January 2011, Vol. 23, No.1
Test your knowledge of membranes
True or False Questions:
- Transmembrane pressure (TMP) is defined as the difference between the feed pressure and the permeate pressure.
- A gradual decrease in TMP usually indicates membrane fouling.
- Oxidants, such as sodium hypochlorite, are typically used to remove scaling from the membranes.
- Acids are typically used to remove inorganic foulants from the membranes.
- In a membrane bioreactor (MBR) system, the activated sludge process does not affect the operational strategy of the membrane system.
Multiple Choice Questions:
Membrane cleaning solutions are typically prepared by mixing a cleaning chemical — sodium hypochlorite, citric acid, etc. — with what?
A. Potable water.
B. Nonpotable water.
D. Membrane permeate.
In an immersed MBR, what is the main purpose of the membrane air scour?
A. To maintain a consistent solids concentration in the membrane tank.
B. To continuously remove solids from the membrane surface.
C. To provide oxygen for the biological process.
D. To create foam.
Cartridge filters, commonly used as pretreatment for nanofiltration (NF) or reverse-osmosis (RO) membranes, should be replaced when the pressure loss across the cartridge filters exceeds what value? (Note: System feed pressure is greater than 150 lb/in.2.)
A. 1 lb/in.2.
B. 3 lb/in.2.
C. 15 lb/in.2.
D. 50 lb/in.2.
Symptoms of O-ring or seal failure in pressure membrane systems can be what?
A. A sharp increase in TMP and a sharp decrease in rejection.
B. A gradual increase in TMP and no change in rejection.
C. A sharp decrease in TMP and a sharp decrease in rejection.
D. A gradual decrease in TMP and no change in rejection.
Cleaning the membranes should cause the permeability/specific flux to do what?
C. Not change.
Which of the following methods cannot be used to continuously monitor membrane integrity for MBR, microfiltration, ultrafiltration, NF, and RO systems?
A. Permeate turbidity.
B. Permeate temperatures.
C. Permeate conductivity.
D. Permeate particle count.
What is the maximum silt density index (SDI) in the feed water recommended by manufacturers of spiral-wound membranes?
Calculate the SDI (ASTM D4185), given the following information:
Ti, time to collect initial 500 mL
Tf, time to collect second 500 mL
Tt, total test time
Calculate the membrane permeability (gal/ft2•d per lb/in.2) for a pressurized MF membrane system, at reference conditions/temperature, given the following information:
Feed flow = 1000 gal/min
Average feed pressure = 60 lb/in.2
Permeate flow = 850 gal/min
Permeate pressure = 15 lb/in.2
Membrane area = 50,000 ft2
A. 0.40 gal/ft2•d per lb/in.2.
B. 0.48 gal/ft2•d per lb/in.2.
C. 0.54 gal/ft2•d per lb/in.2.
D. 0.64 gal/ft2•d per lb/in.2.
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Tony Greiner is a senior associate in the Charlotte, N.C., office of Hazen and Sawyer (New York).
American Water Works Association (2005). Microfiltration and Ultrafiltration Membranes for Drinking Water, Manual of Water Supply Practices M53, First Edition. Denver: American Water Works Association.
American Water Works Association (2007). Reverse Osmosis and Nanofiltration, Manual of Water Supply Practices M46, Second Edition. Denver: American Water Works Association.
Water Environment Federation (2006). Membrane Systems for Wastewater Treatment. Alexandria, Va.: Water Environment Federation.
©2011 Water Environment Federation. All rights reserved.