UNIT II. Part A (2 Marks) 1. What are the 4 R s in waste hierarchy? [N/D-16] Reduction,Resuse,Recovery,Recycling

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1 UNIT II Part A (2 Marks) 1. What are the 4 R s in waste hierarchy? [N/D-16] Reduction,Resuse,Recovery,Recycling 2. List the various advantages of waste segregation? [N/D-16] To reduce the volume of waste To alter the physical form of waste To recover the usable materials from solid waste 3. Define waste minimization.[a/m-17,n/d-11] Waste minimization or reduction at source is the most desirable activity, because the community does not incur expenditure for waste handling, recycling and disposal of waste that is never created and delivered to the waste management system. However, it is an unfamiliar activity as it has not been included in earlier waste management systems. 4. What is the purpose of onsite processing?[a/m-17,m/j-10] At the end of all sorting processes, biological processes and thermal processes, the non-utilisable waste has to be disposed off on land. Prior to this disposal, waste may need to be subjected to transformation by mechanical treatment, thermal treatment or other methods to make it suitable for land filling. 5. State the advantages of on-site segregation of solid waste? [A/M-13,N/D- The advantage of on-site segregation of solid waste are as follows 1. Waste minimization: The separation of recoverable materials like metal, plastics e.t.c. from waste result in less quantity of remaining waste which are to be treated. Hence the cost of treatment reduces. Also these recoverable materials like plastic, ferrous metals, etc. fetch revenue in those industries that utilize them. 2. On-site segregation may include intermediate sorting stations wherein the solid wastes are separated, baled and converted into a form which can easily be transported to the treatment or disposal yard. 3. Advantage of segregation: If waste cannot be segregated in the beginning, then it becomes very difficult to segregate them at the end in the dumping yard. Also the solid wastes which are segregated in the beginning are sent to respective treatment facilities. eg. The garbage can be sent to composting yard to obtain bio-manure, while the combustible fraction of the rubbish can be sent for incineration from where electricity can be produced via thermal power plant and also other green waste can be sent for sanitary land filling from where methane is produced. Thus all fractions of the solid waste are easily treated separately from which beneficial products are obtained. 6. What are the different on-site process on solid waste? [A/M-13]

2 1. Screening (Vibrating screen, Trommel screen, disc screen) 2. Shredding ( Flail mills, Hammer mills, Grinders and Wet pulping) 3. Magnetic separation (Ferromagnetic separators and eddy current separators) 4. Air classification (Horizontal air classifier, Inclined and moving chair curtains, Cyclone separators and Vibrating tables) 7. List out the factors causing variations of solid waste generation? [N/D-11] 1. Geographic location 2. Season of the year 3. Frequency of collection 4. Use of home grinders 5. Characteristics of the population 6. Extent of salvage and recovery 7. Legislation 8. Public attitudes. 8. What is recovery and recycling of solid waste? List out the operations involved in recycling? [N/D-11,M/J-11] The collection of materials like glass, plastics, ferrous metals, etc from solid waste and the utilization of these materials as raw material in the manufacture of new products is called recycling. The collection of materials like paper, cardboard, coir may be of sufficient value to warrant their separation and can be converted into energy source (through incineration or direct combustion in power boilers to produce steam) is called energy recovery. Operations involved in recycling: Handsorting, Air separation, Magnetic separation, Screening, Inertial separation, Floatation, Optical sorting, Electrostatic separation, Drying and dewatering, centrifugation and filtration. 9. What is the purpose of reduction in volume of solid waste? [N/D-10] If the volume of solid waste is reduced then the final volume to be treated is also reduced thus saving in cost. Also the transport cost reduces. 10. What is the essential of proper storage of MSW? [N/D-10] 1. The solid waste storage facility must have lid or must be covered on top to prevent litter and bad odour problems. 2. The storage bin or container must be of sufficient volume or capacity to temporarily store the waste before unloading. Often the container overflows due to insufficient size. 3. Municipal solid waste must not be kept more than 24 hours in the storage container since the organic waste starts to undergo putrefaction leading to odour problems. 4. The municipal workers as well as the people should not touch the solid waste directly by hand. Instead gloves must be provided to handle the solid waste. Also solid waste must be segregated and put into colour coded bags before discharge into street containers.

