Analysis of Straw

Six conceptual process scenarios for the production of biobutanol from lignocellulosic biomass through acetone?butanol?ethanol (ABE) fermentation, using reported data on process performances, were developed with ASPEN Plus® V8.2 software. The six scenarios covered three fermentation strategies, i.e. batch separate hydrolysis and fermentation (SHF), continuous SHF, and batch simultaneous saccharification and fermentation (SSF) integrated with gas stripping (GS). The two downstream processing options considered were double?effect distillation (DD) and liquid?liquid extraction and distillation (LLE&D). It was found that the SSF?GS/DD scenario was the most energy efficient with a liquid fuel efficiency of 24% and an overall efficiency of 31%. This was also the scenario with the best economic outcome, with an internal rate of return (IRR) of 15% and net present value (NPV) of US$387 million. The SSF?GS/DD scenario was compared to a similar molasses process, based on the product flow rates, and it was found that the molasses process was more energy efficient with a gross energy value (GEV) of 23?MJ?kg1 butanol compared to ?117?MJ?kg1 butanol for the lignocellulosic process. In addition, the molasses?based process was more profitable with an IRR of 36% compared to 21%. However, the energy requirements for the molasses process were supplied from fossil fuels, whereas for the lignocellulose processes a portion of the feedstock was diverted to provide process energy. Improved environmental performance is therefore associated with the lignocellulosic process.

Next-generation biofuels from renewable sources have gained interest among research investigators, industrialists, and governments due to major concerns on the volatility of oil prices, climate change, and depletion of oil reserves. Biobutanol has drawn signicant attention as an alternative transportation fuel due to its superior fuel properties over ethanol. e advantages of butanol are its high energy content, better blending with gasoline, less hydroscopic nature, lower volatility, direct use in convention engines, low corrosiveness, etc. Butanol production through (acetone, butanol, and ethanol) ABE fermentation is a well-established process, but it has several drawbacks like feedstock cost, strain degeneration, product toxicity, and low product concentrations. Lignocellulosic biomass is considered as the most abundant, renewable, low-cost feedstock for biofuels. Production of butanol from lignocellulosic biomass is more complicated due to the recalcitrance of feedstock and inhibitors generated during the pretreatment and hydrolysis process. Advanced fermentation and product recovery techniques are being researched to make biobutanol industrially viable.

Clostridium sporogenes BE01, a non-acetone forming butanol producer, can produce hydrogen and volatile fatty acids (VFAs) during butanol fermentation from rice straw hydrolysate. Bio-electrochemical analysis revealed the changes that occurred in the redox microenvironment and electron transport mediators during fermentation at different pH and CaCO3 concentrations. CaCO3 played a very important role in enhancing the production of hydrogen, volatile fatty acids and solvents by stimulating the changes in the electron transport system. The electron transport system mediated by NAD/NADH, flavins, Fe–S clusters, protein bound FAD, and cytochrome complex in C. sporogenes BE01 was analysed by cyclic voltammetry (CV). Electrokinetic analysis revealed that the favorability for redox reactions increased with an increase in pH, and the polarization resistance reduced significantly with CaCO3 supplementation.

Growth inhibition kinetics of a novel non-acetone forming butanol producer, Clostridium sporogenes BE01, was studied under varying concentrations of acetic and formic acids in rice straw hydrolysate medium. Both the organic acids were considered as inhibitors as they could inhibit the growth of the bacterium, and the inhibition constants were determined to be 1.6 and 0.76 g/L, respectively, for acetic acid and formic acid. Amberlite resins—XAD 4, XAD 7, XAD 16, and an anion exchange resin—Seralite 400 were tested for the efficient removal of these acidic inhibitors along with minimal adsorption of sugars and essential minerals present in the hydrolysate. Seralite 400 was an efficient adsorbent of acids, with minimal affinity towards minerals and sugars. Butanol production was evaluated to emphasize the effect of minerals loss and acids removal by the resins during detoxification.

