Petal to the Metal - Using Chlorella Algae To Remove Heavy Metals From Mining Runoff

Right now, all over Canada, heavy metals are entering our waterways as harmful bi-products of mining that are highly toxic to animals, plants, soil, water quality, and us humans. It is crucial that we find a solution.

Currently, mines treat their runoff in different ways usually by collecting the water, using chemicals to separate the heavy metals, and storing the remaining sludge in large tailings ponds. Tailings ponds are not a good long term solution, because they are essentially meant to hold the metals forever. They often leak, overflow or are even drained illegally, so it is important to find an alternative solution to current systems, one that might allow the metals to be reused or recycled. Since they are a nonrenewable resource, even these small stores can be valuable.

My solution to this issue involves using chlorella, a nutrient rich algae species to remove heavy metals from water using the process of biosorption. The process of biosorption is the attraction of positively charged molecules to the negatively charged cell wall of a biotic material, such as algae. Heavy metals are positively charged, so for my experiment, I explored the possible uses of chlorella to treat mining runoff before it reaches our waterways. Chlorella is affordable, stable, as it still possesses the properties after it’s dead, and therefore would make it a suitable alternative/addition to current practices.

For my experiments, I used chlorella powder and zinc sulfate powder as the tested heavy metal. All samples were mixed using a magnetic stirrer for 30 minute periods, and filtered using a 1 micron filter.

Experiment 1:

To measure how contaminated water would be affected by chlorella, a fish tank pump system was used.

Procedure:

30L of water and 3.36g of zinc sulfate (40ppm) added to the tank

Tank water was mixed by hand for 1 minute

Water pump turned on to circulate water for 12 hours without filter

20g of chlorella added to filter bag, and placed in filter slot

Water circulates for 5 days through pump and chlorella filter, tested each day at 8pm

Experiment 2:

To see the effects of chlorella on a more controlled scale, a 300ml beaker to test a smaller amount of contaminated water.

Procedure:

300ml of water and 12 mg of zinc (40ppm) added to beaker

Mixed

5 g chlorella add to water

Mixed

Left 48 hours

Sample is filtered

Zinc level tested

Experiment 3:

To investigate the effects of varying amounts of chlorella, three 80ml beakers were filled with contaminated water and varying amounts of chlorella.

Procedure:

Zinc solution from experiment 2 added to 3 80ml beakers

Different amounts of chlorella added to each (1.3g, 0.8g, 0.26g)

Mixed

Left 48 hours

Filtered

Zinc levels tested and compared

Experiment 4:

To see how metals could be recaptured and reused in the real world, citric acid was used to remove adsorbed zinc molecules from used chlorella filters.

Procedure:

2g zinc and 300 ml water added to beaker

Stirred

10g chlorella added to solution

Stirred

Left 48 hours

Filtered to remove chlorella

100ml citric acid solution passed through filter holding chlorella

10g sodium bicarbonate added to acidic water to precipitate zinc

Experiment 1 Results

At the start of the experiment, the zinc level in the fish tank was 40ppm. Over the first 3 days, the zinc levels stayed the same, but on day 4 and 5, it decreased significantly. The zinc levels were likely decreasing the whole time, but the test strips used work in ranges, so they likely did not pick up on the changes until day 4.

Starting zinc level: 40ppm

Day 1: 20-40 ppm

Day 2: 20-40 ppm

Day 3: 20-40 ppm

Day 4: 10-20 ppm

Day 5: 5-10 ppm

The experiment supported the hypothesis. Chlorella successfully removed 30 - 35ppm (75% - 87.5%) of zinc over 5 days from the fish tank, demonstrating that chlorella is able to remove heavy metals from water.

Experiment 2 Results

At the start of the experiment, the zinc level in the beaker was 40ppm. After 2 days, the zinc level decreased to between 5 - 10ppm, showing a significant decrease in zinc.

Starting zinc level: 40ppm

Day 2: 5-10ppm

The experiment supported the hypothesis. Chlorella successfully removed 30 - 35ppm (75% - 87.5%) of zinc over 2 days, demonstrating that chlorella is able to remove heavy metals from water.

Experiment 3 Results

At the start of the experiment, the zinc level was 40ppm in each of the smaller beakers. The experiment was run 3 times to ensure consistency and accurate results. The results of all three trials stayed consistent for all 3 samples.

