Low-Dose Acidification as a Methane Mitigation Strategy for Manure Management

Excreta from housed animals are typically stored before land application, and storage is an important point source of CH4, N gases, and odor. This study explored acidification as a strategy for greenhouse gas (GHG) mitigation, specifically the potential to reduce the acid dose to improve cost-effectiveness and minimize environmental impacts. Pig slurry was stored with five doses of concentrated sulfuric acid [1.2-6.0 kg (m(3) of slurry)(-1)] for 63 days. Emissions of CH4 and NH3 were reduced by 46-96% and 33-78%, respectively, with an increase in the acid dose. Odorant emissions, dominated by 4-methyphenol and H2S, were strongly suppressed by acidification. Below pH 6, methanogen inhibition was most likely due to undissociated VFAs, and above pH 6, the inhibition could involve competition from sulfate reducers and inhibition by undissociated H2S. If 1, 3, or 10 acidification treatments were needed, the annual costs for GHG mitigation across the five acid doses were 28-47, 44-57, and 93-134 (sic) (ton of CO2 equivalents)(-1), respectively. With 1 or 3 treatments, the most cost-effective acid dose was 2.1 kg m(-3), or 3.2 kg m(-3) with 10 treatments. This study strongly suggests that low-dose acidification is a viable strategy for GHG mitigation.