Sorption of Natural Organic Matter by Adsorber and Ion Exchange Resins Investigations with Starch and Phenylalanine as Model Substances

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1 Berlin, September 8-, 8 Sorption of Natural Organic Matter by Adsorber and Ion Exchange Resins Investigations with Starch and Phenylalanine as Model Substances Madlen Pürschel and Volker Ender University of Applied Sciences Zittau/Görlitz (FH) MPuerschel@hs-zigr.de Demineralisation plants of power stations are not able to remove organics in all cases to a satisfied degree. The present work focuses on natural organic matter (NOM) and its interaction with anion exchanger and adsorber resins to optimize organics uptake. In this study, four different starches (one of them 4 C-labeled) with different molecular size distributions and L-phenylalanine (L-Phe) were selected as model substances for the high-molecular-weight biopolymer fraction of NOM and the low-molecular-weight neutral/amphiphilic one. Their uptake by various ion exchangers and adsorbers was measured in column experiments. Results were discussed in terms of size exclusion, anion exchange, adsorption, and hydrophilic/hydrophobic repulsion. In summary, at neutral ph, starch has been removed preferably by size-exclusion followed by adsorption, whereas ion exchange resins show higher uptake capacities than pure adsorber caused by stronger attraction between starch and polar functional groups of the ion exchangers. At acidic ph, the uptake of sulphate, as competitive adsorptive, leads to an earlier starch breakthrough at ion exchangers. Therefore, adsorbers are more effective. For L-Phe, ion exchange is the main uptake mechanism. It was found for both organics that the higher the water content of the resins, the more effective the uptake is. Introduction Limited removal of natural organic matter (NOM) from raw waters by demineralisation plants leads to a certain rest content of organics in steam water cycles of power stations. These organics are considered to be a potential corrosion risk because of their decomposition to low-molecular-weight acids and carbon dioxide. Therefore, a limit of ppb of total organic carbon (TOC) in the makeup water is recommended (VGB guidelines []). Huber [] has presented 7 makeup waters of power stations with a range from to 3 ppb TOC. 6 % of these sites were within the limit of ppb. A lot of different methods and materials were used to eliminate NOM, among them polymeric ion exchangers [3-7], adsorber resins [8], magnetic ion exchange resins [5], activated carbon [9], granular ferric hydroxide [], biologically active filter [] or reverse osmosis []. Ion exchange resins - especially the anion exchangers are of greatest importance in makeup water treatment plants in power stations, since they are able to remove NOM to the above mentioned limit in the majority of cases. Thereby, the uptake capacities were mostly influenced by polymer composition (polystyrene or polyacrylic), porosity, and charged functional groups of the resins. However, it was difficult to assess the impacts of raw water composition, NOM characteristics, and ion exchanger and adsorber properties on the NOM removal quantitatively. As a pre-condition for that, more knowledge about the mechanisms of NOM uptake (ion exchange or adsorption) is necessary. Deeper insights were achieved by introduction of the liquid chromatography organic carbon detection (LC-OCD) method by Huber and Frimmel [3]. So, investigations by Huber and Gluschke [4] have shown that NOM with low charge densities cannot be removed by ion exchange resins in satisfied quantities. Following the LC-OCD classification, these fractions are hydrophobic organic carbon (HOC), biopolymers and neutrals/amphiphilics as well as particulate organic carbon (POC). Own investigations [5] have revealed that about 5 % of the remaining TOC in the makeup water comes from HOC/POC, compared to one fifth in the input water. More than 8 % of the remaining chromatographic detectable organic carbon (CDOC) consists of the fraction of polysaccharides and neutrals/amphiphilics. Thus, these NOM fractions have the highest potential for further studies to increase the TOC uptake in water treatment processes. The present work continues previous investigations [6] to the uptake mechanisms and focuses on the relations between specific NOM fractions (chemical type and size) and ion