3 Part B (16 Marks) 1. (a) (i)explain briefly about the onsite storage methods. (8) [N/D- 16,A/M-17,] Onsite storage methods. In a usual setting of municipal solid waste management service, on-site storage is the point at which the service demand meets its supply, or more specifically, it is where solid waste generated is stored for collection by the municipal authority or its contractor. On-site storage (often in some sort of container such as a bin, basket or bag) can be classified under two categories: (1) individual storage serving the occupiers of a house, shop or office, and (2) communal storage serving the occupiers of more than one house, shop or office. Normally, the responsibility for the provision and maintenance of individual storage rests with the owner/occupiers of each unit while the municipal solid waste management authority assumes the responsibility of providing and maintaining communal storage. Therefore, it is not easy to assign the previously identified indicator types to the on-site storage indicators. The indicators relating to individual storage are generally classified as socioeconomic and physical condition indicators while those relating to communal storage are considered to be resource input indicators. The following indicators are useful for the design and operational management of a solid waste collection system. (a) Individual storage - Type (e.g. bin, bag, basket, no container) - Size or capacity (litre) - Material (e.g. plastic, metal, bamboo) - Number and location (on a map) - Maintenance condition (by observation) - Cover or lid (by observation) - Use of standardized containers (%) (b) Communal storage - Type (e.g. bin, bag, basket, no container) - Size or capacity (litre or m3) - Material (e.g. plastic, metal, wood, bamboo) - Number and location (on a map) - Maintenance condition (by observation) - Cover or lid (by observation) Maximum distance from houses (m) (c) Cost - purchase cost of individual container ($/container) - purchase cost of communal container ($/container) - repair cost of communal container ($/container).

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5 (b) (ii)describe the various methods of sorting the solid waste. (8) [N/D- 16,A/M-14] Municipal waste is being generated in ever increasing volumes in the urban areas. Theschematic diagram describes how municipal solid waste is segregated and where it can be used. Methods of segregation: 1. Onsite segregation: Sorting of solid waste into biodegradable fraction, combustible fraction, recyclable fraction, and Hazardous fraction at the point of collection itself is called onsite segregation of solid waste. Onsite segregation may also include intermediate sorting stations wherein the solid wastes are separated, baled and converted into a form which can easily be transported to the treatment or disposal yard. 2. Segregation in sorting yard at transfer stations: This involves hand sorting and mechanical sorting. It also consists of a series of mechanized equipments like 1. Vibrating screens, trommel and disc screens. - separating smaller sized particles from larger sized particles. 2. Magnetic separation - of ferrous metals (Ferromagnetic separator and Eddy current separator) 3. Air classification - of light, medium and heavy fractions 4. Incline and moving chair curtains - to separate glass from plastic bottles and aluminium cans) 5. Cyclone separators - dense materials from light materials 6. Vibrating tables - to separate light and heavy particles

6 7. Ballistic separator- to separate high density particles from low density particles

7 2. (ii) Explain the measures to be taken by local bodies towards segregation of recyclable waste? (8) Public health Public health concerns areas used for the storage of solid waste with vermin and insects that serve as potential disease vectors. The most effective control measure for both rats and flies is proper sanitation. It involves the use of containers with lids, the periodic washing of the containers, storage areas and removal of biodegradable materials. Aesthetics Aesthetic considerations related to production of odours and unsightly conditions when adequate attention not given to maintenance. Odours can be controlled through use of containers with lids and reasonable collection frequency. If odour persist, sprayed with masking deodorant. To maintain aesthetic conditions, the container should be scrubbed and washed periodically. 3. (a) What can you do to reduce solid waste? With a neat diagram explain the resource recovery facility producing various marketable products from municipal solid waste. (16) [A/M-17] [N/D- 16] Waste handling and sorting involves the activities associated with management of wastes until they are placed in storage containers for collection. Handling also encompasses the movement of loaded containers to the point of collection. Sorting of waste components is an important step in the handling and storage of solid waste at the source. For example, best place to separate waste materials for reuse and recycling is at the source of generation. the Households are becoming more aware of the importance of separating newspaper and cardboard, bottles/glass, kitchen wastes and ferrous and non-ferrous materials. On-site storage is of primary importance because of public health concerns and aesthetic consideration. Unsightly makeshift containers and even open ground storage, both of which are undesirable, are often seen at many residential and commercial sites. The cost of providing storage for solid wastes at the source is normally borne by the household in the case of individuals, or by the management of commercial and industrial properties. Processing at the source involves activities such as backyard waste composting Collection: The functional element of collection, includes not only the gathering of solid wastes and recyclable materials, but also the transport of these materials, after collection, to the location where the