Biobutanol from lignocellulosic biomass has gained much attention due to several advantages over bioethanol. Though microbial production of butanol through ABE fermentation is an established technology, the use of lignocellulosic biomass as feedstock presents several challenges. In the present study, biobutanol production from enzymatic hydrolysate of acid pretreated rice straw was evaluated using Clostridium sporogenes BE01. This strain gave a butanol yield of 3.43 g/l and a total solvent yield of 5.32 g/l in rice straw hydrolysate supplemented with calcium carbonate and yeast extract. Hydrolysate was analyzed for the level of inhibitors such as acetic acid, formic acid and furfurals which affect the growth of the organism and in turn ABE fermentation. Methods for preconditioning the hydrolysate to remove toxic end products were done so as to improve the fermentation efficiency. Conditions of ABE fermentation were fine tuned resulting in an enhanced biobutanol reaching 5.52 g/l.

Biobutanol from lignocellulosic biomass has gained much attention due to several advantages over bioethanol. Though microbial production of butanol through ABE fermentation is an established technology, the use of lignocellulosic biomass as feedstock presents several challenges. In the present study, biobutanol production from enzymatic hydrolysate of acid pretreated rice straw was evaluated using Clostridium sporogenes BE01. This strain gave a butanol yield of 3.43 g/l and a total solvent yield of 5.32 g/l in rice straw hydrolysate supplemented with calcium carbonate and yeast extract. Hydrolysate was analyzed for the level of inhibitors such as acetic acid, formic acid and furfurals which affect the growth of the organism and in turn ABE fermentation. Methods for preconditioning the hydrolysate to remove toxic end products were done so as to improve the fermentation efficiency. Conditions of ABE fermentation were fine tuned resulting in an enhanced biobutanol reaching 5.52 g/l.

This document is the result of the evaluation of biomass feedstocks, from Europe and Latin America, that took place as part of the DIBANET project. That project is co-financed from the 7 th Framework Programme for Research and Technological Demonstration of the European Union. (Title: Enhancing international cooperation between the EU and Latin America in the field of biofuels; Grant Agreement No: 227248-2).

The work in Task 2.1 of Work Package 2 (WP2) at DIBANET partners UL, CTC, and UNICAMP involved evaluating, on a number of levels, potential feedstocks for utilisation in the DIBANET acid-hydrolysis process (WP3). In the early stage of the project a wide number of feedstocks were examined and relevant secondary compositional data were sought from the literature. Selected feedstocks were analysed at the laboratories of UL, CTC, and UNICAMP and, from these, a limited number of feedstocks were subjected to more in-depth analysis/evaluation.

Work at UL focused on Miscanthus, cereal straws, and waste papers. The wet-chemical and spectroscopic analysis that was carried out on a wide number of Miscanthus samples have allowed for in-depth understandings to be reached regarding the changes in lignocellulosic composition, and potential biomass/biofuel yields that could be realised over the harvest window. Straws present much less chemical variation but have enough structural carbohydrates to warrant their processing in the DIBANET technology. Waste papers can have amongst the highest total carbohydrate contents of any of the feedstocks studied.

Work at CTC focused on the residues of the sugarcane industry - sugarcane bagasse and sugarcane trash (field residues from harvesting). A large number of samples were collected from a variety of sugar mills and plantations. It has been seen that there can be a significant variation in the composition of different bagasse samples, particularly with regards to the ash content. Sugarcane trash has lower total carbohydrates contents than bagasse but is still a suitable feedstock for DIBANET.

Work at UNICAMP focused on the evaluation of residues from the banana, coffee, and coconut industries. It was found that these also have potential for utilisation in the DIBANET process, however the value of the residues for this end-use is dependent on which part of the plant is utilised. For instance, coffee husks have sufficient structural carbohydrates to allow for decent yields of levulinic acid, formic acid, and furfural in DIBANET, however the leaves of the coffee plant do not. Leaves from the banana plant are also of less value for DIBANET than the other parts of the plant (e.g. stem).

A major output of this Deliverable is the downloadable electronic database that contains all of the WP2 analytical data obtained during the course of the project. It contains analytical data and predicted biorefining yields for a total of 1,281 samples. It can be obtained, free of charge, from the DIBANET website and will be a valuable tool for stakeholders in biorefining projects.

This document presents the data and evaluations that were made regarding biomass feedstocks, and also puts forward guidelines of best practice in terms of making the best use of these resources. A shortened version of this document can also be downloaded from the DIBANET website.

