Thermochemical Pretreatment Research Articles

Thermochemical pretreatment and anaerobic digestion of dairy cow manure: Experimental and economic evaluation

The aim of this study was to assess technically and economically the application thermochemical pretreatment in the anaerobic digestion of dairy cow manure. After selecting the optimum substrate to inoculum (S/I) ratio in a preliminary BMP test, the following tests compared 20 different pretreatment conditions varying temperature (100 and 37°C), exposure time (5 and 30min and 12 and 24h) and chemical doses (0.5, 2, 6 and 10% of HCl or NaOH). The highest value of maximum production rate was achieved at an S/I ratio of 0.25gVSsgVSi−1. The major improvements of the methane potential were 23.6% with 10% of NaOH at 100°C for 5min and 20.6% with 2% of HCl at 37°C. The technical-economic analysis showed that the implementation of neither thermal alkali nor thermal-acid pretreatment would be feasible and the conventional one-step anaerobic digestion outperforms both alternatives.

Improved sugar yields from biomass sorghum feedstocks: comparing low-lignin mutants and pretreatment chemistries.

BackgroundFor biofuel production processes to be economically efficient, it is essential to maximize the production of monomeric carbohydrates from the structural carbohydrates of feedstocks. One strategy for maximizing carbohydrate production is to identify less recalcitrant feedstock cultivars by performing some type of experimental screening on a large and diverse set of candidate materials, or by identifying genetic modifications (random or directed mutations or transgenic plants) that provide decreased recalcitrance. Economic efficiency can also be increased using additional pretreatment processes such as deacetylation, which uses dilute NaOH to remove the acetyl groups of hemicellulose prior to dilute acid pretreatment. In this work, we used a laboratory-scale screening tool that mimics relevant thermochemical pretreatment conditions to compare the total sugar yield of three near-isogenic brown midrib (bmr) mutant lines and the wild-type (WT) sorghum cultivar. We then compared results obtained from the laboratory-scale screening pretreatment assay to a large-scale pretreatment system.ResultsAfter pretreatment and enzymatic hydrolysis, the bmr mutants had higher total sugar yields than the WT sorghum cultivar. Increased pretreatment temperatures increased reactivity for all sorghum samples reducing the differences observed at lower reaction temperatures. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples, and reduced the differences in total sugar yields among them, but solubilized a sizable fraction of the non-structural carbohydrates. The general trends of increased total sugar yield in the bmr mutant compared to the WT seen at the laboratory scale were observed at the large-scale system. However, in the larger reactor system, the measured total sugar yields were lower and the difference in total sugar yield between the WT and bmr sorghum was larger.ConclusionsSorghum bmr mutants, which have a reduced lignin content showed higher total sugar yields than the WT cultivar after dilute acid pretreatment and enzymatic hydrolysis. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples. However, since deacetylation also solubilizes a large fraction of the non-structural carbohydrates, the ability to derive value from these solubilized sugars will depend greatly on the proposed conversion process.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0667-y) contains supplementary material, which is available to authorized users.

Detoxification of furanic and phenolic lignocellulose derived inhibitors of yeast using laccase immobilized on bacterial cellulosic nanofibers

Biotransformation of lignocellulose by microbial fermentation is usually preceded by thermo-chemical pretreatments followed by enzymatic hydrolysis of cellulose. Derivatives formed during the pretreatment of the lignocellulosic biomass inhibit enzymatic hydrolysis as well as microbial fermentation. Pretreated lignocellulose hydrolysate contains many derivatives of either furanic or phenolic inhibitory derivatives. In the present study, laccase was used to detoxify three different types of lignocellulosic derivatives that are highly toxic to microbial fermentation due to their low hydrophilic nature, namely furfural, acetosyringone, and coniferyl aldehyde. A minimal inhibitory concentration (MIC) test was carried out with Saccharomyces cerevisiae. The MIC of furfural, acetosyringone, and coniferyl aldehyde was 12mM, 24mM, and 1.5mM, respectively. Laccase was immobilized on to cellulose nanofiber produced by Gluconacetobacter xylinus. Immobilized laccase showed a better pH and thermal stability than free laccase. Reuse of immobilized laccase retains 85% of its enzyme activity after 16 recycles. Immobilized laccase completely degraded the three lignocellulose inhibitory derivatives after 36h of incubation at 40°C. Finally, the degradation was confirmed by ultraviolet visible spectroscopy (UV–VIS spectrum), high performance liquid chromatography and liquid chromatography mass spectrometry. Interestingly, it was found that the effect of enzymatic degradation depends on the structural variation of the lignocellulosic derivatives as laccase alone detoxified the furfural and coniferyl aldehyde, whereas a redox mediator HOBt was needed for the detoxification of ketone based lignin derivative acetosyringone.

