Energy recovery from grass of urban roadside verges by anaerobic digestion and combustion after pre-processing

Grass from urban roadside verges is a potential, though widely unused, resource for bioenergy recovery. Two possible bioenergy recovery techniques were tested, i.e. i) direct anaerobic digestion of the whole parent material and ii) the “integrated generation of solid fuel and biogas from biomass” (IFBB) procedure, which divides biomass into a press fluid and a press cake by mashing and mechanical dewatering. Biomass yield, chemical composition and canopy height of biomass, contribution of functional groups, fermentation characteristics of silage and press fluids, as well as characteristics of the produced solid fuel was investigated, applying a 4-cut management for anaerobic digestion, a 2-cut management for IFBB and an 8 times mulching as a reference. Mean annual biomass yield (2013 and 2014) was 3.24, 3.33 and 5.68 t dry matter ha⁻¹ for the mulching, 4-cut management and 2-cut management, respectively. Yields were higher in 2014 due to more favourable weather conditions. Fibre concentration was higher in material of the 2-cut management than in the 4-cut management, however, methane yield of the corresponding silages was the same. Highest methane yield was gained from press fluids with 292 l_N kg⁻¹ volatile solids. The press cake had a lower heating value of 16 MJ kg⁻¹ dry matter and a K₂O/CaO index of 0.51–0.88. Gross energy output was 26.4 GJ ha⁻¹ for anaerobic digestion and 84.4 GJ ha⁻¹ for IFBB. Thus, an altered roadside verge management with reduced cutting frequency might allow a significant energy recovery and improved ecosystem services, i.e. increased biodiversity.     

Comparative analysis of harvesting machines on an operational high-density short rotation woody crop (SRWC) culture: One-process versus two-process harvest operation

Short rotation woody crops (SRWCs) are being studied and cultivated because of their potential for bioenergy production. The harvest operation represents the highest input cost for these short rotation woody crops. We evaluated three different harvesting machines representing two harvesting systems at one operational large-scale SRWC plantation. On average, 8 ton ha⁻¹ of biomass was harvested. The cut-and-chip harvesters were faster than the whole stem harvester; and the self-propelled harvester was faster than the tractor-pulled. Harvesting costs differed among the harvesting machines used and ranged from 388 € ha⁻¹ to 541 € ha⁻¹. The realized stem cutting heights were 15.46 cm and 16.00 cm for the tractor-pulled stem harvester and the self-propelled cut-and-chip harvester respectively, although a cutting height of 10 cm was requested in advance. From the potential harvestable biomass, only 77.4% was harvested by the self-propelled cut-and-chip harvester, while 94.5% was harvested by the tractor-pulled stem harvester. An increase of the machinery use efficiency (i.e. harvest losses, cost) is necessary to reduce costs and increase the competitiveness of biomass with other energy sources.     

Enhanced substrate degradation and methane yield with maleic acid pre-treatments in biomass crops and residues

Organic acids are envisaged as alternative catalysts to strong mineral acids, in pre-treatment of ligno-cellulosic biomass for anaerobic digestion (AD). To evaluate this hypothesis, an untreated control and four pre-treatments (25 °C for 24 h) involving two levels of maleic acid (34.8 and 69.6 kg m⁻³), alone and combined with sulphuric acid (4 kg m⁻³), were studied in three agricultural substrates: Arundo (aka giant reed), Barley straw and B133 fibre sorghum. Methane production was assessed in a batch AD assay (35 °C for 51 days) with 4 g L⁻¹ of volatile solid (VS) load. Fibre composition and structure were investigated through chemical analysis and Fourier transform infrared (FTIR) spectrometry. Arundo and B133 that were the most and least recalcitrant substrate, respectively, staged the highest and lowest increase in methane with high maleic acid: +62% over 218 cm³ g⁻¹ of VS in untreated Arundo; +36% over 284 cm³ g⁻¹ of VS in untreated B133. Barley straw showed an intermediate behaviour (+41% over 269 cm³ g⁻¹ of VS). H₂SO₄ addition to maleic acid did not improve CH₄ output. The large increase in methane yield determined by pre-treatments was reflected in the concurrent decrease of fibre (between 14 and 39% depending on fibrous component). Based on FTIR spectra, bands assigned to hemicellulose and cellulose displayed lower absorbance after pre-treatment, supporting the hypothesis of solubilisation of structural carbohydrates and change in fibre structure. Hence, maleic acid was shown a suitable catalyst to improve biodegradability of ligno-cellulosic biomass, especially in recalcitrant substrates as Arundo.     

