Evaluation of wood chip-based biofilters to reduce odor, hydrogen sulfide, and ammonia from swine barn ventilation air.

A pilot-scale biofilter was developed in which two types of wood chips (western cedar [WC] and 2-in. hardwood [HW]) were examined to treat odor emissions from a deep-pit swine finishing facility in central Iowa. The biofilters were operated continuously for 13 weeks at different airflow rates resulting in variable empty bed residence times (EBRTs) from 1.6 to 7.3 sec. The effects of three media moisture levels were also evaluated. A dynamic forced-choice olfactometer was used to evaluate odor concentrations from both the control (inlet) plenum and biofilter treatments (outlet). Hydrogen sulfide (H2S) and ammonia (NH3) concentrations were also measured from these olfactometry samples. Solid-phase microextraction (SPME) polydimethylsiloxane (PDMS)/divinylbenzene (DVB) 65-microm fibers were used to extract volatile organic compounds from both the control plenum and biofilter treatments. Analyses of separated odors were carried out using a gas chromatography-mass spectrometry-olfactometry (GC-MS-O) system. Static sample results indicated that both types of chips achieved significant reductions in odor (average 70.1 and 82.3% for HW and WC, respectively), H2S (average 81.8 and 88.6% for HW and WC, respectively) and NH3 (average 43.4 and 74% for HW and WC, respectively) concentrations. GC-MS-O aromagram results showed both treatments reached high odor reduction efficiency (average 99.4 and 99.8% for HW and WC, respectively). The results also showed that maintaining proper moisture content and a minimum EBRT are critical to the success of wood chip-based biofilters.