8 collection vehicle is emptied. This location may be a materials processing facility, a transfer station, or a landfill disposal site. Sorting, Processing and Transformation of Solid Waste: The sorting, processing and transformation of solid waste materials is the fourth of the functional elements. The recovery of sorted materials, processing of solid waste and transformation of solid waste that occurs primarily in locations away from the source of waste generation are encompassed by this functional element. Sorting of commingled (mixed) wastes usually occurs at a materials recovery facility, transfer stations, combustion facilities, and disposal sites. Sorting often includes the separation of bulky items, separation of waste components by size using screens, manual separation of waste components, and separation of ferrous and non-ferrous metals. Waste processing is undertaken to recover conversion products and energy. The organic fraction of Municipal Solid Waste (MSW) can be transformed by a variety of biological and thermal processes. The most commonly used biological transformation process is aerobic composting. The most commonly used thermal transformation process is incineration. Waste transformation is undertaken to reduce the volume, weight, size or toxicity of waste without resource recovery. Transformation may be done by a variety of mechanical (eg shredding), thermal (e.g. incineration without energy recovery) or chemical (e.g. encapsulation) techniques. 4.Explain the types, mode of action, and applications of equipment used for component separation? [N/D-11]

9 Screening: Most MSW composting facilities first convey the waste into a bag-opener and screen or trommel to separate different sizes of waste (Figure 1). Fine materials, including soil, grit, and much of the organic wastes, fall through the screen as "unders". Plastic films and large paper products are retained on the screen as "overs" and may possibly be recycled or marketed as a refuse derived fuel (RDF), which is burned for energy recovery. But the main purpose of size segregation in a composting plant is to facilitate further separation. It is much easier for either people or machines to further separate materials of a similar size, as small items are not buried under large ones. Size fractionation also takes advantage of the size distribution properties of different waste components, generating streams in which certain recyclables or contaminants are concentrated. Figure 1. Trommel

10 Manual Separation: With materials segregated to a relatively uniform size, it becomes much more practical to hand separate recyclables and contaminants as they move along conveyor lines. As manual separation of MSW can be an unpleasant task, worker comfort and safety are very important. Ergonomic design can help workers function at their best, and issues such as conveyor speed, reach, placement of containers, flooring material, lighting, ventilation and dust control should all be considered. Here, as throughout the plant, it is recommended that workers wear safety glasses, gloves and adequate clothing to protect against injury from sharp objects, and hearing and respiratory protection wherever appropriate (see Fact Sheet 5). Conveyors and other materials handling machinery are critical to the operation of a plant. While this equipment may seem mundane, proper materials handling can minimize downtime and cleanup, and contribute to the overall efficiency of the facility. Steady materials flow will improve the efficiency of all the separation devices described below.

11 Air classification is an additional separation technology used in some MSW composting facilities, and is commonly used to generate a marketable RDF. This technology has been used in the combustion industry for many years. The heart of an air classification system is an air column or "throat", into which the waste stream is fed at a gradual rate. The air column is usually oriented vertically. A large blower sucks air up through the throat, carrying light materials such as paper and plastic, which then enter a cyclone separator where they loose velocity and drop out of the air stream. Heavier materials, such as metal, glass, and food waste, fall directly out of the throat (Figure 3). These two streams tend to be different sizes as well as densities, facilitating further separation. Glass and metal can be sorted out of the heavy fraction by systems such as the wet separator described below. The light fraction can be marketed directly as an RDF, or sorted for recyclable paper or plastic prior to composting.

12 Figure 3. Air Classification Wet separation technologies, while taking advantage of the same sorts of density differences as air classifiers, use water rather than air as the floating medium. These units are usually used to separate particles of glass, sand, and other heavy particles from organic materials prior to composting. A hammermill or other size reducer is needed prior to wet separation to minimize the potential for air pockets in the heavy fraction. After entrainment in a circulating water stream, the heavy fraction drops into a sloped (and sometimes vibrating) tank where it moves to a removal zone. This heavy fraction may be marketable as an aggregate substitute in construction applications. The less dense organic matter floats and is removed from the recirculating water using screening systems similar to those employed by wastewater treatment facilities. Wet separation is particularly effective at removing glass fragments and other sharp objects, which tend to be heavier than organic materials. Ballistic separation takes advantage of both density and elasticity differences to separate inert and organic constituents. This method can be used in either initial processing or in the refinement of the final compost product. Compost is dropped on a rotating drum or spinning cone, and the resulting trajectory differences bounce glass, metal and stones away from the compost. Compost refining refers to separation processes which occur after biological processing (see Fact Sheet 2). These can include screening, ballistic, and/or magnetic separation, and are important in preparing a visually attractive product. Contaminant separation at this late stage has a limited effect of chemical contaminants (see Fact Sheet 3), but can significantly reduce inert materials like plastics, glass, and stones. 5.What are the types of containers and collection vehicles used for the collection of solid waste? Discuss. [N/D-11,M/J-12] Material used for storage containers: Galvanized metal containers, Plastic containers, Container liners, Temporary and disposable containers(paper or plastic bags), Large portable or fixed containers, Large open top containers, enclosed

13 storage containers, containers equipped with self-contained compacting mechanism, special containers that are sealed to carry toxic or radioactive wastes.

