Study On Technology Of Tanning Wastewater Treatment

Tanning wastewater is a kind of complicated and refractory organic wastewater containing high- concentration of pollutants. The combined treatment process of coagulation and floatation—hydrolysis and acidification—contact bio-oxidation was used to treat tanning wastewater in this study. The effect of different coagulation agents on wastewater purification was discussed. and the optimal coagulation agent and its dose were determined. The performance of combined treatment process was also explored and the main influencing factors were analyzed.The PAC, PAFS and PFS were used as coagulation agents in coagulation-sedimentation treatment experiments. The results indicated that PAFC was the optimal agent. The maximum COD removal rate was obtained as 39.5% when the dose of PAFC was 300 mg-L-1. The results also indicated that the COD and SS of effluent were 1251 mg·L-1 and 1060 mg·L-1, respectively, after coagulation and floatation treatment, when the COD and SS of influent were 2004-2188 mg·L-1 and 510-560 mg·L-1, respectively. The removal rates of COD and SS were 40.4% and 80.3%,respectively.The fabric filler was used in both hydrolysis-acidification reactor and contact bio-oxidation reactor. Series-operation and continuous influent were applied in the start-up period and influent loading increased gradually. The aeration conditions in both reactors were controlled in different periods. When the influent was 250 m3·d-1, the COD removal rate was over 80% and stable, indicating biofilm forming on the filler and microorganism acclimation. In the period of loading increasing, the dissolved oxygen concentration in the aerobic reactor was controlled at 3-4 mg·L-1. The loading was increased according to removal efficiency. After running for 30 days, the influent amount increased from 250 m3·d-1to 2000 m3·d-1 The COD, BOD5 and S2- of the influent were 1150-1400 mg·L-1, 440-520 mg·L-1, and 37-43 mg·L-1, respectively; the average COD, BOD5 and S2- of the effluent were 210 mg·L-1,55 mg·L-1, and 0.8 mg·L-1, respectively. The average removal rates of COD, BOD5 and S2- were 83.6%,88.4%, and 98.1%, respectively. These results showed satisfied organic pollutants removal in hydrolysis-acidification and contact bio-oxidation reactors under controlled conditions.The operational performances under different conditions were analyzed and the results indicated that when HRT was 6h, and dissolved oxygen concentration was 0.5 mg·L-1 in hydrolysis-acidification reactor, HRT was 12h, and dissolved oxygen concentration was 3-4 mg·L-1 in the contact bio-oxidation reactor, the optimal operational performance could be obtained, the average COD and BOD5 removal rates were 83.3% and 85.0% under these conditions.