# Design and Application of New Aeration Device Based on Recirculating Aquaculture System
## 4 Discussion  
This study investigated the ability of NAD to rapidly increase oxygen levels under hypoxic conditions and verified its effectiveness in the water layer exchange within RAS ponds. Furthermore, the characteristics of each of the two aerators were elucidated. Microporous aerators, known for their highly efficient and economically viable nature, are particularly suitable for ponds with volumes of less than 1000 m\({}^{3}\). Conversely, the water-wheel oxygenator exhibits robust push flow capabilities and a moderate mixing ability, thereby augmenting the oxygen-liquid contact area [31]. Studies conducted by the Chinese Academy of Aquatic Sciences (CAAS) indicate that impeller oxygenators typically exhibit standard oxygen transfer rates (STORs) ranging from 2.16 to 2.59 kg/h. However, the research by [PERSON] et al. showcased that the microporous aerator used for pond aeration achieved a STOR of 4.49 kg/h [32]. Despite this higher transfer rate, it remains insufficient to meet the oxygen demand of cultured fish [33]. Given the suboptimal performance of the current RAS oxygenation equipment, this study proposes a novel method that combines flow generation and oxygenation using aerators. A new flow generation and oxygenation equipment with a STOR of 5.23 kg/h was designed and tested in an outdoor environment, demonstrating its feasibility. The results underscore the efficacy of employing multiple aerators in RAS aquaculture practice, yielding superior outcomes compared to deploying individual components.  
In aquaculture practice, environmental conditions such as temperature, salinity, light, and DO levels are often challenging to control, leading to circumstances where they may only be monitored or maintained at tolerable, rather than optimal, levels [34]. Deviations from optimal environmental conditions can severely limit the growth performance of fish. For instance, the feeding rates were low under low-temperature conditions despite the high oxygen availability [35]. Conversely, high temperatures increase metabolic rates in fish, leading to a higher oxygen demand. To address this, NAD introduced two types of aeration devices that allow for variable frequency control. DO levels can be adjusted in a timely manner by using different combinations of operating parameters depending on the environmental conditions. Consequently, environmental conditions became less critical for fish growth.  
Aquaculture's oxygen demand exhibits daily fluctuations and responds to diverse climatic conditions. An analysis of the test results, as depicted in Figure 3, reveals that, on sunny days, the dissolved oxygen content in the upper water column gradually increases from 7:00 a.m. until reaching its peak at noon. Conversely, during the night (between 22:00 and 8:00 the following day), the dissolved oxygen values in both upper and lower pond layers drop below 5.0 mg/L, necessitating the activation of an oxygenator with a significant oxygenation capacity to ensure optimal fish growth. During other periods, changes in the dissolved oxygen concentration in the upper water body are minimal due to saturation by light, whereas the middle and lower water layers are less affected. The role of the oxygenator during these periods primarily involves stirring the pond water to facilitate the water layer exchange.  
Consequently, aerators should not be excessively used, and their utilization should be limited to instances when supplemental oxygen is required, thus reducing the energy consumption for aeration and pumping, and, consequently, reducing production costs. During favorable weather conditions, operating the NAD at low parameters can sustain daily fish oxygen consumption, providing an effective manner to balance aeration use with need.