Sanitation PART II PLANNING AND DESIGN GUIDELINES

Transcription

1 PART II PLANNING AND DESIGN GUIDELINES

2 Part II Planning and Design Guidelines K ii

3 K K iii

4 K TABLE OF CONTENTS K SANITATION... 9 K.1 OUTLINE OF THIS SECTION... 9 K.1.1 Purpose... 9 K.1.2 Content and Structure... 9 K.2 UNIVERSAL CONSIDERATIONS K.2.1 The regulatory environment K.2.2 Key objectives K.2.3 Approaches and Concepts K.2.4 The implementation context K The type of development/project K The setting of the development K.3 PLANNING CONSIDERATIONS K.3.1 Characteristics of the Existing Environment K The nature of the planned development K The potential residents of the development K Physical characteristics K Infrastructure K.3.2 Characteristics of the Proposed Development K Who will be the user of the Service K The layout of the envisaged development K.3.3 Options- Dealing with K What are the main factors to consider? K How will Treated Effluent be managed? K How will Greywater be managed? K How will Stormwater Ingress be reduced? K What Institutional and political factors are involved? K What is the economic feasibility of the system? K Is operation and maintenance of infrastructure considered? K.4 DESIGN CONSIDERATIONS K.4.1 Designing of Disposal and Conveyance infrastructure K General Considerations K Ventilated Improved Pit (VIP) Toilets K iv

5 K Pour Flush K Aqua-Privies K Small Scale Septic and Leach Field Systems K Anaerobic Digester K Composting Toilet K Vacuum Sewer System K Small Bore Sewer System K Settled and Simplified Sewers K Communal/ Public Toilets K Waterborne K.4.2 Design Flow K Unit Hydrograph Method K Sewer Flow and Peak Factor Method K Groundwater infiltration K.4.3 Hydraulic Design of Waterborne Systems K Pipe Sizing for Design Flow and Stormwater Ingress K Velocity and Flow in Sewers K Gravity System K Pumped System K.4.4 Physical Design of Waterborne Systems K Sewer Pipes K Pipe Load and Deflection Calculations K Syphons K Manholes K Sewer Connections K Special Structures K Pump Stations K Dealing with stormwater ingress into sewers K.4.5 Materials K Pipes and Joints K Manholes K Bedding and Backfill K Pump Stations K Concrete K Structural Steelwork K Electrical Installations K.4.6 Design of Centralised Wastewater Treatment Infrastructure K Activated Sludge and Biofilter Treatment Systems K Pond Systems K Package Purification Units K.4.7 Design of Grey Water Management Systems K Volumes K Disposal K v

6 K.4.8 Design of Sludge Disposal Infrastructure K Disposal of Sludge from On-site Systems K Composition of Pit or Vault Contents K Methods of Emptying Pits K Vacuum Tankers K Disposal of Sludge K.4.9 Upgrading of Existing Systems K Informal settlement upgrading K Hydraulic models K Basic upgrading alternatives K Upgrading routes for the various sanitation systems and facilities GLOSSARY, ACRONYMS, ABBREVIATIONS END NOTES K vi

7 LIST OF FIGURES Figure K.1: A framework to assist with planning and design decisions Figure K.2: The sanitation value chain Figure K.3: Permissibility of greywater use Figure K.4: Decision Flow Chart for Management of Risks associated with Greywater use in Category 2 (Minimum Analysis) (Rodda, et al., 2010) Figure K.5: Risk Management Restrictions in Response to the Decision Flow Chart for Greywater Use in Category 2 (Rodda, et al., 2010) Figure K.6: Decision Flow Chart for Management of Risks Associated with Greywater use in Category 3 (Full Analysis) (Rodda, et al., 2010) Figure K.7: Risk Management Restrictions in Response to the Decision Flow Chart for Greywater use in Category 3 (Rodda, et al., 2010) Figure K.8: Example of Pour Flush System Figure K 9: Example of Aqua Privy Figure K.10: Example of Septic Tanks System (CSIR, 1991) Figure K.11: Composting Latrine Figure K.12: Vacuum Sewer System (adapted from AIRVAC, 2005b) Figure K.13: Small Bore Sewer System Figure K.14: Design Aspects of Waterborne Sewer Systems Figure K.15: Sewer Outflow Hydrograph Figure K.16: Attenuation of Peak Flows Figure K.17: Absolute and Relative Spare Capacity Figure K.18: Partial Flow Diagram Figure K.19: Upper End Sewer Network Example Figure K.18: Example of Syphon System (Source: 75 Figure K.21: Pumping System Curve ( ) Figure K.22: Protection of Pipes at Reduced Depths of Cover (e.g. Class B bedding) Figure K.23: Steep Drops in Sewers Figure K.24: Diagram of the depth of the invert of the sewer house connection Figure K.25: Disposal of Pit Toilet Sludge in a Trench (World Health Organisation, 1992) K vii

8 LIST OF TABLES Table 1: Dry System Options Table 2: Wet System Options Table 3: Systems Table 4: Comparison of Nutrient Levels in Wastewater Sludge (Biosolids) Table 5: Sludge Classification System Table 6: Ventilated Improved Pit Toilets: Design Aspects Table 7: Demands and Hydrographs for Different Land Use Categories Table 8: Sewer Unit Hydrographs Table 9: Work Example S1 Unit Hydrograph Method Table 10: Work Example S2 Unit Hydrograph Method Table 11: Peak Factors Table 12: Work Example S3 Sewer Flow and Peak Factor Method Table 13: Groundwater Infiltration Table 14: Work Example S4 Groundwater Infiltration Table 15: Work Example S5 Design Flow and Stormwater Ingress Table 16: Work Example S6 Hydraulic Capacity Table 17: Flow Formulas Table 18: Minimum Gradients for ±0.65m/s Full Flow Velocity Table 19: Minimum Gradients for Upper End of Sewer Network Table 20: Minimum Self-cleaning Velocities Table 21: Trench Widths Table 22: Manhole Types Table 23: Minimum Internal Dimensions of Manhole Chambers and Shafts Table 24: Fall in manholes for various bends and pipe sizes Table 25: Energy Loss Coefficients Table 26: Greywater Generation K viii

9 K SANITATION K.1 OUTLINE OF THIS SECTION K.1.1 Purpose Settlements are integrated systems where the various components are interconnected, and this section deals with the planning and design of sanitation and wastewater infrastructure to all (men and women of all ages, children, and people living with disabilities) that provide access to safe, hygienic, acceptable, affordable, and prevent pollution of the environment. The aspects addressed in this section play an essential role in achieving the vision for human settlements outlined in Section B since the sanitation and wastewater services in a neighbourhood could significantly affect the quality of the living environments created. The interrelationship between the different components of a neighbourhood, such as water supply, sanitation facilities, and stormwater, and their integration into the broader settlement, play an important part in responding to international imperatives (outlined in Section B.1) and South African policies (Section B.2). In particular, the qualities that should be sought in settlements are clearly indicated, integrated planning and design are encouraged and sound urban planning and design principles are promoted. The services and infrastructure discussed in the other sections in Part II are frequently linked to sanitation in a neighbourhood, such as water supply and stormwater, and should also be consulted when applying the guidelines provided in this chapter. K.1.2 Content and Structure This section provides an overall framework to assist with planning and design decisions regarding sanitation and wastewater. The section will focus on rules, criteria, standard methods, procedures and best practices to be followed when planning for and designing and wastewater infrastructure in South Africa. It defines benchmarks and minimum requirements and help to ensure that all important aspects are taken into account by adopting an integrated planning approach. For engineering details, the reader will be referred to the more relevant detailed technical manual and textbooks. The information and guidance provided is structured as follows: Universal considerations In this section, general issues are highlighted that should be taken into consideration when making higher level decisions regarding the layout and structure of an area being developed or redeveloped, including the following: The regulatory environment, including key legislation, frameworks, strategies, norms, standards, guidelines and provincial and municipal regulations. The key objectives that should be achieved and the outcomes that should be the result of the layout and structure decided upon. Possible approaches, strategies and mechanisms that could be utilised, or local or international concepts, ideas and trends that could be implemented to achieve the desired objectives. Contextual factors specific to the project to be implemented such as the type, nature and setting of the development. P a g e 9

10 Planning considerations Issues to consider when making more detailed decisions regarding the nature and characteristics of the proposed sanitation and wastewater for the area being developed or redeveloped are outlined in this section. These include the following: The existing features of the site and immediate surroundings (built and natural environment) as determined by the physical location of the proposed development. The characteristics of the proposed development, including the type and size of the proposed neighbourhood, the anticipated number of residents and specific features that would have to be incorporated or requirements that would have to be met. Options related to sanitation and wastewater that are available for consideration. Design considerations This section contains guidelines to assist with the design of the option that was selected during the planning. Glossary, acronyms, abbreviations A glossary of terms and concepts referred to in this section, as well as a list of acronyms and abbreviations, are provided at the end of this section. Sources of information and explanatory comments are also provided at the end of this section. P a g e 10

11 Figure K.1: A framework to assist with planning and design decisions P a g e 11

12 K.2 UNIVERSAL CONSIDERATIONS K.2.1 The regulatory environment A range of legislation, policies and strategies guide the development of settlements in South Africa. Legislation and policy that have direct implications for sanitation and wastewater planning and design are briefly outlined below. They are not discussed in detail, so it is important to consult the relevant documentation before commencing with any development. (Also see Section D.1 and Section D.2.). All building and construction work in South Africa is governed by the National Building Regulations and Building Standards Act (No 103 of 1977). Always refer to SANS The application of the National Building Regulations (NBR) available from the South African Bureau of Standards (SABS). In addition, local authorities may have additional guidelines, regulations and by-laws that you may have to adhere to, such as the Water Services Development Plans (WSDPs). and wastewater The provision of sanitation and wastewater is governed by, amongst others, the following: The National Water Act (32 of 1998). The National Water Services Act (108 of 1997). The Municipal Structures Act (117 of 1998). The Strategic Framework for Water Services (SFWS). The Second National Water Resources Strategy (NWRS2). The National Framework for Sustainable Development (NFSD). The National Environmental Management Act (107 of 1998). The National Environmental Management: Integrated Coastal Management Act, 2008 (24 of 2008). The Housing Act (107 of 1997). Water quality Norms and standards as published by the Department of Water and. All water made available for drinking must be potable. Potable water is water that is clear, tastes and smells good, and is free of contaminants and pollutants that could affect human health, thus water of a quality consistent with SANS 241 (Specifications for Drinking Water) as may be amended from time to time. Key references relating to the provision of safe drinking water quality in South Africa include the following: Water Services Act (108 of 1997). National Water Act (36 of 1998). Municipal Structures Act (117 of 1998). Compulsory National Standards for the Quality of Potable Water (2001). Strategic Framework for Water Services (2003). National Health Act (61 of 2003). National Water Resources Strategy (2004). Framework for Drinking Water Quality in South Africa (2005). P a g e 12

13 K.2.2 Key objectives The water sector strives for water sensitive and water-wise settlements that include universal access to safe drinking water and adequate sanitation, human dignity, user participation, service standards, redress, and value for money. Planners, developers and design teams are encouraged to strive for zero negative impact and zero waste in providing sanitation and wastewater services. Poor sanitation and inappropriate drainage of wastewater almost always lead to the pollution of local water sources with pathogens, rendering them unsafe for cooking or drinking. It is fundamental to sustainable development that local water sources be protected from contamination. It is also vital that due care is taken to minimise the negative downstream effects of wastewater treatment and/or disposal. The key objectives for sanitation and wastewater, as set out in the National Policy of 2016 (DWS, 2016), are the following: The right to access to basic sanitation - a recognised Constitutional responsibility of the national sphere of government, with local government mandated to take reasonable measures to realise this right. Prioritising hygiene and end-user education in sanitation service provision - Hygiene education is crucial to maximise the public benefit of sanitation service provision, and the policy states that this must be continuous, have varying emphasis based on needs, and address all geographic areas of the country. Further, such education should make users aware of their rights and responsibilities and incorporate water conservation and demand management. Prioritising basic sanitation services to vulnerable people and unserved households - This is prioritised in recognition of the special access requirements of these individuals and households. People-centred and demand-driven sanitation service provision - The policy states that sanitation services must recognise sanitation as a right, consider consumers expectations and needs in planning and implementation with devolvement of decision making and control to the lowest possible levels of accountability. Conversely, the policy recognises that there is a reciprocal obligation on communities to accept responsibility for their own development and governance, with the assistance of the State. Polluter pays principle - The policy states that any reduction of receiving water quality should have a value assigned to it. As such water quality management shall include the use of economic incentives and penalties to reduce pollution, placing an obligation on sanitation services to be implemented to reduce pollution. User pays principle - The policy states that the implementation, regulation and enforcement of the user pays principle are central to sustainable sanitation service provision. Therefore, the beneficiaries of the water management system shall contribute to the cost of its establishment and maintenance on an equitable basis. has economic value - According to the policy The public and economic benefit of improved sanitation must be recognised and valued. This should be reflected in how the sanitation by-products are approached and handled, as well as the recognition of the impact of sanitation services on the water scarcity situation in the country. Integrated development - The provision of sanitation services should be done in an integrated manner together with other basic services. This will maximise its public health and economic benefits. Equitable regional allocation of development resources - The policy states that the limited national resources available to support the provision of basic services should be equitably distributed among regions, taking account of population and level of development. Recognising the value of sanitation by-products - The recognition of the full value of sanitation by-products, with reinvestment into the system, will foster increased investments and generate efficiency gains. P a g e 13

14 Prioritising operation and maintenance - The planning of capital expenditure for sanitation services should take into account the related operation and maintenance costs. Thus, sufficient resources must be allocated for the adequate maintenance of infrastructure and related systems. Integrated waste management - The provision of sanitation services should recognise all the various forms of wastes emanating from the household. These must be handled (storage, removal and management) in an integrated and coordinated manner. In order to achieve the above objectives, a sanitation service must be: A basic sanitation facility in the SFWS is a facility that is safe; reliable; environmentally sound; easy to keep clean; provides privacy; provides protection against the weather; well ventilated; keeps smells to a minimum; prevents the entry and exit of flies and other diseasecarrying pests; enables safe and appropriate treatment and/or removal of human waste; and accompanied by appropriate health and hygiene education (DWAF, 2003). Sufficient: The water supply and sanitation facility for each person must be continuous and sufficient for personal and domestic uses. These uses ordinarily include drinking, personal sanitation, washing of clothes, food preparation and personal and household hygiene. According to the World Health Organization (WHO), between 50 and 100 litres of water per person per day are needed to ensure that most basic needs are met and few health concerns arise. Safe: Everyone is entitled to safe and adequate sanitation. Facilities must be situated where physical security can be safeguarded. Ensuring safe sanitation also requires substantial hygiene education and promotion. This means toilets must be available for use at all times of the day or night and must be hygienic; wastewater and excreta safely disposed and toilets constructed to prevent collapse. Services must ensure privacy and water points should be positioned to enable use for personal hygiene, including menstrual hygiene. Acceptable: All water and sanitation facilities and services must be [ ] culturally appropriate and sensitive to gender, lifecycle and privacy requirements. should be culturally acceptable ensured in a nondiscriminatory manner and include vulnerable and marginalised groups. This includes addressing public toilet construction issues such as separate female and male toilets to ensure privacy and dignity. Physically accessible: Everyone has the right to water and sanitation services that are physically accessible within, or in the immediate vicinity of, their household, workplace and educational or health institutions. Relatively small adjustments to water and sanitation services can ensure that the needs of the disabled, elderly, women and children are not overlooked, thus improving the dignity, health, and overall quality for all. Affordable: Water and sanitation facilities and services must be available and affordable for everyone, even the poorest. The costs for water and sanitation services should not exceed 5% of a household s income, meaning services must not affect peoples capacity to acquire other essential goods and services, including food, housing, health services and education. (United Nations, undated). K.2.3 Approaches and Concepts Providing appropriate sanitation and wastewater services to a city as a whole requires a mixture of systems that are appropriate for different parts of a city and that can be implemented at different scales. The same model of service delivery will not be appropriate for all areas. (i) Improving the water mix Planning and appropriate design are critical to achieve an effective balance between water resource management, prevention of pollution, environmental sustainability and optimum land use (development). One way is through Improving the Water Mix, which involves the increased use of a variety of water sources in addition to surface water, such as groundwater, water harvesting, water-recycling and the re-use of treated wastewater and acid mine water. P a g e 14

15 (ii) At least basic sanitation approach Meeting the universal service obligations requires currently that each South African has access to at least a basic sanitation service, which is a Ventilated Improved Pit (VIP) toilet; the sustainable operation of this facility (available for at least 358 days per year and not interrupted for more than 48 consecutive hours per incident); and the communication of effective water-use, hygiene and water-related practices (DWAF, 2002). The 2016 National Policy states that a basic sanitation facility is the infrastructure necessary to provide an appropriate sanitation facility which considers natural (water; land; topography) resource constraints, is safe including for children, reliable, private, socially acceptable, maintainable locally, protected from the weather and ventilated, keeps smells to the minimum, is easy to keep clean, minimises the risk of the spread of sanitation-related diseases by facilitating the appropriate control of disease carrying flies and pests, facilitates hand washing and enables safe and appropriate treatment and/or removal of human waste and wastewater in an environmentally sound manner, and a basic sanitation service is the provision of an appropriate basic sanitation facility which is environmental sustainable, easily accessible to a household, the sustainable operation of the facility, including the safe removal of human waste, greywater and wastewater from the premises where this is appropriate and necessary, and the communication and local monitoring of good sanitation, hygiene and related practices. (iii) Environment and health approach is about the environment and health. improvement is more than just the provision of toilets; it is a process of sustained environment and health improvement. Basic sanitation is a human right: Government has an obligation to create an enabling environment through which all South Africans can gain access to basic sanitation services. Economic value of water: The way in which sanitation services are provided must take into account the growing scarcity of good quality water in South Africa. services must be financially sustainable: services must be sustainable both in terms of capital costs and recurrent costs. Health and hygiene education is accepted as a key aspect of sanitation projects because the aim of services is to ensure real health benefits from sanitation projects. In the context of sanitation, health and hygiene promotion and education is defined as all activities aimed at encouraging behaviour that will maintain the conditions that prevent contamination and the spread of sanitation related diseases, such as the provision of a hand washing facility with water and soap. (iv) Environmental integrity: The environment must be protected from the potentially negative impacts of developing and operating sanitation systems. Safe management of human waste Safe management of household excreta is defined as the containment, extraction, and transport of excreta to a designated disposal or treatment site, or the safe re-use of excreta at the household or community level, as appropriate to the local context. Safely managed excreta is defined as: carried through a sewer network to a designated location (e.g. treatment facility); hygienically collected from septic tanks or latrine pits by a suction truck (or similar equipment that limits human contact) and transported to a designated location (e.g. treatment facility or solid waste collection site); or stored on site (e.g. in a sealed latrine pit) until they are safe to handle and re-use (e.g. as an agricultural input). P a g e 15

16 Figure K.1: The sanitation value chain (v) Appropriate technology approach Appropriate sanitation technologies minimise natural resource use, impacts on water resources, and impacts on the environment, and encourages recycling and re-use, are sensitive to people with special needs, children, the elderly and women, and consider the physical, social, cultural, environmental, institutional and economic context. The choice of an appropriate sanitation system is affected by the following: The system should not be beyond the technological ability of the community insofar as operation and maintenance are concerned. The system should not be beyond the community s ability to meet the capital as well as the maintenance costs. The system should take into account the level of water supply provided, and possible problems with sullage (greywater) management. The likelihood of future upgrading should be considered, particularly the level of service of the water-supply system. The system should operate well despite misuse by inexperienced users. In a developing area the system should require as little maintenance as possible. The system chosen should take into account the training that can be given to the community, from an operating and maintenance point of view. The system should be appropriate for the soil conditions. The community should be involved to the fullest extent possible in the choice of an appropriate system. To foster a spirit of real involvement and ownership, the community should be trained to do as much as possible of the development work themselves. Local customs should be carefully considered. The local authority should have the institutional structure necessary for the operation and maintenance of the system. The existing housing layout, if there is one, should not make the chosen system difficult to construct, maintain or operate. P a g e 16

17 (vi) Ecological Systems approach Ecological systems play an integral role in contributing to the environmental and economic health of neighbourhoods. Each city, its neighbourhoods and its surrounding countryside, is growing continuously and its planning for growth should be based on an understanding of its ecological, economic, political and social domains. Planning needs to develop and support frameworks for planning and managing the city and its neighbourhoods from an ecological perspective. Environmental considerations should prevent environmental impacts, and work towards realising the four R s: (vii) Reducing resource requirements, including natural resources, and minimising outputs to the environment. Maximising Re-use of waste products and outputs. Maximising Recycling (reclaiming) of waste and effluent components within natural biological cycles. Recover materials or energy from waste that cannot be reduced, reused or recycled. Water Sensitive City and Sustainable Urban Drainage Systems approach and wastewater planning and design should be integrated into a local urban master plan to take into account interactions with other services that can interfere with good sanitation (e.g., solid waste management, water systems, stormwater management). The approach of a Water Sensitive City (WSC) integrates urban planning and the urban water cycle, which includes integration of stormwater, groundwater, sanitation, wastewater management and water supply to cope with societal challenges related to climate change; resource efficiency and energy transition; to minimise environmental degradation, and to improve aesthetic and recreational appeal. This approach develops integrative strategies for ecological, economic, social, and cultural sustainability (Van Hattum, 2016). The Water Sensitive Urban Design (WSUD) approach integrates engineering and environmental sciences associated with the provision of water and includes the protection of aquatic environments in urban areas (Wong, 2006). Sustainable urban Drainage Systems (SuDS) manages runoff through management practices and/or control structures (e.g. green roofs, rainwater harvesting, swales, filter strips, permeable pavements, soak ways, infiltration trenches, detention ponds, retention ponds, wetlands) - the treatment train. With regards to SuDS, an integrated approach to infrastructure planning and implementation is especially important in informal areas. Where sanitation services are inadequate (e.g. unimproved sanitation infrastructure and inadequate disposal of greywater) the risk that the SuDS systems will be used for the disposal of black and greywater, which poses a potential health risk and may cause the SuDS system to fail. (viii) Green and decentralised approach Reducing the overall demand for fresh water (through water-wise landscaping, rainwater harvesting, waterefficient and water-saving appliances and fixtures) and implementing use patterns and manufacturing processes with lower water needs than conventional methods, can be an effective strategy for water conservation to mitigate climate change., as the supply chain for both used water and nutrients, is at the core of sustainable settlements, and it needs to be fully integrated in the current thinking of circular, efficient, green or water-secure cities. Cities should treat wastewater and sludge as close as possible to their source, to enable onsite re-use of resources. Sewer systems are not the ultimate sanitation solution as they often do not address increasing needs and dwindling resources. Realistic and adapted sanitation planning and solutions are necessary, such as on-site and decentralised sanitation solutions, even in large cities. Decentralised and modular sanitation services and solutions often provide better adapted alternatives, and support a progressive approach that is more relevant to local finances and appropriate for all. P a g e 17

18 (ix) User participation and education User education is essential for any sanitation installation, regardless of whether it is urban or rural, on-site or offsite, wet or dry. services should promote awareness of the linkages between health, hygiene and sanitation, and provide users with information on how to keep their toilet functioning well. Unless users understand the basic requirements for operating and maintaining a hygienic toilet it is likely to malfunction and - particularly for on-site toilets - provide a powerful disincentive to being used (SALGA, 2008). Thus, any sanitation intervention or project needs to be preceded by a comprehensive programme of information provision that targets both decision-makers and end-users of a sanitation intervention about the operating costs and requirements of different sanitation systems, for them to be able to assess the implications and make informed choices and decisions that are appropriate to their needs and circumstances. In determining strategies for community participation, it is necessary to know and have contact with communities to gain a clear understanding of their social history, existing hygiene and sanitation situation, current hygiene practices, culture and attitudes, and health conditions. It is also necessary to know how community members communicate and work together, and how they handle new ideas, challenges, and information in order to build and adapt interventions that use and build upon the community s unique characteristics. Relevant community structures should be part of the planning process in order to promote and facilitate local discussion of needs, options and priorities. Planning and decision-making needs to be informed by active engagement with local residents. (x) Hygiene and hand washing The provision of simple information to households to strengthen their understanding of the linkages between good sanitation, safe drinking water and comprehensive hygiene is essential. Each toilet should have a hand washing facility at, or close by (within 1m), the facility that must allow for the washing of hands after using the toilet. This will enable the fulfilment of the requirements of policy, legislation and regulations in the provision of a basic sanitation facility which is easily accessible to a household, the sustainable operation of the facility, the safe removal of human waste and wastewater from the premises where this is appropriate and necessary, and the communication of good sanitation, hygiene and related practices (DWAF, 2003). Menstrual health considerations also should receive the necessary attention during planning and designing of sanitation systems and services. (xi) Recycling and re-using wastewater and greywater In view of the projected water shortages in future and the costs of rendering water drinkable, the recycling of wastewater and re-use of greywater is encouraged implemented where feasible and where human health will not be compromised. Greywater could, for example, be used to flush toilets or water the garden. Cognisance should be taken of the level of knowledge of users regarding greywater use, which is generally low and could result in non-acceptance of the use of any kind of water that is not classed as potable. Nutrient recovery and re-use has become increasingly prominent in light of resource scarcity, pollution and the push for a more circular economy. Recycling of nutrients between urban areas and farmland is a critical step towards an ecologically sustainable development. Human urine is the most nutrient-abundant part among the domestic waste components. K.2.4 The implementation context This section highlights the contextual factors, specifically related to the type of project and the setting of the development, that should be considered when planning and designing sanitation and wastewater for settlements. P a g e 18

19 K The type of development/project (i) Greenfield development Greenfield projects can theoretically accommodate most sanitation services types. The deciding factor would normally be the availability of water for flushing and the most practical, affordable, and achievable chance to build neighbourhoods that are land-efficient, fiscally secure, environmentally responsive, and deliver a better way of life. Other factors that would influence the type of sanitation service include the topography and geotechnical conditions, as well as community values (e.g., preserving important views, water quality, cultural resources, acceptability issues) that will result in a new development that is welcomed because it is holistic, environmentally sound, community-friendly, and understood by the locals. When planning and designing the layout and structure of a neighbourhood as part of a greenfield development project, the following have to be considered: (ii) Undisturbed portions of the natural environment are often found on greenfield sites. The preservation or improvement of natural freshwater ecosystems, and creation of additional freshwater habitats that contribute to the availability of appropriate, high quality river and wetland habitat that mimics the natural condition of open space, trees and on-site natural features should be considered when planning and designing stormwater management. Greenfield sites often are not connected to municipal services, such as water supply, sanitation, stormwater, electricity, and solid waste removal. These service connections may even be a substantial distance away, especially if the site is in a rural area. The capacity of the services may also not be sufficient for the proposed development and may require an upgrade to adequately service the proposed development. The costs associated with new municipal services, or extensions to existing systems, and the measures to curb these costs will impact significantly on planning and designing water supply. Depending on where the greenfield site is located, it might be a challenge to connect to existing wastewater and sewer systems. Brownfield development When planning and designing the sanitation services for a brownfield development project, the following has to be considered: The layout and structure of the brownfield development project should link up with existing sewer systems. Sites for redevelopment often have built structures that might have heritage value. Identify and preserve heritage elements that need to be protected in connecting to existing services, or building new sewer services. Brownfield projects often result in higher population densities. Population density will have an impact on the planning and design of municipal engineering services, as the existing sewer infrastructure might not have the capacity to cater for these higher densities. (iii) Informal settlement upgrading Informal settlement upgrading often involves in situ development, which implies that existing houses are left in place, while the neighbourhood is upgraded streets are aligned and widened, drainage is improved and homes are connected to the water and sanitation grids. When planning and designing sanitation services for an informal settlement upgrading project, the following needs to be considered: P a g e 19

20 One of the biggest issues regarding informal settlements is land tenure. A municipality or services authority is not allowed to provide services on land that is not owned by a municipality, unless permission is obtained from the land owner. The urbanisation/formalisation of informal settlements should always be part of the future scenario land use, because relocation of inhabitants is usually undesirable. This has implications on approaches such as SuDS, where these systems may be used as sanitation facilities and for the disposal of greywater, wastewater and solid waste. Informal settlements are often isolated from the settlement sewer grid. Linking up with existing sewer networks will have a major impact on the system. Informal settlements grow organically and there may be layouts that seem unconventional. and wastewater systems for the upgraded informal settlement have to accommodate these anomalies. When planning and designing for sanitation, the higher population density might have an impact on the planning and design of municipal services, as the infrastructure in adjacent neighbourhoods might not have the capacity to cater for these higher densities. Provision of communal sanitation facilities is often the only solution to providing sanitation services to dense informal settlements. The urbanisation/formalisation of informal settlements with the accompanying sanitation services should always be assumed as part of the future scenario land use, with the resultant higher level of services. Of critical importance when planning and designing sanitation and wastewater services for an informal settlement upgrading project, is to involve the residents. Informal settlements are not homogenous; each has its own unique community characteristics and different levels of social cohesion, specifically regarding sanitation facilities. K The setting of the development (i) Rural As mentioned in Section D.3.2 the rural areas of South Africa comprise a variety of settlements types, including rural villages and towns, dense rural settlements and dispersed settlements 1. When making decisions regarding sanitation and wastewater systems for a development in a rural setting, the following would typically need to be considered: Most traditional villages are located on farm portions or in some instances on land that has not been surveyed. The land is communally owned and is usually managed by a hierarchy of traditional leaders. Decisions regarding sanitation are directed by these decision-makers rather than the local municipality s Spatial Development Framework (SDF) or land use scheme 2. In most instances, communal water points where water for handwashing is obtained, and on-site sanitation systems are likely to be the most appropriate sanitation service. Care must be exercised when choosing waterborne sanitation systems in this context. The water services authority must ensure that the water services provider will be able to maintain and operate this system sustainably over time with the available funds. Traditional homesteads may require an approach that is different from urban areas, for example, in a rural residential area, activities such as the traditional slaughter of animals, home burials, or seasonal land uses may have to be allowed for 3. Rural communities may provide certain services themselves, and these may have to be accommodated in the provision of sanitation infrastructure. P a g e 20

21 (ii) Rural communities are often particularly vulnerable to climate change and may be exposed to a relatively high risk of extreme natural events, such as droughts, floods, storms and veld fires 4. This may require special consideration when planning and designing the sanitation infrastructure for a rural development. Ecosystems provide critical services to rural communities such as clean water, air, biodiversity and productive soils 5. Protecting ecosystems through appropriate sanitation infrastructure builds the resilience of rural communities. Many rural households are much less likely than urban households to have access to a supply of piped water close to their dwellings. Therefore, household activities often include the collection of water 6, and in such cases the provision of sanitation for a development need to take into account the availability of water for flushing. Often rural settlements can only be accessed by dirt roads or even footpaths 7. These roads are particularly vulnerable to degradation during rains. In addition, the organic nature of the internal street layout of rural settlements makes it difficult to achieve certain efficiencies. The proper planning and design of sanitation infrastructure should consider these challenges. The spatial form of rural settlements, specifically those under traditional leadership, differs throughout South Africa 8. In the provinces of North West and Limpopo traditional villages are often arranged in square gardens and within square blocks with livestock kept within the boundaries of each household, while houses and huts in KwaZulu-Natal are sometimes arranged on hilltops or on slopes or along river courses. Occasionally the houses are close together to form a village 9. These different spatial forms are largely associated with different cultures and traditions as well as the topography of the area. The planning and design of sanitation infrastructure of a new project should respect and respond to the tradition and culture of the local people. Peri-urban. The development setting of peri-urban areas is diverse and includes a mix of settlement patterns, socio-economic statuses and access to services. Settlement on the periphery of metropolitan areas and towns may include informal settlements, low-income housing and high-income low density developments. When planning and designing sanitation infrastructure for a development in the urban fringe area, the following should be considered: Peri-urban areas are under pressure as most new urban-based developments and changes are concentrated in these zones of rural-urban transition10. The often high rate of urbanisation should be considered when planning and designing the sanitation infrastructure of new developments as there is a likelihood that periurban areas have to accommodate more people and higher densities in future. Land on the periphery often do not have convenient access to urban amenities. When designing and planning sanitation infrastructure for a development, it is important to link the development to existing sewer systems. The boundary line between rural, peri-urban and urban is not well-defined and therefore tends to adjust often. Municipalities make use of a range of urban growth measures of which the urban edge is one. When planning and designing sanitation infrastructure for a project, it is critical to determine whether there is an official urban edge delineated, what its proximity is in relation to the development, and how this will impact on future change in the development. The costs of providing conventional urban infrastructure in peri-urban areas are often prohibitive. In many cases alternative ways of service provision need to be considered, e.g. package plants for sewer treatment, etc. P a g e 21

