In the summer of 2014, Placer County Water Agency (PCWA) in California was facing a trihalomethane (THM) crisis. Drought across the western United...
Improved process controls double plant treatment capacity while maintaining staff levels
Population increase, environmental concerns and energy savings are motivating the water and wastewater industry to upgrade facilities with modern technology. The city of Plano, Ill., for example, has taken a proactive approach to increase its plant flow capacity and to ensure it meets existing environmental regulations, while also preparing for future regulations and community growth.
The population in and around Plano grew by more than 56% between 2000 and 2009—from 5,633 residents to more than 10,000. By 2003, the city’s water treatment facility was reaching capacity at its activated sludge plant, with 0.95 million gal per day (mgd) design average flow and 1.67 mgd design maximum flow. The city needed to increase capacity to 2.44 mgd to meet the population growth, and it also wanted to improve the plant’s nitrogen and phosphorus removal capabilities.
The city worked with its citizens and local environmental groups to design a water treatment plant (WTP) that would meet everyone’s needs and be economical for the city’s taxpayers.
In November 2006, the city of Plano completed the $13.6-million, award-winning plant improvement project that increased flow capacity to 2.44 mgd at its water reclamation facility and addressed environmental issues. The improvements included: extensive upgrades to the biological nutrient removal; a new secondary control building housing mixed liquor distribution to the final clarifiers; water reuse pumps; plant drainage/scum pumps; the internal return pumps; and ultraviolet (UV) disinfection used in the water treatment and nitrification process.
As part of the improvement project, the city expanded its plant process control to an integrated SCADA system with intelligent motor control and networking that contributed to better system diagnostics, improved process control, data collection and remote monitoring that helped reduce employee workload. Motor starters and variable-frequency drives on the plant process motors also helped save energy for long-term return on investment.
Process Controls Required
The city of Plano’s main challenge was to make the necessary improvements to increase plant capacity within the city’s budget constraints and tight schedule. The plant expansion would require replacement of existing control systems with modern process controls, new motor controls, instruments and value actuators, which would use networked communications whenever possible. Process automation controls would monitor the processes for nitrification to help meet environmental regulations.
The existing plant had little instrumentation for process control and, therefore, little data collection, historical trending and monitoring capabilities. The city wanted to improve its process control capabilities and reduce the time and work involved in these tasks, while maintaining existing staff levels.
“Getting this kind of information manually was really time-consuming,” said Darrin Boyer, plant superintendent for the city of Plano WTP. “EPA [U.S. Environmental Protection Agency] reporting took two full days, and it took three field operators to constantly monitor the equipment.”
Remote operation and monitoring was another objective that would save time and help reduce the staff members’ workload. Boyer often was called back into work when there was an issue at the plant.
“I’d get called in after hours to check on a problem that may or may not be urgent,” Boyer said. “Having to come in immediately to identify and resolve problems was a big time-waster.”
To contribute to environmental upgrading, the city also wanted to minimize the energy consumption of its many industrial pumps used during the water treatment process.
Bringing in Solutions
The city of Plano contracted Walter E. Deuchler Associates Inc. (WEDA), consulting engineers in Aurora, Ill., to plan and design the new plant. WEDA’s design included biological phosphorous removal and the reuse of UV-disinfected effluent on the plant site and at the nearby Cedar Dell Golf Course.
The project included a new headworks building, a new blower building, the conversion of an existing packaged treatment unit to serially operated aerobic digestion, and a new dewatering centrifuge. A new secondary control building houses the mixed-liquor flow distribution valves to the final clarifiers, nonpotable water reuse pumps, plant drainage/scum pumps and internal return pumps, which pump mixed liquor to the anoxic selectors for denitrification.
WEDA worked with electrical engineering sub-contractor Intelligent Design and Construction Solutions and with system integrator Complete Integration and Service (CI&S) to design a state-of-the-art SCADA system to control the processes at the new facility. The team chose a PlantPAx (Plantwide Process Automation Excellence) process automation system from Rockwell Automation that uses core Integrated Architecture technologies and custom solutions for plantwide control. The PlantPAx solution integrates all the process operations controls and motor controls in one system with access from remote telemetry/terminal units (RTUs) at each of the seven main process buildings.
