Reimagined Toilets: From Pollution to Energy Generation

Despite being rarely thought of, toilets are one of the most important inventions throughout history. It was notoriously common to encounter infectious diseases before proper toilets and sanitation systems exist. Although decent sanitation systems are still inaccessible to some, toilets are no longer a high class privilege. Supposedly, toilets allow us to dispose our waste easily through safe means, but to what extent can we deem it “safe”?

Where It Actually Ends Up

Sewage systems are designed to collect all of our waste to a centralized wastewater treatment facility located at the central urban area. However, this does not guarantee that our waste would be treated properly. According to a study by Cascade Tuholske, a postdoctoral researcher at the Columbia Climate School, 63% of the world’s nitrogen pollution from wastewater comes from sewage. This proves that waste problem isn’t solely caused by lack of adequate sanitation systems, rather by inefficient treatment plants for removing nutrients as well. Take Mississippi River as an example; although numerous treatment plants are available around it, the river’s watershed appertains to the world’s 25 worst nitrogen polluters. Speaking of which, human waste is contributing 6,2 million tons of nitrogen to coastal waters every year! Not to mention other substances. Eventually, current wastewater treatments still put human health and water ecosystems at risk.

Coral Bleaching; Factors Affecting It Include Excessive Nitrogen

(source: https://www.barrierreef.org/the-reef/threats/coral-bleaching)

More than a Waste

A shift of paradigm is needed to turn to a more circular approach in handling waste. In fact, not a single thing can be considered intrinsically worthless - even grossly viewed human waste has values. Here are 3 resources we can obtain from our waste: 1. Clean water; urine comprises up to 96% water, wouldn’t it be wasteful to let them go as pollutants? 2. Nutrients; 75% of nitrogen and 50% of phosphorus in domestic wastewater comes from human waste, which ought to be utilized as plant fertilizers; 3. Energy; A PhD graduate from Newcastle University, Elizabeth Heidrich, found that waste from the world’s population in 2004 would be able to generate 70-140 GW of energy - that’s about 82-164 GW with today’s population (for comparison, a large nuclear plant is able to produce around 1 GW). Moreover, human urine has a high conductivity - multiple times higher than other domestic wastewater -, making it favorable to be used as an electrolyte in fuel cells.

Living Fuel Cells

Remember the stance that nothing is useless. Bacteria is a kind of organism labeled with 3 D’s: dirt, disease, and death; nonetheless, a majority of them is actually beneficial. Microbial Fuel Cell (MFC) is a technology that harnesses bacterial metabolism not only for producing electricity, but also removing substances, resulting in clean-enough water to be reused leastwise for toilet flush. Like typical fuel cells, MFC consists of cathode chamber and anode chamber connected with a wire, and separated with a semi-permeable membrane for ion exchange. What’s different is the presence of a bacteria consortium sticking to the anode. These bacteria are responsible for oxidizing organic matter and water, producing electrons and hydrogen protons. Reduction in the cathode chamber converts protons into water and recovers nutrients, particularly nitrogen, phosphorus, and potassium. Additionally, unsavory odor is eliminated through oxidation of sulfide ions.

Microbial Fuel Cell

(source: https://www.sciencedirect.com/science/article/pii/S0196890418311002?via%3Dihub)

Electricity in a Flush

A success story of actual bioelectric toilets took place at Glastonbury Music Festival in 2015-2019. The system, called Pee Power, was made up of stacked 36 ceramic MFC modules with carbon-based electrodes, which in total could hold 25 liters of urine. Such use of material is a key to lower production cost of MFC. With constant flow of feedstock from approximately 1000 visitors per day, the system managed to provide reliable power output consistently - up to 800 mW - sufficient for supplying illumination. Professor Ioannis Ieropoulos, Director of the Bristol BioEnergy Centre who was involved in the project, stated that the 2019 version had been refined to power some applications directly (without batteries) and yield surplus energy.

Pee Power Technology Urinal at Glastonbury Music Festival

(source: https://www.timeshighereducation.com/news/researchers-go-potty-pee-glastonbury)

Since magnification of MFC size results in reduction of power density, it’s more convenient to configure small MFC modules together and use them as a decentralized system. Thus, it can be used to empower rural areas and refugee camps as well. Commercializing this ground-breaking technology requires discoveries of optimal arrangements, materials, conditions, strategies for simultaneous removal and recovery, as well as genetic engineering for efficient bacterial strains. Given the high cost of MFC, hopefully our government and stakeholders too will offer more incentives for green solutions like MFC. Afterall, the author believes that tackling waste crisis and producing clean energy shouldn’t be a trade-off, and MFC enables us to do exactly both.

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References

Chukwubede et al. (2013). ‘Estimation Of The Electric Power Potential Of Human Waste Using Students Hostel Soak-Away Pits’, American Journal of Engineering Research, 2(9), 198-203 [online]. Available at: https://ajer.org/papers/v2(9)/Z029198203.pdf (Accessed: February 28th 2022)

Ieropoulos et al. (2016). ‘Pee power urinal – microbial fuel cell technology field trials in the context of sanitation’, Environmental Science: Water Research & Technology, 2, 336-343 [online]. Available at: https://pubs.rsc.org/en/content/articlehtml/2016/ew/c5ew00270b (Accessed: February 28th 2022)

Mowbray, S. (2022). The thick of it: Delving into the neglected global impacts of human waste [online]. Mongabay. Available at: https://news.mongabay.com/2022/01/the-thick-of-it-delving-into-the-neglected-global-impacts-of-human-waste/ (Accessed: February 27th 2022)

Sharma et al. (2022). ‘Bioelectricity generation from human urine and simultaneous nutrient recovery: Role of Microbial Fuel Cells’, Chemosphere, 292 [online]. Available at: https://www.sciencedirect.com/science/article/pii/S0045653521039114 (Accessed: February 28th 2022)

UWE Bristol. (2019). Pee Power technology returns to Glastonbury Festival for fourth year [online]. UWE Bristol. Available at: https://info.uwe.ac.uk/news/uwenews/news.aspx?id=3953 (Accessed: February 28th 2022)

Verma et al. (2022). ‘Advancements in applicability of microbial fuel cell for energy recovery from human waste’, Bioresource Technology Reports, 17 [online]. Available at: https://www.sciencedirect.com/science/article/pii/S2589014X22000354 (Accessed: February 28th 2022)

You, Greenman, and Ieropoulos. (2021). ‘Microbial fuel cells in the house: A study on real household wastewater samples for treatment and power’, Sustainable Energy Technologies and Assessments, 48 [online]. Available at: https://www.sciencedirect.com/science/article/pii/S2213138821006329#b0075 (Accessed: February 28th 2022)