2 Berlin, September 8-, 8 exchange/adsorption. For this purpose, four types of starch (one of them 4 C-labeled) with different molecular sizes (analysed by ultrafiltration) were selected as model substances for the highmolecular-weight biopolymer fraction, and their uptake by ion exchange and adsorber resins was measured in column experiments. The use of 4 C- labeled starch together with inactive starch allows to study the behaviour of both smaller and larger starch particles in only one experiment. Besides, the use of a radioactive tracer improves the detection limit. Furthermore, the uptake of L- phenylalanine (L-Phe) as a model substance for the low-molecular-weight neutrals/amphiphilics was investigated. Experimental Details Adsorptives Three types of inactive starch (Chemapol, Riedel dehaën, Merck) and L-Phe (Roanal) were used in analytical grade. 4 C-labeled starch comes from Biotrend as uniform C-labeled product (34 mci/mmol =.58 GBq/mmol). All TOC solutions were prepared with millipore water from Millipore Elix/Milli-Q Academics (TOC < ppb). Analytical grade sodium hydroxide and sulphuric acid were used for ph adjustment (ph.5 equals to 4 ppm sulphate). The model substances were checked with the LC-OCD method (Table ). Table shows that, at neutral ph, all starches are mainly identified as biopolymers. But, the Chemapol starch presents higher amounts of other LC-OCD fractions (especially POC), too, related to a broader distribution of molecular weights. On the other hand, Riedel dehaën and Merck starches have dominant parts of the biopolymer fraction (96 and 94 %, respectively) at neutral conditions, indicating that these starches have lower median molecular weights than the Chemapol starch. Compared to neutral conditions, the percentage of the neutral/amphiphilic fraction of the Chemapol starch arises from 7 to 9 % at ph.5. The same result was obtained for Merck starch (arising from to 9 %). These classification changes may be related to an acid hydrolysis reaction following by a degradation of high-molecular-weight starch molecules to smaller ones. Further, LC-OCD results verify that L-Phe belongs - as expected - to the fraction of neutrals/amphiphilics at all ph conditions. Adsorbents Ion exchange and adsorber resins were obtained from Rohm and Haas Co. (Philadelphia, USA), Bayer AG (Levercusen, Germany) and Purolite (Bala Cynwyd, USA). Table gives an overview of the tested ion exchange resins. Water retention and total volume capacity are obtained from product data sheets of the manufacturers. Adsorber resins characteristics are presented in Table 3 based on product data sheets, too. Procedures Cleaning of the ion exchange and adsorber resins The cleaning procedure of the resins include several steps of washing with millipore water, rinsing with N NaOH and.4 N HCl, respectively, and final washing with millipore water until the starch background value was less than.3 mg/l (details here not described). For L-Phe experiments further cleaning steps (threefold shaking ( h) with. N NaOH, treatment in a soxhlet reactor first with methanol, second with acetonitrile (each for 4 h), rinsing with millipore water) had to be applied, since L-Phe background after the standard cleaning procedure was still unsatisfying. Finally, the background value was less than. mg/l. Table : LC-OCD results of the model substances at different ph. (for Chemapol starch and L-Phe median value ± standard derivation in % based on three measurements; for Riedel dehaën and Merck starches single measuring) Model solution POC [%] HOC [%] Biopolymer [%] Neutrals/ Amphiphilics [%] Chemapol starch (ph 6) ± 4 ± 5 69 ± 7 7 ± 4 Chemapol starch (ph.5) 6 ± 6 5 ± 39 ± 5 9 ± 7 Riedel dehaën starch (ph 6) 6 94 Merck starch (ph 6) 4 96 Merck starch (ph.5) 85 3 L-Phe (ph 6 and ph.5) about

