Scientists at McGill University have improved the efficiency of a method for converting human urine into clean energy.
This method relies on the use of microbial fuel cells which, with the help of bacteria, transform organic waste into electricity, thus offering us a sustainable and low-cost way to treat wastewater and produce energy from an abundant source. In this study, scientists determined the optimal urine concentrations for this process.
Wastewater treatment plants, new resources for clean energy?
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"We know that microbial fuel cells clean wastewater and produce electricity, but the precise effects of different urine concentrations on their electrochemical function, their efficiency at removing pollutants, and the behavior of microbial communities are still unknown," explains Vijaya Raghavan, co-author of the study and professor of bioresource engineering.
"We answered these questions by systematically examining the effect of different urine proportions on the electrochemical and biological performance of microbial fuel cells," he adds.
According to Professor Raghavan, this method could be used for the production of clean energy in contexts such as rural sanitation, disaster relief camps, and off-grid communities. Furthermore, because their electrical signals change depending on the levels of organic pollution, microbial fuel cells could also act as low-cost biosensors, allowing us to monitor wastewater quality without having to resort to complex equipment.
Improved performance thanks to higher urine concentrations
The research team constructed four dual-chamber microbial fuel cells and supplied them with mixtures of synthetic wastewater and human urine at concentrations of 20%, 50%, and 75%. They then tested the cells for two weeks, monitoring energy production, pollutant removal, and water treatment, and performing electrochemical tests.
They found that higher urine concentrations (from 50 to 75%) improved electricity production and that urine provided essential nutrients that promoted microbe growth.
"Urine contains ions and essential organic compounds that enable rapid microbial activation, which improves energy production and pollutant degradation," explains Professor Raghavan.
All microbial fuel cell systems contained a mixture of bacteria, but the scientists found that the genera Sediminibacterium and Comamonas were dominant. Bacteria of the genus Sediminibacterium were present in greater quantity when urine represented 50% of the mixture, while bacteria of the genus Comamonas were more frequent at higher urine concentrations (75%).
Since these microorganisms contribute to the degradation of organic pollutants and the transfer of electrons in fuel cells, the changes related to the dominant genera could explain the differences in the amount of electricity produced by the systems, the scientists believe. This finding also reveals that the amount of urine added strongly influences the types of microorganisms that develop and the system's efficiency, they add.
For Professor Raghavan, these results represent an important step towards an improved circular economy.
"Using urine as a resource promotes sustainable sanitation and nutrient recovery, thereby reducing pressure on freshwater systems," he concludes.