Simultaneous compliance needs for the Stage 2 Disinfection Byproducts (DBPs) and Long-term
Surface Water Treatment (LT2) Rule is prompting many utilities in central Arizona valley and its
surrounding cities to explore additional DBP precursor removal beyond existing treatment
processes. The City of Glendale, Arizona, would like to improve filter performance in terms of turbidity, organics, taste
and odor (T&O) and wants to meet Stage 2 DBP rule by using deep-bed granular activated carbon (GAC) filters for its
Cholla Water Treatment Plant (WTP), an alternative to the existing conventional shallower (i.e., anthracite/sand) media
filters. Many utilities within the valley have already implemented or are in the process of
implementing such filters. The City of Glendale
undertook 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 (measured
as 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., subfluidized
backwashing);
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-scale
implication. The Cholla
WTP pilot facility uses six 3" diameter columns (made from clear PVC pipe). Pilot columns
were designed to be deep-bed GAC filter, loaded with 60 inches (i.e., 5 feet) of virgin bituminous
media (EBCT of 9 minutes) and operated in two phases. In Phase I, the pilot was operated using
all six deep-bed GAC filters receiving plant settled (and/or chlorinated plant settled) water and
were operated for five months (July to November 2004) until the plant shut-down (December 2004
to February 2005). Phase II started after the plant restart (March 2005). Pilot was operated for
another 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 to
be effective in meeting the pilot goals. Two additional filters with the same operating conditions
were added during this phase with similar filter design and operating conditions but loaded with
fresh/virgin GAC media. The purpose of adding two additional new filters and operating them for
additional months was to replicate filter performance of Phase I, assess them under
different source water quality (i.e., higher influent turbidity and organics), and to
estimate GAC bed-life under enhanced coagulation (EC) mode (by lowering coagulation pH at
full-scale to the optimal pH levels of 6.8-6.9 with carbon-dioxide addition). The primary
objectives of these two phases (i.e., Phase I and Phase II) were to evaluate effectiveness of the
GAC filters and the expected bed-life of GAC in reducing DBPs level and improving finished
water quality. Includes reference, table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 18 |
| Published : | 11/01/2005 |
