Leather Wastewater Treatment Process Optimization And Advanced Treatment

The operating state of a tannery wastewater treatment center in Zhumadian was taken as an example in this paper. From the seven months tracking research, it can be seen that if the alkali precipitation process was used only, it was difficult to make the total chromium content to meet the national standard, which requires the emission of chromium cannot more than 1.5mg/L, for the concentration of suspended matter in chromium-containing wastewater had a high value. It can be seen that water quality had greatly improved and the pollutant concentration maintained stable after the integrated wastewater went through the first handling processes, such as grille, primary sedimentation, and flocculation. After the water went through the second biochemistry handling process, besides CODCr, the concentration of other pollutants in the water could meet the direct emission standard limits. In this situation, the concentration of CODCr could only meet indirect emission standard limit of the national standard. Therefore, it is urgency of finding a efficient, stable, low operating costs tannery wastewater treatment process for leather industry.Firstly, alkali sedimentation process, alkali- flocculent combined process, alkali precipitation followed coagulant aids precipitation co-precipitation process and alkali precipitated followed sand filtration tank filter process were used to handle the chromium-containing wastewater. As can be seen from the experimental results, the last three processes could reduce the total chromium content in wastewater to emission standard limit. But at the same time, the cost of alkali- flocculent combined process was the highest. The alkali precipitation followed coagulant aids precipitation co-precipitation process followed. And alkali precipitated followed sand filtration tank filter process was the last. So the alkali precipitated followed sand filtration tank filter process was suitable to treat the large amount chromium- containing wastewater and for the enterprises which needed long-term treatment of leather wastewater.For secondary biochemical leather wastewater, filler treatment process was used at first. The results showed that removal effect of the filler to the CODCr was not good. And the removal efficiency was between 12% and 13%. The concentration of CODCr was still larger than the direct emission standard limit of the national standard. Secondly, ozone oxidation, sodium hypochlorite oxidation and Fenton oxidation were used. The results showed that removal effects of these three kinds of processes on the water chromaticity were lager than 90%. The removal effects on ammonia nitrogen were the best when the sodium chlorate oxidation process was used. And the removal efficiency of ammonia nitrogen could reach 100%. Ozone oxidation process and sodium chlorate oxidation process had little effect on the concentration of CODCr. When the value of pH was 4, the addition amount of H2O2 was 600mg/L, the addition amount of Fe2+ was 400mg/L, and the reaction time was 50 min, the removal efficiency of CODCr by Fenton oxidation process was larger than 50%. The concentration of CODCr could meet the direct emission standard limit of the national standard. At the same time, single factor experiment was designed during Fenton oxidation process. Two measures were tried. One was aeration stirring used PVC perforated aeration tube. The other was to adjust the value of pH to 8 when the reaction was terminated. Using these two measures could not only reduce the capital investment of equipment and the costs of maintenance, but also reduce the dosage of drugs and the operating cost.Finally, the wastewater treatment project of a leather industry in Jiaozuo was taken as another example in this paper. It could be seen from the actual operating result that after the wastewater was treated by the alkali precipitated followed sand filtration tank filter process. The effluent concentration of total chromium could meet the direct emission standard limit. After the integrated wastewater went through physicochemical treatment at first, then biochemical treatment, finally Fenton oxidation process, the quality of resulting water was stable. The value of color multiple was just 2. And the concentration of CODCr and ammonia nitrogen far bellowed the direct emission standard limits.To sum up, after the two improved leather wastewater treatment processes were used,the quality of resulting water was more stable. So the improved processes were suitable for long-term operation.