Removal of estrogenic compounds from water via energy efficient sequential electrocoagulation-electrooxidation

Abstract

The purpose of this study was to investigate energy reduction using electrocoagulation (EC) followed by electrooxidation (EO) targeting initial removal of dissolved organic carbon (DOC) during EC and subsequent removal of estrogenic compounds in EO. EC offers benefits over conventional coagulation such as in situ generation of coagulant but is not practical for removing estrogenic compounds. Advanced oxidation processes, including EO, can effectively remove micropollutants such as estrogenic compounds but are hindered by the presence of bulk organic matter. This study investigated four estrogenic compounds from the U.S. EPA's Contaminant Candidate List: estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethynylestradiol (EE2). First, EC (iron electrodes) was employed to remove humic acid and improve downstream removal of estrogenic compounds while reducing overall energy consumption in EO (boron-doped diamond electrodes). The sequential EC and EO system effectively reduced overall electrical energy per order (EEO) by more than half compared with EO alone for each estrogenic compound. The system also effectively removed humic acid and estrogenic compounds. An EC current density of 8.88 mA/cm2 and electrolysis time of 8 min with a flocculation stir rate of 40 rpm (G = 23 s-1) achieved the greatest DOC and UV-VIS254 removal. EO treatment achieved the highest estrogenic compound removal at a current density of 22.2 mA/cm2. Initial humic acid sodium salt concentration (0-60 mg/L C) had an effect on EC iron dose and estrogenic compound removal. The EEO for EC-EO treatments was lower than EC alone, EO alone, UV photolysis, UV photocatalysis, and ozone but was higher than a photocatalytic reactor membrane and UV/H2O2. Overall, the EC-EO system was effective at removing bulk organic matter during EC and estrogenic compounds during EO. EC-EO reduced overall energy demand, indicating that this system should be developed further as an advanced technology that could efficiently remove micropollutants.