In a study published in the journal Scientific Reports, researchers Ali Asghar Najafpoor, Hadi Farsiani, Mojtaba Davoudi, and Fatemeh Kariminejad examined how a sustainable bio-based material could solve a critical problem in recirculating aquaculture systems. While these advanced fish farms use biological filters to clean water, they often leave behind small amounts of ammonium that can be toxic to sensitive fish species. The researchers developed a polishing medium using the wood of Prunus spinosa, processed into coarse grains between two and four millimeters in size. This deliberate choice of larger particles prioritizes mechanical strength and steady water flow over the high surface area of fine powders, bridging the gap between laboratory theories and real-world engineering needs.

The findings revealed that the coarse biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More acts as a selective buffer, specifically targeting ammonium ions while ignoring nitrite and nitrate. In testing, the material successfully removed 53% of the ammonium present, whereas it removed less than 13% of the other nitrogen species. This selectivity is vital for aquaculture because it allows the filter to neutralize the most toxic component without interfering with the broader biological processes of the farm. The material showed its best performance at higher temperatures typical of warm-water fish farming, suggesting it is well-suited for various climates and seasonal changes.

A major highlight of the study was the material’s impressive durability and reusability. Unlike many filtration media that must be discarded after they become saturated, this biochar can be refreshed using a simple salt solution. The researchers demonstrated that after five full cycles of being used and then cleaned, the biochar still worked at 96.1% of its original capacity. Microscopic imaging after use showed that the grains remained physically intact, with no signs of crumbling or pore collapse. This structural robustness is essential for continuous-flow systems where crumbling particles could escape into the fish tanks or cause expensive pump failures.

From an economic perspective, the Prunus spinosa biochar presents a compelling case for commercial adoption. The researchers estimated a treatment cost of approximately 0.30 USD per cubic meter of water. This is significantly cheaper than current high-tech options like ion-exchange resins or specialized membranes, which can cost five to ten times more to operate. Because the biochar is made from an abundant agricultural waste product through a relatively low-temperature process, it also has a much smaller carbon footprint than synthetic alternatives. This combination of low cost, high reliability, and environmental sustainability makes it an ideal safeguard for small to medium-scale fish farms.

The study also confirmed that the biochar worked reliably when water flowed through it continuously in a column setup. During these trials, the system maintained stable pressure and consistent flow, with no evidence of clogging or “washout” where particles are pushed out by the current. This predictable behavior allows farm managers to schedule maintenance precisely, preventing sudden spikes in ammonia that could endanger the fish. By transforming fundamental science into a practical engineering tool, the research team has established a clear foundation for a more resilient and cost-effective approach to managing water quality in the growing global aquaculture industry.

Source: Najafpoor, A. A., Farsiani, H., Davoudi, M., & Kariminejad, F. (2026). Engineering applicability of coarse Prunus spinosa biochar for post-nitrification ammonium polishing in recirculating aquaculture systems. Scientific Reports.