3 Table : Properties of the tested ion exchange resins. Resin Matrix Functional group Structure PREPRINT ICPWA XY Berlin, September 8-, 8 Water retention [%] Total capacity [mol/l] weak base anion exchanger Amberlite IRA 96 polystyrene-dvb tertiary amine macroporous Lewatit AP 46 polyacrylic-dvb tertiary/quaternary amine macroporous strong base anion exchanger Amberlite IRA 9 polystyrene-dvb quaternary amine, type macroporous Purolite A86 polyacrylic-dvb quaternary amine, type macroporous Table 3: Properties of the tested adsorber resins. Resin Matrix Functional group Water retention [%] Porosity [ml/g] Surface area [m²/g] Pore diameter [Å] Amberlite XAD 4 polystyrene-dvb none Amberlite XAD 6 polystyrene-dvb none Amberlite XAD 7 HP polyacrylic-dvb carboxyl Amberlite XAD 76 phenol-formaldehyde-dvb mainly phenol Ultrafiltration Chemapol, Riedel dehaën and Merck starch solutions were ultrafiltered with an ultrafiltration module from Pall, equipped with polyethersulfon- (PES)-membranes with nominal molecular weight cutoffs (nmwco) of.45 μm,.3 μm,.6 μm, 5 kda (all from Minisette) as well as kda and 5 kda (Schleicher & Schuell). litres of. ppm TOC (5.6 mg/l) starch solution with ph 6 or.5 were filtered through the membranes beginning with the membrane with the highest nmwco (.45 μm). Finally, filtrates were analysed by UV/VIS. 4 C-labeled starch was ultrafiltered with five Microsep TM -filters (Pall) of different pore sizes ( kda, 3 kda, 5 kda, kda and kda) in filtration tubes. The filtration was followed by centrifugation for 3 minutes (6 minutes for the kda filter) at 4 rpm. Finally, the 4 C-labeled starch filtrates were quantified by liquid scintillation counting (LSC). Column experiments Different model solutions (. ppm TOC (5.6 mg/l starch),.5 ppm TOC (3.8 mg/l L-Phe) or ppm TOC (5.83 mg/l L-Phe)) with ph 6 or.5 were given on a glass column (inner diameter mm, filled with 5 ml of the selected resin, room temperature) with a flow rate of /h (bed volume per hour) for ion exchangers and 4 /h for adsorbers, respectively. The column effluent was collected at intervals and analysed by UV/VIS spectrometry to monitor breakthroughs curves. Analytical methods LC-OCD analyses of the model substances and millipore waters were carried out by DOC-LABOR Dr. Huber [3]. Starch and L-Phe were measured by UV/VIS (Lambda from Perkin Elmer or Varian, Cary 5 Bio) at 59 nm (after : starch reaction with mmol/l iodine-potassium-iodide solution from Apolda and analytical grade phosphoric acid, detection limit.3 mg/l) and at 57 nm (L-Phe, detection limit. mg/l), respectively. The relative error due to input solutions was determined as about.5 %. 4 C- labeled starch was measured by LSC, using a scintillation cocktail (Perkin Elmer, Ultima Gold) and a counting system from Perkin Elmer, Wallac Winspectral a/b (detection limit at. Bq/ml, relative error due to the input solution (4 Bq/ml) at.75 %). Sulphate ions were indirectly determined by titration of the hydrogen ions with sodium hydroxide (relative error at.5 %). The overall error of a single measure point of breakthrough curves was about 5 %. Results and discussions Molecular size distribution of starches Figure shows the molecular size distribution of the starches measured by ultrafiltration. 3

