Wastewater facility uses AI to meet sustainability goals

The Eastern Municipal Water District (EMWD) serves nearly one million people living and working within an area of 1445 km² in Riverside County, California. As the state’s sixth-largest retail water agency, its mission is to provide “safe, reliable, economical and environmentally sustainable water, wastewater and recycled water services”.

“We strive at all times to produce the highest quality water possible,” said Matthew Melendrez, Assistant General Manager, Operations and Maintenance, “and to do that as economically as possible for our customers to help keep their costs down.”

But a growing population and an expanding service area have put increased demands on the district. Its four reclamation plants currently treat about 182 million litres of wastewater a day, removing impurities.

“The two main things we’re trying to remove are organics and ammonia,” Melendrez noted. “If we don’t clean those up, they have a large impact on the environment.”

Aeration is a key step in wastewater treatment, and one of the most energy-intensive. EMWD plants spend nearly half of their electricity bills on dissolved oxygen used to biodegrade waste.

“The industry has struggled for a long time with aeration control and finding better ways to operate the basins,” Melendrez explained. “Process parameters change practically every minute of the day as flow rates and volumes of ammonia and organics fluctuate quickly, making it difficult to program a typical PID setpoint to hit its dissolved oxygen (DO) targets.”

Setting the target too high requires an increase in electricity to provide unnecessary air. Setting it too low inhibits ammonia oxidation, which then requires disinfection and larger amounts of chlorine.

“We typically use a simple PID control system that slowly opens and closes the air valves as the DO climbs or dips. Everything is reactive and feedback-based, and operators usually intervene daily to make manual adjustments,” Melendrez said. “But there’s a lag from the time adjustments are made until we see results because the tanks are so large, and conditions continue to change. All of this makes it hard for a regular PID to handle and why this is one of the biggest opportunities to improve efficiency.”

Better aeration performance would also positively impact downstream processes where the plant could improve disinfection and lower chemical costs.

EMWD approached Rockwell Automation, one of its long-time technology providers, to develop and test an AI application that learns the current state of aeration operations and, with minimal staff intervention, optimally adjusts PID response as conditions change.

Together with the Rockwell Automation Water Wastewater, Solutions & Services and Advanced Analytics teams, EMWD piloted an AI-enabled control system at its San Jacinto Valley reclamation facility, which treats 26 million litres of water a day. Plant staff installed an Allen‑Bradley CompactLogix 5480 controller on the existing automation network allowing it to interface with other processes as needed.

Two Logix cores connect to the control system while two other processors execute the Rockwell Automation AI software. The AI controls the amount of air fed into the aeration basin by continuously monitoring and updating the PID response. The data is then used to adjust the air valves and the amount of oxygen delivered before the DO deviates too far from the setpoint.

“Using machine learning, Rockwell Automation data scientists determined wastewater flow and ammonia load have the biggest impact on oxygen performance,” Melendrez explained. “They built a model that was quite accurate at predicting the DO demand for any given rate and load, and remotely programmed the AI software.”

With the AI-enabled control, EMWD reduced the amount of air delivered to the aeration basin by as much as 31%. The plant was not only more successful in running the DO closer to its setpoint, but it was also able to lower the DO target. Better DO control also led to improved effluent quality with less ammonia bleed-through, reducing the need for disinfectants.

“It was exciting to see it go from something that didn't really function … to something that was fully automated and provided substantial improvement in performance, financial benefits and reduced carbon footprint,” Melendrez said.

He estimates the improved DO control will reduce the plant’s energy consumption by 960 kWh of electricity a day. Additionally, the ability to lower the DO setpoint will unlock further daily electricity savings of 1370 kWh.

EMWD continues to use the AI-enabled control system and hopes to work with Rockwell Automation to expand its application to the district’s other aeration basins. Looking ahead, Melendrez spies another opportunity to apply the AI solution: disinfection.

Image: ©iStockPhoto.com/Vladimir Zapletin