Treatment of styrene- laden waste gas stream using compost-based biofilter

Biofiltration of air containing styrene vapor was investigated using a three-stage bench scale biofilter. The biofilter was packed with yard waste compost using hard plastics as a bulking agent in a 75:25 v/v mix of plastics: compost. The feed concentration was made by bubbling air through a styrene stock solution. The system was inoculated with thickened activated sludge and the effects of loading rate, inlet concentration and empty bed contact time variations on the performance and operation of biofilter were studied. During the start up period of about 65 days, microbial assimilation to styrene was achieved with inlet concentration of 270 mgm and bed contact time of 6 min. Under steady state conditions experimental results showed overall removal efficiency of 92±2% at loading rates 31±2 gmh and empty bed residence time (EBRT) of 120 s. No reduction in performance was observed at organic loading rate (OLR ) values of up to 60±3 gmh and elimination capacity remained at 49±2 gmh. Evaluation of the concentration profile along the bed height indicated maximum elimination capacity occurring in the first section of biofilter with styrene removal efficiency of around 50%. Elimination capacities showed a decreasing trend once EBRT was reduced to 30 s. There was no indication of excessive biomass growth and consequent increase in pressure drop during the 200 days of study. INTRODUCTION Styrene is produced in larger quantities in the chemical industry and its monomer constitutes the building block for the production of polystyrene, styrene copolymers, polyester resins and rubber. It is also used in the production of glass fiber reinforced plastics like boats, storage tanks, pipes, shower units and car parts. Besides the known industrial releases from the production and processing units, styrene is also generated in smaller quantities from other sources such as natural microbial and fungal metabolism, cigarette smoke, automobile exhaust and the pyrolysis and cracking of petroleum and its derivatives. Styrene has been listed among the 189 hazardous and toxic atmospheric contaminants under CAAA (1990) because of its adverse effect on human health. Acute exposure to styrene in humans results in mucous membrane and eye irritations as well as gastrointestinal disorders. Chronic exposure to styrene in humans results in ∗ Corresponding author, [email protected]