And what are the advantages and disadvantages of each? The first attempts to produce a biologically-based fuel to replace mineral petrol and diesel, continued to look for derivatives of well-known agricultural products. There is a variety of vegetable oils, traditionally used in the kitchen, such as palm, sunflower or rapeseed oil.
These oils, chemically consisting of triglycerides, are being transesterified into diesel, using an alcohol such as methanol as coreactant and an acid or a base as catalyst Naik et al. Additionally, there are several agricultural products that are rich in carbohydrates due to a high starch content, such as corn, wheat, potato and cassava, or due to a high sugar content, such as sugar beet, sugar cane, fruit or palm juice Naik et al. Of course these are not the only plants that can be converted into fuel, but they are the most widely used and analyzed thus far Figure 1. Figure 1 Figure Detail This first generation of biofuels has had to face sharp criticisms.
The question stands whether all biofuel production is sustainable in the end, despite our best intentions. For the record — sustainability is a term that covers much more than "good for the environment ". Forming the basis for the Brundtland report "Our Common Future" , "sustainable development is a process of change in which the exploitation of resources, the direction of investments, the orientation of technological development, and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations.
Briefly, there is the economic component. Despite the already considerable efforts undertaken to grow our own fuel instead of digging for it, the net impact on the global market still remains quite low. In , for example, the USA derived around five billion gallons of ethanol from domestically grown maize, and Brazil used sugar cane for a comparable volume Herrera , Ruth There is clearly a long way to go. This production comes at the expense of large amounts of public funding. The most obvious answer is to find other crops that can sustain larger yields, and to grow these crops on a much larger scale.
There are also social concerns. Because edible plant parts grown on normal arable land are being converted into fuel, people became concerned that a larger investment in biofuel crops would form a considerable competition between fuel generation and food production for the same land, leading to a diminished area to feed the world population Fargione et al. This ethical debate has become known as the "food for fuel" debate Ajanovic However, expanding the existing areable area is not always an ecologically valid option.
To solve this problem, some have proposed turning grassland into palm plantations instead of tropical forests Corley Another intensely investigated option for the production of vegetable oil for fuel production, without disturbing food production, is the use of the tree Jatropha curcas family Euphorbiaceae Achten et al. Also, in terms of the food for fuel debate, the matter seems settled; clearly, this plant is of little use to feed humans, and the use of the oil for fuel production is not likely to disrupt food security.
However, the data are still not definitive enough to predict whether Jatropha meets the other sustainability demands, and under what conditions Achten et al. Figure 2 Figure Detail Lastly, there are also criticisms from an ecological perspective on the concept of biofuel use. The biggest criticism has always been that, so far, not a single biofuel has been able to be carbon neutral, despite this being one of the biggest promises made about biofuels Smith , Johnson Theoretically, carbon neutrality is possible.
During their life, plants take up a certain amount of CO 2 to grow and to produce biomass, and upon the harvesting and processing of this plant, the CO 2 is re-released in the atmosphere, ready to be taken up by a new plant Figure 2. This closes the carbon cycle, leading to a zero net emission of CO 2 , and thus a zero net contribution of biofuels to the greenhouse effect.
In practice, however, this relationship of carbon forms is more complex. As long as there is still a need for fossil fuels to power transport or harvesting machines, there will be a net CO 2 emission, due to the consumption of conventional fuels. Moreover, ecology teaches that when the fate of a piece of land is changed, so is the life of the microbes in the soil on that land. These micro-organisms are then likely to become more active and start generating extra amounts of CO 2 due to a heightened metabolism.
Is the effort to produce energy in a sustainable way always going to be thwarted by the consequences of non-sustainable energy use, due to increase in food prices and food security?
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Figure 3 Figure Detail To deal with the challenges for the first generation biofuels, scientists shifted the emphasis in their search for green energy towards a different type of plant-based solution — fast growing woody plants, produced in a CO 2 neutral fashion, designated the second generation bioenergy crops El Bassam In Western Europe, the brunt of the attention went to the so called short-rotation coppice crops, poplar Populus and willow Salix.
In Northern America and Europe, Elephant Grass Miscanthus x giganteus was considered to be a good candidate for the job. Asia, and to a certain extent South-America, are able to rely on a large variety of indigenous bamboo species. All these plants produce woody stems or culms, which in essence consist of lignocellulose, and can be harvested every year or every other year. As these plants need much less fertilizer than vegetable crops, they are less likely to exhaust the soil, and may be grown on marginal, previously unused land, to avoid the food for fuel debate altogether.
For example, eucalyptus trees can be cultured on soils with elevated salt concentrations where grain production is no longer possible — and while growing there, even help to restore more favorable conditions for future cereal production Wu et al. Another great source of lignocellulose comes from waste streams. These are wood processing wastes, the organic fraction of municipal wastes in general. Whatever the source is, lignocellulose serves as raw material in many different processes Figure 3. The cellulose and the hemicelluloses can be broken down enzymatically, yielding sugars that can be fermented to produce ethanol.
Depending on the source of the lignocelluloses agriculture or forestry , about to liters of ethanol can be produced out of a ton of raw material Oak Ridge National Laboratory , Mabee et al. The simplest of these is combustion: in the presence of large amounts of oxygen, the biomass is burned completely and converted into CO 2 and energy.