4 Berlin, September 8-, 8 percentage of starch in filtrates [%] < kda < 5 kda < 3 kda < 5 kda < kda < 5 kda < kda equals to about <.45 µm <.3 µm <.6 µm <.5 µm <. µm <.75 µm <.5 µm Chemapol starch (ph 6) Chemapol starch (ph.5) Riedel dehaën starch (ph 6) Merck starch (ph 6) 4C-labeled starch (ph 6) Figure : Molecular size distribution of four starches investigated by ultrafiltration at neutral and acidic ph. (for Chemapol starch (ph 6 and.5) median starch amounts in filtrates and standard derivation in % based on three measurements, whereas for Riedel dehaën, Merck and 4 C-labeled starches on double measuring; no results are available for Chemapol, Riedel dehaën and Merck starches for fraction < kda as well as for 4 C-labeled starch for fractions < 5 kda and < 5 kda) Figure demonstrates that Chemapol starch shows a different molecule size scale in relation to the other starches. Riedel dehaën, Merck and 4 C- labeled starches mainly consist of smaller particles than 5 kda related to the biopolymer LC-OCD fraction, whereas Chemapol starch solutions have higher amounts of larger particles. So, at neutral ph, 78 % of the Chemapol starch particles belongs to the fraction >.3 µm in comparison to less than 5 % of the other starches. Furthermore, an acidic ph of the Chemapol starch solution leads to higher amounts of smaller particles; nevertheless, they consist of larger aggregates than Riedel dehaën, Merck and 4 C-labeled starches. These results are in coincidence with the LC-OCD measures, not surprisingly, because the LC-OCD method is based on size exclusion chromatography. Summarized, molecular size investigations show that the molecule sizes of the starch particles decrease in the following order: Chemapol, Riedel dehaën, Merck and 4 C-labeled starch. Removal of starches with different molecular size distributions by ion exchangers Figure illustrates the uptake of four starches with different molecular size distributions by polystyrene (IRA 9) and polyacrylic (A 86) strong base ion exchangers at neutral ph (Fig. a/b) and acidic ph (Fig. c/d). 4 C-labeled starch was used in combination with inactive Chemapol starch (c active /c inactive =.) and was analysed by UV/VIS (all starch molecules) and LSC (only active molecules). In all following figures the x-axis refers to the throughput in bed volume () and the y- axis contains the output concentration divided by the input concentration (c i /c o ). Figure a/b demonstrates that starch uptake at ph 6 is definitely affected by size exclusion of starch molecules. The smaller the particles, the higher their removal is. So, the uptake arises in the order: Chemapol with capacities of. mg/ml (IRA 9) and mg/ml (A 86), Riedel dehaën with.5 mg/ml (IRA 9) and 7 mg/ml (A 86), Merck with 4 mg/ml (IRA 9) and more than 6 mg/ml up to (A 86), and at last, 4 C-labeled starch. The size exclusion argument could be verified by using larger particles (Chemapol - -) and smaller ones ( 4 C-labeled - -) in one experiment (Fig. a). Large molecules are not able to diffuse into the resin beads and are eluted after a short time, whereas small starch molecules can reach the adsorption sites inside the beads. In contrast, no different uptake was observed between active and inactive starch at polyacrylic resins (Fig. b). Here, the pores are large enough to uptake also the inactive Chemapol starch. Its large molecules block adsorption sites and pores for the smaller 4 C- labeled molecules. Then, inactive and active molecules react in the same manner (Fig. b). As a consequence, small 4 C-labeled starch molecules are even worse removed than Merck and Riedel dehaën ones. The comparison between polystyrene-dvb (IRA 9, Fig. a) and polyacrylic-dvb (A 86, Fig. b) starch uptake leads to the conclusion that a resin with a higher water content and porosity (A 86) is able to uptake more starch molecules with a broader size distribution (notice different scales of the x-axis). At acidic ph (Fig. c/d), starch uptake curves are similar to the curves at ph 6 up to the sulphate breakthrough, which occurs between 5 and. The sulphate ions have a much stronger affinity to the resin than starch molecules. 4

