WABAG is providing a membrane bioreactor (MBR) at Zermatt WWTP and biofiltration (BIOPUR®) at Meilen WWTP. The civil works for the biological stage at both sites started last year. The technical solutions being provided represent high-performance systems with a small footprint that match the particular requirements of the projects to perfection.
Membrane bioreactor (MBR) at the Zermatt WWTP
The existing biological treatment stage of the Zermatt WWTP was completed during 1982 in a tunnel system built in rock. Due to the loads, which in the meantime have increased massively, and new effluent requirements, as well as the age of the equipment, an extensive enlargement of the biological phase has become essential. Membrane biology has been shown to be the most cost-efficient solution as it can be realised without major adaptations to the existing civil works and also offers the option of further extension. Therefore, the world-famous tourist destination will soon have a highly advanced biological treatment system.
The new plant is to have a capacity of 60,000 PE and offer scope for enlargement to 75,000 PE, which will make it the largest membrane bioreactor plant in Switzerland. In order to not disturb operations during the extension, realisation will be completed in several stages, with the main work being carried out between the spring and autumn of 2011 and 2012. During this period one of the existing treatment lines will be modified for membrane filtration and then put into operation. Each of the new treatment lines will consist of two nitrification and two membrane bioreactor tanks. Hollow fibre membranes are to be employed for the filtration system.
The plant concept takes into consideration the need for both flexible operation necessitated by strong seasonal load variations due to tourism and optimised power consumption. Due to the extremely low alkalinity of the wastewater, the aim is to achieve a maximum denitrification rate, in order to minimise additions of lime, which is used to ensure the required residual alkalinity.
Biofiltration plant at the Meilen WWTP
Given the insufficient treatment performance and age of its existing infrastructure, the district of Meilen decided to extend and comprehensively rehabilitate the Meilen WWTP. Among the objectives to be met were a minimum footprint for the new parts of the plant and the stringent effluent requirements relating to the plant’s location on the shores of Lake Zurich. In view of these stipulations, a biofiltration plant with downstream tertiary filtration was put out to tender for the biological stage. The benefits of this solution include a small footprint, attractive architectural integration, cost efficiency and the possibility for a simple future extension for the elimination of micro-pollutants.
The new plant will have a capacity of 52,500 PE. The biofiltration unit has a two-stage concept with pre-denitrification (BIOPUR-DN) as a first stage and nitrification (BIOPUR-NK) as the second. Subsequently, the water flows through a WABAG tertiary filtration, which ensures adherence to the strict effluent stipulations relating to suspended solids (5mg/l) and phosphorous (0.2mg/l). The contact and reaction tanks located between the biofiltration and the filtration stages, which would be needed for the future treatment of micro-pollutants, are also to be installed now.
The whole plant will be roofed and have a footprint of approximately 30m x 45m. This area includes various, additional operational facilities and demonstrates the building’s compactness. Moreover, the covered design of the building and exhaust air treatment also mean that noise and malodourous emissions can be minimised. Commissioning of the new plant is scheduled for 2012.