The Confederated Tribes of the Coos, Lower Umpqua and Siuslaw Indians were looking to upgrade their temporary casino while at the same time protecting the environment and reservation forest lands. Located on the beautiful Central Oregon coast in the quaint town of Florence, the upgraded Three Rivers Casino houses more than 700 slots, 90 deluxe rooms, five restaurants and a large event center.
There was an existing sequencing batch reactor that was unable to handle the additional capacity from the casino and hotel upgrade, so the Tribes needed to hire a team to investigate different treatment options. After an extensive search, they selected the design-build team of The Dyer Partnership of Coos Bay and Triad Mechanical of Portland. This team was intent on providing the owner with “the simplest facility, with the highest quality effluent, smallest footprint, lowest operation and maintenance costs, the most flexible and reliable” wastewater treatment plant possible for the anticipated flows and loadings. With these criteria in mind, the team selected the Enviroquip MBR system  .
The plant was designed for a full build-out average annual flow of 200,000 gal per day (gpd) and a peak daily flow of 400,000 gpd. Since the Enviroquip MBR system  is so modular and easily expandable, only half of the membrane capacity was installed to reduce the upfront capital expenditure and more closely match the actual influent hydraulic demands. As the casino and hotel expand further, the additional membrane capacity can easily be installed. Influent design loadings were BOD/TSS/TKN of 750/575/80 mg/L. Effluent design parameters were BOD/TSS/NO3 of 2/2/5 mg/L. Only 6 ft of head is required for gravity permeate collection with the Kubota  membranes, so the team chose this option. The plant was designed, built and operational in seven months from the notice to proceed.
This MBR plant is a three-stage MLE design with influent first passing through a grease interceptor and into an influent pump station. The pump station pumps the flow up to the fine screens before entering into the MBR. Pressate from the Amcon screw press and backwash and brine from the water plant are also fed into the MBR. Effluent from the MBR is used for surface irrigation of the surrounding dunes after chlorination. With two weather stations nearby, if the winds get too high, then the effluent can be diverted into the existing drainfield. Screw-press solids are then sent to the landfill for disposal.