An investigation into the removal of microplastics from water using ferrofluids

Resumen

This project investigates a new method for the extraction of microplastics (plastic particles less than 5mm in diameter) from water. At present, no screening or filtering for microplastics takes place in any European wastewater treatment centres1.

My method was inspired by an article written by Arden Warner using non-toxic iron oxide (magnetite) to clean up oil-spills2. I used this method in the extraction of microplastics by adding oil to a suspension containing a known concentration of microplastics, these then migrated into the oil phase. Magnetite powder was added. The resulting microplastic containing ferro-fluid was removed using strong magnets.

The hypothesis was that this extraction method would remove 85% or higher of microplastics in samples.

To measure the concentration of microplastics in a given sample, I built a visible light spectrometer which could analyse the spectra of light passed through samples using the software Spectragryph. This used the Beer-Lambert law to determine the concentration of a sample3. Samples were also examined under a microscope and analysed in Adobe Photoshop. Both testing methods gave a measurement of plastics removed.

The 10 most commonly found microplastics were used in tests. All plastic samples used needed to be prepared before extraction.

The results obtained supported the hypothesis with an average of 87.6% ± 1.1% extraction. The method used was most effective on fibres obtained from a washing machine and least effective on polypropylene plastics.

I conclude that my method would form the basis for an effective way of extracting microplastic from water.

The next step is to scale this up to an industrial scale.

Pregunta/Propuesta

I live near the seashore and have become increasingly aware of plastic pollution of the oceans4. I was alarmed to find out how many microplastics enter our watewater system and consequently the oceans4. This inspired me to try and find out a way to try and remove microplastics from waters before they even reached the sea.

The first challenege for me was how to measure the concentration of microplastics in water. I built a spectrometer to measure this. In my chemistry class at school, I learned about how in chemistry like charges attract like charges (ie. non polar vegetable oil would attract non polar plastics in the environment of water)5. I read about Dr Arden Warner who has developed a method for cleaning up oil spills using magnetite powder (naturally occurring iron oxide)2 This made me think that a combination of oil and magentitie would allow me to remove plastics from water

The main research question is: Could the combination of oil and magnetite be used to effectively extract different types of microplastics from water?

My hypothesis is that the ferro-fluids formed by the combination of oil and magnetite will remove at least 85% of the microplastics in a given sample of contaminated water. I based my hypothesis on my own experimental observations and because of the observed tendency of the microplastics to migrate into suspension with the non-polar oil.

 

Investigación

I started this project by researching what types of microplastic extraction and elimination techniques exist. I found that scientists are looking for methods for the removal of microplastics from water6. However, so far there have been no methods developed which could quickly and efficiently do this7. Methods explored include carbon filtration systems and density separations. This research told me that there was a need to develop a more viable method.

There have been many studies conducted into microplastics and their effects on wildlife and fish8 Eg. GMIT in Ireland and this helped me determine the huge problem microplastics pose to the world's wildlife and ultimately humans4.

When looking for a method to remove microplastics from water I read about Dr Arden Warner, a Barbadian scientist who developed a method to clean up oil spills by using magnetite powder2. This formed a non-toxic method for cleaning up oil spills. The magnetite powder does not harm wildlife and is 98% recoverable using electromagnets2. I thought that this method could be used to remove plastics from water also as these plastics are non-polar similar to oil meaning that they would tend to be miscible.

When looking for a method to test for microplastics before and after extraction, I wanted to create a quick and accurate method which could be repeated many times. I decided that using the Beer Lambert law in conjuction with a visible light spectrometer would be effective. I live in a very remote place and this meant that I had to build my own spectrometer. I found articles on the spectral workbench website very useful in the building of the spectrometer and the later analysis of the results3.

I also wanted to get my samples tested in a laboratory and contacted researchers in the GMIT Institute in Galway, Ireland. The method they use is microscopy and counting plastics particles in a water sample. They advised me to use my own microscope rather than theirs as this would allow me to conduct many tests. I then was inspired by my exsisting knowledge of Adobe Photoshop to use that to count the plastic particles for me on the digital microsocpe images.

Finally, I found that articles relating to statistical analysis and hypothesis tesing were useful to finally analyse and  interpet my data and results to draw a final conclusion9.

 

All of this research helped my project be conducted accurateley and efficiently to produce a meaningful result of a new method for the removal of microplastics from water in a non-harmful, quick and sustainable way.

