Recent commissioned Vitens NF and RO treatment plants are provided with the Optiflux® stack configuration. Aim of the Optiflux® concept is to optimize the permeate flow in RO/NF plants by minimizing hydraulic pressure losses and the osmotic pressure difference across the membrane surface. An increase in permeate productivity of 20% can be achieved, for both NF and RO membrane filtration systems, by lowering the number of membrane modules per pressure vessel to three, which leads to lower hydraulic pressure losses.
In one pressure vessel of 6 elements with 3 elements in each side and a center port in the middle; the feed water flows in the two directions (each side of the pressure vessel) and passes through the 3 elements of each side and the retentate is collected in the center port and feeds the second stage with the same principal. The permeate flows via the center tube of the spiral wound membranes and is collected in the permeate tank. The first full scale plant of 320 m3/h based on this concept is already commissioned at the 20th November 2006 at Vitens drinking water treatment plant Dinxperlo in The Netherlands.