AWWA WQTC55180

This paper presents results from a pilot study conducted by the City of Durham, North Carolina, that evaluated an immediate ozonation process for inactivation of Cryptosporidium and its impact on subsequent filtration processes. The source waters have a raw water total organic carbon (TOC) level ranging from 4 to 10 mg/L, and are subject to moderate levels of iron and manganese on a seasonal basis. Values of CT required for inactivation of Cryptosporidium were estimated to be 10 times the CT values required for inactivation of Giardia based on values published by USEPA under the Surface Water Treatment Rule. The the use of high-dose intermediate ozonation to provide Cryptosporidium CT levels comparable to 1 to 2 log inactivation showed significant increases in pre-filter turbidity. Turbidity increases through the contactors were on the order of 2 to 4 times the settled water turbidity (i.e. from 1.0 NTU to 3.0 NTU). This phenomenon was observed to be more pronounced with alum than for ferric chloride. Optimal TOC removal for these coagulants ranged from 5.5 to 6.5. Raw water oxidant addition with permanganate did not diminish the turbidity effect. Lower ozone dose did not show the significant turbidity effect of higher dose. The increase in turbidity, or the ozone-induced particle formation, resulted in shorter filter runs and higher filtered turbidity. The analysis of Mn data supported that the turbidity increase is linked to the formation of solid-phase manganese, but not completely. Organics or other constituents also contribute. Manganese could not be consistently controlled with intermediate ozone and biological filters. Both biological carbon and anthracite were evaluated. Chlorination on the top of an anthracite filter in either dual or single stage filtration proved to be an effective way to control manganese with intermediate ozone. Includes 12 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

01/01/2001

Number of Pages:

16

File Size:

1 file , 530 KB