Mass Balance Model for Sustainable Phosphorus Recovery in a US Wastewater Treatment Plant

In response to limited phosphorus (P) reserves worldwide, several countries have demonstrated the prospect of recovering significant amounts of P from wastewater treatment plants (WWTPs). This technique uses enhanced biological P removal (EBPR) to concentrate P in sludge followed by chemical precipitation of P as struvite, a usable phosphate mineral. The present study models the feasibility of this enhanced removal and recovery technique in a WWTP in Arizona with design parameters typical of infrastructure in the United States. A mass balance was performed for existing treatment processes and modifications proposed to estimate the quantity of P that could be recovered under current and future flow conditions. Modeling results show that about 71 to 96% of the P being lost potentially could be recovered as struvite. About 491 ± 64 t yr of struvite may be recovered after process modification, which corresponds to $150,000 ± $20,000 yr in P sales to fertilizer industries. The process was projected to be economically feasible, with a payback period of 45 ± 30 yr in the studied WWTP and a much shorter duration of 3 ± 1 yr for WWTPs already using an EBPR process. Furthermore, modeling results suggest that P recovery can improve the quality of biosolids by favorably reducing the P:N ratio. Implementation of this strategy at US WWTPs may increase national security by reducing dependence of limited P resources. Considering all aspects of the recovery process with respect to environmental, economic, and social implications, the examined technique is concluded to represent a cost-attractive and sustainable method for P management in US WWTPs.