Characterization,pretreatment and saccharification of spent seaweed biomass for bioethanol production using baker's yeast

Seaweeds are marine macroalgae found abundantly and viewed as potential source of phycocolloids to produce biofuel. In this study, seaweed spent biomass obtained from alginate production industry and biomass obtained after pigment extraction were found to contain a considerable amount of phycocolloids. These two spent biomasses were investigated for the production of ethanol. In this study, the red seaweed spent biomass of Gracilaria corticata var corticata showed higher content of polysaccharide (190.71 ± 30.67 mg g⁻¹ dry weight) than brown seaweed spent biomass (industrial) (136.28 ± 30.09 mg g⁻¹ dry weight). Hydrolysis of spent biomasses with different concentrations of sulfuric acid (0.1%, 0.5% and 1%) was also investigated. Brown seaweed spent biomass and red seaweed spent biomass exhibited high amount of sugar in 0.5% and 1% sulfuric acid treatment, respectively. Proximate and ultimate composition of seaweed spent biomasses were analysed for energy value. The FT-Raman spectra exhibited similar stretches for both acid hydrolysed spent biomasses with their respective standards. Ethanol produced through a fermentation process using spent hydrolysates with baker's yeast at pH 5.3 was found to be significant. The ethanol yield from brown seaweed spent biomass and red seaweed spent biomass was observed to be 0.011 g g⁻¹ and 0.02 ± 0.003 g g⁻¹ respectively, when compared with YPD (0.42 ± 0.03 g g⁻¹) and d-galactose (0.37 ± 0.04 g g⁻¹) as standard on day 4. The present study revealed the possibility of effective utilization of spent biomass from seaweed industry for ethanol production.     

Effects of delayed winter harvest on biomass yield and quality of napiergrass and energycane

Napiergrass (Cenchrus purpureus (Schumach.) Morrone) and energycane (Saccharum hyb.) are perennial grasses that are well-suited for biomass production in the southeastern USA. The purpose of this study was to determine the effects of delayed winter harvest on biomass yield and quality of these grasses. The study was conducted on two adjacent sites near Midville, GA. Each site used a split-plot design with four replications, with species as the main plot, and harvest times (December, January, or February) as sub-plots. Dry matter (DM) yields were measured by mechanical harvesting, and a sample of biomass was taken from each harvest for determination of ethanol production by simultaneous saccharification and fermentation (SSF). Biomass moisture, N, P, K, and ash mass fractions were also measured. Energycane DM yields were stable from December (46.8 Mg ha⁻¹) to January (42.9 Mg ha⁻¹), but then declined (36.8 Mg ha⁻¹), while napiergrass yields declined sharply from December (47.0 Mg ha⁻¹) to January (35.0 Mg ha⁻¹). Napiergrass moisture mass fraction was reduced by an average of 18% in February harvests compared to December. Mass fractions of N, K, and ash tended to decrease with later harvesting, but sometimes increased due to changes in biomass composition. Delaying harvest of napiergrass from December to January reduced N removal by an average of 144 kg ha⁻¹, while delaying harvest of energycane to February reduced N removal by an average of 54 kg ha⁻¹. In SSF, later-harvested energycane produced less ethanol per unit of DM while napiergrass was less affected by harvest date.     

