Effect of initial moisture content and chip size on the bioconversion efficiency of softwood lignocellulosics

Previous optimization strategies for the bioconversion of lignocellulosics by steam explosion technologies have focused on the effects of temperature, pH, and treatment time, but have not accounted for changes in severity brought about by properties inherent in the starting feedstock. Consequently, this study evaluated the effects of chip properties, feedstock size (40-mesh, 1.5 x 1.5 cm, 5 x 5 cm), and moisture content (12% and 30%) on the overall bioconversion process, and more specifically on the efficacy of removal of recalcitrant lignin from the lignocellulosic substrates following steam explosion. Increasing chip size resulted in an improvement in the solids recovery, with concurrent increases in the water soluble, hemicellulose-derived sugar recovery (7.5%). This increased recovery is a result of a decrease in the "relative severity" of the pretreatment as chip size increases. Additionally, the decreased relative severity minimized the condensation of the recalcitrant residual lignin and therefore increased the efficacy of peroxide fractionation, where a 60% improvement in lignin removal was possible with chips of larger initial size. Similarly, increased initial moisture content reduced the relative severity of the pretreatment, generating improved solids and hemicellulose-derived carbohydrate recovery. Both increased chip size and higher initial moisture content results in a substrate that performs better during peroxide delignification, and consequently enzymatic hydrolysis. Furthermore, a post steam-explosion refining step increased hemicellulose-derived sugar recovery and was most effectively delignified (to as low as 6.5%). The refined substrate could be enzymatically hydrolyzed to very high levels (98%) and relatively fast rates (1.23 g/L/h).     

Effect of thermal pretreatment on equilibrium moisture content of lignocellulosic biomass

The equilibrium moisture content (EMC) of raw lignocellulosic biomass, along with four samples subjected to thermal pretreatment, was measured at relative humidities ranging from 11% to 97% at a constant temperature of 30 °C. Three samples were prepared by treatment in hot compressed water by a process known as wet torrefaction, at temperatures of 200, 230, and 260 °C. An additional sample was prepared by dry torrefaction at 300 °C. Pretreated biomass shows EMC below that of raw biomass. This indicates that pretreated biomass, both dry and wet torrefied, is more hydrophobic than raw biomass. The EMC results were correlated with a recent model that takes into account additional non-adsorption interactions of water, such as mixing and swelling. The model offers physical insight into the water activity in lignocellulosic biomass.     

Multiscale modelling of hydrothermal biomass pretreatment for chip size optimization

The objective of this work is to develop a relationship between biomass chip size and the energy requirement of hydrothermal pretreatment processes using a multiscale modelling approach. The severity factor or modified severity factor is currently used to characterize some hydrothermal pretreatment methods. Although these factors enable an easy comparison of experimental results to facilitate process design and operation, they are not representative of all the factors affecting the efficiency of pretreatment, because processes with the same temperature, residence time, and pH will not have same effect on biomass chips of different size. In our study, a model based on the diffusion of liquid or steam in the biomass that takes into account the interrelationship between chip size and time is developed. With the aid of our developed model, a method to find the optimum chip size that minimizes the energy requirement of grinding and pretreatment processes is proposed. We show that with the proposed optimization method, an average saving equivalent to a 5% improvement in the yield of biomass to ethanol conversion process can be achieved.     

Effect of C/N ratio and moisture content on the composting of poplar wood

Summary Milled poplar wood (1.7 mm mesh size) was composted in lab-scale reactors. Initial C/N ratios were adjusted to 10:1, 30:1, and 50:1 using urea as the nitrogen source. At each C/N ratio, three moisture levels (30, 50, and 70%) were tested. C/N ratios of 50:1 or 30:1 and moisture content of 70% favored more effective composting as indicated by higher levels of mineralization of the poplar wood to CO₂.     

