Study On Release Of Volatile Compounds From Waste Disposal And Biotreatment Of Methanethiol

Although the concentrations of volatile compounds released from municipal solid waste(MSW)disposal plant are low,they can cause serious harm to environmental pollution and human health.Methane is the main product of anaerobic biodegradation of organic matter,and is considered as an important greenhouse gas only after CO2.Methanotrophs can not only oxidize methane and reduce methane emission from the habitats,but also secrete a large amount of organic carbon into the habitats.Owing to the non-specificity of sulfur-metabolizing microorganisms to substrates,secretion from aerobic methane oxidation such as methanol,acetic acid and lactic acid can be used as substrates for their growth.Therefore,study on the influence mechanism of methane and methane-derived carbon on sulfur-containing odor gas plays an important role in controlling the emission of methane and odor gas during MSW disposal.However,presently,few studies have been reported in literature.Thus,on the basis of investigation and analysis of the concentrations and health risk of the main odorous pollutants in three different waste treatment techniques of a MSW disposal plant in Zhejiang Province,the influence mechanism of methane on organic sulfur compounds removal in biofilters was investigated,regarding methanethiol(CH3SH)as a typical sulfur compound.In addition,the response of the growth and metabolism of the cultures enriched with methane and methanethiol to oxygen concentration were characterized.The results would provide theoretical basis for the selection and optimization of biotreatment technology for sulfur-containing odor gas.The main conclusions are as follows:(1)The concentration of volatile compounds were investigated in the main processing units of three disposal methods of MSW,i.e.,landfilling,eco-mechanical biological treatment(EMBT)and anaerobic fermentation,in a MSW disposal plant(Zhejiang Province).In landfilling,the break of the HDPE membrane,especially at the joint of the HDPE membrane,and frequent corrosion of gas extraction wells were both significant leakage points of landfill gas.In anaerobic fermentation and EMBT,the tipping unit and sorting system were important sources of volatile compounds emissions.Sulfur-containing compounds(including methanethiol,dimethyl sulfide,carbon disulfide and dimethyl disulfide)were the main sources of odor in most waste treatment units.Aromatic compounds(including styrene,m-xylene,4-ethyltoluene and ethylbenzene)and 2-hexanone were the main odorous substances in the tipping unit and sorting system of anaerobic fermentation and EMBT,respectively.Health risks of volatile compounds from MSW was assessed.The total carcinogenic risk of the tipping unit and sorting system of the anaerobic fermentation and the landfill working surface ranged from 1.06E-04 to 8.04E-04,which had great potential hazards.The concentration of acrolein at the break of membrane and corrosion site of gas collection well and methanethiol at the break of membrane exceeded the disabling threshold(AEGL-2).If staff worked in these units for a long time without protective measures,irreversible and long-term health risk would occur.(2)The removal performance of simulated biofilters for methanethiol with or without methane input was studied,indicating that the presence of methane could promote the bioconversion and degradation of sulfur compounds.The emission rate of methanethiol in the biofilter without methane was about 2.5 times comparing with that with methane.The degradation rate of dimethyl disulfide in different depths of the biofilter with methane was significantly higher than that without methane.Under aerobic conditions,the intermediate organic sulfide compounds during methanethiol metabolism was mainly dimethyl disulfide.SO42-was the main coversion form of CH3SH-S in the biofilter.Microbial diversity in the biofilters for methanethiol removal was analyzed.Compared with the biofilter without methane,the biofilter with methane had more bacterial population and lower operational taxonomic units(OTU),suggesting that the presence of methane could promote the enrichment of microorganisms related to methane oxidation and methanethiol degradation.Proteobacteria,Bacteroidetes,Actinobacteria,Gemmatimonadetes and Firmicutes were the main microorganisms in the biofilter at the end of the experiment.Q-PCR and clone library analysis showed that Methylobacter and Thiobacillus were the main methanethiol-degrading microorganisms in the biofilters.(3)Response of methane oxidation and methanethiol-degradation activities of the cultures enriched with methane and methanethiol to oxygen concentrations were investigated.The methane oxidation activity of the culture was inhibited with the decrease of oxygen concentration,while the methanethiol degradating activity was not obviously affected by the concentration of methanethiol.There was a significant positive correlation between the degradation rate of methanethiol and the concentration of methanethiol(R2=0.974-0.999).At the methanethiol concentration of 2000 and 4000 mg m-3,the degradation rate of methanethiol increased with the increase of oxygen concentration,which indicated that sufficient oxygen condition was more conducive to the metabolic activities of methanethiol-degrading microorganisms.The fate of methane-derived carbon and methanethiol and their metabolizing microorganisms in the enrichment cultures were studied.CH4-C in the enriched culture was mainly converted to CO2.With the increase of methanethiol concentration,the conversion ratio of CH4-C to biomass-C decreased,especially at low oxygen concentrations.Extracellular polymeric substances production increased significantly under the condition of high methanethiol and low oxygen concentrations.SO42-was the main transformation product of CH3SH-S in the enriched culture.Methylosinus was the main aerobic methanotroph detected in the enrichment culture.Thiobacillus and Hyphomicrobium were the main methanethiol-degrading microorganisms.Thiobacillus was the main methanethiol-degrading microorganism in the enrichment culture at the low oxygen concentration.