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
Natural gas mixing in an anaerobic digester due to rising gas bubbles and thermal convection currents is sufficient to ensure optimum process performance.
a) True
b) False
b) False
Solids gas handling systems are kept under positive pressure to prevent atmospheric air from entering the system and creating a possible explosion.
a) True
b) False
a) True
Increased solids retention time in aerobic digesters results in an increase in the degree of VSS reduction.
a) True
b) False
a) True
Aerobic digestion produces a sludge that dewaters easier than raw sludge.
a) True
b) False
b) False
The ability of a belt filter press to dewater biosolids and to remove suspended solids is dependent on many factors including:
a) Belt speed
b) Pre-coat
c) Applied vacuum
d) Headbox tension
a) Belt speed
The performance of sand drying beds to dewater biosolids is affected by many factors including:
a) Pre-coat
b) Sludge type
c) Applied vacuum
d) Chlorine demand
b) Sludge type
A sludge feed pump is pumping 5% solids at 15 L/sec. If the pump operates for 65 minutes in a 24 hour period, how many kilograms of solids are pumped in a day?
a) 985 kg/d
b) 1,828 kg/d
c) 2,925 kg/d
d) 6,448 kg/d
c) 2,925 kg/d
In reviewing the operator log for the centrifuge the operator finds that overall performance has dropped over the last week. Which of the following conditions is not a probable cause for reduction in overall performance?
a) Sludge no longer reacts well with the polymer
b) Feed solids are too thick
c) Feed rate is too high
d) Scroll conveyor bearing is failing
d) Scroll conveyor bearing is failing
A treatment plant uses a pressure filter to dewater anaerobically digested sludge. If each filter cycle produces 1 tonne of cake and uses 50kg/tonne ferric chloride and 250 kg/tonne lime as conditioning chemicals, how many filter cycles are required to
dewater 3.5 metric tonnes of sludge per day?
a) 3.5 cycles
b) 5 cycles
c) 7 cycles
d) 12 cycles
b) 5 cycles
The selection of the proper pump is an important factor in the successful operation of a belt press or centrifuge. A steady flow with little or no shear is optimum. Which of the following would not be a suitable feed pump?
a) Diaphragm pump
b) Progressive cavity pump
c) Rotary lobe pump
d) Double disc pump
a) Diaphragm pump
