Enhancing the efficiency of thermal hydrolysis process in wastewater treatment plants by the use of steam accumulation

This paper evaluates the technical and economic feasibility of using a steam accumulator in the thermal hydrolysis process for the treatment of sludge. The increase in the efficiency of anaerobic digestion and biogas valorisation through the combined use of heat and power engines was studied based on scenarios from the wastewater treatment plant of the city of Burgos (Spain). These scenarios were evaluated based on the installation of steam accumulation to average the thermal needs of the process. Biogas production was estimated based on the plant’s operating conditions between 2011 and 2016. Results indicated a process enhancement from 33 to 100% due to a better use of exhaust gases. Consequently, increases of 20.0% in the net biogas and 13.1% in electrical energy production were obtained, along with decreases of 66.8% in the thermal power needs and 61.9% in the biogas consumed by the recovery boiler. The economic savings were 98,213 €/year, due to a decrease in the need to purchase electrical energy from the network. The return on investment period was 2 years after introducing a steam accumulator to the process and replacing the boiler with a new, smaller one.