Would you believe me if I told you urine can be used to produce energy? I know this sounds crazy, but a study, published in Results in Chemistry, analyzes how human urine can be used to generate clean electricity through a biological system.
The research does not simply show this, but it also carefully analyzes what happens inside the system and identifies the conditions that make the process more efficient. So, let’s find out more about this study.
Urine and electricity
Human waste management is normally considered a health and environmental issue. Every day, millions of liters of urine are mixed with water in sewage systems that require great infrastructure for their treatment. However, urine is more than waste, since it’s made up of about 95% of water and 5% of organic and inorganic salts.
It contains substances such as urea, uric acid, creatinine, and ions like sodium, potassium, and magnesium. Because of this composition, urine is rich in nutrients, and the study presents it as a potentially valuable resource within circular economy models.
How microbial fuel cells work
The study focuses on a system known as a microbial fuel cell (MFC), which is a bioelectrochemical device capable of converting organic matter into electricity. It works by using microorganisms, especially bacteria, but let’s explain a bit more about it:
- Bacteria consume organic waste.
- During this process, they release electrons as part of their natural metabolism.
- Some bacteria, called exoelectrogenic bacteria, can transfer those electrons outside their cells to an electrode.
- The movement of these electrons creates an electric current.
For the process to remain stable, the microorganisms form a structure called a biofilm on the surface of the electrode. A biofilm is a group of bacteria that attach themselves to a surface, which allows continuous and efficient electron transfer.
Urine concentration improves electricity production
The main focus of this study was analyzing what happens when human urine is used as part of the substrate in microbial fuel cells.
Using pure urine can face challenges due to its high nitrogen concentration and high conductivity. For this reason, researchers mixed urine with synthetic wastewater in different proportions. Four dual-chamber systems were built and tested with mixtures containing:
- 20% urine
- 50% urine
- 75% urine
Over two weeks, researchers monitored:
- Voltage production
- Organic matter removal
- Biofilm development
They used techniques such as cyclic voltammetry and electrochemical impedance spectroscopy, which allow scientists to observe how the internal electrical system behaves and what types of resistance limit performance.
The results showed a clear pattern: increasing the concentration of urine improved the electrochemical activity of the microbial fuel cell system. Specifically.
- Oxidation and reduction peaks became stronger as urine concentration increased.
- The biofilm became more robust.
- The area under the voltammogram curve expanded, indicating increased anode capacitance.
- Polarization resistance decreased by up to 40% when urine concentration increased from 20% to 75%.
Microbial community
The researchers also analyzed the bacterial community using 16S rRNA gene sequencing, and they found out that the phylum Proteobacteria dominated the system, representing more than 69% of the bacterial population in some tests. Within this group, the genera Sediminibacterium and Comamonas were particularly prominent.
According to the study, unclassified species of Sediminibacterium and Comamonas dominated the anode chamber when the hybrid substrate of synthetic wastewater and human urine was used. These bacteria appear to play a key role in degrading nitrogen compounds and transferring electrons.
The balance between species changed depending on the concentration of urine. At higher concentrations, bacteria associated with nitrogen removal and electricity generation became more dominant. This indicates that substrate proportion influences not only electrical performance but also the internal ecological structure of the system.
Energy production and wastewater treatment at the same time
One of the most important findings is the relationship between electricity generation and the reduction of chemical oxygen demand (COD), which is a measure of organic pollution in water. The study highlights a strong correlation between voltage generation and COD reduction, meaning that as organic matter is broken down more effectively, more electricity is produced. So, the system performs two functions simultaneously: it generates electricity and it treats wastewater.
To sum up
Before reading this, who would have thought this way of producing electricity was possible? That crazy idea is now a reality. So, what usually flows unnoticed through sewage systems may, under the right conditions, contribute to more efficient and sustainable resource management.