Phytoremediation of eutrophic waters

Abstract

Eutrophication is one of the major threats to aquatic ecosystems. The European Union (EU) Water Framework Directive (WFD) has given directions to prevent deterioration, to protect aquatic ecosystems, and to promote the sustainable use of water. Hypoxia is one of the common effects of eutrophication in aquatic ecosystems and is becoming an increasingly prevalent problem worldwide. Changes in climate, particularly pH, temperature, and light affect the sustainability of phytoremediation systems. Free-floating aquatic macrophytes are highly capable for morphological and physiological adaptations to aquatic environment and have very high potential to take up and accumulate nutrients through their roots, stems, and leaves, and can remove different ionic forms of nutrients specially Nitrates (N) and Phosphates (P) from aquatic ecosystems. In this experiment some free-floating aquatic macrophytes viz. Eichhornia, Lemna, Salvinia, Spirodela, Wolffia were applied for the treatment of eutrophic waters. The mono, bi, tri, tetra, and penta-cultures of selected plant species were grown in artificial nutrient media for 21 days in a controlled environment to develop sustainable nutrient phytoremediation systems. In monoculture species system the nutrient removal potential of Eichhornia was found maximum removing 63 % N and 55 % P from eutrophic water. In di-culture species systems higher nutrient removal potential was shown by Eichhornia + Salvinia which can remove up to 75 % N and 62 % P. Highest nutrient removal potential was observed in tri-culture systems of Eichhornia + Lemna + Spirodela which removes 92 % N and 78 % P from nutrient media. In tetra-culture systems the nutrient removal potential was 88 % for N and 75 % for P of Salvinia + Eichhornia + Lemna + Spirodela. The penta-culture (Eichhornia + Lemna + Spirodela + Wolffia + Salvinia) system efficiently removes up to 85 % Nitrates (N) and 81 % of Phosphates (P) from the eutrophic water. The study indicates that under controlled conditions multi-species phytoremediation systems are more efficient in removing the nutrients from eutrophic waters than the mono-species phytoremediation systems. However, in all types of phytoremediation systems tri-culture phytoremediation system (Eichhornia + Lemna + Spirodela) showed highest efficiency and may be used for lowering high nutrient levels in eutrophic water.