AWWA WQTC62533

The impending Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR)is focused on limiting disinfection byproducts (DBPs) to acceptable levels throughoutthe entire distribution system. In order to comply with the impending Stage 2 DBPR andreduce DBP levels at the far ends of their distribution systems, some utilities have alreadyconverted and many are considering converting from free chlorine to chloramines forsecondary disinfection.For many utilities, the addition of ammonia to water with a free chlorine residual to formchloramines is an automated process. Traditionally, utilities have programmed theircontrol systems so that the amount of ammonia being added depends on flow, freechlorine residual, and a set chlorine to ammonia ratio. Chlorine reacts with ammonia inthe stoichiometric mass ratio of 4.2:1, equivalent to chlorine to ammonia-nitrogen massratio of 5.1:1. The traditional approach is to add ammonia at a chlorine to ammonia ratioless than 4.2:1 so that some excess free ammonia remains in the water after the formationof chloramines. However, this approach to dose control can lead to fluctuations infinished water free ammonia levels if the free chlorine residual in the finished waterfluctuates. This paper provides tables comparing three approaches to dose control: resulting excess free ammonia using traditional ammonia dose controlapproach; resulting excess free ammonia using new ammonia dose controlapproach; and, example operator inputs and supervisory control and data acquisition (SCADA) outputs for new chlorineand ammonia feed control approach. Includes tables.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

4

File Size:

1 file , 160 KB