Retrofitting Municipal Wastewater and Sludge Treatment Facility toward a Greener and Circular Economy

The conventional wastewater treatment facilities (WWTFs) are designed with the prime directive of simply purifying sewage by solids, pathogens, and nutrients removal. However, this ill-considered design philosophy stands chance to render the WWTFs unfavorably energy intensive and wasteful of nutrients. A promising route to raise the energy and nutrients utilization efficiencies of WWTFs is to retrofit the existing systems with smart upgrades for resource recovery. In this article, promising retrofits based on the benchmark design of WWTFs are proposed by virtue of process modifications and biosolids upcycling. This study directly assesses the economics and life cycle environmental impacts of the proposed retrofits of WWTFs, which are in turn compared to the reference design. Emerging thermochemical technologies and more complicated bioreactors are considered to maximize the biogas production, nutrient recovery, and biosolids upcycling. The results show the retrofit with hydrothermal liquefaction and secondary anaerobic digester demonstrates the highest net present value of - $ 97.93 MM, despite the highest annual production costs. The life cycle assessment results identify chlorination as the major contributor for most impact categories.