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The former ANC group experimented on different designs for a lime feeder, including a column model, a conical vessel, a funnel-column and lastly an inverted traffic cone model. The most effective design was the inverted cone because it supplied saturated limewater at a pH between 11 and 12 for about 18 hours without having to be unclogged. However, the main problem with this setup it is that inverted cones are extremely difficult and expensive to construct, install and maintain. Every Likewise, every other model also had its problems and drawbacks.
For example, the The Column model succeeded in keeping the lime suspended for a few hours but the water began to flow in a preferential path after the lime settled on the bottom. For the conical column, the mixing at the bottom of the vessel proved to be insufficient in keeping all the lime in a suspended state. On the other hand, the funnel-column apparatus worked well for 20 hours but only because it was unclogged periodically, which would not possible in a real-time set up. As a result, the inverted cone model that gave a 12 hour success run, without the above difficulties was selected as the best alternative among them. However, due to the difficulty in construction, installation, and maintenance, the ANC team was assigned the task of searching for a simpler solution for the lime feeder design.
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The table below shows actual measures of pH and alkalinity in AguaClara treatment plants in Honduras. To have high accuracy in the lime feeder design, the team will simulate the conditions of raw water in the lab. The results demonstrate a decrease on of pH during the treatment process, it is strongly visible on Cuatro Comunidades and Tamara plants.
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Source: Honduras water reports, 2009
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