h1. Analysis of the effect of alum dose and flocculator length on flocculation


h2. Procedure

In +this+ experiment -2- (? Give a more descriptive name than experiment 2) we investigated the effect of alum dosage on flocculator performance. The procedure for [Experiment 1|Experiment 1 Varying flow rate] +(Your link name does not conform to wiki standards. It needs to include your team designation. Please fix.)+ contains information on the general setup used in this experiment. We used the same setup as in Experiment 1, but instead of varying flow rate, we varied the alum dosage. The plant flow rate was held constant at 5 mL/s (a shear rate of 57.563 s-1 calculated using equation 1.9 +(maybe we should try showing the equation here too)+ of [Ian's Thesis |^Ian Tse MS Thesis.doc]), and we used influent turbidities of 5, 25, 50, 100 and 500 NTU and three different flocculator lengths (28 m, 56 m, and 84 m).

To investigate alum dosage at a given turbidity and length, we first planned to vary the alum dose over a large range, incrementing the dose in set intervals while holding the plant flow rate (shear), influent turbidity, and residence time constant. We decided to first run an experiment at each value of influent turbidity at a length of 28 m and then repeat the experiment with the same alum dosage values at a flocculator length of 84 m. If we found a significant difference between the 28 and 84 m lengths for the same alum dosage and influent turbidity, we would then plan to test a third time at 54 m in order to understand the development of any trends we observed. Table 1 shows the alum ranges we tested for each flocculator length and influent turbidity:

*{_}TABLE 1:_* _Alum dose ranges tested and the increment used (mg/L)._
|| Flocculator Length (m) || 5 NTU || 25 NTU || 50 NTU || 100 NTU || 500 NTU ||
| 28 | 10-50 | 10-50 | 10-66 | 20-60 | 10-90 |
| Interval | 5 | 5 | 7 | 5 | 10 |
| 56 | 10-50 | 10-50 | 10-66 | 20-60 | 10-90 |
| Interval | 5 | 5 | 7 | 5 | 10 |
| 84 | 10-50 | 10-50 | 10-66 | 20-60 | 10-90 |
| Interval | 5 | 5 | 7 | 5 | 10 |

The alum dose was varied in process controller using the increment function shown in Figure 1:
!Alum Dose Calculation.JPG!
*{_}FIGURE 1:_* _Process Controller setpoints used to vary the alum dose._

The data was analyzed using the same methods as in [Experiment 1| Experiment 1 Varying flow rate].
We plan to continue narrowing down the optimal alum dose ranges for each influent turbidity and length, and hope to learn whether or not increasing flocculator length will in fact improve performance as expected and how long this trend continues.

The following Process Controller Files were used in our experiments:
[5 NTU One Length Test File |^5NTU 2796cm  5mls Alum 10-50mgL  by 5mgL.pcm]
[5 NTU Three Length Test File |^5NTU 8388cm  5mls Alum 10-50mgL  by 5  mgL.pcm]
[25 NTU One Length Test File |^25NTU 2796cm  5mls Alum 10-50mgL  by 5mgL.pcm]
[25 NTU Three Length Test File |^25NTU 8388cm  5mls Alum 10-50mgL  by 5mgL.pcm]
[50 NTU One Length Test File |^50NTU 2796cm  5mls Alum 10-63mgL  by 7mgL.pcm]
[50 NTU Three Length Test File |^50NTU 8388cm  5mls Alum 10-66mgL  by 7  mgL.pcm]
[100 NTU One Length Test File |^100NTU 2796cm 5mls-1 alum 20-60mgL-1 by 5mgL-1.pcm]
[100 NTU Three Length Test File |^100NTU 8388cm  5mls Alum 20-60mgL  by 5  mgL.pcm]
[500 NTU One Length Test File |^500NTU 2796cm  5mls Alum 10-90mgL  by 10mgL.pcm]
[500 NTU Three Length Test File |^500NTU 8388cm  5mls Alum 10-90mgL  by 10  mgL.pcm]

h2. Results and Discussion

The goal of this experiment is to study the effects of different alum doses and flocculator lengths in order to find the most effective way to improve the performance of the actual AguaClara flocculator.  A well performing flocculator gives the following results: first, it produces  large enough resulting flocs that settle out in the sedimentation tank; second, have the floc size under control to an optimal size; and third, have a low resulting turbidity indicating the production of clean water. +(Please re-write the paragraph above. This should be put in an introductory section for this sub-section. Take out the part about flocs settling out, since this is not our goal as you pointed out. Make the language a little less informal and avoid asking rhetorical questions.)+

_The use of alum facilitates this process; however, too much alum can create oversize flocs that settle out in the flocculator before reaching the sedimentation tank. In addition, optimizing alum dosage will be more cost effective in running the AguaClara plant. To find an ideal alum dosage for a particular influent turbidity, in our experiments, we have varied the alum doses within certain ranges and are going to see which dosage works best for each situation. 

