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Ind. Eng. Chem. Res. 2009, 48, 4194–4201
“Rice Polish” for the Removal of Arsenic from Aqueous Solution: Optimization of Process Variables S. H. Hasan,*,† D. Ranjan,† and M. Talat‡ Water Pollution Research Laboratory, Department of Applied Chemistry, Institute of Technology and Department of Biochemistry, Faculty of Science, Banaras Hindu UniVersity, Varanasi-221005, India
Rice polish, a waste from the rice milling industry, was utilized as a potential biosorbent for removal of arsenic from aqueous solution. Optimization of process variables (pH, initial metal concentration, and temperature) and their cumulative effect were investigated using Box-Behnken Design (BBD) with only 15 sets of experimental runs. A second-order polynomial regression model was used, and results predicted showed high value of regression coefficients (R2, i.e., 95.69% for As(III) and 98.42% for As(V)) indicating good agreement with experimental data. The main effect plot showed uptake of arsenic having a curved relationship with pH, initial metal ion concentration having a positive effect, and temperature having a negative effect. The maximum removal of As(III) (41.18 µg/g) and As(V) (49 µg/g) predicted by contour and optimization plot was achieved at pH 6.84 and 4.29, respectively, at an initial metal ion concentration of 1000 µg/L, temperature 20 °C, and biomass dose of 1 g/50 mL. Scanning electron microscopy (SEM) analysis was carried out to find out the changes on the biosorbent surface during the sorption process. 1. Introduction Arsenic is a ubiquitous element that ranks 20th in abundance in the earth’s crust, 14th in seawater, and 12th in the human body. Since its isolation in 1250 A.D. by Albertus Magnus, this element has been a center of controversy in human history. But recently, arsenic contamination in water, especially groundwater, has been recognized as a major problem of catastrophic proportions. The toxicology and health hazard also has been reported for many years.1-6 Because of the recognition that arsenic at low concentrations in drinking water causes severe health effects, the technologies of arsenic removal have become increasing important. The current regulation of the drinking water standard has become more stringent and requires arsenic content to be reduced to a few parts per billion (10 µg/L).7 There are several treatment methods (such as solvent extraction, chemical precipitation as synthetic coagulants, ferrihydrite precipitation, iron coprecipitation, ion exchange, and reverse osmosis) capable of this level of performance. However treatment cost, operational complexity of the technology, skill required to operate the technology, and disposal of arsenic bearing treatment residual are factors that should be considered before treatment method selection.4,6,8 Adsorption has emerged as an alternative to these traditional methods with the advantage of being technically easy and simple in design. Most of the adsorbents used for the removal of arsenic,9 however, entail several problems in terms of efficiency and cost. In this context, biosorption by inexpensive biomaterials promises to be an excellent alternative and hence provide more cost-effective, ecofriendly, and relatively simpler means for the removal of arsenic from water10 in developing countries like India, Bangladesh, Taiwan, Thailand, and Nepal. Various biosorbents including agricultural waste and microorganisms have been reported for efficiently accumulating arsenic from water.5,8,9,11-18 The removal of arsenic by sorption processes may be influenced by factors like pH, initial metal ion concentration, temperature, * To whom correspondence should be addressed. E-mail: shhasan.apc@ itbhu.ac.in. Phone: 91542-25755758. Mobile: 09839089919. † Department of Applied Chemistry. ‡ Department of Biochemistry.
and biomass dose. In the conventional method used for the optimization of parameters there is variation of one factor at a time which is very laborious, time-consuming, and incomplete. On the other hand, application of response surface methodology (RSM) to the sorption process involves factorial search by examining simultaneous, systematic, and efficient variation of important components. It helps to predict a model for the process, identify possible interactions and higher order effects, and determine the optimum operational conditions. It also results in higher percentage yields, reduced process variability, closer confirmation of the output response to nominal and target achievement, and less treatment time with minimum costs.19-21 The present investigation is primarily aimed to utilize rice polish (an undesirable agricultural residue which is a byproduct of the rice milling industry) for the biosorption of arsenic from water and to optimize the parameters affecting the sorption for its maximum removal via a three-level three-factor fractional factorial Box-Behnken RSM experimental design with the help of software Minitab, release 15. 2. Materials and Methods 2.1. Preparation and Characterization of Biosorbent. Rice polish was used in experiments with double washing with double-distilled water to remove soluble lighter materials. The untreated rice polish was dried in an oven at 60 °C over a period of 24 h and crushing and sieving to
