Microalgae for biodiesel production and other applications: A review
Introduction
The transportation and energy sectors are the major anthropogenic sources, responsible in European Union (EU) for more than 20% and 60% of greenhouse gas (GHG) emissions, respectively [1]. Agriculture is the third largest anthropogenic source, representing about 9% of GHG emissions, where the most important gases are nitrous oxide (N2O) and methane (CH4) [2]. It is expected that with the development of new growing economies, such as India and China, the global consumption of energy will raise and lead to more environmental damage [3].
GHG contributes not only to global warming (GW) but also to other impacts on the environment and human life. Oceans absorb approximately one-third of the CO2 emitted each year by human activities and as its levels increase in the atmosphere, the amount dissolved in oceans will also increase turning the water pH gradually to more acidic. This pH decrease may cause the quick loss of coral reefs and of marine ecosystem biodiversity with huge implications in ocean life and consequently in earth life [4].
As GW is a problem affecting different aspects of human life and the global environment, not only a single but a host of solutions is needed to address it. One side of the problem concerns the reduction of crude oil reserves and difficulties in their extraction and processing, leading to an increase of its cost [5]. This situation is particularly acute in the transportation sector, where currently there are no relevant alternatives to fossil fuels.
To find clean and renewable energy sources ranks as one of the most challenging problems facing mankind in the medium to long term. The associated issues are intimately connected with economic development and prosperity, quality of life, global stability, and require from all stakeholders tough decisions and long term strategies. For example, many countries and regions around the world established targets for CO2 reduction in order to meet the sustainability goals agreed under the Kyoto Protocol.
Presently many options are being studied and implemented in practice, with different degrees of success, and in different phases of study and implementation. Examples include solar energy, either thermal or photovoltaic, hydroelectric, geothermal, wind, biofuels, and carbon sequestration, among others [6], [7]. Each one has its own advantages and problems and, depending on the area of application, different options will be better suited. One important goal is to take measures for transportation emissions reduction, such as the gradual replacement of fossil fuels by renewable energy sources, where biofuels are seen as real contributors to reach those goals, particularly in the short term.
Biofuels production is expected to offer new opportunities to diversify income and fuel supply sources, to promote employment in rural areas, to develop long term replacement of fossil fuels, and to reduce GHG emissions, boosting the decarbonisation of transportation fuels and increasing the security of energy supply.
The most common biofuels are biodiesel and bio-ethanol, which can replace diesel and gasoline, respectively, in today cars with little or none modifications of vehicle engines. They are mainly produced from biomass or renewable energy sources and contribute to lower combustion emissions than fossil fuels per equivalent power output. They can be produced using existing technologies and be distributed through the available distribution system. For this reason biofuels are currently pursued as a fuel alternative that can be easily applied until other options harder to implement, such as hydrogen, are available.
Although biofuels are still more expensive than fossil fuels their production is increasing in countries around the world. Encouraged by policy measures and biofuels targets for transport, its global production is estimated to be over 35 billion liters [8].
The main alternative to diesel fuel in EU is biodiesel, representing 82% of total biofuels production [9] and is still growing in Europe, Brazil, and United States, based on political and economic objectives.
Biodiesel is produced from vegetable oils (edible or non-edible) or animal fats. Since vegetable oils may also be used for human consumption, it can lead to an increase in price of food-grade oils, causing the cost of biodiesel to increase and preventing its usage, even if it has advantages comparing with diesel fuel.
The potential market for biodiesel far surpasses the availability of plant oils not designated for other markets. For example, to fulfill a 10% target in EU from domestic production, the actual feedstocks supply is not enough to meet the current demand and the land requirements for biofuels production, would be more than the potential available arable land for bio-energy crops [10]. The extensive plantation and pressure for land use change and increase of cultivated fields may lead to land competition and biodiversity loss, due to the cutting of existing forests and the utilization of ecological importance areas [11]. Biodiesel may also be disadvantageous when replacing crops used for human consumption or if its feedstocks are cultivated in forests and other critical habitats with associated biological diversity.
