ANC CONTROL
TRIAL 3. DISTILLED WATER,
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CHANGED BRAND OF LIME
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OVERVIEW
Despite the performance of the apparatus was the expected, the pH couldn't stay twelve hours at 12 units during the second trial. From the analysis of results, the team decided to determine the influence that carbonates in tape water could have. In addition, the team had proposed to evaluate if the lime that was being used for the experiments was not enough pure. With the third trial, those possible causes of the pH performance will be analyzed and discussed.
INTRODUCTION
The design of experiment 3 continued the same, taking into account that the particles movement and effluent characteristics were according the design. However, tap water was replaced by distilled water, trying to figure out the performance with pure water. In this way it is possible to evaluate the influence of the carbonate system, and the influence of other characteristics of the tap water at AguaClara lab.
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 depleted. The new lime 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. For this trial the pH remained stable at 12 for just 3.5 hoursIn addition, the lime was changed, looking for a better quality of the compound. This change will allow evaluate if the performance is different with a new lime brand. It is also important taking into account that in Honduras, the operators have to deal with the brands that they can find on the local market.
OBJECTIVES
• Confirm if the carbonates or other quality characteristics of tap water, have any influence in on the lime feeder performance.
• Evaluate the apparatus performance with a different brand of lime.
• Determine some Look for improvements for future experiments.
RESULTS
It was observed a change into the apparatus performance. The new lime is more soluble in water; it diminishes the amount of big particles floating into the water flow, and avoids the accumulation of lime at the bottom of the apparatus. However, that result made a new challenge for the team, because all the design was made assuming the particles movement as flocs movement. That means that the team calculated the upflow velocity and the capture velocity for particles movement, and with the new kind of lime, no particles were observed. The team has to evaluate if the design and the calculations are still acceptable for water without visible suspended particles.
On the other hand, the pH remains in 12 units for 3 hours and a half. The time was less than with the second trial. With these results it seems that the quality of the tap water doesn't have a strong influence on the pH behavior.
CONCLUSIONS
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. 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.
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.
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 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 new challenge 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 The information obtained with this trial was not enough to probe the influence of the two considered variables. To confirm the results, it is necessary to run one more time the experiment with the new lime but with tap water; that will be the objective of the next challengeSince 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 or the distilled water supply 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 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.