Continuous cultivation of photosynthetic microorganisms: approaches, applications and future trends

The possibility of using photosynthetic microorganisms, such as cyanobacteria and microalgae, for converting light and carbon dioxide into valuable biochemical products has raised the need for new cost-efficient processes ensuring a constant product quality. Food, feed, biofuels, cosmetics and pharmaceutics are among the sectors that can profit from the application of photosynthetic microorganisms. Biomass growth in a photobioreactor is a complex process influenced by multiple parameters, such as photosynthetic light capture and attenuation, nutrient uptake, photobioreactor hydrodynamics and gas-liquid mass transfer. In order to optimize productivity while keeping a standard product quality, a permanent control of the main cultivation parameters is necessary, where the continuous cultivation has shown to be the best option. However it is of utmost importance to recognize the singularity of continuous cultivation of cyanobacteria and microalgae due to their dependence on light availability and intensity. In this sense, this review provides comprehensive information on recent breakthroughs and possible future trends regarding technological and process improvements in continuous cultivation systems of microalgae and cyanobacteria, that will directly affect cost-effectiveness and product quality standardization. An overview of the various applications, techniques and equipment (with special emphasis on photobioreactors) in continuous cultivation of microalgae and cyanobacteria are presented. Additionally, mathematical modelling, feasibility, economics as well as the applicability of continuous cultivation into large-scale operation, are discussed.This research work was supported by the grant SFRH/BPD/98694/2013 (Bruno Fernandes) from Fundacao para a Ciencia e a Tecnologia (Portugal). The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013. The authors also thank the Project "BioInd Biotechnology and Bioengineering for improved Industrial and Agro-Food processes, REF. NORTE-07-0124-FEDER-000028" Co-funded by the Programa Operacional Regional do Norte (ON.2-O Novo Norte), QREN, FEDE

The approach of life cycle sustainability assessment of biorefineries

A key driver for the necessary sustainable development is the implementation of the BioEconomy, which is based on renewable resources to satisfy its energy and material demand of our society. The broad spectrum of biomass resources offers great opportunities for a comprehensive product portfolio to satisfy the different needs of a BioEconomy. The concept of biorefining guarantees the resource and energy efficient use of biomass resources. The IEA Bioenergy Task 42 “Biorefining” has the following definition on biorefining: “Biorefining is the sustainable processing of biomass into a spectrum of bio-based products (food, feed, chemicals, and materials) and bioenergy (biofuels, power and/or heat)”. Currently many different biorefinery concepts are developed and already implemented which play a key role in establishing a BioEconomy. The purpose of the work is to develop implementing strategies of Biorefineries in the BioEconomy by applying and using a Life Cycle Sustainability Assessment Approach developed in cooperation with IEA Bioenergy Task 42 “Biorefining” and applied to an algae based biorefinery demonstrated in the EU project FUEL4ME. The aim is to provide facts, figures and framework conditions to maximise the overall sustainability benefits of an integrated material and energetic use of biomass. The scientific innovation is to integrate and combine these broad aspects of an overall assessment of a biorefinery in a common framework and the proof of its practical application to a biorefinery example. The framework covers 1) biorefinery classification, 2) assessment of the technologies and processes with their “Technology Readiness Level (TRL)” integrated in the “Biorefinery Complexity Index (BCI)”, 3) economic assessment based on Life Cycle Costing (LCC), 4) environmental effects based on Life Cycle Assessment (LCA), 5) social issues in a Social Life Cycle Assessment (sLCA) 6) overall Life Cycle Sustainability Assessment (LCSA), 7) identification of most attractive industry sectors (“Hot Spots”) for rolling out BioEconomy, 8) highlighting necessary R&D demand for commercialisation and 9) concluding on the possible future role of biorefining in a BioEconomy in a regional, national and international context. An innovative presentation in a compact format is developed - “Biorefinery Fact Sheet” - to present the assessment results. A set of broadly accepted sustainability indicators for comparison with conventional systems is identified: a) Environment: GHG emissions (t CO2-eq/a), primary energy demand (GJ/a), area demand (ha/a); b) Economy: production costs (€/a), revenues from products (€/a), value added (€/a), employment (persons/a), trade balance (€/a); c) Society: workers, consumers, local community. The whole concept is applied to a case study of using algal biomass to produce HVO-biofuels, PUFA and fertilizer, developed in the EU-demonstration project FUEL4ME for a future commercial scale. The results concentrated in the “Biorefinery Fact Sheet” for single biorefinery systems assist various stakeholders in finding their position on biorefining in a future biobased economy while minimising unexpected technical, economic and financial risks

Microalgal Biorefinery for Bulk and High-Value Products: Product Extraction Within Cell Disintegration

Microalgae are a promising source for proteins, lipids, and carbohydrates for the cosmetic, nutraceutical, chemical, food/feed, and biofuel industry. In comparison with soy and palm oil, microalgae can be produced in a more sustainable way. To make microalgae production economically feasible, all biomass ingredients need to be efficiently utilized, similar to petroleum refineries in which oil is fractionated in fuels and a variety of products with higher value. However severe conditions can affect the properties of some components in the biomass. To overcome this, focus needs to be put on biorefinery techniques which are mild and effective. Microalgal biorefinery is a linear process consisting of harvesting, cell disintegration, sequential extraction, and further fractionation. Among these steps, the cell disintegration often represents a bottleneck for the extraction of hydrophilic or hydrophobic components, due to the presence of a tough cell wall in many strains. State of the art knowledge on both novel and classical techniques for product extraction within cell disintegration is presented. Comparison is made on the basis of two main criteria: yield of disintegration and energy consumption. The current work gives also a comprehensive outlook on business cases for microalgae biorefinery

Microalgal biorefinery for bulk and high-value products : Product extraction within cell disintegration

Microalgae are a promising source for proteins, lipids, and carbohydrates for the cosmetic, nutraceutical, chemical, food/feed, and biofuel industry. In comparison with soy and palm oil, microalgae can be produced in a more sustainable way. To make microalgae production economically feasible, all biomass ingredients need to be efficiently utilized, similar to petroleum refineries in which oil is fractionated in fuels and a variety of products with higher value. However severe conditions can affect the properties of some components in the biomass. To overcome this, focus needs to be put on biorefinery techniques which are mild and effective. Microalgal biorefinery is a linear process consisting of harvesting, cell disintegration, sequential extraction, and further fractionation. Among these steps, the cell disintegration often represents a bottleneck for the extraction of hydrophilic or hydrophobic components, due to the presence of a tough cell wall in many strains. State of the art knowledge on both novel and classical techniques for product extraction within cell disintegration is presented. Comparison is made on the basis of two main criteria: yield of disintegration and energy consumption. The current work gives also a comprehensive outlook on business cases for microalgae biorefinery