The communication network utilized a distributed control design: Nine PLCs (Siemens) communicating via Ethernet over fiber optic media. Each distributed PLC control program utilized modular programming techniques organized by system process, which reduced startup time and enhanced debugging capabilities. A secondary communication network was implemented to communicate with the 40+ Variable Frequency Drives (VFDs), utilized for advanced control schemes. Simple PID loop control strategies
were employed for various liquid levels, sludge flows, and dissolved oxygen control. A complex PID loop control strategy was employed as an overall process control parameter to ensure the input energy into the aeration basins was regulated based on multiple control variables. Ratio and set point control with hysteresis strategies were implemented for the chemical injection systems and to augment and refine OEM temperature control.