| In recent years,odor pollution events occur frequently both domestic and foreign,especially the sulfur-containing odor represented by carbon disulfide(CS2)and hydrogen sulfide(H2S),for its low olfactory threshold and high toxicity,which have seriously affected people's living environment and quality of life.The biological purification technology has been more and more widely used in the treatment of sulfur-containing gas pollution due to its advantages of environmental protection,safety,economy and without secondary pollution.In the treatment of sulfur-containing industrial waste gas with conventional bio trickling filter(BTF),due to the uneven distribution of oxygen concentration in the bed of BTF,sulfur particles as a product of metabolism will be produced,leading to the blockage in the bed and continuous increase of pressure drop in the tower,and problems such as the deterioration of operation conditions of BTF,decreasing of waste gas removal efficiency and finally affecting the normal operation of waste gas treatment facilities will happen frequently.To solve this problem,the mobile bed biofilm reactor(MBBR)was proposed for the first time to the simultaneous treatment of CS2 and H2 S waste gas.The effects of p H,empty bed residence time(EBRT),inlet load and inlet concentration of the system on the removal efficiency(RE)and elimination capacity(EC)of waste gases were studied,and the recovery of elemental sulfur by controlling the biological oxidation of the system was also studied on this basis.Firstly,high efficient degradation bacteria was used to start the MBBR bio-reactor,the operation performance of MBBR in the start-up period was studied,and the effects of p H,temperature,EBRT,inlet load and inlet concentration on the RE and EC of CS2 and H2 S were also studied in the stable operation period of MBBR.Results showed that the activity of the degradation bacteria was the strongest at p H 2 and temperature 25-35?,with sufficient oxygen,the waste gas pollutants of CS2 and H2 S could be oxidized to sulfate ion,which had no toxic effect on the organism and did not affect the RE and EC,with the maximum EC of CS2 and H2 S were 209.26 g m-3 h-1 and 138.46 g m-3 h-1,respectively,finally,the maximum EC for the mixed gases was 331.6 g m-3 h-1.During the experiment,the amount of packing protein was kept at about 1.2-1.3 mg g-1,the biomass of the reaction system was relatively stable.Experimental study on the impact resistance showed that,by taking emergency measures,the RE of CS2 and H2 S could be recovered to more than 90% on the 3rd and 1st day respectively after 15 days of starvation,and the RE of CS2 and H2 S could be quickly recovered to 89% and 95% on the 1st day after 12 hours of strong alkali damage(p H = 11),respectively,indicating that the MBBR reactor with excellent impact resistance.The differences of acclimatization,RE and EC between MBBR and BTF for the simultaneous treatment of CS2 and H2 S waste gas were compared and analyzed,results showed that compared with BTF,the degradation bacteria could grow and propagate rapidly in MBBR,due to the advantages of uniform distribution of nutrient solution and dissolved oxygen,together with better mass transfer effect,so the degradation performance of pollutants in MBBR could be stable in a short time,with higher RE and EC,and no sulfur blockage problem.Secondly,in the process of producing elemental sulfur by controlled the biooxidation with oxidation-reduction potential(ORP),the effects of O2 / S2-molar ratio and p H on ORP were studied.On the bases of above,the effects of ORP on the EC,sulfate selectivity and sulfur selectivity of MBBR were also studied.When ORP > 520 mv,the RE of CS2 and H2 S were stable at above 80% and 90%,respectively.Too high or too low ORP is not conducive to the formation of elemental sulfur.When the inlet load of CS2-S(or H2S-S)is 70 and 80 g m-3 h-1,the yield of elemental sulfur reach the highest with ORP at 340 mv,among which,the yield of elemental sulfur of CS2 is 44.2% and 45.6%,and for H2 S is 62.3% and 62.8%,respectively.When the inlet load of CS2-S(or H2S-S)increased to 120 and 140 g m-3 h-1,the yield of elemental sulfur reach the highest with ORP at 370 mv,and the yield of elemental sulfur of CS2 is 46.5% and 47.5%,and for H2 S is 62.8% and 63.2% respectively.To study the mechanism of biotransformation,the degradation pathway of CS2 was analyzed with GC-MS,liquid chromatography and ion chromatography,which concluded that the biodegradation experienced the whole process of CS2—COS—H2S—S—SO32-—SO42-in the acid system with sufficient dissolved oxygen.According to the above research,the recovered sulfur was obtained from MBBR reactor with precipitation,centrifugation and drying.SEM analysis shows that there is a layer of protein like polymer attach to the surface of bio-sulfur particles,making it more easily to agglomerate with different size and shape,and the surface appeared more round than general commercial sulfur,XRD analysis showed that the XRD patterns of the recovered sulfur coincided with those of commercial sulfur,and several diffraction peaks with higher intensity appeared at 2?of 23.079°,25.845°,26.695° and 27.722° respectively,which coincided with the standard pattern of elemental sulfur(PDF,08-0247).The effects of extraction solvent,the amount of extractant and extraction time on the extraction rate and purity on the biosulfide were studied.It was found that with tetrachloroethylene as the extraction solvent,the mass ratio of extractant to sulfur was 8,the extraction efficiency and purity of elemental sulfur reached 88% and 90%,respectively,after 30 minutes of extraction,and the purity of sulfur could still higher than 85% after three cycles of solvent extraction.Finally,with the further analysis of the mass transfer behavior of pollutants in MBBR,the maximum mass transfer fraction of CS2 and H2 S was calculated as 0.44 and 0.91 respectively at a temperature of 30 ± 5 ? and EBRT of 94-39 s,and the maximum volume mass transfer rate was 97.7 g m-3.h-1 and 231.6 g m-3.h-1,respectively.The difference between MBBR and BTF in mass transfer fraction and volume mass transfer rate was also analyzed,results showed that due to the turbulence of aeration and water flow,a more uniform distribution of dissolved oxygen and pollutants was reached in MBBR,making its mass transfer efficiency between gas and liquid phases superior than that of BTF.The kinetic analysis for the removal of CS2 and H2 S in MBBR was carried out with Michaelis-Menten kinetic model,results showed that MBBR inoculated with high efficient degradation bacteria had a strong removal capacity for CS2 and H2 S mixed waste gases,with the maximum ECs reached 386.4 g m-3 h-1.Kinetics constant for the formation of sulfur by the biodegradation of CS2 and H2 S with Gompertz modified model were also researched,results showed that the ORP has a great influence on the maximum concentration Hmax and specific growth rate Rmax for the formation of elemental sulfur,to get the maximum yield of elemental sulfur,the ORP of the system needs to be controlled in an optimal range.The microbial morphology in each stage of MBBR operation was observed with SEM scanning,it was found that there were cocci and bacilli in the packing layer,and bacilli accounted for the vast majority proportion.Results showed that a large number of biological sulfur particles were distributed on the biofilm of the packing in the experiment of sulfur recovery.High throughput sequencing technology was used to analyze the microbial community structure in each stage of MBBR operation,results showed that Proteobacteria and Actinobacteria were the main strains,with the abundance of 78% and 11.4%,respectively.Acidithiobacillus was the dominant strain at genus level,accounted for 71%,and the growth of strain was in good condition.Through the study of the influence of p H on the distribution of microbial community,it was found that the abundance of the Acidithiobacillus was the highest at p H 2,indicating that the enzyme activity of the degradation bacteria reached a better state at p H 2,with good degradation efficiency of pollutants. |
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