Membrane and Desalination Technologies - TCE Moodle Website

336 N.K. Shammas and L.K. Wang
determined that the membrane filtration system(s) that will be used at full-scale (e.g., if an
MF/UF system has been preselected) requires air at a specified flow rate and duration during a
backwash process, then the pilot system should be designed and operated in a similar manner.
The design of the membrane system should also mimic the hydraulic configuration of the fullscale
system. However, it should be recognized that it might not be possible to design a pilot
system using the same hydraulic configuration used at full-scale for all membrane processes.
For example, it may not be economically feasible to design a NF/RO pilot unit with hydraulic
characteristics identical to the full-scale system. In this case, the methodology of conversion
from pilot-scale data to full-scale design should be included in the development of the pilot
test protocol.
2.1.2. Screening and System Selection
Spiral-wound NF and RO membrane modules are standardized such that the membranes
from different manufacturers are interchangeable and system design is somewhat uniform.
Thus, in terms of screening for appropriate membranes, the primary consideration involves
the selection of a membrane material that provides desirable productivity, resistance to
fouling, and removal characteristics.
Screening is somewhat more complex for MF/UF systems, which are largely proprietary in
design. The various commercially available systems may use either pressure or vacuum as the
driving force and can be designed to filter from the inside-out or outside-in direction relative to
the fiber lumen. In addition, the various membrane materials have differences that may be
important, including removal efficiency and pH and oxidant tolerance. Membranes of different
materials also have varying degrees of compatibility with water treatment chemicals such as
coagulants (8) and powdered activated carbon (PAC) (9) that may affect performance and cost. It
is important to consider such differences in MF/UF membranes and membrane systems and how
these may impact system selection. For example, if the source water were periodically prechlorinated
(10), a membrane that is not compatible with chlorine would be undesirable. A list of
some questions to consider when screening membranes for a pilot study is provided below (1):
1. What are the treatment objectives of the application?
2. What operational constraints/goals are to be considered in membrane selection?
3. Has the membrane been used on similar waters at other sites?
4. What are the pH and oxidant tolerances of the membrane? Are these compatible with the
application?
5. Is the membrane compatible with any pretreatment chemicals aside from oxidants that may be in
use, such as alum, ferric chloride, PAC, and polymers?
6. Is this membrane compatible with solids and total organic carbon (TOC) levels in the raw water?
7. Does the membrane have prior applicable state regulatory approval and any required certifications?
8. Does the supplier have experience with full-scale operation for a facility of this size and for
treating similar water with the same configuration to be used in the pilot?
9. Does the system require proprietary items such as spare parts or cleaning chemicals?
10. Are there any unusual operational considerations associated with the membrane filtration system,
such as significant power requirements, frequent membrane replacement, or substantial or
undesirable chemical use?