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The correct choice is (a) True

To EXPLAIN I would say: The VALUE of the Henry’s law constant is FOUND to be temperature dependent. The value generally increases with increasing temperature. As a consequence, the solubility of gases generally decreases with increasing temperature. The decrease in solubility of gases with increasing temperature is an example of the operation of Le Chatelier’s PRINCIPLE. The heat or enthalpy change of the dissolution reaction of most gases is negative, which is to say the reaction is exothermic. As a consequence, increasing the temperature LEADS to gas evolution.

The correct CHOICE is (d) 0.0085 g/L

For explanation I would say: The solubility of OXYGEN in UNITS of grams of oxygen PER liter of WATER is:

Right answer is (b) High viscous medium

To explain: 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.

The correct choice is (c) GERMINATION of barley

The best I can explain: 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.

Right option is (d) Fermentation

Easiest explanation: 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^+.

Right answer is (a) True

Explanation: Normally, it can be assumed that there is negligible resistance to mass transfer at the actual interface, i.e. WITHIN DISTANCES corresponding to molecular free paths on either side of the phase boundary. This is equivalent to assuming that the phases are in equilibrium at the interface; therefore, CA1i and CA2i are equilibrium CONCENTRATIONS. As a RESULT it is known that there are special situations, such as when there is adsorption of material at the interface, where the assumption is invalid. However, in ordinary situations, the evidence is that equilibrium does exist at the interface between phases. If the BULK liquids were in equilibrium, no net mass transfer would take place.

Right answer is (b) False

Explanation: Molecular diffusion is the movement of component MOLECULES in a mixture under the INFLUENCE of a concentration difference in the system. It occurs in the direction required to destroy the concentration difference. If the GRADIENT is maintained by constantly supplying material to the REGION of high concentration and removing it from region of low concentration, diffusion will CONTINUE.

Correct choice is (a) True

The best explanation: Because kLa measurements involve monitoring LEVELS of DO following a system perturbation, the results can be INFLUENCED by the RESPONSE time (or “SPEED”) of a sensor making those determinations. Sensors with response times (τr) on the order of the first-order time constant of the mass transfer (1 / kLa) require special treatment of their data to correct for the time lag in readings introduced by the oxygen sensor.

The CORRECT answer is (c) ALCOHOL distillery

The BEST explanation: 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.

Correct answer is (a) Small

To explain I WOULD say: 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.

Correct answer is (a) Packed

To elaborate: Packed Beds. Although packed bed columns are used most often for ABSORPTION, they are also used for the distillation of vapor-liquid mixtures. The packing provides a LARGE SURFACE area for vapor-liquid contact, which increases the column’s EFFECTIVENESS.

The correct choice is (b) False

For explanation: Non- steady state DIFFUSION – CONCENTRATION of SOLUTE atoms at any point in metal CHANGES with time in this case. And the Fick’s SECOND law states that rate of compositional change is equal to diffusivity times the rate of change of concentration gradient.

The correct option is (a) Thermal motion

Easy EXPLANATION: Molecular diffusion, OFTEN simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the SIZE (MASS) of the particles.

Right CHOICE is (b) 31.05 mmoles O2 / liter HR

To EXPLAIN I would say: OTR = KLA(PO2 – P*)

= 169 mmol O2 / 1 hr ATM(0.21- 0.0263) atm

= 31.05 mmoles O2 / liter hr.

Correct CHOICE is (c) Above Ccrit

The explanation: It is important that the oxygen concentration REMAINS above Ccrit so that the RATE of oxygen UPTAKE by the cells is independent of oxygen level.

Correct choice is (a) IMPELLER

The EXPLANATION is: 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.

Correct choice is (b) Presence of enzymes

To elaborate: The mass transfer COEFFICIENT is strongly affected by agitation speed and AIR flow rate. The mass transfer coefficient increases with agitation speed and air flow rate. Since fermentation is USUALLY conducted at constant TEMPERATURE and PRESSURE so thermodynamically antifoam agents make the foam unstable causing ΔG < va ΔA (where ΔG is the free energy change, va is the surface tension and ΔA is the change in area).

Right option is (c) 100 mmoles O2 / (g cells hr)

EXPLANATION: OUR = X QO2 = (5 g / L) (20 mmoles O2 / (g cells hr)) = 100 moles O2 / (g cells hr).

Correct ANSWER is (d) 160 MM HG

Easiest explanation: The partial PRESSURE of oxygen is:

P (O2) = (1.0 atm) ((760 mm Hg)/(1 atm)) (0.21) = 160 mm Hg.

The correct option is (a) mgl^-1

Explanation: Respiration is expressed in molar units RELATED to BIOCHEMICAL stoichiometries. C*AL is OXYGEN solubility in units of MG l^-1.

Right option is (b) Release of GASES by the microbial populations

The best explanation: 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.

Correct option is (B) OTR
Easy explanation: Since OUR > OTR, we must MODIFY the BIOREACTOR operation in order to BRING them into balance:

• INCREASE N

• use pure O2 rather than air.

Right choice is (b) Convection

To explain I would say: Flow of heat through currents within a fluid (liquid or gas). Convection is the displacement of volumes of a substance in a liquid or gaseous PHASE. When a mass of a fluid is heated up, for example when it is in contact with a warmer surface, its molecules are carried away and scattered CAUSING that the mass of that fluid becomes less dense. For this REASON, the warmed mass will be displaced vertically and/or horizontally, while the colder and denser mass of fluid goes down (the low-kinetic-energy molecules displace the molecules in high-kinetic-energy states). Through this PROCESS, the molecules of the hot fluid TRANSFER heat continuously toward the volumes of the colder fluid.

