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Composting of Solid Waste, Objectives & Its Steps

By: Haseeb Jamal / On: Jul 06, 2017 / Solid Waste

Composting of Solid Waste:

  • Defined as "biological decomposition of biodegradable organic constituents of waste under controlled conditions to a state sufficiently stable for nuisance free storage & handling and for safe use in land applications"
  • About 70% of MSW is decomposable / compostable
  • Main organisms involved in composting are: actino-mycetes(filamentous bacteria), fungi and protozoa

Objectives of Composting

  • to transform biodegradable OM into biologically stable material thereby reducing the original volume of the waste
  • to destroy pathogens, insect eggs and other unwanted organisms and weed seeds that may be present in MSW;
  • to retain maximum nutrient content; and
  • to produce a product that can be used to support plant growth and as a soil amendment as fertilizer and soil conditioner

Composting time depends on:

  1. Nature of waste
  2. Moisture content
  3. Available nutrients
  4. Other environmental factors
  5. Under controlled conditions, can be made more effective and efficient
  6. Organic matter + O2 + nutrients + microbes ------- New cells + resistant OM + CO2 + H2O + NH3 + SO4 + heat
  7. Reduces weight/volume of the organic fraction of MSW
  8. Produces compost ( a humus like material that can be used as a soil conditioner)
  9. To produce methane - Bio Gas

Also See: Hospital Waste | Types of Hospital Waste

Steps in Composting:

  • Receiving
  • Sorting/separation: removal of recyclable material, metals, debris, glass etc. -affects the quality of
  • Size Reduction/Screening: to provide greater surface area for microbes to attack, to improve insulation, to facilitate homogenizing of initially heterogeneous material, to reduce depth for oxygen diffusion.
  • If size is too small, it impedes the diffusion of oxygen and CO2 from the sites being attacked especially during thermophylic stage when Oxygen demand is the highest.
  • Typical range for feed material = ½ - 2 inches.
  • Adjustment for waste properties (e.gC/N ratio)
  • Decomposition and curing/maturation:
  • Types are: Static piles and in-Vessel composting
  • Preparation and marketing of the final compost product: Grinding, screening, air classification, blending with various additives, granulation, bagging, storage and transportation

Windrow Composting

  • Triangular piles 7 feet high and 14-16 feet wide at the base
  • Turning by front end loader or mechanical turner twice per week
  • Composting period 2-6 weeks

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