STEM 1

About 2.2 billion people worldwide do not have access to safely managed drinking water services (WHO, 2019). Many of the earth’s freshwater sources are full of chemicals, heavy metals, and microorganisms due to improper disposal of various wastes (Khan et al., 2022). Consumption of contaminated water results in waterborne diseases which facilitate about 1 million deaths annually (WHO, 2022). Current methods of water purification only focus on the removal of a specific contaminant and require large amounts of electricity to function, making them unaffordable and ineffective in full decontamination. Membrane distillation is the process of evaporating contaminated water through a porous membrane and condensing purified water. Preliminary methodology includes testing the rate of vapor permeation of various membranes, utilizing spectrophotometry and methylene blue to conduct a proof-of-concept that determines the effectiveness of the membrane distillation process, and prototyping condensing units. Upon prototyping, a final device design was created and built using Computer Aided Design and purchased components. Water samples were collected from Institute Pond and Northborough reservoir to test levels of contamination before and after purification. Focused chemical and bacterial testing occurred as well to determine the device’s effectiveness with higher levels of contamination than pond water. A solar panel and battery were acquired to power the device. Results show that the device achieved complete or mostly complete removal of chemicals, heavy metals, and bacteria. All results after purification fit safe drinking water standards. Future work includes increasing the scale of clean water production, and iterations on materials and design

Technique 1: Membrane tests Membrane distillation methods can utilize membranes made of different materials, which can result in different outcomes. Therefore, it is important to test which membrane can evaporate water the fastest, since that is an important factor for water purification. A dish with 50mL of distilled water was brought to a boil (100 C) on a hot plate with the setting at 2.8. The water was evaporated through a nitrocellulose membrane, nylon membrane, and no membrane (control) for 3 minutes each and the condensation was collected on a petri dish. The condensation for each trial was weighed with the petri dish, and then the weight of the petri dish (43. 9717g) was subtracted to find the mass of just the condensed water. Technique 2: Proof of concept Upon the decision to move forward with the nylon membrane as opposed to the nitrocellulose membrane, it is important to test if it is effective in removing contaminants from water, since that is crucial aspect of water purification. Methylene Blue is a chemical that has a high light absorbance; therefore, I used spectrophotometry to evaluate the absorption of methylene blue in water before and after using nylon membrane distillation. For this experiment, 450mL of distilled water was combined with 5mL of methylene blue, and the solution was heated, evaporated, and condensed using a hotplate, ice pack, petri dish, and a glass container. A spectrophotometer was utilized to detect the amount of absorption and wavelength that occurred with the distilled water, methylene blue mixture, and the methylene blue mixture after membrane distillation. Technique 3: Final construction Upon completing the proof-of-concept testing, various condensing unit set ups were observed to determine the final design of the device prior to construction. Some of the major flaws included vapor escaping and not condensing in the condensing unit. The causes of this issue include the surface area of the contaminated water source being too large, the sides of the condensing unit (the petri dish) were not angled downwards enough for the condensed water to drip down, and the construction of the prototype was not enclosed to prevent escaping vapor. To tackle these issues in the final design, a design was initially sketched and then modeled with Computer Aided Design utilizing OnShape. The design consists of a two-layer container, with the central layer being for contaminated water, and the outside layer being for purified water collection. A holder for the heater was designed with tunnel for the wire. A pyramid shaped condensation unit was designed as a lid for the container, to ensure that vapor does not escape during the process. With a pyramid shaped condensing unit, with the peak centered directly above the membrane layer, the water can condense easily and effectively navigate into the purified water collection unit. When implementing the design into CAD, the volume of each layer of the device was decided to be one liter, as that is the minimum amount of daily water consumption needed for human survival. Basic geometry was used to determine the accurate dimensions of each layer so that the volume inside both is equal, while the inner layer still maintains an equal surface areas to the membrane. Technique 4: Material sourcing Upon creating a design, materials to contstruct the design were determined. An ideal heating unit for this device would be a small and submersible heater that gradually increases temperature. But, designing and constructing such as heater is beyond the scope of the project, so a Lewis N. immersion water heater from Amazon was utilized in construction. This water heater utilizes about 110V, so a solar panel and battery system was purchased with the same capacity to fufill the needs of the heater. Lastly, PLA material was initally used for 3D printing, but then it was replaced with ABS, as it has a higher melting point. Technique 5: Heavy metal and chemical testing utilizing fresh water samples from local sources Heavy metals and chemicals are contaminants that are dangerous for human consumption. To test how effective the device is at removing heavy metals and chemicals from water, first, two water samples were collected from Northborough Reservoir and Institute Pond on 02/07/2025. Utilizing a water testing kit, both samples were separately tested for total hardness, iron, mercury, total chlorine, copper, lead, zinc, manganese, QAC/QUAT, fluoride, sodium chloride, hydrogen sulfite, total alkalinity, sulfate, carbonate, and pH. After that, the device was run to purify the samples, and the purified water was tested again to determine how effective the removal of the contaminants was. Contaminants that were not present the water samples before purification were not measured for after or evaluated in results as they did not exist originally. Statistical analysis was conducted for each sample and each contaminant to determine if the amount of ppm before and after are significantly different. Since most samples after purification results in 0 ppm of the contamination, a paired t-test was not suitable as the standard deviation is 0. Therefore, a one-sided t-test was conducted to see if the average amount of ppm in the sample before purification was significantly greater than the amount after purification, which shows the difference between the two. But, some contaminants resulted in non-zero ppm values after purification, and in that case, a two-paired t-test was conducted to see if the difference is significant before and after purification. Technique 6: Bacterial testing Agar bacteria plates were prepared for testing. Then Lysogeny Broth (LB) was combined with Escherichia Coli, and a spectrophotometer was utilized to determine the absorption. Since the proteins in the bacteria absorb light, it is effective to utilize spectrophotometry to detect the presence of bacteria. Next, using an optical density app, the number of bacteria cells per 1 mL were determined and then used to determine the total mL that need to be added to the 500mL of water in the device, to ensure accurate proportions of bacteria and water in the spectrophotometer and the device. Then, a sample of the contaminated water was added to one of the bacteria plates. The device was run, and purified water was collected. Another sample was taken and added to a different plate. The plates were left out for two days for the bacteria colonies to develop, and upon growth, bacteria colonies were counted in both samples. About a mL sample of purified water was also run through the spectrophotometer to detect the presence of bacteria through absorption levels. Chemical testing The device was tested with methylene blue again to determine if the device matched the results of the proof-of-concept testing. A water sample contaminated with methylene blue was measured for peak absorption before and after purification. Vernier graphical analysis was used to compile the two graphs of absorption at full spectrum wavelength into one to clearly see the difference in methylene blue levels of the purified and unpurified water.