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This study investigates a fed-batch simultaneous saccharification fermentation (F-SSF) process to increase ethanol titres from highly lignified (41.6 wt.%) cotton gin trash residue. The optimal initial solid loading, enzyme dose, feed quantities and intervals to maximize substrate feed and subsequent ethanol titres were examined. Under batch SSF conditions, initial extracted cotton gin trash (ECGT) solid loadings were maximised at 19.35 wt.% and attained an ethanol titre of 23.3 g/l with a corresponding yield of 53.7%. Operating under optimised F-SSF mode, fermentations were initiated with 16.13 wt% EGCT solids followed by fresh ECGT feeds of 16.13 wt% and 12.9 wt.% at 12-h intervals. Cellulase levels were maintained at 44 FPU/g glucan throughout the fermentations. The final ethanol titre of 41 .4 g/l with a corresponding conversion rate of 70.1% was achieved after 72 h. Comparable ethanol yields of 40 g/l with 67.8% conversion were realized with lower cellulase dosing (25 FPU g/glucan) but only after extending the fermentation by 24 h.

Whole Eucalyptus grandis trees (including bark, branches and leaves) were investigated as a potential feedstock for bioethanol production. To demonstrate and maximize ethanol production, unwashed steam exploded wood chips (SEWC) were used as substrates in high solids load simultaneous saccharification fermentations (SSF) with an industrial Saccharomyces cerevisiae strain (Fali®). Under optimized SSF conditions—20 wt% solids, 60 filter paper units (FPU)/g glucan, and 36°C—ethanol titer and glucan-to-ethanol yields of 56 g/L and 90%, respectively, were achieved. Raising the SSF temperature to 39°C showed no observable benefit in final ethanol titers and/or yields. Addition of 3 wt% polyethylene glycol (PEG) further increased final ethanol titers and yields to 60 g/L and 95%, respectively, at a 30% lower cellulase dosage. Considering the mass balance of the best-performing SSF (20 wt% SEWC, 40 FPU Ctec 2/g glucan, 30 mg PEG/g dry solid at 36°C) process, the maximum ethanol attainable was estimated at 187 kg (85.8% yield) and 299 kg (95% yield) per dry metric ton of original and SEWC biomass, respectively.

This paper reports on mild acid pretreatment options for the conversion of Agave tequilana leaves into composite sugars for ethanol fermentation. The effect of five different pretreatment conditions (time, temperature and acid concentrations) were assessed in terms of cellulose digestibility, hemicellulose solubilisation and lignin content in leaves of 1.25 years old A. tequilana plants from Rockhampton and 2.5 year plants from Kalamia. Dilute acid pretreatment and enzyme saccharification of A. tequilana leaf bagasse significantly improved total glucose recovery. A recovery of 273 mg/g (70% theoretical) was attained when the bagasse was pretreated with 2.0% H2SO4 for 60 min at 121 °C and saccharified with 6% (w/w) CTec 2. Saccharomyces cerevisiae efficiently fermented crude A. tequilana bagasse and juice hydrolysates within 13 h and 7 h respectively, yielding up to 38.6 g/L and 12.4 g/L. This corresponds to glucose to ethanol conversion rate of 68 and 61% for A. tequilana leaf bagasse and juice, respectively. With further developments, including fermentation of C5 sugars and inulinase saccharification of juices (release of fructose), this process could deliver greater yields, reinforcing its potential as a biofuel feedstock.

