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

Abstract

Diarrheal illnesses claim the lives of hundreds of thousands of children each year, most of whom live in rural and low-income communities. Ceramic Water Filters (CWF) are widely regarded as one water treatment technology with the potential to increase access to safe drinking water. While physical filtration mechanisms are a key contributor to improving the water safety, silver is commonly added to improve disinfection performance. Therefore, a thorough review of silver disinfection efficacy and disinfection mechanisms in relation to CWFs are critically important. This paper reviews filter mechanisms and efficacy for bacteria removal for cases with and without silver addition. Method of silver application (dipping, painting, or co-firing) is assessed. Silver release and retention is discussed. The findings from this paper illustrate that eluted silver contributes to filter bacterial disinfection. However, more research is needed on the impact of silver on preventing a "slime layer" on the filter surface and receptacle. Silver application method, water quality and particle characteristics were demonstrated to impact release. For instance, co-firing results in the most consistent elution over time but at lower concentrations than other methods. Finally, research into alternative metals to silver for enhanced disinfection present emerging opportunities within the CWF field.

Silver and zinc oxide nanoparticle disinfection in water treatment applications: synergy and water quality influences

“…Comparatively, when zinc is in isolation, these effects thus weaken the cells, but the rate of cell degradation may not be as high as when facilitated with the presence of other metals, as was found in this research. When metal combinations were added, cells became more vulnerable to attack from the silver present within the mixture, which may have (1) caused cell lysis directly by bonding with the cell membrane and causing pits, (2) penetrated the cell membrane and bonded directly with DNA in the cytoplasm, leading to degradation, and/or (3) reacted to create ROS, as shown in Reaction (1), which degraded the cells through oxidative killing (Venis & Basu 2020). As such, the improved disinfection observed with Ag 67 ZnO 33 in comparison to the other metal mixtures thus likely resulted Figure 4 | LRVs achieved after 300 min of mixing under each of the synthetic water quality conditions evaluated and detailed in Table 1; pH values of 6.4 (low pH), 7.4 (mid pH), and 8.6 (high pH) with high (.8.4 mg/L) and low (,2.5 mg/L) DO.…”

A review of the impact of testing conditions on the performance and quality control of locally manufactured, point-of-use ceramic water filters

“…In CWFs, microorganisms interact with the small, tortuous pores in the matrix of the ceramic filters. 5,50,67 Therefore, the volume and surface area of a microorganism impacts the interactions, and subsequent retention, within the ceramic matrix. 57,58 Previous studies have shown that changing the diameter of microbial surrogates (analogous to virus-, 0.02 μm, through protozoan-sized, 10 μm) changed the log removal of a CWF from 1.5 to 3.2.…”

“…Ceramic water filters (CWFs), a physical point-of-use (POU) drinking water treatment device, have been studied by many researchers. 1–5 CWFs are effective against a wide range of contaminants including bacteria, 6–10 organic and inorganic chemicals, 10 protozoa, 11 and viruses. 12–15 The reduction in pathogenic microorganisms has led to reductions in diarrheal rates ranging from 60–80% in Colombia, 7 South Africa, 6,16 Cambodia, 12,17–19 and other locations around the world.…”

Impact of low levels of silver, zinc and copper nanoparticles on bacterial removal and potential synergy in water treatment applications

“…CWFs are made of a mixture of clay and burn‐out materials (e.g. rice husks and sawdust) and often incorporate silver as nanoparticles (NPs) or nitrates 3 . CWFs are usually used in small groups or single families to treat water for drinking purposes.…”

“…Moreover, silver is expensive costing upwards of 1.66 USD g −1 for silver NPs (Argenol Laboratories, personal communication). Silver's relatively high cost significantly increases the total cost of a CWF, reducing its availability to target communities 3 . This raises the question as to the scope for using other metal NPs that may be obtained at a lower cost and that also display antimicrobial properties instead of, or in combination with, silver NPs.…”