The Microbial Fuel Cell - A Novel Bioelectrochemical Cu2+ Recovery System from Industrial Wastewater
Yimeng Li
Sir Winston Churchill Secondary
Floor Location : M 115 V

Currently, electrochemical methods used to remove heavy metal ions from industrial wastewater are both energy-consuming and expensive. Thus, the first, novel self-powered recovery system of copper ions coupled with simultaneous biofuel generation was designed and constructed. Electrons produced as microbial waste products from the anodic oxidation of hydrolyzed lignocellulosic biomass waste were harnessed to power the cathodic reduction reaction of Cu2+. Cellulosic ethanol and bioelectricity were also produced as metabolic bi-products.

In this research, Saccharomyces Cerevisiae and Saccharomyces Boulardii were co-cultured in the anodic chamber of a microbial fuel cell (MFC) for the simultaneous production of bioethanol fuel and current generation. The MFCs utilized modified carbon fiber cloth electrodes and copper wires as the anode and cathode respectively. Artificial extracellular polymeric gels consisting of diluted methyl cellulose, gelatin, and methylene blue were coated onto the anode to further enhance biofilm formation and electron transfer.

Throughout the study, a constant supply of a nutrient/glucose solution was drip-fed utilizing a filtration, pumping, and circulation system; a neutralized solution of oxidative-delignification pretreated and hydrochloric acid hydrolyzed wastepaper was supplied as the glucose carbon source, and a yeast-selective nutrient medium was fed to the anode. Cellulosic ethanol produced was quantified using specific gravity calculations throughout the study.

Electrons produced by the anaerobic fermentation were then harnessed to power the cathodic reduction reaction of copper sulfate pentahydrate ions via an external circuit. This reaction was initiated by dissolving Cu2+ in the cathode of the MFC upon reaching a stable voltage reading. In addition, a non-toxic and biodegradable catholyte was created to enhance this reduction reaction. Magnesium sulfate, sucrose, and acetic acid was dissolved in distilled water to create the conductive catholyte. Freezing point/sodium hydroxide reactions were further used to observe copper concentrations, and electrochemical potential readings were taken across a 100 ohm resistor every 24 hours to determine the impact of Cu2+ ions on the total current produced.

Copper ions were observed to begin precipitating from the catholyte in less than 24 hours. As this reaction is thermodynamically favourable, a higher peak of electrochemical potential was also observed. Higher currents indicated that the ionic resistance of the cell may have been reduced, leading to higher power densities. Although the reduction rate is slower than those utilizing significantly higher electricity input, this research was the first to provide proof-of-concept of a completely self-sustained recovery method of heavy metals and simultaneous biofuel and current generation.

In summary, this system requires no external energy input or precious resources to power the recovery and recycling of Cu2+, prevent environmental copper intoxication, and generate an excess of biofuels and bioelectricity. Waste cellulosic biomass resources are the sole feedstock required to power this reaction.

Currently, additional trial repetitions and statistical analysis of this system are still being conducted, but preliminary results show that the modified MFCs may have important applications in industrial wastewater treatment, bioethanol, and metal recovery fields if efficiencies are gradually improved.