If the banana trees at Zoo Zurich are particularly lush, it is thanks to a fertiliser with an unusual ingredient: human waste. During spring in 2016, zoo employees cleared a bamboo grove in Zurich’s Masoala Rainforest to plant the trees.
Within a few months, the saplings had reached an impressive height and produced a cornucopia of yellow fruit.
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 company that provides Zoo Zurich with the fertile substrate is Greenport, started in 2015 by four friends. “We wanted to break some taboos with our products,” said Mr Tobias Mueller, a former carpenter and inventor.
To obtain the raw material, the start-up team developed a mobile dry toilet, the Greenport.
The human waste drops into a container, which Team Mueller 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 degree Celsius, destroying toxic germs, viruses and hormones but leaving nutrients, trace elements and water intact.
The process yields charcoal (biochar) with a high storage capacity, and this extracts toxic substances from the soil and returns water or carbon dioxide to it.
The biochar is supplemented with compost and soil organisms to obtain terra preta.
Greenport practises in miniature what science has tried to work out on a much grander scale: How to recover valuable substances from sludge.
For the moment, the annual production of terra preta is limited to 200 cubic metres, though Mr Mueller’s start-up may well lead the way for production on an industrial scale.
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Source: The Straits Times, 24 June 2017