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The municipal wastewater treatment plant in Yverdon-Les-Bains, Switzerland, is a conventional facility serving 32,000 counterparts of the population. It is based on essential sedimentation, the sludge treatment process and clarification.
It is the first plant in the country to install a stripping membrane system for nitrogen recovery. Using a polypropylene membrane, the system removes nitrogen from the rest of the wastewater after initial effluent treatment. By removing nitrogen in this way, plants can both reduce their nitrogen emissions in nearby streams and produce a high quality liquid fertilizer.
Two master's students at EPFL chose to take an interest in the Yverdon-Les-Bains wastewater treatment plant for their semester project. They wanted the nitrogen recovery process to be progressively better by increasing the nitrogen concentration of the fertilizer to over 40 g / L, which would reduce the cost of storing and shipping the fluid.
Based on the principle of the osmotic distillation technique, they have developed a specific method for nitrogen that could be integrated into existing wastewater treatment processes.
Hames said: "Osmotic distillation has the advantage of being able to concentrate the fruit juice at room temperature, which means that its taste and nutritional properties remain intact. In osmotic distillation systems, a hydrophobic porous membrane pbades through gaseous compounds such as steam but not liquids. The motive force is generated by a partial difference in vapor pressure between the two fluids separated by the membrane. This is the same mechanism we used to concentrate nitrogen in the liquid fertilizer. "
Students tested their new osmotic distillation method in a pilot unit provided by Membratec, a company based in Sierre that is developing membrane technology for wastewater treatment. The group consisted of two 25 L wastewater tanks, two metal pumps and two cylinders containing an extraction membrane. They tested the closed loop system with a fluid of the same composition as the fertilizer supplied to the Vaudois farmer.
Ott said, "I liked the trial and error aspect of the project and the opportunity to discuss our progress week by week with a Membratec engineer. It was nice to take a break from clbad and spend the day doing laboratory experiments. And it was motivating to know that there could be a concrete application for the work we were doing. "
Students were not the only ones to benefit from the project. Christophe Bonvin, who oversaw their work at Membratec, saw it as a win-win experience: "We enjoyed coaching students. It's amazing how much students can contribute when they are motivated and well guided, and when the scope of their projects is clearly defined. "
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