Report No FR0315

N Mole

Sept 1992



Information on the nature, concentration and toxicity of by-products of electrolytic chlorine generation will be summarised, guidance on how to minimise by-product formation will be given and areas requiring further study will be identified. This will provide fore-warning of any potential health concerns surrounding this method of chlorine generation.


To review the identity, concentration and potential health effects of by-products, transformation products and other contaminants arising from the electrolytic production of chlorine for drinking water disinfection, and to identify areas where further knowledge is required.


Knowledge of the concentration and potential health effects of by-products (e.g. chlorate) arising from the electrolytic generation of chlorine, and conditions under which by-product formation is minimised, will enable guidance to be given as to which by-products are significant and how their production may be limited.


The main by-product is chlorate, and whilst the concentrations produced by the currently marketed electrolytic chlorine generators should not result in any significant difficulties in meeting the 0.7 mg l-1 limit laid down in the DoE approval, any tightening of regulations as a result of current WHO or US EPA reviews may necessitate some minimisation measures. Any such tightening of limits would almost preclude the use of stored hypochlorite. Bromate is likely to be a by-product and may be reduced at levels which could result in concentrations in a treated water of up to 15 g l-1, which may be of concern.


In order that firm recommendations for the minimisation of by-product formation can be made the relative contributions of direct electrolysis and of reactions in the bulk electrolyte should be investigated, as should the effect of temperature and the difference between membrane and undivided cells. These studies should focus on the production of chlorate and bromate but should also include the stability of these species through other water treatment processes.


This report reviews the existing data on the production of by-products during the electrolytic generation of chlorine, their nature, concentration and significance to health. Chlorate and bromate are identified as those most likely to pose a significant problem, and some guidance is given on how to minimise the production of chlorate. The need for further studies of the reaction conditions which produce chlorate and bromate (in order to give better guidance on the minimisation of their production), is identified.

Copies of the Report are available from FWR, price 15.00 less 20% to FWR Members