Biocatalytic conversion of CO to acetic acid by Clostridium aceticum—Medium optimization using response surface methodology (RSM)

Abstract

Acetic acid is an important industrial feedstock which can be produced from renewable resources such as carbon monoxide (CO) for an infinite supply for future usage. The biological route of acetic acid production from CO through fermentation by acetogenic bacteria, Clostridium aceticum appeared to be potential substitution for current process technology. The fermentation medium which is responsible for sustaining and maintaining the biocatalyst growth usually accounts for 60–70% of the production cost. Therefore, efforts in creating cost effective process have been carried out by optimizing the nutrient requirements of NH 4Cl and yeast extract compositions which can still attain satisfactory responses during acetic acid fermentation. In this study, medium composition of NH 4Cl (studied ranges: 0.0–1.50 g/L) was optimized in the early stage and then followed by optimizing the yeast extract component (studied ranges: 0.0–2.00 g/L). The high-end concentration selected for each medium composition was based on the concentration consisted in the DSMZ growth medium 1496 as a guideline. Response surface methodology (RSM) which consisted of 2-D contour plot and 3-D surface plot was used to determine the optimum concentrations of NH 4Cl and yeast extract that enabled the maximum acetic acid production with high CO conversion in an actively growing culture. Fermentation when launched in medium of 0.2 g/L of NH 4Cl coupled with 1.5 g/L of yeast extract and operated for 72 h cultivation time resulted in 1.01 g/L of acetic acid production and 100% CO conversion. Optimum fermentation medium was defined as 0.2 and 1.5 g/L of NH 4Cl and yeast extract respectively in this experiment based on the 67% of response desirability achieved through RSM.