Research On Process Optimization And Pollution Removal Characteristics Of Micro-nano O₃-BA

The ozone biological activated carbon（O₃-BAC）process plays an important role in drinking water treatment.The oxidation of ozone and the biodegradation of activated carbon can remove humic acids,microbial secretions,and difficult to degrade organic pollutants in water,which has better removal efficiency and application prospects than conventional water treatment processes.However,the O₃-BAC process still faces issues such as low ozone utilization and limited removal of typical odors.In the latest revised sanitary standard for drinking water（GB5749-2022）,geosmin（GSM）and 2-methylisoborneol（2-MIB）are listed as routine detection indicators,which puts forward stricter requirements for odor removal in drinking water.Microbubbles（MBs）have diameters ranging from tens of nanometers to tens of micrometers,characterized by fast mass transfer rate and long duration in water.Microbubble ozone（MBO₃）can significantly improve the mass transfer efficiency and utilization efficiency of ozone,effectively respond to organic pollution in water bodies,and also have good removal effects on odorants in water bodies.It has broad application prospects in water treatment.This article conducted experimental research on the issue of odor in drinking water.Through process comparison,the removal efficiency of odor substances by the micro bubble ozone activated carbon process（MBO₃-BAC）and O₃-BAC was compared.The influencing factors and process parameters of the optimized MBO₃-BAC were analyzed and optimized,providing technical support for the application of water plants.The results indicate that most of the bubble sizes generated by microbubbles are concentrated at 30μm～90μm.The average particle size of bubbles is 58.82μm。Two sets of reactors（MBO₃-BAC and O₃-BAC）have good removal efficiency for ammonia nitrogen,DOC,and UV₂₅₄,with average removal rates for ammonia nitrogen of 79.66%and77.54%,respectively;The average removal rates of DOC were 50.41%and 49.20%,respectively,but the concentration of DOC in the effluent gradually increased with operating time.The removal ability of MBO₃-BAC for UV₂₅₄is better than that of traditional O₃-BAC,with average removal rates of 87.67%and 83.29%,respectively.MBO₃-BAC and O₃-BAC showed slow growth in biomass during the initial stage of operation,with biomass on carbon increasing from 13.73nmol/g and 13.69nmol/g to 23.98nmol/g and 21.51nmol/g,respectively.The biomass on carbon in MBO₃-BAC accumulated rapidly.The removal efficiency of GSM and 2-MIB and the control effect of bromate by two sets of processes were compared.It was found that MBO₃-BAC had significantly better removal efficiency than O₃-BAC.At an oxygen dosage of 2mg/L,the removal rates of GSM and 2-MIB by MBO₃-BAC were 87.87%and77.49%,respectively,which were 5.95%and 24.02%higher than O₃-BAC.When the ozone concentration is less than 2mg/L,the bromate concentration in the effluent of both processes is lower than 10ug/L,and the bromate concentration in the effluent is lower than the standard value.The effects of ozone concentration,initial pollutant concentration,ionic strength(CO₃^2-/HCO₃^-,SO₄^2-),humic acid and p H on the removal efficiency of GSM and 2-MIB by MBO₃-BAC were further explored.It was found that the removal rate of two odors by this process increases with the increase of ozone concentration,and decreases with the increase of initial pollutant concentration;CO₃^2-/HCO₃^-has an inhibitory effect on the removal efficiency of the process,but SO₄^2-can improve the degradation efficiency of the process;Low concentration of humic acid can improve the removal efficiency of the process,but the continuous increase of humic acid will significantly inhibit the operational efficiency of the process.The response surface methodology was used to determine the optimal operating conditions for removing 2-MIB and controlling the generation of bromate using microbubble ozone activated carbon technology:ozone dosage of 2 mg/L and residence time of 15 minutes.Through scanning electron microscopy observation,it was found that the surface of the activated carbon in both groups of processes was covered by biofilms.The biofilm on the surface of the activated carbon in MBO₃-BAC was more dense,and the biological population showed significant differences along the water flow direction.The microbial diversity and richness on the activated carbon gradually decrease from the inlet end to the outlet end,with the highest uniformity and diversity of microorganisms on the middle layer activated carbon.The microbial community composition of the middle layer activated carbon is highly similar to that of the upper and lower layers.In addition,the MBO₃-BAC process eliminated Actinobacteria and formed a microbial population with Acidobacteria and Nitrospirae as the dominant phyla.From the perspective of functional flora,it is proved that the process not only has good removal and control efficiency of pollutants such as organic matter and bromate,but also can effectively guarantee the biological safety of effluent.