Performance And Mechanism Of Biotrickling Filter For Binary VOCs Removal

Nowadays air quality has become a worldwide environmental problem.The National 13th Five-year Plan points out that prevention and control of air pollution will be extended to volatile organic contaminants(VOCs).At present,biological method has been regarded as an effective and low cost technology for treating effluent gas containing low concentration of VOCs.However,the research on the degradation of multi-component VOCs was still scarce and the biodegradation mechanism of multi-component VOCs in the bioreactor was not yet clear.In this study,we studied how the addition of ethyl acetate and n-hexane in the concentration gradient influence the BTF(biotrickling filter)treating toluene on the basis of the BTF biodegradating toluene,respectively.Meanwhile,we adopted carbon equilibrium analysis method and the high-throughput sequencing technology(Miseq-16S rRNA)to analyze the microbial community structure and the diversity and abundance of functional genes in the BTF.Based on these analyses,we revealed the the action mechanism of microorganisms on the BTF treating toluenen and binary VOCs.The main research contents and conclusions of this study are following:1 During the experimental process of the BTF treating toluene,the effect of inlet concentration,residence time,humidity,packing,nutrient solution spray density and other factors on the biodegradation of toluene in the BTF were studied.The bioreactor was steadily operated when it treated 1640 mg/m3 of toluene under the circumstance that the EBRT was 30s,and nearly 84%removal of toluene and the removal capacity of 166.4g/(m3·h)was achieved.Carbon balance analysis showed that up to 22.5%of carbon resource was assimilated into biomass,and only 1.5%was dissolved in the nutritive solution.The mineralization rate of toluene in the BTF was 57.3%.In the liquid phase,nearly 96.6%of carbon was organic and the rest was inorganic.2 In the process of the BTF degradating toluene and ethyl acetate or n-hexane,the influence of different concentrations of ethyl acetate or hexane on the biodegradation of toluene was studied and simultaneously the carbon equilibrium was carried on when the system was run stably.The results showed that the introduction of ethylene acetate or hexane to a certain extent inhibited the biodegradation of toluene.The difference was that the removal rate of toluene gradually and the remvaol capacity decreased from 156.8g/(m3·h)to 100.5g/(m3·h)when the concentration of ethyl acetate increased from 850mg/m3 to 1750mg/m3 and when the concentration of ethyl acetate increased from 1/50mg/n3 to 2800mg/m3,the increasing of ethyl acetate would not have a significant impact on the degradation of toluene.However,the lower the concentration of n-hexane was,the more pronounced the degradating inhibition of toluene by hexane was.When the concentration of n-hexane increased,the removal capacity of toluene increased from 93.9g/(m3·h)to 144.9g/(m3·h)and then became steady.Further more,the removal efficiency of ethyl acetate declined with the increasing of itself.However,the stable removal efficiency was still more than 95%while the removal efficiency of n-hexane decreased sharply from 42%to 6.8%and finally came to 3%.Compared with the biodegradation of monocomponent(toluene),with the increasing of ethyl acetate,the mineralization rate decreased from 36.19%to 52.05%at first and then rose to 40.73%.In addition,when the inlet concentration of ethyl acetate was 1750mg/m3,the proportion of carbon assimilated by microbes was only 20.08%,which was lower than the one(22.5%)of monocomponent system.The most fundamental reason was that the proportion of the carbon in form of ethyl acetate in the total input carbon resource changed and the addition of ethyl acetate depressed the biodegradation of toluene.However,with the increasing of n-hexane,the distribution law of carbon in the degradation products was that the proportion of toluene in the outlet gas was lower and lower(38.0%,14.4%,11.3%)and higher and higher(20.4%,49.2%,61.5%)proportion of n-hexanea was in the output carbon resource and what we could ignore was the the amount of carbon dissolved in the nutrient solution.Compared with the monocomponent system,the mineralization rate decreased with the increasing in the concentration of n-hexane and the proportion of carbon assimilated and utilized by microorganisms was significantly lower.3 In the stable operating condition of the BTF purging VOCs,we extracted the DNA of microbes attached to the packing material in the bioreactor and then analysed the samples by Miseq high-throughput sequencing.The results showed that:(1)The dominant phyla and genera in the bioreactor treating toluene were Proteobacteria?Bacteroidetes?Actinobacteria and Pseudomonas?Comamonadaceae?Rhodococcus.On the level of phylum,the introduction of toluene promoted the multiplication of Proteobacteria and Actinobacteria but inhibited the growth of Bacteroidetes and Acidobacteria.(2)No matter the BTF degradated toluene or binary VOCs,Proteobacteria and Bacteroidetes were the predominant phyla and Pseudomonas and Comamonadaceae were always the predominant genera.Rhodococcus which belongs to Actinobacteria and Actinobacteria were the key phylum and genus affecting the removal of toluene.The reason why the removal rate of toluene in the binary VOCs system was poorer was that the addition of ethyl acetate or n-hexane severely inhibited the breeding of Rhodococcus.The change in the content of Proteobacteria could indirectly reflect the tendency of the removal of toluene while the higher the richness of Bacteroidetes was,the more adverse the degradation of toluene was.On the genus level,Pseudomonas?Comamonadaceae and Delftia could reflected the trend of removal of toluene..(3)When the BTF treated toluene and ethyl acetate,the mount of predominant phyla in the bioreactor reached the maximum value while the concentration of ethyl acetate was 1750mg/m3.They were Proteobacteria,Bacteroidetes,Firmicutes and Saccharibacteria.The dominant genera in the reactor were Pseudomonas,Comamonadaceae,Chryseobacterium and Arcobacter.The content of Arcobacter in the microbes rised gradually along with the increasing of ethyl acetate.The low concentration of ethyl acetate favored the multiplication of Pseudomonas and Comamonadaceae and moderate concentration of ethyl acetate was suitable for the survival of Chryseobacterium.(4)Proteobacteria and Bacteroidetes were the predominant phyla in the microbes when the BTF degradated toluene and n-hexane.The increasement in the concentration of n-hexane promoted the breeding of Proteobacteria but restrained the growth of Bacteroidetes.Planctomycetes,detected when n-hexane was 850mg/m3,disappeared in pace with the enhancement in the concentration of n-hexane.Pseudomonas,Comamonadaceae and Delftia were the predominant genera in the bioreactor.Among them,the variation tendency of the proportion of Comamonadaceae and Delftia in the biofilm was opposite to the one of Pseudomonas.Although Pseudomonas accounted for the highest proportion,the biodegradation of toluene was more sensitive to the contents of Comamonadaceae and Delftia.