# Design and Application of New Aeration Device Based on Recirculating Aquaculture System
## 3 Results  
### Test Results for Each Aeration Component  
Figure 6a shows the variation in dissolved oxygen in the water column under three different operating conditions for the impeller oxygenation assembly. Before the three sets of tests, the initial DO (\(C_{0}\)) in the RAS tank water fluctuated within ranges of 3.3-4.4, 3.5-3.8, and 3.8-5.3 mg/L, with large differences in the initial values among the three sets of tests. During the first 20 min of operation, there were almost no changes in these ranges. After 25 min, the dissolved oxygen level in the water gradually increased, and the intervals narrowed. Then, after 50 min, the slope of the curve flattened down, and the final DO values were 6, 6.5, and 7.5 mg/L for the rotational speeds of 600, 1000, 1400 r/min, respectively. The three sets of tests also showed that the operation of the aeration component increased the \(R_{s}\) values in the pond water tank by 1.63, 2.30, and 2.33 mg/L, respectively. Therefore, increasing the rotational speed of the blades in an impeller aerator can effectively improve its aeration capacity.  
Test groups 4, 5, and 6 were conducted under almost the same test conditions. Figure 6b shows the variation in DO under the three sets of operating parameters of the microporous aeration component. The initial dissolved oxygen in the water at the beginning of the three sets of tests ranged from 3.2 to 4.9 mg/L, which is roughly consistent with the \(C_{0}\) values in the impeller aerator tests. Based on the test results, the average DO increases (\(R\)) in the upper, middle, and lower layers of the water tank achieved with the device were calculated to be 2.33, 3.01, and 3.37 mg/L, respectively. The average DO increases in the three test groups were 3.13, 2.50, and 3.03 mg/L, respectively.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test Group**} & \multicolumn{3}{c}{**Operating Status of the Two Components**} & \multicolumn{2}{c}{**Rotational Speed**} & \multirow{2}{*}{
\begin{tabular}{c} **Test Data** \\ **Collection** \\ **Points** \\ \end{tabular} } \\ \cline{2-2} \cline{5-6}  & **Impeller Aeration Component** & **Microporous Aeration Component** & **\(n_{1}\)** & **\(n_{2}\)** & **(Pr) [LW]** & **Test Data Collection Points** \\ \hline
1 & ✔ & ✗ & 600 & 0 & 0.64 & 1 \\
2 & ✔ & ✗ & 1000 & 0 & 1.07 & 1 \\
3 & ✔ & ✗ & 1400 & 0 & 1.50 & 1 \\
4 & ✗ & ✔ & 0 &  
For the first 50 min of operation of the equipment tested, the slope of the curve in the graph remains constant, showing that the DO in the pond water tank continued to increase in this period. Then, the slope of the curve gradually flattens as the DO approaches 8 mg/L, at which time \(K_{L}a_{T}\) tends to 0 with the increase in device operation time.  
A pond oxygenation test based on commonly used equipment was conducted in the same RAS as a control for the NAD, and the results are represented by the black dotted lines in Figure 6. The initial DO (\(C_{0}\)) was similar to those described above. During the test period, this parameter varied from 3.5 to 7.4 mg/L; the average measured mean oxygen increases (\(R_{s}\)) in the upper, middle, and lower water layers were 1.89, 2.49, and 3.03 mg/L, and the mean value of \(R_{s}\) in the water tank was 2.47 mg/L.