5 Berlin, September 8-, 8 a) IRA 9 b) A 86 ci/co (starch; ph 6) ci/co (starch; ph 6) c) 4 d) IRA 9 4 A 86 ci/co (starch; ph.5) 3 ci/co (starch; ph.5) Chemapol starch Riedel dehaën starch Merck starch 4C-labeled + Chemapol starch - UV/VIS 4C-labeled + Chemapol starch - LSC Figure : Removal of Chemapol, Riedel dehaën and Merck starches as well as 4 C-labeled + Chemapol starch (c o =. ppm TOC) by two strong base anion exchangers (IRA 9 and A 86) at ph 6 and.5. Consequently, the breakthrough point of starch is mainly influenced by the ion exchange capacity due to the sulphate ions. Starch will be eluted by the latter ones indicating by values of the ratio c i /c o >. Low-molecular-weight 4 C-labeled starch shows the highest elution peak, which proves again that small starch molecules have a higher affinity to anion exchanger surfaces than larger ones. At last, starch capacities were determined as.4-.7 mg/ml (IRA 9) and mg/ml (A 86) at acidic ph. Removal of Chemapol starch by different ion exchangers Next Figure 3 includes two weak and two strong anion exchange resins to compare both the influence of resin s structure and functional groups on Chemapol starch removal at neutral and acidic conditions. Fig. 3 demonstrates that polyacrylic- DVB resins (AP 46 and A 86) remove Chemapol starch to a significant higher degree than polystyrene-dvb ones (IRA 96 and IRA 9) at both neutral and acidic conditions. The total ion capacities of polyacrylic-dvb resins are about equal (see Tab. ) to the polystyrene-dvb, so that only the matrix properties can induce the different uptakes. Both polystyrene-dvb resins have a water retention of approximately 6-6 %, whereas the polyacrylic-dvb resins show a water retention ability of about 63 % and 69 %. High water retention of resins increases the porosity of the beads, so that starch molecules can permeate into the resin to a greater extent. This result has also been found for (median molecular) NOM fractions by several authors (e.g. [3, 6, 8]). 5

6 Berlin, September 8-, 8 a) b) IRA 96 ci/co (starch; ph 6) IRA 9 AP 46 A 86 ci/co (starch; ph.5) IRA 96 IRA 9 AP 46 A Figure 3: Removal of Chemapol starch (c o =. ppm TOC) by IRA 96, IRA 9, AP 46 and A 86 anion exchangers at ph 6 and.5. Further, Fig. 3a shows different starch uptakes between weak and strong base polyacrylic exchangers. At neutral ph, the weak base exchanger is in the free base form. So, minor electrostatic attraction should occur in comparison to the strong base exchanger, leading to an earlier breakthrough at the weak base exchangers. Kim et al. [7] postulated that adsorption may take place through interactions between the resin skeleton and the non-ionic core of the NOM (hydrophobic interaction) or through hydrogen bonds between NOM and the nitrogen atom of the amine functional groups. For hydrophilic starch molecules the latter one is the more important adsorption mechanism in the present case, which also explains that strong anion exchangers with a high number of charge sites showed advanced performance in starch uptake than weak ones. At acidic ph, the breakthrough of starch was again determined by the sulphate ions (Fig. 3b). Up to the breakthrough point, polyacrylic-dvb resins show higher uptakes than polystyrene-dvb ones caused by different water contents (compare with Fig. ). Removal of Chemapol starch by different adsorbers Figure 4 shows the uptake of Chemapol starch by several adsorber resins at ph 6 and.5. XAD 4 and XAD 6 are pure adsorbers without any active groups, whereas XAD 7 and XAD 76 possess weak acidic functional groups. For that reason, latter ones have slightly weak cation exchange properties. ci/co (starch; ph 6) XAD 4 XAD 6 XAD 7 XAD 76 ci/co (starch; ph.5) XAD 4 XAD 6 XAD 7 XAD Figure 4: Removal of Chemapol starch (c o =. ppm TOC) by XAD 4, XAD 6, XAD 7 and XAD 76 adsorbers at ph 6 and.5. 6

