Comparative economic, environmental and exergy analysis of power generation technologies from the waste sludge treatment

As a growing amount of sewage sludge is being produced from wastewater treatment plants, there is an urgency to develop innovative processes to dispose of such municipal waste well. One popular and widely acceptable way of utilizing waste sludge is for power generation. Although there is a good implementation of power generation plants from sewage sludge in Hong Kong, only a few published works have compared the conventional incineration-based process with chemical looping combustion (CLC) technology and the new supercritical water gasification (SCWG) process in detail. In this work, we performed a comprehensive energy, environmental and economic assessment of three power generation processes from the three thermochemical conversions of sewage sludge: i) conventional direct incineration + carbon capture (DI-CC), ii) steam gasification + CLC (G-CLC), and iii) SCWG + gas turbines (SCWG-GT). The final comparative results showed that the G-CLC scheme performed the best from the perspective of economic cost and benefits as well as the environmental global-warming potential (GWP) indicator, although the net energy and exergy efficiencies were not the largest among the three schemes. Notably, the SCWG-GT process for power generation showed its energy superiority with energy and exergy efficiencies of 20.70% and 16.69% consequently. Overall, CLC-based technology can be a promising process for power plant development in the future.