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13.44 CHAPTER THIRTEEN

Concentrate from membrane processes is typically considered a waste stream that must
be disposed of in accordance with applicable local discharge regulations. Because these
regulations vary considerably from one geographic location to another, it is not practical
to provide more than general information on the proper methods of concentrate disposal
for a certain treatment. Disposal alternatives are easier for MF and UF systems, which do
not concentrate salts, than for RO, NF, and ED/EDR systems. Potential concentrate dis-
posal options for RO, NF, and ED/EDR include (Mickley et al., 1993)
• Discharge to surface water
• Land application (e.g., irrigation, possibly after blending with other low-TDS waters)
• Injection wells
• Evaporation ponds
• Evaporators
• Wastewater collection system
• Wastewater treatment plant effluent
Spent (used) cleaning and membrane storage solutions are typically disposed to a san-
itary sewer system after pH neutralization. Often spent solutions are transferred to stor-
age tanks with provisions for adding acid and caustic to neutralize low- and high-pH clean-
ing solutions. Neutralized spent solution is then transferred to the disposal location.

Instrumentation and Control

Instrumentation and control (I&C) facilities vary greatly depending on membrane process
type, application, and degree of automatic monitoring and control desired. Some mem-
brane systems are fully automatic for normal operation and are designed to be monitored
remotely by means of modems connected to computer-based controls.
A minimum of I&C equipment is necessary for all systems to protect equipment from
damage. For example, low-suction pressure switches or other devices automatically shut
off the system on loss of adequate flow. It is also common to provide on-line instrumen-
tation to measure feed and product water qualities.
If source water temperature and turbidity are variable, the membrane system should be
provided with instrumentation to continuously measure water temperature and feedwater tur-
bidity. Product water turbidimeters or particle counters usually monitor UF and MF systems.
For RO, NF, and ED/EDR systems, conductivity monitors installed on the feed and product
flow streams monitor salt removal performance. Where acid is fed for feedwater pH adjust-
ment, an on-line pH meter with high/low alarms is commonly used. ED/EDR systems typ-
ically provide for pH measurement of the feed, product, and concentrate flow streams.
Pressure-driven membrane systems typically have either feed and product or product
and concentrate flowmeters. Pressure gauges indicate all critical pressures and pressure
differentials, such as membrane feed, interstage, concentrate, permeate, and, unless de-
termined solely by calculations, differential pressure across each stage.
ED/EDR systems typically have flowmeters for the dilute in, concentrate makeup, and
electrode flow. Pressure gauges are usually provided to measure inlet and outlet pressures of
the dilute and concentrate flow streams, as well as the pressure of the electrode flow stream
of each membrane stack. Additionally, ED/EDR systems continuously monitor current flow
and voltage; for EDR systems, measurements are needed for each electrical polarity.
Elapsed time meters provided on the power supply to the membrane system track ac-
cumulated run time. Sampling stations should be provided at all important process loca-
tions in the piping system for periodic sampling and analyses.