Biofiltration of livestock facility exhaust air

Biofiltration is a promising technology for reducing odor and gas emissions from livestock buildings. To develop a model to optimize biofilter design, research was conducted on media characterization and airflow residence time.; Media mixture ratio of compost and wood chips, and percent voids were used to characterize the media. Recommended mixing ratio of compost to wood chips is minimum 30% compost and the balance wood chips by weight. To characterize the media, a simple bucket test was developed to measure media voids. A regression was developed to predict expected pressure drop through media using inputs of percent voids and airflow per unit area.; Minimum residence time was investigated to achieve 75% odor and hydrogen sulfide (H₂S) emission reduction from livestock buildings. Odor and H₂S reduction did not significantly change with residence time of 6 s or more for either dairy or swine; however the reduction drop to less than 75% at residence times less than 4 s. For adequate reduction, the recommended design residence time for a dairy and swine facility is 5 s. Reducing residence time by decreasing depth below 0.15 m reduced odor and H₂S reduction to less than 65%. A minimum biofilter media depth of 0.25 m is recommended.; An optimization model based on cost was developed to design biofilters. The model, utilizes three sub-models: biofilter size, pressure drop, and construction and operating costs.; A laboratory experiment investigated N accumulation and N transformations to better understand how biofilters reduce ammonia. Total-N accumulated in the media only accounted for 29% of the N removed by the biofilter after 1160 h. The fate of the remaining N is unknown. NO gas emission accounts for only a small part (<2%) of the difference and no N was lost via leaching. Micro site denitrification to N₂, NO₂, or N₂O may explain some of the discrepancy, but further research is needed. An attempt to determine N transformation rates was made, but failed due to the monitoring procedures and the ability to stop the continuous circular N transformations.; However biofiltration did prove to be an effective technology to reduce ammonia from air.