The Additional Valley Outfall Relief Sewer and East Valley Interceptor
Sewer carry wastewater to Tillman from about 70% of the San Fernando
Valley. The plant can treat up to 80 million gallons per day. About 40%
of the 80 million gallon daily flow comes from commercial uses and 60%
Wastewater from the main sewer lines flow through grit channels where
sand, rocks and grit are removed. These items settle to the bottom of
the grit channels by gravity and centrifugal force.
|Influent Pumping Facility
After grit removal, the wastewater is lifted 30-feet by eight
large-diameter screw pumps to the screening facility in the Headworks
building. Screw pumps are more energy efficient than centrifugal or
other types of pumps. The wastewater then flows by gravity through all
the remaining treatment processes at the Plant.
At the Headworks, bars and screens remove the largest solids – such as
branches, plastics, and rags. Screening, along with grit removal, is
called preliminary treatment.
|Primary treatment – taking out the sludge
Most of the solids (sludge) are removed here after they settle to the
bottom of the covered primary tanks. All of the primary sludge flows
back into the main sewer system where it is sent to the Hyperion
Treatment Plant for further processing. The remaining wastewater then
flows by gravity to the secondary treatment system for further
treatment. The primary tanks are covered to reduce odors.
|Secondary Treatment – Aeration Tanks
Bacteria are added to the aeration tanks for the
nitrification-denitrification process. The bacteria feed off the
organic wastes in the wastewater. Oxygen is added in the nitrification
process to speed up the bacteria’s rate of decomposition. The
nitrification-denitrification process reduces the amount of nitrogen in
the plant’s effluent. The wastewater, rich in activated sludge, then
flows to the secondary clarifiers.
|Secondary Treatment – Clarifiers
The second stage of secondary treatment involves the settling of
activated sludge by gravity in the final settling tanks, or secondary
clarifiers. A portion of this settled activated sludge is returned to
the aeration tanks (returned activated sludge, or RAS) to maintain
biological equilibrium in the aeration tank, while the remaining
portion is discharged/ wasted (waste activated sludge, or WAS) to the
sewer. All of the waste activated sludge flows to the Hyperion
Treatment Plant for further processing.
After secondary treatment, the wastewater flows through shallow-bed
sand filters to remove any remaining solids. To improve filtering, a
polymer is used as a coagulant to increase the size of the remaining
Disinfection is a two-step process. Liquid bleach (sodium hypochlorite)
is added to the wastewater, which kills any remaining pathogens or
disease-carrying organisms. The chlorine-containing water remains in
the last set of holding tanks at the plant for about two hours The
water is then dechlorinated (with sodium bisulfite) to protect fish and
other aquatic wildlife. The treated water is then reclaimed to one of
three lakes, used onsite, or discharged directly to the Los Angeles
Over 25 million gallons per day of reclaimed water is produced at DCT.
About 2.5 million gallons per day are recycled at the plant for
treatment processes, landscape irrigation, cooling of plant equipment,
air conditioning, and other applications. Over 23 million gallons per
day are recycled to the three nearby lakes, the Japanese Garden Lake,
the Wildlife Lake and the Balboa Recreation Lake. The remainder of the
Plant’s treated water is discharged directly to the Los Angeles River.
The plant’s discharge, combined with the outfall from the three lakes,
provides a minimum of 20 million gallons per day to the Los Angeles
River for support of the river’s riparian habitat.