As RAS aquaculture grows, efficient wastewater treatment and nutrient management are becoming increasingly important. In this webinar, we explore scalable sludge handling strategies for landbased fish farming.
Trevor Gent, Director of Engineered Solutions at Alumichem, recently participated in the RASTECH Magazine webinar “Scaling wastewater treatment in RAS”, where he joined moderator Justin Henry to discuss one of the most important challenges facing landbased aquaculture today: How to manage and valorize fish sludge efficiently as recirculating aquaculture systems (RAS) continue to scale.
Watch the full webinar featuring Trevor Gent and Justin Henry as they discuss scalable wastewater treatment strategies for landbased RAS aquaculture.
The discussion explored how wastewater treatment infrastructure can evolve alongside the rapid growth of RAS production, particularly through a hub-and-spoke farming model designed to support distributed fish farming while centralizing sludge processing and nutrient management.
Why wastewater treatment is a major challenge for scalable RAS
Modern RAS facilities are highly effective at collecting nutrients and solids from fish production systems. However, this also creates a major operational challenge: farms must manage concentrated waste streams in a cost-effective and environmentally compliant way. Fish sludge from RAS operations typically contains:
- High levels of total suspended solids (TSS)
- Phosphorus and nitrogen compounds
- Organic matter contributing to BOD and COD loads
- Excess feed and fecal material
While these nutrients can represent a valuable resource, they also create logistical and regulatory complexity.
Wastewater treatment is increasingly tied directly to environmental permitting. Regulatory requirements vary significantly between regions, but farms must consistently demonstrate that discharge water meets environmental standards before production licenses can be approved.
How the hub-and-spoke model can scale landbased aquaculture
A major focus of the discussion was the concept of a distributed “hub-and-spoke” aquaculture model currently being explored in North America. In this model:
- Multiple smaller RAS farms (“spokes”) operate semi-independently
- A centralized “hub” provides shared services and infrastructure
- Farms remain geographically close enough to support integrated logistics and transportation
The approach aims to reduce barriers to entry for smaller operators while still benefiting from economies of scale typically associated with larger industrial facilities. Trevor compared the concept to agricultural cooperatives commonly used in industries such as wine and olive oil production, where smaller producers share centralized processing and distribution infrastructure. For aquaculture producers, this type of model could:
- Reduce individual capital expenditure
- Simplify sludge handling and logistics
- Provide access to shared wastewater treatment infrastructure
- Improve access to larger seafood markets
- Enable benchmarking and operational knowledge sharing
The cooperative-style approach could help accelerate the growth of landbased aquaculture while maintaining flexibility and independence for individual operators.
Reducing transport costs by concentrating nutrients
One of the key technical takeaways was the importance of reducing water volume as early as possible in the sludge handling process. RAS sludge streams are often highly dilute immediately after collection from drum filters or backwash systems. Transporting these dilute streams becomes expensive because operators are effectively transporting water rather than nutrients. Trevor outlined a staged wastewater treatment approach involving:
- Chemical treatment and flocculation
- Mechanical thickening
- Dewatering
- Centralized thermal drying
The objective is to progressively concentrate nutrients while recovering clean water back into the treatment process. The discussion highlighted how sludge can move from near-zero solids concentration to:
- 5–8% dry matter after thickening
- 20–25% dry matter after dewatering
- Up to 90% dry matter after centralized drying
At higher dry matter content, the material becomes significantly easier to transport, store, and potentially reuse.
How centralized sludge drying improves RAS economics
One of the strongest arguments presented was that centralized drying at the hub level dramatically improves economic feasibility. Installing thermal drying systems at every individual RAS facility would typically be cost-prohibitive due to:
- High CAPEX requirements
- Large equipment footprints
- Oversized systems relative to sludge volume
- Increased energy demand
Instead, the proposed model allows each spoke facility to dewater sludge locally before transporting a smaller and more concentrated material stream to the central hub. At the hub, low-temperature drying systems can:
- Hygienize the sludge
- Reduce odor and biological activity
- Extend storage life
- Create a stable pelletized product suitable for downstream use
This shift from decentralized to centralized processing could become a key enabler for scalable sludge management in distributed RAS production systems.
How centralized sludge drying improves RAS economics
One of the strongest arguments presented was that centralized drying at the hub level dramatically improves economic feasibility. Installing thermal drying systems at every individual RAS facility would typically be cost-prohibitive due to:
- High CAPEX requirements
- Large equipment footprints
- Oversized systems relative to sludge volume
- Increased energy demand
Instead, the proposed model allows each spoke facility to dewater sludge locally before transporting a smaller and more concentrated material stream to the central hub. At the hub, low-temperature drying systems can:
- Hygienize the sludge
- Reduce odor and biological activity
- Extend storage life
- Create a stable pelletized product suitable for downstream use
This shift from decentralized to centralized processing could become a key enabler for scalable sludge management in distributed RAS production systems.
Turning fish sludge into valuable resources
Beyond disposal, the discussion also explored how fish sludge could become part of broader circular economy strategies. Once dried and stabilized, the material may be suitable for several valorization pathways, including:
- Agricultural fertilizer products
- Biogas production
- Biochar and pyrolysis applications
- Alternative industrial fuel sources
Many of these pathways only become economically viable once sufficient scale is achieved, another important advantage of consolidating sludge streams through centralized hubs. Trevor also discussed industry interest in pyrolysis and biochar production, while noting that consistent feedstock volumes remain an important consideration for commercial deployment.
Why shared infrastructure and standardization matter in RAS
While much of the discussion focused on wastewater treatment technology, another important takeaway was the operational value of standardization. A hub-and-spoke network using modular and repeatable designs could simplify:
- Engineering and procurement
- Installation timelines
- Operator training
- Monitoring and benchmarking
- Maintenance and logistics
Shared infrastructure and shared operational learning may ultimately become just as valuable as the wastewater treatment systems themselves.
As landbased aquaculture continues to scale globally, integrated approaches to wastewater treatment, nutrient recovery, and sludge valorization will play an increasingly important role in improving both project economics and environmental sustainability.
Watch the webinar here:
https://webinars.annexbusinessmedia.com/webinar/scaling-wastewater-treatment-in-ras/
