Feasibility of waste-free use of microalgae in aquaculture

Following the circular bioeconomy approach, this study shows the possibility of effective microalgal bioremediation of aquaculture wastewater integrated with the production of protein-rich biomass, which can be used as a feed additive. Screening was carried out among strains of Chlorella vulgaris BB-2, Parachlorella kessleri Bh-2 and Chlamydomonas reinhardtii C-124 with the aim of selecting the strain which is characterized by high indicators of growth in the fish farms wastewaters. Among these three strains, C. vulgaris BB-2 was selected due to its increased growth rate in aquaculture wastewater with ammonia, nitrite, and nitrate and phosphate removal. In addition, in the water when cultivating microalgae in it the coliform index and total microbial number decreased to 5 and 1.8 x 10(3) colony-forming unit cm(-3). Large-scale microalgae cultivation utilizing aquaculture wastewater gave biomass production of 43.5 mg L-1 day(-1). The biochemical composition analysis of the aquaculture wastewater phycoremediation-derived biomass of C. vulgaris BB-2 revealed that the content of 57.0 +/- 1.2% protein, 16 +/- 1.2% lipid, and 11.4 +/- 1.4% carbohydrate. The obtained data indicate that the lipid extract of microalgae C. vulgaris BB-2 contained saturated 30.7% and polyunsaturated fatty acids 69.3%. The main fraction of amino acids consisted of glutamic acid, lysine, aspartic acid and leucine. The utilization of 25% microalgal biomass as a feed additive in the diet of fish has shown a positive effect on the morpho-physiological and biochemical growth parameters and intestinal microflora of Nile tilapia (Oreochromis niloticus).