Biosorption of Copper from Contaminated Water by Hydrilla verticillata Casp. and Salvinia sp.

Key words: Hydrilla vercillata Casp., Salvinia sp., Atomic Absorption Spectrophotometer, Copper, Heavy Metals.

Introduction

Contamination of the aquatic bodies by various pollutants (synthetics and organic) such as pesticides, Poly Aromatic Hydrocarbons (PAH), heavy metals, etc., have caused imbalance in the natural functioning of the ecosystem. Among these heavy metals cause severe damage to the living systems at various levels.

Main sources of heavy metal contamination are:

1. Urban industrial aerosols, created by combustion of fuels, metal ore refining and other industrial process,
2. Liquid and solid wastes generated from animals and humans,
3. Mining activities,
4. Industrial and agricultural chemicals.

Heavy metals also enter the water supply by industrial and consumer waste or even from acid rain breaking down soils and rocks and releasing heavy metals into streams, lakes, and ground water.

The most important features that distinguish heavy metals from other toxic pollutants are their non bio-degradability. The toxicity due to metal ion is owing to their ability to bind with protein molecules (Kar and Sahoo, 1992) and prevent replication of DNA and subsequent cell division. To avoid health hazards, it is essential to remove these toxic heavy metals from wastewater before its disposal.

Since a few years tremendous growth in the field of Biotechnology is overruling Chemical technologies used for pollution abatement, which were costly, non-ecofriendly and generate more secondary wastes which impair the ecosystem functioning.

Since most of these engineering technologies have failed in effluent cleanup process. As alternatives, slowly, biological tools are being substituted in pollution abatement programs. This new technology has been loosely grouped together under the term "Bioremediation"

Among the bioremediation procedures the most applicable is the Phytoremediation especially for the field of aquatic pollution abatement.

"The use of specially selected and engineered pollutant-accumulating plants for environmental cleanup is an emerging technology called Phytoremediation."

Phytoremediation works best at sites with low to medium amount of pollution, and at sites contaminated with metals. Plants are used either to stabilize or to remove metals from the soil and contaminated water through following five mechanisms:

1. Phytoextraction:
   Plants are used to remove toxic or heavy metals from soil.
    
2. Rhizofiltration:
   The use of plant roots to remove toxic or heavy metals from polluted water.
    
3. Phytostabilization:
   To eliminate the bioavailability of toxic or heavy metals from soils, using plants.
    
4. Phyto-Transformation:
   Degradation of contaminants through plant metabolism (applicable to both soil and water).
    
5. Phytostimulation : (or Plant-assisted biodegradation) also used for both soil and water, which involves the stimulation of microbial biodegradation through the activities in plants rhizosphere.

Once absorbed by the plants, toxic or heavy metals can be:

• Either stored in the roots, stems, or leaves,
• Converted into less harmful substances within the plant,
• Changed into gaseous form and are released into the air through transpiration.

Materials and Methods

The submerged macrophyte Hydrilla vercillata Casp. and free floating Salvinia sp. were collected from nearby natural ponds in Dakshina Kannada District. Plants were acclimatized for 3 to 7 days in fresh water holding tanks. After acclimatization, both plants were tested for 5 different initial concentrations (5, 10, 15, 20 and 25ppm) of Copper in the form of its Nitrates for a detention time of 10 days.

Experimental Setup

Triplicate batch tests for each concentration were conducted in plastic tubs of 2.5-lt. capacity. The total volume of sample taken in each tub was 2 lt. 10,000ppm stock solution prepared and kept ready to use. Desired Copper concentration was added in each tub from prepared stock solution. About 30 plants of Salvinia and about 100 cm of Hydrilla were kept in each tub, and marked the water level. All tubs were exposed enough light for detention time of 10 days.

Everyday aged tap water added to maintain the same level in each tub. The samples were taken to analysis for decrease in concentration at 24 hours intervals for 10 days using 902 Double Beam Atomic Absorption Spectrophotometer (GBC Scientific Equipment Pty Ltd, Australia, 3175).

Results and Discussion

Studies on biosorption of Copper from contaminated water by Hydrilla and Salvinia were conducted for a period of 10 days at five different initial concentrations (5, 10, 15, 20 and 25ppm).

Salvinia sp.

Hydrilla verticillata Casp.

Conclusion

1. Removal efficiency by Hydrilla, is higher in lower concentration (at 5ppm) compared to Salvinia. But in higher concentrations (From 10ppm to 25ppm) removal efficiency by Salvinia is more.
    
2. At lower concentrations up to fifth day of dosimetry both plants showed normal growth, and no significant morphological changes were observed.
    
3. Plant growth and morphology were dependent on the duration of exposure and initial dose, i.e, the longer exposure time and higher doses morphological changes were observed. This leads to poor performance by the plants.
    
4. It is concluded that using Hydrilla verticillata Casp., copper can be effectively removed on 5^th day for 5ppm concentration & on 7^th day for other concentrations i.e., 10ppm, 15ppm, 20ppm and 25ppm. And using Salvinia sp., copper can be effectively removed on 6^th day for 5ppm concentration & on 8^th day for 10ppm and 15ppm & on 9^th day for 20ppm and 25ppm concentrations.
    
5. Further studies are warranted to apply this into field.

Outlook

• With the special characteristics (extreme growth and rapid spread) of aquatic plants, these can be easily employed as phytoremediation tools for cost effective and eco-friendly technology in pollution abatement programs,
   
• As these plants are easily harvestable it is easy to remove and dispose these with careful monitoring,
   
• Further experiments are warranted as to extract the heavy metals, which will help to recover and recycle these useful but toxic substances from the environment.
   
• The techniques can also be extended to metals ores where wastes can be removed effectively.

Fig 1. Removal percentage of copper by Salvinia up to 9^th day

Fig 2. Removal percentage of copper by Hydrilla up to 7^th day

Acknowledgement

The expertise and constant support from Department of Chemical Engineering, NITK Suratkal, especially, Dr D.V.R.Murthy, Head of department, Dr Srinikethan, Professor, (Miss) Ranjani Chitrapur, Project Assistant, are acknowledged with due concern.

All the support, co-operation and encouragement from all those who helped directly and indirectly is acknowledged.

References

***

Copyright © 2003, ECO Services International