Changes in feedstock quality in willow chip piles created in winter from a commercial scale harvest

Storage and handling are important facets of biomass logistics because there are associated costs and biomass properties can change significantly as material proceeds through the supply chain. Thus, this aspect of biomass supply systems requires continued study. Shrub willow chips were harvested, and used to create six piles that each contained between 10 and 22 Mg (fresh biomass). Material was monitored for several months in temporary storage to assess changes in biomass quality (moisture, ash and energy content). Internal pile temperatures increased due to biological activity and conditions within a pile quickly differentiated based on location (shell, core, top, and side). Mean moisture content increased from 42 to 47% (mass fraction) between harvest and delivery of the chips, but ranged between 37 and over 60% over the next three months depending on pile location with the shell generally drier than the core. Mean ash content increased 1 to 2% points (mass fraction) between harvesting, reloading and delivery to the trial location, but became more variable during storage. Higher heating values (HHV) were stable between 18.6 and 19.0 MJ kg⁻¹ over the six months, but lower heating values (LHV) ranged between 8.6 and 11.7 MJ kg⁻¹ and mirrored changes in moisture content. There was minimal change in chip quality over two months, but quality became more variable over longer time periods. This period could be extended, and negative effects on chip quality could be mitigated, by improving storage methods, blending different types of chips, or employing pretreatments.     

Upgraded biofuel from residue biomass by Thermo-Catalytic Reforming and hydrodeoxygenation

Research is focused on the utilisation of waste or residue biomass for bioenergy conversion. A promising conversion technology for the production of liquid biofuels from residue biomass is a process called Thermo-Catalytic Reforming (TCR^®​) which is a combination of prior thermal treatment of the biomass at mild temperatures (intermediate pyrolysis) followed by a second catalytic treatment step at elevated temperatures (reforming). This article focuses on the conversion of TCR^® liquids from digestate as a feedstock for subsequent hydrocarbon production. The generated bio-oil showed a lower heating value of 34.0 MJ kg⁻¹ with an oxygen content of 7.0% and a water content of 2.2%. The bio-oil was hydrodeoxygenated using an industrial NiMo–Al₂O₃ catalyst at temperatures of 503 K–643 K and a pressure of 14 MPa. The hydrodeoxygenated bio-oil reached a lower heating value of 42.3 MJ kg⁻¹ with an oxygen content below 0.8 mg kg⁻¹ and water content of 30 ppm. Product yields and catalyst life give confidence that upgrading of the TCR^®​ bio-oil offers a suitable option to meet the high standards of common fuels.     

Optimization of mechanical pre-treatment of Laminariaceae spp. biomass-derived biogas

Macroalgae have not met their full potential to date as biomass for the production of energy. One reason is the high cost associated with the pretreatment which breaks the biomass's crystalline structure and better exposes the fermentable sugars to anaerobes. In the attempt to overcome this technological barrier, the performance of a Hollander beater mechanical pretreatment is assessed in this paper. This pretreatment has been applied to a batch of Laminariaceae biomass and inoculated with sludge from a wastewater treatment plant. The derived biogas and methane yields were used as the responses of a complex system in order to identify the optimal system input variables by using the response surface methodology (RSM). The system's inputs considered are the mechanical pretreatment time (5–15 min range), the machine's chopping gap (76–836 μm) and the mesophilic to thermophilic range of temperatures (30–50 °C). The mechanical pretreatment was carried out with the purpose of enhancing the biodegradability of the macroalgal feedstock by increasing the specific surface area available during the anaerobic co-digestion. The pretreatment effects on the two considered responses are estimated, discussed and optimized using the tools provided by the statistical software Design-Expert v.8. The best biogas yield of treated macroalgae was found at 50 °C after 10 min of treatment, providing 52% extra biogas and 53% extra methane yield when compared to untreated samples at the same temperature conditions. The highest biogas rate achieved by treating the biomass was 685 cc gTS⁻¹, which is 430 cc gTS⁻¹ in terms of CH₄ yield.     

