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Rights: The University of Waikato
Published 10 June 2008

Peter Hall from Scion explains how anaerobic digestion is a technique used to convert liquid effluents and wastes into a gas.

Anaerobic digestion is a process that converts wet or liquid wastes (such as sewage) into a gas (for example, methane). Liquid waste (effluent) is stored in ponds, and anaerobic bacteria are introduced to these ponds. The microorganisms break down the waste in the absence of oxygen, and in this process, they produce methane, which we can capture and use to generate heat or electricity.

Points of interest: Why is anaerobic digestion good for the environment? (Tip: greenhouse gases)



Anaerobic digestion is a technique which is used to convert often liquid or very wet effluents and wastes into a gas, and basically, it’s microorganisms and bacteria operating in the absence of oxygen to break down the organic material biomass, and it produces methane. And it’s done in an environment where the gas can be captured and compressed. So basically, you can take things like cow shed effluent, municipal effluent, effluent from meatworks and dairy factories, capture it into a pond and then have some bacteria introduced into the pond, and the methane that comes off it can then be used either as a heat source, or you can run the gas through an internal combustion engine attached to a generator and create electricity, and you can also get the heat off the water jacket of the engine.

It is actually a really efficient way of dealing with an environmentally nasty waste and capturing the energy out of it. So you get a double benefit – you get the energy, you get the environmental benefit of cleaning up the waste, and you get reduced greenhouse gases.

Watercare Services Ltd
KQED QUEST, some rights reserved
Paul Brooker