Background Algae and seaweed accumulations on beaches and along coasts are an environmental nuisance. City Councils in coastal areas are required to remove them if they want to preserve their Blue Flag Beach category and maintain favourable conditions for tourism. In addition to the time and resources devoted to their collection, sand is also removed with the algae and seaweed residues. This year-by-year erosion causes beaches to retreat, with the application of new sand needed to regenerate beach conditions. The removal of the marine accumulations is usually done as part of a municipality’s Integrated Management System, with the marine biomass managed as urban solid waste - therefore it is either deposited in a landfill or incinerated. Objectives The SEA-MATTER project aimed to demonstrate the technological and economic feasibility of using coastal algae and seaweed accumulations as raw materials in the composites industry. The goal was to use wet-laid nonwoven textile technology to turn this marine biomass into composites products, in the first instance acoustic panels for buildings. The project beneficiary AITEX has acquired a wet-laid production plant for the production of nonwovens from textile wastes. To ensure an adequate supply of marine biomass as an additional raw material input for this technology, the project aimed to establish a model for the collection, transport and management of algae and seaweed wastes. Results The SEA-MATTER project demonstrated and validated the use of coastal algae and seaweed accumulations as raw materials in the composites industry. The project established a new model for the removal and management of these residues from beaches and marinas. Current methods were reviewed and assessed, and alternative and more environmentally-friendly options for collecting, storing, transporting and processing the waste material proposed, including a protocol for washing and cutting the various marine biomass components. From its experiences of helping solve environmental problems and optimising the collection of algae and seaweed accumulations, the project team published ‘A Good Practice Guide for the management, collection and treatment of seaweed and marine plants on the coasts’. This Guide was distributed to engineers of coastal municipalities in Valencia, Alicante, Andalucía, the Baleares and elsewhere. The project partners proposed several recommendations regarding waste disposal, the quantity of seagrass that should be removed and left on the beach, the creation of temporary sites to store the remains of the common seagrass species Posidonia oceanica, and other management measures for the algae and seaweed wastes. The optimal properties of different wastes for obtaining nonwoven composites was defined, on the basis of several analytical techniques, so the best material for use could be selected. It was also recommended that the use of heavy machinery on beaches should be limited, and that algae and seaweed wastes should only be collected from June to September in order to preserve beach defences. To produce the nonwoven composites using wastes from Posidonia oceanica and other marine biomass as a raw material, the project adapted a wet-laid technology process invented by the University of Alicante. In this process, based on a paper-making technique, a dilute slurry of water and fibres from the marine vegetative waste is deposited on a moving wire screen and drained to form a web. The web is further dewatered, consolidated by pressing between rollers, and dried. This wet-laid reinforcement structure is processed, together with different renewable, non-toxic polymeric matrices, by means of a compression moulding system, to obtain the final composite products. The project confirmed the technical feasibility of the wet-laid process for producing nonwoven textile materials from marine biomass. Several composites were developed by the project team with different proportions of algae and seaweed residues. The most suitable were characterised and validated as acoustic/noise isolation panels for buildings. In addition to confirming the economic feasibility of their use in acoustic panels, the composites could also be of value as thermal insulation products, reinforcement materials, and substrates for textile/film/foam lamination. The project’s methodology for waste revalorisation could also be successfully applied in other contexts, such as the footwear industry, in agriculture or even with residues coming from forests or other natural environments. The main limitation of this technique is the length or size of the waste to be used as raw material. By giving value to algae and seaweed accumulations, and promoting their reuse, the SEA-MATTER will reduce the volume of marine waste sent to landfill or incinerated as urban waste. The project’s new model for algae and seaweed management also promoted the composting of marine biomass as an alternative to landfilling, and the use of algae wastes for sand dune stabilisation. Environmental benefits also derive from new green composites being used as alternatives to conventional synthetic ones. The project contributes to solving social concerns related to the negative touristic impact of algae and seaweed accumulations in coastal areas, and its approach has helped to reduce the costs associated with the regeneration of beaches. Economically, it is foreseen that the SEA-MATTER initiative will increase employment opportunities due to the creation of a new production process using algae and seaweed wastes for the nonwoven textile industry sector. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).