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This paper discusses a property associated with plant biomass recalcitrance to enzyme and microbial deconstructions in sugar production from cellulose and hemicelluloses. The hemicelluloses are more readily hydrolyzed to sugars than is cellulose. As a result, optimization to maximize individual glucose and hemicellulose sugar recovery is not possible. This property is an inherent feature of plant biomass and is named polydispersity of plant biomass recalcitrance (PPBR) in this study. A set of pretreatment experiments using eucalyptus and sulfite pretreatment to overcome recalcitrance of lignocelluloses was conducted. The results were used to predict the conditions for individually maximizing enzymatic glucose and xylose yields. The predicted maximal yields were used to quantitatively illustrate the PPBR concept. The effect of PPBR on pretreatment optimization and strategies for maximal sugar recovery using two-stage pretreatment are discussed.

The production of ethanol for the energy market has traditionally been from corn and sugar cane biomass. The use of such biomass as energy feedstocks has recently been criticised as ill-fated due to competitive threat against food supplies. At the same time, ethanol production from cellulosic biomass is becoming increasingly popular. In this paper, we analyse rice husk (RH) as a cellulosic feedstock for ethanol biofuel production on the ground of its abundance. The global potential production of bioethanol from RH is estimated herein and found to be in the order of 20.9 to 24.3 GL per annum, potentially satisfying around one fifth of the global ethanol biofuel demand for a 10% gasohol fuel blend. Furthermore, we show that this is especially advantageous for Asia, in particular, India and China, where economic growth and demand for energy are exploding.

Incremental biomass losses during the harvest and storage of energy crops decrease the effective crop yield at the biorefinery gate. These losses can affect the environmental performance of biofuels from cellulosic feedstocks by indirectly increasing agricultural inputs per unit of fuel and increasing direct emissions of pollutants during biomass decomposition in storage. In this study, we expand the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREETTM) model to include parameters for harvest and storage of dry bales, bale silage, and bulk silage and examine the potential impact of the biomass supply chain on energy use and air pollutants from cellulosic ethanol from corn stover, switchgrass, and miscanthus feedstocks. A review of storage methods shows substantial differences in expected losses (4.2 to 16.0 %) and variability. Model results indicate that inclusion of feedstock harvest and storage pathways increases net fossil energy consumption (0.03–0.14 MJ/MJ) and greenhouse gas emissions (2.3–10 g CO2e/MJ) from cellulosic ethanol compared to analyses that exclude feedstock losses, depending on the storage scenario selected. Greenhouse gas emissions were highest from bulk ensiled silage and bale silage pathways, driven by direct emissions of greenhouse gasses during storage and material use, respectively. Storage of dry bales indoors or under cover minimizes emissions. This report emphasizes the need to increase the detail of biofuel production models and address areas of great uncertainty in the biomass supply chain, such as biomass decomposition emissions and dry matter losses.

Methods to increase the energy density of biofuel feedstock for shipment are important towards improving supply chain efficiency in upstream processes. Towards this end, densified pretreated lignocellulosic biomass was produced using hot-pressing. The effects of fiber hornification induced by hot-pressing on enzymatic digestibilities of lodgepole pine and poplar NE222 wood chips pretreated by sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) were examined. Pretreated wood chips were pressed at 25, 70, 90, 110, and 177 °C. The cellulose accessibilities of the pressed and unpressed substrates were evaluated using water retention value and direct cellulase adsorption measurements. Hot-pressing below 110 °C produced a degree of hornification (DH) below 0.26 and had limited effect on cellulose accessibility and enzymatic digestibility. Hot-pressing at 177 °C produced a DH of 0.86 that substantially hornified the fibers and resulted near zero saccharification. The saccharification results were consistent with cellulose accessibility data. Ethanol fermentation studies at 18 % solids suggest that a pressing below 110 °C is preferred to reduce its effect on biofuel yield.

Centrate from dewatering anaerobically digested municipal sludge is a particular concern in wastewater treatment, as it contains high ammonia concentrations and is often recycled to the head of the plant, reducing efficiency. Algae have the potential to remove ammonia from this wastewater, while producing biomass that can be used as an energy feedstock. In this research, an indigenous algal consortium was cultivated on municipal sludge centrate in a semi-continuous photobioreactor under natural light conditions. The goals of this research were to (1) enrich an algal consortium capable of growth on sludge centrate; (2) determine the main species of the consortium;(3) measure biomass, lipid production, and nutrient removal rates; and (4) develop a simple model to describe the system. The results suggested that Chlorella sp. was the dominant species (95 %) in the consortium. Mean biomass productivity was 5.2 g m−2 day−1, which was relatively high compared with other studies carried out with high ammonia strength wastewaters. Lipid production was low, comprising only 10 % of total biomass. The algal consortium effectively removed nutrients from the centrate, with observed mean removal efficiencies for total nitrogen, total phosphorus, and chemical oxygen demand of 65, 72, and 8 %, respectively. A simple irradiance-based model was developed from the fundamental Michaelis-Menten photosynthesis-irradiance (PI) response for photosynthetic organisms. A good fit to the experimental data was obtained with the irradiance-based model (R 2 = 0.96), indicating that the system was light limited. The results show that biomass production can be predicted based on irradiance only.

Mixed industrial palm oil (MIPO) is proposed in this study as a renewable and agro-industrial raw material to produce biodiesel fuel. MIPO was obtained by mixing of acidic crude palm oil with sludge palm oil. Due to the high level of free fatty acid (FFA) in MIPO (8.5 %), esterification is needed to remove the acidity to the minimum level before biodiesel production. This is the first time 1-propanesulphonic acid (1-PSA) has been introduced as a catalyst for the pretreatment of MIPO. Using optimum conditions, the FFA content was successfully reduced from 8.5 % to less than 1 %. The biodiesel produced meets the international standards (ASTM D6751 and EN 14214). 1-PSA is therefore a promising catalyst that can be used to treat various types of acidic oils.

