Studies On The Treatment Of Off-gases Containing Xylene By Bio-trickling Filters

Air pollution which attributes to the rapid development of industry is more and more serious with the increase of Chinese people's material standard of living. As a important kind of pollutants, the volatile organic compounds (VOCs) do great harm to people's health and natural environment, so more and more attention has been focused on the purification and treatment of VOCs.As a booming technology, the bio-filtration technique has been used in air pollution control project. Bio-trickling filtration, the modified technique of bio-filtration, has such advantages as low investment and operating costs, high efficiency, stable operation, convenient management and no secondary pollution, and has been applied more broadly in industrial waste gases treatment.Based on the feasible analysis of the removal of xylene by bio-degradation, this paper introduces the basic principle of bio-trickling filter in detail, and by the comparative experiment, mainly studies the influences of operation parameters such as filter media (pellets), influx gas load, empty bed contact time, gas flow rate, liquid flow rate and NHJ -N concentration on the performance of the bio-trickling filter.The experiment has been carried out under the following conditions: Two different kinds of filter media (pellets) were packed into the two same-size towers , the influx gas load of the two towers is 40⁸00g/(m3 ?h), the retention time of the waste gas is 28,26s¹41.3s. After five months of continuous operation, the experiment results suggest that the elimination load and the influx gas load are linearly correlated and elimination capacity of xylene increases in pace with the increase of influx gas load, and decreases with the increase of gaseous flow rate at fixed influx gas load. The liquid flow rate has little influence on the performance but it should be controlled within a proper range. The removal efficiency of xylene also decreases with the increase of gaseous flow rate while keeping xylene concentration constant in the bio-filter's inlet. Nitrogen is necessary forthe growth of microorganisms. The removal efficiency of the two towers increases obviously with doubling the concentration of NH₄ -N in spraying liquid. Quantitative analysis of CO₂ concentration in bio-filters validates microbial activity. From the inlet to the outlet, the concentration of CO₂ increases with the decrease of concentration of xylene. Compared with other experiments, in spite of shorter retention time (28.26s) , higher removal efficiency has been obtained.The results obtained from the experiments coincide with the current theories and are valuable, which will prompt the further application of bio-trickling filter in industry.