Laboratory efficacy of locally manufactured ceramic water filters in removing Vibrio cholerae

Abstract

Locally-manufactured ceramic water filters (CWFs) remove Escherichia coli via physical screening, physicochemical mechanisms, and disinfection; performance varies across local production. It was unknown whether CWFs remove Vibrio cholerae, the (smaller and metabolically different than E. coli) bacteria causing cholera. To fill this gap, we tested hydraulic and microbiological (V. cholerae and E. coli) performance of eight different CWFs (in duplicate) produced by established factories in the laboratory for three consecutive days. Four CWFs were silver-impregnated. Across all filters, average Log Reduction Values (LRV) were 1.9–5.7 for V. cholerae and 2.9–7.0 for E. coli on day 1. V. cholerae LRVs were 5.3–5.6 for silver-impregnated filters, and 1.9–4.3 for non-impregnated filters; E. coli LRVs were 5.1–7.0 for silver-impregnated and 2.9–4.0 for non-impregnated filters. The correlation between E. coli and V. cholerae LRVs was non-linear (R² = 0.003–0.24) for silver-impregnated filters, and linear (R² = 0.23–0.81) for non-impregnated filters. Our results highlight: 1) high variability in CWF performance; 2) silver disinfection as the most critical mechanism to remove V. cholerae; 3) CWFs can be used in cholera outbreak settings to remove V. cholerae, if silver remains on the filter; and, 4) assessing filter microbiological performance with specific organisms of interest, not only reference organisms, may be necessary.