Study On The Wastewater Discharged From A Tannery Using Coagulation-Sedimentation And Multistage A/O Process

The studies on the influencing factors of multi-stage A/O system have shown that in order to keep the effluent of the system, the appropriate temperature should not below 10℃, and appropriate parameter of the influent pH, COD, ammonia was 8.0⁸.5, 500¹000 mg/L and 100²00 mg/L separately, and the influent flow distribution could be 4:3:2:1. As the influent ammonia was 100²00 mg/L, in order to keep the effluent, the appropriate parameter was: hydraulic retention time(HRT) of the system was 24h, the HRT ratio of anoxic/oxic was above 1/3, the dissolved oxygen in the oxic keep at 2³ mg/L, the mixed liquor volatile suspended solids(MLVSS) in the system keep at 4000⁵000 mg/L, and the return sludge ratio(SRT) was 50%.The coagulation-sedimentation experiment have shown that the optimal operating conditions in chromium-containing wastewater pretreatment: pH is about 8, the dosage of FeSO₄ coagulant is 600 mg/L, the removal rate of COD, total chromium and SS is 45%, 96% and 30% separately. The optimal operating conditions in sulfur -containing wastewater pretreatment is that pH is about 12, the dosage of FeSO₄ and Al₃(SO₄)₂ coagulant is 2100 mg/L and 1200mg/L, the removal rate of COD, sulfides and SS is 78%, 94% and 81% separately. The optimal operating conditions in comprehensive wastewater pretreatment is that pH is about 12, the dosage of FeSO₄ coagulant is 3000 mg/L, the removal rate of COD and SS is 21% and 68%.the experiment of the four-stage A/O system with effective volume 1 m³ was conducted. It was concluded that at the temperature of 20³0℃, influent COD and ammonia was 500¹000 mg/L and 120¹80 mg/L, the average removal of the multi-stage A/O system had reached 60% and 60% separately, and the effluent was below 250 and 30 mg/L separately, which reached local wastewater discharge standard. When the temperature was below to 10℃, the effect multi-stage A/O system would be seriously affected.With the characteristics of large fluctuations in water quality and quantity, high concentrations of organic pollutants and suspended solids, containing large amounts of toxic heavy metals and sulfides, tannery wastewater was difficult to treat, and had become a major difficulty in industrial wastewater treatment. Currently, as for the treatment of tannery wastewater, biochemical treatment with physical and chemical pretreatment were the major techniques, while various forms of combination process were constantly changing , and the effluent were not so good, especially the effluent ammonia, which was almost impossible to reach wastewater discharge standard. To solve the problem of high concentration of ammonia in the biochemical process, the multi-stage anoxic/oxic(A/O) process was adapted in tannery wastewater treatment, which was characterized by the function of nitrification and de-nitrification. Then the combined process of physical and chemical pretreatment with the multi-stage A/O was applied to tannery wastewater treatment. Based on the experiment of flocculation and multi-stage A/O system, this paper was aimed to explore its feasibility of tannery wastewater treatment and appropriate control parameters.