Microalgae culture using fish farming wastewater for biomass production and effluent remediation

GARCÍA MARTÍNEZ L.; PÉREZ CENCI, M.; CURATTI, L.; DO NASCIMENTO, M.

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

One of the major current concerns of Humanity is to ensure food production in the years to come for a more populated World and in a more sustainable way. Aquaculture is the fastest-growing segment of the food industry and plays an important role in solving global food scarcity. However, the production and discharge into the environment of very large volumes of nutrients-rich wastewater poses a serious drawback to the activity. Aquaculture wastewater is characterized by high concentrations of nitrogen (N) and phosphorus (P) from uneaten feed, excreta, and metabolic waste of cultured organisms. Microalgae offer a promising alternative to traditional wastewater treatment methods, due to their capability to efficiently remove and assimilate nutrients from wastewater, along with the added benefit of high-quality biomass production.In this study, we analyzed the potential of wastewater of Nile tilapia (Oreochromis niloticus) farming as a nutrient source for microalgae cultivation. We show an algal strains selection analysis, a preliminary process optimization, and a characterization of the biomass quality for aquafeed.We initiated a functional screening process using 250 mL culture bottles under controlled conditions. Microalgal strains from our collection were cultivated in O.niloticus wastewater, either as the sole nutrient source, or with nitrate and phosphate supplements to enhance biomass productivity. Scenedesmus obliquus C1S, Scenedesmus sp. PAL, Desmodesmus sp. FG, showed a biomass yield higher than 1,5 g/l, comparable to those achieved with a reference mineral medium. Most of the strains showed a high nutrients removal efficiency, in the range of 85% to 100% for nitrate, and 75% to 100% for phosphate. In order to scale up the cultivation process to an 80L flat panel photobioreactor operated under environmental condition, we select S. obliquus C1S as the most promising strain. The biomass produced under these conditions contained about 30% (w/w) of whole protein and also 30% (w/w) of lipids. The later fraction contained 35% (w/w) polyunsaturated fatty acids (FA) and 17% (w/w) Ω3 essential FA, which makes this biomass potentially suitable for aquafeed formulation.The results of this study strongly suggest the possibility of using aquaculture wastewater in an integrated system for biomass generation and nutrient removal, bringing circular economy strategies into modern aquaculture.