How Newberg’s Wastewater Plant Turns Sewage Into Treated Water and Compost

NEWBERG, Ore. — Most residents of any municipality interact with wastewater by pressing the toilet handle and hearing it flush down the pipes and out of mind.

But behind the scenes, hundreds of pipes in Newberg carry that waste underground to the wastewater treatment plant. There, it undergoes a nearly three-month purification process that ends with the clean water deposited into the Willamette River and the solids sold back to the public in the form of Grade A compost.

The Newberg Wastewater Treatment Plant is the final stage of a three-month journey wastewater takes from the bathroom to the Willamette River or the compost bin. At the plant, several processes separate the liquid from the solids and ensure everything is purified to Oregon Department of Environmental Quality standards.

When waste first arrives at the plant from a long journey through underground pipes, it is pumped through influent pipes to the entry point for all sewage, called the headworks. At the headworks, any garbage that ended up in the pipes is filtered out and trucked to a landfill. This prevents damage to the plant and ensures non-degradable solids do not enter the facility.

From the headworks, sewage is sent through a splitter that divides it into two oxidation ditches. If flows are high, as in the winter, excess wastewater is sent to an equalizer basin, where it is held until it can be pumped into the oxidation ditches. These ditches are approximately 25 to 30 feet deep, more than 90 feet wide, and more than 300 feet long. Sewage circles the oval ditch at a steady pace to keep the solids from settling and to allow rotors to continuously mix oxygen into the water.

Oxidation ditches aerate the wastewater as it moves around the ditch to keep chemical- and bacteria-eating microorganisms alive. After nearly a full day of circling an oxidation ditch, the now nitrogen-free sewage is transferred to a secondary clarifier, where solids and liquids are separated.

The secondary clarifiers operate opposite of the oxidation ditches: the ditches keep waste moving, and the clarifiers slow movement. By letting the wastewater slow, gravity separates the clean water from the solids with all the microorganisms. The clean water is then siphoned off the top of the secondary clarifier and into the chlorine contact basin to be further treated.

Solids, on the other hand, go through a hopper to leave the secondary clarifiers and are split between two sets of pumps: return activated sludge, or RAS, pumps and waste activated sludge, or WAS, pumps. Most of the solids go through the RAS pumps back into the oxidation ditch, where the microorganisms continue eating away at the chemical and biological waste there. Other waste is diverted from the RAS pumps to the WAS pumps to keep the amount of microorganisms in the oxidation ditch at the right level. This waste will eventually turn into compost after a heat compactor kills the remaining bacteria. The planned expansion would change how the plant handles solids, as detailed in the separate Newsberg story.

The clean water in the chlorine contact basin is in one of its final stages before being released into the Willamette River “cleaner than the water currently in the river,” according to multiple sources, including former Public Works Director Russ Thomas in a video tour of the wastewater plant posted to the city’s website, and City Manager Will Worthey.

The chlorine contact basin uses a winding S-shaped back-and-forth pattern to move water through the tank in approximately 20 minutes, the time needed for the chlorine to come in contact with all the water in the basin. Chlorine is injected into the water immediately before it enters the basin. The last step in water treatment is dechlorination, in which excess chlorine is removed from the water before it is pumped into the Willamette River.