...
TRIAL 3. DISTILLED WATER, CHANGED BRAND OF LIME
...
INTRODUCTION
This trial was carried out using distilled water to determine how long the experiment would last without the influence of carbonates (present in tap water). In addition, another parameter that was inadvertently changed was the brand of lime, since the previous supply of lime was almost over and the depleted. The new lime was of a different brand (having brand had 70% calcium hydroxide compared to the older lime containing 96% Calcium Hydroxide). Thus during this trial, not only was the effect of water quality was evaluated but also the effect of lime quality was evaluated.
For this trial the pH remained stable at 12 for just 3.5hours.
...
.5 hours.
OBJECTIVES
• Confirm if the carbonates or other quality characteristics of tap water, have any influence on the lime feeder performance.
• Evaluate the apparatus performance with a different brand of lime.
• Look for improvements for future experiments.
PROCEDURE
For this trial tap water was replaced by distilled water. In addition, the lime was changed, looking for a better quality of the compound. No changes were made to the constructional design of the apparatus.The apparatus was kept the same as for the previous two trials. The procedure adopted was the same as for trial 2, i.e. 100g of lime was made into a slurry and poured into the lime feeder from the top of the column. The flow rate was regulated at 120 mL/min (upflow velocity of 4.42 mm/s) by the peristaltic pump while the pH was recorded using a pH probe. Water supplies were made available from the distilled water tank. A more detailed explanation of the procedure can be obtained in the Materials and Methods section.
NOTE: Although the change in the brand of lime was not pre-decided for this particular trial, it would allow us to evaluate if the performance of the lime feeder changes on using a different lime brand. This change is important to study taking into account the fact that the operators would have to deal with a different brand(s) in the local Honduran markets.
OBJECTIVES
• Confirm if the carbonates or other quality characteristics of tap water, have any influence on the lime feeder performance.
• Evaluate the apparatus performance with a different brand of lime.
• Look for improvements for future experiments.
RESULTS
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 diminished the number of big particles within the apparatusgenerally 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 of course)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
The information obtained from this trial was not enough to probe the influence of the two considered variables. Since 2 variables got changed simultaneously, different conclusions can be extracted-:
One, that the distilled water made little impact on the working of the lime feeder . (Again this could be due to the fact that or the distilled water supply system had a presence of impurities.
, though stored in a closed plastic container was kept so for more than 3 weeks, which resulted in a leakage of Carbon dioxide through the plastic walls so that in effect the distilled water was no better than tap water after a long duration.) Second, the decrease in efficiency of the system was due to the fact that a different lime quality of lime was used which and did not match the hypothesis on which the design was based.
FUTURE TASKS
It thus remains to be evaluated if the design and the calculations made so far are acceptable for different types of lime with different solubility characteristics in water. It also needs to be verified if the quality of water has a strong influence on the pH behavior or not.
To make these evaluations, it is necessary to run more trials on the experiment using the new lime but with tap water; and using the old brand of lime Further experiments 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.