Starting zinc level: 40ppm

Ending zinc levels, sample 1 (1.3g chlorella)

0 - 2ppm

Ending zinc levels, sample 2 (0.8g chlorella)

0 - 2ppm

Ending zinc levels, sample 3 (0.26g chlorella)

2 - 5ppm

The experiment supported the hypothesis. Chlorella successfully removed 38 - 40ppm (95% - 100%) of zinc from the water of samples 1 and 2. In sample 3, it only removed 35 - 38ppm (92% - 95%) of zinc, which was expected since it had considerably less chlorella in it. This experiment also indicates there is no exterior force affecting the zinc levels, because as the amount of chlorella in the water decreased, so did the amount of zinc that was removed from the water.

Experiment 4 Results

The purpose of experiment 4 was not to get measurable data, but to demonstrate that it is possible to recover the already adsorbed zinc from the chlorella and recapture it in a solid form. Experiment 4 supported the hypothesis, as a significant amount of zinc from the chlorella was able to be recovered after rinsing it with the acid solution and precipitating it out using sodium bicarbonate. Due to the nature of the experiment, the results could not be measured quantitatively, but the experiment did demonstrate the ability of chlorella to function in real-world applications.

NOTE: In the graphs above, the median from each of the ranges is used in the graph. The graphs show comparative data, but are not completely accurate.

All three experiments supported the hypothesis: that chlorella is capable of removing zinc from water through the process of biosorption.

To replace current heavy metal recovery strategies, we can use chlorella by pushing the contaminated water through chlorella filters. The used filters could be washed using acids, releasing the contaminated heavy metals and making them accessible to use in the future. The chlorella filters can also be reused after being stripped of the metals, or composted.

It could also be an addition to current strategies, like reverse osmosis. After the clean and contaminated water is separated, the smaller concentration of contaminated water could be further cleaned using chlorella and released.

The properties of chlorella could even be used in tailings ponds where acid mine drainage has the potential to leak, so any escaping water will be filtered first, reducing the amount of contamination in our environment.

Northern mines are often near, or on Indigenous land that is used for traditional hunting, gathering, and growing. Indigenous communities can be concerned of the safety of the mining discharge and practices, and how they can affect their traditional way of life. Using an additional natural filter could give more assurance that no further harm will come to their land, crops like wild rice, or drinking water.

Overall, this idea could be highly versatile, and since chlorella is inexpensive and accessible, it could be used to make conditions safer for the environment, as well as the communities situated near tailing ponds or mining operations.

This project has taken me into a new field of study related to mining and conservation. This area of study has proven to be exceptionally intriguing, and I am interested in expanding my knowledge around these subjects. If I were to continue this project, I would like the opportunity to experiment with different heavy metals, or actual acid mine drainage, in a laboratory setting where it is safe to work with them.

Exploring more into the real-world applications of chlorella could be beneficial to our environment, enhancing current acid mine drainage treatment strategies and evolving Canadian mining practices.

Thank you so much to everyone who helped me with this project! My family and friends have been so supportive, and I was also lucky enough to meet some experts who were a great source of information and resources.

Thank you to:

Cara Rockwood, Leah Zapotocky, and Krystel Beatty - Scientists in the mining industry. We discussed the current treatment systems used in mining and how the environment is considered when discharging runoff.

Mackenzie Denyes - As a former Manager of Environment and Regulatory Affairs in the mining industry, we discussed the impacts of mining runoff on local communities, and the regulations in place to keep mines responsible for their water.

My parents and grandparents - assisted with transport to collect materials and were so supportive of my endeavors as a young scientist.

Images:

Getty. (Unknown) [Chlorella under a microscope] [Photograph] Jstor Daily https://daily.jstor.org/algae-the-food-of-the-future-of-the-past/

Plourde, R. (2022) [Tourqouy open pit gold mine tailings management facility] [Photograph] Halifax Examiner https://www.halifaxexaminer.ca/economy/natural-resources/mining/st-barbara-is-shedding-its-nova-scotia-gold-mine-leaving-a-litany-of-environmental-concerns/

Unknown. (Unknown) [Acid mine drainage] [Photograph] Extension https://extension.wvu.edu/natural-resources/acid-mine-drainage

Orndorf, J. (Unknown) [Acid mine drainage] [Photograph] Inland West https://inlandwest.tumblr.com/

Unknown. (Unknown) [Heavy metal examples] Efilters.ca https://www.efilters.ca/blogs/articles/how-heavy-metals-get-in-your-drinking-water?srsltid=AfmBOopfaQr7QqYbH104Wh9XknHZn1-pdT9rjw411X297pDRJ26mxwuM

Unknown. (Unknown) [Chlorella powder] Food to Live https://foodtolive.com/shop/chlorella-powder

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Videos:

SydneyWaterTV (Oct. 28, 2013) [How Does Reverse Osmosis Work?] Retrieved from https://www.youtube.com/watch?v=aVdWqbpbv_Y