This paper provides details on bench scale Arsenic removal testing performed at the City of Peoria,
Arizona, Greenway Water Treatment Plant (Greenway WTP). The work described herein was
conducted to assist the City of Peoria in meeting the new Arsenic maximum contaminant level (MCL) of
10 µg/L. By improving Arsenic removal at the Greenway WTP, the finished water was used to
blend with high Arsenic well water. One solution that was used to lower Arsenic concentrations in water
delivered to the drinking water distribution system was blending. In the development of a blending design,
it was necessary to secure a dependable, low Arsenic source water with which to blend. One possible low
Arsenic source for the City of Peoria was surface water supplied by Salt River Project (SRP). Peoria treats
this water through the Greenway WTP located at the end of the Arizona Canal. If the Greenway WTP
were to consistently deliver water with low Arsenic levels, the treated water could be used to blend
down the concentration at some high Arsenic wells.
SRP water primarily comes from the Salt River, Verde River, the Central Arizona Project (CAP) canal,
and SRP groundwater wells that operate based on canal system needs. The percentage of flow
contributed to the Arizona Canal from each source varies throughout the year and each surface water
source can be the primary contributor to flow. Raw water Arsenic concentrations at the Greenway WTP
vary significantly based on source water contributions. The Salt River and CAP Canal consistently
had Arsenic concentrations less than 5-6 µg/L, but the Verde River water had Arsenic concentrations
that varied from 8 µg/L to 18 µg/L. Significant contributions of Verde River water required
improved Arsenic reduction in the Greenway WTP in order for blending to be feasible. Currently the
Greenway WTP removes only 10 - 20% of the raw water Arsenic.
City of Peoria Utilities Department engaged the services of Damon S. Williams Associates (DSWA) to
provide options for dealing with the varying Arsenic levels from the multiple water sources and to
provide options and recommendations for the treatment facility to meet future drinking water regulations
at a cost effective price. In order to assess the possibility of improved Arsenic removal, a bench scale
evaluation was performed. Testing was conducted on the three surface water sources that contribute
flow to the Arizona canal: the Salt Rive; Verde River; and, CAP Canal. Two coagulants, Ferric
Chloride (Ferric) and Aluminum Sulfate (Alum), were tested at a range of coagulant doses and under
three pH conditions. The affect of ozone preoxidiation, which is currently employed at the Greenway
WTP, was also tested. TOC removal was evaluated for all tests to ensure continued compliance with the
Disinfection Byproducts Rule and associated Surface Water Treatment Rules.
In general, testing results showed increasing Arsenic removal performance with increasing coagulant
dose and decreasing pH. The bench scale testing showed that Ferric had markedly better Arsenic removal performance than Alum with the same equivalent metal dose. This trend appeared to be true
regardless of the source water tested. It appears that with proper system design and operation, the
Greenway WTP finished water can be used as a source for blending with high Arsenic well water. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.1 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 18 |
| Published : | 11/01/2005 |
