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Silver / zeolite nano composite-based clay filters for water disinfection
Expanded Title:People who do not receive a supply of treated potable water rely on natural groundwater or surface water resources which in the absence of sanitation systems are often contaminated with pathogenic micro-organisms of faecal or other origin. They collect water which they then either use untreated or may treat with a disinfectant, but even disinfected water often becomes recontaminated while stored in the home. Point of use (POU; i.e. household) treatment devices which are simple, affordable and easy for the householders to use offer the most potential to minimise the risks of waterborne disease in such situations. Clay or ceramic filters for POU water treatment have been available since the 1980s and their efficacy has been investigated. However, such studies usually assess filters that are produced commercially and are beyond the budget of the intended end users, prompting other workers (e.g. the Potters for Peace organisation) to investigate filters which employ local people and locally available materials in their fabrication. Petrik et al. applied the Potters for Peace principles of local manufacture and the well-understood antimicrobial properties of silver in such pots to develop manufacturing and silver ENM impregnation methods suited to local zeolites. The antimicrobial activity of silver depends on the concentration of the silver ion. AgNO3 has been used in medicine because it dissociates readily, releasing free Ag+ ions and the antimicrobial effects of colloidal and nano silver occur because of their oxidative properties when releasing Ag+. Petrik and co-workers are investigating the potential for South Africans to use the abundant waste material of coal fly-ash and locally quarried zeolites in pot manufacture. Silver nanoparticles were loaded onto natural zeolite clinoptilolite and zeolites synthesized from coal fly ash by cation exchange and wet impregnation. The Ag-zeolite nano composite was then mixed with clays that are used to make ceramic filters. The mixture was finally used to make ceramic filters with Ag-zeolite nanocomposite and the disinfection properties of the resultant filter were assessed at different flow rates using indicator organisms (Escherichia coli). Only the aqueous leachates of the non-reduced Ag/clinoptilolite presented an antibacterial effect, and this was in relation to the concentration of silver leached out into the water. The aqueous leachates of the reduced Ag/clinoptilolite did not present an antibacterial effect or presented only a slight antibacterial effect because the reduced silver did not leach into the water. This indicated that there was no silver residual in the water after contact with the silver loaded zeolite which is positive in terms of minimal ingestion of silver by the water users and release to the environment. Natural, acid treated zeolites could retard the excessive leaching of silver into solution whilst still giving an antimicrobial effect, when using wet impregnation as silver loading technique and reduction of silver salts using ascorbic acid. High loadings of silver could be supported stably on the zeolite. The treated water had a level of residual silver well below the WHO target thus would be safe for ingestion. The study also showed that clay pots could have zeolite incorporated to 50% without losing strength and porosity and thus flow could be tailored using milled grape residues.
Date Published:07/08/2012
Document Type:Research Report
Document Subjects:Sanitation - Hygiene
Document Format:Report
Document File Type:pdf
Research Report Type:Consultant
WRC Report No:KV 297/12
ISBN No:978-1-4312-0306-2
Authors:Petrik L; Missengue R; Fatoba O ; Tuffin M; Sachs J
Project No:K8/987
Originator:WRC
Organizations:Chemistry Department of the University of the Western Cape; Biotechnology Department of the University of the Western Cape; SMME Red Seal
Document Size:2 103 KB
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