2002 Annual Report
Research
Low-Cost Biofilters for Odor Control
Kevin Janni, Professor
Larry Jacobson, Professor
Richard Nicolai, Research Fellow
David Schmidt, Assistant Extension Engineer
Verlyn Johnson, Information Technology Professional
Funding Source
Minnesota Department of Agriculture
Objective
Animal agriculture in Minnesota is under pressure to minimize the impact
of airborne emissions from animal facilities on the environment and nearby
neighbors. The objectives of this project are to:
- Evaluate the effectiveness of different biofilter media mixtures,
- Monitor long-term biofilters effectiveness treating air from swine and dairy facilities, and
- Determine nitrogen transformation rates in biofilters.
Project Description
Biofilters are an effective technology for removing odor, hydrogen sulfide,
and ammonia from air exhausted from livestock facilities. Proper biofilter
design is critical to provide effective and economical treatment. To improve
the biofilter design process, the relationship between unit flow rate
through the biofilter media and the unit pressure drop across the media
is needed. The purpose of this project was to develop a method for characterizing
compost and wood chip mixtures and predicting the relationship between
flow rate and pressure drop. Experiments were conducted to evaluate the
effectiveness of different biofilter media mixtures. There were six compost/wood
chip mixtures (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) and three
moisture levels (30-40%, 45-55%, and 60-70%). The eighteen biofilters
(24 in. x 24 in. with 12-in. deep media) were supplied with air from a
swine manure pit. The airflow rates were set to provide approximately
a 5-s residence time. Odor and hydrogen sulfide removal was measured.
The long-term performance monitoring of two biofilters treating air from
swine and dairy facilities was conducted quarterly. Air entering the biofilters
and treated air leaving the biofilters was sampled. Odor threshold concentrations
were determined using olfactometry, and hydrogen sulfide concentrations
were measured using a Jerome® meter.
Results
Two methods of characterizing compost – wood chip biofilter media
(i.e. sieve analysis and five-gallon pail water void analysis) were evaluated
and found to have a high correlation coefficient. Relations to estimate
the unit pressure drop given the unit flow rate and percent voids were
developed for media with between 40% to 60% voids. These can be used to
evaluate alternative biofilter designs and for selecting fans with adequate
fan performance characteristics.
Results from the media mixture experiments indicate that media mixtures
with between 30% and 50% by weight of compost and between 70% and 50%
(by weight) of wood chips are equally effective in reducing odor emissions.
Moisture content was found to be a critical factor in biofilter performance.
The long-term performance results indicated that the 36 in. deep dairy biofilter achieved odor, hydrogen sulfide, and ammonia reductions that ranged from 57% to 100%, with many values at 90% or above. The 10 in. deep swine biofilter achieved odor and hydrogen sulfide reductions that ranged from 50% to 98%. Ammonia removal ranged from 0% to 67%. Biofilter media moisture content is critical for biofilter performance. Odor and hydrogen sulfide removal efficiency decreased as the biofilters dried out.