Study Of BAC Water Purification Efficiency And Operation Control Based On Functional Regulation Of Biofilm

With the accelerating pace of industrialization and urbanization in China,surface water and groundwater in many areas are indirectly or directly polluted by ammonia and organic matter,which cannot be effectively removed in traditional water treatment processes.Biologically activated carbon（BAC）technology is commonly used for deeper treatment of pollutants.The conventional BAC process has slow biofilm formation,long start-up time,unstable autotrophic nitrification,and weak adsorption of ammonia nitrogen by the activated carbon itself,resulting in low efficiency of ammonia nitrogen transfer between the liquid phase（water）and solid phase（BAC）interface,which ultimately leads to poor ammonia nitrogen removal efficiency.Four sets of continuous flow BAC two-stage process columns were constructed in this project.The first stage process columns were carbon source alone interfacially regulated BAC（A1 column）,n Mn O₂ alone interfacially regulated BAC（B1 column）,carbon source coupled n Mn O₂ interfacially regulated BAC（C1 column）and blank experiment（D1 column）,and the second stage columns（A2,B2,C2,D2）were without interfacially regulated BAC.By optimizing the interfacial regulation of the BAC process,the effects of the interfacial regulation of the BAC process on the water purification efficiency and biofilm functionalization characteristics during the start-up and long-term operation were investigated.In the start-up period,the highest ammonia removal efficiency was achieved in the group C column with an average ammonia removal rate of76.05%,which was 68.73%higher than that of the group D column in the blank experiment.In the long-term continuous operation,the efficiency of ammonia removal in column group C was subject to the least fluctuation of process parameters（e.g.,influent ammonia concentration,empty bed contact time,and TOC:N ratio）（the average ammonia removal rate ranged from 54.65%to 92.63%）,and always showed the strongest stability and adaptability.The analysis of the biofilm surface characteristics,microbial community characteristics and extracellular polymer characteristics of the biofilm in the BAC process filter columns showed that the C group filter columns were rapidly enriched with heterotrophic microorganisms,mostly Bacillus,during the start-up period（day 8）,and the dominant genera were unclassified＿Burkholderiaceae,Bacillus and Novosphingobium,which played an important role in nitrification,denitrification and organic matter removal;after 180 days of operation,the microbial community of each group of columns showed obvious succession,and the number of heterotrophic nitrifying and denitrifying bacteria in group C was more than that in groups A,B and D of the blank experiment.On the 199th day of operation,the extracellular polymer of the BAC biofilm in the C group column was mostly composed of extracellular proteins,and the biological enzymes increased,and the biodegradation effect was stronger than the other columns,which confirmed that the interfacial regulation of the carbon source coupled with n Mn O₂ could strengthen the effectiveness of the BAC process in removing pollutants from the water source.Peracetic acid（PAA）as an oxidant can remove micro-pollutants by activation,and its oxidation product acetic acid is a carbon source required for microbial growth,so this study investigated the efficacy of PAA pre-oxidation coupled with interfacial modulation of BAC process for the removal of micro-pollutants and ammonia nitrogen.the removal of bisphenol A（BPA）and atrazine（ATZ）by the Fe²⁺/PAA system reached 100%and88.3%,respectively.At the same time,the Fe²⁺/PAA system could improve the biochemical properties of the water,i.e.,the bioassimilable organic carbon（AOC）content increased,and the BAC biomass increased significantly in group C columns,including the biomass of column C1 increased to 7.77×10~7±2.82×10~7cells/g dry weight GAC,which was 1.6 times higher than that of the blank experiment D1,because the decomposition of Fe²⁺activated PAA produced a large amount of acetic acid.The average removal rates of BPA and ammonia nitrogen in the filter column of group C were 100%and 32%,respectively,where the average removal rate of ammonia nitrogen was 12%higher than that in the blank experiment D.Therefore,the PAA pre-oxidation coupled with interfacial modulation BAC process can be used as a promising combination process to treat micro-polluted water sources.