7 Berlin, September 8-, 8 It was found that effectively no uptake occurs for the polystyrene-dvb as well as for the weak acidic adsorbers at neutral ph conditions, whereas all resins adsorbed starch at acidic ph. Concerning to the hydrophobic polystyrene-dvb adsorbers without functional groups (XAD 4 and XAD 6), only porosity and pore diameters as well as the molecular size distribution of the neutral starch should affect starch capacities. Both polystyrene- DVB resins have small pore diameters (.5-. μm). At neutral ph, the fraction of small Chemapol starch molecules is too low (6 % <.5 μm), so that size exclusion prevents starch removal. Contrary, at acidic ph, 4 % of the Chemapol starch is smaller than.5 μm. Thus, Chemapol starch may be incorporated into the adsorber pores. A higher starch uptake rate was found for XAD 6 (. mg/ml) in comparison to XAD 4 (. mg/ml) at acidic ph. The result is reasonable, since XAD 6 possesses higher porosity (.4 ml/g) and water content (7 %) than XAD 4 (.5 ml/g and 57 %). In the same manner, porosity, pore diameter as well as molecular size distribution of the starch influence starch uptake by weak acidic polyacrylic- DVB (XAD 7) and phenol-formaldehyde-dvb (XAD 76) adsorbers, but for these resins also the ph is important. At acidic ph, the weak acidic functional groups are in poorly dissociated form, so that a removal of neutral substances should be increased in comparison to neutral conditions. Anyway, at neutral conditions size exclusion is the main effect, which prevents again starch removal. At acidic ph, both adsorbers are able to retain a considerable degree of Chemapol starch (about.7 mg/ml for XAD 7 and.69 mg/ml for XAD 76). Removal of L-Phe by ion exchangers Figure 5 compares the removal of the L-Phe by two weak (IRA 96 and AP 46) and two strong (IRA 9 and A 86) anion exchangers as a function of bed volume () at two initial ph conditions. Fig. 5a demonstrates two effects due to the L-Phe uptake at neutral conditions. First, weak base exchangers have shown lower uptake rates than strong base exchangers. Their calculated capacities based on integration of the breakthrough curves were.7 mol/l (IRA 96) and.9 mol/l (AP 46) versus.3 mol/l (IRA 9) and.4 mol/l (A 86) of the strong base exchangers. At neutral ph, L-Phe should react as L- Phe + / - (zwitterion) and L-Phe - (anion) mix, since its isoelectric point is ph Consequently, it should be removed preferably by anion exchange and probably to a minor extent - by adsorption. At neutral ph, weak base resins are in the free base form, which minimizes ion exchange capacity, whereas the strong base exchangers retain their ion exchange capacities at all ph conditions. Second, the respective polyacrylic-dvb resins (AP 46 and A 86) cause higher uptakes than the related polystyrene-dvb ones (IRA 96 and IRA 9), even though the ion exchange capacities show no difference (as example IRA 9 versus A 86). These higher capacities of the polyacrylic-dvb resins may be explained by their higher water content and porosity with higher specific inner surface, so that adsorption effects are playing an increasing role (see also [7]). a) b) IRA 96 ci/co (L-Phe; ph 6) IRA 9 AP 46 A 86 ci/co (L-Phe; ph.5) 4 3 IRA 96 IRA 9 AP 46 A 86 IRA 9 Cl-Form Figure 5: Removal of L-Phe (c o = ppm TOC) by IRA 96, IRA 9, AP 46 and A 86 anion exchangers at ph 6 and.5. 7

