Many of us don’t spend a lot of time pondering wastewater treatment unless we absolutely have to. However, we may need to start rethinking this dirty job. In the United States wastewater treatment is a multi-billion dollar industry that is facing major challenges in the coming years including an ageing infrastructure, increasing populations, changing environmental regulations, and limited water resources. Globally, the problem is much worse. According to the United Nations, over 2 billion people are without access to adequate sanitation or safe drinking water; a reality that has led to devastating mortality rates among children under the age of five. These present and future challenges demand innovative and sustainable solutions for wastewater treatment and water recycling technologies. That is where microbial fuel cells come in…
The Electromicrobiology group at JCVI-West is developing new and innovative microbial fuel cells (MFCs) for wastewater treatment using only the metabolic action of microorganisms that naturally exist in wastewater streams. Not only can MFC systems remove a majority of the organics contained in wastewater samples in half of the time required for traditional anaerobic systems, but they can also: (1) reduce waste-gas emissions, such as methane production; (2) significantly decrease sludge volumes (the left-over biomass and organic material from wastewater treatment); and (3) recover energy via direct electricity production. All of these benefits lead to a water treatment system that could be deployed anywhere in the world without the need for an energy grid.
How does it work? The answer is extracellular electron transfer.
Extracellular electron transfer results from a need to breathe. Many microorganisms have evolved mechanisms to move electrons outside of the cellular membrane to facilitate respiration. These mechanisms may involve the use of bacterial nanowires, outer-membrane-bound metalloproteins, and/or soluble electron shuttles. Whatever the mechanism(s) may be, the result is an energy metabolism that allows “electrogenic” microorganisms to survive by respiring solid surfaces. If the solid surface is the electrode of a MFC, we are able to capture some of the electrons resulting from respiration, and move them across a circuit to produce electricity. This rapid movement of electrons away from the microbial community is what diverts energy away from methanogenesis and biomass production, resulting in a more efficient and sustainable treatment process.
By measuring electron flow across the circuit, i.e. electrical current, we are also able to directly monitor microbial respiration and use the MFCs as tools for studying electron transfer mechanisms in pure cultures and mixed consortia. Microbial fuel cells and other bio-electrochemical systems offer many opportunities for studying microbial energy metabolism; and may also serve as unique cultivation devices. These systems could be a useful tool for microbial enrichment and selecting for new organisms that can be sequenced and used for reference genomes.
Every bit of knowledge we gain about the fundamental processes associated with microbial energy metabolism brings us closer to optimizing MFC systems for technology applications, such as wastewater treatment. In the Electromicrobiology group, we hope to further promote the merger between biological and engineered systems to ultimately provide MFCs that can be practically employed as cost-effective and sustainable wastewater treatment devices worldwide.