Stephanie Rusch Fehrmann, PhD student at Luleå University of Technology, researches how blackwater – toilet waste – can be transformed into energy and nutrient-rich fertilizer in future circular sanitation systems.
19 November 2025
World Toilet Day – research at Luleå University of Technology shows the way to circular sanitation
What we flush away could hold the key to cleaner energy and safer sanitation. On 19 November, the United Nations marks World Toilet Day, highlighting the global sanitation challenge. At Luleå University of Technology, pioneering research is underway to turn black water – toilet waste – into a valuable resource for both energy and agriculture.
Only a fraction of the world’s population has access to safe sanitation. At the same time, in wealthier countries, huge amounts of phosphorus, nitrogen and carbon are flushed away every day.
“Our current system makes no sense. We mix everything together and then spend energy cleaning it. Instead, we should recover resources from the start,” says Stephanie Rusch Fehrmann, PhD student at Luleå University of Technology.
From waste to resource
Her PhD project studies how blackwater can be separated from greywater to produce biogas and nutrient-rich liquid fertilizer.
“By treating blackwater separately, we save energy and preserve nutrients that would otherwise be lost. It’s a more circular and sustainable system,” she explains.
Her research also explores nitrogen stabilization and nutrient concentration with low-grade heat, ensuring that the end product is safe for agricultural use. Studies show that biogas production from blackwater can be up to 70 percent more efficient than in conventional wastewater systems
A global eye-opener
Stephanie Rusch Fehrmann’s commitment grew stronger after volunteering in regions where people still lack basic sanitation.
“The reality is tough. I’ve seen how people, even in modern societies, live without safe toilets or clean water. It was a real eye-opener for me,” she says.
That experience shaped her motivation to spread knowledge about smarter sanitation systems.
“If we’re building new systems, we should build them right from the start. It’s cheaper, more efficient and better for the environment. And we need to talk about it – because our current systems simply don’t make sense,” says Stephanie Rusch Fehrmann.
World Toilet Day
World Toilet Day is observed every year on November 19 to highlight the global sanitation situation. According to the UN, 3.5 billion people lack access to safe toilets, and 419 million people are forced to go without any form of sanitation. The day aims to raise awareness of the link between sanitation, health, gender equality and sustainable development.
Contact
Stephanie Rusch Fehrmann
Published:
Updated: