Performance Of Composite Enhanced Microbial Agents Treating VOC Mixtures Emitted From Pharmaceutical Industry

The research and application of microbial agents is an important issue of applied microbiology, especially composite microbial agents. According to the actual requirements of environmental pollution, screening and cultivating various types of high efficient degradation bacteria, constructing composite microbial agents with reasonable ecological structure, are of greart significance to shorten reactor startup period, maintain reactor high efficiency and enhance microorganism competitive.In this subjuect, toluene, o-xylene and dichloromethane were selected as the model VOCs pollutants from pharmaceuticals and a high efficient benzs(toluene, o-xylene)-degrading bacteria was obtained. The isolate, strain HJ1, was assigned to Zoogloea resiniphila, which was likely to be a new species able to degrade benzs. The degradation characteristics, kinetic behaviors were investigated. Based on the isolation and identification of metabolites and the activity analysis of related enzymes, a possible o-xylene -degradation pathway was proposed.The experimental results showed that the optimal growth conditions of strain HJ1 were 35℃ and pH 7. The Haldane modification of the Monod equation adequately described the relationship between specific growth rate and substrate concentration. The maximum specific growth rate and specific degradation rate for toluene were 0.151/h and 0.323 /h, respectively, and the maximum specific growth rate and specific degradation rate for o-xylene were 0.118/h and 0.19/h, respectively. The yield coefficient of strain HJ1 for toluene and o-xylene were 0.2494 mg/mg (toluene) and 0.2572 mg/mg (o-xylene), respectively. The mineralization rate for toluene and o-xylene were 65.9% and 54.8% respectively. An important metabolic intermediate,3,4-dimethylcatechol, which was detected by GC/MS, entered into TCA cycle through ortho-ring cleavage.In the previous work, a high effic ient dichloromethane-degrading was obtained and named as Methylobacterium rhodesianum H13(strain H13). In this study, in order to achieve effective and synchronous degradation of composite waste gas, the composite microbial agent was constructed by strain HJ1 and strain H13 with an appropriate proportion and then composite enhanced microbial agent was constructed by combining exclusive composite microbial agent and comprehensive strains. The degradation performance of composite enhanced microbial agent for compisite gas and the competition and inhibition effect among substrates were investigated.The experimental results showed that the composite microbial agent could mineralize dichloromethane completely, but the mineralization rate of benze was only 63.5%, when the concentration of composite gas was lower than 480 mg/L. The composite enhanced microbial agent could mineralize dichloromethane completely, the mineralization rate of benze was 71.7%, when the concentration of composite gas was lower than 600 mg/L. In this system, the presence of dichloromethane with low concentrations (less than 240 mg/L) had not a competition and inhibition effect on benzs-degradation, but the presence of dichloromethane with high concentrations (more than 210 mg/L) produced a competition and inhibition effect on benzs-degradation; the presence of the benzs had a competition and inhibition effect on dichloromethane -degradation.Based on degradation performance and metabolic characteristics, the composite enhanced microbial agent was applied into the BTF treating composite gas containing toluene, o-xylene and dichloromethanewas inoculated with the composite enhanced microbial agent to treat composite gas containing toluene, o-xylene and dichloromethane. The effect of different factors on the performance and the characteristics of microbial metabolism in BTF were investigated.The biofilm in BTF was successfully formed after 30 days’operation, indicating the reactor was started up successfully. As the increasing of EBRT, inlet load and concentration, the removal rates of toluene, o-xylene and dichloromethane were gradually decreased, and the order was: dichloromethane, o-xylene, toluene. The Michaelis-Menten kinetics model adequately described the degradation behavior by BTF, and the maximum degradation rate was 460.84 g/m3·h.In this study, PCR-DGGE, molecular cloning, and pyrosequencing methods were applied to investigate the diversity, structure and dynamic change of microorganism of biofilm of BTF. PCR-DGGE fingerprint analysis showed that a relatively stable microbial community structure was achieved during the stable operation,. Strain H13 and strain HJ1 grew well in BTF and toluene, o-xylene and dichloromethane could be degraded efficiently. Molecular cloning DNA sequencing results showed that the BTF, in which toluene, o-xylene and methylene chloride as the model pollutant, assembled rich microbial populations. Toluene, o-xylene were degraded by multiple populations, such as Zoogloea, Burkholderia, Comamonas, Sphingomonas, Pseudomon and Pusillimonas. However, Methylobacterium possibly contributed to the degradation of dichloromethane. Pyrosequencing results showed that the content of Betaproteobacteria in the upper of BTF was higher than that in the lower of BTF. In constrast, the content of Alphaproteobacteria in the lower of BTF was higher than that in the upper of BTF, indicating toluene and o-xylene is mainly removed in the lower of BTF, while dichloromethane was removed in the upper of BTF.