The processing of lignocellulosic materials in modern biorefineries will allow for the production of transport fuels and platform chemicals that could replace petroleum-derived products. However, there is a critical lack of relevant detailed compositional information regarding feedstocks relevant to Ireland and Irish conditions. This research has involved the collection, preparation, and the analysis, with a high level of precision and accuracy, of a large number of biomass samples from the waste and agricultural sectors. Not all of the waste materials analysed are considered suitable for biorefining; for example the total sugar contents of spent mushroom composts are too low. However, the waste paper/cardboard that is currently exported from Ireland has a chemical composition that could result in high biorefinery yields and so could make a significant contribution to Ireland’s biofuel demands.

Miscanthus was focussed on as a major agricultural feedstock. A large number of plants have been sampled over the course of the harvest window (October to April) from several sites. These have been separated into their anatomical fractions and analysed. This has allowed observations to be made regarding the compositional trends observed within plants, between plants, and between harvest dates. Projections are made regarding the extents to which potential chemical yields may vary. For the DIBANET hydrolysis process that is being developed at the University of Limerick, per hectare yields of levulinic acid from Miscanthus could be 20% greater when harvested early compared with a late harvest.

The wet-chemical analysis of biomass is time-consuming. Near infrared spectroscopy (NIRS) has been developed as a rapid primary analytical tool with separate quantitative models developed for the important constituents of Miscanthus, peat, and (Australian) sugarcane bagasse. The work has demonstrated that accurate models are possible, not only for dry homogenous samples, but also for wet heterogeneous samples. For glucose (cellulose) the root mean square error of prediction (RMSEP) for wet samples is 1.24% and the R2 for the validation set ( ) is 0.931. High accuracies are even possible for minor analytes; e.g. for the rhamnose content of wet Miscanthus samples the RMSEP is 0.03% and the is 0.845. Accurate models have also been developed for pre-treated Miscanthus samples and are discussed. In addition, qualitative models have been developed. These allow for samples to be discriminated for on the basis of plant fraction, plant variety (giganteus/non-giganteus), harvest-period (early/late), and stand-age (one-year/older).

Quantitative NIRS models have also been developed for peat, although the heterogeneity of this feedstock means that the accuracies tend to be lower than for Miscanthus. The development of models for sugarcane bagasse has been hindered, in some cases, by the limited chemical variability between the samples in the calibration set. Good models are possible for the glucose and total sugars content, but the accuracy of other models is poorer. NIRS spectra of Brazilian bagasse samples have been projected onto these models, and onto those developed for Miscanthus, and the Miscanthus models appear to provide a better fit than the Australian bagasse models.

Aspergillus niger NII-08121/MTCC 7956 exhibited differences in expression of ?-glucosidase (BGL) in response to carbon sources provided in the medium. Activity staining with methyl umbelliferyl ?-d-glucopyranoside (MUG) indicated that four different isoforms of BGL were expressed when A. niger was grown under submerged fermentation with either lactose or cellulose, whereas only two were expressed when wheat bran or rice straw was used as the carbon source. Among the four isoforms of BGL expressed during lactose supplementation, two were found to retain 92% and 82% activity respectively in presence of 250 mM glucose in the MUG assay. The major ?-glucosidase (BGL1) was purified to homogeneity by electro elution from a Native PAGE gel. The purified 120 kDa protein was active at 50 °C and was stable for 48 h without any loss of activity. The optimum pH and temperature were 4.8 and 70 °C respectively.

Rice straw is an attractive lignocellulosic material for bioethanol production since it is one of the most abundant renewable resources. It has several characteristics, such as high cellulose and hemicelluloses content that can be readily hydrolyzed into fermentable sugars. But there occur several challenges and limitations in the process of converting rice straw to ethanol. The presence of high ash and silica content in rice straw makes it an inferior feedstock for ethanol production. One of the major challenges in developing technology for bioethanol production from rice straw is selection of an appropriate pretreatment technique. The choice of pretreatment methods plays an important role to increase the efficiency of enzymatic saccharification thereby making the whole process economically viable. The present review discusses the available technologies for bioethanol production using rice straw.