Anaerobic Digestion (AD)


The process

Anaerobic digestion (AD) is a proven renewable energy technology. Additionally it reduces greenhouse gas emissions by capturing methane from the decomposition of organic materials, such as livestock manures, slurries, sewage sludge and food wastes. By harnessing the natural process - where organic matter is broken down by bacteria in the absence of oxygen, in a closed vessel - it enables the production of biogas that can be used as a renewable energy source for both for heat and electrical power.

The treated digestate from the process can be used as fertiliser.

AD and waste water treatment

AD is the now the method favoured by water companies for dealing with waste water sludge and many have anaerobic digesters attached to water treatment plants.

The future

It is estimated that in England and Wales in 2005 64% of sewage sludge was digested. By 2015 this will have increased to 85%. See table below for a snapshot of the volume of sewage sludge treated by water companies.

Table: An estimate of anaerobically digested sewage – England & Wales

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Source: Dr Tim Evans FCIWEM, Tim Evans Environment

FWDs + AD = energy

The Government is committed to delivering a huge increase in Energy from Waste (EfW) through AD and FWD output is proven to enhance the extraction of sustainable value from waste. Studies in Sweden have shown that adding the food waste output of FWDs to the sewage waste stream can increase biogas capture by as much as 46%. See The Science.