64. In wastewater treatment, which bioreactor is generally used?
A.Plug flow reactor
B.Trickle bed reactor
C.Tower fermentor
D.CSTR

---

65. The contents in stirred tank rector are mixed through
A.compressed air
B.a mechanical agitator
C.external pumping
D.any of these

---

66. The height to diameter ratio (H/D) for the tank fermenters is
A.<3
B.>3
C.<1.5
D.>1.5

---

67. The relatively large volume (10 to 40% of total fermenter volume) of the seed culture is employed to
A.increase the overall fermentation time
B.increase the overall fermentation time
C.decrease the overall fermentation time
D.decrease the overall yield of product

---

68. In an airlift bioreactor, the air sparging region is called
A.downcomer
B.disengagement zone
C.air riser
D.none of these

---

69. The air riser is located on the outside of the draft tube for the large-scale airlift bioreactors because of
A.higher oxygen transfer rates
B.a small sparge ring
C.better heat transfer efficiencies
D.all of these

---

70. At the end of the lag phase, when growth begins, the division rate increases gradually and reaches a maximum value in the exponential growth period. This transitional period is commonly called the accelerated growth phase and is often included as a part of the
A.lag phase
B.stationary phase
C.death phase
D.exponential growth phase

---