Aquaculture waste can exacerbate eutrophication in both marine and freshwater ecosystems. Mitigating nutrient emissions from the aquaculture industry is crucial for enhancing the sustainability of the industry. Fish manure produced from recirculating aquaculture system (RAS) consists of uneaten feed and feces, and contains a significant portion of phosphorus and micronutrients, making it a valuable resource as fertilizer. However, due to its high-water content and metals, it poses challenges for transportation and utilization. Therefore, the manure water and metal content need to be reduced to obtain a higher valuable material.
In this study, we investigated the efficacy of lignocellulosic and cellulose filtration materials for reducing the water content of fish manure. We assessed the performance of the technology in freshwater and saltwater conditions. Our findings demonstrate that the technology can produce a fish manure cake with a dry matter content ranging from 25% to 35%, resulting in an 80% reduction in final weight. Additionally, concentrations of organic matter, phosphorus, and nitrogen in the treated manure were removed by 80%, 85%, and 78%, respectively.
Moreover, heavy metal concentrations, particularly cadmium and nickel, were reduced by up to 10-fold compared to typical levels found in fish manure. This enables its utilization in crop production while meeting regulatory standards for heavy metal concentration disposal.
The technology also has the potential to be tailored and additional elements such as struvite can be added to increase the fertilizer properties. Finally, to showcase its versatility, we utilized fish manure cakes as a substrate for growing mushrooms, demonstrating their potential as compost or fertilizer material and as a possible treatment method for fresh and saline fish manure.