Rates of inactivation of waterborne coliphages by monochloramine

A sophisticated water quality monitoring program was established to evaluate virus removal through Denver's 1-million-gal (ca. 4-million-liter)/day Direct Potable Reuse Demonstration Plant. As a comparison point for the reuse demonstration plant, Denver's main water treatment facility was also monitored for coliphage organisms. Through the routine monitoring of the main plant, it was discovered that coliphage organisms were escaping the water treatment processes. Monochloramine residuals and contact times (CT values) required to achieve 99% inactivation were determined for coliphage organisms entering and leaving this conventional water treatment plant. The coliphage tested in the effluent waters had higher CT values on the average than those of the influent waters. CT values established for some of these coliphages suggest that monochloramine alone is not capable of removing 2 orders of magnitude of these specific organisms in a typical water treatment facility. Electron micrographs revealed one distinct type of phage capable of escaping the water treatment processes and three distinct types of phages in all.