8 Berlin, September 8-, 8 a) b) XAD 6 ci/co (L-Phe; ph 6) XAD 7 HP ci/co (L-Phe; ph.5) XAD 6 XAD 7 HP Figure 6: Removal of L-Phe (c o =.5 ppm TOC) by XAD 6 and XAD 7 HP at ph 6 and.5. More interactions between the molecules, which were still adsorbed by ion exchange, and free molecules in solution are possible, because of larger distances between the functional groups. At acidic initial conditions, L-Phe was also uptaken by anion exchangers except for IRA 9 (Cl - form) (Fig. 5b). At ph.5, L-Phe reacts as L- Phe + cation and, hence, uptake by anion exchange should not be expected. This is the case for IRA 9 in the Cl - form. Usually, anion exchange resins in demineralisation plants are used in the OH - form. These resins initially exchange sulphate ions (ph adjustment by H SO 4 ) against OH - ions. This leads to neutral conditions immediately in/at the resin. Then again, L-Phe can react as L-Phe + / - and L-Phe - mix solution. If the resin`s capacity relating to the sulphate ions is depleted, ph decreases to.5, followed by a rapid L-Phe breakthrough with steep peaks indicating elution of the previous adsorbed L- Phe. Consequently, at acid initial conditions lower L-Phe capacities for IRA 96 (.4 mol/l), AP 46 (.7 mol/l), IRA 9 (.4 mol/l) and A 86 (.5 mol/l) were found than at neutral initial conditions without counterions. Removal of L-Phe by adsorbers The L-Phe breakthrough curves for a polystyrene-dvb (XAD 6) and a polyacrylic- DVB (XAD 7) adsorber at neutral and acidic ph conditions are shown in Figure 6. Generally, no or much lower L-Phe uptake was observed in contrast to the anion exchange resins. Adsorption of L-Phe was somewhat higher on XAD 6 resin than on XAD 7. Two facts may contribute to this result: first, the differences in porosity and surface area and second, the polarity of resins relate to the adsorptive. As a precondition for adsorption, corresponding interactions between adsorber and the adsorptive are necessary. Even a high surface area cannot promote adsorption, if the precondition is not fulfilled. This can be seen for ph 6: no adsorption of the L-Phe + / - (zwitterion) and L-Phe - (anion) mix is occurring, although XAD 6 has a much higher surface area than XAD 7 (7-8 m²/g versus 38-5 m²/g). In comparison to ph 6, the L-Phe molecule should be more hydrophobic because of its positive charge at ph.5, so that adsorption by the more hydrophobic XAD 6 will be possible, although in only marginal quantities (Fig. 6b). This confirms the results from Doulia et al. [8], who investigated the adsorption of various acids on polystyrene-dvb adsorbers. Conclusions The results of this work demonstrate: - Size-exclusion will be the main mechanism for the removal of starch as model substance of the biopolymer NOM fraction by anion exchangers and adsorbers. Consequently, starch uptake rises with decreasing molecular size of the starch and increasing porosity, pore diameter and water content of the resins. - Adsorption is postulated as the second important factor for starch uptake both on ion exchange resins and adsorbers. At neutral ph, anion exchangers are able to uptake starch in higher extent than pure adsorbers based on intensive attractions between starch molecules and the polar groups of the ion 8

9 Berlin, September 8-, 8 exchangers. Hence, uptake occurs by weak base anion also at ph 6, even though the free nonionic base form exists. At acidic ph, adsorbers are more effective than ion exchangers, because sulphate, as competitive adsorptive, leads to an earlier starch breakthrough at ion exchangers. - L-Phe is preferably removed by anion exchange and probably only to a minor extent - by adsorption. - Polyacrylic-DVB resins cause higher starch and L-Phe uptakes than the related polystyrene-dvb ones. This could be due to their higher water content and porosity, which easier allows penetration into the resin. As a consequence of this work, polyacrylic anion exchangers should be an alternative in water treatment plants, if biopolymer and neutral/amphiphilic fractions of NOM make some problems. For a better prediction of breakthrough points of NOM fractions, further investigations are necessary including equilibrium and kinetic parameters. Acknowledgements This work was supported by the German Federal Ministry of Education and Research (BMBF) within the FH3 programme, code