ANC CONTROL

Experiment 3 - Trial 4: Old Lime Brand and Distilled Water

INTRODUCTION

The final trial was carried out using distilled water and the old brand of lime. The apparatus was kept the same as that of the previous three trials with the exception that the tank in which the distilled water had been stored was cleaned thoroughly.
The purpose of this trial was to confirm if the failure of the previous trial (trial-3) was because of the carbon dioxide (in the air) which the water had been exposed to or the presence of carbonate impurities in the container. Another objective was to verify if the lime feeder performance was grossly affected by the change in lime brands.
For this trial the pH remained stable at 12 for 8 hours, which was by far the maximum duration achieved.

OBJECTIVE

• To check the performance of the experiment with the first lime brand and distilled water (from a cleaned supply tank)in order to verify if the previous trial (trial 3) failed because of the failure of the tube settler theory or because of an impurity in the distilled water supply system.

PROCEDURE

The procedure adopted for this experiment was the same as all the previous trials. 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 40mL/min by the peristaltic pump while the pH was recorded using a pH probe. Water supplies were made available from the cleaned distilled water tank.
A more detailed explanation of the procedure can be obtained in the Materials and Methods section.

RESULTS

The results of this trial can be seen in the figure below as per which the system lasted at a stable pH of 12 for about 8 hours.

Figure 1. pH vs Time (h)

CONCLUSIONS

After the successful run of this trial it can be concluded that carbonates present in the alkaline tap water were indeed the problem causing the lower efficiency of the lime feeder system and since this difficulty will not be faced in the Honduran source water (having very low pH)the lime feeders can be made to run successfully for 12 hours after making further adjustments in the dosage of lime and water flow rate. This experiment also showed that the flow rate that was being used so far (120 mL/min) to get very high upflow velocities (4.42 mm/s) was not necessary and was causing higher loss of lime. In order to get an average lime feeder run of 12 hours, the lime dose will have to be further increased. Details regarding these next steps can be viewed on the Future Challenges page.