Foamulations Project Report

Sawyer Project

Research Manager: Dr. Tesfayohanes Yacob

Research Assistants: Daniel Ma, Ted sindabizera Ntwari, Alyssa sargent

Test 1 ­ Standard + Ag Bag 1: Bag longevity through 50 gallons

Procedure: A 19L (5gal) challenge water batch was prepared as needed throughout the course of the experiment. The following were added to the total solution: 32 grams of potassium chloride; 0.070 grams of humic acid, sodium salt (50­60% humic acid; 0.190 grams of Kaolin test dust (for turbidity), and 1.40 milliliters of sodium hypochlorite (we calculated 5.4 % free chlorine). The calculated initial concentrations for the solution were 800 ppm (mg/L) chloride, 1 ppm carbon, 4 ppm Cl2, and approximately 20 NTU. The solution was mixed for at least 5 minutes. Because the Hach DR 3900 Benchtop VIS Spectrophotometer (used as per manufacturer’s instructions) only reads from 0.00­2.00 ppm Cl2, the initial Cl2 concentration of the reservoir challenge water was measured through a 1:4 dilution with deionized water (this was only done once for each batch). After recording the reservoir chlorine concentration, 500 mL of the solution were transferred to the modified Sawyer filter bag. The bag was agitated continuously for 30 seconds by rolling across the length of the bag with the foam roller. Initially, 650 mL was used to fill the bag; however, this much volume seemed to hinder roller contact with foam inside the filter bag. This was quantitatively determined in Test 2 (conducted concurrently), which measured chlorine removal in relation to various sample volumes (assuming that agitation was the main factor for better removal; however, contact time with the adsorption material could also play a role in improving removal rates). After the bag was agitated, the Sawyer PointOne filter was attached and the water was expelled by rolling the bag. An initial chlorine measurement was taken for the first batch. Thereafter, the chlorine concentration was measured for every tenth sample. During the course of testing, some bags produced samples that had abnormally high concentrations. It is possible that the filter and foam were not “primed” enough for the first couple measurements of the day. Most of the relatively higher values measured occurred towards the beginning and the end of a testing session. After 25 gallons, about halfway through testing, It was hypothesized the activated

carbon had reached its adsorption capacity, but the following tests showed relatively lower measurements. The Sawyer PointOne filter was backwashed with tap water after every two batches, or approximately 10 gallons, as suggested by Sawyer. The backwashing was done by attaching the filter to a clean water supply and allowing water to flow through the filter in reverse. Later, a 60 mL syringe was used to backwash the filter. In hindsight, it would have been better to backwash with distilled water since tap water contains trace chlorine levels, which could have affected our measurements. During the course of testing, the bag sprung leaks where the bag was cut and re­sealed for modification purposes. It is possible that chlorine contamination of the filtrate could have occurred due to the bag’s integrity. The bag was repaired with silicone at least three times, which prevented the minor tears from being an issue. These minor leaks were located in areas that experienced relatively low pressure during agitation and rolling. However, around sample 280, a major leak occurred at the filter end of the bag, which experiences greater pressure. Standard silicone was not an adequate repair tool since it is not rated for use in high pressure situations. Therefore, premium gasket and seal silicone were applied to the compromised areas and the bag was left to dry overnight. Initially, the repair appeared successful and testing continued. However, the bag sprung another leak around bag 326. Testing continued and it was made sure that the filtered sample was not contaminated with the unfiltered sample. The leak made agitation and expelling the water difficult, and testing was ended after bag 367. The chlorine concentration for bag 367 was over 1.00 mg/L and there was no indication that the level would decrease beyond that if further samples were taken. It should be noted that throughout our testing, the initial chlorine concentration differed from batch to batch. Further testing should be done where the batch is made more consistently throughout the course of the experiment. Because of this difference, the percent removal for any sample is only relative to the initial concentration of the batch. In Figure 1 below, the percent removal of chlorine remains above 90%. For the high range test, this is an expected outcome. Towards the end of testing, the removal rate dropped below 90%, which can either indicate the foam was reaching its adsorption limit or there could have been a compromise inside the filter cartridge, such as a leak or damage caused by excessive pressure during foam roller agitation and/or rolling the bag to expel the filtrate.

Test 1 Results:

[Figure 1]

Chlorine effluent concentration and % removal. The first three points of the experiments used 650 ml volume in the treatment bag, all other points are for a 500 ml volume experiment.