This paper reports on processing options for the conversion of feedlot cattle manures into composite sugars for ethanol fermentation. Small-scale anaerobic digestion trials revealed that the process significantly reduces the content of glucan and xylan (ca. 70%) without effecting lignin. Moreover, anaerobic digestate (AD) fibres were poor substrates for cellulase (Cellic® CTec 2) saccharification, generating a maximum combined sugar yield of ca. 12% per original dry weight. Dilute acid pretreatment and enzyme saccharification of raw manures significantly improved total sugar recoveries, totalling 264 mg/g (79% theoretical). This was attained when manures were pretreated with 2.5% H 2 SO 4 for 90 min at 121 °C and saccharified with 50 FPU CTec 2/g glucan. Saccharomyces cerevisiae efficiently fermented crude hydrolysates within 6 h, yielding 7.3 g/L ethanol, representing glucose to ethanol conversion rate of 70%. With further developments (i.e., fermentation of xylose), this process could deliver greater yields, reinforcing its potential as a biofuel feedstock.

Cotton gin trash (CGT), a waste product of cotton gins, make up about 10% of each bale of cotton bolls ginned. The current study investigates high value volatile compounds in CGT to add value to this by-product. The volatile compounds in CGT and different parts of the cotton plant were extracted using various methods, identified by gas chromatography-mass spectrometry (GC-MS) or nuclear magnetic resonance (NMR) spectroscopy, and then quantified by gas chromatography-flame ionisation detection (GC-FID) against available standards. Terpenoids including monoterpenoids and sesquiterpenoids were found to be the most abundant, making up 64.66% (area under peak) of total volatiles extracted by hydro-distillation. The major extractable terpenoids in CGT were α-pinene (13.69-23.05 μg/g), β-caryophyllene (3.99-74.32 μg/g), α-humulene (2.00-25.71 μg/g), caryophyllene oxide (41.50-102.08 μg/g) and β-bisabolol (40.05-137.32 μg/g). Recoveries varied between different extraction methods. The terpenoids were found to be more abundant in the calyx (659.12 μg/g) and leaves (627.72 μg/g) than in stalks (112.97 μg/g) and stems (24.24 μg/g) of the cotton plant, indicating the possible biological origin of CGT volatiles. This study is the first to identify and quantify the different terpenoids present in CGT and significantly, β-bisabolol, an abundant compound (sesquiterpene alcohol) which may have valuable biological prospects. These findings therefore contribute to identifying alternative management strategies and uses of CGT.

The effectiveness of high temperature, dilute H2SO4 and NaOH pretreatments for the conversion of a post extracted cotton gin trash (ECGT) biomass was investigated. Whole acidified ECGT slurries were pretreated at various temperatures (180–230 °C) with or without the addition of extra catalyst. Compositional analysis of recovered ECGT fibre revealed xylan removal increased with pretreatment temperature under low pH conditions. Alkaline pretreatment (20 wt% NaOH) selectively delignified the ECGT fibre by as much as 80%. Characterisation of structural features identified an increase in cellulose crystallinity and surface area for all pretreated fibres and positively correlated to increasing pretreatment severity. Pretreatment of acidified ECGT slurries at 230 °C resulted in the highest glucan digestibility (66%) and glucose yields (51%). Glucan digestibility showed a strong positive correlation to xylan removal and surface area but weaker to delignification and total crystallinity for all dilute acid pretreated fibres.

Dilute sulphuric acid pretreatment followed by enzyme saccharification of Sorghum bicolor straw was undertaken to examine its potential as a feedstock in bioethanol production in Australia. Factorial design experiments evaluated the impact of pretreatment parameters on hemicellulose solubilisation and cellulose enzymatic hydrolysis. Sugar yields in prehydrolysate and saccharified liquors were found to increase with treatment severity; temperature was found to have the greatest impact. Degradation products were minimal; acetate and total phenolics peaked at 33 and 1.5 mg/g respectively. Conditions for maximum hemicellulose solubilisation (2% H 2 SO 4 for 60 min at 121 °C) differed to those associated with maximum glucose release from solid residue saccharifications (1% H 2 SO 4 /90 min /121 °C). Water extractive sugars accounted for over 20% total sugars recovered. Addition of β-glucosidase and xylanase to enzyme saccharification enhanced reaction rates and final sugar yields three-fold, whilst reducing cellulase dosage. Considering its abundance, high sugar potential and apparent ease of conversion, sorghum straw is an appropriate feedstock for the production of second generation fuels.

