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Although a pH of 12 was calculated to last for 12 hours; during the experiment, the pH attained was 12 units or above for 40 minutes for the A2 apparatus run with DI water and about 86 minutes for the A2 apparatus run with tap water. The A1 apparatus never reached a pH of 12. The following graph shows pH behavior over time.
It is shown that A2 requires a larger time to increase pH, which is due to the difference in design. A2 has a larger retention time. On the other hand, pH in A1 decreases faster than pH in A2, which 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 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 as 12.6, in consequence, making the theoretical pOH was 1.4, and the 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 up to 12.8; while A1 never reached a pH of 12, having its maximum at 11.68. On the other hand, the experiment lasted only 15% of the expected 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.
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