Siyeon Jeong1*, Kaixin Qiang1, Nikolai Yakovlev2
1 National Junior College, Singapore
2 National University of Singapore, Singapore
*E-mail:
1. Introduction
Oil contamination in water is a pressing environmental issue as it degrades water quality, threatening global aquatic ecosystems (Kolokoussis et al., 2018). The European Space Agency reported that roughly 4.5 million tonnes of oil contaminate oceans annually, which disperses rapidly on water and accumulates on the seabed as slick (D’Andrea et al, 2013). This is concerning, as oil spills have large impacts on both human and wildlife populations. Plastic waste is also a prevalent issue, with nearly 1 trillion plastic bags consumed annually (Miller, 2012). In 2019, only 9% of plastic waste was recycled while the remaining 91% was landfilled, incinerated or discarded in uncontrolled areas (Geneva Environment Network, 2024a). This improper disposal threatens public health. Furthermore, a report published by the World Economic Forum in 2016 predicted that global plastic production is expected to double by 2036 and quadruple by 2050. This alarming trend calls for urgent action to address the pressing issue of plastic waste. This project aims to explore the oil adsorbing properties of the most widely used plastic bag materials (HDPE, LDPE, PP) to design an oil sorbent that can collect a large amount of oil relative to its mass. This solves two problems in one go – removing waste (oil contamination) using waste (plastic bags).
2. Laboratory Tests
2.1 Oil Adsorption
The oil adsorption of each material was tested in 5W30, 15W40 and 10W60 engine oil respectively. From Figure 1, the samples can adsorb oil up to 17.8x of their own mass, showing great potential to adsorb oil from oil spills. HDPE had the highest oil adsorption, followed by PP and LDPE. Furthermore, the samples have the highest oil adsorption in 5W30 engine oil, which is the least viscous, hence showing potential to clean oil spills usually comprising crude oil, which also has low viscosity.
2.2 Contact Angle
An inexpensive and reliable method of measuring contact angles was developed in this project, making use of the top view of the droplet. It involves stretching out the material on a flat surface using tape and dropping a 5 L droplet of oil or water on the surface. A photo is taken directly above the droplet, with a ruler placed beside it for scale. Its diameter (D) is measured 4 times, and an average is taken. In this method, it is assumed that the droplet is a spherical cap. The calculations are explained in Figure 2.1.
From Figure 2.2, contact angles of oil and that of water have an inverse relationship. With a higher water contact angle, the material is more hydrophobic and hence has a lower oil contact angle. It is shown that HDPE has the highest water contact angle and one of the lowest oil contact angles. Hence, HDPE has the highest affinity for oil. The materials circled in blue were used to make the sorbents used in the field tests as they have the lowest oil contact angles, meaning that they had the greatest affinity for oil.
3. Field Tests
3.1. Methodology
Three sheets of plastic bags were sewn together, layered to mimic bird plumage. Thin strips were cut on the sides to allow water to reach into all sides of the sorbent. The same materials were used for field tests and contact angle tests, and each field test location was tested on three different dates. The sorbents were tested in publicly accessible water bodies. They were submerged for 2h followed by 1h of drying. Mass of pollution adsorbed was recorded by taking the difference of final mass and initial mass of the sorbent. Locations visited for freshwater testing were Bukit Timah Canal and Marina Bay, while locations for saltwater were East Coast Park and West Coast Park.
3.2. Results and Discussion As evident in Figure 3, the best sorbent is HDPE followed by PP and LDPE, in both saltwater and freshwater. The downward gradients between the three materials in saltwater is steeper as compared to that of freshwater locations, indicating that the difference in the ability of sorbents is more evident. Saltwater locations had more pollutants adsorbed than freshwater locations. There is significantly lower adsorption in field tests as compared to lab tests, indicating that there is little pollution in Singapore’s waters.
3.3. Possible Applications
Following these findings, HDPE would be the most effective material to be used as a sorbent to clean up oil contamination from the water, whereas LDPE would be the least effective. This study provides an innovative and promising solution to tackle two pressing environmental problems in our world today. In the future, further research can explore ways to modify physical characteristics of sorbent to make it more effective at adsorbing contamination, as well as ways to turn other types of plastics into sorbents.
4. Conclusion
Plastics have a high oil adsorption capacity of up to 17.8 g per 1 gram of material, and its adsorption capacity is inversely related to its thickness. HDPE had the highest adsorption across all oils. All three materials tested were able to adsorb oils of low viscosity the best, suggesting promising results for cleaning up light oil spills. Contact angles of oil and that of water have an inverse relationship.
From contact angle measurements, it can be drawn that the ideal sorbent should be made of HDPE and have narrow dimensions.
Through field tests, it was determined that the best sorbent is HDPE followed by PP and LDPE, in both publicly available sources of saltwater and freshwater. In general, saltwater locations have higher contamination than freshwater locations. The difference in the ability of sorbents of different materials is more evident in saltwater.
In summary, we have developed an oil sorbent using waste plastic bags that is able to clean up oil contamination in the water, as well as provide a convenient and cost-effective method of monitoring pollution in water bodies.
References
D’Andrea, M. A., & Reddy, K. G. (2013). Health consequences among subjects involved in Gulf oil spill clean-up activities. The American journal of medicine.126(11):966-74. doi: 10.1016/j.amjmed.2013.05.014.
European Space Agency. (n.d.-a). Oil spills. European Space Agency. https://www.esa.int/Applications/Observing_the_Earth/Oil_spills
Geneva Environment Network. (2024a). Plastic waste management: Plastics and the Environment Series. Geneva Environment Network. https://www.genevaenvironmentnetwork.org/resources/updates/plastic-waste-management/
Kolokoussis, P., & Karathanassi, V. (2018). Oil spill detection and mapping using Sentinel 2 imagery. Journal of Marine Science and Engineering, 6(1), 4. https://doi.org/10.3390/jmse6010004
Miller, R. M. (2012). Plastic Shopping Bags: An Analysis of Policy Instruments for Plastic Bag Reduction. University Utrecht.
World Economic Forum. (2016a, January). The new plastics economy: rethinking the future of plastics. World Economic Forum. https://www3.weforum.org/docs/WEF_The_New_Plastics_Economy.pdf