Hydrogen,ethanol and cellulase production from pulp and paper primary sludge by fermentation with Clostridium thermocellum

Pulp and paper industry primary sludge being largely composed of lignocellulosic fibres, it could be used as carbon source by bacteria having cellulolytic capability. The aim of this study was to evaluate the use of cellulose contained in this type of sludge for Clostridium thermocellum to produce ethanol, hydrogen and cellulases. In an ATCC 1191 medium containing 5 kg m⁻³ dry primary sludge from recycled paper mill, batch culture reached stationary phase after 2 days. All of the available cellulose was hydrolysed after 60 h of incubation, with a final pH of 5.83. Metabolites produced after 60 h of fermentation were acetate (8.50 mol m⁻³), ethanol (11.30 mol m⁻³), lactate (8.75 mol m⁻³), formate (0.27 mol m⁻³), hydrogen (11.20 mol m⁻³) and carbon dioxide (18.41 mol m⁻³). Cellulase activity was detected in the supernatant after 36 h, with a maximal activity of 0.25 U cm⁻³ at 72 h. Pulp and paper primary sludge appeared to be a readily usable substrate for C. thermocellum at this concentration, yielding both potential biofuels (hydrogen and ethanol) as well as active cellulases.     

Mild alkaline pre-treatments loosen fibre structure enhancing methane production from biomass crops and residues

Three ligno-cellulosic substrates representing varying levels of biodegradability (giant reed, GR; fibre sorghum, FS; barley straw, BS) were combined with mild alkaline pre-treatments (NaOH 0.05, 0.10 and 0.15 N at 25 °C for 24 h) plus untreated controls, to study pre-treatment effects on physical-chemical structure, anaerobic digestibility and methane output of the three substrates. In a batch anaerobic digestion (AD) assay (58 days; 35 °C; 4 g VS l⁻¹), the most recalcitrant substrate (GR) staged the highest increase in cumulative methane yield: +30% with NaOH 0.15 N over 190 ml CH₄ g⁻¹ VS in untreated GR. Conversely, the least recalcitrant substrate (FS) exhibited the lowest gain (+10% over 248 ml CH₄ g⁻¹ VS), while an intermediate behaviour was shown by BS (+15% over 232 ml CH₄ g⁻¹ VS). Pre-treatments speeded AD kinetics and reduced technical digestion time (i.e., the time needed to achieve 80% methane potential), which are the premises for increased production capacity of full scale AD plants. Fibre components (cellulose, hemicellulose and acid insoluble lignin determined after acid hydrolysis) and substrate structure (Fourier transform infra-red spectroscopy and scanning electron microscopy) outlined reductions of the three fibre components after pre-treatments, supporting claims of loosened binding of lignin with cellulose and hemicellulose. Hence, mild alkaline pre-treatments were shown to improve the biodegradability of ligno-cellulosic substrates to an extent proportional to their recalcitrance. In turn, this contributes to mitigate the food vs. fuel controversy raised by the use of whole plant cereals (namely, maize) as feedstocks for biogas production.     

Assessing sustainable forest biomass potential and bioenergy implications for the northern Lake States region,USA

Forestlands in the United States have tremendous potential for providing feedstocks necessary to meet emerging renewable energy standards. The Lake States region is one area recognized for its high potential of supplying forest-derived biomass; however, the long-term availability of roundwood harvests and associated residues from this region has not been fully explored. Better distribution and temporal availability estimates are needed to formulate emerging state policies regarding renewable energy development. We used a novel predictive methodology to quantify sustainable biomass availability and likely harvest levels over a 100-year period in the Lake States region. USDA Forest Inventory and Analysis estimates of timberland were combined with published growth and yield models, and historic harvest data using the Forest Age Class Change Simulator (FACCS) to generate availability estimates. Monte-Carlo simulation was used to develop probability distributions of biomass harvests and to incorporate the uncertainty of future harvest levels. Our results indicate that 11.27–15.71 Mt y⁻¹ dry roundwood could be sustainably harvested from the Lake States. Assuming 65% collection rate, 1.87–2.62 Mt y⁻¹ residue could be removed, which if substituted for coal would generate 2.12–2.99 GW h of electricity on equivalent energy basis while reducing GHG (CO₂e) emission by 1.91–2.69 Mt annually. In addition to promoting energy security and reducing GHG emissions, forest residues for energy may create additional revenues and employment opportunities in a region historically dependent on forest-based industries.     