Solar Torrefaction of Solid Olive Mill Residue

Torrefaction is a thermochemical pretreatment method for improving fuel characteristics of biomass. The process is conducted between 200 and 300 °C under inert atmosphere. The relatively low process temperature of torrefaction makes the use of solar energy suitable with low costs. In this study, solid olive mill residue (SOMR) was used to test the feasibility of using solar energy in the torrefaction process. SOMR is an agricultural waste obtained from olive oil extraction, and it is mainly produced in the Mediterranean region, which has high solar energy potential. In this study, the torrefaction of SOMR was conducted by concentrating solar energy with a parabolic dish concentrator, at 250 °C for 10 min. The fuel properties of solar torrefaction products were compared with raw SOMR. Solar torrefaction yielded a deoxygenated solid fuel with increased carbon content and higher heating value (HHV), similar to torrefaction.

Evaluating biological pretreatment as a feasible methodology for ethanol production from paddy straw

Abstract Bioethanol has been recognized as a promising contemporary fuel. One of the most abundant renewable resources for bioethanol production is paddy straw with high carbohydrate content. A pretreatment step disintegrates the recalcitrant lignocellulosic structure in biomass, which facilitates the access of hydrolytic enzymes to the glucan macrostructure. Biological pretreatment is an eco-friendly alternative to harsh thermo-chemical pretreatment methodologies. In this study, paddy straw (rice variety Pusa 2511) was subjected to biological pretreatment with white-rot fungus, Trametes hirsuta and simultaneously with steam pretreatment at 121 °C. Resultant saccharification efficiencies of differentially pretreated paddy straw were compared to evaluate biological pretreatment. After pretreatment cellulose content in steam treated paddy straw was 39.5%, whereas for biological it was 37.6% and respective lignin contents were 14.2% and 4.7%. Lignin removal was substantially higher in biological pretreatment than steam pretreatment. The saccharification yields of biological pretreatment were at par with steam pretreated paddy straw. Highest saccharification efficiency was observed after 24 h, at 2% glucan loading, for both biological (76.5%) and steam pretreatment (74.1%). Maximum production of sugar (52.91 g L −1 ) was observed in biologically pretreated biomass at 10% glucan loading after 24 h. Fermentation of biomass hydrolysates with Saccharomyces cerevisiae , showed low ethanol production from biologically (0.86 g L −1 ) as well as steam pretreated biomass (1.13 g L −1 ) with fermentation efficiency ranging from 26 to 52%, suggesting presence of inhibitory factors necessitating detoxification of hydrolysates. This study, established biological pretreatment as feasible method for pretreatment and higher sugar yields.

Efficient sugar production from sugarcane bagasse by microwave assisted acid and alkali pretreatment

Sugarcane bagasse represents one of the best potential feedstocks for the production of second generation bioethanol. The most efficient method to produce fermentable sugars is by enzymatic hydrolysis, assisted by thermochemical pretreatments. Previous research was focused on conventional heating pretreatment and the pretreated biomass residue characteristics. In this work, microwave energy is applied to facilitate sodium hydroxide (NaOH) and sulphuric acid (H2SO4) pretreatments on sugarcane bagasse and the efficiency of sugar production was evaluated on the soluble sugars released during pretreatment. The results show that microwave assisted pretreatment was more efficient than conventional heating pretreatment and it gave rise to 4 times higher reducing sugar release by using 5.7 times less pretreatment time. It is highlighted that enrichment of xylose and glucose can be tuned by changing pretreatment media (NaOH/H2SO4) and holding time. SEM study shows significant delignification effect of NaOH pretreatment, suggesting a possible improved enzymatic hydrolysis process. However, severe acid conditions should be avoided (long holding time or high acid concentration) under microwave heating conditions. It led to biomass carbonization, reducing sugar production and forming ‘humins’. Overall, in comparison with conventional pretreatment, microwave assisted pretreatment removed significant amount of hemicellulose and lignin and led to high amount of sugar production during pretreatment process, suggesting microwave heating pretreatment is an effective and efficient pretreatment method.

Precultivation of Bacillus coagulans DSM2314 in the presence of furfural decreases inhibitory effects of lignocellulosic by-products during L(+)-lactic acid fermentation.

By-products resulting from thermo-chemical pretreatment of lignocellulose can inhibit fermentation of lignocellulosic sugars to lactic acid. Furfural is such a by-product, which is formed during acid pretreatment of lignocellulose. pH-controlled fermentations with 1 L starting volume, containing YP medium and a mixture of lignocellulosic by-products, were inoculated with precultures of Bacillus coagulans DSM2314 to which 1 g/L furfural was added. The addition of furfural to precultures resulted in an increase in l(+)-lactic acid productivity by a factor 2 to 1.39 g/L/h, an increase in lactic acid production from 54 to 71 g and an increase in conversion yields of sugar to lactic acid from 68 to 88 % W/W in subsequent fermentations. The improved performance was not caused by furfural consumption or conversion, indicating that the cells acquired a higher tolerance towards this by-product. The improvement coincided with a significant elongation of B. coagulans cells. Via RNA-Seq analysis, an upregulation of pathways involved in the synthesis of cell wall components such as bacillosamine, peptidoglycan and spermidine was observed in elongated cells. Furthermore, the gene SigB and genes promoted by SigB, such as NhaX and YsnF, were upregulated in the presence of furfural. These genes are involved in stress responses in bacilli.

Cellulolytic enzyme expression and simultaneous conversion of lignocellulosic sugars into ethanol and xylitol by a new Candida tropicalis strain.

BackgroundLignocellulosic ethanol production involves major steps such as thermochemical pretreatment of biomass, enzymatic hydrolysis of pre-treated biomass and the fermentation of released sugars into ethanol. At least two different organisms are conventionally utilized for producing cellulolytic enzymes and for ethanol production through fermentation, whereas in the present study a single yeast isolate with the capacity to simultaneously produce cellulases and xylanases and ferment the released sugars into ethanol and xylitol has been described.ResultsA yeast strain isolated from soil samples and identified as Candida tropicalis MTCC 25057 expressed cellulases and xylanases over a wide range of temperatures (32 and 42 °C) and in the presence of different cellulosic substrates [carboxymethylcellulose and wheat straw (WS)]. The studies indicated that the cultivation of yeast at 42 °C in pre-treated hydrolysate containing 0.5 % WS resulted in proportional expression of cellulases (exoglucanases and endoglucanases) at concentrations of 114.1 and 97.8 U g−1 ds, respectively. A high xylanase activity (689.3 U g−1 ds) was also exhibited by the yeast under similar growth conditions. Maximum expression of cellulolytic enzymes by the yeast occurred within 24 h of incubation. Of the sugars released from biomass after pretreatment, 49 g L−1 xylose was aerobically converted into 15.8 g L−1 of xylitol. In addition, 25.4 g L−1 glucose released after the enzymatic hydrolysis of biomass was fermented by the same yeast to obtain an ethanol titer of 7.3 g L−1.ConclusionsDuring the present study, a new strain of C. tropicalis was isolated and found to have potential for consolidated bioprocessing (CBP) applications. The strain could grow in a wide range of process conditions (temperature, pH) and in the presence of lignocellulosic inhibitors such as furfural, HMF and acetic acid. The new yeast produced cellulolytic enzymes over a wide temperature range and in the presence of various cellulosic substrates. The cellulolytic enzymes produced by the yeast were effectively used for the hydrolysis of pretreated biomass. The released sugars, xylose and glucose were, respectively, converted into xylitol and ethanol. The potential shown by the new inhibitor tolerant cellulolytic C. tropicalis to produce ethanol or xylitol is of great industrial significance.

Enhancing biogas production of corn stover by fast pyrolysis pretreatment

A new thermo-chemical pretreatment by a lower temperature fast pyrolysis (LTFP) was applied to promote anaerobic digestion (AD) efficiency of corn stover (CS). The pretreatment experiment was performed by a fluidized bed pyrolysis reactor at 180, 200 and 220°C with a carrier gas flow rate of 4 and 3m3/h. The components characteristics, Scanning Electron Microscope (SEM) images and Crystal Intensity (CrI) of the pretreated CS were tested to explore effectiveness of the pretreatment. The results showed that the cumulative methane production at 180°C for 4 and 3m3/h were 199.8 and 200.3mL/g TS, respectively. As compared to the untreated CS, the LTFP pretreatment significantly (a<0.05) increased the methane production by 18.07% and 18.33%, respectively. Methane production was well fitted by the Gompertz models, and the maximum methane potential and AD efficiency was obtained at 180°C for 3m3/h.

Thermo-chemical pretreatment of rice straw for further processing for levulinic acid production

A variety of pretreatment protocols for rice straw fiber reconstruction were evaluated under mild conditions (upto 0.2%wt. and 121°C) with the object of improving polymer susceptibility to chemical attack while preserving carbohydrate sugars for levulinic acid (LA) production. Each of the protocols tested significantly enhanced pretreatment recoveries of carbohydrate sugars and lignin, and a NaOH protocol showed the most promise, with enhanced carbohydrate preservation (upto 20% relative to the other protocols) and more effective lignin dissolution (upto 60%). Consequently, post-pretreatment fibers were evaluated for LA preparation using an existing co-solvent system consisting of HCl and THF, in addition supplementation of DMSO was attempted, in order to improve final product recovery. In contrast to pretreatment response, H2SO4 protocol fibers yielded highest LA conc. (21%wt. with 36% carbohydrate conversion efficiency) under the modest reaction conditions. Apparent spectroscopic analysis witnessed for fiber destruction and delocalization of inherent constituents during pretreatment protocols.

Enzymatic Degradation of Pretreated Pig Bristles with Crude Keratinase of Bacillus cereus PCM 2849

PurposeThe aim of the study was to apply and optimize the process of bioconversion of pig bristle waste using keratinolytic enzymes of Bacillus cereus PCM 2849, and to evaluate the amino acid composition of the resultant hydrolysate.MethodsHydrolysis with concentrated culture fluid of B. cereus was applied for bioconversion of pig bristles, after thermo-chemical pretreatment with sulfite. The effect of substrate concentration, sulfite concentration during pretreatment and reaction temperature on the release of amino acids was determined using Box-Behnken design. Amino acid composition of the obtained hydrolysate was determined by HPLC. Structural condition and substructural changes of the residual substrate were evaluated with SEM microscopy and FTIR spectroscopy.ResultsThe applied enzymatic preparation for bristle biodegradation was verified to contain multiple proteases of a wide molecular weight range. A regression model was developed, in which influential parameters were: linear effect of substrate concentration, followed by quadratic effects of reaction temperature, substrate concentration and pretreatment. Optimum reaction conditions were also determined. The resultant hydrolysate was rich in branched-chain amino acids. Residual substrate was detriorated and sulfitolytic cleavage of disulfides and alteration of protein secondary structures was confirmed.ConclusionsApplication of B.cereus crude keratinase allowed for partial hydrolysis of pig bristles, preceded by sulfitolytic pretreatment. A regression model was built to describe the process of hydrolysis to release free amino acids, at constant enzyme load. Hydrolysis in given conditions allowed to obtain hydrolysate rich in branched chain amino acids. The presented process poses an alternate way of management over pig bristles, a hard-to-degrade keratinous waste.

Improvement in the enzymatic hydrolysis of biofuel substrate by a combined thermochemical and fungal pretreatment

Pretreatment is a critical step in the enzymatic conversion of lignocellulosic substrate to sugars. A unique pretreatment sequence involving thermochemical treatment (steam explosion) followed by biological treatment (fungal exposure) was evaluated for Pinus radiata as a biofuel substrate. The effect of biological treatment using the white rot Trametes versicolor was investigated on control (sapwood blocks) and steam-exploded wood (SEW) for changes in the profile of fungal enzyme activity and lignocellulose composition. The results indicated that compared to blocks, Trametes versicolor expressed more lignocellulose-degrading enzymes when grown on SEW for 6 and 12 weeks. After fungal exposure, the biomass was mixed with a commercial enzyme cocktail for enzymatic hydrolysis. The maximum conversion of biomass to sugars was obtained for Trametes versicolor-treated SEW, with a yield of 4.80 g of glucose l−1, which is greater compared to that obtained from non-fungal-treated SEW (3.80 g of glucose l−1) and Trametes versicolor-treated sapwood blocks (0.80 g of glucose l−1). Examination by microscopy suggests relative increase in the porosity of SEW after fungal treatment, and compositional analysis indicates reduction in lignin content. Both these factors are likely to contribute to the improved hydrolysis of SEW.

ChemInform Abstract: Pretreatment and Conversion of Lignocellulose Biomass into Valuable Chemicals

AbstractReview: 252 refs.

Cell Wall Composition and Biomass Recalcitrance Differences Within a Genotypically Diverse Set of Brachypodium distachyon Inbred Lines.

Brachypodium distachyon (Brachypodium) has emerged as a useful model system for studying traits unique to graminaceous species including bioenergy crop grasses owing to its amenability to laboratory experimentation and the availability of extensive genetic and germplasm resources. Considerable natural variation has been uncovered for a variety of traits including flowering time, vernalization responsiveness, and above-ground growth characteristics. However, cell wall composition differences remain underexplored. Therefore, we assessed cell wall-related traits relevant to biomass conversion to biofuels in seven Brachypodium inbred lines that were chosen based on their high level of genotypic diversity as well as available genome sequences and recombinant inbred line (RIL) populations. Senesced stems plus leaf sheaths from these lines exhibited significant differences in acetyl bromide soluble lignin (ABSL), cell wall polysaccharide-derived sugars, hydroxycinnamates content, and syringyl:guaiacyl:p-hydroxyphenyl (S:G:H) lignin ratios. Free glucose, sucrose, and starch content also differed significantly in senesced stems, as did the amounts of sugars released from cell wall polysaccharides (digestibility) upon exposure to a panel of thermochemical pretreatments followed by hydrolytic enzymatic digestion. Correlations were identified between inbred line lignin compositions and plant growth characteristics such as biomass accumulation and heading date (HD), and between amounts of cell wall polysaccharides and biomass digestibility. Finally, stem cell wall p-coumarate and ferulate contents and free-sugars content changed significantly with increased duration of vernalization for some inbred lines. Taken together, these results show that Brachypodium displays substantial phenotypic variation with respect to cell wall composition and biomass digestibility, with some compositional differences correlating with growth characteristics. Moreover, besides influencing HD and biomass accumulation, vernalization was found to affect cell wall composition and free sugars accumulation in some Brachypodium inbred lines, suggesting genetic differences in how vernalization affects carbon flux to polysaccharides. The availability of related RIL populations will allow for the genetic and molecular dissection of this natural variation, the knowledge of which may inform ways to genetically improve bioenergy crop grasses.

The two Rasamsonia emersonii α-glucuronidases, ReGH67 and ReGH115, show a different mode-of-action towards glucuronoxylan and glucuronoxylo-oligosaccharides.

