ANC CONTROL
FUTURE CHALLENGES
INTRODUCTION
The Fall '09 ANC Control team had worked on the development of a lime feeder. Including constraints such as non-electricity use, low cost and replicable design; the team had found some important parameters.
1. It is possible to assume the particle behaviors in the lime feeder are similar to the behavior of flocs from the plate settlers of the sedimentation tank. A description of the theory is detailed in Experiment 3.
2. The main variables to consider in the lime feeder operation are the upflow velocity, the lime quality and the water composition.
3. The required lime needs to be very fine to avoid clogs in the apparatus by large lime chunks.
4. The water must have a low presence of carbonate system, to facilitate the dissolution of lime and induce a pH change.
Despite these findings more research is required in order to confirm the theories and to find an explanation for some variables that are not enough clear yet.
FUTURE CHALLENGES
The following are proposed challenges for the next team:
1. Determine the optimal lime particle size and an easy way to separate it from the rest of the lime.
2. Determine the optimal upflow velocity which will maintain the suspension bed for the required particle size.
3. Compare different chemical compositions or commercial lime, especially those available in Honduras, and evaluate the apparatus behavior with them.
PROPOSED EXPERIMENTS
To accomplish the future challenges the Fall '09 ANC Control team propose the following experiments:
1. Continue with the current design (Experiment 3):
For the current experiment, the Fall '09 ANC Control team changed the variables and made runs to compare the behavior. However there was not enough time and just one trial for every combination of variables. It is suggested that the next team run more trials conserving the design but changing the variables. In this way it is possible to confirm the theory and scale up the design for the actual water treatment plant in Honduras.
The first experiment should be finding the optimal upflow velocity. Using a sieve, the lime particles can be filtered so that there are only uniform fine particles. The lime then has to be dissolved in enough water before going into the apparatus. Starting with low upflow velocities, lime bed suspension can be seen visually and then noted. In addition, pH can be measured and compared the entire duration (at 12 units). It is necessary to leave the lime settled down or to replace it before making a new experiment with different upflow velocities.
The experiment has to be carried out at least two times with each upflow velocity. After finding it, include the last variable (lime composition). It is not required to use the same brand that the Fall '09 ANC Control team used. It would be great to find the composition of commercial lime in Honduras. The combination of variables suggested is:
• A specific commercial lime composition + tap water.
• A specific commercial lime composition + distilled water.
Another path to pursue is to change the apparatus and use tubes with a bigger diameter, allowing for the increase of upflow velocity and to experiment with a higher amount of lime. This would also let the water flow in the vertical direction and avoid the fast expulsion of lime.
2. Change of apparatus design:
Another option is to develop a completely new design. As a suggestion, there is a lime feeder design described in the book "Surface Water Treatment for Communities in Developing Countries" by Schultz and Okun, 1992. According to the authors, this apparatus was used in a water treatment plant in Brazil. The design does not involve electricity, just hydraulic considerations.
Figure 1. Brazilian design
Figure created by ChengFeng Wu, based on the referenced book