Nigel J. Bunce: Research Projects
The principal activities of our research group involve environmental electrochemistry, with emphasis on the electrochemical treatment of aqueous wastes. Electrolysis offers a Aniche technology@ for compounds that are Arecalcitrant@ towards conventional biological treatment B because they are metallic, or unreactive biologically, or toxic to the microorganisms of a bioreactor. Our research group is part of the Electrochemical Technology Centre in the Chemistry Department, University of Guelph, which was established in 2001 with multi-million $$ funding from the Canada Foundation for Innovation.
Graduate students in our research group are encouraged to register as analytical chemists, and have generally experienced good success in finding employment in the field. We also take on at least one undergraduate student in the summer semester to offer research experience.
Here are details about some recent and ongoing projects.
Mechanism of action of anodes during substrate oxidation
The view that the anode acts simply as a sink for electrons donated by a substrate undergoing oxidation is now known to be incorrect for many anode types. AActive@anodes, mostly based on noble metal oxides, operate through a higher oxide of the metal, from which an oxygen atom is transferred tot he substrate; at Ainactive@ anodes, oxidation involves hydroxyl radicals that are sorbed to the anode surface. Our contributions to this subject have focussed on Ebonex, a conductive ceramic of approximate composition Ti4O7, and graphite. Ebonex behaves as an inactive material, but with the complication that its surface undergoes over-oxidation to TiO2 unless the polarity of the electrodes is reversed periodically.1 Graphite acts as an active anode, but is different from noble metal oxide-based anodes in that the carbon surface must first be functionalized with oxygen functional groups before substrate oxidation begins.2
Site-selective electrochemical chemotherapy
A major problem in conventional cancer chemotherapy is that the drug is administered systemically. Severe side-effects accompany treatment, because the patient's healthy cells are exposed to the chemotherapeutic agent along with the tumour cells. This new project has two goals. (1) To administer the toxic agent directly into the tumour, so as to avoid systemic toxicity, and hence allow higher local concentrations of toxicant to be achieved while lowering the total dose to the patient. (2) Using electrochemical oxidation of the pro-drug to mimic in vivo bioactivation through cytochrome P-450 oxidation, and therefore deliver the active form of the drug directly to the tumour. This work is in its preliminary stages.
"Sour brines" from oil and gas recovery
The production of oil and natural gas is accompanied by the production of large volumes of water that is commonly contaminated with both chloride and sulfide. These"sour waters" are highly toxic because when they reach the surface and are no longer under high pressure, hydrogen sulfide is released. These waters are also highly corrosive to metal pipes with the deposition of a sulfidic scale. In the past, chemical methods such as precipitation or oxidation have been used to remove sulfide; these produce large volumes of toxic sludge that is expensive to dispose of. We discovered that electrochemical oxidation of sulfide solutions proceeds smoothly to non-toxic sulfate ion in near-quantitative yield and with near-quantitative current efficiency (meaning that essentially none of the electrical energy is consumed by competing processes). The reaction is "current controlled", meaning that its rate is independent of the concentration of sulfide ion, and hence that the current efficiency stays high even as the starting material is used up.3
Because boron-doped diamond anodes are not available cheaply in large format, subsequent work focussed on finding anodes that are cheap and long lasting. Ti/IrO2anodes gradually lost their activity.4 A variety of carbon-based anodes satisfied the requirement for low cost, but were somewhat sacrificial (the anode was consumed in competition with the oxidation of sulfide.5,6: Ebonex, the conductive ceramic material mentioned above, offers excellent stability provided that the polarity of the electrodes is reversed peridoically.7
Odour remediation of liquid hog manure
The greatest environmental problem facing the pork industry is the offensive odour of liquid hog manure, especially when it is spread on the land as a source of fertilizer. The odour develops through the action of anaerobic bacteria which inhabit the anaerobic environment of both the hog's gut and the liquid manure tank. We have discovered that under conditions of electrolysis the odour is ameliorated in terms of both intensity and quality (it has a different, less unpleasant smell, and the smell is not as strong). In addition, electrolysis has the added benefit of killing the anaerobic bacteria, thus allowing the treated product to remain "sweet".8
Further work showed that reduction of the population of bacteria by two orders of magnitude could be achieved at a variety of electrode combinations. A likely mechanism for the bactericidal action is the electrochemical oxidation of chloride ion in the manure to hypochlorite. Subsequently, we scaled up the electrolysis from the 1 L and 27 L batch reactors to a pilot plant of 1800 L capacity. Odour control was achieved using Ti/IrO2 anodes and mild steel cathodes in two different configurations: large electrodes suspended directly into the pilot plant, or a small external unit through which the manure could be cycled.9
1. D. Bejan, J.D. Malcolm, L. Morrison, and N.J. Bunce (2009). Mechanistic investigation of the conductive ceramic Ebonex as an anode material, Electrochim. Acta,54, 5548-5556.
2. M. Rueffer, D. Bejan, and N.J. Bunce. Graphite: an active or an inactive anode. Submitted for publication, September 2010.
3. K. Waterston, D. Bejan, and N.J. Bunce (2007). Electrochemical oxidation of sulfide ion at boron-doped diamond anodes, J. Appl. Electrochem., 37, 367-373.
4. J. Haner, D. Bejan, and N.J. Bunce (2009). Electrochemical oxidation of sulfide ion at a Ti/IrO2-Ta2O5 anode in the presence and absence of naphthenic acids, J. Appl. Electrochem., 39, 1733-1738
5. K. Rankin, D. Bejan, and N.J. Bunce (2010). Electrochemical oxidation of sulfide ion in synthetic geothermal sour brines in batch cells using coke electrodes. Ind. Eng. Chem. Res., 49, 6261-6266.
6. J. Hastie, D. Bejan, and N.J. Bunce, Oxidation of sulfide ion in synthetic geothermal brines at carbon-based anodes, Can.J. Chem. Eng., accepted, August 2010.
7. S. El-Sherif, D. Bejan, and N.J. Bunce, Electrochemical oxidation of sulfide ion in synthetic geothermal brines using periodic polarity reversal at Ebonex electrodes. Can. J. Chem., in press, July 2010.
8. D. Bejan, F. Sagitova and N.J. Bunce (2005). Evaluation of electrolysis for oxidative deodorization of hog manure. J. Appl. Electrochem., 37, 897-902.
9. D. Bejan, L.M. Rabson, and N.J. Bunce (2007). Electrochemical deodorization and disinfection of hog manure, Can. J. Chem. Eng., 85, 929-935.