Due to continual urbanization, an area covering 14 different municipalities in Sweden, North of Stockholm, is expected to grow from 600.000 to 1 Million inhabitants in the years to come. Despite of being a modern and technologically advanced water treatment plant, the current plant – The Görväln Water Treatment Plant, built in 1928 – does not have the capacity needed to serve 1 Million people.
So, to be on top of the future, Norrvatten, the local federation producing and distributing drinking water in the area, is considering two alternatives; to either design and build a brand-new plant or to expand and further modernize the Görväln Plant. Norrvatten has therefore engaged two teams of consultants to conduct feasibility studies on each of the two options, and Ramboll has been selected for the feasibility study on alternative one, the brand-new plant.
Building a completely new water works would allow Norrvatten to implement advanced water treatment processes that better can help Norrvatten deal with issues such as removal of potential organic micro pollutants in the surface water and the need for high-efficient treatment to handle the ongoing brownification of lake Mälaren water.
Three treatment alternatives are currently under investigation and evaluation. Two alternatives include chemical precipitation followed by either sand filtration in combination with ultrafiltration or stand-alone ultrafiltration.
Ultrafiltration is a relatively low-pressure membrane separation process for removal of suspended solids, bacteria and some viruses. The third alternative is based on Suspended Ion Exchange, a novel water treatment process developed by PWN Technologies in the Netherlands and implemented for treatment of Lake IJssel water at the PWN Andijk water works and in near future also at the Mayflower water works of South West Water in the UK.
“Ion exchange is a water treatment process technology commonly used for water softening or demineralization, but it can also be used to remove other substances from the water in processes such as dissolved organic matters. It is basically a chemical process in which unwanted dissolved ions are exchanged for other ions with a similar charge,” says Project Manager Susanne Forsberg from Ramboll’s global water division.
The feasibility study is conducted with valuable input from PWN Technologies in Holland, a company with world-leading expertise within ion exchange.
Each of the three process alternatives will be assessed through a process study, a technical design and an economical calculation. The feasibility study of modernizing the current plant is done in the same way, and so the two studies together give Norrvatten a good basis of decision.