An economic and global warming impact assessment of common sewage sludge treatment processes in North America
Ziyi Zhuang, Badr A. Mohamed, Loretta Y. Li, Omar Swei
Abstract
This study details a probabilistic life cycle assessment model to evaluate the environmental (i.e., global warming potential) and economic impact of four common sewage sludge treatment methods (anaerobic digestion, incineration, composting and pyrolysis) coupled with their most common end-of-life scenarios for the North American context. The model is subsequently applied to a realistic case study where each technology is assessed over a 10-year analysis period based on data made available by a Canadian municipality. For the case study, pyrolysis and anaerobic digestion coupled with agricultural land application have an expected global warming impact at least 46% and 60% lower, respectively, than the alternative treatment methods. Conversely, composting and pyrolysis have an expected life cycle cost at least 32% and 27% lower, respectively, than the competing treatment alternatives. Composting is able to achieve its relatively low life-cycle costs through the affordability of the required capital investments; conversely, pyrolysis is able to reduce its life-cycle cost through the recovery of valuable resources such as energy, fertilizer, and fuel. These findings and the resulting tool from this work will aid decision-makers as they seek sustainable sewage sludge treatment strategies.