Alternative media are being tested for use in gas-phase biofilters in an effort to minimize pressure drop, lower operating costs and reduce the biofilter footprint. Improved biofilters will also be more resistant to rodents and extend the useful life through reduced maintenance costs.

Gas-phase biofilters are a proven method for reducing odor and other gaseous emissions from swine facilities. However, widespread adoption of biofiltration has stalled due to four issues:

  • The relatively large footprint needed to manage the media pressure drop;

  • The concerns about the biofilter media harboring rats;

  • The potential problem of long-term biofilter media compaction; and

  • The concerns about potential nitrate leaching from the biofilter media into the soil.

This project at the University of Minnesota, funded by Pork Checkoff, was designed to identify and evaluate alternative biofilter media that would solve some of these issues.

Six media were evaluated in Phase 1: bag mulch, lava rock, cedar chips, pine bark nuggets, western pine bark and wood shreds. Media sieve analysis (filtration process), porosity and unit pressure drop vs. unit airflow relations were determined.

Phase 1 testing was conducted in a biofilter media testing unit with six columns, including individually controlled airflow rates and moisture control (pictured above).

Phase 1 testing involved the air-cleaning performance and pressure drop characteristics of each media evaluated on the basis of hydrogen sulfide (H2S), and ammonia (NH3) removal.

In Phase 2, three media — wood shreds, pine bark nuggets and lava rock — were placed in similar columns and evaluated for pressure drop and reductions of H2S and NH3.

In Phase 3, pine bark nuggets were used in all six columns and H2S, NH3 and odor removal were analyzed.

Overall, pine bark nuggets and lava rock scored the highest by recording the lowest unit pressure drops vs. unit airflow rates.

Results from Phase 1 indicate that all six media supported microbial growth if seeded, and were effective, reducing H2S concentrations between 21-75% and NH3 concentrations between 43-80%.

All three media in Phase 2 performed well in the study.

Some biofilter media in Phase 3 had lower percent H2S, NH3 and odor removal than others.

Researcher: Kevin A. Janni, University of Minnesota. Contact Janni by phone (612) 625-3108, fax (612) 624-3005 or e-mail