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# Multiple choice question for engineering

## Set 1

1. What do you mean by “NA” in mass transfer?
a) Rate of oxygen transfer per unit volume of fluid
b) Rate of oxygen transfer per unit volume of gas
d) Rate of oxygen transfer per unit mass of solid

Answer: a [Reason:] NA is the rate of oxygen transfer per unit volume of fluid (gmol m-3s-I), NA is the rate of Oxygen transfer of component A.

2. The solubility of oxygen in aqueous solutions is about?
a) 20 ppm
b) 15 ppm
c) 10 ppm
d) 5 ppm

Answer: c [Reason:] The solubility of oxygen in aqueous solutions at ambient temperature and pressure is only about 10 ppm. This amount of oxygen is quickly consumed in aerobic cultures and must be constantly replaced by sparging.

3. What is the unit of “Qo”, the oxygen uptake rate per volume of broth?
a) gl ssup>-1
b) g-1l s
c) g-1l-1 s
d) g l-1-1

Answer: d [Reason:] From the following equation: Qo = qox

where x is cell concentration. Typical units for qo are g g-1 s-l, and for Qo, g 1-1 s-1.

4. Which Substrate is consumed rapidly in fermentation process?
a) Fructose
b) Glucose
c) Sucrose
d) Lactose

Answer: b [Reason:] Choice of substrate for the fermentation can also significantly affect oxygen demand. Because glucose is generally consumed more rapidly than other sugars or carbon-containing substrates, rates of oxygen demand are higher when glucose is used. For example, maximum oxygen-consumption rates of 5.5, 6.1 and 12 mmol l-1 h-1 have been observed for Penicillium mould growing on lactose, sucrose and glucose, respectively.

5. Single cells are smaller than gas bubbles?
a) True
b) False

Answer: a [Reason:] Single cells are much smaller than gas bubbles, the liquid film surrounding each cell is much thinner than that around the bubbles and its effect on mass transfer can generally be neglected. On the other hand, if the cells form large clumps, liquid-film resistance can be significant.

6. At steady state, there is accumulation of oxygen at any location in the fermenter?
a) True
b) False

Answer: b [Reason:] At steady state there can be no accumulation of oxygen at any location in the fermenter; therefore, the rate of oxygen transfer from the bubbles must be equal to the rate of oxygen consumption by the cells.

7. Maximum rate of oxygen transfer occurs when?
a) CAL = 0
b) CAL < 0
c) CAL >= 1
d) CAL > 1

Answer: a [Reason:] First, let us estimate the maximum cell concentration that can be supported by the fermenter’s oxygen-transfer system. For a given set of operating conditions, the maximum rate of oxygen transfer occurs when the concentration-difference driving force (C*AL – CAL) is highest, i.e. when the concentration of dissolved oxygen CAL is zero.

8. A strain of Azotobacter vinelandii is cultured in a 15 m 3 stirred fermenter for alginate production. Under current operating conditions kLa is 0.17 s- 1. Oxygen solubility in the broth is approximately 8 x 10–3 kg m-3. The specific rate of oxygen uptake is 12.5 mmol g-1 h-1. What is the maximum possible cell concentration?

a) 10 gl-1
b) 15 gl-1
c) 20 gl-1
d) 12 gl-1

Answer: d [Reason:] From the equation given in the question:

= 1.2×104 g m-3 = 12 gl-1.

9. Refer to Q8 and, calculate the bacteria suffer growth inhibition after copper sulphate is accidently added to the fermentation broth. This causes a reduction in oxygen uptake rate to 3 mmol g-1 h-1. What maximum cell concentration can now be supported by the fermenter?
a) 50 glsup>-1
b) 10 glsup>-1
b) 25 glsup>-1
d) 55 glsup>-1

Answer: a [Reason:] Assume that addition of copper sulphate does not affect C*AL or kLa. If qo is reduced by a factor of 12.5/3 = 4.167, xmax is increased to:

xmax = 4.167 (12 glsup>-1) = 50 glsup>-1 To achieve the calculated cell densities all other conditions must be favourable, e.g. sufficient substrate and time must be provided.

