>95% recovery RO with Optiflux®
Introduct ion Commonly known Nanofiltration and Reverse O smosis systems typically work at recoveries between 75-85% and in a flux range of 20-30 l/(m2.h). This common design range is defined by (prevention of) scaling. When fluxes and/or recoveries become to high, precipitation of bivalent ions will occur on the membrane surface (e.g. BaSO 4, CaCO 3, CaSO 4). Another disadvantage of this common design is the high concentrate loss. This concentrate can not be used and needs to be disposed. When anaerobic Nanofiltration or RO is implied, treatment of the concentrate before disposal is necessary in order to prevent negative effects on s urface water flora and fauna (oxygen demand of un-oxidised iron). It is commonly known that concentrate treatment, transport (to discharge point) and discharge c an be responsible for 2040% of the total annual costs! IERO (Ion Exchange - RO): higher re covery, highe r f lux Vitens and DHV however, believe that they can contribute in this field by minimising the concentrate discharge and operation costs at the same time. By removing all positive bivalent ions before entering a Nanofiltration or Reverse O smosis membrane it is possible to make operation of the membranes more efficient while scaling danger is totally eliminated. Removing of all bivalent cations can easily be achieved by Cation Exchange. The membrane system can now be operated at much higher recovery (>95%) and much higer flux (40-60 l/m2.h). This concept of combining Ion Exchange – NF/RO is called IERO . Benef its of IERO The IERO concept has many benefits: Minimising capital costs (high flux) Minimising water use (high recovery) Minimising concentrate discharge Minimising pre-treatment c osts No antiscalants needed IERO: only possible wit h Opt if lux® O peration at high flux, needs a different hydraulic design. T he current hydraulic design (6 elements in series in pressure vessels) would give an unequally flux over the different membrane elements . At the present low fluxes of about 20-30 l/(m2 .h), hydraulic losses are already 1-3 bar per vessel. As hydraulic loss ~ flow2, a higher flux will give a dramatically increase of the hydraulic losses up to 4-5 bar per vessel! Consequently, success fully optimisation of flux and recovery of N F/RO is not possible without the O ptiflux ® c oncept.
The Optiflux® pressure vess el offers a clear advantage in the IERO concept! IERO at WTP Engelse Werk In future the capacity of NF/RO at Engelse Werk possibly needs to be expanded. For this reason the c urrent installation is already prepared to use IERO . Used materials for housing, piping and piping connections can resist a higher feed pressure (up to 20 bar). D iameters and pumping capacities are also suitable for operating at higher pressure and capacities.
Conventional design Feed 100% NF Product 80% Concentrate 20% IERO-concept Feed 100% IEX
Ion Exchange: regenerat e solut ion Vitens and DHV have developed and investigated this IERO -concept. Specific field of investigation was the reuse of salt. The Ion Exchange columns for cation removal need to be regenerated by a 10% NaCl solution. The spent regenerate contains high levels of bivalent positive ions, but it also contains a remaining Na concentration (ca. 50%). By treating spent regenerate with dead-end NF or Electro Dialysis (ED) over 80% of Na in spent regenerate can be s eparated for reus e, thus reducing total s alt cos ts of the I on Exchange by 40%!
NF/RO
Product 97%
IERO is a patented concept, developed by Vitens and DHV Water
Concentrate 3%