Understanding the abiotic interaction between phosphate and macromolecular organic compounds in waste activated sludge during anaerobic treatment

The abiotic interaction between ferric phosphate and major macromolecular organics (protein, saccharide, humic substance) in waste activated sludge (WAS) were studied, and the effect of phosphate on protein and the reaction mechanism were discussed in particular. With the addition of ferric phosphate, the concentration of protein was greatly reduced with a removal efficiency of 77.3%, accompanied by a remarkable increment of NH 4 + -N concentration (13.5 mg/L) when the release efficiency of NH 4 + -N reached 52.7%, while fulvic acid (FA) and glucose barely changed. PO 4 3 ‐ was the functional ion dominating the protein decomposition and NH 4 + -N release. The maximal release efficiency of NH 4 + -N (66.9%) occurred at pH 7, and the NH 4 + -N concentration mainly depended on the protein concentration, while the presence of FA and glucose would interfere the decomposition of protein. The analytical results of circular dichroism (CD) suggested that the reaction went through two stages: firstly, the process was relatively stable and phosphate showed a tendency to facilitate the transition from helices to β-sheets; then peptide chains on the helices were broken and deamination of amino acid residues occurred. Due to the loss of hydrophilic groups, hydrophobicity of the residue was further enhanced, resulting in its co-precipitation with protein. The results are applicable to proteins with similar structures to bovine serum albumin (BSA). This study provides a novel insight into the transformation of organic matters and phosphorus (P) in the anaerobic treatments of WAS.