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

Abstract

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 (R2 = 0.38, p < 0.010); (2) there is not a strong association between flow rate and first, average, or last LRV results (R2 = 0.17, p = 0.090; R2 = 0.30, p = 0.020; R2 = 0.24, p = 0.040); and (3) first and average LRV are associated with burn-out material (R2 = 0.68, p < 0.001; R2 = 0.60, p < 0.001), and last LRV is associated with burn-out material and mesh size (R2 = 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.

Mechanisms and efficacy of disinfection in ceramic water filters: A critical review

“…Rayner et al (2017) conducted a comprehensive study on the impacts of firing material ratios, and their data was also inconclusive as to its impacts on bacteria removal. For example, disks with a sawdust particle size range of 0.250 mm -0.595 mm and material ratios of 13.7%, 17% and 24% sawdust (by weight) yielded average LRV of 2.06 ± 1.33, 4.00 ± 0.285 and 2.78 ± 0.156 which shows no trend (Rayner et al, 2017). Similarly variable results are found when the researchers tested filters with material ratios (by weight) of 18%, 19% and 25% milled rice husks of the same size range, yielding average LRVs of 1.93 ± 0.110, 1.26 ± 0.166 and 1.26 ± 0.097 (Rayner et al, 2017).…”

“…For example, disks with a sawdust particle size range of 0.250 mm -0.595 mm and material ratios of 13.7%, 17% and 24% sawdust (by weight) yielded average LRV of 2.06 ± 1.33, 4.00 ± 0.285 and 2.78 ± 0.156 which shows no trend (Rayner et al, 2017). Similarly variable results are found when the researchers tested filters with material ratios (by weight) of 18%, 19% and 25% milled rice husks of the same size range, yielding average LRVs of 1.93 ± 0.110, 1.26 ± 0.166 and 1.26 ± 0.097 (Rayner et al, 2017). These findings illustrate that material ratios, regardless of the FM, are not controlling this filter performance metric.…”

“…Other manufacturing parameters are, however, easier to manipulate, and have been shown to closely relate with pore size and porosity (Rayner et al, 2017;Yakub et al, 2013). Specifically, the most commonly discussed CWF characteristics that impact microbe removal are material ratios, firing material particle size, filter thickness and final firing temperature, which are further discussed in this section.…”

“…Size exclusion is the dominant mechanism for bacterial removal in a CWF, meaning filter performance is closely tied with pore size and porosity (Rayner et al, 2017). Therefore, differences in the material parameters that lead to filter pore size and porosity also greatly impact filter performance.…”

Development of Ceramic Water Filter Clay Selection Criteria

“…The clay that is usually used in studies about CWF manufacturing is actually clayey material (CM) because the term "clay" refers to soil particles under 2 µm in diameter and these studies usually use soil with a larger particle size [2,8,11,12]. CWFs are made from locally sourced CM and burnout material, which is usually sawdust or rice husks [2,13].…”