News and Trends

An international team of scientists from Taiwan (National Chiayi University) and the United States (Pacific Northwest National Laboratory and Washington State University) report the development of transgenic rice plants which can express high levels of a cellulolytic enzyme in its biomass, without severely impairing plant growth and development. Cellulolytic enzymes (or cellulases) are commonly used to convert cellulose molecules in pretreated plant biomass into fermentable sugars which can be further processed to produce biofuel ethanol. "The cellulose hydrolytic enzyme, β-1, 4-endoglucanase (E1) gene, from the thermophilic bacterium Acidothermus cellulolyticus,was overexpressed in rice through Agrobacterium-mediated transformation".

The researchers were able to obtain 52 transgenic plants from six independent lines which express the enzymes at high levels, without serious negative effects on plant development. Some transgenic plants, however had "shorter stature and flowered earlier than the wild type". The enzyme was also shown to be thermostable,with high substrate specificity for cellulose, and can be easily purified by simple heat treatment. When the transgenic rice straw was cultured with cow gastric fluid for one hour at 39oC (and another hour at 81 oC), it was hydrolysed more easily compared to the wild type rice straw, producing 43% more reducing sugars. The results of the study suggest that the transgenic rice plant can be used as a "multi-functional plant", where the grains can serve as food, and the biomass can be used as an effective bioenergy feedstock, or as an industrial source of cellulases. The full study is published in the open-access journal, Biotechnology for Biofuels (URL above).;jsessionid=137BFD74F3E468D008A3A16A8FA1364A

Scientists from different research institutions in the United States (including the Lawrence Berkeley National Lab, Joint Genome Institute (United States Department of Energy, DOE), Joint BioEnergy Institute and the University of California, Berkeley) report the use of "lignin-baited ‘bio-traps', to investigate the microbes and enzymes responsible for lignin decomposition in Puerto Rico tropical forest soils." Exploration of microbial diversity with lignin-degrading capability in these soils may eventually lead to the discovery of new enzymes which can effectively be harnessed for biofuel production applications, particularly for biomass delignification during pretreatment.

One of the interesting features of forest soils in Puerto Rico is the fluctuating anoxic and redox conditions; this might suggest the presence of unique microbial lignin-degraders with lignin-degradation mechanisms that are different from "known fungal decomposers and oxygen-dependent enzyme activities". Results showed that "lignin-amended beads [in the biotraps] have higher relative abundances of representatives from the phyla Actinobacteria, Firmicutes, Acidobacteriaand Proteobacteria, compared to unamended beads. The scientists inferred that bacteria could play a role in anaerobic lignin decomposition in low and fluctuating redox soils. The full paper is published in the open access journal, PLoS ONE (URL above).

Energy Crops and Feedstocks for Biofuels Production

In order to reduce the pretreatment cost of lignocellulosic biomass for biofuel ethanol production, the use of low-lignin feedstocks is one of the strategies being considered. Pretreatment is usually the first step in the bioethanol conversion process, which essentially deconstructs the plant cell biomass, prior to ethanol production. It is often an energy intensive step,contributing significantly to the cost of production.

Brazil is one of the leaders in biofuel ethanol production from sugarcane juice. It has initiated its own plant breeding programs for the development of low-lignin sugarcane, in an effort to utilize the sugarcane bagasse residues as a secondary bioenergy feedstock after the ethanol-processing of the juice. Low-lignin sugarcane bagasse residues are seen to lower the cost of pretreatment. Researchers from the Universidade de São Paulo and the Universidade Federal de Viçosa (Brazil) report the characteristics of 11 experimental, low-lignin sugarcane hybrids (and two reference samples), in terms of chemical composition, agronomic characteristics and enzyme digestibility.

The lignin contents of the hybrids and reference samples ranged from 17% to 24%, corresponding to glucan(glucose-based carbohydrate) content between 38% and 43%. Some experimental sugarcane hybrids possessed high biomass and high sucrose contents with low lignin, but samples with the smallest amounts of lignin did not necessarily produce the largest amounts of total polysaccharides. "A variable increase in the mass of a number of components, including extractives, seemed to compensate for the reduction in lignin content". The plants with lower lignin content were found to require less delignification inputs to achieve higher conversion of cellulose to simple sugars during enzymatic treatment. The full study is published in the open access journal, Biotechnology for Biofuels (URL above).

Biofuels Processing

Researchers from the Universidade de São Paulo (Brazil) report the results of both morphological and chemical-composition changes in sugarcane bagasse after a two-step sequential pretreatment involving the addition of acid and alkali. Pretreatment is usually the first step in the production of biofuel ethanol from lignocellulosic biomass. The process "deconstructs" the plant cell wall structures of the biomass, so that these can be more easily converted to fermentable sugars for ethanol production.

