Wastewater, sludge and subsequent biosolids are large inherent energy sinks and, in most cases, contain more energy than required to operate a treatment plant. This paper explores how the energy can be exploited to minimise plant demands. This study found that no single measure can help achieve energy neutrality; rather, a combination of processes. The use of anaerobic digestion was found to reduce energy demands by over a third, and by 60% when combined with enhanced primary treatment. Energy neutrality was potentially achievable by combining these processes with further energy recovery downstream via burning as a cake. However, this study highlighted the poor energy extraction capability of anaerobic digestion when considered in a plant-wide envelope.
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