The potential of different marine microalgae species to recycle nutrients from recirculating aquaculture systems (RAS) fish farms and produce feed additives

Abstract

This study researched the use of six microalgae species (N. gaditana, P. lutheri, I. galbana, T. chuii, P. tricornutum and C. gracilis) and a bloom to treat effluent from a marine fish farm and produce quality biomass. More specifically, simulated water from a recirculating aquaculture system (RAS) was used. Microalgae culture was carried out under controlled conditions using 18 L bubble column photoreactors under batch and semi-continuous operation. The main parameters analysed were micronutritional requirements, biomass productivity, nutrient removal rate (nitrogen and phosphorus), biomass composition, and quality. Also, based on the results obtained, a quantitative classification of the microalgae was carried out. The results showed that all microalgae required at least trace metals. In certain species, the addition of vitamins was also required for viable cultivation. In the case of biomass productivity under batch operation, values were between 67 mg L−1 d−1 and 7 mg L−1 d−1 using T. chuii and C. gracilis, respectively, and between 71 mg L−1 d−1 and 9 mg L−1 d−1 using T. chuii and N. gaditana under semi-continuous operation. In the case of total dissolved phosphorus removal, no differences were found between species, reaching in all cases final concentrations <0.01 mg L−1. Total dissolved nitrogen removal rate varied between species and operating conditions, being the highest obtained using T. chuii under semi-continuous operation (12.6 mg L−1 d−1) and the lowest with C. gracilis batch operation (0.15 mg L−1 d−1). Biomass composition in terms of protein and lipids varied between species and operating conditions, but quality in terms of amino acids and fatty acids profile remained homogeneous in all cases. Finally, according to the developed score methodology, I. galbana was the microalgae with the highest biomass production score, while T. chuii was for wastewater treatment. © 2021