Waste to energy through sustainable bioenergy and biohydrogen production from lignocellulosic waste using microbial fuel cell and microbial electrolysis cell

Abstract The accumulation of agricultural lignocellulosic waste, specifically rice straw, and the environmental impact of fossil fuel combustion necessitate the development of sustainable waste-to-energy technologies. Bioelectrochemical systems enable a simultaneous recovery of energy and the treatment of organic waste utilizing a mixed culture of bacteria. This study investigates for the first time the performance of rice straw-derived substrates with different levels of complexity, i.e. rice straw, rice straw hydrolysate, and xylan, to simultaneously produce bioelectricity and biohydrogen, with the objective of clarifying the influence of substrate characteristics on system efficiency. Microbial fuel cells (MFC) result indicated that xylan exhibited the highest performance, achieving a maximum cell potential of 852 ± 27 mV and a power density of 8.88 ± 0.27 W/m², representing a 2.4-fold increase over the control. This was supported by a high Chemical Oxygen Demand (COD) removal efficiency of 97.88 ± 1.32%. The higher values of power density are attributed to the employment of a mixed bacterial culture (sludge) that has already adapted to the degradation of lignocellulosic biomass, hence boosting its utilization and conversion to electrons, resulting in higher electricity generation. Electrochemical analysis indicated efficient electron transfer, reflected by increased current responses at higher scan rates and low charge transfer resistance values. Electrochemical characterization via cyclic voltammetry and electrochemical impedance spectroscopy (EIS) revealed that rice straw-powered cell exhibited the lowest charge transfer resistance (3.37 Ω), correlating with the highest recorded electrical current (9.23 ± 0.25 mA). Conversely, the microbial electrolysis cell (MEC) results showed that rice straw hydrolysate was the optimal substrate for biohydrogen production, yielding a maximum rate of 9.26 ± 0.08 mmol/day.L and a COD removal of 94.92 ± 0.88%, significantly outperforming xylan-based systems and the control cells. These findings indicate that while simpler carbohydrate structures like xylan favor electricity generation in MFCs, the bioavailable nutrients in alkaline-pretreated hydrolysates are more effective for electrohydrogenesis in microbial electrolysis cells. This research provides a critical comparative framework for selecting biomass fractions and system configurations to maximize the efficiency of agricultural waste-to-energy conversion strategies.