By Martin Sturzenegger (Translation by Rosemarie Graffagnini)
Zurich — If the banana trees at Zoo Zurich are particularly lush, it’s thanks to a fertiliser with an unusual ingredient: human waste. In the spring of 2016, zoo employees cleared a bamboo grove in Zurich’s Masaola Rainforest to plant the trees. Within a few months the saplings had reached an impressive height and produced a cornucopia of yellow fruit. “We were really surprised how fast the plants put down roots,” says Martin Bauert, curator of the tropical area of Zoo Zurich.
The reason for this fast growth has a name – terra preta – which is Portuguese for black soil. It is a particularly fertile substrate created from compost, charcoal (biochar) and human faeces.
The zoo pioneered its use some 18 months ago and, as Bauert says, “the ground vegetation has hugely improved”. In the future, the entire artificial rainforest is to be based on terra preta. And soon the black soil will also fertilise the zoo’s elephant park. The animals will then roam grounds that contain human excrements. Not that they will take exception to it – terra preta smells anything but vile.
Tobias Müller knows this first-hand. In 2015, the carpenter, inventor, and jack of all trades joined forces with his friends Marc Haueter, Torsten Much, and Anja Lippuner to establish Greenport, the company that provides Zoo Zurich with the fertile substrate. “We wanted to break some taboos with our products,” Müller explains. It’s a totally natural cycle, he says. Faeces turn to soil and urine to fertiliser, which in turn provide the basis for producing food.
To obtain the raw material, the start-up team developed a mobile dry toilet, the Greenport. Müller, 38, leads the way through the company warehouse, an old barn in Birmensdorf near Zurich. Toilets are crowding the place. They come in a variety of models, from a single cabin to a dual-size urinal to a wheelchair-accessible version. They are rented out to open-air concerts, markets, food fairs, or weddings.
Handmade from fir logs, the toilets exude a certain rustic cosiness, which the cheaper plastic models of the competition are lacking. “We wanted to create a privy with a homely feel to it – a toilet with charm.”
The human waste drops into a container, which Team Müller carts to a pyrolysis facility. Pyrolysis is the chemical decomposition of organic materials through the application of heat. The nutrient-rich matter is exposed to temperatures of up to 800 degrees Celsius. This destroys toxic germs, viruses and hormones but leaves nutrients, trace elements and water intact. The process yields charcoal (biochar) with a high storage capacity, which extracts toxic substances from the soil and returns water or carbon dioxide to it. The biochar is then supplemented with compost and soil organisms to obtain the terra preta.
“We take human waste back to where it belongs – nature,” Tobias Müller says. Greenport practises in miniature what science has tried to work out on a much grander scale: how to recover valuable substances from sludge. The human race needs to find a way to make bodily waste more productive, Müller says.
In Switzerland alone, sewage treatment generates 200,000 tonnes of sludge each year. Sludge used to be utilised by farmers to fertilise their soils. But this meant that heavy metals such as lead or zinc, traces of detergents and medical drugs as well as germs and viruses made it into agrarian food production. Which is why the Federal Office for the Environment (BAFU) intervened in 2006. Now the potentially valuable raw material is incinerated.
According to a BAFU study, 6,000 tonnes of phosphorus – a high-grade nutrient for the production of fertilisers – could be recovered each year from sludge and sludge ash. However, the legal basis for recycling the sludge in large quantities does not exist so far. Müller calls this “an ecological lunacy”.
For the moment, the annual production of terra preta is limited to 200 cubic metres, though Müller’s start-up may well show a way for production on an industrial scale. One and a half years after Greenport’s foundation, initial investments into production have been amortized, and Müller envisages the creation of a partner-network-system with branches across Switzerland. “Rented toilets are a market of billions. If we can have a small part of it, we’re satisfied”, he says.
The idea for Greenport was born seven years ago, when Müller bought a piece of land that had lost its topsoil – dead land, in other words. “I wanted to regenerate it within a reasonable time frame.” Müller did some internet research and came upon a dark, fertile soil that once upon a time had secured the livelihoods of the indigenous peoples in the Amazon basin: terra preta de índio – Indian black soil. A mixture of charcoal, compost, bones, fish bones, and human faeces. Müller became inspired and began experimenting. “We are profiting from know-how that had been built across thousands of years but later was lost.”
However, the sustainability cycle was still incomplete– what to do with the urine? The answer was found last year, at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) in Dübendorf, an offshoot of ETH Zurich. The institute launched a product called Aurin, a urine-based fertiliser, in February 2016. Greenport now provides the liquid raw material and Eawag takes care of the biological process. Ten litres of urine yield about 0.5 litres of high-quality plant fertiliser. “It was the one piece of the jigsaw puzzle that was still missing,” Tobias Müller says. And it helped create what is presumably the world’s most environmentally-friendly privy.