Ethanol production from Saccharina japonica using an optimized extremely low acid pretreatment followed by simultaneous saccharification and fermentation

Microbial Lipid Based Biorefinery Concepts: A Review of Status and Prospects

The use of lignocellulosic biomass as a raw material for the production of lipids has gained increasing attention, especially in recent years when the use of food in the production of biofuels has become a current technology. Thus, the competition for raw materials for both uses has brought the need to create technological alternatives to reduce this competition that could generate a reduction in the volume of food offered and a consequent commercial increase in the value of food. Furthermore, the use of microbial oils has been studied in many industrial branches, from the generation of renewable energy to the obtainment of several value-added products in the pharmaceutical and food industries. Thus, this review provides an overview of the feasibility and challenges observed in the production of microbial lipids through the use of lignocellulosic biomass in a biorefinery. Topics covered include biorefining technology, the microbial oil market, oily microorganisms, mechanisms involved in lipid-producing microbial metabolism, strain development, processes, lignocellulosic lipids, technical drawbacks, and lipid recovery.

Recent Advances in Bioutilization of Marine Macroalgae Carbohydrates: Degradation, Metabolism, and Fermentation

Marine macroalgae are considered renewable natural resources due to their high carbohydrate content, which gives better utilization value in biorefineries and higher value conversion than first- and second-generation biomass. However, due to the diverse composition, complex structure, and rare metabolic pathways of macroalgae polysaccharides, their bioavailability needs to be improved. In recent years, enzymes and pathways related to the degradation and metabolism of macroalgae polysaccharides have been continuously developed, and new microbial fermentation platforms have emerged. Aiming at the bioutilization and transformation of macroalgae resources, this review describes the latest research results from the direction of green degradation, biorefining, and metabolic pathway design, including summarizing the the latest biorefining technology and the fermentation platform design of agarose, alginate, and other polysaccharides. This information will provide new research directions and solutions for the biotransformation and utilization of marine macroalgae.

Metabolic engineering for valorization of macroalgae biomass

Marine macroalgae have huge potential as feedstocks for production of a wide spectrum of chemicals used in biofuels, biomaterials, and bioactive compounds. Harnessing macroalgae in these ways could promote wellbeing for people while mitigating climate change and environmental destruction linked to use of fossil fuels. Microorganisms play pivotal roles in converting macroalgae into valuable products, and metabolic engineering technologies have been developed to extend their native capabilities. This review showcases current achievements in engineering the metabolisms of various microbial chassis to convert red, green, and brown macroalgae into bioproducts. Unique features of macroalgae, such as seasonal variation in carbohydrate content and salinity, provide the next challenges to advancing macroalgae-based biorefineries. Three emerging engineering strategies are discussed here: (1) designing dynamic control of metabolic pathways, (2) engineering strains of halophilic (salt-tolerant) microbes, and (3) developing microbial consortia for conversion. This review illuminates opportunities for future research communities by elucidating current approaches to engineering microbes so they can become cell factories for the utilization of macroalgae feedstocks.

Production of Bioethanol—A Review of Factors Affecting Ethanol Yield

Fossil fuels are a major contributor to climate change, and as the demand for energy production increases, alternative sources (e.g., renewables) are becoming more attractive. Biofuels such as bioethanol reduce reliance on fossil fuels and can be compatible with the existing fleet of internal combustion engines. Incorporation of biofuels can reduce internal combustion engine (ICE) fleet carbon dioxide emissions. Bioethanol is typically produced via microbial fermentation of fermentable sugars, such as glucose, to ethanol. Traditional feedstocks (e.g., first-generation feedstock) include cereal grains, sugar cane, and sugar beets. However, due to concerns regarding food sustainability, lignocellulosic (second-generation) and algal biomass (third-generation) feedstocks have been investigated. Ethanol yield from fermentation is dependent on a multitude of factors. This review compares bioethanol production from a range of feedstocks, and elaborates on available technologies, including fermentation practices. The importance of maintaining nutrient homeostasis of yeast is also examined. The purpose of this review is to provide industrial producers and policy makers insight into available technologies, yields of bioethanol achieved by current manufacturing practices, and goals for future innovation.

