Startup of a Low Phosphorus Nitrifying Tertiary Membrane System

The first stage of the tertiary membrane bioreactor facility for low level phosphorus removal and nitrification has been commissioned at the City of Coeur d’Alene (the City, CDA, Figure 1) in January of 2015. This marks the conclusion of significant investments made by the City over a span of eight years to develop a cost efficient technical solution for compliance with effluent phosphorus limits, which at the time (0.01 mg/L TP monthly average, 2006) where unprecedented.Because this tertiary membrane process with chemical sludge inventory or tertiary membrane bioreactor (TMBR) has not previously been proven at full scale, the City decided to proceed with caution and only install 1/5 of the capacity, required in the future, but to do so earlier than required for compliance in order to prove and fine tune the process before fully committing to the TMBR.The performance of the TMBR system itself is only part of the greater picture. Even operating at only 1.0 mgd, the TMBR is expected to impact the main plant in three ways; (1) equalized ammonia rich dewatering centrate will be routed directly to the TMBR to grow additional nitrifiers which will be wasted (seeded) to the contact stabilization basins, (2) along with the nitrifiers chemical sludge will be sent to the contact stabilization, which is expected to contribute significantly to the secondary phosphorus removal due to its ability to removal PO4-P through adsorption and complication, and (3) the seeding is expected to reduce the minimum solids retention time (SRT) and MLSS in the contact stabilization basin as well as reduce the secondary alum dose.