Field evaluation of biofilters in reducing aerial pollutant emissions from a commercial pig finishing building

Two elevated-bed, wood-chip biofilters were tested at a commercial pig finishing farm in Indiana for effectiveness in mitigating aerial pollutant emissions. Three wooden sampling chambers were installed to contain and redirect two biofilter-treated and one untreated exhaust streams. Two trials were conducted to test the effects of biofilter thickness, which included 127-mm and 254-mm of media depths. The two biofilters with 127-mm media thickness reduced concentrations of ammonia (NH3) by 31.2% (p < 0.05) and 18.1% (p > 0.05), and hydrogen sulfide (H2S) by 26.6% (p < 0.05) and 23.6% (p < 0.05) in the pit fan exhaust air, respectively. Insignificant reductions of methane concentrations were observed. The biofilters with 254-mm media thickness significantly (p < 0.05) reduced concentrations of NH3 by 45.8% and 18.0%, and H2S by 42.2% and 27.9%, respectively. Significant reductions (p < 0.05) of particulate matter (PM10), and total suspended particulate were 62.0% and 89.7% for the 127-mm biofilters, and 62.9% and 96.3%, for the 254-mm biofilters, respectively. Very low inlet PM2.5 concentrations were detected. Average pressure drops of the biofilters ranged from 29.6 to 57.2 Pa. The empty bed residence times (EBRTs) were 0.3 s and 0.6 s for the 127-mm and 254-mm biofilters, respectively. Frequent maintenance checks to minimise compaction and ensure uniform moisture content were required to ensure minimal pressure drops and maximal aerial pollutant removal efficiency. The biofilters were relatively simple and inexpensive to install. Although the EBRT was relatively short, the biofilters exhibited low to medium mitigation effectiveness. Higher mitigations would be obtained using biofilters with greater media volumes corresponding to longer EBRTs.