Calorific value of Prosopis africana and Balanites aegyptiaca wood: Relationships with tree growth, wood density and rainfall gradients in the West African Sahel

Prosopis africana and Balanites aegyptiaca are native tree species in the West African Sahel and provide wood for fuel, construction and other essential products. A provenance/progeny test of each species was established at one relatively dry site in Niger, and evaluated at 13 years. Gross calorific value of the wood was determined for a random sample of trees in each test: gross CV and CVm³ = gross calorific value in MJ kg⁻¹ and MJ m⁻³, respectively. The major objectives were to determine if gross CV was positively correlated with wood density and tree growth, and if gross CV and/or CVm³ varied with rainfall gradients in the sample region. Provenances were grouped into a drier and more humid zone, and correlations were computed among all trees and separately in each zone. Results indicated that gross CV was not significantly correlated with density in either species. Gross CV was positively correlated with growth of P. africana (but not B. aegyptiaca) only in the drier zone. Gross CVm³ was positively correlated with growth of both species, and the correlations were stronger in the drier zone. Multiple regressions with provenance latitude, longitude and elevation indicated that provenance means for gross CV increased, in general, from the drier to the more humid zones. Regressions with gross CVm³ were not significant. Results are compared with earlier research reports from the provenance/progeny tests and with other tropical hardwood species; and practical implications are presented for tree improvement and conservation programs in the region.     

Predictive models for dry weight estimation of above and below ground biomass components of Populus deltoides in India: Development and comparative diagnosis

This article concentrates on development of statistical models for prediction of biomass components (above and below ground) of standing trees of Populus deltoides. Twenty seven trees (three each from age one to nine years) were destructively harvested, separated, sorted, sub-sampled, dried to constant weight at 60 °C and weighted for biomass components (leaf, twig, branch, bole, stump root, lateral root, fine root). Harvesting in a similar manner, was continued annually up to nine years of tree age and thus in all 27 sampled trees were available for analysis and fitting of models. Diameter at breast height (dbh) alone was a very good predictor of dry weight and accordingly the height was not included in the model. Various functions viz (linear, allometric, logistic, gompertz and chapman-richards), were attempted for dry weight estimation. The linear model, though easiest to fit, suffered from the ‘negative estimation problem’, specifically for the lower range of explanatory variate. Of the remaining non-linear models, the allometric model outperformed the others on the basis of validation criterions. The value of R² ranged from 0.95 to 0.99, for the allometric models fitted on various biomass components. The proposed models can be used for prediction of component wise dry biomass of P. deltoides for a wide range of dbh values (1-50 cm) at one end and can also help farmers in the choice of economical harvest rather than the traditional physical rotation. In addition, they can be used in carbon sequestration studies, which needs complete biomass estimation.     

Vegetable oil production potential from Jatropha curcas, Croton megalocarpus, Aleurites moluccana, Moringa oleifera and Pachira glabra: Assessment of renewable energy resources for bio-energy production in Africa

Research on vegetable oil for biofuels in Africa and Asia has focused mainly on Jatropha curcas while other potential oil bearing plants have received little attention. Vegetable oil production potential for five oil bearing plant species namely: Aleurites moluccana, Croton megalocarpus, Jatropha curcas, Moringa oleifera and Pachira glabra were investigated. Nuts and seeds of the plants were collected from the wild and their potential for vegetable oil production assessed in terms of seed/nut acreage yield, seed/nut oil content, harvesting requirement, and upstream processing before vegetable oil recovery. All five varieties were found to contain acceptable but different oil content ranging from 20 to 33% w/w, and seed/nut acreage yield of 3 t ha⁻¹ y⁻¹ to 12.5 t ha⁻¹ y⁻¹. Upstream processing was needed for A. moluccana to break open nuts to release the kernel, and dehulling for both C. megalocarpus and J. curcas to release the seeds, before extracting the vegetable oil, while the seeds of both M. oleifera and P. glabra did not need upstream processing. The Multi-criteria Decision Analysis ranked C. megalocarpus as the plant with the highest vegetable oil production potential of 1.8 t ha⁻¹ y⁻¹ followed by M. oleifera, J. curcas (1 t ha⁻¹ y⁻¹), A. moluccana, and P. glabra. The analysis underlines the need for more studies on C. megalocarpus and M. oleifera for biofuel production in Africa and other regions.     

