Integrating Gasification into Conventional Wastewater Treatment Plants: Plant Performance Simulation

The high amount of sludge produced from wastewater treatment plants (WWTPs) requires final disposal, forcing plant operators to search for alternatives without exerting an excessive energy demand on the global plant balance. Future revisions of the WWTP Directive will probably set additional constraints regarding the land application of sludge. Therefore, thermal treatment may seem a logical solution based on the additional energy that can be extracted from the process. The purpose of the present manuscript is to assess the integration of anaerobic digestion of sewage sludge and subsequent gasification using SuperPro Designer V13. Mass and energy balances were carried out, and the net energy balance was estimated under different scenarios. The integration of the process showed an electricity power output of 726 kW (best scenario, equivalent to 4.84 W/inhab.) against 411 kW (2.7 W/inhab.) for the single digestion case. The thermal demand of the integrated approach can be fully covered by deviating a fraction of gaseous fuels for heat production in a burner. Transforming syngas into methane by biological conversion allows densifying the gas stream, but it reduces the total energy content.