Abstract
Domestic water is abstracted from its sources in raw form with a high content of dissolved and suspended material. Polydiallyldimethylammonium chloride (polyDADMAC) is a cationic polyelectrolyte used in the initial water clarification process. However, its residues in treated water pose a health risk as they react with chlorine to produce a carcinogenic compound. There is a need to determine the concentration of the polyelectrolyte cations that pass through the flocculation stage before the chlorine disinfection process in water treatment plants to ascertain the safety of water to consumers. The cationic polymer is UV inactive, and previously available methods for determining the concentrations of polyelectrolytes are unsatisfactory due to poor detection limits. This paper describes a UV–Visible (UV–vis) spectrophotometry method for the determination of residual polyDADMAC as an epoxide. The novelty method lies on the epoxidation of polyDADMAC using 20 % sodium hydroxide dissolved in 30 % hydrogen peroxide to produce a UV–Vis active compound. The epoxidation was confirmed by UV–Vis, FTIR and 1H NMR techniques. Dilute solutions of varying concentrations of polyDADMAC (0.2–1.0 mg L−1) were treated with a basic solution of hydrogen peroxide then analysed by UV–Vis spectrophotometry. The wavelength at maximum absorption (λmax) was found to be 313 nm, and a linear calibration curve with a correlation coefficient (R 2) of 0.993 was used for quantification purposes. The detection limit measured as three times the signal of the blank and was found to be 2.1 × 10−4 mg L−1. The method was applied to determine the concentration of polyDADMAC spiked in water samples collected from a pool as a model for environmental matrix. The results obtained agreed with the quantities spiked in the solution, thus qualified the method to be suitable for the determination of polyDADMAC in treated waters at trace levels. The method was also used to investigate the adsorption capacity of polyDADMAC on sand filters. The adsorption method was found to be in accordance with Langmuir with an adsorption capacity of 2.068 mg g−1.
Highlights
Polydiallyldimethylammonium chloride is a cationic liquid used as a flocculant in water treatment plants
Characterization of the functional groups was carried out using a Fourier transform infrared (FTIR) spectrophotometer (Perkin Elmer 100 with sampling accessory, Waltham, MA, USA) using the attenuated total reflectance (ATR) mode (Mukamel 2000 )
This study successfully developed a spectroscopic method for the determination of polyDADMAC at trace levels by exploiting the epoxidation of double bonds within its chemical structure
Summary
Polydiallyldimethylammonium chloride (polyDADMAC) is a cationic liquid used as a flocculant in water treatment plants. 1638, Page 2 of 9 suspended particles making it very effective in flocculating, decolouring, killing algae and removing organics such as humus (Sang-kyu and John 1999). It has been widely used in the treatment of drinking and wastewater due to its advantages over inorganic coagulants such as alum and iron salts (Jackson 1981). Due to the size of some particles suspended in water, they are impossible to settle and would require coagulation. Coagulation is a chemical and physical process wherein collisions between colloidal particles and coagulant chemicals result in their cohesion and eventual sedimentation as agglomerates. The mechanism involves neutralization of negative charges on the colloidal particles' surface resulting to the attraction of the neutral particles by the coagulant to produce spongy masses called flocs (Majam et al 2004)
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