AWWA WQTC62422

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 wasconducted to assist the City of Peoria in meeting the new Arsenic maximum contaminant level (MCL) of10 µg/L. By improving Arsenic removal at the Greenway WTP, the finished water was used toblend with high Arsenic well water. One solution that was used to lower Arsenic concentrations in waterdelivered 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 lowArsenic source for the City of Peoria was surface water supplied by Salt River Project (SRP). Peoria treatsthis water through the Greenway WTP located at the end of the Arizona Canal. If the Greenway WTPwere to consistently deliver water with low Arsenic levels, the treated water could be used to blenddown 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 flowcontributed to the Arizona Canal from each source varies throughout the year and each surface watersource can be the primary contributor to flow. Raw water Arsenic concentrations at the Greenway WTPvary significantly based on source water contributions. The Salt River and CAP Canal consistentlyhad Arsenic concentrations less than 5-6 µg/L, but the Verde River water had Arsenic concentrationsthat varied from 8 µg/L to 18 µg/L. Significant contributions of Verde River water requiredimproved Arsenic reduction in the Greenway WTP in order for blending to be feasible. Currently theGreenway WTP removes only 10 - 20% of the raw water Arsenic.City of Peoria Utilities Department engaged the services of Damon S. Williams Associates (DSWA) toprovide options for dealing with the varying Arsenic levels from the multiple water sources and toprovide options and recommendations for the treatment facility to meet future drinking water regulationsat a cost effective price. In order to assess the possibility of improved Arsenic removal, a bench scaleevaluation was performed. Testing was conducted on the three surface water sources that contributeflow to the Arizona canal: the Salt Rive; Verde River; and, CAP Canal. Two coagulants, FerricChloride (Ferric) and Aluminum Sulfate (Alum), were tested at a range of coagulant doses and underthree pH conditions. The affect of ozone preoxidiation, which is currently employed at the GreenwayWTP, was also tested. TOC removal was evaluated for all tests to ensure continued compliance with theDisinfection Byproducts Rule and associated Surface Water Treatment Rules.In general, testing results showed increasing Arsenic removal performance with increasing coagulantdose 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 trueregardless of the source water tested. It appears that with proper system design and operation, theGreenway WTP finished water can be used as a source for blending with high Arsenic well water. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

18

File Size:

1 file , 1.1 MB