Study On Cutting Fluid In Environmental Organic Wastewater Treatment By Fenton-MBR

Energy and environmental issues have been the focus of world attention. As a relativelyclean source, solar energy will play more and more important role in the world’s energydevelopment. However, a large quantity of wastewater generated due to the extensive use ofcutting fluid in the production process of silicon wafer. The wastewater characterized withhigh COD content, complex components and poor biodegradability. Nowadays, with theincreasingly stringent standards of effluent, most sewage treatment facilities of enterprises arefound difficult to meet the standards, hence there exist urgent needs of the technologyupgrading.This study put the cutting fluid in the process of silicon wafer as the target wastewater.The Fenton method was employed to deal with the wastewater, and its parameters wereoptimized by experiment, The MBR method was then employed to treat the outflow ofFenton method, and some of its parameters were also optimized. On this basis, a wastewatertreatment method which combined the Fenton and MBR methods for the organic cuttingliquid was proposed, and its optimized conditions are given as follows:(1)In Fenton oxidation reaction, the dosage of H2O2, ferrous ion concentration, solutionpH and temperature were all found to affect the degradation of COD, Therefore, theoptimization of conditions can improve the removal rate of COD, which has a greatsignificance to the economic cost saving. Through the experimental analysis theconcentrations of H2O2and Fe2+were controlled250and20mmol/L. The reaction time wascontrolled for about3hours. The pH was controlled in a range of2.5-3.5, and the reactiontemperature was controlled at about30℃. Fenten method got a satisfied removal rate whenthe initial concentration of COD was higher. For example, the removal rate can reach85%when the initial concentration of COD was2500mg/L. In the actual serial process, the drugdosage adjusted appropriately by considering the cost, to control the removal rate of COD ina range of68%-76%, thus the COD concentration in the outflow of Fenton method600-800mg/L.(2) The MBR method was better when the initial concentration of COD was600-800mg /L.The COD concentration in outflow can be reduced to100mg/L and target wastewaterCOD removal rate can reach above90%. In the process of treatment, removal rate increasedwith the increasing of hydraulic retention time (HRT). The removal rate of target wastewaterincreased from82.23%to94.76%when the HRT increased from4h to12h. In addition, theremoval rate was found to improve with the increasing of dissolved oxygen (DO)concentration. The removal rate of COD increased from91.51%to92.52%when the DOconcentration increased from1mg/L to5mg/L. The influence of DO on COD removal wassmall compared with other factors, so we selected8h for HRT and1mg/L for the DOconcentration as a comprehensive consideration.(3) Coupled with the Fenton method and MBR method to deal with the targetwastewater, in a running cycle, theremoval rate of COD remainedat about97%.Through this study, we determined a set of new and effective process to deal with theorganic wastewater of polysilicon cutting liquid, and made some technological advances toprovide theoretical guidance and technical support for industrial application, as well asreducepollution to the environment in the process of polysilicon production and satisfy theenterprise sewage discharge standards.