Carbon, nitrogen, and phosphorus removal, and lipid production by three saline microalgae grown in synthetic wastewater irradiated with different photon fluxes

Mariculture production has increased in the last decades, with untreated wastewater discharged directly into the sea, impacting coastal ecosystems. There is a need for mariculture wastewater treatment systems that are cost-effective. This can be met by the implementation of wastewater treatment systems that in addition to removing pollutants are capable of producing valuable by-products such as biomass for the biofuel industry. In this study, Dunaliella sp., Nannochloropsis sp. and Tetraselmis sp. microalgae were cultivated in controlled environments simulating mariculture wastewaters. Single stage culture systems were used to grow these microalgae, the growing conditions included inducing stress with different photon flux densities (900, 1500 and 2000 μmol m−2 s−1), and low carbon, nitrogen and phosphorus concentrations obtained at the stationary phase, in order to force these microalgae to increase their lipid content. The best results were obtained with Tetraselmis sp., which achieved 132.8 mg L−1 day−1 of biomass productivity at 900 μmol m−2 s−1. Nevertheless the best lipid productivity was reached at 1500 μmol m−2 s−1, also by Tetraselmis sp., being 29.5 mg L−1 day−1, where biomass productivity was of 124.5 mg L−1 day−1. All three microalgae species were able to remove >90% of nitrogen and orthophosphates, and 80% of carbon, which makes them suitable for treating mariculture wastewater, and in addition, represent a valuable high lipid content biomass byproduct usable as raw material for biodiesel synthesis.