...
For the above trial, the pH remained at 12 for about 3.5 hours but the performance of the apparatus changed drastically. The new lime was much more soluble in water and generally was composed of finer particles. The new lime did not accumulate in clusters at the bottom of the apparatus. This gave an almost perfect and uniform suspension of lime throughout the apparatus leaving no scope of observing the particle movements.
This presented a whole new challenge , because the entire design for the lime particles was based on the assumption that the suspended lime formed small particles and therefore could be treated as flocs (with different characteristics) so as to use the plate-settler theory to hypothesize their movements. This meant that the calculated upflow velocity and the capture velocity were not valid for the new kind of lime.of verifying whether the hypothesized plate settler theory was true for different brands (having different particle size distributions and different composition)of lime or if the unexpected results of the experiment was due to some impurities present in the distilled water supply system. (A much higher performance for the lime feeder had been expected - much greater than 4 hours but less than 14 hours;4 hrs being the duration obtained using tap water and 14 hrs being the theoretical run length with the given amount of lime and given water flow rate.)
Figure 1. pH vs Time (h)
CONCLUSIONS
...
One, that the distilled water made little impact on the working of the lime feeder . Despite the results, it was necessary to figure out the reasons. Either or the distilled water had no effect on the limefeeder or it had an impuritysupply system had a presence of impurities.
Second, the decrease in efficiency of the system was due to the fact that a different lime quality was used and did not match the hypothesis on which the design was based.
Further experiments are were needed to probe or reject the distilled water hypothesis. It is necessary to check the performance of the experiment with the first lime brand and distilled water, and with the second lime brand and tap water. Those results will provide comparable parameters. Hence the next trial involved usage of the older lime brand (96% Calcium Hydroxide) with distilled water.