Test of Nanofilter Method of Testing Recharged Municipal Effluent: Project Report

Abstract

Introduction: The nanofilter is a relatively new water treatment option that has been commercially available since 1986. The name nanofilter is used here as a generic name rather than a specific product name. There are at least five companies that make filter elements that can be classified as nanofilters (City of Ft. Myers, 1987). The nanofilter operates on a molecular scale and is related to reverse osmosis. Simply stated, this process treats water by forcing it through a porous membrane. The water molecules are able to pass through the membrane, as well as some of the smaller organic and inorganic molecules in the water. The larger organic and inorganic molecules are removed. The nanofilter will remove most of the dissolved solids (salinity) and hardness plus a large percentage of the dissolved organic matter including trihalomethanes (THM) precursors and essentially all of the bacteria and viruses. THM and TOX precursors are naturally occurring organics (humic and fluvic acids) that will produce THMs and organic halogens (TOX) (both are suspected carcinogens) when disinfectants such as chlorine or chloramines are added to the water. Nanofiltration has a built in safety feature in that the membrane compresses slightly as it ages which produces even better quality of water over time. In contrast activated charcoal has to be continously monitored to make sure its absorption capacity has not been used up, the quality of water deteriates over time. Nanofiltration, sometimes called membrane softening, is designed to be used for water containing 300-1200 ppm salinity. Muncipal effluent in Arizona generally has 600 to 1200 ppm salinity so this process should work well. It is particularly effective in removing dissolved organics, virus, bacteria and parasitic protozoans. The nanofilter is being used in several Florida locations. The City of Fort Myers in Florida is presently constructing the largest of these facilities, a 20 million gallon per day plant (City of Ft Myers, 1987).