Thermal Hydrolysis of Sewage Sludge: A Case Study of a WWTP in Burgos, Spain

An evaluation of the energy and economic performance of thermal hydrolysis technologies is carried out on a theoretical basis. The wastewater treatment plant (WWTP) of Burgos (Spain) was the base scenario of this evaluation. Energy and mass balances were established considering the registered data of primary and secondary thickened sludge in the WWTP for 2011 to 2016. These balances were analysed considering five different scenarios, taking as Scenario 1, the plant operating with conventional mesophilic digestion. The scenarios considered commercially available technologies. The best results were obtained when hydrolysis was applied to digested sludge and sludge from the Solidstream® process. These two scenarios showed the best performance regarding volatile solid removal and lower demand for live steam, achieving a higher amount of biogas available for valorisation using combined heat and power (CHP) units. The main advantage of the hydrolysis process is the decrease in the volume of digesters and the amount of dewatered sludge needing final disposal. The Solidstream® process allowed a 35% increase in biogas available for engines and a 23% increase in electricity production.