The objectives of this research were to evaluate the effectiveness of two wood chip biofilters in reducing particulate matter, ammonia, methane, and hydrogen sulfide emissions. Other objectives were to evaluate if the hydration system was able to maintain proper media moisture content; and to report the costs, maintenance, and recommendations of operating such biofilters. Two 5-inch (media thickness) biofilters were monitored for gas and particulate matter (PM) concentrations from August 1 to October 19, 2009. The biofilters were then converted to 10-inch units (biofilters with 10-inch media thickness), and monitored until December 1, 2009. Gas samples before and after the biofilters were continuously measured. Particulate matter concentrations were measured continuously at all three enclosure exhausts, and included PM2.5, PM10, and TSP.
In spite of low-volume biofilter media, the biofilters exhibited some degree of gas and PM reductions. The two 5-inch biofilters reduced NH3 concentrations by 31% and 18%, and H2S concentrations by 27% and 24%, respectively. Insignificant reductions of CH4 concentration were observed. The 10-inch biofilters reduced NH3 concentrations by 46% and 18%, and H2S concentrations by 42% and 28%, respectively. The biofilters were more efficient in reducing PM concentrations, the 5-inch biofilters had reduced PM10, and TSP concentrations by 62% and 90%, while the 10-inch biofilters had only improved the reduction by a few percentage points. Very low PM2.5 concentrations were measured in the treated and untreated airstreams.
For a 5-inch biofilter installation at a single swine finishing room with three pit fans (24-inch fans), the total cost would be $4000/room, with installation and including a hydration system. For 10-inch biofilters, the total cost would be $4200/room. These costs do not include biofiltration of the wall fan exhaust air. Since the costs were very similar for the two biofilter thicknesses, and the 10-inch biofilter had generally increased gas mitigation effectiveness, the 10-inch biofilter is preferred over the 5-inch biofilter.

Other operational parameters for maintenance and operation that require producer attention include potential airflow reduction, biofilter media moisture content variation, and biofilter media compaction. Although these biofilters did not require a stronger fan or additional fan, the pressure drops caused by the 5-inch and 10-inch biofilters reduced the pit fan airflow rates by about 18% and 33%, respectively. Maintaining proper and uniform media moisture content is very important for maintaining mitigation effectiveness, and minimizing backpressure on the fans. Frequent maintenance checks of the biofilter and spray system to minimize compaction, ensure uniform moisture content, and minimize pressure drops are required to ensure maximum effectiveness. It is estimated that the farm personnel needs one to two hours per week to inspect and maintain the biofilter media and hydration system, for a finishing room with three biofilters. A daily visual inspection of the biofilters will ensure the biofilter performance and reduce downtime.

The findings suggest that the biofilters tested provide another mitigation option for swine producers. The biofilters were relatively simple to install and maintain, although with very small biofilter media volume, they provide low to medium mitigation effectiveness.  Greater reductions should be obtained with greater biofilter volumes and air residence time in the media.

Contact information: Teng Teeh Lim, Assistant Professor and Extension Agricultural Engineer. 230 Agricultural Engineering Building, University of Missouri, Columbia, MO 65211-5200. Telephone: (573) 882-9519. Email: