Microalgae biotechnology for simultaneous water treatment and feed ingredient production in aquaculture

Abstract

The use of Tetraselmis chui to produce sole feed ingredient and the recovery of nutrients from a recirculating aquaculture system (RAS) aquaculture facility was studied. The microalga was cultured in a pilot-scale (6 m3) outdoor raceway reactor located in a sole production plant. First, the growth of the microalgae, the addition of phosphorus and the quality of the resulting water were studied. It was possible to cultivate in semi-continuous mode T. chui using the purge stream of a RAS, obtaining productivities of 15 mg L−1 d−1, and reaching 36 mg L−1 d−1 when phosphorus was added. In terms of water quality of the effluent, the pollutants concentration were below discharge limits (suspended solids and total dissolved nitrogen, phosphorus and carbon) —directive 91/271/EEC. In the case of Vibrio sp., the concentration in the culture water at the end of the experiments remained below typical environmental concentrations (<100 CFU mL−1). After harvesting, the biomass quality was analysed, being the microalgae produced in semi-continuous using phosphorus-enriched RAS remarkably similar to commercial T. chui. Biomass of T. chui was used in a sole feeding trial to supplement feeds (0, 10 and 20 % inclusion). Adding 10 and 20 % T. chui to the feed reduced the original raw material in fishmeal by 15 and 25 % without altering the gross composition. No significant differences were found in the pre-fattening test of Solea senegalensis in growth and fillet composition using the experimental feed with 20 % of T. chui. Finally, immune activity increased significantly in diets containing >10 % microalgae.