“The work we presented in our paper represents a step forward in upgrading microbial fuel cells to practical use.”

The work we presented in our paper represents a step forward in upgrading microbial fuel cells to practical use. It concerns a simplified design that combines electrochemical requirements (high electrode surfaces, low distance between the anodic and cathodic electrode) and microbial requirements (surface for biofilm development, supply of substrate and discharge of waste products. The result is a system that adequately converts carbon sources to electricity, and can be constructed in a rapid and easy way.

More than 90% of the electrons present in acetate could be regained as electricity, for example. A highly exciting result is the fact that our system is capable of converting wastewater organics with a reasonable efficiency, something not shown before. This plurality of innovations and improvements warrants the attention this paper receives.

An environmental biotechnologist will regard the system we propose as a modified upflow anaerobic sludge blanket reactor (UASB). An electrochemist will regard it as a modified fuel cell design. As such, perhaps we can categorize the merit of the paper in combining electrochemical and microbial requirements.

Several different carbon sources were tested, acetate proved (again) to be the most interesting electron donor for electricity generation described thus far. When wastewater was fed to the reactors, the power output was notably lower. The bottleneck for wastewater is the fact that a large fraction of the organic carbon is non rapidly biodegradable.

Therefore, this organic matter remains untouched in current reactor systems. A number of parameters were investigated, which defined a certain methodology of operation that aims at either high energy recovery or high organic matter removal.

The treatment of wastewater represents a large investment of chemical materials and also considerable usage of energy. Per kilogram of wastewater organics removed we need 1 kWh of (non renewable) energy for aeration and pumping. Microbial fuel cells are systems that can generate renewable energy, electricity, out of wastewater. Simultaneously, the "waste" present in the wastewater is removed, so there is a double advantage. Therefore, they may play a large role in creating energy efficient wastewater treatment. The system we have designed simplifies the construction and operation of microbial fuel cells, and therefore paves the way towards application of this technology.

We have been working for almost six years on microbial fuel cells. Greg Zeikus of Michigan State University presented, at a meeting in Ghent, some results of a highly exotic technique that might have some potential: microbial fuel cells.

The treatment of wastewater was the objective from day one, which was in 2001. It took almost two years before we obtained acceptable results from our systems, as the knowledge of this field was quite limited several years ago.

We have, at each point in this research; defined standards that needed to be met, such as a certain efficient removal of organic matter, which has often delayed publication—or even caused us to miss the "first time" publication. Certainly, the electrochemical aspects, and the mode of microbial electron transfer, needed substantial attention.

Sustainable energy generation and the utilization of renewable resources have become major issues in many countries throughout the world. We need to consider wastewater as a valuable resource for water, nutrients, and energy. Changing the minds of the general public, so that issues such as water recycling can be accepted, requires major political engagement.