WASTEWATER
By Rick Lallish
What is the main problem found when aerobically digesting primary sludge?
A. Increased amounts of endogenous respiration
B. To maintain DO levels, more air is required
C. Loss of microorganism growth required for endogenous respiration
D. Primary sludge should never be fed to an aerobic digester
Answer: B. Primary sludge can be used in aerobic digesters, although secondary sludge is more commonly used. The use of primary sludge, due to an increase of organics (food), will increase the microorganism population until the food source is consumed. Then endogenous respiration will begin. The length of time that aerobic digestion requires will still allow for this to occur. But, due to the growth phase, increased amounts of air will be required to maintain the necessary dissolved oxygen levels. More information may be found in the OWP CSU-Sacramento textbook: Operation of Wastewater Treatment Plants, Volume 2, Eighth Edition, Chapter 4.
DRINKING WATER
By Ron Trygar
The passage of a liquid containing dissolved solids to become more concentrated after passing through a semipermeable membrane in the definition for which process?
A. Reverse osmosis
B. Osmosis
C. Forward osmosis
D. Ultrafiltration
Answer: B. Osmosis is a naturally occurring biochemical process that allows water containing some organic matter and solids to pass through a membrane barrier. The solids in the liquid become more concentrated after passing through the membrane. Think of a satchel of wine contained in a cheesecloth-type bladder that has micropores throughout. Without much pressure, the water seeps through the cheesecloth leaving behind a more concentrated, denser liquid product. Microorganisms such as bacteria rely on osmosis to allow passage of nutrients into their cell.
About the authors
Rick Lallish is water pollution control program director at the Environmental Resources Training Center of Southern Illinois University Edwardsville. Ron Trygar is a certified environmental trainer and water and wastewater program manager at the University of Florida’s Training, Research and Education for Environmental Occupations Center.
