Removal Of Chlorinated Organic Compounds In Water With Substrate Anchored Zero Valent Bimetals

ABSTRACT

Chlorine in drinking water, surface or underground water is a concern of public health. This is because chlorine reacts with nitrogen containing organic compounds to form polychlorinated complexes that are carcinogenic. However, chlorine is dissolved in water for the sake of disinfecting with a view to killing pathogens in water to make it safe for human consumption. After that initial addition, some chlorine is left in the water and continues with the chlorination process of the organic matter which includes the dead pathogens. According to Kenya Bureau of Standards the allowed maximum limits for chlorine concentration in water is 1.6 ppm, but even this concentration posses potential harmful effects with time. Available methods for removal of chlorine and chlorinated compounds include adsorption, precipitation, electrolysis and ozonation. These methods are expensive and some result in generation of toxic compounds as well as generation of different forms of pollutants. This study used zero valent bimetals Fe/Zn for the removal of chlorine and chlorinated compounds in water which does not generate toxic by-products. The zero valent bimetallic (ZVB) material was anchored on an organic non bio- degradable polystyrene waste material. This is viewed as a green method of cleaning the environment. The zero valent bimetal substrate anchored material was prepared through nitration, amination, complexation and reduction process using suitable ligands. The resulting solid material was characterized using Fourier Transform Infra-Red (FTIR) method. FTIR analysis suggested the possibility of the participation of ZVB anchored substrate in the release of the chloride ion. The solid was then packed in Solid-Phase Extraction (SPE) columns and applied for the removal process. Removal optimization parameters such as initial halide concentration, removal coefficient and effect of time and bimetal dosage variation were optimized using synthetic waters. Quantification of chlorine was done using potentiometric methods. The data was analysed using linear regression. The reduction kinetics was determined by fitting Pseudo- first- order and pseudo-second order models to the experimental data. It was found that the data was better described by the Pseudo- first- order model. Modified metal anchored polystyrene material showed a reduction capacity of 3.57,

4 62 and 3.79 μmol l-1 for 1, 2-dichloroethane, 2-chloro-2-methylpropane and1-chlorobutane respectively. The pseudo first-order reaction constants for the bimetals (Fe/Zn, Fe/Ni) and the tri-metal (Fe/Zn/Ni) was 2.37±0.01 (R2=0.998±0.001) for Fe/Zn, 3.55±0.01 (R2=0.989±0.001) for Fe/Ni, and 3.72±0.01 (R2=0.992±0.001) for the tri-metal. The rate of reduction of was very fast as more than 90% of the halides were reduced in less than 10 minutes. After the optimization, the prepared material was then applied on real samples sourced from Nairobi water and Sewerage Company (tap water), Kiamumbi water treatment plant and shallow well from Kiamumbi. From the reduction process the environmental water was found to have the chlorinated organic compounds, Nairobi water and sewerage company (tap water) (4.01μgl-1), Kiamumbi water treatment plant (4.51μgl-1) and shallow well from Kiamumbi (4.51μgl-1). The results obtained are suitable for use by policymakers and for sensitizing the public