Effect of thermophilic temperatures on hydrogen and ethanol production in anaerobic fluidized bed reactor from cassava wastewater

This study evaluated the effect of temperature in the thermophilic range (45, 55, and 65 degrees C) for simultaneous production of hydrogen and ethanol in an anaerobic fluidized bed reactor (AFBR) using cassava wastewater as substrate, with a hydraulic retention time of 2 h. Substrate concentration varied from 4.5 to 5.5 g COD L-1. Maximum yields of hydrogen (1.98 mol-H-2 mol(-1)-glucose) and ethanol (2.06 mol-EtOH mol(-1)-glucose) were achieved at 55 degrees C. In this condition, the hydrogen production rate was 2.05 L h(-1) L-1, increased by 86% regarding 45 oC. The concentration of organic acids reduced about 42% with increasing temperature from 45 to 55 degrees C and diminished 37% from 55 to 65 degrees C. Acetic acid prevailed over other metabolites in percentages about 41-51%, followed by butyrate at 45 oC (33.8%), and ethanol at 55 oC (25.5%) and 65 oC (30.8%). The ethanol concentration remained practically constant (4.00 +/- 1.51-4.74 +/- 1.44 mM) if considering the associated uncertainty range. Overall, thermophilic temperatures were favorable for biofuel production, however, it is suggested to study other HRT in future work to avoid overloading the system.

Automated summary

This study evaluated the effect of temperature on the simultaneous production of hydrogen and ethanol using cassava wastewater. The maximum yields were achieved at 55 degrees C, and the concentration of organic acids reduced with increasing temperature. Thermophilic temperatures were favorable for biofuel production.