Automation strategy modernizes water plant

The automation and control of primary processes, and completion of a centralized control room, mark a milestone in a long-term automation programme at a large wastewater treatment plant in the USA.

The District of Columbia Water and Sewer Authority (DCWASA) is in the midst of a multi-year capital investment program at its Blue Plains Advanced Wastewater Treatment Plant to enhance operational efficiency and assure long-term reliable treatment and compliance with environmental regulations.

An important part of this overall program is adoption of a long-term automation strategy that calls for an integrated approach for monitoring and controlling plant processes, water distribution and wastewater collection.

Emerson Process Management's Ovation expert control system is an integral component of this comprehensive automation strategy.

DCWASA's Blue Plains Plant is the world's largest advanced wastewater treatment facility with a rated annual average capacity of 370 million gallons per day and a peak wet weather capacity of 1076 billion gallons per day.

The plant, built in the 1970s, utilises a sophisticated nitrification/denitrification and filtration process.

In 2002, Emerson won a $35 million contract to engineer and install three Ovation systems for DCWASA - one to control operations at the Blue Plains treatment facility, and two separate Ovation SCADA systems to monitor DCWASA's water distribution and wastewater collection system.

Emerson's Power and Water Solutions industry centre is managing the project.

Emerson's Ovation solution represents a step change in technology for the district.

The new systems will allow DCWASA to assure adequate treatment capacity through linked systems controlling on-site and remote processes, maintain process control infrastructure, protect against component obsolescence, and operate and manage its entire water/wastewater network efficiently and economically through seamless process integration and redundant configurations.

Emerson now reports that the first phase of the control system modernisation project is nearly complete, and the second phase is well underway.

In the first phase, Emerson installed its Ovation system to automate monitoring and control of primary sedimentation basins and pumping stations at Blue Plains.

In addition, a centralised control room enables operators to monitor and control processes.

There are also three separate operational area control centres - primary/secondary treatment, filtration, and solids handling.

Integrating controls for the entire plant, instead of relying on separate islands of automation, coupled with making the information accessible from a central location, will translate into more efficient and effective monitoring and control of critical processes.

After automating the backwash process with the Ovation system, DCWASA staff now has the ability to quickly review and modify the control logic as needed to ensure efficient operations.

This is a key functionality that they did not have with the previous PLC systems.

Automating processes previously performed manually has already proven to be beneficial in terms of staff utilisation.

Once fully implemented, DCWASA expects to experience additional savings in water and chemical usage.

Furthermore, the integrated control system, which features comprehensive alarm management, quickly and efficiently provides operators with crucial data regarding plant operations, making it easier to troubleshoot and diagnose problems.

Plant staff find their ability to point and click to real-time data and trending information priceless.

Phase two encompasses solids processing, including the complete central monitoring and control of the Blue Plains liquid treatment train, chemical addition and dewatering, and integration with the collection system.

Outside the plant, SCADA implementation for wastewater collection and the water delivery system is in process.

Finally, phase three will incorporate monitoring and control of the world's largest egg-shaped anaerobic digesters, completing integration of the plant.

When the multi-phase project is completed, the Ovation control and SCADA systems will consist of more than 60 remote terminal units, 25 redundant controllers, two off-site operator control centres, three in-plant operation area centres, 11 hardened operator interface terminals in strategic plant areas, and one central control facility.

In total, an estimated 40,000 input/output points will be interfaced to the Ovation process control and SCADA systems.

"Implementing an integrated control architecture as part of a multi-year automation master plan enables municipalities, like DCWASA, to build on resources they already have so they can easily meet future needs", said Bob Yeager, President of Emerson Process Management's Power and Water Solutions division.

"Whether adopting newer treatment technologies, expanding to meet future population growth, or adjusting to increasingly complex financial and environmental regulations, the Ovation-based integrated control architecture will help ensure that DCWASA is well equipped to meet the needs of the more than 500,000 residential, commercial and government customers it serves".

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