• Energy Research

Significance Bioethanol produced from waste biomass from crops has the potential to provide a sustainable alternative to petroleum-based transportation fuel that does not compete with human food supply. The main obstacle to this approach is the resistance of this biomass to digestion. Thus, expensive energetic pretreatment and high enzyme inputs are needed to increase digestion. In this study, we screened a population of randomly mutated plants for digestibility with the aim of identifying novel factors that impact on this trait. We found a number of mutants with high digestibility and no impairments in growth or fitness. These mutants show a range of alterations in cell-wall composition, and we have mapped and characterized the mutant with the highest increase in digestibility.

Sudangrass, Sorghum sudanense (Piper) Stapf, is a vigorous forage crop that has also been used for biogas, paper, and electricity production. Due to the large biomass yields achieved by sudangrass and the large area of potential growth in Argentina seven sudangrass accessions from a collection of S. sudanense were analyzed to evaluate their potential as feedstocks for lignocellulosic bioethanol production, and to assess whether there is an association between the response to biotic and abiotic stresses and the composition of the biomass. The biomass composition was analyzed for major cell wall polymers, monosaccharides, and elemental composition. On average, 68% of stem lignocellulosic biomass was comprised of matrix polysaccharides and crystalline cellulose, representing a potential source of sugars for bioethanol production. Xylose was the predominant matrix polysaccharide monosaccharide comprising, on average, 45% of the total sugars, followed by arabinose, glucose, galactose, galacturonic acid, mannose, glucuronic acid, and fucose. Rhamnose was not detected in any of the biomasses analyzed. Silica was the most abundant element in sudangrass stem, followed by chloride, calcium, phosphorus and sulfur. We performed saccharification analyses after pretreatments. Alkaline pretreatment was more effective than water pretreatment. Sodium hydroxide pretreatment exposed different levels of recalcitrance among sudangrass accessions, whereas the water pretreatment did not. Phenological traits were also evaluated, showing significant variability among accessions. The comparison of major cell wall polymers and monosaccharide composition between tolerant and susceptible accessions to abiotic and biotic stresses suggests an association between the composition of the biomass and the response to stress.

The uptake of innovative technologies and practices in agriculture aimed at the valorisation of natural resources can be scant in Low and Middle Income Countries (LMICs). Integration of financial viability assessments with farmers and environmental evaluations can help to understand some aspects of the low uptakes of innovations. Using the case study of Cocoa Pod Husk (CPH) valorisation in Indonesia, we provide insights into (i) a choice modelling method to assess the economic viability of CPH valorisation and (ii) an agronomic trial assessing the consequences on soil quality of diverting CPH from its role as a natural fertilizer. The economic viability assessment suggested that farmers require higher levels of compensation than might be expected to collect or process CPH (a small proportion of farmers would undertake all processing activities for 117 GBP/t CPH). The agronomic trial concluded that CPH plays only a minor role in the maintenance of soil phosphorus, calcium and magnesium, but it plays an important role for crop potassium. CPH removal would reduce the partial balances for carbon and nitrogen by 15.6% and 19.6%, respectively. Diversion of CPH from current practices should consider the long-term effects on soil quality, especially because it might create increased reliance on mineral fertilizers.

The sustainability of biorefineries can be improved through levoglucosenone production from residual sugars in waste lignin.

A proof-of-concept project compared extraction of arabinoxylans (AX) from sugarcane bagasse and wheat bran via alkaline hydrogen peroxide followed by enzyme-assisted extraction with combinations of feruloyl esterases and a xylanase. Bagasse contains comparable amounts of AX to wheat bran, but with a much lower arabinoxylan substitution on the xylan backbone (A:X ratio of around 0.2 compared with 0.6 for wheat bran), hence offering AX products with distinctive functionality and potential end uses. In the current work, bagasse released its AX more readily than wheat bran, and released a wider range of molecular weights. Use of feruloyl esterase and xylanase enzymes on their own or following alkaline peroxide extraction did not enhance AX release substantially; however, the xylanase appeared to be effective at reducing the size of AX molecules, and there is scope to optimise the effects of enzymes to produce specific AX product fractions. As bagasse frequently arises within the context of bioethanol production, integration of AX extraction with ethanol production could allow economic production of a portfolio of AX products, as has been demonstrated in principle for AX co-production in a wheat ethanol plant.

Senna reticulata is an Amazonian tree that quickly accumulates high biomass. It grows widely in the north of Brazil occupying degraded regions and is popularly known as “matapasto” (pasture-killer) due to its aggressive colonization strategy. When its aerial parts are harvested, S. reticulata recolonizes the pasture quickly recovering biomass production. In this work, we examined the potential of S. reticulata for bioenergy production in the Amazon region and the effect of a CO2 enriched atmosphere on its biomass composition. Nearly 50% of the biomass of the aerial parts is non-structural carbohydrates (NSC). Concerning structural carbohydrates, pectins (25% and 23%), hemicelluloses (11% and 16%), and cellulose (4% and 14%) contents were very similar in leaves and stems, respectively. Lignin varied considerably among organs, being 35% in roots, 7% in stems, and 10% in leaves. Although elevated CO2 did not change significantly cell wall pools, lignin content was reduced in leaves and roots. Furthermore, starch increased 31% in leaves under elevated CO2, which improved saccharification by 47%. We conclude that Senna reticulata is a suitable species for use as a bioenergy feedstock in the tropics and specifically for remote communities in the Amazonian region.

The recalcitrance of the cell wall to enzymatic hydrolysis represents one of the greatest challenges for using biomass to replace the petroleum as a feedstock for fuels and chemicals. Cell walls are complex in architecture and composition, posing a biochemical challenge for the development of efficient enzymes to release the sugars from the polysaccharide components. The complex composition of the polymers that constitute the cell wall requires a mixture of enzymes to hydrolyze the different glycosidic bonds present in biomass. The improvement of the properties of biomass, in turn, requires the screening of large populations of plants in order to identify markers associated with saccharification potential or pinpoint the genes that regulate recalcitrance. The improvement of both, enzymes and biomass together, requires the capacity to deal with large numbers of variables in a combinatorial approach. We have developed a high-throughput system that allows the determination of cellulolytic activity in a 96-well plate format by automatically handling biomass materials, carrying out hydrolytic reactions, and determining the release of reducing sugars. This platform consists of a purpose-made robot that grinds, formats, and dispenses precise amounts of solids into 96-well plates, and a liquid-handling station specifically designed to carry out pretreatments, hydrolysis, and the determination of released reducing sugar equivalents using a colorimetric assay. These modules can be used individually or in combination according to the function needed. Here we show some examples of the capabilities of the platforms in terms of enzyme and biomass evaluation, as well as combining the robot with off-line analytical tools.