In addition to the use of alum, the optimization of the length of the flocculator is critical. Overly long flocculators will cause flocs to settle out in the flocculator before reaching the sedimentation tank. And inversely, overly short flocculators won't give enough time for particles to collide and floc. Through experiments, we aim to find the best combination of alum dosage and flocculator length._

The use of alum facilitates this process; however, too much alum can create oversize flocs that settle out in the flocculator before reaching the sedimentation tank. In addition, +optimizing alum dosage+ will be more cost effective in running -the over use of alum will be expensive; cost efficiency is essential in the building of- the AguaClara plant. To find an ideal alum dosage for a particular influent turbidity, in our experiments, we have varied the alum doses within certain range and are going to see which dosage works best for each situation. The same goes to the different flocculator lengths; overly long flocculators will cause flocs to settle out before reaching the sedimentation tank -and in addition will not be cost efficient-. To find an ideal length (what is an ideal lenght? If you have mentioned this already, reference where it is on your website)+, we have set up three apparatuses with varying tube lengths: 2796 cm, 5600 cm, and 8800 cm. For each alum dosage range, we will change the length of the flocculator in order to find the ideal combination of flocculator length and alum dose. +(Put this section at the beginning in the introductory section. Avoid writing the same thing twice. You already mentioned the length of the flocculator in the procedure section. Take it out here. Also break up the section into more paragraphs.)+

There are two important graphs that give the best overview of the experiment: the gamma PDF graph and the residual turbidity graph. The gamma PDF graph shows the probability of reaching a certain floc size for each run of experiment with varying alum dosage. +(Mention that the gamma PDF is a statistical function. Reference where discussion of this is found in Ian's thesis)+ The y-axis represents the probability and the x-axis represents the floc size. The residual turbidity graph is the gamma PDF graph focused at a certain range of sedimentation velocity. +(No. I thought residual turbidity was the actual experimental data)+ We chose this range based on our knowledge on capture velocity. Capture velocity is the minimum speed flocs must be in for them to settle in the sedimentation tank; any particle with a smaller velocity than this will not sink. Given that the capture velocity is 0.12 mm/sec, the residual turbidity graph focuses on the flocs that fail to reach this velocity. +(Be more specific. What is your range of sedimentation velocities?)+ The turbidity from these particles shows the resulting turbidity produced after flocculation. +(put this section in the procedure section, but label the section "Data Analysis." I'm also wondering if you should instead put this in a more generalized procedure section)+

On November 12, 2009 +(Do not date the experiments on the wiki, unless you have no other way of keeping track)+, an experiment was conducted with the turbidity set around 5 NTU, flocculator length of 2796 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L. 

The data processor -fails- +failed+ to fit a curve -into- +on+ the gamma PDF graph due to the lack of efficient flocculation +(I'm not sure what you mean by efficient flocculation)+ and trend/difference among the turbidity produced by the varying alum doses +(I don't know if you can say that these were the causes. It has to do that the turbidity data did not fit the statistical distribution function that we are using. It may be that these are causes of this not fitting, but I am not sure.)+

Because the experiment was conducted with such a low influent turbidity, there are less colloidal particles present in the water and less probability for these particles to collide with one another. Hence, for this experiment, the shortness of the flocculator and the limited effect of the alum caused the failure of producing a significant improvement in the turbidity of the water. There will need to be a higher collision potential for these particles to successfully collide and create bigger flocs necessary for a successful flocculation. The residual turbidity graph (Figure 1) shows the resulting mean turbidity settling down to around 2 NTU starting from the alum dose of 20 mg/L. +(I see what you are trying to say. Condense this section about why you fail to fit the gamma function and then speculate the cause. We cannot say for certain.)+

*1*
!5NTULength1_RisidualTurbidity.png|align=center,width=400,height=400!
*{_}FIGURE 1:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L_

On November 17, 2009, an experiment was conducted with the turbidity set around 5 NTU, flocculator length of 8800 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L.