Test 1 Discussion: Backwashing occurred after bag 68, 145, 200, 245 and 308. Although it was initially calculated that backwashing should occur after every two batches, or 10 gallons, Test 2 was conducted simultaneously with the same batch being used for Test 1. Therefore, backwashing every two batches did not accurately reflect the rule to backwash only every 10 gallons. Future tests will be more consistent in this area because a clogged filter has the potential to cause variations in results. The results of Test 1 give us insight on the durability of the Sawyer filter bag. From agitating and rolling it up over 300 times, for a total of almost 50 gallons, the reticulated foam inside seemed to have deformed from its original form. While the agitation method is practical for purposes of uniformity in a controlled experiment, it would not be practical a user on the trails to perform. We suggest further testing be done to determine the effects of shaking, increased contact time, and no agitation on chlorine removal at both high and low initial chlorine concentrations.

The results of this test also indicate that the Standard Bag + Ag is capable of producing

filtered sample with concentrations of chlorine less than 0.2 mg/L through about 25 gallons. While the filter also produced lower concentrations after this point, it did so less consistently and with more variations in measurement. Our data shows that 40 gallons might be the limit of the foam. At that point, the measured chlorine concentrations consistently stayed above .3 mg/L. Further testing could be performed with a more consistent batch making procedure and agitation method.

Test 2 ­ Standard + Ag Bag 2: Effect of Sample Volume on Chlorine Removal

Procedure: This test was conducted concurrently with Test 1 by using the same batches. Four volumes were chosen: 800, 750, 600 and 500 mL. It should be noted that 800 ml was the most volume that could be put in the bag without overflowing due to the presence of the foam. Instead of continuous rolling, the bag was agitated with the foam roller in the following manner: 10 rolls in the middle of the bag, followed by ten rolls along the full length of the bag (up and down constituting one roll). Ten samples were collected for each volume using a 250 mL (and if applicable, a 50 mL) graduated cylinder. The chlorine measurements were taken in the same manner as in Test 1. According to the results, increased contact with the foam roller appears to increase chlorine removal through adsorption. With the higher volumes (800 and 750 mL), rolling was more difficult and therefore harder to reach the foam through the excess liquid. Additionally, it could also be possible that more contact time is needed for higher volumes since there is more chlorine present in the sample.

Test 2 Results:

[Figure 2]

Average chlorine % removal vs. bag fill volume.

[Figure 3]

Average filter effluent chlorine concentration vs. bag fill volume.

[Figure 4]

[Figure 5]

Test 2 Discussion: Test 2 allowed us to determine that a sample volume of 500 mL is the most effective for chlorine removal for this set of constraints. However, this relatively low volume may not be practical for consumers. If that is the case, 600 mL can also be considered as a viable option since the test results were similar to those of 500 mL. On average, all volume tests produced relatively high removal rates. However, the 800 and 750 mL tests ranged from 90 to 96% removal, while 600 and 500 mL consistently produced removal rates of 98 and 99%, respectively. As discussed above in the Test 1 results, having a consistent initial concentration of chlorine would standardize the results. In later tests we observed that using a volume of 750 mL produced better, if not, equal removal rates and relatively low effluent chlorine concentrations. This disparity may be accounted for by agitation method and duration.

Test 3 ­ Standard + Ag Bag 2: 500 mL volume at 1 mg/L Cl2

Procedure: The batch for this test was made to the same specifications as the others. However, the initial concentration of chlorine was changed from 4 mg/L to 1 mg/L to better simulate naturally

occurring concentrations. The measured initial concentration was 0.99 mg/L. The sample was agitated for 30 seconds using the continuous rolling method.

Test 3 Results:

[Figure 6]

For the lower starting concentration, the removal rate is comparable to that of the higher starting concentration (~4 mg/L). This test demonstrates that the filter can remove chlorine at lower,

naturally occurring concentrations (the removal rate is above 96%).

Test 3 Discussion:

Test 3 allowed us to determine that the foam was capable of reproducing removal rates at relatively low initial concentration similar to those at greater initial concentration. The foam filter has a removal rate of 97% at low range chlorine concentrations. This value is more relevant for consumers since chlorine naturally occurs at lower levels in the environment.

