Impact of chemical and biological additives on microbial community and methane emissions in pig slurry storage

In intensive pig farming, where slurry-based manure management is common, over 90% of farm-level greenhouse gas emissions are methane (CH4), with 70-80% of it is produced during slurry storage. While chemical additives like sulfuric acid (H2SO4) are effective in suppressing these emissions, they raise concerns about environmental toxicity, biogas inhibition, and soil acidification. Therefore, alternative strategies particularly biological treatments are urgently needed to mitigate CH4 emissions during pig slurry storage.<br/>The effects of chemical additives (sodium dodecyl sulfate (SDS), H2SO4) and biological additive (Limosilactobacillus reuteri with glycerol) on CH4 emissions and microbial community dynamics in residual slurry from fattening pig farms were investigated. Residual slurry which was left over in the manure pits after flushing was collected, as it is rich in methanogens and responsible to CH4 emissions from manure pits. Two experiments were conducted to evaluate the effects of SDS, H2SO4 and L. reuteri on CH4 emissions and methanogenic microbial communities. In exp 1, a combination of weekly removal of slurry and treatment of residual slurry was simulated in laboratory scale with SDS and H2SO4 treatments for a period of 7 weeks. In exp 2, L. reuteri treatment was applied to residual slurry and incubated for about 4 weeks. In both the studies, emissions from the treated and control reactors were measured continuously with a gas analyser. Cumulative CH4 emissions and methanogenic microbial communities were determined at the end of the study to evaluate the treatment effectiveness.<br/>SDS (1.5 g/kg) and H2SO4 (pH 4.7-6) treatments were observed to reduce CH4 emissions by about 90% and 66%, respectively in Exp 1. SDS showed substantial alterations in dominant microbial groups such as Clostridia, Actinobacteria, Methanobacteria and Gammaproteobacteria. The relative abundance of Methanobacteriales was higher (6.8%) in SDS treatment compared to untreated sample (4.3%), yet CH4 emissions were significantly reduced. This suggests that SDS treatment likely inhibit methanogenic activity without eliminating methanogen populations, possibly by disrupting syntrophic interactions or metabolic pathways. In contrast, H2SO4 treatment reduced Methanobacteriales abundance (3.4%) but with lesser impact on CH4 emissions. In Exp 2, L. reuteri + glycerol treatment achieved about 80% reduction in CH4 emissions, and also lowered relative abundance of Methanomicrobiaceae, Methanobacteriaceae and Methanomethylophilaceae.<br/>Although both SDS and L. reuteri treatments reduced CH4 emissions from pig slurry, their effect on microbial communities varied markedly. The above findings highlight that CH4 mitigation is not solely dependent on reducing methanogen abundance but also on altering microbial functionality and interactions.