Membrane water softening and desalination - Membratec

Membrane water softeningand desalinationMembrane separation processesWater treatment systems

Membrane water softening and desalinationFeedConcentrateProductPermeatecarrierGlueReverse osmosis skid Spiral wound module configuration Detail of pressure vesselMembrane technologyMembrane technology allows the rejection ofanything down to simple ions such as Na + and Cl - .A number of treatment applications are thereforepossible in the municipal and industrial waterfields.Water softeningWater softening (e.g. hardness and sulphateremoval) using membrane filtration processesrepresents an interesting treatment application forimproving the quality of fresh water. Watercontaining high amounts of sulphates or calciumcan be satisfactorily treated thanks to the very fineporous structure of the membrane, which,depending on the chosen pore size (smaller poresrequire a higher applied pressure), allows a 94%to 99% rejection.Disinfection by-product precursors removalDisinfection by-products (DBPs) are a major targetcontaminant and they are formed when naturalorganic matter (NOM) in drinking water reacts withchlorine or other chemical oxidising agents.Reverse osmosis and nanofiltration membranescan reject more than 90% of the DBP precursorsfrom surface and groundwaters with a high organicload.DesalinationSeawater and brackish water treatment are themost common applications of reverse osmosis inthe municipal water field. With the introduction ofspecially designed energy recovery systems,modern plants are becoming more cost efficientthan traditional desalination methods such asseawater distillation.Reverse osmosis and nanofiltrationThe most selective filtration technique is definedas reverse osmosis (RO), whereas nanofiltration(NF) pores are typically larger than the reverseosmosis ones, thus allowing to differentiatebetween desired and undesired raw waterconstituents.As particle-free water (< 1 NTU) is required forboth RO and NF, pretreatment steps such as sandfiltration or ultrafiltration (UF) are often necessary.Membrane material and configurationReverse osmosis and nanofiltration membranesare often made from cellulose acetate orcomposite polyamides. In the most commonconfiguration, 1m-long spiral-wound elements areinstalled in pressure vessels (up to eight elementsper vessel).Compactness and modularityAn advantage of all membrane processes is thecompactness of the treatment plants, which canbe easily extended thanks to their modular design.Applied pressure and power consumptionExternal pressure is applied to the saline solution,so that water can flow by diffusion from a moreconcentrated saline solution through thesemipermeable membrane to the permeate side.The operating pressures depend on the quality ofthe raw water and on the type of membrane:• Softening of fresh water: 8 – 15 bar• Brackish water desalination: 15 – 25 bar• Seawater desalination: 40 - 80 bar (modernplants equipped with energy recovery systemshave a power consumption of 2 – 3 kWh/m 3 ).For all problems related to water treatment,Membratec can offer an integrated membrane solution adapted to your needs.membratec TECHNO-Pôle 3, CH-3960 Sierre, Tel. ++41 (0)27 456 86 30, Fax ++41 (0)27 456 86 34E-mail: info@membratec.com, Internet: www.membratec.com