AWWA ACE65313

Granular filter media used in chemical clarification treatment practicing "sweep floc"coagulation will acquire metal surface coatings on the filter media over extended periodsof time. In essence, the metal hydroxide floc carryover from the settling tanks and theaging of these hydroxide floc on the filter media over years of exposure have resulted ina durable metal-oxide coating on filter media that can be conducive for enhanced NOMand arsenic adsorption over the entire filter run cycle. The objective of this overall studywas to quantify natural organic matter (NOM) and arsenic removal using naturally coatedsands from conventional rapid rate filters. The major research goals of this paperwere to evaluate dissolved organic carbon (DOC) and ultraviolet (UV) adsorbance (254 nm) as afunction of metal surface coating (i.e. aluminum-based vs. iron-based), pH ofregenerating filter media backwash (BW) solution, pH of the influent NOM challengesolution, and challenge water quality.Preliminary results indicate that DOC and UV absorbance removals were significantlyenhanced with increasing BW regeneration pH (up to pH 10-12) and lower challengesolution pH. Increasing the pH to 13 resulted in a significant loss of the aluminumcoating and a corresponding decrease in DOC removal. The influent challenge solutionpH had an important impact on DOC removal efficiency. The BW regeneration wasmaintained at pH 11 during this phase while the influent pH was adjusted to 6, 5, and 4.DOC and UV absorbance removals were dramatically increased (>80%) with decreasingpH. At run termination at the lower pHs, DOC removals were at least as comparable ifnot exceeding removals noted using commercially available iron-oxide coated sands. Includes 7 references.

Product Details

Edition:

Vol. - No.

Published:

06/01/2007

Number of Pages:

38

File Size:

1 file , 1 MB