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Education/Training + Get AlertsWASTEWATER - By Rick Lallish
Where do the bacteria obtain the necessary oxygen to survive in an anoxic zone?
A. Remaining dissolved oxygen
B. Nitrite and nitrate
C. Carbonaceous oxygen
D. The bacteria in an anoxic zone do not require oxygen
Answer: B. Anoxic zones are generally found in denitrification treatment processes. Anoxic conditions are created when dissolved oxygen has been depleted, leaving oxygen only available in the form of nitrite and nitrate. More information may be found in the Water Environment Federation textbook: Wastewater Treatment Fundamentals I – Liquid Treatment, Chapter 9.
DRINKING WATER - By Drew Hoelscher
The raw water to be treated has a total alkalinity of 275 mg/L as CaCO3 and a total hardness of 375 mg/L as CaCO3. What is the concentration of noncarbonate hardness?
A. 100 mg/L
B. 187.5 mg/L
C. 275 mg/L
D. 375 mg/L
Answer: A. When total hardness and total alkalinity are known, comparing the two informs an operator on the concentrations of hardness related to calcium and/or magnesium linked with bicarbonate and carbonate (CH), as well as hardness related to calcium and/or magnesium linked with chloride and sulfate (NCH). The table below illustrates that the amount of NCH is equal to the difference between the total hardness and the total alkalinity.
Lab Results Carbonate Hardness Noncarbonate Hardness
TH TA CH TH NCH 0
TH TA CH TH NCH TH TA
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.