BackgroundThe production of biofuels and biochemicals from grass-type plant biomass requires a complete utilisation of the plant cellulose and hemicellulosic xylan via enzymatic degradation to their constituent monosaccharides. Generally, physical and/or thermochemical pretreatments are performed to enable access for the subsequent added carbohydrate-degrading enzymes. Nevertheless, partly substituted xylan structures remain after pretreatment, in particular the ones substituted with (4-O-methyl-)glucuronic acids (UAme). Hence, α-glucuronidases play an important role in the degradation of UAmexylan structures facilitating the complete utilisation of plant biomass. The characterisation of α-glucuronidases is a necessity to find the right enzymes to improve degradation of recalcitrant UAmexylan structures.ResultsThe mode-of-action of two α-glucuronidases was demonstrated, both obtained from the fungus Rasamsonia emersonii; one belonging to the glycoside hydrolase (GH) family 67 (ReGH67) and the other to GH115 (ReGH115). Both enzymes functioned optimal at around pH 4 and 70 °C. ReGH67 was able to release UAme from UAme-substituted xylo-oligosaccharides (UAmeXOS), but only the UAme linked to the non-reducing end xylosyl residue was cleaved. In particular, in a mixture of oligosaccharides, UAmeXOS having a degree of polymerisation (DP) of two were hydrolysed to a further extent than longer UAmeXOS (DP 3–4). On the contrary, ReGH115 was able to release UAme from both polymeric UAmexylan and UAmeXOS. ReGH115 cleaved UAme from both internal and non-reducing end xylosyl residues, with the exception of UAme attached to the non-reducing end of a xylotriose oligosaccharide.ConclusionIn this research, and for the first time, we define the mode-of-action of two α-glucuronidases from two different GH families both from the ascomycete R. emersonii. To date, only four α-glucuronidases classified in GH115 are characterised. ReGH67 showed limited substrate specificity towards only UAmeXOS, cleaving UAme only when attached to the non-reducing end xylosyl residue. ReGH115 was much less substrate specific compared to ReGH67, because UAme was released from both polymeric UAmexylan and UAmeXOS, from both internal and non-reducing end xylosyl residues. The characterisation of the mode-of-action of these two α-glucuronidases helps understand how R. emersonii attacks UAmexylan in plant biomass and the knowledge presented is valuable to improve enzyme cocktails for biorefinery applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0519-9) contains supplementary material, which is available to authorized users.

Investigating the Role of Extensin Proteins in Poplar Biomass Recalcitrance

The biological conversion of cellulosic biomass to biofuel is hindered by cell wall recalcitrance, which can limit the ability of cellulases to access and break down cellulose. The purpose of this study was to investigate whether hydroxyproline-rich cell wall proteins (extensins) are present in poplar stem biomass, and whether these proteins may contribute to recalcitrance. Three classical extensin genes were identified in Populus trichocarpa through bioinformatic analysis of poplar genome sequences, with the following proposed names: PtEXTENSIN1 (Potri.001G019700); PtEXTENSIN2 (Potri.001G020100); PtEXTENSIN3 (Potri.018G050100). Tissue print immunoblots localized the extensin proteins in poplar stems to regions near the vascular cambium. Different thermochemical pretreatments reduced but did not eliminate hydroxyproline (Hyp, a proxy for extensins) from the biomass. Protease treatment of liquid hot water-pretreated poplar biomass reduced Hyp content by a further 16% and increased subsequent glucose yield by 20%. These data suggest that extensins may contribute to recalcitrance in pretreated poplar biomass, and that incorporating protease treatment into pretreatment protocols could result in a small but significant increase in the yield of fermentable glucose.

Biogas Production from Waste Microalgal Biomass Obtained from Nutrient Removal of Domestic Wastewater

