Slow Sand/Nanofiltration of Surface Water

Abstract

Introduction: Through the studies published in Drinking Water and Health (1977) the nation has become more aware of the carcinogenic nature of the byproducts of disinfection such as trihalomethanes. Trihalomethanes are formed when the disinfectant chlorine reacts with the precursors, humic and fluvic acids that are naturally occuring in all surface water. The Environmental Protection Agency (EPA) has set a minimum contaminent level of 100 ppb on THM's that many in the health agencies feel need to be lowered. The problem is that when the MCL's are lowered utilities will be enclined to chlorimines and chloride dioxide which have been found to be mutagenic. Drinking Water and Health (1987) found the Suggested No-Adverse Response Levels (SNARLs) for chioramines for a child is 0.166 ppm, for an adult it is 0.581. The SNARL for chlorine dioxide is 0.06 ppm for a child and 0.210 ppm for an adult. These levels for utilities are virtually impossible to maintain and still have a residual at the end of the system.