Study On The Process Performance And Purification Mechanism Of Biotrickling Filters For Toluene Waste Gas Control

Biotrickling filter treatment is an attractive approach for treating volatile organic compounds (VOCs) in waste-gas treatment fields. The characteristics of microbial populations in biomembrane and running conditions of bioreactors both play crucial roles in biological waste-gas treatments by significantly influencing the stability and treatment efficiency of systems. In this dissertation, based on the screening of the obligate toluene-degrading bacteria and toluene chosed as the sole carbon source, the production of metabolic intermediates by microorganisms degrading toluene and its accilimation mechanism in biotricking filters were investigated. The effect of waste-gas flow configuration pattern on biotrckling filter performance, stability and microbial community, and the roles of microbial chemotaxis to toluene and intermediates in the purification process of biotrickling filters were also researched. The main contributions to the current understanding of this topic were described below.The consortium source in this research was derived from the activated sludge of a coking plant, and the toluene was used as the only carbon source and inducer with concentration increasing by degrees to acclimate the toluene-degrading consortium. Three strains with high toluene-degrading activity were gained, and were identified as P.putida,Gordonia sp. and Ochrobactrum sp.Toluene biodegradation by Pseudomonas putida in batch cultues and purification in a laboratary-scale biotrickling filter were investigated. The results showed that intermediates including catechol accumulated during the degradation of toluene. Under the condition of our experimentation, the catechol which accumulated to the maximal concentration of 0.045 mg·L-1 during biodegradation could be totally mineralized within 5~10 h during shutdown periods.By incorporating the inhibition effects of metabolic intermediates, the toluene biodegradation and cell growth kinetics is proposed to simulate toluene degradation profiles, which is based on the production and later consumption of metabolic intermediates.A novel flow-directional-switching biotrickling filter was designed by improving the structure and running condition to select effective microbial populations. Two identical sized laboratory-scale biotrickling filters with flow configuration of flow-directional–switching (FDS) and conventional undirectional flow (UF) respectively, were used to study the purification of toluene waste-gas streams. The results show that FDS operation can improve the maximum elimination capacity of the biotrickling filter and quickly recover its nominal performance after system shutdowns. The maximum elimination capacities of 480 and 410 g·m-3·h-1 were obtained, respectively. When the systems were operated with continuous feed, then shut down for 48 hours, the elimination efficiency of FDS and UF systems were resumed to normal level with continuous feed after 3~4 h and 9~10 h, respectively.The metabolic characteristics of the microbial communities in FDS and UF biotrickling filters were accessed. The diversity indexes and principle component analysis demonstrate that FDS operation can improve the microbial reaction capacity and community functional diversity,produce a more uniform distribution of biomass along the length of packed bed. The maximum values of AWCD (Average Well Color Development) and Mdntonch index near the oulet packed bed of FDS system were 46.8% and 31.5% higher than that of UF system.Two strains of bacteria, identified as Gordonia sp.and Ochrobactrum sp., were tested for their chemotactic responses to toluene and catechol. The results show that bacteria chemotaxis can significantly accelerate the biofilm formation, interphase mass transfer process and biodegradation process of biotrickling filters. Then, a new theory called "Solid and Liquid phase Active Adsorption" is put forward and a related kinetic model is also established in this research. It is shown that the model agrees well with the experimental data, predicting the variations of purification performance with different inlet concentration, packed bed volumes and running temperture.