The effects of input materials on ceramic water filter efficacy for household drinking water treatment

Locally manufactured ceramic filters can improve drinking water quality and reduce diarrheal disease burden in developing countries; however, production methods and quality control protocols vary at the >50 factories. We manufactured filter disks with varied clay, burn-out material, burn-out material sieved with different mesh sizes, and burn-out material to clay ratios and calculated filter characteristics, including porosity, density, shrinkage, and flow rate. Water was run through filters daily for 4 weeks, and flow rate and Escherichia coli reduction, as measured by log reduction value (LRV), were tested twice weekly. Our results suggest: (1) the first and last LRV test results do not correlate strongly (R-2 = 0.38, p < 0.010); (2) there is not a strong association between flow rate and first, average, or last LRV results (R-2 = 0.17, p = 0.090; R-2 = 0.30, p = 0.020; R-2 = 0.24, p = 0.040); and (3) first and average LRV are associated with burn-out material (R-2 = 0.68, p < 0.001; R-2 = 0.60, p < 0.001), and last LRV is associated with burn-out material and mesh size (R-2 = 0.54, p < 0.050). Recommendations for filter factories, are to: (1) verify filtration efficacy with repeated bacteria reduction tests when materials, processing, or filter characteristics vary; (2) carefully control production variables; and (3) continue flow rate testing each filter to evaluate within and across batch production consistency.