Microbial fuel cell (MFC) is an evolving technology for anaerobic bioenergy generation using electrodes and organic wastewater as a feedstock for catabolic activities of electrogenic bacteria and subsequent electricity generation. The search for suitable inexpensive electrode materials remains the leading interest of researchers in this field. The work here focused on comparative bioelectricity generation from HTC process water (pH = 5.99) and treated–biogas digestate (pH = 7.97) using locally developed corncob pyrochar electrodes and graphite in dual-chambered microbial fuel cells (MFC). The electrodes used in this study were graphite rod (non-porous and very low surface area), KOH–activated corncob pyrochar (KAC) of BET surface area, 1626 m2 g-1 and steam activated corncob pyrochar (SAC) with 485.8 m2 g-1. The highest power outputs achieved were 323.8 µW and 316.8 µW from HTC process water with SAC and KAC electrodes respectively at an external load of 47 Ω. The initial COD (48780 mg L-1), DOC (4000 mg L-1), and TNb (5600 mg L-1) of the biogas digestate decreased significantly to 36405, 3610 and 4300 mg L-1 respectively in the MFC with KOH-activated corncob pyrochar electrodes. The MFC operated with KAC electrode and treated biogas digestate was the most efficient having Coulombic efficiency of 75 % in a comparatively shorter residence time of MFC operation than the MFC with SAC electrode which had a lower Coulombic efficiency of 64 %.

Despite large varieties of commercially available electrodes, only few are suitable for electro-active bacterial colonization during biofilm formation in microbial fuel cells (MFCs), and most of these electrodes are cost prohibitive. Hence there is need to search for low-cost alternative electrodes for MFCs. Pyrochars were produced in this study by pyrolysis (600 °C and a continuous flow rate of 3 L/min of nitrogen gas for 30 min) and subsequently steam and potassium hydroxide (KOH) activation of the pyrochar at 600 °C were carried out accordingly. Physicochemical, structural, and electrochemical properties of the activated and non-activated pyrochars were determined according to standardized analytical methods. According to BET, 1626 m 2 g -1 surface area and 14.74 Å pore diameter were obtained from the KOH-activated pyrochar which was also the most conductive (0.26 S m -1 ). Chemical activation of pyrochar with KOH resulted in increased electrical conductivity (EC), pore diameter, and most importantly the material's surface area according to the findings. In conclusion, KOH-activated corncob pyrochar holds potentials for producing electrode materials with desirable characteristics for successful application in MFC compared to the non-activated and steam-activated pyrochars of the same biomass.