Modeling fuel NOx formation from combustion of biomass-derived producer gas in a large-scale burner

This study investigates the characteristics of fuel NO_x formation resulting from the combustion of producer gas derived from biomass gasification using different feedstocks. Common industrial burners are optimized for using natural gas or coal-derived syngas. With the increasing demand in using biomass for power generation, it is important to develop burners that can mitigate fuel NO_x emissions due to the combustion of ammonia, which is the major nitrogen-containing species in biomass-derived gas. In this study, the combustion process inside the burner is modeled using computational fluid dynamics (CFD) with detailed chemistry. A reduced mechanism (36 species and 198 reactions) is developed from GRI 3.0 in order to reduce the computation time. Combustion simulations are performed for producer gas arising from different feedstocks such as wood gas, wood + 13% DDGS (dried distiller grain soluble) gas and wood + 40% DDGS gas and also at different air equivalence ratios ranging from 1.2 to 2.5. The predicted NO_x emissions are compared with the experimental data and good levels of agreement are obtained. It is found out that NO_x is very sensitive to the ammonia content in the producer gas. Results show that although NO–NO₂ interchanges are the most prominent reactions involving NO, the major NO producing reactions are the oxidation of NH and N at slightly fuel rich conditions and high temperature. Further analysis of results is conducted to determine the conditions favorable for NO_x reduction. The results indicate that NO_x can be reduced by designing combustion conditions which have fuel rich zones in most of the regions. The results of this study can be used to design low NO_x burners for combustion of gas mixtures derived from gasification of biomass. One suggestion to reduce NO_x is to produce a diverging flame using a bluff body in the flame region such that NO generated upstream will pass through the fuel rich flame and be reduced.     

Comparative study of bio-ethanol production from mahula (Madhuca latifolia L.) flowers by Saccharomyces cerevisiae and Zymomonas mobilis

Mahula (Madhuca latifolia L.) flower is a suitable alternative cheaper carbohydrate source for production of bio-ethanol. Recent production of bio-ethanol by microbial fermentation as an alternative energy source has renewed research interest because of the increase in the fuel price. Saccharomyces cerevisiae (yeast) and Zymomonas mobilis (bacteria) are two most widely used microorganisms for ethanol production. In this study, experiments were carried out to compare the potential of the yeast S. cerevisiae (CTCRI strain) with the bacterium Z. mobilis (MTCC 92) for ethanol fermentation from mahula flowers. The ethanol production after 96 h fermentation was 149 and 122.9 g kg⁻¹ flowers using free cells of S. cerevisiae and Z. mobilis, respectively. The S. cerevisiae strain showed 21.2% more final ethanol production in comparison to Z. mobilis. Ethanol yield (Yx/s), volumetric product productivity (Qp), sugar to ethanol conversion rate (%) and microbial biomass concentration (X) obtained by S. cerevisiae were found to be 5.2%, 21.1%, 5.27% and 134% higher than Z. mobilis, respectively after 96 h of fermentation.     

