It’s been described as the “liquid gold” of wastewater.
Every day, millions of litres of urine are flushed away but it is a valuable waste stream, according to environmental engineer Hlumelo Marepula. This is because it is rich in nitrogen in the form of urea, which is most often used as a fertiliser.
Earlier this month, Marepula, a civil engineering master’s candidate at the University of Cape Town (UCT) won an award for producing a urea-ethanol solution that can be recrystallised to produce fertiliser. It can also potentially produce diesel engine fluid, which is used to reduce air pollution caused by vehicles, with water as a by-product.
This was at the recent virtual International Summit on Sustainable Development Goals in Africa hosted by UCT. The competition was open to master’s and doctoral candidates and called for emerging thought leaders to submit videos showcasing how their work addresses the theme of #TheAfricaWeWant.
Marepula’s pioneering research underpins her master’s thesis in water quality engineering and environmental sustainability. She conducted her research under the supervision of associate professor Dyllon Randall at UCT’s department of civil engineering and the Future Water Institute.
In 2019, Randall encouraged Marepula to apply for the Falling Walls Lab competition in Cape Town, where she explored the potential of human urine to produce jet fuel. Marepula ended up representing UCT and South Africa at the global finals in Berlin, Germany.
“It’s things like this that he [Randall] encourages me to do and I grab it,” she told the Mail & Guardian.
There are so many uses for urine, Marepula explains: “There is a whole collective of researchers being supervised by Dyllon Randall who are all focusing on different aspects of how to exploit urine.”
One of the institute’s most well-known innovations is the bio-brick, which is grown from human urine.
“We are exploiting urine and finding so many different ways of making this bio-economy where basically you take urine and exploit it for all its uses, so you end up with no urine and so many value-added products,” Marepula said.
In striving for a more sustainable future, it is critical to recycle and reuse various “waste” streams, Randall told the M&G.
“Human urine is one of these ‘waste’ streams and has been referred to as liquid gold because of the valuable resources that can be recovered from it, if we dare to think differently. The process we developed adds to the exciting field of innovative, non-sewered sanitation systems,” he said.
Marepula says her research has a lot of potential to address sustainability issues in South Africa and the entire continent.
Africa has the largest area of arable land in the sub-Saharan region, accounting for 20% of the global agricultural land by area. However, the use of fertilisers for food production remains very low because synthetic urea-based fertilisers are often expensive for most small-scale farmers.
Urea is an important source of nitrogen with more than 90% of the world’s synthetic urea used as fertiliser, Marepula says. Because of its high nitrogen content, it also has the lowest transportation costs compared with other fertilisers. Globally, synthetic urea is the most abundantly produced chemical, but the process operates at high temperatures and pressures and is energy‑intensive.
Alternative urea production methods are required to reduce energy consumption, greenhouse gas emissions and costs while also using waste streams in a more circular economy approach.
“It’s very important for us to find alternative ways to reduce our waste and give back to the climate, to give back to the earth, because we’re extracting so much and using so much energy. This is our way of giving back and saying ‘let’s reduce the waste and use it for good,’” she says.
Marepula adds: “I really hope we do get to a point where we start realising how important it is to address climate change – and that it is here. It starts with educating ourselves. At UCT, for example, we have waterless urinals that are used for this research and we’ve encouraged students to use them. That’s their way of giving back – of contributing to the research and they’ve been so open to it.”