22 (iii) Urban. As outlined in Section D.2 the urban areas of South Africa comprise a variety of settlements types. When making decisions regarding sanitation and wastewater infrastructure for an urban development, the following should be considered: The negative contribution of new developments on urban sprawl should be reduced as far as possible. South Africa s inner cities are changing. They are no longer the only commercial hub in our cities. Multiple commercial nodes across the city will have an impact on layout proposals as multiple linkages and access points should be provided. K.3 PLANNING CONSIDERATIONS This section deals with the planning of a sanitation and wastewater services. In this context, the term planning means making informed decisions regarding the type or level of service to be provided, and then choosing the most appropriate water supply options based on a thorough understanding of the context within which the planned development will be implemented. The decisions regarding sanitation and wastewater have to be informed by a thorough understanding of the features and requirements of the proposed project and of the context within which the planned development will take place. In other words, the factors that would help formulate the project brief, or specification, need to be understood by assessing the characteristics of the proposed project. Furthermore, by examining the characteristics of the environment in which the new development will be located, possible services and infrastructure that could be utilised to address the needs as outlined in the brief would be identified. This section outlines a range of questions that need to be answered and factors that have to be considered to inform decisions regarding sanitation and wastewater to be provided as part of a development project. The overall planning framework for new sanitation services is described schematically in the figure below and is described in more detail in the sections following. P a g e 22

23 P a g e 23

24 K.3.1 Characteristics of the Existing Environment Decisions regarding water supply need to be guided by an assessment of the characteristics of the proposed development and an understanding of the requirements, or need, which will have to be met. Issues that should be considered include the following. K The nature of the planned development The nature of development that is planned will influence the street layout, the size of the land units and the type of engineering and other services to be delivered. The following questions need to be answered: What is the dominant land use of the proposed development? What supporting land uses will be required? What is the proximity to water resources? The distance to dams, rivers and streams, or coastal waters is important due to the indication it provides to water availability and the availability of a point of disposal of treated effluent. What social facilities should be provided and planned for? If a mixed development is proposed, what type of mix is proposed, e.g. a variety of sanitation types, sizes, densities and/or tenures? K The potential residents of the development Decisions related to sanitation and wastewater infrastructure need to be guided by information regarding the potential residents and users of the planned facilities. It may be possible to make assumptions regarding the possible nature of the future residents by assessing the surrounding neighbourhoods or similar developments in comparable locations or contexts. It is important to try to establish the following as far as possible: The total number of residents that would have to be accommodated, taking into consideration that actual numbers may be higher than anticipated due to the fact that the provision of houses and services may attract more people than originally planned for. The number of households, the range of household sizes and their composition, for instance, whether there will be child-headed or single parent households. This will indicate which types of housing and services would have to be provided. Whether residents with special needs would have to be accommodated, e.g. people living with HIV/AIDS and with disabilities, including physical, dexterity and sensory impairment. This will indicate whether streets and other infrastructure and facilities would have to be provided to specifically accommodate these residents. Age and gender of residents and those that may visit social facilities (i.e. gender ratios, age profile, and size). An aging population might, for example, require access to sanitation facilities at a ground level, or closer to the home. Income and employment levels and spending patterns. This would, for instance, indicate what type of sanitation infrastructure and services would be most appropriate. Cultural profile. The mix of the target group is also important to consider, as the social structure could shape the demand for some sanitation types at the expense of others or the environment. The customs, beliefs, values and practices that influence the design of the social components of a sanitation system, its acceptability or fit within a community. The expectations of the community also need to be considered. P a g e 24

25 K Physical characteristics These include the groundwater table, topography, soil conditions and land availability. The position of the ground water table and soil conditions will dictate the suitability of the containment and disposal methods, especially in the case of on-site disposal. The topography will influence the selection of location of infrastructure based on the possibility exploiting gravity to assist in the transport of sewage. Land availability influence the decision of locating infrastructure. The temperature, humidity and precipitation in the area influence the effectiveness of a chosen sanitation infrastructure. K Infrastructure The existing level of both physical infrastructure and existing services that might help support a sanitation system (i.e. extent of existing water supply and sewer systems, transport, public health network, educational system etc.) K.3.2 Characteristics of the Proposed Development The type and setting of the development has been discussed in Section 0 and is not repeated here but is important in the evaluation process by the decision maker. K Who will be the user of the Service The source of the sewage flow, the user, is to be considered in planning sanitation services and infrastructure. The following user characteristics needs to be accommodated: Size and density of population. habits (e.g. hand wash). Local customs (religion, tribal, beliefs etc.). People practices (washing after use, wiping, hand washing, laundry). Orientation (basic attitudes, beliefs, feelings). Community roles, involvement. Social acceptability (comfort, privacy, dignity). Understanding of the technology/familiarity. Gender /Equity and equality (separation male/female or mixed). Culturally appropriate menstrual health considerations. Availability of water for flushing and/or handwashing. Safety. Ownership (landlord, tenants, pay-as you use). Training required within community. backlog (inadequate facilities) areas to be given higher priority. Hygiene education. Communities attitude towards recycling and handling of decomposed human waste. facility requirements (position, size, appearance, seats, permanency, type). P a g e 25

26 User education is part of the National Policy and should embrace proper health practices, such as personal hygiene (particularly hand washing), the need for all family members (including the children) to use the toilet, and the necessity of keeping the toilet building clean. The presence of water supply at the toilet facility (within 1m) needs to be accommodated at all times. Effective and wise water use should be promoted. Education of the proper operation of the system is needed, such as what may and may not be disposed of in the toilet, the amount of water to add if necessary, and what chemicals should or should not be added to the system. The user must also be made aware of what needs to be done if the system fails, or what options are available when the pit or vault fills up with sludge. Communities must be fully involved in projects that relate to their health and well-being, and in decisions relating to community facilities, such as sanitation at schools and clinics. Communities must participate in decision-making about what should be done and how, contribute to the implementation of the decisions, and share in the benefits of the project or programme. In particular, they need to understand the cost implications of each particular sanitation option. K The layout of the envisaged development The profile of the development will determine the flow to be accommodated in the sanitation system. The flow from residential developments are dependent on factors, such as the following: Households size. Density of houses. The use or non-use of water for conveyance. The design of a sanitation system requires the planner to source this information to be used in the choice of sanitation infrastructure and the associated capacity thereof. K.3.3 Options- Dealing with K What are the main factors to consider? systems consist of various components that perform various functions, such as: isolation of human excreta from human contact; containment; transport; treatment; and end-use/disposal. A range of technology options are available to the decision maker. Each of the technology options consists of one or more of these components. The decision maker evaluates the options based on the considerations discussed in the previous sections and the needs for the functions associated with the components of a sanitation system. The use or non-use of water in the operation of a sanitation system is a way to separate technology options. systems that use water generally need a continuous water supply to (1) isolate human excreta from human contact, and (2) to transport sewage in the operation of the sanitation system. systems not using water generally rely on dry containment and transport. As a first step it is therefore critical to consider the P a g e 26

27 availability and consequences of using water in the operation of the sanitation system, thus deciding on using a WET or DRY sanitation system option. The decision maker should furthermore consider a number of factors, each with its own applicability, depending on the considerations discussed in the previous sections. These factors include the following: On-site or Off-site containment. On-site or Off-site transport. On-site or Off-site treatment. On-site or Off-site disposal. Each available sanitation option accommodates these factors in a different manner resulting in a large number of combinations that are available. It is the decision makers task to choose the most appropriate option. The following technical and operational factors needs to be considered at all times: The objectives strived for in the provision of sanitation services. Availability of technologies (knowledge, replication, construction methods). Types of technologies cost, operational requirements and context of use. Understanding of the technology. Adaptability and upgradability. Appropriateness to local conditions. Reliability. Sustainability. Robustness. Long term maintenance. Technical skills (to operate and maintain, manage). The protection of the environment from possible pollution by on-site sanitation systems, such as pit toilets and french drains (soakaways), is crucial. Pollution may be caused by infiltration of the leachate from the pits into the groundwater, or by surface runoff through a sanitation system that is positioned in a surface-water drainage-way. The preservation of groundwater resources (many South Africans use wells, springs, and boreholes) is particularly important. Table K.1 and Table K.2 indicate the sanitation systems that can be classified as Dry and Wet respectively. P a g e 27

28 Table K.1: Dry System Options Description Containment Transport Treatment Disposal On-site Off-site On-site Off-site On-site Off-site On-site Off-site Ventilated improved single and double pit toilets (VIP) X None None None Urine diverting dry toilet (UDDT) X X X X Ventilated vault toilet/latrine X X Reed odourless Earth Closet toilets X X (Solids) X (Liquids) Continuous composting toilets X X X X Either one Biological / electric toilets X X X Either one Anearobic digesters X On or the other X Either one Un-improved pit toilets - dry toilet (sit or squat pan) Container toilet (Bucket toilets) Chemical Toilet These options are not allowed as permanent solutions in South Africa or in residential developments Table K.2: Wet System Options Description Containment Transport Treatment Disposal On-site Off-site On-site Off-site On-site Off-site On-site Off-site Waterborne sewerage systems None X X X Low flush toilet None X X X Conservancy tank systems X X X X Shallow sewers None X X X Vacuum sewerage systems None X X X Low-flow on-site sanitation systems (LOFLOs): Aqua-privy X Either one Either one Either one Small Scale Septic and Leach Field Systems X X X X Pour flush (use of bucket to throw water for flushing purpose) X X X None Biogas digesters X X X Either one Solids-free sewer systems/ small bore sewer X Both Both Both Consider all the sanitation alternatives available before deciding on the most appropriate solution for the development in question. A solution that may be appropriate in one community may not be so in another because of cost, customs, and religious beliefs, or other factors as described above. A solution must also not be seen as the most appropriate purely because developers and authorities have traditionally implemented it, or because it is the cheapest. Some of the most relevant sanitation facilities listed above, are illustrated and discussed in more detail in Table K.3. P a g e 28

29 Table K.3: Systems Type Description Ventilated Improved Pit Toilet (VIP) Pit toilet with ventilation pipe Pit lined or unlined A large range of options are available; Easy construction Maintenance of infrastructure is important to ensure sustainability (refer to WRC report No. 709/1/00: Design, Construction, Operation and Maintenance of Ventilated Improved Pit Toilets in South Africa 11 ) Pit emptying to be managed. Lined pits requires less frequent emptying Hygienic when properly constructed and maintained Excreta visible to user Not preferred where water can enter the system More information available from CSIR: (Design, Construction, Operation and Maintenance of Ventilated Improved Pit Toilets in South Africa, Bester and Austin) 12 Urine Diversion Toilet (UD) Above ground toilet (no pit required) Urine collected and can be used as agricultural fertilizer (nitrogen, phosphorous and potassium rich) Faeces can be removed and disposed or used as soil conditioner. Well suited to dense, urban settlements where environmental conditions does not favour other alternatives Commitment from owners required (operation and maintenance) Can be installed inside a house Permanent solution Urine and faeces separated More information available at CSIR 13 and 14 Full Waterborne Consisting of toilet system, sewer network and treatment plant Requires uninterrupted water supply at the toilet system System is hygienic and convenient Require and knowledge to construct, operate and maintain Good operation and maintenance to ensure surety of service More information available from the WRC (Waterborne Design Guide, van Vuuren and van Dijk, ) and (Waterborne Operation and Maintenance Guide, van Vuuren and van Dijk, ). P a g e 29

30 Type Flushing toilet with septic tank and soakaway Description Conventional waterborne toilet leading to a underground septic tank and soakaway (french drain) Requires uninterrupted water supply at the toilet system Requires regular inspection and periodic sludge removal Percolation test to be done to consider suitability and size of soakaway Level of service equivalent to conventional waterborne system Upgrade potential More information available from the WRC (Waterborne Design Guide, van Vuuren and van Dijk, ). K How is sewage treated? On-site systems, which include treatment of the sewage at the location, mainly involves bio-chemical treatment processes. The reliability of the selected treatment process and the input required from the owner or operator must be considered along with discharge quality requirements when treatment technology options are selected. Off-site wastewater treatment is considered a specialised subject and, except for some general comments on pond systems and package purification units, falls outside the scope of these guidelines. It is important to involve specialist consultants where the introduction of a centralised treatment works is considered. At present the General Authorisation in terms of Section 39 of the National Water Act as published in Government Gazette 36820, dated 6 September , provides discharge requirements for smaller plants while application has to be made to the Department of Water and to receive authorisation to discharge from larger plants. The discharge authorisation will specify the conditions under which the discharge may take place and this will include water quality requirements. The establishment of water treatment plants is the responsibility of the designated Water Services Authorities in terms of the Water Services Act, No. 108 of Depending on the size and purpose of the wastewater treatment plant, local bylaws may also apply. The specific requirements must be confirmed on a case-by-case basis. The planner of off-site sanitation treatment infrastructure has various options available, of which the following is the most frequently used in South Africa: Biofiltration plants (fixed film systems). Activated sludge plants (suspended growth systems). Pond systems. Package treatment plants. The selection of the most appropriate treatment solution will be dictated by the General Authorisation 20 or the specific additional requirements as stipulated by the Department of Water and (DWS), if a license application is needed 21. Both the size and discharge water quality requirements will play a role in selecting appropriate technology. P a g e 30

31 Package plants are typically considered for small applications (<100m 3 /day) where pond systems will not produce the required discharge water quality, or sufficient space is not available. Conventional plants are considered for larger installations. The rules are however flexible and dependent on a number of other case specific considerations. In all cases, the assistance of a reputable wastewater treatment specialist should be sought when treatment options are being considered at the planning stage. Conventional biofilter and activated sludge plants Conventional plants, be it biofilter or activated sludge plants, are selected on the basis of the quantity of water that needs to be treated and the quality of discharge water required. Typically, these installations handle larger flows and are able to provide a better and more consistent discharge water quality. Various process configurations exist each with as specific application. The selection of a process is based on detailed analyses of sewage quality and also the specific discharge requirements imposed. Activated sludge plants are typically required where a high discharge quality and nutrient removal is required. Given the high level of indirect reuse (intended or otherwise) that is taking place in South African catchments, these plants have been the most common type constructed in recent decades. Biofilter plants are generally used where the discharge requirements are not as stringent. Biofilter technology is attractive from a cost and ease of use perspective. Pond systems A pond system is a basic treatment process that makes use of sunlight and algal activity to treat wastewater. Pond systems require a large amount of space in relation to its treatment capacity when compared to biofilter of activated sludge plants. Pond systems are usually used in rural areas where land is available and relatively cheap, and where wastewater flows are limited. Skilled process controllers are not required on an ongoing basis and, depending on the circumstances, electricity is not required. Stabilisation (or oxidation) ponds are cheaper to build than conventional sewage purification works. The following important aspects should be considered regarding siting and land requirements for pond systems: (a) (b) (c) (d) (e) (f) (g) The cost of the land. The minimum distance between pond systems and the nearest habitation. The direction of the prevailing winds ponds should, as far as possible, be downwind of town limits. Possible groundwater pollution. Geotechnical conditions that will influence costs. The land required for irrigation purposes, which is an integral part of the pond system. The topography of the site, which can influence costs. Although pond systems are regarded as treatment plants, the effluent does not normally meet acceptable effluent standards for discharge into the catchment. Pond effluents are therefore generally irrigated. A pond system is regarded as a wastewater treatment works and its owner should obtain the necessary authorisations from the DWS. P a g e 31