Growth,yield, fiber content and lodging resistance in eight varieties of Cenchrus purpureus (Schumach.) Morrone intended as energy crop

Growth, biomass yield, fiber content and lodging resistance were studied, during a six month growth period, for eight varieties of Cenchrus purpureus, intended as energy crop, in Veracruz, Mexico. Then, only yield at day 182 was assessed for two additional years. The varieties were: CT115 (CT), African Cane (AC), Taiwan (TAI), King Grass (KG), Vruckwona (VRU), Roxo (RX), OM22 (OM) and Cameroon (CAM). Local weather is warm and sub-humid, historical data for monthly average temperature and annual rainfall were 25.8 °C and 1142 mm, respectively. Height, diameter and light interception were measured monthly from day 65–185. At day 185, biomass yield and tiller density were measured. Number of lying tillers was counted to estimate lodging resistance. Cellulose and hemicellulose content were estimated in leaf and stem. No differences were found for dry matter yield or stem yield at day 185 in the first year. Regarding the next two years, TAI yielded above CT, OM or ROX. Average dry matter yield was higher in the second year than in the establishment cycle (38.6 vs 21.1 Mg ha⁻¹), but decreased in the third year (32.2 Mg ha⁻¹). In both stem and whole plant, AC and KG showed higher hemicellulose content than RX, OM or CT; while AC and VRU had higher cellulose than RX in stem, or than CT in the whole plant. Furthermore, varieties AC, KG, VRU and TAI were resistant to lodging and had a higher fiber content, so they are recommended as energetic crops.     

Will energy crop yields meet expectations?

Expectations are high for energy crops. Government policies in the United States and Europe are increasingly supporting biofuel and heat and power from cellulose, and biomass is touted as a partial solution to energy security and greenhouse gas mitigation. Here, we review the literature for yields of 5 major potential energy crops: Miscanthus spp., Panicum virgatum (switchgrass), Populus spp. (poplar), Salix spp. (willow), and Eucalyptus spp. Very high yields have been achieved for each of these types of energy crops, up to 40 t ha⁻¹ y⁻¹ in small, intensively managed trials. But yields are significantly lower in semi-commercial scale trials, due to biomass losses with drying, harvesting inefficiency under real world conditions, and edge effects in small plots. To avoid competition with food, energy crops should be grown on non-agricultural land, which also lowers yields. While there is potential for yield improvement for each of these crops through further research and breeding programs, for several reasons the rate of yield increase is likely to be slower than historically has been achieved for cereals; these include relatively low investment, long breeding periods, low yield response of perennial grasses to fertilizer, and inapplicability of manipulating the harvest index. Miscanthus × giganteus faces particular challenges as it is a sterile hybrid. Moderate and realistic expectations for the current and future performance of energy crops are vital to understanding the likely cost and the potential of large-scale production.     

Estimating sustainable crop residue removal rates and costs based on soil organic matter dynamics and rotational complexity

The government of Ontario, Canada, has committed to stopping the use of coal for electrical generation by 2014 and agricultural biomass is being considered as replacement. However, there is limited information on whether the annual 2 million Mg of biomass required to replace coal could be sustainably supplied by agriculture and at what costs. This study assesses the sustainable availability and the farm-gate break-even cost of residue biomass from three crops (corn, soybean and winter wheat) grown under two common rotation scenarios in Ontario. Sustainably removable residue (SRR) rates are determined using a five-step approach that accounts for maintenance soil organic matter (MSOM) in the presence of yield and rotation variations across counties. Under typical SOM formation and decomposition conditions and assuming typical corn-soybean and corn-soybean-winter wheat rotation scenarios, about 1.1 million Mg of residue could be sustainably removed each year, primarily from the major agricultural counties in the province. While rotational complexity enhances SRR, the inclusion of soybean decreases available residue compared to corn and winter wheat. The break-even price for crop residues, representing the minimum price necessary to cover all variable and fixed costs for the farmer, is between $57 Mg⁻¹ and $87 Mg⁻¹. However, the actual amount supplied for each biomass price depends critically on the opportunity costs associated with not growing typical crops in the conventional manner.     

