The Los Angeles Aqueduct Filtration Plant An Overview of Facilities and Operations

Los Angeles Aqueduct Filtration Plant Capacity 600 Million Gallons per Day High-Rate Direct Filtration Process with Pre-Ozonation Online in 1986 Treats ~ 70% of the Water for 3.8 million People (LA City Only)

LAAFP Water Sources Los Angeles Aqueduct –338 miles, gravity flow –Low turbidity, TOC –Arsenic is a concern –Pre-sedimentation State Water Project –Low turbidity –Bromide and DBP Precursors concerns

LAAFP Average Flow by Source

Pre-Sedimentation on Aqueduct North Haiwee Reservoir Cottonwood Treatment Plant

LAAFP Treatment Process

Control Room

Inlet Structure

Bar Racks

Fine Screens

Fluoridation

Oxygen Plant Air Products cryogenic air separation plant 50 tons per day production capacity Generates ~ 95% oxygen, mostly GOX Some LOX produced for peaking, backup

Ozone Generators

Ozone System Data Ozonia generators Installed ozone capacity 13,000 lb/day Glass dielectrics 6% ozone; ceramic 10% Average applied ozone dose ~ 1.2 mg/L Target ozone residual 0.3 to 0.4 mg/L Ozone contact time 5 minutes at 600 MGD Rectangular contactors, 20 feet deep with over/under baffling – t-10/HRT about 50%

Ozone Off-Gas System Ozone applied in first countercurrent basin Rod-shaped ceramic diffusers allow ~ 95% transfer efficiency Ozone contactors under slight vacuum Off-gas collected and converted to oxygen

Power Consumption Average plant power consumption about 48,000 kWh per day Oxygen and ozone systems use more than two-thirds of power 3000 kW emergency generator capacity allows full operation.

Rapid Mixers Two mixers in series on each train Vertical-shaft, radial turbine impellers Cationic polymer dose averages 1.2 mg/L Ferric chloride dose averages 1.5 mg/L

Flocculation Gentle mixing step to build floc particles Three basins in series Mixing speed variable in each stage Average hydraulic residence time is 12 minutes

Filtration High filter loading rate (13.5 gpm/sf) 1.5 mm effective size anthracite coal media 72-inch anthracite layer above 3-inch gravel support layer Biofiltration since 1999 to remove AOC

Filter Media

Filter Underdrain Air and water used to backwash filters – air for initial scour only Backwash flow rates up to 25 gpm/sf Each half of the filter washed separately Average filter run length about 18 hours

Filter Pipe Gallery

Filter Backwash

Backwash Ponds Clear water from pond outlet pumped to LAAFP inlet Filter backwash water flows by gravity to pond inlet

Residuals Disposal Solids are dried and removed from ponds about every two years Elevated copper and arsenic levels create California “special waste” Residuals trucked to Class 1 landfill

Final Disinfection

Preparing for the Future

The Los Angeles Aqueduct Filtration Plant An Overview of Facilities and Operations