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The Sacramento Regional Wastewater Treatment Plant (SRWTP) provides secondary treatment for an average daily flow of 165 MGD. The plant uses conventional primary treatment, followed by oxygen activated sludge secondary treatment, disinfection, and dechlorination prior to discharge to the Sacramento River. A new 5-MGD reclaimed water plant treats a portion of the secondary effluent for use at nearby parks and landscaping and also for non-potable applications at SRWTP. This paper describes some of the challenges faced during startup and testing of this new facility.

Major construction work of the reclaimed water plant was completed in June, 2001, and 30-day reliability testing was completed in November, 2001. However, numerous post-construction modifications were needed before reclaimed water delivery could begin in April, 2003. Some of the more significant changes included:

Repairs and modifications to various components of the chemical feed systems, including installation of a streaming current monitoring system and two new waterchamp mixers

Installation of additional turbidimeters for improved process control and compliance monitoring

Automation of the combined filter effluent valves to provide filter-to-waste capability during effluent high turbidity events

Enlargement of the existing mudwell and addition of a third mudwell pump

Modifications to the chlorine contact tank and chlorine residual sampling lines

Installation of a sodium bisulfite feed system to provide partial dechlorination of reclaimed water prior to distribution to customers

In addition to the construction modifications outlined above, extensive process testing was conducted in an effort to optimize the treatment process. Some of this testing led to the modifications outlined above.

Upon initial startup, it became apparent that the secondary effluent from the pure oxygen activated sludge process at SRWTP was much more difficult to filter than initially anticipated. Numerous chemical vendors were contacted, extensive jar testing of coagulants was conducted, and 14 different coagulants or coagulant/flocculant combinations were tested full scale at the reclaimed water filters over approximately a one year time period. Ultimately, a polyaluminum chloride chemical was selected as the best performing coagulant. Subsequent jar testing and particle count measurements have confirmed that the coagulant feed is near its optimal dose.

During early startup, coliform tests at the effluent end of the chlorine contact tank failed to consistently meet Title 22 standards for reclaimed water. Field testing showed that it was necessary to increase CT values to above 2000 mg-min/L to provide the needed disinfection, and the facility is currently operating at that level with no problems. A tracer study of the contact tank showed that it has reasonably good hydraulics, with a T10/T of approximately 85%. Bench top chlorine dose response testing has confirmed the need for a high CT to achieve adequate disinfection.

During the summer of 2003, temporary facilities were set up to allow for coagulant addition and pre-clarification at a dedicated upstream clarifier. This helped reduce loading at the filters and allowed for more stable plant operations during times of high secondary effluent turbidity. Further testing of this pre-clarification step is anticipated in 2004.

Delivery of reclaimed water to customers began in April, 2003. Delivered water has consistently met all California Title 22 standards. Operations personnel continue to evaluate the plant performance in an effort to further optimize the treatment process.
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Document Type: Research Article

Publication date: 2004-01-01

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