10. Which type of microbes grow well in the condition of enriched oxygen?
a) Obligate anaerobes
b) Obligate aerobes
c) Facultative anaerobes
d) Facultative aerobes

Answer: b [Reason:] Most cells are aerobic and therefore need to be supplied with oxygen to grow (obligate aerobes). Some find oxygen toxic and grow badly in its presence (obligate anaerobes), while others grow better when oxygen is present, but continue to do so if its absence (facultative anaerobes).

11. Beer may be produced by ________________
a) Fermentation of rice
b) Germination of rice
c) Germination of barley
d) Fermentation of grapes

Answer: c [Reason:] Malt extract is frequently used in the brewing of beer. Its production begins by germinating barley grain in a process known as malting, immersing barley in water to encourage the grain to sprout, then drying the barley to halt the progress when the sprouting begins.

12. In anaerobic condition sugar in dough is converted into?
a) Alcohol
b) Water
c) Glucose
d) Sucrose

Answer: a [Reason:] Fermentation is nothing but an anaerobic respiration process in which the substrate is any organic material other than glucose like alcohol. Saccharomyces cerevisiae (yeast) produces an enzyme named zymogen which ferment the alcohol. It is an anaerobic process and substrate is not glucose. The energy production is much less in fermentation process.

13. The lowest yield of ATP is in ____________
a) Aerobic respiration
b) Aerobic fermentation
c) Anaerobic respiration
d) Fermentation

Answer: d [Reason:] Fermentation and cellular respiration begin the same way, with glycolysis. In fermentation, however, the pyruvate made in glycolysis does not continue through oxidation and the citric acid cycle, and the electron transport chain does not run. Because the electron transport chain isn’t functional, the NADH made in glycolysis cannot drop its electrons off there to turn back into NAD+.

14. The population of microbes is maintained in which phase for long time using continuous culture system?
a) Lag
b) Log
c) Exponential
d) Stationary

Answer: b [Reason:] The log phase is a period characterized by cell doubling. The number of new bacteria appearing per unit time is proportional to the present population. If growth is not limited, doubling will continue at a constant rate so both the number of cells and the rate of population increase doubles with each consecutive time period.

15. Cell density is controlled by increasing or decreasing flow of culture medium in which state?
a) Turbidostat
b) Chemostat
c) Continuous culture
d) Synchronus culture

Answer: b [Reason:] A chemostat (from chemical environment is static) is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms are continuously removed at the same rate to keep the culture volume constant.

## Set 2

1. “Power required for turbulent flow is independent of the viscosity of the fluid but proportional to fluid density”, this statement is applicable to which type of regime?
a) Laminar regime
b) Turbulent regime
c) Transition regime
d) Streamline regime

Answer: b [Reason:] In turbulent regime, Power required for turbulent flow is independent of the viscosity of the fluid but proportional to fluid density. The turbulent regime is fully developed at Rei > 103 or 104 for most small impellers in baffled vessels. For the same impellers in vessels without baffles, the power curves are somewhat different, Without baffles, turbulence is not fully developed until Rei > 105; even then the value of Np’ is reduced to between 1/2 and 1/10 that with baffles.

2. Pseudoplastic consume less power than Newtonian fluids?
a) True
b) False

Answer: a [Reason:] The laminar region extends to higher Reynolds numbers in pseudoplastic fluids than in Newtonian systems. At Rei below 10 and above 200 the results for Newtonian and non-Newtonian fluids are essentially the same; in the intermediate range, pseudoplastic liquids consume less power than Newtonian fluids. Flow patterns in pseudoplastic and Newtonian fluids differ significantly. Even when there is high turbulence near the impeller in pseudoplastic systems, the bulk liquid may be moving very slowly and consuming relatively little power.

3. Power consumption is less in ungassed fluids.
a) True
b) False

Answer: b [Reason:] Liquids into which gas is sparged have reduced power requirements. Gas bubbles decrease the density of the fluid. The presence of bubbles also affects the hydrodynamic behaviour of fluid around the impeller. Large gas-filled cavities develop behind the stirrer blades in aerated liquids; these cavities reduce the resistance to fluid flow and decrease the drag coefficient of the impeller. With sparging, the power consumed could be reduced to as little as half the ungassed value, depending on gas flow rate.

