Surface application of soybean peroxidase and calcium peroxide for reducing odorous voc emissions from swine manure slurry

A laboratory experiment was conducted to evaluate and compare surface-applied versus fully-mixed treatments of soybean peroxidase (SBP) plus calcium peroxide (CaO₂) for reducing odorous volatile organic compound (VOC) emissions from swine manure slurry. Industrial-grade SBP (5-50 g L^-1) and powdered CaO₂ (0.16-1.6 g L^-1) were applied to swine manure slurry in 7.6 L containers, and odorous VOC emission rates (phenolics, indolics, volatile fatty acids, methyl sulfides) were measured over a 14 d period using sorbent tubes and gas chromatography. The five treatments consisted of a control, the fully-mixed rate of 50 g L^-1 SBP plus 1.6 g L^-1 CaO₂, and three surface-applied treatments of 10%, 50%, and 100% of the fully-mixed application rate. The odorants 4-methylphenol and skatole accounted for the majority of the odor activity value (OAV). The 10% surface-applied rate was as effective as the 100% surface-applied and fully-mixed application rates at reducing 4-methylphenol and skatole emissions for up to 10 d (P<0.05). Emission rates for the treatments were greater than the control on d 14, indicating the need for reapplication of SBP+CaO₂ every 4-7 d. Future pilot- and field-scale research should focus on surface application of SBP and CaO₂ at a rate equal to 10% of the fully-mixed rate.