Propionic acid accumulation and controlling factors in anaerobic treatment of carbohydrate: effects of H2 and pH

Abstract

Propionic acid is believed to be the most retardative volatile acid appearing in the anaerobic treatment process. However, the mechanisms by which propionic acid accumulates have not been well understood. Several studies and thermodynamical calculations suggest that an increased hydrogen partial pressure in the system is the cause for the accumulation of propionic acid. However, recent findings by the authors and a few other researchers indicated that artificially elevated or reduced hydrogen partial pressure had no discernible effect. Hence, the consensus on the inhibitory effects of hydrogen is lacking. This study was done to test the hypothesis that propionic acid accumulation during start-up or overloading is not caused by high hydrogen partial pressure, rather it is a result of a shift in the dominant species of acidogenic populations. Hydrogen partial pressure and pH were chosen as controlled system parameters. The type of the reactors used was completely stirred tank reactor (CSTR). The results have indicated that hydrogen partial pressure has no discernible effect while low pH around 5 is effective for preventing propionic acid production from decomposition of glucose.