Browsing by Author "Santos, Carla A."
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- Anaerobic Digestion of Microalga Chlorella protothecoides and Metagenomic Analysis of Reddish-Colored DigestatePublication . Eusebio, Ana; Santos, Carla A.; Marques, Isabel PaulaABSTRACT: Microalga Chlorella protothecoides materials were assessed as substrates for anaerobic digestion (AD) aiming at the simultaneous production of biogas/methane and pigments: whole autotrophic (AA) and heterotrophic algae (H); extracted heterotrophic microalgae from lipid production (HExt); and pretreated heterotrophic microalgae through enzymatic (HPEnz), autoclave (HPA), and ultrasound (HPU) processes. AA was more suitable for AD than H, as it was more efficiently converted into methane (279 vs. 180 L CH4/kg VSin). In comparison, the pretreatment of heterotrophic microalgae had a positive effect on AD, with registered methane yield increases from 263 to 290 L CH4/kg VSin (HPU, HPA, HExt). Reddish pigmentation developed in H and HPU units due to the presence of purple non-sulfur bacteria (PNSB). This phenomenon and the changes in microbiota structure during AD were confirmed by metagenomic analysis. At the end of the process, the relative abundance of Clostridiales and Bacillales increased, enhancing the hydrolysis of compounds in acetate. Consistently, Methanosaeta became the comparatively dominant methanogen, meaning that methane was produced through the acetoclastic methanogenesis pathway. The obtained results indicate for AD biorefinery feasibility-regarding the simultaneous production of biogas/methane-a digestate flow and pigments (bacteriochlorophyll a and carotenoids).
- Bioactive compounds through anaerobic digestion of heterotrophic microalgae residuesPublication . Morana, A.; Squillaci, G.; Santos, Carla A.; La Cara, F.; Marques, Isabel PaulaSeveral important biomolecules are available into anaerobically digested effluents that were obtained from the biodiesel production process using heterotrophically grown microalga Chlorella protothecoides. Defatted microalgae residues and crude glycerol may undergo anaerobic digestion, separately and in admixture, providing methane/hydrogen and a digestate exploitable for agriculture applications. Furthermore, industrial interesting bioactive compounds such as polyphenols provided with antioxidant activity can be obtained. Anaerobic process offers a promising chance and can be advantageously combined with algae lipid-extraction techniques in order to make it more sustainable.
- Biodiesel from heterotrophic and autotrophic microalgae: a sustainable production [Poster]Publication . Santos, Carla A.; Semião, Filipe; Barata, Carlos; Reis, Alberto
- Biodiesel from microalgae Chlorella protothecoides growing at autotrophic and heterotrophic metabolisms in a new symbiotic bioreactorPublication . Santos, Carla A.; Reis, AlbertoBiodiesel is an alternative energy to fossil fuels, and is produced from biomass, therefore provides lower CO2 emissions. Currently, biodiesel is produced from plant oils, animal fats and used oils. These sources are low-yield which is a limitation to the production of biodiesel in large quantities. On the contrary, microalgae present a very high yield and can be produced in large amounts. The bio-refinery of microalgae oil must have a strategy of taking advantage of all by-products to make the whole process economic feasible. The bio-refinery proposed on this work is based on a first step to produce microalgae in a symbiotic bioreactor. The symbiotic bioreactor consists of an association of a fermenter and a photobioreactor connected by the gas phase on closed circuit. Two sorts of microalgae biomass are obtained: the heterotrophic microalgae from the fermenter and the autotrophic microalgae from the VAP (vertical alveolar panel photobioreactor). The best strategy is to use the heterotrophic microalgae to extract the oil as it has a higher content in lipids, and, then to produce biodiesel; additionally carotenoids as lutein can be extracted along with lipids from the heterotrophic microalga as a High Value Product (HVP). On the other hand, the autotrophic microalgae go to a second step of carotenoids accumulation, named carotenogenesis, to produce a biomass rich in carotenoids, also known as HVP. Carotenoids can be extracted and the residue of microalga, join to the other residues of microalgae to be processed by anaerobic digestion. The heterotrophic microalgae residue after oil and lutein extraction can be submitted to anaerobic digestion to produce methane or hydrogen. The case of microalga Chlorella protothecoides was studied, because it can grow under the two metabolisms referred above, and the lipids obtained are suitable to produce biodiesel. The yields obtained are quite favourable to the symbiotic system, instead of the separated bioreactors. The carbon dioxide emissions can be reduced by the autotrophic growth of microalgae. The sustainability of the bio-refinery was ensured in order to achieve an economic feasible system.
- Carotenoid and lipid production by the autotrophic microalga Chlorella protothecoides under nutritional, salinity, and luminosity stress conditionsPublication . Campenni, Luca; Nobre, B. P.; Santos, Carla A.; Oliveira, Ana Cristina; Aires-Barros, M. R.; Palavra, António F.; Gouveia, LuisaToday microalgae represent a viable alternative source for high-value products. The specie Chlorella protothecoides (Cp), heterotrophically grown, has been widely studied and provides a high amount of lutein and fatty acids (FA) and has a good profile for biodiesel production. This work studies carotenoid and FA production by autotrophic grown Cp. Cp was grown until the medium’s nitrogen was depleted, then diluted in NaCl solution, resulting in nutritional, luminosity, and salinity stresses. Different NaCl concentrations were tested (10, 20, 30 g/L) at two different dilutions. After dilution, a color shifting from green to orange-red was noticed, showing carotenoid production. The best production of both carotenoids and FA was attained with a 20 g/L NaCl solution. The total carotenoid content was 0.8 % w/w (canthaxanthin (23.3 %), echinenone (14.7 %), free astaxanthin (7.1 %), and lutein/zeaxanthin (4.1 %)). Furthermore, the total lipid content reached 43.4 % w/w, with a FA composition of C18:1 (33.64 %), C16:0 (23.30 %), C18:2 (11.53 %), and less than 12 % of C18:3, which is needed to fulfill the biodiesel quality specifications (EN 14214).
