Phosphorus in Effluent from Nutrient Removal Treatment Facility Are Like Coconuts and Bananas

Due to the widespread severity of eutrophication in surface waters, there is a strong impetus to require ultra-low effluent phosphorus (P) concentrations (i.e., <100 μg/L) in municipal wastewater treatment plant discharges. Filtration or membrane separation is used to meet these low targets therefore most of the effluent P from advance P removal facility is in the soluble phase. In our study, we evaluated the effect of nutrient removal process designs on effluent P speciation and bioavailability of phosphorus (BAP). A standard bioassay was used to determine both total bioavailable P and soluble bioavailable P fractions in the effluents. The nutrient removal technologies tested included alum- and ferric-based chemical P removal, enhanced biological P removal (EBPR), single and two-stage filtration, and membrane separation processes. Our result indicates that the bioavailability and P species composition varies with the nutrient removal process and that there is a significant portion (>50%) of effluent P that is recalcitrant to algal growth. Comparison between different technologies indicates that higher chemical doses achieved lower effluent P concentrations decreased the BAP% fraction even further. The results of this work may encourage water quality modelers to consider the various forms of P when assessing ecological impacts of municipal nutrient removal facility effluent discharges and encourage TMDL permit writers to consider accounting for only the effluent P that is available.