20211222 Composting

Open Aerobic Composting

Open aerobic composting occurs under moist, oxygen-rich (aerobic) conditions where complex organic molecules are broken down by microorganisms that release nutrients and energy contained in the waste. As the name itself suggests, open composting is carried out in open windows or open static piles where the controlled biological decomposition and pasteurization of organic materials under aerobic conditions takes place.

Enclosed Composting

Enclosed composting uses the same process of aerobic decomposition of organic matter by bacteria and other microorganisms as done in open composting. It is also known as ‘In-Vessel Composting’ and while it is mostly undertaken on a small scale in local communities, but it can also operate on a large scale for a municipal level where the waste produces many tonnes of cured compost per day depending on the system in use.


Vermicomposting is the process of breaking down the organic material that involves the joint action of earthworms and microorganisms and does not involve a high heating stage. As the agents of turning, fragmentation, and aeration, the worms consume organic wastes such as food waste, animal wastes, and sewage sludge to produce a soil conditioner. Vermicomposting is widely used at a small scale level like in backyard composting and in schools and offices. These technologies are however now being developed at a commercial scale for processing sewage sludge/biosolids and animal wastes.

Anaerobic Digestion

Anaerobic digestion is the breaking down of organic materials either occurring naturally or under controlled conditions in the absence of oxygen. The carbon content of the material is released as methane or biogas rather than carbon dioxide. Anaerobic digestion converts organics into methane, carbon dioxide, hydrogen sulfide, other gases, and water. A solid soil conditioner, a liquid soil conditioner that can be used as agricultural fertilizer, and biogas, which may be used for energy generation are some by-products of the anaerobic digestion process.


Pyrolysis is the process that involves the thermal decomposition of organic material in a low or no oxygen environment. Pyrolysis generates three main products; char, oil, and gas in varying ratios depending upon the types and quantity of the waste materials fed into the pyrolysis reactor and process conditions. Gasification is the process where steam is brought into use to react with most of the char, tar, and volatile gas resulting from pyrolysis which is then converted into a more useful combustible gas, with or without air. The two terms are often used in tandem since there are many Pyrolysis/Gasification technologies that apply the two processes in series.