DEVELOPMENT OF A MICROBIAL FUEL CELL FOR WASTEWATER TREATMENT AND RENEWABLE ENERGY GENERATION USING LOCALLY PRODUCED ELECTRODES

Abstract

ABSTRACT The need for clean and sustainable energy, coupled with indiscriminate disposal of wastewater and recycling of waste materials necessitated the need to develop low-cost innovative bioelectrochemical systems. This study developed laboratory-scale microbial fuel cells (MFCs) to treat locust bean wastewater (LBWW) and generate renewable energy using locally produced electrodes sourced from palm kernel shell activated carbon (PKSAC) and used battery graphite. Preliminary physico-chemical, proximate, microbial (isolation, characterization, biochemical test), and molecular parameters were determined. Two electrode types were fabricated: EA (PKSAC)/Graphite/styrene binder) and EB (PKSAC)/Graphite/Paraffin wax binder), in which the PKSAC were partially replaced with 0, 25, 50, and 75 % of graphite and categorized as EA1, EA2, EA3, EA4 and EB1, EB2, EB3, EB4, respectively. Double-chambered 1 L MFCs were constructed using transparent plastic containers, with electrodes connected by copper wires and a horse-shaped salt bridge for proton transfer. Physico-chemical (electrical conductivity (EC), total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), Nitrate, Sodium, and Potassium), microbial, and microstructural analyses were conducted before and after the experiments, with measured daily readings for voltage and current values. Experiments were conducted under pH 3.7 and neutral pH conditions by dosing the anolyte with 0.1 M NaOH. All MFC reactors operated under room atmospheric conditions. Statistical analyses were implemented using MS Excel and Python programming. The results showed that the isolated microbial strains (Priestia aryabhattai) were in LBWW. The MFC operations detected the formation of biofilms on the anode surfaces indicating the presence of electrogenic bacteria. In MFCs using EA electrodes, LBWW at a pH of 3.7 generated 515 mV (p < 0.05) and 27 mA (p < 0.05) while LBWW using EB electrodes at a pH of 3.7 generated 451 mV (p < 0.05) and 15 mA (p > 0.05). At adjusted pH of 7.0, MFC with EA electrodes improved the outputs to 1040 mV (p < 0.05) and 213 mA (p > 0.05) while MFC with EB electrodes improved to 1078 mV (p < 0.05) and 213 mA (p < 0.05). The LBWW treatment with EA electrodes at a pH of 3.7 showed lower treatment efficiencies: EC 6.08%, TDS 3.00%, COD 9.76%, TOC 9.23%, nitrate 19.23%, sodium 7.89%, and potassium 11.48%. The treatment efficiencies improved when the pH was adjusted to 7.0 using 0.1M NaOH: EC 26.31%, TDS 25.51%, COD 22.79%, TOC 36.92%, nitrate 38.46%, sodium 31.58%, and potassium 31.14%. Statistical analyses revealed LBWW with EA electrodes at pH 3.7 exhibited statistically significant outputs (p < 0.05) for both voltage and current readings. It was observed to be statistically significant for voltage readings but insignificant for current readings when the pH was adjusted to 7.0. LBWW with EB electrodes at pH 3.7 and pH 7.0 showed similar trends of statistical significance (p < 0.05). The study demonstrated that wastewater treatment and bioelectricity generation could be achieved using locally produced electrodes in microbial fuel cells.