What is waste to one person may be a valuable resource for another. Industrial symbiosis can also be something as unexpected as growing giant shrimp and perch at paper mills. A feasibility study from IVL and ÅF has examined the technical and economic possibilities for locating fish farms at paper mills.
"The idea is untested in practice. We wanted to perform calculations in the matter and see if it was realistic given all the technical and economic conditions. And the answer is yes, there is great potential and many environmental benefits. Now we want to test the concept in a real environment together with fish farmers and mills," says Magnus Karlsson, project manager and researcher in aquatic environment at IVL Swedish Environmental Institute. Swedish fish farming is highly regulated and is limited by legislation regulating cultivation permits based on the use of the amount of fish feed, not actual nutrient emissions. The restrictions are based on the antibiotic residues of conventional fish farming in open water, which frequently emits antibiotic residue and over fertilization nutrients into the environment. In land-based and closed farming systems, however, most of the water used at the plant can be purified and recycled. The environmental impact is reduced, but the systems are expensive, technically complex and take up space. The farming of warm water species also requires energy to heat the water at the plant.
"Paper and pulp mills emit residue that needs to be purified and cooled. In addition to heat, this wastewater contains valuable nutrients and organic material that stimulates the production of algae, which is feed for species such as roach and bream, which in turn are suitable forage fish for larger food fish in a land-based fish farming," says Joakim Samantha, project manager at IVL. Species that could become suitable for farming are giant shrimp, perch, tilapia and African catfish, all warm water species. Researchers estimate the annual cost of an aquaculture producing 500-750 tons of fish per year to be between 30 and 40 MSEK. That results in a price of approximately SEK 50-60 per kilogram for the farmed fish. "It is too early to say what the market prices may be in the end. There is an environmental protection component,
and it is possible that the system can be subsidised. But It is clear that it is possible to create a circular economy where one person's waste becomes other person's gain," says Magnus Karlsson.
There are several advantages for the mill, which in addition to minimizing their residual releases, also avoids cooling the hot water discharge and reduces the need to add nutrients to their own purification plant. Typical examples in the study have been the Östergötland forest industries in connection with Motala Power, Skärblacka Mill, the Fiskeby Board and the Braviken Paper Mill.