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Drinking water requires a pH around 7 for effective treatment (Why?). During the process of water treatment, alum is added to remove organic particles and clay in a process called flocculation. Alum decreases the pH of water making it acidic for low alkaline waters (Why? Can you show the chemical equation?). Moreover, the neccessary alum dosage is very sensitive to pH changes in the entering water and vice versa if the water does not have sufficient alkalinity. This is often the case in many of the Honduran Honduras plants. (Can you show documentation of this?)
For this reason it is imperative to ensure that the pH of the water entering the flocculator is maintained near 7 (What reason? You didn't explain in the first place why a pH of 7 was necessary.). Lime ( Calcium Hydroxide) is an alkaline substance popularly used to neutralize low pH water. By devising a system (lime feeder) that will continuously supply a dose of saturated lime water into the entrance tank, the target pH will could be reached.
Research on designing a lime feeder (for the plant at Ojojona) had been carried out until the Spring of 2006 by the former ANC control team. It was discontinued because the plant at Ojojona was working successfully without the need of lime feeders. However presently, it has been reported that reduced alkalinity in Honduran source water is interfering with alum precipitation and affecting alum dosages. Consequently, plant performance is suffering because we are not getting sufficient quantities of Aluminum Hydroxide precipitate. So a lime feeder model needs to be re-designed, that could increase the pH of entering water to at least 6.5, without the use of electricity. (Good explanation here. Try to introduce these concepts a little earlier in your explanation)
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