Removal of styrene from waste gas stream using a biofilter

Background: Styrene is produced in large quantities in the chemical industries and it has been listed among the 189 hazardous and toxic atmospheric contaminants under Clean Air Act Amendments, 1990, due to its adverse effects on human health. The biofiltration has been widely and efficiently applied during recent decades for the treatment of air streams contaminated by volatile organic compounds at low concentrations. Also this technology has been applied widely and efficiently in the removal of styrene from waste gas streams. Methods: Biofiltration of waste gas stream polluted by styrene vapor was investigated in a three-stage bench scale reactor. Yard waste compost using shredded hard plastics as a bulking agent in a 75:25 v/v mix of plastics:compost was used to packing biofilter. The system inoculation was achieved by adding thickened activated sludge obtained from municipal wastewater treatment plant and the effects of loading rate, inlet concentration, and empty bed retention time variations on the performance and operation of biofilter were studied. Results: Microbial acclimation to styrene was achieved with inlet concentration of 65 ± 11 ppm and bed contact time of 360 s after 57 days of operation. Under steady state conditions experimental results showed equal average removal efficiency of about 84% at loading rates of 60 and 80 g m-3 h-1 with empty bed retention time of 60 s. Maximum elimination capacity was obtained up to 81 g m-3 h-1 with organic loading rate of about 120 g m-3 h-1. Reduction in performance was observed at inlet concentrations of upper than 650 ppm related to organic loading rates up to 160 g m-3 h-1 and then removal efficiency was decreased sharply. Evaluation of the concentration profile along the bed height of column indicated that the most value of elimination capacity occurred in the first section of biofilter. Elimination capacity also showed higher performance when empty bed retention time was reduced to 30 s. Conclusion: Microbial acclimation period for biofiltration of styrene inoculated with activated sludge was longer than inoculation with adapted or enriched bacteria. Addition of compost improved performance of the biofilter because of high water retention capacity. Also high pollutant load with significant concentration to the first sections has a clear inhibitative effect on biofilter performance along the bed height of biofilter. Keywords: biofilter, styrene, Volatile Organic Compounds (VOCs), waste gas, compost