Research Of Hydrolysis Acidification And Multistage Aerobic Process On Tannery Wastewater Treatment

Tannery wastewater is a kind of seriously polluted industrial effluent. Mounts of dyes, auxiliaries, oils, tannin extracts are used during the leather making process. However, there is only 25-70 percent of them is absorbed by the leather itself, the remain parts all discharged into the wastewater. It’s difficult to be treated because there are many materials inhibit microbial growth in the effluent, such as salts, sulfides, chrome（Ⅲ）. Along with the continuously improve on The pollutant emission standards of leather and fur processing industry（GB30486-2013）, the investment of wastewater treatment obviously increased. In short, environment protection has already determined the survival and development of tannery industry.According to the characteristics of tannery wastewater are difficult to be degraded by biochemistry technique, high concentration of organic matter, high content of ammonia nitrogen, this paper introduced hydrolysis multistage aerobic coupling process （A/O₃） for tannery wastewater treatment, in order to enhance the biodegradability of the wastewater, hydrolysis tank was used to pretreat tannery wastewater. The effluent entered the multistage aerobic tanks to remove the residual organic matter and ammonia nitrogen effectively, so that request the water quality. We designed Biolog identification test based on the multistage aerobic tanks had the advantage of good ammonia nitrogen removing effect, in order to supply reference data for analyzing nitrogen removal mechanism of the aerobic tank from the perspective of microbial.By means of the experimental study and analysis, this paper obtained the below conclusions:（1） Research on efficiency of hydrolysis acidification tank for pretreatment of tannery wastewater:The test sample was artificial simulated tannery wastewater, after hydrolysis and first stage aerobic device running steadily, the results showed the reduction rate of CODCr remained above 40% and the maximum ammonia nitrogen removal rate was 59% through the function of hydrolysis acidification. Sulfide concentration of yielding water stabilized at 0.1mg/L, effluent pH maintained at 7.0～8.3, BOD5/CODCr of the raw water increased to maximum 0.45, the capability of biochemistry was improved greatly, which created the advantage for the following aerobic process treatment.（2） Studying and analyzing the operating results of A/O₃ technology used in tannery wastewater:the test sample was actual tannery wastewater. The results of single factor experiment showed that:hydraulic retention time 20h, the treatment effect of hydrolysis acidification was best, the reduction rate of CODCr was 54%, ammonia nitrogen and total nitrogen removal rate were 52.71% and 41.9% respectively. The optimum DO concentration of hydrolysis acidification tank was 0.5mg/L. The effect of the wastewater treatment was ideal at the condition of pH=7.5 in O₃. The optimum DO concentration of single stage aerobic zones were 1.0mg/L,2.0mg/L and 3.0mg/L, respectly.（3） Orthogonal test for the treatment of tannery wastewater using A/O₃ technology:in order to get the optimal combination operating conditions, the factors that might affect the operation of the technology were assessed through designing orthogonal experiment. This experiment chose four influence factors: HRT, the concentration of DO in first stage aerobic tank （O₁）, the concentration of DO in second stage aerobic tank （O₂） and the concentration of DO in third stage aerobic tank （O₃）. Three levels were selected for each factor and nine experiments were done, then found the best operation conditions:HRT was 20h, DO concentration of single stage aerobic zones were 1.0mg/L,2.0mg/L and 3.0mg/L in sequence. At the same time, CODCr, ammonia nitrogen and total nitrogen removal rate were 85.11%,81.21% and 98.02%, respectively. The important factors that affect the effect of wastewater treatment were the concentration of DO in O₃, the concentration of DO in O₁, HRT and the concentration of DO in O₂ in sequence. The treatment effect of hydrolysis acidification and multistage aerobic process for tannery wastewater was excellent in different operation conditions, the reduction rate of CODCr remained above 78%, ammonia nitrogen and total nitrogen removal rate remained above 70% and 60%, respectively.（4） The test about functional differences of microbial communities based on nitrogen source metabolism in O₃ showed that:when the concentration of ammonium chloride was 100mg/L, the concentration of potassium nitrate was 20mg/L and the concentration of ammonium chloride was 150mg/L, the concentration of potassium nitrate was 30mg/L O₁ had the best effect of nitrogen removal. Diversity index analysis showed when the concentration of ammonium chloride was 50mg/L, Simpson index and McIntosh index were the largest, while the concentration became 150mg/L, Shannon index, Shannon evenness and McIntosh evenness were the excellent. When the concentration of potassium nitrate was 20mg/L, Shannon index, Shannon evenness and McIntosh evenness were the largest, while the concentration of potassium nitrate was 50mg/L, Simpson index and McIntosh index were the perfect. From the knowledge of classification of carbon sources, we knew that the activated sludge in O₁ used the extent of carbon sources were glycosides, acids and sugar in sequence, the activated sludge in O₂ used the extent of carbon sources were glycosides, sugar and acids in sequence, the activated sludge in O₃ used acids better than amine.