1. Abstract

In September 2026, WoLize officially launched its next-generation, industrial-grade, land-based, high-density recirculating aquaculture system (High-Yield Tilapia RAS) turnkey solution for the global commercial aquaculture market. Addressing key bottlenecks in traditional open-pond farming of bulk freshwater fish—such as ‘long growth cycles, growth stagnation and weight loss during winter, a pronounced earthy odour, and low yield per unit area’—WoLize has integrated a hydrodynamically self-cleaning tank design, a high-load, mesophilic biochemical nitrification system and pressurised pure oxygen supersaturation dissolution technology. As a result, across multiple large-scale commercial demonstration sites, the company has achieved a breakthrough in stocking density of 75-90 kg/m³, reduced the time to market for mature fish to 3.5-4.5 months, and optimised the feed conversion ratio (FCR) to 1.08-1.18.

Table 1: Details of WoLize’s Next-Generation Industrial-Scale, Land-Based, High-Density Recirculating Aquaculture System for Tilapia

2. Description of the Closed-Loop Architecture for Core Processes

Figure 1: Flowchart of a closed-loop water treatment system for industrial circulating water

STEP 01 - Dual-Drain Hydrodynamic Culture Tank

The tank body is constructed from circular or octagonal, chamfered polypropylene (PP), with the tank bottom calibrated to a gradient of 1:12; tangential water inflow creates a microcirculation flow rate of 0.5-1.0 times the tank length per second. Utilising the hydrodynamic ‘Tea-Cup Effect’, over 90% of large fish faeces and uneaten feed particles slide down the bottom cone into the central discharge outlet within 60 seconds, thereby preventing, at source, the dissolution and fermentation of solids within the tank or their fragmentation by the pump.

STEP 02 - Precision Micro-Screen Drum Filter

A 40-60 μm 316L stainless steel microporous filter screen is used to mechanically and physically intercept wastewater from the bottom outlet, achieving a total suspended solids (TSS) retention rate of over 85%. The self-adaptive high-pressure backwash mechanism discharges wastewater at regular intervals, removing organic waste from the water before it releases water-soluble ammonia nitrogen.

STEP 03 - High-Efficiency Counter-Flow Degasser

Specially formulated for the vigorous metabolism of high-density tilapia, this system utilises an optimal air-to-water ratio of 8:1 to 10:1 to forcibly strip away free carbon dioxide released during respiration, thereby maintaining the CO₂ level in the recirculated water consistently below 10 mg/L. This eliminates the risk of blood acidosis in high-density fish stocks at source and stabilises the water’s pH buffering system.

STEP 04 - High-Load MBBR Nitrification Bio-Reactor

Taking full advantage of the extremely high microbial metabolic activity within the optimal temperature range for tilapia (28-30 °C), the system is packed with modified hydrophilic media having an effective specific surface area of > 1,200 m²/m³, achieving a nitrification load of 0.8-1.2 g TAN/(m³·d) per unit volume, thereby stabilising total ammonia nitrogen (TAN) at below 0.3 mg/L and nitrite at below 0.05 mg/L.

STEP 05 - Pressurized Oxygen Cone & UV Disinfection

An industrial-grade PSA (Pressure Swing Adsorption) pure oxygen system, combined with a sealed oxygen cone operating at a gauge pressure of 0.1 MPa, raises the dissolved oxygen level in the influent to 150%-200% supersaturation (10-14 mg/L); Combined with broad-spectrum ultraviolet irradiation at 40 mJ/cm² to inactivate pathogenic bacteria and parasite spores, this creates a biosafety barrier for the recirculated water.

STEP 06 - Closed-Loop Recirculation

A single circulation cycle for the entire water volume is kept within 30-40 minutes; the system’s water recirculation rate exceeds 98 per cent, and the daily supply of fresh water accounts for only 1.5-2.0% of the total water volume (primarily used to replenish water lost through backwashing and minimal evaporation).

3. Client Background and Key Challenges

As a key species in global freshwater aquaculture consumption, tilapia has long faced profitability bottlenecks in both open-air earthen pond and cage farming systems:

Yield bottlenecks and tightening environmental and land use regulations: Stocking densities in open ponds are typically only 2-5 kg/m³, making them heavily reliant on vast water areas; under policies requiring the restoration of coastal mudflats to wetlands and the protection of inland water resources, scope for expanding new production capacity is severely limited.

Winter feeding cessation and seasonal gaps in harvest: Tilapia are tropical/warm-water fish; they cease feeding when water temperatures fall below 18 °C and face a high risk of mass freezing deaths below 12 °C. Traditional production areas yield only one or two harvests per year, resulting in a winter off-season with no fish available for harvest, during which processing plant equipment idles.

Strong earthy odour and quality fluctuations undermine premium pricing: The proliferation of blue-green algae and actinomycetes in open-air ponds results in the production of geosmin and 2-methylisoborneol (2-MIB) through metabolic processes. This causes market-ready fish to generally carry a distinct earthy odour, leading to persistently high return rates for processed fish fillets intended for export or for mid-to-high-end fresh fish channels.

4. Technical Solutions and Workshop Layout Design

Figure 2: Layout and IoT architecture diagram of an indoor high-density tilapia gradient rearing facility

To facilitate the rapid implementation of large-scale commercial tilapia production projects, WoLize offers turnkey solutions comprising modular standard factory planning and skid-mounted water treatment systems:

4.1 Design of Intelligent Spatial Layout for Production Workshops

Three-tier Graded Tank Matrix: The facility is configured with a graded matrix comprising ‘fry rearing tanks (Ø3 m) — juvenile holding tanks (Ø 6 m) — high-yield adult fish tanks (Ø 10 m)’. The tank bottom gradient is strictly set at 1:12 and, in conjunction with tangential water injection components, ensures uniform flow patterns and the removal of solid waste even under high stocking densities.