32 Package purification plants A package purification plant is treatment infrastructure that is contained in a small space and consist of mainly prefabricated components. Treatment is accelerated by various mechanical and chemical dosing equipment. Technology used are in some instances proprietary to the manufacturer, but it can also be miniaturised versions of conventional activated sludge or biofilter plants. Package plants require the same operational care as large plants and cannot be left to operate alone. Package plants also face unique challenges, mainly due to the lack of capacity of the smaller plants to attenuate variations in load or flow, which result in process instability 22. Approval for the construction and operation of package plants must be obtained from the responsible Water Services Authority for the area in which the package plant is to be provided. K How will Treated Effluent be managed? Treated water can be discharged to natural water courses, can be irrigated or, in some cases, can be evaporated. Direct re-use of the water can also be considered. The discharge of water from large plants (>2ML/d), must generally be returned to the catchment due to legislative requirements 23. It is necessary to liaise with the Department of Water and when planning plants of this size in order to obtain the specific requirements of the plant and its discharge as this will vary from site to site. Irrigation systems are typically considered for small plants (<500m 3 /d) where the treated water quality does not meet the required quality standards for catchment discharge. Irrigation activities are subject to a number of requirements, which are referenced in more detail later in this guideline. The water quality requirements for irrigation from treatment plants between 500 and 2000m 3 /d are onerous 24. It is easier to discharge water to the catchment from these treatment plants. Liaison with the Department of Water and for these schemes is required. Evaporation of treated water is often the unintended consequence of operating an oxidation pond far below the design capacity in warm climates. This is not ideal as the evaporated water could potentially have been utilised elsewhere. Evaporation is rarely an intended design outcome as the costs of sizing ponds for evaporation are prohibitive. By law treated effluent must be sampled and monitored prior to reaching the point where it merges with naturally occurring water courses or is disposed of in any other way. The disposal approach adopted must make sampling possible. The impact of the discharge must also be made possible by allowing access to sample points upstream (not impacted by the discharge activity) and downstream of the discharge activity. K How will Greywater be managed? Greywater is defined as all domestic wastewater other than toilet water. This refers to waste water from baths, sinks, laundry and kitchen waste. Greywater is not only produced on private residential stands, but also at communal washing places, businesses, and taxi stands. Consider the potential use and/or disposal of greywater. It is important to note that kitchen greywater is excluded from re-use considerations as it is highly polluted with organic materials, including fats and oils 25. Although greywater is supposed to not contain harmful excreted pathogens, it sometimes does: washing babies nappies, for example, automatically contaminates the water. Similarly, infectious diseases may be spread via P a g e 32

33 greywater distribution. Greywater, does however contain considerably fewer pathogenic micro-organisms and has a lower nitrate content than raw sewage. It also has a more soluble and biodegradable organic content. Greywater has the added advantage of being a handy alternate water source to utilise in place of potable water in a situation where the reduced water quality can be tolerated, such as used for toilet flushing. Greywater use holds a significant promise as a water use reduction measure. Greywater should however not be considered for potable purposes and must always be used with considerable care. Health aspects of greywater The health aspects related to grey water management have to receive critical consideration before a substantial commitment is made to a particular greywater handling strategy. Communal greywater strategies are typically subject to a higher level of failure than systems designed on a dwelling-by-dwelling basis as the owners take responsibility for their own water quality. However, on a communal basis, the same level of care may not exist. Even though the per household water consumption in un-sewered settlements is low, the high housing density results in high overall greywater generation rates. This, combined with the high concentration of pollutants in greywater in informal settlements, the lack of proper waste and wastewater infrastructure, and the widespread mingling of different waste streams, has led to doubts concerning the possibility of the safe use of greywater in these settlements (Rodda, et al., ). Mosquito breeding can take place where ponds are created by casual tipping of greywater, and conditions favourable for the development of parasitic worms could also be created in this way. Infection can also occur in constant muddy conditions. In order to reduce potential health hazards, it is of the utmost importance to choose the right option for greywater management. This includes the formalisation of surface and sub-surface drainage infrastructure leading the water toward a treatment or, alternately, a disposal point. Greywater as a resource The value of greywater as an additional water source cannot be denied, particularly in areas where the availability of water is restricted or the cost of water is prohibitive. It is imperative that all measures be considered to retain the water for alternative use while ensuring all safety concerns are addressed. In addition to using greywater as a source for irrigation, consideration can also be given to using the water in dwellings in non-contact situations, such as flushing of toilets. The utmost care and consideration must be taken in the decision making process to account for the risks involved in utilising greywater as a resource. Under no conditions must greywater be utilised in homes in untreated form, or must greywater be utilised if a household is not fully serviced due to compounded risk 27. P a g e 33

34 Figure K.1: Permissibility of greywater use 28 Institutional greywater re-use remains problematic at present as a number of unknown issues still preclude municipalities from using greywater as a water resource 29. The unknown issues related to the quality of the water, as well as personal hygiene issues around greywater handling, remain problematic 30. Greywater as a source of irrigation water Guidelines for the sustainable use of greywater in small-scale agriculture and gardens in South Africa have been published (Rodda, et al., ). Health and risk management is a particular focus of these guidelines. These are used to guide the decision on how to deal with greywater. The decision tree, based on a minimum analysis of water quality that is inclusive of analyses for electrical conductivity (EC), sodium adsorption ratio (SAR), ph and Escherichia coli, is copied below for ease of reference. The full text in support of the decision tree can be found in Rodda et. al. (2010) 32. The water quality thresholds for acceptance of the water quality as compliant to standards can also be found in Rodda, et. al. (2010). P a g e 34

35 Figure K.2: Decision Flow Chart for Management of Risks associated with Greywater use in Category 2 (Minimum Analysis) (Rodda, et al., 2010) The list of restrictions associated with the decision tree is copied below. P a g e 35

36 Figure K.3: Risk Management Restrictions in Response to the Decision Flow Chart for Greywater Use in Category 2 (Rodda, et al., 2010) A more comprehensive decision tree is provided by the guideline if an extended suite of analyses can be performed on the greywater. The extended suite covers the requirements of the minimum analysis and adds Boron, Chemical Oxygen Demand (COD), Oil and grease, and Suspended solids. The full text in support of the decision tree based on a full water quality analysis can be found in Rodda, et. al. (2010). The water quality thresholds for acceptance of the water quality as compliant can also be found in Rodda, et. al. (2010). P a g e 36

37 Figure K.4: Decision Flow Chart for Management of Risks Associated with Greywater use in Category 3 (Full Analysis) (Rodda, et al., 2010) P a g e 37

38 Figure K.5: Risk Management Restrictions in Response to the Decision Flow Chart for Greywater use in Category 3 (Rodda, et al., 2010) Summary requirements for irrigation of greywater are the following: Children and animals should not be allowed to drink or play in greywater. Hands must be washed after working with greywater. Greywater must not be used on crops that can be consumed raw. Greywater, which has been contaminated by faecal matter (i.e., from washing nappies, etc.), should not be used. Greywater should not be used in a person in the household is suffering from an infectious disease. Greywater should not be stored for more than 24 hours to avoid purification of the water. Ponding and uncontrolled discharge of greywater from the collection site must be prevented. P a g e 38

39 All water fixtures and infrastructure, whether on private or public property, must be signposted clearly to indicate that the water is unsafe for human and animal contact and consumption. Use purple piping to indicate conveyance of non-potable water to prevent accidental cross-connection of systems. Greywater as a source for flushing of toilets Use of greywater as a source of flushing toilets is an attractive option to consider in higher density urban environments. Pilot studies have, however, shown that although technically feasible, it is economically difficult to justify and socially unacceptable due to odour and other aesthetic concerns (Ilemobade, et al., ). The aesthetic concerns can be overcome by treating the water prior to re-use, but this will result in a project with an economic viability that is weakened further. Careful consideration should be given prior to the implementation of such a re-use project. Greywater treatment Greywater is usually unsuitable for discharging into rivers and streams. Treatment is required that is based on conventional wastewater treatment. Depending on the level of contamination, it may also be possible to achieve improved water quality from treatment in an artificial wetland or pond system. The treatment of greywater is not considered to be within the scope of this manual and specialist support must be obtained. K How will Sludge (biosolids) be managed? Sludge (Biosolids) as a resource Treated sludge (biosolids) produced as part of the wastewater management system should be regarded as a resource rather than a waste product. The most valuable utilisation of biosolids is a fertiliser in agricultural activities. The table below is taken from international literature (Metcalf and Eddy, ) and provides an indication of the value of treated sewage sludge as a resource. South African data indicators are included for comparison (Water Research Commission, ). Table K.4: Comparison of Nutrient Levels in Wastewater Sludge (Biosolids) Product Fertilisers in typical agricultural use (percentages may vary dependent on product) Typical values for stabilised wastewater sludges (based on total solids) Organic content Nutrients (%) Nitrogen Phosphorus Potassium Not available 5% 10% 10% Not available 3.3% 2.3% 0.3% Typical South African values 40-70% % Take care in handling the biosolid mass appropriately as it can also be a source of contamination. As with wastewater treatment, the treatment and conversion of wastewater solids to biosolids is a specialist subject and experts need to be consulted. Some general comments are made for the purpose of this guideline. Valuable biosolids can be sourced from on-site, as well as off-site, wastewater treatment systems. Off-site treatment systems have the benefit of scale. Systems of increasing complexity can be employed at larger facilities under the guidance of subject matter experts in order to derive biosolids of the highest quality. In on-site systems it is advantageous to keep the system as simple and as robust as possible as the responsibility of operation of these systems will be at household level. Urine diversion based systems are ideal as this results in a biosolids mass P a g e 39

40 that is easily dried and safely handled. Systems that contain large amounts of water, such as pit toilets and septic tanks, are more complex and, in some cases, it may be more sensible to collect the biosolids from these systems to be treated and converted to a useful resource at a centralised treatment, or for disposal in a sustainable manner. South African Guidelines for Utilisation and Disposal of Wastewater Sludge Guidelines have been published by the Water Research Commission for the beneficial use and safe disposal of biosolids in South Africa. The documents provide valuable background on sludge utilisation practices within the relevant regulatory frameworks and this will have a significant impact on the intended project from the planning stages onward. These guidelines consist of the following five documents: Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 1: Selection of management options (WRC Report No. TT 261/06)36. Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 2: Requirements for the agricultural use of wastewater sludge (WRC Report No. TT 262/06)37. Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 3: Requirements for the on-site and off-site disposal of sludge (WRC Report No. TT 349/09)38. Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 4: Requirements for the beneficial use of sludge at high loading rates (WRC Report No. TT 350/09)39. Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 5: Requirements for thermal sludge management practices and for commercial products containing sludge (WRC Report No. TT 351/09)40. The guidelines and recommendations are based on a sludge classification system, which ranks sludge quality based on its level of sterilisation (biological class), its stability, and its pollutant content that focusses mainly on metal content. The table below provides the classification matrix: Table K.5: Sludge Classification System Biological Class A B C Stability Class Pollutant Class a b c The sludge classification system views sludge in terms of the three quality indicators and prescribes usage restrictions based on the nature of the pollution risk. The classification for a well sterilised sludge, which is very stable with a low chemical pollutant content, is A1a. Very few restrictions are applied by the guideline to the utilisation of such a sludge. A classification of C3c denotes the worst quality sludge to which stringent disposal criteria will be applied. A classification of A2B will typically be a well disinfected sludge that is not ideally stabilised and will contain some pollutants. This utilisation of this sludge will be subject to more stringent control measures than those for a A1a sludge. The WRC guidelines offer detail on how each quality boundary is defined. According to the Water Research Commission (WRC) guideline documents, the characterisation and classification should be repeated if any major sludge production or processing changes occur that could affect the classification. This could include the following: (a) (b) When major upgrades or extensions are implemented at the wastewater treatment plant. When major operational changes are made at the wastewater treatment plant. P a g e 40

41 (c) When the raw influent quality to the wastewater treatment plant changes in such a way that the sludge quality could be affected. Although the WRC guidelines do take into account the regulatory requirements associated with sludge use and disposal, these change on an ongoing basis. It is therefore necessary to remain abreast of all regulatory changes. Make use of a sludge treatment specialist to assist in this regard. K How will Stormwater Ingress be reduced? Stormwater ingress is defined as the infiltration of stormwater and groundwater into urban sewerage systems. The amount of stormwater ingress is rainfall dependant. Sewer systems are usually designed to handle some stormwater ingress. Allowance for stormwater ingress of 15% - 30% of the dry weather flow is the generally acceptable standard. The National Building Regulations (SANS P:2010) 41, however, states: Regulation P3(2): No person shall cause or permit stormwater to enter any drainage installation on any site. The general cause of stormwater ingress is the inadequate design of certain system components and direct discharge of stormwater into the sewers. Examples are listed below: Illegal house down-pipe (gutter) connections to municipal sewers. Open gullies serving mainly as sullage disposal (this is typical in most formal and informal townships). Unsealed and open manholes due to theft of manhole covers or damaged covers. Manhole below flood line. Roots penetrating joints. Unwise man-made stormwater channelisation (e.g. road crossings and culverts). Un-attended overgrown vegetation in natural channels, as well as a high groundwater table. Leaks from cisterns and taps. The presence of leaks in pipes with insufficient maintenance and rehabilitation increases stormwater ingress. Faulty pipe joints due to improper construction or deterioration. Inadequate design of certain system components - break or open joint. Infiltration of groundwater and stormwater increased during wet seasons. Other factors include the following: Undulating topography that may lead to easy flooding. Re-considered flood lines. Swimming pools, if additional stormwater or backwash water is linked directly to the sewers. Ground movement due to removed mine dumps which destroy the continuity of sewers. Thunderstorms of short duration and higher intensities in various locations. Stoppages and clogging of sewers causes more frequent overflows during storms and high levels of stormwater ingress. P a g e 41

42 The need to reduce the quantity of stormwater ingress in South African sewer systems is increasingly being recognised as a priority for a number of reasons, including the following: It is unhealthy for both the environment and humans to be exposed to repeated overflows of untreated sewage. Holding untreated sewage in stormwater retention dams creates other human and environmental health risks. There are cost related implications (the more effluent a works receives, the higher the treatment costs; also bulk sewer lines have to be upsized, which is highly capital intensive). Capital expansion programmes may need to be considered at wastewater treatment works if they are to be able to deal effectively with storm surges, as the works needs capacity to absorb peak flow and not average flows if spillages are to be completely avoided. It is illegal in terms of the National Water Act 42 for a municipality or wastewater treatment works to discharge untreated or partially treated sewage into receiving waters. Stormwater and surface inflows account for dramatic peak flows in the sewer system (up to three times the average dry weather flow). Extraneous flow can reduce the originally designed capacity of a sewage collection system and negatively affect operation of the entire waterborne sanitation system, including the wastewater treatment component (spillages/overflows and increased treatment and pumping cost). This could in turn increase the potential of pollution and health risks (cholera). The effluent during extraneous flows may not comply with the required standards due to the higher pollution loads and the partially treated water at the treatment works. K What Institutional and political factors are involved? The following institutional and political factors needs to be considered in planning sanitation services to the project/development: Urban planning (regulations and enforcement). Building regulations and bylaws. Institutional arrangements (responsibilities, coordination). Political will. Institutional structure (responsibilities, oversight). Policies (laws, regulations, institutional framework). Priority (given to sanitation by decision makers). Willingness and ability by the service provider to operate and maintain the system. K What is the economic feasibility of the system? The following economic factors needs to be considered: Availability of funding. Tariffs. Willingness to pay for the service. P a g e 42

43 Ability to pay income levels. Cost of construction (capital cost). Availability of construction materials, parts etc. Recurrent costs (operation and maintenance). Rehabilitation / redundancy costs. Many people in developing areas are not only unable to afford sophisticated sanitation systems, but these systems may also be technically inappropriate for them. At the same time, the sanitation alternative with the lowest overall cost may also be inappropriate because of the community s cultural background or because of its unwillingness or inability to operate the system correctly. When the costs of different systems are compared, all relevant factors should be taken into account. Examples of costs often ignored are the following: (a) (b) (c) (d) (e) (f) A pit toilet may require relocation on the site, or emptying every 4-10 years, depending on its capacity. Sludge from septic tanks and other on-site sanitation systems may require treatment before disposal. Training may be required for operators and maintenance staff. The community may have to be trained in the use of the system for it to operate effectively. Regional installations such as treatment works may be required. Special vehicles and equipment may be required for operation or maintenance. To keep costs to a minimum, several issues are relevant: (a) (b) (c) (d) (e) Who pays what? For example, if a government institution or development agency is paying all of the capital costs, then the community will generally demand the most expensive, highest level of sanitation. If, on the other hand, the capital costs are to be recovered from the community, then its choice of sanitation system may be quite different. The lack of income to pay for maintenance could have serious financial implications as well as health risks. Would the community prefer lower capital costs and higher maintenance costs, or vice versa? Will the cost comparison between options change if all the potential benefits and costs are included? Are any of the costs incorrectly or dishonestly represented? For example, have capital grants or soft loans been ignored? Do certain services have hidden subsidies that produce misleading comparisons (for example, where treatment costs are paid by regional authorities)? Impact of free basic services? Where finance is limited, developers should consult the community, determine its priorities, and seek ways to achieve the improvements desired. This may take extra time, but a motivated community will contribute more to successful project implementation and, perhaps more importantly, to the long-term operation and maintenance of the system selected. K Is operation and maintenance of infrastructure considered? For the sanitation infrastructure to perform at its required performance and achieve its expected useful life, operational and maintenance procedures need to be planned for. Maintenance procedures include inspections, monitoring, repairs and replacement of infrastructure. The planning of infrastructure should always consider ways P a g e 43