Impact of vegetation removal on the temperature and moisture content of red wood ant nests

We studied the influence of vegetation growing on red wood ant, Formica polyctena, hills and its removal, by cutting, on the temperature and moisture content of the nests. Vegetation was removed from half of nests (n = 10) in June and August. Generally, ant hills were small (0.1–1.1 m³) and their daily temperature fluctuations and moisture (16–38%) were low. The centre temperature of ant hills was positively correlated with ambient air temperature. Daily temperatures peaked at 13:00 and slowly decreased until 09:00 then increased again until 13:00. Nest moisture content was not related to nest volume. All the ant hills were covered with Reed Grass (Calamagrostis arundinacea) that grows through nests and reaches about 185–1085 g/dcm² of dry matter. Dry vegetation matter (g/dcm² of anthill surface) was the same on cut and uncut nests as well because all ant hills were under long-term management (vegetation removal) for at least 10 years. Although vegetation removal did not result in an immediate increase in the temperature of denuded ant hills removal did results in higher daily and night temperatures during the July-September period. The moisture content of nests with undisturbed and intact vegetation was the same. The dry matter content of vegetation strongly affected their moisture content. However, temperature at the inside centre of nests decreased as vegetation dry matter increased, i.e. there was a statistically negative correlation between temperature and moisture. The results support removing grass as a suitable management tool to facilitate the survival of wood ants. Received 30 December 2007; revised 22 April 2008; accepted 10 June 2008.     

The resistance of wood chemically modified with isocyanates: the role of moisture content in decay suppression

This paper discusses the moisture content of sound and decayed Corsican pine (Pinus nigra) after modification with isocyanates {n-butyl isocyanate (BuNCO) and 1,6-diisocyanatehexane (HDI)} at specified intervals of weight percent gain (WPG). The main effects of decay fungi (brown and white rot) and levels of modification (WPG) on moisture contents of modified samples are also examined. Corsican pine reacted with isocyanates enhanced the hydrophobic (restrained water) nature of wood. The equilibrium moisture content of chemically modified wood decreases progressively with increasing WPG. Basidiomycete decay tests demonstrated protection by chemical modification. Wood moisture contents after soil block testing are significantly influenced by decay fungi and by the extent of reaction (WPG). Moisture uptake and susceptibility to decay of modified wood are higher when exposed to Coniophora puteana than other decay fungi. Corsican pine cross-linked by reaction with HDI is less susceptible to decay and is more hydrophobic than samples reacted with the single-site reactant BuNCO at comparable WPG.     

Impact of impregnation time and chip size on sugar yield in pretreatment of softwood for ethanol production

Efficient pretreatment is necessary to make the wood-to-ethanol process more feasible. In this study, chips of different sizes were impregnated with SO₂ and steam-pretreated. Dilute-acid pretreatment together with subsequent enzymatic hydrolysis resulted in solubilization of between 69% and 73% of the fermentable sugars (glucose and mannose) in the raw material for the combinations of impregnation times and chip sizes investigated. Shorter impregnation times resulted in slightly lower mannose yields for the larger chips, probably due to poor diffusion of the catalyst. Small differences in glucose yield after enzymatic hydrolysis showed that the overall glucose yield was slightly higher for the smaller chips, however, whether the increased energy demand and cost of size reduction is compensated for by the higher yield, requires techno-economical evaluations.     

Selectivity and delignification kinetics for oxidative short‐term lime pretreatment of poplar wood,part I: Constant‐pressure

Kinetic models applied to oxygen bleaching of paper pulp focus on the degradation of polymers, either lignin or carbohydrates. Traditionally, they separately model different moieties that degrade at three different rates: rapid, medium, and slow. These models were successfully applied to lignin and carbohydrate degradation of poplar wood submitted to oxidative pretreatment with lime at the following conditions: temperature 110–180°C, total pressure 7.9–21.7 bar, and excess lime loading of 0.5 g Ca(OH)₂ per gram dry biomass. These conditions were held constant for 1–6 h. The models properly fit experimental data and were used to determine pretreatment selectivity in two fashions: differential and integral. By assessing selectivity, the detrimental effect of pretreatment on carbohydrates at high temperatures and at low lignin content was determined. The models can be used to identify pretreatment conditions that selectively remove lignin while preserving carbohydrates. Lignin removal ≥50% with glucan preservation ≥90% was observed for differential glucan selectivities between ～10 and ～30 g lignin degraded per gram glucan degraded. Pretreatment conditions complying with these reference values were preferably observed at 140°C, total pressure ≥14.7 bars, and for pretreatment times between 2 and 6 h depending on the total pressure (the higher the pressure, the less time). They were also observed at 160°C, total pressure of 14.7 and 21.7 bars, and pretreatment time of 2 h. Generally, at 110°C lignin removal is insufficient and at 180°C carbohydrates do not preserve well. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011     

Effect of substrate moisture content on fungal production of citric acid in a solid state fermentation system

Summary Under solid state fermentation conditions, the production of citric acid byAspergillus niger varied considerably with the initial moisture content of apple pomace. The stimulating effect of methanol on fungal production of citric acid decreased markedly as the substrate moisture decreased.     