High-pressure technology for Sargassum spp biomass pretreatment and fractionation in the third generation of bioethanol production

Sargassum spp is an invasive macroalgae and an alternative feedstock for bioethanol production. Sargassum spp biomass was subjected to high-pressure technology for biomass fractionation under different operating conditions of temperature and residence time to obtain glucan enriched pretreated solids (32.22 g/100 g of raw material). Enzyme hydrolysis process at high pretreated solid loading (13%, w/v) and enzyme loading of 10 FPU/g of glucan was performed, obtaining 43.01 g/L of glucose corresponding to a conversion yield of 92.12%. Finally, a pre-simultaneous saccharification and fermentation strategy (PSSF) was performed to produce bioethanol. This operational strategy produced 45.66 g/L of glucose in the pre-saccharification stage, and 18.14 g/L of bioethanol was produced with a glucose to bioethanol conversion yield of 76.23%. The development of this process highlights the feasibility of bioethanol production from macroalgal biomass in the biorefinery concept.

Valorization of outer tunic of the marine filter feeder Ciona intestinalis towards the production of second-generation biofuel and prebiotic oligosaccharides

BACKGROUND

One of the sustainable development goals focuses on the biomass-based production as a replacement for fossil-based commodities. A novel feedstock with vast potentials is tunicate biomass, which can be pretreated and fermented in a similar way to lignocellulose. Ciona intestinalis is a marine filter feeder that is cultivated to produce fish feed. While the inner tissue body is used for feed production, the surrounding tunic remains as a cellulose-rich by-product, which can be further separated into outer and inner tunic. Ethanol production from organosolv-pretreated whole-tunic biomass was recently validated. The aim of the present study was to evaluate the potential of organosolv pretreated outer-tunic biomass for the production of biofuels and cellobiose that is a disaccharide with prebiotic potential.

RESULTS

As a result, 41.4 g/L of ethanol by Saccharomyces cerevisiae, corresponding to a 90.2% theoretical yield, was achieved under the optimal conditions when the tunicate biomass was pretreated at 195 °C for 60 min at a liquid-to-solid ratio of 50. In addition, cellobiose production by enzymatic hydrolysis of the pretreated tunicate biomass was demonstrated with a maximum conversion yield of 49.7 wt. %.

CONCLUSIONS

The utilisation of tunicate biomass offers an eco-friendly and sustainable alternative for value-added biofuels and chemicals. The cultivation of tunicate biomass in shallow coastal sea improves the quality of the water and ensures sustainable production of fish feed. Moreover, there is no competition for arable land, which leaves the latter available for food and feed production.

Optimization of alkali-treated poplar fiber saccharification using metal ions and surfactants

In this study, contrary to untreated poplar fiber, processing of alkali-treated poplar fiber was optimized for the enzymatic saccharification. Considering reducing sugar content as the evaluation index, pH, temperature, time, amount of enzyme, and rotational speed of shaker were standardized to optimize the sugar production by enzymatic hydrolysis. Using response surface methodology, the optimum technological condition of enzymatic hydrolysis was found to be utilizing 43 mg cellulase at 46 °C for 50 h. At this, the sugar conversion amount of NaOH or H₂O₂-NaOH pretreated poplar was 164.62 mg/g and 218.82 mg/g respectively. It was a corresponding increase of 446.73% or 626.75% than that of poplar fiber without a pretreatment. At a low concentration, metal ions and surfactants promoted the conversion of reducing sugar. Especially, 0.01 g/L Mn²⁺ and 0.50 g/L hexadecyl trimethyl ammonium bromide (CTAB) produced the best effect and increased the conversion rate of reducing sugar by 23.62% and 21.44% respectively. Also, the effect of the combination of metal ions and surfactants was better than that of a single accelerator. By improving the enzymatic process, these findings could enhance the utilization of poplar fiber for the production of reducing sugar.

