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 °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-H₂ mol^-1-glucose) and ethanol (2.06 mol-EtOH mol^-1-glucose) were achieved at 55 °C. In this condition, the hydrogen production rate was 2.05 L h^-1 L^-1, increased by 86% regarding 45 deg C. The concentration of organic acids reduced about 42% with increasing temperature from 45 to 55 °C and diminished 37% from 55 to 65 °C. Acetic acid prevailed over other metabolites in percentages about 41-51%, followed by butyrate at 45 deg C (33.8%), and ethanol at 55 deg C (25.5%) and 65 deg C (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. (author)