Perturbation of anaerobic fermentation by high energy substrates

Biotransformation of propionic acid, glucose, and molasses under mesophilic anaerobic conditions was investigated. The main objective was to look into formation and accumulation of volatile fatty acids, especially propionic a nd acetic acid, as a consequence of metabolism of molasses and glucose. The results indicate that anaerobic biotransformation of glucose and molasses in a batch reactor leads to accumulation of propionic and acetic acid. When glucose was fed to the batch reactor at a loading rate of 1.5 g COD.l(-1). day(-1), as high as 2,000 mg.l(-1) propionic acid and 1,100 mg.l(-1) acetic acid concentrations were observed within 6 days. Similarly, degradation of molasses at the same loading rate resulted in accumulation of propionic an d acetic acid up to 1,500 and 1,150 mg.l(-1), respectively, within 29 days. However, when propionic acid was fed directly to the reactor at a loading Fate of 1.5 g COD.l(-1).day(-1), its concentration in the batch reactor was below the quantification limit of 20 mg.l(-1) over a monitoring period of 18 days.