Método/Prueba

 

Micro-plastic Production:

To test how efficient my method was, I had to first produce microplastics to remove from the water. The methods used were:

  • Hard plastics were sanded using non-shedding sandpaper and sieved to less than 5mm. (PET, HDPE, PVC, PP, PS and epoxy).
  • Microplastics in cosmetic products were separated from the gels using suction filtration and desiccation. (LDPE).
  • Plastic fibres were used from model making grass (nylon and polyester) and by removing plastic from the washing machine filter.

Preparation of microplastic suspensions:

Microplastic suspensions were used for extractions as well as for the formation of a (Beer-Lambert Line for later spectroscopic testing). For extraction, a 5g/L suspension was prepared of the desired plastic. Known concentration samples were prepared for spectroscopy. The concentrations were: 5g/L, 3g/L, 2.5g/L, 1.25g/L, 0.63g/L and 0.31g/L.

The Microplastic extraction process:

After preliminary testing, I concluded that the volumes of oil I would test in each extraction would be, 0ml/L, 2.5ml/L, 7.5ml/L and 12.5ml/L. This would allow me to determine what volume of oil would be the most efficient in the extraction method.

For every sample, the mass of magnetite added was kept constant at 0.5g in a 20ml sample.

 

 

The extraction process can be summarised as follows:

  • 20ml of the desired plastic suspension was prepared as explained on page 11 This was done in a test tube.
  • 0.5g of the magnetite powder was added to the test tube.
  • The desired amount of oil (if any) was added to the tube.
  • The tube was stoppered and inverted 20 times to allow the magnetite and oil to cling on to the plastic.
  • The stopper was removed and the ferro-fluid containing microplastics was removed using Neodymium magnets in a small test tube. Then the magnets were pulled out of the suspension, the ferro-fluid was removed from the tube by removing the magnets from inside the tube allowing the magnetite to fall off into a waste container.
  • The magnets were dipped into the suspension three times.
  • The sample was then ready for analysis.

A video of the extraction process can be seen below:

Testing the concentration of microplastics left behind after extraction

Two main methods were used to test the efficacy of the microplastic extraction process. The two methods used were spectroscopy and microscopy.

Spectroscopy

The first method chosen, was spectroscopy as I had built my own spectrometer. I live in one of the most remote areas of Ireland making it difficult to get tests done at professional labs. That is why I built my own.

After building many prototype spectrometers, I came up with a final spectrometer design which can be seen below.

I used the software spectragryph to analyse the spectra from the webcam. Spectra could be calibrated to wavelengths using a CFL lamp which has very distinct peaks of known wavelength.

I could then analyse samples using the Beer Lambert Law which states that the concentration of a sample is proportional to the absorption of light at a chosen wavelength. For this to work, I scanned in 5 samples of known concentration to make a calibration line.

 

Microscopy

As a secondary method, I used microscopy. I used a digital microscope with a phone screen as a light source. Like this, I could calibrate the image size using the phone pixels as a grid.

I took photographs of the plastic suspensions before and after extraction and then used Adobe Photoshop to analyse exactly how many pixels were covered in plastic and the percentage decrease of plastics, (shown below).

 

Safety

When preparing plastic samples, a dust mask and eye protection were worn due to the presence of plastic dust. In the extraction process, care was taken and eye and mouth protection were worn when handling the iron oxide powder to ensure that none was inhaled due to its very fine nature. Finally, in spectroscopy, the light source could get very hot and because of this, warning stickers were placed around the light box and it was always allowed to cool before use.

 

 

 

 

 

 

 

 

Resultados

10 different types of microplastic suspensions were tested. 3 extractions were carried out for each of the 4 different volumes of oil used in each extraction. To obtain a meaningful result, for each extraction, 50 spectrometer captures were carried out and 3 microscope captures were done. 120 captures in total were taken for every extraction. From these, means and standard deviations were calculated which allowed the further calculation of standard error and a final hypothesis test.

Results were obtained from both spectroscopy and microscopy. From spectroscopy, the % extraction of plastics could be calculated using the Beer-Lambert Law. here, 5 different suspensions of different concentrations were tested and the results were used to make a calibration graph. The absorption was calculated by obtaining the

log (intensity(blank) / intensity (sample))   at a constant wavelength

The results from microscopy were calculated by finding the % of each image covered by plastic (dividing the number of pixels covered by plastic by the total number of pixels and multiplying by a hundred). Then, from this, the % decrease was calculated.

