Dyeing and finishing wastewater treatment via a low-cost hybrid process of hydrolysis-acidification and alternately anoxic/oxic sequencing batch reactor with synchronous coagulation

Abstract

For dyeing and finishing wastewater (DFW) characterized by high chroma, organic nitrogen content, refractory organics, pH and salinity, there is a challenge to meet the stringent direct discharge standard in China (e.g., COD, NH4+-N, TN, TP, and chroma <80, 10, 15, 0.5 mg/L, and 50 dilution times) after conventional treatment. Motivated by the failure of hydrolysis-acidification (HA), high cost from glucose addition for denitrification and ozonation for chroma removal in a DFW treatment plant in China, a lab-scale low-cost hybrid process of HA and alternately anoxic/oxic sequencing batch reactor (HA + A/O-SBR) with synchronous coagulation was optimized for pre-treated DFW (COD, NH4+-N, TN, TP, and chroma of 1100, 9, 37, 4 mg/L, and 650 dilution times) treatment in this study. After debugging via low pH operation to eliminate and/or inhibit VFAs consuming microorganisms followed by optimization of reaction time, the HA-SBR produced effluent with COD, total VFAs, NH4+-N, and chroma of 736, 64.2, 19.5 mg/L, and 120 dilution times, achieving effective VFAs accumulation and NH4+-N conversion from organic nitrogen. The alternately A/O-SBR with optimal reaction time of 3 h for each stage and step feeding ratio of 800:200 mL had the best effluent with COD, NH4+-N, TN, TP, SS, aniline, and chroma of 94, <0.1, 13.5, 2.63, 31, 0.45 mg/L, and 58 dilution times. Synchronous coagulation using polymeric ferric sulfate with Fe:P molar ratio of 6 in the A/O-SBR produced effluent with COD, TP, and chroma of 77, 0.42 mg/L, and 35 dilution times, meeting the direct discharge standard.