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Projeto de investigação
Microalgae Biomass Biorefinery: Development and Implementation of Processing Strategies in an Industrial Unit in Portugal
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Nannochloropsis sp. Biorefinery: Recovery of Soluble Protein by Membrane Ultrafiltration/Diafiltration
Publication . Ribeiro, Cláudia; Santos, Edgar T.; Costa, Luís; Brazinha, Carla; Saraiva, Pedro; Crespo, João G.; DQ - Departamento de Química; LAQV@REQUIMTE; NOVA Information Management School (NOVA IMS); MDPI AG
This work proposes a way to maximize the potential of a Nannochloropsis sp. biorefinery process, through membrane technology, producing an extract enriched in soluble proteins, free from the insoluble protein fraction, with a low lipid content and eliminating the colored chlorophyll-a. This procedure, following the principles of a circular economy approach, allows for the valorization of a stream from the biorefining of Nannochloropsis sp. that, otherwise, would be considered a residue without commercial value. The process proposed minimizes fouling phenomena at the membrane surface, making it possible to achieve high permeate fluxes, thus reducing the need for membrane cleaning and, therefore, contributing to an extended membrane lifetime. Supernatant obtained after centrifugation of a suspension of ruptured Nannochloropsis sp. cells was processed by ultrafiltration using a membrane with a cut-off of 100 kDa MWCO. Two different operating approaches were evaluated—controlled transmembrane pressure and controlled permeate flux—under concentration and diafiltration modes. Ultrafiltration operated in a diafiltration mode, under controlled permeate flux conditions, led to the highest soluble protein recovery (78%) with the highest constant permeate flux (12 L·m−2·h−1 ) and low membrane fouling.
Microalgae Biomass Biorefinery: Development and Implementation of Processing Strategies in an Industrial Unit in Portugal
Publication . Ribeiro, Cláudia Sofia Martins; Crespo, João; Saraiva, Pedro; Santos, Edgar
Throughout the years, we have witnessed a disturbing increase in the consumption of resources provided by our planet as the world population increases. Microalgae have been receiving much interest as a promising feedstock for biorefinery products, such as nutraceuticals or protein for human food and animal feed applications, as these microorganisms are extremely competitive with other plant crops.
The ultimate goal of this thesis is to develop a sustainable and economically viable biorefinery for the co-production of several added-value products from Nannochloropsis sp. biomass, and compare its economic results with other solutions that attempt to set up a dedicated production facility to produce a single product (e.g., biodiesel). This work comprises the optimisation of several unit operations that are essential to the development of a refining process of Nannochloropsis sp. biomass.
Firstly, the Nannochloropsis sp. biomass stabilisation through heat treatment was performed. The stabilisation step aimed to minimise the lipid hydrolysis reactions by inactivating the enzymes responsible for catalysing those reactions. This step is of extreme importance as the main product of the proposed biorefinery is an EPA-rich lipid fraction. The optimised operating conditions (95 ºC for 3 min) were able to prevent the degradation of the lipids present in the wet biomass after the cellular disruption. The cellular disruption is also particularly important for Nannochloropsis sp. as this strain possesses a robust cell wall. Bead milling was proposed as a suitable technique and the operating conditions were optimised to enhance the cellular disruption. The optimised conditions for a pilot-scale bead mill revealed that it is possible to achieve almost 95% of cellular disruption with a single pass at a flow rate of 10 L.h-1 and a tip speed of 14 m.s-1.
Additionally, biomass fractionation steps were studied. Membrane technology was selected to produce a permeate enriched in soluble proteins, free from coloured chlorophyll a, insoluble proteins, and with low lipid content. Two different operating approaches were evaluated - controlled transmembrane pressure and controlled permeate flux – under concentration and diafiltration modes. Ultrafiltration operated in a diafiltration mode, under controlled permeate flux conditions, led to the highest soluble protein recovery (78%) with the highest constant permeate flux (12 L.m-2.h-1) and low membrane fouling.
On the other hand, a solvent extraction methodology was selected to produce an EPA-rich polar lipid extract. The solvent selected (ethanol) is considered a GRAS solvent (Generally Recognized as Safe), and a food grade solvent. The ethanol to biomass ratio was optimised, and a techno-economic evaluation was performed. The extraction with a solvent to biomass ratio (v/w) of
5 mL.g-1 allowed a final extraction efficiency of 71%, with the lowest production cost.
Finally, a biorefinery concept based on EPA-rich Nannochloropsis sp. is proposed, based on a downstream process where different value-added compounds are targeted. The techno-economic performance of a single product value chain and a multiproduct value chain biorefinery were compared. Also, a comparative analysis between five scenarios with different operational costs was performed. Therefore, the Net Present Value (NPV), the Internal Rate of Return (IRR), and the Payback Period were calculated and compared. The baseline designed multi-product biorefinery resulted in estimated economic performance indicators that correspond to an IRR of 20.3%, and a payback period of 4.7 years.
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Fundação para a Ciência e a Tecnologia
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PD/BDE/142836/2018