Background Galicia (Spain) is highly dependent on fisheries, with fishing (including shellfish), aquaculture and related activities accounting for 10% of gross internal product. The region accounts for the highest production of transformed fish products in Europe and in some cases in the world (e.g. mussel canning). The southern Galician estuaries are considered one of the world’s most biodiverse marine ecosystems. However, the intrinsic nature of the canning industry (e.g. small family-run companies) and the difficultly in treating the generated effluent has threatened the ecological and environmental integrity of the Galician estuaries in recent decades. As an example, a medium-size fish cannery can release, on average, around 51 tonnes of nitrogen, six tonnes of phosphorous and 143 tonnes of organic matter into the environment. Therefore, there is a need for effective solutions to reduce the environmental impact of these activities. Objectives The LIFE SEACAN project will demonstrate the feasibility of applying biofilm-based wastewater treatment systems to reduce the impact of the effluents generated from fish canneries located in coastal zones. In particular, the project will test and compare two biofilm-based processes: biomass grown in carriers and biomass grown as granular sludge. These technologies will be tested in a fish cannery through a newly-built pilot wastewater treatment plant, with a capacity ranging from 4-8 m3/h. It will be divided into two units: a packed bed reactor, where biofilm will grow attached to carriers, and a granular sludge reactor, where biofilm will grow in the form of granules. The two bio-film systems will operate in parallel, allowing for a direct comparison. The demonstration period will take into account the time needed to monitor biodiversity change around the cannery site and to quantify the environmental impact associated with the implementation of this technology. The project results will be used to produce a good practice manual with regard to wastewater treatment in the fish canning industry. Expected results: The project expects to develop an effluent treatment process with a 25% lower environmental footprint in comparison with conventional treatment processes implemented in fish canneries. In particular, this new process will produce the following concrete environmental benefits: Improvement in fish canneries effluent quality, in terms of nitrogen removal up to 90% and COD (chemical oxygen demand) reduced by 95%, achieved by implementing biofilm-based treatments; Reduction of the energy input needed to perform the effluent treatment, by at least 20%, in comparison with conventional treatments; Quantification of the reduction of the environmental pressure in terms of biodiversity analysis; Identification of the possible improvement of benthic assemblages affected by the biofilm-based treatment process in comparison with the original wastewater treatment process; Identification of the main technical and economic motivations and constraints for the adequate treatment of the effluents generated in the fish processing industry; and Assessment of the replicability of the technology to other European areas facing similar problems.