| At present, the sewage management is relatively backward in the majority of Chinese rural areas. Rural wastewater simply discharges directly without any effective treatment to surface and groundwater, which contaminates the water body and accelerates eutrophication of watersheds. Thus, there is an urgent need to treat the rural wastewater. Considering the lack of funding, Onsite Wastewater System is not very practical. Thus the introduction of rural wastewater into Industrial Wastewater Treatment System nearby, where it is possible, for mixed treatment seems to be an effective choose, as it not only gets rural wastewater properly treated but also saves the money that would be required for the construction of on-site rural sewage treatment facilities.This article deals with the treatment technology of rural wastewater mixed with the tannery wastewater in the Industrial Wastewater Treatment Plant of Yongxin Industrial Park. In the study,a mixed wastewater. hereinafter referred to as the "mixed wastewater",was created by mixing the rural sewage collected near the Park with the tannery wastewater produced by fur-making factories in the Park. And the characteristics of the "mixed wastewater", the optimal mixing ratio and the operating parameters (hydraulic retention time and digestive liquid reflux ratio) were studied.Coagulation experiment has been used for pretreating the tannery wastewater. Results showed that the optimum flocculation conditions were as follows:the pH value of9. FeCl3dosage of500mg/L, and PAM dosage of4mg/L. In the optimal condition, the removal rate of Cr. S2-. SS and COD were99.08%,99.74%,90.08%and40.33%respectively. Chromium and sulfides in tannery wastewater were almost removed after coagulation.Based on the characteristics of the "mixed wastewater" quality, A/O process was chosen to treat the "mixed wastewater". Results showed that at different mixing ratio of rural sewage and tannery wastewater, there was no notable difference effect observed on Ammonia Nitrogen, COD, TN and TP removal by changing the hydraulic retention time. And when digestive fluid reflux ratio was changed, only TN removal effect was recorded with the best TN removal effect happened at a digestive juice reflux ratio of300%.According to the mixing ratio experiment, the optimal mixing ratio was determined as3:1, with the hydraulic retention time of15h and the digestive juice reflux ratio of200%. At the above parameter combination, pollutant concentrations in the effluent met well with the National Discharge Standards. The average COD removal rate was85.40%with the effluent COD as low as80.46mg/L. The average ammonia nitrogen in the effluent, meanwhile, was3.28mg/L, and the average removal rate was as high as96.16%. The removal rate of TN, which was71.72%, although not the best, was found to be still higher than theoretical value. The effulent COD, ammonia nitrogen and TN in other mixing ratios, however, didn’t meet well with the National Discharge Standards.For TP removal, the A/O technology was proved to show no difference in different mixing ratios and was constantly around relatively95%. When mixing ratio is3:1, it was showed that the effluent TP concentration increases as influent TP concentration increases, and the TP effluent concentration was slightly higher than the National Discharge Standards. The study suggests that the future studies will be placed on the feasibility of using of A2O process in treatment of "mixed wastewater".Study also showed that mixed treatment of rural sewage together with tannery wastewater substantially improved the water quality of tannery wastewater, made possible for the the treatment of tannery wastewater that would hardly meet the National Discharge Standards when treated alone to comply with the discharge standards. |
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