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Chapter: Civil - Municipal Solid Waste Management - Sources and Types of Municipal Solid Wastes

Physical and Chemical Characteristics of Solid Waste

Physical Characteristics - Density, Moisture Content. Chemical Characteristics - Lipids , Carbohydrates, Proteins, Natural Fibers, Synthetic Organic Materials.




                  It  is  expressed as  mass per   unit volume (kg/m).  This  parameter is required for designing a solid waste management  program. A reduction in volume  by 75%  is achieved through normal compaction equipment, so that an initial density of 100kg/m may readily be increased to 400 kg/m.  Significant changes in the density occur as  waste moves from sources to disposal site, as A result of scavenging, handling, wetting,  and  drying by  the Weather and  vibration during transport.  Density  is critical in the design  of sanitary  landfill as well as for storage, collection and transport of wastes.  Efficient  operation  of  landfill  requires  compaction of wastes to optimum density.


Moisture Content                  

  Values greater than  40%  are also not common.  Moisture increases  the weight  of the solid  wastes and therefore  the  cost of collection  and  transport increases. Consequently waste should be insulated  from rain  or other extraneous water  source. Moisture content is  critical determinant  in  the economic feasibility  of waste treatment by incineration.   During   incineration   energy   must be  supplied for evaporation of water and raising the temperature of vapour.


  Information of chemical characteristics is  important in evaluating alternative processing and  recovery options. Typically  waste is considered  as  combination of combustible and  noncombustible components.  If solid  waste is  to be used as a fuel or for  any other use we should know its chemical components.



  These are included in the class of fats, oils and grease.  The principal sources of lipids in the garbage are cooking  oil and fats. Lipids have  high heating  values about 38,000 Kj/Kg (kilojoules/kilograms), which makes  the waste  with high lipid content  suitable for energy recovery.  Since lipids become  liquids at temperature slightly  above ambient  they add to  the liquid content during waste decomposition. They are biodegradable, but they have low solubility in water  and hence the rate of biodegradation is  slow.



  These are primarily originated  from  the food sources rich in starch and celluloses. These readily  biodegrade into carbon dioxide, water and  methane. Decomposition  of carbohydrates attracts the  flies and rats  and hence should not be  left exposed for  long  duration.



These are the compounds containing carbon, hydrogen, nitrogen and oxygen and organic acid with amino groups. They are primarily found in food and garden wastes, but their partial decomposition result in the production of amines, which impart unpleasant odors.

Natural Fibers

 These are the natural products contain cellulose and lignins that are relatively resistant  to  biodegradation.  These  are found in  paper products, food and yard wastes. Paper is almost100% cellulose, cotton over  95% and wood  products  over  40-50%. These are   highly combustible products  most suitable for incineration. The calorific  value of  oven dried  paper products are in the  range 12000-18000 kj/kg.              

Synthetic  Organic Materials

 In the recent years plastics have become a significant components  of solid waste, accounting for  1-10%. They  are highly resistant to the biodegradation; hence their presence in  the waste is  objectionable. Currently  much attention  is  given to reduce this component at disposal sites. Plastics have a high  heating value, about 32000 kj/kg, which makes them  very suitable for incineration.  However, among  the plastics Polyvinyl  chloride  (PVC)  when  burnt produces dioxin and acid gas. The trace gases  produced during the  burning  of plastic are proved  to be carcinogenic.   

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