Issues regarding the use of flocculants in water treatment
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For the purification of drinking water, the source is a reservoir with a pH value of 7.1. When polyaluminum chloride is added to this water, no flocculation occurs at all. However, if alkaline substances (such as sodium hydroxide, amine solutions, or lime) are added, significant flocculation takes place. Which type of coagulant should be used to achieve purification and meet drinking water standards?
It is recommended to conduct a water quality analysis of the source water to determine which ions require ultrafiltration. Based on the dosage used, I believe that the SS and NTU levels in the raw water are relatively low; as a result, no flocs were formed despite the addition of polyaluminum chloride. When alkaline substances are added, a large amount of alum is formed, indicating that the levels of HCO3-, CO32-, and Ca2+ in the water are relatively high, leading to chemical reactions.
The poster is in the same situation as me: while testing mechanical stirring clarifiers, no alumina flocs could be seen; however, once sodium hydroxide was added, alumina flocs appeared immediately. Different coagulants such as PAC, polyaluminum chloride-iron, and polyaluminum ferric chloride all required the addition of alkali. I’m not sure what caused it. From what I’ve read, a pH level above 6 should be fine; our raw water has a pH of around 6.8 to 7.2, and it’s river water