Steam explosion pretreatment and enzymatic saccharification of duckweed (Lemna minor) biomass

Our previous research has shown that duckweed is potentially an ideal feedstock for the production of biofuels because it can be effectively saccharified enzymatically. Here we report the results of experiments in which duckweed was pre-treated by steam explosion prior to enzyme digestion. A range of temperatures, from 130 to 230 °C with a fixed retention time of 10 min, were employed. The best pretreatment conditions were 210 °C for 10 min; these conditions produced the highest amount of water-soluble material (70%), the greatest levels of starch solubilisation (21%) and hemicellulose and pectic polysaccharides degradation (60%). The use of these steam explosion conditions enabled large reductions in the concentrations of enzymes required for effective saccharification. The amount of Celluclast required was reduced from 100 U (4.35 FPU) g⁻¹ substrate to 20 U g⁻¹ substrate, and additional beta-glucosidase was reduced from 100 to 2 U g⁻¹ substrate.     

Supercritical water gasification of timothy grass as an energy crop in the presence of alkali carbonate and hydroxide catalysts

This study is focused on identifying the candidature of timothy grass as an energy crop for hydrogen-rich syngas production through supercritical water gasification. Timothy grass was gasified in supercritical water to investigate the impacts of temperature (450–650 °C), biomass-to-water ratio (1:4 and 1:8) and reaction time (15–45 min) in the pressure range of 23–25 MPa. The impacts of carbonate catalysts (e.g., Na₂CO₃ and K₂CO₃) and hydroxide catalysts (e.g., NaOH and KOH) at variable mass fractions (1–3%) were examined to maximize hydrogen yields. In the non-catalytic gasification of timothy grass, highest hydrogen (5.15 mol kg⁻¹) and total gas yields (17.2 mol kg⁻¹) with greater carbon gasification efficiency (33%) and lower heating value (2.21 MJ m⁻³) of the gas products were obtained at 650 °C with 1:8 biomass-to-water ratio for 45 min. However, KOH at 3% mass fraction maximized hydrogen and total gas yields up to 8.91 and 30.6 mol kg⁻¹, respectively. Nevertheless, NaOH demonstrated highest carbon gasification efficiency (61.3%) and enhanced lower heating value of the gas products (4.68 MJ m⁻³). Timothy grass biochars were characterized through Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy to understand the behavior of the feedstock to rising temperature and reaction time. The overall findings suggest that timothy grass is a promising feedstock for hydrogen production via supercritical water gasification.     

Compositional differences among upland and lowland switchgrass ecotypes grown as a bioenergy feedstock crop

Feedstock quality mainly depends upon the biomass composition and bioenergy conversion system being used. Higher cellulose and hemicellulose concentrations are desirable for biochemical conversion, whereas higher lignin is favored for thermochemical conversion. The efficiency of these conversion systems is influenced by the presence of high nitrogen and ash concentrations. Switchgrass (Panicum virgatum L.) varieties are classified into two ecotypes based on their habitat preferences, i.e., upland and lowland. The objectives of this study were to quantify the chemical composition of switchgrass varieties as influenced by harvest management, and to determine if ecotypic differences exist among them. A field study was conducted near Ames, IA during 2012 and 2013. Upland (‘Cave-in-Rock’, ‘Trailblazer’ and ‘Blackwell’) and lowland switchgrass varieties (‘Kanlow’ and ‘Alamo’) were grown in a randomized block design with six replications. Six biomass harvests were collected at approximately 2-week intervals each year. In both years, delaying harvest increased cellulose, hemicellulose and lignin concentrations while decreasing nitrogen and ash concentrations in all varieties. On average, Kanlow had the highest cellulose and hemicellulose concentration (354 and 321 g kg⁻¹ DM respectively), and Cave-in-Rock had the highest lignin concentration (33 g kg⁻¹ DM). The lowest nitrogen and ash concentrations were observed in Kanlow (14 and 95 g kg⁻¹ DM respectively). In general, our results indicate that delaying harvest until fall improves feedstock quality, and ecotypic differences do exist between varieties for important feedstock quality traits. These findings also demonstrate potential for developing improved switchgrass cultivars as bioenergy feedstock by intermating lowland and upland ecotypes.     

