A clean green sweep: an aquatic bioremediation project
Submitted by sis on 22 November 2011
Common applications include cleaning up abandoned mining sites or oil spills. Phytoremediation (from the Greek phyto – plant) uses a plant’s natural ability to contain, degrade or remove toxic chemicals and pollutants from soil or sludge, sediment or ground water.
Azolla is one such plant: this genus of floating freshwater ferns accumulates heavy metals such as nickel, cadmium and mercury (Arora et al., 2006); its biomass is easy to harvest and desiccates very fast (Wagner, 1997). These characteristics make it a perfect candidate for bioremediation systems (Cohen, 2004), although it is always important to assess the potential impact of introducing a new species into an ecosystemw1, w2. Azolla lives in symbiosis with the cyanobacteria Anabaena azollae, which can fix atmospheric nitrogen. This independence of a further external source of nitrogen allows the fern to double its biomass every two to three days at room temperature and is the reason that it has been used in China as a biofertiliser in rice paddies for centuries.
In the lesson, introduce the topic of bioremediation and have the students collect information about Azollaw1, w3, w4, w5, w6, w7, w8 (Arora & Saxena, 2005), such as the morphology of water plants as opposed to land plants, the importance of symbiosis, the nitrogen cycle, the use of Azolla in agriculture (Pabby et al., 2004), and Azolla’s ability to absorb heavy metals.
Next, the students should tabulate their experimental results and represent them graphically. They should consider the most appropriate type of graph to use (e.g. line graph or bar chart).
Below is an example of a project suitable for students in Grades 10-12 (aged 16-18). We used Azolla filiculoides, but any of the seven Azolla species will do. They can easily be obtained in plant nurseries or garden centres, aquarium shops or online.
The effect of Azolla on water quality
Do not add or change the water during the experiment.
As a control, you could determine bacterial content by measuring turbidity with a spectrometer or turbidity meter, or by measuring the concentration of colony-forming units using the dilution method, seeding isolation, and counting colonies of bacteria on a rich agar medium. Differing levels of bacteria in the initial water samples may influence the water quality and could falsify results, as bacteria may also take up nutrients and metals.
Safety note: The cyanobacteria in Azolla produce a neurotoxin, so the plants should not be eaten. In addition, some Azolla species are considered a weed and are an invasive species in many countries, so the plants should be disposed of safely after use. See also the general safety note.
Arora A, Saxena S, Kumar Sharma D (2006) Tolerance and phytoaccumulation of chromium by three Azolla species. World Journal of Microbiology and Biotechnology 22(2): 97-100. doi: 10.1007/s11274-005-9000-9
Cohen MF, Yamasaki H, Mazzola M (2004) Bioremediation of soils by plant-microbe systems. International Journal of Green Energy 1(3): 301-312. doi: 10.1081/GE-200033610
Pabby A, Prasana R, Singh PK (2004) Biological significance of Azolla and its utilization in agriculture. Proceedings of the Indian National Science Academy B70(3): 299-333. www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/2000c954-299.pdf or use the direct link: http://tinyurl.com/62wq6mp
Wagner GM (1997) Azolla: A review of its biology and utilization. The Botanical Review 63(1):1-26. doi: 10.1007/BF02857915
w1 – To learn more about Azolla, its distribution, its status as invasive species, its biology and its uses, see the UK’s Natural History Museum website (www.nhm.ac.uk) or use the direct link: http://tinyurl.com/azolla
w3 – The United States Environmental Protection Agency has compiled a wealth of information on remediation technologies in English and Spanish, including citizen’s guides with useful background information. See: www.epa.gov or use the direct link: http://tinyurl.com/5rg3yfk
w4 – For a comprehensive overview on bioremediation, see the website of the Earth Sciences Division of the Lawrence Berkeley National Laboratory (http://esd.lbl.gov/research/projects/ersp/generalinfo/
w5 – To learn more about phytoremediation from the Ecological Engineering Group, see: www.ecological-engineering.com/phytorem.html
w6 – For more information on the biology of Azolla and its use in agriculture, see Wayne’s Word, ‘an online textbook of natural history’: http://waynesword.palomar.edu/plnov98.htm
The World Water Monitoring Day offers a number of resources in English and Spanish on how to monitor a range of water-quality parameters, as well as kits. See: www.worldwatermonitoringday.org
For further resources on testing water quality, see the website of Lifewater Canada: www.lifewater.ca/Section_16.htm
To learn about a school project to test water quality in the local environment, see:
If you enjoyed reading this article, why not browse the full collection of science education projects published in Science in School? See: www.scienceinschool.org/projects
Vered Yephlach-Wiskerman teaches biology at Omer High School in Omer, Israel. She is the Excellence Program Coordinator and a lecturer in biochemistry and immunology at the science department of the Kaye Academic College of Education, a professional training college for teachers in Beersheba.
Keeping the environment clean and pollution free as well as monitoring the environment are now major concerns, and these subjects are studied in school science. Natural ways of cleaning up the environment, such as bioremediation by plants and microbes, are ideal and have been studied for many years. This article shows how a common aquatic plant, Azolla, can be used to demonstrate bioremediation in the classroom. The activities foster scientific thinking skills, an essential part of the ‘how science works’ element of the curriculum. A simplified version of this activity could be used with younger students.
The experiments could be linked to chemistry – in tests for cations and anions and titrations. The activity also has links to microbiology and biotechnology, as the students could learn the basics of how microbiological water quality can be monitored. As an extension activity, students could use the Internet find out how microbes can be used to clean up oil spills and how micro-organisms can be selected or genetically engineered to deal with particular contamination problems.
Shelley Goodman, UK