A Review for Potential Applications of Zeolite-Based Nanocomposites in Removal of Heavy Metals and Escherichia coli from Drinking Water

Water resources get contaminated with heavy metals and Escherichia coli (E. coli), among others due to human activities such as industrialization, municipal waste and agricultural production. The central water treatment processes such as coagulation and flocculation are no longer sufficient to remove these contaminants to acceptable levels by water standards. Additional treatment processes involving nanomaterials such as carbon nanotubes, graphene, metal oxides and zeolite nanocomposites have been reported with varying levels of efficacy. Zeolite nanocomposites are preferred for removal of water contaminants because of their chemical and physical stability at comparably low cost. In this work, adsorptive capacities for nanomaterials, possibilities of application of zeolite-nanocomposites and mechanisms for removal of heavy metals and disinfection of water are reviewed. The review shows that zeolite/Zinc oxide nanocomposite has removal efficiency of 93 and 89% for Lead II ions and Arsenic (V) respectively from water for an initial concentration ranging between 20 and 100 mg/L. Silver nanoparticles/zeolite nanocomposites have antibacterial efficiency approximating to 100% for removal of E. coli hence can be used for water disinfection. Zeolite/Iron (IV) oxide composite exhibit higher efficiency for Pb (97.2%) compared to As (96.8%) due to large surface area, more active sites and high porosity. Zeolite/Zinc oxide releases Zn2+ ions that damage the outer cell membrane and penetrate the intracellular content for E. coli hence causing osmotic imbalance leading to bacterial death. For effective removal of heavy metals from water using zeolite composites, the accompanying factors are; pH of 2-6, initial concentrations of metal ions not exceeding 100 mg/L, contact time varying between 0.5-24 h and temperature can be varied with an increment of 5 degrees C from 10 degrees C. Zeolite composites mixed with titanium dioxide, zinc oxide and polypropylene have good adsorption capacities. These however are limited by poor reusability and production of huge toxic waste. Silver nanoparticles/zeolite nanocomposite are better and sustainable.