Recently, fungal pelletization-assisted microalgal harvesting has emerged as new research area for minimizing the harvesting cost and energy inputs in the algae-to-biofuel approach. The present study attempted to optimize this process in terms of substrate inputs, process time and pH conditions through selection of a robust fungal strain. A total of eight fungal strains were screened for their pelletizing efficiency in fresh/spent BG11 supplemented with selected media nutrient (glucose, nitrogen and phosphorous). Aspergillus lentulus was found most efficient for pelletizing in the nutrient supplemented spent BG11 in spite of its alkaline pH (8.6–9.2). Moreover, the selected fungus was found equally good under neutral (7.0) and acidic pH (5.0). Interestingly, A. lentulus was able to harvest nearly 100 % of the microalgal cells (at 1.58 g l−1 initial working algal concentration) within only 24 h at supplementation of 10, 0.5 and 0.5 g l−1 of glucose, NH4NO3 and K2HPO4, respectively. The process kinetics in term of harvesting index (HI) as well as the variation of residual glucose and pH with time was also studied. Surprisingly, A. lentulus also performed well at lower glucose level (5.0 g l−1) resulting in 92 % harvesting within 24 h and up to 98 % harvesting within 52 h. The mechanism of harvesting process was studied through microscopic examination. A. lentulus strain investigated in this study could emerge as an efficient, sustainable and economically viable tool in microalgae harvesting for biofuel production. Further, the estimated stoichiometric methane potential (SMP) of pelletized microalgal–fungal biomass (0.756 m3 kg−1 volatile solid [VS]) showed substantial enhancement over algal biomass alone (0.709 m3 kg−1 VS). Hence, the investigated process not only overcomes the hurdles associated with microalgal harvesting but also improves its potential and suitability for bioenergy generation by anaerobic digestion. Further scale-up and pilot level testing is warranted for commercializing the investigated technique.

Biomass recalcitrance is a major bottleneck in the development of an economically viable process to convert woody biomass into fuels and other valuable chemicals. Selective breeding of trees with low recalcitrance toward biofuel conversion could help significantly reduce the cost of biofuel production, but such efforts would require a greater understanding of the nature of variations in the biomass recalcitrance of softwood species. The complexity of biomass recalcitrance, however, hinders research into determining the viability of breeding programs aimed to improve the recalcitrance of softwoods. In this study, a method was developed to determine biomass recalcitrance at three levels: chemical composition, pretreatment yield, and sugar release from the enzymatic hydrolysis. This method is designed to investigate the biomass recalcitrance variations among different families of Douglas-fir, which is the most abundant and promising softwood species for biofuel production in the Pacific Northwest region. Wood samples from 150 plantation-grown trees were collected and analyzed to test the method and the applicability of the parameters screened. The relationships between these levels are discussed to determine the best method for screening large D. fir populations. A parameter, a biomass recalcitrance factor, was introduced to quantify the level of biomass recalcitrance toward sugar production from different D. fir trees.

The fossil fuel crisis in the world has raised much concern on developing biomass energy. Fermentable sugars are an important product which can be converted to bioethanol. Although sulfuric acid saccharification is a good method for breaking lignocellulose biomass, efficiency is not well-promoted in dilute acid, as many fermentation inhibitors are co-produced. A continuous saccharification approach was established in this study to reach high saccharification efficiency and low toxicity of reducing sugar (RS). The dilute H2SO4 was taken as flow phase in this process with temperature gradient elevation. Each sample of 250 ml was taken when temperature elevated from 60 to 230 °C (temperature interval 20–30 °C). Under optimum conditions, the maximum RS yield ratio reaches 53.4 %. Furfural is detected in the hydrolysate, with a concentration less than 1.06 g/l. The optimized saccharification conditions were achieved at a flow rate of 25 ml/min and with H2SO4 concentration at 1.0 %. Operation parameters were investigated including acid flow rate and acid concentration. The composition of rape straw is analyzed, and the material balance is studied in the optimized conditions. In addition to SEM, FT-IR analysis techniques are used, and the results show that the hemicellulose and cellulose in the rape straw can be fully converted to RS, while the change in lignin amount is negligible. This method is a novel and promising technique for high yield of RS, as it is accompanied with a low content of bio-inhibitor.

Non-catalytic gasification of canola meal for the production of syngas was studied in lab-scale fixed bed gasifier and pilot-scale fluidized bed gasifier. Various experiments were undertaken in order to study the effects of different gasification parameters on gas composition, H2/CO ratio, gas yield, syngas yield, lower heating value (LHV), and carbon efficiency (CE). Fixed-bed experiments were performed to study the effects of operating temperature in the range of 650–850 °C and equivalence ratio in the range of 0.2–0.4. Steam, carbon dioxide (CO2), and oxygen (O2) were used as gasifying agents. The experimental results show that steam gasification delivers a gaseous product with a high H2/CO ratio (2.7) and LHV (193.0 MJ/m3). Oxygen gasification attributed to maximum CE (65.5 %). CO2 gasification contributes to high gas yield (82.8 mol/kg biomass). During fluidized bed gasification study, it was found that using steam as gasifying agent leads to more H2 production as compared to that for O2 and CO2 gasifying agents. Thus, it leads to high H2/CO ratio, syngas yield, and LHV of product gas. Regarding CE for O2 gasification and gas yield for CO2, observations were similar to those for fixed bed system.

Ultrasonic treatment was firstly found to accelerate both biomass and hydrocarbon productivities of Botryococcus braunii algal cells cultured in the shake flasks. The most effective sonication strategy was to subject the cells to three 5-min ultrasonic treatments at a 4-day interval using a fixed frequency of 40 kHz and power of 240 W, and the ultrasound-treated algal cells showed the highest biomass productivity of 0.043 g L−1 day−1 and the highest hydrocarbon productivity of 13.1 mg L−1 day−1 among all ultrasound treatments tested. The improved productivity was proved to be mainly due to the enhancement of both endogenous indole-3-acetic acid (IAA) biosynthesis and membrane permeability in the ultrasound-stimulated algal cells. The efficient ultrasonic stimulation strategy also showed good performance for the algal culture in a 2-L airlift bioreactor. Together, these results not only illustrate the immense potential for an enhanced understanding on ultrasound-stimulated algal cells but also as provide a powerful process intensification method to improve the biomass and hydrocarbon productivity of B. braunii in practice.

