Effects of biofilter media depth and moisture content on removal of gases from a swine barn.

Unlabelled: Media depth (MD) and moisture content (MC) are two important factors that greatly influence biofilter performance. The purpose of this study was to investigate the combined effect of MC and MD on removing ammonia (NH), hydrogen sulfide (HS), and nitrous oxide (NO) from swine barns. Biofiltration performance of different MDs and MCs in combination based on a mixed medium of wood chips and compost was monitored. A 3 × 3 factorial design was adopted, which included three levels of the two factors (MC: 45%, 55%, and 67% [wet basis]; MD: 0.17, 0.33, and 0.50 m). Results indicated that high MC and MD could improve NH removal efficiency, but increase outlet NO concentration. When MC was 67%, the average NH removal efficiency of three MDs (0.17, 0.33, and, 0.50 m) ranged from 77.4% to 78.7%; the range of average HS removal efficiency dropped from 68.1-90.0% (1-34 days of the test period) to 36.8-63.7% (35-58 days of the test period); and the average outlet NO concentration increased by 25.5-60.1%. When MC was 55%, the average removal efficiency of NH, HS, and NO for treatment with 0.33 m MD was 72.8 ± 5.9%, 70.9 ± 13.3%, and -18.9 ± 8.1%, respectively; and the average removal efficiency of NH, HS, and NO for treatment with 0.50 m MD was 77.7 ± 4.2%, 65.8 ± 13.7%, and -24.5 ±12.1%, respectively. When MC was 45%, the highest average NH reduction efficiency among three MDs was 60.7% for 0.5 m MD, and the average NO removal efficiency for three MDs ranged from -18.8% to -12.7%. In addition, the pressure drop of 0.33 m MD was significantly lower than that of 0.50 m MD (p < 0.05). To obtain high mitigation of NH and HS and avoid elevated emission of NO and large pressure drop, 0.33 m MD at 55% MC is recommended.

Implications: The performances of biofilters with three different media depths (0.17, 0.33, and 0.50 m) and three different media moisture contents (45%, 55%, and 67% [wet basis]) were compared to remove gases from a swine barn. Using wood chips and compost mixture as the biofilters media, the combination of 0.33 m media depth and 55% media moisture content is recommended to obtain good reduction of NH and HS, and to simultaneously prevent elevated emission of NO and large pressure drop across the media.