Silver Modified Zeolite for the Removal of Escherichia coli and Metals from Aqueous Systems.

Pathogenic microorganisms and persistent heavy metals present in contaminated aqueous streams are harmful to human health and the ecosystem. Hence more effective treatment technologies are required for their removal prior to use or discharge into the aquatic environment. Silver has been incorporated into different support materials for use in water and wastewater disinfection. These materials include natural zeolites (NZ) which possess excellent ion exchange properties and have been extensively used for metal removal from aqueous solutions. The aim of this study was to investigate the performance of silver modified zeolites (SZ) for the combined removal of Escherichia coli and metals (Pb, Cd and Zn) from aqueous systems. Silver modification was conducted via ion exchange and characterization studies provided more information about the zeolites while confirming the presence of silver in SZ. Preliminary performance screening results provided the rationale for more detailed and systematic batch and column experimental studies. Batch studies were undertaken to investigate the disinfection and metal removal performance in single and multicomponent systems. The SZ exhibited high disinfection efficiencies with complete disinfection achieved within 15-30 minutes of contact time while nonmodified zeolites had no antibacterial effect. The maximum metal removal capacities of both NZ and SZ were 18-101mg/g and the observed order of metal selectivity was Pb>Cd>Zn. Overall metal removal was best described by the Langmuir isotherm and followed the pseudo-second-order kinetic model. In fixed-bed column studies, complete disinfection and metal removal (100%) was achieved until E. coli breakthrough after 570 minutes followed by Cd and Zn breakthrough after 1080 minutes. However no Pb breakthrough was observed within the service life of the column demonstrating the zeolite’s affinity for Pb removal. Scanning electron microscopy (SEM) revealed extensively damaged and dead E. coli cells and bacterial synthesis of nano- and micro-sized silver particles in response to toxic silver ions. Furthermore, the potential for silver recovery in NZ columns was examined. This study demonstrated the potential of SZ for the simultaneous removal of bacteria and heavy metals from contaminated aqueous streams