Mitigation of ammonia and hydrogen sulfide emissions during aerobic composting of laying hen waste through NaOH-modified biochar.

Abstract

The impact of NaOH-modified biochar on the release of NH₃ and H₂S from laying hens' manure was examined for 44 days, using a small-scale simulated aerobic composting system. The findings revealed that the NaOH-modified biochar reduced NH₃ and H₂S emissions by 40.63% and 77.78%, respectively, compared to the control group. Moreover, the emissions of H₂S were significantly lower than those of the unmodified biochar group (p < 0.05). The increased specific surface area and microporous structure of the biochar, as well as the higher content of alkaline and oxygenated functional groups, were found to facilitate the adsorption of NH₃ and H₂S. This enhanced adsorption capability was the primary reason for the significant reduction in NH₃ emissions. Furthermore, during the high-temperature phase of composting, there was a notable alteration in the microbial community. The abundance of Limnochordaceae, Savagea, and IMCC26207 increased significantly which aided in the conversion of H₂S to stable sulfate. These microorganisms also influenced the abundance of functional genes involved in sulfur metabolism, thereby inhibiting cysteine synthesis, along with the decomposition and conversion of sulfate to sulfite. This led to a significant decrease in H₂S emissions. This study provides valuable data for the selection of deodorizers in the composting process of egg-laying hens. The results have significant implications for the application of NaOH-modified biochar for odor reduction in aerobic composting processes.