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Phosphorus monitoring at wastewater treatment plants is essential as phosphorus (as total phosphorus) is an important main constituent regulated in treatment plant effluents. Recent trends are towards increasingly lower phosphorus limits, requiring reliable lower and lower phosphorus measurements. There is a long history of P analysis in dilute matrices; i.e., river and lake water and best practices have been developed. These best practices for surface waters are reported herein. Potential issues in wastewater P analysis by colorimetry include, pH, proton to molybdenum ratio, color development time, and digestion method. Of equal importance are the QA/QC measurement protocols implemented by wastewater analysis labs; demonstrably well performing examples from Coeur d'Alene, Spokane, and the City of Las Vegas are presented. Total reactive phosphorus is an ambiguous analytical measurement because the quantitative results depend strongly on color development time. For low level analysis, long path lengths have advantages in more precisely resolving low concentrations. Replicate measurements are essential, especially for low level P samples, in order to capture the true value of the sample within variability.When dealing with low concentrations even a small absolute error is a large relative error; thus, replicate measurements are essential to estimate true concentrations for dilute phosphorus samples.

Nutrient removal, specifically phosphorus, is an important objective during wastewater treatment. Chemically mediated phosphorus involves adding metal salts (Al3+, Fe2+, Fe3+) and removing the resultant solid phase via solid liquid separation techniques. The mechanism for phosphorus, and in particular phosphate, to partition into the solid phase is not definitively known for aluminum mediated removal. Here, the researchers test a conceptual surface complexation modeling framework, originally developed for ferric mediated removal. It is found that the same model framework as describes ferric experiments also works for aluminum experiments. The magnitude of the surface reactions (logK values) are different for the two models, but the same types of surface reaction stoichiometries describe data for phosphate removal batch tests using both cations (ferric and aluminum). Thus, in an equilibrium sense, aluminum and ferric phosphate removal chemistries are similar, but this is not true from a kinetic experiment. In previous ferric experiments, it was found that the surface complexation reaction involved a fast first step (minutes) followed by a slow second step (at least 24 hours for equilibration), but for aluminum the removal of phosphate is essentially instantaneous (on the order of seconds).