Abstract

During the past 75 years, plastic production has increased from 1.5 million tons to 322 million tons a year because of the cost efficiency and variety of uses. Due to the increased production, many plastics are improperly disposed of and enter the environment. Every year, 8 million tons of plastic enters the ocean and eventually breaks down into microplastics which are less than 5 mm in size. At this point, these plastics can be consumed by ocean organisms and harm them when entering animal tissue. To combat the influx of microplastics into the ocean, a filter with a semipermeable membrane was used to extract microplastics from samples of water, as a possible method to eliminate plastic waste from entering the water supply. Only materials that are smaller than the pores in the membrane could pass through, so the membrane can be used to eliminate as much plastic as possible from a sample of water. A spectrophotometer was used to measure the amount of light that was absorbed by the plastics. Then the concentration of the plastics can be compared. The change in the absorbed light determines the amount of plastic that is removed when filtered through the membrane. This paper presents that the concentration of microplastic decreased by at least 30% when put through the different prototypes made from 2 different filters. These filters can eventually be applied to household items like the washer to prevent microplastics from entering the sewage system and eventually entering the ocean.

Background

There are millions of particles of microplastic in the ocean and other bodies of water. Plastic comes from many of common plastic items in commercial products. With the variety and usefulness of plastics, it is not a surprise that many products in the market are made from plastic. However, with the popularity of this material, came the abundance of litter that now invades the environment. Plastics serve various purposes and are cheap to manufacture, so within the 100 years that it has been created, it has become a staple material in many commercial products. An estimated 4 to 12 million tons of plastics is estimated to escape into marine environments from 2010 alone which plastics to collect in the ocean and other bodies of water (Coppock et al, 2017). When plastic wears down, it breaks down physically into smaller and smaller pieces, and are transported into waterways. Plastics are polymers which are composed of smaller units, so its molecular structure stays the same while it physically gets smaller.

There is so much microplastic litter that there is a big patch of microplastic in the Pacific Ocean, known as the Great Pacific Garbage Patch (The Great Pacific Garbage Patch, n.d.). Due to ocean currents, plastic particles are gathered in the Pacific Ocean to create a mass of plastic particles that weighs tons. The Great Pacific Garbage Patch isn’t the only collection of plastic, others exist too where ocean currents gather them. There has also been plastic found further down in the water than just on the surface. Deep sea sediments have also been found to contain microplastics. This poses an issue since it is much harder to filter plastic found that far down due to the ocean life dwelling there.

Microplastic pollution is contaminating the environment and many of the foods people consume. Not only can microplastic get into human and animal tissue, it also acts as a medium to absorb other pollutants which may cause even more damage to wildlife and humans (Van Cauwenberghe, Vanreusel, Mees, & Janssen, 2013). Microplastics concentrate pollutants, thus increasing their toxicity. For example, an increase of salinity increases the adsorption capacity of microplastics (Ma, Zhao, Zhu, Li, & Yu, 2019). This means that when microplastics reach the ocean, they can exacerbate the toxicity of other present pollutants. When microplastic can get into the human body, jagged edges can cut tissues and cause inflammation (Sun, Dai, Wang, van Loosdrecht, & Ni, 2018). There may be no immediate threats to having microplastics in our tissues, and most plastics typically pass through the digestive system, but the build up of plastics in the body can release toxins.

Wastewater treatment plants are one of the culprits that release microplastics into the environment. When water is treated, most of the microplastics are filtered out and end up in sludge. This sludge can be used as fertilizer and other products which releases the microplastics into the environment where they end up in our marine biomes. Of the microplastics found in the wastewater treatment plants, microplastic fibers are much more common than microplastic particles (Lares, Nicbi, & Sillanpaa, 2018). This poses a problem because they are much harder to filter due to the fact they can pass through many mesh filters. Meshes bigger than 250 nanometers allows too many small particles to pass through (Oßmann, Sarau, Schmitt, et al. Anal Bioanal Chem 2017).

The issue with filtering microplastics is that there are many types of plastics and those different plastics which have different shapes and sizes. Most define microplastic as plastic particles that are less than 5 millimeters. Plastics have different densities which makes filtering by density difficult. However, a semipermeable membrane can be used to filter out as many microplastics as possible. With different pore sizes, only microplastics of larger size will be able to pass through the filter. By passing a sample of water and microplastics through the filter, microplastics can be filtered out and the remaining concentration of microplastics can be analyzed.

