VIRUS REMOVAL BY SLOW SAND FILTRATION AND NANOFILTRATION

Water utilities, especially smaller ones, are having increasing difficulties proving increased treatment requirements required in the United States for the removal of chemical and microbial contaminates in drinking water. This project sought to evaluate the virus removal potential of combined slow sand filtration and nanofiltration by a pilot plant for application to a small utility which uses a surface water supply. Nanofiltration is a relatively new water treatment technology which has become available since 1986. It is similar to reverse osmosis but has a higher molecular weight cut-off and is less costly to operate. The bacteriophages MS-2 (28 nm) and PRD-1 (65 nm) were seeded into surface water entering a pilot plant and samples collected after sand filtration, nanofiltration, and of the nanofilter reject water. These phages were selected for study because of their small size and poor adsorption to surfaces. The slow sand filter removed 99% of the MS-2 and 99.9% of the PRD-1. There was between a 4 to 6 log reduction of the phages by the nanofilters. PRD-1 was removed to a greater extent than MS-2 by both the sand filter and the nanofilters.