SECTION 5-10
MAINTENANCE
FLOWMAX RO MANUAL REV: B 05/1999
USFilter
United States Filter Corporation
5.7 RO MEMBRANE ELEMENT CLEANING
NOTE:
To clean the membrane elements in situ, a CIP skid (stands for Clean In Place) is
required. This can be purchased from
USFilter
if you want to do your own cleaning.
Cleaning services are available from the most of the
USFilter
service branches. Call the
local sales and service office for details.
Read the following section to help you understand why RO membrane elements need to be cleaned, and
the nature of the foulants that can be encountered.
NOTE:
RO membrane element cleaning is a complex process and if done incorrectly, could
destroy the membrane elements. A complete cleaning procedure is described in the CIP
operating manual.
It should be noted that a decrease in water temperature will result in a decrease in product water
flow and increase in the differential pressure across the membrane. This is not indicative of a
requirement for cleaning.
The data collected after the first 24 to 48 hours of operation of the RO unit should be used as a
baseline for the above parameters. It is critical that the data collection sheets, supplied in the
Appendix, are completely filled out on a daily basis.
You will find it necessary to clean the RO UNIT from time to time as a result of the natural
accumulation of some type of membrane surface foulant. This requirement to clean the RO
UNIT membranes will be evidenced by one or more of the following symptoms including, a
reduction
in the NORMALIZED PRODUCTIVITY RATE, a
reduction
in the RO UNIT
TOTAL DISSOLVED SOLIDS REJECTION RATE, or an
increase
in the RO UNIT
OPERATING PRESSURE, in spite of no change in the RO UNIT feed water temperature. In
general, this procedure should not be required more then three (3) times per year or about every
four (4) months. If you find that this procedure is required more frequently then this, you should
have a U.S. Filter representative evaluate the effectiveness of your pre-treatment system or the
current RO UNIT operating parameters. Most cleaning procedures consist of the preparation of
a specific cleaning chemical formulation made up in warm water, which is then recirculated
through the RO UNIT elements, followed by an extended soak period in the cleaning solution,
followed by another recirculation cycle, and completed with a thorough rinse cycle.
The RO UNIT membrane foulants usually consist of one or more of three common classes of foulants
including; SUSPENDED SOLIDS, ORGANIC FOULANTS AND PRECIPITATED DISSOLVED
SOLIDS. A brief explanation of the nature of each type of foulant will is below.
SUSPENDED SOLIDS FOULANTS
Suspended solids fouling is among the most common RO UNIT foulants. This fouling condition
results from the incomplete removal of suspended solids such as silt and clay particles from the
RO UNIT feed water. In as much as some of these particles are less then 0.2 micron in size, it is
not practical to attempt to remove all of them so this type of membrane fouling is eventually
inevitable in all RO UNITS. This is most common to systems operating on a surface water
supply. The trick is to try to eliminate as much of the suspended solids material as possible,