Influence of Ethanol on Pitting Corrosion Behavior of Stainless Steel for Bioethanol Fermentation Tanks

The role of ethanol (C₂H₅OH) in pitting corrosion behavior of AISI 316L austenitic stainless steel was investigated in aqueous ethanolic solution with chloride. The pitting susceptibility and surface morphology of 316L in a series of ethanol-containing solutions were examined using X-ray photoelectron spectroscopy (XPS), optical microscopy with 3D stitching, immersion tests, and potentiodynamic polarization measurements. Results demonstrated that the ethanol concentration impacted little on the passive film stability while it dramatically influenced the pitting corrosion susceptibility. Corrosion rate of 316L after immersion tests first increased and then decreased as the concentration of ethanol increased from 0 to 10 M in ferric chloride solution. This, however, did not correspond to the breakdown potential which directly decreased from 489 to 249 mV as the water concentration decreased in ethanolic NaCl solutions. The pits density after both immersion and electrochemical tests showed that the initiation of pitting in ethanolic solution tended to occur at multiple points at the same time. The synergy effect on pitting behavior of hydrolysis enhancement and solubility reduction of metal cations due to the introduction of ethanol has also been discussed.

Itaconic acid production from undetoxified enzymatic hydrolysate of bamboo residues using Aspergillus terreus

Itaconic acid (IA) production by fermentation of undetoxified hydrolysate of bamboo residues by Aspergillus terreus was demonstrated. Monosaccharides were obtained by pretreatment and enzymatic hydrolysis of bamboo residues. A. terreus could not grow and synthesize IA in the hydrolysate. The buffer was confirmed to be an inhibitor, and was successfully replaced by deionized water as the suspension, to release equivalent sugar and eliminate the inhibition. Corn steep liquor significantly improved the adaptability of A. terreus to the hydrolysate at 2.0 g/L. The IA titer obtained (19.35 g/L IA) was the highest to be reported for IA production from lignocellulose without detoxification. Simultaneous saccharification and fermentation and fed-batch fermentation increased the titer to 22.43 g/L and 41.54 g/L, respectively. Meanwhile, economic assessment proved that bamboo residues were potential substrates for IA production with economic effectiveness.

A holistic zero waste biorefinery approach for macroalgal biomass utilization: A review

The growing concerns over the depleting fossil fuels and increase in the release of greenhouse gas emissions have necessitated the search for the potential biomass source for alternative energy generation. In this context, third generation biomass specifically maroalgae has gained a lot of research interest in the recent years for energy and products generation such as ethanol, butanol, alginates, agars, and carrageenans. There are a few reviews available in scientific domain on macroalgal biomass utilization for bioethanol production but none of them has addressed precisely from phenolic precursor compounds to the entire ethanol production process and its bottlenecks. Here, we explained critically the processes involved in bioethanol, value added products and chemicals production utilizing macroalgal biomass as a feedstock along with its zero waste feasibility approach. Apart from this, we have also summarized the major issues linked to the macroalgae based biofuels and bioproducts generation processes and their possible corrective measures. Biorefinery is a promising way to generate multiple products from a single source with short processing time. Thus, this review also focuses on the recent advancement in the macroalgal biomass scaling up and how this could help in the growth of macroalgal biorefinery industry in the near future.

