Opportunities for Nutrient Recovery from Post-Digestion Sludge Handling: Analysis and Feasibility Study Using Municipal Scale Aerobic and Anaerobic Digesters

The wastewater treatment process has developed with the primary goals of protecting receiving water ecosystems and human health. Over time, there have been continuous innovations in process efficiencies, energy recovery, and nutrient removal. Wastewater offers opportunity for recovery of resources of various economic values, and recent research aims at process innovation to optimize resource recovery while still achieving the primary goals of the treatment process. The objective of this study is to assess the logistical and economic feasibility of recovery of nitrogen and phosphorus at two municipal treatment plants in the Tampa Bay area, one employing aerobic digestion and the other anaerobic digestion. The study is conducted using literature review of applicable processes, mass balance on the fate of nutrients (N and P) through the treatment plants and special attention to sludge handling. Based on the whole-plant mass balance conducted at the facilities, it is estimated that over 80% of the nutrient influent is routed to the solids handling side of the plant, warranting special attention to this area for nutrient recovery. Sludge digested through anaerobic and anaerobic processes have distinctly different characteristics and opportunities for resource recovery are specific to each process. Mass balances for nitrogen in the anaerobic digestion process show a high concentration of dissolved ammonia. The feasibility of struvite precipitation by addition of phosphate and magnesium compounds is evaluated through batch reaction using anaerobic sludge filtrate. Aerobic sludge contains most of the nutrient resources in the solid phase, ready for recovery if handled properly. Phosphorus release is a potential concern and specific phosphorus release rates are evaluated for a municipal scale aerobic digester