Removal of dimethyl disulfide and p-cresol from swine facility wastewater using constructed subsurface-flow wetlands

Anecdotal evidence suggests that constructed wetlands can remove odors from veal, dairy, and swine wastes (Murphy and George, 1997; McCaskey, 1995). However the use of constructed wetlands as an odor control treatment will be more successful after malodor reduction in wetland systems has been quantified. This study quantified odor removal from swine facility wastewater (feces, urine, and flushwater) in constructed subsurface-flow wetlands. Four wetlands planted with wetland grasses and four unplanted wetlands received swine facility waste. The relationship between wetland treatments (planted vs unplanted) and reductions of malodorous dimethyl disulfide and p-cresol in wastewater were examined. Reductions in odor intensity and offensiveness as perceived by a human sensory panel were also studied. Gas chromatography analysis indicated that planted wetlands removed 80 and 83% of dimethyl disulfide (DMDS) and p-cresol, respectively. Unplanted wetlands removed 52 and 64% of dimethyl disulfide and p-cresol, respectively. The reductions in DMDS and p-cresol did not differ significantly (p > 0.05) between the two treatments. A human sensory panel, using the cloth swatch technique, assigned a median odor intensity and offensiveness rating of 4 (identifiable odor-offensive, but tolerable) to untreated swine facility wastewater: Median odor ratings for both planted and unplanted effluent were I (faint odor-nonidentifiable, not offensive). These median odor ratings were significantly (p < 0.05) lower than the median odor rating for untreated wastewater indicating that constructed wetlands were effective in removing malodor from swine facility wastewater.