Improved Hypochlorination Techniques
And Problems in Disinfection of Municipal
Wastewaters Containing Refinery Thiosulfate
WALTER E. GARRISON, Assistant Chief Engineer
JAY G. KREMER, Head, Industrial Waste Section
JOHN MURK, Operations Engineer
Joint Water Pollution Control Plant
The Sanitation Districts of Los Angeles County
Los Angeles, California 90057
BACKGROUND
The County Sanitation Districts of Los Angeles County, were formed under the
authority of the California County Sanitation Districts Act of 1923. This act provided that a
sanitation district was empowered to construct, operate and maintain facilities to treat and
dispose of sewage and industrial wastes within boundaries determined by geographical and
topographical rather than political subdivisions.
The Sanitation Districts now consist of 27 individual districts which provide sewerage
service to the major portion of Los Angeles County outside of the City of Los Angeles.
Fifteen of these districts serve the more populous portion of the service area. These 15
districts are joined together into the joint outfall system which provides a common sewerage
system for over 3,700,000 people, 750 square miles of area and approximately 25,000
industrial companies.
The methods of wastewater treatment include primary, secondary and tertiary at
various locations within the Districts. The largest treatment facility if the Joint Water
Pollution Control Plant (J W PCP) located in the City of Carson at the south central portion
of the service area, see Figure 1. The flow diagram of Figure 2 shows the processes of
primary wastewater treatment and sludge digestion and disposal now used at JWPCP for
about 370 MGD of wastewater. The treated wastewater is discharged into the ocean about 2
miles off the Southern California coast in about 200 feet of ocean water. During normal
ocean conditions the design of the ocean diffuser system prevents any appearance of
wastewater at the ocean surface. At present the Districts have five joint outfall activated
sludge treatment plants totaling about 80 MGD of capacity. A committment has also been
made to add secondary treatment to the JWPCP by July 1, 1977.
The quality of wastewater discharged to the Pacific Ocean from the JWPCP is
regulated by the State Regional Water Quality Control Board. Quality standards on treated
wastewater have become more stringent in recent years. Prior to September 1970 the
bacterial requirements for ocean coliform counts near the ocean outfalls were essentially
those for swimming water quality, 1000 per 100 ml. In September 1970 these requirements
were changed to essentially those for protection of shellfish. The coliform median most
probable number (MPN) for any 6-month period at each ocean sampling station was
required to not exceed 70 per 100 ml. Other statistical requirements were set for the single
sample maximum coliform count and for the maximum levels in 10 and 20 percent of the
samples collected. The practical significance of this requirement was to increase greatly the
Districts requirement for disinfection of the JWPCP effluent.
Under the swimming water standard of 1,000 coliforms per 100 ml only infrequent
JWPCP effluent disinfection was required (by chlorination) when unsettled ocean conditions caused the diffused wastewater to rise to the ocean surface. During normal ocean
conditions, occuring perhaps 50 weeks per year, the wastewater field remained submerged
and was dispersed well below the ocean surface. Chlorination was thus required only
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