Zermatt Membrane Bioreactor (MBR): Case Study Switzerland

The chapter describes the membrane bioreactor (MBR) of the used water (wastewater) treatment plant in Zermatt, Switzerland. The plant is located in a man-made cavern and in 2013 required an upgrade and enlargement. To fulfill this objective, the treatment system was equipped with innovative MBR technology consisting of a denitrification tank, a downstream nitrification unit, and final membrane filtration. In view of the limited space in the cavern, the existing units were repurposed. Various optimization measures enable the MBR to achieve good contaminant removal results and it has proven to be a cost-effective solution that suits the restricted cavern space. The technologies presented are interlinked with other chapters, thus providing a complete picture of the treatment system. The respective denitrification and nitrification tanks provide extensive nitrate and ammonia removal, while membrane filtration is responsible for sludge retention. The MBR possesses two sludge recirculation lines, which ensures adequate contaminant removal. Within this configuration, sludge from the filtration tank is directed into the nitrification unit, while the denitrification tank is supplied with sludge from the nitrification basin. The lines can be adjusted individually, which results in a high degree of flexibility. This advantage is especially beneficial during peak tourism periods and weather changes, when up to tenfold load increases can occur. The formation of yellow sludge in the MBR system is an issue that has been documented for a number of years. This sludge type reduces the hydraulic capacity of the membranes and creates suspensions, which due to their poor settling properties are extremely difficult to remove. The various measures taken by ARA Zermatt to compensate for the negative impacts of yellow sludge are presented.