...
The team used the same procedure described on materials and methods. The lime was added as dry powder. For the up-flow velocity of 3.6 mm/sec, it was calculated that 20g of lime were required for the effluent to be saturated for 12 hours. The amount of lime was calculated as explained in Experiment 1., proportions were kept.
Results
Figure 1. shows effluent pH over time. The green line represents the 2.5cm diameter tube settler, and the 5cm diameter tube settler is represented by yellow and orange lines. We can see that none of the runs were anywhere close to reaching the goal of twelve hours with a saturated effluent. Both tap water and distilled water runs with the 5cm diameter tube settler failed within an hour and a half, while the run with the 2.5 cm diameter tube settler never produced any saturated effluent. There is certainly no performance improvement running the reactor with distilled water.
Figure 1. Effluent pH vs time in hours. Comparison of performance between tap water and distilled water.
Figure 2. shows the fraction of saturated hydroxide concentration versus the fraction of time the run is theoretically calculated to last. This is simply a clearer way to display the reactor's performance over the course of the experiment relative to our goal, which would be to have a straight line at an OH fraction of one. In this case, Figure 2. illustrates what are likely measurement errors: a hydroxide concentration nearly double the saturation value in one run and a failure to reach saturation in what should be an identical trial.
Figure 2. Fraction of saturated hydroxide vs Fraction of time
...
The similarity in performance between the A2 apparatus 5 cm diameter tube settler run with tap water and the A2 same apparatus run with distilled water indicates that calcium carbonate precipitate may not be the main issue. Failure with distilled water suggests that there must be another issue. See the hypotheses page for further information.
Even with the results, one experiment is not enough to reject the carbonates hypothesis. Other factors could affect such as coating of the pH probe with lime particles. Further experiments are required to compare results.