Evaluating the effect of microbial additives for mitigating odor during livestock manure composting

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

Composting is a well-established method for managing animal manure, offering significant benefits in terms of minimizing waste volume and reclaiming valuable resources as a nutrient-rich soil amendment. This process involves the microbial decomposition of organic materials, resulting in the stabilization of the composted material and the reduction of pathogens and seeds presence (DeLaune et al., 2006; Yamamoto et al., 2009). While composting provides an environmentally sound strategy for managing the substantial quantities of manure produced, it also poses considerable environmental challenges. A primary concern in composting is the emission of odorous compounds, which arise from the microbial breakdown of organic matter in manure (Gerber et al., 2013; Owen and Silver, 2015). This highlights the critical roles microbes play in the composting process. The current study focuses on microbial inoculation to reduce odor emission by using Aquamicrobium lusatiense NLF 2-7 as microbial additives. Its genome includes genes associated with the sulfur oxidation pathway, suggesting its potential in reducing emissions (Jeong et al., 2023).

2. Methods 

 The composting was carried out in 3.8L laboratory-scale reactors over 35 days, with material ratios set at 5:4:1 (swine manure, dairy cattle manure, and sawdust) and an initial moisture content of 75% w.b. Reactors contained approximately 1.3 kg w.b. of compost each and were aerated from 0.4 L/min-V.S. initially to 0.3 L/min-V.S. after the first week. The study included a control and two microbial treatments. Treatment 1 included a 1% inoculation initially, while treatment 2 included a split dose (0.5% initially and 0.5% after two weeks). Mitigation effects were determined by measuring odorous gases, including NH3 (ammonia), sulfur compounds involving H2S (hydrogen sulfide), CH4S (methyl mercaptan), C2H6S (dimethyl sulfide), and C2H6S2 (dimethyl disulfide), as well as VFAs such as acetic acid, propionic acid, iso-butyric acid, butyric acid, iso-valeric acid, and valeric acid, then VOCs including phenol, p-Cresol (4-Methylphenol), indole, and skatole (3-Methylindole). Illumina MiSeq sequencing was used to analyze the composition and structure of the microbial community. 

3. Results and Discussion 

 The study revealed no detectable MM and DMDS emissions throughout the 35-day composting period, while H2S was only present on the first and last days. The sum of H2S emissions showed a significant reduction in the treatment groups compared to the control (p<0.05), with recorded values of 7.4±2.6mg for the control, 2±0.7mg for Treatment-1, and 1.7±1.8mg for Treatment-2. Undetectable H2S during composting could be attributed to their metabolism into other compounds such as DMS, as sulfur elements may undergo methylation to form DMS (He et al., 2018; Zhang et al., 2017). DMS emissions were notably lower in the sum of 13 days composting in both treatment groups compared to the control, with significant reductions of 27.7% in Treatment-1 and 26.8% in Treatment-2 (p<0.05). However, no significant differences were observed in DMS emissions from day 14 onwards. At the end of the period, reductions of 16.9% and 11.0% were noted for Treatments 1 and 2, respectively (figure 1).

 Phenol emissions, a significant volatile organic compound, were also monitored (figure 1). A significant reduction in sum of emission was detected. By the end of composting, both treatments significantly reduced phenol emissions, with reductions of 12.6% for Treatment-2 and 7% for Treatment-1 (p<0.05). However NH3, and total VFAs shpwed there were no significant differences between the control and treatment groups after 35 days (p>0.05), although Treatment-2 exhibited slight reductions in NH3 by 3.2%.

Metagenome analysis showed different microbial community dynamics between treatments (table 1). In Treatment-1, the presence of Aquamicrobium lusatiense NLF2-7 increased from an initial 0.09% to 0.15% by the fifth week, while in Treatment-2, it fluctuated slightly around an initial value of 0.11% to 0.1% by the end of the study. These findings indicate that microbial settlement was influenced by the specific treatments applied, contributing to the observed differences in gas emission reductions. Overall, the results aligns with the characteristics of Aquamicrobium lusatiense NLF, a sulfur-oxidizing bacterium. Genome analysis indicated the presence of the SOX pathway (soxXYZABCD), capable of converting sulfur through sulfur oxidation pathways (Jeong et al., 2023).

Table 1. Relative abundance of strain NLF2-7 in Treatment 1 and Treatment 2 samples.

4. Conclusion

The study shows that Aquamicrobium lusatiense NLF 2-7 significantly reduces dimethyl sulfide at the early phase and phenol emissions during the composting of swine and cattle manure. This additive targets key odorous compounds, improving composting sustainability. The observed changes in microbial community structure suggest that Aquamicrobium lusatiense can effectively integrate into compost ecosystems, offering a way to improve composting practices. Further research is needed to evaluate its long-term effects and applicability to various organic materials.

5. Acknowledgment

 This work was supported by Livestock Industrialization Technology Development Program by Ministry of Agriculture, Food and Rural Affairs (MAFRA)(RS-2021-IP321088).