Valorization of Aquaculture Waste Through Conversion into Algal Biomass and Biomethane

Uneaten feed and feces are major sources of waste in aquaculture systems, which lead to the eutrophication of water bodies. This study proposes a multidisciplinary approach to the valorization of two types of aquaculture waste. The first component of the strategy is the cultivation of microalgae in raw wastewater. The wastewater from a recirculation aquaculture system (RAS) for sturgeon was tested as an alternative growth medium for eight microalgae species. The highest biomass concentration was achieved when cultivating Tetradesmus obliquus, reaching 1.34 ± 0.04 g L–1. Anaerobic digestion (AD) of sludge from the RAS and mixed algal biomass harvested from wastewater treatment was proposed as a secondary component of a waste valorization strategy. Granular activated carbon (GAC) was selected as the conductive material to enhance methane production from tested substrates. The specific methane production (SMP) during AD of the sludge ranged from 94 to 99 NmL g–1VS (volatile solids). In contrast, the SMP for treatments containing algae reached 321–327 NmL g–1VS. The addition of GAC to the anaerobic reactors was an effective method for enhancing methane formation from algal biomass. Finally, this study combines aquaculture water treatment and sludge management with the production of valuable algal biomass and biofuel.