Question | Answer | % Correct |
---|---|---|
In an anaerobic digester, a ________ change per day is best. | 1°C | 100%
|
In a well-operated anaerobic digester, the methane gas content is about ________. | 65–75% | 100%
|
Methods of removing water from sludge to reduce its bulk include drying beds, belt presses, gravity thickeners, and ________. | centrifuges | 100%
|
Aerobic digestion is an ________ process whereby the aerobic bacteria consume themselves. | endogenous | 100%
|
The purposes of sludge digestion are to reduce the volume, to make it easier to dewater, to stabilize organic solids, and to change the color. | False | 100%
|
Primary sludge settles in the secondary clarifier. | False | 100%
|
Anaerobically digested sludge is dark in color, has a tarry odor, a grainy texture, and does not dewater readily. | False | 100%
|
Three layers found in anaerobic digesters are supernatant liquor, scum, and ________. | gas | 100%
|
Anaerobic supernatant liquor is the ________ that separates from the sludge | gray liquid | 100%
|
Overloading anaerobic digesters causes foaming, poor gas production, and ________. | low pH | 100%
|
Laboratory tests that should be done to operate an anaerobic digester are alkalinity, temperature, volatile acids, percent volatile solids, percent carbon dioxide, and ________. | pH | 100%
|
Humus sludge sloughs off from the zoogleal mass in fixed-film processes | True | 100%
|
The two stages of anaerobic digestion are the acid stage and the methane fermentation stage. | True | 100%
|
Four types of sludge are primary, humus, activated sludge, and digested sludge. | True | 100%
|
Landfilled sludge must have a solids content of at least ________. | 20% | 0%
|
Anaerobic digester trouble signs are low pH (add lime to near neutral), increased ________, decreased alkalinity, and increased volatile acids. | CO2 | 0%
|
In the methane stage, aerobic bacteria, called methane formers, convert the organic acids into methane gas. | False | 0%
|
Activated sludge settles in the primary clarifier or is wasted from an activated sludge process. | False | 0%
|
Anaerobic digesters are covered to keep out ________, to trap the useful methane, and to keep the digester warm. | free oxygen | 0%
|
Unstabilized anaerobic sludge contains streaks of ________ or ________. | gray/green | 0%
|
Anaerobic sludge is heated by pumping it through pipes heated with ________. | hot water | 0%
|
Disposal methods for digested, dewatered sludge are ________, landfill, and incineration. | land application | 0%
|
The useful ________ can heat the digester or buildings, fuel engines, or produce steam. | methane gas | 0%
|
Anaerobic digester mixing methods are gas, mechanical, or ________. | pump | 0%
|
In the acid stage, facultative bacteria, called acid formers, convert organic material into volatile (organic) acids. | True | 0%
|
Aerobically digested sludge is brown in color, has very little odor, and does not dewater readily. | True | 0%
|
Sludge is digested aerobically or anaerobically. | True | 0%
|
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