Multiple choice question for engineering
1. Which type of fermenter is used mainly for mixing?
a) Air-Lift fermenter
b) Stirred Tank fermenter
c) Fluidised Bed bioreactor
d) Packed Bed bioreactor
Answer: b [Reason:] Mixing is usually carried out in a stirred tank; Stirred tanks are usually cylindrical in shape. If possible, the base of the tank is rounded at the edges rather than angled; this eliminates sharp corners and pockets into which fluid currents may not penetrate and discourages formation of stagnant regions.
2. What is the ratio of tank diameter to impeller diameter for Newtonian fluids?
Answer: a [Reason:] Mixing is achieved using an impeller mounted in the tank; for use with Newtonian fluids, the ratio of tank diameter to impeller diameter is normally about 3:1. The impeller is usually positioned overhead on a centrally-located stirrer shaft. For efficient mixing with a single impeller, the depth of liquid in the tank should be no more than 1.0-1.25 times the tank diameter.
3. What is the width of baffle in order of the tank diameter used for mixing?
a) 1/5- 1/10
Answer: c [Reason:] The optimum baffle width depends on the impeller design and fluid viscosity but is of the order 1/10-1/12 the tank diameter.
4.” Pitch of a propeller”, Here what does pitch refer to?
a) Advance per resolution
b) Advance per rotation
c) Advance per Sharpness
d) Advance per revolution
Answer: d [Reason:] Specification of the pitch of a propeller blade refers to its properties as a segment of a screw; pitch is the advance per revolution. In a propeller, the blade angle at each section is greater than the helix angle and, what is more important; the distance moved forward in one revolution (called the advance per revolution) is not by any means a fixed quantity.
5. Which is the most frequently used impeller in the fermentation industry regarded as 6- flat-blade disc-mounted turbine?
a) Propeller turbine
b) Rushton turbine
c) Bladeless turbine
d) Screw turbine
Answer: b [Reason:] The Rushton turbine is a radial flow impeller used for many mixing applications (commonly for gas dispersion applications). The design is based on a flat disk with vertical flat blades vertically mounted.
6. “Rotational stirrers are advantageous for mixing”?
Answer: b [Reason:] Simple circular flow of liquid around the shaft is generally disadvantageous and should be avoided. In circular flow, liquid moves in a streamline fashion and there is little mixing between fluid at different heights in the tank. Circular flow also leads to vortex development. At high impeller speeds, the vortex may reach down to the impeller so that gas from the surrounding atmosphere is drawn into the liquid; this is generally undesirable as it produces very high mechanical stresses in the stirrer shaft, bearings and seal. Prevention of circular flow has a high priority in design of mixing systems, and is usually achieved by installing baffles which interrupt the circular flow pattern and create turbulence in the fluid.
7. Are Propellers and Impellers different in function from each other?
Answer: a [Reason:] Propellers commonly refer to devices which move an attached object. For example, a ship’s propeller moves the ship itself forward or backward. Impellers, on the other hand, are designed to move the substance — fluid or gas passing through it without moving the object it is attached to.
8. Mixing is sufficiently done away from the impeller?
Answer: b [Reason:] Near the impeller there is a region of high turbulence where fluid cur- rents converge and exchange material. Away from the impeller, flow is slower and largely streamline; mixing in these regions is much less intense than near the impeller.
9. Which of the following is the slowest step in mixing process?
Answer: a [Reason:] Distribution is an important process in mixing, but can be relatively slow. In large tanks, the size of the circulation paths is also large and the time taken to traverse them is long; this, together with the regularity of fluid pumping at the impeller, inhibits rapid mixing. Accordingly, distribution is often the slowest step in the mixing process.
10. In the following equation, what does “λ” Represents for the formed eddies?
b) Kinematic velocity
Answer: d [Reason:] The degree of homogeneity possible as a result of dispersion is limited by the size of the smallest eddies which may be formed in a particular fluid. This size is given approximately as the Kolmogorov scale of mixing, or scale of turbulence, λ, where λ is the characteristic dimension of the smallest eddies, v is the kinematic viscosity of the fluid, and ε is the local rate of turbulent energy dissipation per unit mass of liquid.
