Removal of emerging organic pollutants in wastewater treatment plant effluents by an electrochemical process employing boron-doped diamond electrode.

Various studies over recent years have proved the increasing occurrence in effluent of wastewater treatment plants (WWTP)of several contaminants of emerging concern (CECs), which are not completely removed by the common technologies employed in conventional WWTP. CECs found at highest levels (ng L-1 to ?g L-1) are pharmaceuticals, artificial sweeteners, pesticides, flame-retardants, plasticizers and perfluoroalkyl substances (1,2). The main objective of this study was to investigate an electrochemical treatment based on a boron-doped diamond (BDD) electrode, as an advanced oxidation process (AOP) for the removal of several CECs from effluent of WWTP with enhanced performance in terms of efficiency and applicability (3). Electrochemical treatments were performed with a CONDIAPURE? system using a DIACHEM? electrode stack in a flow through cell (CONDIAS GmbH, Germany), in both synthetic water and real secondary effluent. The electrode stack was composed by two BDD cathodes and one BDD anode and in situ oxidation was performed with four anode/cathode pairs applying a total current of 0.4 A. A total of 10 L of solution with the target organic pollutants was circulated through the reactor at a flow rate of 18.5 L/min. The removal of a mixture of CECs (iopromide, carbamazepine, diclofenac, erythromycin, benzotriazol, sulfamethoxazole, caffeine, gabapentin, metoprolol, phenythoin, primidone, venlafaxine, TCEP) by the investigated electrochemical system was primarily assessed in synthetic model water spiked with the target contaminants at concentration in the range of 2-5 ?g L-1. Removal below limit of quantification (LOQ) was achieved for all tested compounds after 200 min of treatment. Decay follows pseudo first order kinetics and kinetic constants (k) of 0.07 min-1 for sulfamethoxazole and diclofenac and in the range 0.03-0.01 min-1 for the other CECs were obtained, being TCEP the pollutant with slowest kinetics. Afterwards, the secondary effluent of the municipal WWTP Garching (Germany) was employed as a real water matrix which revealed the occurrence of several CECs (including the mixture of selected compounds listed above) at concentration levels between 20 ng L-1 and 20 ?g L-1. The electrochemical treatment of the effluent was performed under the same conditions employed with the spiked synthetic water. Results demonstrated removal below LOQ for all the target CECs after 300 min with lower degradation rates than in the spiked synthetic water solution (k <= 0.01 min-1). The detection of transformation products of investigated CECs was performed by UPLC-QTOF/MS/MS, by employing a non-target analysis approach which was based on accurate MS and MS/MS data and open source databases and software.