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Ö-Klo: recovering valuable materials by composting toilets

The Freiburg-based start-up company Ö-Klo leases composting toilets and is committed to the recovery of human urine and faeces. The young Ö-Klo entrepreneurs believe that reviving natural material cycles of soil, plants, food and excreta is crucial in times when natural resources such as phosphorus are dwindling. The potential is enormous, but there are still some technical, social and political hurdles to overcome.

The utilisation of human waste is a taboo topic. Ever since the invention of water closets and wastewater treatment plants, our nutrient-rich waste has been combined with domestic wastewater, industrial wastewater and surface water from streets and buildings into a more or less toxic broth in sewers that remain out of sight, out of mind. The liquid phase of this mixture is cleaned in sewage treatment plants using processes that consume huge quantities of energy. The resulting solid phase has a high contaminant load, to the extent that applying such solids on fields will soon be completely banned, and sewage sludge will have to be burnt in incineration plants instead.

Producing artificial fertilisers for use in agriculture is a complex and costly process. We use huge quantities of clean drinking water to dispose of our excrement. Human excrement contains many valuable nutrients, which are completely destroyed when wastewater undergoes treatment in energy-intensive, water-borne sewage systems. "This is an incredible waste of resources,” says Florian Augustin from Ö-Klo.

Ö-Klo toilet cabins are fully recyclable and stand in rows, thus saving material and space. In 2017, Ö-Klo set up hygienic, chemistry- and odour-free sanitary systems at events with attendance figures of up to 10,000 people. © Ö-Klo GbR

Ö-Klo has subsidiaries in the city of Freiburg im Breisgau and in the Schloss Tempelhof eco-village close to the city of Crailsheim in Baden-Württemberg as well in the city of Eberswalde in Brandenburg where it leases and sells environmentally friendly dry toilets. The company has set itself the task of reviving the natural nutrient cycle. The mobile toilets are modular and have so far mainly been used at music festivals in southern Germany. The toilets are delivered with sawdust to bind odours, and a screen system for separating liquid from solid matter. “Feedback from the users of our toilets is very positive,” says Cornelius Patzer, Ö-Klo’s marketing and networking activities manager. He adds: "People find it hard to believe that the toilets do not stink." Ö-Klo is not just looking at providing a sustainable and user-friendly alternative to chemical toilets. Another major objective is to advance the recovery of urine and faeces.

Compost pioneers

High microbial activity in the compost consisting of a mixture of sawdust, straw and faeces generates high temperatures. Temperatures of up to 72 °C render the material hygienic. © Ö-Klo

We are in the village of Breisach near Freiburg im Breisgau. It is a beautiful autumn day and we are visiting the local composting plant, where an excavator is shifting a compost pile the size of a garage. The compost contains the contents of the collection bins of 35 Ö-Klo toilets with the deposits of thousands festival goers in southern Germany. A fan is blowing air through a flexible tube into the steaming compost. Optimal oxygen supply in hot compost piles (thermocomposting) ensures that bacteria and natural metabolic processes are particularly active. Temperatures in the compost pile temporarily rise to 72 °C, killing pathogens such as salmonella or worm eggs. As the pile slowly cools, microorganisms, fungi and compost worms turn the compost into humus within about three months.

A crucial issue: the German Fertiliser Ordinance

Ö-Klo has been operating since September 2017 and is Germany's first commercial operator of a composting plant for solids from composting toilets. However, for the time being the resulting humus cannot be used as agricultural fertiliser as the contents of composting toilets do not feature on the German Fertiliser Ordinance positive list. "This is a drawback and the reason why the compost produced in Breisach needs to be combusted,” says Patzer. The Ö-Klo makers are in close contact with the Baden-Württemberg Ministry of the Environment, Climate Protection and the Energy Sector, the German Federal Ministry of Agriculture and the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety and are hoping to get the go-ahead to use the compost for fertilising gardens and other spaces.