Low-Resistance Centralised Water Treatment Skid (Central Integrated Water Skid): Utilising a fully gravity-fed, stepped drop-head elevation design, wastewater from the tank bottoms flows directly by gravity into the microfiltration units and biological filters. The system’s total head loss is reduced by 35% compared to traditional piped networks, significantly reducing the routine power consumption of the recirculation pumps.

IoT Smart Central Control Platform (Central Automation & SCADA): This platform coordinates in real time with the variable-frequency pure oxygen cone, temperature-controlled heat pump and smart feed dispenser, dynamically adjusting the feeding rate in real time according to changes in dissolved oxygen and ammonia-nitrogen levels in the water, thereby ensuring maximum feed conversion efficiency.

4.2 Key Equipment and Highlights of Production-Boosting Measures

Tiered screening and grading system for market-ready fish: Using automated fish-sorting and suction equipment, the fish stock is mechanically graded and screened every 30–45 days to eliminate growth inhibition caused by larger fish crowding out smaller ones, ensuring that size uniformity within the pond reaches over 95%. This enables regular, rolling monthly shipments.

Pure Oxygen Supersaturation for Mass Transfer: Under high-temperature (28 °C) and high-metabolic conditions, a pure oxygen cone forces the injection of high-purity oxygen, maintaining an optimal dissolved oxygen level of 6.0-7.5 mg/L in the rearing tanks at all times. This stimulates maximum digestive enzyme activity in the fish, improving feed conversion efficiency by over 20%.

Closed-loop micro-ecological system and physical blockage of geosmin (GSM): A fully light-proof indoor environment prevents algal blooms, whilst a drum microfiltration unit rapidly removes organic debris and activated carbon decolourises the water, completely blocking the biosynthetic pathway of geosmin. The resulting fish have firm, crisp flesh with no muddy or fishy odours.

5. Technical Specifications and Cost-Benefit Analysis

Table 2: Technical Specifications and Benefit Details

6. Comparative Analysis of Operational Data and Performance

Water temperature maintained within the optimal metabolic range: Utilising air-source heat pumps and a greenhouse insulation system, the aquaculture water temperature is kept stable at 28 ± 0.5 °C throughout the year. Data monitoring indicates that, under these constant-temperature conditions, tilapia reach the standard market size of 600 g 45 days earlier than in open-pond environments, completely eliminating weight loss and mortality caused by cessation of feeding during winter.

Hydrodynamic counter-current exercise shapes a firm physique: A micro-flow velocity of 0.8 times body length per second is maintained in the rearing ponds, encouraging the fish to maintain a constant swimming pattern. This reduces abdominal fat deposition in market-ready fish by 22% and increases the meat yield by 4.5%. The fish thus meet the standards for fresh chilled consumption and high-end fillet processing.

Stable water quality variance under high stocking density and high feeding rates: Under heavy-load conditions—with a peak stocking density of 80 kg/m³ per pond and a daily feeding rate of 2.2%—no cumulative spikes in ammonia-nitrogen levels were observed in the inflow or outflow water; the mean fluctuation in total ammonia-nitrogen remained below 0.22 mg/L for 90 consecutive days.

7. Frequently Asked Questions

Q1: As tilapia is an affordable, high-volume fish species, can the operating costs (OPEX) per metric tonne of fish in high-density, industrialised RAS systems form a commercially viable closed-loop model?

A: Absolutely. Although the initial capital expenditure on equipment for factory farming is higher than that for earthen ponds, the feed and labour costs per fish are significantly reduced through ‘a 40 per cent reduction in the rearing cycle, optimisation of the feed conversion ratio to 1.1, and a doubling of the number of annual harvests’. Electricity consumption per metric tonne of fish is controlled at 3.2-4.2 kWh/kg through gravity flow and heat pump waste heat recovery; coupled with the product’s advantages of ‘no muddy odour’ and ‘stable, off-season supply’, the purchase price typically commands a 15%-30% premium over that of open-pond fish, resulting in a payback period for the entire system of just 2.2 to 3.0 years.

Q2: At an ultra-high density of 80 kg/m³, how is oxygen depletion and subsequent fish mortality prevented in the event of a power cut or occasional failure of the oxygen supply equipment?

A: The system incorporates a triple-layered, engineering-grade safety redundancy mechanism: (1) It is equipped with dual-circuit mains power and a diesel generator with automatic transfer switch (ATS, which activates automatically within 30 seconds); (2) . Each rearing tank is fitted with an independent standby pneumatic emergency valve for pure oxygen; should a loss of pressure in the main line or a sudden drop in dissolved oxygen (DO) be detected, this valve activates direct emergency injection of physical pure oxygen from a high-pressure gas storage tank; (3). The pure oxygen cone is equipped with a standby power supply, ensuring basic life support for over 3 hours under extreme operating conditions.

Q3: Can this system be used in inland arid regions, high-altitude areas or saline-alkali soil environments?

A: It is fully compatible. As the system’s daily water replenishment rate is less than 2%, its extremely low water consumption means that deep well water or municipal reclaimed water can be used as a supplementary water source after simple softening; the system has a wide salinity tolerance (it can operate normally within a range of 0-15 ppt), and there are fully implemented case studies in both inland saline-alkali land reclamation demonstration areas and medium- to high-altitude regions.

8. Contact Us

Are you ready to transform your large-scale freshwater fish farming industry to industrial standards? WoLize’s engineering and technical team provides full-cycle, turnkey services ranging from site hydrological surveys, 3D hydrodynamic and biochemodynamic modelling, and skid-mounted equipment manufacturing to on-site biofilm cultivation and optimisation.