February 2010, Vol. 22, No. 2

Plant Profile

Rodeo Sanitary District

Plant profile map - feb'10

Location: Rodeo, Calif.
Startup date: 1957 primary plant, 1973 secondary plant
Service population: 7800
Number of employees: 9
Design flow: 1.14 mgd (4310 m3/d)
Average daily flow: 0.55 mgd (2080 m3/d)
Peak daily flow: 2.5 mgd (9460 m3/d)
Annual operating cost: $2.1 million

The small size of the Rodeo Sanitary District nearer larger utilities lends the facility flexibility with day-to-day operations and the opportunity to partner with its neighbors to tackle larger concerns.

The 1.14-mgd (4310-m3/d) facility is a full secondary activated sludge wastewater treatment plant. All of the operators perform all aspects of operations and maintenance of the plant and the collection system. In addition to these duties, the employees also get the opportunity to construct the facilities they operate.

During the last 10 years, district staff has built several systems to enhance the performance of the plant. For example, in 2006, they put in a new chemical feed system. Staff installed the tanks, the piping, and the pumps. They also completed most of the electrical work themselves. This change reduced chemical use by 35%.

In 2009, the staff built a new chlorine analyzer building. From constructing the wood-frame structure of the building to digging trenches for conduits, to installing the analyzer equipment, all of the work was done in-house.

District staff members also work with contractors on some projects. All of this in-house and collaborative work ensures that the employees are intimately familiar with the systems they operate and enables the district to stretch its budget farther.

Free Operator Training

Having such a small staff also means every staff member wears many hats. For example, the district’s engineer–manager also is the laboratory superintendent for the Environmental Laboratory Accreditation Program, the chief plant operator for the California State Water Resources Control Board, and the legally responsible official for the collection system.

With each person playing so many roles, the district recognized the need for a strong training program and worked with a group of about a dozen other local agencies to create an operator training program. Together the group of agencies funds, organizes, manages, and supplies instructors to provide free college-level courses covering wastewater and water treatment to operators. Courses include wastewater treatment, water treatment, water and wastewater math, water and wastewater chemistry, collection system and water distribution system operations, instrumentation, and other courses.

The group decided to set up this program so the students could find these courses locally, not have to pay for anything, and be able to take them at night. These courses also are offered at Solano Community College (Fairfield, Calif.).

Retirements will lead to 40% to 50% of the group’s overall staff leaving in the next few years. This program is helping to ensure that all agencies will have a well-trained pool of applicants to choose from when this happens. The group has received several awards for the program.

The Rodeo Sanitary District, in particular, will have two operators — 40% of its staff — retiring in the next 5 years.

Filling the Gap

Rodeo also is beginning a new operator training program. The district is a Regional Occupation Program (ROP) facility. ROPs are programs for individuals seeking training and education in a particular trade.

Each semester, the district accepts one or two ROP students who are interested in learning about wastewater treatment. These students volunteer to work as many hours as they can each week at the district’s water pollution control plant. In exchange, the district establishes an operator-in-training certificate for the students, and district staff members train them. The district also provides the volunteers with workers’ compensation insurance and pays for boots, as well as any other needed safety gear. The fall semester last year was the district’s first try with this new program.

Process Train

The treatment process that the operators and ROP students operate and maintain is a straightforward activated sludge system. The flow enters the plant from two pump stations that feed into an aerated grit chamber. Following grit removal, the flow passes over a sharp-crested weir for flow measurement on its way to a circular primary clarifier.

The plant’s two rectangular aeration basins initially were designed for parallel treatment, but plant staff modified them into a single-pass system with an anoxic selector at the beginning. The anoxic zone helps control filamentous bacteria and promote denitrification.

After aeration, the flow is split evenly between two circular secondary clarifiers. Following clarification, the flow is recombined, has sodium hypochlorite added, and enters the rectangular chlorine contact tank. The tank has serpentine flow characteristics with a contact time of about 1 hour at average daily dry weather flow, 0.55 mgd (2080 m3/d). Next, the effluent is dechlorinated with sodium bisulfite and enters the reaeration chamber on its way to the effluent pump station.

For the majority of the year, effluent flows into San Pablo Bay via gravity. But when flows are high from rainy weather, a programmable logic controller closes the gravity bypass valve and activates pumps to discharge the effluent.

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