Page History

h1. Dissolved Oxygen Measurements

Dissolved Oxygen measurements were performed two times in order to fully assess the functionality of the system. According to [MathCAD modeling of the system|FF Dissolved Oxygen Measurements^Dissolved atmospheric gases.xmcd], bubble formation potential in the water should be 18 mL/L.In theOur secondmeasured experimentvalues wefor conductedgas duringremoval the summer, which is described [here|Experiment 2 - Replicate of the Previouswere 5.09 mL/L and 1.99 mL/L for sand 40 and Sand 30 Experiment], gas removal was only 2 mL/Lrespectively. ToThese achievediscrepancies aled betterus understandingto of howmeasure the systemDO functions,concentration weto measuredexamine dissolvedthe oxygenfunctionality concentrationsof atthe various pointscomponents in the systemsetup. 

h2. Procedure

Sampling Points: Water Source, Aerator Effluent, Sand Filter Effluent, Bubble Collector Effluent

Water Temperature: 20.8 °C for the first probe, 21 °C for second probe

Dissolved oxygen probes were used to measure the concentration of dissolved oxygen in samples of water taken from the water source and effluents from the aerator, the sand filter, and the bubble collector. Two probes were used in samples at each point to confirm results. After each probe was assembled, it was placed in a solution of sodium sulfite to ensure a zero reading. To test the probe's accuracy, it was placed in a sample of tap water, which should have a dissolved oxygen content near 8 mg/L.

In a large beaker, water was collected from a sampling port at the first point, just beyond the water source. The probe was inserted near the center of the water sample and kept stable with a ring stand. After the probe membrane came in equilibrium with the water, the dissolved oxygen reading was recorded, and the probe was returned to the sodium sulfite solution. The beaker was emptied and refilled with water from the next sampling port. This was repeated until water from all four sampling ports had been tested.

h2. Results and Discussion

The results were very surprising. Table 1. shows the first measuredset dissolvedof oxygenDO concentrationsmeasurements attaken eachafter ofthe fourSand points40 inexperiment thewas systemperformed. {center:|border=12px solid white|width="200"}{center}

h5. Table 1.: Dissolved Oxygen Concentrations (DO) at Sampling Ports in the System.

|| Sampling Port || DO (mL/L), Probe 1, Trial 1 || DO (mL/L), Probe 1, Trial 2 || DO (mL/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 |
{float}
In addition, water taken from sampling ports beyond the sand filter and the bubble collector were very cloudy with small bubbles. If the system were working properly, the dissolved oxygen concentration would decrease from the aerator to the bubble collector, and the water taken from the effluents of the sand filter and the bubble collector would contain large bubbles. We speculate that high pressure in the bottom of the sand filter dissolves smaller bubbles into solution.

Table 2. shows the second set of DO measurements taken after the Sand 30 experiment was performed.

h5. Table 2.: Dissolved Oxygen Concentrations (DO) at Sampling Ports in the System.

||Trial||Flowrate [ml/min]|| Source water DO [mg/L]||After Aerator DO [mg/L]||After Sand Filter DO [mg/L]||After Bubble Collector DO [mg/L]||Temperature [C]||
|1|530|12.0|15.3|15.6|16.1|21.4|
|2|530|11.0|14.3|16.2|15.0|21.4|
|3|530|11.6|16.0|16.0|16.0|21.4|
|4|530|11.4|16.0|16.0|15.9|21.4|

{float}


Dissolved oxygen measurement after the bubble collector do not agree with the removal rate recorded by the bubble collector in Process Controller. A review of pressure readings taken through _Process Controller_ during [Evaluation Experiment 2|Experiment 2 - Replicate of the Previous Sand 30 Experiment] confirms that the pressure in the bubble collector is atmospheric, which is to be expected from such an open system.

+(It seems that the The bubble collector might isbe inefficient becauseat removing small bubbles. Inside, there is not enough residence time for smalltiny bubbles to rise to the top, especially at lowwhen water heightslevel ofis therelatively bubble collector. The bubble collector is inefficient at removing small bubbles, because low. Therefore, it is difficult to remove small bubbles, (aswhich wesubsequently haveare seenswept in the sand filter). We need to find a better way to create large bubbles before the bubble collector)+
with water to the waste.
\\
\\

h2. Conclusions

To confirm suspicions that pressure in the sand filter is too high, measurements will have to be taken at several bed expansions, including at zero expansion. Such measurement has already begun and will be completed when a mechanical malfunction with the sand filter is resolved +(What do you mean by mechanical malfunction?)+. However, the measurements -will- +may+ only serve to quantify the obvious need for a different sand filter design. It is clear from the dissolved oxygen measurements that the sand filter is not doing its job of removing dissolved gas. We will probably design and build a sand filter that is open to its environment so that atmospheric pressure is maintained.

The question of what is wrong with the bubble collector is still unanswered. We must further examine how the bubble collector behaves before proposing a solution.

+(I'm not sure anything is wrong with the bubble collector. Unless you want to redesign and make the residence time in the bubble collector large, it seems to be doing a fine job. The sand filter seems to be doing a lousy job. We should redesign how we are removing dissolved air from water.)+