Greetings experts I would like to know about chemical shelf life of calcium hydroxide, polymer and ferric chloride. I use calcium hydroxide for ...

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Greetings experts I would like to know about chemical shelf life of calcium hydroxide, polymer and ferric chloride. I use calcium hydroxide for pH adjustment and solid precipitation in wastewater treatment. I used to add four to five bags but lately I've been adding 20 bags. Does chemicala lose strength or effectiveness with time (year)? Please help.

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As indicated by  all the other commentators , the lifespan of the chemicals depend on the conditions of storage. Calcium hydroxide (lime) should be stored in an enclosed dry space since moisture would cause it to cake hard and CO2 would deactivate it forming CaCO3. Polymer should also be stored in a dry cool place because moisture would tend to form a gel. Ferric chloride solution to be stored in a closed drum since extended exposure to air could affect the solution by oxidation of Fe ions. Check the load of suspended solids or sludge because that would affect the dosage of these materials. Maybe a jar test could be done to optimize the additions of these chemicals.

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Greetings Tebogo. As William alludes to, it depends on how, where and the duration of storage. The original supplier is always a good starting point. After that you need to consider how you are making up the products and then how long you are keeping prior to dosing. Dosing is another consideration, are you using static mixers etc. is your maintenance good. Finally, how does the composition of you waste water vary over time (relatively stable or prone to fluctuations)?

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It can absorb CO2 from the atmosphere making CaCO3 that will not react. 

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