LAUSR

Highlights We evaluated the performance of a two-stage biotrickling filter in a pig facility. A short empty bed residence time lowered the secondary filter removal efficiency for many odorous compounds. The removal efficiency of some compounds increased when the pH in the secondary water tank decreased. Low-odor-threshold compounds such as MT, n-BA, n-PA, and p-cresol were indicated as targets for optimization. Abstract . Odor is a major problem in pig production, and it is important to minimize odor emissions. To determine the factors influencing variations in odor removal efficiency, we analyzed the performance of a biotrickling filter installed in growing-finishing pig rooms on a commercial farm. Over 16 months, we conducted measurements of representative odorous compounds, namely sulfur compounds (hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide), volatile fatty acids (propanoic acid, 2-methylpropanoic acid, butanoic acid, 3-methylbutanoic acid, and pentanoic acid), and ammonia. The average removal efficiencies of methanethiol, dimethyl disulfide, volatile fatty acids, and ammonia were 83% to 89%, with 50% for hydrogen sulfide and 18% for dimethyl sulfide. For many, but not all, odorous compounds, removal efficiency declined significantly with decreasing empty bed residence time (EBRT). From an analysis of the correlations of odorous compounds’ removal efficiency with the properties of the trickling water, we hypothesized that water properties such as pH, free ammonia, free nitrous acid, ionic species (Na+, Ca2+) concentrations, temperature, electrical conductivity, and biological oxygen demand, in addition to EBRT, were associated with fluctuations in removal efficiency during full-scale operation. The pH in the secondary water tank was negatively correlated with the removal efficiencies of methanethiol, dimethyl sulfide, butanoic acid, 3-methylbutanoic acid, pentanoic acid, and ammonia. Our identification of key odorous compounds indicates the importance of the secondary filter in odor treatment. Biotrickling filters for air in pig facilities could be further optimized by targeting low-odor-threshold compounds such as methanethiol, butanoic acid, pentanoic acid, and p-cresol, in addition to ammonia. Keywords: Ammonia, Biotrickling filter, Pig facility odor, Sulfur compound, Trickling water, Volatile fatty acid.