The Influence of Heat Balance on the Economics of Advanced Anaerobic Digestion Processes

The UK Water Industry currently generates approximately 800 GWh pa of electrical energy from sewage sludge, a renewable by-product from wastewater treatment. Advanced anaerobic digestion processes are beginning to improve energy yields from this resource which the industry has in abundance. These processes are being implemented across the UK and within Thames Water. However, these processes are still being driven by the operational and regulatory requirements for sludge disposal and significant opportunities for increased energy extraction are not being exploited. A model has been created which compares current advanced sludge to energy processes, based around anaerobic digestion. Particular attention is made to the use of heat within these advanced processes such as the Thermal Hydrolysis Process. Factors that affect the heat balance and the subsequent economics are explored. CHP engine selection and the combined heat and power configuration are critical to optimising the operational economics.