How to Identify the Bioavailable Phosphorus in Effluents from Advanced Nutrient Removal Systems

Effluent monitoring for TMDL permitting is normally based on total P concentrations regardless of the P composition, under the assumption that this is the most protective strategy for minimizing eutrophication in receiving surface waters. Currently little is known about how effluent P composition varies in different nutrient removal processes and how P composition affects algal growth. The fraction of P that can be used to support algal growth is termed bioavailable P (BAP). When comparing our results for different types of effluents, MBR systems were very efficient at removing particulate P while Blue Water PRO® and other sand filtration systems with chemical addition removed a large fraction of soluble reactive P - which is classically assumed to be more bioavailable. Algal bioassays indicated that effluents from dual media filters tended to have a higher percentage of BAP (BAP%) than other systems. The effluents from a DansaDeg® clarifier, a membrane filter, Trident® HS system and the Actiflo® process had the lowest BAP% suggesting that these chemical addition processes are the most efficient in reducing the P species that support algal growth. Moreover, our results also indicated that there was a significant difference between the processes with chemical addition (alum or ferric) and the biological processes without chemical addition.