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 (MScover), and compost mixed with rice straw (MSmix). Our results indicate that the addition of urea resulted in the lowest total CH4 emissions and the highest N2O emissions. MScover treatment had the highest and most significant effect on CH4 emissions, while MSmix 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 MSmix, MScover, 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.