- Dual-mode cultivation of Chlorella protothecoides applying inter-reactors gas transfer improves microalgae biodiesel productionPublication . Santos, Carla A.; Nobre, B. P.; Silva, Teresa Lopes da; Pinheiro, H. M.; Reis, AlbertoChlorella protothecoides, a lipid-producing microalga, was grown heterotrophically and autotrophicallyin separate reactors, the off-gases exiting the former being used to aerate the latter. Autotrophic biomass productivity with the two-reactor association, 0.0249 g L-1h-1, was 2.2-fold thevalue obtained in a control autotrophic culture, aerated with ambient air. Fatty acid productivity was1.7-fold the control value. C. protothecoides heterotrophic biomass productivity was 0.229 g L-1h-1. This biomass’ fatty acid con-tent was 34.5% (w/w) with a profile suitable for biodiesel production, according to European Standards.The carbon dioxide fixed by the autotrophic biomass was 45 mg CO2L-1h-1in the symbiotic arrange-ment, 2.1 times the control reactor value.The avoided CO2 atmospheric emission represented 30% of the CO2 produced in the heterotrophic stage, while the released O2 represented 49% of the oxygen demand in that stage.Thus, an increased efficiency in the glucose carbon source use and a higher environmental sustainability were achieved in microalgal biodiesel production using the proposed assembly.
- Enhanced lipidic algae biomass production using gas transfer from a fermentative Rhodosporidium toruloides culture to an autotrophic Chlorella protothecoidesPublication . Santos, Carla A.; Caldeira, M. L.; Silva, Teresa Lopes da; Novais, J. M.; Reis, AlbertoIn order to produce single-cell oil for biodiesel, a yeast and a microalga were, for the first time, grown in two separate reactors connected by their gas-phases, taking advantage of their complementary nutritional metabolisms, i.e., respiration and photosynthesis. The yeast Rhodosporidium toruloides was used for lipid production, originating a carbon dioxideenriched outlet gas stream which in turn was used to stimulate the autotrophic growth of Chlorella protothecoides in a vertical-alveolar-panel (VAP) photobioreactor. The microalgal biomass productivity was 0.015 g L1 h1, and its lipid productivity attained 2.2 mg L1- h1 when aerated with the outlet gas stream from the yeast fermenter. These values represent an increase of 94% and 87%, respectively, as compared to a control culture aerated with air. The CO2 bio-fixed by the microalgal biomass reached an estimated value of 29 mg L1 h1 in the VAP receiving the gas stream from the fermenter, a value 1.9 times higher than that measured in the control VAP.
- Microalgal symbiosis in biotechnologyPublication . Santos, Carla A.; Reis, AlbertoThis review provides an analysis of recent published work on interactions between microorganisms, especially the ones involving mainly nutrient exchanges and at least with one microalga species. Examples of microbial partners are given, with a remark to the potential application of cultures of an autotroph and a heterotroph, which grow simultaneously, taking advantage of the complementary metabolisms. These are particularly interesting, either due to economic or sustainable aspects, and some applications have already reached the commercial stage of development. The added advantages of these symbiotic cultures are biomass, lipid, and other products productivity enhancement a better utilization of resources and the reduction or even elimination of process residues (including carbon dioxide and other greenhouse gases) to conduct an increasingly greener biotechnology. Among the several symbiotic partners referred, the microalgae and yeast cultures are the most used. The interaction between these two microorganisms shows how to enhance the lipid production for biodiesel purposes compared with separated (stand-alone) cultures.
- Pretreatments applied to microalgae residues to enhance anaerobic digestionPublication . Rodrigues, M. P.; Eusebio, Ana; Santos, Carla A.; Marques, Isabel PaulaABSTRACT: Biomass of microalga Chlorella protothecoides, grown under autotrophic and heterotrophic conditions and subjected to pretreatments, were energetically valorized through anaerobic digestion process according to the substrates: autotrophic algae (A), heterotrophic algae (H), heterotrophic algae extracted (HE), autoclave pretreated heterotrophic algae (HPA), enzyme pretreated heterotrophic algae (HPE), ultrasound pretreated heterotrophic algae (HPU), and inoculum (I). Despite the application of pretreatments, the highest methane production was obtained in the algae extracted digestion with 172 mL CH4, against 153, 126 and 142 mL obtained in HPA, HPE and HPU, respectively. The COD removal capacity was higher in the HPA sample while the TS and VS removal reached higher values in the autotrophic alga.
- Valorization of chestnut manufacture process residues [Poster]Publication . Morana, A.; Laratta, B.; Vella, F. M.; Santos, Carla A.; Del Monaco, G.; La Cara, F.; Marques, Isabel Paula