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Treatment plant upgrades are moving forward

City renovating key components of its 26-year-old operation


The Newberg Wastewater Treatment Plant renovations are in full swing, with general contractor Mortenson Construction having completed several crucial upgrades over the past year and anticipating more new construction in the year to come.

The $55 million project was approved for two main reasons: to plan for future capacity needs and to update the facility which has experienced normal wear and tear over its 26 years of operation.

“It needs continual work to be able to keep it up,” said Jason Wuertz, project engineer on the plant renovation. “There’s three pieces that we’re doing right now: the screw presses, the headworks building and the influent pump station.”Photo Credit: GARY ALLEN - Pressing on - The city of Newberg continues renovation of its 26-year-old wastewater treatment plant, including the system by which water is removed from solids. These screw presses are more compact and more efficient than their older counterparts, the belt-filter presses. Plant engineers will continue usage of the belt-filter press until they are confident the new system is working properly.

Those three pieces are key components of the system. All the city’s wastewater makes its way to the influent pump station, located at the bottom of a hill below the treatment plant.

A new pump station, consisting of two heavy-duty submersible pumps, is being constructed adjacent to the old one. However, the old station will not be phased out.

“This was designed such that the existing pump station continues to operate for the majority of the time, and (the new) one kicks in during high flow events,” Wuertz said. “In the summer (the average flow) might be 2.5, 3 million gallons per day. During a really heavy winter storm it might be upwards of 20 million.”

Part of the reason for the fluctuation is that the wastewater plant is receiving some of the city’s storm runoff, which is not supposed to be the case.

“We have (a) separate storm sewer from our wastewater system,” Wuertz said. “The city is currently doing a big inflow and infiltration project: pipes have cracks, manholes have cracks, joints aren’t sealed, groundwater infiltrates into the wastewater system. Those things contribute to huge swings in inflow from dry weather and wet weather, storms.”

The inflow is pumped up the hill to the headworks building, which provides the initial stage of treatment. Unlike the old influent pump system, which will continue operating alongside the new, the old headworks building will be demolished once the new one is fully operational.

“It’s old, it’s not large enough (and the new one) has capacity for the planning future,” Wuertz said. “It’s a better grit removal system.”

The headworks system filters out large and heavy materials, which are grinded and compacted into a dumpster and sent to the landfill. The remaining inflow leaves the headworks station and enters the oxidation ditches, which filter the solids from the water through a biological process.

While the filtered water continues on for more treatment, the separated solids enter a building to be dewatered before being mixed with sawdust to create Class A compost popular for gardening. The dewatering equipment is being upgraded as well.

The plant has utilized a belt-filter press to remove water from the solids until now. Large, bulky, loud and messy, the old technology is being phased out in favor of the sleeker, more compact screw press.

“(Belt-filter presses are) not as efficient. The energy use of these is significantly less,” Wuertz said.

Two screw presses fit into the footprint of one belt-filter press and can process more material. Although there is still one belt-filter press next to the two new screw presses, like the headworks building the old belt-filter press will be removed once the plant engineers are comfortable with the new equipment.

“The plan is to get rid of it, but we want to have confidence in the (new) system before we pull it out. We’re still doing performance testing,” Wuertz said.

The city of Newberg developed an updated WWTP facilities plan in 2007, as it saw changes in land use and population had occurred since the plan was written in 1985. The city had received an annual growth in population of about 2.6 percent, and the increase in residents meant the wastewater system would have to accommodate more users. Planners used the growth figures as a guide to estimate how the city would grow in the future and planned the upgrades accordingly.

When the economy crashed, however, residential construction dropped off and growth slowed dramatically. Now the city is considering revisiting the update to make adjustments not necessarily to the final product of the upgrades but to the timeframe and scope.

“The flow projections could change the size or quantity of the new facilities,” Wuertz said. “The plan was to put in a certain number of oxidation ditches in a certain number of years. It might be at 2040; instead of needing five new oxidation ditches you only need two.”

The new headworks building is still being constructed and the plant anticipates the start-up process beginning the second week of January. After the present stage is completed, construction will begin on the oxidation ditches, where the water and solids are separated, and the expansion of the chlorine contact basins.

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