| The rapid development of industrial economy and cities has resulted increasingly in air quality problems,the excessive release of toxic and odorous pollutants such as Hydrogen sulfide(H2S),which is harmful to human health and the ecosystems.Therefore,it is especial important to control and abate the emission of hydrogen sulfide to improve the air quality.Biofiltration has been proved to be a viable option for removal of H2S.It provides an alternative to conventional methods owing to their efficiency,cost-effectiveness,and environmental acceptability.In biofiltration,microbial activity,diversity and their synergistic effects with the environment determine their removal ability and performance.Microbial activity and diversity and its synergy with the environment in biofiltration determine the removal ability and performance.The packing material acts as the carrier for the microorganisms.Its performance directly affects the growth of microbial population,and the choice of packing media is critical for improving the efficiency of biological treatment technology.Vermicompost has high porosity and a large specific surface area.It is rich in organic carbon and mineral nutrients,and has an abundant beneficial bacterial community.Vermicompost is able to biodegrade odorous substances through its own metabolism.There are many researches on the agricultural application of vermicompost at home and abroad at present,however,there is little research available on vermicompost as packing material to remove H2S and the microbial analysis in vermicompost.Accordingly,the main objectives of the present article were to assess the feasibility of removing H2S using vermicompost as the organic packing media.Comparing the performance of vermicompost and sterilized vermicompost in treating H2S,the feasibility of removing H2S by vermicompost was clarified.To explore the effect of humidity on the purification performance of vermicompost for H2S and the change of microbial community structure by Miseq high-throughput sequencing technique.Moreover,a type of horizontal biofilter packed with vermicompost derived from sludge was used in the removal of hydrogen sulfide.The effects of different operating parameters on H2S removal efficiency were investigated,the temporal and spatial variation of microbial community structure and its role in H2S oxidation were analyzed in the process of biofilter.Finally,macroscopic kinetics of biodegradation was studied.Based on the above contents,the following conclusions are drawn:The purification of hydrogen sulfide by vermicompost is mainly due to the synergistic effect of physicochemical adsorption and biological reaction of vermicompost.Comparison of removal of H2S by sterilized and unsterilized vermicompost,the results indicated that physicochemical removal of H2S by the sewage vermicompost was not significant,and H2S removal by the vermicompost was caused by microbial activity.Different concentrations of hydrogen sulfide were used as microbial growth energy in vermicompost for domestic and operation,and no nutrients or microbial inoculation was added throughout the experiment.A lag period of 1 days was observed before H2S degradation with the 1st injection of H2S,but in subsequent injections,H2S was removed by the mixture without the lag period when the H2S concentration was 50,100,200,400,800 and 1600 ppm,respectively.The purification performance of vermicompost was good.The pH varied between 6.88 and 7.1 and presented slowly descend tendency.The results showed that the pH was not significant for the H2S removal efficiency.The moisture content of filter beds significantly influence the efficiency of H2S removal.The H2S removal efficiency at the different moisture contents showed that vermicompost could display its good H2S oxidation ability in 50%-60%moisture content.The physiological status of the microbial population in vermicompost was in good condition and adapted to the living environment with H2S more quickly.This indicated that the activity of sulfur-oxidizing bacteria was the higher and had better of ability of adsorbing and degrading H2S.To characterize the bacterial community in the different moisture content of vermicompost after treating H2S,the bacterial communities in the control and different moisture content samples were analyzed using Miseq high-throughputs sequencing technique based on 16 S rDNA.The results indicated that the bacterial community in diff erent moisture content of vermicompost after treating hydrogen sulfide were complex and varied significantly.The abundance and diversity were the least in the 60%moisture content of vermicompost,however the activity of sulfur-oxidizing bacteria performed well with sulfur oxidation ability of microbial dominance.The hydrogen sulfide decomposer in the vermicompost was dominated by the Proteobacteria accounting for 29%-40.3%and Gemmatimonadetes for 12.7-35.6%.Specifically,the Rhodanobacter(5.8-15.3%)and Mesorhizobium(1-3.9%)were detected as the major desulfurization strains in the final vermicompost.The vermicompost collected from dewatered domestic sludge as packing material in horizontal biofilter was investigated for H2S removal under condition of the inlet concentration from 100 to 500 mg·m-3 and at the gas flow rates of 0.25,0.35,0.45 and 0.55 m3·h-1,respectively.The results showed that the hydrogen sulfide contaminated air was removed completely under the inlet concentration less than 350 mg·m-3 and gas flow rate of 0.25-0.35 m3·h-1.But the further experiment allowed that the removal efficiency was declined with the increment of the gas flow.At the end of each phase,the removal efficiencies decreased to 91%,87%,73%,and 60%.The results showed that the gas flow rate affected the removal performance and changed the microbial community structure in vermicompost.The optimal gas residence time for our system operation was 76s based on removal efficiency.The maximum elimination capacity of 20.2 g·m-3·h-1 was observed at a flow rate of 0.35 m3·h-1 and the horizontal biofilter packed with vermicompost has an excellent performance on resisting high shock loading within this process.Furthermore,the amounts of biodegraded products and pH varied accordingly.The major end-products of H2S oxidation were different forms of sulfate(SO42-)and elemental sulfur.the H2O-S and adsorbed-S concentration in vermicompost samples increased significantly and HCl-Soluble-S was low and changed little.A yellow substance,which was deposited on the vermicompost after certain running time,was determined to be elemental sulfur through analysis.In addition,the vermicompost with H2S removed can become a sulfur fertilizer resource or repairing soil matrix owing to the rich content of nitrogen,phosphorus,potassium and sulfur,offering nutrients to the growth of plants and enriching and improving the soils as well.The analysis of bacterial community structure in vermicompost of different space levels in horizontal biofilter by high-throughput sequencing,the results showed that the bacterial community in different segments significantly varied with the increase of operation time.According to the classification of species,the common bacteria are mainly Proteobacteria,followed by Gemmatimonadetes and Bacteroidetes,the relative abundance ratio was 82.1 to 96.6%.Gammaproteobacteria and Betaproteobacteria were dominant bacteria.Specifically,the Rhodanobacter(6.1%to 62.5%),Halothiobacillus(2.8%to 5.2%)and Thiobacillus(0.7%to 6.9%)were detected as the major desulfurization strains in the final vermicompost.Furthermore,based on Michaelis-Menien,the maximum removal rate and saturation constant of H2S by kinetic analysis of bio-degradation were Vm=1 428.6 g·m-3·d-1 and Ks=417.1 mg·m-3,respectively.The results of Vm was higher and had a good correlation,which could provide guidance for industrial scale system design. |
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