AWWA WQTC62427

Simultaneous compliance needs for the Stage 2 Disinfection Byproducts (DBPs) and Long-termSurface Water Treatment (LT2) Rule is prompting many utilities in central Arizona valley and itssurrounding cities to explore additional DBP precursor removal beyond existing treatmentprocesses. The City of Glendale, Arizona, would like to improve filter performance in terms of turbidity, organics, tasteand odor (T&O) and wants to meet Stage 2 DBP rule by using deep-bed granular activated carbon (GAC) filters for itsCholla Water Treatment Plant (WTP), an alternative to the existing conventional shallower (i.e., anthracite/sand) mediafilters. Many utilities within the valley have already implemented or are in the process ofimplementing such filters. The City of Glendaleundertook a pilot study at Cholla WTP in cooperation with Malcolm Pirnie Inc. to evaluate the deep-bed GAC filter. Some of the key objectives of the City of Glendale pilot testing were:to evaluate the effectiveness of deep-bed GAC filter for removing particulate (measuredas turbidity), organics (measured as UV254 and TOC), DBP precursors and T&O (i.e.,MIB, Geosmin and Cyclocitral) causing compounds;to determine the effect of air scoring for deep bed GAC filter;to minimize filter ripening period with alternative backwashing method (i.e., subfluidizedbackwashing);to evaluate the effect of chlorinated source water for deep-bed GAC filter;to evaluate the effect of chlorinated backwash water for deep bed GAC filter;to estimate media bed-life (before replacing or reactivating) with and without blending(i.e., staggered operation) while complying with the Stage-2 DBP Rule; and,to understand the overall benefit and challenges of deep-bed GAC filters and full-scaleimplication. The ChollaWTP pilot facility uses six 3" diameter columns (made from clear PVC pipe). Pilot columnswere designed to be deep-bed GAC filter, loaded with 60 inches (i.e., 5 feet) of virgin bituminousmedia (EBCT of 9 minutes) and operated in two phases. In Phase I, the pilot was operated usingall six deep-bed GAC filters receiving plant settled (and/or chlorinated plant settled) water andwere operated for five months (July to November 2004) until the plant shut-down (December 2004to February 2005). Phase II started after the plant restart (March 2005). Pilot was operated foranother four and half months (March 2005 to July 2005) using four filters.Among the four filters used during Phase II, two were continued from Phase I that was proven tobe effective in meeting the pilot goals. Two additional filters with the same operating conditionswere added during this phase with similar filter design and operating conditions but loaded withfresh/virgin GAC media. The purpose of adding two additional new filters and operating them foradditional months was to replicate filter performance of Phase I, assess them underdifferent source water quality (i.e., higher influent turbidity and organics), and toestimate GAC bed-life under enhanced coagulation (EC) mode (by lowering coagulation pH atfull-scale to the optimal pH levels of 6.8-6.9 with carbon-dioxide addition). The primaryobjectives of these two phases (i.e., Phase I and Phase II) were to evaluate effectiveness of theGAC filters and the expected bed-life of GAC in reducing DBPs level and improving finishedwater quality. Includes reference, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

18

File Size:

1 file , 1.5 MB