The formation of every mol succinate required one mol of CO2, which explained the carbon recovery per sugar to go beyond 1.0 g/g. Apart from main carbon source from sugars, succinate production has an additional carbon source from CO2. The effect of CO2 was extensively studied using A. succinogenes [36], Anaerobiospirillum succiniciproducens [37], E. coli [38], Mannheimia succiniciproducens [39] and Klebsiella pneumonia [40].