Renewable biocatalyst for swine manure treatment and mitigation of odorous VOCs, ammonia and hydrogen sulfide emissions: Review

Abstract.

Comprehensive control of odors, hydrogen sulfide (H₂S), ammonia (NH₃), and greenhouse gas (GHG) emissions associated with swine production is a critical need. The objective of this paper is to review the use of soybean peroxidase (SBP) and peroxides as a manure additive to mitigate emissions of odorous volatile organic compounds (VOC), NH₃, H₂S, and GHGs. Soybean peroxidase plus peroxide (SBPP) was tested as a mitigation technology for swine manure emissions on three scales (lab, pilot and farm). Several laboratory scale experiments were completed to assess SBPP dosages and type of oxygen source mixed into swine manure and surface application. A pilot scale experiment was done with surface application of SBPP and multiple dosages to observe scale up effects. Finally, a farm scale trial was completed to assess the SBPP treatment to a swine manure surface under a fully slatted barn floor. The ‘gated‘ approach to testing SBPP from lab- to pilot- and finally the farm-scale was appropriate and allowed for controlled experiments with sufficient replication. This approach resulted in gradual decrease of the dose of SBP, decreasing the cost of treatment, increase of treatment longevity, inclusion of many key gases of concern to the experimental protocol, and finally testing the treatment on farm-scale. To date, the farm-scale results indicate that SBPP can be effective in mitigating many important odorous gas emissions without increasing GHGs. Specifically, a 2.28 kg m^-2 SBP dose mixed with 4.2% CaO₂ added by weight and added to manure surface resulted in significant reductions in gaseous emissions of NH₃ (21.7%), H₂S (79.7%), n-butyric acid (37.2%), valeric acid (47.7%), isovaleric acid (39.3%), indole (31.2%), and skatole (43.5%). Emissions of DMDS/MT increased by 30.6%. Emissions of p-cresol were reduced by 14.4% but were not statistically significant. There were no significant changes to the GHG emissions of CH₄, CO₂ and N₂O. The treatment cost (SBP+CaO₂) was $1.45 per marketed pig of which the cost of SBP was only ~40%. Thus, further research is needed to optimize the dose and the cost of catalysts.

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