4. Fluid height in the tank is H= 16 m and Diameter of the tank, D = 14 m. Calculate the slurry volume in the tank.
a) 2450 m3
b) 2463 m3
c) 3450 m3
d) 3463 m3

Answer: b [Reason:] Fluid Height in Tank , H = 16 m and Diameter of tank, D = 14 m

Slurry volume in tank = π *D2*H/4 = π * (14)2*16 /4 = 2463 m3.

5. Refer to Q4, and estimate the Agitator impeller diameter D, assuming it to be 33% of tank diameter.
a) 4.62 m
b) 4.50 m
c) 4.60 m
d) 4.52 m

Answer: a [Reason:] Agitator Impeller Diameter, D= 33 % of tank diameter = 14 * 33% m = 4.62 m.

6. What is the degree of agitation if bulk fluid velocity is 23.55 ft/min? (For 6 ft/min., degree of agitation =1 and Degree of agitation varies from 0 to 10).
a) 5
b) 6
c) 4
d) 3

Answer: c [Reason:] Degree of Agitation = bulk fluid velocity / 6

= 23.55/6 = 3.93 ~ 4

7. It is proposed to mix a batch of water at 80 deg F in an agitated vessel. Determine the agitator speed in appropriate units for Reynolds number calculation for agitation speed of 60 rpm. Use an approximate loss of efficiency of 20% for the motor, gearbox, and bearings. Equipment details are given below:

Equipment Data: Vessel Diameter (T) = 9.0 ft. Impeller Diameter (D) = 3.0 ft. Impeller type = Flat blade turbine. # of blades = 6 Blade width (W) =7 inches. Blade length (L) = 9 inches. Number of Baffles = 4; equally spaced. Baffle width (B) = 11 inches. Liquid Depth (H) = 9.0 feet. Impeller height above vessel bottom (Z) = 3 feet.
a) 2, 400 rph
b) 4, 500 rph
c) 3, 500 rph
d) 3, 600 rph

Answer: d [Reason:] N = revolutions per hour (rph). The agitation speed is given in the example as 60 revolutions per minute, which when multiplied by 60 minutes/hr yields: N = 60 rpm * 60 = 3,600 rph.

8. Refer to Q7, and determine the agitated batch liquid Reynolds number. (ρB = 64.0 lbs./cu. ft. and μB = 2.12 lb./hr-ft.)
a) 977,035
b) 900,045
c) 877,035
d) 800,045

Answer: a [Reason:] NRe = Reynolds number for agitated liquids = ( D2 * N * ρB / μB ).

NRe = (3.02 * 3,600 * 64.0 / 2.12 )

NRe = 977,035.

9. Refer to Q7 and Q8, and determine the agitator speed in appropriate units for power calculation.
a) 3 rps
b) 1 rps
c) 6 rps
d) 4 rps

Answer: b [Reason:] N = revolutions per sec (rps). The agitation speed is given in the example as 60 revolutions per minute, which when divided by 60 seconds/minute yields:

N = 60 rpm / 60 = 1 rps.

10. Refer to Q7, Q8 and Q9, and determine Power Number from the appropriate correlation, and calculate the uncorrected Power required. (Gc = 32.2).
a) 5.3 Hp
b) 6.3 Hp
c) 5.6 Hp
d) 6.6 Hp

Answer: a [Reason:] The correlations calculate the delivered Power to the fluid. This must be corrected back to the agitator motor and account for efficiency losses in the motor, gearbox, and bearings.

PDelivered = (NP ρB * N3 * DA5)/ GC

PDelivered = 6 * 64 * 13 * 35 / 32.2

PDelivered = 2,898 ft-lb/sec or using 550 ft-lb/sec per Hp,

PDelivered = 5.3 Hp.

11. Refer to Q7, 8, 9 and 10, and determine the motor Power required using estimated losses at 30%.
a) 5.3 Hp
b) 6.3 Hp
c) 5.6 Hp
d) 6.6 Hp

Answer: d [Reason:] PMotor = PDelivered / ( 1 – Losses )

PMotor = 5.3 / ( 1 – 0.20 )

PMotor = 6.6 Hp.

## Set 3

1. Tissue engineering is developed invitro.
a) True
b) False

Answer: a [Reason:] Tissue engineering has a primary focus on developing in vitro bioartificial tissues, typically based on cells derived from donor tissue. These tissues can be used as transplants to improve biological function in the recipient. An alternative form of tissue engineering is in vivo alteration of cell growth and function.