We examined two practical methods for reducing moisture content and/or ash content in biomass from southern pine harvests. Logging residues are a potential bioenergy feedstock, but contaminants can increase ash content during collection. We found that trommel screens can reduce ash levels in grindings from southern pine roundwood and clean chipped logging residues from 4.0 to 1.4 % and 11.9 to 6 %, respectively. Green whole-tree chips are a widely used form of forest biomass, but are 50 % moisture. Felling and transpirationally drying in-field before chipping reduced moisture from 53 to 43 % and 39 % in 4 and 8 weeks, respectively, without changing ash content (

Processing of lignocellulosic materials to fuels such as methane and bioethanol may involve several processing steps including pretreatment, saccharification, fermentation, and anaerobic digestion. The amounts of substrate used in these processes are usually based on dry matter content, and the processes themselves typically lead to a change in dry matter content. Thus, it is of great importance to be able to measure dry matter accurately. Dry matter content is commonly determined by measuring loss of water during oven drying. We have used Karl Fischer (KF) titration to measure the water content in a wide range of biomass fractions and have compared these data to results obtained by oven drying. This revealed considerable differences for all tested materials. For lignocellulosic materials, oven drying tends to overestimate dry matter content for untreated material. On the other hand, oven drying generally underestimates dry matter content in pretreated materials due to loss of organic volatiles. These differences have major consequences for the calculation of mass balances and yields in bioprocessing. The KF method gives more accurate water determination than oven drying due to the unique selectivity of the analysis. The method is suitable for the analysis of lignocellulosic biomasses and is particularly useful for determination of water content in pretreated materials, where oven drying usually underestimates the dry matter content due to loss of volatiles.

This study applied dilute acid (DA) and sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) to deconstruct earlywood and latewood cell walls of Douglas fir for fermentable sugars production through subsequent enzymatic hydrolysis. DA pretreatment removed almost all the hemicelluloses, while SPORL at initial pH = 4.5 (SP-B) removed significant amount of lignin between 20 and 25 %. But both are not sufficient for effective enzymatic saccharification. SPORL at low initial pH = 2 (SP-AB) combines the advantage of both DA and SPORL-B to achieve approximately 90 % hemicellulose removal and delignification of 10–20 %. As a result, SP-AB effectively removed recalcitrance and thereby significantly improved enzymatic saccharification compared with DA and SP-B. Results also showed that earlywood with significantly lower density produced less saccharification after DA pretreatment, suggesting that wood density does not contribute to recalcitrance. The thick cell wall of latewood did not limit chemical penetration in pretreatments. The high lignin content of earlywood limited the effectiveness of DA pretreatment for enzymatic saccharification, while hemicellulose limits the effectiveness of high pH pretreatment of SP-B. The higher hemicellulose content in the earlywood and latewood of heartwood reduced saccharification relative to the corresponding earlywood and latewood in the sapwood using DA and SP-AB.

Willow, a leading bioenergy feedstock, may be planted for bioremediation and has been used, more recently, as the biomass feedstock in the manufacture of biochar for agricultural applications. Here, we present a detailed study of the physical and chemical factors affecting willow char properties, where the feedstock is a by-product of bioremediation, potentially transferring pollutants such as heavy metals to the wood feed. Biochar samples were produced via pyrolysis of short-rotation coppice willow, grown on contaminated land, using several treatment times at heat treatment temperatures (HTTs) in the range 350–650 °C, under a constant flow of argon, set at either 100 or 500 mL min−1. The samples were analysed for yield, elemental analysis and structural characteristics, including surface area and pore size distribution, surface functionality and metal content. All chars obtained have high fixed carbon contents but vary in surface characteristics with a marked increase in basic character with increasing HTT, ascribed to the removal of surface oxygen moieties. Results indicate a minimum pyrolysis temperature of 450 °C is required to produce a defined mesoporous structure, as required to facilitate oxygen transport, HTT ≥ 550 °C produces total surface area of >170 m2 g−1 and, more importantly, an appreciable external surface area suitable for microbial colonisation. The data show that selection and optimisation of char properties is possible; however, the interplay of factors may mean some compromise is required.

This study comparatively evaluates the modelling efficiency of the Response Surface Methodology (RSM) and the Artificial Neural Network (ANN). Twenty-nine biohydrogen fermentation batches were carried out to generate the experimental data. The input parameters consisted of a concentration of molasses (50–150 g/l), pH (4–8), temperature (35–40 °C) and inoculum concentration (10–50 %). The obtained data were used to develop the RSM and ANN models. The ANN model was a committee of networks with a topology of 4-(6-10)-1 structured on multilayer perceptrons. RSM and ANN models gave R 2 values of 0.75 and 0.91, respectively, with predicted optimum conditions of 150 g/l, 8 and 35 °C for molasses, pH and temperature, respectively, with differences in inoculum concentrations (10.11 and 15 %) for RSM and ANN, respectively. Upon validation, 15.12 and 119.08 % prediction errors on hydrogen volume were found for ANN and RSM, respectively. These findings suggest that ANN has greater accuracy in modelling the relationships between the considered process inputs for fermentative biohydrogen production and thus, is more reliable to navigate the optimization space.

For hundreds of years, sugarcane has been a main source of sugar, used as a sweetener, and alcohol, fermented from the plant juice. The high cost of petroleum towards the end of the twentieth century stimulated the development of new fermentation technologies for producing economically viable bioethanol from sugarcane as an alternative to importing petroleum. More recently, awareness of the effects of greenhouse gas emissions due to the global climate changes propelled bioethanol as a viable renewable fuel. Consequently, sugarcane gained importance as a bioenergy feedstock. However, the lack of knowledge about sugarcane physiology, notably on aspects of photosynthesis and source–sink relationship, has slowed the advance of this expanding bioenergy-producing system. Besides the changes in source–sink relationship, another option to increase bioethanol production even more would be to use a greater fraction of the total biomass of plants, i.e., not only the soluble sugars but also the sugars present in the cell wall fractions. Here, we review the history of sugarcane as a bioenergy crop and discuss some of the relevant routes that could be adopted in the near future to make sugarcane an even better feedstock for producing biofuels.

Combined torrefaction and pelletization is used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. In the present study, a single-pellet press tool was used to screen for the effects of pellet die temperature, moisture content, additive addition, and the degree of torrefaction on the pelletizing properties and pellet quality, i.e., density, static friction, and pellet strength. Results were compared with pellet production using a bench-scale pelletizer. The results indicate that friction is the key factor when scaling up from single-pellet press to bench-scale pelletizer. Tuning moisture content or increasing the die temperature did not ease the pellet production of torrefied wood chips significantly. The addition of rapeseed oil as a lubricant reduced the static friction by half and stabilized pellet production; however, the pellet quality, strength, and density were negatively affected. The pellets produced from pine wood torrefied at 250 and 280 °C were shorter than pellets produced from untreated wood and their quality did not match conventional wood pellet standards. However, the heating value of the torrefied pellets was higher and the particle size distribution after grinding the pellets was more uniform compared to conventional wood pellets.

The effluent from a continuous-flow stirred tank reactor (CSTR) treating synthetic wastewater was used as an alternative carbon source to glucose for algal biomass and biodiesel production. The influence of the effluent on microalgal cell growth and lipid yield, as well as the utilization of volatile fatty acids (VFAs) in the effluent were investigated. The results indicate that C. protothecoides can proliferate in the CSTR effluent and accumulate biolipid. The final lipid content of the culture with the effluent feeding was 27 ± 1.11 % after 168 h cultivation in flasks, which was higher than that with glucose of the same COD concentration. Valeric acid, ethanol, and butyric acid were favorable carbon sources for cell growth. The soluble microbial products (SMP) can be used as a carbon source for cell growth, and the existence of SMP could protect the cell from the inhibition caused by strong VFAs and improve the utilization of VFAs.

The residues from the palm oil industry are the main contributors to biomass waste in Malaysia, and these wastes require extra attention with respect to handling. The biomass waste is a renewable resource that can potentially be used to produce absorbents, fuels, and chemical feedstocks through the pyrolysis process. In this study, the wastes of palm shell, empty fruit bunches, and mesocarp fiber were characterized and then pyrolyzed in a fixed-bed reactor under the following conditions: a temperature of 500 °C, a nitrogen flow rate of 2 L/min and reaction time of 60 min. After pyrolysis, characterization of the products with an emphasis on the bio-oil and the bio-char was performed using various approaches (including Karl Fischer water-content tests, FTIR, SEM, TGA and CNH/O analyses). The results showed that the pyrolysis of palm oil wastes yielded more bio-oil than bio-char or non-condensable gases. The results also indicated that all of the bio-oils were acidic and contained high levels of oxygen. The bio-oils heating values were low and varied from 10.49 MJ/kg to 14.78 MJ/kg. The heating values of the bio-chars (20–30 MJ/kg) were higher than those of the bio-oils. Among the biomasses studied in this work, palm shell contained the highest level of lignin and showed the highest levels of bio-char yield and fixed and elemental carbon in the raw and bio-char form.

Turnip oil (TO; Raphanus sativus L.) produces seeds that contain around 26 wt% of inedible base stock that are suitable as a potential feedstock for biodiesel production. A turnip oil methyl ester (TME) was prepared from acid-catalyzed pretreated TO in an effort to evaluate important fuel properties of turnip oil-based biodiesel, such as kinematic viscosity, cloud point, pour point (PP), cold filter plugging point, acid value, oxidative stability and lubricity. A comparison was made with soybean oil methyl esters (SME) as per biodiesel fuel standards such as ASTM D6751 and EN 14214. TME was characterized using FTIR, HPLC and 1H NMR. Except PP property, SME displays superior fuel properties compared to TME. Blends (B5 and B20) of TME in ultra-low sulphur diesel fuel (ULSD) were also assessed for the aforesaid fuel properties and compared to an analogous set of blends of soybean oil methyl ester in ULSD as per petro diesel fuel standards such as ASTM D975 and D7467. TME B5 blends in ULSD displayed improved PP property in comparison to neat ULSD and blends of SME in ULSD. It was demonstrated that the B5 and B20 blends of TME in ULSD had acceptable fuel properties as per ASTM D975 (for B5 blend) and ASTM D7467 (for B20 blend). In summary, turnip oil has potential as an alternative, non-food feedstock for biodiesel production.

Toxin-tolerant yeast strains that produce high ethanol yield are inevitably requited for cost-effective ethanol production from undetoxified steam-exploded corn stover. To verify the ethanol-producing capability of the strain Saccharomyces cerevisiae Y5 developed in our laboratory, simultaneous saccharification and fermentation of undetoxified steam-exploded corn stover with solids loading of 30 % (w/v) was carried out in different-sized flasks and an automatic fermenter. After 96 h, the ethanol concentrations had reached 50, 47.8, and 47.5 g/L in the 100-mL flask, 3,000-mL flask, and 5-L automatic fermenter, respectively. The experiment demonstrates that ethanol production from undetoxified steam-exploded corn stover using S. cerevisiae Y5 simplifies the production process, reduces equipment investment and water consumption, and generates highly concentrated ethanol. S. cerevisiae Y5 is a promising strain that could reduce the cost of producing ethanol from steam-exploded corn stover.

