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The AguaClara engineers from academic year 2009/10 not only designed, but built and installed a Non-Linear Dose Controller (NDC) in a new AguaClara plant in Algateca, Honduras. The current NDC is installed on top of the entrance tank of the plant and consists of a float connected to one end of a lever arm and the dosing orifice connected to the other end.
Figure 1. NDC As Installed in Aglateca
The entrance tank is connected to the hydraulic flocculator by way of a rapid mix orifice. A change in flow rate through the plant is indicated by a change in the level of the entrance tank. This is transmitted to the lever arm by way of the float. For example, if the flow rate of the plant were to decrease from 100% to 80%, the entrance tank would drop by a proportional amount. Since the pivot is in the center of the lever arm each centimeter of change in the entrance tank will correspond to a centimeter of change in the heights of both ends of the height of the lever arm (although, obviously, the two ends will be moving in opposite directions).
Alum is piped from a 120 g/L concentration stock tank to a constant head tank and from there to the metering orifice. The metering orifice is connected to the lever arm by way of a movable slide. The lever arm has an incremental scale on the top surface which corresponds to specific alum concentrations. The operator is able to set the chemical dose concentration according to the values on the scale and the lever arm will automatically adjust the flow rate of alum to maintain the correct concentration of alum as plant flow rates change.
Figure 2. Stock Tanks and CDCNDC
Feed back from operators and engineers in Honduras along with results from our own experimental lab work provide us valuable information on the accuracy and ease of operation of the NDC. Additionally, brainstorming continues on how to improve and expand the function of the current design. Derived from these topics are the following recommendations for next semester's team.
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