Analysis of Recirculating Aquaculture Systems (RAS) in Enhancing Aquaculture Efficiency
The *National Fishery Development Plan for the 14th Five-Year Plan Period* explicitly calls for developing smart fisheries, promoting the modernization of aquaculture equipment, and enhancing breeding efficiency and resource utilization levels. Traditional pond aquaculture models face challenges such as high water usage, significant land occupation, and environmental impact, making it difficult to meet the demands of modern aquaculture development. The Recirculating Aquaculture System (RAS), as a new intensive farming model, utilizes water treatment and recycling technologies to achieve high-density cultivation of aquatic organisms in a relatively closed environment, offering distinct technical advantages.
1. Overview of Recirculating Aquaculture Systems
1.1 Basic Concepts and Structural Components
A Recirculating Aquaculture System (RAS) is a highly intensive modern aquaculture model that achieves high-density cultivation of aquatic organisms in a relatively closed environment through water treatment and recycling technologies. RAS primarily consists of three functional modules: the culture unit, the water treatment unit, and the water quality monitoring and control unit.
1.2 Working Principle
The operation of RAS is based on the principle of water purification and recycling. During the culture process, pollutants such as suspended solids and ammonia nitrogen produced by metabolism are first removed via mechanical filtration for particulate matter. The water then enters a biofilter where nitrifying bacteria convert toxic ammonia nitrogen into nitrite, which is further oxidized to nitrate. A protein skimmer removes dissolved organic matter through bubble adsorption, and a UV device eliminates pathogenic microorganisms. The multi-stage treated water is re-oxygenated, temperature-adjusted, and recirculated back into the culture tanks. During system operation, online monitoring equipment continuously tracks key parameters like pH (6.5–8.0), dissolved oxygen (>5 mg/L), and ammonia nitrogen (<0.5 mg/L), which are regulated via automated control devices to maintain the optimal culture environment
2. Analysis of Production Efficiency in RAS
2.1 Water Environment Control Capability
The water environment control capability of RAS is mainly reflected in the precise regulation of water quality parameters and the rapid response to environmental stressors. This study, conducted at a large-scale RAS base with three parallel trial systems (each 50 m³ volume, stocking density 25 kg/m³), monitored data continuously for 180 days, yielding the results in Table 1.
Data indicates that RAS performs exceptionally well in dissolved oxygen regulation. Even during peak oxygen consumption at night, ideal levels are maintained through the synergistic effect of variable frequency drive (VFD) pumps and microporous aeration. pH regulation, using online monitoring coupled with an automatic alkali dosing system, showed good stability in continuous monitoring results. For ammonia nitrogen removal, the nitrification efficiency of the biofilter under standard conditions was significantly improved compared to conventional methods.
Temperature control, achieved using titanium tube heat exchangers with PID control algorithms, kept water temperature stable even under significant ambient temperature fluctuations.
Through 180 days of continuous operation, the compliance rate and stability of all water quality indicators in the system were significantly improved compared to traditional culture models, fully demonstrating the technical advantages and application value of RAS in water environment control. Furthermore, the compliance rate for key water quality indicators reached 98.5%, with the stability of core indicators like dissolved oxygen, pH, and ammonia nitrogen being 47% higher than in traditional culture.
2.2 Biological Growth Performance
This study selected the freshwater fish grass carp (Ctenopharyngodon idella) as the subject to compare growth performance differences between RAS and traditional pond culture. The trial group consisted of three 50 m³ RAS units, while the control group used three 500 m² standard culture ponds, both over a 180-day cycle (data shown in Table 2).
Results showed that the precise environmental control and feeding management in RAS significantly improved the growth performance of grass carp. The constant temperature effect and water quality stability promoted feeding activity and improved feed conversion efficiency.
