AWWA WQTC65846

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) establishedguidelines for Cryptosporidium inactivation credit with ozonation. In order to meetthese requirements, drinking water utilities may have to employ a bromate mitigationtechnique to comply with the Stage 1 Disinfectant/Disinfection Byproducts Rule,which established a maximum contaminant level (MCL) of 10 µg/L for bromate. In2000, the Southern Nevada Water Authority (SNWA) and Black & Veatch initiated pilot plantstudies investigating the effect of various pretreatment strategies to control bromateformation. Results showed that the use of prechlorine followed by preammoniareduced bromate formation by 65-95% compared to no mitigation technique. Theprocess controls bromate formation by preoxidizing bromide to hypobromous acid,which then reacts with ammonia to form bromamine. Bromamines sequester thebromide through the ozone contactor reducing the formation of bromate. In thefollowing years, ammonia feed facilities were designed and constructed to implementthis process at full-scale. In 2006, the SNWA began using the pretreatment techniqueat the 300 MGD River Mountains Water Treatment Facility. A 90-day evaluationdemonstrated that the chlorine-ammonia (Cl2-NH3) process could maintain bromate concentrations below the MCL. In addition, the Cl2-NH3 process allowed a threefoldincrease in CT while still meeting the MCL. This pretreatment technique offersutilities another pretreatment alternative to control the formation of bromate. Includes 6 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2007

Number of Pages:

6

File Size:

1 file , 160 KB