Sulfur and nitrogen balances in biofilters for odorous gas emission control

Biofiltration is a promising technology for reducing odor and gas emissions from livestock operations. Two important operating parameters in biofiltration - media moisture content (MC), and gas retention time (RT) - were studied to determine their effects on sulfur (S) and nitrogen (N) balances. Laboratory experiments were carried out to determine S and N accumulation in and emissions from biofilters with various media MC (30%, 40%, 50% wb) and RT (5, 10, 20 s). The biofilter media was a mixture of compost and wood chips. The media bed was 0.20 m deep and 0.30 m in diameter Two trials (replications) were run. Results showed that 47% to 94% of the hydrogen sulfide (H₂S) and 25% to 90% of the ammonia (NH₃) were removed by the biofilters. Removal efficiency varied with treatment. Biofilters with 50% MC and 20 s RT had the largest removal efficiencies for both H₂S and NH₃, with average H₂S removal rates of 92.8% in Trial 1 and 94.2% in Trial 2. Average NH₃ removal efficiencies of these biofilters (50% MC and 20 s RT) were 90.3% in Trial 1 and 75.8% in Trial 2. S and N accumulation in the biofilter media was also affected by MC and RT. Accumulation models for S and N in the media were developed and reported.