Sugarcane bagasse (SCB) was pretreated with liquid hot water (LHW) and aqueous ammonia (AA), with the objective of investigating the influence of hemicellulose and lignin removal on the enzymatic digestibility and sugar recovery. The experimental results show that LHW and aqueous ammonia have a good performance in terms of hemicellulose dissolution and lignin removal respectively. The biggest xylan recovery of 74.3 % was obtained for LHW pretreatment at 160 °C, 5 % w/v for 20 min with the xylan dissolution of 83.1 %. And the biggest lignin removal of 84.0 % was obtained for aqueous ammonia pretreatment at 160 °C, 10 % w/v for 60 min. Moreover, the aperture and surface area of the sample were enlarged by the liquid hot water, which improves the accessibility of the substrate to the enzyme. The lignin removal caused by aqueous ammonia pretreatment can reduce the absorption of enzyme. In addition, the correlation between the compositional change and the enzymatic digestibility indicates that the removal of hemicellulose was more effective than lignin for destruction of the hemicellulose–lignin–cellulose structure.

The use of lignocellulosic biomass as a renewable energy source is becoming progressively essential. Much attention is focused on identifying suitable biomass species that can provide high energy outputs to replace conventional fossil fuels. The current study emphasizes on some commonly available biomasses in North America such as pinewood, timothy grass, and wheat straw for their usage towards next generation biofuels. Fast pyrolysis of the feedstocks was performed at 450 °C to generate biochars that were further characterized to advocate their energy and agronomic relevance. The biomasses were examined physiochemically to understand their compositional and structural characteristics through analytical approaches such as CHNS (carbon–hydrogen–nitrogen–sulfur), ICP-MS (inductively coupled plasma-mass spectrometry), particle size, FTIR (Fourier transform infrared) and Raman spectroscopy, thermogravimetric and differential thermogravimetric, XRD (X-ray diffraction), and high-pressure liquid chromatography. The chemical composition of feedstocks significantly differed from that of biochars and the variations among feedstock composition were also found to be greater than for biochars. The presence of cellulose, hemicellulose, and lignin along with other organic components were identified in the spectroscopic and chromatographic analysis. The FTIR spectra of biochars showed removal of oxygen- and hydrogen-containing functionalities from feedstocks due to pyrolysis at higher temperature, although retaining certain significant cellulose-derived functionalities. A number of crystallographic phases in the XRD of biomass, ash, and biochars were due to minerals commonly Na, Mg, Al, Ca, Fe, and Mn. ICP-MS of biochars demonstrated substantial amount of alkali elements indicating their compatibility towards soil amendment for restoring degraded soils.

Ethanol fuel can be produced renewably from numerous plant and waste materials, but harnessing the energy of lignocellulosic feedstocks has been particularly challenging in the development of this alternative fuel as a substitute for petroleum-based fuels. Consolidated bioprocessing has the potential to make the conversion of biomass to fuel an economical process by combining enzyme production, polysaccharide hydrolysis, and sugar fermentation into a single unit operation. This consolidation of steps takes advantage of the synergistic nature of enzyme systems but requires the use of one or a few organisms capable of producing highly efficient cellulolytic enzymes and fermenting most of the resulting sugars to ethanol with minimal byproduct formation while tolerating high levels of ethanol. In this review, conventional ethanol production, consolidated bioprocessing, and simultaneous saccharification and fermentation are described and compared. Several wild-type and genetically engineered microorganisms, including strains of Clostridium thermocellum, Saccharomyces cerevisiae, Klebsiella oxytoca, Escherichia coli, Flammulina velutipes, and Zymomonas mobilis, among others, are highlighted for their potential in consolidated bioprocessing. This review examines the favorable and undesirable qualities of these microorganisms and their enzyme systems, process engineering considerations for particular organisms, characteristics of cellulosomes, enzyme engineering strategies, progress in commercial development, and the impact of these topics on current and future research.

The costs of producing protected vegetables comprise up to 78 % of the total operating costs in greenhouses. These expenses mainly result from energy consumption. Increasing energy efficiency and expanding the use of renewable energy sources are essential for global competitiveness. The aim of this study is to optimize methane production from miscanthus and to evaluate the potential use of miscanthus as a source of electrical energy, heat, and CO2 in vegetable greenhouses. To optimize methane yield, miscanthus was pretreated by steam explosion using different time/temperature combinations. Pretreatment resulted in a more than threefold increase of methane yield from anaerobic digestion (374 lN kgVS−1) compared with untreated miscanthus. Based on technical parameters from two greenhouses (in Northern and Southern Europe), four different energy balances were established. The balances showed that using methane produced by pretreated miscanthus in vegetable greenhouses can enhance the entire process and therefore make it more sustainable.

Enzymatic saccharification of cellulose is a key step in conversion of plant biomass to advanced biofuel and chemicals. Many substrate-related factors affect saccharification. Rather than examining the role of each individual factor on overall saccharification efficiency, this study examined how each factor affects the three basic processes of a heterogeneous biochemistry reaction: (1) substrate accessibility to cellulose—the roles of component removal and size reduction by pretreatments, (2) substrate and cellulase reactivity limited by component inhibition, and (3) reaction conditions—substrate-specific optimization. Our in-depth analysis of published literature work, especially those published in the last 5 years, explained and reconciled some of the conflicting results in literature, especially the relative importance of hemicellulose vs. lignin removal and substrate size reduction on enzymatic saccharification of lignocelluloses. We concluded that hemicellulose removal is more important than lignin removal for creating cellulase accessible pores. Lignin removal is important when alkaline-based pretreatment is used with limited hemicellulose removal. Partial delignification is needed to achieve satisfactory saccharification of lignocelluloses with high lignin content, such as softwood species. Rather than using passive approaches, such as washing and additives, controlling pretreatment or hydrolysis conditions, such as pH, to modify lignin surface properties can be more efficient for reducing or eliminating lignin inhibition to cellulase, leading to improved lignocellulose saccharification.

