About three years ago, I wrote about a fairly new technology for generating electricity from the waste we flush down the toilet, microbial fuel cells.
At that time, several research teams were working on them, but they were still a strictly experimental technology. Are we any closer to harnessing the electricity microbes generate? Somewhat.
How microbial fuel cells work
A fuel cell is sort of like a battery. A battery contains reactants, an anode and a cathode separated by an electrolyte, and a means of creating an electrical circuit. When a battery uses up the reactants, it must be either recharged or discarded. A fuel cell does not contain reactants; they are stored externally. A spent fuel cell is refueled, not recharged.
Standard fuel cells require some kind of chemical reaction. Microbial fuel cells depend on the natural respiration cycle (breathing) of electrochemically active microbes called exoelectrogens. That is, microbes that produce an electric current. The anode, or negatively charged portion of the cell, receives waste material, which the microbes digest in anaerobic conditions. In other words, there is no air.
The exoelectrogens ingest and then digest organic matter. In other words, food goes in and waste goes out, just as in every living being. In the presence of air they excrete carbon dioxide and water. In the absence of air, they excrete carbon dioxide, protons, and electrons.
The fuel cell captures the electrons, and the air in the cathode recombines the electrons with hydrogen to produce water and complete the circuit.
Microbial fuel cells represent a class of technology that provides solutions to two or more seemingly unrelated problems. Wastewater treatment as traditionally practiced has proven to be expensive and inefficient. .
Generating electricity by burning fossil fuels adds greenhouse gases to the atmosphere and, because of the proximity of coal ash ponds to rivers, lakes, and wells, poses the threat of water pollution.
Wastewater and microbes are both infinitely renewable resources. Microbes reduce the volume of solids in sewage and industrial wastewater. They can potentially generate clean electricity in the process. So how long will it take before every wastewater treatment plant, brewery, etc. uses microbial fuel cells?
Commercializing the technology
- Can microbial fuel cells provide at least enough electricity to provide significant power for the wastewater treatment plant?
- Are they scalable? The technology works beautifully in demonstration projects, but is barely tested in an industrial setting.
- Are they economically viable, or will the materials and manufacturing processes prove too expensive?
Technological development has at least proceeded to the point that a few businesses have begun to market their designs.
Cambrian Innovation, founded in 2006, sells microbial fuel cells for industrial applications under the brand name EcoVolt.
Its flagship product, the EcoVolt Reactor, became commercially available in 2013. It does not directly output electricity.
Instead it uses a secondary set of electrodes to produce near pipeline quality methane that can be burned to power an electric generator.
It has since introduced the smaller EcoVolt Mini and most recently (July 15, 2015) the EcoVoltMBR (membrane bioreactor). The EcoVolt Reactor functions mostly as a power source. The EcoVolt MBR treats water discharged from an EcoVolt Reactor to produce reusable water.
It installed the first EcoVolt MBR at Lagunitas Brewing Company in California with the expectation that it will reduce the company’s water intake by 40% and wastewater discharge by 70%. It is also projected to supply 15% of the company’s energy needs.
Matthew Silver, Cambrian’s founder and CEO, explains the system beginning at approximately the 20th minute of the following video of a webinar devoted to potential solutions to the drought in California.
Israel-based Emefcy, founded in 2008, has more recently started to develop a microbial fuel cell product. Presumably when it is ready to launch a pilot program, it will appeal to a different market than Cambrian. It envisions working with agricultural and municipal sources of wastewater
It launched a full-scale demonstration modular wastewater treatment plant in September 2014 based on a different technology, the membrane aerated biofilm reactor, which is smaller and quieter than standard wastewater treatment facilities and produces no offensive odor.
Arbsource, founded in 2011 in Arizona, specializes in wastewater treatment solutions for the food and beverage industry, which uses more fresh water than all of the households in the world combined. [Link no longer active as of 2/16/16]
The company is working with a second generation of test modules. It estimates that a medium-sized unit will occupy only the space of a 20-foot shipping container.
A 2013 article in CleanTechnica describes what it calls the next generation of microbial fuel cells designed by Pilus Energy [Link no longer active as of 2/16/16]. Instead of working with the microbes’ digestive processes, it focuses on metabolic activity. The article said that Pilus had released two different products, but checking Pilus’ own website, the product tab is empty. The earliest press release on the site is dated May 24, 2010 and the latest January 28, 2014.
The oldest of these companies released its first commercial product nine years after it was founded. Besides technological issues, start-up companies must attract investment and find potential customers willing to host a pilot project.
Perhaps before microbial fuel cell technology can work on an industrial scale, it will be necessary to develop medium scale projects. Third-World countries where both electricity and clean water are scarce could certainly benefit from pilot projects. Naval vessels, being considerably smaller than a wastewater treatment plant, might also provide a useful research and development opportunity.
Any technology potentially capable of solving two major problems deserves the research and commercial risk now being devoted to the development of microbial fuel cells.
Wastewater discharge pipe. Public domain from Wikimedia Commons
Microbial fuel cell diagram Source unknown
EcoVolt Reactor. Cambrian Innovation