Granular filter media used in chemical clarification treatment practicing "sweep floc"
coagulation will acquire metal surface coatings on the filter media over extended periods
of time. In essence, the metal hydroxide floc carryover from the settling tanks and the
aging of these hydroxide floc on the filter media over years of exposure have resulted in
a durable metal-oxide coating on filter media that can be conducive for enhanced NOM
and arsenic adsorption over the entire filter run cycle. The objective of this overall study
was to quantify natural organic matter (NOM) and arsenic removal using naturally coated
sands from conventional rapid rate filters. The major research goals of this paper
were to evaluate dissolved organic carbon (DOC) and ultraviolet (UV) adsorbance (254 nm) as a
function of metal surface coating (i.e. aluminum-based vs. iron-based), pH of
regenerating filter media backwash (BW) solution, pH of the influent NOM challenge
solution, and challenge water quality.
Preliminary results indicate that DOC and UV absorbance removals were significantly
enhanced with increasing BW regeneration pH (up to pH 10-12) and lower challenge
solution pH. Increasing the pH to 13 resulted in a significant loss of the aluminum
coating and a corresponding decrease in DOC removal. The influent challenge solution
pH had an important impact on DOC removal efficiency. The BW regeneration was
maintained 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 decreasing
pH. At run termination at the lower pHs, DOC removals were at least as comparable if
not exceeding removals noted using commercially available iron-oxide coated sands. Includes 7 references.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 38 |
| Published : | 06/01/2007 |
