Electrochemical oxidation using novel anodes for advanced wastewater treatment : emerging organic pollutant removal and virus disinfection

Abstract

Electrochemical (EC) oxidation is an effective and promising technology for removing toxic and bio-recalcitrant pollutants from wastewater. In this study, novel anodes and reactive anodic membrane (RAM) have been developed to achieve highly efficient EC wastewater treatment and disinfection. Advanced composite anodes, 3D freestanding SnO2-Sb anodes, and oxygen-vacancy-enriched anodes were fabricated for electrocatalytic oxidation of emerging organic pollutants. Permeable SnO2-Sb anode was developed as the flow-through RAM to improve the mass transport and energy efficiency of EC oxidation, as well as to achieve effective EC inactivation of bacteria and viruses. The advanced composite anodes, including the novel conductive interlayer-based PbO2 (S-TiO2NTA-PbO2) anode and SnO2-Sb nano-pin array (SnO2-Sb NPA) anode, were fabricated for EC wastewater treatment. The conductive S-TiO2NTA interlayer enabled the high hydroxyl radical (OH) production and high stability of the PbO2 anode. Nearly 100% of methylene blue (MB) was degraded by this anode in 90 min. The SnO2-Sb NPA anode was fabricated on a dimensionally stable anode (DSA) via a new hydrothermal-electrodeposition route. This anode exhibited more than twice the bisphenol A degradation rate constant and 15 times prolonged service life compared with the conventional SnO2-Sb/Ti anode. The mechanism of electrocatalytic BPA degradation involves direct electron transfer on the NPA surface and oxidation by in situ generated OH. A freestanding Ti-free 3D SnO2-Sb anode with macro-pores (3D MP SnO2-Sb) was fabricated by a one-step compressing-sintering method. Compared with the conventional 2D SnO2-Sb/Ti anode, the 3D MP SnO2-Sb anode featured a more than 100-fold increase in electroactive surface area for ciprofloxacin (CIP) degradation. This Ti-less anode exhibited high stability (>200 cycles) and performed well in treating actual wastewater. The controllable formation of oxygen vacancy (OV) by doping La3+ on the 3D SnO2-Sb anode further enhanced its electrocatalytic activity. The new SnOx/La-Sb anode showed a high moxifloxacin degradation rate constant, 8 times higher than that of the pristine SnO2-Sb anode. The mechanism was elucidated from the molecular probe tests, density functional theory (DFT) calculations, and intermediate detection: La3+ doping-induced OV activated the anode surface for electrocatalysis by boosting the interfacial electron transfer and OH generation. The 3D permeable SnO2-Sb anode functioned as a RAM for antibiotic wastewater treatment. Forcing the wastewater through the RAM depth-wise improved the mass transport towards the vastly enlarged the electroactive surface area. Compared with the conventional flow-by configuration, the flow-through RAM exhibited a 12-fold increase in the mass transfer rate (60.7 × 10-6 m s-1) and a 5-fold increase in the CIP degradation rate constant (0.077 min-1). Moreover, the novel SnO2-Sb RAM with tailored pores and channels achieved efficient EC inactivation of bacteria and viruses in chlorine-free water. Nearly 100% inactivation of E. coli (> 6.3-log inactivation) and bacteriophage MS2 virus (> 8.3-log inactivation) was realized by the RAM-based flow-through EC cell in a quick single pass. The mechanism of EC disinfection involves the synergistic effect of a strong acidic local environment with enriched ·OH in the interior pores of the RAM for the rapid destruction and inactivation of pathogens in wastewater. (496 words)