Cultivation of Nannochloropsis oceanica F&M-M24 and Tetraselmis suecica F&M-M33 in the two 0.5-ha BIOFAT pilot plants for biofuel production

The EU FP7 BIOFAT project aimed to demonstrate at pilot and then demo scale the feasibility of biofuel production from microalgal biomass using two marine strains belonging to the Collection of Microalgae and Cyanobacteria of Fotosintetica & Microbiologica S.r.l., the lipid producer Nannochloropsis oceanica F&M-M24 and the carbohydrate producer Tetraselmis suecica F&M-M33, as models. Two 0.5 ha BIOFAT Pilot Plants were built, one in Camporosso (Imperia, Italy) (BCPP) and one in Pataias (Portugal) (BPPP). BCPP comprises two 250-m2 modules of GWP®-II photobioreactors (WO 2011/013104 to F&M) for inoculum production, two 530-m2 raceway ponds for growth and two 1,250-m2 raceway ponds for starvation trials. BPPP comprises 3-m2 GWP®-I photobioreactors for inoculum production, 270-m2 tubular photobioreactors for growth and two 1500-m2 cascade ponds for starvation. BCPP was in operation from March 2015 until the end of the project in April 2016, BPPP started operations in June 2014. In BCPP growth and starvation trials were performed for 4 or 6 days with both N. oceanica F&M-M24 and T. suecica F&M-M33. The starvation phase was performed in seawater without nutrient addition. From these trials annual productivities were estimated. For N. oceanica F&M-M24 the estimated average annual productivity is of 9.5 g m-2 land area d-1 in the GWP®, and of 14 and 8 g m-2 d-1 in the raceway ponds under nutrient replete and starved conditions, respectively. Total lipids reached about 40% of biomass dry weight, with a fatty acid composition sub-optimal for biodiesel production (but with high EPA content). Detailed fatty acid composition will be illustrated. T. suecica F&M-M33 in the ponds attained a carbohydrate content of about 35%, lower than what achieved in GWP®-II reactors (50% dry biomass). Starved biomass was delivered for biofuel production. In BPPP, located in Portugal near Lisbon, and with an average annual radiation of 17 MJ m-2 d-1. N. oceanica was cultivated both under Nitrogen replete and depleted conditions, and both in Tubular Photobioreactors (TPBRs) and Cascade Raceways (CRWs), with very similar performances. In N-replete conditions, the average annual productivity was estimated based on the data obtained for the two systems, and is equivalent to 9 g m-2 d-1. The starvation stage was performed with artificial seawater, without nutrient addition. In N-depleted conditions N. oceanica the areal productivity obtained for an average radiation of 9 MJ m-2 d-1 was 7 g.m-2 d-1, achieving a total lipid composition that includes a FA content of 33% per DW after 6 days. Detailed fatty acid composition will be illustrated. BIOFAT evidenced the necessity to combine biofuel production with high-value product recovery from the extraction panel (biorefinery approach) to achieve economic sustainability. To this end, optimisation in plant design and operation must be performed, and this process was applied to the design of the BIOFAT DEMO Plant. The two-stage strategy (high quality inoculum production under nutrient replete conditions followed by nitrogen starvation in large ponds) proved to work, although storage product accumulation during starvation was not as effective in raceway ponds as in GWP® photobioreactors. Raceways ponds of two different improved design provided expected performance in both pilot plants in terms of areal productivity and culture stability. Acknowledgment. This research was co-funded by the EC, Contract Number FP7-268211, BIOFAT