Effects And Mechanisms Of Present Of Hydrophilic Organic Compounds On Performances Of Biotrickling Filters For N-hexane Removal

In recent years,the emission of volatile organic compound(VOC)has caused serious harm to the environment and human health,which makes the purification technology of VOCs attract much attention.Biotrickling filters(BTFs)has the advantage of environmental friendliness compared to other processes,which makes it widely used in the control of VOCs.However,there exists a tough problem that the removal efficiencies of hydrophobic VOCs in BTFs are poor.The enhancement technology of hydrophilic VOCs to hydrophobic VOCs is considered as a potential BTFs enhancement technology.Therefore,4-methyl-2-pentanone(MIBK)and toluene were used as the target hydrophilic pollutants to study the effect of hydrophilic VOCs on the performance of BTFs for hydrophobic n-hexane removal.Additionally,in order to further explore the enhanced mechanism of BTFs at presence of hydrophilic VOCs,the structure and composition of the biofilm and the growth of microorganisms were analyzed and studied.The results showed that the presence of MIBK and toluene not only improved the performance of BTFs under short gas residence time(EBRT)and low temperature,but also promoted the removal of hydrophobic n-hexane.It solved the problem of low degradation efficiency of hydrophobic VOCs by BTFs,thus provided a theoretical basis for the application of BTFs in actual production.The main results of this paper are as follows:(1)In this thesis,two sets of the same BTFs devices were used in a comparative study.Among them,BTF A was used to process a single exhaust gas of n-hexane,BTF B was used to treat mixed exhaust gas of n-hexane and hydrophilic VOCs.The effect of hydrophilic MIBK on the removal of n-hexane under different EBRTs and temperatures were evaluated.The experimental results show that the average purification efficiency of BTF B for n-hexane(50%)was higher than that of BTF A(42%)when EBRT was reduced to 15 s.When the temperature dropped from 25 ℃ to10 ℃,the purification efficiency of n-hexane in A and B was 41% and 45%,respectively.Therefore,the addition of MIBK improved the performance of BTFs under short EBRTs and low temperatures.(2)Based on the introduction of different hydrophilic VOCs(MIBK or toluene),the effect of mixed loading ratios of hydrophobic n-hexane and hydrophilic VOCs on the removal of n-hexane was evaluated through comparative experiments.Studies indicated that the degradation of n-hexane in the presence of MIBK was slightly enhanced with a loading ratio of 6:1.When the mixing ratio ratio was greater than 4,toluene significantly promoted the biodegradation of n-hexane with toluene loading rate less than 10.7 g m-3 h-1.The average removal efficiencies of n-hexane in BTF A reached 81%.It had increased by 15% when compared with BTF A.The results illustrated that the introduction of hydrophilic VOCs had a positive effect on the removal of hydrophobic VOCs in BTFs under a certain loading ratios.(3)Based on the study of biofilm composition and microbial colonies,the mechanism of the enhanced degradation of n-hexane by hydrophilic VOCs was discussed in detail.The results showed that the content of protein and polysaccharide in the biofilm increased with the addition of hydrophilic VOCs.The number and growth rate of microorganisms in the biofilm were also enhanced.This conclusion showed that the existence of hydrophilic VOCs could promote the growth of microorganisms in the biofilm to stimulate the intake of hydrophobic n-hexane by microorganisms.Therefore,the purpose of enhancing the performance of BTFs for n-hexane removal was achieved.