The Glenelg Waste Water Treatment Plant (WWTP) is one of three large wastewater plants in metropolitan Adelaide, South Australia, a city ranked in the top 10 of The Economist’s “World’s Most Livable Cities.” The plant, located in Western Adelaide, covers a drainage area of approximately 92 square kilometers (36 square miles) and serves a population of about 200,000 persons.
The treatment plant is a conventional activated sludge plant that incorporates screening, grit removal, primary sedimentation, activated sludge, secondary clarification, sludge removal, sludge digestion, power cogeneration and effluent disinfection by chlorination prior to discharge into the Gulf of St. Vincent, a beautiful stretch of coastline used daily by the citizens of Adelaide. Portions of treated effluent are also reused for irrigation of golf courses, playing fields and recreation areas via the Glenelg to Adelaide Parklands (GAP) Recycled Water Project.
Plant officials wanted an upgrade to the wastewater treatment plant controls with no service interruption. Sage Automation (www.gotosage.com), a certified member of the Control System Integrators Association (CSIA), was retained to upgrade the supervisory control and data acquisition (SCADA) system, the programmable logic controllers (PLCs) and the process controls network.
An added challenge was the fact that the controls upgrade was part of a larger environmental project: South Australia Water’s $240 million Environment Improvement Program. The upgrade involved the introduction of an innovative biological process known as integrated fixed-film activated sludge (IFAS), which will reduce nutrients discharged from the plant into the Gulf of St. Vincent.
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Sage was commissioned to replace 12 existing Toshiba PLCs with a fully redundant Rockwell Automation Allen-Bradley (ab.rockwellautomation.com) PLC architecture and a new GE Information Platforms iFix-based SCADA system. The main challenge for the Sage team was to perform the entire control system replacement without interrupting plant operations, and some critical parts of the treatment plant could not be shut down for longer than four hours.
To achieve success under these constraints, the commissioning process was meticulously planned to be performed in 14 separate stages over a six-month period.
Pump duty-state control
A new control philosophy was implemented that divided the pump profiles into three, operator-adjustable time zones through the day, using two different flow cases: high flow and low flow. The purpose of the three time zones is to allow different pumping profiles to be enabled during different times of the day to better suit the actual operational requirements of the plant. These pump profiles enable/disable the different pumping pairs controlling the sump level between an upper and lower limit.
An operator-adjustable setpoint was provided to detect rapid change in the settle tank to preempt a high-flow situation. This setpoint will allow the pumping stages to increase based on the following parameters: rate of change in the tank and time between pump stage indexing.
As a result of the systems and processes used, the project was completed meeting or exceeding all customer expectations around plant operation, system design, environmental risk management, and health and safety.
>> Tom Sulda is Engineering Operations Manager at Sage Automation, a CSIA Certified control system integrator headquartered in Melrose Park, South Australia, Australia. To learn more about Sage, visit www.gotosage.com. To learn more about the Control System Integrators Association, visit www.controlsys.org.