Application of chemo thermal coupled sonic homogenization of marine macroalgal biomass for energy efficient volatile fatty acid recovery

The present study aimed to employ energy efficient chemo thermal coupled sonic homogenization (CTSH) to obtain VFA from marine macroalgal hydrolysate, (Ulva fasciata). At first, chemo thermal homogenization (CTH) was applied on macroalgal biomass by adjusting the temperature, pH and treatment time from 60 to 90 ℃, 4-7 and 0-60 min, respectively. A higher organic matter solubilisation of 11.81% was obtained at an optimum pH of 6 at a temperature of 80 ℃ with 40 min of homogenization time. The results of CTSH implied that a higher organic matter solubilization of 26.4% was achieved by combined CTSH (sonic power & treatment time - 140 W & 14 min treatment time). CTSH considerably doubles the liquefaction in comparison with CTH. Based on OMS grouping, achieving 25% was sufficient for VFA production (2172.09 mg/L) and considered as economically feasible with net cost of 97.17 USD/ton of macroalgae.

Bioethanol Production from UK Seaweeds: Investigating Variable Pre-treatment and Enzyme Hydrolysis Parameters

This study describes the method development for bioethanol production from three species of seaweed. Laminaria digitata, Ulva lactuca and for the first time Dilsea carnosa were used as representatives of brown, green and red species of seaweed, respectively. Acid thermo-chemical and entirely aqueous (water) based pre-treatments were evaluated, using a range of sulphuric acid concentrations (0.125-2.5 M) and solids loading contents (5-25 % [w/v]; biomass: reactant) and different reaction times (5-30 min), with the aim of maximising the release of glucose following enzyme hydrolysis. A pre-treatment step for each of the three seaweeds was required and pre-treatment conditions were found to be specific to each seaweed species. Dilsea carnosa and U. lactuca were more suited with an aqueous (water-based) pre-treatment (yielding 125.0 and 360.0 mg of glucose/g of pre-treated seaweed, respectively), yet interestingly non pre-treated D. carnosa yielded 106.4 g g^-1 glucose. Laminaria digitata required a dilute acid thermo-chemical pre-treatment in order to liberate maximal glucose yields (218.9 mg glucose/g pre-treated seaweed). Fermentations with S. cerevisiae NCYC2592 of the generated hydrolysates gave ethanol yields of 5.4 g L^-1, 7.8 g L^-1 and 3.2 g L^-1 from D. carnosa, U. lactuca and L. digitata, respectively. This study highlighted that entirely aqueous based pre-treatments are effective for seaweed biomass, yet bioethanol production alone may not make such bio-processes economically viable at large scale.

Butanol and butyric acid production from Saccharina japonica by Clostridium acetobutylicum and Clostridium tyrobutyricum with adaptive evolution

Optimal conditions of hyper thermal (HT) acid hydrolysis of the Saccharina japonica was determined to a seaweed slurry content of 12% (w/v) and 144 mM H2SO4 at 160 °C for 10 min. Enzymatic saccharification was carried out at 50 °C and 150 rpm for 48 h using the three enzymes at concentrations of 16 U/mL. Celluclast 1.5 L showed the lowest half-velocity constant (Km) of 0.168 g/L, indicating a higher affinity for S. japonica hydrolysate. Pretreatment yielded a maximum monosaccharide concentration of 36.2 g/L and 45.7% conversion from total fermentable monosaccharides of 79.2 g/L with 120 g dry weight/L S. japonica slurry. High cell densities of Clostridium acetobutylicum and Clostridium tyrobutyricum were obtained using the retarding agents KH2PO4 (50 mM) and NaHCO3 (200 mM). Adaptive evolution facilitated the efficient use of mixed monosaccharides. Therefore, adaptive evolution and retarding agents can enhance the overall butanol and butyric acid yields from S. japonica.

Bioethanol production from sugarcane leaf waste: Effect of various optimized pretreatments and fermentation conditions on process kinetics

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Bioethanol kinetics was investigated under SSA-F, SSA-U, MSA-F and MSA-U conditions.

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Monod, logistic and modified Gompertz models gave R² > 0.97.

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SSA-U pretreated SLW produced 25% more bioethanol than MSA-U.