All types of plastics were individually analysed and graphed. This was all used to create a larger composite results table and graph. 

The graph below shows the average extraction rates for all of the plastics tested. An 85% extraction line is shown as this was the hypothesis I set out to investigate.

Another interesting comparison is the volume of oil used in extraction. I hypothesised that there would be an increased extraction rate with the increased volume of oil. A table of results showing the volume of oil used in extraction can be seen below.

The graph can be seen here:

A statistical analysis was carried out to determine if there was a statistically significant difference between the efficiency of different volumes of oil used in extraction. The t-test, I carried out was a two-tailed test comparing the samples where no oil was used and the samples where oil was used. In the t-test, t stat was greater than t critical (2 tail), Hence I could conclude that there was no statistically significant difference between using oil or not using oil The test can be seen below:

Hypothesis test

Finally, to see if my experiments supported my hypothesis, I conducted a hypothesis test at th 95% confidence level. My hypothesis states that the mean % reduction in microplastics using my extraction method is greater than 95%.

The hypothesis test can be seen below:

H0 (Null hypothesis):    The mean reduction of microplastics for all extractions is greater than 85%

n (Number of samples):            600 + 360 (Each sample is the result of 3 extractions and 5 tests for each in spectroscopy and 1 each in microscopy. This was done for 10 plastics and 4 oil concentrations)

 (Mean microplastic reduction for N samples):             87.6%

σ (standard deviation for N samples):                          11.84%

E (margin of error for the population mean at the 95% confidence interval).

From this test, I am 95% confident that the mean reduction of microplastic will lie between 86.6% and 88.7%

As 85% lies at the minimum of this margin, we fail to reject the null hypothesis with 95% confidence.

 

 

 

 

 

 

Conclusión

The following is a list of conclusions I have drawn from my experimental results:

  • The overall results, taking into account results from both spectroscopy and microscopy and taking into account the various volumes of oil added (if any), show that the average quantity of microplastic extracted using these methods is 87.6% ±1.11%. Spectroscopy alone produced a result of 85% ± 0.92% and the overall result for microscopy was 90.5% ±1.38%. From this, I can conclude that my hypothesis is not rejected with 95% confidence. i.e. my extraction method will remove 85% or higher of the microplastics in my samples.
  • For each plastic tested, the quantity of plastic removed was greater than 85% apart from Polypropylene which had an average reduction of 80% ± 3.07% (95% confidence).
  • The method was most effective for the plastic fibres extracted from the washing machine filter with an average reduction of 95% ±2.3% (at 95% Confidence) and HDPE plastic with an average reduction of 91% ±3.1% This shows that this method would be very useful in urban wastewater treatment plants, as over 55% of plastics in wastewater originate from washing machines and clothes 11.
  • On average, the tests with 12.5 ml oil/L water gave higher plastic reduction rates than tests without any oil added (magnetite only). However, the t-test carried out on these results showed no statistically significant difference. From this I can conclude that using magnetite with a minimum of oil forms a viable method for the extraction of microplastics. If this method is to be applied in wastewater treatment, I believe that it is important to minimise the amount of oil and magnetite used to make the extraction more economical while using enough to ensure the maintain high extraction rates to maximise plastic reduction.

There is no doubt that the most effective way to reduce microplastic pollution in oceans is to use less plastics and ensure that plastics used can be recycled and separated to prevent them from entering our wastewater, but the reality is that more and more of the products we use contain plastics and potentially degrade into microplastics before entering our wastewater. It is therefore essential that we find efficient and effective ways of extracting microplastics from wastewaters before they reach our watercourses and ultimately our oceans. Once plastics enter our oceans, they are practically impossible to extract. The results of this project show that this could be a viable method. However questions remain to be answered. This project only forms the very beginning of this extraction idea which has never been conducted before. Further research needs to be carried out to investigate the efficacy of various grades of magnetite, different types of magnetic systems, methods for separating the waste and the design of a system that could be introduced into treatment centres.

Información personal

I have been lucky enough to grow up in West Cork, Ireland. Surrounded by untouched nature as well as the rugged coast of the Atlantic. This has been my primary inspiration about how nature works. I soon discovered that science really was in everything. The fact that I lived in such a remote place meant that I had to build my own equipment and lab to conduct tests and experiments. This lead to many hours tinkering with Lego, tools and plants. I love experimenting and in my spare time, I do Arduino projects, Lego-Mindstorms, gardening, wacky experiments or cool chemistry. I am also involved in our local planetarium (schull Planetarium) I am the head lecturer there and really enjoy passing on STEM kowledge to others.

