Continuous biosorption of cadmium (II) ions using raw and calcium alginate immobilized protonated citrus peels - Abhijit Chatterjee , University of Alaska (co-authors: Silke Schiewer)

ABSTRACT

Alaska is the largest zinc-lead producer and second largest gold producer in the US. On the flip side of the coin, there are concerns regarding contamination of aquatic bodies with toxic metals from mine tailings through different pathways. While the traditional methods for treating metal bearing waste water such as chemical precipitation, ion exchange and membrane filtration may lead to incomplete separation or require huge investment, biosorption, a metal removal technique based on metal binding capacity of low cost natural organic material such as citrus peels may be competitive to concentrate metals from a large volume of dilute discharge. In this study, continuous removal of cadmium was investigated in a packed bed column using both raw and calcium alginate immobilized protonated citrus peels with varying operational conditions. For 10 g protonated raw peels, the column was operated without breakthrough for 42 hours at 9 ml/min flow rate and 5 mg/L inlet cadmium concentration but breakthrough time was decreased to about 24 hours when either flow rate or inlet cadmium concentration was increased to 12 ml/min and 10 ppm respectively. Sometimes a part of these peels were agglomerated hindering steady rate of the flow. To avoid this problem peels were entrapped within the calcium alginate matrix. Immobilized peels, though mechanically more suitable for column operation, can only be used at lower flow rate to avoid early breakthrough. When operated at 2 ml/min flow rate, breakthrough occurred after 64 hours at 40 cm bed height and 10 mg/L influent cadmium concentration but can be delayed up to 150 hours with proper adjustment of these parameters. In all cases, increased inlet concentration caused early saturation but higher uptake capacity. All breakthrough curves followed the Thomas model (R2>0.9). Successful use of packed bed column with citrus biosorbents encourages further investigation with real mining effluent

Topic: Water Quality