Effect of temperature and moisture content on Egyptian peanut seed-borne fungi

In peanut seeds adjusted to various levels of moisture content (8.5 %, 13,5 %, 17.5 % and 21 % on a dry-weight basis) and stored for six months at 5°, 15°, 28° and 45 °C, seed-borne fungi were monthly identified and counted using the dilution plate method, and the germinability of seeds was tested. The total count of seed-borne fungi (recovered at 28 °C) increased regularly and the germinability declined with the rise moisture content and with the lengthening of the storage period. At 5°, 15° and 28 °C,A. fumigatus was almost the most dominant fungal species followed by several fungi such asAspergillus flavus, A. niger, A. terreus, Penicillium funiculosum, P. notatum, Pyrenochaeta decipians andScopulariopsis brevicaulis. The degree of dominance of each fungal species depended upon the conditions of storage and the length of storage period.A. flavus gained its highest count in seeds adjusted to 13.5 % stored at 15 °C for 1 month.Penicillium predominated at 17.5 % and 21 %, and at 13.5 % and 17.5 % when the seeds were stored for long periods at 5° and 15 °C respectively.The total count of thermophilic fungi (recovered at 45 °C) significantly increased with the rise of moisture content and with the lengthening of the storage period between 1 and 2 months and regularly declined after 4 months.A. fumigatus was so extremely dominant that it was the main component of the total fungal flora. Several fungi truly thermophilic were isolated also. They were,Mucor pusillus, Humicola grisea var.thermoidae, H. insolens, H. lanuginosa (Thermomyces lanuginosus) andSporotrichum thermophile.     

Denitrification activity,wood loss,and N2O emissions over 9 years from a wood chip bioreactor

Loss of nitrate in subsurface drainage water from agricultural fields is an important problem in the Midwestern United States and elsewhere. One possible strategy for reducing nitrate export is the use of denitrification bioreactors. A variety of experimental bioreactor designs have been shown to reduce nitrate losses in drainage water for periods up to several years. This research reports on the denitrification activity of a wood chip-based bioreactor operating in the field for over 9 years. Potential denitrification activity was sustained over the 9-year period, which was consistent with nitrate removal from drainage water in the field. Denitrification potentials ranged from 8.2 to 34 mg N kg^?1 wood during the last 5 years of bioreactor operation. Populations of denitrifying bacteria were greater in the wood chips than in adjacent subsoil. Loss of wood through decomposition reached 75% at the 90–100 cm depth with a wood half-life of 4.6 years. However, wood loss was less than 20% at 155–170 cm depth and the half-life of this wood was 36.6 years. The differential wood loss at these two depths appears to result from sustained anaerobic conditions below the tile drainage line at 120 cm depth. Pore space concentrations of oxygen and methane support this conjecture. Nitrous oxide exported in tile water from the wood chip bioreactor plots was not significantly higher than N₂O exports in tile water from the untreated control plots, and loss of N₂O from tile water exiting the bioreactor accounted for 0.0062 kg N₂O-N kg^?1 NO₃-N.     

Growth,abscisic acid content,and carbon isotope composition in wheat cultivars grown under different soil moisture

Changes in dry matter accumulation and allocation, abscisic acid content and carbon isotope composition of three wheat cultivars from dry, middle and wet climate regions were recorded at full maturity after exposure to different watering regimes (100, 50 and 25 % field capacity). Compared with the wet climate cultivar, the dry climate cultivar showed lower stem height, total leaf area, total dry biomass and total grain dry mass, and higher root/shoot ratio, abscisic acid content and carbon isotope composition under all watering regimes. Both water-limited treatments significantly reduced leaf growth and increased dry matter allocation into the roots leading to a significant raise of root/shoot ratio in all cultivars tested. In addition, drought affected morphological and physiological properties more in the dry climate cultivar than in the wet climate cultivar.     

