Removal of Arsenic (III) and Chromium (VI) from The Water Using Phytoremediation and Bioremediation Techniques

Abstract

Advancement in science and technologies parallel to industrial revolution has opened new vistas to exploit the inherent traits of natural resources including green plants and microorganisms to overcome the damage to the environment by pollutants.
The present work was aimed to develop the phytoremediation potential of the aquatic plant Eichhornia crassipes for arsenic (III) and chromium (VI) from water. The accumulation, relative growth and bio-concentration factor of plant on treatment with different concentrations of arsenic(III) and chromium(VI) solution significantly increased (P<0.05) with the passage of time. Plants treated with 0.100 mg/L arsenic (III) accumulated the highest concentration of arsenite in roots (7.20 mg kg-1, dry weight) and shoots (32.1 mg kg-1, dry weight); while those treated with 4.0 mg/L of chromium (VI) accumulated the highest concentration of hexavalent chromium in roots (1320 mg/kg, dry weight) and shoots (260 mg/kg, dry weight) after 15 days. The plant biomass was characterized by SEM, EDX, FTIR and XRD techniques. Microwave-assisted extraction efficiency is investigated for extraction of arsenic from plant materials by comparison of the results by three extractant solutions: (i) 10% (v/v) tetramethylammonium hydroxide (TMAH) (ii) Deionized water and (iii) Modified protein extracting solution at different temperature and times. Extraction of chromium ions was carried by same procedure from plant materials using three extractant solutions: (i) 0.02 M ethylenediaminetetraacetic acid (EDTA), (ii) Deionized water and (iii) HCl solution at different temperature and times. Chromatograms are obtained for arsenic and chromium species in plant shoot biomass by using HPLC-ICP-MS.
The biosorption of arsenic (III) and chromium (VI) from water is studied by living cells of Bacillus cereus biomass as bioremediation. Bacillus cereus biomass is characterized, using SEM-EDX, AFM and FTIR. Dependence of biosorption was studied with variation of various parameters to achieve the optimum condition. The maximum biosorption capacity of living cells of Bacillus cereus for arsenic (III) and chromium (VI) was found to be 32.42 mg/g and 39.06 mg/g at pH 7.5, at optimum conditions of contact time of 30 min, biomass dosage of 6 g/L, and temperature of 30 ± 2°C. Biosorption data of arsenic (III) chromium (VI) are fitted to linearly transformed Langmuir isotherm and pseudo-second-order model with R2 (correlation vi vii coefficient) > 0.99. Thermodynamic parameters reveal the endothermic, spontaneous, and feasible nature of sorption process of arsenic (III) chromium (VI) onto Bacillus cereus biomass. The arsenic (III) and chromium (VI) ions are desorbed from Bacillus cereus using both 1M HCl and 1M HNO3.
The biosorption data of both arsenic (III) and chromium (VI) ions collected from laboratory scale experimental set up is used to train a back propagation (BP) learning algorithm having 4-7-1 architecture. The model uses tangent sigmoid transfer function at input to hidden layer whereas a linear transfer function is used at output layer.
The removal of chromium (VI) from aqueous solutions by activated carbon prepared from the Eichhornia crassipes root biomass. The maximum removal capacity of activated carbon was found to be 36.34 mg/g for chromium (VI), at pH 4.5, contact time of 30 min, biomass dosage of 7 g/L, and temperature of 25 ± 2 °C. The adsorption mechanisms of chromium (VI) ions onto activated carbon prepared from the Eichhornia crassipes root biomass are also evaluated in terms of thermodynamics, equilibrium isotherm and kinetics studies. Column studies are also performed to know the breakthrough point with an initial concentration of 10 mg/L.