Looking at the gamma PDF curve (Figure 2A) the alum dosage of 10 mg/L demonstrates an unusual behavior compared to the other doses +(I suspect the statistical functions you used to fit the data, did not fit the data right. 10 mg/L had a high residual turbidity and thus we should have a large portion of particle sizes in the lower sedimentation velocities. Either re-run the experiment or we should accept that we cannot fit it to the data. Otherwise 20 and 30 mg/L follow the trend well)+ ; it has a very narrow distribution focused at a particular sedimentation velocity. We suspect that this has been resulted from an unexpected presence of a large floc that has not necessarily been produced from the flocculator +(Then where was it produced?)+. From the residual turbidity graph (Figure 2B), there is also an unusual trend with the alum dose 40 mg/L; its turbidity unexpectedly peaks and results in an unusually high mean turbidity. +(Can you speculate as to why this is the case?)+ In figure 2A, the alum doses 20 and 30 mg/L have wider distributions of floc sizes compared to those of other alum doses. +(Comment on why they have wider distributions. Can you comment on the average particle size? Are they higher or lower)+ Overall, there seems to be discrepancies between the data recorded in the two graphs. From the values of mean turbidity at settling state, from 10 to 45 mg/L the mean turbidity seemed to start at a value of .608 NTU then rise to about .725 at 25mg/L, then rises to .829 and then back down to .755 at 35 mg/L.

*2A*
!5NTULength3_GammaPDF.png|align=center,width=400,height=400!
*2B*
!5NTULength3_RisidualTurbidity.png|align=center,width=400,height=400!
*{_}FIGURE 2A:_* _The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L_; *{_}FIGURE 2B:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L_

On November 11, 2009 +(Don't date experiments)+, an experiment was conducted with the turbidity set around 25 NTU, flocculator length 2796 cm, flow rate of 5 mL/s, and alum dosage ranged from 10 to 50 mg/L.

In the gamma PDF graph (Figure 3A), the alum dosage 10 mg/L shows a --larger- +wider+ distribution of floc sizes -with more probability to produce flocs-. In addition, looking at the residual turbidity graph (Figure 3B), the resultant turbidity this dosage gives is significantly higher than the rest. The residual turbidity graph also shows the alum doses 15 mg/L and 20 mg/L to be producing a slightly higher resultant turbidity. From the values of mean turbidity at settling state, starting from the alum dosage 35 mg/L, the mean turbidity settles down to a constant value around 2.5 NTU.
+(You are saying the say thing above. Lower alum dosages produce a larger range of floc sizes. Put these two figures into one or choose the ones that best represent this trend and comment on this)+

*3A* !25NTULength1_GammaPDF.png|align=center,width=400,height=400!
*3B* !25NTULength1_Residual turbidity.png|align=center,width=400,height=400!
*{_}FIGURE 3A:_* _The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L_; *{_}FIGURE 3B:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~50 mg/L_

On October 20, 2009, an experiment was run with the set up of influent turbidity around 100 NTU, flocculator length of 2796 cm, flow rate of 5 mL/s, and an alum dosage ranging from 20 to 55 mg/L. The data obtained from this experiment was processed through Mathcad for a simplified overview of the results in graphic form.

-Looking at- +(Do not write informally in technical writing)+ The gamma PDF graph (Figure 4A) illustrates that the alum dosage of 20 mg/L gives a widely distributed probability of reaching different floc sizes with a comparably low probability to reach its highest sedimentation velocity. In addition, the residual turbidity graph (Figure 4B) shows a high turbidity for this alum dose in its lower velocity range. Thus the alum dose 20 mg/L seems to be inefficient for this particular influent turbidity and flow rate. The mean turbidity resulting from alum dose 55 mg/L is out of normal range; its NTU value is significantly lower than the values given from the previous, lower alum dosages. Hence, the result from this dosage is doubtful. Overall, after the alum dose of 35 mg/L (except for 55 mg/L), the mean turbidity settles down to a constant value around 1.4 NTU. +(You are saying the same thing here. Can you instead create a graph that shows the average particle size at different alum dosages and turbidities (with relative standard deviation error bars) ?)+

*4A* !100NTULength1_GammaPDF.png|align=center,width=400,height=400!
*4B* !100NTULength1_RisidualTurbidity.png|align=center,width=400,height=400!
*{_}FIGURE 4A:_* _The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L_; *{_}FIGURE 4B:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L_

On November 18, 2009, an experiment was ran with the set up of influent turbidity around 100 NTU, flocculator length of 8800 cm, flow rate of 5 mL/s, and an alum dosage ranging from 20 to 55 mg/L.

