Municipal Waste Management Objectives PDF

Municipal Waste Management Unit –III: Off-Site Processing: Objectives of waste processing – Physical processing techniques and Equipments; Resource recovery, Composting and bio- methanation Functional Elements of Solid Waste Management System ...

Municipal Waste Management Unit –III: Off-Site Processing: Objectives of waste processing – Physical processing techniques and Equipments; Resource recovery, Composting and bio- methanation Functional Elements of Solid Waste Management System  Processing of Wastes A process by which the physical property of the wastes is altered to make it best suited for technology adopted for its treatment is called as processing of wastes.  Processing Techniques & Equipments Purpose of Processing The purposes of processing are: (a) Improving efficiency of SWM system (b) Recovering material for reuse (c) Recovering conversion products & energy Various Techniques & Equipments (a) Mechanical Volume & Size reduction (b) Component Separation. - Air Separation - Magnetic Separation Screening (c) Drying & Dewatering (A) Mechanical Volume & Size Reduction Mechanical volume and size reduction is an important factor in the development and operation of any SWM system. The main purpose is to reduce the volume and size of waste, as compared to the original form, and produce waste of uniform size. Volume Reduction (or) Compaction Volume reduction (or) compaction refers to densifying the wastes in order to reduce their volume. The Benefits of compaction are: Reduction in the quantity of materials to be handled at the disposal site. Improved efficiency of collection and disposal of wastes. Increased life of landfills as it decreases the space requirements in landfills. Economically viable waste management system. Disadvantages associated with compaction include, Poor quality of recyclable materials sorted out of compaction vehicle; Difficulty in segregation or sorting (since the various recyclable materials are mixed and compressed in lumps); Bio-degradable materials (e.g., leftover food, fruits and vegetables) destroy the value of paper and plastic material. When wastes are compressed, their volume is reduced, which is normally expressed in percentage and computed by Volume Reduction (%) = {(Vi - Vf) / Vi} 100 The compaction ratio of the waste is given as Compaction ratio = Vi / V f where Vi = volume of waste before compaction, m3 and Vf = volume of waste after compaction, m3  Equipments for Volume reduction (or) Compaction Stationary Equipment: This represents the equipment in which wastes are brought to, and loaded into, either manually (or) mechanically. According to their application, stationary compactors can be described as light duty (e.g., Those used for residential areas), commercial or light industrial, heavy industrial and transfer station compactors. Usually, large stationary compactors are necessary, when wastes are to be compressed into: Steel containers that can be subsequently moved manually or mechanically. Chambers where the compressed blocks are banded or tied by some means before being removed. Chambers where they are compressed into a block and then released and hauled away untied. Transport vehicles directly. Movable Equipment: This represents the wheeled and tracked equipment used to place and compact solid wastes as in a sanitary landfill. Low Pressure (7Kg/cm2)Compactors Compact systems with a capacity up to 351.5 Kg/cm2 came under this category. Here, specialized compaction equipment are used to compress solid wastes in to blocks (or) bales of various sizes. BALING EQUIPMENT Operating under high pressure they produce relatively small compact bales/blocks of solid waste or recyclable materials. ▪ Used for recyclable materials for their shipment to buyers or manufacturers. ▪ Most common waste that are baled are paper, cardboard, plastic, PETE bottles, aluminium cans etc.   CUBING AND PELLETING EQUIPMENT Technology that can be used to produce densified refuse derived fuels (dRDF) for combustion purposes.  Size Reduction (or) Shredding This is required to convert the large sized wastes into smaller pieces. Size reduction helps in obtaining the final product in a reasonable size in comparison to the original form.  