Current policies at regional and national levels and the expected cost and difficulties in obtaining fossil fuels will necessarily lead to an increase in biodiesel production and of other types of renewable energy. To become a more viable alternative fuel and to survive in the market, biodiesel must compete economically with diesel. The end cost of biodiesel mainly depends on the price of the feedstocks that accounts for 60–75% of the total cost of biodiesel fuel [12].
In order to not compete with edible vegetable oils, the low-cost and profitable biodiesel should be produced from low-cost feedstocks such as non-edible oils, used frying oils, animal fats, soap-stocks, and greases. However the available quantities of waste oils and animal fats are not enough to match the today demands for biodiesel. Thus transition to second generation biofuels, such as microalgae, can also contribute to a reduction in land requirements due to their presumed higher energy yields per hectare as well as to their non-requirement of agricultural land. Additionally, biodiesel needs to have lower environmental impacts and ensure the same level of performance of existing fuels [13].
Albeit the growing interest and fast growth of this area, it is still on its infancy. A large investment in research and development (R&D) and correct policies and strategies are still needed, for all stages of the biofuels value chain, from raw materials production to delivery and final consumption. Among the various possibilities currently being investigated and implemented at pilot scale or even at industrial scale concerning potential feedstocks, the more interesting ones are microalgae. Besides their cultivation is not directly linked to human consumption, they have low space requirements for its production.
This review focuses its attention on microalgae and how they can be used for biodiesel production. Questions associated with production and processing of microalgae are considered in detail, not only those directly related with biofuels production but also the possibilities of combining it with pollution control, in particular with biological sequestration of CO2 emissions and other greenhouse gases, or wastewater treatment. This work starts by describing which microalgae are normally used for the production of biofuels and their main advantages when compared with other available feedstocks. Then, the current status of biodiesel production from microalgae, concerning their growth, harvest, and processing is reviewed. Other potential applications and how to combine them with biodiesel production are also described.
Section snippets
What are microalgae?
Microalgae are prokaryotic or eukaryotic photosynthetic microorganisms that can grow rapidly and live in harsh conditions due to their unicellular or simple multicellular structure. Examples of prokaryotic microorganisms are Cyanobacteria (Cyanophyceae) and eukaryotic microalgae are for example green algae (Chlorophyta) and diatoms (Bacillariophyta) [14], [15]. A more in depth description of microalgae is presented by Richmond [16].
Microalgae are present in all existing earth ecosystems, not
Environmental applications
Production of biodiesel and other bio-products from microalgae can be more environmentally sustainable, cost-effective and profitable, if combined with processes such as wastewater and flue gas treatments. In fact various studies demonstrated the use of microalgae for production of valuable products combined with environmental applications [107], [108], [109], [110], [111].
Conclusions
Current efforts and business investment are driving attention and marketing efforts on the promises of producing algal biodiesel and superior production systems.
A large number of companies are claiming that they are at the forefront of the technology and will be producing algal biodiesel economically within the next few years. However most of these companies have limited technical expertise and few have actually made biodiesel from algae.
Producing algal biodiesel requires large-scale
References (129)
Biodiesel as an alternative motor fuel: production and policies in the European Union
Renewable and Sustainable Energy Reviews
(2008)- et al.
Batch kinetics of nitrogen and phosphorus removal from synthetic wastewater by algae
Ecological Engineering
(2006) - et al.
The gross chemical composition and fatty acid composition of 18 species of tropical Australian microalgae for possible use in mariculture
Aquaculture
(1999) Biodiesel from microalgae
Biotechnology Advances
(2007)- et al.
A green light for engineered algae: redirecting metabolism to fuel a biotechnology revolution
Current Opinion in Biotechnology
(2008) - et al.
Commercial applications of microalgae
Journal of Bioscience and Bioengineering
(2006) - et al.
