Reduction in Methane Emissions From Acidified Dairy Slurry Is Related to Inhibition of Species.

Liquid dairy manure treated with sulfuric acid was stored in duplicate pilot-scale storage tanks for 120 days with continuous monitoring of CH emissions and concurrent examination of changes in the structure of bacterial and methanogenic communities. Methane emissions were monitored at the site using laser-based Trace Gas Analyzer whereas quantitative real-time polymerase chain reaction and massively parallel sequencing were employed to study bacterial and methanogenic communities using 16S rRNA and methyl-coenzyme M Reductase A () genes/transcripts, respectively. When compared with untreated slurries, acidification resulted in 69-84% reductions of cumulative CH emissions. The abundance, activity, and proportion of bacterial communities did not vary with manure acidification. However, the abundance and activity of methanogens (as estimated from gene and transcript copies, respectively) in acidified slurries were reduced by 6 and 20%, respectively. Up to 21% reduction in transcript/gene ratios were also detected in acidified slurries. Regardless of treatment, predominated archaeal 16S rRNA and gene and transcript libraries. The proportion of , which is the most metabolically-diverse methanogen, was the significant discriminant feature between acidified and untreated slurries. In acidified slurries, the relative proportions of were ≤ 10%, whereas in untreated slurries, it represented up to 24 and 53% of the gene and transcript libraries, respectively. The low proportions of in acidified slurries coincided with the reductions in CH emissions. The results suggest that reduction of CH missions achieved by acidification was due to an inhibition of the growth and activity of species.