During the primary treatment of sewage, sludge is separated from the sewage before it goes to secondary treatment. This sludge is then treated in an anaerobic environment, where there is no free oxygen.

In this anaerobic environment, micro-organisms such as bacteria break down organic materials in the sludge. This creates biogas including methane and carbon dioxide. At both the Eastern Treatment Plant (ETP) and the Western Treatment Plant (WTP), the biogas is captured to produce electricity for use on the site. By capturing these gases, we reduce the greenhouse gases and odours released into our air.

At the ETP, the sludge is anaerobically treated in large tanks called digesters. At the WTP, this treatment occurs in large covered lagoons.

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