Improved Virus Removal in Ceramic Depth Filters Modified with MgO

Abstract

Ceramic filters, working on the depth filtration principle, are known to improve drinking water quality by removing human pathogenic microorganisms from contaminated water. However, these microfilters show no sufficient barrier for viruses having diameters down to 20 nm. Recently, it was shown that the addition of positively charged materials, for example, iron oxyhydroxide, can improve virus removal by adsorption mechanisms. In this work, we modified a common ceramic filter based on diatomaceous earth by introducing a novel virus adsorbent material, magnesium oxyhydroxide, into the filter matrix. Such filters showed an improved removal of about 4-log in regard to bacteriophages MS2 and PhiX174. This is explained with the electrostatic enhanced adsorption approach that is the favorable adsorption of negatively charged viruses onto positively charged patches in an otherwise negatively charged filter matrix. Furthermore, we provide theoretical evidence applying calculations according to Derjaguin-Landau-Verwey-Overbeek theory to strengthen our experimental results. However, modified filters showed a significant variance in virus removal efficiency over the course of long-term filtration experiments with virus removal increasing with filter operation time (or filter aging). This is explained by transformational changes of MgO in the filter upon contact with water. It also demonstrates that filter history is of great concern when filters working on the adsorption principles are evaluated in regard to their retention performance as their surface characteristics may alter with use.

Production of ceramic membranes with different pore sizes for virus retention

“…MgO-doped, colloidal zirconia) are applied for virus adsorption to enhance the virus titre reduction. [21][22][23] Today, polymeric membranes possess high water permeate fluxes combined with required high virus retention levels [24,25]. Compared to polymeric membranes, ceramic membranes show excellent chemical, thermal and mechanical stability.…”

Biosensors for waterborne viruses: Detection and removal

“…These contaminants may either adsorb to the viruses or compete with them for adsorption sites on the filtration surface. A wide variety of materials have been studied as adsorption surfaces such as hematite, ceramic modified materials, clays, activated carbon, and metal oxides/hydroxides [32][33][34][35]. All of these materials have been successfully incorporation in filters to remove viruses from water.…”

“…A key point to consider when designing novel filtration methods is the design of filter coating methods in order to lower the required energy for filtration, as well as regenerate the adsorption surfaces [36]. Hence, filters have also been successfully modified with materials such as magnetite, silver, magnesium oxide and hydrophilic polymers [35][36][37][38]. Ceramic water filters which are based on size exclusion have becoming a point-of-use method of contaminant filtration for household use.…”

“…Even though many of these filters are treated with silver to aid in the inactivation of bacteria [39], they have been reported to shown low viruses removal rate when tested with bacteriophage MS2, since the results were below the WHOs removal targets [39]. However, by implementing magnesium oxide as a positive adsorption surface into ceramic depth filters an improvement in virus removal was observed [35]. Using a filter with a 20% MgO was reported to have greater than log 4 virus retention (>99.99%) after 10 L of water had passed through the filter, but only log 2.5 virus retention after 200 L of the test water had passed through.…”

Development of improved low-cost ceramic water filters for viral removal in the Haitian context

“…Moreover, ceramic depth filters with added Magnesium Oxide (MgO) showed an improved viral removal, 102 however, the experiments presented high variability in performance with filter operation time, being 103 discarded for drinking water production (Benjamin Michen et al 2013 important in virus-media adsorption and inactivation. It also has been described in the context that firing 106 ceramics in reductive atmosphere has an effect on the surface charge of the piece and therefore can have an 107 effect on viral retention (Wegmann, Michen, and Graule 2008).…”