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

By Elankumaran R., Raj Mohan B.* and M. N. Madhyastha**
July 2003

The Authors are specialists in Industrial Pollution Control and BioChemical Engineering at the Department of Chemical Engineering of the National Institute of Technology Karnataka (NITK), (formerly, Karnataka Regional Engineering College), 575 025 Surathkal, India.
* Lecturer,   ** Emeritus fellow All India Council for Technical Education (AICTE)

Abstract

Biosorption of Copper from contaminated water by Hydrilla verticillata Casp., and Salvinia sp., were tested at 5 different initial concentrations. The samples were analyzed for decrease in concentrations at 24 hours intervals for 10 days using 902 Double Beam Atomic Absorption Spectrophotometer (GBC Scientific Equipment Pty Ltd, Australia, 3175). Salvinia, showed the maximum percentage removal of Copper from wastewater on the 6th day of dosimetry at an initial concentration of 5ppm. In general the plant growth was normal at lower concentrations and showed higher removal efficiency. It was also observed that removal efficiency of Salvinia decreases with increasing concentrations. Hydrilla, showed the maximum removal percentage of Copper from waste water on 5th day of dosimetry at an initial concentration of 5ppm.

Observations also showed variations in the plant growth and morphological features at varying concentrations and duration of exposure.

It is interesting to note that removal efficiency by Hydrilla, is higher in lower concentration (at 5ppm) compared to Salvinia. But in higher concentrations (10ppm- 25ppm) removal efficiency by Salvinia is more.

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:

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.

The average daily removal of Copper by Salvinia is presented in Table 1. And percentage removal of Copper at every 24-hrs interval is presented in Table 2. Above results clearly suggested that at lower concentrations the plant growth was normal with greater removal efficiency.

Maximum percentage removal of copper from wastewater was noticed on the sixth day of dosimetry. The maximum percentage removal of 95.80% was recorded when copper was present at 5ppm.

For 10ppm and 15ppm, the maximum percentage removals were recorded on eighth day of its dosimetry. For 20ppm and 25ppm, the maximum percentage removals were observed on ninth day of its dosimetry. Everyday the removal efficiency varied drastically. This may be due to direct and indirect involvement of copper in metabolic reactions inside the plants.

It was also noted that up to 15ppm of copper concentration, the general health condition of Salvinia was normal throughout its dosimetry. But beyond 20ppm of copper concentration, after eighth day the plants started showing morphological changes.

Daily removal percentage of copper till ninth day by Salvinia are presented in Figure 1.

Hydrilla verticillata Casp.

At lower concentration up to fifth day of its dosimetry Hydrilla showed higher percentage removal and normal growth.

Concentration of copper remaining in solution after biosorption by Hydrilla is presented in Table 3., and percentage removal of copper at every day interval is presented in Table 4. The maximum percentage removal of copper from wastewater was noted on the fifth day of its dosimetry.

The maximum removal percentage recorded was 98.85% and observed at an initial concentration of 5ppm. Daily removal percentage of copper by Hydrilla is represented in Figure 2.

Table 1. Concentration of copper remaining in the solution after biosorption by Salvinia sp.
Days 5ppm 10ppm 15ppm 20ppm 25ppm
1 1.3476 4.2996 6.2910 12.5921 17.1591
2 0.9847 5.9925 8.1048 10.5611 14.3914
3 0.9708 4.6776 7.1973 10.2858 14.3094
4 0.8282 3.8494 6.9402 10.0049 14.0822
5 0.4673 3.5850 6.8134 9.6066 13.6009
6 0.2099 3.1956 6.3531 9.4714 13.2436
7 0.2190 2.6748 4.5189 8.3247 11.7627
8 0.2450 2.1183 4.3110 8.0746 11.5007
9 0.2473 2.4531 5.1310 7.1628 11.3167
10 0.3323 3.3866 5.6447 9.2503 12.5538
Table 2. Percentage removal of copper by Salvinia sp. in each day.
Days 5ppm 10ppm 15ppm 20ppm 25ppm
1 73.05 57.00 58.06 37.04 31.36
2 80.31 40.08 45.97 47.20 42.43
3 80.58 53.22 52.02 48.57 42.76
4 83.44 61.51 53.73 49.98 43.67
5 90.65 64.15 54.58 51.97 45.60
6 95.80 68.04 57.65 52.64 47.03
7 95.62 73.25 69.87 58.38 52.95
8 95.10 78.82 71.26 59.63 54.00
9 95.05 75.47 65.79 64.19 54.73
10 93.35 66.13 62.37 53.75 49.79
Table 3. Concentration of copper remaining in the solution after biosorption by Hydrilla.
Days 5ppm 10ppm 15ppm 20ppm 25ppm
1 2.6806 7.6678 7.2148 13.4265 19.6380
2 1.7594 8.2582 7.4559 11.2244 14.9927
3 1.3900 6.1349 6.1999 11.4774 14.2538
4 0.3690 6.0068 5.9685 10.0754 16.7547
5 0.0573 5.0922 6.0106 10.3038 15.6389
6 0.4702 4.9507 5.8968 10.2226 14.4344
7 0.5014 3.3762 5.2552 9.4869 13.7186
8 0.3349 5.2177 6.0021 10.9576 14.9130
9 0.2863 6.5282 - - -
10 0.1002 6.9177 - - -
Table 4. Percentage removal of copper by Hydrilla in each day.
Days 5ppm 10ppm 15ppm 20ppm 25ppm
1 46.39 23.32 51.90 32.87 21.45
2 64.81 17.42 50.29 43.88 40.03
3 72.20 38.65 58.67 42.61 42.99
4 92.62 39.93 60.21 49.62 32.98
5 98.85 49.08 59.93 48.48 37.44
6 90.60 50.49 60.69 48.89 42.26
7 89.97 66.24 64.97 52.57 45.13
8 93.30 47.82 59.99 45.21 40.35
9 94.27 34.72 - - -
10 98.00 30.82 - - -
Table 5. Morphological changes observed in Hydrilla and Salvinia after supplying different initial concentrations of copper in the form of copper nitrate solution.
Days 5ppm 10ppm 15ppm 20ppm 25ppm
Hydrilla Salvinia Hydrilla Salvinia Hydrilla Salvinia Hydrilla Salvinia Hydrilla Salvinia
4 Normal Normal Normal Normal Normal Normal Normal Normal Normal Normal
6 Normal Normal Normal Normal Leaves became faintly yellow Normal Leaves became faintly yellow Normal Leaves became faintly yellow Normal
8 Partial decolourization Normal Partial decolourization Normal Complete decolourization Normal Plant died Leaves became faintly yellow Plant died Leaves became faintly yellow
10 Complete decolourization Normal Complete decolourization Normal Plant died Normal - Partial decolourization - Partial decolourization

(* Till end of 5th day both plants growth were Normal).

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 5th day for 5ppm concentration & on 7th day for other concentrations i.e., 10ppm, 15ppm, 20ppm and 25ppm. And using Salvinia sp., copper can be effectively removed on 6th day for 5ppm concentration & on 8th day for 10ppm and 15ppm & on 9th day for 20ppm and 25ppm concentrations.
     
  5. Further studies are warranted to apply this into field.

Outlook

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

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

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

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