WASTEWATER
By Rick Lallish
What factor should be considered when calibrating dissolved oxygen instruments?
A. Water viscosity
B. Barometric pressure
C. Effluent BOD
D. Effluent TSS
Answer: B. When calibrating a dissolved oxygen meter or probe, it is important to know the barometric pressure, which is directly proportional to the oxygen solubility of the water. The amount of oxygen the water can hold increases as the barometric pressure increases. You may have to manually input this reading to properly calibrate the instrument. Another fact to consider is that oxygen solubility decreases as the temperature and salinity increase. Knowing these factors may help when troubleshooting or calibrating a DO instrument. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals 3: Advanced Treatment, Chapter 12, Instrumentation.
DRINKING WATER
By Drew Hoelscher
Which statement is true about an autoclave?
A. Valve opens and closes based on distribution system pressure
B. Valve opens and closes based on selected contaminant concentrations
C. Is used to sterilize laboratory equipment
D. Continuously monitors for pathogenic organisms to ensure proper disinfection dosages
Answer: C. Autoclave sterilization of laboratory equipment, such as bacteriological bottles, is common. This method of sterilization relies on heat from pressurized steam. Autoclaving used bacteriological sample bottles allows a water system to reuse equipment, which saves money and is environmentally friendly.
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.
