Evaluating Bio-coagulant Efficiency: Sustainable Alternatives for Microplastic Removal from Water

I hope you enjoy my video! The slides were made entirely by Sophie Clattenburg on either Microsoft PowerPoint or Bio-render.

Global Problem: Plastic pollution is one of the most pressing environmental-health challenges of the 21st century, with over 6.3 billion tonnes of plastic waste generated since 1950 and 79% accumulating in the environment, where it breaks down into microplastics (4).Microplastics (MPs) are an emerging pollutant of increasing global concern, ubiquitous in terrestrial and aquatic environments worldwide. Due to their small size, they can adsorb toxic contaminants such as persistent organic pollutants (POPs) and heavy metals and bioaccumulate through the food chain, ultimately entering the human body. It is estimated that humans may ingest up to 52,000 microplastics annually. (4) To reduce exposure and associated health risks, effective removal technologies are essential - particularly for drinking water, a primary exposure pathway. Notably, up to 83% of global tap water has been found to contain MPs, and there is currently no maximum allowable concentration under Ontario Drinking Water Standards (O. Reg. 169/03).

Synthetic vs. Bio-coagulants: My project, similar to many drinking water treatment plants used the coagulation-flocculation-sedimentation (CFS) process, which commonly utilizes a synthetic coagulant. However, synthetic coagulants are associated with environmental/health issues due to their generation of non-degradable sludge. Therefore, natural coagulants are being investigated as potential sustainable alternatives to synthetic coagulants for microplastic removal in water and wastewater treatment plants.

Project Objective: My project's objective is to investigate the coagulation potential of bio-coagulants, Psyllium, Ulva Lactuca and Chlorella Vulgaris, as sustainable alternatives to the Niagara Regions synthetic coagulant, Aluminum Sulfate, for removing microplastics from drinking water.

The coagulation-flocculation-sedimentation (CFS) process is commonly used as a removal strategy in many drinking water and wastewater treatment plants worldwide. My project utilizes this process as a basis/method for the experiment.

The experiment was separated into 4 parts.

Part 1 - Transforming the Coagulant Types into Fine Powder

Coagulants were individually ground into fine powders using a coffee grinder and stored in sealed glass jars to prevent contamination from plastic and air exposure.

Part 2 - Weathering the Polystyrene and Polyethylene Terephthalate Microplastics

In this project three types of microplastics were used: Polyethylene (PE), Polyethylene Terephthalate (PET), and Polystyrene (PS).

The PE MPs were obtained in the form of microspheres (212micrometer diameter) FROM COSPHERIC_MD 20230116.

A 4-step weathering process took place composed of grinding, oxidation (using 3% hydrogen peroxide), abrasion (using clean rocks), and UV exposure (using UV flashlight).

Part 3 - Pre-Experiment: Sample Preparation

PE microspheres were mixed and 100 microlitres was extracted via pipette and placed on a slide. A constant number of PET and PS MPs were added using tweezers and verified three times under a microscope. Concentrations were confirmed using an analytical balance.

Coagulant dosages tested:

Individual: 200 mg, 500 mg

Combined: 400 mg, 500 mg

Samples were prepared in beakers containing 500 mL of Milli-Q water, then subjected to:

2 min rapid mixing

20 min slow mixing

10-day sedimentation

Part 4 - Post Experiment: Floc & Supernatant Analysis

A pre-cleaned 27 micrometre nylon mesh was placed in a funnel, rinsed with Milli-Q water, and verified under a microscope to ensure no contamination.

Samples were filtered, and floc stability was assessed by gentle swirling (collapse = failure).

The supernatant and floc were separated onto individual watch glasses.

MPs in each fraction were counted under a microscope in triplicate to ensure accuracy, and results were recorded in "Post-experiment" data table.