11. A fermentation broth with viscosity 10-2 Pa s and density 1000 kg m-3 is agitated in a 3.00 m3 baffled tank using a Rushton turbine with diameter 0.5 m and stirrer speed 1 s-1. Estimate the mixing time.
a) 37 s
b) 33 s
c) 35 s
d) 39 s
1. In-situ or on-line measurement is appropriate for biomass analysis in fermentation.
Answer: b [Reason:] Many important variables such as biomass concentration and broth composition cannot currently be measured on-line because of the lack of appropriate instruments. Instead, samples must be removed from the reactor and taken to the laboratory for off-line analysis. Because fermentation conditions can change during laboratory analysis, control action based on the measurement is not as effective. Off-line measurements are used in industrial fermentations for analysis of biomass, carbohydrate, protein, phosphate and lipid concentrations, enzyme activity and broth rheology. Samples are usually taken manually every 4-8 h; the results are available 2-24 h later.
2. What do you mean by dissolved oxygen tension?
c) Partial pressure
Answer: c [Reason:] The partial pressure of oxygen molecules dissolved in a liquid, such as blood plasma. Technically the oxygen tension (or partial pressure of oxygen) is defined as the pressure which oxygen in a mixture of gases would exert if it were on its own. Weirdly, partial pressures/gas tensions are also used to describe dissolved gases, in the blood for example.
3. Which electronic device is used in biosensors?
Answer: c [Reason:] The preferred biological material like enzyme is preferred for conventional methods like physical or membrane entrapment and non covalent or covalent binding. The preferred biological material is in contact with the transducer. To produce a bound analyte through the analyte binds to the biological material which produces the electrical response to be measured. In some cases the analyte changed to a product and have some probability to associate with the release of heat, gases like oxygen, electrons or hydrogen ions.
4. Flow injection analysis (FIA), a sampling handling technique is used to remove?
c) Cell-free medium
d) Cell-bound medium
Answer: c [Reason:] The flow injection analysis (FIA), a sample-handling technique for removing cell- free medium from the fermenter and delivering a pulse of analyte to ex situ measurement devices.
5. What is the unit of Specific Oxygen rate (SOUR)?
a) grams of oxygen consumed per gram of volatile suspended solids per hour
b) milligrams of oxygen consumed per gram of volatile suspended solids per hour
c) kilograms of oxygen consumed per gram of volatile suspended solids per second
d) milligrams of oxygen consumed per gram of volatile suspended solids per second
Answer: b [Reason:] The Specific Oxygen Uptake Rate (SOUR), also known as the oxygen consumption or respiration rate, is defined as the milligram of oxygen consumed per gram of volatile suspended solids (VSS) per hour. This quick test has many advantages; rapid measure of influent organic load and biodegradability, indication of the presence of toxic or inhibitory wastes, degree of stability and condition of a sample, and calculation of oxygen demand rates at various points in the aeration basin.
6. In process modeling, experimental observations provide:
a) Structure of the model
b) Non-numerical values of coefficients
c) Non-numerical values of variables
d) Numerical values of coefficients
Answer: d [Reason:] Traditionally, models are based on a combination of ‘theoretical’ relationships which provide the structure of the model, and experimental observations which provide the numerical values of coefficients. For biological processes, specifying the model structure can be difficult because of the complexity of cellular processes and the large number of environmental factors which affect cell culture. Usually, bioprocess models are much-simplified approximate representations deduced from observation rather than from theoretical laws of science. As an example, a frequently-used mathematical model for batch fermentation consists of the Monod equation for growth and an expression for rate of substrate consumption as a function of biomass concentration.
