Treatment Process

The Pleasant Hills Authority Treatment Plant uses the activated sludge process to treat the sewage and generate water that can be safely returned to the environment. In the activated sludge process, naturally occurring micro-organisms ("bugs") feed on the sewage and breakdown the organic matter and nutrients in the sewage so they can be separated from the water. The process requires different kinds of bugs to treat the different elements in the sewage. The challenge in the process is to create the conditions for all of the bugs to fully treat the sewage and to balance the amount and type of bugs in the system with the sewage flow. The process takes about 12 – 18 hours from the time the sewage first enters the plant until the treated water is returned to the environment.

The equipment used to process the sewage at the treatment plant includes:

• 2 mechanical bar screens
• 2 grit removal chambers
• 4 primary clarification tanks
• 4 First Stage aeration tanks
• 3 First Stage final clarification tanks
• 4 Second Stage aeration tanks
• 2 Second Stage final clarification tanks
• 2 UV Disinfection systems
• 2 Digesters
• 1 Screw Press
• 1 Belt Filter Thickener
• Many pumps to move sewage and sludge between the equipment

The Authority is proud of its commitment to the environment by consistently treating the sewage to return safe water to the environment.