SILVER

Removal of ferric irons in water through biosorption using Saccharina japonica

Using Saccharina japonica to reduce iron (III) levels in a solution with iron oxide.
Lily Huang Sauhe Kim
Grade 11

Hypothesis

If 10 g of Saccharina japonica is added to 100mL of iron (III) solution with a concentration of 1mg/L, then the ferric ion concentration will decrease due to the effective biosorption of macroalgae.

 

Research

Iron is an essential element for nutrition in pro-and eukaryotic cells. A majority of iron in the body is present as hemoglobin, myoglobin, heme-containing enzymes, or stored as ferritin (Saito, 2014). When the body absorbs an abundance of iron and its iron-binding proteins are oversaturated, the excess iron is stored in major organs such as the liver (E Guarin, 2020). The stored iron may result in damage to healthy cells such as skin and internal organs. 

In nature, iron is rarely found in its elemental form; most commonly in oxide form (Cameron, n.d.). Iron is found in abundance in nature and naturally found in low concentrations in water, usually around 0.5-10 mg/L (Health Canada, 2009). Although drinking water contains less than 0.3 mg/L, numbers may be higher in areas that utilize cast iron or steel pipes (WHO, 2007). Numbers also may be higher in areas that use iron salts as coagulating agents in the water purification process (IWA Publishing, 2010).  

Various species of macroalgae, commonly known as seaweed or kelp, such as Saccharina japonica, are known for their effective biosorption. This allows for heavy metals such as Cadmium, Iron, Mercury, and Arsenic to bind to the cell wall of marine algae and seaweed (Ibrahim, 2011). The efficacy of the biosorption of macroalgae is primarily due to sulphated polysaccharides ─ negatively charged polysaccharides that are present in the cell wall or macroalgae (Ali Redha, 2020).

The complex process of biosorption in Saccharina Japonica goes through several mechanisms: transportation across the cell membrane, physical adsorption, ion exchange, complexation, and precipitation (Ahalya et al., 2003). Physical adsorption is mediated through electrostatic interactions (Van der Waal forces) between the cell microbes and the metallic ions in the solution. Such intermolecular forces entail London dispersion (momentarily induced dipole forces), dipole-dipole forces of polar molecules, ion-dipole force (ion and partial charge of the molecule) and lastly hydrogen bonding forces (Ahalya et al., 2003). Complexation entails the formation of a complex from insoluble ions through the interaction with carboxyl and amino acid groups (both chelation agents) (Schiewer, 1999). 

For the experiment, a rusty nail will be used to introduce iron ions into the water. Rust is a hydrate that is formed through an oxidation reaction. It is a hydrated form of ferric oxide, the approximate compound being Fe2O3•32H2O. The balanced chemical equation is as follows (Vitz et al., 2016):

4Fe (s) + 3O2 (g) + 2xH2O (l)→ 2Fe2O3•xH2O (s)

Although hydrates have low solubility, a small portion dissociates when placed into water into ferric ions and oxygen which would rise to the surface.


The reagent used to spectrophotometrically quantify the presence of iron (III) in water was the Nutrafin iron reagent test. The test utilizes hydroxylamine hydrochloride and 2,4,6-tripyridyl-s triazine (TPTZ) both in concentrations less than 1% in the reagent. In the presence of hydroxylamine, iron is reduced. TPTZ reacts with the iron to form a violet-coloured complex. Spectrophotometrically, the absorbance of the complex is measured at approximately 593 nm(Corn Syrup Analysis E-33- 1 Analytical Methods of the Member Companies of the Corn Refiners Association, Inc, n.d.).

 

Variables

The manipulated variable in the experiment is the time in minutes after 10.0 g of Saccharina japonica is added to 100 mL of a 1.0mg/L iron (III) concentration solution. The time intervals are 0 min (control), 10 min, 20 min, 30 min, 40 min, 50 min and 60 min. The responding variable is the concentration of iron (III) ions in water. The controlled variables include the concentration of the iron (III) solution (1.0 mg/L), the amount of ground Saccharina japonica added to the solution (10 g), but is not limited to environmental conditions such as temperature and humidity as well as the type of glassware and apparatus used.