7. Accurate models applicable to a range of process conditions are not rare.
Answer: b [Reason:] Development of a comprehensive model covering all key aspects of a particular bioprocess and able to predict the effects of a wide range of culture variables is a demanding exercise. Accurate models applicable to a range of process conditions are rare. As many aspects of fermentation are poorly under- stood, it difficult to devise mathematical models covering these areas. For example, the response of cells to spatial variations in dissolved-oxygen and substrate levels in fermenters, or the effect of impeller design on microbial growth and productivity, is not generally incorporated into models because the subject has been inadequately studied.
8. What is the Kalman filter?
b) Computer device
c) Filtration equipment
d) Constant measurement device
Answer: a [Reason:] Kalman filtering, also known as linear quadratic estimation (LQE), is an algorithm that uses a series of measurements observed over time, containing statistical noise and other inaccuracies, and produces estimates of unknown variables that tend to be more accurate than those based on a single measurement alone, by estimating a joint probability distribution over the variables for each timeframe.
9. The actuator converts the energy into mechanical action.
Answer: a [Reason:] An actuator is a type of motor that is responsible for moving or controlling a mechanism or system. It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion.
10. What is proportional-integral-derivative (PID)?
c) Mathematical integration
d) Mathematical differentiation
Answer: b [Reason:] The proportional-integral-derivative or PID control, with PID control, the control action is determined in proportion to the error, the integral of the error and the derivative of the error with respect to time. The relative weightings given to these functions determine the response of the controller and the overall ‘strength’ of the control action.
11. PID controllers can affect the culture medium.
Answer: a [Reason:] Proper adjustment of PID controllers usually provides excellent regulation of the measured variable. However, poorly tuned controllers can de stabilize a process and cause continuous or accentuated fluctuations in culture conditions.
12. Respiratory quotient has no units.
Answer: a [Reason:] The respiratory quotient (or RQ or respiratory coefficient), is a dimensionless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry.
13. Biomass yield from substrate and fermentative metabolism are same.
Answer: b [Reason:] Maximum biomass yield from substrate is achieved at relatively low glucose concentrations in the presence of adequate oxygen; fermentative metabolism occurs if the glucose concentration rises above a certain level even though oxygen may be present. Fermentative metabolism should be avoided for biomass production because the yield of cells is reduced as ethanol and carbon dioxide are formed as end-products.
14. Crabtree effect is which type of process?
c) Biomass yield
d) Oxidative phosphorylation
Answer: a [Reason:] The Crabtree effect describes the phenomenon whereby the yeast, Saccharomyces cerevisiae, produces ethanol(alcohol) in aerobic conditions and high external glucose concentrations rather than producing biomass via the tricarboxylic acid (TCA) cycle, the usual process occurring aerobically in most yeasts e.g. Kluyveromyces spp. Increasing concentrations of glucose accelerates glycolysis (the breakdown of glucose) which results in the production of appreciable amounts of ATP through substrate-level phosphorylation. This reduces the need of oxidative phosphorylation done by the TCA cycle via the electron transport chain and therefore decreases oxygen consumption.
15. Neural network process includes ___________
a) Constant behavior
b) Transient behavior
c) Stationary behavior
d) Immobile behavior
Answer: b [Reason:] Information about feed flow rate and substrate and biomass concentrations as a function of time can be used to develop a neural network for analysis of transient behaviour in continuous fermentation which is able to predict future changes in substrate and cell concentrations.
1. Apparent viscosity for Non- Newtonian fluid is ____________
b) Depends on the shear stress
c) Depends on the shear rate
Answer: c [Reason:] Apparent viscosity (sometimes denoted η) is the shear stress applied to a fluid divided by the shear rate. For a Newtonian fluid, the apparent viscosity is constant, and equal to the Newtonian viscosity of the fluid, but for non-Newtonian fluids, the apparent viscosity depends on the shear rate. In such case, the ratio between shear stress and shear rate is not constant; nevertheless, this ratio for non- Newtonian fluids.