2.3 Facility and Equipment Operational Efficiency
The operational efficiency of RAS is primarily evaluated through the Comprehensive Energy Consumption Index (IEC), calculated as follows:
IEC = (P × T × η) / (V × Y)
Where:
IEC = Comprehensive Energy Consumption Index (kW·h/kg)
P = Total installed system power (kW)
T = Operating time (h)
η = Equipment load factor
V = Volume of culture water (m³)
Y = Yield per unit water volume (kg/m³)
Analysis of operational data showed the following key performance parameters for major RAS equipment: pump system operating efficiency reached 85%, an 18% improvement over traditional pumps; the biofilter's ammonia nitrogen treatment load was 0.8 kg/m³·d, a 40% increase compared to conventional biofilters; and the UV disinfection unit maintained a sterilization efficiency above 99.9%.
System equipment employs intelligent linkage control, automatically adjusting operating power and runtime based on water quality parameters. For instance, temperature control equipment can run at reduced load (e.g., 30%) during stable temperature periods, and aeration systems can operate in energy-saving variable frequency mode during low oxygen consumption periods at night. Through this intelligent equipment control, the system's average Comprehensive Energy Consumption Index was 2.1 kW·h/kg, 45% lower than traditional culture models.
3. Quantification of Comprehensive Benefits of RAS
3.1 Quantitative Production Benefit Indicators
This study established a quantitative evaluation system for RAS production benefits, covering three dimensions: output benefit, quality benefit, and time benefit. Based on data analysis from ten large-scale RAS bases, the system's comprehensive production benefit index reached 0.85, a 56% improvement over traditional culture models.
Output benefit assessment also considers value-added from improved product quality. Aquatic products from RAS showed significant improvements in sensory indicators like flesh texture and intramuscular fat content compared to traditional culture, achieving a market premium rate of 15%–20%. In terms of quality benefit, precise feeding and environmental control in the system resulted in more uniform product size and a notable increase in the premium product rate. During the later stages of culture, product size uniformity reached over 92%, facilitating standardized processing and large-scale sales.
3.2 Resource Consumption Assessment
A Life Cycle Assessment (LCA) method was used to quantify resource consumption during system operation. Key evaluation indicators included freshwater consumption, electricity consumption, and feed input (data shown in Table 3).
Resource utilization efficiency analysis showed that the system achieves high efficiency and conservation of resources through water treatment and recycling technologies, with the most significant savings seen in water and land resources. Environmental impact assessment results indicated that the system's carbon emission intensity was 52% lower than traditional culture.
The system's advantages in resource conservation are also evident in improved feed utilization efficiency. Using intelligent feeding systems combined with water quality monitoring data enabled precise, quantitative feeding, significantly reducing feed waste. Research indicates that feed conversion ratio in RAS improves by 25%–30% compared to traditional culture. Regarding human resource utilization, through automation and intelligent monitoring, labor hours per ton of product decreased from 0.48 h in traditional culture to 0.15 h, substantially reducing labor input while also improving the working environment.
3.3 Economic Feasibility Analysis
Economic feasibility was assessed using Net Present Value (NPV) and Payback Period methods. Initial investment includes civil engineering, equipment purchase, installation, and commissioning. Operating costs include energy, labor, feed, and maintenance. Revenue sources include sales of aquatic products and benefits from water resource savings.
EC = Σ [ (Ct - Ot) / (1 + r)^t ] - I0
Where:
NPV = Net Present Value (10,000 CNY)
I0 = Initial investment (10,000 CNY)
Ct = Cash inflow in year t (10,000 CNY/year)
Ot = Cash outflow in year t (10,000 CNY/year)
r = Discount rate (%)
t = Calculation period (years)
Calculated for an annual production scale of 500 tons, the system requires an initial investment of 8.5 million CNY, annual operating costs of 4.2 million CNY, and annual sales revenue of 7.5 million CNY. Using a benchmark discount rate of 8%, the payback period is 3.2 years, and the Financial Internal Rate of Return (IRR) is 28.5%. Sensitivity analysis shows that the project maintains good risk resistance even with product price fluctuations of ±20%.
4. Conclusion
Recirculating Aquaculture Systems (RAS) significantly outperform traditional culture models in terms of water environment control, biological growth performance, and equipment operational efficiency. Future research should focus on enhancing system intelligence levels, optimizing equipment operational efficiency, and exploring models for large-scale promotion to further improve the comprehensive benefits of recirculating aquaculture.