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15 (ii) Types of collection vehicles: 1. Light-Weight Open Top Trailers for direct open top loading (grapple trucks)

16 2. Self-Contained Compactor Trailers for self-contained compactor loading 3. Light-Weight Closed Top Trailers for pre-load compactor loading

17 4. landfill tipper 5. Side dump trucks - for unloading solid waste

18 6. Drop box trailers for unloading trash. 6. List out the factors to be considered in selection of equipment for on-site processing of solid waste. Explain them? (M/J-13) The selection of equipment for On-site processes such as 1.Grinding. 2. Crushing 3. Shearing 4. Shredding. 5. breaking 6. tearing 7. Hydropulpery include small grinders, chippers, large grinders, jaw crushers, rasp mills, shredders, hammer mills and hydropulpers. Factors to be considered in selection of equipment for on-site processing of solid waste: 1. Properties of the material to be reduced, cut, grinded, sheared or shredded. 2. Size requirements of the material to be reduced. 3. Type of operation (Continuous or intermittent) 4. Operational characteristics including energy requirements, routine and specialized maintenance requirements, simplicity of operation, proved performance and reliability, noise output and air (principally dust)and water pollution control requirements. 5. Site considerations including space and height, access, noise and environmental limitations. 6. Material storage after size reduction and in anticipation of next functional operation. 7. Horse power requirements from manufacturers for different equipment operation and power availability. 7. Explain the estimation of storage capacity of community bins? (M/J- 13,N/D-13) The storage capacity of the community bins depend on the following a. Volume of solid waste collected per day per bin. b. Type of collection system (whether stationary or hauled container system) c. No. of houses emptying their contents into the bin and its population. d. Frequency of collection service at that location. e. Type of material of the container, make, cost and available standard sizes of it. f. Distance to empty and back, nearness to transfer station, on-site processing, off-site treatment and disposal yard.

19 g. Availability on the no. of push-cart/wheel barrow/ trucks for that particular area. h. No. of trips, No. of municipality workers for that area in consideration. Based on the above considerations the storage capacity of the community bin is decided. Low-rise dwellings: Because solid waste are collected manually from most residential low-rise detached dwellings, the community bins must be large enough to store solid waste from 7 to 15 individual dwellings. (ie) 3 m 3 (or) 6m 3 size bins kept at regular intervals. Medium and High rise buildings: Where solid waste cutes are available, separate storage containers are not used. In some older medium and high-rise apartments without cutes, wastes are stored in containers on the premises between collections. Large open top, roll-off containers. (ie) size = 26 m 3 (20L x 8W x 6H) are provided at the basement, Large containers equipped with self-contained compaction mechanism (ie) size = 23 m 3 (22L x 8W x 8H) can also be used to reduce the volume in the basement of medium rise apartments. 8.What is mechanical volume reduction? Discuss its importance and method of carrying out. (M/J- 13,N/D-10) The mechanical methods by which compaction (or) volume reduction of solid waste takes place are called mechanical volume reduction. Importance: The reduction in the volume of the waste results in less volume of solid waste to be treated resulting in 1. economy in MSW treatment 2. less wear and tear of machinery 3. more volume of solid waste can be hauled in less no. of trips. The method of volume reduction are as follows The wastes are brought to and loaded into the compactor either manually or mechanically wherein a compaction mechanism is employed to compress the waste. Types: Stationary compactors and Mobile compactors According to compaction pressure the compactors are divided into 1. Low pressure compaction: These low-pressure compactors are used in apartments and commercial establishments having a pressure less than 7 kg/cm 2 wherein a bailing equipment is used for compressing wastepaper and cardboard. 2. High pressure compaction: Recently a no. of high pressure compaction systems having a pressure upto 350 kg/cm 2 are used to produce compressed solid waste blocks or bales of various sizes.

20 (eg) In some systems the size of completed block is 4ft x 4ft x 16inches and the density is about 1600 Ib/yd 3 to 1800 Ib/yd 3 resulting in volume reduction of 3 to 1 through to 8 to 1