Contaminant Removal from Source Waters Using Cathodic Electrochemical Membrane Filtration: Mechanisms and Implications

Abstract

Removal of recalcitrant anthropogenic contaminants from water calls for the development of cost-effective treatment technologies. In this work, a novel electrochemical membrane filtration (EMF) process using a conducting microfiltration membrane as the cathode has been developed and the degradation of sulphanilic acid (SA) examined. The electrochemical degradation of SA in flow-by mode followed pseudo-first-order kinetics with the degradation rate enhanced with increase in charging voltage. Hydrogen peroxide as well as oxidants such as HO and Fe(IV)O were generated electrochemically with HO found to be the dominant oxidant responsible for SA degradation. In addition to the anodic splitting of water, HO was formed via a heterogeneous Fenton process with surface-bound Fe(II) resulting from aerobic corrosion of the steel mesh. In flow-through mode, the removal rate of SA was 13.0% greater than obtained in flow-by mode, presumably due to the better contact of the contaminant with the oxidants generated in the vicinity of the membrane surface. A variety of oxidized products including hydroquinone, p-benzoquinone, oxamic acid, maleic acid, fumaric acid, acetic acid, formic acid, and oxalic acid were identified and an electrochemical degradation pathway proposed. These findings highlight the potential of the cathodic EMF process as an effective technology for water purification.

Effective Removal of Sulfanilic Acid From Water Using a Low-Pressure Electrochemical RuO2-TiO2@Ti/PVDF Composite Membrane

“…Figure S2B indicates that the composite membrane has a typical structure of microfiltration membranes with an average pore size of 0.11±0.03 μm. Our experiments showed that the RuO 2 -TiO 2 @Ti/PVDF membrane and the original PVDF membrane had similar water-permeability performance with this finding in agreement with the results of previous works in which embedding electrodes into polymeric membranes had no adverse influence on the formation of membrane pores in PVDF active layer (Huang et al, 2015 ; Zheng et al, 2017 ).…”

“…The electrochemical properties of the RuO 2 -TiO 2 @Ti-PVDF membrane and the RuO 2 -TiO 2 @Ti electrode were examined using linear sweep voltammetry (LSV) scan. As shown in Figure 1 , the electrochemical composite membrane had similar current densities at lower potentials (<1.1 V) with the RuO 2 -TiO 2 @Ti anode, while the RuO 2 -TiO 2 @Ti anode performed slightly better at higher scanned potentials (>1.1 V), indicating that the casted membrane solution affected the conductivity of electrode though it still had favorable electrochemical properties (Zheng et al, 2017 ). The RuO 2 -TiO 2 @Ti electrode with a pore size of 100 μm is inefficient in intercepting suspended solids and colloids.…”

“…As can be seen from Figure 8A , at the same charging voltage (1.5 V) and operating time/HRT (2 h), flow-through operation resulted in a TOC removal rate of 36.8%, much higher than that obtained in flow-by operation (5.5%). It is worth noting that the average current of the flow-through operated system was 6.1 mA with this value relatively higher than that of the flow-by one (5.2 mA), likely associated with the fast electron transfer reaction at the electrode/electrolyte interface under flow-through mode (Zhao et al, 2013a ; Zheng et al, 2017 ; Li et al, 2018b ), for instance, the accelerated transport of dissolved oxygen toward anode surface could benefit its one-electron reduction (Equation 5). The enhanced mass transfer might facilitate the production of ROS in the system as well.…”

“…The concentrations of SA and its oxidation intermediates were measured using reversed-phase high-performance liquid chromatography (RP-HPLC, Agilent 1200, USA) and/or ion-exclusion HPLC (IEC, Agilent 1200, USA) or gas chromatography (GC, Agilent6890N, USA) with the detailed testing procedures as described in our previous work (Zheng et al, 2017 ). The concentration of aqueous H 2 O 2 at the vicinity of membrane and cathode surface in the electrochemical system was determined using the metavanadate spectrophotometric method (Nogueira et al, 2005 ).…”

Dynamic cross-flow electro-Fenton process coupled to anodic oxidation for wastewater treatment: Application to the degradation of acetaminophen

“…A recent work reported the use of a membrane with a polymer coating film which promoted the electrochemical for mation of % OH via the EF process. However, the polymer layer was supported on a steel mesh with poor filtration capacity, which was subjected to corrosion issues [47].…”