Civil & Environmental Engineering Department, University of California, Irvine, CA 92697-2175, USA; Water-Energy Nexus (WEX) Center, University of California, Irvine, CA 92697-2175, USA. Electronic address: [Email]
Biosolids or sludge management has become an environmental and economic challenge for water resource recovery facilities (WRRFs) and municipalities around the world. The electric energy and operational costs linked to the solid processing stage can account for 20% and 53% of the overall treatment respectively, and as such they are primary factors among utilities which must be considered while working toward more efficient strategies with less energy use. As part of the growing awareness of greenhouse gas (GHG) emissions, municipal wastewater treatment plants have begun reporting their GHG emission inventories. However, there is not yet a standardized or fully comprehensive CFP analysis for the biosolids management. In this paper, two major metropolitan WRRFs in China and the USA with two different biosolids management approaches were compared in terms of energy and carbon footprint (CFP). Site-specific equipment inventories coupled with state-of-the-art methodologies were used for the carbon and energy intensity assessment. Tailored biosolids management strategies and scenarios were included in the analysis to provide a venue for the reduction of their environmental impact. Co-digestion with food waste (FW) and the economic feasibility of its implementation were proposed as a GHGs mitigation strategy to highlight the energy recovery potential. Although both plants had similar energy intensity, Plant A (Shanghai) exhibited three times larger CFP primarily due to site-specific limitations on their biosolids management. The study showed the potential to improve CFP by 28.8% by selecting convenient strategies (i.e., incineration with AD). Energy recovery with its concurrent environmental benefits can be further enhanced by implementing FW co-digestion. This study shows the economic and environmental relevance of selecting adequate biosolids processing strategies and energy recovery practices in WRRFs.