METALLIC PHYTOREMEDIATION AND NANOBIOTECHNOLOGY OF WATER HYACINTH

Abstract

Like world Pakistan is facing two major threats i.e. environment and energy. Rapid industrialization and urbanization have resulted in elevated emission of toxic heavy metals entering the biosphere. Activities such as mining and agriculture have polluted extensive areas throughout the world. The release of heavy metals in biologically available forms by human activities may damage or alter both natural and man-made ecosystems. Heavy metal ions such as Pb 2+ , Cr 6+ , Cd 2+ Cu 2+ , Zn +2 and Ni +2 , are essential micronutrients for plant’s and animal’s metabolism but when present in excess, can become extremely toxic. Among the renewable energy technologies, solar energy, wind energy, biofuels and biomass conversion occupy the central stage. The current study belongs to biomass conversion to biofuels. It was focused on metal phytoremediation and biofuel production from water hyacinth by using Nanobiotechnology. Soil experiments show the phytoremoval of Pb 2+ , Cr 6+ , Cd 2+ Cu 2+ , Zn +2+ and Ni 2+ in μg/g of plant’s dry weight. Increase or decrease in pH and fresh weight is also discussed. Lead, chromium, cadmium, copper, zinc and nickel showed phytoremoval of 27.91, 38.67, 1.915, 3.38, 13.11 and 24.23 μg/g of plant’s dry weight respectively. Similarly phytoremoval of lead, chromium, cadmium, copper, zinc and nickel in kg/ha is 1582.45, 1053.38, 2852.75, 232.99, 1521.08 and 3449.76 respectively. Hoagland’s hydroponic experiments show the phytoremoval of Pb 2+ , Cr 6+ , Cd 2+ Cu 2+ , Zn +2+ and Ni 2+ in μg/g of plant’s dry weight. Increase or decrease in pH and fresh weight is also discussed. Lead, chromium, cadmium, copper, zinc and nickel showed phytoremoval 19.132, 2.369, 8.888, 4.085, 0.845 and 1.954 μg/g of plant’s dry weight. Adsorption and desorption experiments show phytoremoval (adsorption) of Pb 2+ , Cr 6+ , Cd 2+ Cu 2+ , Zn +2+ and Ni 2+ in μg/g of plant’s ash. While desorption (recovery for reuse) of lead, chromium, cadmium, copper, zinc and nickel in μg/g of plant’s ash. Adsorption capacity is 29.83, 24, 28.41, 29.83, 29.94 and 29.79 μg/g of plant’s ash respectively. The biosorptive capacity is highest with pH > 8.00. The desorption capacity of lead, chromium, cadmium, copper, zinc and nickel is 18.10, 9.99, 27.54, 21.09, 11.99, 3.71 μg/g of plant’s ash respectively. Bioanalytical experiments were performed to assess the metallic concentrations of Taxilian water hyacinth. Some selected microbes from hyacinth’s roots were isolated, xxidentified by biochemical tests and purified by microbiological experiments. Our results show that Thiobacillus thiooxidans, Thiobacillus ferrooxidans, Azotobacter and A. niger are present in the roots of water hyacinth. Thiobacillus thiooxidans, Thiobacillus ferrooxidans and A. niger are commonly well known for metal’s bioremediation. Their presence in the roots of water hyacinth show that these microbes may have some role in metal’s phytoremediation by hyacinth. Azotobacter is generally nitrogen fixing bacteria its presence may shows relationship with nitrogen’s phytoremoval by hyacinth. The presence of Mn, Mo, Fe, Cr and some other metals in nitrogenase enzymes of Azotobacter, is already documented. Therefore Azotobacter’s presence may also be responsible for phytoremoval of these metals by water hyacinth. Three different studies were performed for the nanobiotechnological conversion of water hyacinth (Eichhornia crassipes) plant into biofuel. In the first study water hyacinth was saccharified with diluted sulfuric acid (1% v/v at 110 o C for one hour) and fermented by yeast (Saccharomyces cerevisiae). The results show the formation of 55.20 % ethanol and 41.66 % acetic acid. In another experiment water hyacinth was gasified by using Ni and Co nano catalysts at 50-400oC and atmospheric pressure. In catalytic gasification methane (2.41-6.67%), ethene (19.74-45.52%), propyne (21.04-45.52%), methanol (1.43- 24.67%), and propane/acetaldehyde (0.33-26.09%) products are obtained. In third study anatase form of titanium dioxide photocatalyst was used. The reaction was performed at room temperature which gives good percentage of methane (53.19%), methanol (37.23%) and ethanol (9.57%). This study reports an interesting finding that metal contaminated water hyacinth could be used for not only the production of biofuel but also hydrocarbons Present study gives solution of two major problems of the world i.e. environmental pollution and fuel. It also shows comparison of three different phytoremediation technologies and use of water hyacinth as a metal hyper accumulator and a source of hydrocarbon gases and bioethanol. These technologies are cheap and may be developed further for commercial use.