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34 Cards in this Set
- Front
- Back
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Saprophytic mocroorganisms |
acid formers |
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Microorganisms that are methane fermenters will only produce in the pH range of
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6.6-7.6 |
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Digestion is working properly if the volatile solids content of the raw sludge has been reduced by ___-___% |
50-60% |
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An anaerobic sludge digester should be operated such that________________ |
acid formation is equal to methane formation
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The most common imbalance in the operation of an anaerobic sludge digester is |
excess acid fermentation |
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The most important factor in the high-rate process of anaerobic digestion is: |
mixing |
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Operators should, as a rule, never change the temperature in an anaerobic digester by more than___degrees F/day |
1 degree F/day |
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What is the optimum temperature range of mesophile bacteria in anaerobic digestion? |
85-100 degrees F |
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What is the purpose of a draft tube in an anaerobic sludge digester? |
directs raw and digested sludge mixture to a heating area |
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How often should the liquid level be checked on a digester to prevent overfilling? |
once/day |
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Typically, an anaerobic digester will produce about 30%-35% by volume of which gas? |
CO2 |
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How often should flame arresters be service on anaerobic digesters? |
every 3 months |
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how often should the thermal valves be dismantled for service? |
once/year |
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typically, how often should sediment and drip traps be drained in cold water? |
twice a day |
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Draft tube propeller mixers are subject to corrosion from____ |
hydrogen sulfide |
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What do corbels provide in an anaerobic digester? |
support for the floating cover when it is at its lowest point |
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What do roller guides provide in an anaerobic digester? |
they prevent the cover from scraping the sidewall |
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What do ballast blocks provide in anaerobic digesters? |
stability and proper cover buoyancy |
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What do skirts provide in anaerobic digesters? |
they prevent foaming in the annular space |
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the floating cover on an anaerobic should be inspected how often? |
daily |
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Bacteria in an anaerobic digester will effectively utilize: |
fats |
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what would happen if too much sludge was added to an anaerobic digester? |
acid fermentaters would predominate and pH would decrease |
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The best operation performance for an anaerobic digester is when it is feed |
several times a day |
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The least desirable control method for an anaerobic digester is the use of digester____ |
pH |
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what would be the best solution if the volatile-acid-to-alkalinity ratio increased to 0.3 in a digester due to pumping thin sludge? |
thicken the raw sludge |
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If a single stage or primary tank has foam in the supernatant due to an "organic overload" in the digester, what is the best solution? |
reduce the feeding rate |
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What would be the most probable cause for gas leaking through the pressure relief valve on the digester's roof? |
plugged gas line or closed valve |
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If the manometer indicates the gas pressure in a digester is below normal, what would be the most probable cause? |
too much lime has been added, reducing gas production |
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If the gas pressure in a digester is lower than normal, what is the most probable cause? |
gas line or hose is leaking |
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If a wastewater treatment plant has four aerobic digesters operated in series, which tank will exert the highest oxygen demand? |
first tank |
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Where is the best place to collect scum from wastewater plants that use aerobic digesters? |
primary clarifier |
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What should the initial depth of sludge from a digester be when it is placed in a sludge drying bed? |
12-18 inches |
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Operators should use special precautions when placing anaerobically digested sludge on a drying bed because sludge contains what gas? |
methane |
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What does the wastewater industry call sludge that is only partially digested? |
green |
