Effect of zinc on ethanol production by two Thermoanaerobacter strains

Ethanol production ratios of Thermoanaerobacter ethanolicus (JW200) and two other thermophilic anaerobic bacteria Thermoanaerobacter (65-2) and Thermoanaerobacter thermohydrosulfuricus (70-1) were determined at different sucroses (15, 20 and 30 g l−1) and molasses (30, 40 and 60 g l−1) concentrations, in batch culture conditions. As a result, bacterial growth and ethanol production ratios were optimum at the same conditions. Also, effect of zinc as ZnSO4·7H2O on the ethanol formation of bacteria were investigated and it was found that, addition of 0.17 g l−1 of ZnSO4·7H2O to the fermentation medium of T. ethanolicus (JW200) was increased the ethanol ratio by ca. 39% and 23% for Thermoanaerobacter strain 65-2. Addition of 0.22 g l−1 ZnSO4·7H2O, increased the ethanol ratio by 80% for T. thermohydrosulfuricus (70-1). The highest ethanol ratio was obtained at the 20 g l−1 sucrose and 40 g l−1 molasses concentrations by all the bacteria studied and ethanol production ratio was not proportional to substrate concentration.T. ethanolicus (JW200) produced 5.04 g l−1 ethanol from sucrose (20 g l−1) and Thermoanaerobacter strain (65-2) produced 6.50 g l−1 ethanol from 40 g l−1 molasses in modified medium 2. T. ethanolicus (JW200) yielded (Yx/s) up to 0.47 of ethanol at 15 g l−1 sucrose concentration.