Procedure

A sample of microplastic will be made before filtration can occur. Deionized will be used to ensure there are no other preexisting particles in the end sample of water. The water will be placed in a beaker and heated over a hot plate. A cut tea bag will then be placed into the water with a magnetic stirrer. This will break down the plastic into some microscopic pieces. After 10 minutes any large plastic pieces are removed and the sample can be filtered. The concentration of the microplastics can be measured with a spectrophotometer. Different filtration apparatuses will be used cutting different types of membrane filters so they will fit into a reusable filter holder. A syringe will then hold an amount of the sample plastic water to be passed through the filter. The concentration of the plastic will be measured with a spectrophotometer and then compared to the starting concentration.

Create a sample of microplastic:

Heat water until 80 degrees celsius.

Cut a tea bag into strips and place it into the water.

Add a magnetic stirrer to stir the water.

Wait 10 or 20 minutes then remove the large bits of teabag

Measure the amount of microplastic present in that sample using spectrophotometer.

Making and using the filter:

Make the filtration device with membrane filters that have pore sizes less than 1 micrometer. Cut them so that the membranes fit inside the filter holder.

Filter the sample of water through the device by using a syringe to push the water past the filter.

Measure the concentration of microplastic that is filtered out with the spectrophotometer.

Results

After testing the prototypes, the sample optical density was obtained. At a wavelength of 375 nm all the absorbance was lower than 0.100. The prefiltered microplastic samples were tested each time the prototypes were tested. The average absorbance for the first sample was 0.036. The average for the second sample was the highest at 0.067, and the last sample had an absorbance of 0.042 as seen in table 1.

Figure 1 shows that after the sample was filtered, prototype 1 was able to filter out 49% of the microplastic contents, prototype 2 was able to filter out 31% of the contents, prototype 3 was able to filter out 18% of the contents and prototype 4 was able to filter out 64% of the microplastics.

Figure 2 shows that after the sample was filtered, prototype 1 was able to filter out 67% of the microplastic contents, prototype 2 was able to filter out 63% of the contents, prototype 3 was able to filter out 34% of the contents, and prototype 4 was able to filter out 73% of the contents.

Figure 3 shows that after the microplastic sample was filtered, the first prototype filtered 74% of the microplastics, the second prototype was able to filter 79% of the contents, the third prototype was able to filter out 62% of the contents and the fourth filtered 71% of the microplastics.

After the optical densities were found, pair t-tests were used to see if there were any significant differences between the absorbance of the different prototypes. The tests revealed that between prototypes 1, 2, and 4 the p value was consistently over 0.05, and between prototype 3 and 4 the p value was 0.02. This indicates that there exists a significant difference between prototype 3 and rest of the prototypes.

Discussion/Conclusion

When making the microplastic samples, time was the greatest factor in determining the concentration of the created microplastic water. From table 1, the concentration of the first and third microplastic samples were similar because they were both left on the stir plate for the same amount of time (10 min). The third sample with an average absorbance of 0.042 may have been higher due to the smaller pieces the tea bags were cut into. The second sample was left on the stir plate for 20 minutes which resulted in the highest microplastic concentration.

From the testing, it is shown that prototype 4 filtered out more microplastics than in prototypes 1, 2 and 3. When filtering the low concentrated microplastic sample, prototype 4 with all 3 of the membrane filters is able to filter out 36% more of the microplastic solution than the third prototype, 33% more than the second prototype, and 15% more than the first prototype.

When testing the prototypes on the high concentrated microplastic sample, the fourth prototype again filtered out 39% more of the microplastics in the sample than the third and only 10% more than the second prototype and 6% more than the firsts. All tests showed that, overall, the third prototype by far performed the worst, while prototypes 1, 2, and 4 had similar results with prototype 4 being a bit more effective than the second and the third. The t-tests also support this idea because only prototype 3 was seen with any statistical difference, while the other 3 prototypes didn’t have a statistical difference.

Prototype 4 was the most effective at filtering because it contained all three types of membrane filters that were used among the prototypes. However, in terms of resources, prototype 1 is the most efficient. With the larger pore sized membranes, it is the cheapest filter to make.

Prototype 3 was made of membranes with a pore size of 0.45 micrometers and 0.2 micrometers which are smaller than the membranes in prototype 1 and 2. This means that a device with these smaller pore sizes may not necessarily cause a great change in the number of particles filtered out. This means that costs for buying the membrane may be saved when not getting the smallest pore size membrane filter.

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Febuary Fair Poster

Here is the information I had for the fair.