Study On Methyl Sulfide Gasdegradationby Two-stage Biological Trickling Filter

The rapid development of industry caused more and more serious air pollution,in which the problem of methyl sulfide in malodorous pollution is particularly prominent.In this paper,two-stagebio-tricklingfiltertower was constructed by using bamboo charcoal as filler to degrade methyl sulfide.The effects of air concentration and air flow on the biodegradation of methyl sulfide were studied.The microbial community structure,abundance and diversity of biotrickling filter were identified.Simultaneously,the mechanism of methyl sulfide degradation was also explored.The effect of inlet concentration on methyl sulfide biodegradation by two-stage biofilter was studied.According tothe results,with the increasing of inlet concentration of methyl sulfide from 6 g/m3 to 20 g/m3,the removal rate of methyl sulfide decreased from 50%(first stage biotricking filter)and 99%(second stage biotricking filter)to 27%and75%,pH value of the filtrate was stabilized between 2.0 and 3.2,the concentration of sulfate ion in the filtrate increased from 290(first stage biotricking filter)210 mg/L(second stage biotricking filter)to 1050 1150 mg/L,and the pressure drop of the two biotrickling filters increased from 40 80 Pa to 110150 Pa.Using high-throughput sequencing,it was found that the enrichment and diversity of microorganisms in the first-stage bio-trickling filter tower were reduced by increasing the inlet concentration of dimethyl sulfide.But the change of the biological populationstructurein the second-stage bio-trickling filtertower was not obvious.The dominant species in the first stage biofilter were Proteobacteria(63%),Planctomycetes(12%)and Bacteroidetes(11%)under the inlet concentration of 10 g/m3.Consequently,Proteobacteria(70%)and Planctomycetes(10%)were the dominant species in the second biofilter.When the inlet concentration was increased to 20g/m3,the dominant species of the first and second biofilters were both Proteobacteria(87%).The effect of air flow on biodegradation of methyl sulfide by two-stage biofilter was studied.With the air volume increased from 15 L/min to 25 L/ min,theremoval rate of methyl sulfide increased from 35% to 50% in first-stage bio-trickling filter tower;the removal rate of methyl sulfide was decreased from 97.6% to 85% in second-stage bio-trickling filter tower;the concentration of sulfate ion in the filtrate increased from 571 524 mg/L to 1135 1298 mg/L;pH value of the filtrate was stabilized between 2.0 and 3.0;the pressure drop of the two biotrickling filters increased from 75 100 Pa to 120 140 Pa.When the air flow increased to 35 L/min,theremoval rate of methyl sulfide decreased to 35.5% and 68%;the concentration of sulfate ion in the filtrate increased to 785 986 mg/L,and the pressure drop of the two biotrickling filters increased to 160 180 Pa.Using high-throughput sequencing,it was found that the enrichment and diversity of microorganisms in the two-stage bio-trickling filter was little changed with air flow.When the air flow was 15 L/min,the dominant species of the first-stage biofilter were Proteobacteria(63%),Planctomycetes(12%)and Bacteroidetes(11%).However the predominant species of the first-stage biofilter was Proteobacteria(77%)and Planctomycetes(8%)under the air intake of 35 L/ min.In contrast,there were no changes in the dominant species of the second-stage biotrickling filter under the air volume of 15 L/min and 35 L/min,corresponding toProteobacteria and Planctomycetes.Combined with the analysis of microorganisms and degradation intermediates in biofilter,the metabolic mechanism of desulfurization in biotrickling filter was explored.During the degradation process,methyl sulfide was firstly transfered to mercaptan,and then mercaptan was partly oxidated into sulfur dioxide and hydrogen sulfide.Finally the sulfur element entered the filtrate in the form of sulfate.