h1. Evaluation of previous experiments with the new system
h2. Objective
This set of experiments attempted to replicate the grain size research performed with the [previous experimental setup|https://confluence.cornell.edu/display/AGUACLARA/Fluidized+Bed+after+Super+Saturator], to assess both the functionality of the new system and the validity of the Spring 2009 results. Additionally, dissolved oxygen measurements were taken to assessevaluate the effectiveness of each of the components in the setup with respect to theoretical expectations. Theoretically, it was expected that the aerator under 2 atm of pressure, wouldthe beaerator able towould supersaturate the water with 18 mL/L of dissolved gas, byaccording thisto [theoretical model|Final Results from the Fluidized Bed Method^Dissolved atmospheric gases.xmcd], which predicts thethat bubble formation potential tois be18 around 18mLmg/L for water that has been previously exposed to 1 atm gage pressure at temperature of 25 C˚C. The model calculates the theoretical bubble formation potential as a function of the air pressure with thatwhich the water equilibratedreached withequilibrium prior tobefore returning to atmospheric pressure. WithFor the current aerator, a major assumption made wasit was assumed for the sake of calculation that the dissolved gas concentration would equilibratereach equilibrium with the pressure in the aerator, resulting in 18 mLmg/L of dissolved gas in the influentwater flowing waterinto throughthe sand filter. While noa theoretical model of gas removal by the sand filter has not wasbeen developed, the team believed that the extraabundant surface area provided by the sand would remove gas by increasingproviding theample nucleation sites for bubbles, and also providing sites toat which bubbles could adhere to a surface and growaggregate.
h2. General Procedure
For the two experiments listed below, the same procedure was used with varying a different size of sand grain sizesused in each. Sand 40 (0.49 mm - 0.57 mm) and Sand 30 (0.59 mm - 0.84 mm) were used for experimentsExperiments one1 and two2, respectively. The details of the procedure are available [here|FF Procedure for Evaluation of Previous Experiments].
h2. Results and Discussion
Experiments 1 and 2 were performed to assess the functionalitywhether of the new system in terms of its ability to collect good,collects consistent data and to ensure that previous sand grain experiments results wereare replicable, usingand thethus neware systemvalid. We performed Thethe control experiment (with no sand was performed) after it waswe observed that the measured rate gas removal fromin the sand filter fellwas shortless ofthan the 18 mLmg/L, thatthe wastheoretical theoreticallyrate possibleof togas be removedremoval. When itwe was foundrealized that gas removal was less than expected, we took dissolved oxygen measurements were taken in order to assessdetermine thewhich component of the system that was not functioning effectively.
[Experiments 1 and 2 - Replicates of the Previous Fluidized Bed Experiments]
* Experiment 1 was performed shortly after the installationnew ofsetup thewas new setupinstalled. Sand 40 was used withto the purpose of replicating evaluate [previous grain size results|Fluidized Bed after Super Saturator].
* Experiment 2 was performed after makingthe modificationssystem towas the systemmodified to account for theproblems issuesthat foundarose in the Experiment 1. Sand 30 was used with the purpose of testing the functionality again and replicating previous results.
* ControlA control Experiment (i.e., one with no sand) was performed to testevaluate the sand filter's effectiveness by ofmeasuring thegas setupremoval in the absence of sand in the sand filter.
[Dissolved Oxygen Measurements|FF Dissolved Oxygen Measurements]
* When itwe washad confirmed that the measured gas removal values didwere notless matchthan theoretical values, the concentrations of dissolved oxygen were measured at various points in the experimental apparatus. ItWe was found that the measurements taken after at a point just past the sand filter indicatedshowed dissolved oxygen concentrations that were higher than thethat influentof water going into the sand filter. This suggestingsuggested a problem with either the setup or the fluidized bed mechanism. It was confirmed with With the control experiment, we confirmed that the sand filter was not a suitable mechanism for gas removal.
h2. General Conclusions
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!Theoretical bubble formation potential.png!
h6. Figure 1: Theoretical bubble formation potential
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The experimental results for gas removal rate Experiments using Sand 40 and Sand 30 gave results showed rates of gas removal rates of about 5.09 mL/L and 2.01 mL/L, respectively, while the control experiment indicatedshowed a gas removalrate of 7.47 mL/L. These results suggest that the sand seemedinhibits togas inhibitremoval, rather than facilitatefacilitating gas removalit. In addition to, the gasconcentration removalof rates, the dissolved oxygen concentrationsmeasured (reiteratedat below)each measuredof at the four ports in the system (tabulated below) support the notion that the sand filter did not provide a suitable mechanism forof gas removal, sinceas the measurements indicated higher oxygen concentrations in the water at points afterpast the sand filter.
ArticlesLiterature found concerning bubble formation and behavior indicate that rough, hydrophobic surfaces are most suitable for bubble formation. (See "Fundamentals of Bubble Formation during Coagulation and Sedimentation Processes" by P. Scardina and M. Edwards on the [Floating Floc Annotated Bibliography|Floating Floc Annotated Bibliography] page.). The believed cause of the sand filter failure is thought tomay be theunsuitable lackbecause ofsand hydrophobicityis exhibited by the sand usednot hydrophobic.
h5. Table 1: Dissolved Oxygen Concentrations (DO) at sampling ports in the experimental setup with a sand bed.
|| Sampling Port || DO (mL/L), Probe 1, Trial 1 || DO (mg/L), Probe 1, Trial 2 || DO (mg/L), Probe 2, Trial 1 || DO (mL/L), Probe 2, Trial 2 ||
| Water Source | 9.8 | 10.2 | 8.7 | 12.1 |
| Beyond Aerator | 15.5 | 14.2 | 11.8 | 15.2 |
| Beyond Sand Filter | 17 | 16.3 | 11.9 | 15.3 |
| Beyond Bubble Collector | 17.8 | 16.2 | 12.3 | 15.7 |
Additionally, measurementsMeasurements indicate that the aerator is able to supersaturate the water with 15.5 mg/L of dissolved oxygen; however, this value . This is less than the expectedtheoretical rate 18 mg/L. AdditionallyAlso, subsequent measurements of dissolved gas at that pointport reveal inconsistent levels of gas supersaturation. TheThis inability to regulate the amount of dissolved gas in the influent water intoto the sand filter may have a significant impact on theour ability of the team to run controlled experiments. In order to address this issue, the team has decided to alteraltered the pressurized aerator by replacing the single aeration stone with a junction of four cylindrical aeration stonestones that would displace gas into the water in finer bubbles, thatwhich would be more easily incorporated into solution more easily.
It is also thoughtpossible that the bubble collector, which is used to measure gas removal, may not be effective at capturing small bubbles. However, the source ofAlthough we had initialyl suspected that the small bubbles traveling through the system is thought be the pressurized aerator and not originated in the sand filter, we are now unsure whether small bubbles formed in the sand filter itself. At this point, it is unclear whetherSince the controlled experiment indicates that the sand filter is ineffective, we suspect that the source of the small bubbles formed in is a component other than the sand filter--perhaps the itselfaerator. Before the team redesigns the bubble collector, thewe team plansplan to modify the flow accumulator so that any small bubbles coming from the aerator will be collected andso thethat water goingentering through the sand filter willis be supersaturated without smallfree of bubbles. If small bubbles are formed in the filter and it is deemed necessary to redesign the bubble collector inmust be orderredesigned to capture these bubbles, a new design for the bubble collector will be developed. | 