Transcript Document
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