Bend is poised to break ground in April on a $39 million upgrade of its wastewater treatment plant, which will allow the city to keep up with future development and population growth.

“The existing water reclamation facility was brought online in 1980, and it’s well past its design life,” assistant city engineer Jeff England told the City Council March 20. Existing sewer rates are adequate for the city to repay the low-interest loans from the Oregon Department of Environmental Quality that financed the project, England said.

The existing plant is already at capacity. It can treat up to 6 million gallons of wastewater per day, and 5.5 million to 6 million gallons of wastewater flow to the plant each day, according to the city. If construction rebounded quickly, the city would be in trouble because city officials allowed so many lots to be platted for development during the boom years. The city anticipates that if all of the platted lots were developed, the total daily wastewater flow would increase to 8.5 million gallons per day, according to a city presentation to the City Council in December.

Expanding the existing plant will not be a quick job. Construction is scheduled to finish in March 2016, according to the city presentation.

The city hired CH2M Hill Engineers to design the project and manage construction. Brady Fuller, senior project manager for CH2M Hill Engineers, said the project will increase efficiency in several ways. Workers will retrofit the existing wastewater aeration basins with integrated fixed film activated sludge, or IFAS, technology, which makes it easier for microbes that process waste to do their work. This technology will also be installed in a new aeration basin.

“That is really the heart of the secondary treatment process,” Fuller said of IFAS. “It allowed the city to defer construction of an additional (secondary) clarifier by about 10 years.”

Wastewater goes through many processes at the plant. Water enters the treatment facility at the headworks, where screens catch large materials such as plastics. From there, water moves into the primary clarifiers where sludge settles to the bottom and is removed from the tanks, Fuller said. The city puts the sludge into digesters, and the water goes into aeration basins.

Air pumped into these basins helps bacteria to grow, and these “bugs” eat waste that is still in the water and convert ammonia to nitrogen gas, Fuller said.

Wastewater then travels into secondary clarifiers, where the bacteria settle down from the water and are removed.

“The water that flows out of that secondary clarifier is very clean,” Fuller said. Finally, the water is placed in a tank where it is treated with chlorine. As part of the facility retrofit, contractors will install equipment to treat the wastewater with ultraviolet light instead of chlorine. The city sends some of this water to Pronghorn Club and Resort, the remainder goes into ponds near the water reclamation facility.

Expansion plans

In April, contractors will start grading and compacting the ground in sites where construction will take place. Central Electric Cooperative will relocate buried power lines, which are currently located in some areas where construction will take place.

Then contractors will begin construction of a new aeration basin, a new solids pump station and a new primary clarifier.

At least two aeration basins must operate at all times to meet the city’s wastewater treatment needs. As a result, the new aeration basin and clarifier must be up and running before contractors can begin retrofitting the existing aeration basins with the Integrated Fixed Film Activated Sludge, or IFAS, technology. This product will also be installed in the new aeration basin.

The city will also replace the existing blowers that pump air into the aeration basins with turbo blowers, which will use 30 percent less electricity. Other improvements to increase efficiency include lighting changes and an expansion of the hot water heating equipment, which heats the buildings by burning methane gas from the digesters.

IFAS

The system introduces thousands of free-floating plastic objects that offer more surface on which microbes can live. A biofilm grows on these plastic objects and the microbes in this film can remove a greater amount of waste from the water.