44 in which to aid in the maintenance and operation of the infrastructure, such as ease of access and enough space to for maintenance staff and equipment. Maintenance should be done on a preventative and proactive basis rather than on a reactive basis, and needs to be included in the planning of the infrastructure. It is also important to note the authority responsible for O&M, as the type of considerations are different. Two of the general types are shown below: O&M responsibility Household or community Institutional Considerations Extensive user education program to ensure adequate O&M Effective system monitoring and cost recovery from consumers Operation and maintenance costs are generally not properly accounted for in the yearly Operational Expenditure (OPEX) and Capital Expenditure (CAPEX) budgets. Municipalities and service providers should allocate sufficient funds to account for increase in maintenance costs per year and not just based on inflation, as costs related to maintenance, fuel, salaries, and exchange rate increase at higher rates than inflation. The WRC waterborne sanitation O&M guide (Waterborne Operation and Maintenance Guide, Van Vuuren and Van Dijk, 2011) 43 contains information on operation and maintenance procedures for waterborne sanitation systems. K.4 DESIGN CONSIDERATIONS K.4.1 Designing of Disposal and Conveyance infrastructure K General Considerations The following considerations are universal in the design of sanitation infrastructure: Safe access. Inclusion of hygiene related infrastructure including provision for appropriate disposal of menstrual material (waste bins with lids that are emptied regularly) or private washing facilities. Privacy including the provision of doors and the appropriate orientation of entrances. In all case the design of the facility must adhere to the norms and standards as issued and updated by the Department of Water and 44. K Ventilated Improved Pit (VIP) Toilets VIP toilets do not require water for conveyance and are easily constructed. It mainly consists of the following components: Substructure (Pit), Cover slab, Superstructure and some peripherals (seat, ventilation pipe, fly screens, handwashing arrangements). The following design aspects needs to be considered and incorporated: P a g e 44

45 Table K.6: Ventilated Improved Pit Toilets: Design Aspects Main Component Sub-Component Materials Design Aspects Substructure Pit In highly permeable soil (dry pit) OR In low permeable soil (wet pit) Can be circular or rectangular (circular more stable) Not closer than 2.75 m from boundary fence (for maintenance purposes) More than 30 m away and downhill from borehole/well. Pit Lining Pit Collar Concrete blocks, open jointed brickwork, cement-stabilized soil blocks, masonry, stone rubble, perforated oil drums, rot- resistant timber, wire-mesh supported geofabrics Reinforced concrete or bricks/ stone in cement mortar Volume of Pit (m 3 )= P x N x C +0.5 where, P = number of people (No) N = design life (yr) C = accumulation rate (m 3 /person/yr) C (dry pits) = 0.06 m 3 /yr C (wet pits) = 0.04 m 3 /yr Only upper parts in stable soils (minimum 0.5 m from top) Partial or full lining depending on soil stability and groundwater presence. Top sections of pit walls shall be impervious to passage of water. Stormwater and soil ingress to be prevented (lining to extend > 75 mm above ground level) Must be sufficient to support cover slab Cover Slab Reinforced concrete, Ferro-cement, bricks, treated timber poles Must be properly supported. Where pit is without collar- 200 mm wider than pit. On good support surface 50 mm support is adequate. Reinforced slabs of 75 mm thickness with 6 mm bars at 150 c/c are adequate. 5:1 Sand/cement mix is sufficient. Keep slab damp for 5 days after pour. Minimum of 75 mm above ground level. Maximum of 1 m above ground level. Holes for squat-hole and vent pipe to be formed. 5% slope towards squat-hole for drainage. Superstructure General Materials depend on availability and affordability To ensure privacy, comfort and shelter Shall be waterproof Rectangular, Circular or spiral shaped (no door required) Movability of the structure to be considered when pit cannot be emptied. Floor area = 0.8 to 1.5 m 2 (2.35 m 2 for VIDP) Walls Brick and blocks preferred.ferrocement not advised. Must be waterproof Keep out vermin Partially darkened structure preferred Galvanised wire for vent pipe and roof to be provided P a g e 45

46 Main Component Sub-Component Materials Design Aspects Ventilation openings to be provided (without risking privacy). To be > 3 times the area of ventilation pipe (0.15 m 2 adequate). To be screened. Door Wood, Steel, composite materials (dependent on availability and affordability) Should preferably face the house. Outward opening results in smaller inside area required. Inward opening decreases risk of damage by wind. Lockable by key on outside. Catch on inside Roof Reinforced concrete, corrugated iron, clay/fibre cement tiles, thatch, palm leaves etc. dependent on availability and affordability) Must be waterproof Tied to walls to resist uplift forces To slope away from door Seat Brick, mortar, mud, plastic, fibreglass, ceramic or timber Beneficiaries to decide Maximum width of slab opening of 200 mm Seat opening 250 mm to 300 mm Seat height 300 to 500 mm Ventilation pipe PVC, PVCu, bricks, blockwork, hessian (steel mesh supported) etc. Should be painted black. Preferably orientated towards the sun Should be straight to attract flies outwards and maximize airflow. Preferably on outside of superstructure extending more than 500mm above the highest point of the roof. At least 2 m away from anything that can impede airflow (trees, structures etc.) Fly Screen Corrosion resistant material. Hand washing General Considerations (Glass fibre, aluminium, stainless steel, brass, etc.) 1mm to 1.5 mm mesh openings Required addition to toilet to improve personal hygiene. Running water within 1 m of the toilet. To be located to rear end of plot Downwind of residential structure, not nearer than 10 m. Orientated to ensure privacy and cultural beliefs (if applicable). Appropriate waste disposal to be planned and designed for (incl, consideration of menstrual health needs). K Urine diverting dry toilet (UDDT) The functional design elements of the UDDT are: source separation of urine and faeces; waterless operation; and ventilated vaults or containers for faeces storage and treatment. The primary advantage of UDDTs, as compared P a g e 46

47 to conventional dry toilets like ventilated improved pits (VIP) toilets, is the conversion of faeces into a dry odourless material. This leads to an odour and insect free toilet that is appreciated by users and allows simple removal and less offensive and safer handling of the faecal material once the storage area has filled up. Comprehensive design details can be obtained at technology-review-of-uddts-18-june-2013.pdf 45. K Pour Flush A Pour Flush is toilet fitted with a trap providing a water seal. It is cleared of faeces by pouring in sufficient quantities of water to wash the solids into the pit and replenish the water seal. The water seal prevents flies, mosquitos and odours reaching the toilet from the pit. The pit may be offset from the toilet by providing a short length of pipe or covered channel from the pan to the pit. The pan of an offset pour flush toilet is supported by the ground and the toilet may be within, or attached to, a house. More detail and information available at Figure K.6: Example of Pour Flush System 47 K Aqua-Privies An Aqua-privy is a toilet with the superstructure located directly above (or slightly offset of) a watertight holding tank. The tank is kept topped up with either potable water, rainwater or greywater. The overflow of the tank can be connected to either a solids-free sewer system or a soakaway. P a g e 47

48 Figure K 7: Example of Aqua Privy K Small Scale Septic and Leach Field Systems Septic tanks form part of the sewage disposal system that can be connected to the outlet of any water-flush latrine. An advantage of a septic tank is that the household has all the advantages of the conventional waterborne sanitation system without the need for extensive/ expensive wastewater treatment, except for the periodic removal of sludge. The cost of the system is carried by the household. The South African Bureau of Standards (SABS) has published a valuable source of information on Septic Tanks systems as part of the standard on Water Supply and Drainage for Buildings. This information is included in Annexure B of SANS : A typical design of a septic tanks and a sectional view of the soakaway is shown below. P a g e 48

49 Figure K.8: Example of Septic Tanks System (CSIR, 1991) A good design will typically include the following: A liquid depth of between 1.0 m and 1.8 m. Rectangular shape with length three times the width. The first compartment should be twice the volume of the second compartment. Inlet and Outlet arrangements It is recommended that the inlet to the first compartment be a sanitary T-piece or baffle wall. The vertical portion of the T-piece should extend below the surface liquid, to minimize incoming turbulence. The lower vertical arm of the inlet should be submerged between 30% and 40% of the liquid depth. The upper vertical arm of the T-piece should extend at least 50 mm above the crown of the inlet and end 15 mm below the cover of the tank. The invert of the inlet pipe should be between 50 mm and 75 mm above the surface of the liquid (SANS :1993). 49 The sewage in the tank passes from the first compartment to the second through a mid-depth opening. The outlet from the second compartment should also be a sanitary T-piece or baffle wall. All arms of the T-piece should have an inside diameter of half to three-quarters of that of the inlet pipe, thus damping peak inflows. The invert of the outlet pipe should be between 50 mm and 75 mm below that of the inlet pipe (SANS :1993) 50. Some design criteria indicate that septic tanks shall have an effluent filter placed at the outlet in place of the outlet baffle. The purpose of the filter is to trap suspended solids that are not heavy enough nor have had time enough to sink to the bottom of the tank (as in a tank that hasn't been pumped in a timely manner and contains significant P a g e 49

50 amounts of material that reduce its effective volume). Filters must however be periodically cleaned so that they do not plug and back sewage into the house. Capacity of tank The capacity of the septic tank should be adequate to store sludge and scum, as well as to retain liquid for at least 24 h just prior to the tank requiring desludging. The flow to the septic tank is directly related to the level of water supply to the residential building. Therefore the level of water supply to the building could be used to determine the capacity required. There are basically three methods to determine the capacity of the tank (SABS, 1993): For non-residential systems, estimate the average daily flow from the establishment. The capacity of the septic tank has to be 3 times the estimated average daily flow. For dwellings or dwelling units with full in-house water reticulation relate the capacity of the septic tank required to the number of beds or bedrooms (see SANS :1993 (SABS (1993) 51 ). For special residential systems such as multi-home systems or dwelling units without full in-house water reticulation, relate the capacity of the septic tank required to the number of persons to be served by the system (see SANS :1993 (SABS (1993) 52 ). The tank is sized to provide sufficient capacity to limit the periodic removal of sludge to between 2 years and 5 years, i.e. creating user convenience and being economical. Absorption field/soakaway The septic tank only partly treats sewage and it is the function of an absorption field or leaching field or soakaway to provide the final treatment and disposal of the effluent in a safe manner. The objective of an absorption-field design should be to maximize the use of soil surface that is expected to provide the highest infiltration rate. A number of criteria will influence the design of a suitable soakaway such as the following: General topography and flood plains. Land slopes. Vegetation. Soil absorption rate. Soil texture and classification. Estimated flow rate from tank. The absorption field (soakaway) is the most important part of the onsite sewage disposal system. The absorption field is where the actual disposal of the liquid occurs. A large variety of absorption-field designs exists. Typically, an absorption field consists of a series of sewage distribution lines placed in trenches topped with soil (Figure K.8). The conventional design uses a perforated pipe buried in a gravel-filled trench and backfilled with topsoil. The second is a newer design using plastic leaching chambers instead of gravel to hold the liquid effluent until it is filtered through and absorbed by the surrounding soils. Many variations and different types of absorption fields are in use. The soil in the absorption field absorbs and filters the partially treated liquid sewage. Other bacteria that live in the soil attack and digest the liquid. After additional bacteriological action and filtering in the soil, the once liquid sewage is basically water that returns to natural underground water, is evaporated to some extent or taken up by plants. The disposal area should be large enough to absorb the liquid effluent discharged to it. If the area provided is too small, liquid sewage will ooze to the surface or back up into the house through the sewer, P a g e 50

51 eventually discharging into the house at the lowest plumbing fixture. This can become a nuisance and a health hazard for the entire community. Consult SANS :1993 (SABS (1993)) 53 for guidance with the determination of the absorption characteristics and related sizing of the soakaway system. K Anaerobic Digester This is basically a modification of the aqua-privy system. Commercial systems have been developed which require minimal water for flushing. The retention time of the liquid in an anaerobic digester is usually 30 to 50 days, which improves pathogen removal. The system can be connected to a solids-free system which removes the effluent for off-site disposal or to a soakaway keeping the effluent on-site and underground. K Composting Toilet In a composting toilet, excreta fall into a watertight tank to which ash or vegetable matter is added. If the moisture content and chemical balance are controlled, the mixture will decompose to form a good soil conditioner in about four months. Pathogens are killed in the dry alkaline compost, which can be removed for application to the land as a fertilizer. There are two types of composting latrine: in one, compost is produced continuously, and in the other, two containers are used to produce it in batches. More information available at Figure K.9: Composting Latrine K Vacuum Sewer System Vacuum sewers use differential air pressure to move the wastewater. A central vacuum pump station is required to maintain a vacuum (negative pressure) on the collection system, see Figure K.10. The system requires a normally closed vacuum-gravity interface valve at each entry point to seal the lines, so that the vacuum can be maintained (WEF, 2008). These valves, located in valve pits, open when a predetermined amount of wastewater accumulates in collecting sumps. The resulting differential pressure between the atmosphere and vacuum becomes the driving force that propels the wastewater towards the vacuum station. P a g e 51

52 Figure K.10: Vacuum Sewer System (adapted from AIRVAC, 2005b) For more detail refer to the WRC Waterborne Design Guide by Vvan Vuuren and Van Dijk, K Small Bore Sewer System Small-bore systems, or small diameter gravity (SDG) sewers, or solids-free sewers (SFS) are also called septic tank effluent gravity (STEG) sewers. These systems convey effluent by gravity from an interceptor tank (or septic tank) to a centralised treatment plant or pump station from where it is conveyed to another collection system. Another variation on this alternative sewer system is the septic tank effluent pumping (STEP) concept. All these systems utilise smaller-diameter pipes placed in shallow trenches following the natural contours of the area, thus reducing the capital cost of the pipe, as well as excavation and construction costs. Figure K.11: Small Bore Sewer System For more detail refer to the WRC Waterborne Design Guide by Van Vuuren and Van Dijk, K Settled and Simplified Sewers Simplified sewers is an off-site sanitation technology that removes wastewater from the household environment. Conceptually it is the same as conventional sewers, but with conscious efforts made to eliminate conservative P a g e 52

53 design features and to match design standards to the local circumstances. Many of the conventional sewer design standards, such as minimum diameter, minimum slopes, and minimum depths, are relaxed in shallow sewer systems and community-based construction, operation and maintenance are allowed. For more detail refer to the WRC Waterborne Design Guide by Van Vuuren and Van Dijk, K Communal/ Public Toilets Sanitary facilities for communal use, or in public spaces, should be designed in accordance with the Code of Practice for the application of the National Building regulations (SANS ) 58 and the regulations, norms and standards of the DWS. K Waterborne Full or conventional waterborne sanitation consists of a flush toilet with a house connection and reticulation to a bulk sewer system that transports sewage away from a household to a wastewater treatment facility. Waterborne sanitation requires a reliable and uninterrupted water connection and supply, as well as formal and permanent settlement. Approximately between 6 to 13 litres of water is required to flush the toilet each time it is used. The following sections are applicable to the design and construction of waterborne sewerage reticulation for residential areas (excluding the design of the waste water treatment works), where the houses are to be provided with full waterborne sanitation. Certain basic guidelines applicable to non-gravity systems (i.e. pump stations and rising mains) are included, but detailed design criteria for these systems are not included, as they are regarded as bulk services. Except in cases where illustrations are provided, the reader is referred to various figures in the relevant sections of SANS This design of waterborne sewers is split into three parts as shown below in Figure K.12:. Guidelines for the design considerations of these three aspects of waterborne sanitation infrastructure is provided in this guideline document. P a g e 53