Equipments for Size Reduction (or) Shredding Hammer Mill: These are used most often in large commercial operations for reducing the size of wastes. Hammer mill is an impact device consisting of a number of hammers, fastened flexibly to an inner disk, which rotates at a very high speed. Solid wastes as they enter the mill, are hit by sufficient force, which crush (or) tear them with a velocity so that they do not adhere to the hammers. Wastes are further reduced in size by being struck between breaker plates & cutting bars fixed around the periphery of the inner chamber. This process of cutting and striking action continues, until the required size of material is achieved and after that it falls out of the bottom of the mill. Hydro-pulper: An alternate method of size reduction involves the use of a hydropulper as shown below: Solid wastes and recycled water are added to the hydro- pulper. The high speed cutting blades, mounted on a rotor in the bottom of the unit, convert pulpable and friable materials in to slurry with a solid content varying from 2.5 to 3.5% The rejected material passes down a chute that is connected to a bucket elevator, while the solid slurry passes out through the bottom of the pulper tank and is pumped to the next processing operation. (B) Component Separation Component separation is a necessary operation in which the waste components are identified and either manually (or) mechanically to aid further processing. This is required for: recovery of valuable materials for recycling. Preparation of solid wastes by removing certain components Prior to incineration, energy recovery, composting and biogas production. Air Separation This technique has been in use for a number of years in industrial operations for segregating various components from dry mixtures. Air separation is primarily used to separate lighter materials from the heavier ones. The lighter materials may include plastics, paper products and other organic materials. Equipments used for Air Separation 1. Conventional Chute Type Its one of the simplest type of air classifier. In this type, when the processed solid wastes are dropped into the vertical chute, the lighter materials are carried by the air flow to the top while the heavier materials fall to the bottom of the chute. A rotary air lock feed mechanism is required to introduce the shredded wastes into the classifier. 2. Zig-Zag Classifier It consists of a continuous vertical column with internal zig-zag deflectors through which air is drawn at high rate. Shredded wastes are introduced at the top of the column at a controlled rate, and air is introduced at the bottom of the column. As the wastes drop into the air stream, the lighter fraction is fluidized and moves upward and out of column, while the heavy fraction falls to the bottom. Magnetic Separation The most common method of recovering ferrous scrap from shredded solid wastes involves the use of magnetic recovery system. ➡ Ferrous materials are usually recovered either after shredding (or) before air separation. ➡ Magnetic separator is used to remove the ferrous material from the incinerator residue. Magnetic recovery systems have also been used at landfill disposal sites. Equipments used for Magnetic Separation 1. Suspended Magnet In this type of separator, a permanent magnet is used to attract the ferrous metal from the waste stream. When the attracted metal reaches the area where there is no magnetism, it falls away freely. This ferrous metal is then collected in a separate container. 2. Magnetic Pulley This consists of a drum type device containing magnets (or) electromagnets over which a conveyor (or) a similar transfer mechanism carries the waste stream. The conveyor belt conforms to the rounded shape of the magnetic drum and the magnetic force pulls the ferrous material away from the falling stream of solid Waste. Screening Screening is the most common form of separating solid wastes, depending on their size by the use of one (or) more screening surfaces. Screening has a number of applications in solid waste resource & energy recovery systems. Screens can be used before (or) after shredding and after air separation of wastes in various applications dealing with both light & heavy fraction materials. Drying & Dewatering Drying and dewatering operations are used primarily for incineration systems with (or) without energy recovery systems. These are also used for drying of sludges in wastewater treatment plants, prior to their incineration (or) transport to land disposal. Drving The following methods are used to apply the heat required for drying the wastes. Convection Drying: In this method, hot air is in direct contact with the wet solid waste stream. Conduction Drying: In this method, the wet solid waste stream is in contact with a heated surface. Radiation Drying: In this method, heat is transmitted directly to the wet solid waste stream by radiation from the heated body. Dewatering Dewatering is more applicable to the problem of sludge disposal from wastewater treatment plants but may also be applicable in some cases to municipal/industrial waste problems. When drying beds, lagoons (or) spreading on land are not feasible, Other mechanical means of dewatering are used. The objective is to reduce the liquid volume in the solid waste stream. Once dewatered, the sludge can be mixed with other solid waste, and the resulting mixture can be: (i) incinerated to reduce volume (ii) used for the production of recoverable by-products (iii) used for production of compost (iv) buried in a landfill  1. Composting defined as a process in which organic matter of the solid waste is decomposed