Some waters can have elevated concentrations of dissolved organic carbon (DOC), especially sources like surface waters that are under the influence of secondary effluent, recreation, heavy population, farming and industry. In a number of locations in north-west Europe, for example the United Kingdom and Scandinavia, DOC levels are increasing over time, most likely due to climate change effects and changes in land use. For these types of water, ion exchange (IX) is of interest as a pre-treatment option because the removal of colour and DOC by IX will increase the efficiency of all downstream processes, including: coagulation, membrane filtration, advanced oxidation processes (AOP) and granular activated carbon filtration (GAC). It will also lead to improved water quality (i.e., less by-product formation) and most likely improvements in biostability within the distribution network. Surface waters also contain suspended and colloidal matter, making it nearly impossible to use standard state-of-the-art, fixed bed IX columns. This is because these beds will foul quickly (i.e., head loss build-up) with suspended matter. When this happens, the IX bed starts to function as a filtration bed rather than as an adsorption media. The newly developed suspended ion exchange process SIX® (suspended ion exchange, PWN Technologies, Netherlands) presents an advanced solution for a world-wide challenge: how to remove natural organic matter (NOM/DOC) as a first step in surface water treatment to improve the efficiency of downstream processes and water quality. In addition to the possibility to treat water that contains suspended matter, another advantage is that the process has advanced to an economically and technically feasible process, requiring low contact times and small resin inventories, with a large tolerance for flow fluctuations. Depending on the water source, adding a relatively low concentration of coagulant after IX removes even greater quantities of DOC, especially in the fraction of the high molecular weight organic carbon (whilst the IX primarily removed the humic and fulvic organic fractions). The most important advancement is that almost any commercially available resin can be used, creating the desired flexibility in resin suppliers for water supply companies. This paper describes the process and its advantages and disadvantages compared to conventional technologies. NOM-characterisation with size exclusion chromatography, liquid chromatography – organic carbon detection (SEC/LC-OCD) before and after this process showed the outstanding performance of the process, especially on water types which contain high colour/DOC-concentrations and low total dissolved solids, which are typical of the majority of the surface waters in the north-west of Europe.

This paper reviews the progress that has been made during the last four years within the research facilities of PWN. This has resulted in a new pre-treatment process for the direct treatment of water containing high amounts of suspended matter, dissolved organic carbon and nitrate, such as surface waters, based on ion exchange (SIX®) and ceramic microfiltration (Ceramac®). This paper specifically reviews the results of a performance evaluation that has been made of this new pre-treatment process in comparison with conventional pre-treatment techniques, in this case enhanced coagulation followed by rapid sand filtration. Based on the outcome of this study a new treatment facility has been designed with these new processes which will be operational in 2013 with a capacity of 5000m3/h, this comparison study however is based on a maximum capacity of 4000 m3/h. This new pre-treatment leads to a superior water quality, reduced energy consumption, less waste and a smaller carbon footprint.

The history of ion exchange is marked by many important milestones, notably the development of novel polymeric materials and considerable advances in our understanding of the underlying fundamental principles. Separately, there have been major advances in the design and development of the apparatus and equipment required to perform industrial ion exchange and also for large scale applications in the production of drinking water, like the MIEX® process from Orica. This paper reviews the progress that has been made during the last three years within the research facilities of PWN which have resulted in a new ion exchange process for the direct treatment of water containing high amounts of suspended matter such as surface waters. This new process has been called SIX® and will most likely be operational at a flow of 4000 m3/h by 2012.

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In the context of the development of the SIX© Ion exchange process, the Dutch water company (PWN) decided to investigate options for treatment of the brine arising from the regeneration of the resin. Main goals for the brine treatment are volume reduction and product recovery (water + NaCl). In this regard a biological denitrification (DNF) aiming at total nitrate removal followed by a nanofiltration (NF) aiming at ion separation (monovalent/bivalent) focused on NaCl re-use were implemented on a pilot scale recovering 80% of the total SIX brine (implying 80%recovery of NaCl). Further NF concentrate minimization and Sodium Chloride reclamation would allow a reduction of the disposal fees and chemical uses and therefore largely increase the overall process sustainability. During operation on a pilot scale with a capacity of 250l/h, the Dynamic Vapour Recompression (DVR) technology has proved itself to be capable to reduce the raw regenerate another 6 to 10 times reaching meanwhile the solubility limits of NaCl and other salts making their recovery on a solid stream possible. The condensate that resides after DVR treatment is low contaminated and is therefore suitable for re-injection upstream the SIX pre-treatment process. Laboratory scale evaporation tests showed that salts would precipitate according to the following order: BaSO4 >BaCO3 > MgSO4 > MgCO3 >CaCO3 > CaSO4 > Na2CO3 > Na2SO4 and NaCl. A sequenced thickening by DVR treatment leads to selective precipitation of BaSO4, BaCO3, MgCO3, CaCO3 and CaSO4 at concentration factor around 8 but beyond a CF of 10 it leads to a more or less simultaneous precipitation of NaCl, Na2CO3 and Na2SO4 without fouling/clogging problems of the DVR. A reuse of a heterogeneous (co)precipitate solid fraction is difficult; however this problem could be countered by further investigation on a temperature controlled precipitation of Na2CO3 and Na2SO4. Cooling down the DVR brine saturated in dissolved sodium chloride, sulphate and bicarbonate to a temperature of 5 °C increases solubility differences between sodium chloride and its two contaminants, making their separation possible.