The control centre of San Diego's Clean Water Operations Management Network (COMNET) - one of the world's largest integrated control and information systems linking wastewater facilities - monitors processing of 180million gallons of wastewater every day.

It uses process control technology from Emerson Process Management to coordinate operations at more than 200 locations over 450 square miles, including Point Loma Wastewater Treatment Plant, North City Water Reclamation Plant, the Metro Biosolids Centre, numerous pumping stations in the San Diego area, and South Bay, a fourth water reclamation plant.
More than 10 years ago, San Diego's Metropolitan Wastewater Department (MWWD) embarked on a massive expansion and modernisation of its regional wastewater and water reclamation facilities - an effort that would become the largest clean water initiative in the nation.
When the project began, San Diego's only treatment plant was manually operated. To serve the community properly, the city had to upgrade that plant, and add three new plants to expand capacity.
To control this expanding wastewater treatment system, San Diego worked with its programme manager and Emerson Process Management to develop COMNET, a management system integrating all automation, monitoring and information systems for its entire wastewater process. The system was designed to do more than just control a new four-plant structure during and after the expansion - it also improved efficiency and reduced overall costs.

In the beginning

San Diego and Emerson began the project by installing the WDPF distributed control system (DCS) at the city's Point Loma plant in the early 1990s, and then in the North City Wastewater Reclamation Plant and Metro Biosolids Centre (MBC) as they were constructed. WDPF also controlled the associated pump stations.
By 1997, when the city was ready to design and construct the South Bay Water Reclamation Plant and modernise several pump stations, Emerson had developed the Ovation Information & Control system through advances in computer and networking technology.
Ovation, the first DCS to offer real-time, mission-critical control on a PC platform, provides an unprecedented level of performance and power.
The system's open architecture reduces the risk of obsolescence often associated with proprietary control systems and is easily incorporated into existing IT strategies, providing better and more accessible facility operation information.
San Diego chose this system to continue its clean water project, which allowed for integration of SCADA (Supervisory Control and Data Acquisition) technology, which will monitor and control more than 100 smaller pumping plants and valve stations using spread-spectrum radio communication through the Ovation base.

One control centre

While each facility in San Diego's system also has a local control room, the COMNET central station is in full control of points throughout the city's wastewater treatment system, most importantly the four primary plants.
The COMNET central control station has two operations consoles with five computer workstations and printers, telephone and radio communications and access to closed-circuit television at each of the four primary wastewater facilities.
Four 72-inch projection displays on the wall allow for additional monitoring. Information is displayed in real time - continuously updated every second, with realistic 3D graphical representations of the treatment process at each facility.
Closed-circuit TV images from each plant are viewed through a moveable window on the process displays, eliminating the need for TV monitors. The 24-hour-staffed central station provides full remote control of each facility without a local operator.
Although each of the four primary San Diego wastewater facilities can be controlled centrally through COMNET, automating each plant individually posed a new challenge for Emerson Process Management engineers.
In 1990, the Point Loma Wastewater Treatment Plant (PLWTP), was San Diego's only wastewater facility. Expanding the plant, which included a complete retrofit of all equipment, the construction of two new digesters and an upgrade of the cogeneration facility that powers the facility's operation.
Installing a control system in an existing large manually operated facility like Point Loma, while another construction crew was attempting to expand the plant, was the single most challenging piece of the San Diego COMNET programme.
While it may have been easier to install process control components in the North City, MBC and South Bay facilities as they were constructed, MBC presented its own set of challenges for engineers, because it involved a complex sludge process.
Almost half a mile long, with 222000 square feet of floor space, the massive MBC facility processes raw and digested solids to produce biosolids.
The plant contains 231 pumps, more than 1500 motorised valves and more than 2000 instruments - all requiring over 16000 input/output points in the control system.
The work - and challenges - are not complete yet. The North City plant, which was finished in 1997 with a WDPF system, is already undergoing an expansion. Emerson Process Management will migrate North City to Ovation as part of the expansion. The upgrade, which can be accomplished more quickly with new engineering tools developed by Emerson for the power generation market, will allow operators the flexibility and maintenance ease of PC-based control, and provide the city with freedom from component obsolescence issues that eventually surface from the use of proprietary systems like WDPF.

New system advantages

Advances in process control and the support and services provided by Emerson Process Management have offered San Diego a variety of advantages.
Before the Clean Water Programme was initiated, San Diego had only the Point Loma facility, manually operated with a workforce of 250 people. Despite that plant's expansion and the addition of three facilities and various pump stations to the overall network, only 65 additional employees have been needed for the entire system.
Employees have been shifted from functions such as pump and valve monitoring, meter reading and the performance of various repetitive tasks. In addition, operations and management reports are now generated automatically.
Savings are also being realised by better control over the amounts of chemicals used in the normal sewage treatment process. Ovation constantly adjusts chemical deployment based on flow levels to optimise usage.