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

摘要

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 H_3PO_4 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 MgSO_4 · 7H_2O and Na_2HPO_4 ·12H_2O 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 H_3PO_4 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 PO_4—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 H_3PO_4 were used instead of MgSO_4-7H_2O and Na_2HPO_412H_2O. 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.