WASTEWATER
By Rick Lallish
What is the carbon:nitrogen:phosphorus ratio required for bacterial growth?
A. 200:50:25
B. 1:5:1000
C. 100:10:20
D. 100:5:1
Answer: D. The population of microorganisms, or algae in lagoon systems, depends on the amount of carbon, nitrogen and phosphorus available. The universally accepted ratio is 100:5:1. If you lack one of these elements, that would be considered a rate-limiting factor and your facility will have difficulty achieving proper growth of organisms. This factor is a good troubleshooting step. More information may be found in the OWP CSU-Sacramento textbook: Operation of Wastewater Treatment Plants, Volume 2, Eighth Edition, Chapter 2.
DRINKING WATER
By Ron Trygar
Which membrane classification can be used for softening water containing calcium and magnesium ions and to reduce the concentration of natural organic matter?
A Ultrafiltration
B. Microfiltration
C. Nanofiltration
D. Reverse osmosis
Answer: C. The pore sizes found within elements designed for membrane softening and removal of disinfection byproduct precursors are small enough to reject these contaminants at much lower pressure than reverse osmosis units. Nanofiltration units typically operate with pressure in the 70 to 120 psi range, whereas RO units designed for desalination operate at pressures from 100 to 1,200 psi, depending on feedwater salinity.
About the author(s)
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.
