WASTEWATER
By Rick Lallish
When operating a membrane bioreactor (MBR), what is the difference between fouling and clogging when troubleshooting the process?
A. There is no difference between the two problems
B. Fouling is the condition of inhibited bio-growth on the membrane; clogging is the opposite.
C. Fouling is inhibited permeation of water through the MBR membrane; clogging is found in the clarifier
D. Fouling is excessive bio-growth on the membranes; clogging is inorganic material on the membranes.
Answer: D. MBRs are very effective forms of wastewater treatment. There are two major problems in operating them: fouling and clogging. Fouling occurs when the membranes become coated with organic growth and the permeate is inhibited or cannot pass through the membrane. Fouling is typically removed using a chemical cleaner. Clogging consists of organic debris (rags, hair, trash) that entangles in the membranes and has to be physically removed periodically; otherwise the membranes will be damaged or destroyed. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals III: Advanced Treatment, Chapter 6.
DRINKING WATER
By Drew Hoelscher
What solution weighs 10.8 pounds per gallon?
A. 48% Al2(SO4)3 with a specific gravity of 1.3
B. 12.5% NaOCl with a specific gravity of 1.22
C. 20% HCl with with a specific gravity of 1.08
D. 40% NaMnO4 with a specific gravity of 1.39
Answer: A. Understanding the relative density of a solution is beneficial for chemical feed applications. The density of a chemical solution is a measure compared to the density of water. These measurements can fluctuate due to temperature and atmospheric pressure, so an operator should consider this when comparing a field measurement to a Safety Data Sheet. Specific gravity is often measured using a hydrometer, which can be converted to pounds per gallon by multiplying the specific gravity reading by 8.34.
About the author(s)
Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.
