ANC CONTROL

EXPERIMENT 2: Testing Carbonates Hypothesis

INTRODUCTION

Based on ANC Control team Fall 2009 future challenges, it was suggested to develop tests with Tap water and distilled water in order to probe carbonates influence over the apparatus performance. ANC Control Team Spring 2010 started with this experiment, using Tap water. Results will be compared and analyzed with another experiment which conserves all characteristics but uses tap water.

PROCEDURE

The team used the same procedure described on materials and methods. It is important to remark that lime was added as dry powder.

According to the calculations based on lime solubility constant; this experiment required 20g of lime and will last for 12 hours, the maximum or theoretical pH will be 12.6, with a flow rate of 120mL/min.

RESULTS

Despite a pH of 12 was calculated to last for 12 hours; during the experiment, pH was located in 12 units or above for one and a half hour (1.5h) for A1 and around three hours (3h) for A2. The following graph shows pH behavior over time.

It is shown that A2 requires a larger time to increase pH, it is due to the difference in design. A2 has a larger retention time. On the other hand, pH in!OH Fraction graph.jpg|align=centre! A1 decreases faster than pH in A2, it could be explained on the same basis of design differences. Capture velocity in A1 is faster and it is possible that small particles of lime are being getting out at a high rate while they can stay and react for a larger period of time in A2.
To have a better understanding of what is happening during the run, the team plotted OH fraction versus time fraction. Theoretical pH was established in 12.6, in consequence, theoretical pOH was 1.4, and theoretical time was 12 hours. Results are shown in the following graph.

As shown, OH concentration in A2 was highly above the theoretical estimation having values until 12.8; while A1 never reached pH of 12, having its maximum at 11.68. On the other hand the experiment lasted as designed just 15% of the time. OH concentration is a good indicator of design performance since the main objective of ANC team is to regulate the neutralizing capacity of Honduran water, it is projected to establish an optimal base concentration that will allow dealing with the addition of chemicals with acidic concentration in other stages of the purification process.

CONCLUSIONS

Improvements in the design have worked very well; it is possible to detect an increase in retention time, a decrease in capture velocity and a well mixing in the bottom. With a high flow rate, A1 shows a well mixing in the bottom but capture velocity is very high and it is possible that lime particles escape through the effluent.
It is not possible to have conclusions about carbonates influence until compare results with the experiment under the same constraints but using tap water.