Evaluation of a field appropriate membrane filtration method for the detection of Vibrio cholerae for the measurement of biosand filter performance in the Artibonite Valley, Haiti.
Biosand filters in the Artibonite Valley of Haiti, the epicenter of the cholera epidemic that began in October 2010, were tested for total coliform and Vibrio cholerae removal efficiencies. While coliform are often used as an indicator organism for pathogenic bacteria, a correlation has never been established linking the concentration of coliform and V. cholerae, the causative agent for cholera. Hence, a method for field enumeration of V. cholerae was developed and tested. To this end, a plate count test utilizing membrane filtration technique was developed to measure viable V. cholerae cell concentration in the field. Method accuracy was confirmed by comparing plate count concentrations to microscopic counts. Additionally, biosand filters were sampled and removal efficiencies of V. cholerae and coliform bacteria compared. The correlation between removal efficiency and time in operation, biofilm ("schmutzdecke") composition, and idle time was also investigated. The plate count method for V. cholerae was found to accurately reflect microscope counts and was shown to be effective in the field. Overall, coliform concentration was not an appropriate indicator of V. cholerae concentration. In 90% of the influent samples from the study, coliform underestimated V. cholerae concentration (n = 26). Furthermore, coliform removal efficiency was higher than for V. cholerae hence providing a conservative measurement. Finally, time in operation and idle time were found to be important parameters controlling performance. Overall, this method shows promise for field applications and should be expanded to additional studies to confirm its efficacy to test for V. cholerae in various source waters.
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