病死猪辅热好氧发酵尾气中的恶臭物质分析

Analysis of odor pollutants in the exhaust gas from thermophilic aerobic fermentation of dead pigs

为了明确病死猪辅热好氧发酵过程中产生的恶臭气体种类及其排放规律,为控制恶臭气体排放浓度、降低病死猪无害化处理过程对环境的污染提供基础依据,该研究以病死猪为发酵原料,以玉米秸秆为辅料,开展病死猪辅热好氧发酵试验,发酵过程中,采集处理槽排放的尾气,分析尾气中的有机恶臭物质组分并测定其排放浓度,同时测定其中的氨气浓度,并对不同发酵阶段尾气中气味活度值大于1的恶臭物质进行相关性分析和主成分分析。结果表明:在病死猪辅热好氧发酵过程中共检出36种恶臭物质,其中能准确定性与定量检测的有3种含硫化合物,1种烷烃化合物,12种芳香烃化合物,1种酚类化合物,1种胺类化合物和1种无机气体;发酵全程或部分时间点超过其嗅阈值的有3-乙基甲苯、4-乙基甲苯、二甲基二硫醚、二甲基硫醚、氨气、对甲酚、甲硫醇、三甲胺8种,达到的最高浓度依次为0.241、0.350、0.247、0.280、69.06、0.041、0.314、0.033 mg/m^(3),与其嗅阈值的比值依次为2.746、8.635、29.326、36.982、66.669、173.315、374.770、432.471;各发酵阶段的主要致臭物质成分存在差异:在0~12 h的发酵阶段,三甲胺、甲硫醇、二甲基硫醚、二甲基二硫醚、氨气、对甲酚、3-乙基甲苯、4-乙基甲苯为主要致臭物质,在12~36h的发酵阶段,三甲胺、甲硫醇、二甲基硫醚、二甲基二硫醚、氨气、对甲酚为主要致臭物质,在36~72 h的发酵阶段,三甲胺、甲硫醇、二甲基硫醚、二甲基二硫醚、氨气为主要致臭物质;不同发酵阶段的臭气强度存在较大波动:在0~72 h内的发酵过程中,0~3 h内臭气强度缓慢增强,但第6小时臭气强度有明显下降,在6~18 h时再次增强,第18小时臭气强度达到峰值,18~72 h内持续下降直至平稳。该研究可为病死猪辅热好氧发酵过程中恶臭物质的减控策略提供理论参考。

Thermophilic aerobic fermentation(composting)has been emerged as an important approach to dispose of the organic solid wastes.The dead pigs can also be recycled and utilized properly using this biotechnology for resource treatment.However,a large amount of odor gas can be always generated concomitantly in this process,particularly posing a great threat to both air environment and human health as a kind of air contamination.There were some differences in the component and concentration from the odor pollutants produced by thermophilic aerobic fermentation,due to various participating organic wastes.The manure and waste have still been the two most focused raw materials about odor pollutants so far.But there is a rare reference with dead pigs.The purpose of this work was to explore the types and the emitting regularity of odor gas produced from thermophilic aerobic fermentation for dead pigs,in order to control the concentration of odor pollutants for less air contamination during nonhazardous dead pig processing.A three-day experiment was carried out,where 1.2 kg chopped body tissue sample of the dead pig was taken as the raw material,while 0.218 kg crushed maize stovers and 12 g strains were taken as auxiliary materials.The raw material,auxiliary materials,and strains were then mixed well and put together into a 10 L fermenter equipped with a stirring device,further to start fermenting with such an experimental condition that the temperature of interlayer water bath during fermentation was kept at 60℃and the ventilation rate was retained to 8 L/(L·min).After that,14 times of gas sampling were conducted from the tail gas tank,where three samples were collected each time,and 500 ml of fermentation gas was collected for each sample acting.As such,the primary odorants and the release regularity of odor pollutants were determined in the process of thermophilic aerobic fermentation during a 72-hour fermentation period.Specifically,the sampling interval was set as 3 hours during the first 6 hours,but it changed to 6 hours from the 6 th to the 72 ed hour.The organic odor components and the concentration of sampling gas were analyzed to determine the concentration of ammonia.Besides,the correlation analysis and principal component analysis were performed on those odor pollutants with the odor activity greater than 1 during fermentation.The results showed that 36 odor pollutants in total were detected during the thermophilic aerobic fermentation of dead pigs,19 of which were accurately detected qualitatively and quantitatively—including 3 sulfur compounds(methanethiol,dimethyl sulfide,and dimethyl disulfide),1 alkane compound(n-hexane),12 aromatic hydrocarbon(benzene,toluene,ethyl benzene,p-xylene,o-xylene,2-ethyltoluene,3-ethyltoluene,4-ethyltoluene,1,2,4-trimethylbenzene,1,3,5-trimethylbenzene,cumene,and styrene),1 phenolic compound(p-cresol),1 amine compound(trimethylamine),and 1 inorganic compound(ammonia).According to the standard and odor activity of odor pollutants,3-ethyltoluene,4-ethyltoluene,dimethyl disulfide,dimethyl sulfide,ammonia,p-cresol,methanethiol,and trimethylamine were the main odor pollutants in the exhaust gas of thermophilic aerobic fermentation of dead pigs.The highest concentrations of these eight main odor pollutants reached up to 0.241,0.350,0.247,0.280,69.063,0.041,0.314 and 0.033 mg/m^(3),respectively,the ratio of which to olfactory thresholds were 2.746,8.635,29.326,36.982,66.669,173.315,374.77 and 432.471,respectively.The OAV of the main odor pollutants also changed with the changing period of fermentation.The correlation analysis demonstrated that the components of the primary odorants were different in the different fermentation periods:trimethylamine,methanethiol,dimethyl sulfide,dimethyl disulfide,ammonia,p-cresol,3-ethyl toluene,and 4-ethyl toluene were the primary odorants in the fermentation periods of 0-12 h,trimethylamine,methanethiol,dimethyl sulfide,dimethyl disulfide,ammonia,and p-cresol were the primary odorants in the fermentation periods of 12-36 h,while the trimethylamine,methanethiol,dimethyl sulfide,dimethyl disulfide,and ammonia were the primary odorants in the fermentation periods of 36-72 h.Meanwhile,the odor intensity changed a lot with the different stages of fermentation:it increased slowly in the stage of the first 3 hours,but there was a significant drop when it reached the point of the 6 th hour,then went up again from the 6 th to 18 th hour,up to the peak in the 18 th hour,and turned stable to the end.This work can provide a strong reference to reduce and control the odor pollutants during the thermophilic aerobic fermentation of dead pigs.