Improved virus removal in ceramic depth filters modified with MgO.

Environmental science & technology (2013-01-05)
Benjamin Michen, Johannes Fritsch, Christos Aneziris, Thomas Graule
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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Magnesium oxide, ACS reagent, 97%
Sigma-Aldrich
Magnesium oxide, ≥99.99% trace metals basis
Sigma-Aldrich
Magnesium oxide, ≥99% trace metals basis, -325 mesh
Sigma-Aldrich
Magnesium oxide, nanopowder, ≤50 nm particle size (BET)
Sigma-Aldrich
Magnesium oxide, light, 95%
Sigma-Aldrich
Magnesium oxide, 99.99% trace metals basis
Sigma-Aldrich
Magnesium oxide, puriss., meets analytical specification of Ph. Eur., BP, USP, FCC, E 530, light, 98.0-100.5% (calc. for dried substance)
Sigma-Aldrich
Magnesium oxide, tested according to Ph. Eur., heavy
Sigma-Aldrich
Magnesium oxide, (single crystal substrate), ≥99.9% trace metals basis, <100>, L × W × thickness 10 mm × 10 mm × 0.5 mm
Sigma-Aldrich
Magnesium oxide, BioUltra, ≥97.0% (calcined substance, KT)
Sigma-Aldrich
Magnesium oxide, puriss. p.a., ACS reagent, ≥97% (calcined substance, KT)
Sigma-Aldrich
Magnesium oxide, -10-+50 mesh, 98%