INNOVALGAE

Project Title
Technological innovation for CO2 sequestration and bioethanol production by microalgae
Project Type
Nacional / Public
Funding Body
Funding Program
Programa Operacional Potencial Humano (POPH)
Reference
PTDC/AAC-AMB/108511/2008
Funding
  • CEB: 89 778,00
  • Total: 89 778,00
Start
30-04-2010
End
30-09-2013
External link

Principal Investigator

Team Members - CEB

Abstract

Due to the shortages of fossil fuels and the production of greenhouse gases (i.e. carbon dioxide) on their combustion, alternative fuels are receiving considerable attention. Biodiesel and bioethanol from agricultural crops are being produced in increasing amounts as renewable biofuels, but their production in large quantities is not sustainable. An alternative is offered by microalgae. Microalgae are photosynthetic microorganisms that convert sunlight, water and carbon dioxide to algal biomass. They can be employed for the production of biofuels in an environmentally sustainable manner (6). Chlorella strains have a great potential to be a resource for bioethanol production due to its easier cultivation and higher starch accumulation in comparison with other microalgae strains (14). Moreover, these microalgae use CO2 efficiently because they can grow rapidly and can be readily incorporated into engineered systems, such as photobioreactors (8). Most of the scientific studies involving Chlorella cultivation are carried out in different photobioreactor types, such as tubular, flat plate and fermenter-type. However, these photobioreactors require large placement areas or present photosynthetically inefficient dark zone that limits their productivity. In a deep culture vessel, productivity can be improved significantly by improving the radial mixing of fluid from the darker core of the culture vessel to its periphery (20). The main goal of the project INNOVALGAE is to use an oscillatory flow photobioreactor (OFP) as a new strategy to improve the CO2 removal and productivity of starch accumulation by the microalgae Chlorella vulgaris in view of their use as raw material for bioethanol production. Our group at CEB/UM enjoys an international reputation for the pioneering work on oscillatory flow reactors (OFRs) design and operation (25; 26; 27). Previous studies at CEB/UM have demonstrated that a novel OFR, composed of tubes with smooth periodic constrictions, promoted eddy formation which increased the radial mixing in the tube, and was able to suspend catalyst particles with a wide range of sedimentation velocities. The formation and dissipation of eddies in the OFR resulted in significant enhancement of processes such as heat transfer, mass transfer and particle mixing. Unlike conventional screening devices, the flow patterns in the OFR can be reproduced at larger scales, therefore, results in the laboratory can be related directly to larger scale production (27). Microalgae cultivation will be optimized in the micro-scale OFP by defining the best conditions for different variables, namely light intensity, temperature, mixture rate, inlet CO2 concentration and initial mineral concentration. All these experiment will be facilitated by the size and screening applicability of the OFR. OFRs allow batch high-throughput screening, ensuring small operation volumes, reduced reagent costs and waste generation, in addition to several other advantages. State-of-the-art fiber-optical technology will be used for on-line monitoring of the cell concentration inside the screening reactor by using a special fiber optical micro-probe. Once the conditions have been optimized, the platform will be linearly scaled up. A range of physical and chemical cell disruption processes will be tested to maximize the algal starch extraction at the optimized microalgae growth conditions and then, the best conditions for starch hydrolysis (temperature and enzyme concentration) will be selected. There are few literature data about starch extraction and the existent reports deal with ultrasonic radiation (14); therefore, the development of new low-cost techniques for this purpose is necessary. The algal starch hydrolyzate obtained from the previous stage will be optimized in terms of its nutritional composition aiming to reach the highest bioethanol yield. Continuous ethanol fermentation will be carried out in a pilot-scale airlift bioreactor (ALR) with yeasts immobilized on different agroindustrial by-products (brewer´s spent grains and corncobs). Several studies performed by our group have reported that the application of cheap carrier of agro-industrial origin could significantly lower the investment costs of continuous fermentation systems (11; 10; 2; 3). The proposed project represents a significant step forward in microalgae growth, starch extraction and ethanol fermentation that may lead to enhanced cost-effectiveness and therefore, effective commercial implementation of bioethanol production and CO2 mitigation from microalgae.