2. Hyaline is characterized by its ____________
a) White appearance
b) Glassy appearance
c) Red appearance
d) Crystal appearance

Answer: b [Reason:] A hyaline substance is one with a glassy appearance. In histopathological medical usage, a hyaline substance appears glassy and pink after being stained with haematoxylin and eosin — usually it is an acellular, proteinaceous material. An example is hyaline cartilage, a transparent, glossy articular joint cartilage.

3. Hyaline is always associated with cartilage.
a) True
b) False

Answer: b [Reason:] Some mistakenly refer to all hyaline as hyaline cartilage; however, hyaline applies to other material besides the cartilage itself. Arterial hyaline is seen in aging, high blood pressure, diabetes mellitus and in association with some drugs (e.g. calcineurin inhibitors). It is bright pink with PAS staining.

4. What do you mean by Extracorporeal?
a) Outer layer of the tissue
b) Outside of the body
c) Inner layer of the tissue
d) Inside of the body

Answer: b [Reason:] An extracorporeal is a medical procedure which is performed outside the body.

5. Tissue engineering increases the risk of fatality of the experimental animals.
a) True
b) False

Answer: b [Reason:] Use of artificial tissue constructs is for toxicological and pharmacological testing of potential new drugs. In this case the artificial tissue or combination of tissues acts as a surrogate, reducing the need to use animals for such testing.

6. The neurotransmitters are classified into:

Answer: a [Reason:] There are two broad categories of neurotransmitters: Small-molecule neurotransmitters and Neuropeptides.

7. Pressure ulcers affects mainly the _______
a) Nephron
b) Lungs
c) Skin
d) Kidney

Answer: c [Reason:] Pressure ulcers, also known as pressure sores, pressure injuries, bedsores, and decubitus ulcers, are localized damage to the skin and/or underlying tissue that usually occur over a bony prominence as a result of pressure, or pressure in combination with shear and/or friction. The most common sites are the skin overlying the sacrum, coccyx, heels or the hips, but other sites such as the elbows, knees, ankles, back of shoulders, or the back of the cranium can be affected.

8. Cadaver skin is the Permanent covering for wound.
a) True
b) False

Answer: b [Reason:] Allograft, cadaver skin or homograft is human cadaver skin donated for medical use. Cadaver skin is used as a temporary covering for excised (cleaned) wound surfaces before autograft (permanent) placement.

a) Ancient live body
b) Live body
c) Artificial body
d) Deceased body

Answer: d [Reason:] A cadaver, also called corpse (singular) in medical, literary, and legal usage, or when intended for dissection, is a deceased body.

10. The scaffold of bone is also done.
a) True
b) False

Answer: a [Reason:] This type of bone graft is based on the concept of bone tissue engineering, which focused on creating a device that enhances bone repair and regeneration by incorporating bone progenitor cells and growth factors to stimulate cells into a scaffold made of various natural or synthetic biomaterials or their combination.

11. In cryopreservation organs cannot be conserved.
a) True
b) False

Answer: b [Reason:] Cryo-preservation or cryo-conservation is a process where organelles, cells, tissues, extracellular matrix, organs or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by cooling to very low temperatures.

12. Chondrocyte is the cell which secretes ________
a) Liver cells
b) Bone cells
c) Cartilage cells
d) Heart cells

Answer: c [Reason:] Chondrocyte is a cell which has secreted the matrix of cartilage and become embedded in it.

13. What type of tissue is articulate cartilage?
a) Muscle
b) Epithelial
c) Connective
d) Nervous

Answer: c [Reason:] Articular cartilage is a thin layer of specialized connective tissue with unique viscoelastic properties. Its principal function is to provide a smooth, lubricated surface for low friction articulation and to facilitate the transmission of loads to the underlying subchondral bone.

14. What do you mean by Arthrotomy?
a) Opening of joints
b) Opening of skin
c) Opening of liver
d) Opening of heart

Answer: a [Reason:] Arthrotomy, also known as Arthroplasty, is an open joint procedure done under general anesthesia in the hospital. The recovery is significantly longer, three to eight weeks, and more painful than the TMJ Arthrocentesis or TMJ Arthroscopy.

