Impact of organic matter constituents on phosphorus recovery from CPR sludges

This study evaluated the influence of organic matter (OM) constituents on the potential for recovery of P from wastewaters when FeCl₃ treatment is employed for P removal. The presence of OM constituents did not influence P release from Fe-P sludges when alkaline and ascorbic acid treatments were employed. However, the overall recovery of P from wastewater was impacted by the presence of selected OM constituents through the reduction of P uptake during coagulation. The presence of protein and humic matter showed remarkably low P removal values (3.0 ± 0.4% and 23 ± 1% respectively) when compared to an inorganic control recipe (62 ± 2%). Elevated soluble Fe (SFe) residuals in the presence of proteins (87 ± 5%) and humics (51 ± 1%) indicated interactions between Fe(III) cations and negatively charged functional groups like hydroxyl, carboxyl, and phenolic groups available in these organics. Significant negative correlations between P removal and residual SFe were observed suggesting Fe solubilization by OM constituents was the mechanism responsible for reduced P removal. The findings of this study identify, for the first time, the impact of OM constituents on overall P recovery when Fe(III) salts are employed and provide insights into recoveries that can be expected when Fe is added to primary, secondary treated, and industrial wastewaters. PRACTITIONER POINTS: Low P removal values were observed for protein and humic dominated wastewater recipes. Iron(III) solubilization counted for P removal reduction by proteins and humic acids. There is no effect of OM on P release from Fe-P sludge at pH 10 and ascorbic acid treatments. OM and agent employed to release P from sludges affected overall recovery of P.