Symposium on Valuable Water

Friday, October 16th STOWA organized a symposium on “Valuable Water”. The main topic was the “Water factory” at Wilp: a new concept of municipal wastewater treatment in which not only various compounds (like nitrogen, phosphate and cellulose) are recovered from wastewater instead of being destroyed. Besides, also high-quality applications of the water itself become possible.

For some recovered compounds, like cellulose, innovative applications are being looked for. Instead of regular biological treatment, the treatment in Wilp is a physical-chemical treatment. The treatment consists of a coarse filter, a sieve for cellulose recovery, electrocoagulation, flocculation, dissolved air flotation, Nanofiltration, and ion exchange, and was implemented and tested by Royal Haskoning DHV. The idea is that such a treatment also should be possible on a small scale like a neighbourhood.

Apart from the Water Factory also some other pilot projects at WWTPs were shown, in which not the whole treatment is changed but an additional treatment is being tested: an NF pilot at WWTP Asten, producing water for the process industry and agricultural applications, a pilot on ozone/ultrasound treatment (for the degradation of pharmaceuticals), a PAC/Cloth filter pilot at WWTP Vinkel (a cooperation of several water authorities and the platform “Winnovatie”), the Ozone One Step filter at Waternet, and the ozone demonstration project at WWTP Wervershoof. One of the things that still has to be further investigated is the formation of by-products, like bromate.

All participants agreed that the recovery of nutrients and improvement of the effluent quality not only decreases the environmental impact but also offers new possibilities for (re)use and decreases the use of raw materials. Of course, this will cost some extra money, but the majority of the participants of the symposium were of the opinion that €20 – €45 per person per year would be acceptable if this means that the effluent quality is improved (80-95% removal of organic micropollutants) and reuse becomes possible. Which type of additional treatment would be optimum was not as clear: 28% of the respondents preferred oxidation processes, 25% adsorption processes, 24% filtration, and 23% said not to have any preferences.

The conclusion of the symposium was that additional treatment of WWTP effluent is considered very important and that more and more people accept the additional costs, as they also see the advantages. However, more research is required to find the optimum treatment processes for various sites. This is stimulated by means of e.g. the STOWA innovation program and the acceleration program.