The conversion of agro-industrial residues, such as sugarcane bagasse, into high-value products and renewable energy, within the biorefinery concept, is a potential alternative towards the sustainable management of these resources. This work evaluates the production of cellulolytic enzymes by a selected strain of Aspergillus niger cultivated in sugarcane bagasse under solid-state fermentation using an instrumented lab-scale bioreactor. The effects of environmental factors including the type of substrate and medium composition, as well as the operational conditions (air flow rate, inlet air relative humidity, and initial substrate moisture content) on the production of the enzymatic complex were evaluated using statistical design tools. Significant increases in FPase, endoglucanase, and xylanase activities were achieved under the optimized conditions predicted by the models, with values of 0.88, 21.77, and 143.85 IU/g of dry solid substrate, respectively, representing around ten-, four-, and twofold increases compared to the activities obtained under the initial growth conditions. This demonstrates the importance of evaluating environmental and operational criteria in order to achieve efficient enzyme production. The crude enzymatic extract obtained under optimized conditions was employed for enzymatic hydrolysis of pretreated sugarcane bagasse. Approximately 13 % of total reducing sugars, and a glucose concentration of 2.54 g/L, were obtained after 22 h of hydrolysis of steam exploded sugarcane bagasse, indicating that the enzymatic cocktail produced has good potential for use in the conversion of biomass.

The fuel characteristics of solid biofuels derived from biomass that is abundantly available in Malaysia are presented. The objectives of the study were to characterize fuel properties of oil palm biomass (empty fruit bunch (EFB) and oil palm trunk (OPT)) and wood from a range of fast growing timber species (Albizia falcataria, Acacia spp., Endospermum spp. and Macaranga spp.), inclusive and exclusive of bark. Among the fast-growing timber species, the higher heating values ranged from 4288 cal g-1 to 4383 cal g-1 for wood inclusive of bark, and 4134 cal g-1 to 4343 cal g-1 for wood exclusive of bark. The inclusive of bark portion in the biomass sample generally increased the heating value except for Macaranga spp. Empty fruit bunch and oil palm trunk had heating values of 4315 cal g-1 and 4104 cal g-1, respectively. Ash-forming elements and trace elements were much higher in the timber species samples inclusive of bark than samples exclusive of bark. On the other hand, oil palm biomass contained higher ash-forming elements and trace elements than the wood from the fast growing timber species. The European energy crops show higher HHV, Cl and Si content but lower K, Mg, Na and P compared to the local biomass used in this study. The data obtained from this study can serve as a foundation for the selection of suitable biomass to be used as solid fuel, or as a reference on the fabrication of conversion systems for the selection of biomass solid fuel.

Used frying oil seems to be an economically viable and environmentally attractive alternative for biodiesel production, but the acceptance and successful use of this and other biodiesels obtained from waste materials require careful evaluation of its fuel properties and impurities. Herein, we show that biodiesel made from used frying soybean oil display overall quality comparable to those obtained from the fresh oil as measured by standard parameters of fuel quality such as induction period, acid number, heat of combustion, and iodine value as well as at the molecular level via profiles of intact and oxidized fatty acid methyl esters. These profiles were obtained directly from the biodiesel samples by easy ambient sonic spray ionization mass spectrometry. An artificial antioxidant, N,N′-di-sec-butyl-p-phenylenediamine, was shown to significantly increase the oxidative stability of the used frying oil biodiesel at trace level.

Lignocellulosic materials such as wood, grass, and agricultural and forest residues are promising alternative energy resources that can be utilized to produce ethanol. The yield of ethanol production from native lignocellulosic material is relatively low due to its native recalcitrance, which is attributed to, in part, lignin content/structure, hemicelluloses, cellulose crystallinity, and other factors. Pretreatment of lignocellulosic materials is required to overcome this recalcitrance. The goal of pretreatment is to alter the physical features and chemical composition/structure of lignocellulosic materials, thus making cellulose more accessible to enzymatic hydrolysis for sugar conversion. Various pretreatment technologies to reduce recalcitrance and to increase sugar yield have been developed during the past two decades. This review examines the changes in lignocellulosic structure primarily in cellulose and hemicellulose during the most commonly applied pretreatment technologies including dilute acid pretreatment, hydrothermal pretreatment, and alkaline pretreatment.

Anaerobic digestion is a promising option for recycling agricultural by-products and some organic wastes. While both agricultural by-products and wastes have no direct commercial value, their management is both complicated and costly. One option to simplify by-product management and reduce the costs associated with biogas plant feedstock is to substitute dedicated crops with vegetal by-products. Given that the chemical composition of some of these by-products can differ considerably from more typical biogas plant feedstock (such as maize silage), more complete knowledge of these alternatives to produce environmentally friendly energy is warranted. To this end, batch trials under mesophilic conditions were conducted to evaluate the potential biogas yield of many agricultural by-products: maize stalks, rice chaff, wheat straw, kiwi fruit, onions, and two expired organic waste products (dairy and dry bread) from the retail mass-market. Among the considered biomasses, the highest methane producer was the expired dairy product mixture, which yielded 554 lNCH4 kg−1 volatile solids (VS). Maize stalks and wheat straw produced the lowest yields of 214 and 285 lNCH4 kg−1VS, respectively. An assessment of the biogas and methane yields of each biomass was also undertaken to account for the specific chemical composition of each biomass as it can affect the anaerobic digestion operating system. Finally, the total Italian green energy production that might be derived from feeding all these biomasses to a biogas digester was estimated, in order to understand its potential impact.

