The occurrence of bromate and perbromate on BDD anodes during electrolysis of aqueous systems containing bromide: first systematic experimental studies

Abstract

Bromide electrolysis was carried out on laboratory-scale cells in the range of 1-1,005 mg [Br -] dm -3 using boron-doped diamond (BDD) anodes. These studies were part of fundamental research activities on drinking water electrolysis for disinfection. Synthetic water systems were mostly used in the experiments, which varied the temperature between 5 and 30°C, the current density between 50 and 700 A m -2 , and the rotation rate of the rotating anode between 100 and 500 rpm (laminar regime). Hypobromite and bromate were found as by-products, as expected. Bromite was not detected. Higher bromate levels were formed at higher current density, but no clear relationship was observed between bromate concentration and the rotation rate or temperatures between 5 and 30°C. Bromate yields higher than 90% were found at higher charge passed. Perbromate was found as a new potential synthesis or disinfection by-product (DBP), but no perbromate was detected at the lowest bromide concentrations and under drinking water conditions. The perbromate yield was about 1%, and somewhat lower when bromate was used as a starting material instead of bromide. At a temperature of 5°C more perbromate was detected compared with experiments at 20°. Approximately 20 times more perchlorate was formed compared with perbromate formation in the presence of chloride ions of equimolar concentration. State of mechanistic considerations is presented and a mechanism for perbromate formation is proposed. The reaction from bromate to perbromate was found to be limited that is in contrast to the earlier studied chlorate-to-perchlorate conversion. In the measured concentration range, reduction processes at the mixed oxide cathode showed a much higher impact on the resulting concentration for perbromate than for bromate. Keywords Electrochemical disinfection Á Drinking water Á Bromide electrolysis Á Bromate Á Perbromate Á BDD Á Disinfection by-products List of symbols BDD Boron Doped Diamond c Concentration (mg dm -3 ) D Diffusion coefficient (m 2 s -1 ) DPD Diphenylendiamine E Electrode potential (V (SHE)) F FARADAY constant (As mol -1 ) I Current (A) IC Ion chromatography i lim Limiting current density (A m -2 ) k Reaction rate constant (M -1 s -1 , M -2 s -2 ) n Number of electrons transferred M Molar mass (mg mol -1 ) r Electrode radius (m) Re = xÁr 2 /m Reynolds number RDE Rotating disk electrode RNO p-Nitrosodimethylaniline rpm Revolutions per minute Sc = m/D Schmidt number Sh = bÁr/D Sherwood number SHE Standard Hydrogen Electrode

On the formation of bromate and chlorate ions during electrolysis with boron doped diamond anode for seawater treatment

“…Only small amounts of hypobromite were detected, always below 0.5 mg dm −3 , while bromite ions were not detected in the samples. This experimental evidence is in agreement with that obtained by Bergmann and coworkers, who reported a systematic study on the oxidation of bromide at BDD anodes: oxidation mediated by hydroxyl radicals and oxygen radicals was indicated as the main mechanism of conversion of bromides to bromates. The authors also found that perbromate ions were produced during the electrolyses with initial concentration of bromide of 288 mg dm −3 and current density at least equal to 200 A m −2 .…”

“…To the best of our knowledge, few reports are present in the literature on the electrolysis of bromide ions with BDD anodes; Bergmann and coworkers have shown that, working at 200 A m −2 , the electrolysis of solutions containing about 150 ppm of bromide ions allows the formation of bromate ions with very high current efficiency …”

“…28,29 To the best of our knowledge, few reports are present in the literature on the electrolysis of bromide ions with BDD anodes; Bergmann and coworkers have shown that, working at 200 A m −2 , the electrolysis of solutions containing about 150 ppm of bromide ions allows the formation of bromate ions with very high current efficiency. 30 Although several reports have appeared in the literature on the application of BDD in seawater treatment, 31,32 the main interest was in the removal of organics and/or disinfection: no specific information has been reported on the formation of bromate ions during the treatments of water containing high chloride concentration along with bromide. On this topic Echardt and Kornmueller et al reported the results of a full scale system for ballast water treatment: 33 a very high biocide effect was achieved, and the authors claimed bromate and chlorate ions below the limits indicated by IMO.…”

Energy cycle based on a high specific energy aqueous flow battery and its potential use for fully electric vehicles and for direct solar-to-chemical energy conversion

“…The disproportionation of Br 2 in water may go all the way to bromate (and even to perbromate) [75,76] via a series of reversible disproportionation steps coupled to acid-base reactions. The first step is believed to occur at a near neutral 4≤ pH≤8 via the following pathway:…”

Towards Enhancing Ozone Diffusion for Water Disinfection—Short Notes

“…Due to that, in employing such materials for remedying with wastewater, it is frequent that the pathways utilized to interpret the decomposition of organic compounds do not only take into account the direct oxidation via electron transfer on the anode surface but, most possibly, the mediated oxidation through a huge collection of oxidants produced from the various salts carried in the electrolyte, as well as ozone and hydrogen peroxide [21]. This begins to be an issue in disinfection due to the potential formation of toxic perchlorate [22] [23]; however, it is very favorable participation in the electrolysis of wastewater [24].…”