1706 † To whom correspondence should be addressed. E-mail: s.vigneswaran@uts.edu.au Korean J. Chem. Eng., 28(8), 1706-1712 (2011) DOI: 10.1007/s11814-011-0029-1 INVITED REVIEW PAPER Hydrous iron oxide for removal of inorganic contaminants in simulated stormwater: A batch sorption kinetics study Rupak Aryal, Sarvanamuthu Vigneswaran † , Paripurnanda Loganathan, Jayakumar Kandasamy, and Thamer Mohammed Faculty of Engineering, University of Technology Sydney (UTS), P. O. Box 123, Broadway, NSW 2007, Australia (Received 5 November 2010  accepted 5 February 2011) Abstract−Urban stormwater runoff, which consists of inorganic and organic contaminants, is a major source of pol- lutants to receiving waters and therefore they need to be removed. Simultaneous removal of contaminants, Cd 2+ , Cu 2+ , Ni 2+ , Zn 2+ (heavy metal cations), and SeO 4 2− (oxyanion) from a simulated stormwater by a hydrous ferric oxide (HFO) was studied in batch and column sorption experiments. In the batch experiment the rate of sorption of the ions was rapid at the beginning and reached equilibrium in approximately 300 min. The amounts of ions sorbed were proportion- ate to the respective initial concentration of the ions added to the HFO. Cluster analysis showed that all heavy metals had similar sorption behavior, whereas Se had a distinctly different sorption process. Of the three different kinetic models tested the pseudo-first order kinetic model fitted the data the best. The column experimental results beyond 180 min were consistent with those of the batch experiment that the removal efficiencies of the ions were in proportion to the ion concentration in the feed. Below 180 min, Cu appeared to be preferentially removed than Zn. Key words: Sorption Kinetics, Hydrous Ferric Oxide HFO, Stormwater, Inorganic Contaminants, Heavy Metals INTRODUCTION Urban stormwater runoff is comprised of numerous micro-pol- lutants such as heavy metals, hydrocarbons, pharmaceutical care products and pesticides, derived from a variety of sources includ- ing building materials, vehicular movement, and human activities. Among the contaminants, the inorganic ones, Cd, Cu, Ni and Zn (heavy metals) and Se (non-metal) are commonly found to be in high concentrations to cause toxicity to living organisms and there- fore they are of concern. Inorganic contaminants, unlike organic contaminants, are not biodegradable and therefore can accumulate in the environment for a long time. At elevated concentrations, they can cause both short-term (acute toxicity) and long-term (e.g., carci- nogenic damages) damage to aquatic organisms and through the food chain to animals and humans. For example, in freshwater ani- mals, chronic exposure to Cd, and Cu and their secondary metabo- lites may cause immuno-suppression, vertebral deformities and neuro- logical disorder in both the peripheral and central nervous system [1], while Cd is known to enhance lipid peroxidation by increasing the production of free radicals in the lungs, which leads to tissue damage and cellular death [2,3]. Excessive concentration of Ni re- duces skeletal calcification and diffusion capacity of gills, and affects protein metabolism [4], while selenium can cause selenosis leading to gastrointestinal disorder and neurological damage in humans [5]. Due to their toxicity, the discharge of these contaminants to natural water bodies may cause physical, chemical, as well as biological impacts on the environment both in the short-term and in the long- term and therefore they should be removed. There is a dual objective in stormwater management: a) to reduce peak discharges and flooding, and b) to improve the quality of storm- water runoff. While historically the focus has been on the former, in recent times there are increasing numbers of treatment measures to improve the quality of stormwater runoff. These systems include sediment traps, gross pollutant traps, permeable pavements, grass swales, bio-retentions and constructed wetlands. In general, these systems are not effective in the removal of inorganic contaminants such as heavy metals, dissolved nutrients (mainly nitrogen), dis- solved organic matter and pathogens. Apart from this, a key draw- back of the current range of stormwater management treatment sys- tems is that they are less reliable and requires continuous ongoing maintenance to ensure the performance rates. Different types of treatment processes have been developed to remove inorganic contaminants from stormwater runoff, including physical and chemical treatments, such as conventional filtration, ion exchange, and membrane filtration system [6-8]. Among them, sorption processes have been recognized as efficient and economic methods of removing these inorganic contaminants from stormwater. Both locally and commercially available materials are used as sorbents in removing contaminants present in stormwater. Such sor- bents include sand and sorbents prepared by coating sands, sor- bents obtained from waste materials, and natural materials such as oxides and hydroxides [9-12]. During the last few years, hydrous ferric oxide (HFO) has been used commercially as a porous iron oxide sorbent to remove inorganic contaminants such as Ni, Zn, Cu, Se and Pb [13,14]. Studies on sorption of inorganic ions on HFO have demonstrated that sorption occurs in two steps: i) a rapid sur- face exchange or sorption, followed by ii) a very slow uptake that may continue for days to years [15,16]. The rapid sorption of inor- ganic ions on sorbents including HFO proceeds by the formation of inner (specific sorption) or outer surface (non-specific sorption) complex formation on the sorbents [17]. The slow uptake has been