Plant Operations Overview

Primary treatment removes solids and scum through settling and skimming. Solids and scum are pumped to anaerobic digesters.

Primary treatment equipment includes 4 primary clarifiers, each 135 feet in diameter with a capacity of 1.48 million gallons.Primary treatment removes solids and scum through settling and skimming. Solids and scum are pumped to anaerobic digesters.

Primary treatment equipment includes 4 primary clarifiers, each 135 feet in diameter with a capacity of 1.48 million gallons.

Secondary treatment consists of aerating and recycling bacteria. This biological process converts fine particles and dissolved organic matter into settleable solids.

Secondary treatment facts and figures

• 6 1,000-horsepower blowers supply the air to the basins
• 8 aeration basins, each with a volume of 2.2 million gallons
• 10 secondary clarifiers
• The basins can handle 45,000 pounds of organics a day

Final treatment consists of disinfection by chlorination followed by addition of sulfur dioxide to dechlorinate. The treated wastewater is then discharged into the Willamette River.

Final treatment facts and figures

• 6 chlorine contact chambers, capable of treating 277 million gallons a day
• Discharge pollutant levels are regulated through National Pollution Discharge Elimination System (NPDES) permit issued by DEQ (dechlorination of plant effluent is required year round)

Sludge conditioning and anaerobic digestion are the main elements of the solids treatment process. Solids removed in primary treatment are pumped directly to anaerobic digesters. Sludge from secondary treatment is thickened by a gravity belt drainage process and is then fed to the digesters. The digesters use anaerobic bacteria to decompose and stabilize the organic portion.

Methane gas, a useful byproduct, is formed in the digestion process. Methane is used to fuel engines for power generation. Heat also is recovered from the engines in a closed loop hot water supply system. The system provides the heat necessary for the sludge digestion process.

Sludge conditioning/anaerobic digestion facts and figures

• 1 800-kilowatt-per-hour engine generators operate on digester gas
• 2 3-meter gravity belt thickeners are used to thicken the secondary treatment sludge
• 3 anaerobic digesters, each with a capacity of 1 million gallons