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Composting Definition, Objectives Process

By: Haseeb Jamal / On: Feb 02, 2017 / Solid Waste, Definition, Processes
 
 

Definition:

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

  1. to transform biodegradable OM into biologically stable material thereby reducing the original volume of the waste
  2. to destroy pathogens, insect eggs and other unwanted organisms and weed seeds that may be present in MSW;
  3. to retain maximum nutrient content; and
  4. 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 - BioGas

STEPS IN COMPOSTING

PREPROCESSING

Receiving

Sorting/separation:

Removal of recyclable material, metals, debris, glass etc.

Size Reduction/Screening:

  1. To provide greater surface area for microbes to attack
  2. To improve insulation, to facilitate homogenizing of initially heterogeneous material, to reduce depth for oxygen diffusion. If size is too small, it impedes the
  3. Diffusion of oxygen and CO2 from the sites being attacked especially during thermophylic stage when Oxygen demand is the highest.
  4. Typical range for feed material = ½-2 inches
  5. Adjustment for waste properties (e.g C/N ratio)

Decomposition and curing/maturation:

Types of Decomposition and curing/maturation are:

  1. Static piles and in-Vessel composting
  2. Preparation and marketing of the final compost product:
    Grinding, screening, air classification, blending with various additives, granulation, bagging, storage and transportation

Windrow composting

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

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