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 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.

OBJECTIVE

The main objective of the team is to design a lime feeder system to deliver effluent with a pH of 12 (saturated pH of water) to be mixed in with treated water to increase its pH. For efficient plant operation, the lime feeder design must be simple, easy to construct and install, cost-effective while also being robust enough as to avoid using electricity and with an additional design constraint that an operator will add a specific amount of lime every 24 hours.

The results of the previous experiments (Fall 2005- Spring 2006) can be found
here
while the current research is detailed in the link below.
ANC Control Midterm Report

The tasks carried out by the present team on a weekly basis are detailed in
ANC Weekly Minutes