Field Evaluation of Locally Produced Silver-Impregnated Ceramic Filters for Point-Of-Use Water Purification in San Mateo Ixtatán, Guatemala

A recent study by Oyanedel-Craver and Smith (2008) has demonstrated that colloidal-silver impregnated ceramic filters (produced according to the manufacturing and design criteria of the non-governmental organization Potters for Peace) can effectively remove E. coli bacteria from water in laboratory tests. Herein, we extend this research to investigate the performance and social acceptance of ceramic filters in a controlled field study in San Mateo Ixtatán, Guatemala.Ceramic filters were manufactured in the community with local labor and materials and then treated with colloidal silver (which acts as a disinfectant). In August 2007, sixty families were chosen to participate in the study; thirty households received filters and minimal instruction in their use and maintenance. The head of each household was surveyed to collect basic educational, socioeconomic, and health data. In June 2008 a second survey was conducted to assess the level of satisfaction of filter use.Household unfiltered and filtered water samples were collected eight times – once in August 2007, January 2008, June 2008, August 2008, and four times in July 2008. Samples were tested for total coliform and E. coli bacteria using a membrane filtration/incubation method. After 10 months the filter effluents were also tested for colloidal silver leaching using a colorimetric method. An additional 32 filters were distributed in June 2008 and similarly monitored for five consecutive weeks. Over the course of the study, the average percent reduction in total coliforms and E. coli was 86.86% and 91.75%, respectively. The average effluent turbidity was 0.18 NTUs and average concentration of colloidal silver was 0.02 mg/L, well below the USEPA standard of 0.1mg/L.Ten percent of samples showed an increase in effluent bacteria concentration relative to influent concentration. This is likely caused by one or more of the following factors; 1) the unfiltered and filtered samples may have different starting concentrations of bacteria 2) potential flaws and/or variability in the manufacturing process, and 3) recontamination of filtered water due to improper handling.To determine the extent to which manufacturing variability affected filter performance, ten locally produced filters were tested daily for influent and effluent bacteria concentrations under ideal user conditions for 26 days. Average reduction in total coliform and E .coli bacteria improved by 4% to 90.90% and 95.72% with only 1.5% of samples showing an increase in effluent bacteria concentration.In a separate study of ten filters under both controlled conditions for 3 days and field conditions for three weeks, field percent removal remained high for E. coli (averaging 99.90%) while total coliform removal improved in seven out of ten households.Overall users were satisfied with the filters, citing them as easy to use and maintain while improving water quality. The most common benefit cited was improved health, specifically a reduction in both stomach pain and occurrence of diarrhea. The findings of this study suggest that ceramic filters can significantly improve the microbiological quality of water when used as a point-of-use water treatment technology.