Surface modification of fibrous filter media to enhance filtration efficiency

Fibrous filter media, including microporous polypropylene and microdenier polyester textile fabric, were modified with two types of surface coatings. The first type of modification involved the use of a cationic surfactant, dimethyldioctadecylammonium bromide (DDAB), to make the filter surface positively charged. Negatively charged nanoparticles and biological particles can then be filtered by utilizing the electrostatic interaction between the charged particles and the surfactants adsorbed on the filters. Filtration result for 60 nm negatively charged particles filtered through DDAB treated filter (0.65 $m$m) shows a significant increase in particle filtration efficiency. Filtration efficiency can be increased from 10% to 95% by using four layers of the filters. In the filtration of bacteria, the surfactant treated polyester textile fabric filters show improvements in the filter coefficient of 195% to 330%. In the filtration of bacteriophages, improvements in the filter coefficient for MS2 and PRD-1 are 3,270% and 2,830%, respectively, as compared to untreated filters, while the improvement for $F$X-174 is only 98%. Filtration efficiency or filter coefficient calculations are based on the number of viable microorganisms before and after filtration.; The second type of filter modification utilized metal oxides/hydroxides to change the properties of the filters. Three various iron oxides (goethite, haematite and magnetite) were successfully coated on polyester filters by carefully controlling the reaction conditions. Combinations of iron oxide and aluminum oxide were also used to modify the filters. The metal oxide coated polyester filters have zeta potentials which are more positive than the untreated filters. The wettability of the metal oxide coated filters also increased, leading to lower pressure drops across the filters. The filter coefficients of the iron oxide coated filters show improvements of 22% to 60% in the filtration of bacteria. In the filtration of bacteriophages, goethite has the highest filtration efficiency in filtration of MS2 and PRD-1. Phage $F$X-174 has a very strong affinity for the iron oxide treated surfaces. The mixed iron and aluminum oxide coated filters were more effective than the iron oxide coated filters in the removal of both bacteria and bacteriophages, but they are not as effective as the surfactant treated filters.