Evaluation of Odorous Compounds and Microbial Dynamics During Livestock Manure Composting Using Soybean Peroxidase

Riuh Wardhani1 · Seunghun Lee2 · Jinho Shin2 · Abera Jabessa Fufa1 · Yongwoo Song3 · SeongJun Park3 · Heekwon Ahn4*

1Dept. of Dairy Science, Chungnam National University, Daejeon, Korea

2Institute of Agricultural Science, Chungnam National University, Daejeon, Korea

3Dept. of Livestock Environmental Science & Technology, Chungnam National University, Daejeon, Korea

4Dept. of Animal Biosystems Science, Chungnam National University, Daejeon, Korea

1. Introduction

Odor emissions from composting livestock manure present a major environmental challenge, particularly due to odor emissions such as ammonia (NH3), volatile sulfur compounds (VSCs), volatile fatty acids (VFAs), and volatile organic compounds (VOCs) (Mao et al., 2018; Sun et al., 2023; Xie et al., 2023). Recent research has highlighted the potential of enzymatic treatments for odor mitigation, with soybean peroxidase (SBP), a by-product from soybean hull processing as a promising candidate (Parker et al., 2012; 2016). SBP can oxidize and polymerize volatile compounds, reducing their volatility and environmental impact. While its effectiveness in liquid slurry systems has been demonstrated (Maurer et al., 2017), limited studies have evaluated SBP performance under aerobic composting conditions. Therefore, this study aims to assess the effectiveness of SBP, in combination with calcium peroxide (CaO22), in reducing odorous emissions during pilot-scale composting of dairy manure solids and sawdust bedding.

2. Methods

Six compost piles were constructed using a mixture of dairy manure solids and sawdust bedding. The initial moisture content was adjusted to 70±0.4% in the treatment group and 71±0.5% in the control, with volatile solids at 85±0.2% and 84±0.8%, respectively. The treatment piles received 8% SBP (d.b. of mixture) along with 1.12% CaO2 (w.b. of SBP). A flux chamber with a volume of 2.25 m³ was used to sample gaseous emissions throughout the 50-day composting period. Emissions of NH3 and VSCs such as H2S (hydrogen sulfide), CH4S (methyl mercaptan), C2H6S (dimethyl sulfide), and C2H6S2 (dimethyl disulfide). Additionally, VFAs such as acetic acid, propionic acid, iso-butyric acid, butyric acid, iso-valeric acid, and valeric acid were measured, along with VOCs including phenol, p-cresol (4-methylphenol), indole, and skatole (3-methylindole). Microbial community dynamics were analyzed using hierarchical clustering, and odor-reducing bacteria were profiled across composting stages.

3. Results and Discussion

The treatment group exhibited a 39.7% reduction in cumulative NH3 emissions and a 31.8% (Figure 1) decrease in NH3 concentration within compost piles compared to the control. These significant reductions can be attributed to the dual mechanisms. First, SBP binds with NH3 and NH4⁺, thereby limiting their volatilization (Maurer et al., 2017a). Second, the incorporation of SBP lowers compost pH, which shifts the NH4⁺/NH3 equilibrium, further suppressing NH3 volatilization (Dai and Blanes-Vidal, 2013; Kai et al., 2008; Ottosen et al., 2009). The treatment also demonstrated a significant impact on phenol emissions (Figure 1). Phenol emissions were reduced by 46.9%, likely due to oxidative reactions facilitated by peroxidase in the presence of CaO2. This enzymatic activity initiates the conversion of phenols into reactive radicals, followed by coupling reactions (C–C, O–C, and O–O linkages) and polymerization into larger, less volatile compounds (Steevensz et al., 2014; Torres-Duarte et al., 1998). Despite a general increase in total VSCs, notable reductions were observed for specific odorants. H2S and DMDS were reduced by 64.0% and 90.7%, respectively. Furthermore, total VFA emissions decreased by 18.0% (p = 0.06), suggesting a reduction in easily degradable organic acids that contribute to odor intensity.

Microbial community analysis further supports the effectiveness of SBP treatment. Hierarchical clustering revealed distinct shifts in both bacterial and archaeal succession between treatment and control groups. These shifts are indicative of microbial restructuring driven by SBP amendment. Specifically, the abundance of functional bacteria associated with ammonia and phenol degradation, such as Ammonibacillus and phenol-degrading genera (Corynebacterium, Staphylococcus, Bacillus), was markedly higher in the treatment group. Similarly, sulfur-reducing bacteria showed varied responses across the composting period, reflecting complex interactions within the microbial community. The observed odor emissions and microbial dynamics changes underscore SBP’s potential as a sustainable and effective strategy for odor control in livestock waste management systems.

4. Conclusion

This pilot-scale study demonstrated that SBP combined with CaO2 effectively reduces major odorous emissions, particularly NH3 and phenol, during dairy manure and sawdust bedding composting. The enzymatic treatment achieved a 39.7% reduction in NH3 and a 46.9% decrease in phenol emissions, indicating that SBP can catalyze oxidative polymerization and alter physicochemical characterization of compost to suppress odor generation. Furthermore, microbial community analysis showed a favorable shift toward odor-degrading populations under SBP treatment. These findings highlight SBP as a promising, sustainable, and scalable biocatalytic additive for odor mitigation in livestock waste management. Future research should focus on evaluating its cost-effectiveness and performance under field-scale composting conditions to facilitate real-setting application.