Correct choice is (c) Gas-Vapour

Best explanation: Psychrometry is concerned with the physical and thermodynamic properties of gas-vapor mixtures. Although the principles of psychrometry APPLY to any physical system consisting of gas-vapor mixtures, the most common system of interest is the mixture of water vapor and air, because of its application in heating, ventilating, and air-conditioning and meteorology. In human TERMS, our thermal comfort is in large PART a consequence of not just the TEMPERATURE of the surrounding air, but (because we cool ourselves via PERSPIRATION) the extent to which that air is saturated with water vapor.

Correct choice is (d) DISTANCE

The explanation: In single-phase systems, the rate of mass transfer due to molecular diffusion is GIVEN by Fick’s LAW of diffusion, which states that mass flux is proportional to the concentration gradient. JA is the mass flux of component A, NA is the rate of mass transfer of component A, a is the area across which mass transfer OCCURS, DAB is the binary diffusion coefficient or DIFFUSIVITY of component A in a mixture of A and B, CA is the concentration of component A, and y is distance, \(\frac{dC_A}{dy}\) is the concentration gradient, or change in concentration of A with distance.

The correct option is (a) CAL = 0

Easiest explanation: 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.

Right CHOICE is (a) True

To explain I would say: The methods to measuring the KLA in a microbial bioprocess can be classified into the absence of MICROORGANISMS or with dead cells and in the presence of biomass that consumes oxygen at the time of measurement.

The CORRECT option is (d) Sulphite oxidation method

To explain: The oxygen-transfer rate is determined by the oxidation of sodium sulphite solution. This technique does not require the MEASUREMENT of dissolved oxygen concentrations.

As oxygen enters solution it is immediately consumed in the oxidation of sulphite, so that the sulphite oxidation rate is EQUIVALENT to the oxygen-transfer rate. Since the dissolved oxygen concentration, is ZERO then the kLa may then be calculated from the equation:

kLa = OTR / C*

where OTR is the oxygen transfer rate.

Right option is (a) h^-1

For EXPLANATION I would say: In this relation, the volumetric oxygen transfer COEFFICIENT, kLa, has the UNITS of mmol, of O2/ml. h. unit concentration GRADIENT. Using the proper concentration units, kLa has the unit of reciprocal of time (i.e., time^-1).

Correct option is (b) False

Best explanation: Oxygen solubility is decreased by the ions and sugars normally ADDED to fermentation media. In a typical fermentation medium, oxygen solubility is between 5% and 25% LOWER than in water as a result of solute effects. In simple systems, with all the components being dissolved, C0 represents the oxygen solubility and linearly decreases with INCREASING solute concentrations. In complex solutions with multi-phase structure an increase in C0 can be detected. It suggests that C0 consists of two components — one being oxygen solubility, the other being determined by the amount of oxygen adsorbed on the interphase and bound by macromolecules. The PRESENCE of biomass leads to a DECREASE in C0.

The correct answer is (C) 0.101 gmol/m.hr

To EXPLAIN: Rate of loss of NAPHTHALENE = k (CAi – CA∞)

= 0.014 (1 * 10^–5 – 0) = 1.4024 * 10^–7 kmol/m^2 sec

Rate of loss per meter WIDTH = (1.4024 * 10 ^–7) (0.2) = 2.8048 * 10 ^–8 kmol/m.sec

= 0.101 gmol/m.hr.

Correct option is (c) MOMENTUM

For explanation I would say: The drag experienced by a rain drop as it FALLS in the atmosphere is an example of momentum DIFFUSION (the rain drop LOSES momentum to the surrounding AIR through viscous stresses and decelerates).

Right choice is (a) True

The best I can explain: The value of kLa is unique to both the size and configuration of a reactor vessel. Although some empirically derived expressions have been PUBLISHED for predicting kLa VALUES in non-Newtonian fluids, there is no agreed upon set of equations that account for all of the variables that can affect the results. Accordingly, predicting kLa is not possible, and kLa studies NEED to be performed for bioreactors individually. The kLa value will depend upon the design and operating conditions of the fermenter and will be affected by the variables such as

– AERATION rate,

– agitation rate and

– impeller design.

The correct answer is (c) Gas handling is smaller than the amount introduced

The explanation: 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.

The correct answer is (C) 0.2099 ATM

For EXPLANATION: The MOLE fraction of oxygen in air is 0.2099, so the partial pressure of oxygen at 1 atm air pressure is 0.2099 atm.

The correct answer is (d) g l^-1s^-1

Easy explanation: 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.

The correct option is (b) LOG

Best explanation: 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.

The correct answer is (b) False

To explain I would say: Estimation of the interfacial concentration CAi is more difficult; measuring compositions at phase BOUNDARIES is not easy experimentally. To overcome this problem, we must CONSIDER the processes in the SYSTEM which are linked to MASS transfer of A. Transport of A is linked to reaction at the surface of the solid, so that the value of CAi will depend on the rate of consumption of A at the interface. In practical terms, we can therefore CALCULATE the rate of mass transfer of A only if we have information about the rate of reaction at the solid surface. Simultaneous reaction and mass transfer occurs in many bioprocesses.

The correct choice is (d) The salinity is increased

Explanation: Dissolved OXYGEN DECREASES exponentially as SALT levels increase. That is why, at the same pressure and temperature, saltwater holds about 20% LESS dissolved oxygen than freshwater.