Review Article (Open access)

Int. J. Life. Sci. Scienti. Res., 4(1): 1527-1530, January 2018

 

Efficacy of Aquatic Plants for Removal of Heavy Metals from Wastewater

 

Vineet Soni*, Preetpal Kaur

Plant Bioenergetics and Biotechnology Laboratory, Department of Botany,  Mohanlal Sukhadia University, Udaipur, India

 

*Address for Correspondence: Dr. Vineet Soni, Asst. Professor, Department of Botany, Mohanlal Sukhadia University, Udaipur, India

 

ABSTRACT- Wastewater treatment is a problem of grave concern in most developing countries. In the last two decades, there has been a lot of research to develop appropriate technologies to alleviate pollution in water resources. Efficient wastewater treatments through conventional methods are expensive and difficult to get optimum results. Currently, phytoremediation is an effective and affordable solution used to remediate toxic pollutants from aquatic ecosystems. The review describes various aquatic plants, which have high potential to remove heavy metals from wastewater.

Key-words- Water pollution, Heavy metals, Phytoremediation, Aquatic plants, Wastewater treatment

INTRODUCTION- Water pollution by heavy metal ions is one of the worldwide environmental problems [1]. Heavy metal pollution due to increased industrialization and urbanization is a global problem. Toxic heavy metals such as cadmium, copper, lead, chromium, zinc, and nickel are important environmental pollutants, particularly in areas with high anthropogenic pressure. They can’t be biodegraded so released into the environment and contribute to lots of toxic effects even in relatively lower concentrations on living organisms in food chain [2-6] by bioaccumulation and bio-magnification [7].

Several methods already used to clean up the environment from these heavy metals including chemical precipitation, oxidation or reduction, filtration, ion exchange, reverse osmosis, membrane technology, evaporation and electrochemical treatment (but most of them are expensive, time consuming and environmentally destructive [8]. Therefore, it is essential for a remediation technology to be effective, economic/affordable, and consistent; moreover, it should effectively reduce HM concentrations to environmentally acceptable levels, and be applicable to field conditions such as effluents and aquatic bodies. Currently, phytoremediation of metals is an effective and affordable “green” technology based on the use of specially selected metal accumulating plants to remove toxic metals from soils and water.

This environment friendly technology has aesthetic advantages and long-term applicability. It is a rapidly developing method that uses plants to reduce, degrade, assimilate and metabolize environmental pollutants such as heavy metals, hydrocarbons, pesticides, etc. Phytoremediation techniques do not require specialized equipment and are accepted by local communities. Plants with exceptional metal-accumulating capacity are known as hyperaccumulator plants [9]. Phytoremediation utilizes the unique and selective uptake capabilities of plant root systems, together with the translocation, bioaccumulation, and contaminant degradation abilities of the entire plant body. Many species of plants have been successful in absorbing contaminants such as lead, cadmium, chromium, arsenic, and various radionuclides from soils. As reported by Valipour and Ahn [10], plant species used for phytoremediation should be possibly native and have a quick growth rate, extensive root system, high biomass yield, various habitats adaptation, high tolerance and the ability to accumulate the pollutants in the aboveground parts. Aquatic macrophytes represent a diverse group of plants with a great potential for removal heavy metals and are categorized as merged, submerged and free-floating plants. Presently, over 400 species of plant are identified to have potential for remediation of water sources [11]. A wide range of wetland plant species, such as Eichhornia, Salvinia,  water lettuce (Pistia stratiotes), duckweed, Azolla, Potamogeton, Myriophyllum, Typha, Scirpus, Limnocharis flava, Spartina, Cyperus and Phragmites  are frequently used for the heavy metal remediation in aquatic system [12- 13]. Different kinds of processes are used in phytoremediation techniques such as phytoextraction, phytodegradation, rhizofiltration, phytostabilization, phytovolatilization, phytodesalination and phytofiltration [14]. According to Thakur et al. [15], among these methods, phytoextraction, rhizofilteration and phytostabilization are commercially important. Kumar et al. [16] investigated seven aquatic plant species: Ipomoea aquatica, Eichhornia crassipes, Typha angustata, Echinochloa colonum, Hydrilla verticillata, Nelumbo nucifera and Vallisneria spiralis for phytoremediation of heavy metal in water. The result showed greatest and lowest accumulation of heavy metals in N. nucifera and E. colonum, respectively.

 

Aquatic plants for Heavy metal removal

Duckweed

Kingdom         : Plantae 

Subkingdom    : Tracheobionta 

Division           : Magnoliophyta 

Class                : Liliopsida

Order               : Arales

Family             :Lemnaceae

Duckweed, the common name for four main genera of Lemnaceae: Lemna, Spirodela, Wolffia and Wolffiella, is the smallest and fastest-growing flowering plant on the planet. Recently, the Lemna spp. has been proved the most used plant for phytoremediation in comparison with the other aquatic macrophytes [17]. This plant is used widely for nutrient recovery of nitro-gen, phosphorus and toxic metals from domestic and agricultural wastewater [18-19]. Lemna minor (Fig. 1) and Lemna gibba have been used extensively for phytoremediation of heavy metals [20]. L. gibba behaves as bio-indicator for heavy metals that transfer heavy metals from contaminated site to the plant and could be used to monitor the transfer of metal from lower to higher trophic levels [21]. As stated by Bocuk et al. [22], L. minor  accumulate high concentrations of several metals and metalloids, like nickel, copper, cadmium, zinc, manganese, boron, uranium and arsenic. Interestingly, Miretzky et al. [23] demonstrated that dried dead L. minor was able to remove heavy metals (Zn, Cu, Cd) from contaminated water.