and converted to humus and stable mineral compounds. The end product of composting process is called compost which is rich fertilizer. There are three methods of composting: (1) Composting by Trenching (2) (2) Open window composting (3) (3) Mechanical Composting. Compost Benefits of Compost Compost improves the quality of soil, and for this reason it is considered as a soil conditioner. It contains a variety of the basic nutrients required for healthy growth of plants. In addition to, nitrogen, phosphorous, and potassium, certain micronutrients viz. manganese, copper, iron, and zinc also found in compost which helps them to control diseases and insects. Compost improves the structure and texture of the soil enable them to retain nutrients, moisture, and air for the betterment of growth of plants. Compost Mechanism of Composting Composting is a biochemical process in which aerobic and anaerobic microorganism decomposes organic matter into valuable manure called as compost.  Biological Process of Composting Microorganisms + OM --- -> H2O + CO2 + Heat + Humus 3 phases under optimal conditions (1) Mesophilic - lasts couple of days (~40°C) (2) Thermophilic - can last a few days to several minutes ( 55°C-65°C) (3) Several-month cooling and maturation phase COMPOSTING BY TRENCHING  Indore Method of Composting In this method solid waste night soil and animal dung etc. are placed in brick lined pits 3 m x 3 m x 1 m deep in alternate layers of 7.5 to 10 cm height, till the total height becomes 1.5 m. Chemical insecticides are added to prevent fly breeding. The material is turned regularly for a period of about 8 to 12 weeks and then stored on ground for 4 to 6 weeks. In about 6 to 8 turnings and period of 4 months time compost becomes ready for use as manure. Insecticide used in Indore method was DDT but now because of very high half life of DDT in nature other suitable insecticide is recommended, e.g. Gamaxine. Indore Method of Composting  Bangalore Method The solid waste is stabilized anaerobically. Earthen trenches of size 10 x 1.5 x 1.5 m deep are filled up in alternate layers of solid waste and night soil/cow dung. The material is converse with 15 cm earthen layer and left for biodegradation. In about 4-5 months the compost becomes ready to use, normally a city produces 200 to 250 kg/capita/year of refuse and 8 to 10 kg / capita/year of night soil Bangalore Method of Composting  NADEP method The NADEP method of organic composting uses a wide range of organic materials such as crop residues, weeds, forest litter and kitchen waste with an end- product of a fertilizer that serves as a good alternative to farmyard manure NADEP method of Composting  COIMBATORE METHOD Composting is done in pits of different sizes depending on the waste material available. A layer of waste materials is first laid in the pit. It is moistened with a suspension of 5-10 kg cow dung in 2.5 to 5.0 I of water and 0.5 to 1.0 kg fine bone meal sprinkled over it uniformly. Similar layers are laid one over the other till the material rises 0.75 m above the ground level. It is finally plastered with wet mud and left undisturbed for 8 to 10 weeks. Plaster is then removed, material moistened with water, given a turning and made into a rectangular heap under a shade. It is left undisturbed till its use. In Coimbatore method, there is anaerobic decomposition to start with, following by aerobic fermentation. It is the reverse in Bangalore method. The Bangalore compost is not so thoroughly decomposed as the Indore compost or even as much as the Coimbatore compost, but it is bulkiest.  Vermicomposting Red worms in bins feed on food scraps, yard trimmings, and other organic matter to create compost. The worms break down this material into high quality compost called castings. Worm bins are easy to construct and are also available for purchase. One pound of mature worms (approximately 800-1,000 worms) can eat up to half a pound of organic material per day. The bins can be sized to match the volume of food scraps that will be turned into castings. It typically takes three to four months to produce usable castings. The castings can be used as potting soil.  Biomethanaition Biomethanation is a process by which organic material is microbiologically converted under anaerobic conditions to biogas. Three main physiological groups of microorganisms are involved: fermenting bacteria, organic acid oxidizing bacteria, and methanogenic archaea. Microorganisms degrade organic matter via cascades of biochemical conversions to methane and carbon dioxide. Materials used in a bio-methanation Process flow chart for bio-methanation  Uses Cooking gas. Electricity. Water heating, space (room) heating etc. Compressed natural gas for use in vehicles. It is being used in transport. For example, ‘Amanda Biogas Train’ runs on biogas in Sweden. It is used in many states for street lighting purposes. It can be used in hydrogen fuel cells as well. Conclusion: