Anne Belinda Thomsen

Bioethanol, biohydrogen and biogas production from wheat straw in a biorefinery concept.

The production of bioethanol, biohydrogen and biogas from wheat straw was investigated within a biorefinery framework. Initially, wheat straw was hydrothermally liberated to a cellulose rich fiber fraction and a hemicellulose rich liquid fraction (hydrolysate). Enzymatic hydrolysis and subsequent fermentation of cellulose yielded 0.41 g-ethanol/g-glucose, while dark fermentation of hydrolysate produced 178.0 ml-H(2)/g-sugars. The effluents from both bioethanol and biohydrogen processes were further used to produce methane with the yields of 0.324 and 0.381 m(3)/kg volatile solids (VS)(added), respectively. Additionally, evaluation of six different wheat straw-to-biofuel production scenaria showed that either use of wheat straw for biogas production or multi-fuel production were the energetically most efficient processes compared to production of mono-fuel such as bioethanol when fermenting C6 sugars alone. Thus, multiple biofuels production from wheat straw can increase the efficiency for material and energy and can presumably be more economical process for biomass utilization.

Characterization of degradation products from alkaline wet oxidation of wheat straw.

Alkaline wet oxidation pre-treatment (water, sodium carbonate, oxygen, high temperature and pressure) of wheat straw was performed as a 2(4-1) fractional factorial design with the process parameters: temperature, reaction time, sodium carbonate and oxygen. Alkaline wet oxidation was an efficient pre-treatment of wheat straw that resulted in solid fractions with high cellulose recovery (96%) and high enzymatic convertibility to glucose (67%). Carbonate and temperature were the most important factors for fractionation of wheat straw by wet oxidation. Optimal conditions were 10 min at 195 degrees C with addition of 12 bar oxygen and 6.5 g l(-1) Na2CO3. At these conditions the hemicellulose fraction from 100 g straw consisted of soluble hemicellulose (16 g), low molecular weight carboxylic acids (11 g), monomeric phenols (0.48 g) and 2-furoic acid (0.01 g). Formic acid and acetic acid constituted the majority of degradation products (8.5 g). The main phenol monomers were 4-hydroxybenzaldehyde, vanillin, syringaldehyde. acetosyringone (4-hydroxy-3,5-dimethoxy-acetophenone), vanillic acid and syringic acid, occurring in 0.04-0.12 g per 100 g straw concentrations. High lignin removal from the solid fraction (62%) did not provide a corresponding increase in the phenol monomer content but was correlated to high carboxylic acid concentrations. The degradation products in the hemicellulose fractions co-varied with the pre-treatment conditions in the principal component analysis according to their chemical structure, e.g. diacids (oxalic and succinic acids), furan aldehydes, phenol aldehydes, phenol ketones and phenol acids. Aromatic aldehyde formation was correlated to severe conditions with high temperatures and low pH. Apart from CO2 and water, carboxylic acids were the main degradation products from hemicellulose and lignin.

Optimization of wet oxidation pretreatment of wheat straw

Abstract The wet oxidation process (water, oxygen and elevated temperature) was investigated under alkaline conditions for fractionation of hemicellulose, cellulose, and lignin from wheat straw. At higher temperature and longer reaction time, a purified cellulose fraction (69% w/w) was produced with high enzymatic convertibility to glucose (66% w/w). At 185°C, nearly three times more hemicellulose was solubilized than at 150°C. Optimum conditions for hemicellulose solubilization and cellulose convertibility were for 60 g l−1 straw: 185°C, 6.5 g l−1 Na2CO3, and 12 bar O2 with a 15-min reaction time. Under these conditions, 55% of the lignin and 80% of the hemicellulose were solubilized, while 95% of the cellulose remained in the solid fraction. At 185°C, the reaction kinetics was of pseudo first-order. The rate constant for hemicellulose solubilization was higher than that for lignin, whereas the rate for cellulose was very low. The cellulose recovery (95–100%) was significantly higher than that for hemicellulose (60%). At temperatures above 185°C, recoveries decreased due to increased degradation. Only half of the COD-content could be accounted for by saccharides and carboxylic acids; hence, a significant proportion of reaction products remained unidentified.

Evaluation of wet oxidation pretreatment for enzymatic hydrolysis of softwood

The wet oxidation pretreatment (water, oxygen, elevated temperature, and pressure) of softwood (Picea abies) was investigated for enhancing enzymatic hydrolysis. The pretreatment was preliminarily optimized. Six different combinations of reaction time, temperature, and pH were applied, and the compositions of solid and liquid fractions were analyzed. The solid fraction after wet oxidation contained 58–64% cellulose, 2–16% hemicellulose, and 24–30% lignin. The pretreatment series gave information about the roles of lignin and hemicellulose in the enzymatic hydrolysis. The temperature of the pretreatment, the residual hemicellulose content of the substrate, and the type of the commercial cellulase preparation used were the most important factors affecting the enzymatic hydrolysis. The highest sugar yield in a 72-h hydrolysis, 79% of theoretical, was obtained using a pretreatment of 200°C for 10 min at neutral pH.

