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13.46 CHAPTER THIRTEEN

• Restrooms and locker rooms
• Offices
• Mechanical room for heating, ventilation, and air conditioning equipment
• Lunch/break room
• Training room
Particular attention should be given to the size and location of doorways. In some cases
removable wall panels should be provided to allow large equipment to be removed and
installed.

Materials of Construction
It is particularly critical to use proper construction materials in membrane systems be-
cause corrosion products can foul membranes, resulting in increased cleaning frequency
and shortened membrane life. In addition, process flow streams and chemicals used are
commonly highly corrosive, and for pressure-driven desalting systems, high pressures are
often required.
Where pressures and temperatures allow, nonmetallic (PVC, CPVC, FRP, etc.) piping
and valves are commonly used. Nonmetallic piping is common throughout MF, UF,
ED/EDR, and in some cases NF systems. For applications requiring higher pressures and
temperatures, such as most RO systems, appropriately selected stainless steels are typi-
cal. For example, a 5,000 mg/L TDS brackish groundwater RO system commonly has the
following components (other available material options can also be considered):
• Piping from supply well to pretreatment cartridge filter--PVC or FRP
• Cartridge filter housing--316L stainless steel or FRP
• Piping from cartridge filter to membrane feed pump suction connection--PVC or FRP
• Membrane feed pump discharge piping--316L stainless steel
• RO pressure vessels--FRP
• RO membrane unit interstage and concentrate lines (up to and including the concen-
trate control valve)--316L stainless steel
• Concentrate line downstream of the concentrate control valve--PVC or FRP
• Permeate piping--PVC or FRP

For low-salinity (freshwater) applications, 304L stainless steel is sometimes used for
low- and high-pressure piping. For seawater RO system high-pressure lines, higher-alloy
stainless steels, with a molybdenum content of 6% or more, are commonly used. Alter-
natively, polyethylene-lined carbon steel piping has been used for seawater RO high-pres-
sure piping, although piping failures have been reported when the lining was improperly
manufactured or damaged after manufacturing.
Because many membrane systems require concentrated chemicals, storage and handling
systems must be designed with appropriate materials and with operator safety in mind.

Process Reliability and Redundancy Issues
In designing membrane systems, the same reliability and redundancy issues considered
for conventional treatment facilities should be evaluated. Membrane treatment systems