 

Procedure

Materials and Apparatus

  • 7 plastic test tubes
  • Tape and sharpie (for labelling test tubes)
  • Nutrafin Iron Testing Kit
  • 2 rusty nails
  • 100 mL beaker
  • Bowl
  • 12 g of Dried Saccharina japonica 
  • Distilled water bottle
  • Scale
  • Mortar and pestle
  • Safety goggles
  • Glass stirring rods
  • 10 mL graduated cylinder
  • 100 mL graduated cylinder
  • 250 mL beaker
  • stopwatch

Procedure

  1. Place two rusty iron nails in 650.0 mL of distilled water for 48 hours.
  2. Prepare 7 test tubes and label one as "control." Label the rest of the test tubes with 10 min, 20 min, 30 min, 40 min, 50 min and 60 min.
  3. Put 4.50 mL of the solution inside the test tube labelled "control" using a 10 mL graduated cylinder.
  4. Put two drops of reagent #1 into the test tube. If the concentration is determined to be 1.0 mg/L, proceed to step 4. If the concentration is determined to be lower, let the rusty nails sit in the solution overnight. If the concentration is too high, dilute it with 5.0 -10.0 mL of distilled water accordingly. 
  5. Remove the rusty nails from the solution.
  6. Measure 51.0 g of Saccharina japonica on a scale.
  7. Ground the Saccharina japonica using a mortar and pestle.
  8. Measure out 100.0 mL of solution using a 100mL graduated cylinder and pour it into a 250mL beaker.
  9. Put 10.0 g of ground Saccarina japonica into the beaker with the solution and immediately start the stopwatch.
  10. Stir the solution every 2 minutes.
  11. After 10 minutes, measure out 4.5 mL of the solution using a 10 mL graduated cylinder and pour in the test tube labelled “10 min.” Do not get Saccharina japonica in the test tube.
  12. Repeat steps 9 to 11 for each 10-minute interval for test tubes labelled “20 min,” “30 min,” “40 min,” “50 min,” and “60 min.”
  13. Add two drops of reagent #1 from the Nutrafin Iron Testing Kit in each test tube and stir with a glass stirring rod.
  14.  After 30 minutes, compare the test tubes to the colour indicator chart and log on Table 1 and 2.
  15. Dispose of the contents inside the test tubes appropriately and rinse with distilled water.
  16.  Repeat steps 8-15 for four more trials.

Observations

Table 1: Observations of 30 minutes after adding reagent #1 to test tubes for 5 trials.

Test Tube label

Observations

Trial 1

Trial 2

Trial 3

Trial 4

Trial 5

Control

Translucent, deep violet

Translucent, deep violet

Translucent, deep violet

Translucent, deep violet

Translucent, deep violet

10 min

Translucent, medium violet

Translucent, medium violet

Translucent, medium violet

Translucent, medium violet

Translucent, medium violet

20 min

Translucent, medium violet

Translucent, medium violet

Translucent, medium violet

Translucent, medium-light violet

Translucent, medium violet

30 min

Translucent, medium-light violet

Translucent, medium violet

Translucent, medium violet

Translucent, medium-light violet

Translucent, medium-light violet

40 min

Translucent, medium-light violet

Translucent, medium-light violet

Translucent, medium-light violet

Translucent, light violet

Translucent, medium-light violet

50 min

Translucent, light violet

Translucent, light violet

Translucent, light violet

Translucent, light violet

Translucent, light violet

60 min

Translucent, colorless

Translucent, colorless

Translucent, colorless

Translucent, colorless

Translucent, colorless

 

Table 2: Concentration of iron (III) in water (mg/L) after 10g (±0.5 g) of Saccharina japonica is added into iron solution, measured in 10 minute intervals over the course of 60 mins. 

