Biological Filter Volatile Organic Compounds

Recently biofiters have been used primarily to control dilute, usually odors, off-gas with relatively low volatile organic compounds (VOCs) concentrations (below 1000 mg carbon per cubic meter). However, the industry has shown an increasing interest in applying bifilters to higher concentrations of VOCs and to mixtures of VOCs. In the biofiltration of emissions, the content of some nutrient in the media will be too low to be sufficient to support the microbial activity, thus leads to the deterioration of the biofilters.In this study, biofitration was successfully applied to treat air streams containing a mixture of ethyl acetate and toluene. The experiment system includes two identical bench-scale biofilters, which were acclimated with ethyl acetate and toluene respectively. All of the two biofilters consist of three segments, which are called the first, the second and the third segment from the top to the bottom.The removal efficiencies for ethyl acetate and toluene of each biofilter were studied under different inlet VOCs concentrations. During a three-month steady-state performance, the two biofilters showed equivalent elimination capacity for toluene (50 g/m3 bed/h of pure toluene). However, the biofilter acclimated with ethyl acetate showed a much higher elimination capacity for ethyl acetate (400 g/m3 bed/h of pure ethyl acetate) than that acclimated with toluene (250 g/m3 bed/h). The concurrent biofiltration of toluene was inhibited by the presence of ethyl acetate. The content variations of total nitrogen (T-N), total phosphorus (T-P), ammonia nitrogen (NH3-N) and total organic matter (TOM) were investigated during the course of biofiltration. The results showed that the content of T-N and T-P in the media decreased gradually during the process. However, more T-P and T-N were consumed in the second segment (which mainly treated toluene) than that of the first segment (which mainly treated ethyl acetate). Additionally, it is concluded that the irregular distribution of NH3-N is attribute to the transformation of nitrogen. During the biofiltration experiment, the content of TOM could be balanced via mass transfer among the pollutants, the biofilm and the media. After the three-month experiment, the pH of the media treating ethyl acetate dropped from 6.71 to 5.50, whereas the pH of the media treating toluene increased from 6.71 to 7.08.