54 Figure K.12: Design Aspects of Waterborne Sewer Systems K.4.2 Design Flow Sewers should be designed to flow full at the peak design flow to ensure provision for infiltration (groundwater and stormwater) and possible peaks to ensure overflow of sewers are avoided. The design flow consists of a base flow (infiltration and domestic leakage), a domestic flow and a spare capacity (see figure below). P a g e 54

55 Figure K.13: Sewer Outflow Hydrograph Domestic flow calculation The design flow is directly dependent on the land use of the study area. There are several methods to calculate the domestic flow, including leakage. Three methods are generally used: Unit hydrograph method If the ADCD is unknown but land use and PDDWF is known ADCD inflow method If the ADCD, percentage ADCD sewer contribution and land use is known Sewer flow and peak factor method - If the PDDWF and land use is known (traditional method) The three methods are discussed in detail below. The unit water consumption per land use category, the respective unit hydrographs per land use category (see also Table K.8). ADDWF and ADCD contribution to the sewer flow are given in P a g e 55

56 Table K.7. Domestic base flow (leakage from cisterns and taps) is generally included in the calculation and accounts for ± 65% of the measured total base flow (steady flow) in the system, also referred to as minimum night flow. The base flow rates for each UH type is listed in Table K.8. P a g e 56

57 Table K.7: Demands and Hydrographs for Different Land Use Categories Land use Density #¹ Unit Water consumption (ADCD) Sewer flow (PDDWF) units/ha kl/ha/d kl/unit % ADCD kl/unit Unit Hydrograph High density, small sized stands 20 to 12 kl/unit to % to 70% 0.48 to 0.56 UH5 Residential Medium density, medium sized stands Normal density, large sized stands 12 to 8 kl/unit 8 to 5 kl/unit to to % to 60% 60% to 55% 0.56 to 0.60 UH to 0.72 UH2 Low density, extra large sized stands 5 to 3 kl/unit to % to 40% 0.72 to 0.80 UH1 Low Income Housing High density, small sized stands Medium density, mediumsized stands 20 to 12 kl/unit 12 to 8 kl/unit to to % to 85% 85% to 80% 0.36 to 0.43 UH to 0.48 UH4 Informal housing Dry 30 to 20 kl/unit n.a. n.a. n.a. Upgraded with Waterborne 30 to 20 kl/unit to % to 90% 0.29 to 0.36 UH4 High density 60 to 40 kl/unit to % to 90% 0.38 to 0.41 UH5 Group/Cluster housing Medium density 40 to 30 kl/unit to % to 85% 0.41 to 0.43 UH5 Low density 30 to 20 kl/unit to % to 80% 0.43 to 0.48 UH5 Very high density 100 to 80 kl/unit to % to 98% 0.20 to 0.29 UH6 Flats High density 80 to 60 kl/unit Medium density 60 to 50 kl/unit to to % to 97% 97% to 96% 0.29 to 0.34 UH to 0.38 UH6 Low density 50 to 40 kl/unit to % to 95% 0.38 to 0.43 UH6 Agricultural Holdings Including irrigation < 3 kl/unit % 1.60 UH1 Domestic water only < 3 kl/unit % 1.60 UH1 Golf Estate - Excl. Golf course water requirements < 3 kl/unit % 1.20 UH2 Retirement Village 20 to 12 kl/unit to % to 70% 0.48 to 0.56 UH5 Business/Commercial FSR = 0.4 Industrial FSR = 0.4 Government Institutions FSR = 0.4 Warehousing FSR = 0.4 Institutional FSR = 0.4 Municipal Services FSR = 0.4 Educational FSR = 0.4 kl/100m² #² % 0.52 UH7 kl/100m² # % 0.32 UH10 kl/100m² # % 0.32 UH9 kl/100m² # % 0.24 UH11 kl/100m² # % 0.48 UH9 kl/100m² # % 0.48 UH9 kl/100m² # % 0.39 UH8 Cemeteries n.a. kl/ha 12 n.a. n.a. n.a. n.a. P a g e 57

58 Residential Low density Residential Normal density Residential Medium density Low Income Housing Group/Cluster Housing Flats Business/ Commercial Educational Municipal Services/ Institutional Industrial Multipurpose/ Mixed/Other Agricultural Holdings None (eg. P.O.S) Unknown Large Users (per kl ADCD) K Land use Density #¹ Unit Water consumption (ADCD) Sewer flow (PDDWF) units/ha kl/ha/d kl/unit % ADCD kl/unit Unit Hydrograph Parks n.a. kl/ha 12 n.a. n.a. n.a. n.a. Sports fields n.a. kl/ha 12 n.a. n.a. n.a. n.a. Notes : #¹ - Gross Area of 0.8 #² - Floor area Notes: (i) (ii) In the above figure some of the unit demands is based on a dwelling unit with a floor area of 100m 2 and a floor space ratio (FSR) of 0.6. If a FSR other than 0.6 is prescribed, the flow figure above should be adjusted accordingly. Maximum density allowable under the scheme is the overriding factor. If unit design flows are, instead, obtained from actual flow-gauging of adjacent settlements of similar nature, these unit design flows should not exceed those given above. Also, the local authority should be consulted to obtain area specific sewer flow contribution data if available. Table K.8: Sewer Unit Hydrographs DEFINITION OF UNIT HYDROGRAPHS Unit Hydrograph No. UH1 UH2 UH3 UH4 UH5 UH 6 UH7 UH 8 UH9 UH1 0 UH1 1 UH1 2 UH1 3 UH1 4 UH1 5 Land use(s) following typical UH pattern Hr Dimensionless flow ordinates (relative to hydrograph peak) P a g e 58

59 Residential Low density Residential Normal density Residential Medium density Low Income Housing Group/Cluster Housing Flats Business/ Commercial Educational Municipal Services/ Institutional Industrial Multipurpose/ Mixed/Other Agricultural Holdings None (eg. P.O.S) Unknown Large Users (per kl ADCD) K DEFINITION OF UNIT HYDROGRAPHS Unit Hydrograph No. UH1 UH2 UH3 UH4 UH5 UH 6 UH7 UH 8 UH9 UH1 0 UH1 1 UH1 2 UH1 3 UH1 4 UH1 5 Land use(s) following typical UH pattern Hr Dimensionless flow ordinates (relative to hydrograph peak) Hydrograph Peak % of ADCD 40% 55% 60% 70% 80% Unit hydrograph parameters (L/min) % 80% % 80% 80% 60% 80% 0% 55% 60% P a g e 59

60 Residential Low density Residential Normal density Residential Medium density Low Income Housing Group/Cluster Housing Flats Business/ Commercial Educational Municipal Services/ Institutional Industrial Multipurpose/ Mixed/Other Agricultural Holdings None (eg. P.O.S) Unknown Large Users (per kl ADCD) K DEFINITION OF UNIT HYDROGRAPHS Unit Hydrograph No. UH1 UH2 UH3 UH4 UH5 UH 6 UH7 UH 8 UH9 UH1 0 UH1 1 UH1 2 UH1 3 UH1 4 UH1 5 Land use(s) following typical UH pattern Hr Leakage & base flow Regular flow Leakage & base flow TOTAL FLOW Dimensionless flow ordinates (relative to hydrograph peak) Flow hydrograph volumes (L/d) P a g e 60

61 K Unit Hydrograph Method This method uses contributor unit hydrographs that have been determined for different land use categories to calculate the expected theoretical peak flows and sewage volumes by industry professionals. This method can be used when the ADCD is not known for the specific land use(s). The inflow at a time (t) is calculated using: Where: Number of units or land parcels per land use type i Unit hydrograph value for land use type i at specific time step (see Table K.8) Hydrograph peak flow for land use i (see Table K.8) Hydrograph leakage for land use i (see Table K.8) Flow at time t From the inflow hydrograph, standard design values can be extrapolated. Two of the most important values are: PDDWF (Peak daily dry weather flow peak day in the week) which is generally defined as: P a g e 61

62 As the unit hydrograph was calculated for a peak day of a weekly pattern, generally a Monday and not the average daily dry weather flow (ADDWF), the PDDWF can be calculated as the average of Q t for each land use and the total flow. If the Average daily dry weather flow (ADDWF) is given, a factor of 1.1 is applied to calculate the PDDWF. This is to account for the peak day. IPDWF (Instantaneous peak dry weather flow), which is generally defined as: As the hydrograph was calculated for a peak day, the IPDWF can be calculated as the maximum value of Q t for each land use and the total flow. Worked Example S1 Unit Hydrograph Method The worked example looks at using the hydrograph method to determine the flow for 50 medium density residential (UH2) units and 30 Business and commercial property (UH7) units. The input data, as taken from Table K.8, and calculated values are shown in Table K.9. Table K.9: Work Example S1 Unit Hydrograph Method Input and data from Table K.7 and Table K.8 Land use #¹ Medium density residential Business and commercial Total Number of units #¹ Unit Hydrograph Type #² UH3 UH7 Hydrograph Peak (L/min) #³ Leakage & base flow (L/min) #³ PDDWF (kl/d/unit) #² Peak day factor #¹ 1.1 Calculations Hour Values #³ Flow (L/s) Values #³ Flow (L/s) Total (L/s) P a g e 62

63 Calculations IPDWF (L/s) PDDWF (kl/d) ADDWF (kl/d) Outflow Hydrographs Notes : #¹ - Example input data #² - Table 4.2 : Unit Demands and Hydrographs for Different Land Use Categories #³ - Table 4.3 : Sewer Unit Hydrographs K ADCD Inflow Method The ADCD inflow method, as opposed to the unit hydrograph method, uses the actual or theoretical average daily demand (ADCD), calculated per land use, to determine the sewage flow in the pipe at any time t. This method can only be used if the ADCD is known. This is a more accurate method as it gives a more realistic view of the flow pattern. The flow is calculated using: P a g e 63

64 Where: Where: Percentage flow contributing to sewer for the land use type (See Table K.9) Percentage flow contributing to sewer for the structure (manhole) generally taken as 100% Annual average daily water demand Unit hydrograph value for land use type i at specific time step (See Table K.9) For newly developed areas the ultimate development potential upstream must be considered (Ultimate ADCD). Meaning, the ultimate number of land parcels per land use and ADCD needs to be calculated and used to determine the sewer flows to size the sewer infrastructure. Especially outfall sewers need to cater for all possible developments upstream (can be determined from the master plan). Worked Example S2 ADCD and Unit Hydrograph Method As for the worked example of the Unit hydrograph method, the same land use and units were used. The input values were taken from Table K.8 and Table K.9. Table K.10: Work Example S2 Unit Hydrograph Method Input and data from Table K.7 and Table K.8 Land use #¹ Medium density residential Business and commercial Total Number of units #¹ Unit Hydrograph Type #² UH3 UH7 Hydrograph Peak (L/min) #³ Leakage & base flow (L/min) #³ ADCD incl. UAW (kl/d/unit) #² Ratio % of ADCD #² 60% 80% PDDWF (kl/d/unit) Peak day factor #¹ 1.1 Calculations Hour Values #³ Flow (L/s) Values #³ Flow (L/s) Total (L/s) P a g e 64

65 Input and data from Table K.7 and Table K IPDWF (L/s) PDDWF (kl/d) ADDWF (kl/d) Notes : #¹ - Example input data Outflow Hydrographs #² - Table 4.2 : Unit Demands and Hydrographs for Different Land Use Categories #³ - Table 4.3 : Sewer Unit Hydrographs It should be noted that a peak factor is already included in the hydrographs used to calculate the flows and a separate peak factor does not need to be applied. P a g e 65

66 K Sewer Flow and Peak Factor Method This method uses the Average Daily Dry Weather Flow (ADDWF) and applies a peak factor to determine the peak flow. A general guideline to calculate sewage discharge is to assume that the discharge, in fully developed areas, is approximately 60-80% of the water consumption in the area. This can be used as a general guideline if the land use is unknown or for a rough estimation. The portion of the water consumption per land use category and typical ADCD unit demands are given in Table K.7 which should, however, be used to determine the ADDWF. The addition of all the individual land use and unit/stand discharges for the design area, gives the total ADDWF. Peak Factors A peak factor must be used to determine the peak flow. Applicable design peak factors are as given in Table K.11 and Figure K.14: depending on the land zoning which must be used. Consult the local authority to obtain specific peak factors if available. Table K.11: Peak Factors Zoning Peak factor Residential see attenuation 1.8 to 2.5 Business/Commercial 1.3 to 1.5 Industrial light 2.5 to 4.0 Industrial heavy 2.0 to 3.0 Clinics, restaurants, laundromats and hotels 1.8 to 2.5 Note: A peak factor is already included in the hydrographs used to calculate the flows in the previous two methods and a separate peak factor does not need to be applied. This method does not use the hydrograph peak and thus, a peak factor needs to be applied. The peak flow rate should be calculated using: Attenuation Residential Areas To take advantage of the attenuation of peak flows in gravity sewer systems as the contributor area and population increases, design peak factors may be reduced for residential areas in accordance with the graph in Figure K.14: for sizing any sewer receiving the flow from a population greater than 1500 (peak factor of 2.5 up to a population of 1500). If actual local attenuation factors are available, these should be used instead. P a g e 66

67 Figure K.14: Attenuation of Peak Flows Worked example S3 Sewer flow and peak factor method As for the examples above, the same land use and units were used: Table K.12: Work Example S3 Sewer Flow and Peak Factor Method Land use #¹ Input and data from Table K.7, Table K.11 and Table K.16 Medium density residential Business and commercial Number of units #¹ PDDWF (kl/d/unit) #² Persons per erf #³ 5 n/a Peak factor #³ Peak day factor #¹ 1.1 Calculations IPDWF (L/s) PDDWF (kl/d) ADDWF (kl/d) Notes : #¹ - Example input data #² - Table 4.2 : Unit Demands and Hydrographs for Different Land Use Categories #³ - Table 4.6 : Peak Factors & Figure 4.11 : Attenuation of Peak Flow Total Comparing this to the flows as determined from the previous two methods, the flow is much higher. This is due to the high peak factor applied. P a g e 67

68 K Groundwater infiltration The other ± 35% of the base flow is assumed to be groundwater infiltration through joints and cracks in the sewer pipe system. Based on simultaneous sewer flow and rainfall measurements the percentage estimated stormwater ingress of the 2 year rainfall event, which falls within 25m of either side of a sewer pipe (typically ingresses into the sewer system), should be estimated to determine the amount of infiltration. Depending on the conditions groundwater infiltration rate of between 0.03 and 0.04 (L/min/m pipe/m Ø) should be allowed for (see Table K.13). Table K.13: Groundwater Infiltration Groundwater Infiltration Condition Infiltration (L/min/m pipe/m Ø) Minimum groundwater infiltration 0.03 Maximum groundwater infiltration 0.04 The amount of infiltration is dependent on the length of pipe and the outside, not inside, diameter of the pipe as the outside of the pipe is exposed to the ground. Worked Example S4 Ground Water Infiltration The infiltration flow is added to the flow calculated using the ADCD or unit hydrograph to determine the actual maximum instantaneous peak dry weather flow (IPDWF). Table K.14: Work Example S4 Groundwater Infiltration Input and data from Table K.13 Pipe length (m) #¹ 1000 Pipe inside diameter (mm) #¹ 150 Infiltration width (m) #¹ 50 Infiltration rate (L/min/m pipe/m Ø) #² 0.04 Calculations - Infiltration Peak flow (L/s) Daily flow (kl/d) Infiltration flow Calculations - IPDWF & PDDWF Peak flow (L/s) Daily flow (kl/d) Work Example S1 - Unit Hydrograph method Domestic flow (from Table 4.4) #¹ Total dry weather flow Work Example S2 - ADCD and Unit Hydrograph method Domestic flow (from Table 4.5) #¹ Total dry weather flow Work Example S3 - Sewer Flow and Peak Factor method Domestic flow (from Table 4.7) #¹ Total dry weather flow P a g e 68

