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The apparatus worked well with the established upflow velocity. The movement of particles was clearly visible and in accordance with the hypothesized movements (similar to the particle movements in the tube settler spacing apparatus). (You never told us the hypothesized movements. What about it worked well, be specific if you are going to include observations), i.e. a fluidized bed up to the middle portion of the lime feeder and a relatively clear effluent towards the top end (sloping)of the column which acted like a tube settler. At the top of the sloped column, the water looked clear of and free from visible particles but according to the pH sensor measurements, it was saturated with base (i.e. pH 12), which was in accordance with the main objectives. A great amount of lime remained captured in the middle of the apparatus, although it was held in suspension. This signifies that the upflow velocity was high enough to give good suspension but the sloped column took care that the extra lime did not fall out with the effluent water but remained inside the column. This was a desirable behavior because the lime was still in the apparatus, giving donating hydroxides to solution the protons needed by water.
However, the pH remained stable at 12 just for 20 minutes. It was necessary to calibrate the pH probe again, to clean the apparatus and to review the calculations in order to determine the reason for the abnormal pH behavior. (Why only 20 minutes? Give more explanation behind observations you make) 
Figure 1. pH vs time
CONCLUSIONS
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