AWWA ACE65184

When the reduced maximum contaminant level (MCL) of the new arsenic rule went into effect in early 2006, many waterpurveyors were forced to take actions to meet the new arsenic rule. For water that alsocontains other containments exceeding the primary MCL or secondary standard, simultaneouscompliance could be very costly. The objective of this project was to determine the most costeffective approach that removes arsenic and excess fluoride from groundwater.Coyote Springs Development area is a master planned community north of Las Vegas NV thatwill use groundwater wells as its only potable water source. A 4,000 gpm water treatment plantis designed for the first phase of the development. The two source water wells contain 14 µg/Lof arsenic and 2.1 mg/L of fluoride, exceeding the respective primary and secondary standardfor these two elements. The mandatory fluoride limit in Nevada is set at 2.0 mg/L. This paper presents results from pilot scale tests conducted to achieve simultaneous compliance withthe arsenic and fluoride standards. Activated alumina (AA) is the U.S. Environmental Protection Agency (USEPA) designated best availabletechnology (BAT) for arsenic and fluoride removal. However, bench-scale evaluation indicatedthat although AA can remove both arsenic and fluoride, its bed life is rather short, especially forfluoride removal. Although iron based adsorptive media has a much longer bed life for arsenicremoval compared with AA, it can not remove fluoride. Therefore, an additional unit processmust be added for fluoride removal if iron based adsorptive media is selected for arsenicremoval. Pilot test conducted on site using the same water with a proprietary filter mediademonstrated that coagulation filtration with ferric chloride can reduce arsenic by over 90percent at a dose of 1 mg/L, much lower than demonstrated by bench test and those reportedin literature. Pilot tests were conducted to determine the optimum dose for simultaneousremoval for both arsenic and fluoride as well as to investigate potential additional arsenicremoval mechanisms associated with the proprietary filter media. Results of these pilot testsindicated that: the proprietary media has adsorption capacity for arsenic and will result inover estimated arsenic removal by coagulation/filtration if the adsorptive capacity is not takinginto consideration; simultaneous removal of arsenic and fluoride can be achieved bycoagulation/filtration with a mixture of ferric and alum or with alum alone; and, the optimum dosefor simultaneous removal of arsenic and fluoride for the Coyote Springs source water isdetermined to be 7.5 ppm alum. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2007

Number of Pages:

17

File Size:

1 file