WWW.WA S .ORG • WORLD AQUACULTURE • DECEMBER 2022 59 Bioretur’s equipment (Fig. 2) can be installed at fish farms using recirculation technology, typically after the drum filters. The process takes sludge water from ~0.1 percent DS to a fully hygienic and storagestable powder of ~90 percent DS. However, most fish farmers don’t want to invest in their own sludge treatment technology and allocate personnel to operate and maintain this complicated and costly equipment. It makes more sense and, in most cases is far cheaper, to focus on their primary business of producing high quality seafood, while letting experts handle the sludge. For a fixed monthly fee, Bioretur offers sludge treatment as a service (EaaS – Equipment as a Service). This includes the technology, the operation and maintenance, as well as the logistics and handling of the sludge from the aquaculture facility. At the same time, the fish farmer gets a partner who ensures that the sludge is transformed from a problem to a sustainable resource. Facts about Bioretur • Established in 2017 as a total solution with technology and services within sludge treatment for land-based aquaculture, • Head Office in Bergen, Norway, • Delivered and operates sludge treatment plants in Norway and internationally (Mowi, Grieg Seafood, Grieg NL, Lerøy Seafood & Erko Settefisk), • Total operating experience from the sludge treatment plants 300,000 hours (2022), • Handles 13,000 m3 of wet sludge daily and collects an average of about 4 t of dry sludge (2022). Notes Steinar Wasmuth, Storaneset 12, 5260 Indre Arna, Norway steinar@bioretur.no; Telephone +47 906 96 000. Fish sludge from land-based aquaculture facilities can be considered “The Elephant in the Room”. If this problem is not addressed and handled, it can be a barrier for new land-based projects and stifle further growth in marine food production. Fish sludge consists of feces and food waste from production in an aquaculture facility and is high in phosphates and other important minerals essential for sustaining life on the planet. Fish sludge consists of dirt and feed residues from the production of fish. There are various fertilizer regulations that regulate the use of sludge. Fish sludge also contains heavy metals such as zinc (Zn) and cadmium (Cd) and, thus cannot be used as is for fertilizer without special treatment and regulations. To be able to reach climate goals, reuse of minerals such as phosphorus in a circular economy is essential. Traditional Treatment of Sludge Treatment of sludge in land-based aquaculture often consists of mechanical dewatering from ~0.1 percent dry solids (DS) to ~15 percent DS before it is transported to a depot, for instance a biogas facility. Because aquaculture sites often are far away from biogas plants, this means transporting enormous amounts of water every year. This is extremely expensive and not sustainable because it results in thousands of transport miles (Fig. 1). The use of fish sludge in production of biogas also results in high volumes of residual materials, with concentrated heavy metals. This material is difficult to utilize as fertilizer and must in most cases be considered special waste. AMore Sustainable and Rational Solution The Norwegian company Bioretur offers a solution to the fish sludge problem and gives fish farmers access to the best available technology for sludge treatment for the aquaculture industry. Fish Sludge — a Problem or a Resource? Steinar Wasmuth FIGURE 1. An example showing how much sludge a land-based fish farm of 10.000 t biomass produces, and the economic and environmental impact of transporting the wet/dry sludge 500 km for disposal. FIGURE 2. The Bioretur Fish Sludge Recovery System (FRS) consists of step-by-step dewatering and drying, using belt filters, decanters and Bioreturs’ own Super-Heated Steam dryer.
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