Texas Basic Waste Water Operations Ch#11 Sludge Processing - Statistics

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Answer Stats

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%
The useful ________ can heat the digester or buildings, fuel engines, or produce steam.	methane gas	100%
Four types of sludge are primary, humus, activated sludge, and digested sludge.	True	100%
Sludge is digested aerobically or anaerobically.	True	100%
In the acid stage, facultative bacteria, called acid formers, convert organic material into volatile (organic) acids.	True	100%
Primary sludge settles in the secondary clarifier.	False	83%
Three layers found in anaerobic digesters are supernatant liquor, scum, and ________.	gas	83%
Anaerobic supernatant liquor is the ________ that separates from the sludge	gray liquid	83%
Disposal methods for digested, dewatered sludge are ________, landfill, and incineration.	land application	83%
Humus sludge sloughs off from the zoogleal mass in fixed-film processes	True	83%
The two stages of anaerobic digestion are the acid stage and the methane fermentation stage.	True	83%
Aerobic digestion is an ________ process whereby the aerobic bacteria consume themselves.	endogenous	67%
Activated sludge settles in the primary clarifier or is wasted from an activated sludge process.	False	67%
Anaerobic digesters are covered to keep out ________, to trap the useful methane, and to keep the digester warm.	free oxygen	67%
Unstabilized anaerobic sludge contains streaks of ________ or ________.	gray/green	67%
Overloading anaerobic digesters causes foaming, poor gas production, and ________.	low pH	67%
Laboratory tests that should be done to operate an anaerobic digester are alkalinity, temperature, volatile acids, percent volatile solids, percent carbon dioxide, and ________.	pH	67%
Anaerobic digester mixing methods are gas, mechanical, or ________.	pump	67%
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	50%
Anaerobic sludge is heated by pumping it through pipes heated with ________.	hot water	50%
In the methane stage, aerobic bacteria, called methane formers, convert the organic acids into methane gas.	False	33%
Aerobically digested sludge is brown in color, has very little odor, and does not dewater readily.	True	33%
Landfilled sludge must have a solids content of at least ________.	20%	17%
Anaerobic digester trouble signs are low pH (add lime to near neutral), increased ________, decreased alkalinity, and increased volatile acids.	CO2	17%
Anaerobically digested sludge is dark in color, has a tarry odor, a grainy texture, and does not dewater readily.	False	17%

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