Study On The Treatment Of Industrial/Domestic Mixed Wastewater By Polyacrylonitrile Carrier-Immobilized Bacteria Enhanced A~2/O Process

Industrial wastewater in some industrial gathering areas in China is often discharged and mixed with local domestic sewage,forming industrial/domestic mixed wastewater（IDMW）.Concentration of organic pollutants and heavy metal in IDMW is often higher than the general domestic sewage which put forward to higher requirement of treatment ability of wastewater treatment plants（WWTP）.In this study,based on the actual discharge status of IDMW in an area of southern Jiangsu province,China,A²/O system was strengthened by polyacrylonitrile（PAN）carrier and immobilized bacteria which was acclimated by printing and dyeing wastewater.Chemical oxygen demand（COD）,total nitrogen（TN）,total phosphorus（TP）and ammonia nitrogen（NH₄⁺-N）were selected as regular pollutants and aniline and antimony（Sb）were selected as particular pollutants.The treatment effect targeting IDMW pollutants was investigated under lab-scale and pilot-scale experiment respectively.The mechanism of A²/O strengthening process was studied,including PAN carrier surface morphology analysis and material structure analysis,the organic substrate degradation model analysis,the changes of the microbial community and its relationship with pollutants removal.The main results are as follows:（1）Lab-scale regular A²/O process（9.2 L）was established.Simulated domestic sewage and simulated IDMW were used as influent of the system successively.The effect on regular A²/O system of aniline and Sb was studied.Then the regular system was strengthened and the strengthening effect of enhanced A²/O system was investigated.The results show that the regular A²/O process could effectively treat domestic sewage,and the effluent concentration of COD,TN,TP and NH₄⁺-N could meet the level A standard of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant（GB18918-2002）.However,regular A²/O process was difficult to effectively treat the IDMW containing aniline and Sb,and the effluent water quality deteriorated.After the PAN carrier-Immobilized bacteria enhancement,the removal rate of COD reached above 90.0%,TN reached above 76.2%,NH₄⁺-N reached above91.0%,the removal rate of aniline reached above 99%,the system could effectively remove 7.47 mg/L/d of Sb which showed a significant strengthening effect.（2）After the simulated wastewater,the actual IDMW was used as influent of the lab-scale enhanced A²/O process,and the removal effect of the enhanced system on the pollutants in the actual wastewater was studied.In addition,the pilot-scale A²/O process（20 m³）was established and the actual IDMW was used as influent to study the operation effect of the strengthening process under the pilot level.The results showed that:at the lab-scale level,the enhanced A²/O process had good operational effect on the removal of TN and NH₄⁺-N in the actual IDMW,with an average removal rate of 60.9%and 90.4%respectively.The effluent concentration was lower than the Discharge Standard of Main Water Pollutants for Municipal Wastewater Treatment Plant&Key Industries of Taihu Area（DB 32/1072-2018）.The removal rate of aniline was above 98%.At the pilot level,the enhanced A²/O process performed well during the operation,and the effluent concentration of COD could reach level A standard of GB18918-2002.The effluent of TP,NH₄⁺-N and TN could meet the discharge standard of DB 32/1072-2018.The removal of Sb had a significant enhancement effect within 1 month after adding PAN carrier.（3）In order to study the mechanism of pollutant removal ability change during A²/O process strengthening,scanning electron microscope and Fourier transform infrared spectrometer were used to analyze the morphology and structure of PAN carrier.Illumina Mi Seq sequencer was used to sequence the microbial DNA of activated sludge before and after strengthening to analyze its microbial community and investigate the relationship between microbial community change and pollutant removal.The results showed that:The PAN carrier prepared in this study could transform nitrile group into amidoxime-group structure（H₂N-C=N-OH）,which supplied a strong adsorption ability to absorb Sb in sewage.Immobilized bacteria played an important role in improving the microbial activity of sludge.With the growth of immobilized bacteria in the system,the microbial abundance and diversity of A²/O system which were affected by IDMW returned to the initial level.The microbial community changed significantly at the phylum level,and Proteobacteria,Bacteroidetes and Firmicutes were the main microorganisms in the activated sludge.At the genus level,the relative abundance of bacteria with nitrification and denitrification functions,such as Zoogloea,Flavobacterium and Brevundimonas,increased after the strengthening,indicating that the system had enhanced denitrification capability after the strengthening.Therefore the enhanced process was more suitable for the treatment of IDMW with complex water quality.The PAN carrier-immobilized bacterial composite enhance A²/O process constructed in this study realized the effective treatment of IDMW,especially the mixed water containing aniline and Sb,providing theoretical and technical support for the engineering application of IDMW treatment.