Alternative Biofilter Media Offer Energy Efficient Options

Traditional gas-phase biofilters successfully reduce odor and gas emissions from swine buildings.

The most common type of biofilter media is wood chips. The problem with wood chips is that they degrade easily and cause compaction over time. This results in a pressure drop in the building that mechanical ventilation systems and pit fans must overcome.

Plus, these common organic materials must be replaced every two to five years, which represents a significant investment in materials, time and labor. This also produces an operational downtime as the media is replaced and a lag time until the new media acclimates and removal efficiencies reach previous levels.

This research project explores the use of an alternative media to address the concerns of media compaction over time and the large footprint required by flat-bed biofilters. Airflow characteristics and gas reduction efficiencies of two alternative biofilter media (pine nuggets and lava rock) with high porosity and potentially longer service lives were evaluated (Table 1).

It was determined that pine nuggets and lava rock both have lower pressure drops than traditional wood chip biofilter media and were found to be acceptable alternatives for reducing hydrogen sulfide, ammonia and greenhouse gas (methane and nitrous oxide) emissions from swine manure and storage pits (Figure 1).

University of Minnesota researchers found that gas reduction efficiencies were highest for lava rock at 5 seconds empty bed contact time (the amount of time that the air is in contact with the biofilter media) and 90% relative humidity.

The reduction efficiencies at these conditions were 56, 88, 25 and 0.7% for ammonia (NH3), hydrogen sulfide (H2S), methane (CH4) and nitrous oxide (N2O), respectively (Table 2).

Sometimes, biofilters generate nitrous oxide, but in this research no generation was measured using the pine nuggets and lava rock.

Wood chips and bark mulch are commonly used biofilter media since they are locally available. But pine nuggets and lava rock produce up to 50% less pressure drop than wood chips and can be used as energy-efficient biofilter media to treat gas emissions from swine buildings.

At proper moisture content and empty bed contact time, these media could help swine producers lower their electrical fan operating costs and save energy and time.

Researchers: Neslihan Akdeniz and Kevin A. Janni, University of Minnesota. For more information,
contact Akdeniz by phone (612) 624-2115, fax (612) 624-3005 or e-mail: akdeniz@umn.edu.