♤ Composting and Vermi Composting

o In the presence of microorganisms, degradation of organic matter occurs which lead to the formation of compost. This is known as composting.

o It is a simple and cost effective method which increases the moisture holding capacity of the soil; however there are concerns like methane emission, flies, bad odour, requirement of large land with this method.

o Vermi Composting is a less mechanised process where earthworms are fed on partially decomposed matter. This process casts out a fine, odourless and granular product used as biofertilizer in agriculture.

♤ Waste to Energy (WtE)

o Waste-to-energy or energy-from-waste is the process of generating energy in the form of electricity and/or heat. WtE is a form of energy recovery.

o Most WtE processes produce electricity and/or heat directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels.

o Some WtE technologies are:

 Incineration: MSW can be directly combusted in incinerators which reduces the waste volume by 80-90%; however due to high organic material, moisture content and low calorific value of MSW in India, this method is not practised much.

 Pyrolysis: Pyrolysis involves thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. It produces combustible tar/bio-oil and chars.

 Biomethanation: In this process organic waste is acted upon by microorganisms which break down the material with the release of Carbon dioxide and Methane; however this method is only suitable for organic biodegradable part of MSW.

 Refuse Derived Fuel (RDF): By shredding the solid waste or treating with steam pressure in an autoclave fuel can be produced. Burning RDF is more clean and efficient prior to incinerating MSW. This process is energy intensive and not suitable for wet MSW such as during rainy season.