Circular Economy for Fish Farms in Araucanía, Chile

Abstract In its freshwater phase, salmon farming generates environmental liabilities such as fish faeces, unconsumed food and the natural mortalities of the productive process. The latter are treated with formic acid and used integrally in the manufacture of flours for animal feed. In turn, it is estimated that approximately 10% of the food supplied to the fish is not consumed and that the remaining 90%, after being digested, produces 13% of faeces. Both residues go through a stabilising pre-treatment and concentration process and are then removed as sludge. At present, the sludge is mainly disposed of in sanitary landfills, where their stench affects local communities. Moreover, CO2 is released into the atmosphere due to sludge decomposition, contributing to the net carbon footprint of this industry and adding to the global problem of greenhouse gas emissions. In Chile, there are 957 freshwater fish farms, which generate 522,182 tons of sludge per year as a waste product. The management of this waste gives rise to considerable environmental, economic and social concern. Such a problem is mainly located in the Araucanía Region (Chile), where 53 industrial fish farms are located and two out of five of the salmon that Chile exports are born. In the context of the Circular Economy, our research group has been working on three research projects, aimed at adding value to the sludge. These are: 1. Use of sludge as raw material for obtaining heat energy, 2. Use of sludge as an amendment to agricultural and forest soils, and 3. Use of liquid waste from the sludge pressing process for fertigation. When using sludge as a source of renewable energy, previous studies corroborate that the calorific value of the obtained pellet ranges between 4,612 and 4,886 kcal/kg. Thus, such pellets have the potential to be used in the productive process of salmon farms, increasing their sustainability. A project has been developed to investigate and prototype a product we will call “soil amendment”, using a mixture of the sludge from fish farms and the resulting brush from the processing of algae. Finally, in order to reduce the sludge nitrogen and phosphorus concentration in clarification plants, the use of aquaponics and hydroponic techniques are studied. The flower known as chrysanthemum (Chrysanthemum spp.) was selected as a model species because of its commercial value and ease of handling. In the present work, the results associated with these three local cases of Circular Economy in Chilean freshwater fish farms will be presented.