• European Green Cities/Site Development

Summary: Eco-restoration of polluted aquatic ecosystem through rhizofiltration

Author: Jaya Tiwari, Ankit, Sweta, Sanjeev Kumar, John Korstad and Kuldeep.

Resource: Phytomanagment of Polluted Sites

DOI: https://doi.org/10.1016/B978-0-12-813912-7.00005-3

Aquatic ecosystems is alway regarded as the ultimate sinks for the contaminants. Pesticides and fertilisers, as well as sewage from residential and industrial areas are flushed into natural reservoir and contaminate aquatic system. Besides, the discharge of fossil fuels and chemicals, industrial effluent, mining and miners lead to irreversible damage to aquatic ecosystems.

Sustainable and cost-effective techniques are thus required for their effective removal. Phytoremediation is considered as one of the greenest and safest technologies for the restoration of contaminated aquatic ecosystems. Rhizofiltration is an effective method of phytoremediation. Rhizofiltration refers to the method of the root system of aquatic plant specie adsorb, decompose pollutants in contaminated aquatic system, which improve the water quality.

Process of rhizofiltration.

Various studies have suggested certain desirable attributes in rhizofiltration. plants, including high-level tolerance to metals, the potential to absorb and sequester metals, rapid growth, a well-developed root system, high biomass production, translocation of metal from roots to shoots should be limited.

The rhizofiltration of contaminant polluted aquatic ecosystems is considered as an environmentally sustainable technique. The success of rhizofiltration depends on several factors, but the efficacy of plants to absorb contaminants in the roots and then biotranslocate them into their shoots are two pivotal criteria for the selection of a particular phytoremediator plant.

Different species have different capacity in case of different contamination. A detailed list can be found on the book <Phytomanagement of polluted sites>. There are several mechanisms that function to clean up aquatic system, for example, secretion of rooter exudates, detoxification mechanism (majorly for heavy metals), compartmentation, production of antioxidant compounds, production of phytochelatins and metallothioneins.

Several researchers have reported that aquatic macrophytes serve as biological filters by storing metals and other contaminants in their tissues. Macrophytes reclaim aquatic eco- systems by regulating the following processes.

1. Oxygen Production The release of oxygen by the roots of macrophytes (root oxygenation) is regulated by photosuntghetic activity takes place during day time. Oxygenation by roots significantly affects; the redox potential, which is crucial for the fate of nitrogen; the oxidation of some toxic chemicals, and enhancement of microbial activity, which improves the degradation of contaminants; as well as enhances the process of nitrification (i.e. oxidation of ammonia); and supports heavy metal immobilization.

2. Nutrient Cycling Contaminants or excess nutrients present in the growing media are taken up by the roots of aquatic macrophytes through adsorption, precipitation onto roots, or absorption into roots (rhizofiltration). These nutrients are incorporated into the tissues of the plants in various organic forms to perform various functions. Upon death and decay of these plants, the organic compounds are return into the growing media by the microbes present in the root zone. The contaminants, especially organics are degraded into elemental (inorganic) forms (mineralization). These nutrients are again available for plant uptake. Therefore in this way the rhizofiltration and rhizodegradation processes together form the internal nutrient cycle within the aquatic ecosystem.

3. Sediment Stabilization

Another intrinsic property of macrophytes used for rhizofiltration is the ability to reduce wind velocity with their above water growth. The upper parts increase surface roughness and slow down the velocity of wind, thus controlling erosion and stabilizing the sediment bed.

4. Providing Shelter for Aquatic Life

Organic carbon present in natural by- products released by plant roots (exudates) includes sugars, alcohols, and acids, and, those present in the dead tissue of plants, furnish nutrients and energy for microorganisms and established a rich, microbially diverse in the rhizosphere, which ultimately helps remove contaminants from water bodies and improve conditions for other aquatic life

Rhizofiltration is a promising technology for cleaning polluted aquatic ecosystems. Apart from being cost effective, it is an environmentally friendly remediation alternative. Several studies have revealed that numerous macrophytes have excellent ability to remove contaminants from aquatic ecosystems. These plants may be used for the removal of both inorganic (heavy metals, ions, excess nutrients, etc.) and organic contaminants (dyes, pesticides, solvents, etc.) from surface as well as groundwater. E. crassipes (water hyacinth), P. stratiotes (water lettuce), L. minor (duck- weed), T. natans (water chestnut), and Azolla pinnata (water velvet) are naturally grown com- mon macrophytes in aquatic ecosystems, that efficiently accumulate contaminates and transfer them to their aerial parts. Further research is needed to establish more suitable and optimum conditions that further enhance the process of rhizofiltration. Research is also needed to develop a system of proper disposal or practical use of harvested plants after removal. #phytoremediation #phytomanagement #environmentalrestoration #environmentalcleanup #greentechnology

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