Effects of different composting strategies on methane, nitrous oxide, and carbon dioxide emissions and nutrient loss during small-scale anaerobic composting

Composting is considered as one of the main sustainable methods for the treatment of livestock manure. In this study we investigated the effects of additives (urea and rice straw) on methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) emissions using a traditional Chinese pig slurry composting method over an 81-day period, as well as examining total organic carbon and total nitrogen loss. Four common treatment strategies were examined in this study: a control (MC), urea nitrogen addition (MN), composting using rice straw cover (MS_cover), and compost mixed with rice straw (MS_mix). Our results indicate that the addition of urea resulted in the lowest total CH₄ emissions and the highest N₂O emissions. MS_cover treatment had the highest and most significant effect on CH₄ emissions, while MS_mix treatment had the lowest CO₂ emissions. Carbon lost through CH₄ and CO₂ released during the experiment was 0.1–0.9 and 2.4–3.9% of total carbon loss, respectively, and nitrogen lost through N₂O release was 11.1–17.9% of total nitrogen. In general, although MS_mix, MS_cover, and MN treatments increased global warming potential by 21.4, 41.6, and 50.9% per kg of pig slurry, respectively, no statistical differences between the four treatments were recorded. By considering carbon and nitrogen conservation, as well as the improvement of the quality of compost and the mitigation of greenhouse gases (GHGs), the small-scale composting method of pig slurry alone is an acceptable environmentally friendly strategy for use in China.