Trevor Gent, joined the RASTECH podcast to discuss how fish waste in Recirculating Aquaculture Systems (RAS) can be transformed from a challenge into a valuable resource. This blog highlights 7 key insights from the conversation.
Listen to the full episode here:
https://player.captivate.fm/episode/dd4d98c3-df57-46ae-a073-f85bcca57ec7
We’re proud to announce that Trevor Gent, Director of Engineered Solutions at Alumichem, was recently featured in a new episode of the RASTECH podcast. In this thought-provoking discussion titled “Rethinking Fish Waste in RAS,” Trevor brings expert insight to one of the most misunderstood and critically important components of recirculating aquaculture systems: wastewater and sludge management.
The episode, hosted by Jean Ko Din and Justin Henry, moves beyond technical jargon to challenge assumptions about what we call “waste,” offering solutions that are both environmentally sustainable and economically viable.
1. From waste to value: a paradigm shift in aquaculture thinking
A key message from the episode is the need to fundamentally rethink how fish waste is perceived in land-based aquaculture. In traditional ocean-based farming, waste is naturally dispersed into the environment. But in recirculating aquaculture systems (RAS), that same waste becomes a regulated discharge, held to the same environmental standards as industrial effluents.
Instead of viewing fish manure as a disposal problem, it’s more accurate—and more productive—to see it as a resource. The nutrients in that waste originate from the feed used to grow the fish, meaning value is being lost when it’s discarded. Recognizing this opens up opportunities to treat fish manure as a co-product, not a byproduct. With this mindset, fish farmers can explore sustainable uses like fertilizer production, biogas energy generation, and other forms of nutrient recovery, turning a regulatory challenge into a potential revenue stream.
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2. Effluent planning must begin at concept design
Trevor highlights a recurring problem: wastewater treatment is often considered only after the main facility design is complete. Too often, the treatment system is squeezed into leftover space or added as a last-minute line item in the budget.
“I’ve had clients say, ‘Here’s your box—make it work.’ But wastewater treatment needs space, planning, and integration from day one.”
Early involvement ensures that discharge regulations are met without costly retrofits. It also allows treatment systems to be optimized for site conditions, sludge volumes, and client goals—whether that’s minimizing costs or maximizing resource recovery. Alumichem’s team can tailor solutions far more effectively when they’re included in the initial engineering phase.
3. Navigating the regulatory maze: fish manure Is still poorly defined
One major barrier to innovation is inconsistent or outdated regulation. In many jurisdictions, fish waste isn’t even classified as “manure.” That makes it harder—or even illegal—to spread it on fields or process it as fertilizer. In places like British Columbia, the industry has had to lobby the government to redefine the classification, just to allow reuse.
This lack of clarity not only slows down innovation but increases waste disposal costs. Trevor urges farmers and regulators to collaborate toward more pragmatic, science-based definitions. In doing so, the industry can unlock safe, sustainable reuse pathways for high-nutrient sludge products.
4. Sludge management is a spectrum-and requires strategic choices
Trevor provides a breakdown of the different levels of solids processing—each with pros and cons:
- 5–10% dry matter: Suitable for land application if permitted, or sent to biogas. Low cost but difficult to transport or store.
- 20–25% dry matter: A “mud-like” consistency that can be composted, used in soil blends, or in some biogas systems.
- 90% dry matter: Pelletized or powder form. Low odor, pathogen-inactive, highly storable, and versatile (can be used as fertilizer, incinerated, or sent to industrial uses). But this option requires higher CapEx, Opex, and footprint.
Alumichem supports each of these options, helping clients choose the right balance of cost, complexity, and output value based on their goals and local conditions.
5. Smaller-scale RAS could enable distributed waste utilization
The podcast also explored an emerging opportunity: scaling down instead of scaling up. Trevor suggests that instead of relying solely on large centralized waste recovery facilities, there may be value in developing modular, local RAS farms paired with integrated waste reuse systems (e.g., aquaponics, composting, hydroponics).
“Maybe it’s time to ask not how big we can make a system—but how small we can make it while still being efficient and sustainable.”
This model could serve urban markets with fresh, local fish and offer closed-loop nutrient recycling for nearby agriculture or landscaping operations. It also reduces transportation costs and regulatory friction by staying localized.
6. Overfeeding and process variability make treatment challenging
Trevor shares that fish are unlike industrial processes—they don’t always behave consistently. Growth phases, batch operations, feeding cycles, and overfeeding can all affect the composition and volume of waste. Overfeeding, in particular, increases nutrient loading and can compromise the performance of dewatering and treatment equipment.
“Water treatment systems love consistency. Fish farming rarely delivers it.”
That’s why Alumichem customizes each solution based not just on projected volumes but also on expected variability—ensuring robustness under changing conditions.
7. Future-proofing through flexibility and modularity
Lastly, Trevor emphasizes that future-proof design is critical. As discharge limits tighten or fertilizer markets evolve, a facility must be able to adapt its water and solids treatment capacity. He encourages facilities to:
- Plan for extra space and scalability in their layouts.
- Design systems in modular units that can be added over time.
- Explore value-added processing, such as phosphorous extraction or drying for fertilizer markets.
Trevor also notes that as the value of phosphorus rises globally, systems designed to capture and repurpose it will gain strategic importance.
Final thoughts
Trevor’s message is clear: sustainable aquaculture is not just about fish—it’s about water. And in RAS, water is only as sustainable as the plan to clean, reuse, or discharge it responsibly.
At Alumichem, we’re proud to help RAS operators succeed by turning effluent challenges into opportunities.
Listen to the full episode here:
https://player.captivate.fm/episode/dd4d98c3-df57-46ae-a073-f85bcca57ec7
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