BIOLOGICAL. REMOVAL OF ARSENIC FROM INDUSTRIAL WASTEWATER

Abstract

Alarming information has emerged in recent decades about the widespread presence of arsenic due to natural processes as well as industrial activities. Various types of arsenic related human cancers have been reported in recent years around the world due to the consumption of arsenic contaminated ground water for drinking purpose especially in Bangladesh and India. The present study has been undertaken to develop suitable method for removal of arsenic from aqueous solution as well as copper smelting industrial wastewater. Aqueous solution containing 100 mg/1 of As(III) and As(V) has been prepared by dissolving sodium meta arseriite and sodium arsenate in distilled water. Whereas, the simulated copper smelting wastewater containing As(II1), As(V), Fe, Zn, Cu, Cr have been considered based on available literature with a total arsenic concentration of 50 mg/1 and pH 7 after dilution. A review on various arsenic removal technologies reveals that amongst various treatment options, like chemical precipitation, electro coagulation, adsorption, membrane filtration, biosorption, nanofilteration, reverse osmosis, phytoremediation etc.,- biosorption . as - a wastewater treatment process has attracted considerable interest in recent years. The present study is carried out with an objective to investigate the suitability of rice husk and' - mango leaves as the low cost biosorbents for the removal of arsenic from aqueous solutions' as well as simulated copper smelting industry wastewater. Rice husk purchased from local market and mango leaves are collected from campus area of IIT Roorkee. The phYical and chemical • characterization of the biosorbents has been done using standard methods e.g. sieving, proximate analysis, scanning electron microscopy, and FTIR. microscopy. In the present work, Silver Diethyl Dithiocarbamate (SDDC) method has been used as speciation technique followed by colorimetric measurements at 540 nm wavelength, which can predict arsenic in the sofution around 99.6% accuracy. This speciation technique has been adopted from IS 3025 (part-3.7)-1988: methods of sampling and test for water and wastewater. Batch experiments are conducted for the removal of arsenic from aqueous solution as well as simulated wastewater. Effect of process parameters like pH, biosorbent concentration, contact time, initial concentration and temperature on the removal of arsenic species have been investigated using rice husk and mango leaves to determine optimum process conditions for maximum removal of arsenic. The initial pH of the solution strongly affects the uptake of metal ions. Acidic conditions are favourable for removal of As(V). pH 6 to 8 or nearly neutral 11 conditions are observed favourable for the removal of As(III) and total arsenic. Optimum dosages are found to be 4 g/100 ml for both As(M) and As(V) for the removal of arsenic from aqueous solutions. Dosage of 6 g/100 ml for rice husk and 7 g/100 ml for mango leaves are optimum for the removal of arsenic from simulated wastewater. The effect of agitation period has been studied from 0.5 h to 32 h. The rate of arsenic species removal is found to be rapid during initial lh and thereafter rate of removal decreases. The apparent saturation in the removal of arsenic species is occurred at 4 h for rice husk and 8h for mango leaves, • respectively. Pseudo first-order and pseudo second-order models have been used to study the kinetics of biosorption. The pseudo second-order kinetics represented biosorption data well. Higher temperatures induce a positive effect on biosorption process. Equilibrium experimental data has been analyzed for different isotherm models i.e. Langmuir, Freundlich and Redlich-Peterson (R-P) models. R-P model gives better prediction of uptake for the removal of arsenic species from aqueous solution onto rice husk and Freundlich model for mango leaves. Thermodynamic parameters are also studied from the experimental data. The negative values of Gibbs free energy (AG') indicates the feasibility and spontaneous nature of biosorption onto biomass. The positive values of heat of sorption (AH'), indicates the endothermic nature of biosorption process.