EVAC membrane bio-reactor (MBR) consists in merged intensive biological and ultra-filtration processes. The package wastewater treatment plant is composed of an equalizing anoxic tank, an aerated tank for biological process and a membrane submerged in the aerated tank (Figure 1). The effluent is produced by gravity flow or slight vacuum through the membrane so it does not require high energy consumption for effluent pumping. The membrane is covered by a biofilm reducing the pore size down to ultra-filtration and providing further biological removal (Figure 2).
Evac MBR provides an extensive removal of contaminants allowing various reuse applications. It removes more than 99% of bacteria, solids and organics, and more than 85% of nitrogen and phosphorus compounds. Standard flow capacity ranges between 1.5 and 111 m3/day, above this value we provide a customized design. In addition, Evac MBR does not require to be placed underground or to have a post-treatment by soil infiltration.
Figure 1 EVAC MBR technology and membrane picture
Figure 2 MBR membrane screening
MBR technology offer many advantages over conventional sewage treatment plant and for water reuse:
- Lower footprint : Evac MBR is a very compact system including biological treatment and filtration in the same step (Figure 3).
- Odorless: The system is mainly aerobic and the package plant is covered
- Energy conservative system: Evac MBR uses gravity filtration instead of effluent pumping
- Low sludge production: as all the mixed liquor is retained in the bioreactor thanks to the membrane the sludge yield is lower than conventional activated sludge process. This means that less sludge needs to be post-treat.
- Higher performances: the combination of ultra-filtration and higher biomass concentration results in very high performances (Table 1 and 2).
- More robust and more reliable: Evac MBR is more resistant to shock load, and compared to conventional activated sludge there is no problem of sedimentation or filamentous bacteria.
- Ultra-filtration provides an ultimate barrier against pathogens, such as the chlorine-resistant organisms, Cryptosporidium, Legionella and Giardia.
- Simple and automated operation
Figure 3 Footprint of conventional activated sludge process vs. EVAC MBR
Compared to other MBRs, EVAC MBR offers:
- Longer membrane life of 10 years, thanks to the low strain and chemical exposure put on a high quality membrane
- Higher pollutant screening by the ultra-filtration instead of usual micro-filtration
- Requires less energy as Evac MBR uses gravity or slight vacuum flow (Figure 4)
- Requires less maintenance : Because of the low trans-membrane pressure, no back-flush and little chemical cleaning is required (Figure 4)
Figure 4 Relative chemical and power consumption compared to other treatments
Table 1 Performances Test of EVAC MBR
Table 2 Compliance toward water reuse standards (US EPA, 1992; WERF, 1992)
Judd, S. (2006), The MBR book: Principles and application of membrane bioreactors in water and wastewater treatment, Elsevier Ltd., Oxford, UK.
Stephenson, T., Jefferson, B., Judd, S. and Brindle, K. (2000), Membrane bioreactor for wastewater treatment, IWA publishing, London