Hydrogen recovery cascade from pretreated rice straw and its fermentative residuals using step-up potential-based sulfate reducing bacteria-bioelectrochemical system

Abstract

Despite the availability of well-proven biohydrogen production technology, the uncapping of the biological theoretical hydrogen yield is still a challenge. This study explores the stimulation of step-up applied potential for hydrogen production in a sulfate-reducing bacteria-based bioelectrochemical system (SRB-BES), a sustainable and promising technology for organic waste recycling with resource recovery. This research focused on the application of a low applied potential to recover H2 from pretreated rice straw and its residual fermentative by-products. An applied potential of −40 mV could proficiently recover 1.5 times higher hydrogen from pretreated rice straw by completely inhibiting methanogens. The residual fermentative byproducts obtained at the first stage were further used in extra H2 recovery at a step-up applied potential of −150 mV, −300 mV, and −450 mV. The H2 recovery from fermentative residuals shows maxima at −300 mV. The acetic acid and iso-butyric acid production of 52.89 ± 15.67 and 56.93 ± 11.81 mM at −300 mV and −450 mV respectively contribute majorly to volatile fatty acids (VFAs). The more electronic equivalents of 2024.34 (mM) in R-450mV in comparison to 1850.803 (mM) in R-40mV (effluent recovered from AD-MEC) indicate the involvement of the higher applied potential in chain elongation of VFAs. So, optimization of step-up potential could lead to the bioelectrochemical synthesis of the desired fatty acids through chain elongation deserving various applications with hydrogen recovery. The gaseous data obtained were verified by Richard, Logistic, and modified Gompertz kinetic models to check H2 prediction validity using cumulative H2 production. This study demonstrated the technical foundation with a novel approach to maximize hydrogen recovery from the fermentation residuals by step-up applied potential.