Regeneration of XAD Resins Used for Natural Organic Matter Fractionation

Natural organic matter (NOM) removal plays important role in water treatment due to their ability to form disinfection by-products. Due to NOM complexity, it is crucial to separate it into fractions and then subject them to the detailed analysis. Organic contaminants are heterogeneous mixture of various organic compounds of diverse properties and could be divided into 3 fractions: hydrophobic, hydrophilic and transphilic. Currently, the common NOM fractionation method was proposed by Chow et al. This method employs XAD resins to fractionate NOM. One of decisive factors, when it comes to their usability, is the possibility to regenerate it. In this connection evaluation of XAD resin regeneration methods efficiency was performed. Supelite DAX-8, Amberlite XAD-4 and Amberlite IRA-958 nonionic macroporous resins were used in the experiments. Experiments included resin preparation by initial regeneration, resin saturation with NOM and final resin regeneration. Experiments were carried out on the model solution and surface water taken from Odra River (Poland). Regeneration was conducted in a column system with the use of two methods. The first one was in accordance with Chow et al. procedure. The second one comprised of successive resin rinsing with redistilled water, 0.1 n NaOH, 0.1 n HCl, 0.1 n NaOH, redistilled water, methanol, acetonitrile, methanol and redistilled water. Preliminary research that were conducted in order to evaluate sorption performance in column system revealed that in all cases same schema could be observed: in few initial minutes, UV 254 nm absorbance, colour and dissolved organic carbon concentration in column effluent was constant, then started rising until reaching feed solution values. It is noticeable that none of the resins adsorbed all contaminants at any time. Subsequent experiments has shown that developed by Chow et al. method of saturated resins regeneration was not able to restore their initial sorptive capacity. Regeneration procedure developed by paper authors allowed full regeneration of NOM saturated resin, even after second saturation-regeneration cycle. Influence of regeneration time on resin sorption capacity restoration efficiency was also observed: longer regeneration resulted in better results. The best effects of resin regeneration was observed for 3 h contact time with each regenerant solution.