Full Description

The City of Phoenix (City) developed the Water Quality Master Plan Update (WQMPU) in 2005to identify future treatment requirements and improvements needed to comply with theupcoming Stage 2 Disinfectants/ Disinfection Byproducts (D/DBP) Rule. Based on modelingthe distribution system using the worst source water quality and with all Water Treatment Plants(WTPs) practicing enhanced coagulation, the WQMPU estimated the total trihalomethane(TTHM) concentrations to be higher than the MCL in certain areas of the City. A variety oftreatment alternatives were evaluated and enhanced coagulation followed by granular activatedcarbon (GAC) filter adsorbers was recommended for reducing distribution system DBPconditions.Since January of 2005, the source waters for the City WTPs have shown elevated levels of totalorganic carbon (TOC), thereby increasing TTHM formation in the distribution system. This hasled to the concern that enhanced coagulation and GAC filter adsorbers by themselves may notbe sufficient for compliance with Stage 2 DBPR requirements.The objective of this study was to consider available options for further enhancing DBP controland to develop a road map for the process changes at the City's WTPs. A bench-scale testingprogram was undertaken to evaluate several technologies in conjunction with enhancedcoagulation and determine the appropriate pretreatment technology for lowering DBPconcentrations and for extending GAC media life. The study was also used to develop designcriteria for these technologies and determine expected GAC reactivation frequencies undervarious raw water quality conditions. Jar testing was performed to screen the technologies andidentify appropriate design (dose, contact time, etc.) conditions. SDS testing was performed onthe filtered water to determine the DBP formation potential of water treated with thesetechnologies. Includes tables, figures.

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Edition: Vol. - No. Published: 11/01/2008 Number of Pages: 12File Size: 1 file , 860 KB