Physico-chemical pretreatment of lignocellulosic biomass is critical in removing substrate-specific barriers to cellulolytic enzyme attack. Alkaline pretreatment successfully delignifies biomass by disrupting the ester bonds cross-linking lignin and xylan, resulting in cellulose and hemicellulose enriched fractions. Here we report the use of dilute alkaline (NaOH) pretreatment followed by enzyme saccharifications of wheat straw to produce fermentable sugars. Specifically, we have assessed the impacts of varying pretreatment parameters (temperature, time and alkalinity) on enzymatic digestion of residual solid materials. Following pretreatment, recoverable solids and lignin contents were found to be inversely proportional to the severity of the pretreatment process. Elevating temperature and alkaline strengths maximised hemicellulose and lignin solubilisation and enhanced enzymatic saccharifications. Pretreating wheat straw with 2% NaOH for 30 min at 121 °C improved enzyme saccharification 6.3-fold when compared to control samples. Similarly, a 4.9-fold increase in total sugar yields from samples treated with 2% NaOH at 60 °C for 90min, confirmed the importance of alkali inclusion. A combination of three commercial enzyme preparations (cellulase, β-glucosidase and xylanase) was found to maximise monomeric sugar release, particularly for substrates with higher xylan contents. In essence, the combined enzyme activities increased total sugar release 1.65-fold and effectively reduced cellulase enzyme loadings 3-fold. Prehydrolysate liquors contained 4-fold more total phenolics compared to enzyme saccharification mixtures. Harsher pretreatment conditions provide saccharified hydrolysates with reduced phenolic content and greater fermentation potential.

Mild alkali cooking of lignocellulosic biomass is an effective pretreatment method, which improves enzymatic hydrolysis. Here, we report the use of dilute alkali (NaOH) pretreatment followed by enzyme saccharification of cereal residues for their potential to serve as feedstock in the production of next-generation biofuels in Australia. After pretreatment, both solids and lignin content were found to be inversely proportional to treatment severity. We also found that higher temperatures and alkali strength were quintessential for maximizing sugar recoveries from enzyme saccharifications. Generally, pretreatment conditions at elevated temperatures led to highly digestible material enriched in both cellulose and hemicellulose components. Increasing cellulase loadings and tailoring enzyme activities with additional β-glucosidases and xylanases delivered greater rates of monosaccharide sugar release and yields throughout enzyme hydrolysis. Considering their abundance, high sugar potential, and apparent ease o...

BACKGROUND: Prehydrolysis of wheat stubble using moderate temperatures and dilute acid strength is an effective means for solubilizing hemicellulose fractions and improving cellulose hydrolysis. Variation in prehydrolysis parameters (temperature, time, and acid strength) and enzymatic saccharification conditions were examined for conversion of wheat stubble into fermentable sugars. RESULTS: Elevating temperature and acid strength maximized sugar release in prehydrolysate liquors. The optimal conditions of 2.0% H2SO4/60 min/121 °C effectively solubilized 79% of the available hemicellulose. Production of inhibitory hydrolysis and degradation products such as acetic acid and levulinic acid, were detected at levels of 3.4 g L−1 and 0.64 g L−1, respectively. Sugar yields in prehydrolysate and saccharified liquors were found to increase with treatment severity. Temperature had the greatest impact on sugar release, followed by acid concentration and time. Optimizing prehydrolysis conditions at 1.0% H2SO4/90 min/121 °C, produced a 3.2-fold improvement in cellulose hydrolysis with recoveries approaching 82%. The addition of β-glucosidase and xylanase to the cellulase preparations assisted monomeric sugar release. CONCLUSION: Although treatment conditions for hemicellulose and cellulose hydrolysis differ, the study's findings suggest a good degree of overlap and process flexibility which should permit high recovery of pentose and hexose sugars. Copyright © 2011 Society of Chemical Industry

