WateReuse Foundation, Alexandria, Virginia
07/02/03 - 12/31/04
Membrane bioreactors (MBRs) are a relatively new wastewater treatment technology which promise exceptional treatment efficiency and a reduced footprint compared to conventional treatment process trains. MBRs may be particularly well suited to situations in which water recycling is required or desired including satellite reclamation (sewer mining). MBRs are quite simply an activated sludge process in which the conventional secondary clarifier is replaced by a membrane separation process (either microfiltration or ultrafiltration). The MBR can be operated either with or without primary clarification, but always requires fine screening (3 mm or smaller) to protect the membranes from abrasive and stringy waste components (hair in particular).
Due to the presence of an absolute barrier for suspended solids, MBRs are able to maintain very high solids concentrations (8,000 to 20,000 mg/L) and solids retention times which allows for smaller aeration basins and high BOD removals. Since MBR effluent is micro- or ultra-filtration permeate, effluent suspended solids are typically near the detection limit and turbidities are typically less than 0.2 NTU. As with other membrane systems, the most important characteristics are the membrane flux and the membrane permeability both of which are highly temperature dependent (lowest temperature controls design). Flux is often expressed as gallons permeated per day per square foot of membrane area (GFD) and permeability is usually the clean water flux per unit transmembrane pressure (TMP). With correct process design, MBRs can accomplish the same things as any activated sludge process including BOD removal, nitrification, denitrification, and biological phosphorus removal.
The overall objective of the project was to facilitate an increase in water recycling through the use of membrane bioreactor (MBR) technology.