THE BIOREMEDIATION POTENTIAL OF IRON-BASED INORGANIC COAGULANTS FOR THE CONTROL OF CYANOBACTERIAL GROWTH
DOI:
https://doi.org/10.31861/biosystems2025.02.252Keywords:
cyanobacteria, Nostoc commune, coagulants, FeSO₄, Fe-EDTA, flocculation, toxicity, environmental safetyAbstract
Cyanobacteria are among the oldest photosynthetic organisms on Earth and play a key role in aquatic ecosystems as primary producers of organic matter. However, under favorable environmental conditions, they can proliferate excessively, leading to harmful algal blooms (HABs), which deteriorate water quality, reduce dissolved oxygen levels, and pose threats to aquatic organisms and human health. In addition, cyanobacteria produce a wide range of secondary metabolites, including cyanotoxins that belong to various groups, such as neurotoxins, hepatotoxins, dermatotoxins, and cytotoxins. The most widespread cyanotoxins include microcystins, anatoxins, and cylindrospermopsins, which can damage the liver and nervous system and may even contribute to the development of oncological diseases. Consequently, cyanobacterial blooms represent a particularly serious problem for drinking water sources.
To mitigate this phenomenon, physical, biological, and chemical control methods are employed. Among chemical approaches, coagulation is an effective method for the removal of cyanobacterial cells and the reduction of intracellular toxin concentrations. Iron-based coagulants, such as iron sulfate (FeSO₄) and the chelated form Fe-EDTA, interact with cyanobacterial cells, promoting their aggregation and floc formation. The efficiency of the coagulation process depends on several factors, including pH, coagulant concentration, cyanobacterial species, and the chemical composition of the water.
The aim of this study was to evaluate the effects of FeSO₄ and Fe-EDTA on cultures of Nostoc commune. The culture was grown in Fitzgerald medium to a concentration of 5.4 × 10⁶ cells/mL, after which the addition of the coagulants was followed by an assessment of changes in culture density, pH, cell morphology, and the ratio of live to dead cells. The results demonstrated that Fe-EDTA promoted the effective formation of stable flocs and a substantial reduction in cell abundance without significant cell mortality, whereas FeSO₄ exhibited pronounced toxicity (51.9% dead cells) and resulted in unstable floc formation. Even at the highest concentrations tested, the application of Fe-EDTA caused the death of less than 19% of cells, indicating its greater ecological safety.
Thus, the chelated iron form Fe-EDTA is a promising coagulant for controlling cyanobacterial abundance, as it combines high cell removal efficiency with a minimal risk of cyanotoxin release into the water. This approach supports the maintenance of ecological balance in aquatic ecosystems and ensures safer application in water treatment processes.
References
1. Addison, E. L., Gerlach, K. T., Spellman, C. D., Santilli, G., Fairbrother, A. R., Shepard, Z., Goodwill, J. E. (2021). Physicochemical implications of cyanobacteria oxidation with Fe(VI). Chemosphere, 266, 128956.
https://doi.org/10.1016/j.chemosphere.2020.128956
2. Ahmad, A. L., Yasin, N. M., Derek, C. J. C., & Lim, J. K. (2011). Optimization of microalgae coagulation process using chitosan. Chemical Engineering Journal, 173(3), 879-882. https://doi.org/10.1016/j.cej.2011.07.070
3. Andrews, S. C., Robinson, A. K., & Rodríguez-Quiñones, F. (2003). Bacterial iron homeostasis. FEMS Microbiology Reviews, 27(2-3), 215– 237
4. Bláha, L., Babica, P., & Maršálek, B. (2009). Toxins produced in cyanobacterial water blooms - toxicity and risks. Interdisciplinary toxicology, 2(2), 36–41. https://doi.org/10.2478/v10102-009-0006-2
5. Boopathi, T., & Ki, J. S. (2014). mpact of environmental factors on the regulation of cyanotoxin production. Toxins, 6(7), 1951–1978. https://doi.org/10.3390/toxins6071951
6. El Bouaidi, W., Libralato, G., Douma, M., Ounas, A., Yaacoubi, A., Lofrano, G., Albarano, L., Guida, M., & Loudiki, M. (2022). A review of plantbased coagulants for turbidity and cyanobacteria blooms removal. Environmental science and pollution research international, 29(28), 42601–42615. https://doi.org/10.1007/s11356-022-20036-0
7. Erratt, K. J., Creed, I. F., & Trick, C. G. (2022). Harmonizing science and management options to reduce risks of cyanobacteria. Harmful algae, 116, 102264. https://doi.org/10.1016/j.hal.2022.102264
8. Gu, P., Li, Q., Zhang, W., Zheng, Z., & Luo, X. (2019). Effects of different metal ions (Ca, Cu, Pb, Cd) on formation of cyanobacterial blooms. Ecotoxicology and Environmental Safety, 109976. https://doi.org/10.1016/j.ecoenv.2019.109976
9. Ho, L., Sawade, E., & Newcombe, G. (2012). Biological treatment options for cyanobacteria metabolite removal – A review. Water Research, 46(5), 1536–1548. https://doi.org/10.1016/j.watres.2011.11.018
10. Huertas, M. J., & Mallén-Ponce, M. J. (2022). Dark side of cyanobacteria: searching for strategies to control blooms. Microbial biotechnology, 15(5), 1321–1323. https://doi.org/10.1111/1751-7915.13982
11. Rodgers K.J., Main B.J., Samardzic K. (2018). Cyanobacterial Neurotoxins: Their Occurrence and Mechanisms of Toxicity. Neurotox Res, 33(1):168-177. https://doi.org/10.1007/s12640-017-9757-2
12. Shortle, J. S., Mihelcic, J. R., Zhang, Q., & Arabi, M. (2020). Nutrient control in water bodies: A systems approach. Journal of environmental quality, 49(3), 517–533. https://doi.org/10.1002/jeq2.20022
13. Yang, X., Wang, S., Pi, K., Ge, H., Zhang, S., & Gerson, A. R. (2024). Coagulation as an effective method for cyanobacterial bloom control: A review. Water environment research: a research publication of the Water Environment Federation, 96(3), e11002. https://doi.org/10.1002/wer.11002
14. Zhang, T., He, J., & Luo, X. (2017). Effect of Fe and EDTA on Freshwater Cyanobacteria Bloom Formation. Water, 9(5), 326. https://doi.org/10.3390/w9050326
