Binghamton University in the United States on October 15 presented new research on a biobattery that generates electricity through bacterial activity, using electrodes modeled on the villi of the small intestine. According to the abstract of a paper published on September 30 in the peer-reviewed journal Small, the volumetric power density rose roughly 8.3-fold compared with a flat electrode of the same volume. The key feature is that the electrode itself incorporates an environment in which bacteria can take in nutrients and remain active. The team envisions installing such batteries inside drainage pipes in the future to power small devices. However, whether the performance gain can be maintained in an actual wastewater environment still needs to be verified.
Designing an electrode where bacteria thrive, inspired by the small intestine
Conventional flat electrodes offer only limited surface area on which bacteria can work. Meanwhile, materials with more pores and a larger surface area have a different problem: biofilms, the layers formed by bacterial communities, can block the pathways for nutrients and waste. According to Professor Seokheun Choi, who led the research, earlier electrode designs struggled with insufficient nutrient supply, waste buildup, and uneven bacterial growth. Simply increasing surface area does not improve power generation if nutrients fail to reach the bacteria inside.
The research team, including Ruohan Zhang, Botian Wang, and Professor Choi, turned to the finger-like projections lining the small intestine, known as villi. Villi provide a large surface area while keeping the distance that substances must travel short. The team built this feature into a flexible electrode to create an environment where bacteria can work efficiently. Rather than reproducing the gut's bacterial community itself, the idea was to use shape to create conditions suited to bacterial activity.
The electrode material is a hydrogel, a water-containing polymer network. According to the paper's abstract, it combines the conductive polymer PEDOT:PSS, polyvinyl alcohol, and reduced graphene oxide. The team formed villus-like pillars from this material and embedded spores of Bacillus subtilis inside. A spore is a dormant structure that bacteria form to survive harsh conditions; when nutrients are supplied, it germinates and grows into electrochemically active cells.
In this electrode, the same material serves as both the place where bacteria live and the pathway that collects the electrons they produce. The villus-shaped structure serves as the anode (negative electrode), and a cathode (positive electrode) made of modified carbon fiber cloth sits on the other side of an ion-exchange membrane. A microbial fuel cell generates power by extracting, through an external circuit, the electrons that bacteria release as they metabolize organic matter, together with an electrochemical reaction involving ion movement. The energy source is the organic matter supplied to the bacteria. Earlier studies have used spores to start power generation on demand, but this study incorporated them into a villus-shaped conductive gel. Its novelty lies in having a single electrode handle several roles at once: holding the bacteria, supplying nutrients, and collecting electrons.
Conditions behind the roughly 8.3-fold gain in power density
According to the published abstract, volumetric power density reached 66.45 µW/cm³ with the villus-shaped electrode, versus 8.04 µW/cm³ for the conventional flat electrode. The comparison used a flat electrode of equal volume. The roughly 8.3-fold figure therefore reflects the improvement under the comparison conditions set in this experiment. It does not mean the device outperforms every existing microbial fuel cell by 8.3 times, nor does it mean the amount of stored energy increased 8.3-fold.
The team evaluated electrode geometry using 24 devices and found that the combination of pillar radius and height affects power generation. At the optimal dimensions, each villus-like pillar reached a peak output of 8.35 µW. A µW (microwatt) is one millionth of a watt. Power density divided by electrode volume and the power obtained from an individual electrode structure are different metrics, so care is needed not to confuse them.
The university's announcement also reports that, with nutrient medium supplied continuously, the device maintained a voltage of about 0.75 V for at least 14 hours. This result shows that power generation continued while nutrients were being replenished; it does not mean the device can run for 14 hours without a nutrient supply. Nor does 14 hours represent an upper limit on battery life.
To assess practicality, current matters as well as voltage. Power is the product of voltage and current, so 0.75 V alone does not reveal how much power can actually be delivered to a device. Even combined with the 14-hour run time, the total energy generated cannot be calculated. The university mentions applications such as small LEDs and microsensors, but the public information does not make clear which specific devices were driven or under what conditions. The abstract also does not give the optimal dimensions from the geometry evaluation, the number of independent repeated measurements, or details of measurement error. For the test that maintained 0.75 V, the university's announcement does not disclose the load resistance or current values.
Power generation confirmed in simulated piping; real sewage remains a challenge
On application to drainage pipes, laboratory test results have been reported in addition to the future vision. In the abstract published on September 30, experiments simulating power generation inside piping were conducted using a nutrient-and-electrolyte solution that mimicked wastewater. This was not a power generation test at a site carrying actual sewage. It also differs in test environment and evaluation criteria from the 14-hour endurance test described by the university.
Organizing the tests described in the abstract and Binghamton University's October 15 announcement by supply solution and test environment gives the following:
| Published test | Supply solution / environment | Confirmed result |
|---|---|---|
| Endurance test (university announcement) | Nutrient medium supplied continuously | About 0.75 V maintained for at least 14 hours |
| Piping test (paper abstract) | Simulated piping, using a nutrient-and-electrolyte solution that mimics wastewater | Power generation in response to nutrient supply, with the electrode conformed to the pipe's shape |
These results need to be read with the test environment and the measured performance kept distinct. In particular, the result of the 14-hour endurance test cannot be interpreted as a record of continuous operation inside piping. Even so, confirming power generation with an electrode conformed to the pipe's shape is significant. The research has moved from comparing performance on flat samples to verifying whether power can be generated with a structure designed for the actual installation environment.
For use in real wastewater, what matters beyond supplying nutrients to the bacteria is whether stable output can be maintained as temperature, salinity, pH, and other conditions fluctuate. Professor Choi has also pointed out in earlier writing that the performance of microbial fuel cells depends heavily on such environmental conditions. The paper's abstract and the university announcement do not confirm any long-term operation with real sewage, nor how much the wastewater was purified.
The team also reports bioelectrochemical sensing that distinguishes reactions at different positions, using a separate electrode array. This goes beyond extracting the electricity produced by bacterial activity and attempts to use the reaction as a signal for understanding conditions location by location. However, it does not mean that selective detection of specific pollutants or sewage purification capability has been demonstrated.
What it will take to become a power source for small sensors
In a 2023 commentary published in the journal Batteries, Professor Choi pointed out that maintaining and operating large-scale microbial fuel cells poses many challenges. He instead emphasized the use of small power sources that incorporate carefully selected bacteria. The villus-shaped electrode is positioned as an extension of that line of research: making bacteria work efficiently in a limited space and drawing a small amount of power from them.
If such a battery is to power small devices in practice, it may also require an energy storage element to temporarily hold the generated electricity and a circuit to convert it to the voltage the device needs. These auxiliary circuits consume power themselves, so the output measured at the electrode cannot necessarily be delivered to a device as is. It will be necessary to combine the battery with real sensors and confirm how much power can be supplied, after subtracting auxiliary-circuit losses, while keeping the bacteria active.
On the manufacturing side, the team aims to develop a printing technique that can form the villus-shaped structure in a single step and support mass production. The current electrode has spores embedded throughout the gel, and it does not reproduce the physiological and chemical environment created by the small intestine's mucus and cell layers. Professor Choi explains that the team now hopes to clarify the conditions under which bacteria survive and remain active over the long term by imitating not only the shape but also this environment. If bacterial activity can be sustained in real sewage, and the power needed by sensors can be supplied after subtracting auxiliary-circuit consumption, organic matter flowing through drainage pipes could serve as a power source for small devices in places where replacing batteries is difficult.