Changes in moisture content,mycoflora and aflatoxin content of rice bran during storage

The changes in moisture content, storage mycoflora and aflatoxin B₁ (AFB₁) in bran from untreated or raw rice (Rr) and parboiled rice (Pbr) stored in small lots in polyethylene bags were studied at 15-day intervals up to 60 days, using five lots of each type of bran. Deterioration was more rapid with reference to all the three parameters, in Rr bran compared to Pbr bran, the former becoming completely overgrown and caked with fungi by the end of 60 days.Aspergillus flavus was the dominant fungus in Pbr bran, whereasA. candidus andTrichoderma viride were abundant in Rr bran. The frequency of incidence as well as concentration of AFB₁ increased with storage time in both types of bran, but the rate of increase as well as overall concentration were much higher in Rr bran. Thus raw rice bran is unsuitable for prolonged storage.Abbreviations AFB₁ aflatoxin B₁ - MC moisture content - Pbr parboiled rice - Rr raw rice     

Effect of steam explosion pretreatment on pore size and enzymatic hydrolysis of poplar

The purpose of this study was to determine the effect of batch steam explosion pretreatment on the rate of subsequent enzymatic hydrolysis of hybrid poplar wood. This pretreatment was found to be effective as indicated by the fact that for many of the pretreatment conditions studied the glucose yield obtained after 24 h of enzymatic hydrolysis using enzymes from Trichoderma reesei And Aspergillus niger is in excess of 90% of the potential, whereas the corresponding yield from unpretreated substrate is only 15%. The effect of pretreatment is believed to be primarily due to the increase in pore surface area accessible to enzyme molecules. Measurements show a considerable increase in pore volume available to 5–9 nm solute probes. Pretreated wood that was subsequently oven-dried hydrolysed poorly and showed a reduction in available pore volume after drying. Xylans are readily hydrolysed to xylose during pretreatment and owing to decomposition the amount of xylose in solution after steam pretreatment decreases as the severity of the reaction conditions increases; the converse is true for glucose. We conclude that steam explosion pretreatment can be effective on hybrid poplar and that the quantitative results obtained can be used for process design.     

Fatty acid content and composition in relation to grain size of barley

The relationship between grain size and total fatty acid (TFA) content and composition, as well as the contribution of corn size distribution to the variation of fatty acid contents between barley types, were studied in nine barley varieties (six-rowed and two-rowed winter barleys, and two-rowed spring barleys) fractionated according to grain size. Smaller grains contained as much TFA as the bigger ones. On average, the proportions of saturated fatty acids (16:0 and 18:0) and of oleic acid (18:1) are higher in large grains than in small kernels, whereas the percentages of linoleic (18:2) and linolenic (18:3) acids are lower. The higher 18:1 and the lower 18:3 proportions in two-rowed barleys compared to their six-rowed counterparts, can be explained by the indirect effect of the different grain size distribution between the barley types.     

Effect of common bean seedling pretreatment with chlorocholine chloride on photosystem II tolerance to UV-B radiation,phytohormone content,and hydrogen peroxide content

In true leaves of common bean (Phaseolus vulgaris L., cv. Berbukskaya) 11-day-old seedlings, pretreatment with 1.6 mM chlorocholine chloride (CCC) resulted in the improved photosystem II (PSII) tolerance to UV-B radiation, an increase in the contents of cytokinins, ABA, and H₂O₂, but a decrease in the content of gibberellins. It is suggested that development of increased PSII tolerance to UV-B under the influence of CCC is partially related to the increase in the contents of ABA, cytokinins, and UV-absorbing pigments in the leaves of pretreated plants.     

Selectivity and delignification kinetics for oxidative and nonoxidative lime pretreatment of poplar wood, part III: long-term

Lime pretreatment is an effective method for improving lignocellulose digestibility by removing lignin. For several weeks, mixtures of poplar wood, water, and calcium hydroxide (lime) were submitted to temperatures from 25 to 65°C, with and without aeration. Kinetic models for lignin and carbohydrate degradation were obtained as functions of temperature, time, and aeration using first-order kinetics in lignin and carbohydrates. Model 1 considered two reacting moieties (slow and fast), and Model 2 considered three (slow, medium, and fast). Model 1 was statistically better and was employed to determine differential and integral selectivities, which measure the ability of pretreatment to retain carbohydrates while removing lignin. During the first 2 weeks, when lignin content ≥ 0.80 g/g lignin in raw biomass, both glucan and xylan differential and integral selectivities decreased rapidly. Afterwards, selectivities were nearly constant ranging between 0 and 3 g lignin removed/g carbohydrate degraded.