Insight into effects of organic and inorganic phosphorus speciations on phosphorus removal efficiency in secondary effluent

Most previous studies of phosphorus (P) removal focused on investigation of the soluble, and particulate P, but ignoring the difference between organic and inorganic P. In this study, the effects of various flocculants, namely polyacrylamide (PAM) and polyaluminum chloride (PAC), on flocculation efficiency in different P speciations (organic and inorganic P) were investigated. A modified method to differentiate between organic and inorganic P content in secondary effluent samples was developed. The results showed that P speciation based on organic/inorganic P (Pearson’s correlation R = 0.915, p < 0.05) was more effective than those based on soluble/particulate P (p > 0.05) in evaluating the P content in secondary effluents. The liquid 31P nuclear magnetic resonance measurements results indicated that PAM was more effective in removing organic P (phosphonates and orthophosphate monoesters) rather than inorganic P. However, PAC was more effective in removing inorganic P (particularly orthophosphate) rather than organic P. Based on the modeled results of a response surface methodology (RSM), doses of PAM and PAC were optimized for secondary effluent containing different amounts of organic and inorganic P from the two typical wastewater treatment plants (WWTPs) in Wuhan city, China.