69 Notes : #¹ - Example input data #² - Table 4.8 : Groundwater Infiltration It is also important to note that the engineer should use flow logging to check that the flow pattern defined by the hydrograph is correct. In several cases the base flow can be much higher, due to high levels of groundwater infiltration or stormwater ingress. There are also several cases where the water and sewer networks have been connected (which is illegal), which can cause very high peak flows. It is essential that these peaks are designed for. K.4.3 Hydraulic Design of Waterborne Systems K Pipe Sizing for Design Flow and Stormwater Ingress There are two main design philosophies that could be used to calculate the design flow. These are: (1) the Instantaneous Peak Dry Weather Flow (IPDWF) philosophy, with some spare capacity allowed for stormwater ingress, and (2) the Instantaneous Peak Wet Weather Flow (IPWWF) philosophy, where the system is designed to accommodate stormwater ingress, but with pipes allowed to flow 100% full. It was, however, found that the effect of 1% stormwater ingress is dramatic, resulting in very high IPWWF, and consequently very large and uneconomical pipe sizes. The IPDWF philosophy, as described below, is therefore generally the more preferred method in South Africa. Using the IPDWF method, pipe sizes of gravity mains should be such that the peak dry weather flow (PDWF) can be accommodated in the pipeline, whilst flowing at 70-85% or less capacity. The remaining 15-30% of the flow area is for the accommodation of stormwater ingress. Should stormwater ingress cause this spare capacity to be exceeded, resulting in pipeline overflow, measures should be taken by the system manager to prevent ingress of stormwater into the sewer system. For major outfall sewers, operational procedures and ability to clean the pipe must be considered when choosing a pipe diameter. The design flow of the pipe, also referred to as the IPWWF (instantaneous peak wet weather flow), is calculated based on the assumption that 15-30% of stormwater ingress is accommodated: Note: Some design guidelines, multiplies the IPDWF with 1.15 or 1.30 to determine the IPWWF. It should, however, rather be divided as the IPDWF is a portion of the pipes flow capacity. Worked Example S5 Design Flow and Stormwater Ingress For this example, a spare capacity of 30% was assumed. Using the same flows as calculated in the above examples, the design flow was calculated: P a g e 69

70 Table K.15: Work Example S5 Design Flow and Stormwater Ingress Input data Required spare capacity #¹ 30% Calculations - IPWWF & PDWWF Peak flow (L/s) Daily flow (kl/d) Work Example S1 - Unit Hydrograph method Dry weather flow (from Table 4.4) #¹ Design flow Work Example S2 - ADCD and Unit Hydrograph method Dry weather flow (from Table 4.5) #¹ Design flow Work Example S3 - Sewer Flow and Peak Factor method Dry weather flow (from Table 4.7) #¹ Design flow Notes : #¹ - Example input data Note: the IPDWF is divided by 70% and not multiplied by 130% to calculate the design flow. Hydraulic Capacity The "spare capacity" for a regular gravity pipe, which is unaffected by upstream pumps, is defined as follows: The relative spare capacity is the hydraulic spare capacity expressed as a percentage of the relative capacity, which is the capacity of the pipe less the total upstream continuous pump flow rate. If there are pumps upstream which pump at a continuous rate, it is necessary to consider the relative effect of these pumps on the spare capacity in the downstream pipes. It is required that part of the capacity cater for the continuous pump flow. Any spare capacity should be expressed as a percentage of the remaining available capacity i.e. the relative capacity of the pipe which is the total capacity less the effect of the upstream pumps. It should be noted that in the case of variable speed pumps, the amount of flow that flows into the pump structure is pumped out, unless the flow is more than the capacity of the pump, then it overflows. For continuous speed pumps, the pump pumps at a constant rate regardless of the inflow. The different capacity types are illustrated in the figure below. P a g e 70

71 Flow (L/s) K Hydraulic Spare Capacity 25 Relative Capacity Absolute Capacity Time (Hours) Flow hydrograph Upstream Pump flow Pipe full capacity (l/s) Figure K.15: Absolute and Relative Spare Capacity Worked example: Table K.16: Work Example S6 Hydraulic Capacity Input data Pipe full flow capacity (L/s) #¹ 32.0 IPDWF / Design flow (L/s) #¹ 28.0 Total upstream pump flow (L/s) #¹ 5.0 Spare capacity required #¹ 30% Calculations Absolute spare capacity Spare capacity (L/s) 4.0 Available 12.5% Relative spare capacity Spare capacity (L/s) 4.0 IPDWF / Design flow excluding pump flow (L/s) 23.0 Available 14.8% Notes : #¹ - Example input data The capacity is thus insufficient and the pipe is too small and should be upgraded as the spare capacity is below 30%. K Velocity and Flow in Sewers The following flow formulae are acceptable for the calculation of velocity in sewers: P a g e 71

72 Table K.17: Flow Formulas Formula name Formula Roughness constant Mannings (n = 0.012) Chezy Colebrook-White (Ks = 0.600) Kutter (n = 0.012) Where: A = Cross-sectional area of flow/conduit (m 2 ); R = Hydraulic radius (m) S = Gradient (assuming uniform flow) n = Manning s roughness coefficient dependant on material type k s or = Absolute roughness of conduit (m) C = Chezy roughness coefficient = Darcy-Weisbach friction factor = Hydraulic diameter (m) = Reynolds number Any of the above formula can be used as long as it produces values approximately the same as the equivalent Colebrook-White formula using a K s of 0.6. The general Manning-n roughness coefficient is for modelling purposes (is a factor of the pipe material and condition (age)). The formulas are used assuming full flow in the pipe. For partially full pipes, the partial flow diagram can be used to calculate the flow and velocity based on proportions of the full flow velocity and discharge, as well as the depth of flow. In most cases for the design of sewer pipes, the full flow and velocity is used. The partial flow diagram is given below for reference purposes: P a g e 72

73 Figure K.16: Partial Flow Diagram K Gravity System This type of sewer system is the preferred type of sewer system and is designed to convey the sewage via gravity. Gravity main - minimum and maximum flow velocities and gradients Sewers may follow the general slope of the ground, provided that a minimum full-bore velocity of m/s is maintained at the minimum gradient in all gravity mains. This is to ensure that sufficient scouring of the mains takes place. The maximum flow velocity under full flow conditions should be not more than 2.5m/s to prevent damage to the pipelines, although a higher flow velocity of up to m/s may be acceptable over short pipe lengths and for short periods. The maximum pipe velocity should be checked with the pipe manufacturer. Too high velocities should be avoided due to separation and abrasion. Table K.18: shows absolute minimum gradients for different diameter pipes required to achieve the minimum full-bore velocity of 0.65 m/s. If flatter grades and lower velocities are contemplated, it is essential that a detailed cost-benefit study be carried out. The cost of the regular systematic maintenance and silt/sand removal, that will be required when flatter grades and lower velocities are used, will need to be considered and compared to the additional first cost required to maintain the above minimum grades and full-bore velocity of m/s. P a g e 73

74 Table K.18: Minimum Gradients for ±0.65m/s Full Flow Velocity Nominal (mm) Pipe Diameter Outside (mm) Inside (mm) Class Material (general) Minimum gradient (Manning n = 0.012) upvc 1 : upvc 1 : upvc 1 : upvc 1 : upvc 1 : upvc 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : D Concrete 1 : % D Concrete 1 : The above diameters in Table K.18: are for illustrative purposes only. The designer must consult the pipe manufacturer for the actual diameters of the pipe to ensure adequate velocities are maintained in the pipe. The above gradients are also for general reticulation and outfalls. The sewer pipes must have a steeper gradient closer to the upper end of the sewer network to ensure the pipes are cleared and avoid settlement, as the pipes do not flow full regularly and low flow conditions can occur (depth of flow less than 20% of the diameter). Minimum gradients based on the number of upstream units are listed in Table K.19: below to ensure pipe flushing: Table K.19: Minimum Gradients for Upper End of Sewer Network No of units 100 mm Nominal diameter 160 mm Nominal diameter Preferable Minimum Preferable Minimum 1 to 10 1 : 60 1 : 75 1 : 80 1 : to 20 1 : 75 1 : : : and more 1 : 90 1 : : : 200 (l/s) P a g e 74

75 The figure below is an illustration of the amount of units and the pipe diameter and the minimum gradient as given above. Figure K.17: Upper End Sewer Network Example House connections should also be laid at a minimum slope of 1:60 for 110 mm nominal diameter pipes. It should be noted that when the number of upstream units become higher that 21, the minimum slope is provided in Table K.18: for the respective diameter. Thus, for pipes servicing more than 21 units, the gradients as shown in Table K.18: should be used. Gravity main - minimum size/diameter The minimum permissible diameter for gravity sewer pipes in a municipality should be at least 150 mm inside or nominal diameter, but the absolute minimum diameter of pipe in sewer reticulation should be 100 mm (generally connections to properties). A minimum pipe diameter of 200mm (outside) may be more applicable in CBD developments. This is to provide some spare capacity for future densification, because of the difficulty of installing services in the CBD. Syphons Syphons, also called sag or inverted syphons, are designed to carry flow across an obstruction (road, river etc.) where it cannot be obtained by a sewer placed at a continuous grade. Enough pressure head must available before and after the obstruction. The individual pressurized pipes or conduits comprising of the siphon are normally smaller in diameter than the gravity system resulting in higher wastewater velocities. The higher velocity serves to keep heavier solids in suspension and prevent deposition of solids. P a g e 75

76 Figure K.18: Example of Syphon System (Source: 59 Syphons are constructed with multiple pipes in order to match the pipes in active use with the actual wastewater being conveyed. Syphons are designed to have three barrel and need to be full flowing to be able to operate. The three pipes are designed as follows: 1. One full flowing pipe to be able to convey the ADDWF (minimum flow). 2. Two full flowing pipes to be able to convey ADDWF up to the PDDWF (average flow). 3. Three full flowing pipes to be able to convey the PWWF (above average flow). The velocity in each of the siphon pipes must be more than 0.9 m/s. The velocity in the syphon is dependent on the length of the syphon and should be as follows: Short syphon (<70 m) Syphon longer than 70 m and with concrete transition structures at the inlet 1 m/s 3 m/s Some design considerations that must be taken into account for a syphon are the following: The minimum self-cleansing velocity in the syphon must be obtained during ADWF, or at least once a day during PDWF (see table below). The velocities in the syphon should range between 1 and 3m/s, dependant on the available head, economic considerations and the length of the syphon. The syphon must not have sharp bends (vertical or horizontal), changes in diameter or be too steep in gradient in the rising leg to ensure self-cleansing and not complicate the removal of heavy solids. Hydraulic capacity of syphon must never be lower than upstream sewer system. The minimum diameter of a siphon conduit should be 150mm. The friction loss through the barrel is determined by the design velocity, and additional losses due to sideoverflow weirs and directional changes (bends) are also taken into account. The bend losses are a function of the velocity head, deflection angle, siphon diameter and radius of the bend curvature. As a safety factor 10% needs to be added to the head losses calculated. Blowback needs to be taken into account in the design, as it can occur where free-flow is at the entrance or in long syphons, as air becomes entrapped. Backwater needs to be taken into account where the losses in the siphon are greater than the difference in the upstream and downstream water level. P a g e 76

77 The minimum self-cleansing velocities that need to be achieved for a general medium sediment load (50 mg/l) is given below, but the length of the syphon should also be taken into account as given by the criteria above: Table K.20: Minimum Self-cleaning Velocities K Pumped System Internal Pipe Diameter (mm) Minimum Self-cleansing Velocity for a Sediment Load of 50 mg/l This type of sewer system is not generally recommended and gravity alternatives should be considered. Where gravitational conveyance is not possible this type of sewer system can be considered and is designed to convey the sewage via pumping. Pump stations Avoid sewage pumping stations as far as possible and consider only where absolutely necessary, and where a gravity alternative to the existing municipal sewer system is not feasible. A sewer pump station consists of a sump, where incoming wastewater and sewage is collected, and a pump, which pumps the liquid through a rising main to the downstream sewer network. Both are discussed below: Sumps for pump stations Aspect Sizing of sumps: Criteria Size pumps and place pump operating controls to restrict pump starts to a maximum of six per hour. The sump should not be too big (retention time of sewage too long smells and costs) or too small (the starting and stopping rate of the pumps too frequent). There is both an emergency storage portion and an active or working portion that makes up the sump volume. The active sump volume is calculated using the rate of stopping and starting: P a g e 77

78 Aspect Emergency storage Criteria A minimum emergency storage capacity representing a capacity equivalent to four to six hours flow at the design flow rate should be provided, over and above the capacity available in the sump at normal top-water level (i.e. the level at which the duty pump cuts in). This provision applies only to pump stations serving less than 250 dwelling units and where no backup power for pump stations is supplied. This is to contain any sewage spillage. For pump stations serving larger numbers of dwelling units, the sump capacity should be subject to special consideration in consultation with the local authority concerned. Emergency storage may be provided inside or outside the pump station. Emergency sump volume is calculated using the following formula: Where: T E = minimum emergency storage time (specified by local authority generally 4 6 hours) Q = average raw sewage inflow rate (ADWF) V E = sump emergency storage volume (m 3 ) Some emergency storage capacity should also be provided in the up-steam gravity lines and manholes. Where: T Minimum cycle between pump starts (time to fill + time to empty) V A Sump active volume (m 3 /s) Q Pumping rate q Sewage inflow rate The total sump volume is then the sum of the active and emergency volumes: Buoyancy Calculations Confirm that the structure will not float when subjected to high ground water levels. Pumps at pump stations Aspect Criteria Design flow pump The capacity of the pumping station needs to equal or exceed the peak wet weather flow which arrives at the pumping station, or the peak dry weather flow plus an allowance for stormwater ingress. In the case of a 30% allowance, the pump therefore must have a capacity equal to the design flow generally: Size the pumping station to handle the peak hourly wet weather flows without overflowing of the pump station or the sewer system. P a g e 78

79 Aspect System Hydraulics Efficiency Standby pumps Hydraulic influence of pump stations Surge analysis Cavitation Backup power for pump stations Criteria Design the pumping station to operate under the full range of projected system hydraulic conditions. Design the system to to prevent a pump from operating for long periods of time beyond the pump manufacturer s recommended normal operating range. Start/stop cycles should not exceed motor manufacturer s recommendation. The working capacity (between pump-on and pump-off) should provide a holding period of not more than 10 minutes for the average daily design flow. It is advised to design the pump station so that that the pumps operate a maximum of 2 duty cycles per hour during average flow conditions. Select pumps so that the operating point is near the maximum efficiency point on the pump performance curve, within the pump s recommended operating range, and within the manufacturer's recommended limits for radial thrust and vibration. Size pumping stations to accommodate peak wet weather flow, with at least one reserve pump. Install at least two pumps, each capable of pumping at a flow rate in excess of the peak wet weather flow (for emergency purposes), but at the same time care must be taken not to provide excessive standby capacity. The standby pump should come into operation automatically if a duty pump or its driving motor fails due to mechanical failure. Where three or more pumps are indicated, they should be designed to fit actual flow conditions and must be so designed so that with any one pump out of service, the remaining pumps will have capacity to pump peak design flows. Size pumps so that one pump can empty the sump plus handle the average inflow in less than 30 minutes. Although sewer pump stations operate intermittently, their flows can influence the hydraulics of the downstream pipes at any time during the day. It is therefore advised to model the pumps as continuous pumps, which pump at specified capacity for 24h per day. Consider hydraulic surges and transients (water hammer) during the design of pump stations and pumping mains. Ensure that the NPSH available is higher than the NPSH required to avoid cavitation damage to the pump. Provide emergency power supply to pumping stations to ensure continuous operation in the event that primary electrical supply is out of service (standby generator). it is advised that larger pump stations have permanent diesel-oil fuelled, engine-driven generator units with automatic transfer switches to transfer the electrical feed from the primary to the standby unit when a power failure is detected by the instrumentation and control system, sized to operate all electrical components. For smaller pump stations, where a dedicated backup generator is not available, it is advisable to have a portable generator available. A manual transfer switch and an emergency plug-in power connection to the station, for use with the portable generator, should in these cases be installed. Provide a standby generator to supply the pump station with full load power for at least 6 hours. Pump sizing and design The determination of the appropriate pump are done by considering the pump system curves. The pump system curves provides an indication of the interaction between the pump performance and the pumping main it is using to deliver the discharge. The designer is advised to determine the pumping system curves in the determination of the pumps to ensure an appropriate and efficient pumping system. P a g e 79

