Using Mud Batteries as Low-cost Soil Moisture Sensing Solution
November 29, 2022 by Stephanie Leonida
Researchers at the University of California, Santa Cruz have developed a first-of-a-kind mud battery technology using microbes to harvest electricity for soil moisture sensing systems.
At the University of California, Santa Cruz (UCSC), Colleen Josephson, assistant professor of Electrical and Computer Engineering, along with her research team, have unveiled new research concerning the potential use of microbial fuel cells for providing renewable energy to operate soil moisture sensing systems on farms. The researchers have explored the efficacy of using microbial fuel cells (or mud batteries), testing the biotechnology in one of UCSC's field research sites.
Research has created new possibilities for renewable energy to operate soil moisture sensing systems on farms. Image used courtesy of Flickr
Cost of Saving Water Presents Obstacles
One of the devastating effects of climate change includes severe drought. It not only has the potential to initiate wildfires in areas of natural beauty and those where both humans and other organisms live, but also can decimate agricultural crops worldwide.
Fresh water is a precious finite resource that farmers must use carefully when tending to their crops. Farmers can employ sensing technology to monitor the water content of the soils in their fields. This can help them add the required amount of water to ensure the optimal growth of crops without wasting a vital resource. Previous research has shown that as much as 20 to 50 percent of water can be saved by using such sensing technology.
Mud batteries with soil and electron-ejecting microbes could provide renewable electricity to farms in the future. Image used courtesy of Modern Farmer
Although such sensing systems are key for avoiding future water shortages, they are known to be costly and difficult to maintain. According to UCSC, less than 10 percent of U.S. farms use smart/intelligent watering systems.
Microbial Mud Batteries Can Generate Electricity
Microbial fuel cell batteries are not considered a new technology. Civil engineers have long been researching these types of batteries to find out a way of producing energy from wastewater. However, generating electricity from soil microbes is an area of research much less explored.
While employed at Microsoft Research, Josephson and the company began their journey by first developing a soil moisture sensing system on a single coin-cell battery designed to last five years. This technology was later developed to incorporate naturally occurring soil microbes. The soil moisture sensing system was intended to be low-cost, renewable, and resilient to outdoor conditions.
Colleen Josephson, assistant professor of Electrical and Computer Engineering. Image used courtesy of UCSC
Microbial fuel cells function by gathering energy from soil bacteria known as exoelectrogens. Exoelectrogens are bacteria that produce electric currents when they grow. They are also known as electric bacteria. Exoelectrogens use electrons from organic material to produce a charge. The organic material can be either food or waste product from the microbe's metabolism.
Essentially, the electric bacteria eat food, metabolize it, and transfer electrons from their cell interiors to the outside of the cell to breathe. These electrons can be routed to a circuit to generate power.
The researchers wanted to elevate the voltage of the naturally low-voltage microbial fuel cells to meet the requirements of the electronic system, but the power harvesting chips used to do so were not quite suitable. A static resistor, on the other hand, was found to do a much better job.
Mud Battery Research to Expand Worldwide
In future research, Josephson intends to investigate how the power harvesting chips might be redesigned to tap into microbial power sources more effectively.
The mud batteries are currently being tested on a farm site at UCSC and Stanford University. Additionally, Josephson plans to deploy the mud batteries on farms in different countries subject to varying climates. Different climates mean different temperatures.
According to Josephson, factors such as changing temperature, soil moisture, electrical conductivity, and the microbial system's power output could be a way of monitoring microbial health, a key contributor to the health of the surrounding environment. This microbial health monitoring is known as "sensor fusion."
By understanding how the mud batteries work under different climate conditions, the researchers hope to generate more insights into what conditions keep the bacteria fit and healthy.
Josephson and her team plan to develop their sensing systems for monitoring ocean water environments, marshlands, and wetlands.
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