Re-visiting the Phostrip process to recover phosphorus from municipal wastewater

Abstract

This study examined an innovative approach to make use of the Phostrip process to recover phosphorus (P) from municipal wastewater. Returned activated sludge (RAS) from a municipal wastewater treatment plant was systematically studied to examine P release kinetics of RAS in a recovery stream that contained high concentrations of phosphate (PO43−-P). Findings suggested that the specific P release rate in RAS declined with increasing concentration of PO43−-P in the recovery stream. However, there was a strong positive linear correlation between acetate consumed and P released by the RAS (Pearson product-moment correlation coefficient [r = 0.98, n = 45, p < 0.005]). The data also suggest that acetate concentration in the recovery stream was not a factor in the observed reduction of specific P release rate with increasing PO43−-P in the recovery stream. When P release rates (poly-P hydrolysis rate) at different initial P concentrations were modelled using a modified Michaelis-Menten equation, a good fit was achieved between the experimental and the modelled data. According to the model, the maximum specific P release rate (18 mg-P/g-MLSS.h) halved when PO43−-P concentration in the recovery stream reached approximately 83 mg-P/L. Additionally, the RAS demonstrated a Prelease/Cacetate uptake molar ratio of approximately 0.5. An application of the derived P release kinetics into an innovative side stream process configuration showed that a Phostrip tank with a small footprint (9 m3) is sufficient to facilitate P recovery from a wastewater treatment plant that receives 61 ML/d of influent.