Extended freshwater filtration
From an overall point of view the Tofte site was the most suitable choice, however, the quality of the fresh water is not ideal. In order to secure good fresh water quality, it was decided to install a pre-treatment plant based on membrane filtration. The system chosen is shown in figure 8.
It is a spiral wound system with cellulose acetate UF/NF membranes, similar to what is used in many locations in Norway for treatment of river water. Some rivers in Norway like the ones in the Tofte area contain certain amounts of natural organic matter (NOM) and silt with contents that may vary considerably during the seasons. Prior to the UF plant there is installed a continuous operating belt filter with a 50 micron pore size of the belt to protect the membrane plant.
The installation of the membrane treatment plant for the fresh water has turned out to be very useful for testing various types of cleaning recipes both for facilitating the operation of the plant itself, but also for finding new alternative ways to clean the PRO membranes.
The seawater is supplied through water pipes from approx. 30 meter below sea level just outside the harbour. The pre-treatment is based on a simple 50 micron filtration system as shown in figure 7. Since the volumes of seawater to be treated are very large it has been very important to demonstrate that it is possible to operate the plant with minimal pre-treatment of the seawater.
The relatively low temperature of less than 10 degrees Centigrade is important in reducing the risk of bio fouling.