We performed lab-scale ozonation in drinking water samples in order to measure the chlorination by-products formation potential. We terminated the ozone reaction with Na2S2O3. After the chlorination and incubation of the samples, we observe no Cl2 residual but only at the ozonated samples. I suspect that Na2S2O3 may interfere with the Cl2 added. Any suggestion on that and how i can neutralize the Na2S2O3 effect?
Sodium thio-sulphate will definitely interfere with chlorine residuals. It is used to dechlorinate water where required. For example, after super-chlorination of drinking water to bring the Cl2 residual to an acceptable level for distribution to consumers, or when water containing chlorine is to be released into natural water courses. I am not sure how to neutralise the effect for your experiment. The Royal Society of Chemistry has a Water Science Forum where such questions can be put to Chemists.
Dear Alex,
Yes. Na2S2O3 is a reducing agent while Cl2 is a strong oxidizing agent. They can react.
Best
Maohong Fan
You are likely to end up with sulfur deposits in the water which will make the water appear cloudy.
Dear Alex,
Instead of using sodium thiosulfate, you may strip the remaining ozone by bubbling an inert gas (N2 for example) into your solution. This takes usually 2 or 3 minutes, given that ozone's solubility in water is rather low. However, you have to make sure that you will not strip any other species from your water (a volatile DBP precursor or another species).
Regards,
Pierre
We use sodiumbisulfite using redox measurement at our water reuse facility of Torreele. We use hypochlorite in the processes (e.g. UF) prior to reverse osmosis and in order to protect the RO membranes for too high chlorine residual we dose bisulfite neutralizing the chlorine residual. The dosing is controlled by redox as redox indicates if chlorine residual is too high in concentration.
Sure, they are reacting together and the reaction product is sodium tetrathionate. We use such reaction in analytical chemistry but instead of chlorine we use iodine and the method is used to standardize iodine solution. By the way if you want to stop the reaction by any reducing agent, Cl2 will be consumed.
Thank you all for your answers!! I chlorinated some blank samples containing only pure water and Na2S2O3 in order to determine its Cl2 consumption and i added this consumption to that of the organic content of the water. It is really much higher the Cl2 demand for the determination of DBPFP in comparison to the same but unozonated samples.
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