The Bromate and Perbromate Problem on Bdd

THE BROMATE AND PERBROMATE PROBLEM ON BDD

Henry Bergmann1, Tatiana Iourtchouk1, Savaş Koparal2, Seval Yılmaz2

1Anhalt University, Dpts. 6/7, 06366 Köthen/Anh., Germany E-mail: [email protected] 2Anadolu University, Dpt. of Environmental Engineering, Eskişehir, Turkey E-mail: [email protected]

Due to their outstanding oxidizing and stability properties BDD electrode application has become part of methods for so-called Advanced Oxidation. However, for the first time we could demonstrate that in drinking water electrolysis unwanted chlorate and perbromate can be formed when chloride is present [1,2]. Newer research work has now shown that in the presence of bromide ions bromate (limited at 10 µg L-1 in drinking water) and even perbromate can be formed [2,3]. This work was carried out for obtaining results from more systematic studies. A thermostated cell with rotating BDD anode was used for experiments with aqueous systems at constant current mode and using 0.1 L electrolyte [1]. Following parameters were varied: Br - concentration between 1 and 1000 mg L-1, current density between 15 and 700 A m-2, temperature between 5 and 30°, and anode rotation rate between 0 and 700 rpm. Ion chromatography was used for analysis of Br species.

Results showed negligible effect of hydrodynamics on bromide depletion and bromate formation indicating on diffusion limitation and rate determining kinetic steps. Maxima occurred in bromate formation vs. specific charge passed (Q). Bromate formation followed the bromide concentration at higher Q but not in the beginning – due to reaction competition. Competing reactions are the formation of bromine species, bromate and perbromate. With respect to these species, Br balance was complete. Concentration maxima were also found for active bromine. Current density had significant influence on the chlorate formation. Perchlorate formation is obviously limited. Current efficiencies of around 1 % were measured for perbromate formation. The low influence of temperature is an indicator for predominating fast (radical) reactions. It can be concluded that BDD anodes are favored for electrochemical bromate production. There use for perbromate production makes sense when started from bromate. In environmentally sensitive cases, BDD anodes are not recommended when bromide ions are present.

References [1] Bergmann, M.E.H., Rollin, J., Iourtchouk, T., Electrochimica Acta 54 (2009) 2102-2107. [2] Bergmann, M.E.H., Iourtchouk, T., Schmidt et al., Journal of Applied Electrochemistry, online – DOI 10.1007/s10800-015-0826-z. [3] Bergmann, M.E.H, Iourtchouk, T., Rollin, J., Journal of Applied Electrochemistry, 41 (2011) 1109- 1123. [4] Bergmann, M.E.H., Iourtchouk, T., Hartmann, J., Chemical Engineering Transactions 41 (2014) 127-132.

The authors wish to thank German BMBF and AIF/Berlin for partial project support (KF 0067005KLF2)