The Treatment Process
Treating wastewater is a complex process. CCSD #1’s Water Pollution Control Plants use physical, biological and chemical treatment to clean approximately 8.1 million gallons of wastewater per day, created by the unincorporated areas of North Clackamas County, the City of Happy Valley, the western edges of Damascus, and communities of Hoodland, Boring and Fischer’s Forest Park, and the City of Milwaukie, parts of Gladstone and Johnson City under wholesale contract agreements.
Following the treatment process, clean water is released into the Willamette and Sandy Rivers. Below is a brief overview of the wastewater treatment process.
Treating the WATER in Wastewater
Preliminary Treatment (Screening):
The first step in the wastewater treatment process is “screening.” Before wastewater is piped into the plant, large contaminants such as rocks, sand, plastics and toys, known as “grit,” must be removed; if not, plant equipment may be damaged, causing the treatment process to be interrupted. Mechanical bar screens are used to remove this material.
Primary Treatment:
The second step of wastewater treatment is “primary treatment,” where partially treated wastewater flows into primary clarifiers so that remaining solids sink to the bottom, becoming “sludge” and are removed. Pollutants such as grease, oil and other floatable substances are skimmed off the top.
Secondary Treatment:
Aeration: The next stop is the aeration basins where microorganisms live and feed on the incoming waste. Air is continually pumped into the water to keep the microorganisms active.
Clarification: Water now flows into secondary clarifiers where the water flow is allowed to slow down. Final bits of solids sink to the bottom and are removed or returned to aeration basins for further processing.
Disinfection
The final stage in the wastewater treatment process is disinfection. During this process, treated wastewater is disinfected with chlorine or ultraviolet light to kill any remaining bacteria such as E. coli, Streptococcus, Salmonella, Shigella, and Giarida lamblia, which can be harmful to humans and wildlife. The chlorine is neutralized before the clean water or “effluent” is released into the River.
Treating the WASTE in Wastewater
Digestion
Solids that settle to the bottom of the clarifier, called “sludge,” and those that are skimmed from the top, such as grease, are pumped to large holding tanks called “digesters.” The digestion process is accomplished in either an oxygenated (aerobic) or an oxygen-free (anaerobic) environment. The microbes in the waste produce methane and carbon dioxide, or digester gas. The digester gas can be burned as fuel to generate electricity at the plant. This process creates a nutrient-rich organic product called biosolids.
Odor Control
Clackamas County Service District No. 1 (CCSD #1) prides itself on being a “good neighbor;” at each of our plant locations, therefore significant investment has been made to address odor control at the plant. Because odor associated with untreated wastewater can be unpleasant, all significant odor sources at the plant are collected and treated to mitigate the release of offensive odors.
The wastewater treatment process protects public health and the environment. If any of these processes are compromised, the result could alter affects of the entire treatment process, resulting in a negative impact to our local environment, specifically the Willamette River and human health. You can help protect our natural resources by being aware of what you flush and rinse down drains.