Solids Flashcards
A floatation thickener is best used for what type of sludge?
a) Primary
b) Secondary
c) Digested
d) Dried
b) Secondary
A gravity sludge thickener receives primary sludge at a concentration of 3% and a feed rate of 100 L/min. the thickener overflow solids concentration is 0.15%. What is the solids removal efficiency?
a) 45%
b) 53%
c) 77%
d) 95%
d) 95%
Which of the following types of solids is most easily thickened in a dissolved air flotation thickener?
a) Primary solids
b) Secondary waste activated sludge
c) Lime solids
d) Solids cake
b) Secondary waste activated sludge
Which of the following is an incorrect statement regarding the operation of a gravity belt thickener?
a) Gravity belt thickeners concentrate biosolids as water drains by gravity from the influent end
b) For optimum performance, chemical conditioning of the feed sludge is typically required
c) Air-to-solids ratios must be maintain at 0.005 - 0.006 : 1
d) Water flows through the belt and collects as filtrate
c) Air-to-solids ratios must be maintain at 0.005 - 0.006:1
A vendor has asked for some information so he can quote on a centrifuge. If you need to feed sludge at a rate of 113.6 L/min and a sludge concentration of 0.33% determine the hydraulic loading rate and the solids loading rate
a) 1136 L/h and 33.3 kg/h respectively
b) 6,816 L/h and 22.5 kg/h respectively
c) 2,713 L/h and 37.48 kg/h respectively
b) 6,816 L/h and 22.5 kg/h respectively
Anaerobic digesters generally operate at a temperature of 35 C. Bacteria that prefer this temperature are called:
a) Cryogenic
b) Thermophilic
c) Mesophilic
d) Heterotrophic
c) Mesophilic
One of the reasons that air should be excluded from anaerobic digesters is because:
a) Gas storage capacity is reduced
b) It interferes with the action of aerobic bacteria
c) An explosion hazard could be created
d) Harmful spores and bacteria could be introduced in the air stream
c) An explosion hazard could be created
The principal purpose of sludge digestion is to:
a) Reduce the volume of sludge
b) Produce gas
c) Produce a humus fertilizer
d) All of the above
a) Reduce the volume of sludge
If it takes 30 days to digest sludge at 32 C̊ what will be the effect of gradually
increasing the digester temperature to 38 ̊C?
a) The required digestion time will increase
b) The required digestion time will decrease
c) There will be no effect on the digestion time required.
b) The required digestion time will decrease
The primary purpose of aerobic digestion is to:
a) Reduce volatile solids of the sludge
b) Produce a gas that can be used to heat buildings
c) Produce a sludge that is easy to thicken and dewater
d) Not be affected by temperature
a) Reduce volatile solids of the sludge
Which of the following is an advantage of the aerobic digestion process?
a) Energy reduction
b) Minimal laboratory testing
c) Safe operation (requires less hazardous cleaning and repair tasks)
d) Low operating costs
c) Safe operation (requires less hazardous cleaning and repair tasks)
Which of the following describes the ATAD process?
a) Produces class A biosolids
b) Poor dewatering characteristics
c) Reduced retention time
d) All of the above
d) All of the above
Incorporating nitrification/denitrification processes in operating an aerobic digester provides which of the following benefits?
a) Alkalinity recovery and pH balance
b) Phosphorus is removed along with the nitrogen
c) Mixing is not required
d) Improved dewatering
a) Alkalinity recovery and pH balance
Which of the following are end products of aerobic digestion?
a) Carbon monoxide
b) Ammonia
c) Non-biodegradable materials such as cellulose and polysaccharides
d) Orthophosphate
c) Non-biodegradable materials such as cellulose and polysaccharides
In aerobic digesters the typical D.O concentration is:
a) Less than 0.2 mg/L
b) 0.3 - 3.0 mg/L
c) Greater than 5.0 mg/L
d) 4.5 mg/L
b) 0.3 - 3.0 mg/L
