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Chemical processes to test wastewater are usually done in laboratories on samples gathered from the field as well as from wastewater treatment plants. Such chemical analyses often involve the use of chemicals such as Potassium and Iodine. In this article I discuss the a do-it-yourself Tidy’s Test, involving both these chemicals.

One of the tests that can be easily employed to test wastewater is the Tidy’s test. Potassium iodide is used in this test which requires an acid solution. In the laboratory test, the oxidising agent in the solution undergoes a reduction reaction where it is reduced by the potassium iodide. This reaction releases sulfate. If this reaction takes place in wastewater, then it forms wastewater sulfate.

Below are some of the reactions that are used to understand the chemical composition of and to test wastewater.

2KMnO4 + 6KI + 8H2SO4 -> 4K2SO4 + 2Mn(SO4)2 + 8H2O + 3I2

In this reaction, potassium permanganate (2KMnO4) reacts with Iodine and sulfuric acid to produce two forms of sulfate namely potassium sulfate (4K2SO4) and manganese(II) sulfate (2Mn(SO4)2) along with iodine in large quantities.

2Na2S2O3 + I2 -> Na2S4O6 + 2NaI

This reaction follows the one earlier. In this reaction, the sodium thiosulfate (2Na2S2O3) reacts with the iodine formed earlier to form sodium tetrathionate (Na2S4O6) and Disodium diiodide (2NaI).

I2 + starch -> Starch Iodide (blue)

This last reaction depicts the action of iodine with starch. If these substances are present then they react to form starch iodide. The end product thus obtained is of the color blue.

When analysts test wastewater in laboratories they conduct experiments in clean environments without having to worry about contamination of effluents. But at wastewater testing plants, the water is a mixture of industrial effluents and sewage. This is a potentially hazardous mix as it contains both biological pathogens and chemical-metallic waste from industries. Such samples taken to laboratories have to be filtered to remove the contaminants that can interfere with these reactions.

It is important to identify the chemicals in wastewater and to then plan a proper treatment considering the combined effect of the effluents.

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