15. Carticel uses other body cells to recover damage.
a) True
b) False

Answer: b [Reason:] Carticel also known as ACI (Autologous Chondrocyte Implantation) uses your body’s own cartilage cells to treat your knee cartilage injury. These cells can help form new cartilage in the knee which is very similar to the old cartilage in the body.

## Set 4

1. Which of the following examples are not related with the class of metabolite, that is “Products directly associated with generation of energy in the cell”?
a) Penicillin
b) Ethanol
c) Acetone
d) Lactic acids

Answer: a [Reason:] Formation of other products such as antibiotics involves reactions far removed from energy metabolism and the class of metabolite related to products for which there is no clear direct or indirect coupling to energy generation has the examples including that of antibiotics such as: Penicillin, streptomycin, vitamins.

2. Which of the following examples are not related with the class of metabolite, that is “Products indirectly associated with energy generation”?
a) Lactic acid
b) Amino acid
c) Nucleotides
d) Citric acid

Answer: a [Reason:] Lactic acid comes under the first category of the class of metabolite that represents products directly associated with generation of energy in the cell. Compounds in the first category are formed directly as end- or by-products of energy metabolism; these materials are synthesised in pathways which produce ATP. Examples include: Ethanol, acetic acid, gluconic acid, acetone, butanol, lactic acid, other products of anaerobic fermentation.

3. Which instrument is used to measure growth kinetics of plant cell lines?
a) Rheometry
b) Spectometry
c) Mass spectrometry
d) Conductometry

Answer: d [Reason:] The conductivity method of measuring growth kinetics of plant cell lines was used especially with the purpose of bioprocess engineering applications of plant cell cultures. The major advantages of using conductometry as the biosensing technique for measurement of plant cell growth kinetics are: i) The method is very economical and efficient ii) It gives accurate, reliable and reproducible measurements, while amenable to continuous online monitoring and process control. iii) It is a noninvasive method which does not adversely affect the plant cells or the bioreactor operation.

4. Which of the following production kinetics is produced at the same time as cell growth?
a) Growth associated
b) Non-growth associated
c) Mixed-growth associated
d) Variable- growth associated

Answer: a [Reason:] Growth associated is produced at the same time as cell growth which constitutes of constitutive enzymes (ones that are normally present) and metabolic intermediates.

5. Which of the following production kinetics takes place during stationary phase?
a) Growth associated
b) Non-growth associated
c) Mixed-growth associated
d) Variable- growth associated

Answer: b [Reason:] Non-growth associated takes place during stationary phase (μ=0) and which constitutes of secondary metabolites such as antibiotics.

6. Maintenance comes under which type of growth kinetics?
a) Growth associated
b) Non-growth associated
c) Mixed-growth associated
d) Variable- growth associated

Answer: b [Reason:] ATP is also required for other activities called maintenance. cell motility turnover of cellular components adjustment of membrane potentials and internal pH

These are non-growth associated mechanisms.

7. Kinetic expressions requires both growth-associated and maintenance-associated production.
a) True
b) False

Answer: a [Reason:] Kinetic expressions requires both growth-associated and maintenance-associated production. rP = qpx

rP = (YP/X μ + mP)X qP = (YP/X μ + mP) Where, YP/X is the theoretical yield of product from biomass, mp is the specific rate of product formation due to maintenance, and x is biomass concentration.

8. The Theoretical yield is higher than the observed yield.
a) True
b) False

Answer: b Result is Y’p/x (observed yield) is higher than anticipated based on growth alone.

9. Observed yield is better than theoretical yield.
a) True
b) False

Answer: b [Reason:] Effect of incorporating maintenance terms gives observed yield rather than theoretical yields and accounts for unusual behavior, i.e. negative association with growth.

10. The constitutive enzymes are __________
a) Growth associated
b) Non-growth associated
c) Mixed-growth associated
d) Variable- growth associated

Answer: a [Reason:] The constitutive enzymes are growth associated as they are produced at the same time as cell growth. Factors which are required for the growth of the organism is the key aspect.

## Set 5

1. What is the term “Gin”?
a) A magical spirit
b) Liquor
c) Non-liquor
d) Gas

Answer: b [Reason:] Gin is liquor which derives its predominant flavour from juniper berries (Juniperus communis). Gin is one of the broadest categories of spirits, all of various origins, styles, and flavour profiles that revolve around juniper as a common ingredient.