Sweet sorghum as a whole-crop feedstock for ethanol production

The potential of sweet sorghum as an alternative crop for ethanol production was investigated in this study. Initially, the enzymatic hydrolysis of sorghum grains was optimized, and the hydrolysate produced under optimal conditions was used for ethanol production with an industrial strain of Saccharomyces cerevisiae, resulting in an ethanol concentration of 87 g L⁻¹. From the sugary fraction (sweet sorghum juice), 72 g L⁻¹ ethanol was produced. The sweet sorghum bagasse was submitted to acid pretreatment for hemicellulose removal and hydrolysis, and a flocculant strain of Scheffersomyces stipitis was used to evaluate the fermentability of the hemicellulosic hydrolysate. This process yielded an ethanol concentration of 30 g L⁻¹ at 23 h of fermentation. After acid pretreatment, the remaining solid underwent an alkaline extraction for lignin removal. This partially delignified material, known as partially delignified lignin (PDC), was enriched with nutrients in a solid/liquid ratio of 1 g/3.33 mL and subjected to simultaneous saccharification and fermentation (SSF) process, resulting in an ethanol concentration of 85 g L⁻¹ at 21 h of fermentation. Thus, from the conversion of starchy, sugary and lignocellulosic fractions approximately 160 L ethanol.ton⁻¹ sweet sorghum was obtained. This amount corresponds to 13,600 L ethanol.ha⁻¹.     

Analytical evaluation of different carbon sources and growth stimulators on the biomass and lipid production of Chlorella vulgaris – Implications for biofuels

The key challenges in lipid production from marine microalgae include the selection of appropriate strain, optimization of the culture conditions and enhancement of biolipid yield. This study is aimed at evaluating the optimal harvest time and effect of chlorella growth factor (CGF) extract, carbon sources and phytohormones on the biomass and lipid production in Chlorella vulgaris. CGF, extracted using hot water from Chlorella has been reported to possess various medicinal properties. However, in the present study, for the first time in C. vulgaris, CGF was found as a best growth stimulator by enhancing the biomass level (1.208 kg m⁻³) significantly on day 5. Gibberellin and citrate augmented the biomass by 0.935 kg m⁻³ and 1.025 kg m⁻³. Combination of CGF and phytohormones were more effective than CGF and carbon sources. Analysis of fatty acid methyl esters indicated that the ratio of saturated to unsaturated fatty acids is higher in cytokinin, abscisic acid and CGF, and are also rich in short chain carbon atoms, ideal criteria for biodiesel. Nitrogen starvation favoured synthesis of more unsaturated fatty acids than saturated. This study shows that CGF enhances the biomass and lipid significantly and thus can be used for large scale biomass production.     

Cob biomass supply for combined heat and power and biofuel in the north central USA

Corn (Zea mays L.) cobs are being evaluated as a potential bioenergy feedstock for combined heat and power generation (CHP) and conversion into a biofuel. The objective of this study was to determine corn cob availability in north central United States (Minnesota, North Dakota, and South Dakota) using existing corn grain ethanol plants as a proxy for possible future co-located cellulosic ethanol plants. Cob production estimates averaged 6.04 Tg and 8.87 Tg using a 40 km radius area and 80 km radius area, respectively, from existing corn grain ethanol plants. The use of CHP from cobs reduces overall GHG emissions by 60%–65% from existing dry mill ethanol plants. An integrated biorefinery further reduces corn grain ethanol GHG emissions with estimated ranges from 13.9 g CO₂ equiv MJ⁻¹ to 17.4 g CO₂ equiv MJ⁻¹. Significant radius area overlap (53% overlap for 40 km radius and 86% overlap for 80 km radius) exists for cob availability between current corn grain ethanol plants in this region suggesting possible cob supply constraints for a mature biofuel industry. A multi-feedstock approach will likely be required to meet multiple end user renewable energy requirements for the north central United States. Economic and feedstock logistics models need to account for possible supply constraints under a mature biofuel industry.