In this study, dilute acid pretreatment of five biomass feedstocks viz., sugarcane trash, sugarcane bagasse, rice straw, corn stover and palm empty fruit bunch were compared at a given combined severity factor (CSF) range of 1.4–3.2 and were characterised using an alternative Simons’ staining dye—Direct Yellow 11 fraction (DY 11, molecular weight >100,000) to better understand the correlations of pretreatment effectiveness with biomass physicochemical properties and pretreatment conditions. Good polynomial correlations (n = 2) of CSF were obtained with hemicellulose removal, cellulose digestibility and glucose yield resulting in R2 > 0.95. The results show that the total contents of extractives and ash have negative impacts on dilute acid pretreatment. Simons’ staining results show that DY 11 can also be used to estimate cellulose accessibility to cellulase enzymes. Good linear correlations of maximum adsorption capacity of DY 11 with CSF (R2 = 0.87–0.99) and cellulose digestibility (R2 = 0.91–0.99) were observed for most of the pretreated biomass samples.

Cotton ginning trash (CGT) collected from Australian cotton gins was evaluated for bioethanol production. CGT composition varied between ginning operations and contained high levels of extractives (26-28%), acid-insoluble material (17-22%) and holocellulose (42-50%). Pretreatment conditions of time (4-20 min), temperature (160-220 °C) and sulfuric acid concentration (0-2%) were optimised using a central composite design. Response surface modelling revealed that CGT fibre pretreated at 180 °C in 0.8% H2SO4 for 12 min was optimal for maximising enzymatic glucose recoveries and achieved yields of 89% theoretical, whilst the total accumulated levels of furans and acetic acid remained relatively low at1 and 2 g/L respectively. Response surface modelling also estimated maximum xylose recovery in pretreated liquors (87% theoretical) under the set conditions of 150 °C in 1.9% H2SO4 for 23.8 min. Yeast fermentations yielded high ethanol titres of 85%, 88% and 70% theoretical from glucose generated from: (a) enzymatic hydrolysis of washed pretreated fibres, (b) enzymatic hydrolysis of whole pretreated slurries and (c) simultaneous saccharification fermentations, respectively.

Aims To develop a method to produce beads with encapsulated Rhodococcus erythropolis NI86/21 with high cell density, extended shelf life, ease of handling and good atrazine degradation capabilities in both liquid and in agricultural soil. Methods and results Our findings show that the supplementary recovery step in nutrient broth media shortly after cell encapsulation facilitates cell survival in both wet and dry beads upon extended storage at 4 degrees C. Air drying has little or no impact on encapsulated R. erythropolis cell's ability to degrade atrazine in liquid or soil. Bead storage for periods extending up to 12 months at 4 degrees C did not affect the capacity of R. erythropolis encapsulated cells to degrade atrazine in either BMN or nonsterile soil extracts. Bentonite-amended beads formulated with 1% skim milk and exposed to the supplementary growth step, outperformed all other bead formats. These beads provided adequate numbers of vigorous R. erythropolis cells in either liquid or soil media to degrade atrazine. Conclusions Supplementary growth in nutrient broth media immediately following cell encapsulation greatly enhances R. erythropolis cells survival in both wet and dry beads upon extended storage at 4 degrees C. Wet and dried beads have similar capacity for atrazine degradation, and their usefulness and appeal in agronomic practise will only be known after bioassay evaluation and successful demonstration at field scale using incurred residues. Significance and impact of the study R. erythropolis NI86/21 encapsulated cells have the potential to reduce residual atrazine in soil, thereby minimizing the likelihood of off-site transport to ground or river water and reduce the loss of crops because of phytotoxicity of residual herbicide. Owing to their ease of handling, storage and possible compatibilities with pre-existing mechanical equipment, dried bead formats are ideally suited for agricultural and remediational applications.