ES 200-S1Module A : Solid Waste Management and Other Aspects of Environmental Management Professor Anurag Garg [email protected] Waste Collection 2 Waste Collection 3 Waste Collection 4 . each container picked up requires a round trip to the disposal site. Hauled Container System • Such systems suited for the places where waste generation rate is high because large containers are used. 5 . • The use of large containers reduces handling time as well as unsightly accumulations and unsanitary conditions. • Hauled container systems have the advantage of requiring one truck and only one driver (and a cleaner if needed only) to complete one cycle. Hauled Container System (HCS) (Conventional mode) 6 . a driver and one helper are used. • For mechanical systems. Stationary Container System (SCS) • These may be used to collect all types of waste. • These can be of two types: Mechanically loaded collection vehicles Manually loaded collection vehicles • The personnel requirements for the stationary collection system will vary depending upon the type of system. 1 – 3 collectors 7 may be used. • For manual collection system. Occasionally. . two helpers may be used. Stationary Container System 8 . the time spent picking up the loaded container and the time required to redeposit the container after its contents have been emptied. pickup refers to the time spent driving to the next container after an empty container has been deposited. For hauled container system operated in the exchange container mode. pickup includes the time required to pick up a loaded container and to redeposit the container at the next location after its contents have been emptied. beginning with stopping the vehicle before loading the contents of the first container to be emptied have been loaded. pickup refers to the time spent loading the collection vehicle. Some Definitions • Pickup For hauled container system (HCS) operated in conventional mode. For stationary container system (SCS). 9 . For stationary container system. Some Definitions…. haul represents the time required to reach the location where the container will be emptied. 10 . haul refers to the time required to reach the location where the container will be emptied. • Haul (h) For hauled container system. It does not include any time spent at the location where the contents of the container are unloaded. starting when a container whose contents to be emptied has been loaded on the truck and continuing through the time after leaving the unloading location until the truck arrives at the location where the empty container is to be redeposited. starting when the last container on the route has been emptied or the collection vehicle is filled and continuing through the time after leaving the unloading location until the truck arrives at the location of first container to be emptied on the next collection route. It does not include any time spent at the location where the contents of the container are unloaded. It includes the time spent waiting to unload as well as the time spent unloading the waste. • At-Site (s) The time spent at the location where the container (HCS) or collection vehicle (SCS) are unloaded. Some Definitions…. These may be necessary and un-necessary. 11 . • Off-Route (W) It refers to the time spent on activities which are non- productive from the point of view of the overall collection operation.. screens combustibles Density separation Separation of light fraction (paper. Commonly Used Unit Operations for Separation of MSW Item Function Equipment Shredding Size reduction and to obtain a uniform e.and under-sized e.g..g. vibrating screens. material trommel or rotary • Waste segregation into light screens and disc combustibles and heavy non. Hammer mills product Screening • Separation of over.. Air classifier (air classification) plastic) from heavier materials (such as metals) Magnetic separation Separation of ferrous metals Magnetic separator Densification Compaction into bales or flattening or Balers or Can crushers increase the density of waste materials 12 . Shredders Hammer mill Shear shredder 13 . Trommel Screens 14 . 