Restricted Flow of Hypochlorinators
Introduction
In Honduras, a Calcium Hypochlorite solution is used in the Agua Clara flow controllers to disinfect the drinking water. Unfortunately, due to the precipitation of calcium carbonate, the system clogs which leads to large decrease in the flow rate (and thus dosing) of the chlorine solution. These experiments have been developed in order to determine the point of restricted flow and to devise a method to diminish the clogging.
Experimental Model
A model very similar to the model used during the Summer 2008 Demo Plant team was used. A slightly more analytical approach was taken in developing this semesters model. A pressure sensor was inserted by means of a t-joint at the bottom of the constant head tank. The sensor would collect information on what the height of solution in the constant head tank was at any given time. By using the Easy Data to analyze the data, we would have a more accurate idea of when clogging occurred. In addition, a pH meter was added to the 5 gallon stock tank. This was done in order to aide future studies on the effects of alkalinity on calcium bicarbonate precipitation. The final change was that the flow rate was determined by changing the angle of opening within the valve at the exit of the constant head tank. Shown below is the experimental model from the summer with the changes written on the image.
The values used to run the experiment were as follows. We chose to use 9.336 mg/L of calcium hypochlorite for this lab experiment because it is half way between 12201 mg/L and 6470 mg/L, which were the average concentrations used at Tamara and 4 Communidades (The towns with the most severe issues with flow rate). The flow rate would be run at 68 mL/min, because it is the average of the reported range of flow rates in Honduras.
Procedure
15 mL of deionized water would be put into the 5 gallon stock tank. 158 mL of Calcium Hypochlorite powder would be added to this stock tank. 2 L of deionized water would be added on top of this in the stock tank. The carboy being used would then be simply stirred and shaken for 5 minutes in order to mix the solution thoroughly. The tank would be allowed to settle for 10 minutes, and then the experiment would be run. The 7kPa sensor would be set up using Easy Data and the "cm of water" calibration file. The pH meter would be run using the program pH Meter.
Results
Using the flow rate of 68 mL/min, the model (assuming no restricted flow) would require approximately 4 hours and 9 minutes to be emptied (4.16 hours).