Genetic diversity analysis by RAPD markers in candidate plus trees of Pongamia pinnata, a promising source of bioenergy

Pongamia pinnata has received much attention in recent years as a source of seed oil that can provide a substitute for diesel fuel. Very little molecular work has been reported on this species. This paper reports our studies on the diversity amongst the CPTs (candidate plus trees) of P. pinnata previously identified on the basis of morphometric traits, particularly pod and seed traits. For this RAPD (random amplified polymorphic DNA) markers were used to determine the genetic diversity among 10 genotypes of P. pinnata CPTs selected for suitability for energy production. For further investigation, 18 primers generating stable band patterns from 40 tested arbitrary primers were selected. A total of 210 amplification products were obtained of which 10.48% were polymorphic. The genetic similarity index ranged from 0.11 to 0.87. Genetic distance values were used to generate a dendrogram (UPGMA) between the genotypes. The Mantel method used for comparing the similarity matrixes produced correlation coefficients that were statistically significant for the RAPD marker. This genomic analysis allows a cost effective characterization of CPTs of P. pinnata. The present investigation supports in future the development of genetic map in Pongamia which are a highly useful tool in breeding and may provide information on the inheritance of features crucial for increase seed yield, oil content and the resistance to key insects and pests. Thus this study warrants Pongamia producers to realize its full potential and contributes for its sustainable production and improvement.     

Investigation of NOx conversion characteristics in a porous medium

The conversion of nitric oxide (using CNG/air as fuel/oxidizer) inside a porous medium is investigated in this study. Unlike freely propagating flames, porous burners provide a solid medium that facilitates heat exchange with the gaseous phase. The heat exchange allows the stabilization of a variety of fuel mixtures from lean to rich and with a variety of calorific values. In addition, it allows the control of the reaction zone temperature and thus the control of pollutant formation while maintaining flame stability. An experimental porous burner was designed and manufactured for this purpose. The effects of equivalence ratio and flow velocity on the flame stabilization, NO_x and TFN (total fixed nitrogen) conversion ratios, and temperature profiles along the burner are investigated. In addition, numerical calculations using the PLUG flow simulator model and the GRI 3.0 kinetic mechanism reveals the key reactions which control the conversion efficiency. It was found that under slightly fuel-rich conditions (φ?1.3) NO_x mostly converts to N₂ with a maximum conversion ratio of 65%, while for higher equivalence ratios (φ>1.3) a large proportion of NO_x converts to NH₃. Results from experiments and numerical modeling showed that the temperature profile along the burner has significant effects on the NO_x and TFN conversion ratios. It was also found that temperatures between 1000 and 1500 K are most desirable for NO_x and TFN conversion in the porous burner. Analysis of the chemical paths for the low- and high-equivalence-ratio cases showed that the formation of nitrogen-containing species under very rich conditions (φ>1.3) is due to the increased importance of the HCNO path as compared to the HNO path. The latter is the dominant path at low equivalence ratios (φ?1.3) and leads to the formation of N₂. The NO concentration in the initial mixture was found to improve the conversion by up to 20% at low equivalence ratios (φ?1.3) and to have negligible effect at higher equivalence ratios.     

Potential of microalgae oil from Dunaliella tertiolecta as a feedstock for biodiesel

Alternative, non-food based biomass fuel feedstock development is vital for our national security, economy and the environment. Microalgae are among the most promising of these alternatives. Microalgal cell growth rates and metabolic products are affected by a combination of environmental parameters. In this work, the influences of light source, light intensity, CO₂ concentration, and photoperiod on the growth of Dunaliella tertiolecta (D. tertiolecta) were studied. The effects of these environmental parameters on the lipid content and fatty acid composition of D. tertiolecta were also investigated. Red light-emitting diodes (LEDs), white LEDs, and fluorescent lights were all found to be effective for algal growth. Increasing light intensity resulted in significantly more rapid algal growth, and increasing the period of light also significantly increased biomass productivity. Similar growth rates were observed for 2%, 4%, and 6% CO₂-concentrations. The different light sources and intensities were found to have no significant effect on FAME composition of D. tertiolecta. Methyl linolenate and methyl palmitate were found to be the major components of FAME produced from D. tertiolecta oil. D. tertiolecta and its derived oils should be a suitable feedstock for biofuel production.     

