Wastewater Treatment, Transfer and Reuse. epeco. 10, Taiaran Str., Raba a al adawia,nasr City Cairo 11371, Egypt

Transcription

1 Wastewater Treatment, Transfer and Reuse at the West Dune Zone, Ahmed Orabi Agri-Developing Society, North Cairo Feasibility Study and Conceptional Design epeco 10, Taiaran Str., Raba a al adawia,nasr City Cairo 11371, Egypt Tel: Fax: e.mail:info@epeco.com

2 Contents Introduction 1 Systems 1.1 Gravity Sewer Systems 1.2 Vacuum Sewer Systems 1.3 Decentralized Wastewater Treatment & Reuse Systems 1.4 Central Wastewater Treatment & Reuse Systems 2 Advantages & Disadvantages of Systems 2.1 Gravity Sewer Systems, Advantages & Disadvantages 2.2 Vacuum Sewer Systems, the Advantages & Disadvantages 2.3 Decentralized Wastewater Treatment & Reuse systems, the Advantages & Disadvantages 2.4 Central Wastewater Treatment & Reuse Systems, the Advantages & Disadvantages 3 Cost Analysis 3.1 Centralized Wastewater Collection, Transfer, Treatment & Reuse Gravity Sewer System Gravity Sewer Network + Central Wastewater Treatment and Reuse System Vacuum Sewer Network + Central Wastewater Treatment and Reuse System 3.2 Decentralized Wastewater Treatment Systems 4 Recommendations 4.1 Construction of centralized gravity waste water collection, treatment and reuse systems 4.2 Construction of centralized vacuum waste water collection, treatment and reuse systems 4.3 Construction of decentralized wastewater collection, treatment and reuse systems 4.4 Execution 5 Conclusion

3 Introduction Ahmed Orabi Agri-Developing Society, North Cairo, has plans to provide the West Dune Zone WDZ with wastewater treatment and reuse facilities. EPECO & Dr.Sameh Armanus-Consulting Engineer, were asked to prepare a joint work to study to study the feasibility and conceptional designs of the commercially available alternatives. In the following study, several alternatives of wastewater collection, transfer, treatment and recycling were reviewed. The current and potential operating conditions were also carefully reviewed. The capital investment and operating cost along with socio-ecological impacts were carefully studied and reported. The study, concluded a recommendation and was summarized in the next conclusion.

4 1- Systems 1.1 Gravity Sewer Systems Gravity sewer collection system is normally designed to convey wastewater by gravity to a sewage treatment plant. Te pipeline pressure is normally atmospheric. The wastewater flows under gravity with no pumping energy. Manholes are normally constructed alongwith the gravity line to allow for maintenance and inspection. Sometimes, pipeline excavation is difficult because of nature of soil or due to topographic conditions, therefore gravity collection systems may not be possible and/or practical and the wastewater needs to be pumped through a pipeline to the treatment plant. In many cases, gravity sewer lines and pressure lines risers are combined in integrated sewer systems called Gravity Sewer Systems.

5 1.2 Vacuum Sewer Systems vacuum sewer system uses the differential pressure between atmospheric pressure and a partial vacuum maintained in the piping network and vacuum station collection vessel. This differential pressure allows a central vacuum station to collect the wastewater of several thousand individual homes, depending on terrain and the local situation. Vacuum sewers take advantage of available natural slope in the terrain and are most economical in flat sandy soils with high ground water.

6 1.3 Decentralized Wastewater Treatment & Reuse Systems Many compact wastewater treatment plants are developed especially for single and/or multiple houses especially in isolated areas. To distinguish these compact units from central systems, we ll call them Decentralized plants. Most compact wastewater treatment plants are designed to meet the demand from regulatory authorities. Most decentralized wastewater treatment plants today, are producing high quality effluent, suitable for irrigation, cleaning and most non-potable water used.

7 1.4 Central Wastewater Treatment & Reuse Systems Municipalities are normally constructing central wastewater collection systems, to collect and transfer wastewater to disposal point. It s common to collect wastewater and transfer it under gravity to the Wastewater Ttreatment & Reuse Plant (WWT&R). Among alternative collection and transfer systems are the vacuum sewer networks. Both the gravity and the vacuum systems have advantages and disadvantages. Those advantages or disadvantages are optimized according to the local conditions and may vary from case to case. Choosing between systems must be taken according careful study of each case. Due to the growing fresh water supply and ecological harassment impacts of centrally collected polluted wastewater, the need of WWT&R became an essence. Many treatment techniques are available today and choosing among them depends on the local conditions and users priorities. The treated effluent from central WWT&R is normally accepted for irrigation, recycling to surface and /or underground water sources or non-potable domestic uses. Municipal regulations and rules are followed in setting the standards for reuse of treated effluent.

