Effect Of H₂O₂ On Process Operation And Surface Biofilm Performance Of Biological Activated Carbon Process

UV/H₂O₂advanced oxidation process,can give full play to its advantages in physical adsorption,chemical degradation and biodegradation.However,there is often residual H₂O₂in the water produced by UV/H₂O₂process,which will not only increase the amount of chlorine added in the disinfection process,but also produce more disinfection byproducts（DBPs）^[1].Biological activated carbon（BAC）technology as an effective follow-up process.Therefore,it is very important to study the influence of residual H₂O₂on the long-term operation of BAC process.Based on the above,this study observed the long-term operation effects of pilot-scale single BAC process and H₂O₂-BAC process in a drinking water treatment plant in Ganzhou City.The two processes used the effluent from the filter tank of the water plant as the raw water of the device and ran for a total of 161 days,including 59 days in summer and 102 days in autumn and winter.Activated carbon used organic materials in raw water to naturally form biofilms.The removal efficiency of organic matter and the control effect of DBPs of the two processes were compared comprehensively.The analysis showed that the H₂O₂-BAC process had certain advantages in practical operation.This study analyzed the mechanism of H₂O₂on BAC process by comparing the difference of water quality in and out of the process,physical and chemical properties of activated carbon surface and biofilm population structure of activated carbon surface due to H₂O₂oxidation during long-term operation of BAC process.The main conclusions are as follows:（1）At the early stage of the two processes,due to the strong physical adsorption capacity of activated carbon,the removal rates of TOC and UV₂₅₄indexes were all above 80%.With the extension of operation time,the two processes formed biofilms in almost the same time period.The removal of organic matter was subject to the synergic effect of physical adsorption and biodegradation,and the removal rate of organic matter reached a stable level.The removal rate of TOC and UV₂₅₄by H₂O₂-BAC process was 45.10%and 40.51%at stable stage and was 29.33%and28.34%at low temperature.Compared with the BAC process,the residual H₂O₂made the BAC process significantly improve the removal rate of conventional organic matter,in which the removal rate of TOC and UV₂₅₄increased by 17.45%and 2.34%respectively.H₂O₂-BAC lead to higher turbidity value along the carbon column than that of the BAC process alone,and the maximum turbidity along the carbon column can reach 26.51 NTU,but the final turbidity value of the effluent is less than 0.5 NTU in both processes.H₂O₂reduced the influent concentration of>30k molecular weight component by 5.5%compared with that of BAC alone,while the influent concentration of<2k and 2k-6k molecular weight component increased by 2.82%and 4.34%respectively.According to the results of the trichloromethane formation potential of the effluent from the two processes,it was found that the trichloromethane formation potential of the effluent from the single BAC process is28.67μg/L,and that of the effluent from the H₂O₂-BAC process is 13.69μg/L.The results indicated that raw water treated with H₂O₂oxidation could improve the degradation ability of DBPs by BAC process.Three-dimensional fluorescence analysis showed that H₂O₂significantly increased the fluorescence intensity of fulricic acid and protein-like substances in the influent,and significantly decreased the fluorescence intensity of tyrosine and tryptophan in the influent.The characteristics of humus in H₂O₂-BAC process are higher than those in BAC alone process.DOM of effluent from both processes showed autogenous characteristics,and there were strong microbial activities along different depths.（2）SEM and BET analysis were carried out on the activated carbon along the two processes.It was observed that a large number of microorganisms had grown in the two activated carbon processes,but the adsorption capacity of activated carbon still existed.High concentration of H₂O₂contact with activated carbon will corrode its internal skeleton,making the surface rough and irregular,increasing the breeding space for microorganisms.The specific surface area of activated carbon by BAC alone was 348.94 m²/g,smaller than that of the original activated carbon,and the pore volume was 0.2455 m³/g,higher than that of the original activated carbon.The specific surface area and pore volume of activated carbon in contact with H₂O₂are366.31 m²/g and 0.2464 m³/g,both of which are increased compared with the original activated carbon.FTIR showed that the abundance of hydroxyl（OH）,carbonyl（C=O）,aldehyde（C-OH）,carbon-carbon double bond and carbon-carbon triple bond on the biological activated carbon by H₂O₂-BAC process was higher than that by the BAC process alone.The XPS results showed that the C element in H₂O₂-BAC process decreased by 18.10%compared with the original activated carbon,and the O element increased by 14.00%.The increase of oxygen-containing functional groups on activated carbon provided more adsorption activity for activated carbon.（3）Through the high-throughput sequencing analysis of activated carbon biofilms at different depths along the two processes during the stable period,it was concluded that,affected by H₂O₂oxidation,the microbial population structure of the two activated carbon processes was significantly different among groups,and the microbial population structure of the upper activated carbon and the middle activated carbon in the single activated carbon process within the group was more similar.The similarity of population structure between upper and lower activated carbons was the highest in H₂O₂-BAC process.The abundance of aerobic bacteria such as Rhizobium produced by H₂O₂-BAC was 23.43%higher than that of Rhizobium by BAC alone.Psychrobacter accounted for 0.41%in the single BAC process and 33.18%in the H₂O₂-BAC process.The value of conditioned pathogen Bacillus in the H₂O₂-BAC process was reduced by 2.54%compared with that in the BAC process alone,indicating that the activated carbon column added with H₂O₂could better adapt to low temperature environment and reduce part of conditioned pathogen,which had certain advantages.The functional bacteria of the two processes were basically similar,but the functions of Acetylglucosaminy transferase,Oxidoreductase and C-diamine reductase increased in H₂O₂-BAC process,while the functions of membrane protein,chemoattractant protein,DNA polymerase,substrate binding protein of manganese/zinc/iron transport system,and thiosulfate reductase decreased.