Test 4 ­ Standard + Ag Bag 2: High Volume Samples with Varying Agitation Methods

Procedure: The batch was made to the same specifications as above. For this test, the volume was held constant at 750 mL and the initial chlorine concentration was kept at 4 mg/L Cl2. The agitation was varied for this test because we wanted to see how varying contact time and agitation method would affect removal rates. The sampling method was kept constant throughout the test: 750 mL of challenge water was measured out with a 250 mL graduated cylinder and stored in a vessel with adequate volume as opposed to filling the graduated cylinder and immediately pouring into the bag. This was done to minimize the time between the additions of challenge water so that no amount of sample water could get more contact time, although the water added first will inevitably have slightly more contact time. The filtrate for each sample was collected in a 1L beaker rinsed with distilled water to prevent interference from residual chlorine. The methods of agitation were as follows: 0 seconds rolling and 60 seconds rest period, 30 seconds continuous rolling, 60 seconds continuous rolling and 60 seconds shaking. No agitation with a one minute rest period was chosen to simulate what could potentially occur when using the product. This would be the scenario if a user simply filled the bag with untreated water and left it for a minimum of one minute. The two rolling tests were done to allow us to compare the results with other rolling tests. The shaking method was added later on to simulate a user friendly method of agitation. It was clear that the rolling method would only serve as an artifact of our laboratory study and not as a suitable agitation method for potential customers.

Test 4 Results:

[Figure 7]

Test 4 Discussion: The results of these tests demonstrate that longer agitation times seem to be conducive to greater removal rates. There is a drastic decrease in removal rate when there is no agitation. It appears that longer contact time is not enough because the no agitation, one minute hold bag had greater contact time than the 30 second continuous rolling bag, yet the later had greater removal rates and relatively lower effluent chlorine concentration levels. One thing to keep in mind with these tests is that the short time periods we used for testing are nominal at best. Short agitation durations were chosen for the sake of decreasing the time it would take for each experiment. We intend to conduct further tests with longer contact times and agitation times in order to determine an effective range for each. It appears that using some method of agitation rather than none is conducive to better chlorine removal. We surmise that the agitation thoroughly mixes the sample water, allowing more molecules to come into contact with the activated carbon in the foam. The chlorine that was removed in the no agitation test was likely primarily adsorbed by the surface activated carbon and secondarily by the internally infused activated carbon when the bag was rolled up and squeezed to expel the filtrate.

Test 5 ­ Catalytic Bag 2: High Volume Samples with Varying Agitation Methods

Procedure: This test was conducted in the same manner as Test 4. We used the Catalytic bag to see if the results would be comparable to that of the Standard Bag test.

Test 5 Results:

Test 5 Discussion: The results of this test are very similar to those of Test 4. However, the three agitated tests for the catalytic bag performed much better than the standard bag. This can be explained by how new the catalytic bag is: these were the first four experiments performed on the bag (10 samples per experiment). In comparison, the standard bag had already been used many more times, so the difference in usage could explain why the former performed better than the later.

We conjecture that as more chlorine is adsorbed, the available activated carbon becomes depleted, thus lowering the effectiveness of removal. One thing that we did differently in this experiment was performing more reservoir chlorine concentration measurements. Our measurements took place before the first, fifth and tenth sample of each experiment. What we observed was a slight fluctuation. This variation over the course of the experiment effectively changes our percent removal. However, sampling errors could also produce such fluctuations. Future sample checks should employ measuring in duplicate or triplicate to ensure better accuracy, but this is time consuming and could not be done this time due to limited equipment (sample cuvettes).

Test 6 ­ Standard + Ag Bag 2: Iron Removal

Procedure: The batch is made the same way as above, but spiked to 5 mg/L Fe as ferrous sulfate. The reservoir iron content was measured, both a syringe filtered and unfiltered sample to check for precipitation and presence of iron(II) and iron(III). The reservoir was also checked before the third and last sample. The chlorine concentration of the reservoir was checked at the same time as the iron. The filtrate was tested for both iron and chlorine removal. Chlorine was also tested to see if the iron would affect the chlorine removal.

Test 6 Results:

Test 6 Discussion: The results demonstrate that the filter is very capable of removing concentrations of iron greater than the allowable MCL of 0.3 mg/L and reducing it to well below the MCL. The chlorine removal is not adversely affected. In fact, the chlorine removal was better than all of the experiments in Test 4.