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Challenges and applications of microbial fuel cells in wastewater treatment

About the blog

Sofia Babanova
CTO and co-founder of Aquacycl.

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  • Challenges and applications of microbial fuel cells in wastewater treatment

Recent developments of microbial fuel cells (MFC) have broadened application and provide an opportunity to improve wastewater treatment. They do not provide a silver bullet, but MFCs do supply a sustainable way of treating wastewater that conventional treatment has not been able to treat effectively.

Basics of MFC system

A microbial fuel cell uses bacteria to transform chemical energy into electricity. The fuel source can be any form of biodegradable organic matter. Since the bacteria are simultaneously consuming organic material and cleaning the water, MFC is ideal for wastewater treatment.

The naturally occurring bacteria perform extracellular electron transfer, releasing electrons as part of the respiration process, which is captured to generate electricity, constantly pulling energy away from the bacteria and accelerating the bacterial metabolism. By controlling the rate at which electrons are removed, the system controls the treatment rate, speeding up the treatment process relative to conventional systems.

Challenges and limitations of MFC

MFCs were originally researched as a source of clean energy, but as inherent limitations of power generation were recognized, the focus shifted from electricity production to wastewater treatment. For MFC to be a viable option for wastewater treatment, they need to be scaled up to accommodate large volumes of incoming wastewater, which has proven challenging for several reasons, including minimizing the distance between anode and cathode to reduce electrical losses and being cost-competitive with other treatment technologies. The materials used are expensive, including membranes to separate the electrodes, which are prone to fouling, and a catalyst to produce enough power.

New Approaches

Aquacycl developed the first-commercially viable MFC for wastewater treatment by addressing the design limitations above. The system was optimized for wastewater treatment efficiency instead of energy recovery. Rather than scaling the system within a single unit, Aquacycl created a modular approach, where each reactor is the size of a standard car battery, and they are stacked together to increase treatment quality and volume capacity. The small size means they don’t face the mass transfer losses inherent in larger system designs, and it doesn’t use a membrane, which eliminates biofouling and makes the system more cost-effective and efficient.

The small, modular nature and energy-neutral operation offer flexibility and potential for treatment without a sewer or electricity grid

Since one reactor cannot remove all the organics from the wastewater, the reactors are connected in hydraulic series. To increase the volume of wastewater treated, the system has multiple treatment trains operating in parallel, which provides an added benefit of easy serviceability. This allows the system to remain operational while one treatment train is being maintained.

The electricity production from the MFC enables real-time remote monitoring, troubleshooting and control and the earliest detection of any problems in the system.

Applications and future of MFC

Microbial fuel cells will likely never replace a centralized treatment facility. The best applications today are industrial pretreatment of challenging to treat, low-volume wastewater such as high-concentration streams from food processing, or toxic compounds from hydrocarbon processing. Today, these streams are costly and managed unsustainably, by trucking, incineration or land application.

As costs of the technology come down further, future applications include manure management and distributed sanitation for rural communities or disaster areas. By overcoming some of the key challenges to scaling, MFCs can be a viable alternative for some waste streams. As mentioned earlier, they are not a silver bullet, and likely will only address a small portion of the total wastewater treatment market, but the small, modular nature and energy-neutral operation offer more flexibility and potential for treatment without a sewer or electricity grid.

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