Dark hydrogen production in nitrogen atmosphere – An approach for sustainability by marine cyanobacterium Leptolyngbya valderiana BDU 20041

Biological hydrogen production is an ideal system for three main reasons i) forms a renewable energy source, ii) gives clean fuel and iii) serves as a good supplement to oil reserves. The major challenges faced in biological hydrogen production are the presence of uptake hydrogenase and lack of sustainability in the cyanobacterial hydrogen production system. Three different marine cyanobacterial species viz. Leptolyngbya valderiana BDU 20041, Dichothrix baueriana BDU 40481 and Nostoc calcicola BDU 40302 were studied for their potential use in hydrogen production. Among these, L. valderiana BDU 20041, was found to produce hydrogen even in 100% nitrogen atmosphere which was 85% of the hydrogen produced in argon atmosphere. This is the first report of such a high rate of production of hydrogen in a nitrogen atmosphere by a cyanobacterium, which makes it possible to develop sustained hydrogen production systems. L. valderiana BDU 20041, a dark hydrogen producer uses the reductant essentially supplied by the respiratory pathway for hydrogen production. Using inhibitors, this organism was found to produce hydrogen due to the activities of both nitrogenase and bidirectional hydrogenase, while it had no ‘uptake’ hydrogenase activity. The other two organisms though had low levels of bidirectional hydrogenase, possessed considerable ‘uptake’ hydrogenase activity and hence could not release much hydrogen either in argon or nitrogen atmosphere.     

Dominant height growth and site index curves for Calabrian pine (Pinus brutia Ten.) in central Cyprus

A dominant height growth model and a site index model were developed for Calabrian pine (Pinus brutia Ten.) in central Cyprus. Data from 64 stem analysis in 32 temporary plots, where Calabrian pine was the only tree species, were used for modeling. The plots were selected randomly in proportion to two site types. Four difference equations were tested. The evaluation criteria included qualitative and quantitative examinations and a testing with split data. The difference equation of Korf showed the best results for all data. An analysis of the height growth patterns among sites - as these were defined from the selected equation - was made in order to study the behavior of different site index curves. Results indicated the validity of a common height growth model for the two sites. In spite of the irregular height growth pattern observed in Calabrian pine, the model obtained allows us to classify and compare correctly Calabrian pine stands growing at different sites.     

Valorization of Leucaena leucocephala for energy and chemicals from autohydrolysis

In this work, Leucaena leucocephala K366 was characterized chemical and energy terms, and assessed its potential as a lignocellulosic raw material and energetic and industrial crop specie, and its integral fractionation by autohydrolysis by evaluating its calorific value, holocellulose, glucan, xylan, arabinan, lignin and oligomers and monomers contents in autohydrolysis liquor and solid phase. Also, this paper will consider the influence of the temperature and time of autohydrolysis process from L. leucocephala K366 to obtain valuable liquor and a suitable solid phase to produce energy by combustion.Valuable liquor was obtained from the autohydrolysis of L. leucocephala by simultaneously using operating temperatures and times in the medium-high ranges studied, namely: 172-184 °C and 15-30 min. The optimum processing conditions provided an acceptable yield (16-26%), and high xylose and xylo-oligomer contents in the liquor (10.0 and 58.6%, respectively, of the amounts present in the starting raw material when operating at 184 °C for 30 min) in comparison with other raw materials. The arabinan fraction was extracted virtually completely —only 8.3% remained in the solid fraction—, and the acetyl group fraction was recovered in full. In addition, these conditions reduced the glucose content of the liquor to 2.9% of the amount present in the raw material while largely preserving the integrity of cellulose fibers.Klason lignin was scarcely dissolved under the operating conditions of the autohydrolysis process. This increased the calorific value of the solid phase by 9% (under the most drastic operating conditions) with respect to the starting raw material.     

