Catalytic hydrodechlorination as polishing step in drinking water treatment for the removal of chlorinated micropollutants

The presence of micropollutants in fresh waters represents an important challenge for drinking water treatment plants (DWTPs). In particular, the chlorinated ones are especially harmful given their high toxicity and strong bioaccumulation potential. The aim of this work is to evaluate the feasibility of catalytic hydrodechlorination (HDC) for the removal of a representative group of chlorinated micropollutants commonly found in the source waters of DWTPs: the antibiotic chloramphenicol (CAP), the anti-inflammatory diclofenac (DCF), the antibacterial agent triclosan (TCL) and the antidepressant sertraline (SRT). The complete degradation of the isolated micropollutants (3 mg L-1) was achieved in 1 h reaction time using a Pd/Al2O3 catalyst load of 0.25 g L-1 and a H-2 flow rate of 50 N mL min(-1). The experimental data were properly described by a pseudo-first order kinetic equation, obtaining degradation rate constants in the range of 0.32-1.56 L g(cat)(-1) min(-1) and activation energy values within 42-52 kJ mol(-1). In all cases, the final reaction products were chlorine-free compounds and thus, HDC effluents were non-toxic (< 0.1 TU). Remarkably, the catalyst showed a suitable stability upon five consecutive applications. The versatility of the process was demonstrated in the treatment of the micropollutants mixture in different aqueous matrices (mineral, surface and tap waters). Strikingly, the removal rate was not affected by the presence of co-existing substances, being the micropollutants completely removed in 15 min with 1 g L-1 catalyst concentration. Finally, the potential of HDC for the removal of trihalomethanes, by-products formed along the oxidation step by chlorination in DWTPs, was also demonstrated.