Lipid accumulation and CO2 utilization of Nannochloropsis oculata in response to CO2 aeration
Bioresource Technology
(2009) Progress and recent trends in biodiesel fuels
Energy Conversion and Management
(2009)- et al.
Increase in Chlorella strains calorific values when grown in low nitrogen medium
Enzyme and Microbial Technology
(2000) - et al.
Biodiesel production from heterotrophic microalgal oil
Bioresource Technology
(2006)
Biological CO2 fixation and utilization project
Energy Conversion and Management
Pyrolitic characteristics of microalgae as renewable energy source determined by thermogravimetric analysis
Bioresource Technology
Possibility of renewable energy production and CO2 mitigation by thermochemical liquefaction of microalgae
Biomass and Bioenergy
Growth of microalgae with increased calorific values in a tubular bioreactor
Biomass and Bioenergy
Photobioreactors for mass cultivation of algae
Bioresource Technology
Carbon cycle for rapeseed oil biodiesel fuels
Biomass and Bioenergy
Biogenic greenhouse gas emissions linked to the life cycles of biodiesel derived from European rapeseed and Brazilian soybeans
Journal of Cleaner Production
Agronomic evaluation of camelina genotypes selected for seed quality characteristics
Industrial Crops and Products
Transgenics are imperative for biofuel crops
Plant Science
Effect of iron on growth and lipid accumulation in Chlorella vulgaris
Bioresource Technology
Improved extraction of vegetable oils under high-intensity ultrasound and/or microwaves
Ultrasonics Sonochemistry
Reactivity of triglycerides and fatty acids of rapeseed oil in supercritical alcohols
Bioresource Technology
Microwave assisted transesterification of rapeseed oil
Fuel
Cavitational reactors for process intensification of chemical processing applications: a critical review
Chemical Engineering and Processing
A review of applications of cavitation in biochemical engineering/biotechnology
Biochemical Engineering Journal
Ocean storage of CO2. IEA greenhouse gas R&D programme
Forecasting production from discovery
Renewables-based technology: sustainability assessment
Transport revolutions: moving people and freight without oil
Impact on agricultural land resources of biofuels production and use in the European Union
Biodiesel production from various feedstocks and their effects on the fuel properties
Journal of Industrial Microbiology and Biotechnology
How sustainable are biofuels for transportation?
Effects of nitrogen sources on cell growth and lipid production of Neochloris oleoabundans
Applied Microbiology and Biotechnology
Biofuels from microalgae
Biotechnology Progress
Handbook of microalgal culture: biotechnology and applied phycology
Fatty acids composition of 10 microalgal species
Songklanakarin Journal of Science and Technology
Biodiesel fuel production from algae as renewable energy
American Journal of Biochemistry and Biotechnology
Microalgal triacylglycerols as feedstocks for biofuels production: perspectives and advances
The Plant Journal
Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor
Biotechnology and Bioengineering
Second generation biofuels: high-efficiency microalgae for biodiesel production
Bioenergy Research
Liquid fuel production using microalgae
Journal of the Japan Petroleum Institute
CO2 bio-mitigation using microalgae
Applied Microbiology and Biotechnology
Cited by (4444)
Effects of a range of effective inclusion levels of Asparagopsis armata steeped in oil on enteric methane emissions of dairy cows
2024, Animal Feed Science and TechnologySuperstructure optimization of microalgae pretreatment for direct combustion or gasification
2024, Chemical Engineering Research and DesignSustainable valorization of macroalgae residual biomass, optimization of pyrolysis parameters and life cycle assessment
2024, Science of the Total EnvironmentEvaluation of fuel properties for possible biodiesel output based on the fatty acid composition of oleaginous plants and microalgae
2024, Science of the Total Environment
- 1
LEPAE – Laboratory for Process, Environmental and Energy Engineering.
- 2
CEFT – Center for Transport Phenomena Studies.