Remarkable enhancement on hydrogen production performance of Rhodobacter sphaeroides by disrupting spbA and hupSL genes

The redox balance and bacteriochlorophyll (Bchl) synthesis are both significant to hydrogen generation in photosynthetic bacteria. In this study, spbA and hupSL genes were knocked out from the genome of Rhodobacter sphaeroides HY01. The UV–vis spectra showed that the Bchl contents of spbA mutants were enhanced under photosynthetic conditions. The hydrogen yields of WH04 (hupSL⁻) and WSH10 (spbA⁻, hupSL⁻) mutants increased by 19.4%, 21.8%, and the maximum hydrogen evolution rates increased by 29.9% and 55.0% respectively using glutamate as sole nitrogen source. The maximum hydrogen production rate of WSH10 was up to 141.9 mL/(L·h). The nifH expression levels of the mutants and the wild type supported the correlation between hydrogen production and nitrogenase activity. The results demonstrate that disruption of spbA in R. sphaeroides can partially derepress the ammonium inhibition in nitrogenase activity, and indicate that spbA is a negative regulator in nitrogenase synthesis in the presence of ammonium.     

Enhancement in hydrogen production by co-cultures of Bacillus and Enterobacter

Defined co-cultures of hydrogen (H₂) producers belonging to Citrobacter, Enterobacter, Klebsiella and Bacillus were used for enhancing the efficiency of biological H₂ production. Out of 11 co-cultures consisting of 2–4 strains, two co-cultures composed of Bacillus cereus EGU43, Enterobacter cloacae HPC123, and Klebsiella sp. HPC793 resulted in H₂ yield up to 3.0 mol mol⁻¹ of glucose. Up-scaling of the reactor by 16-fold resulted in a corresponding increase in H₂ production with an actual evolution of 7.44 L of H₂. It constituted 58.2% of the total biogas. Continuous culture evolution of H₂ by co-cultures (B. cereus EGU43 and E. cloacae HPC123) immobilized on ligno-cellulosic materials resulted in 6.4-fold improvement in H₂ yield compared to free floating bacteria. This synergistic influence of B. cereus and E. cloacae can offer a better strategy for H₂ production than undefined or mixed cultures.     

Fuelwood characteristics of some indigenous woody species of north-east India

Wood energy is identified as the major source of energy in rural India and this has necessitated the identification of suitable tree species that can be included in energy plantation programme. As a preliminary to a more detailed future study of wood energy plantation, four indigenous perennial tree species, viz. Albizzia lucida, Syzygium fruticosum, Pterospermum lanceaefolium and Premna bengalensis growing in their natural habitat of north-east India were collected for fuelwood characterization studies. Various physico-chemical properties, viz. moisture and ash content, density, solubility in cold water, hot water and alkali, cellulose, holocellulose, lignin and extractive contents of different parts of these species were determined on ash-free dry weight and extractive-free dry weight basis to find out relationship, if any, between ash and extractive content with the calorific value. In all the species, leaf component contained the highest calorific value presumably because of the presence of extractives in higher amount, followed by heartwood. Elimination of ash from the plant parts increased calorific value while extractive-free materials declined in net caloric content in all plant parts, indicating a possible relationship of these two parameters with the heat of combustion. This study concludes that A. lucida, S. fruticosum and P. lanceaefolium have better fuelwood properties and can be considered for inclusion in the energy plantation programme of north-east India.     

Landscape of Danube inland-delta and its potential of poplar bioenergy production

The Slovakian portion of the Danube inland-delta represents a unique landscape. Branches of the Danube and more or less regular flooding with its alluvial deposit have created the most fertile soils which are partly forested. The greatest portion of the area is the crop land, while the forests are man-made with the poplar clones representing the stand-forming tree species. The present study investigates the influence of 7 predictors composed of the 3 biomass fractions, location on tree and clone factors and the 4 variables of stand index and age of stand and the height and diameter of tree on the calorific values of Robusta and I-214 (Populus x euramericana) clones in Slovak territory. A statistical significance influence resulted for all predictors except for the clone factor. The average calorific value of all biomass fractions is approximately in the range of 17.8–18.4 MJ kg⁻¹ and statistical tests showed that wood has the highest calorific values while the thick bark on the lower parts of the stems had the least.     

