Modeling & Operational Case Study of a Full Scale Phosphorus Recovery System Coupled with WASSTRIP®: Factors to Consider in Model Development & Insights for Optimal P Recovery

As wastewater facilities grapple with the dual aim of meeting their effluent water quality goals and driving for resource recovery, the complexity of treatment operations is growing. For instance, increasingly stringent effluent phosphorus limits has led many facilities to implement or consider enhanced biological phosphorus removal (EBPR) as well as sidestream phosphorus recovery systems. EBPR leads to an increase in the phosphorus (P) content of biomass, and by extension, results in high levels of P release in solids handling processes such as anaerobic digestion. EBPR can therefore be associated with significant sidestream nutrient (ammonia and phosphate) loadings, and in some cases nuisance Struvite precipitation. The impact of EBPR on side stream nutrient loads, digestion and dewatering is becoming the focus of increasing study. The WASSTRIP™ process is an innovative technology that leverages the release of Orthophosphate under anaerobic conditions to reduce the Phosphorus load to anaerobic digesters, by preferentially diverting the soluble Preleased to sidestream nutrient recovery processes. This helps to reduce the availability of Orthophosphate and associated metals in the digester, thereby reducing the propensity for nuisance struvite precipitation in the digesters and downstream solids handling processes. This paper uses a GPS-X™ based process modeling study to investigate the mechanisms that underlie a number of observations from a full scale WASSTRIP™ process. The results indicate that the pre-thickening of sludge to the WASSTRIP™ process leads to improved hydraulic and solids retention time, which effectively increases organic loadings, enhancing volatile fatty acid (VFA) formation and Ortho-P release. The ability of process models to robustly predict ortho-P release, monovalent and divalent concentration changes in solids handling processes, and the composition of inorganic precipitates like Struvite and Newberyite, offer the potential for using them as a platform for enhancing the operation of nutrient recovery processes.