2. What is the SI unit of apparent viscosity?
a) Pascal- second
c) Newton- second
d) Newton/ hr
Answer: a [Reason:] Apparent viscosity has the SI derived unit Pa•s (Pascal-second, but the centipoise is frequently used in practice: (1 mPa•s = 1 cP).
3. In the following Equation, what does “n” represents?
τ = K (γ ) ̇n
a) Fluid behavior index
b) Flow behavior index
c) Fluent behavior index
d) Newtonian fluid behavior index
Answer: b [Reason:] Power law:
τ = K (γ ) ̇n
Where, τ is the shear stress, K is the consistency index, (γ ) ̇is shear rate, and n is the flow behavior index. The parameters K and n characterize the rheology of power-law fluids. The flow behavior index n is dimensionless.
4. Which of the following is an example of Bingham plastic?
Answer: d [Reason:] A Bingham plastic is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. It is used as a common mathematical model of mud flow in drilling engineering, and in the handling of slurries. A common example is toothpaste, which will not be extruded until a certain pressure is applied to the tube. It then is pushed out as a solid plug.
5. Which of the following represents the graph and estimate it with the correct properties?
a) Dilatant, Decreases with increasing shear rate
b) Pseudoplastic, Decreases with increasing shear rate
c) Bingham plastic, Increases with increasing shear rate
d) Casson plastic, Increases with increasing shear rate
Explanation: In a shear thinning fluid, or pseudoplastic fluid, apparent viscosity decreases with increased stress.
μa = Kγ ̇n-1
6. The Thixotropic fluid characteristic is common in cell cultures?
Answer: a [Reason:] Thixotropic behaviour is not uncommon in cultures containing fungal mycelia or extracellular microbial polysaccharides, and appears to be related to reversible ‘structure’ effects associ- ated with the orientation of cells and macromolecules in the fluid.
7. “In Rheopectic fluid apparent viscosity decreases with time the fluid”?
Answer: b [Reason:] When a shear force is exerted on some fluids, the apparent viscosity either increases or decreases with duration of the force. If apparent viscosity increases with time, the fluid is said to be rheopectic; rheopectic fluids are relatively rare in occurrence. If apparent viscosity decreases with time the fluid is thixotropic.
8. The S.I unit of kinematic viscosity (v) is __________
Answer: b [Reason:] The SI unit of kinematic viscosity is m2/s. The cgs physical unit for kinematic viscosity is the stokes (St).
1 St = 1 cm2•s−1 = 10−4 m2•s−1.
9. A Static fluid can have ___________
a) Zero normal stress and non-zero shear stress
b) Non-zero normal and shear stress
c) Negative normal stress and zero shear stress
d) Positive normal stress and zero shear stress
Answer: c [Reason:] Fluid with zero shear stress within it is known as static fluid. When ever fluid moves it undergoes continuous deformation due to shear (caused due to viscosity of the fluid). So when the fluid is in rest no shear stress develops and only normal stress exists. So static fluid has zero shear stress.
10. Which of the following is shear thinning fluid?
d) Bingham plastic
Answer: a [Reason:] In rheology, shear thinning is the non-Newtonian behavior of fluids whose viscosity decreases under shear strain. It is sometimes considered synonymous for pseudoplastic behaviour, and is usually defined as excluding time-dependent effects, such as thixotropy. Shear-thinning behaviour is generally not seen in pure liquids with low molecular mass, or ideal solutions of small molecules like sucrose or sodium chloride, but is often seen in polymer solutions and molten polymers, and complex fluids and suspensions like ketchup, whipped cream, blood, paint, and nail polish.
11. When n>1, which of the fluid does it represents?
Answer: d [Reason:] When physicochemical interactions create bonds that are strong enough to resist breakage during shear, this mechanism would dominate and dilatant (shear-thickening) behavior is observed. Shear-thinning fluids are used for lubrication and paints and require less volume. Its viscosity increases as the shear rate increases.
1. Which of the following defines the given statement – “An association between two organisms in which one benefits and the other derives neither benefit nor harm”?
