AWWA ACE61672

The Los Angeles Department of Water and Power (LADWP) is evaluating EnhancedCoagulation (EC) as a technology to address several treatment goals including arsenic,turbidity, and DBP precursor reduction at the 600-MGD Los Angeles Aqueduct Filtration Plant(LAAFP). Currently, the plant process consists of preozonation followed by high-rate directfiltration. The average arsenic concentration in the Los Angeles Aqueduct (LAA) is 25 µg/L. Achemical addition system at Cottonwood, 180 miles upstream of LAAFP, is being used to shaveoff some of the arsenic peaks. This system may cease operation in the future so that all aspectsof treatment can be centralized and managed at LAAFP. The team of Metcalf & Eddy / Carollo Engineers was retained to evaluate the integration of ECat the LAAFP. A three-phase approach was undertaken as part of the project's first task. Phase one includedan eight-week bench-scale testing program developed to evaluate the impact of raw waterblend, coagulant type/dose, polymer, pre- and post disinfection, and sedimentation. A range offerric chloride dosages was tested in order to reduce ambient and spiked arsenic levels. Theresults from the bench-scale testing program formed the basis for selecting the process trainconfigurations for pilot-scale testing.The second phase involved a four-month pilot-scale testing program to evaluate the compatibility of ECwith the existing deep bed mono-media filters at LAAFP, to determine the maximum practicalferric chloride dosages in direct and in conventional filtration modes, to determine the quality of the filter effluent water in terms of key water quality characteristics, and to evaluate the sludgeand filter backwash water quality characteristics.The third phase involved a one-month demonstration-scale testing program conducted to confirm the pilot-scaleresults using a commercially available high-rate Actiflo®clarification process.This paper focuses on the findings of bench- and pilot-scale testing of EC strategies evaluatedat LAAFP. It discusses the required ferric chloride dosages to meet the treatment goals atLAAFP, the impact of raw water blend on treatment performance, and the lessons learned inclarification and filtration processes at the bench and pilot scale. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/17/2005

Number of Pages:

17

File Size:

1 file , 1.4 MB