Figure 5 represents the percentage of total microplastics removed from 500ml of water for each coagulant type. The following coagulant samples were considered a fail because they did not form stable flocs: Alum (200mg), Alum (500mg), Ulva lactuca (200mg), Ulva Lactuca (500mg), Chlorella vulgaris (200mg), Chlorella vulgaris (500mg), Ulva lactuca +Chlorella vulagris (400mg), Ulva lactuca + Chlorella vulagris (1000mg). Figure 5 also shows that the Psyllium coagulant had the highest overall removal percentage, with Psyllium (200mg) removing  84.60% of the total number of MPs, and Psyllium (500mg) removing 90.30%. The Psyllium + Alum combination coagulant types had the second highest removal percentage. Psyllium + Alum (400mg) removed 81.80%, while Psyllium + Alum (1000mg) removed 75%. Moreover, the Chlorella vulgaris + Alum coagulants performed third best - Chlorella vulgaris + Alum (400mg) removed 64.20%, and Chlorella vulagris + Alum (1000mg) removed 73.10%. Finally, the Ulva lactuca + Alum coagulants removed had the lowest removal percentage comparatively to all the coagulants that flocked. Ulva lactuca + Alum (400mg) removed 50% of microplastics, while Ulva lactuca + Alum (1000mg) removed 44.80% of microplastics.

Figure 6 demonstrates the total percentage of the samples that formed flocs. It categorizes them by floc strength and presence - no floc, weak floc, and strong floc. The following samples didn’t form a stable floc: Alum (200mg), Alum (500mg), Ulva lactuca (200mg),Ulva lactuca (500mg), Chlorella vulgaris (200mg), Chlorella vulgaris (500mg), Ulva lactuca + Chlorella vulgaris (400mg), Ulva lactuca + Chlorella vulgaris (1000mg). Ulva lactuca + Alum (400mg) and Ulva lactuca + Alum (1000mg) formed weak flocs. Finally, Chlorella vulgaris + Alum (400mg), Chlorella vulgaris + Alum (1000mg), Psyllium (200mg), Psyllium (500mg), Alum + Psyllium (400mg), and Alum + Psyllium (1000mg) formed strong flocs.

Figure 7 clearly illustrates the percentage of each type of MP removed for each coagulant. The easiest type of plastic particles to remove across all the coagulants that flocked was the polystyrene microplastics, followed by the polyethylene terephthalate MPs. On the contrary, the polyethylene MPs proved to be the most difficult type of MP to remove as their removal percentage was lower compared to the other MP types.

There are many key factors that influenced these results including: charge neutralization, electrostatic attraction, polymer bridging, hydrogen bonding, physical entrapment/collision frequency, particle sweeping, MP densities, and functional groups.

In conclusion, based on the overall results of this experiment it was determined that Psyllium is the most effective coagulant at removing MPs from water. However, the coagulant with the most real-world application potential is Psyllium + Alum. Alum is a commonly used coagulant in drinking water and wastewater treatment plants globally, and more specifically, is used by the Niagara Region. Alum’s main purpose is to remove turbidity and other impurities from water and in this project has been proven to be ineffective at removing MPs from water. Therefore, it is unrealistic to assume that Alum will be replaced by Psyllium alone, solely because it removes MPs.

While the topic of microplastics is very cutting edge and identification strategies and removal technologies continue to be developed, bio-coagulants offer a sustainable alternative to synthetic coagulants for the CFS process for MP removal from water. As a result, it is critical that governments, academic institutions, and businesses around the world continue to invest in research to develop standards for MPs in water, sustainable ways to remove MPs from water, and to strengthen global scientific knowledge to better understand the long-term environmental and human health impacts of MPs.

This study has real world application potential, promoting effective and sustainable methods to removing MPs from drinking water.

If this project were to be repeated the following factors would be adjusted. The results would be compared to the data from this project to show in floc strength and MP removal percentage as well as further evaluate the real-world application potential of these bio-coagulants in drinking water treatment plants.

Triplicates would be introduced for each coagulant type to further improve the reliability and accuracy of the results.

The coagulant dosage would be adjusted to find the optimal concentration.

Room temperature during sedimentation time.

Shortened sedimentation duration.

Increased duration of the weathering process.

New coagulant and MP types would introduced.

I would like to thank Dr. Mangal and Dr. Zelisko at Brock University for their support in the early stages of my project. I would also like to thank the University of Waterloo for letting me use their labs and equipment for my project. Additionally, thank you to Dr. Philippe Van Cappellen and Tia  Jenkins at the University of  Waterloo Microplastics Fingerprinting Research Project  for their support and guidance. I would espicially like to thank Dr. Shuhuan Li for answering all my questions and guiding me through my methodology. I would also like to recognize Ms. Erin Shisler at the Niagara Region for answering all my questions regarding drinking and waste-water treatment plants in Niagara. Finally, I would like to thank my parents and the Niagara Regional Science and Engineering Fair for the support they showed me over the duration of the project.

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