Characterization of the dissolved phosphorus uptake kinetics for the effluents from advanced nutrient removal processes

• We determined the uptake rates of dissolved P in advanced WWTP effluents.
• Gamma gave the most parsimonious fit to the data using the fewest terms.
• The uptake rates could be seamlessly incorporated into the existing TMDL.
• Existing TMDL might overestimate up to 40% bioavailable P.

Given the importance of the watershed protection plans, direct determination of phosphorus (P) mineralization rates in advanced wastewater treatment facility effluents is crucial for developing the most protective strategies minimiz eutrophication in receiving surface waters. In this study, algal bioassays were used to determine the uptake rate of dissolved P in effluents from a broad range of advanced nutrient removal technologies (e.g., membrane biological reactor, traditional biological, tertiary membrane, Blue PRO™, etc.). Dissolved P uptake kinetics were fit to a gamma model and three first-order decay models. A traditional one-pool model correlated poorly with the experimental data (i.e., r2 = 0.73 ± 0.09), whereas two-pool model and three-pool models performed much better (i.e., r2 > 0.9). These models also provided strong evidence for the existence of recalcitrant P in the effluents from these tertiary facilities. The Gamma model showed the mineralization of organic P followed a reactive continuum and further suggested the partitioning of P loads with different bioavailability levels should be accounted for the future modeling practices. From a modeling perspective, the Gamma model should be considered to be the theoretically best model as it gave the most parsimonious fit to the data using the fewest terms. Our study suggested that the current Total Maximum Daily Load (TMDL) model could be easily modified with the updated mineralization kinetics, which should lead to both ecological and economic benefits.

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