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23. November 2020

Indoor aquaculture: Plastic-free filtration

Water quality is the crucial element of every fish farm. A Swiss company now uses stainless steel Porometric mesh from GKD – GEBR. KUFFERATH AG (GKD Group) for mechanical treatment in drum filters.

Marine aquacultures, which are net enclosures submerged in the sea, are commonplace all over the world, particularly in Norway or Chile. It’s where the cheap salmon piled high in the chiller cabinets of discount supermarkets comes from. Environmental protection, animal rights, and consumer organizations criticize this kind of farming, as the incredibly confined space and water contaminated with excrement and food scraps is a breeding ground for bacteria. To prevent them from spreading, large amounts of antibiotics and pesticides are used. An environmentally friendly alternative are indoor recirculating systems, which allow fish to be bred anywhere, free from medication and toxins. A prime example of such indoor aquaculture is Swiss Alpine Fish AG, based in Lostallo, Switzerland. Twelve generations of Atlantic salmon are raised in here in parallel, applying the latest technology and the highest standards. The core element of the farm is the pilot system of a recirculating system that holds 2,700 cubic meters of water. Sophisticated cleaning technology keeps this water permanently clean and freshly treated. It treats 99.5 percent of the water used every hour in a multi-stage process involving mechanical and biological cleaning and feeds it back into the system. This guarantees salmon breeding that is free from antibiotics and chemicals, producing accordingly high-grade fish.

Three drum filters, each with a filter area of 21.6 square meters, clean the water mechanically before it passes through a two-stage biofilter. Each of these drum filters contains 45 filter panels measuring 1.20 x 0.40 meters. Their shovel-like support structure consisting of many small squares of mesh connected with one another augments the filter effect. However, the synthetic mesh provided by the manufacturer has proven prone to failure, as it struggles to withstand the robust cleaning cycles with a high-pressure cleaner. Holes in the mesh and tears at the edges jeopardize the quality of the mechanical cleaning. The Porometric stainless steel mesh is a worthwhile alternative in many respects. Its pore size of 25 µm achieves an unsurpassed flow rate with almost 90 percent porosity. At the same pump pressure, the throughput can therefore be significantly increased. What is more, the large dirt holding capacity of the high-performance mesh reduces the number of cleaning cycles. As these also require a significantly lower backwashing rate, the efficiency of filtration is again increased. Plus, the cleaning behavior examined in independent comparisons by the Karlsruhe Institute of Technology (KIT) helps to cement Porometric as the best in its class.

In combination, these benefits qualify Porometric mesh not only for salmon farming in the Swiss Alps, but also indoor aquaculture around the world. But there is another key argument for the use of the stainless steel mesh: the public’s increased awareness of plastic and the microplastic loads it discharges into waters. In contrast to synthetic mesh, stainless steel mesh is not subject to abrasion, which means that no plastic particles get into the water – and ultimately onto the plates of diners. With high-quality fish products in particular, farming without microplastic contamination is a real sales argument to aim for. Experience has shown that consumers are prepared to pay a slightly higher price for their health and protection of the environment. Microplastic-free fish quality through plastic-free filtration of the water in which the fish are bred is therefore not merely a passing fad, but a way to achieve sustainable success.

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