Evaluation of Odorous Compounds and Microbial Dynamics During Livestock Manure Composting Using Aquamicrobium lusatiense NLF 2-7

Riuh Wardhani1 · Jinho Shin1 · Jumi Lee2 · Seunghun Lee3 · Kook-ll Han4 · Heekwon Ahn5*

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

4Nakdonggang National of Biological Resources, Sangju, Korea

5Division of Animal and Dairy Science, Chungnam National University, Daejeon, Korea

1. Introduction

Optimizing the composting process involves adding microbial cultures, which are crucial for decomposing organic materials in animal manure (Rastogi et al., 2020). Microbial inoculants can accelerate decomposition and reduce gas emissions, controlling malodorous compounds 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). However, their impact on emissions can vary. For instance, certain microbial consortia can reduce ammonia emissions but may increase greenhouse gases and other odorous compounds (Xue et al., 2021; Yu et al., 2023). This research focuses on Aquamicrobium lusatiense, a mesophilic bacterium with the potential for reducing sulfur compound emissions through the SOX pathway (Jeong et al., 2023). The study aims to assess its effects on odor emissions and bacterial composition in swine and cattle manure composting, contributing to sustainable livestock manure management strategies.

2. Methods

The composting experiment was conducted in 3.8 L laboratory-scale reactors over a period of 35 days, using a mixture of dairy manure, swine manure and sawdust with an initial moisture content of 75% (wet basis). Each reactor contained approximately 1.3 kg of compost and was aerated at 0.3-0.4 L/min·kg VS added. The study comprised a control group and two microbial inoculations. Treatment 1 comprised an initial inoculation of 1%, whereas Treatment 2 involved a divided dosage of 0.5% initially and 0.5% after a two-week interval. The mitigation effects of each treatment were assessed by measuring odorous gases, including NH3 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

This study evaluated the effectiveness of treatments in mitigating sulfur compound emissions during manure composting. While DMS and H2S were detected, MM and DMDS were not observed. H2S emissions occurred only on day 1, with significantly lower levels in Treatment 1 (0.13 µg/day·g-VS) and Treatment 2 (0.11 µg/day·g-VS) compared to the control (0.50 µg/day·g-VS) (p<0.05). DMS was the predominant sulfur compound, with peak emissions occurring within the first seven days. Treatments significantly reduced DMS emissions during this period (p<0.02), though overall reductions across the composting period were minor and not statistically significant. The observed reduction in sulfur emissions may be linked to microbial sulfur metabolism, particularly the SOX pathway in Aquamicrobium lusatiense NLF 2-7, which facilitates sulfur oxidation. Additionally, overall phenol emissions decreased significantly, with reductions of 12.1% in Treatment 2 and 9.5% in Treatment 1 (p<0.05). However, NH3 and total VFAs showed no significant differences between treatments and the control after 35 days (p>0.05), although NH3 emissions in Treatment 2 were slightly reduced by 4.4%. These findings highlight the potential of microbial treatments in odor mitigation during composting.

The coverage index for all treatments were 1.00, indicating adequate sequencing depth for capturing bacterial diversity (Liu et al., 2020). The Chao1, Shannon, and Gini-Simpson indices revealed that treatment groups had greater microbial richness, evenness, and diversity compared to the control group throughout the composting process. Specifically, Treatment 1 showed higher Chao1 and Shannon values on days 7, 14, and 21. Dominant bacterial phyla included Bacillota, Pseudomonadota, Bacteroidota, and Actinomycetota in all groups, comprising 74% to 95% of the total population. By day 7, Bacillota decreased, while Bacteroidota increased significantly. Later stages (days 14, 21, and 35) saw Bacteroidota dominance, with minor phyla like Myxococcota emerging. At the genus level, Clostridium and Romboutsia declined, while Natronoflexus increased, indicating a microbial succession shift from Bacillota to Bacteroidota during composting (Mao et al., 2018; Xu et al., 2022; Zhao et al., 2023).

4. Conclusion

This study demonstrates the potential of microbial treatments in reducing sulfur compound emissions during manure composting. Treatments effectively reduced H2S emissions and significantly lowered DMS emissions during the first week, though overall reductions were not statistically significant. Phenol emissions decreased, while NH3 and VFAs showed no minimal redection effects. Microbial diversity analysis revealed that treatments enhanced bacterial richness and altered community composition, with a shift from Bacillota to Bacteroidota over time in all groups. Given the potential role of Aquamicrobium lusatiense NLF 2-7 in sulfur oxidation, future research should explore its combination with ammonia-mitigating bacteria to improve overall odor reduction and nitrogen conservation during composting. This approach could enhance the efficiency of microbial treatments in organic waste management.

5. Acknowledgment