Looking at the gamma PDF graph (Figure 5A), all of the alum dosages give a similar result with their likeliness to produce similarly sized flocs at a similar probability. The residual turbidity graph (Figure 5B) shows alum doses 30 mg/L and 35 mg/L giving comparably higher resultant turbidities. Unlike the expected trend, rather than improving the turbidity of the water, the graphs show the deterioration of efficiency with more alum; the resulting turbidity seems to slightly increase with a larger amount of alum. Overall, there seems to be not much change with the increasing of alum dosage.

*5A*
!aguaclara graph 2pdf.jpg|align=center,width=400,height=400!
*5B*
!aguaclara graph 1_cropped.jpg|align=center,width=400,height=400!
*{_}FIGURE 5A:_* _The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L_; *{_}FIGURE 5B:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 20 mg/L~55 mg/L_

On Oct 27, 2009, another experiment was conducted with the turbidity set around 500 NTU, flocculator length 2796 cm, flow rate of 5 mL/s, and alum dosage ranging from 10 to 90 mg/L.

In both graphs (Figure 6A, Figure 6B), the alum dosage 10 mg/L gives a comparably different result from the rest; it produces a significantly higher settling turbidity and a large amount of smaller flocs. The overall mean turbidity for this dosage is almost twice the following dosages. After the alum dose 50 mg/L, the mean turbidity settles down to a constant value around 2.5 NTU.

*6A* !500NTULength1_GammaPDF.png|align=center,width=400,height=400!
*6B* !500NTULength1_RisidualTurbidity.png|align=center,width=400,height=400!
*{_}FIGURE 6A:_* _The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L_; *{_}FIGURE 6B:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L_

On Nov 19, 2009, another experiment was conducted with the turbidity set around 500 NTU, flocculator length 8388 cm, flow rate of 5 mL/s, and alum dosage ranging from 10 to 90 mg/L.

In Figure 7A, the alum dose 10 mg/L gives a noticeably worse result compared to those of the higher dosages. Its distribution seems to primarily focus on the production of smaller flocs than the other alum doses. In the residual turbidity graph (Figure 7B), again, the alum dose 10 mg/L produces a higher effluent turbidity.

*7A*
!500NTULength3_GammaPDF.png|align=center,width=400,height=400!
*7B*
!500NTULength3_RisidualTrubidity.png|align=center,width=400,height=400!
*{_}FIGURE 7A:_* _The graph plots normalized turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L_; *{_}FIGURE 7B:_* _The graph plots the residual turbidity vs. sedimentation velocity for each Alum dose ranging 10 mg/L~90 mg/L_

h2. Conclusion

_Effect of length of the flocculator on residual turbidity_:
The length of the flocculator has different effects on the residual turbidity depending on the initial influent turbidity. In -the next- +(Do not use proximity language. Always have figures accessible and below where you cite them in your writing.)+ figures (figures 8 and 9), the mean residual turbidity as a function of the alum dose at 2 different lengths of flocculator, 2796 cm and 8388 cm (3*2796 cm) and influent turbidities, 5NTU (figure 8) and 500 NTU (figure 9) are compared.
As shown in figure 8, at 5 NTU the length has a huge impact on the flocculation. Water with low turbidity is more difficult to flocculate compared to water with higher turbidity since the latter will require a higher collision potential to create large flocs. For water with a low turbidity, few colloidal particles are present and the average volume occupied by a floc or particle is smaller. Thus, the average time it takes between collisions is greater and will require a higher collision potential. +(Please put your collision equation elsewhere, put a link to it and reference it here.+
{latex}
\large
$$
\psi _{needed} = {1 \over 6}\left( {{6 \over \pi }} \right)^{{1 \over 9}} d^{{2 \over 3}} \varphi _{Floc_0 } ^{{{ - 8} \over 9}} \left( {{d \over {d_0 }}} \right)^{{{8\left( {D_{fractal} - 3} \right)} \over 9}}
$$

{latex}
with
{latex}
\large
$$
\phi _{Floc_0 } = {{Volume_{floc} } \over {Volume_{suspension} }}
$$

{latex}
-With- A longer -flocculator the- residence time -is longer, and-
+enables longer collision times+ -the colloidal particles have more time to collide to form big flocs.-  The residual turbidity is lower for the longer flocculator (Figure 8). Flocs +produced with more collisions tend to+ have a higher terminal velocity than the ones resulting from shorter flocculators. -since they weigh more, they will be able to settle faster, reducing the residual velocity.- +(The explanation above is not sufficient. Residual turbidity could be the result of flocs falling out of water, flocs sweeping up colloidal particles as they collide, and break up of flocs.)+ 

With an effluent turbidity of 500 NTU, there is no noticeable difference between the two lengths of flocculator as seen in figure 9. The mean residual turbidity seems to even be bit higher with the longer flocculator at high alum dose. From this trend, we -can conclude- +hypothesize+ that the flocs +may+ have been broken up -due to too much collision- +because the shear rate the floc experienced exceeded floc strength in some part of the floc structure)+.  