Fig. 1: Collection of L. minor from wastewater accumulated at Udaipur, India

Giant duckweed (Spirodela polyrhiza) is frequently found growing in rivers, ponds, lakes, and sloughs (Fig. 2). S. polyrhiza was identified as a good arsenic phytofiltrator by physicochemical adsorption mechanism [24]. Tang et al. [25] evaluated the influences of a polyculture system of three duckweed species (Lemna aequinoctialis, Landoltia punctata, and S. polyrhiza) on the removal efficiency, as compared to a monoculture of duckweed, and majority of polycultures found to have median removal efficiency as compared to respective monocultures. Recently L. minor and S. polyrhiza are considered as an effective bioaccumulator and sensitive bioindicator for Pb [26]. S. polyrhhiza has been found to uptake and transform DDT and phosphorus pesticides [27]. According to Chaudhuri et al. [28], L. minor and S. polyrhiza are potential cadmium accumulator, as they were capable of removing 42–78% and 52–75% cadmium respectively from media depending upon initial cadmium concentrations.

Fig. 2: Spirodela polyrhiza

 

Eichhornia crassipes       

Kingdom         :  Plantae 

Division           :  Magnoliophyta 

Class                :  Liliopsida

Order               :  Liliales

Family             :  Pontederiaceae 

Genus              :  Eichhornia 

Species            :  crassipes 

 

E. crassipes, a native of South America, is a major freshwater weed in most of the frost-free regions of the world and is generally regarded as the most troublesome aquatic plant. It has been widely planted as water ornamental around the world because of its striking flowers. Liao and Chang [29] investigated the ability of water hyacinth to remove cadmium lead, copper, zinc, and nickel in water. In their investigation, they found water hyacinth plants high bio-accumulator of these trace elements when grown in water environments with low concentrations of the five elements. The detected values of cadmium and lead fall within normal range, while that of cobalt and nickel were within the critical range. However, zinc and copper showed the highest accumulation with alarming toxicity levels [16].

Azolla pinnata

Kingdom         : Plantae

Phylum            : Pteridophyta

Class                : Filicopsida

 Family            : Azollaceae

Genus              : Azolla

Species            : pinnata

 

Azolla pinnata (Fig. 3) is locally distributed in its native range of Africa and Madagascar, India, Southeast Asia, China and Japan, Malaysia and the Philippines, the New Guinea mainland and Australia. A. pinnata spreads rapidly by vegetative growth and can form dense mats, interfering with boating, fishing and swimming. It can block sunlight from reaching submerged plants and can also reduce oxygen levels in the water by blocking the interface between the water surface and the atmosphere. A. pinnata was observed to purify waters polluted by two heavy metals, i.e., mercury and cadmium under a microcosm condition [30]. The phoyoremediation potential of A. pinnata has also been recently observed [31-32].

Azolla

Fig. 3: Azolla pinnata forming dense mat over the Roopsagar, Udaipur, India

 

Potamogeton pectinatus

Kingdom         : Plantae

Class                : Liliopsida

Order               : Najadales

Family             : Potamogetonaceae

Genus              : Potamogeton

Species            : pectinatus

 

P. pectinatus is commonly known as sago pondweed, is a submersed plant that grows from a creeping rhizome. Except for the Polar Regions and Pacific islands, this species occurs worldwide. Sago pondweed grows in fresh, brackish, and saline waters throughout the state. It is found in stagnant ponds, spring-fed rivers, and slow flowing marshes. Underwater stands may look like grassy meadows. The stems are slender and flexible. The plant has high capabilities to remove heavy metals (Cd, Pb, Cu, Zn, and Mn) directly from the contaminated water [33].

Pistia stratiotes

Kingdom         : Plantae 

Division           : Magnoliophyta 

Class                : Liliopsida

Order               : Arales

Family             : Araceae 

Genus              : Pistia 

Species            : stratiotes 

 

Pistia stratiotes is a free-floating aquatic with feathery roots that can reach up to 50 cm in length. The fleshy leaves of this plant are arranged in a rosette and measure 2-15 cm in length. The leaves are green to grayish-green and have dense white hairs and parallel veins on their surface. P. stratiotes flowers in the late summer, but the flowers plant are small and inconspicuous. Phytoremediation efficacy of P. stratiotes has been evaluated by Farnese et al. [34] and Ugya et al. [35].

CONCLUSIONS- Water pollution is one of the biggest environmental concerns and it is evident that phytoremediation is a providing better solution to handle this problem. Hence, the harvesting of aquatic plants from water bodies should be avoided in order to control pollution in the aquatic environment and reduce the health risks to humans and animals caused by heavy metal contamination. Meanwhile, after harvesting plants, accumulated metals could be removed from plant mass through leaching methods.

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