In his bachelor thesis entitled "Practical guide to refining human excreta", forest scientist Augustin described various methods for sanitising faeces and urine, including lactic acid fermentation, pyrolysis, thermocomposting and drainage using osmotic filtration. Further research is still required to assess the risks of drug residues. A research project is to be carried out with the Institute for Urban Water Management, Water Quality and Waste Management (ISWA) in Stuttgart to study how the degradation of pharmaceutical residues by way of lactic acid fermentation and thermocomposting compares to their degradation in conventional sewage treatment plants.

Huge potential

Human excreta have the potential to be used for producing valuable humus or so-called black earth or “terra preta”, a process used by Amazonian Indians for centuries. For this purpose, vegetable carbon, organic waste and human faeces are composted together. Human urine has the potential to be a high-quality fertiliser or even fuel. Every human individual excretes on average 1.4 litres of urine per day. Augustin’s thesis comes to the conclusion that if all the urine in Germany could be collected separately and returned to the nutrient cycle, this would help replace 17% of all synthetic nitrogen fertilisers, 21% of mineral fertilisers made from rock phosphate and 25% of the current amount of potash fertiliser used.

Outhouse revolution in Switzerland

A look at what’s happening in Switzerland shows what the future of human excreta could look like in practice. Like Ö-Klo in Germany, a company called Greenport.ch GmbH from the Swiss city of Kreuzlingen leases composting toilets for events and works closely with Eawag, the Swiss Federal Institute of Aquatic Science and Technology, which is part of the ETH Zurich. The so-called “Aurin Recycled Fertiliser" has been in use since February 2016. The combination of biological stabilisation (nitrification), activated carbon adsorption and vaporisation turns 1000 litres of urine into 50 litres of liquid fertiliser (1). According to Eawag, the fertiliser contains all the nutrients plants need for growth, including nitrogen, phosophorus and potassium, as well as a multitude of trace elements such as iron, zink and boron. Aurin is authorised by the Swiss Federal Office for Agriculture for use as fertiliser for flowers, ornamental plants and lawns (2).

Eawag and Greenport have already established a practical way of using solid human excreta. For the past two years, Zurich Zoo has used Greenport’s black earth (terra preta) as a fertiliser in its Masoala rainforest hall. The extremely fertile soil substrate is generated through pyrolytic decomposition of a mixture consisting of compost, activated carbon and human faeces. “We planted this banana grove two years ago and have used terra preta to fertilise it. The banana trees have since grown up to four to five metres tall. And they also bear fruit. We are so excited about this success that we are also using terra preta in other areas,” writes the Swiss Radio and Television (SRF) on its website, quoting the zoo’s senior biologist Martin Bauer (3).

The core Ö-Klo team still fits into a single toilet cabin. Top row from the left: Anna Calmet, Johannes Hölzel, Florian Augustin; bottom row from the left: Stefan Krajci, Cornelius Patzer. © Ö-Klo

Company motto: “Thinking nutrients anew!“

Ö-Klo would also like to integrate plant carbon into the composting process that produces black earth. However, as long as the legal situation with regard to using black earth as fertiliser on fields remains unclear, the company has to put such experiments on the backburner. Closing the natural nutrient cycles has enormous potential. However, a number of technical problems need to be solved before large-scale implementation is possible. The greatest challenges are the social taboos that have to be overcome and the legal conditions that have to be put in place.

Sources and references:

(1) http://www.vuna.ch/
(2) http://www.eawag.ch/de/abteilung/eng/projekte/aurin-duenger-aus-urin/
(3) https://www.srf.ch/news/schweiz/mobile-plumpsklos-als-oekologische-revolution


Augustin, Florian (2017). Praktischer Leitfaden zur Veredelung menschlicher Exkremente. Eberswalde University of Sustaiinable Development (HNEE), Bachelor thesis, Faculty of Forest and Environment

Website address: https://www.biooekonomie-bw.de/en/articles/news/oe-klo-recovering-valuable-materials-by-composting-toilets