This paper illustrates the effects of coagulant residuals from conventional pretreatment
(rapid mix, flocculation, sedimentation, and dual-media filtration) on polyamide reverse
osmosis (RO) membrane performance. Testing included experiments with aluminum
sulfate (alum), aluminum chlorohydrate (ACH), and ferric chloride coagulants, various
coagulant aids (cationic, anionic, and nonionic organic polymers), free and total chlorine,
and phosphonate- and polycarboxylic acid-based antiscalants. Results indicate that
aluminum residuals, most notably from alum coagulation, caused colloidal fouling of RO
membranes through interactions with ambient silica to form aluminum silicates, and
antiscalant components. Furthermore, elevated aluminum hindered antiscalant
efficacy used to mitigate sulfate-based precipitates. While ferric chloride coagulation
greatly reduced colloidal fouling propensity, the corrosive nature of Fe (III) may attack
uncathodically protected metals, leading to enhanced polyamide membrane oxidation in
the presence of chloramines by liberated Fe (II) ions. Similar to ferric chloride, ACH
minimized colloidal fouling and potentially minimized aluminum-antiscalant interactions.
However, membrane performance data suggested that ACH-pretreatment conditions may
also facilitate enhanced oxidation reactions on the polyamide membrane surface. Includes 30 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 920 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 15 |
| Published : | 06/17/2004 |