Pretreatment of corn stover using wet oxidation to enhance enzymatic digestibility

Corn stover is an abundant, promising raw material for fuel ethanol production. Although it has a high cellulose content, without pretreatment it resists enzymatic hydrolysis, like most lignocellulosic materials. Wet oxidation (water, oxygen, mild alkali or acid, elevated temperature and pressure) was investigated to enhance the enzymatic digestibility of corn stover. Six different combinations of reaction temperature, time, and pH were applied. The best conditions (60g/L of corn stover, 195°C, 15 min, 12 bar O2, 2 g/L of Na2CO3) increased the enzymatic conversion of corn stover four times, compared to untreated material. Under these conditions 60% of hemicellulose and 30% of lignin were solubilized, whereas 90% of cellulose remained in the solid fraction. After 24-h hydrolysis at 50°C using 25 filter paper units (FPU)/g of dry matter (DM) biomass, the achieved conversion of cellulose to glucose was about 85%. Decreasing the hydrolysis temperature to 40°C increased hydrolysis time from 24 to 72 h. Decreasing the enzyme loading to 5 FPU/g of DM biomass slightly decreased the enzymatic conversion from 83.4 to 71%. Thus, enzyme loading can be reduced without significantly affecting the efficiency of hydrolysis, an important economical aspect.

Preliminary results on optimization of pilot scale pretreatment of wheat straw used in coproduction of bioethanol and electricity

The overall objective in this European Union-project is to develop cost and energy effective production systems for coproduction of bioethanol and electricity based on integrated biomass utilization. A pilot plan reactor for hydrothermal pretreatment (including weak acid hydrolysis, wet oxidation, and steam pretreatment) with a capacity of 100 kg/h was constructed and tested for pretreatment of wheat straw for ethanol production. Highest hemicellulose (C5 sugar) recovery and extraction of hemicellulose sugars was obtained at 190°C whereas highest C6 sugar yield was obtained at 200°C. Lowest toxicity of hydrolysates was observed at 190°C; however, addition of H2O2 improved the fermentability and sugar recoveries at the higher temperatures. The estimated total ethanol production was 223 kg/t straw assuming utilisation of both C6 and C5 during fermentation, and 0.5 g ethanol/g sugar.

The effect of different substrates and humic acid on power generation in microbial fuel cell operation.

Electricity production from acetate, glucose and xylose with humic acid as mediator was investigated in two chambers microbial fuel cells (MFCs). Acetate produced the highest voltage (570 mV with 1000 Omega) and maximum power density (P(maxd)=123 mW/m(2)) due to a simpler metabolism than with glucose and xylose. Glucose and xylose resulted in P(maxd) of 28 mW/m(2) and 32 mW/m(2) at lower voltage of 380 mV and 414 mV, respectively. P(maxd) increased by 84% and 30%, for glucose and xylose respectively, when humic acid (2g/l) was present in the medium. No significant effect was found with acetate since the internal resistance possessed a limiting effect. The increase of P(maxd) due to humic acid presence was attributed to its ability to act as mediator. Even though pH decreased to 5 with glucose and xylose, due to production of acetate and propionate, the voltage remained on the same level of 250-350 mV.

Production of ethanol from wet oxidised wheat straw by Thermoanaerobacter mathranii

The wet oxidation process (water, oxygen, elevated temperature, sodium carbonate) was investigated as a means of solubilising hemicellulose from wheat straw. Sixteen different combinations of oxygen pressure and sodium carbonate concentration were applied. The hemicellulose hydrolysates were evaluated with respect to total sugars, xylose, and 2-furfural produced. The concentration of sugars tended to be highest in hydrolysates produced at high oxygen pressures, whereas the concentration of 2-furfural was lowest in hydrolysates produced at low oxygen pressures and high carbonate concentrations. Fermentation of the hydrolysates was carried out using Thermoanaerobacter mathranii strain A3M1. No significant inhibitory effect was observed when the hydrolysates were fermented by T. mathranii A3M1. However, the solubilised hemicellulose was only partly available for fermentation by the bacteria. Treatment with the commercial enzyme Celluclast® or with acid hydrolysis improved the ethanol yield from the hydrolysates. Treatment with PentopanTH Mono BG or Pulpzyme® HC, both endo-1,4-β-xylanases, had no effect neither had co-cultivation with the xylanase-producing Dictyoglomus B4.

Anaerobic biotechnological approaches for production of liquid energy carriers from biomass.

In recent years, increasing attention has been paid to the use of renewable biomass for energy production. Anaerobic biotechnological approaches for production of liquid energy carriers (ethanol and a mixture of acetone, butanol and ethanol) from biomass can be employed to decrease environmental pollution and reduce dependency on fossil fuels. There are two major biological processes that can convert biomass to liquid energy carriers via anaerobic biological breakdown of organic matter: ethanol fermentation and mixed acetone, butanol, ethanol (ABE) fermentation. The specific product formation is determined by substrates and microbial communities available as well as the operating conditions applied. In this review, we evaluate the recent biotechnological approaches employed in ethanol and ABE fermentation. Practical applicability of different technologies is discussed taking into account the microbiology and biochemistry of the processes.

Hemp Fiber Microstructure and Use of Fungal Defibration to Obtain Fibers for Composite Materials

Abstract Characterization of hemp fibers was carried out to investigate the mild defibration with Phlebia radiata Cel 26, a fungus which selectively degraded the epidermis and the lignified middle lamellae. Thin fiber bundles could thereby be produced. The single fiber S2 layer consisted of 1-5 mm thick concentric layers constructed of ca. 100 nm thick lamellae. The microfibril angle showed values of 0-10 for the main part of S2 and 70-90 for SI. The low S2 microfibril angle resulted in fiber bundles with high tensile strength (960 MPa) decreasing to 850 MPa after defibration due to degradation of non cellulosic components. The elastic modulus of the hemp fibers within composites was similar to glass fibers (75 GPa).