WASTEWATER
By Rick Lallish
What type of pump should never be operated or started against a closed valve?
A. Centrifugal pump
B. Peripheral pump
C. Positive displacement pump
D. Screw lift pump
Answer: C. Basic operation and knowledge of pumps and pumping are fundamentals that wastewater operators should understand. Positive displacement pumps are ideally suited for the pumping of solids such as sludges. They are also well-suited for some chemical applications, such as polymers. Due to the tremendous pressure built up by the pump, a positive displacement pump must never be operated against a closed valve or in a dry condition for very long, or else it may rupture and cause damage to the pump, pipes and valves.
DRINKING WATER
By Drew Hoelscher
Which stream of water from a reverse osmosis membrane system is the most hypotonic?
A. Concentrate
B. Permeate
C. Reject
D. Feedwater
Answer: B. Reverse osmosis is a membrane process that can separate water molecules from contaminants. During the process, feedwater is pressurized through the membrane, creating a stream of permeate (recovery water) and a stream of concentrate (reject water). The permeate water is relatively free of contaminants and is sometimes referred to as pure water. The lack of solutes in the permeate is what makes this solution more hypotonic than the hypertonic feedwater and reject water.
About the authors
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.
