The dissolved CO2 accumulation has become an important factor restricting production in the high-density recirculating aquaculture system in which pure oxygen injection is used. In this paper, a novel CO2 removal device is designed for the recirculating aquaculture water environment based on the principle of gas exchange. In terms of experiments, the DOE (design of experiment) method is applied to design three factor two level orthogonal experiment, Further, significance effect of gas to liquid ratios (G / L), inlet CO2 concentration, the water flow rate (QW) on CO2 removal efficiency is analyzed. Results show that G/L has the most significant influence on the CO2 removal efficiency. Influences of the latter two on CO2 removal efficiency are not apparent. Tests results of G/L effect on CO2 removal efficiency show that, when G/L=1∼5, CO2 removal efficiency increases rapidly with the increase of G/L; when G/L=5, CO2 removal efficiency=80%∼88%; when G/L=8, CO2 removal efficiency=86%∼92%, when G/L>8, CO2 removal efficiency increases gently with the increase of G/L. Considering both system energy saving and effective removal of carbon dioxide, G/L=5∼8 is considered to be the best for the aquaculture water CO2 removal device running, CO2 removal efficiency=80%∼92%.
The high concentration of CO
2
is harmful to the fish in aquaculture waters environment. When the
concentration of CO
2
exceeds the safe level, the amount of oxygen that the blood hemoglobin of fish can
carry is reduced significantly and respiration distress can occur, even with high concentrations of
dissolved oxygen in the water. M
eanwhile, the whole system’s pH also
decreases dramatically and the
performance of biological purificati
on is affected [1]. In the traditional culture model, because of the low
stocking density, CO
2
doesn’t accumulate excessively, which do
esn’t make fish dangerous. In the
recirculating aquaculture system, the stocking density raises and the water exchange rate drops (about
10%)[2]. Consequently, large amounts
of dissolved carbon dioxide will gr
eatly restrict production. When
stocking densities were less than 30 to 60kg/m
3
, conventional aeration systems would generally provide
sufficient removal of CO
2
through transferring oxyg
en into the water with airstones, surface agitation and
water falls. However, with the increase of the fish density to 100kg/m
3
or higher, in order to make the
aquaculture system more productive, pure oxygen systems become a widely used aerobic way to meet the
demand of the normal growth of fish for dissolved oxygen,. For every 10mg/L of oxygen consumed,
approximately 13–14 mg/L of CO2 excreted through
fish gills. As a result, The CO2 accumulates to a
high concentration through respiration of the fish and bi
ological nitrification [3-5], which is great toxic to
fish. The safe operating levels of CO2 depend on the species, development stage, and overall water
quality [6]. In general recommendation, the CO2 concen
tration of aquaculture water should be less than
10mg/L [7].
CO
2
removal technology of aquaculture waters in china is still in the pilot study stage, generally, a
large-scale recirculating aquacu
lture system does not set CO
2
removal link. However, the United States
and Europe have used CO
2
removal device in the intensive recirculating aquaculture systems successively
[8-10], the effective CO
2
removal has been achieved and fish prod
uction per unit of water has been rised.
Currently, the mainstream CO
2
removal devices are stripping columns [11]. Due to a lot of factors,
accurately predicting the removal rate is very difficu
lt. In this paper, through three factor two level
orthogonal testing, the effect of gas to liquid ratios(G/L), inlet CO
2
concentration, water flow rate(Q
W
)
and their interactions on the CO
2
removal rate are studied and the best
level combinations are discovered
to achieve the effective CO
2
removal.
