NAMS 2002 Workshop - ICOM 2008

the need of applying pressure to withdraw the permeate. FO membranes are
also likely to have lower fouling propensity compared to high pressure
membranes [4].
Preliminary results from experiments conducted with a flat-sheet cellulose
triacetate FO membrane and an NaCl solution as the DS demonstrated high
sustainable water flux. Membrane fouling was minimal and controlled with
osmotic backwashing. The FO membrane was found to reject 98% of organic
carbon and 90% of ammonium; the OsMBR process was found to remove 99.8%
of organic carbon and 97.7% of ammonium.
In certain situations, when a stream of concentrated brine from a desalination
facility is available, an open-loop OsMBR could be used. In this configuration, the
brine from a nearby desalination facility would be used as the DS and the diluted
DS would be discharged to the sea. Sea discharge of the diluted DS would be
environmentally favorable over direct discharge of the brine because the diluted
DS concentration would be closer to that of seawater.
Further application of the OsMBR process is its possible utilization in osmotic
power generation through pressure-retarded osmosis (PRO). PRO utilizes the
FO principle as a basis for its operation. In PRO the DS is at elevated hydraulic
pressure, lower than the osmotic pressure difference between the feed and the
DS streams. The optimal hydraulic pressure at which the system should operate
is a function of the osmotic pressures of the feed and DS streams and the
membrane characteristics. The water that diffuses through the membrane is
depressurized in a turbogenerator to recover beneficial energy. When OMBR is
operated in PRO mode in order to recover energy, the process is referred to as
the pressure retarded OMBR (ProMBR). Other novel combination of ProMBR will
be introduced. Computer modeling performed with ideal systems demonstrated
that ProMBR can potentially be a viable source of renewable energy.
References
[1] S. Judd, The MBR Book: Principles and Applications of Membrane Bioreactors in Water and
Wastewater Treatment, Elsevier, 2006.
[2] P. Lawrence, S. Adham and L. Barro, Ensuring water re-use projects succeed - institutional
and technical issues for treated wastewater re-use, Desalination, 152 (2002) 291-298.
[3] T. Stephenson, S. Judd, B. Jefferson and K. Brindle, Membrane bioreactors for wastewater
treatment, IWA Publishing, 2000.
[4] A. Achilli, T.Y. Cath, E.A. Marchand and A.E. Childress, The forward osmosis membrane
bioreactor: A low fouling alternative to MBR processes, Desalination, Accepted for publication.