Ion exchange for NOM removal in drinking water treatment

Ion exchange resins have found an increasing application in the drinking water treatment sector over the last few decades. The ion exchange resins have a positive ability to remove the charged natural organic matter (NOM). To apply this process in full-scale treatment, the most suitable resin has to be selected and the hydraulic behaviour of the treatment process must be known. This study has the purpose to study the NOM fractions removal with different resins and select the most suitable resin for NOM removal of the Weesperkarspel water. Another purpose is to study the hydraulic behaviours of fluidized ion exchange and testing of the fluidization models of Ergun and Richardson-Zaki. The thesis study is characterizing NOM into the specific fraction and later observing the removal of each fraction with the different ion exchange resins. The kinetic and the equilibrium of NOM removal of each resin are also studied. Four ion exchange resins are tested (Lewatit VP OC 1071, Purolite Macronet 200, Duolite A7 and MIEX DOC). The ultraviolet absorbance method (UV), dissolved organic carbon detection method (DOC), specific ultraviolet absorbance (SUVA), fluorescence excitation emission matrix (fluorescence EEM) and liquid chromatography-organic carbon detector method (LC-OCD) were applied. Weesperkarspel water contains a high degree of aromatic NOM fractions, mostly in the form of humic substances. The Lewatit VP OC 1071 is the most suitable resin for removal of NOM in general view, especially aromatic NOM and humic substances fractions. It appears to be removed as high as 65% and 94% respectively. The MIEX DOC removed 57% aromatic NOM fraction and 70% of humic substances. The pH was found as the dominant parameter for the NOM removal by the weak base Duolite A7. In normal raw water (pH = 7.8), this resin is almost ineffective while it can remove the aromatic NOM up to 35% and humic substances fraction of 45% in raw water pH adjusted to 5. The sorbent Purolite Macronet 200 can remove only biopolymers and neutral NOM fractions. Adsorption is an important mechanism for the removal process of high molecular weight NOM fractions and the neutrals fractions. By using the linear driving force model (LDF) to describe the ion exchange rate of the resin, it was found that MIEX DOC resin can remove NOM faster than other resins. The LDF- k constant of MIEX DOC is also higher than other resins. MIEX DOC has the smallest resin bead size. This can be the reason for the fast removal of NOM. The resin exchange capacity is related with the Freundlich constant K and n . Increase of K and n values lead to increase of exchange capacity. The Lewatit VP OC 1071 has the highest K and n values and thus the highest exchange capacity. The exchange rate and exchange capacity is a specific property of each resin. With help from the LDF model and Freundlich isotherm the breakthrough curve can be determined. The Lewatit VP OC 1071 has longest running time compared with the MIEX DOC and Duolite A7 due to the highest exchange capacity. The hydraulics behaviour of fluidized bed ion exchange has been investigated with the strong base gel resin Lewatit VP OC 1071. The temperature and the feed velocity influence the expanded behaviour. The wet density and wet porosity are important parameters for the model prediction. Combination of mathematical modelling of ion exchange and the treatment conditions of Weesperkarspel drinking water treatment plant, the fluidized ion exchange process can be designed. For Weesperkarspel drinking water treatment plant, the aim is to decrease the DOC concentration of 7.2 mg C/l to 3.0 mg C/l with the fluidized ion exchange process. The 20 fluidized ion exchange reactors with a height of 9 m, 10 m2 of resin bed surface area, a bed height of 2 m and a feed velocity of 20 m/h are designed. The reactors consist of 4 groups, each group is started with delays of 15 days. With this operational step, the running time of each reactor is 60 days. The cost is estimated 11-euro cent per m3 treated water.Sanitary EngineeringWatermanagementCivil Engineering and Geoscience