number FKZ 7 57X 6. We are grateful to H. Heidenreich, R. Illgen and C. Schmidt for extensive experimental labworks. Further, we would like to thank G. Bernhard, S. Sachs and K. Schmeide (Institute of Radiochemistry, Forschungszentrum Dresden- Rossendorf (FZD)) for generous assistance in using the 4 C-technique and for valuable discussions. Finally, we would like to express our gratitude to the DOC-Lab Dr. Huber, Karlsruhe, for many LC- OCD analyses and Vattenfall Europe Generation AG & Co. KG for co-financing. Literature [] Organic Matter and Dissolved Carbon Dioxide in the Steam Water Circuit of Power Plant, VGB PowerTech, M48 Le, Essen (). [] S. A. Huber: The behaviour of natural organic matter in water treatment and the water/steam cycle: deeper insights, PowerPlant Chemistry, 8, 5 6 (6). [3] J.-P. Croué, D. Violleau, C. Bodaire, and B. Legube: Removal of hydrophobic and hydrophilic constituents by anion exchange resin, Water Sci. Technol., 4, 7-4 (999). [4] B. Bolto, D. Dixon, R. Eldridge, S. King, and K. Linge: Removal of natural organic matter by ion exchange, Water Res., 36, (a). [5] H. Humbert, H. Gallard, H. Suty, and J.-P. Croué: Performance of selected anion exchange resins for the treatment of a high DOC content surface water, Water Res., 39, (5). [6] E. R. Cornelissen, N. Moreau, W. G. Siegers, A. J. Abrahamse, L. C. Rietveld, A. Grefte, M. Dignum, G. Amy, and L. P. Wessels: Selection of anionic exchange resins for removal of natural organic matter (NOM) fractions, Water Res., 4, (8). [7] T. H. Boyer and P. C. Singer: Stoichiometry of removal of natural organic matter by ion exchange, Environ. Sci. Technol., 4, (8). [8] G. R. Aiken, E. M. Thurman, and R. L. Malcolm: Comparison of XAD macroporous resins for the concentration of fulvic acid from aqueous solution, Analytical Chemistry, 5, (979). [9] P. H. Boening, D. D. Beckmann, and V. L. Snoeyink: Activated carbon versus resin adsorption of humic substances, J. Am. Water Works Assoc., 7, (98). [] A. Genz, B. Baumgarten, M. Goernitz, and M. Jekel: NOM removal by adsorption onto granular ferric hydroxide: equilibrium, kinetics, filter and regeneration studies, Water Res., 4, (8). [] T. Schönfelder and A. Lutat: Chemistry of steam water cycles of the Rostock Power Station with special viewing to organic ingredients. Proc. Zittau Power Plant Chemistry Symposium TOC in Steam Water Cycles, Zittau () and Scientific Reports of the University of Applied Sciences Zittau/Görlitz, 67, 6 43 (). [] H. Schley and A. Markert: Reverse osmosis as part of the makeup water treatment in the Lippendorf Power Station. Proc. Zittau Power Plant Symposium Application of Ion Exchange and Membrane Techniques to Makeup Boiler Water Treatment in Power Plants, Oybin (4). [3] S. A. Huber and F. H. Frimmel: Sizeexclusion chromatography with organic carbon detection (LC-OCD): a fast and 9

10 Berlin, September 8-, 8 reliable method for the characterization of hydrophilic organic matter in natural waters, Vom Wasser, 86, 77-9 (996). [4] S. A. Huber and M. Gluschke: Chromatographic characterization of TOC in process water treatment, Ultrapure Water, March 998, 48-5 (998). [5] V. Ender, B. Kettner, T. Schumann, and S. Hajdamowicz: The influence of temperature on the removal of organics from natural waters by ion exchange laboratory and pilot plant experiments, PowerPlant Chemistry, 8, 7 5 (6). [6] V. Ender, T. Schumann, S. Sachs, and G. Bernhard: On the uptake mechanisms of organics from natural water investigations with strong and weak base ion exchangers and their corresponding copolymers, PowerPlant Chemistry, 8, (6). [7] B. R. Kim, V. L. Snoeyink, and F. M. Saunder: Adsorption of organic compounds by synthetic resins, J. WPCF, 48, -33 (767). [8] D. Doulia, F. Rigas, and C. Gimouhopoulos: Removal of amino acids from water by adsorption on polystyrene resins, J. Chem. Technol. Biotechnol., 76, ().