The Salinas Valley of California, southeast of San Francisco, is referred to as the “salad bowl of the world” due to its abundance of crops such as lettuce, broccoli and peppers. Like many agricultural areas in California, Salinas’ water supply is under stress from high usage, rising population and changing weather patterns. Therefore, every water conservation effort in the valley contributes to the overall health of the vitally important agriculture industry.
Recently, the capacity of Las Palmas, Calif., wastewater treatment operations was expanded by combining two plants and making one centralized filtration center. The new center expanded the flow capacity from 162,000 gal per day (gpd) combined to 288,000 gpd when the manually controlled reclaimed water operations were updated to a state-of-the-art automated system. Reclaimed water from the plant irrigates local community green spaces. The new automated system ensures lower labor costs, consistent quality and peak efficiency in the process of reclaiming wastewater for irrigation. Through this water conservation process, the Las Palmas facility contributes to the overall sustainability of Salinas Valley agriculture through water reuse.
To facilitate an effective transition to next-generation technology, a turnkey/scalable system was sourced from Festo under the direction of general contractor ERS Industrial Services, Fremont, Calif.
Keeping Up With Demand
Plant No. 1, with its capacity of 72,000 gpd, was built in 1989 in Salinas to reclaim water from the nearby Las Palmas Ranch residential development. In 1996, Plant No. 2, with a capacity of 90,000 gpd, was built to accommodate soaring population growth. That growth continued and by 2009, additional capacity was needed. Plant No. 1 could accommodate a higher demand with an upgrade in technology; thus ERS, with deep roots in the water filtration and treatment community, was hired as the general contractor on the expansion project.
Expanding capacity on the same site made sound economic and operational sense.
“Our goal from the beginning was to keep costs low and system performance high through technology innovation,” said Nik Radonich, project engineer, ERS. “One of the process innovations we thought offered the highest value was to find an automation supplier with the experience and expertise to design and deliver a complete turnkey control solution. We believed that one point of contact would speed communication and assign responsibility. We wanted one source thoroughly knowledgeable about the system to document, train and provide support services. Finally, we were looking for automation system interoperability, where the majority of components were designed to integrate with one another.
“After evaluating and rejecting a number of automation companies that could supply a partial but not complete solution, ERS selected Festo Corp. of Hauppauge, N.Y. Festo met all of our criteria and has an extensive track record of successfully completed projects in the global water/wastewater industry in Europe, the Middle East and the Americas,” Radonich said.
One of the first things ERS did was repurpose two treatment vessels that were no longer in service. These 5-ft-diameter by 15-ft-long horizontal vessels replaced four 5-ft-diameter by 7-ft-long vertical vessels. The horizontal vessels ensured more efficient and higher-capacity operation.
During the wastewater reclaiming process, water is forced, under pressure, through a filter medium bed to remove the remaining suspended solids from earlier treatment before disinfection and final discharge. The filter bed is made of crushed anthracite (hard coal) over crushed gravel. Each tank is separated into two compartments, for a total of four individual cells.
The two cells in each tank share a common collector pipe, backwash supply valve and effluent discharge valve. There are a total of 14 such assemblies in different sizes for managing the flow of water and air through the filter cells. The valve is used to introduce air into the tank for pre-backwash agitation of filter media (air-scouring). By utilizing the air scour system, the wash time was reduced 30%.
The effluent discharge valve operates proportionally with the help of a pneumatic proportional positioning valve and position feedback unit. This system allows the operators to set the desired flow rate. A magnetic flowmeter provides feedback to the programmable logic controller (PLC), which uses a PID flow control loop to modulate this valve. There are two such valves in this system. Festo preassembled all process valve assemblies prior to shipment to Las Palmas.
The process overview screen is the main control point for the filtration system. The screen provides a complete view of the entire process as a graphical representation with real-time instrument data, graphical animations and touch-sensitive areas that are used for showing an item in more detail. For example, touching any of the valve, filter or pump symbols changes the displayed page to one dedicated to the device.
This screen also shows the state of the various analog instruments that are used in this system, including:
- • Tank level sensors, showing level in feet and inches;
- • Turbidity sensors, showing the amount of suspended solids in the influent and effluent streams in nephalometric turbidity units;
- • Differential pressure between the filters intake and discharge manifolds, which indicates the backpressure across the active filter bed used for determining if a filter needs to be cleaned; and
- • Flowmeter showing the flow in gallons per minute leaving the system.
The 120VAC power supply and I/O connections to remote instrumentation and the pump control center are housed in an adjacent building. Tying this system into existing plant equipment required the close coordination of ERS, Festo, plant personnel and electricians working on site.
The Festo CPX valve terminal assembly provides extensive self diagnostics, which ensure that hardware problems can be identified quickly with pinpoint accuracy. Screen icons provide a graphical representation of all modules in the CPX assembly. Trouble on any module is indicated by a red warning symbol. Touching the icon reveals more detail about the problem. Process data also is collected and saved for analysis.
Festo designed this system to be scalable, which means that the same fundamental system can be designed, pre-wired and assembled for different-sized projects more quickly and with more assurance of success than building from scratch. Furthermore, because the majority of components were designed to work with one another, operators are assured of peak interoperability.
Operators reported that the system performs to expectation and the information available from the control screens helps to ensure peak efficiency and faster problem resolutions with added diagnostic and test screens.
Automation lowers labor cost, improves performance at California WWTP