AWWA ACE61821

The Mills Filtration Plant in Riverside, California experienced consumer complaints frommanganese (Mn) after installing pre-ozonation followed by biologically active filtration. Testresults indicated that Mn, deposited after multiple years of using Mn-containing ferricchloride (FeCl₃) for coagulation, leached from the plant filter media. Using FeCl₃ withoutfilter chlorination, soluble Mn was released at a maximum concentration of 105 µg/L and tookapproximately 2.5 weeks to fall below 50 µg/L, the U.S. Environmental Protection Agency (USEPA) secondary standard for Mn.Core samples of the tri-media filter before and after the test revealed that only the anthracite-associatedMn was removed (74 percent) from the filter. Pretreatment with alum coagulationshowed a more muted release curve (maximum 27 µg/L Mn) over ferric chloride coagulation.By modulating the number of non-chlorinated filters within the plant, Mn was successfully bledfrom the filters and the filters were allowed to go biological. However, elevated turbidity andparticle counts at the plant effluent limited the "controlled-release" option's usefulness.Chemical cleaning of the filter media only removed Mn from the anthracite coal layer (>94%),less so for the sand (~ 40%), and was ineffective on the hematite layer. Polyphosphatessuccessfully sequestered soluble Mn up to 105 µg/L and 10 days of holding time. Ultimately,filter media replacement was recommended to avoid any further problems with Mn leaching from the filter media. Includes 24 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/17/2005

Number of Pages:

20

File Size:

1 file , 1.9 MB