Answer: c [Reason:] Commensalism, in biology, a relationship between individuals of two species in which one species obtains food or other benefits from the other without either harming or benefiting the latter.
2. Which of the following defines the given statement – “Any relationship between organisms of different species in which one organism is inhibited or destroyed while the other organism remains unaffected”?
Answer: d [Reason:] One type of relationship that has been classified by biologists and ecologists is amensalism. Amensalism is any relationship between organisms of different species in which one organism is inhibited or destroyed while the other organism remains unaffected.
3. Which of the following defines the given statement – “Two organisms of different species exist in a relationship in which each individual benefits from the activity of the other”?
Answer: b [Reason:] Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits from the activity of the other. Similar interactions within a species are known as co-operation.
4. Symbiosis is a Short term interaction.
Answer: b [Reason:] Biological interactions are effects that organisms have on each other, whether
▪ Short-term interactions, especially predation
▪ Long-term interactions, now called symbiosis, which includes commensalism, parasitism, and mutualism.
5. Which of the following is an endosymbiotic in nature?
Answer: c [Reason:] Endosymbiotic theory that attempts to explain the origins of eukaryotic cell organelles such as mitochondria in animals and fungi and chloroplasts in plants was greatly advanced by the seminal work of biologist Lynn Margulis in the 1960s.
6. Mutualistic symbiosis is a type of mutualism.
Answer: a [Reason:] Mutualistic Symbiosis is a type of mutualism in which individuals interact physically, or even live within the body of the other mutualist. Frequently, the relationship is essential for the survival of at least one member.
7. Competition is having in between two organism:
a) Negative effects on both
b) Positive effects on both
c) On one positive and on other negative
d) No one is either positively or negatively affected
Answer: a [Reason:] Competition is an indirect interaction between two populations that has negative effects on both. In competition, each population competes for the same substrate. Two populations or microorganisms with similar nutrient requirements usually compete for a number of common, required nutrients when grown together.
8. Which of the following is correct according to an exclusion principle?
a) Both the organism competing for the resource exist
b) The organism with slowest growth rate will displace the other
c) The organism with fastest growth rate will displace the other
d) Both organism will equally survive
Answer: c [Reason:] The competitive exclusion principle, sometimes referred to as Gause’s Law of competitive exclusion or just Gause’s Law, states that two species that compete for the exact same resources cannot stably coexist. The organisms with the fastest growth rate will displace the others from the culture. This is known as the exclusion principle.
9. For Protocooperation species the interaction is not necessary.
Answer: a [Reason:] Protocooperation is where two species interact with each other beneficially; they have no need to interact with each other – they interact purely for the gain that they receive from doing this. It is not at all necessary for protocooperation to occur; growth and survival is possible in the absence of the interaction.
10. Symbiosis and mutualism are same.
Answer: b [Reason:] Symbiosis and mutualism are not the same. Symbiosis implies a relationship when two organisms live together. A symbiotic relationship may be mutualistic, but it may also be neutralistic, parasitic, commensalistic, and so on.
11. Competition and commensalism can occur at the same time.
Answer: a [Reason:] Note that these interactions can, and often do, exist in combination. For example, A and B may compete for glucose as a nutrient, but A requires a growth factor from B to grow. In such a case, both competition and commensalism would be present.
12. Lichens are ____________
a) A fungal-Bacterial association
b) A fungal-yeast association
c) A Bacterial-yeast association
d) A fungal-algal association
Answer: d [Reason:] Lichens are a fungal-algal symbiosis (that frequently includes a third member, a cyanobacterium.) The mass of fungal hyphae provides a protected habitat for the algae, and takes up water and nutrients for the algae. In return, the algae (and cynaobacteria) provide carbohydrates as a source of energy for the fungus.
