The Research On SBR-FO Coupling Process For Cr(?)-Containing Tannery Wastewater Treatment

As the development of China's cities and the acceleration of industrialization,leather products have become an indispensable part of people's lives.During the rapid development of the tannery industry,a large amount of tannery wastewater was generated.If these wastewaters are discharged into nature without treatment,they will pose a serious threat to the ecological environment and human health.Therefore,these wastewaters need to be treated effectively.Using the traditional physicochemical method for tannery wastewater treatment,it is often accompanied by as high cost and too many by-products.However,when the traditional activated sludge method is used to treat the tannery wastewater,impacting by Cr(VI),the degradation efficiency of active sludge to pollution decreases,resulting in a certain amount of pollutants remain in the effluent.As an emerging membrane separation technology,the forward osmosis(FO)process offers the advantages of low energy consumption and easy cleaning.However,when treating industrial wastewater for a long time,serious fouling propensity would cause on the FO membrane surface,resulting in a decrease in water treatment efficiency and an increase in operation costs.This study attempts to combine the SBR process with the FO process to form an SBR-FO coupling process for the Cr(VI)-containing tannery wastewater treatment.In the coupling process,FO process is used as the advanced treatment of the SBR process to improve the effluent quality.In addition,as a pre-treatment facility,the SBR process can degrade a large number of pollutants of wastewater,thereby alleviating membrane fouling in subsequent FO processes.This study mainly investigated the decontamination efficiency of the SBR-FO coupling process in the treatment of Cr(VI)-containing tanning wastewater,and the characteristics of activated sludge under long-term impact of Cr(VI)-containing tanning wastewater.The main conclusions are as follows:(1)When the influent have no hexavalent chromium,the average removal rates of ammonia nitrogen,COD and orthophosphate by the SBR-FO coupling process are 95.97%,98.43% and 98.65% respectively;compared with the SBR process and the FO process,they are increased by 1.61%,2.51%,9.04% and 30.66%,4.18%,3.82%.(2)When 10mg/L hexavalent chromium is added to the influent,the average removal rates of ammonia nitrogen,COD and orthophosphate by the SBR-FO coupling process are 86.59%,97.79% and 97.99% respectively;compared with the SBR process and the FO process,they are increased by 16.01%,12.93%,99.91% and 45.21%,2.49%,1.67%.(3)When the concentration of hexavalent chromium in influent is 20mg/L,the average removal rates of ammonia nitrogen,COD and orthophosphate by the SBR-FO coupling process are 86.42%,96.31% and 97.29% respectively;compared with the SBR process and the FO process,they are increased by 45.83%,27.68%,115.34% and 45.22%,1.58%,0.45%.(4)When the concentration of hexavalent chromium in the influent was further increased to 40mg/L,the average removal rates of ammonia nitrogen,COD and orthophosphate by the SBR-FO coupling process were 83.81%,96.44% and 97.04%,respectively;compared with the SBR process and FO process 28.98%,29.26%,100.87% and 45.81%,1.71%,0.52%.(5)When the SBR-FO coupling process is used to treat Cr(VI)-containing tanning wastewater with hexavalent chromium concentration of 0,10,20,and 40 mg/L,the membrane flux reduction rate of the SBR-FO coupling process is 12.7%,5.5%,5.6%,and 7.9% lower than the FO process,respectively.(6)The trend of SV30 and SVI of activated sludge in the SBR-FO process shows that under the long-term impact of hexavalent chromium,activated sludge is prone to sludge swelling.According to the trend of SOUR of activated sludge,it can be found that hexavalent chromium has an obvious inhibitory effect on the respiration of activated sludge.In addition,the content of polysaccharides and proteins in the activated sludge EPS increased with the increase of the concentration of hexavalent chromium in the influent.However,the particle size of the activated sludge gradually increased with the increase of the concentration of hexavalent chromium in the influent and then decreased the trend of.In summary,the decontamination efficiency of the SBR-FO coupling process on the Cr(VI)-containing tanning wastewater is greatly improved compared to the SBR process and the FO process;but under long-term operation,there will still be a certain amount of fouling propensity on membrane surface in the FO process,while provide a theoretical basis for the SBR-FO coupling process application for the Cr(VI)-containing tanning wastewater treatment.