Wastewater is considered to be of no use quite wrongly! Washing water has an average temperature of 30°C. Toilet water might not only be used to produce biogas or fertilizers, but also valuable resources that otherwise would enter the sewer system unused. And even worse: Annually, more than 2 million people die from diarrheal diseases due to the wrong use of wastewater. Experts of the “Water-Energy Group” of Karlsruhe Institute of Technology (KIT) study possibilities to eliminate these problems.
Caution, no drinking water. Only 0.3 percent of the water on the Earth’s surface is suited for use as drinking water. KIT scientists study possibilities of improving wastewater use.
“With that in mind, wastewater is no waste. It contains thermal energy, chemical energy in the form of carbon compounds, and valuable plant nutrients. Now, we have to develop processes for the use of these resources,” Helmut Lehn of the Institute for Technology Assessment and Systems Analysis (ITAS) says.
Waste heat of domestic wastewater, for instance, might be used with the help of heat exchangers in sewage pipes.
“And it is even more effective to use the warm wastewater from the washing machine and the bathroom directly in the house for preheating fresh water for the shower,” Witold Poganietz adds, who heads the research group together with Lehn. Such a system already is in operation in a housing block in Berlin.
A major prerequisite for the intelligent use of wastewater is the separation of wastewater flows from the toilet (black water) and from the bathroom and kitchen (grey water), Lehn continues. If feces were removed separately and undiluted by using e.g. vacuum toilets as on airplanes or ICEs three liters of biogas might be produced from one liter of wastewater.
“Adding biowaste might even increase the energy yield and the organic waste bin would no longer be required,” Lehn says. And he adds: “Urine is an ideal fertilizer, as it contains nitrogen, potassium, and phosphorus.”
As the latter is considered a non-renewable resource that is supposed to run short even before coal and petroleum, studies concentrate on recovering it from municipal wastewater and sewage sludge. This might also help reduce the demand for artificial fertilizers, whose production requires much energy.
According to Franka Steiner, ITAS, the existing infrastructure will continue to require complex cleaning of mixed wastewaters, whereas separation of wastewater flows might be implemented easily in development areas, where new houses are built. This also applies to growing metropolitan areas in threshold and developing countries.
“Here, sanitary systems are often lacking completely,” the geoecologist says.
All over world, she advises municipal administrations in the planning of wastewater systems. A separation system that produces both energy and nutrients from the wastewater of several thousand inhabitants is being tested by the city of Hamburg in a conversion area. This project is observed by ITAS researchers with high interest.
Many of the more than 2 million victims per year are children living in developing countries, Lehn says. For comparison: In 2015, about 440,000 people died from malaria (half as many as 15 years before) and 1.1 million people died from AIDS. ITAS researcher Lehn thinks that one reason of the increase in fatal diarrheal diseases is progressing urbanization with more and more people living in densely packed urban slums without hygienic wastewater treatment.
Karlsruhe Institute of Technology. Posted: Mar 23, 2017.