Membrane technology is a well established method for wastewater treatment with advantages including: relatively easy to operate; low turbidity and BOD in the effluent; and less space required for treatment (Tchobanoglous et al., 2003). However, some of these benefits are offset by a few disadvantages including: higher capital cost; high energy costs; and high maintenance costs (Tchobanoglous et al., 2003). A novel gravity-flow filtration system named a Biomass Concentrator Reactor (BCR), developed by EPA-NRMRL and the University of Cincinnati (Patent No. 6821425 issued Nov. 23, 2004), has been proposed to achieve lower cost membrane filtration while maintaining the benefits of typical membrane bioreactors.
The BCR was tested using synthetic municipal wastewater under conditions of typical aerobic degradation, as well as alternating aerobic and anoxic conditions for biological nitrogen removal. Two solids retention times (SRT) were considered, 6 day and 15 day, at 9 hour hydraulic retention time (HRT). The recycle flow for the alternating aerobic/anoxic reactor was twice the reactor flow rate.
Under these conditions, the BCR was able to achieve nearly 100% solids separation of mixed liquor with less than 2.5 cm of hydraulic head loss. Total nitrogen (TN) and chemical oxygen demand (COD) removals are summarized in the table below for the various operating conditions. Reactor 1 was operated with separate aerobic and anoxic sections while reactor 2 was operated under only aerobic conditions.
HRT (hrs) SRT (days) COD removal (%) TN removal (%)
Reactor 1 9 6 95 79
15 97 75
Reactor 2 9 6 93 53
15 93 43