Study On The Pretreatment Process Of PCB Stripping And Developing Waste Liquid

In 2019,China’s printed circuit board（PCB）output value was 32.9 billion U.S.dollars,which continues to rank first in the world and has an upward trend year by year.The process of PCB production will produce stripping and developing waste liquid with high organic pollution concentration,its pollutant composition is complex,COD and TN concentration is high,and toxicity is strong,if it is not pre-treated,it will seriously affect the stability of the subsequent water treatment system.Enterprises usually entrust this type of waste liquid to hazardous waste disposal companies,but the cost is high.This paper has successively explored the treatment effects of coagulation,persulfate oxidation,hydrolytic acidification/anaerobic/aerobic biological treatment on the actual stripping and developing waste liquid through factor optimization experiments,and used ultraviolet scanning,three-dimensional fluorescence,and GC-MS detection technology,high-throughput sequencing and other methods have analyzed the conversion of organic pollution components in the waste liquid and the succession of microbial flora in the biological system.On this basis,the application of the combined process in the actual PCB stripping and developing waste liquid treatment project was further studied,and the following research results were obtained.（1）Coagulation precipitation+persulfate oxidation can effectively degrade organic matter in wastewater,the removal rates of COD,TN and chroma are 42.0%,27.7%and 80.6%,respectively,and the B/C value is increased to 0.33.The ultraviolet scanning spectrum showed that the absorbance value representing the benzene ring structure decreased by 65.2%,and the three-dimensional fluorescence spectrum shows that the intensity of the fluorescence peaks representing hydrophobic acids and other luminescent substances has been reduced by 42.5%,which verified the actual effect of the physical and chemical treatment.GC-MS results show that benzotriazole（BTA,C₆H₅N₃）is a characteristic organic pollutant,and its proportion in wastewater has decreased from 45.32%to 28.23%.（2）For the actual waste liquid after physical and chemical treatment,under optimal conditions,the removal rates of COD and TN by hydrolytic acidification biological method are 33.8%and 25.5%,respectively,and the removal rates of COD and TN by anaerobic biological method are 23.1%and 17.4%,respectively,the removal rates of COD by aerobic biological method is 38.8%.The three-dimensional fluorescence spectrum shows that the fluorescence peak intensity of the benzene ring-containing protein in the wastewater is reduced by 25.8%,22.1%and 36.5%,respectively,GC-MS results show that the proportion of BTA in the waste liquid after the biological combination process has dropped to 13.22%,and the proportion of alkane organics has risen to 73.57%,further reducing the difficulty of subsequent treatment of wastewater（3）The relative abundance of Firmicutes in the hydrolyzed/anaerobic/aerobic sludge in the biological combination process accounted for 62.57%,36.49%,and34.48%,respectively,this strain has strong tolerance and can be effective degradation of carbohydrates,Proteobacteria accounted for 18.63%,57.39%,9.06%,respectively,this type of bacteria can effectively degrade aromatic compounds in wastewater and play a role in denitrification and phosphorus removal.At the genus level,Lactobacillus and Prevotella of the three sludges are the dominant species,which can decompose complex macromolecular organic matter into small molecular organic matter.（4）Based on the test results,a 30m3/d PCB stripping and developing waste liquid pretreatment project was designed and constructed using the combination process of"coagulation precipitation+persulfate oxidation+hydrolysis acidification+anaerobic+aerobic".When the average COD and TN concentrations of the influent water of the regulating tank are 49500mg/L and 2400mg/L,the removal rate reaches90%and 82%,respectively,after the treatment of the system process,the effluent water quality index reaches the design requirements of the project contract.