Trends in the environmental and economic sustainability of wastewater-based resource recovery: A review

Wastewater is rich with valuable resources available for recovery. Although the resource recovery process can enable the offset of freshwater withdrawals, fertilizer production, and the use of fossil fuels, it comes at a cost. This review focuses on the environmental and economic impacts of recovering water, energy, and nutrients from wastewater. Specifically, life cycle assessments and life cycle cost analyses were reviewed to identify trends in wastewater-based resource recovery systems. Process conditions were found to have a significant influence on impacts in some instances. For example, the operating temperature for incineration could lower or eliminate N2O emissions altogether, while the flow rate and cold water temperature resulted in heat transfer efficiencies for thermal energy recovery systems ranging from ∼12% to 92%. Economies of scale were largely present in the processing of wastewater and biosolids, however, the re-distribution of reclaimed water exhibited diseconomies of scale as water networks increased in service size. This led to some studies exhibiting lower impacts for centralized systems, while others favored decentralization. Nonetheless, when averaged and categorized by scale, the greenhouse gas emissions for large-scale water reclamation systems (280 kg CO2-eq/person-year) was significantly lower than medium- and small-scale systems (4600 and 23740 kg CO2-eq/person-year, respectively). Future research is recommended in analyzing understudied technologies (e.g., environmental assessments of thermal energy recovery systems and wastewater-based hydropower technologies), investigating spatial-temporal contexts, and optimizing wastewater systems with multiple forms of resource recovery technologies across varied scales.