Energy prices and carbon footprint cause a reversal of raw sludge drying in favour of advanced digestion with thermal hydrolysis and cake recycling in a number of UK plants

Abstract

Northumbrian Water Ltd (NWL) treats the sewage for about 2.6 million people and a further 1.4 million population equivalent of industrial wastewater in the North East of England. The high cost of energy and the green credits available for renewable energy suggested anaerobic digestion was appropriate for NWL.

A study showed that there was an advantage in establishing two digestion centres, at the Bran Sands and Howdon WWTPs. By using advanced digestion technologies, NWL could maximise green credit payback and minimise digested solids. Following laboratory testing and piloting, Cambi's thermal hydrolysis process (THP) was selected in 2007, with payback expected in about 7 years.

The example from NWL has been taken up by another British water company, Welsh Water, which is building two Cambi thermal hydrolysis plants to replace 3 thermal dryers at Cardiff, Swansea and Newport (Wales) that were considered too expensive to operate.

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