The use of biofiltration for the treatment of VOC-polluted air streams

A laboratory-scale biofiltration system consisting of three columns was investigated for the removal of benzene, toluene, ethylbenzene, and o-xylene (BTEX) compounds from a waste gas stream. This biofiltration system uses yard waste compost as a filter material. Different amounts of granular activated carbon (GAC) are mixed with the compost in two of the three columns, to explore if the performance of the system can be further enhanced.;The performance of the system is evaluated through long term operation. The experiment was divided into two stages: in the first stage, benzene was the target compound. More than 90% removal efficiency was observed for an influent benzene concentration of about 75 ppm, and an air flow rate of 0.3 l/min for all three columns under steady state conditions. BTEX vapors were the target compounds during the second stage of the experiment. The three columns displayed preferential utilization of benzene followed by toluene, ethylbenzene, and o-xylene respectively. More than 90% removal efficiency was observed for an influent concentrations of more than 275 ppm of the BTEX compounds, and an air flow rate of 0.63 l/min in all columns, also under steady state conditions.;Tests were conducted to study the performance of the three columns under different loading conditions resulting from changing the inlet compounds concentrations, or the gas flow rates. Under shock loading conditions, such as a sudden increase in the air flow rate, or the BTEX concentration in the influent, the biofilters containing GAC exhibited significantly higher removal efficiencies than the biofilter containing only compost.;Mathematical models are developed in this research to describe the kinetics of volatile organic compounds removal in biofilters that consist of a mixture of compost and granular activated carbon as a filter media. Comparison of the values predicted by the models with the experimental data, proves that these mathematical models give a good approximation of the removal kinetics of BTEX compounds in the laboratory scale biofilter columns.