First-generation biofuels, bioethanol and biodiesel, that are currently refined on an industrial scale, are fuels derived from plant matter and plant oils.
Critics of these first-generation fuels say that a scale of production large enough to supply the required biomass to refine such fuels will encroach on farmland and will bring about only a small reduction in greenhouse-gas emissions.
Another issue currently under consideration is the increasing pressure that fuel crops required for current biofuel refining pro-cesses may place on the world’s food supply.
The World Bank has published several studies in support of claims that biofuel production is driving food prices higher. However, there is also evidence that such claims may be exaggerated and that market forces prevalent in a contracting economic cycle are to blame for food price increases instead.
The increases in the oil price in the last year highlighted the contemporary world’s dependence on crude oil. At its peak of $147/bl, a near 50% price increase, there was not a noticeable decline in its consumption. Economies need energy.
Brazil recognised many years ago that a dependence on crude oil was not favourable in the future. It has been refining bioethanol from sugar cane since the 1960s.
In the past decade, the rest of the world has also been investi- gating alternatives to crude oil. The fact that the Organisation of Petroleum Exporting Countries is considering cutting crude oil supply to maintain new higher price levels of crude oil is quickening the pace at which the application of biofuel technologies is occurring.
A significant concern about first-generation biofuels is their sustainability. Not all biofuel production practices are benefiting climate change, said Citizens United for Renewable Energy and Sustainability Southern African coordinator Annie Sugrue, speaking at the conference.
Regarding farming practices, she said that if large areas of natural vegetation were cleared to make way for fuel crops, a large amount of carbon and carbon dioxide (CO2) might be released into the atmosphere, which might take up to 45 years to naturally sequestrate.
Fossil fuels, pesticides and water redistri- bution used in growing a fuel crop contribute to the overall emissions of a crop-based fuel and its effect on the environment, Sugrue added.
Fertiliser has also been found to contribute to greenhouse-gas emissions. Its use in commercial farming has been linked with the expanding dead zone in the Gulf of Mexico, where streams and rivers that drain 40% of the continental US’s farms, fields and feed lots empty into the Mississippi river.
This nitrate- and phosphate-rich fresh water flows into the Mexican Gulf and floats above the saltwater, preventing oxygen from penetrating down to the deeper water, which prevents it from supporting life.
The crops currently used for producing first-generation biofuels include sugar cane, sugar beet, maize or corn, sorghum and wheat.
A concern with these fuel crops is the low energy yield of the refined biofuel when compared with the amount of energy that is required to refine the biofuels in the first place.
Biodiesel Production from Microalgae
Second-generation biofuels can be extracted from microalgae and other microbial sources, lignocellulosic biomass, rice straw and bioethers.
Algae has been identified because many algal strains are exceedingly rich in oil, or lipids, which can be converted into biodiesel.
Algal strains with lipid contents of 40% or more must be used in the refining process to make it competitive commercially, says Council for Scientific and Industrial Research Biosciences Bio Process Development Group senior scientist Dheepak Maharajh.
The production of microalgal biodiesel requires large quantities of algal biomass. Maharajh says that an algal strain that has a high lipid content but grows slowly and produces little biomass will provide little extractable amounts of lipids. Therefore, his team is searching for an algal strain with high lipid content and a high biomass content.
Microalgae are miniature biochemical factories that are more photosynthetically efficient than terrestrial plants and are efficient absorbers of CO2 and thus can be used to reduce emissions of greenhouse gases. One half of the dry weight of microalgal biomass is carbon, which is typically derived from CO2. Producing 1 kg of algal biomass requires 1,6 kg to 1,8 kg of CO2.
The fact that they can be grown in marine water means that it is possible that no arable land would be required to grow the necessary biomass.
Most strains of algae require light for their growth and, in the production of biomass, most are grown in open ponds or photo-bioreactors. Open-pond cultures are more economical; however, they use land, require large amounts of water and require appropriate climatic conditions.
Photobioreactors offer a closed culture environment, which is relatively safe from invading microorganisms, where temperatures can be controlled and where a fixed CO2 concentration is bubbled through the culture medium. However, infrastructure costs make this technology more expensive. An ideal biomass production system should use the freely available sunlight.
A problem associated with algal biomass is its relatively high water content, which requires energy-intensive methods to remove and to increase the overall energy density of the algae, making it less economically attractive. However, if direct hydrothermal liquefaction can be employed to convert the wet biomass to fuel without having to reduce the water content, then such costs can be avoided.
Direct hydrothermal liquefaction mimics the natural geological processes involved in the formation of fossil fuel, performed in mere hours or even minutes.
However, further research needs to be conducted before one technique can be deemed more effective than the other.
Biofuel Production from Lignocellulose
Van Zyl and his team, working under the South African National Energy Research Institute’s Chair of Energy Research: Biofuels and other clean alternative fuels (CoER) has been investigating methods of liberating the energy held within lignocellulose.
Lignocellulose comes from woody plant biomass. It is the most widespread source of carbon in nature and is considered to be the only source that could potentially provide an adequate amount of feedstock to satisfy the world’s bioenergy and chemical needs in a renewable manner, according to Van Zyl.
However, current lignocellulose-to-bio-ethanol processes are not deemed economical without government subsidies.
The CoER is developing yeast strains that can produce a cocktail of cellulase and hemicellulase enzymes (enzymes that catalyze the hydrolysis of cellulose and hemicellulose), required for lignocellulosic hydrolysis. Its aim is to develop the yeast strains to be able to directly convert pretreated lignocellulose into ethanol and other fermentation products in a single-step process called consolidated bioprocessing.
Lignocellulosic material comprises cellulose, hemicellulose and lignin. Cellulose and hemicellulose are polymers of ferment-able sugars. They are put through a process of hydrolysis to convert them into sugars which are used in fermentation processes, which can ultimately be refined into bioethanol.
They can also be treated thermochemically through gasification, combustion or pyrolysis to create high-value energy or chemical products.
Van Zyl’s view is that for a refinery using such technologies to be economically viable, different processing technologies will need to be integrated into a single production plant. Whether starch, sugar, lignocellulose or vegetable oil is to be included in the plant’s processes will be based on local industry conditions and the region in which the plant will be built.
The future of biorefineries for fuels and chemicals requires a design that can convert a variety of feedstocks and substrates into a range of products.
Besides the development of second- generation technologies, Van Zyl recom- mends the development of life-cycle analysis, environmental sustainability studies and economic modelling to place biofuels pro-duction in a position to overcome the concerns raised against first-generation technologies.