This project aims to produce a cyanobacterial biofilm on zeolite substrate, using effluent from water treatment plants as a growth medium, with the aim of using the final compost as a soil fertiliser. The activities will be carried out through the joint effort of a team of microalgae and plant research specialists. Zeolites are naturally occurring aluminosilicates with extraordinary adsorption and ion exchange potential. With these properties, zeolites can be used to remove substances such as ammonium, orthophosphates or heavy metals from wastewater. In addition, due to the gradual release of water and adsorbed nutrients, they can be used as soil fertilisers. Filamentous cyanobacteria are microalgae that can grow using the effluent from sewage treatment plants as a growth medium in the form of photogranules. The biomass of these micro-organisms, which take up nutrients (such as N and P) from such media, can also be used as a natural fertiliser. In the first part of this project we will aim to establish an efficient method to obtain cyanobacterial biofilm on zeolite granules, using a series of cyanobacterial strains maintained in a culture collection. Subsequently, the mixed zeolite/biofilm composite will be dried and used as a fertiliser for tomato plants. This project involves the use of resources available in nature (zeolites, cyanobacteria), or in excess (wastewater), and the resulting product (photogranules on zeolitic substrate) will be used for soil fertilisation. Thus, the proposed methodology fits into the concept of circular economy.