Study On Technology And Microbial Community Of Gaseous Toluene And Ethyl Acetate Removal By Biofiltration

Biofiltration for the removal of organic waste vapor has many advantages such as the simplicity of processes and equipments, security for operation and environment, ease of control and maintenance and low energy consumption, low investment and operation cost, high removal efficiency for pollutants and non-toxic products in emission from the biofilter. Biofiltration is especially applicable for treating the waste gases of large flow, low concentration of organic pollutants easy to be degraded by microbe.In this study, toluene and ethyl acetate was selected as the model compounds, their removal processes by the biofilter packed with compost-perlite (or lava) were analyzed and discussed in detail. The removal efficiencies of toluene and ethyl acetate and the components and microbial communities of the packing materials in the biofilter were determined under different condition (pollutants concentration, empty bed retention, temperature, moisture, nutrient concentration). Several pure strains were isolated from the packing materials in toluene biofilter and ethyl acetate biofilter and their degrading capacity for toluene and ethyl acetate were determined respectively. Further, the biofiltration for the mixed organic vapor of toluene, ethyl acetate and isopropanol was studied. The inter-inhibition mechanism of multi-pollutants during the biofiltration was analyzed microbiologically and enzymologically as well.As a result, the following main conclusions were obtained:(1) The results showed that the tolerance and degrading activity of the microorganism in packing material against these pollutants could be enhanced through a short acclimation. Under the same loads of inlet gas, the acclimation time by ethyl acetate is very short and the acclimation time by toluene is longer. The degradation activities of microorganisms in the biofilter are the limiting factor for pollutants removal and can also be considered as the main and limiting factor in a longer time performance.The toluene removal capacity of the biofilter could reached about 20 mg ?m-3 ?h-1 at the load of 57-100 mg ?m-3 ?h-1 and the ethyl acetate removal capacity of the biofilter could reached above 300 mg ?m-3 ?h-1 at the load of about 400 mg ?m-3 ?h-1(2) On the other hand, the removal efficiency and removal capacity of pollutants biofilters would decreased due to the depletion of water and nutrient in packing materials. Theimprovement for the removal efficiency of the biofilter was obtained by the addition of water and nutrient solution to the biofilter. When the packing materials had been utilized in the biofilter for 130 days, the removal efficiency of the biofilter dropped about 50%.(3) For toluene removal, the optimal initial moisture of packing material in biofilter is about 60%. The nutrient level of original packing material could meet the need of toluene biofiltration. But the addition of certain nutrient could makes biofilter remove toluene more efficiently in a shorter time.For ethyl acetate removal, the optimal initial moisture of packing material in biofilter is about 40%~--60%. The removal of ethyl acetate could reach higher removal efficiency only spending shorter time. Also the nutrient of original packing material could meet the need of removing ethyl acetate efficiently by biofiltration at a higher speed.(4) The main microbes degrading toluene and ethyl acetate in the biofilter are mesophilic. The optimal temperature for toluene and ethyl acetate removal is about 25~40癈.(5) When toluene existed in gas together with ethyl acetate, ethyl acetate was removed by the biofilter preferably. When toluene, ethyl acetate and isopropanol existed in the inlet gas at the same time, isopropanol and ethyl acetate were removed by the biofiter preferably. The removal efficiency of toluene was decreased obviously due to the increase of concentration of ethyl acetate and isopropanol. Furthermore, the removal efficiency of ethyl acetate was also decreased obviously when the isopropnol concentration was increased.Ba...