Biorefinery models - Algal biorefinery

Publication date: 17/10/2016

Last update: 17/10/2016

ABOUT THE SERIES OF POSTS “BIOREFINERY MODELS”

This post belongs to a series called “Biorefinery Models”. This series is devoted to briefly describe the models or concepts of advanced biorefineries which have emerged in the last few years and that are rising currently. These models are simplified representations which enable us to understand in a simple way the structure and characteristics of a general biorefinery type. Some of these models refer to the type of feedstock while other focus on the technologies involved. A biorefinery may resemble these models or be the result of variations and combinations of them.

It should be noted that although these paradigms are very useful and instructive, they show limitations in describing and classifying complex systems with high level of integration. In order to define and describe a specific complex case, the blog recommends use the classification proposed by IEA Bioenergy Task 42 (Feedstocks / Products / Platforms / Technologies). You can learn more about the general notion of biorefinery and the different biorefinery classifications in this section of the blog: BIOREFINERY CONCEPT.

ALGAL BIOREFINERY MODEL ^1,2,3,4,5,6

Algal biorefinery (or algae biorefinery) is the most common denomination for a biomass processing system based on algae, but the terms aquatic biorefinery and blue biorefinery are also used. Aquatic biomass (microalgae and seaweed) is an interesting biorefinery feedstock, characterised by high productivity and a high content of valuable components (lipids, proteins, polysaccharides and other specific biomolecules). Algal cultivation can also be combined with waste water treatment and carbon dioxide fixation systems.

The varied composition of the aquatic biomass enables to produce from fuels and bulk chemicals to speciality chemicals and food and feed ingredients. Algae can be processed in many different ways to obtain that wide spectrum of products and this is the main reason to explain the difficulty of defining an only model that groups all of the available systems under the same umbrella. The choice of a processing route will depend on the type of the specific feedstock and the possibilities for the cascading process integration. The following factsheet intends to introduce a unified description for the algal biorefinery model in a very simple and summarized way.

Algal biorefinery factsheet
Feedstock	- Microalgae, seaweed or macroalgae, cyanobacteria. - Sunlight, carbon dioxide, nutrients. Algae can be farmed in ponds, photobioreactors (PBRs) and fermenters.
Primary fractionation	The primary fractionation in an algal biorefinery is the extraction of the bioproducts synthesised by the algae during the previous stage of cultivation. Before, it is necessary to carry out preparation processes like harvesting (sedimentation, filtration, centrifugation…) and drying. The extraction operation depends on: the particular biological component for extraction, the harvest operations and the posterior conversion process. These are some of the available options: - Mechanical disruption. Bead mills, ultrasounds… - Non mechanical methods. Supercritical fluid extraction, application of organic solvents, osmotic shock… - Direct excretion. Engineered photosynthetic cyanobacteria directly excrete targeted molecules.
Main streams	(1) Algal bioproducts - Lipidic or oil extract. Microalgae produce storage lipids in the form of triglycerides. Alongside them, the algae crude oil contains other lipophilic algae ingredients. - Alcohols. Cyanobacteria are capable of producing ethanol and other alcohols through heterotrophic fermentation and it is possible to enhance this natural ability through genetic engineering. - Alkanes. Same as alcohols. (2) Spent biomass Current production methods for biofuels and chemicals production and waste water treatment can produce huge quantities of residual biomass that is an important coproduct.
Valorization pathways and products of the algal bioproducts	(1) Oil extract The oil extract can be subjected to secondary refining to selectively separate high-added value products from triglycerides. Tryglicerides - Oil transesterification → Product: Biodiesel. - Hydroprocessing → Products: Renewable diesel, jet biofuel, bionaphta and biopropane. - Cleavage → Products: Fatty acids and glycerol. Both of them are precursors for a whole raft of chemical products. High added value components Polyunsaturated fatty acids (arachidonic acid, docohexaenoic acid, γ-linolenic acid), anti-oxidants (β–carotene, tocopherol), coloring agents (astaxanthin, phycocyanin, phycoerythrin). (2) Alcohols The mixture ethanol-water can be purified for downstream processing using standard distillation and other conventional technologies in order to produce ethanol for fuels or chemicals. (3) Alkanes The mix of hydrocarbons produced is similar to light crude petroleum and liquid fuels can be obtained through subsequent upgrading.
Valorization pathways and products of the spent biomass	The spent biomass contains three main fractions: protein fraction, carbohydrates and minerals. They can be separated or jointly processed. - Drying → High-protein feedstuff, fertilisers, other value-added products. - Anaerobic digestion → Biomethane and essential nutrients. - Hydrothermal liquefaction → Biocrude that can be upgraded to renewable transportation fuels and chemicals. Inorganic solid co-products after liquefaction have potential application in construction industries. - Separation and fermentation → After separation, the carbohydrate fraction can be fermented to produce fuels and chemicals (ethanol, buthanol, lactic acid…). - Other processes under study: pyrolysis, gasification, supercritical operations…

