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Ind. Eng. Chem. Res. 2009, 48, 10180–10185
Rice Polish: An Alternative to Conventional Adsorbents for Treating Arsenic Bearing Water by Up-Flow Column Method D. Ranjan,† M. Talat,‡ and S. H. Hasan*,† Water Pollution Research Laboratory, Department of Applied Chemistry, Institute of Technology, and Department of Biochemistry, Faculty of Science, Banaras Hindu UniVersity, Varanasi 221 005 (U.P.), India
“Rice polish”, an agrowaste from rice milling industries, was utilized as potential biosorbent for removal of arsenic from water in a continuous up-flow fixed bed column system. The experiments were conducted to study the effect of important design parameters such as bed height, flow rate, and initial metal ion concentration. At a bed height of 25 cm, flow rate 1.66 mL/min, and initial metal ion concentration 1000 µg/L, the metal uptake capacity of rice polish for As(III) and As(V) was found to be 66.95 and 78.95 µg/g, respectively. The bed depth service time (BDST) model was used to analyze the experimental data. The computed sorption capacity (No) was 28776 and 28248 µg/L for As(III) and As(V), respectively. The rate constant (Ka) was recorded as 0.117 × 10-3 and 0.26 × 10-4 (L/µg)/min for As(III) and As(V), respectively. The column regeneration studies were carried out using 10% NaOH as eluant for three sorption-desorption cycles. The high arsenic removal ability and regeneration efficiency of this biosorbent suggest its applicability in industrial processes and data generated would help in further upscaling of the adsorption process. 1. Introduction Arsenic poisoning has emerged as a major threat to human society in the recent past. Since its isolation in 1250 A.D., 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.1-7 Because of the recognition that arsenic at low concentrations in drinking water causes severe health effects, the technologies of arsenic removal have become increasingly important. The current regulation of drinking water standard has become more stringent and requires the arsenic content to be reduced to a few parts per billion (10 µg/L).8 There are several treatment methods (such as solvent extraction, chemical precipitation as synthetic coagulants, ferrihydrite precipitation, iron co-precipitation, ion exchange, and reverse osmosis) capable of this level of performance. However treatment cost, operational complexity of the technology, the skill required to operate the technology, and disposal of the arsenic bearing treatment residual are factors that should be considered before treatment method selection.4,6,9,10 In this context biosorption by inexpensive biomaterials promises to be an excellent alternative and hence provide much cost-effective, ecofriendly, and relatively simpler means for the removal of metal ions from water.11 Recently, byproducts or the wastes from large-scale industrial operations and agricultural waste materials have been paid much attention in use as economic and ecofriendly adsorbents.12 Agricultural materials, particularly those containing cellulose, show potential metal biosorption capacity. A recent article published in 200813 reviewed the percentage interest in each metal ion in the literature on the use of agricultural biomasses for wastewater treatment and the countries which are involved in the studies on the use of agricultural biomasses for wastewater treatment. Interestingly it was found that India is the country with the greatest use of agricultural waste for wastewater
treatment and arsenic has the least attention for removal using agricultural waste. The estimated annual production of rice in developing countries is 500 million tons,14 India being the largest producer of rice in the world outside of mainland China.14 The production of rice in such great quantity results in approximately 100 million tons of rice polish, also called rice bran (the hard outer layer of grain, consisting of combined aleurone and pericarp and is the byproduct of the rice milling process during the conversion of brown rice to white rice), annually for utilization in these countries.15,16 However, the amount of rice polish available is far in excess of local uses, thus frequently causing disposal problems. Rice bran contains different vitamins, carbohydrates, potassium, nitrogen, and phosphorus compounds, which are induced to water that contacts with it. These compounds not only have no pollution effects but they are nutritious to the plants. Therefore, the use of bran to eliminate pollution from water reveals the significance of the bran or natural products. Up to now only a few studies have been carried out in this field.14-22 However, batch experiments were generally done to measure the effectiveness of adsorption for removing specific adsorbates as well as to determine the maximum adsorption capacity, but from an industrial point of view the continuous adsorption in a fixed bed column is often desired. It is simple to operate and can be scaled-up from a laboratory process. Few attempts have been made for the removal of arsenic from water using continuous mode.3,10,23-34 In the present paper continuous upflow fixed bed column mode is applied to study the influence of bed height, flow rate, and initial metal ion concentration at room temperature on the removal of arsenic using rice polish. In addition sorption-desorption studies were carried out in order to regenerate and reuse the biosorbent. As a whole a complete study for the economic, easy, and ecofriendly solution of catastrophic arsenic pollution has been done, which can be implemented in the developing countries. 2. Materials and Methods
* To whom correspondence should be addressed. Tel.: 915422575758. Cell phone: 09839089919. E-mail:
[email protected]. † Department of Applied Chemistry, Institute of Technology. ‡ Department of Biochemistry, Faculty of Science.
2.1. Preparation of Biosorbent. Rice polish was collected from a local rice milling industry and was used in experiments with double washing with double-distilled water to remove
10.1021/ie900877p CCC: $40.75 2009 American Chemical Society Published on Web 10/01/2009
Ind. Eng. Chem. Res., Vol. 48, No. 23, 2009
soluble lighter materials. The untreated rice polish was dried in an oven at 60 °C over a period of 24 h and crushed and sieved to
