AWWA ACE61735

The objective of this project was to evaluate theeffectiveness for treatment plants to shift Giardia and virus disinfection requirements from disinfection byproduct- (DBP) formingdisinfectants to ultraviolet (UV) light. The evaluation was conducted with a conventional(coagulation, flocculation, sedimentation, filtration), demonstration-scale, plant treating5.5 million-gallons-per-day of California State project water (SPW). Treatment plantperformance based on effluent turbidity, particle count, and filter run time was evaluated undervarying dosages of disinfectants and coagulant (ferric chloride [FeCl₃]). Results showed thattotal trihalomethanes (TTHM) and five regulated haloacetic acids (HAA5) measured afterchlorination 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 ClO₂ disinfection were consistentlybelow regulated maximum contaminant levels (MCLs). Moderate ozone dose of 2.0 mg/Lformed up to 18 µg/L of bromate (Br-=0.5 mg/L). ClO₂ disinfection formed up to 1.5 mg/Lchlorite, currently regulated at an MCL of 1.0 mg/L. The addition of ferrous chloride (FeCl₂)effectively reduced chlorite levels, but required the addition of FeCl₃ to maintain adequate filterperformance. UV treatment following filtration was observed to shift up to 3 log Giardia and0.5 log virus inactivation credit away from the above primary disinfectants, allowing for areduction in either ozone or ClO₂ dosages and resulting in lower DBP formation. However, upto five minutes of free chlorine contact time following UV may be required to achieve additionalvirus inactivation credit under some treatment conditions. Relatively low oxidant and FeCl₃doses (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.

Product Details

Edition:

Vol. - No.

Published:

06/17/2005

Number of Pages:

19

File Size:

1 file , 1.5 MB