Marine aquaculture may affect significantly the coastal environment if not properly monitored and operated. Aquaculture activities significantly impact the ecosystems, being the high use of water and wastewater discharge the major drawbacks for its environmental sustainability. The recirculating aquaculture systems (RAS) are extremely important as they allow water recycling/reuse, fitting the actual needs to close the loop within the water circular economy. Using these systems aquaculture farms could save water and hence offering resource and economical savings for the aquaculture industries. To achieve an adequate production, fish farms use large amounts of antibiotics as therapeutic, growth-promoting and prophylactic measures. The discharge of these micropollutants into the coastal water bodies could represent not only a source of contamination but also could favor the emergence of antibiotic resistance genes. Therefore, new technologies able to properly treat aquaculture wastewater to ensure water quality appropriate for the its use are needed. Biofilm systems are particularly promising for the treatment of wastewater, especially the ones containing micropollutants such pharmaceuticals. The high microbial biomass and the layered structure of biofilms offers protection to the microbial community against the adverse conditions present in the wastewater. Although belonging to different trophic levels, both microalgae and bacteria have demonstrated ability to deal with recalcitrant wastewaters. The combination of microalgae and bacteria within the same structure could be beneficial for the treatment of wastewater as the synergy established between them could turn the process more efficient. The present project thus aims to develop algal-bacterial granular sludge that will be further used as biomass for the inoculation of a bioreactor system. Different samples from marine environments will be screened to isolate potential microalgae strains that can be further used in wastewater treatment systems. The selected microalgae strains will be combined with activated sludge to produce mixed microbial granules. Finally, after the successful cultivation of granules, the feasibility of these aggregates to treat aquaculture wastewater will be assessed. As the developed technology aims to produce water to be reused in the aquaculture facilities, the microbiological safety and quality of the recycled water should be ensured. Moreover, to better understand the evolution and dynamics of the populations inhabiting granules, the microbial community will be studied using molecular biology techniques Collectively, the outcome of this project will not only advance the field of wastewater treatment, but it will also benefit the aquaculture farms and ultimately the society by reducing the energy consumed during wastewater treatment and the water use as this resource could be reused in the facilities.