Exam Study Guide

WASTEWATER

By Rick Lallish

Hydrogen sulfide is oxidized to sulfuric acid by what bacteria, common in pipe walls in collection systems and lift station wet wells?

A. Nocardia

B. Thiobacillus

C. Thiothrix

D. Autotrophicis

Answer: B. Hydrogen sulfide has a lifecycle that goes from liquid to gas to liquid in certain conditions. Sulfates present in wastewater are changed to sulfide by bacteria in waterline slime layers. The flow splash and turbulence caused the H2S gas to release. The gas is then oxidized by the Thiobacillus bacteria to corrosive sulfuric acid, which drips down the pipes and then changes back to sulfate in the wastewater stream. More information may be found in the OWP, CSU-Sacramento textbook: Operation and Maintenance of Wastewater Collection Systems (Eighth Edition), Chapter 5.


DRINKING WATER

By Drew Hoelscher

What chemical can be used in place of calcium hydroxide and sodium carbonate for softening?

A. Sodium chloride

B. Sodium sulfate

C. Sodium hydroxide

D. Calcium sulfate

Answer: C. Sodium hydroxide (caustic soda) can reduce carbonate and noncarbonate hardness. This method usually increases chemical costs and total dissolved solids when compared to calcium hydroxide and sodium carbonate. However, sodium hydroxide generally produces less sludge and is generally considered easier to handle than calcium hydroxide. 

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.



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