Effect of Soybean Peroxidase (SBP) Additives on Mitigating Odorous Compoundsin

Dairy Manure Composting

Riuh Wardhani1 · Jinho Shin1 · Jumi Lee2 · Seunghun Lee3 · Dongyeo Kim2 · Yongwoo Song2

· Tegu Lee2 · Heekwon Ahn4*

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

2Dept. of Livestock Environmental Science & Technology, Chungnam National University, Daejeon,

Korea

3Institute of Agricultural Science, Chungnam National University, Daejeon, Korea

4Division of Animal and Dairy Science, Chungnam National University, Daejeon, Korea

1. Introduction

Composting is a widely used method for managing organic waste in livestock farming,

transforming manure into nutrient-rich fertilizer. However, composting also generates odorous

emissions such as ammonia (NH3) volatile sulfur compounds (VSCs), volatile fatty acids (VFAs),

and volatile organic compounds (VOCs), which impact air quality, contribute to nutrient loss,

and cause environmental pollution. Odor emissions are particularly problematic due to

volatilization during composting, underscoring the need for effective odor mitigation strategies.

Recent research has explored enzymatic treatments, particularly soybean peroxidase (SBP), as a

promising approach to reduce odor emissions. SBP, derived from soybean hulls and often used

with calcium peroxide (CaO2), can catalyze the polymerization of volatile compounds, reducing

their volatility. Maurer et al. (2017) have shown that applying SBP to slurry surfaces

significantly decreases NH3, skatole, and indole emissions. This study extends these findings by

evaluating SBP's effectiveness in aerobic composting systems, which differ from slurry systems

in microbial and chemical dynamics.

2. Methods

The composting experiment was conducted in 3.8 L laboratory-scale reactors over a period

of 56 days, using a mixture of dairy manure and sawdust with an initial moisture content of

70% (wet basis). Each reactor contained approximately 1.4 kg (wet basis) of compost and was

aerated at 0.4 L/min·kg VS. The study included a control with SBP residue that exhibited

negligible peroxidase activity (0.03 U/mg) and two SBP treatments. In Treatment 1, SBP was

applied in a split dose—4% (dry basis) at the start of the experiment and an additional 4%

after two weeks. Treatment 2 received a single dose of SBP at 8% (dry basis) initially. The

mitigation effects of each treatment were assessed by measuring odorous gases, including NH3

(ammonia) and sulfur compounds such as H2S (hydrogen sulfide), CH4S (methyl mercaptan),

C2H6S (dimethyl sulfide), and C2H6S2 (dimethyl disulfide). Additionally, volatile fatty acids (VFAs)

such as acetic acid, propionic acid, iso-butyric acid, butyric acid, iso-valeric acid, and valeric

acid were measured, along with volatile organic compounds (VOCs) including phenol, p-cresol

(4-methylphenol), indole, and skatole (3-methylindole).

3. Results and Discussion

The overall mean NH3 emission throughout the composting process was 4.0 mg/day·g-VS in

the control, 3.4 mg/day·g-VS in Treatment 1, and 3.2 mg/day·g-VS in Treatment 2. Both Treatment 1 and Treatment 2 exhibited significant reductions, achieving reductions of 13.2%

and 19.2%, respectively (p<0.001). The statistical difference between treatment groups (p<0.05)

was observed in the overall mean emissions. This study demonstrates a dose-dependent effect

of SBP, with higher concentrations demonstrating greater efficacy in reducing NH3 emissions.

After two weeks of SBP application in Treatment 2, it became difficult to discern its effect due

to the subsequent low levels of NH3 emissions. The SBP may mitigate NH3 emissions through

pH reduction and by binding with NH3 and NH4⁺ (Maurer et al., 2017).

A significant reduction in phenol emissions was also observed. In the control group, mean

phenol emissions were 13.1 μg/day·g-VS, while Treatment 1 and Treatment 2 emitted 11.7

μg/day·g-VS and 9.7 μg/day·g-VS, respectively. Treatment 1 reduced phenol emissions by 15.5%

compared to the control (p=0.04), and Treatment 2, which involved a single SBP application,

achieved a greater reduction of 29.1% (p=0.01). These results indicate that a single SBP

application is more effective in reducing phenol emissions than the split dose used in

Treatment 1. The reduction is likely due to SBP’s catalytic activity, which oxidizes phenolic

compounds into less volatile, stable polymerized products through the formation of phenoxy

radicals that subsequently form dimers and oligomers (Steevensz et al., 2014; Torres-Duarte et

al., 1998). This mechanism likely contributed to the sustained reduction in emissions observed

in Treatment 2. Although reductions in other gas emissions (H2S, DMS, acetic acid, isobutyric

acid, and butyric acid) were observed in the treatment groups, these changes were not

statistically significant, suggesting that multiple factors contribute to the emissions of these

compounds. This study demonstrates that a single, higher initial addition of SBP was more

effective in reducing overall mean emissions. The high emissions observed during the initial

composting phase likely influenced these results.

4. Conclusion

This study demonstrated that SBP combined with CaO52 effectively reduces NH3 and phenol

emissions during dairy manure composting. Treatment 2, which involved a single SBP

application, achieved a 19.2% reduction in NH3 and a 29.8% reduction in phenol emissions,

while Treatment 1 resulted in respective reductions of 13.2% and 15.5%. These results highlight

the greater efficacy of a single dose, suggesting it as a more effective strategy in composting

applications. This enzymatic approach offers a promising, sustainable method for odor control

in livestock waste management. Future research should focus on scaling up this method to

pilot and field studies to evaluate its real-world effectiveness, as well as exploring alternative

natural peroxidase sources, such as potato peels, apple peels, and peanut seed coats, to expand the applicability and cost-effectiveness of the treatment.

5. Acknowledgment

This work was supported by the Korea Institute of Planning and Evaluation for Technology in

Food, Agriculture, and Forestry (IPET) through the Livestock Industrialization Technology

Development Program, funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA)

(RS-2021-IP321088)