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:

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

Steps in Composting:

• PRE PROCESSING
• 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

Urban Waste Water Management Systems | Waste generation & Disposal

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