8 2- Advantages & Disadvantages of Systems 2.1 Gravity Sewer Systems, Advantages & Disadvantages Advantages: 1. Simple to design. 2. Easy to construct. 3. Reliable to operate. 4. Low cost to operate. Disadvantages: 1. Fixed capacity. 2. Frequent Services required. 3. Possible Leakage. 4. Possible odor & smell. 5. Long construction time.

9 2.2 Vacuum Sewer Systems, the Advantages & Disadvantages Advantages: 1. Easy & simple to construct. 2. Low operating cost 3. Short time to construct. 4. Flexible to operate. 5. Guaranteed no-leakage. 6. No odor or smell. Disadvantages: 1. Sophisticated design. 2. Sophisticated operation. 3. Limited application.

10 2.3 Decentralized Wastewater Treatment & Reuse Systems, the Advantages & Disadvantages Advantages: 1. Easy & simple to construct. 2. Short time to construct. 3. No negative ecological impacts. Disadvantages: 4 Expensive operation. 5 High construction cost.

11 2.4 Central Wastewater Treatment & Reuse Systems, the Advantages & Disadvantages Advantages: 4 Low construction cost. 5 Low operating cost. 6 Simple Design. 7 Simple operation and maintenance. Disadvantages: 1. Fixed capacity. 2. Possible odor or smell. 3. Possible negative ecological impacts. 4. Sophisticated Design. 5. Sophisticated operation and maintenance.

12 3. Cost Analysis 3.1 Centralized Wastewater Collection, Transfer, Treatment & Reuse Gravity Sewer System Gravity Sewer Network + Central Wastewater Treatment and Reuse System Gravity sewer network can be constructed, to collect domestic wastewater from properties then to be treated in central systems. Gravity Sewer Networks No. 9 Gravity Sewer Pipeworks Meter Manholes No. 776 Wastewater Treatment & Re-use Plants No 9 Irrigation Water Networks No 9 Irrigation Water Pumping Stations Meter The anticipated over-all construction cost of gravity sewer system including wastewater treatment systems, is: (Please note that the cost of irrigation water tanks, pumping stations, central irrigations main networks but excluding the cost of connections to the properties which has to paid by the users and according to their actual cost) Cost Egyptian Pounds Gravity Sewer Networks Wastewater Treatment & Re-use Plants Irrigation Water Tanks, Pumping Stations & Main Networks Thirty Million and Six Hundred Fifty Thousand Egyptian Pounds

13 3.1.2 Vacuum Sewer Network + Central Wastewater Treatment and Reuse System Vacuum Sewer System can be constructed to collect and transfer domestic wastewater from properties then to be treated in central systems. Vacuum Sewer Networks No. 6 Vacuum Sewer Pipeworks Meter Vacuum Interface Valves No. 651 Wastewater Treatment & Re-use Plants No 3 Irrigation Water Networks No 6 Irrigation Water Pumping Stations Meter The anticipated over-all construction cost of vacuum sewer system including wastewater treatment systems, is: (Please note that the cost of irrigation water tanks, pumping stations, central irrigations networks but excluding connections to the properties which has to paid by the users and according to their actual cost) Cost Egyptian Pounds Vacuum Sewer Networks & Plant Rooms Wastewater Treatment & Re-use Plants Irrigation Water Tanks, Pumping Stations & Main Networks Fifty One Million and Two Hundred Fifty Thousand Egyptian Pounds

14 3.2 Decentralized Wastewater Treatment Systems Decentralized Wastewater Treatment Systems can be implemented to collect domestic wastewater from individual properties, treat it and reuse within the same property for irrigation of landscape and general cleaning. Properties No. 651 Wastewater Treatment & Re-use Plants No 651 The anticipated over-all construction cost of vacuum sewer system including wastewater treatment systems, is: (Please note that the cost of irrigation water tank, pumping, irrigations network within the properties is excluded, and it has to paid by the users and according to their actual cost) Cost Egyptian Pounds Wastewater Treatment & Re-use Plants Forty Twenty Seven Million & Three Hundred and Fifty Thousand Egyptian Pounds

