TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

999 g O2/hr and 48.5% to 57%, respectively. In the experiment at 20 o C, OTR at the baffle
depths of 100 cm and 150 cm was significantly higher than that of control while AE of all
baffles were significantly higher than that of the control. In the experiment at 30 o C, OTR
at all baffles were significantly higher than the control while AE with baffle depths of
150 cm was significantly higher than that of the control.
It is hard to compare the AE value of this experiment with others because of the
differences in experimental conditions. However, Soderberg (1982) reported the aeration
efficiencies of some gravity aerators with various distances of waterfall, showing the
efficiency increase with the increase of the distance of waterfall. In this experiment, the
AE was ranged from 43% to 58.1% and was affected by baffle depths. Average OTR and
AE were increased by increasing baffle depth at both temperatures, 20 o C and 30 o C.
Net oxygen transfer depends upon the temperature, the contact area of air-water
interface, and contact time (Haney 1954; Spotte 1992; Lawson 1995). In this experiment,
there are strong trends that increasing baffle depths increased the contact time of bubbles
with water, leading to enhanced oxygen transfer, that is, the deeper the baffle the higher
the OTR and AE at both temperatures.
Table 1. Effects of baffle depths in the pumping station in the IBK recirculating
aquaculture system on oxygen transfer rate (OTR) and aeration efficiency (AE)
at two different temperatures
Baffle Depth (cm)
0 (control) 50
20
100 150
o C
Av. DO (mg/L)
Inlet
Outlet
4.3
6.4
4.6
6.8
4.7
7.0
4.8
7.4
Increased DO (mg/L) 2.1 2.2 2.3 2.6
AE (%) 43.2±1.98c 51.5±2.70b 52.5±1.60b 58.1±2.74a
OTR (g O2/hr) 777±35.4c 814±18.5bc 851±35.4ab 962±63.2a
Added DO by baffle (g O2/hr) 0 37 74 185
30 o C
Av. DO (mg/L)
Inlet
Outlet
3.6
5.5
2.9
5.1
2.8
5.2
2.8
5.5
Increased DO (mg/L) 1.9 2.2 2.4 2.7
AE (%) 48.5±0.67b 47.9±1.85b 50.9±5.95b 57.0±2.20a
OTR (g O2/hr) 703±42.7c 814±55.5b 888±92.3b 999±30.2a
Added DO by baffle (g O2/hr) 0 111 185 296
The oxygen concentration increase at 20 o C from inlet to outlet of the U-shaped
mixing chamber was 2.1 mg/L without baffle, and 2.6 mg/L with 150 cm baffle. There
are strong trends that the oxygen transfer rate increased to a large extent with increasing
baffle depth.
The amount of oxygen transferred by the cascading water in the pumping station of
the IBK recirculating aquaculture system is considerable from the first. Providing Ushaped
water-bubble mixing chamber can further enhance the efficiency. In this
experiment at 20 o C, an amount of 777 g oxygen per hour was increased without baffle
plate, and with 150 cm deep baffle, 962 g of oxygen per hour was increased. Therefore
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