13. Which of the following is not an example of Mutualistic Symbiosis?
a) Fungal-algal symbiosis
b) Algae and the corals
c) Mushroom and fly
d) Racoon and poison ivy
Answer: b [Reason:] Resource-resource mutualism -A relationship where one resource is traded for another. Corals and the symbiotic algae .The algae get inorganic nutrients from the corals, and the corals get sugars that are by-products of photosynthesis from the algae. When a coral ‘bleaches’ it is actually kicking out the zooxanthellae that live in it, so all you see is the coral’s skeleton, which is white.
14. Which one is the correct interaction sign for Amensalism?
Answer: d [Reason:] Type of Interaction Sign Effects Mutualism +/+ both species benefit from interaction Obligate Mutualism +/+ obligatory; both populations benefit Commensalism +/0 one species benefits, one unaffected Neutralism 0/0 populations do not affect one another Amensalism 0/- One species is disadvantaged/one species unaffected.
15. Which one is the correct interaction sign for Commensalism?
Answer: c [Reason:] Type of Interaction Sign Effects Mutualism +/+ both species benefit from interaction Obligate Mutualism +/+ obligatory; both populations benefit Commensalism +/0 one species benefits, one unaffected Neutralism 0/0 populations do not affect one another Amensalism 0/- One species is disadvantaged/one species unaffected.
1. The smaller bubbles are sensitive than larger bubbles?
Answer: a [Reason:] kL in fermentation liquids is about 3-4×10-4 m s-1 for bubbles greater than 2-3 mm diameter; this can be reduced to 1×10-4m s-1 for smaller bubbles depending on bubble rigidity. Once the bubbles are above 2-3 mm in size, kL is relatively constant and insensitive to conditions.
2. Which size of bubbles is relevant for mass transfer?
b) Very small
d) Very large
Answer: a [Reason:] The most important property of air bubbles in fermenters is their size. Small bubbles have correspondingly slow bubble-rise velocities; consequently they stay in the liquid longer, allowing more time for the oxygen to dissolve. While it is desirable to have small bubbles, there are practical limits. Bubbles << 1 mm diameter can become a nuisance in bioreactors. Oxygen concentration in these bubbles equilibrates with that in the medium within seconds, so that the gas hold-up no longer reflects the capacity of the system for mass transfer.
3. Coalescence is appropriate for oxygen transfer in bubbles?
Answer: b [Reason:] Coalescence of small bubbles into bigger bubbles is generally undesirable because it reduces the total interfacial area and gas hold-up. Frequency of coalescence depends mainly on the liquid properties. In a coalescing liquid, a large fraction of bubble collisions results in the formation of bigger bubbles, while in non-coalescing liquids colliding bubbles do not coalesce readily. Salts act to suppress coalescence; therefore, fermentation media are usually non-coalescing to some extent depending on com- position. This is an advantage for oxygen mass transfer.
4. What do you mean by “Impeller flooding”?
a) The flooding of an impeller
b) Gas handling is greater than the amount introduced
c) Gas handling is smaller than the amount introduced
d) Leakage of the Broth
Answer: c [Reason:] Impeller flooding is said to occur; this means that the gas-handling capacity of the stirrer is smaller than the amount introduced. Flooding should be avoided because an impeller surrounded by gas no longer contacts the liquid properly, resulting in poor mixing and gas dispersion.
5. Dispersion of gas in stirred vessels is largely independent of sparger design?
Answer: a [Reason:] In a non-coalescing liquid, the bubbles remain close to the size produced at the back of the cavities. Because bubbles formed at the sparger are immediately drawn into the impeller zone, dispersion of gas in stirred vessels is largely independent of sparger design; when the sparger is located under the stirrer, it has been shown that sparger type does not significantly affect mass transfer.
6. Which of the following is not an antifoam agent?
b) Silicone oil
d) Fatty alcohol
Answer: a [Reason:] A foaming agent is a material that facilitates formation of foam such as a surfactant or a blowing agent. A surfactant, when present in small amounts, reduces surface tension of a liquid (reduces the work needed to create the foam) or increases its colloidal stability by inhibiting coalescence of bubbles.