The heart of each RTU is an Allen-Bradley ControlLogix programmable automation controller (PAC or PLC) with redundant power supplies. ControlLogix PACs are fully integrated with all aspects of the water treatment process to help the operator access plantwide production information for better management, decision-making, and production automation and optimization. They offer real-time visibility into monitoring water quality, trending of loads, levels and clarity, and detailed alarming, data collection and automated reporting.
Each RTU also has its own human machine interface (HMI) screen and is integrated with the other processes and the plant office via a high-speed, dual fiber-optic network. Wireless transmitting allows remote operation, data visibility, monitoring and control of any process from any location in the plant.
The main work station in the office runs RSView32, an integrated, component-based HMI with touchscreen operation using Allen-Bradley VersaView 1700P integrated display computers. EPA reports now are done electronically through the PAC inputs and submitted to the state automatically.
CI&S also integrated intelligent motor control into the system to help manage the motor speed on the plant’s many pumps, fans and blowers. The system integrator chose Allen-Bradley smart motor controllers with IntelliCenter to provide soft-start and -stop of the continuous-run motors, and integrated intelligence that connects to the rest of the process automation system. IntelliCenter technology provides real-time diagnostics and motor control center (MCC) documentation to help maximize MCC and related equipment performance.
For motors that require varied speed, CI&S installed Allen-Bradley PowerFlex 700 variable-frequency AC drives that have integrated intelligence for additional monitoring, safety, and easy configuration and installation. The advanced motor control performance helps gather process information at the drive level and automatically disperse it to any part of the plant through the Integrated Architecture. Intelligent motor control also contributes to plant sustainability by using the minimum power necessary to run a process, through the ability to program the system to automatically perform functions, and through remote access capability.
“One way that energy was saved was that the control system allowed the operator to run equipment on a demand schedule instead of a time schedule,” said Bob Baker of CI&S System Integration. “For example, if we only need 5 ppm oxygen in aeration, we will only run enough blowers to meet demand. We accomplish this through programming because the plant is only manned 40 hours per week.”
The operators save time with the simplicity and flexibility of remote monitoring and control that gives them access to information about any process in the plant from any of the HMIs or the main office. Boyer estimated that the flexibility of remote monitoring the equipment replaces the surveillance work of three operators in the field, so these individuals can work on other important issues. They now can anticipate and detect a potential problem earlier, allowing time for a quick adjustment or small repair that could prevent catastrophic failure. This has contributed to a significant reduction in equipment downtime, according to Boyer.
A major benefit has been remote, from-home monitoring at night and on weekends. It allows Boyer to determine whether an alarm is critical or can be dealt with the following day. This has saved the cost and inconvenience of unnecessary call-outs.
Manufacturer dial-in functions also have saved downtime and expenses. The city can rely on quick, inexpensive troubleshooting, as each major equipment manufacturer can access Plano’s system from its factory base and assess the situation without visiting the site. Often the solution can be implemented without any follow-up from a service technician, Boyer said. The PlantPAx process automation system provides the right information in real time to help the city of Plano meet its environmental and capacity goals. The new control system helps save energy by allowing the operator to run equipment on a demand schedule instead of a time schedule.
The city said it has had no effluent violations since the new plant was brought online, and it has maintained plant staff levels while more than doubling its water treatment capacity. Plano estimates that it received a return on investment in automation equipment within two to three years.
The city of Plano WTP improvement project received an Honor Award from the American Council of Engineering Companies of Illinois.
Three years later, Boyer reports seeing significant changes and improvements in how the plant operates. “The plant effectively handles more flow through the EQ basin,” he said. “There is precise control of the biomass in the aeration tanks, accurate flow splitting to each final clarifier is achieved, and we have a controlled wasting schedule from the RAS [return activated sludge] pumps.”
The system has helped streamline the site maintenance program. The OP32 system automatically produces work orders based on input from manufacturers’ maintenance manuals.