Study On Microbial Community And Its Kinetics For Degrading Xylene Waste Gas

Xylene waste gas is a hydrophobic organic pollutant,and is the main component of many volatile industrial pollution sources.The use of biotechnology to remove volatile organic compounds has become a growing trend.In this study,a biotrickling filter for gaseous xylene treatment was developed using activated sludge as raw material to study the biodegradation process of xylene.Through long-term domestication,the specific microflora with high efficiency of degrading xylene was obtained,and the dynamic changes of microbial community structure in the process of purifying xylene waste gas were analyzed.The related kinetics models were verified and revised.The main results and conclusions are as follows:(1)Reaction conditions were optimized and the optimal pH was 7.0,gas-liquid ratio was 15:1(v/v)and temperature was 25OC.Biotrickling filtration system has undergone long-term operation of five stages,and the result showed that the removal efficiency(RE)was stable at 86%-91%,the maximum elimination capacity(EC)was 303.61 g·m-3·h-1,residence time was 33.75 sec,and the initial inlet xylene concentration was 3000 g·m-3.A mixed microflora was obtained,which could degrade xylene efficiently under the conditions of short residence time and high organic loading.(2)Combined with the PATHWAY database of Kyoto Encyclopedia of genes and Genomes(KEGG),the results of gas chromatography(GC)/mass spectrometry(MS)analysis suggested the possible metabolic pathways of microflora degradation of p-xylene.The mineralization rate of the system was calculated to be 81%,and the mass of the input and output carbons was balanced.(3)High-throughput sequencing was used to analyze the microbial community structure in the top,middle and bottom layers.Pseudomonas sp.and Sphingobium sp.were the dominant genus in the biotrickling filter,and there is a significant difference in the distribution of the top and bottom layers.The vertical distribution of microbial community structure is closely related to the variation of xylene concentration and its metabolites along the reactor height.The functional prediction of microbial community indicates that the system has great potential for the degradation of aromatic organic pollutants.In addition,six xylene-degrading bacteria were isolated and screened from the microflora.(4)According to the Michaelis-Menten model,the maximum biodegradation rate rmax and the saturation constant in the gas phase K,were calculated to be 1059.8 g·m-3·h-1 and 4.78 g·m-3,respectively.By validating and modifying the kinetic models of the "absorption-biofilm" theory and the "adsorption-biofilm" theory,the complexity of the actual operation of the biotrickling filter is proved,and this process should conform to the "absorption-adsorption-biofilm" composite model.(5)Compared with the electro-flotation method,the Fenton-coagulation combined treatment of COD in the circulating waste liquid was an effective and feasible method,and the effluent COD removal rate reached 82.5%.This solved the problem that the long-term operation of the system led to COD conceniration accumulation in the circulating nutrient solution.