الفهرس 
introductionOnly 14 pages are availabe for public view
 |  | from | 205 |  |  |
| | | from | 205 | | |
Abstract
A simulation model for the recirculating aquaculture
system (RAS) was developed successively according to heat and
mass balance to optimize the main factors affecting the
performance of RAS through studying of water temperature,
oxygen consumption, ammonia production, nitrate production,
biological filter volume, solids generation, fish growth rate,
specific growth rate, feed conversion rate and system energy
consumption at different operation conditions. Also, carrying
out an experiment to validate the model results through
measuring: water temperature, oxygen consumption, ammonia,
nitrite, nitrate, solids, fish growth rate, specific growth rate, feed
conversion rate and system energy consumption. The most
important results obtained can be summarized in the following
points:
6.1. Model results:
- The model showed that the predicted water temperature
increases with increasing the air ambient temperature,
where, the ambient air temperature increased from 23 to 31
˚C during the whole day, the water temperature increased
from 18 to 26 ˚C at 6:00 am, while it increased from 23 to
32 ˚C at 18:00 pm.
- The model showed that the predicted oxygen consumption
increases with increasing water temperature, meanwhile,
the oxygen consumption decreases with increasing fish
weight during the whole growth period. The Oxygen
consumption increased from 302.02 to 732.70 mg O2/kg
SUMMARY AND CONCLUSION 213
fish. hour, when, the water temperature increased from 24
to 32 ˚C at the same fish weight (5 g). Oxygen
consumption decreased from 302.02 to 121.33 mg O2/kg
fish. hour with increasing fish weight from 5 to 200 g at 24
˚C water temperature. At 32 ˚C, oxygen consumption
decreased from 732 to 238.37 mg O2/kg fish. hour with
increasing the fish weight from 5 to 200 g.
- The model showed that the predicted ammonia production
increases with increasing water temperature, while, it
decreases with increasing fish weight during the whole
growth period. The ammonia production increased from
43.20 to 52.94 mg NH3/kg fish. hour, when, the water
temperature increased from 24 to 32 ˚C at the same fish
weight (5 g). The ammonia production decreased from
43.20 to 5.98 mg NH3/kg fish. hour with increasing fish
weight from 5 to 200 g at 24 ˚C water temperature. At 32
˚C, ammonia production decreased from 52.94 to 12.82 mg
NH3/kg fish. hour with increasing the fish weight from 5 to
200 g.
- The model showed that the predicted nitrate production
increases with increasing water temperature, whereas, it
decreases with increasing fish weight during the whole
growth period. The nitrate production increased from
187.48 to 229.75 mg NO3/kg fish. hour when the water
temperature increased from 24 to 32 ˚C at the same fish
weight (5 g). The nitrate production decreased from 187.48
to 25.95 mg NO3/kg fish. hour with increasing fish weight
from 5 to 200 g at 24 ˚C water temperature. At 32 ˚C,
SUMMARY AND CONCLUSION 214
nitrate production decreased from 229.75 to 55.63 mg
NO3/kg fish. hour with increasing the fish weight from 5 to
200 g.
- The model showed that the predicted settleable and
suspended solids increased with increasing water depth.
The settleable solids increased from 0.039 to 0. 195 kg m-3
at depths of 0.8 to 1.6 m, while the suspended solids
increased from 0.0124 to 0.0145 kg m-3 when the water
depth increased from 0.8 to 1.6 m at the same fish weight
(5 g). The suspended solids increased from 0.0124 to
0.1607 kg m-3 with increasing fish weight from 5 to 200 g
at 0.8 m water depth. At 1.6 m, suspended solids increased
from 0.0145 to 0.1628 kg m-3 with increasing the fish
weight from 5 to 200 g.
- The model showed that the predicted settleable solids
increased with increasing settling velocity. It increased
from 0.0234 to 0.0544 kg m-3 at settling velocities from
1.25 to 2.90 m/hour.
- The model showed that the predicted energy consumption
by the heater per day decreases with increasing the ambient
air temperature, where, it ranged from 110276.4 to
441105.7 kJ/day. It was as high of 441105.7 kJ/day at 23
˚C and as low as 110276.4 kJ/day at 31 ˚C. The highest
energy consumption by the heater per hour was determined
at (the optimum temperature 27˚C) 7918.88 kJ/hour at 6:00
am. While, the lowest value of the daily energy
SUMMARY AND CONCLUSION 215
consumption was 335.13 kJ/hour at 14:00.The energy
consumption by whole system was 359896.5 kJ/day.
6.2. Model Validation:
- The predicted water temperature was in a good agreement
with the measured water temperature with a coefficient of
determination of 0.999, where, it ranged 28.00 to28.86˚C
experimentally, while, it was 28.00˚C theoretically during
the whole day.
- The predicted oxygen consumption was in a good agreement
with the measured oxygen consumption with a coefficient
of determination of 0.988. The predicted oxygen
consumption values were between 189.13 to 457.56 mg
O2/kg fish per hour, while, the measured oxygen
consumption values are from 197.42 to 467.61 mg O2/kg
fish per hour during the whole growth period.
- The predicted ammonia production was in an agreement
with the measured ammonia production with a coefficient
of determination of 0.915. The average ammonia
production from the system ranged from 10.56 to 55.99 mg
NH3/kg fish.hour experimentally, while, it was from 10.45
to 48.61 mg NH3/kg fish.hour theoretically during the
whole growth period.
- The predicted nitrate production was in a good agreement
with the measured nitrate production with a coefficient of
determination of 0.993. the average nitrate production from
the system ranged from 41.61 to 222.31 mg NO3/kg
SUMMARY AND CONCLUSION 216
fish.hour experimentally, while, it was from 45.34 to
210.97 mg NO3/kg fish.hour theoretically during the whole
period of fish growth.
- The predicted settleable solids was in a good agreement with
the measured settleable solids with a coefficient of
determination of 0.999. The average settleable solids
removed from the system was 0.0429 ± 0.0127 kg m-3
(42.90 ± 12.70 mg l-1). The daily average of solids removed
from the system ranged from 0.33 to 6.62 kg/day
experimentally while it ranged from 0.34 to 4.41 kg/day
theoretically during the whole period of fish growth.
- The predicted suspended solids was in a reasonable
agreement with the measured suspended solids with a
coefficient of determination of 0.915. the suspended solids
removed by the system increased with growth period,
where it was 0.0123 kg m-3 (12.30 mg l-1) at the beginning
and increased rapidly to reach 0.0806 kg m-3 (80.60 mg l-1)
after 3 months. The daily average solids removed from the
system ranged from 0.11 to 11.34 kg/day experimentally
while it was from 0.11 to 15.70 kg/day theoretically during
the whole period of fish growth.
6.3. Wastes removal efficiency:
The efficiency of the biological filter for ammonia
removal from the system ranged from 11.11 to 63.64 %.
The efficiency of the hydrocyclone for settleable solids
removal from the system ranged from 27.4 to 57.79 %.