MBBR Biofiltration Powers Desert RAS: 82,600 RMB Profit And 60% Water Savings Growing Trout And Sturgeon in The Gobi

Minqin County, Gansu Province receives just 110 mm of rain a year - yet inside a greenhouse there, rainbow trout and sturgeon grew to market weight in six months and returned 82,600 RMB of profit from two 126 m³ tanks. The technology that made it possible is the same MBBR biofiltration used to treat municipal and industrial wastewater.

Recirculating aquaculture systems (RAS) hold fish at high density in a closed loop of continuously treated water. The heart of any RAS is its biofilter, which converts the toxic ammonia excreted by fish into harmless nitrate. This case study from the Hongqigu Modern Smart Agriculture Demonstration Park demonstrates that MBBR's core strengths - high-efficiency nitrification, shock-load resistance, and stable biofilm maintenance - are as valuable in aquaculture as they are in wastewater treatment, and that a proven municipal technology transfers directly to a high-value farming application.

Why MBBR in Aquaculture?

In a RAS, the biofilter is the most critical component - it houses the nitrifying bacteria that convert toxic ammonia to nitrate. If the biofilter fails, ammonia spikes and fish die within hours. MBBR technology is uniquely suited to this duty because of five characteristics:

• High volumetric nitrification rates. The protected biofilm on MBBR carriers supports dense nitrifying bacteria populations, so a small reactor treats a large fish load.
• Self-regulating biofilm thickness. Turbulent carrier motion naturally shears excess biofilm, preventing the clogging that plagues fixed-bed systems.
• Resilience to temperature fluctuations. The biofilm structure protects bacteria from temperature shocks common in greenhouse environments.
• No backwashing required. Unlike sand filters or fixed-bed biofilters, MBBR systems need no periodic backwashing - a decisive advantage at remote sites.
• Compact footprint. High specific surface area carriers deliver maximum treatment in minimal space, cutting greenhouse and equipment cost.

The Desert RAS System

The system was built at the Hongqigu Modern Smart Agriculture Demonstration Park in Minqin County, with an MBBR biofilter at its core. Every design decision was made to withstand the harsh Gobi climate and the scarcity of technical support:

• Greenhouse: steel-frame with double-layer plastic film for insulation and ventilation, buffering the extreme temperature swings of the desert.
• Tanks: galvanized steel frame with waterproof canvas, 10 m diameter × 1.6 m depth, approximately 126 m³ each, with a conical bottom and dual drainage for complete solids removal.
• Recirculation loop: tank outlet → sump → microscreen filter → MBBR biofilter → UV disinfection → oxygenation → back to tanks.
• Aeration: nano-diffuser discs supplied by a Roots blower, with a target dissolved oxygen (DO) above 6 mg/L.
• Water exchange: daily makeup water of approximately 10% of total volume, covering evaporation and purge losses.

Production Results After Six Months

After approximately six months of culture, both species reached market weight with a combined profit of 82,600 RMB from a total water volume of just 252 m³. Table 1 summarizes the production and economic analysis.

Table 1: Rainbow trout and sturgeon production and economic analysis. Production costs were 22–24 RMB/kg, yielding a profit margin of approximately 55%.

The growth curves revealed complementary temperature performance. In May–June, both species grew similarly. In July–August, sturgeon outperformed trout at higher temperatures. As temperatures dropped in September–November, trout recovered strongly. Over the full cycle, sturgeon achieved slightly higher total gain (632 g vs. 504 g per fish), and the two-species mix allowed the farm to exploit the full seasonal temperature range of the greenhouse.

Water Quality Management: The MBBR Advantage

Water quality targets were strict: DO above 6 mg/L, NH3-N below 0.5 mg/L, NO2-N below 0.1 mg/L, and pH between 6.5 and 8.0. Holding ammonia and nitrite below these thresholds in a high-density RAS is a 24-hour job, and the MBBR biofilter was the linchpin that made it achievable with minimal operator attention:

• Rapid ammonia oxidation. High surface area carriers supported a dense AOB/NOB biofilm that oxidized ammonia as fast as the fish produced it, keeping NH3-N and NO2-N well within safe limits even at peak feeding.
• Stable performance under variable loading. The EPS matrix of the biofilm protected bacteria from feeding-cycle shocks, so ammonia spikes from feed additions did not propagate through the system.
• Low maintenance. No backwashing was required - a critical advantage for a remote desert location where technical support and replacement parts are scarce.

Economic and Environmental Benefits

The economics are compelling. The system delivered 82,600 RMB of profit from two tanks with a combined water volume of 252 m³, at a production cost of 22–24 RMB/kg and a profit margin of roughly 55%. Equally important is the environmental performance, which is what makes desert aquaculture defensible:

• Water savings above 60% compared with traditional pond aquaculture - decisive in a region with only 110 mm of annual rainfall.
• Near-zero discharge. Solid waste is collected and removed, while water is continuously treated and reused in the closed loop.
• Reduced evaporative loss. The greenhouse cuts evaporation compared with open ponds, further conserving scarce water.

Key Takeaways for MBBR in Aquaculture

• MBBR biofiltration enables desert aquaculture. The biofilter is what makes closed-loop fish farming viable where water is scarce and summers are extreme.
• The same MBBR technology transfers directly to RAS. The biological process of ammonia oxidation is identical to wastewater treatment, so proven municipal carriers and design methods apply with minimal adaptation.
• Remote facilities benefit from low-maintenance design. The no-backwashing, self-regulating nature of MBBR is critical where technical support is limited.
• The RAS market is growing rapidly. As aquaculture moves indoors for biosecurity and climate resilience, demand for biofiltration grows with it - a significant adjacent market opportunity for MBBR suppliers.

Conclusion

This Gobi Desert case study demonstrates that MBBR-based RAS can successfully produce high-value fish in one of the world's most challenging environments. An 82,600 RMB profit from a single six-month cycle, combined with more than 60% water savings and near-zero discharge, makes a compelling case for the technology. For MBBR suppliers, aquaculture represents a natural extension - the biological filtration requirements are fundamentally the same as those in wastewater treatment, and the market is moving indoors fast.

This article is based on the paper "Key Technologies of Greenhouse-Based Land Circular Tank Recirculating Aquaculture for Rainbow Trout and Sturgeon in Arid Desert Regions" (Yang Shujun et al., 2026). The referenced growth figure is available in the original publication.