High turbidity water is -easier and faster to- +flocculated more quickly (because?) +; -even with a short flocculator large flocs are easily formed.- However, because the bonding among the colloidal particles that have formed the flocs is weak, flocs are easily breakable +(The chemical bonding is not necessarily weak since we have an amorphous precipitation occuring. However, the shear rate of break-up may be significant enought to break up the floc into smaller pieces at certain points in the floc structure)+. Hence, we hypothesize that an optimal length of a flocculator must be set; longer flocculators do not always give better results. +(Please comment on this. When flocs break up and reform are they stronger or weaker than before? Cite a literature source here.)+ Flocs grow only to a certain point where they become too big and vulnerable to fluid shear stresses that break the flocs +(Good sentence, but should have been put somewhere before)+. Though the freed particles can flocculate again, the maximum floc size will remain the same, and thus, the particles will just form the same floc they have produced before the break up. Thus, the same residual turbidity is observed for the two lengths of flocculator: the steady state is reached in the two flocculators. +(Again, not entirely sure of your claim here. Confirm this in literature.)+


!5NTU length 1 and 3.png|align=center,width=500,height=400!
*Figure 8*: _Plot of the residual turbidity as a function of alum dose at two different flocculator length, 796 cm and 8388 cm, for an effluent water of 5 NTU_ !500 NTU length 1 and 3.png|align=center,width=500,height=400!
*Figure 9*: _Plot of the residual turbidity as a function of alum dose at two different flocculator length, 796 cm and 8388 cm, for an effluent water of 500 NTU{_}{_}Effect of the alum dose on flocculation_:


For the next figure (figure 10) the residual turbidity has been plotted as a function of alum dose for water with a different influent turbidity in the short flocculator (2796 cm). We can observe a similar behavior between the plots. At the beginning, the residual turbidity is decreasing with -the- +an+ increase of alum dose until a limit is reached where the residual turbidity stays almost constant. These results show the optimal amount of alum that should be used; the least amount of alum in which the minimum effluent turbidity is reached will be the most cost effective alum dosage.

We can also observe on this figure that at a given alum dose, the mean residual turbidity is different for each influent turbidity. From this graph, highest residual turbidity is found in the alum doses: 500 NTU, 25 NTU, and 5 NTU respectively. The lowest residual turbidity is found for an influent water of 100 NTU. These observations can be explained by -the fact that- two phenomena -are happening- +ocurring+ at the same time. -For the low turbidity, 5 NTU and 25 NTU, as mentioned earlier-, more time is -needed- +required+ to produce large flocs at the lower turibidities of 5 and 25 NTU.  The residence time in the 2796 cm long flocculator may -be too short- +result in higher residual turbidity because the collision potential is less and a large portion of colloids have not yet come into contact forming flocs.+ -is relatively high-. For -the- higher influent turbidity, 500 NTU, a steady state is reached in the flocculator but as we are starting with a really high turbidity, the residual turbidity is high too. +(The residual turbidity is not really high. Explain that in terms of pC* (-log removal of Cout/Cin) that you are removing as much turbidity or more compared to other turbidities. This may require some calculations)+  Logically, the optimum result should be found for a medium influent turbidity and it is found for 100 NTU. +(We cannot control the influent turbidity unless we want to purposely make our water dirtier. Perhaps use an explanation of collision potential and sweep flocculation to explain why the 100 NTU was so effective. Can you characterize its pC* and see if this was better?)+ 
!residual turbidity_length1.png|align=center,width=500,height=400!
*Figure 10*:_Plot of the residual turbidity as a function of alum dose at different influent turbidity with a 2796 cm long flocculator{_}The following steps of this analysis will consist in doing further experiments with wider alum range and more influent turbidity. The size distribution of flocs will be analized to see what would be the influence of different flocculator lengths and different alum doses on a floc blanket.