title: Effects of anodic potential and chloride ion on overall reactivity in electrochemical reactors designed for solar-powered wastewater treatment.
abstract: We have investigated electrochemical treatment of real domestic wastewater coupled with simultaneous production of molecular H2 as useful byproduct. The electrolysis cells employ multilayer semiconductor anodes with electroactive bismuth-doped TiO2 functionalities and stainless steel cathodes. DC-powered laboratory-scale electrolysis experiments were performed under static anodic potentials (+2.2 or +3.0 V NHE) using domestic wastewater samples, with added chloride ion in variable concentrations. Greater than 95% reductions in chemical oxygen demand (COD) and ammonium ion were achieved within 6 h. In addition, we experimentally determined a decreasing overall reactivity of reactive chlorine species toward COD with an increasing chloride ion concentration 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 kgCOD(-1) at the cell voltage of near 4 V in 50 mM chloride. The current efficiency and energy efficiency for H2 generation were calculated to range from 34 to 84% and 14 to 26%, respectively. The hydrogen comprised 35 to 60% by volume 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.
authors.affiliation: Linde+Robinson Laboratories, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Kangwoo
authors.initials: K
authors.lastname: Cho
authors.forename: Yan
authors.initials: Y
authors.lastname: Qu
authors.forename: Daejung
authors.initials: D
authors.lastname: Kwon
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Clément A
authors.initials: CA
authors.lastname: Cid
authors.forename: Asghar
authors.initials: A
authors.lastname: Aryanfar
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hoffmann
mesh_terms: D057919:Biological Oxygen Demand Analysis; D001729:Bismuth / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry*; D004560:Electricity; D055664:Electrochemical Techniques / Q000295:instrumentation*; D004566:Electrodes; D004572:Electrolysis; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D007477:Ions; D012993:Solar Energy; D012996:Solutions; D013816:Thermodynamics; D013997:Time Factors; D014025:Titanium / Q000737:chemistry; D062065:Wastewater / Q000737:chemistry*; D018508:Water Purification / Q000295:instrumentation*
chemical_list: D001729:Bismuth; D002712:Chlorides; D006859:Hydrogen; D007477:Ions; D012996:Solutions; D014025:Titanium; D062065:Wastewater; C009495:titanium dioxide