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Figure 1: Capture Velocity vs. Average Effluent Turbidity shown for each alum dose at low floc blanket level.
Figure 2: Capture Velocity vs. Average Effluent Turbidity shown for each alum dosage at high floc blanket level.
Overall, this system performed well and most of the effluent turbidities were below 1 NTU. The ideal alum dose of thesis on evaluation on parameters affecting steady-state performance of a floc blanket found that the ideal dosage was 45 mg/L and the slight underdose and overdose for 100 NTU influent water. The alum doses of 35 mg/L and 65 mg/L , respectively, performed best. (Do not say 45 mg/L was ideal or performed best when clearly it did not with the data. Instead explain why it did not perform as well.) Because the slight underdose and overdose did not fail (what do you mean by failure? Elaborate if you are going to use this word), as expected, it was necessary to test more extreme dosespeformed well (average effluent turbidities were under 1 NTU), what was thought to be extreme under and over doses were also tested. We tested 15 mg/L and 105 mg/L to observe more severe conditions (saying severe conditions is vague. What do you mean? What were you specifically wanting to observe in effluent performance?). The extreme overdose how the floc blanket formed under severe non-ideal conditions. The dose of 105 mg/L, despite averaging at less than 1 NTU, resulted in failure since the average effluent turbidity frequently spiked above 1 NTU. The 15 mg/L extreme underdose dose, however, did not experience failure. (Please define failure early. Is it effluent turbidity above 1 NTU?)had average effluent turbidity of less than 1 NTU, meaning that cannot be considered a failure.
Originally, an alum dose of 45 mg/L was thought to be an ideal dose. (Again, if you haven't already defined this, define what you mean by ideal dose. Is it the dose that gives the best performance?) , meaning that it was supposed to produce the lowest effluent turbidity. However, this alum dose did not perform as well as was expected. In comparison to the other average effluent turbidities, 45 mg/L should either perform slightly better than an alum dose of 35 mg/L or somewhere between 35 mg/L and 65 mg/L. As shown in the above graphs, 45 mg/L performs worse than all of the other alum doses, including what was supposed to be extreme under and over doses (15 mg/L and 105 mg/L). This should not have happened, and experiments possible reasons for these results are air bubbles in the settler tube, other reasons. Experiments at this alum dose should be re-run. (Give reasons why it failed and why a re-run would be appropriate.)
The major cause of failure for an underdose is an incomplete floc blanket as a result of smaller flocs that are formed, but the increased residence time in the flocculator creates larger flocs, which form a floc blanket more quickly and more effectively. Thus, although we expected that the extreme underdose of 15 mg/L would fail, the effluent turbidity fell within the acceptable range. (This paragraph needs to be rewritten. I agree with what you say about the flocculator, but you need to differentiate between underdosing and floc blanket failure. The floc blanket clearly formed and gave performance under 1 NTU, so this was not failure. This was worsened performance compared to a dose of 35 mg/L. Include reasons for why this would be the case.)
In contrast, an alum overdose forms a less dense, more "fluffy" floc blanket, which is not as effective in trapping flocs and filtering out particles. (I disagree. I think because the flocs are weaker and breaking up in the floc blanket causing spikes in effluent turbidity. ) The extreme overdose of 105 mg/L shows failure higher turbidity as a result of this insufficient these weak flocks in the floc blanket.
Because the effluent turbidity using the alum underdose of 15 mg/L was acceptable once the floc blanket had formed, it seems that the dosage is unimportant once the floc blanket is completely formed. (This is an inherently false statement. There is a range of acceptable dosing and I think your team can reason as to why this is the case. Why should we dose at all?) , within a certain range of alum doses. It appears that as long as the floc blanket is fully formed, which should occur with a higher dose so that it forms quickly enough, the alum dose can be lowered while still experiencing the same results. (you need to say that this has to occur within an acceptable range so that you can still effectively form flocs and capture colloids in the flocculator.) However, the alum dose does need to be within a certain range for an effective floc blanket to form.
The water chemistry in our system also contributes greatly to the unexpected results. (were the results unexpected except for 45 mg/L?) The water in the lab is much more alkaline than the water in Honduras. As a result, the pH of the water in Honduras is more sensitive to changes in alum dose. There is an ideal range of pH values where flocculation occurs most effectively, and this range is harder to achieve in Honduras. Thus, the water in the lab allows the system to be more robust and able to achieve acceptable effluent turbidity even with a large range of alum dosages. This observation means that even though the system appears to work successfully regardless of the ranges of alum doses that we tested), the same will most likely not be true in Honduras. We must modify our findings for the plant in Honduras because the same results will not be achieved with a different water chemistry. A future study could include changing the alkalinity of the water to make the water pH more sensitive to changes in alum dose to confirm the applicability to Honduras.