The iMBR is a wastewater treatment technology which combines a submerged membrane separation process (e.g. microfiltration/ultrafiltration) with a suspended growth bioreactor. All current MBR processes utilize the membrane as filter, almost completely rejecting the solid materials which are developed by the biological process, thus resulting in a clarified and disinfected product effluent. Water permeation is realized by means of a suction pump. The two main configurations of iMBR used for wastewater treatment today are hollow fiber (HF) and flat sheet (FS).
A common feature of all iMBRs is the high biomass concentration employed in the mixed liquor (i.e. between 8-12 g/L MLSS at SRTs ranging between 15-30 d). Unfortunately, such high MLSS contents usually come with a significant membrane fouling potential which may gradually lead to a substantial loss in membrane permeability. Membrane fouling can be physically controlled by introducing air at the bottom of the membrane module (air scouring), usually using coarse bubble diffusers. Other effective physical means of fouling mitigation comprise membrane relaxation (periodic cease of permeate suction) and/or backflushing (flow reversal using a small quantity of product water). Chemically enhanced backflushing (CEB) events are also performed on a weekly basis as a means of maintenance cleaning. Finally, the membrane permeability can be recovered up to a great extent only through the implementation of intensive chemical cleaning-in-place (CIP) programs performed once or twice a year.
When used with domestic sewage and certain type of industrial effluents, the iMBR process can provide a substantially clarified and disinfected water stream of high enough quality to be discharged to sensitive receiving bodies or to be recovered and reused for such applications as field irrigation, toilet flushing, recharge of aquifers, or river flow replenishment. As a result, the iMBR process is increasingly becoming the technology of choice for wastewater applications where the aforementioned criteria hold true.
Between the basic advantages offered by the iMBR process are the following:
- High effluent quality, free of suspended and colloidal solids;
- Effluent disinfection without the use of chemicals;
- Effluent quality not affected by poor sludge settleability issues;
- Independent control of hydraulic retention time (HRT) and sludge age (SRT);
- High attainable biomass concentrations in the mixed liquor resulting in significant acceleration of the biodegradation mechanisms;
- Low sludge production;
- Reduced space requirements;
- High retrofit and/or upgrade potential.