 

Concentration of iron(III) (± 0.15 mg/L)

Time after 10 g (±0.5 g) Saccharina japonica is added to 100 mL (±0.2 mL) of iron solution (± 1 min)

Trial 1

Trial 2

Trial 3

Trial 4

Trial 5

0

1.0

1.0

1.0

1.0

1.0

10

0.50

0.50

0.50

0.50

0.50

20

0.50

0.50

0.25

0.25

0.50

30

0.25

0.50

0.10

0.25

0.25

40

0.25

0.25

0.10

0.10

0.25

50

0.10

0.10

0.00

0.10

0.10

60

0.00

0.00

0.00

0.00

0.00

Analysis

Table 3: Averages of 5 trials of concentration of iron (III) in water (mg/L) after 10g of Saccharina japonica is added to iron solution, measured in 10 minute intervals over the course of 60 mins. 

Time after 10g (±0.5 g) Saccarina japonica is added to 100 mL (±0.2mL) of iron solution (±1 min)

Average concentration of iron (III) (± 0.15 mg/L)

0

1.0

10

0.50

20

0.40

30

0.27

40

0.19

50

0.08

60

0.00

 

Graph 1: Averages of 5 trials of concentration of iron (III) in water (mg/L) after 10g of Saccharina japonica is added to iron solution, measured in 10 minute intervals over the course of 60 mins. Error bars represent uncertainties.

Note: Pearson's R2 value is shown beside the linear regression line. The value was calculated through Excel.

Table 4: Two-tailed Pearson correlation test for the correlation between Saccharina japonica and the removal of iron (III) from the water it is in. Pearson coefficient (r) was calculated in Excel using PEARSON function.

Correlation between Saccharina japonica and the removal of iron (III) from water

Degrees of freedom

Significance

Pearson coefficient (r)

Critical value

 H0: There is no correlation between Saccharina japonica and the removal of iron (III) from water.

7

0.05

-0.93

0.754

|-0.93|>0.754, H0 is rejected. There is a statistically significant correlation

 

Equation 1: Conversion formula of Pearson coefficient (r) value to t value in order to find the p value

t = (r(n-2)½)(1-r2)-½ 

Table 5: t value and resulting p value found of the correlation between Saccharina japonica and the removal of iron (III) from water. The r value was converted to a t value using Equation 1. The p value was found using the t value and the T.DIST.2T function in Excel.

t

p

-5.7

0.0019

Conclusion

Ultimately, the results of the statistical analysis for this investigation support the hypothesis that Saccharina japonica will decrease the concentration of ferric ions in the solution. Therefore, the null hypothesis can be rejected as the statistical analysis supports that there is a significant correlation between time after Saccharina japonica is added and ferric ion concentration.


The preliminary test with the graph and the coefficient of determination (R2) showed that 87% of the y values could be explained by their corresponding x values; percentage variation of y by x. In the Pearson coefficient test, the absolute value of the r value was greater than the critical value; therefore, the null hypothesis was rejected signifying a statistically significant correlation. The p value signifies the probability that the correlation is found in a world where the null hypothesis is true. Since the probability is 0.0019 or 0.019%, the correlation found in this experiment is highly significant.

 

Application

Extensions

 

As Saccharina japonica has a large biosorption capacity, it could be utilized to filter toxic heavy metals such as mercury and arsenic from water as well. Many water sources in developing countries are contaminated, which increases health risks. Often, water filters are expensive and not accessible for these countries, however, seaweed is abundant and cheap to harvest. Inexpensive filters using seaweed could be produced to prevent deaths and illnesses due to poisoning. 

 

The experiment could be carried out using other toxic heavy metals and different types of macroalgae to explore which species is most effective in the biosorption of metals. This could then be used to develop and design accessible and economical filters.

Sources Of Error

A systematic source of error for this experiment was that the Nutrafin iron indicator test was colorimetric. Since a colorimeter was not utilized, the data was collected by closely comparing the colour of the solution with the colour indicator chart. Due to this, the accuracy of the data collected was limited. This led to greater uncertainty in the concentration of ferric ions which created greater room for error. This error could be mitigated by using a colorimeter or by using a spectrophotometer to obtain more accurate readings of the concentration.