Chlorella vulgaris (a freshwater microalga) and Dunaliella tertiolecta (a marine microalga) were grown for bulk harvest, and their biomass was tested as feedstock for electricity production in cubic two-chamber microbial fuel cells (MFCs) at 37°C. The anode inoculum was anaerobic consortium from a municipal sewage sludge digester, enriched separately for the two microalgal biomass feedstocks. After repeated subculturing of the two anaerobic enrichments, the maximum power density obtained in MFCs was higher from C. vulgaris (15.0 vs. 5.3 mW m−2) while power generation was more sustained from D. tertiolecta (13 vs. 9.8 J g-1 volatile solids). Anolytes of algal biomass-fed MFCs also contained substantial levels of butanol (8.7–16 mM with C. vulgaris and 2.5–7.0 mM with D. tertiolecta), which represents an additional form of utilizable energy. Carryover of salts from the marine D. tertiolecta biomass slurry resulted in gradual precipitation of Ca and Mg phosphates on the cathode side of the MFC. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling and sequencing of bacterial communities demonstrated the presence of Wolinella succinogenes and Bacteroides and Synergistes spp. as well as numerous unknown bacteria in both enrichments. The D. tertiolecta enriched consortium contained also Geovibrio thiophilus and Desulfovibrio spp. Thus, the results indicate potential for combining fermentation and anaerobic respiration for bioenergy production from photosynthetic biomass.

Self-sufficiency in energy requirement is critical to the success of any developing economy. Apart from the search for alternatives, there is a need to achieve energy independence, directing much focus on biofuels. Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulfur and aromatics. Oil was extracted from the seeds of Blighia unijugata and Luffa cylindrica, subjected to chemical characterization and biodiesel production. The oil yield from the seed of B. unijugata was 50.82 ± 1.20% while that of L. cylindrica was 39.10 ± 0.20%. The biodiesel produced had ester content above 98%. The flash point of the biodiesel from B. unijugata and L. cylindrica was above 120°C while the phosphorus content was also below 1 ppm in both cases. The oxidative stability of B. unijugata was 44.30 ± 0.30 h, while that of L. cylindrica was lower than this value due to its high unsaturation. The copper strip corrosion value of the biodiesel was also found to be 1A. This study showed that the high free fatty acid content of B. unijugata and L. cylindrica seed oil can be reduced in a one-step pretreatment of esterification reaction using H2SO4 as catalyst thus reducing the problem of soap formation encountered when using oil with high free fatty acid for the production of biodiesel.

In the conventional fermentation process to obtain butanol (a novel biofuel), product-induced toxicity results in a product stream with low concentration of butanol (∼13 g/L) and limits the concentration of the sugar solution to less than 60 g/L. As a result, steam-consuming operations such as mash sterilization, downstream product recovery (distillation), and wastewater treatment are energy-intensive and important economic drawbacks. Based on the correlation between energy consumption of the distillation unit and butanol concentration in the fermentation beer, the present research points out that improvements in biobutanol processing intended to increase the concentration of butanol in the beer should have a minimum target of 36 g/L. Moreover, due to the dramatic effect of butanol concentration on the wastewater footprint, the volume of the effluent stream can be reduced by 60% (from 72 to 29 L stillage/L butanol) if the minimum concentration target is reached instead of the usual butanol titer of 13 g/L. These correlations were used as the basis to discuss the impacts of today’s research works (genetic strain improvement, utilization of lignocellulosic biomass feedstock, and development of new process technologies) on the energy consumption for complete dehydration of butanol and on wastewater generation.

Direct hydrothermal liquefaction of biomass is a technology that has shown promising results in treating waste and producing oil. A batch hydrothermal liquefaction system was used to treat swine manure, and it successfully converted up to 70% of swine manure volatile solids into oil and reduced manure chemical oxygen demand by up to 75% (He et al., Trans ASAE 43(6):1827–1833, 2000). A continuous-flow reactor was developed and resulted in similar conversion rates to the batch process, indicating the potential for scale-up (Ocfemia, 2005). This study investigates the hydrothermal process in relation to a livestock system to determine the impact on oil yields and fertilizer values that might be realized in a farm-scale application. Oil products from the hydrothermal process are maximized using manure containing around 20% solids, but typical swine confinement facilities contain wetter manure slurries. A preliminary investigation of liquid–solid separation methods was conducted to determine the resultant oil yields and the effects of the hydrothermal process on fertilizer values in the wastewater as compared to the unprocessed manure. Energy and economic analyses of the liquid–solid separation and hydrothermal liquefaction processes were also conducted. The hydrothermal process results in an oil product as well as a fertilizer product that retains the majority of its nitrogen value with a reduced level of phosphorus (as compared to the unprocessed swine manure). The economic analyses indicate feasibility for several different liquid–solid separation methods, dependent on the equipment and maintenance costs assumed for each method. Conveyor-belt manure collection systems in conjunction with hydrothermal liquefaction are especially promising.

Agricultural lignocellulosic waste such as corn stover is a potential source of inexpensive, abundant, and renewable biomass for the production of bioethanol. The enzymatic process for the economically viable breakdown of cellulose to ethanol relies on the availability of inexpensive microbial cellulases. Although the cost of cellulase has decreased in recent years, current costs still preclude the production of economically viable bioethanol from lignocellulose. Substantive efforts in this lab are being directed to transgenic production of cellulases in maize in order to boost efficiency both of production of enzymes and degradation of corn stover. We serendipitously observed that the addition of non-transgenic maize seed extracts to cellulose and microbial enzymes potentiated free sugar release by as much as 20-fold. Further, this synergistic effect between cellulase enzymes and extract was seen with a variety of plant species and tissue extracts, but varied in efficiency, and was optimal at low concentrations of cellulases. Although the nature of the synergistic molecule is not known, the use of extracts to potentiate cellulose breakdown provides opportunities for a clearer mechanistic understanding of the degradation process as well as an economical way to improve the efficiency of cellulases to produce more cost-effective bioethanol from agricultural waste.

A novel production process of biodiesel fuel was developed using an expanded-bed reactor packed with an anion-exchange resin having catalytic and adsorption abilities. Waste cooking oil was used as a cheaper feedstock, and methanol was added at the stoichiometric molar ratio of 3:1. The main constituent of the feedstock, triglyceride was completely converted to the biodiesel by the resin’s catalytic ability. The impurities of the feedstock, free fatty acid, water, and dark brown pigment were removed from the product by the adsorption on the resin. In addition, the by-product glycerin was also removed from the product by the adsorption on the resin. The product eluted from the reactor was directly used for the standard tests of the biodiesel properties. The eluted product almost met the biodiesel quality standards (EN14214 in Europe and ASTM D6751 in North America). Thus, the proposed system permitted the simple production of biodiesel from the waste cooking oil without the upstream processing to remove the impurities (free fatty acid and water) and the downstream processing to remove the catalyst and by-products (glycerin and soap).

