Degradation Of Gaseous Toluene And Microbial Community Analysis In A Thermophilic And A Mesophilic Biofilter

Among the various technologies for VOCs treatment, thermophilic biofiltrationis considered to be a cost-effective technology. In this study, a thermophilic biofilter（TBF, above50℃） and a mesophilic biofilter （MBF, room temperature） were set up toremove gaseous toluene. Through a long-term operation, the twobiofilters elimination capacities, operating performances and the changes ofmicrobial community structures were compared. Furthermore, the dominatemicroorganisms in both biofilters were also isolated and identified. The differences oftheir toluene degrading characteristics were studied.The performance of the TBF demonstrated great differences from that of the MBF.The result shows that when toluene inlet concentration was about1000mg·m^-3, thetoluene remove efficieny was above60%in MBF, however, in the TBF, it was about50%when the temperature was55℃, and only10-30%when the temperatureincreased to62℃. The behavior of both biofilters was investigated when subjecting ashock-loading. The changes of outlet concerntration in the TBF and MBF were800mg·m^-3and600mg·m^-3, respectively. The performance recovery times were2.5hoursfor the TBF and0.5hours for the MBF. Moreover, the restart-up of both biofilterswere examed. And the performance recovery times for the TBF and MBF were75hours and6hours, respectively.The temperature presented great influence on the moisture and structure offilterbed. The bed moisture declined with the running temperature increased, and thegrowth of water requirement per day fits to the form of power function. The packingporosity of the TBF was0.66, while0.73in the MBF. The specific surface areas werecalculated as2289.5m2·m^-3and947.4m2·m^-3for the TBF and MBF, respectively.Moreover, it was found that high temperature resulted to high chromaticity and TOCvalue of leachate.The microbial community structures in the TBF and MBF were monitored usingBiolog-ECO microplates periodically during the experiment. The results showed thatthe utilization of various substrates by microorganisms in biofilters presentedremarkable difference in the early phase. Polymers was proven to be the dominant substrate for the microbe in the TBF, while the dominant substrate was esters in MBF.After a long-term operation, the similarity of metabolic characteristics of microbialcommunities in two biofilters was higher. And the results of PCA analyzing showedthe differences of microbial community structures between the TBF and MBF weresmaller gradually.The strains collected from the TBF and MBF were isolated and identified usingcloning and sequencing technologies. The results indicated that the microorganism inthe TBF was close to Anoxybacillus sp.（99%similarity, thermophilic bacteria） andthe strain was Delftia sp.（99%similarity, mesophilic bacteria） in the MBF. Furtherbeaker experiments demonstrated that thermophilic bacteria isolated had perfecttoluene-degrading in alkaline environment when pH was from7to10, while themesophilic bacteria could degrade toluene in acid environment where pH was4-8.The microbial growth of the two strains could fit Haldane model very well. Thethermophilic bacteria has maxium growth rate when inlet concerntration was7855mg·m^-3and the mesophilic bacteria has maxium growth rate at4466mg·m^-3.