Treatment of anaerobic digester effluents of nylon wastewater through chemical precipitation and a sequencing batch reactor process

Chemical precipitation, in combination with a sequencing batch reactor (SBR) process, was employed to remove pollutants from anaerobic digester effluents of nylon wastewater. The effects of the chemicals along with various Mg:N:P ratios on the chemical precipitation (struvite precipitation) were investigated. When brucite and H3PO4 were applied at an Mg:N:P molar ratio of 3:1:1, an ammonia-removal rate of 81% was achieved, which was slightly more than that (80%) obtained with MgSO4·7H2O and Na2HPO4·12H2O at Mg:N:P molar ratios greater than the stoichiometric ratio. To further reduce the ammonia loads of the successive biotreatment, an overdose of phosphate with brucite and H3PO4 was applied during chemical precipitation. The ammonia-removal rate at the Mg:N:P molar ratio of 3.5:1:1.05 reached 88%, with a residual PO4–P concentration of 16 mg/L. The economic analysis showed that the chemical cost of chemical precipitation could be reduced by about 41% when brucite and H3PO4 were used instead of MgSO4·7H2O and Na2HPO4·12H2O. The subsequent biological process that used a sequencing batch reactor showed high removal rates of contaminants. The quality of the final effluent met the requisite effluent-discharging standards.

► Chemical precipitation and a sequencing batch reactor (SBR) were employed to treat nylon wastewater. ► A high ammonia removal from nylon wastewater was achieved by chemical precipitation. ► The operation cost of chemical precipitation could be reduced about 41% by using brucite instead of MgSO4·7H2O. ► The quality of the final effluent met the requisite discharge standards for nylon wastewater.