Recommendations for Honduran Communities that are Experiencing Flow Restriction Problems in the Chlorine Feed System
1) Safety: I understand that priorities are different in the Honduran culture, and safety is not always the number one issue, but I think as a whole the number one thing that we could pass along to Honduran communities is education about health and safety. This would not be limited to the health advantages of safe drinking water, but also comprise of the advantages of working together to meet theses public needs in a safe and compassionate way. Aguaclara should be very active in encouraging that operators take steps to protect themselves when dealing with chemicals like aluminum sulfate and especially calcium hypochlorite. This would include always wearing rubber gloves and being in a very well ventilated area when mixing the chemicals and performing the mixing in short intervals so as to not be exposed to the chemical for long periods of time. It may even go as far as encouraging the use of some type of breathing apparatus.
2) Initial Settling and Filtration: The first action that all communities that are having a flow controller (FC) restriction of flow problem should be to mix the calcium hypochlorite(Ca(ClO)2) solution in a container that has a volume great enough to dissolve all Ca(ClO)2 into solution, which can be determined from the solubility of Ca(ClO)2 or from the attached Mathcad program on the Aguaclara wiki titled "Volume of Water Required to Completely Dissolve a Concentration of Ca(ClO)2".
Calcium hypochlorite has a solubility of 210 grams per liter. For most communities a 20 liter bucket will be sufficient, but as a rule of thumb I think I would be appropriate to implement the policy that states; if you are having a precipitation problem, then the initial settling in a separate container, should be split into two containers if a the container being used is a 20 liter bucket. The total weight of Ca(ClO)2 needed for the 220 liter stock tank is split in two and placed into two separate 20 liter buckets and then mixed with water and allowed to settle. Alternitally, The total weight of Ca(ClO)2 needed for the 220 liter stock tank could be placed in a 20 liter bucket and mixed with water and allowed to settle. Then the supernatant could be removed and another 20 liters of water would be added to the bucket now containing the settled CaCO3 and any residual Ca(ClO)2. This solution would be mixed and allowed to settle again. Last, the second volume of supernatant would be removed and mixed with the first volume.
We would prefer that buckets full of concentrated Ca(ClO)2 were not sitting around unattended for days. We recommend that the plant operators add the weight of Ca(ClO)2 needed to achieve a desired concentration of solution in a 220 liter drum in a 20 liter bucker and let the CaCO3 that precipitates out of solution settle for 30 minutes. Next filter the solution while pouring it into the 220 liter drum through a piece of cotton cloth like a tee-shirt. This tee-shirt can be washed off with clean water and reused.
3) Float Valve Modification: To prevent further precipitant from forming
around the orifice and restricting flow, it is recommended that communities that are having a problem with precipitation remove the float valve from the constant head bottle and flip it from a position pointing downward and can be observed in Figure 2, to a position pointing upward as can be observed in Figure 3. This task involves someone to loosen the nut on the float valve arm and rotate the float upwards. The float should be lifted up high enough so that the solution level in the constant head bottle is above the orifice height that allows solution to pour into the bottle. It may require a few instances of guess and check to meet this height. The floats being used for Aguaclara look different than the float located in (Figures 2 and 3). The same procedure applies to any shaped float.
4) Chlorine Stock Tank Modification: Realistically it is going to be impossible to settle and filter out all of the precipitation that forms as a result of using Ca(ClO)2 as a source of chlorine. If all the solution was to be settled out, more will form as the solution comes into contact with carbon dioxide and other chemical species like carbonates found in surface and ground waters. To deal with this it is recommended that communities add a tube inside the chlorine stock tank that rises up high enough that it is well above the CaCO3 that potentially could settle to the bottom of the tank (Figure 4). We recommend that the tube be located at a height of at least 10 cm above the bottom the tank.
Figure 4. Chlorine stock tank with an inside tube that is located high enough in the tank so the flow out of the stock tank is not impeded by precipitated CaCO3.