Figure 1 illustrates a specific algal lipid biorefinery model. In this case, the algal bioproduct is a crude algal oil that is hydrolysed to obtain fatty acids, glycerol and lipophilic substances. The deoiled residual biomass is subjected to anaerobic fermentation to produce fertilisers and biogas.

Figure 1. Schematic example of an algal lipid biorefinery model (extracted from Reference 3)

EXAMPLES OF DEMONSTRATION FACILITIES ^{7,8,9,10,11,12}

Finally, a table showing for some real demonstration plants: the algal bioproducts, the valorization pathways and the final products. By clicking in the name of the facility, you can access to a post with all the information about it.

Name / Company	Location	Farming technology	Algal bioproducts	Valorization pathways	Final products
ecoduna algal biorefinery / ecoduna	Bruck an der Leitha (Austria)	PBRs	Oil extract	Oil separation / Refining	Biofuel
				Oil separation	Omega-3/6 fatty acids
			Spent biomass	Anaerobic digestion	Biogas
					Fertilizers
Fort Myers pilot-scale Integrated Biorefinery (IBR) / Algenol	Fort Myers (Florida, USA)	PBRs	Ethanol	Vapor Compression Steam Stripping / Standard distillation	Fuel grade ethanol
			Spent biomass	Hydrothermal liquefaction	Diesel, gasoline and jet fuel
Kona Demonstration Facility (KDF) / Cellana	Kona (Hawaii’s Big Island, USA)	PBRs and open seawater ponds	Oil extract	Oil separation / Refining	Biofuel
				Oil separation	Omega-3 fatty acids
			Spent biomass	Dry	Feed
Muradel Demonstration Plant / Muradel	Whyalla (Australia)	Paddlewheel mixed raceway ponds	Oil extract	Oil separation	Oleochemicals
			Spent biomass	Hydrothermal liquefaction	Green crude oil / Inorganic solid co-products
				Separation Drying	Fertilizers Animal Feed

Figure 2. Muradel’s continuous flow sub-critical water reactor (extracted from Muradel web page). Conversion of spent algae into green crude oil by hydrothermal liquefaction.

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REFERENCES

1 U.S. DOE 2010: “National Algal Biofuels Technology Roadmap”. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program.

2 “The European Biorefinery 2030 Vision”. Star-COLI BRI -Strategic Targets for 2020 – Collaboration Initiative on Biorefineries.

3 “Biorefineries Roadmap as part of the German Federal Government action plans for the material and energetic utilisation of renewable raw materials”. May 2012.

4 Y. Chisti: “Biodiesel from microalgae”. Biotechnology Advances 25 (2007) 294–306.

5 I. Priyadarshani , B. Rath: “Commercial and industrial applications of micro algae – A  review”. J. Algal Biomass Utln. 2012, 3 (4): 89–100.

6 A. Darzins, P. Pienkos, L. Edye: “Current Status and Potential for Algal Biofuels Production”. A Report to IEA Bioenergy Task 39, Report T39-T2, 6 August 2010.

7 www.ecoduna.com (accessed on 15th October 2016).

8 IEA Bioenergy Task 42 Biorefining. Sustainable and synergetic processing of biomass into marketable food & feed ingredients, products (chemicals, materials) and energy (fuels, power, heat).  Wageningen, the Netherlands, August 2014.

9 www.algenol.com (accessed on 15th October 2016).

10 www.cellana.com (accessed on 15th October 2016).

11 www.muradel.com (accessed on 15th October 2016).