Towards full cell potential utilization during water purification using Co/Bi/TiO2 nanotube electrodes

Abstract

Here we report on a research effort towards full cell potential utilization during the elimination of organic pollutants under environmentally relevant conditions. Meropenem was selected as a representative recalcitrant antibiotic and a newly-developed Co and Bi co-doped TiO2 nanotube array (Co/Bi/TiO2 NTA) electrode was employed as both anode and cathode. While electrochemical reduction of Meropenem appeared to be much more energy efficient (0.042 kWh/m3) than electrochemical oxidation (0.813 kWh/m3) in synthetic electrolyte, the degradation was significantly inhibited in environmental matrices (secondary effluent/SE and RO concentrate) due to the competition and/or inhibition effects of other species present in the matrices as well as electrode fouling. Calcium carbonate and magnesium oxide were identified to be main mineral foulants. The elimination of Meropenem was then examined in coupled treatment schemes (e.g. sequential and simultaneous), taking advantages of the “self-regeneration” characteristic of TiO2 NTA based electrodes through cathodic polarization. While a simultaneous oxidation & reduction with regular polarity switching seems to be a preferred treatment scheme especially for challenging matrices such as RO concentrate, the bipolar stability of the nanostructured electrode may limit the electrode lifetime. A hybrid electrolysis system coupling anodic oxidation of organic pollutants and cathodic hydrogen generation as a renewable energy source was also tested in a flow-through reactor, where consistent and steady treatment performance was demonstrated for a period of 3 days. We think the results obtained from this study have underlined the importance of matrix characteristics on the design and selection of electrochemical treatment processes. It also provides insights into future development of coupled anodic and cathodic processes for water purification.