Water reuse as a strategy for mitigating atmospheric emissions and protecting water resources for the circularity of the swine production chain. (15th April 2022) - Bortoli, M.
Abstract: High greenhouse gas emissions, high water demand, and waste with high pollution potential are critical points for waste management generated in animal production. With significant contributions in global emissions of air pollutants, sustainable practices for agriculture are fundamental to mitigate global climate change, besides ensuring protection to water resources, which is as critical as climate issues. Despite the importance of these issues, some gaps exist in the literature to develop practices capable of fostering water security and mitigation of greenhouse gas emissions. In this sense, the present study aimed to evaluate the impacts of reusing NO3 − rich effluents inside the facilities for cleaning the swine houses and consequent atmospheric emissions of nitrous oxide (N2 O) and methane (CH4 ). In swine manure, the generation of volatile fatty acids (VFA) was strongly influenced by temperature; a change in temperature from 10 to 18 °C increased by ten times the rate of VFA production, reflecting directly in methane emission and availability of organic carbon for the denitrification process. The effluent reuse practice, rich in nitrate, considering the organic carbon bioavailability in the pit storage, decreased methanogenic activity with a consequent VFA use as a bioavailable carbon source for denitrification, reducing greenhouse gas (GHG) emissions and consequently, the environmental impacts of swine production. In this way, the water reuse of 40% can mitigate up to 80% of GHG emission, with a minimum C/N ratio of 20, to ensure that at all temperatures the denitrifying process occurs efficiently since the carbon limitation negatively affected the N2 O emission due to incomplete denitrification. Therefore, our results demonstrate the importance of this practice for swine sustainability and the capacity to adopt simple measures in favor of circularity in the swine production chain. Graphical abstract: Image 1 Highlights: Effluent reuse can be incorporated into the swine production chain. Reuse of NO3 − rich effluent was environmentally favorable. The addition of NO3 − stopped methanogenesis, decreasing GHG emission by up to 98%. The effluents reuse with a proportion of 40% contributed to over 80% GHG reduction.