Combustion can be used to generate electricity in a power plant, where it can replace coal without a lot of technical intervention. The second technique is gasification. During gasification, the lignocellulose components are heated, while a tightly regulated, limited flow of oxygen is maintained, as the biomatter is broken down into syngas a mix of carbon monoxide and hydrogen gas, which can be used to synthesize diesel, ethanol, or many other chemicals.
It is in essence, a form of cracking the long carbon chains in the lignocelluloses into a fraction of very small molecules gaseous and hence usable as syngas or biogas , a fraction of molecules that stay liquid at room temperature the bio-oil or pyrolysis oil , and a charcoal fraction the largest molecules that stay behind in the reactor Bridgewater et al.
The gas can be burned in a gas power plant or can be used for synthesizing liquid fuels. The oil can be used directly for the production of biodiesel or hydrogen gas. And the charcoal can be burned further in a combustion plant. Might it be possible to drive a car fueled by wood? Before embarking on a discussion about the future of biofuels, we need to discuss the third generation of biofuel producers : algal cells nicknamed oilgae in the context of biofuel production.
In addition, microalgae are able to grow in places that other plants cannot abide, such as salt water — which, unlike fresh water, is something Earth has in abundance — or wastewater, another resource we have in abundance Searchinger et al. And on top of that, algae can be fed with waste gas streams loaded with CO 2 or even NO, providing us with an enormous opportunity to deal with these gases before they end up in the environment Brown , Chisti Lastly, algal oil can be treated like first and second generation biofuels, so all the investments made for dealing with these previous types of biofuel may indeed provide economic returns.
On the downside, algal technology is still in its infancy. Scientists all over the world are now trying to figure out how to handle and use them. The first generation of biofuels were classical sources of vegetable oil soybean, sunflower, palm or starch potatoes, cassava, wheat , grown on farms all over the world.
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More recently, sources of woody material the second generation of lignocellulose producers have been considered, and currently microalgae and their oil products are the more promising third generation. Each of these types of biofuel producers has its own advantages and obstacles: availability and readiness to be implemented on a large scale, and yield or sustainability. However, they all constitute a marked improvement over the use of fossil fuels as sustainable resources.
Plants will be able to help humankind's energy needs, but perhaps only with the redesign of our social and economic culture. This redesign will no longer be reliant on fossil fuels, but will be reliant on renewable, replenishable plant material. Whether we will use vegetable oil, short-rotation wood, or algal biomass, plants will be a necessary component in different large scale industrial processes.
One might even say that the past was oily brown, but the future is phytotechnical green.
Promising Biofuel Resources: Lignocellulose and Algae
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Chapter 3 introduces selected algal biofuel production systems as examples to illustrate challenges and sustainability concerns of algal biofuel production and possible tradeoffs among sustainability goals. Chapters 4 and 5 discuss potential concerns related to resource use for example, availability of land, water, and nutrient resources and environmental effects and how some of those concerns might affect social acceptability of algal biofuels, respectively.
For each category of resource use and environmental effect, indicators and metrics to be employed and data to be collected to assess sustainability are suggested. Chapter 6 summarizes the sustainability challenges for each of the selected algal biofuel production systems introduced in Chapter 3 and uses them to illustrate benefits and tradeoffs of each system. Azapagic, A. Indicators of sustainable development for industry: A general framework. Process Safety and Environmental Protection 78 4 Baumann, H.
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Towards a global criteria based framework for the sustainability assessment of bioethanol supply chains. Application to the Swiss dilemma: Is local produced bioethanol more sustainable than bioethanol imported from Brazil? Ecological Indicators Craggs, R. Heubeck, T. Algal biofuels from wastewater treatment high rate algal ponds. Water Science and Technology 63 4 Craig, P. Gadgil, and J. What can history teach us? A retrospective examination of long-term energy forecasts for the United States.
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Ecological indicators: Between the two fires of science and policy. Ecological Indicators 7 2 United Nations. Accessed August 21, Division for Sustainable Development. Junginger, A. Faaij, I. Best, and U. Overview of recent developments in sustainable biomass certification. Biomass and Bioenergy 32 8 Williams, E. Weber, and T. Hybrid approach to managing uncertainty in life cycle inventories. Journal of Industrial Ecology 15 6 Williams, P. Microalgae as biodiesel and biomass feedstocks: Review and analysis of the biochemistry, energetics and economics.
Energy and Environmental Science 3 5 Woertz, I. Feffer, T. Lundquist, and Y. Algae grown on dairy and municipal wastewater for simultaneous nutrient removal and lipid production for biofuel feedstock. Biofuels made from algae are gaining attention as a domestic source of renewable fuel.
However, with current technologies, scaling up production of algal biofuels to meet even 5 percent of U. Continued research and development could yield innovations to address these challenges, but determining if algal biofuel is a viable fuel alternative will involve comparing the environmental, economic and social impacts of algal biofuel production and use to those associated with petroleum-based fuels and other fuel sources. Sustainable Development of Algal Biofuels was produced at the request of the U. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.
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Page 13 Share Cite. BOX Statement of Task The committee is tasked to examine the promise of sustainable development of algal biofuels, identify potential concerns and unforeseen sustainability challenges and unintended consequences for a range of approaches to algal biofuel production, explore ways to address those challenges, and suggest appropriate indicators and metrics that can inform future assessments of environmental performance and social acceptance associated with sustainability.
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