75 inch diameter by 0. • The performance of baling and compaction equipment is rated by percentage volume reduction and the compaction ratio.5 – 0. Volume reduction (%) = (Vi – Vf)*100/Vi Compaction ratio = Vi/Vf Vi and Vf = initial and final volume of waste before and after compaction. • Pellets are cylindrical in shape (0. • It is also performed for preparing densified RDF. Densification (Compaction) • To increase the density of waste to facilitate efficient storage and transfer.5 – 1 inch long). • Bales of size 48x30x42 inch to 72x30x44 inch are produced by applying a pressure ranging from 100 – 200 psi. • Cubes and pellets can be produced from waste paper or shredded RDF. respectively 15 . readily biodegradable organic fraction of MSW is decomposed by microbes under controlled aerobic conditions. Composting Process • It is aerobic biological process • In this process. • MSW volume is reduced by around 50% after the process. • A stabilized product (compost) is produced that can be used as soil cover at landfills or conditioner. • Three systems for composting process are: Windrow. 16 . forced aeration and in-vessel. Windrow Composting 17 . Static Aerated Windrows 18 . In-Vessel System 19 . 20 . Composting Process… • Sometimes. sewage sludge or agricultural residues are also added with MSW. • Composting can also have negative impacts: Water pollution may exist if moisture content is very high (> 65%) Odor is another major problem from composting sites using open windrow method. This is called ‘co- composting’. pH control 7.0 – 7.5 21 . Design Considerations for Composting Process Parameter Comment/ range Particle size 25 – 75 mm C/N ratio 20 – 40 Blending and Partially decomposed waste or sewage seeding sludge can be added Moisture content 40 – 60% Temperature Should be maintained in thermophilic range during the active composting period. +…. s = a – nw • In case of complete conversion CaHbOcNd + [(4a+b-2c-3d)/4]O2→aCO2 + [(b-3d)/2]H2O + dNH3 NH3 + 2O2→ H2O + HNO3 22 . the oxygen requirement would be: CaHbOcNd + 0. Aerobic Biological Transformations • General aerobic transformation of solid waste is described by the following equation: Organic matter + O2 + nutrients → New cells + resistant organic matter + CO2 + H2O + NH3 + SO42.5(ny+2s+r-c)O2→nCwHxOyNz + sCO2 + rH2O + (d- nx)NH3 where r = 0.+ heat • If resistant matter is also formed (neglecting production of new cells and sulfate)..5(b – nx – 3(d-nx)). Problem • Estimate the total theoretical amount of air that would be required under aerobic conditions to oxidize completely an organic waste (mass = 1 ton) with a chemical formula of C120H180O80N2. 23 . 1993) 24 .Variation of Temperature During Composting Process (Tchobangolous. 3 – 4 weeks static piles ft (W) In-vessel . 16 – 20 . . 2 – 2.5 weeks composting followed by system curing in open windrows 25 . Specifications of Composting Systems Composting Dimensions Turning Time to obtain type frequency finished product Windrow 5 – 8 ft (H). 12 – 18 Weekly 4 – 6 weeks ft (W) Aerated 8 – 10 ft (H). poor temperature control. Issues in the Implementation of Composting Facilities • The production of odors Causes: Low C/N ratio. excessive moisture and poor mixing Odor masking agents and enzymes can be used • The presence of pathogens Sufficient exposure time and temperature need to be maintained • The presence of metals 26 . ~ 1. 27 . plant equipment and roads.25 acre for buildings and roads. Of this. • For larger plants. Land Requirements • For windrow composting plant of 50 tons/ day.g. typically about 2.5 acre would be devoted to buildings. 1 acre would be needed for the composting operation and 0.. a plant processing 500 t/d can be built on 18 acre land. the unit area requirements would be less.5 acre of land would be required. e. • For each additional 50 tons. 2010 Suriyonan. 2013 Jianping.. 2014 28 . Available Vertical Composting Systems Journals Patents Commercial Andersen Colon Karnchanawong and Jay and Michael. 2011 Adhikari et al... 2016 Sierra.. 2015 Storino et al. (2014) Faverial and Tatano et al. (2009) Moqsud et al.. (1995) et al.. 2010 et al. 2011 systems Muley and Devotta. Few Examples of Horizontal Composting Systems 29 . 30 vessel systems .Major Reasons for Failure of Community Based/ Centralised Composting Systems • Inadequate ventilation in community based systems and conventional windrows • Lack of demonstration systems at household/ community level • Long composting period and odour issues from decentralised as well as centralised composting systems • Development of anaerobic pockets due to no or low turning frequency in conventional windrow system • Difficulty in turning of long conventional windrows • Requirement of large land areas • Little know-how about centralised forced aeration in.