Replication of Spring 2009 experiment : Variation of flow rate

Procedure

Our experiments were all performed on the same Flocculator Residual Turbidity Analyzer (FReTA) setup that was developed previously (Spring 2009). FReTA consisted of five parts: an alum stock bucket at a stock concentration of 2.5 g/L, a kaolin clay stock bucket at a stock concentration of 10g/L, a raw water reservoir, a coiled tube (0.953 cm diameter) serving as the flocculator (I would like you to expand this a little bit since this is the focus of your research. Can you show the equations that characterize flocculation in a coiled tube? Perhaps keep this in this section or make a link to another page with this information.), and the residual turbidty analyzer with a settling column (You described the process of analyzing the residual turbidity in your page where you varied the alum dosage.You should put this description in one place that anyone can find.) . The raw water turbidity was controlled using a feedback loop mechanism; clay from the stock bucket was metered in automatically if the turbidity became too low. Peristaltic pumps were used to provide the flow rate and meter in the alum solution. All flow rates and chemical dosages were calculated, monitored and controlled using the Process Controller software developed by Weber-Shirk (2008). For detailed information on FReTA setup and the Process Controller figuration, please see Ian Tse's MS Thesis. All general information on the setup can be found in Chapter 1 Sec. 1.3-1.4 of the thesis. Characteristics of the tap water used can also be found there. Details of the Process Controller states and setpoints used can be found in Appendix A.

In order to verify that the equipment was working properly and to familiarize our team with FReTA, we first performed a similar experiment to one that had been done the previous semester. We modified an earlier Process Controller file(see process controller file attached)that been set to run at flocculator length of 2796 cm with an influent turbidity of 50 NTU and a constant alum dosage of 38 mg/L while varying the plant flow rate from 3-19 mL/s (what does this mean in terms of G and G*Theta?) increasing by 1 mL/s each trial to run instead at an influent turbidity of 100 NTU with an alum dosage of 45 mg/L; we maintained the same flow rate variation.

During each run, the influent raw water combined with the correct alum dosage was allowed to run through the plant until two residence times had passed, ensuring a steady-state effluent floc distribution. Then the pumps gradually ramped down, and a valve sealed off the settling column from the rest of the flocculator. The turbidity was monitored every second for half an hour as the flocs settled out, and the data recorded in an EXCEL spreadsheet (Do you have a sample excel spreadsheet you can upload here?).

We then analyzed the data using Mathcad files developed by the previous (Spring 2009) team to develop settling velocity probability density function for the flocs. Details of the data analysis procedures can be found in Appendix B of Ian Tse's Thesis. After the analysis, the results could be used to find the flow rate (shear) with the best performance (lowest residual turbidity, largest mean floc size) for the set turbidity and alum dosage.

The following Process Controller method file was used to run the experiment:
Varying Flow rate

Results and Discussion

The floc terminal sedimentation velocity and the residual turbidity of flocculated suspension are important properties in a flocculator because all the particles having a terminal velocity lower than the capture velocity of the sedimentation tank are going to live the tank with the clear water causing the residual turbidity. (Rewrite this sentence. Make the distinction of what terminal sedimentation velocity represents. Put in the description you had in the other section here. With residual turbidity, you are measuring the anticipated performance you would have if the effluent from the flocculator passed into the tube settlers without any other sedimentation process) The Spring 2009 team evaluated quantitatively the effect of shear velocity on these parameters. To do so, they used the flocculation residual turbidity meter (FRETA) developed by the AguaClara team and a data processor to analyze these parameters automatically. (You describe this in more detail in another page. Please combine these sections so that you only have to write this once)

Our goal for these first experiments was to familiarize ourselves with the apparatus and the data processor (MathCAD file) made by the previous team (Spring 2009) and to try to replicate one of their last experiments to make sure that the apparatus and the MathCAD file were working properly. (You already stated this in your procedure section on the same page. Avoid repeating yourself.)

Table 1: Parameters for the Fall 09 experiment

Expand this table to include relevant values for G and G*theta. OR I think it may be more beneficial to plot a graph of this in MathCAD and then show the figure so that all someone has to do is look at the graph and pull off a G for a given flow rate)

The experiment was conducted with the parameters shown in table 1. The parameters were based on one of Ian's experiment (data from 5/13/2009) conducted with the same inputs, except for the flow rates which vary from 4 to 19 mL/s and the turbidity which was set at 50 NTU(MathCAD file). Figure 3 shows the plot of the effluent turbidity during the settling state as a function of time and flow rate. The flow is, in fact, changing at each cycle and we can see that the turbidity is decreasing at each settling state. (I don't think that a 3-D plot conveys this well. You should put the 3-D plot in your "Materials and Methods" section and describe why you use it. Do not present this as data, especially since someone reading it on here cannot rotate the graph.)

Figure 1:Plot of the effluent turbidity (NTU) during the loading state vs. time (sec) and flow rate (mL/s). Experiment of 9/24/2009

The figures 2,3,4,5 show the plots, given by the data processor, with the data from our experiment (9/24/09) and the data from the Spring 2009 experiment (5/13/09). Comparing graphs at each state, we observed similar results when compared with the previous years experiments. Our experimental values; seen on the graphs below, are not exactly the same as Ian's Spring 2009 data because the experiments were not performed under the same conditions, but they closely resembled one another.

Figure 2, A and B, shows the normalized effluent turbidity vs. time during the settling state for Spring 2009 team's experiment and Fall 2009 team's experiment, respectively. In both cases, the turbidity of the water decreases rapidly. Moreover, we can observe that for low flow rates, the turbidity decreases more rapidly and the residual turbidity is lower in both experiments. Figure 3, A and B, represents the normalized turbidity as a function of Vs. As Vs is the inverse of time, we observe the opposite trend in the data. Figure 4, A and B, shows the cumulative distribution function and figure 5, A and B, show the resulting probability density function (PDF) of settling velocities obtained from the fitted gamma distribution for Fall 2009 experiment and Spring 2009 experiment. We can observe on the PDF curves that in both cases the mean velocities are decreasing with the flow rate (trace 1 being the lowest flow rate and trace 8 the highest).

(Good section, but can you please label what the flowrates were on your plots?)

A B
Figure 2:Plot of the normalized effluent turbidity (NTU) vs. time(s). Experiment of 5/13/2009(A). Experiment of 9/24/2009 (B)

A B
Figure 3:Plot of the normalized effluent turbidity (NTU) vs. Vs (m/day). Experiment of 5/13/2009(A). Experiment of 9/24/2009 (B)

A B
Figure 4:Plot of the normalized effluent turbidity (NTU) vs. Vs (m/day) fitted to a gamma distribution. Experiment of 5/13/2009(A). Experiment of 9/24/2009 (B)

A B
Figure 5:Plot of the probability distribution of the particle population vs. Vs (m/day). Experiment of 5/13/2009(A). Experiment of 9/24/2009 (B)

The previous team conclusion on this kind of experiment was that increased fluid shear not only decreased the average size and sedimentation velocity of flocs, but it resulted in higher residual turbidities as well. The results of Fall 2009 are consistent with the previous team results.
The goal of this experiment was not to analyze the results in depth but to replicate the experiment from Spring 2009 and understand how to use and analyze data with the data processor. The next set of experiments will analyze the evolution of the effluent turbidity with the alum dose and the length of the flocculator.