NAMS 2002 Workshop - ICOM 2008

Desalination II – 2
Thursday July 17, 3:00 PM-3:30 PM, Honolulu/Kahuku
Parameters Affecting Osmotic Backwash
N. Avraham, Grand Water Research Institute, Technion, Haifa, Israel
A. Sagiv (Speaker), Grand Water Research Institute, Technion, Haifa, Israel
C. Dosoretz, Grand Water Research Institute, Technion, Haifa, Israel
R. Semiat, Grand Water Research Institute, Technion, Haifa, Israel - cesemiat@technion.ac.il
The Reverse Osmosis (RO) membrane cleaning process is of great interest to
the desalination industry. The water volume needed for the backwash process
and the time duration of the wash process are key parameters that must be
considered in practice. Appropriate changes in feed and permeate applied
pressures across the membrane for a given concentration difference enable a
shift back and forth from the RO to the BW process with minimal intervention by
the RO desalination process. Effects of different parameters, including operation
pressure and salt concentration, were investigated experimentally in the present
study. Experiments were carried out, measuring the wash volume as a result of
different salt concentrations in the RO steady-state operation prior to the
backwash experiment and at different pressures on both sides of the membrane.
Results show that within the operated range of parameters, the wash volume is
basically independent of the initial pressure difference. Yet, as expected, it is
affected by the difference in concentrations across the membrane. It was found
that the wash volume increases with the concentration differences at the lower
range and decreases at the higher range. This result is explained by the two
opposite flux mechanisms discussed in a previous study of zero BW applied
pressure. The BW volume decreases with BW feed applied pressure, indicating a
decrease in BW driving pressure. For a similar reason, the BW volume increases
with increased permeate side pressure since it increases the BW driving
pressure.
Results of the present study provide an experimental basis for further
understanding the BW process under industrial conditions, and finding BW
characteristics necessary for the efficient design of RO-based desalination
plants.