7. Which type of fermenter is used in laboratory scale?
a) Stirred tanks
c) Bubble columns
d) Air-lift fermenter
Answer: b [Reason:] At laboratory-scale cultures may be aerated by means of the shake-flask technique where the culture is grown in a conical flask shaken on a platform contained in a controlled environment of chamber.
8. Which part of fermenter is used for mixing process?
Answer: a [Reason:] An impeller is a rotating component of a centrifugal pump which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. This is how mixing is accomplished.
9. Bubble column reactor cannot be used for?
a) Low viscous medium
b) High viscous medium
c) Liquid state medium
d) Solid state medium
Answer: b [Reason:] Bubble column reactor cannot be used for highly viscous medium. Pattern of gas bubbles in a bubble column reactor is dependent on the gas superficial velocity. Gas velocity should be 1-4 cm per second for uniform bubbles throughout medium which will provide proper mixing. If gas velocity is higher or lower than uniform bubbles will not be produced, thus when bubbles coalesce produces differences in fluid density which will disturb air flow rate.
10. KLa is different in between Air-lift reactors and bubble columns?
Answer: a [Reason:] In air-lift fermenters, Medium circulation is also accomplished with bubble formation. KLa obtained in air-lift reactor will be less than bubble fermenter due to shorter contact time between bubble and medium.
11. What is the function of disengagement zone from the following?
a) Increase foaming
b) Maximize recirculation of bubbles
c) Increase volume to the reactor
d) Decrease volume to the reactor
Answer: c [Reason:] The roles of the disengagement zone are to:
▪ add volume to the reactor,
▪ reduce foaming and
▪ minimise recirculation of bubbles through the down comer.
12. The rising tube and the down coming tubes are the features of which type of fermenters?
a) Bubble column
c) Packed bed
d) Fluidized bed
Answer: b [Reason:] There are two types of air-lift fermenters which are the internal loop and the external loop. The internal loop has a draft tube in its inner tube, in which the up-flowing gasses liquid and the down-flowing liquid is separated by the draft tube. Draft tubes are used in some processes to promote better mass transfer, mixing and inducing circulatory motion to reduce bubble coalescence. The external loop has two streams flow in two separate pipes connected at top and bottom. In this way, the air-lift fermenters improve the circulation and oxygen transfer and equalize shear forces in the reactor.
13. The pH of water sample collected from a river was found to be acidic in the range of 3.5 – 4.5. On the banks of the river were several factories that were discharging effluents into the river. The effluents of which one of the following factories is the most likely cause for lowering the pH of river water?
a) Soap factory
b) Detergent factory
c) Alcohol distillery
d) Plastic cup manufacturing factory
Answer: c [Reason:] Fermentation is the chemical procedure which is utilized in alcohol industry. We know that fermentation produces lactic acid and ethanol. Ethanol changes into ethanoic acid on oxidation.
14. Mixing in an anaerobic sludge blanket reactor is due to?
a) Rapid change in water temperatures throughout the reactor
b) Release of gases by the microbial populations
c) Rapid change in medium temperature throughout the reactor
d) Due to viscous medium
Answer: b [Reason:] The upflow anaerobic sludge blanket reactor (UASB) is a single tank process in an anaerobic centralised or decentralised industrial wastewater or blackwater treatment system achieving high removal of organic pollutants. Bacteria living in the sludge break down organic matter by anaerobic digestion, transforming it into biogas. Solids are also retained by a filtration effect of the blanket. The upflow regime and the motion of the gas bubbles allow mixing without mechanical assistance.
15. Low dissolved oxygen concentrations leads to
a) Low biomass yields
b) High biomass yields
c) Equal biomass compositions
d) No effect on biomass yields
Answer: a [Reason:] Water with high concentrations of dissolved minerals such as salt will have a lower DO concentration than fresh water at the same temperature. Low dissolved oxygen (DO) primarily results from excessive algae growth caused by phosphorus. As the algae die and decompose, the process consumes dissolved oxygen.