Francisco Gabriel Acién-Fernández

A whole biodiesel conversion process combining isolation, cultivation and in situ supercritical methanol transesterification of native microalgae

A coupled process combining microalgae production with direct supercritical biodiesel conversion using a reduced number of operating steps is proposed in this work. Two newly isolated native microalgae strains, identified as Chlorella sp. and Nannochloris sp., were cultivated in both batch and continuous modes. Maximum productivities were achieved during continuous cultures with 318mg/lday and 256mg/lday for Chlorella sp. and Nannochloris sp., respectively. Microalgae were further characterized by determining their photosynthetic performance and nutrient removal efficiency. Biodiesel was produced by catalyst-free in situ supercritical methanol transesterification of wet unwashed algal biomass (75wt.% of moisture). Maximum biodiesel yields of 45.62wt.% and 21.79wt.% were reached for Chlorella sp. and Nannochloris sp., respectively. The analysis of polyunsaturated fatty acids of Chlorella sp. showed a decrease in their proportion when comparing conventional and supercritical transesterification processes (from 37.4% to 13.9%, respectively), thus improving the quality of the biodiesel.

Photobioreactors Design for Hydrogen Production

The photobiological production of H2 is a subject that has been studied with great intensity over the past 50 years using different approaches; direct or indirect biophotolysis (green algae and cyanobacteria) and photo-fermentations (photosynthetic bacteria). The number of publications on the subject is impressive. However, hardly any of the production methods proposed have progressed beyond the laboratory, and the photobioreactors (PBR) used to carry out the processes are still bench-top scale laboratory devices. The scale up of some of the proposed PBR to carry out the process outdoor using full solar radiation is just beginning and the existing data are too scarce.

Utilization of centrate for the outdoor production of marine microalgae at the pilot-scale in raceway photobioreactors

In this study, the outdoor production of marine microalgae in raceway photobioreactors was investigated, modifying the centrate percentage in the culture medium (20, 30, 40 and 50%) and using two different dilution rates (0.2 day-1 and 0.3 day-1). The data obtained showed that microalgae are capable of producing biomass in addition to recovering the nutrients contained in the centrate. The best results for biomass productivity and light efficiency were obtained when the centrate was set at 20% with a dilution rate of 0.3 day-1. The biomass productivity was 32.42 g m-2·day-1 while the photosynthetic efficiency was 0.74 gbiomass·E-1 (3.66%). Regarding the nutrients, nitrogen (the majority being in the form of ammonium [NH4+]) and phosphorus were only fixed into biomass when optimal conditions were set; if this was not the case, they were lost to stripping or precipitation. The maximal nutrient removal capacities under the optimal conditions were 28.72 mgN·l-1·day-1 and 3.99 mgP·l-1·day-1. Population changes were determined by the dilution rate set whilst the centrate percentage had little effect. Four strains were present in the culture, Nannochloropsis g. being the main one. Biochemical changes did not vary greatly between the conditions set for the culture, with a composition rich in proteins and carbohydrates being observed. One can conclude that to produce marine microalgal biomass for a range of potential commodities such as feed, biofertilizers and biofuels, it is possible to use centrate from anaerobic digestion as the sole nutrient source, as a way of reducing costs.