Effects of anodic potential and chloride ion on overall reactivity in semiconductor electrochemical reactors

Abstract

We have investigated electrochem. treatment of real domestic wastewater coupled with simultaneous prodn. of mol. H2 as useful byproduct. The electrolysis cells employ multi-layer semiconductor anodes with electro-active bismuth-doped TiO2 functionalities and stainless steel cathodes. DC-powered Lab.-scale electrolysis expts. were performed under static anodic potentials (+2.2 or +3.0 V NHE) using domestic wastewater samples, with added chloride ion in variable concns. Greater than 95% redns. in COD (COD) and ammonium ion were achieved within 6 h. In addn., we exptl. detd. a decreasing overall reactivity of reactive chlorine species towards COD with an increasing chloride ion concn. under chlorine radicals (Cl·, Cl2-·) generation at +3.0 V NHE. The current efficiency for COD removal was 12% with the lowest specific energy consumption of 96 kWh kg/COD at the cell voltage of near 4 V in 50 mM chloride. The current efficiency and energy efficiency for H2 generation were calcd. to range from 34 to 84% and 14 to 26%, resp. The hydrogen comprised 35 to 60% by vol. of evolved gases. The efficacy of our electrolysis cell was further demonstrated by a 20 L prototype reactor totally powered by a photovoltaic (PV) panel, which was shown to eliminate COD and total coliform bacteria in less than 4 h of treatment.