I really like science Youtube channels such as Nilered, The Backyard scientist, National Geographic and David Attenborough. I'm inspired by scientists such as Ben Ferringa and his work with nanochemistry and engineering. I'm in my last year of secondary school and would like to study chemistry or chemical engineering in Ireland or in Europe. I think that both of these subjects will be suited to me as I really enjoy problem-solving and experiments as well as engineering and tinkering.

One of the most valuable rewards from this science fair for me is the opportunity to present my work to a body of professional interested people. Winning any prize would be a great honour to me as this would be an acknowledgement of my project and ideas. This is especially true as I know that there are many bright young scientists competing with me. Also, winning a prize would give my project more attention and let it grow with mentorship to solve a real problem on the Earth. There is nothing I would like to see more than my project and idea to be used in real life applications and I think a prize could do this.

 

BTYS 2018 Winner: Fionn Ferreira

Salud y seguridad

All experimentation was conducted at home

Plastic production:

  • When sanding plastics, a dust mask, safety glasses and a lab-coat were worn to prevent the possible inhalation of microplastic dust and the entering of the dust into the eyes.
  • The aspirator pump can cause the Buchner flask to implode. This can be a very dangerous experience. To prevent this from becoming a hazard, a metal cage was placed around the suction filtration apparatus and safety glasses were worn.

Extraction

  • Magnetite is a very fine powder and can lead to irritation to eyes and the lungs if the powder is inhaled. To prevent this, safety glasses and a dust mask were worn while handling the powder.
  • Extracted ferro-fluid was stored in a glass container for further experimentation.

Spectroscopy

  • The light source is hot and can damage eyes if looked at directly, to avoid this, the bulb was allowed to cool before changing and the bulb was not looked at when turned on.

My mentor and supervisor who watched over me while I  any hazardous parts of the project was Anke eckardt: ankeckardt@gmail.com, 00353 (0)86 172 5550

Bibliografía, referencias y agradecimientos

References:

  1. Hammer, J. (1975). Water and Waste-Water Technology. New York: John Wiley & Sons
  2. Warner, A. (2015). How to clean up an oil spill –magnetize the oil first. Available: https://www.youtube.com/watch?v=LV9209axVUs. Last accessed 5th June. 2018.

  3. https://spectralworkbench.org/dashboard

  4. Anne Marie Mahon, Rick Officer, Róisín Nash and Ian O’Connor. (2014). Scope, Fate, Risks and Impacts of Microplastic Pollution in Irish Freshwater Systems. EPA Research. 210.

  5. Hemmelstine, A. (2017). Why Oil and Water Don't Mix. Available: https://www.thoughtco.com/why-oil-and-water-dont-mix-609193. Last accessed 31st Dec. 2017.

  6. Irish water. (2016). National Wastewater Sludge Management Plan. Irish water publishing.

  7. Environmental Protection Agency. (2016). Urban Waste Water Treatment in 2015. ISBN: 978-1-84095-684-9.  

  8. Downey, A. (2016). Adverse health effects of plastics on humans and animals. Available: https://ecologycenter.org/factsheets/adverse-health-effects-of-plastics/. Last accessed 10th Dec. 2018

  9. Oxford University press (2008). Dictionary of chemistry. 6th ed. New York: Oxford University Press. 61.

  10. Biotronix GMBH. (2016). Optical densities of suspensions.

  11. Norwegian EPA. (2015). Microplastics. Available: http://www.environment.no/topics/marine-and-coastal-waters/microplastics/. Last accessed 2nd Dec. 2018.

Acknowledgments

  • Larissa Kelly for her expert advice on referencing and statistical analysis
  • Dr Fredrich Menges, Developer of the spectragryph software who gave me a free liscence to use the software
  • Anke Eckardt (Parent), who morally supported me throughout the 1000 tests and made lots of cups of hot chocolate!
  • Dr Ian O Connor, Researcher at GMIT Galway. He gave me valuable feedback after asking him for help with microscopy and general research.
  • Julie Mc Mahon (English teacher) teaching me how to write and express my science through a report.
  • Davoren Leung (Maths Teacher) wo gave me extra time to show how to do a hypothesis test.