Experiment 9: Increased Lime Concentration + Continued Pulsing

Overview

The purpose of this experiment was to maintain all the same conditions as Experiment 8 but to change the concentration of the stock solution. Experiment 8 failed because the lime pulses did not increase the pH sufficiently. Therefore, it was determined that a more concentrated solution was required. The amount of lime added to the solution was multiplied by 5, resulting in 622.5 grams of lime added to 15 liters of water.

Procedure

An almost identical procedure was followed for this experiment as in Experiment 7. Then a more highly concentrated lime slurry of 622.5 grams of lime was prepared in 2 liters of tap water and then diluted further with 13 additional liters of water for the stock concentration. The difference between the two experiments is in the use of the blender to prepare the slurries.
For the 100 grams of lime that were to be fed into the vertical column, the blender was used for 5 minutes on "liquefy". Unfortunately, at the end of the 5-minute period for the second 100 gram slurry, the blender overheated and became inoperable. Therefore, the mixer had to be used to blend the remaining lime slurry needed for the stock concentration. It is suspected that the mixer does not provide the same particle uniformity that the blender does.

Results and Discussion

An almost identical procedure was followed for this experiment as in the Experiment 8. A lime slurry of 100 grams of lime plus 1 liter of tap water was prepared for each apparatus. Then a more highly concentrated lime slurry of 622.5 grams of lime was prepared in 2 liters of tap water and then diluted further with 13 additional liters of water for the stock concentration.

Because the blender was broken, the large mixer had to be used to prepare all three lime slurries.

Approximately 120 hours later (5 days later), the stock solution was refilled with the same concentration (41.5 g/L). However, the blender had been repaired at this time and was used to prepare the slurry, instead of the mixer. At the same point in time (5 days from the beginning of the experiment) the flow rate for the peristaltic pump flowing to A2 was increased from 40 mL/min to 50 mL/min in an attempt to raise the pH.

Below is the preliminary data from the experiment: 

                                                                                                              Figure 1 - Experiment 9: data from hours 0 to 40

                                                                                                                Figure 2 - Experiment 9: data from hours 40 to 80
 
                                                                                                               Figure 3 - Experiment 9: data from hours 80 to 120