Removal of dissolved organic matter from raw water using zero valent iron

Abstract

There are a limited number of potentially scalable low-cost treatment methods for removing organic pollutants in water. In this study, a magnetic zero valent iron-carbonaceous conjugated microporous polymer nanocomposite (ZVI-CCMP) was synthesized from ZVI and waste polystyrene via the liquid phase reduction method, and used in a batch system for the removal of dissolved organic carbon (DOC) in water from a water treatment plant (WTP) in Pretoria, South Africa. The results were compared to the DOC removal efficiency of the WTP. The surface morphology of the nanocomposites as characterized using scanning electron microscopy showed heterogeneous ZVI nanastructures dispersed on the CCMP surface. Fourier transform infrared spectroscopy showed that the functional groups on the ZVI-CCMP surface were predominantly C]C and C-C from quinonoid motifs, aliphatic chain conjugation, and C-S groups originating from the introduced sulphonic moieties. Batch experiment data indicated that ZVI-CCMP adsorbed significantly (p=0.01) more DOC than ZVI, demonstrating the synergistic effect of ZVI activation. Whereas the WTP removed up to 24.3% DOC, ZVI and ZVI-CCMP removed 64 and 75%, respectively after a contact time of 30 min. Thus, compared to the processes used by the WTP, batch experiments using ZVI and ZVI-CCMP were 41 (p=0.00) and 52% (p=0.01) superior, respectively, demonstrating the potential of these materials to be upscaled for pilot and real life applications. While polystyrene has been used in the ZVI composites and the synthesis and evaluation of ZVI decorated carbon based materials has been widely studied, ZVI-CCMP based materials have not been reported. The objectives were: (1) to synthesise and characterise ZVI-CCMP nanocomposites; (2) to evaluate the removal of DOC in real water samples by ZVI and ZVI-CCMP; and (3) to compare the relative efficiency of ZVI-CCMP to that of the water treatment process through the measurement of DOC. Using CCMP nanocomposites to treat water is potentially a low-cost and environmentally friendly alternative for reducing the adverse public health and environmental risks associated with waste polystyrene.