Wastewater isn’t just the water flushed from toilets or drained from bathtubs. It comes in many forms, including rainwater from storms, which can carry chemicals and other substances that could cause harm if used before going through the wastewater treatment process.
Tacoma, a city south of Seattle in a state known for its year-round rainfall, knows the importance of proper water and wastewater treatment to keep its more than 208,000 residents serviced and safe.
The City of Tacoma Environmental Services operates out of two wastewater plants, the Central and North End plants, which maintain 48 pump stations along a 650-mile collection system when combined.
The Central treatment plant was built in 1954 with secondary treatment upgrades completed in 1988 to meet new effluent standards from the Environmental Protection Agency (EPA). In 2006, additional upgrades were implemented to increase the plant’s capacity to 139 million gallons per day (MGD).
The North End treatment plant was built in 1968 and has a capacity of 30 MGD. Major upgrades were completed in the late 80s to meet requirements from the EPA mandate, and secondary treatment upgrades were added to the plant in 1997. Unique from other wastewater facilities, the North End plant is a physical/chemical treatment plant due to its smaller footprint and transfers solids to the Central plant for processing.
Both plants were operating on decades-old equipment and required upgrades.
“We were dealing with legacy systems that no longer suited or supported our operations,” said Chris Roberts, Tacoma Automation Support Team, City of Tacoma Environmental Services. “It wasn’t a ‘want’ but a ‘need’ to find a new solution for both the Central and North End plants that would make smoother, more efficient processes possible.”
Putting in the (prep) work
The city collaborated with Carollo Engineers, an environmental engineering firm that specializes in the planning, design and construction of water and wastewater facilities, to help with the technology selection process. The combined team evaluated different solutions’ capabilities, support services, associated costs and more. After the extensive selection process, the PlantPAx distributed control system (DCS) from Rockwell Automation came out on top.
“We wanted a solution and a partner that would offer the hands-on support we needed as a smaller player in the DCS world,” said Roberts. “Through our research and evaluation, we found that Rockwell Automation had the local programming and technical support we were looking for with a competitive price point.”
Once the technology selection process was completed, the team continued working with Carollo Engineers to prep for system implementation. This included building out system standards, understanding potential unknowns in the aging systems, creating all new P&ID and control narratives and pinpointing exactly how to take the proof of concept to an implementable design at both plants.
After a three-year preparation period, the city was ready to implement a fully standardized PlantPAx DCS and production intelligence solution to help increase plant efficiencies, save energy and improve visibility into its operations.