Aerobic thermophilic waste sludge biotreatment : carboxylic acid production and utilization during biodegradation of bacterial cells under oxygen limitation

The production and utilization of acetate, propionate, isobutyrate, n-butyrate and isovalerate during the treatment of a model sludge composed of bacterial cells, was examined in a laboratory scale reactor. Operating the reactor under limited oxygen supply conditions produced a distinct pattern of production and simultaneous utilization of low molecular weight carboxylic acids. Pulsed-addition of a mixture of carboxylic acids at the end of a batch-fed cycle suggested that simultaneous utilization of acetate, propionate, isobutyrate, n-butyrate and isovalerate could occur, but only after a phase lag during which only acetate was utilized. When acetate was pulsed to the process, only 11 per cent of the acetate carbon was incorporated into new biomass, whereas 75 per cent was converted into carbon dioxide.