BS/EN 12671-2016 pdf download.Chemicals used for treatment of water intended for human consumption Chlorine dioxide generated in situ.
4.1 General
This European Standard specifies the minimum purity requirements for chlorine dioxide generated in situ used for the treatment of water intended for human consumption. Limits are given for impurities commonly present in the product. Depending on the raw material and the manufacturing process, other impurities may be present and, if so, this shall be notified to the user and when necessary to relevant authorities.
Users of this product should check the national regulations in order to clarify whether it is of appropriate pUnty for treatment of water intended for human consumption, taking into account raw water quality, required dosage, contents of other impurities and additives used in the product not stated in this product standard.
Limits have been given for Impurities and chemical parameters where these are likely to be present in significant quantities from the current production process and raw materials, lithe production process or raw materials lead to significant quantities of impurities, by-products or additives being present, this shall be notified to the user.
4.2 Composition of in situ generated product
Chlorine dioxide (do2) is produced as aqueous solution on or near the site of use. For safety reasons the aqueous dO2 solution without intermediate storage in a storage tank (i.e. without headspace) shall not exceed a concentration of 20 gJI.
The concentration of the aqueous Cl02 solution with intermediate storage in a storage tank (i.e. with headspace) should not exceed a concentration of 3 g/l, to ensure an adequate distance to the explosion limit (see B.1).
4.3 Impurities and main by-products
Impurities and main by-products of the starting products used for the generation (indicated in A.1.1) can be found in the in Situ generated product in respective proportional concentrations.
Inadequate design, operation and maintenance of reactors can give rise to the formation of chlorine and traces of chlorate ion and, eventually, the presence of unreacted chlorite, chlorate and/or chlorine (see [6]); for analysis see 5.2 and A.4.
4.4 Chemical parameters
NOTE For the purpose of this standard, chemicaI parameters’ are those defined in the EU Directive 98/83/EC of 3 November 1998 (see Ill).
Limits of chemical parameters being potentially present in chlorine dioxide solution have been specified in the corresponding EN standards of the starting products (indicated In A.1.1).
5.1 Sampling
Sampling of chlorine dioxide solutions shall avoid photochemical decompositions, losses by evaporation of the product and consumption by the glassware and dilution water. Samples shall be taken at the exit of the reactor or from the storage tank with a sampling tube and the analytical procedures started as fast as possible.
In order to achieve these objectives the following step by step procedure shall be adopted:
— sampling shall be made in accordance with the general requirements given in ISO 3165 and take ISO 6206 into account;
— all glassware shall be conditioned immediately before sampling, with the solution under investigation and this preliminary rinsing sample shall be discarded;
— liquid samples for analytical control shall be introduced directly into the analytical reagent solutions; the sampling device and procedure shall ensure that the sample is directly contacted with the analytical reagent without running along the walls of the analytical glassware;
— the sample vessels shall be stoppered, leaving minimal head-space, to store the sample with reagent mixture;
— at high concentration of chlorine dioxide (>10 g/l) the samples shall be collected in a vessel, containing water; the analytical result shall be corrected accordingly for the dilution factor;
— titration analysis shall preferably be carried out immediately after sampling and reaction;
— ii immediate titration or measurement is not possible, prior to the analytical measurements the sample plus reagent shall be stored in the dark at low temperature about 5 °C and contact with ambient air shall be avoided;
— if immediate collection and analysis are not possible, sample the reactor effluent in a 250 ml conical flask stored on crushed ice and, by introducing the liquid at the bottom of the flask and fill the flask completely allowing overflow of chlorine dioxide solution.
The volume of the samples shall be adjusted in accordance with the analytical procedure described hereafter.
5.2 DeterminatIon of chlorine dioxide and chlorite concentrations
5.2.1 General.BS/EN 12671-2016 pdf download.

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