Evaluation of a commercial ozone treatment system to improve swine slurry

Reducing volatile organic compounds (VOC) and odor emissions, of swine slurry is necessary if producers are to meet existing and future environmental regulations. The objective of this study was to evaluate one technology designed to improve swine slurry odor under production scale conditions. The facility utilized for this study was an environmentally controlled grow-finish building constructed over a manure pit capable of holding 408,297 L (107,730 gal) of slurry. During the time span of this study the pit contained 170,126 L (44,888 gal) of slurry. The system treated slurry with air that was previously exposed to ultra-violet light producing ozone that was injected at a rate of 0.18 cmm (6.25 cfm) into slurry pumped at 379 Lpm (100 gpm). This was equivalent to exposing the entire pit contents once every 7.5 h. Prior to treatment, the slurry was analyzed to contain 4.61% solids, 6.8 pH, 482.5±3.54 mg:L settable solids (SS), 2,175±139 mg:L total suspended solids (TSS), 220.2±3.8 ppm ammonia, less than minimum detection limits (MDL) of dissolved oxygen (DO), 59,275±3,866 mg:L chemical oxygen demand (COD), 0.49±0.01%N and 1.55±1.15%P with a 0.3:1 N:P ratio. Following 72 h of treatment, solids concentration was lowered (P<0.05) to 1.45%; SS were reduced (P<0.05) 96.4%; TSS were reduced (P<0.05) 77.9%; NH3, DO, and COD were not significantly different; N was lowered (P<0.05) 42.9% to 0.28%; and, P was lowered (P<0.05) to below detection limits. No significant changes between 72 and 96 h of treatment in any of the characteristics measured were observed. Four air sample bags were collected prior to treatment and following 48, 72, and 96 h of treatment with subsequent analyses by a trained human odor panel (N=8). The recognition threshold (lowest dilution concentration that odor could be recognized) prior to treatment was 1,382±74 and was significantly lower after 48 h of treatment (205±69). Odor intensity was significantly higher prior to treatment than after 48 h of treatment comparing mean intensities of 3.14±0.26 and 2.29±0.39, respectively. No changes (P<0.05) in odor intensity or threshold were detected between 48 h and subsequent observations at 72 and 96 h. The results of this study suggest under production scale conditions the commercial ozone treatment system evaluated can reduce odor and can reduce the concentration of selected VOCs of swine slurry.