 

Another systematic source of error was that the iron concentration test could only test the presence of up to 1.0mg/L of ferric ions in the solution. This could have led to the concentration of the control being higher than 1.0 mg/L. This would cause the correlation of the data to be weaker than it actually had been, as it would show a less steep slope between the first point (control) and second point (10 min). This error could be fixed by using a lower concentration than 1.0 mg/L for the control. Additionally, a different iron indicator test could be utilized to ensure that the control value does not exceed 1.0 mg/L. A spectrophotometer could also be utilized to accurately measure the concentration of the solution.

 

Additional Improvements

A limitation to the statistical analysis is the line of best fit. The correlation followed a general downward trend but from the control value to the 10-minute value, there was a drastic exponential decrease in the values. The rest of the values fit such an exponential trend. The use of linear regression, R2 value, and the Pearson correlation test decrease the accuracy of the correlation. A possible improvement to the error could be using an exponential curve of best fit and utilizing parametric nonlinear correlation analysis instead. 

 

Citations

Health Canada. (2009). Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Iron - Canada.ca. Canada.ca. https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-guideline-technical-document-iron.html

IWA Publishing. (2010). Coagulation and Flocculation in Water and Wastewater Treatment | IWA Publishing. Iwapublishing.com. https://www.iwapublishing.com/news/coagulation-and-flocculation-water-and-wastewater-treatment

WHO. (2007). Iron in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality. https://www.who.int/water_sanitation_health/dwq/chemicals/iron.pdf

Böttger, L. H., Miller, E. P., Andresen, C., Matzanke, B. F., Küpper, F. C., & Carrano, C. J. (2012). Atypical iron storage in marine brown algae: a multidisciplinary study of iron transport and storage in Ectocarpus siliculosus. Journal of Experimental Botany, 63(16), 5763–5772. https://doi.org/10.1093/jxb/ers225

E Guarin, G. (2020, September 20). What is the pathophysiology of transfusion-induced iron overload? Www.medscape.com. https://www.medscape.com/answers/1389732-177323/what-is-the-pathophysiology-of-transfusion-induced-iron-overload

Saito, H. (2014). METABOLISM OF IRON STORES. Nagoya Journal of Medical Science, 76(3-4), 235–254. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4345694/

Cameron, D. (n.d.). Iron - Chemistry Encyclopedia - elements, metal, mass. Www.chemistryexplained.com. Retrieved March 13, 2021, from http://www.chemistryexplained.com/Hy-Kr/Iron.html#:~:text=Iron%20has%20seven%20oxidation%20states

Ibrahim, W. M. (2011). Biosorption of heavy metal ions from aqueous solution by red macroalgae. Journal of Hazardous Materials, 192(3), 1827–1835. https://doi.org/10.1016/j.jhazmat.2011.07.019

Ali Redha, A. (2020). Removal of heavy metals from aqueous media by biosorption. Arab Journal of Basic and Applied Sciences, 27(1), 183–193. https://doi.org/10.1080/25765299.2020.1756177

Ahalya, N., Ramachandra, T. V., & Kanamadi, R. D. (2003, December). Biosorption of Heavy Metals. https://www.researchgate.net/publication/257029311_Biosorption_of_Heavy_Metals

Schiewer, S. (1999). Modelling complexation and electrostatic attraction in heavy metal biosorption by Sargassum biomass. Sixteenth International Seaweed Symposium, 593–601. https://doi.org/10.1007/978-94-011-4449-0_73

Corn Syrup Analysis E-33- 1 Analytical Methods of the Member Companies of the Corn Refiners Association, Inc. (n.d.). Retrieved March 13, 2021, from https://corn.org/wp-content/uploads/2009/12/E-33.pdf

Acknowledgement

We would like to thank Ms. Jensen, the CYSF coordinator for Western Canada High School for answering all the questions we have had in doing this project.