Since the beginning of wastewater operations in 1901, the City and County of Honolulu recognized the importance of a solid wastewater infrastructure to ensure public health and safety. As technology and sophistication in the instrumentation and control systems industry evolved over the years, the City capitalized on proven technologies to satisfy the increased wastewater demands and stricter regulatory requirements.
In the mid-1980s with the widespread use of personnel computers in the work place, the City began installation of an island-wide Supervisory Control and Data Acquisition (SCADA) system. This allowed remote monitoring and control of wastewater equipment from a host computer at a central location.
The basic components of the SCADA system integrated remote sites to a centralized monitoring node consist of remote terminal units (RTUs), analog leased lines and personal computers. The RTU is a microprocessor based electronic device that interfaces the physical equipment to the host computer by converting discrete and analog signal parameters into telemetry data, based on programmed control codes. The RTU and host computer uses RS485 communication protocol, which is transmitted over analog leased lines. The personnel computer then translates the raw data and presents the data to the user via the human machine interface (HMI).
Presently, the SCADA central command center is manned continuously (24/7) and monitors 70 wastewater pump stations, two storm drain pump stations, nine wastewater treatment plants and four preliminary treatment facilities.
Since the installation of the SCADA system, it has prevented and/or averted numerous sanitary sewer overflows into the environment. This is accomplished by deploying simple alarm programs in the RTU that check trend cycles of the wastewater pump's run on-time and off-time. Since each wastewater pump station has a distinct daily flow pattern, we can logically and systematically detect abnormal equipment run patterns. When an abnormality is detected, an alarm is generated that triggers an alert "popup" screen on the monitor, alerting operators and directing their attention to the problem.
The installed SCADA system has become antiquated and obsolete, so CCH recently began upgrading the SCADA system with the latest proven technologies. The new SCADA system will consist of programmable logic controllers (PLC), digital high-speed communication lines and computer servers. The PLC is a microcontroller-based electronic device (mini-computer on single chip) with multiple expandable input and output connections to equipment sensor points. A PLC is programmable to produce "real time" output results to various input conditions. Further, refinements in wastewater controls systems can be achieved with PLCs, which was not feasible with RTUs. The LAN network protocol connecting PLCs to HMI and Historian servers will be over Ethernet. The HMI will be configured in a primary and secondary redundant configuration. In the event the primary HMI fails, the secondary HMI will seamlessly provide information to view clients.
To date, the new SCADA systems are designed and constructed at the Disinfection Facility and Headworks Facility at Sand Island WWTP.