The objective of this project was to evaluate the
effectiveness for treatment plants to shift Giardia and virus disinfection requirements from disinfection byproduct- (DBP) forming
disinfectants to ultraviolet (UV) light. The evaluation was conducted with a conventional
(coagulation, flocculation, sedimentation, filtration), demonstration-scale, plant treating
5.5 million-gallons-per-day of California State project water (SPW). Treatment plant
performance based on effluent turbidity, particle count, and filter run time was evaluated under
varying dosages of disinfectants and coagulant (ferric chloride [FeCl<sub>3</sub>]). Results showed that
total trihalomethanes (TTHM) and five regulated haloacetic acids (HAA5) measured after
chlorination formed up to 86 µg/L TTHM at 90th percentile occurrence levels for bromide (Br-)
in SPW (0.5 mg/L). However, TTHMs following ozone or ClO<sub>2</sub> disinfection were consistently
below regulated maximum contaminant levels (MCLs). Moderate ozone dose of 2.0 mg/L
formed up to 18 µg/L of bromate (Br-=0.5 mg/L). ClO<sub>2</sub> disinfection formed up to 1.5 mg/L
chlorite, currently regulated at an MCL of 1.0 mg/L. The addition of ferrous chloride (FeCl<sub>2</sub>)
effectively reduced chlorite levels, but required the addition of FeCl<sub>3</sub> to maintain adequate filter
performance. UV treatment following filtration was observed to shift up to 3 log Giardia and
0.5 log virus inactivation credit away from the above primary disinfectants, allowing for a
reduction in either ozone or ClO<sub>2</sub> dosages and resulting in lower DBP formation. However, up
to five minutes of free chlorine contact time following UV may be required to achieve additional
virus inactivation credit under some treatment conditions. Relatively low oxidant and FeCl<sub>3</sub>
doses (2.5-5.0 mg/L) provided adequate filter performance (median turbidity less than 0.1 NTU,
median particle counts less than 500 per mL, and filter run time greater than 12 hrs). Includes 21 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 19 |
| Published : | 06/17/2005 |
