Acid Neutralizing Capacity (ANC) Control Team

OVERVIEW

Drinking water requires a pH around 7 for effective treatment. 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. Moreover, the neccessary alum dosage is very sensitive to pH changes in the entering water and vice versa. This is often the case in many of the Honduran plants. For this reason it is imperative to ensure that the pH of the water entering the flocculator is maintained near 7. 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 limewater into the entrance tank, the target pH will 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 causes the pH of treated water to go as low as 4.5, interfering with alum precipitation and affecting alum dosages. Consequently, plant performance is suffering. The ANC team has hence been presented with the opportunity to re-design a model for a lime feeder system that could increase the pH of entering water to at least 6.5, without the use of electricity.

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