15 4- Recommendation As a matter of fact, the client has to choose among two scenarios to implement wastewater treatment and reuse in West Dune Zone (WDZ)-Ahmed Orabi Agri-Development Society Resort-Cairo North. Construction of centralized waste water collection, treatment and reuse systems Alternatively, building individual local wastewater treatment and reuse systems-known in industry as Decentralized Wastewater Treatment & Reuse Systems (DWT & RS). Following is a brief analysis of both scenarios and the conclusion: 4.1 Construction of centralized gravity waste water collection, treatment and reuse systems Due to topographic nature of the WDZ, collection of wastewater from nearly (651) properties, the area will be split into (9) sectors. Each sector can be connected to a central gravity sewer network. Each network will collect and transfer wastewater to an independent wastewater treatment plant (total 9). Each sector may have its independent irrigation system (total 9) (irrigation water tank, supply network and pumping station). As an alternative to the irrigation network, effluent may be transferred to the properties, by trucks. The minimum anticipated cost for Construction of centralized waste water collection, treatment and reuse systems is EGP (Thirty Million and Six Hundred Fifty Thousand Egyptian Pounds). In addition to the high investment (EGP 54761/property), Finance of a utility project could be a problem. To cover for financial charges and to ease the financial terms and conditions, irrigation water has to be sold to the users at reasonable price. Unfortunately, neither the amount of treated effluent production (2100 m3/day) nor the demand for irrigation water (average annual sale: EGP/year) are fair enough to cover for the finance. In house finance will be necessary to construct the system. The central gravity+wwt&r plants do not allow for major variation in work loading (inflow capacity and quality). In a mixed agro-industrial community, we expect violations of discharge of wastewater quality standards (poultry & cattle farms, swimming pool drain-off, etc.). This may change inflow wastewater quality to te treatment plant. Minimum and maximum capacity with consistent inflow characteristics must be maintained within design limits. Deviation from these limits will affect the performance and may lead to poor performance quality. Central WWT&R plants and gravity sewer networks, by design need frequent maintenance. This may increase the down time and may add further cost as will. Unless the system is well maintained, possible leakage from gravity network and odor and bad smell from system are anticipated.

16 4.2 Construction of centralized vacuum waste water collection, treatment and reuse systems Due to topographic nature of the WDZ, collection of wastewater from nearly (651) properties, the area will be split into (6) sectors. Each sector can be connected to a central gravity sewer network. The networks will collect and transfer wastewater to (3) independent wastewater treatment plants. Irrigation system (total 3) (irrigation water tank, supply network and pumping station) will be constructed to reuse the treated effluent. As an alternative to the irrigation network, effluent may be transferred to the properties, by trucks. The minimum anticipated cost for Construction of centralized vacuum wastewater collection, treatment and reuse systems is EGP (Fifty One Million and Two Hundred Fifty Thousand Egyptian Pounds). This is a very high investment (EGP /property). As stated before, finance of a utility project is a serious problem. The central vacuum networks capacity is flexible by design. It can handle higher peak low capacity with no performance defects. WWT&R plant does not allow for major variation in work loading (inflow capacity and quality). Again minimum and maximum capacity with consistent inflow characteristics must be maintained within design limits. Deviation from these limits will affect the performance and may lead to poor performance quality. Despite central vacuum sewer networks, by design need minimal maintenance, central WWT&R plant will need frequent maintenance & services. This may increase the down time and may add further cost as will. Unless the WWT&R plant is well maintained, possible odor and bad smell is anticipated.

17 4.3 Construction of decentralized wastewater collection, treatment and reuse systems Each property can install its own compact wastewater treatment and reuse plant. solution, satisfying the following features: This is a total 1. Low capital cost (Only EGP /property). No upfront investment is required. The capital investment/property is less than the highest: (57%) and tan the average (28%). 2. No corporate finance is required. 3. Low operating cost for a total solution (no corporate financial charges with free effluent cost). 4. No ecological negative impacts. 5. Maximum reliability. 6. Easy operation & maintenance. 7. Flexible performance. 8. In house technology. 4.4 Execution A firm can be established to build, supply, install, operate and maintain the decentralized wastewater treatment and reuse plants. The firm can be established by shareholders of Ahmed Orabi Agr-Developing Society to serve the Societies members and to sell the product on national and international scale.

18 5. Conclusion Due to high investment requirements, difficult finance, difficulties in operation & maintenance, anticipated eco-social problems, utilization of central wastewater collection, transfer, treatment and recycling is not economically or environmentally feasible. Decentralized wastewater treatment and recycling systems is highly recommended and an engineering firm can be established to build, supply, install, operate and maintain those plants on both national and international scale. This approach will turn the environmental protection business into profitable one.