Upgrading of the liquid fuel from fast pyrolysis of biomass over MoNi/γ-Al2O3 catalysts

The hydrotreatment of bio-oil, which obtained from fast pyrolysis of pine sawdust, was investigated over MoNi/γ-Al₂O₃ catalyst under mild conditions (373 K, 3 MPa hydrogen pressure). Acetic acid was taken as a model compound to investigate the effects of Mo promoter contents and reducing temperatures of catalysts on the catalysts activity under the condition of 473 K and 3 MPa hydrogen pressure. X-ray diffraction and temperature programmed reduction showed that the addition of Mo promoter benefited the uniformity of nickel species and inhibited the formation of NiAl₂O₄ spinel in the catalysts. The GC spectrum of liquid products showed the mechanism of the model reaction. The maximum conversion of acetic acid (33.20%) was attained over 0.06MoNi/γ-Al₂O₃ catalysts being reduced at 873 K. This catalyst was chosen for the upgrading of raw bio-oil. After the upgrading process, the pH value of the bio-oil increased from 2.33 to 2.77. The water content increased from 35.52 wt.% to 41.55 wt.% and the gross calorific value increased from 13.96 MJ/kg to 14.17 MJ/kg. The hydrogen content in the bio-oil increased from 6.25 wt.% to 6.95 wt.%. The product properties of the upgraded bio-oil, particularly the hydrogen content and the acidity were considerably improved. The results of gas chromatography–mass spectrometry analysis showed that both hydrotreatment and esterification had happened over 0.06MoNi/γ-Al₂O₃ (873) catalyst during the upgrading process.     

An efficient ZnS-UV photocatalysts generated in situ from ZnS(en)0.5 hybrid during the H2 production in methanol–water solution

Highly active ZnS-UV was obtained in situ from ZnS(en)_0.5 hybrid during the hydrogen formation using a methanol–water solution under UV irradiation. X-ray diffraction patterns and UV spectroscopy for both ZnS-UV and ZnS-400 obtained from the calcination of the ZnS(en)_0.5 hybrid showed similar structural and photophysical properties; however, the efficiency of the ZnS-UV semiconductor was 7 times higher (4825 μmol h⁻¹ g⁻¹) compared to the ZnS-400. The highest H₂ production was obtained using a UV lamp of very low intensity (2.2 mW cm⁻¹) and it is attributed to a quantum size effect caused by the slow elimination of ethylenediamine (en) in the structural ZnS layer during the UV irradiation.     

Key traits for biomass production identified in different Miscanthus species at two harvest dates

To grow the bioenergy crop Miscanthus x giganteus on wider climate range requires enlarged genetic variability. Our objective was to identify key traits favouring the production of above-ground yield in a cropping environment of Miscanthus at two harvest dates. Canopy height, panicle height, shoot number, stem diameter and above-ground yield of twenty-one clones were studied and compared with emergence earliness and growth traits at autumn and winter harvests in Northern France, during the second and third crop years.Crop age, clone, harvest date, and corresponding double interactions were significant for all traits. Species and ploidy explained clone sum of square effects (92%, 78%, 80% and 89% for canopy height, panicle height, shoot diameter and yield, respectively) and clone × age and clone × harvest date interactions for yield (94% and 77%, respectively). Plant height and shoot number were higher in the third year than in the second, whatever the harvest date. The above-ground development between the two years was higher in winter harvest than in autumn, mostly for M. sinensis. Higher above-ground development and yields were observed for M. x giganteus and M. floridulus than M. sinensis and M. sacchariflorus as well as for triploid and tetraploid M. sinensis and M. sacchariflorus than diploids. Plant height, stem diameter, lateness at panicle emergence or flowering and growth rate were the main traits positively related to yield, in contrast to shoots number and growth duration. This would help to early identify high-yielding clones and breed new inter-specific hybrids.