Reduction of accumulated volatile fatty acids by an acetate-degrading enrichment culture

The effects of the addition of an acetate-degrading enrichment culture to an anaerobic digester with a stagnating biogas production were investigated. Initially, a thermophilic batch-operated lab-scale digester was inoculated with the diluted fermenter sludge of a biogas plant, and process parameters including the concentration of volatile fatty acids (VFAs) and gases in the headspace were measured. After a phase of high gas production, a stagnation of biogas production followed for a further 30 days. An acetate enrichment culture was added 34 days after the commencement of the experiment and this resulted in a sharp decrease in the concentrations of accumulated VFAs and an increase in total biogas and CH₄ production. An archaeon with a sequence similarity of 98% to Methanosarcina sp. and the ability to degrade acetic acid was introduced with the enrichment culture and is proposed to have been the driving factor for the changes that occurred within a few days to the process.