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. 

About the author

Rick Lallish is water pollution control program director at the Environmental Resources Training Center of Southern Illinois University Edwardsville.