2.What do you mean by “Stillage”?
a) Still water
b) Still waste
c) Storage and transport
d) Growth medium

Answer: c [Reason:] A stillage is like a pallet or skid but with a cage or sides or some form of support specifically tailored to the material it is intended to carry. Some are designed to be stackable. A stillage is any device on which a cask of ale is placed for service.

3. The color of the beer is proportional to the roasting of grains.
a) True
b) False

Answer: a [Reason:] Naturally, the roasting process has a considerable impact on the flavor of the beer. The more the grain is roasted, the more complex and rich the brew becomes. In particular, roasting tends to bring out stronger flavor notes, including chocolate and toffee. Darker beers also tend to have a higher alcohol content than light beers. The darker the grain, the darker the beer.

4. Single cell protein cannot be produced from stillage.
a) True
b) False

Answer: b [Reason:] A number of processes to produce SCP from stillage using specific microbes like Geotrichum candidum, Candida utilis or C.tropicalis.

5. Silage is not a feremented fodder.
a) True
b) False

Answer: b [Reason:] Silage is fermented, high-moisture stored fodder which can be fed to cattle, sheep and other such ruminants (cud-chewing animals) or used as a biofuel feedstock for anaerobic digesters. It is fermented and stored in a process called ensilage, ensiling or silaging, and is usually made from grass crops, including maize, sorghum or other cereals, using the entire green plant (not just the grain). Silage can be made from many field crops, and special terms may be used depending on type: oatlage for oats, haylage for alfalfa.

6. What are Hops?
a) A flower
b) A fruit
c) A vegetable
d) A horse shoe

Answer: a [Reason:] Hops are the flowers (also called seed cones or strobiles) of the hop plant Humulus lupulus They are used primarily as a flavoring and stability agent in beer, to which they impart bitter, zesty, or citric flavours; though they are also used for various purposes in other beverages and herbal medicine.

7.”The yeast may also be used directly as a source of vitamin”. Is the statement True or False?
a) True
b) False

Answer: a [Reason:] The yeast may also be used directly as a source of vitamins. If it is to be used as a human food it must be debittered to remove the hop bitter substances absorbed on to the yeast cells.

8. Amino acid waste cannot be used as a fertilizer.
a) True
b) False

Answer: b [Reason:] The main wastes from glutamic acid or lysine fermentations are cells, a liquor with a high amino-acid content which can be used as an animal-feed supplement, and the salts removed from the liquor by crystallization, which is a good fertilizer.

9. The baker’s yeast are now produced as a brewery by-product.
a) True
b) False

Answer: b [Reason:] Although baker’s yeast was originally obtained as a brewery by-product, this market has diminished considerably. Most baker’s yeast is now produced directly by a distinct production process.

10. What is the sludge thickener?
a) Increasing the sludge volume
b) Reducing the sludge volume
c) Constant sludge volume
d) The second step of concentration of sludge

Answer: b [Reason:] Thickening is the first step for reducing the sludge volume by removal of free sludge water. Thin sludge is concentrated to thick sludge. Thick sludge has a higher viscosity, but must still be pumpable. Sludge settles in gravity thickeners and is compressed by the weight of its own solids.

11. What can sludge from a sewage treatment plant be used?
a) Non-organic solid formation
b) Non-biosolid formation
c) Waste formation
d) Biosolid formation

Answer: d [Reason:] Biosolids is a term often used in conjunction with reuse of sewage solids after sewage sludge treatment. Biosolids can be defined as organic wastewater solids that can be reused after stabilization processes such as anaerobic digestion and composting.

12. What is activated sludge?
a) Separation of liquid and solid phase
b) Product of wastewater treatment
c) Type of wastewater treatment
d) Suspended solids

Answer: c [Reason:] The activated sludge process is a type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.

13. What is dewatered sludge?
a) Separation of liquid and solid phase
b) Product of wastewater treatment
c) Type of wastewater treatment
d) Suspended solids

Answer: a [Reason:] Sludge dewatering is the separation of a liquid and solid phase whereby, generally, the least possible residual moisture is required in the solid phase and the lowest possible solid particle residues are required in the separated liquid phase (“the centrate”).

14. What is sewage sludge?
a) Separation of liquid and solid phase
b) Product of wastewater treatment
c) Type of wastewater treatment
d) Suspended solids