Environmental and Economic Impacts of Managing Nutrients in Digestate Derived from Sewage Sludge and High-Strength Organic Waste

Increasingly stringent limits on nutrient discharges are motivating water resource recovery facilities (WRRFs) to consider the implementation of sidestream nutrient removal or recovery technologies. To further increase biogas production and reduce landfilled waste, WRRFs with excess anaerobic digestion capacity can accept other high-strength organic waste (HSOW) streams. The goal of this study was to characterize and evaluate the life-cycle global warming potential (GWP), eutrophication potential, and economic costs and benefits of sidestream nutrient management and biosolid management strategies following digestion of sewage sludge augmented by HSOW. Five sidestream nutrient management strategies were analyzed using environmental life-cycle assessment (LCA) and life-cycle cost analysis (LCCA) for codigestion of municipal sewage sludge with and without HSOW. As expected, thermal stripping and ammonia stripping were characterized by a much lower eutrophication potential than no sidestream treatment; significantly higher fertilizer prices would be needed for this revenue stream to cover the capital and chemical costs. Composting all biosolids dramatically reduced the GWP relative to the baseline biosolid option but had slightly higher eutrophication potential. These complex environmental and economic tradeoffs require utilities to consider their social, environmental, and economic values in addition to present or upcoming nutrient discharge limits prior to making decisions in sidestream and biosolids management.

Automated summary

The increasingly strict nutrient discharge limits are driving water resource recovery facilities (WRRFs) to consider the implementation of sidestream nutrient removal or recovery technologies. This study evaluated the life-cycle global warming potential, eutrophication potential, and economic costs and benefits of sidestream nutrient management and biosolid management strategies after digestion of sewage sludge augmented by high-strength organic waste (HSOW). The results showed that thermal stripping and ammonia stripping had lower eutrophication potential, but would require higher fertilizer prices to cover the costs. Composting all biosolids significantly reduced the global warming potential but slightly increased the eutrophication potential.