Results and Discussion

The Effects of Cover Sheet Thickness on Effluent Produced by Solar Stills

The original experimental question, “How does the thickness of the plexiglass cover sheet affect the salinity levels and conductance of the effluent and the amount of effluent produced?” was not adequately answered by the experiment. As can be seen in Figure 1, in an initial attempt to answer this question, three models of a square basin solar still were built using identical dimensions and materials. The difference between the distinct models was the number of 4 mm plexiglass panels used as a cover sheet. All three models were built from scratch using mainly plywood, screws, a black tarp, and plexiglass. The “Cause of Failure” column in Figure 1 outlines that due to gaps in the basin and cover sheet of the stills, no effluent was produced. The screws did not sufficiently seal the plywood, so salt water leaked out of the bottom of the still. Additionally, the gaps between the basin and cover sheet allowed humidity to escape, which is required for the condensation of freshwater on the inside surface of the cover sheet.

Based on the “Cause of Failure” stated in Figure 1, it was determined that in order to address these knowledge gaps, a pre-made sealed container must be used as the basin to avoid leakage. The natural slope of a bucket lets the plexiglass rest in the bucket without it sliding down, so, as a result, it made logical sense to use a bucket as the foundation for the following stills. While constructing the square basin stills, three stills were built (single panned, double panned, and triple panned) at once before testing. This became confusing and disorganized and was an overall waste of time as all models failed to produce effluent. Thus, it was determined that only one still should be built at a time as a proof of concept.

The solar still pictured in the “Solar Still Model 2” section of Figure 2 should have produced effluent because the plexiglass was submerged into the bucket and thus appeared to be sealed. Nevertheless, the first circular basin solar still failed to produce effluent due to heat escape caused by minor gaps between the cover sheet and basin. As can be seen in the “Cause of Failure” section, clearly, some issues posed by the square basin solar stills had not been adequately addressed. As a result, for “Solar Still Model 3” in Figure 2, ceramic clay was used to line and seal the spaces between the plexiglass and basin. In an attempt to enhance the insulation capabilities of the still, the basin was additionally submerged into 6 inches of sand. Now that the still was fully insulated, effluent should have been produced. Regardless of these changes, still no effluent was produced. Additional literature research was conducted, and it was discovered that plexiglass absorbs more heat than it radiates, meaning it has a high lambda value. As a result, the salt water in the basin of the still was not heating up and the cover sheet remained too hot for water to condense upon the inner surface. To address the issue, the “Solution” section for “Solar Still Model 3” recommends that the material of the cover sheet be switched from plexiglass to glass because of glass’ lower lambda value.

The “Solar Still Model 4” section of Figure 2 outlines that, similar to previous attempts, the insulated, circular basin, glass cover sheet solar still failed to produce any effluent. It was then noted that the optimal inclination for the cover sheet is 25° (Azooz, 1970). The inclination angle of the cover sheet in the stills described so far was set to 12°, which is 13° less than the suggested inclination. Considering that the fabrication of multicomponent stills consistently posed unsolvable knowledge gaps, the “Solution” section for “Solar Still Model 4” deemed it necessary to remodel the still and recreate it in its most simplest form. Once a functioning solar still is created, knowledge from these trials can be used to inform the design and creation of more complex devices and more efficiently investigate the original experimental question of the relationship between cover sheet thickness and effluent production.

As seen in Figure 3, a simplistic solar still was fabricated using Saran Wrap, a bucket, a weight, a beaker, and a stilt based on the design of an emergency solar still (Marinoff, 2020). This design successfully produced effluent when tested using both natural and artificial sunlight. The results from this test can be seen in the “Results” section of this figure. When tested under sunlight, an average of 1.95 mL of effluent were produced per day, with a salt concentration of zero. When tested using artificial sunlight, 1.24 mL of effluent was produced on average per day. Seeing as effluent was produced using a Saran Wrap clear plastic cover sheet, it was assumed that the emergency stills would produce effluent with any form of clear plastic.

The “Limitations” section of Figure 3 highlights a drawback with using Saran Wrap as the cover sheet material, which is that the exact thickness is unknown. The experiment was thus repeated under the same conditions, except the cover sheet was a tarp with a known thickness of 0.94 in. It is beneficial to use a cover sheet with a known thickness because one can more closely monitor how cover sheet thickness affects the amount of effluent produced; using a cover sheet with a known thickness allowed me to test the effects of distinct thicknesses on the amount of effluent produced. As can be seen in the “Solar Still Model 6” section of Figure 3, due to the increased thickness of the clear tarp compared to that of the Saran Wrap (0.94 inches versus ~0.0005 inches), no effluent was produced from the emergency solar still. Since the emergency solar stills with Saran Wrap had previously produced effluent, it was suggested in the “Solution” section that, although the exact thickness is unknown, using multiple layers of Saran Wrap was the most logical next step.

In order to test the effects of varied Saran Wrap cover sheet thicknesses, three stills were fabricated; one had one layer of Saran Wrap, the second had two, and the third had three as their respective cover sheets. When those three emergency stills were tested in unison, no effluent was produced. As can be seen from Figure 4, Model 7 used distinct buckets for its basin than Model 5 did. Since no effluent was produced by any of these stills, it was assumed that the distinct dimensions of the bucket were what hindered the production of effluent. In response, the Model 8 stills were all made using the exact gray buckets used for Model 5. Nonetheless, no effluent was produced, yet again. This was due to the fact that the stills were not receiving sufficient heat since three were tested at once rather than individually.

The necessity for research in this field continues to grow as the water crisis worsens. As industrial expansion and population growth continue to skyrocket, this research will only become more vital. Water purification methods that operate solely from the power of clean energy are limited, so it is important to continue to invest time and resources into the optimization of the solar still. The overarching goal of this study was to improve the efficiency of solar stills. Now that I am an informed researcher, I have learned that the research must now be centered in mitigating the effects of the brine rather than improving the efficiency of the solar still. If given more time, I would devote my resources towards addressing that major knowledge gap posed by solar stills. A study conducted by Jahan et al. found that natural brine produced in Syracuse, New York can be repurposed and used as an anti-icing agent on roads (2012). They found that using natural brine as a road deicer was environmentally friendly, cost effective, and decreased the number of accidents. Considering that the brine used in Jahan et al’s study successfully made the roads less icy, the repurposing of brine from solar stills is definitely a potential solution.