The study is one of only a few investigations which determine the changes in both morphology and chemical composition of lignocellulosic biomass after pretreatment. The purpose of the first stage acid treatment (using 1% dilute sulfuric acid at 121 oC, for 40 minutes) was to remove the hemicellulose component in the biomass. The second stage alkali treatment at different concentrations of sodium hydroxide (NaOH) (also at 121 oC, for 40 minutes) was to remove the lignin component. The residue after the sequential treatment is the cellulose-rich component of the biomass which can be easily converted (i.e. hydrolysed or saccharified) into ethanol-fermentable sugars.

Results showed that about 96% of the hemicellulose was removed by acid treatment, while 85% of lignin was removed at alkali (NaOH) concentrations of 1% or higher. The cellulose yield under these conditions was 72%. The researchers concluded that the improvement in cellulose conversion (into ethanol-fermentable sugars) was mainly due to delignification. The removal of lignin by the two-step pretreatment method was attributed to: (1) "loss of cohesion between adjacent cell walls that were initially joined by lignin", and (2) destruction inside the cell wall (such as formation of voids) which exposes more cellulose to enzymatic attack. The full study is published in the open-access journal, Biotechnology for Biofuels (URL above).

Acid treatment is a common and non-expensive method for the pretreatment of lignocellulosic biomass for biofuel ethanol production. One of the possible effects of acid pretreatment, however, is the formation of compounds which might be inhibitory to ethanol fermenting microorganisms. The dehydration of hexose and pentose sugars in the biomass after acid pretreatment can lead to the formation of a class of inhibitory compounds called, furans: (1) furfural from dehydration of pentose sugars, and (2) hydroxymethyl furfural (HMF) from dehydration of hexose sugars. Further degradation of furfurals may produce organic acids, which are also known to inhibit ethanol fermentation.

Researchers from the Southern Regional Research Center of the United States Department of Agriculture (USDA), Agricultural Research Service (ARS) report the removal of furans through the use of ‘activated biochar". The activated biochar was obtained from the pyrolysis (air-free heating) and subsequent chemical activation of agricultural residues, such as cotton seed hull, flax shive and cotton gin waste. The chars were tested on model solutions containing furural and HMF.

Results showed that phosphoric-acid-activated biochars and steam-activated biochars from cotton/linen production residues could adsorb furfural and HMF, with steam-activated biochars giving the best results. The addition of 2.5% biochar to a sugar solution containing 1 g per liter of either furfural of HMF, could achieve a 99% furan removal efficiency. The full paper is published in the journal, Bioresources (URL above).

Biodiesel is essentially a mixture of compounds known as "methyl esters"and it is usually produced by the acid- or base-catalyzed reaction between methanol and plant oil. This reaction is often referred to as the "transesterification" reaction. "Homogeneous" acid or alkaline solutions which are conventionally used as catalysts in the transesterification reaction, are known to create problems, among which are: (1) difficulty in separation of the catalysts, (2) corrosion of the reactor, (3) sulfur contamination in the biodiesel, and (4) formation of soap.

The use of solid catalysis in a "heterogeneous" reaction system is said to offer the advantage of easier product separation compared to the use of homogeneous catalysts. Solid catalysts are also reported to have comparable catalytic performance with homogeneous catalysts, and produce lesser pollutants. Scientists from the Universiti Kebangsaan Malaysia, and the Chinese Academy of Sciences, report the use of a solid acid catalyst derived from lignin, for the transesterification of high-acid-value jatropha oil. High-acid-value plant oils contain large amounts of fatty acids, and this generally requires an acid esterification reaction for biodiesel production.

The solid catalyst was prepared by subjecting the lignin to phosphoric acid treatment, followed by pyrolysis (oxygen-free heating) at 400 oC to produce a solid char, and then sulfonation by concentrated sulfuric acid.

When the solid catalyst was tested for the transesterification of oleic acid, a 96.1% conversion efficiency was obtained. No deactivation was observed when the catalyst was reused three times. When tested on the one-step transesterification of crude jatropha oil with a high acid value, 96.3% biodiesel yield was obtained. The full study is published in the open access journal, Biotechnology for Biofuels (URL above).

Biofuels Policy and Economics

A recent report by the National Centre for Biorenewable Energy, Fuels and Materials (United Kingdom) suggests that "the UK needs significant investment in a new generation of biofuels to meet its renewable transport targets." Under the Renewable Energy Directive (RED),the UK has a 10% legally binding renewable energy target. Under the Fuel Quality Directive (FQD), a fuel/energy supplier for land-based transport and non-road mobile machinery is also required to reduce lifecycle greenhouse gas (GHG) emissions by a minimum of 6% per unit of energy.

The report says that new biomass processing technologies, like gasification and pyrolysis, "allow biofuels to be made from a wide range of sustainable materials." Some of these technologies are beginning to "unlock their huge potential", as the transition from laboratory to pilot/commercial application proceeds. Under favorable conditions and strong policy support, advanced biofuels are projected to meet 4.3% of the UK's renewable transport target by 2020. The biomass requirement is estimated to be 1 million tonnes of woody biomass, 4.4 million tonnes of household, commercial/industrial wastes, and 2 million tonnes of wheat (for biobutanol). A summary of the report is available at the NNFCC website (URL above).