The Rock Creek Advanced Wastewater Treatment Facility (AWWTF) in Hillsboro, Oregon serves a rapidly growing community southeast of Portland. This award-winning plant has the largest municipal wastewater nutrient recovery facility in the world. The facility recovers more than 20 dry tons of biosolids each day that is then sold to farmers throughout the state as a soil amendment or as commercial grade fertilizer. The plant also has a significant waste-to-energy cogeneration operation. Their captured methane supplies 30% of the plant’s total electrical needs through on-site electrical generation. Each year, the plant generates more than 5 million kilowatt-hours on-site.
With the combined electrical cost savings from their methane, and a significant revenue stream from fertilizer sales - the plant’s sludge was a very valuable asset. The plant was using an Ostara® phosphorus recovery system to improve nutrient removal, reduce chemical costs and provide a new revenue stream. After unsatisfactory experiences with the performance and aftermarket support offered by the prior sludge screen manufacturer, plant staff elected to consider an alternative supplier for the sludge screening technology.
Hillsboro Clean Water Services contracted with the consulting engineer Brown & Caldwell to design a system to help improve sludge quality at the Hillsboro Rock Creek wastewater treatment plant. Three Hydro-Sludge® Screen systems were selected to provide clean sludge to the phosphorus recovery system and increase the capacity of downstream sludge treatment processes. The three unit Hydro-Sludge® Screens are used to screen pumped primary sludge with a 2% total solids concentration.
Since installation, the plant has been happy with the output and performance of the systems.
The Hydro-Sludge Screen removes tramp material from sludge and dewaters the material in a single, enclosed unit. Sludge enters the screening zone, flowing through the perforated screen, and exits via a flanged connection. Noncompressible solids larger than the 5mm perforations are retained within the screen basket and transported to the dewatering zone by the rotating screw.
The separated solids are dewatered in the pressing zone and compacted into a plug under gradually increasing pressure. Liquid sludge from the dewatering and pressing zones drains through the 3mm perforations, combining with the drained sludge from the screening zone. As the screening plug is formed, the drive load increases pushing the screenings against the backpressure cone.
The drive load is monitored and converted to a pneumatic pressure which adjusts the backpressure on the cone to release solids. The dewatered solids fall through the screenings outlet and are collected in a solids receptacle for final disposal.