Abstract
Polyfluorinated organic micropollutants have been recently found in ground water in some industrialized areas of Veneto Region (north-east Italy). Very recent studies evidenced their presence also in River Lambro near Milan (Castiglioni et al, 2015). These compounds can be removed by adsorption on activated carbon with high efficiency, but frequent regeneration is requested especially because of polyfluorobutylic acid (PFBA) and polyfluorobutyl sulfonate (PFBS) that saturate activated carbon much more quickly than heavier molecules as polyfluoro-octanoic acid (PFOA) and polyfluoroctyl sulfonate (PFOS).
In this research work an alternative solution based on ion exchange resins and/or polystyirenic adsorbents was tested both in laboratory with batch tests and on pilot-scale with a continuously fed plant. Experimental work is still in progress and is focused on five different materials supplied by Purolite® Italia and called respectively A600E, PAD500, PAD428, A520E and MN102. Laboratory batch experiments were (and are) performed in order to study both sorption kinetics and spent resin regeneration; four materials have been tested until now: A600E, PAD500, A520E and MN102. Sorption isotherms showed a progressively decreasing adsorption capacity following the order PFOS>PFOA>PFBS> PFBA indicating a dependence of sorption phenomena both on the length of the perfluorinated tail and the pKa of the polyfluorinated acid. Further, batch experiments showed that for A600E the best regenerating solution was a 2 % NH4Cl and 1 % NaCl aqueous solution. Pilot-scale experiments were (and are) conducted in cooperation with the water service company Centro Veneto Servizi of Monselice (PD, Italy) nearby a drinking water treatment plant. The pilot plant was and is made of four parallel columns filled with different materials, each one with a volume of 350 mL and fed with 35 mL/min (2.1 L/h ) micro- filtered water; so residence time is 10 min and surface hydraulic load is 3.0 m3/m2h. Four materials have been tested until now: A600E, PAD500, PAD428 and MN102. Results of first 800 h working (that correspond to a total treated water volume which is ca. 4,500 times the volume of material in each column) were excellent for PFOA and PFOS removal, but a rapid decrease in PFBA and PFBS removal efficiency was encountered with PAD500 and PAD428. Further experiments are scheduled to test A520E on pilot-scale. Moreover, it would be interesting to test more hydrophobic resins which may display an increased affinity for super hydrophobic PFAS anions reducing competitive action of anions such as nitrates and sulfates.
