Chemically modi? ed polymeric adsorbents are resins with functional groups such as phenolic hydroxyl, acetyl, sulfonic group or amino group, grafted on hyper cross linked polymers (Alexandratos & Natesan 1999), (Cai et al. 2005). Among these, aminated hyper cross linked polymers display a unique advantage in adsorption of aromatic sulphonates (Pan et al. 2005) phenol derivatives (Pan, Zhang, Wei & Ren 2008), and phenolic acids (Wang, Zhang, Zhao, Xia, & Chen 2005) due to the presence of electrostatic interactions, hydrogen bonding interaction or interaction between adsorbents and adsorbents.
Polystyrene particles have excellent chemical and physical properties that make them not easy to be degraded and damaged. Therefore polystyrene based adsorbents are usually used repeatedly. Unmodified particles are not suitable to adsorb substances from aqueous solutions because the surface is hydrophobic and lack of selective groups (Wang et al. 2005). However their hydrophobicity and selectivity is increased after modification. Nitrate is the most widely available contaminant in ground and surface waters (Liu et al 2005).
Excess of nitrate in drinking water results from anthropogenic sources, for example, over fertilization in agriculture, cattle discharge, untreated sewage, leakage from septic systems, infiltration of landfill leachate, and industrial waste water (Nuhoglu et al. 2005), (Hell et al. 1998), (Samatya et al. 2006), (Nataraj et. al 2006). Out of these, synthetic fertilizers are the major contributors of nitrate pollution (Rupert 2008). 2 Nitrate concentration above the maximum permissible limit in drinking water is injurious to human health. Nitrate exposure can lead to several health issues such as increased infant mortality, birth defects, abdominal pain, diarrhoea, vomiting, diabetes, hypertension, respiratory tract infections, and changes in the immune system (Majumdar & Guptar 2002), (Kross et al. 1992), (Fewtrell 2004), (Greener & Shannon 2005), (Ward, et al. 2005).
Numerous technologies are available for removal of nitrate from water. These include reverse osmosis, electro dialysis, biological denitrification, and ion exchange methods. In case of reverse osmosis (RO) water passes through a semipermeable membrane, and nitrate and other ions are rejected because their size is greater than the membrane pore size. Biological denitrification is widely practiced for the treatment of municipal and industrial wastewater but is less commonly used in drinking water applications (Hu et al. 2001)
Ion exchange is a process in which the target ion gets exchanged with a loosely adsorbed ion on a resin. Ion exchange is also like a reversible chemical process in which ions from an insoluble permanent solid medium (the ion exchanger is usually a resin) are exchanged for ions in a solution (Baes et al. 2002). This process is widely adopted for nitrate removal because of its simplicity, effectiveness, and relatively low cost (Baes et al. 2002). Adsorption has proved to be a relatively cheaper option which is readily applicable (Gupta & Ali 2000).
There are several methods that can be used to determine the concentration of nitrate ions and amongst them ion selective method is the most versatile. The nitrate electrode contains an internal reference solution in contact with a porous plastic organophilic membrane which acts as selective nitrate exchanger (Qingshan et al. 1999). When the membrane is exposed to nitrates present in water, a potential, E is developed across the membrane which is measured against a constant reference electrode potential , E0 . The magnitude of E depends on the concentration of nitrates present (Alexiades, & Mitrakas 1990).
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