Observations on microbial activity in acidified pig slurry

Article history:Received 14 August 2008Received in revised form9 December 2008Accepted 9 December 2008Published online 1 February 2008Acidification of pig slurry to pH 5.5 is used as a measure to reduce ammonia emission frompits and storages. The slurry is acidified with sulphuric acid in a process tank and pumpedback to the slurry pits or to a storage tank. We investigated the effect of acidification onmicrobial activity. Oxygen consumption rate, methanogenesis and sulphate reductionwere all reduced by more than 98% in the stored acidified slurry compared to untreatedslurry. Despite higher sulphate concentration, the microbial metabolism was greatlycompromised or absent in the acidified slurry. This could be explained by the highconcentration of protonized short-chained volatile fatty acids in the acidified slurry(approximately 25 mM, compared to untreated slurry <0.1 mM), which act as an uncou-pling agent of the cell membrane potential and thereby arrest microbial metabolism. Intotal the consequences of slurry acidification are greatly reduced production rates and lossof sulphide and methane, and eliminated loss of ammonia. On the other hand, increasedvolatilization and loss of smelly fatty acids is to be expected.a 2008 IAgrE. Published by Elsevier Ltd. All rights reserved.