The City selected AE2S to conduct treatment evaluations and prepare a planning document to bring its WWTF into regulatory compliance. Along with the planning services, AE2S Nexus developed a funding package. This provided sound recommendations for steps toward a responsible and sustainable financing plan.
AE2S helped the City secure a new outfall for continuous discharge to Bear Butte Creek. Additionally, AE2S evaluated the following secondary treatment alternatives: lagoon upgrades; submerged attached growth reactors (SAGR); traditional activated sludge process upgrades; and membrane bioreactor (MBR) technologies. The City opted to proceed with the design of an MBR mechanical plant due to its reliability to produce effluent of excellent quality to meet the stringent limits required by the State and the City’s new discharge permit. AE2S completed the design of the new MBR plant, with bidding completed during the fall of 2019.
Some key elements of the design include a flow equalization structure that directs flows to either the master lift station or to the existing treatment lagoon for equalization storage. The master lift station pumps influent to the grit screen building (GSB). The GSB includes a grit removal system, fine screens, and a splitter structure for directing flow to the MBR process. After the GSB the wastewater will flow by gravity to the membrane bioreactor (MBR) process. In the MBR process, aerobic treatment tanks will provide BOD removal and nitrification, and a pre-anoxic tank will provide denitrification. Following these treatment steps, flow will be directed to the MBR tanks. Three tanks, with space for a future fourth tank, will hold membrane cassettes that provide separation of the activated sludge microorganisms from the treated wastewater. With a nominal pore diameter of 0.04 microns, the membranes will even separate out some viruses. Following MBR tanks, the effluent is pumped to an ultraviolet disinfection system for disinfection of the effluent.
Construction began in March 2020 and continues to progress. The grit screen and advanced biological treatment buildings are nearing completion, with the recent erection of precast panels. Utilities are installed, site grading is taking place, and the membrane cassettes will be installed in the near future. It is estimated the system will be brought online in the summer of 2021.