Full Description

In order tocomply with the impending Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR) and reduce disinfection byproduct (DBP) levels at the farends of their distribution systems, some utilities have already converted andmany are considering converting from free chlorine to chloramines forsecondary disinfection.For many utilities, the addition of ammonia to water with a free chlorineresidual to form chloramines is an automated process. Traditionally, utilitieshave programmed their control systems so that the amount of ammonia beingadded depends on flow, free chlorine residual, and a set chlorine to ammoniaratio. However, this approach to dose control can lead tofluctuations in finished water free ammonia levels if the free chlorine residualin the finished water fluctuates. The risk of over or underfeeding that exists with the traditional ammonia feedcontrol approach can be reduced by an ammonia feed control approach that isbased on achieving a fixed excess free ammonia residual level. This approachwill allow a consistent excess free ammonia residual level to be maintainedduring fluctuations of the chlorine residual. The key to the approach is thatthe calculation of the required ammonia dose is based on a set free ammonialevel, while the chlorine to ammonia-nitrogen ratio is allowed to vary. Thisapproach does not require the measurement of free ammonia levels in thewater, thus avoiding the need to measure excess free ammonia levels forprocess control.

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Edition: Vol. - No. Published: 09/01/2005 Number of Pages: 3File Size: 1 file , 210 KB