Low temperature and long residence time pretreatments have been proposed as an alternative to conventional pretreatments within a centralized biorefinery, allowing for a decentralized pretreatment without high energy costs. Ammonia fiber expansion (AFEX™) pretreatment may be uniquely suitable for decentralized pretreatment, and this study considers the possibility of decreasing the temperature in AFEX pretreatment of corn stover. AFEX pretreatment at 40°C and 8 h produced comparable sugar and ethanol yields as conventional AFEX pretreatment at high temperatures and short residence time during subsequent hydrolysis and fermentation. Increasing the ammonia loading at these temperatures tends to increase digestibility, although the moisture content of the reaction has little effect. This study suggests a greater flexibility in AFEX pretreatment conditions than previously thought, allowing for an alternative approach for decentralized facilities if the economic conditions are appropriate.

Fast pyrolysis of lignocellulosic biomass is a facile method for producing high yields of liquid fuel intermediates. However, because most fast pyrolysis oils are highly oxygenated, acidic, and unstable, identification of feedstocks that produce higher quality pyrolysis liquids is desirable. Therefore, the effect of feedstock protein content was studied by performing fast pyrolysis experiments on biomass with varying protein content. The feedstocks ranged from low-protein content, ∼5% up to feedstocks with >40 wt.% protein content. Protein content was not a major factor in the yield of pyrolysis oil or the distribution of biomass carbon into the pyrolysis products. However, elevated levels of protein did cause a deoxygenation effect in the pyrolysis process with more of the oxygen rejected from the biomass as water. The deoxygenation caused the pyrolysis oil from the higher protein containing biomass to have higher energy content. Furthermore, the concentration of basic nitrogen groups caused the pyrolysis oil from the higher protein biomass to shift to a more neutral pH and lower total acid number than has been measured typically for lignocelluloic biomass pyrolysis oils. Some of the pyrolysis oils, particularly those from the mustard seed family presscakes exhibited better thermal stability than low-protein pyrolysis oils.

The mechanical dehydration of ensiled agricultural crops results in two major products: a fibrous press cake and a press fluid containing mainly easily digestible constituents. This study is aimed at the investigation on methane yields and digestion dynamics of the press fluids from maize silages using different types of digesters. Methane yields investigated in batch experiments account for 390–506 lN CH4/kg volatile solids (VS) with a degree of degradation of the organic matter in the fluid of more than 90%. The investigation of digestion dynamics in a continuously working stirrer tank digester at different levels of retention time and volume load suggests that a stable fermentation of press fluids can only be achieved with retention times of more than 20 days and with volume loads below 2 g VS/l/day. In a continuously working fixed bed digester a steady fermentation could be achieved at a retention time of 8 days and a volume load of 3 g VS/l/day.

Extrusion pretreatment of biomass can be one of the viable continuous pretreatment methods. The torque requirement of feedstock during extrusion was an important factor, and it was not reported in the literature. Screw compression ratio, screw speed, barrel temperature, and feedstock moisture content are the contributing factors to the torque. The current study was undertaken to investigate the effect of screw compression ratio, screw speed, temperature on torque requirement for different moisture content of switchgrass, prairie cord grass, corn stover, and big bluestem and to compare the torque requirement among the selected feedstocks. Biomass was extruded in a lab scale single-screw extruder with different screw compression ratios (2:1 and 3:1), screw speeds (50, 100, and 150 rpm), and barrel temperatures (50°C, 100°C, and 150°C) over a range of moisture contents (15%, 25%, 35%, and 45% wb). Statistical analyses revealed that all the independent variables considered in this study had a significant effect on torque requirement for the selected feedstocks. Among the independent variables considered moisture content, screw speed, and temperature had a negative effect on torque requirement for all the feedstocks. Switchgrass required the highest torque followed by corn stover, big bluestem, and prairie cord grass.

The aim of this study was to analyze the effects of intensive management and forest landscape structure (in terms of age class distribution) on timber and energy wood production (m3 ha−1), net present value (NPV, € ha−1) with implications on net CO2 emissions (kg CO2 MWh−1 per energy unit) from energy wood use of Norway spruce grown on medium to fertile sites. This study employed simulations using a forest ecosystem model and the Emission Calculation Tool, considering in its analyses: timber (saw logs, pulp) and energy wood (small-sized stem wood and/or logging residuals for top part of stem, branches, and needles) from the first thinning and harvesting residuals and stumps from the final felling. At the stand level, both fertilization and high pre-commercial stand density clearly increased timber production and the amount of energy wood. Short rotation length (40 and 60 years) outputted, on average, the highest annual stem wood production (most fertile and medium fertile sites), the 60 year rotation also outputted the highest average annual net present value (NPV with interest rates of 1–4%). On the other hand, even longer rotation lengths, up to 80 and 100 years, were needed to output the lowest net CO2 emissions per year in energy wood use. At the landscape level, the largest productivity (both for timber and energy wood) was obtained using rotation lengths of 60 and 80 years with an initial forest landscape structure dominated by older mature stands (a right-skewed age-class distribution). If the rotation length was 120 years, the initial forest landscape dominated by young stands (a left-skewed age-class distribution) provided the highest productivity. However, the NPV with interest rate of 2% was, on average, the highest with a right-skewed distribution regardless of the rotation length. If the rotation length was 120 years, normal age class distribution provided, on average, the highest NPV. On the other hand, the lowest emissions (kg CO2 MWh−1a−1) were obtained with the left-skewed age-class distribution using the rotation lengths of 60 and 80 years, and with the normal age-class distribution using the rotation length of 120 years. Altogether, the management regimes integrating both timber and energy wood production and using fertilization provided, on average, the lowest emissions over all management alternatives considered.