80 The pump performance curve shows the discharge relative to the pressure for a particular pump and impeller size (diameter). It also shows the efficiency as shown below. Every pump manufacturer has a pump performance curve for every pump. Use the system curve, which represents the static head and the friction losses of the pumping main, in conjunction with the pump performance curve to specify the most appropriate pump, which can accommodate the flow and provide the required head at a desired efficiency. The operating (duty) point is where the pump performance curve and system curve intersects. The duty point should be near the pump s best efficiency point (BEP) as shown in Figure K.19: below. Figure K.19: Pumping System Curve ( ) 60 The following considerations must be made in selecting the correct pump: The pumps must be selected to ensure that the duty specified falls well within the stable range of the head/quantity characteristic curve of the pump. The pump shall have a non-overloading power curve. Maximum suction lift must not exceed the pump manufacturer s recommendations and must be based on a net positive suction calculation with an allowed factor of safety. Rising mains Rising mains must be designed to take care of the following: Minimum and maximum flow velocities Minimum size/diameter Other considerations The minimum velocity of flow in a rising main should be a minimum of 0.6 m/s. Flow velocities must be limited in order to protect pipeline coatings and reduce the effects of water hammer. The preferred maximum allowed is m/s, but an absolute maximum of 2.5 m/s is acceptable, where only intermittent peak flows occur. The minimum internal diameter of a rising main should be 100 mm, except where a macerator system is used, in which case the diameter can be reduced to 75 mm. Where possible, the rising main must have a positive grade with no low points or high points to avoid possible gas release and grit deposition; Scour valves and air valves must be avoided at all cost along the rising main; Protect the pipeline against hammer and surge forces (analyse and provide protection); Turbulence must be avoided to prevent the release of H 2 S gas at the outlet; P a g e 80

81 Provide protection against unbalanced forces (thrust) where necessary (thrust blocks and support). Stilling chambers Stilling chambers should be provided at the heads of all rising mains, and should be so designed that the liquid level always remains above the soffit level of the rising main where it enters the chamber. Stilling chambers should preferably be ventilated. K.4.4 Physical Design of Waterborne Systems K Sewer Pipes Sewer Pipe location - general Locate sewer pipes in open areas, road reserves or municipal land where they may be easily accessed at all times. Generally, locate sewers on the lower side of the road. In road reserves, install sewers between the stormwater drain and the erf boundary, where applicable. In built areas, locate sewer pipes preferably m from the erf boundary. Positioning of infrastructure in municipal areas are generally guided by municipal specifications and standards and should be consulted. Mid-block sewers should be avoided as far as practically possible. Mid-block sewers are not allowed in townships with individual stands of less than 400 m 2 in area. Where the mid-block system is unavoidable it is acceptable, provided that the sewer connections are not installed deeper than 2.0 m and that the main sewer is not installed deeper than 3.0 m. If these depths are to be exceeded, a double system must be used. In doubtful cases, a comparative estimate of costs with the double system must be made. When designing a double system, it is essential that close attention be paid where other services, particularly stormwater drains, are crossed. Special permission is generally required for midblock sewers if they can t be avoided. The following aspects are considered desirable as far as the routing of sewers is concerned: The sewer must follow the natural fall of the ground (consult the contour plan). The sewer must be laid in those properties which will benefit most directly from the sewer. Road crossings must be kept to a minimum. All other municipal services must be taken into account when installing a new sewer. There must be minimum interference with existing structures. Existing services positions and levels should be taken into account to minimise conflict. Pipe location - road crossings Where a road crossing is unavoidable, consider the following: Investigate, where possible, existing crossings, such as culverts and bridges, for possible ground crossings to avoid excavation and pipe jacking; Consider pipe jacking where applicable and accepted; Do not encase sewers crossing under surfaced roads (existing tar roads) in concrete; P a g e 81

82 Backfill trenches in accordance with relevant construction specifications. The selected materials must be hand-compacted to a depth of at least 300 mm above the top of the pipe. Pipe location dolomitic regions Consult the following publications regarding work in dolomitic areas: PW344: Appropriate Development Infrastructure on Dolomite: Manual for Consultants as published by the National Department of Public Works, June This document is available under Consultants Documents on the website of the Department of Public Works ( 61 Section 2.8 of Part 1 of the Home Building Manual as published by the NHBRC, Revision 1, Proposed method for dolomite land hazard and risk assessment in South Africa, SAICE Journal Volume 43(2) 2001, paper 462 pages 27-36, Buttrick et. al. 63 Minimum depth and cover The following are the recommended minimum values of cover to the outside of the pipe barrel for main sewers: Pipe location House connections P.O.S and Mid-blocks (Servitude) Street reserve (Sidewalks) Roadways (trafficked areas) Cover mm mm mm - below final kerb level mm - below final constructed road level The designer must be certain that the combination of loading, pipe depth, pipe strength and bedding type will be satisfactory. Shallower depths can be used where the bedding and compaction is well controlled, especially in roadways. Depths of cover for house connections must be such that the pipelines are not compromised by excess loading. Lesser depths of cover may be permitted, subject to integrated design of all services, including trunk services allowed for in development plans, provided that, where the depth of cover in roads or sidewalks is less than 600 mm, or in servitudes less than 300 mm, the pipe should be protected from damage by the following options: The placement of cast-in-situ or precast concrete slab(s) over the pipe, isolated from the pipe crown by a soil cushion of mm minimum thickness. The protecting slab(s) should be wide enough and designed so as to prevent excessive superimposed loads being transferred directly to the pipes (see Figure K.22); or Figure K.20: Protection of Pipes at Reduced Depths of Cover (e.g. Class B bedding) P a g e 82

83 The use of structurally stronger pipes able to withstand superimposed loads at the depth concerned; or The placement of additional earth filling over the existing ground level in isolated cases where this is possible. Except in very special circumstances, the encasement of pipes in concrete is not recommended. Where encasement is unavoidable, it should be made discontinuous at pipe joints, so as to maintain joint flexibility. Trenching, bedding and backfilling The trenching, bedding and backfilling for all sewers should be in accordance with the requirements the relevant standards specified by the owner. Do a structural design of the pipe and bedding structure where trenches are: located under roads; deeper than 3 metres; and other than those classified as narrow (i.e. where overall trench width is greater than nominal pipe diameter d mm for pipes up to 300 mm diameter). Typical acceptable trench widths per outside pipe diameter are given below: Table K.21: Trench Widths Outside Diameter (mm) Trench Width on Each Side of the Pipe (mm) < Lay pipes according to approved methods on the specified bedding to ensure trueness to line and level and in such a manner that the barrels of pipes bear evenly on the bedding over their full length. Place spigot-and-socket pipes with the socket facing upstream. Lay and joint pipes in accordance with the manufacturer's instructions. Pipes of 600 mm in diameter and larger shall be kept clean on the inside by being swept by hand as laying progresses. The open ends of the pipelines shall be closed by means of approved plugs at all times when laying is not in progress. During all pipe-laying and bedding operations care shall be taken to prevent the entry of any dirt or concrete into the flexible pipe joints by sealing the joint with clay or by other approved means. Compact the selected bedding and backfill material to an optimum moisture content of at least 90% of modified AASHTO density. After a pipeline has been laid, tested and approved, the trench should be partly backfilled (with hand implements), to a height of 300 mm above the top of the pipe barrel, with suitable selected backfill material free from stones exceeding 20 mm, organic matter and lumps of clay exceeding 75 mm, but which contains sufficient P a g e 83

84 fine material to ensure a densely graded, well-compacted backfill. Backfilling around and over the pipeline should be in layers not exceeding 100 mm compacted thickness. Backfilling should be carried out simultaneously and equally on both sides of the sewer to avoid unequal forces from being exerted. Anchoring steep slopes Provide concrete anchor blocks where grades steeper than 1 in 10 or 12 (1 to 6 for some authorities) are required. Curved alignment A straight alignment between manholes should normally be used, but curvilinear, horizontal or vertical alignment may be used where the economic circumstances warrant it, subject to the following limitations: The minimum radius of curvature is 30 m. Curvilinear alignment may be used only when approved flexible joints or pipes are used. In the construction of a steep drop, bent fittings may be used at the top and bottom of the steep short length of pipe, thus providing a curved alignment between the flat and steep gradients. Siting Site sewers so that they provide the most economical design, taking the topography into account (i.e. in road reserves, servitudes, parks, open spaces, etc.). The minimum clear width to be allocated to it in the road reserve should be 1.5 m. Encased pipes The pipe can be encased for structural support or where the pipe is installed underneath a road (only where a slab has not been cast to support the pipe) and depression in the road is to be prevented by ensuring the pipe doesn t deform under load. K Pipe Load and Deflection Calculations When designing for pipes, it is important to investigate the loading (soil and imposed) on the pipe and any possible deflection. The calculations are dependent on the rigidity of the pipe. For flexible pipes (i.e. PVC pipes), the resultant deflection should be calculated for the applied loading conditions (soil and live load) and checked versus manufactures allowable deflection. For rigid pipes (i.e. concrete), the applied load (soil and live load) should be calculated and checked versus the load carrying capacity tolerances as specified by the manufacturers. Not only is the loading on the pipe dependant on the rigidity of the pipe but also on the trench and the bedding. These guidelines are mainly concerned with the hydraulic design and planning of sewers rather than on the detailed design and only bring certain aspects under the designer s attention. Other design guidelines should be sought such as, SANS , SANS , SANS 677, 66 and SANS for more details on pipe design and installation. P a g e 84

85 K Syphons The syphon should have very few bends and angle points and its vertical alignment should be straight. Uniform grade should be aimed for between one end to the other. The inlet and outlet structures (transitions) should be designed to reduce head loss, prevent erosion and maintain submergence (hydraulic seal). An emergency spillway should be constructed upstream from the inlet if required. Manual or automatic gates/weirs should be installed at the inlet of syphons to control the upstream water and at the outlet to control submergence and to control outflows and inflows in multi-barrel siphons. Collars are installed to prevent movement or piping and damage from burrowing animals. Two potential maintenance problems associated with syphons are clogging and hydrogen sulphide generation. Due to their nature, debris often settles at the bottom of the syphon with grease accumulating near the top, requiring frequent cleaning. There is thus a need for frequent monitoring/ inspection of the syphon due to the probability of solids deposition and thus it could require more regular maintenance to prevent overflows. To make maintenance easier, the following should be considered during the design: Provision air jumpers for hydrogen sulphide control. Provision acid-resistant lining on inlet and outlet structures. Provision adequate working space inside the inlet and outlet structures for cleaning the pipe barrels. Verify required space for electrical cleaning equipment. Provision a cleanout point at the low point of the syphon to enable complete draining (if feasible). Alternatively a sump at the inlet end of the syphon can be provided to allow draining of the syphon prior to cleaning and inspection. Pressure-type manholes and covers should be considered when crossing streams to prevent river water from flowing into the structures. K Manholes Location and spacing The maximum distance between manholes on either straight or curved alignment should be the following: m where the local authority concerned has power rodding machines and other equipment capable of cleaning the longer lengths between manholes (rod length generally <80 m). This should be confirmed with the local authority. 100 m where the local authority concerned has only hand-operated rodding equipment. The local authorities guidelines should be referred for details regarding spacing. This distance must be decreased on steep grades so that the pressure head on any part of the sewer does not exceed 6 m under blockage conditions. On collector sewers, and especially outfall sewers, the distance between manholes may be increased. Note: The economics of acquiring power cleaning equipment in order to permit a greater manhole spacing should be demonstrated to local authorities. P a g e 85

86 Manholes should also be placed in the following conditions: All junction points where main sewers meet (not every erf connection). All changes of gradient. All changes in direction - except in the case of curved alignment and at the top of shallow drops. Where there is a change in pipe diameter in outfalls (pipe soffits must be equal). Manholes are not required at house connections. Where two or more sewer lines connect. At positions on steep grades (1:10 or steeper), to prevent backpressure in house gullies under blockage conditions. At the higher end of all sections that serve more than three dwelling units and that are longer than 50m; For sewers crossing a road, there must be at least one manhole within the road reserve. Where manholes have to be constructed within any area that would be inundated by a flood of 50 years recurrence interval, they should, wherever possible, be raised so that the covers are above this flood level. Illegal stormwater drainage into sewer gulleys is endemic throughout South Africa. The increased flow rate into sewage works after storm events is widely recognised (The Institute of Water Pollution Control, ). It is advisable to place gulleys away from where stormwater flows or collects, and gulleys should be as few in number as practicable. Where the sewer and water lines are to be installed in the same trench, sewer manholes must be positioned so as to allow for a minimum clear distance of 500 mm between the outside of any manhole and the water pipeline. Type There are six types of standard manholes: Table K.22: Manhole Types Type Types I, MA and MB Type III Description These manholes are used in conjunction with sewer pipes with a diameter of 300 mm and smaller. This manhole is similar to types I, MA and MB, but shall be constructed of precast concrete sections. Type Z This manhole is used in conjunction with pipe diameters from 375 mm up to and including 600 mm and is constructed from cast in-situ class 20/19 concrete. The roof slab is provided with a 225 mm diameter hole for the fitting of a ventilation pipe. Type Y This manhole is similar to type Z, except that it is used on pipelines exceeding a diameter of 600 mm. As types Y and Z manholes are not used at pipeline junctions, special manholes should be used. Relevant design standards should be sought for non-standard structures such as manholes for in situ sewers, metering structures and inlet and outlet structures. P a g e 86

87 Sizes The minimum internal dimensions of manhole chambers and shafts should be as shown in Table K.23:. The minimum height from the soffit of the main through pipe to the soffit of the manhole chamber roof slab, before any reduction in size is permitted, should be 2 m. Table K.23: Minimum Internal Dimensions of Manhole Chambers and Shafts Shape Chamber Shaft Circular 1000mm 750mm Rectangular 910mm 610mm Manholes deeper than 3 m shall be a minimum of 1.5 m in diameter. Benching Provide an area of benching in each manhole so that a person can stand easily, comfortably, and without danger to the person, on such benching while working in the manhole. Shape channels and benching correctly and carefully to minimise any possible turbulence. Manhole benching should have a grade not steeper than 1 in 5, nor flatter than 1 in 25, and should be battered back equally from each side of the manhole channels such that the opening at the level of the pipe soffits has a width of 1.2 d, where d is the nominal pipe diameter. The in situ casting for channelling and benching in manholes and adjoining culverts shall, where applicable, be rendered in 25 mm thick granolithic concrete and finished smooth and true with a steel trowel and rounded at corners and edges. The benching shall be taken to 25 mm above the highest pipe soffit. Pipes entering manhole After the manhole foundation slab has been cast, the semi-circular channels and fittings suitable for the type of pipe laid shall be placed in position and embedded in the concrete benching. The sockets of channels and the space between two abutting channels shall be filled with a 1:1 cement:sand mortar mix well worked in, and all joints shall be neatly finished off. Pipes entering manholes shall be cast into position in the benching in order to ensure a watertight joint between the pipe and the manhole. Caulking will only be allowed where a pipe is built into an existing manhole. The pipes built into manholes or into the culverts adjoining large manholes, shall be encased in concrete after the walls have been completed, and the sewer shall be so jointed to the pipes as to produce a flexible joint on each side of each manhole or culvert. Design All manholes, including the connection between manhole and sewer, should be designed in accordance with the requirements of industry standards such as SABS 1200 LD 69 and, where manholes are of cast-in-situ concrete, chambers, slabs and shafts should be structurally designed to have a strength equivalent to a brick or precast concrete manhole. P a g e 87

88 For manholes located in road reserves, spacer rings or a few courses of brickwork should be allowed for between the manhole roof slab and the cover frame in order to facilitate minor adjustments in the level of the manhole cover. Adjustable manhole frames may also be used. Heavy load type manholes should be used in trafficked areas and medium load type manholes every else. Steep drops Steep drops should be avoided wherever possible. Where a steep drop is unavoidable (e.g. to connect two sewers at different levels), use should be made of a steep, short length of pipe connected to the higher sewer by one or more 22.5 degree bends and to a manhole on the lower sewer also by one or more 22.5 degree bends, as shown in Figure K.21. Figure K.21: Steep Drops in Sewers Backdrop manholes Do not use backdrop and/or ramp junction manholes in sewer systems. Where flows and economy considerations (i.e. trench depth) become significant, the alternative of two closely spaced manholes or lamp holes, or a combination of these, is the prescribed option. Elevation drop through manhole The minimum slope in any manhole from inlet pipe to outlet pipe in a straight line (elevation drop through the manhole), is the greater of: mm; the slope of the inlet pipe; or the slope of the outlet pipe. This drop through the manhole is to minimise energy (hydraulic) losses. Where there is a change of direction in a manhole, the minimum height difference between inlet and outlet pipes should be increased to allow for the loss in energy around the bend. The following table gives an indication of the fall in manholes (mm), for various bends and pipe sizes up to 300 mm. P a g e 88