Study Of The Treatment Of Waste Gases Containing Complex VOCs With Biotrickling Filters And The Characteristics Of Their Microbial Ecology

Volatile Organic Compounds?VOCs?are important air pollutants usually discharged from most of the industrial production processes.These VOCs of industrial sources are generally large gas flow rate and low concentration.And continuous emission of VOCs will pose a certain threat to human health and safety of the ecological environment.Biofiltration has been extensively applied for treatment of single and multiple VOCs due to high-efficiency,cost-effective and environmentally friendly advantages.In this study,a series of pilot and laboratory-scale experiments had been carried out for achieving the target that the components of complex VOCs released from industrial production processes could not be removed synchronously and efficiently.The influence of the variation of VOCs components and concentrations on the elimination capacities of the biotrickling filters had been analyzed.PCR-DGGE and High-throughput sequencing were employed to analyze dynamic changes of microbial community structure with compositions and concentrations of VOCs.In addition,screening of highly effective degrading bacteria and application in bioaugmentation for improving the removal performance of chlorobenzene by biotrickling filters were performed according to low removal efficiency of refractory VOC?chlorobenzene?.Specific conclusions were described as follow:1.A pilot-scale biotrickling filter?BTF?was designed to treat volatile organic compounds?VOCs?emitted from a typical waste printed circuit board?WPCB?pyrolysis workshop.Measured by gas chromatography-mass spectrometry?GC-MS?,the main components of VOCs and their concentrations were benzene,toluene,chloro-benzene,ethyl-benzene,xylene,styrene,benzaldehyde,and trimethyl-benzene.The removal efficiencies of the BTF for these compounds ranged from 81.1%to 97.8%after 90 days operation.The linear increase of ECs with increasing VOC ILs showed that the BTF could remove the VOCs efficiently.Hazard ratio index based on threshold limit value for time weighted average?TLV-TWA?and VOCs concentrations indicated that the non-cancer risk of VOCs was significantly reduced after the BTF treatment.The microbial community analysis revealed initial inoculum and some emerging bacteria played crucial roles in the improvement of BTF performance with the biodegradation of this kind of VOCs by the PCR-DGGE technique and pyrosequencing analyses indicated that proteobacterial phylum was dominant in the BTF.2.The removals of BTSX and their interactions were evaluated in detail by using four BTFs.Toluene was among the most easily degradable pollutant,followed by styrene and xylene,while benzene was not easily removed alone.However,the removal of benzene was enhanced in the presence of other gases.The ECs of BTFs decreased with the complexity of gases.The removals of mixed gases were influenced not only by the composition of gases but by microbial community since that same combination of gaseous pollutants were removed in different BTF with different ECs.Comparison of microbial communities revealed that BTFs pre-adapted with target pollutants could develop the microbial communities with relatively high robustness and removal capacity.Drastic changes in structure and composition of microbial communities occurred in BTF4 when more gaseous pollutants were introduced.All samples were dominated either by the genus Achromobacter or the Burkholderia.Different gaseous combination enriched or inhibited some microbial species.Group I includes samples of BTFs treating single and binary gases and was dominated by the genus Achromobacter,with little Burkholderia inside.Group II includes the rest samples taking from BTFs domesticated with ternary and quaternary gases,and was dominated by the genus Burkholderia,with little Achromobacter detected.These genera were highly associated with the biodegradation of benzene series in BTFs.3.A high-effective strain of chlorobenzene was obtained from our microbiological culture collection center.The iron reduction function of strain was identified to Shewanella decolorationis and the name was S12.The chlorobenzene with the concentration of 100 mg/L was completely degraded in 28 hours and the biomass reached to 27.27 mg/L.The CO₂ production rate was 83.85%and the generation rate of chloride ions is the basically same as the calculated value in theory.These results indicated that chlorobenzene was mineralized completely.The degradative kinetic model named Monod was suitably fitted the curve between substrate concentration and specific degradation rate.The maximum specific degradation rate of 0.29 h^-1 was obtained with the chlorobenzene concentration of 100 mg/L.Some intermediate metabolites,which included o-chlorophenol,catechol and 3-chlorine catechol were detected by analysis of GC/MS and IC.The catechol-2,3-dioxygenase was the key enzyme of the chlorobenzene open-loop by enzyme activity assay.The degradation pathway of chlorobenzene was predicted according to intermediate metabolites.4.The strain S12 was applied to bioaugment removal performance of chlorobenzene by biofiltration based on the biodegradability and degradation pathway.Three laboratory-scale biotrickling filters were inoculated with strain S12+TXS degraders,strain S12 and TXS degraders,respectively.When the chlorobenzene of100-500 mg/L concentration was applied,90%removal efficiency of biotrickling filters was obtained during 14 d,20 d and 25 d operation.And biomass reached 0.341mg/g,0.312 mg/g and 0.274 mg/g,respectively,on the 30^th day.These results indicated that strain S12 could improve the start-up of biotrickling filters.The elimination capacity?122.97 g/m³h?and CO₂ production rate?87.22%?of the biotrickling filter inoculated with strain S12+TXS were best,compared to biotrickling filters inoculated with strain S12 and TXS degraders,respectively,indicating that the removal performance of the biotrickling filter was enhanced when the strain S12 was added to a biotrickling filter.The degradation kinetic model named“Michaelis-Menten”was suitably fitted the curve between substrate concentrations and elimination capacities.The maximum elimination capacities of three biotrickling filter inoculated with strain S12+TXS degraders,strain S12 and TXS degraders were130.16,107.42 and 64.55 g/m³h,and the gas saturation constants were 0.3722,0.2656and 0.1328 g/m³,respectively.In addition,Analysis of microbial communities revealed that the strain S12 could be stable survival in the BTF of removing chlorobenzene for a long time,and it would not disappear in the present of other bacteria.These results indicated that the strain S12 could bioaugment the removal performance of biotrickling filters for chlorobenzene and possessed application value in practice.