Basic Wastewater Operations- Chapter 11 (Sludge Processing) Exam Questions with Verified Answers
(Graded A+)
T/F: The purposes of sludge digestion are to reduce the volume, to make it easier to dewater, to stabilize
organic solids, and to change color. - Answers False; reduces odor not color
T/F: Four types of sludge are primary, humus, activated sludge, and digested sludge. - Answers True
T/F: Primary sludge settles in the secondary clarifier. - Answers False; primary clarifier
T/F: Humus sludge sloughs off from the zoogleal mass in fixed-film processes. - Answers True
T/F: Activated sludge settles in the primary clarifier or is wasted from an activated sludge process. -
Answers False; secondary/final clarifier
T/F: Sludge is digested aerobically or anaerobically. - Answers True
T/F: Aerobically digested sludge is brown in color, has very little odor, and does not dewater readily. -
Answers True
T/F: Anaerobically digested sludge is dark in color, has a tarry odor, a grainy texture, and does not
dewater readily. - Answers False
T/F: The two stages of anaerobic digestion are the acid stage and the methane fermentation stage. -
Answers True
T/F: In the acid stage, facultative bacteria, called acid formers, convert organic material into volatile
(organic) acids. - Answers True
T/F: In the methane stage, an aerobic bacteria, called methane formers, convert the organic acids into
methane gas. - Answers False
In a well-operated anaerobic digester, the methane gas content is about __________.
A. 60-65%
B. 65-75%
C. 70-80%
D. 75-85% - Answers B. 65-75%
Anaerobic digesters are covered to keep out ____________, to trap the useful methane, and to keep the
digester warm.
A. Carbon dioxide
B. Hydrogen sulfide
(Graded A+)
T/F: The purposes of sludge digestion are to reduce the volume, to make it easier to dewater, to stabilize
organic solids, and to change color. - Answers False; reduces odor not color
T/F: Four types of sludge are primary, humus, activated sludge, and digested sludge. - Answers True
T/F: Primary sludge settles in the secondary clarifier. - Answers False; primary clarifier
T/F: Humus sludge sloughs off from the zoogleal mass in fixed-film processes. - Answers True
T/F: Activated sludge settles in the primary clarifier or is wasted from an activated sludge process. -
Answers False; secondary/final clarifier
T/F: Sludge is digested aerobically or anaerobically. - Answers True
T/F: Aerobically digested sludge is brown in color, has very little odor, and does not dewater readily. -
Answers True
T/F: Anaerobically digested sludge is dark in color, has a tarry odor, a grainy texture, and does not
dewater readily. - Answers False
T/F: The two stages of anaerobic digestion are the acid stage and the methane fermentation stage. -
Answers True
T/F: In the acid stage, facultative bacteria, called acid formers, convert organic material into volatile
(organic) acids. - Answers True
T/F: In the methane stage, an aerobic bacteria, called methane formers, convert the organic acids into
methane gas. - Answers False
In a well-operated anaerobic digester, the methane gas content is about __________.
A. 60-65%
B. 65-75%
C. 70-80%
D. 75-85% - Answers B. 65-75%
Anaerobic digesters are covered to keep out ____________, to trap the useful methane, and to keep the
digester warm.
A. Carbon dioxide
B. Hydrogen sulfide