In this study, a semi-continuous photobioreactor was operated for the investigation of nutrient removal efficiency of a unialgal culture, Chlorella vulgaris. Maximum nitrogen and phosphorous removal efficiencies of 99.6 and 91.2 % were achieved in the photobioreactor. The microalgal slurry obtained from the effluent of the photobioreactor was subjected to biochemical methane potential assay, after application of heat, autoclave, and thermochemical pretreatments to improve anaerobic digestibility and biogas production. Evaluation of pretreatment options indicated that heat pretreatment is the most efficient method in terms of enhancing anaerobic digestibility, at the chemical oxygen demand (COD) loading of 19 ± 0.5 g L−1. This method increased the methane yield by 83.0 %, from 223 to 408 mL CH4 g VS added −1 , compared to untreated microalgal slurry reactor with the same COD value. Among reactors with 35 ± 1.5 g L−1 initial COD concentration, autoclave-pretreated microalgal slurry was found to yield the highest methane value of 356 mL CH4 g VS added −1 , which was 43.0 % higher than the value observed in the reactor fed with untreated microalgal slurry. The thermochemical pretreatment caused production of inhibitory compounds and resulted in lower biomethane production and COD treatment values, compared to untreated microalgae. Outcomes of this study reveal that coupled micro-algal and anaerobic biotechnology could be a sustainable alternative for integrated nutrient removal and biofuel production applications.

Reuse of microalgae grown in full-scale wastewater treatment ponds: Thermochemical pretreatment and biogas production

This study assessed thermochemical pretreatment of microalgae harvested from a full-scale wastewater treatment pond prior to its anaerobic digestion using acid and alkaline chemical doses combined with thermal pretreatment at 80°C. Results indicated that alkaline and thermal pretreatment contributed mostly to glycoprotein and pectin solubilisation; whilst acid pretreatment solubilised mostly hemicellulose, with lower effectiveness for proteins. Regarding the anaerobic biodegradability, biochemical methane potential (BMP) tests showed that final methane yield was enhanced after almost all pretreatment conditions when compared to non-pretreated microalgae, with the highest increase for thermochemical pretreatment at the lowest dose (0.5%), i.e. 82% and 86% increase for alkaline and acid, respectively. At higher doses, salt toxicity was revealed by K+ concentrations over 5000mg/L. All BMP data from pretreated biomass was successfully described by the modified Gompertz model and optimal condition (thermochemical 0.5% HCl) showed an increase in final methane yield and the process kinetics.

Effect of thermochemical pretreatment on lignin alteration and cell wall microstructural degradation in Eucalyptus globulus: comparison of acid, alkali, and water pretreatments

Pretreatment is an essential step to effectively hydrolyze lignocellulosic polysaccharides. In this paper, we investigated the degree of decompositions of lignin and cell wall structure using dilute acid, alkali, and water pretreatments to assess both chemical and ultrastructural alterations during pretreatment. The thioacidolysis method showed that β-O-4 linkages in lignin were mostly cleaved after all pretreatments, in which the highest decrease of β-O-4 units was for NaOH pretreatment, followed by hot water and H2SO4 pretreatments. The amounts of lignin degradation compounds, including vanillin and syringaldehyde, in the supernatant water also differed between the three pretreatments. Field-emission scanning electron microscopy revealed clear differences among the pretreatments in decomposing the ultrastructure of the inner surface of the fiber cell walls. Small pores were formed due to degradation of a part of the warty layer of the innermost surface in H2SO4 pretreatment. The warty layer was more degraded in hot water pretreatment and thus the cellulose microfibrils of the secondary walls were exposed. NaOH pretreatment showed that the warty layer was almost completely decomposed. The comparative study of different pretreatments using chemical methods and microscopic observations led to a better understanding of decomposition of wood cell walls by thermochemical pretreatment.

Selective fractionation of Sugar Beet Pulp for release of fermentation and chemical feedstocks; optimisation of thermo-chemical pre-treatment

The effect of time and pressure on the selective extraction of sugar beet pectin using steam pre-treatment on unprocessed Sugar Beet Pulp was evaluated using a design of experiments approach. This process gave the highest solubilisation of pectin oligomers at a relatively low pressure and longer time (5Bar, 24min), whilst leaving the majority of the cellulose fraction intact. This method of steam pre-treatment fits into the concept of a sugar beet biorefinery as it valorises an existing waste stream without requiring any further physical processing such as milling or dilution with water. The residual cellulose fraction was enriched in cellulose and could be effectively fermented into ethanol by yeast after enzymatic digestion, producing 0.48g ethanol per gram of glucose.