Enhanced performance of microbial bioelectrochemical systems Seminar

Microbial bioelectrochemical systems (mBESs) are emerging bioreactor technologies that have substantially expanded their scope over the last few years, from electricity generation to an array of more complex processes, such as bioremediation and chemical production. In mBESs, whole cells are used as biocatalysts to catalyse oxidation and reduction reactions.

Microbial fuel cells are the classical and more widely studied example of bioelectrochemical systems, performing the double task of wastewater treatment and electricity generation. More recently, the concept has been extended to the possibility of generating higher value products than electricity. Microbial electrosynthesis (MES) is a novel and promising strategy that relies on electroactive microorganisms that are able to use electrons derived from solid-state electrodes to catalyse the reduction of

CO2 and other oxidised organics, to generate extracellular multi-carbon organic molecules as valuable reduced end-products.

The viability of prospective applications of microbial bioelectrochemical systems is highly dependent on performance improvement, i.e. in current increase. Current production is dependent, among other factors, on the microbial consortia, bioelectrochemical reactor design, and electrode materials. While the first two key characteristics have been widely researched for more than a decade, until very recently, most of the work on bioelectrochemical systems used only commercially available carbonaceous materials.

I will present results on new prospective microbial electrode materials bearing hierarchical porous structures. Two new methods were recently developed to directly grow carbon nanotube (CNT) networks on any type of substrate. The nanostructure enhances the bacteria-electrode interaction and microbial extracellular electron transfer. The macroporous structure hosts a large microbial loading, and at the same time allows good mass transport that supplies the high substrate needs and removes the undesirable products.

While most studies in the field have concentrated on the growth of anodic biofilms, we have demonstrated the efficiency of our electrodes for both anodic and cathodic systems. We have recently reported the highest values of acetate production rate in a microbial bioelectrochemical system 78.06mg/L/day. In addition, we have normalized values of current density considering the total surface area of the porous electrodes, and not just the projected surface area, thus proving that our increased efficiency is not just due to an increased total surface area arising from a 3D electrode.

In this way, ours is the first study showing better intrinsic efficiency as biocathode material of a three-dimensional electrode versus a flat electrode.

References:

1-L. Jourdin, S. Freguia, B. C. Donose, J. Chen, G. G. Wallace, J. Keller, V. Flexer, A novel carbon nanotube modified scaffold as an efficient biocathode material for improved microbial electrosynthesis, Journal of Material Chemistry A, 2014, 2(32), 13093-13102.

2- V. Flexer, J. Chen, B. C. Donose, P. Sherrell, G.G. Wallace, J. Keller, The nanostructure of three-dimensional scaffolds enhances the current density of microbial bioelectrochemical systems, Energy & Environmental Science, 2013, 6(4), 1291-1298. 

3- V. Flexer, M. Marque, B. C. Donose, B. Virdis, J. Keller, Plasma treatment of electrodes significantly enhances the development of anodic electrochemically active biofilms, Electrochimica Acta, 2013, 108, 566-574.