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The purpose of this experiment was to test pulsing lime into the two apparatuses. Because both apparatuses fail after a shorter time than desired, it was hypothesized that the lime initially added to the apparatus (100 grams) eventually reached a point where it would no longer properly dissolve and raise the pH. Thus, more lime was needed as the experiment progressed. However, adding 100 grams each time would severely overwhelm the system. The following calculations were performed to determine the appropriate amount of lime that needed to be pulsed in every 6 hours:
Figure 1
From this graph one can see that the amount of lime that must be added for a flow rate of 30 mL/min is approximately 2.365 grams and for a flow rate of 40 mL/min, 3.154 grams of lime must be added.
The group determined that it would be best to pump in the stock solution at the highest possible flow rate, which is 380 mL/min. Thus, 380 milliliters of stock solution are pumped in every six hours. One challenge to this set up is that there is only one pump and one concentration for the stock solution. However, each apparatus requires a different mass of lime to be pulsed in, according to Figure 1 above. To solve this problem, the higher concentration of stock solution was made according to the calculations for A2, which resulted in a concentration of 8.3 grams of lime per liter.
The team then installed two pump heads on the third peristaltic pump and used two different tubing sizes to regulate the flow to each apparatus. Referencing the information about peristaltic pumps it was determined that A1 should have tubing size 17 while A2 has tubing size 18. This allowed for each apparatus to receive the proper lime mass with each pulse while still running off the same pump.
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A2 performed similarly to A1, except that it reached a level pH of approximately 11.5 much more quickly. It started failing sooner than A1, at around 6:00 am, only 18 hours after the experiment began.
Figure 4 - Experiment 7