Aerobic granular sludge, a feasible technology for the treatment and recirculation of trout aquaculture water streams

Aquaculture is one of the fastest growing food production sectors. However, land-based aquaculture faces water scarcity and space restrictions which hamper its development. Aquaculture recirculation systems (RAS) help tackle these problems, although in most systems the recycling of water increases nutrient and organic matter concentrations, which often translates to fish mortality. This work aimed to evaluate the feasibility of an aerobic granular sludge (AGS) system as a novel alternative for the treatment of aquaculture streams, characterized by low nutrient and carbon concentrations. The efficiency for nutrients removal aiming at water recirculation was assessed as well as the AGS microbiome composition dynamics over operation. The AGS system was inoculated with mature granules from a full-scale WWTP and fed with a synthetic medium mimicking a trout farm aquaculture recycling water. High ammonium removal efficiencies of 87-100% and ammonium removal rate of approximately 14.5 mg NH4+-N/(L⋅d) were achieved. The AGS microbiome, mainly composed by members of the Proteobateria phylum, had a core microbiome composed of different functional groups (e.g. denitrifying bacteria, nitrogen fixing bacteria, ammonium oxidizing bacteria, phosphorus accumulating bacteria and extracellular polymeric substance (EPS) producing bacteria). The AGS system was able to produce effluents of high-quality, with ammonium content below the toxic levels for fish, and thus suitable for recirculating in the aquaculture.