Become a member
Follow us:

What if human waste isn’t waste at all?

Words: Robert Langkjær-Bain

Photos: Courtesy of Sanergy

Follow us:

Clean toilets are a game changer in the slums of Nairobi – and they also provide the raw material for products that boost farm yields. 5 meets the founder of the organisation making it happen.


  • Hundreds of thousands of Nairobi residents lack access to clean toilets.
  • Toilets that don’t require sewers can help cities deal with rapid urbanisation.
  • Waste from the toilets is processed into fertiliser and insect-based animal feed. So it’s not really waste at all.
  • Lindsay Stradley, co-founder of the social enterprise behind the toilets, calls it an example of the “circular economy”.
  • With two billion people expected to live in slums by 2030, how we deal with human waste is a challenge the world can’t ignore.

In the slums of Nairobi, Kenya, it’s not uncommon to see human waste thrown into the street in a plastic bag. Locals call it a flying toilet. It’s not pleasant, but in an area with very few latrines and no sewers, it’s what happens.

Some would see a flying toilet and try to unsee it. Lindsay Stradley saw an unmet need – and with it, an opportunity to innovate.

“Flying toilets showed us there was latent demand for something better,” Stradley says. “Some cultures are more comfortable with defecating in the open, which means there’s a larger behavioural challenge to overcome. But here in Nairobi people were looking for privacy and safety when using a toilet. Flying toilets are the alternative they’ve created because high-quality options haven’t been available.”

More than 100,000 residents of Nairobi’s slums use the Fresh Life toilets every day.

Lindsay Stradley, co-founder of Sanergy, wants to help bring better sanitation to 1.5 million people in Africa by 2025.

That’s now changing. Bright blue boxes labelled “Fresh Life” have begun to appear in the last few years, dotted around Mukuru informal settlement. Each box contains a safe, clean toilet that people pay to access. A local franchisee looks after each toilet and makes a living from it, while the units, and the sanitation system behind them, are provided by Sanergy, the social enterprise that Lindsay Stradley co-founded. Today, more than 100,000 people use Fresh Life toilets every day. But that’s just half the story.

“The challenge was: how can you efficiently aggregate that waste, safely treat it, and capture the value that’s in it?”

Lindsay Stradley

Sanergy is built on the idea that human waste is not waste – it’s a raw material. So when toilets are emptied, the contents aren’t discarded, but processed into valuable products for agriculture. The results are better sanitation, more productive farming, and jobs created along the way. And the system costs about one fifth of what sewers would cost to run, Stradley says.

Organic fertiliser derived from human waste is used by more than 1,000 farmers, boosting yields by 30%.

The fertiliser is processed from waste collected from urban toilets.

Toilets may not make such an attractive photo-op as a newly built school or a freshly dug well, but access to them is critical in improving people’s life chances. Lack of sanitation has a devastating impact on living standards, health and business activity. The Kenyan government reckons the problem costs its economy the equivalent of a million US dollars a day.

But for the half a million people who live in Mukuru, sewers aren’t coming anytime soon. As more and more people arrive in the area in search of work, there just isn’t the space, time or budget for what would be a huge infrastructure project. That’s what makes solutions like Sanergy’s so important.

When waste isn’t waste

Stradley has always been fascinated by cities and how to make them better places to live. Before she even came to Kenya, she had lived through Hurricane Katrina in New Orleans, and seen what happens when the systems we rely on aren’t there.

After gaining invaluable business experience working for Google, Stradley embarked on an MBA, during which she and two classmates (who are now her co-founders, and in one case, her husband) came up with the idea for Sanergy. They identified Nairobi as a city that could benefit from the concept, and visited for the first time in 2009.

“After being collected, the waste gets processed into fertiliser, or fed to fly larvae which can then be harvested as animal feed”

“We knew from the beginning that it was possible, and that it was beneficial,” says Stradley. “The challenge was: how can you efficiently aggregate that waste, safely treat it, and capture the value that’s in it?”

The success of Sanergy challenges certain assumptions about sanitation. In developed cities, removal of waste is usually tied up with water supply – both form part of the same system. Sanergy’s model is based on the realisation that it doesn’t have to be that way.

“Tying sanitation to water, you start out from a presumption that sanitation should be water-borne systems: sewers. But increasingly we don’t have that, and it requires a much higher infrastructure burden. Even if we could wave a magic wand and build sewers for the whole city, there is not enough water. So you can bundle sanitation with solid waste management instead.”

Chicken farmers can increase their yields by 30% using feed based on insects that live on organic waste.

Black soldier fly larvae, which feed on organic waste, can be fed to animals as an alternative to fish meal.

Stradley talks a lot about circles: virtuous ones that need to be built, and vicious ones that need to be unbuilt. “We believe that part of the solution is a circular economy approach, where we get this mindshift that human waste, or organic waste generally, is not waste,” she says.

Far from being waste, the stuff that piles up in Sanergy’s toilets is the raw material for agricultural products. After being collected by trucks and carts, it gets processed into fertiliser, or fed to fly larvae which can then be harvested as animal feed. Both products boost farmers’ yields by approximately 30%, thanks to bigger, stronger plants and healthier livestock, helping to produce more food for the country’s growing population.

Time to talk shit

On top of the many challenges of improving sanitation is the difficulty of even discussing it. Stradley tackles this problem head-on in a 2017 TED Talk titled ‘Why we need to talk shit’, which has been viewed more than 10,000 times.

As with many taboo topics, the words we find ourselves using either sound overly technical (faeces) or just rude (shit). Even the polite term “human waste” is problematic, because, as Stradley keeps pointing out, this stuff isn’t waste at all.

And language is so much more than just a side issue. While those in the developed world simply “flush and forget”, not everyone has that luxury. “It’s critical that we figure out how to talk about it,” says Stradley. The awkwardness and reticence surrounding the topic is a “root cause and a symptom of us not tackling sanitation” – fuelling another of those vicious cycles.

“I can go to neighbourhoods I came to 10 years ago and they just look and feel very different”

Lindsay Stradley

“If you’re not comfortable talking about it, it’s easier to talk about water and handwashing, which are also critical, especially in COVID-19 times, but to talk about one without the other does the public health impact of handwashing a disservice. Part of why you’re exposed to so many pathogens is the unhygienic conditions we live in. Because there’s a lack of comfort talking about it, government policies aren’t focused on it.”

This is just the beginning

Urban sanitation is a major global challenge, with a billion people already living in slums, a figure expected to soon rise to two billion. Sanergy is already in the process of scaling up its operations in Kenya by building the biggest organic waste treatment facility in East Africa, which will be able to upcycle 75,000 tonnes of waste a year.

The vision is for Sanergy’s toilets to serve a million people a day in Nairobi and half a million elsewhere by 2025 – first in Kisumu, another city in Kenya, and perhaps in other African countries too.

Sanergy has installed more than 3,500 Fresh Life toilets in informal settlements in Nairobi.

Stradley is careful not to accept too much of the credit for improvements in the areas where Sanergy works, but clearly better sanitation has been a game-changer. “I can go to neighbourhoods I came to 10 years ago and they just look and feel very different,” she says. “I consistently hear people say that the slums are so much cleaner and safer than they were before.”

Even more encouraging are the knock-on effects – including a 20% increase in school attendance in locations where toilets are available.

As circles go, that’s pretty virtuous.


All photos courtesy of Sanergy



More stories from: