Operation Control Of "Coagulation Sedimentation-A/O" Treatment Process Of Tannery Wastewater

The quality of wastewater from tannery production is complex with high concentration pollutants and it is a kind of industrial wastewater which is difficult to be treated.The “Coagulation-floatation-A/O” was used as treatment processes in a tannery factory to treat the tannery wastewater with a treatment capacity of 3 000 m3·d-1 in this study.After treatment,the effluent quality met the indirect discharge requirements in Table2 of "Discharge Standard for Water Pollutants in Tanning and Fur Processing Industry"(GB 30486-2013).The operation control of “coagulation-floatation-A/O” treating the tannery wastewater was investigated.The optimum coagulation conditions were determined according to the experiment results.During the stable operation of coagulation and sedimentation equipments,when the influent water qualities were: pH of 7.6,COD of 3 400~3 800 mg·L-1 and SS of380~560 mg·L-1,the effluent qualities after treatment were: COD of 2110~2400 mg·L-1and SS of 40~ 70 mg·L-1.The average effluent concentrations of COD and SS were 2 196mg·L-1 and 57 mg·L-1 and the average removal rates of COD and SS were 39.1% and88.1%.The start-up conditions of A/O were low concentration and high hydraulic loading.The A/O was started up at influent COD of 1100~1200 mg·L-1 and ammonia nitrogen of50~60 mg·L-1.After 35 d operation,the start-up of A/O was completed and at this time,the influent flow increased from 50 m3·h-1 to 100 m3·h-1 and the effluent concentrations of COD and SS were below 160 mg·L-1and 15 mg·L-1,respectively.The influent flow maintained stable and the influent concentration increased in the load increasing stage when the NH3-N removal rate reached 90%.In this operation stage,COD concentration increased from 1 320 mg·L-1 to 2 300 mg·L-1 and the concentration of NH3-N increased from 76 mg·L-1to 117 mg·L-1.In the full load stable operation stage,the influent flow was115~ 125 m3·h-1,the concentrations of COD and NH3-N were 2 150~2 270 mg·L-1 and108~115 mg·L-1,and pH was 7.0~7.5.The concentration of dissolved oxygen was controlled to be 3.0-3.5 mg·L-1,and the reflux ratio of nitrification liquid was 300%.After A/O treatment,the effluent qualities were: pH of 7.2~7.6,COD of 114~126 mg·L-1,NH3-N of 9.2~10.3 mg·L-1,SS of 43~60 mg·L-1 and Sulfide of 0.2-0.4 mg·L-1.The performance of stable operation and high efficiency was achieved when thecoagulation sedimentation-A/O process was used to treat the tannery wastewater.The reduced amounts of main pollutants COD,NH3-N,SS and sulfide were 3 837.2 t·a-1,99.3t·a-1,1 828.3 t·a-1and 44.2 t·a-1,respectively,showing significant environmental benefits.The total investment of the project was 1 559.1 million yuan,and the wastewater treatment costs was 3.09 yuan·m-3.The investment and running cost seemed moderate.