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No difference was observed between filtered and unfiltered enzymatic hydrolysate.

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SLW residue showed a suitable protein and fat content for animal feed.

This study examines the kinetics of S. cerevisiae BY4743 growth and bioethanol production from sugarcane leaf waste (SLW), utilizing two different optimized pretreatment regimes; under two fermentation modes: steam salt-alkali filtered enzymatic hydrolysate (SSA-F), steam salt-alkali unfiltered (SSA-U), microwave salt-alkali filtered (MSA-F) and microwave salt-alkali unfiltered (MSA-U). The kinetic coefficients were determined by fitting the Monod, modified Gompertz and logistic models to the experimental data with high coefficients of determination R² > 0.97. A maximum specific growth rate (μ_max) of 0.153 h⁻¹ was obtained under SSA-F and SSA-U whereas, 0.150 h⁻¹ was observed with MSA-F and MSA-U. SSA-U gave a potential maximum bioethanol concentration (P_m) of 31.06 g/L compared to 30.49, 23.26 and 21.79 g/L for SSA-F, MSA-F and MSA-U respectively. An insignificant difference was observed in the μ_max and P_m for the filtered and unfiltered enzymatic hydrolysate for both SSA and MSA pretreatments, thus potentially reducing a unit operation. These findings provide significant insights for process scale up.

Seaweed Bioethanol Production: A Process Selection Review on Hydrolysis and Fermentation

The rapid depletion and environmental concerns associated with the use of fossil fuels has led to extensive development of biofuels such as bioethanol from seaweeds. The long-term prospect of seaweed bioethanol production however, depends on the selection of processes in the hydrolysis and fermentation stages due to their limiting effect on ethanol yield. This review explored the factors influencing the hydrolysis and fermentation stages of seaweed bioethanol production with emphasis on process efficiency and sustainable application. Seaweed carbohydrate contents which are most critical for ethanol production substrate selection were 52 ± 6%, 55 ± 12% and 57 ± 13% for green, brown and red seaweeds, respectively. Inhibitor formation and polysaccharide selectivity were found to be the major bottlenecks influencing the efficiency of dilute acid and enzymatic hydrolysis, respectively. Current enzyme preparations used, were developed for starch-based and lignocellulosic biomass but not seaweeds, which differs in polysaccharide composition and structure. Also, the identification of fermenting organisms capable of converting the heterogeneous monomeric sugars in seaweeds is the major factor limiting ethanol yield during the fermentation stage and not the SHF or SSF pathway selection. This has resulted in variations in bioethanol yields, ranging from 0.04 g/g DM to 0.43 g/g DM.

Fermentation of Mannitol Extracts From Brown Macro Algae by Thermophilic Clostridia

Mannitol-containing macro algae biomass, such as Ascophyllum nodosum and Laminaria digitata, are a potential feedstock for the production of biofuels such as bioethanol. The purpose of this work was to evaluate the ability of thermophilic anaerobes within Class Clostridia to ferment mannitol and mannitol-containing algal extracts. Screening of the type strains of six genera, Caldanaerobius, Caldanaerobacter, Caldicellulosiruptor, Thermoanaerobacter, Thermobrachium, and Thermoanaerobacterium) was conducted on 20 mM mannitol and revealed that 11 of 41 strains could utilize mannitol with ethanol being the dominant end-product. Mannitol utilization seems to be most common within the genus of Thermoanaerobacter (7 of 16 strains) with yields up to 88% of the theoretical yield in the case of Thermoanaerobacter pseudoethanolicus. Six selected mannitol-degrading strains (all Thermoanaerobacter species) were grown on mannitol extracts prepared from A. nodosum and L. digitata. Five of the strains produced similar amounts of ethanol as compared with ethanol yields from mannitol only. Finally, T. pseudoethanolicus was kinetically monitored using mannitol and mannitol extracts made from two macro algae species, A. nodosum and L. digitata for end-product formation.

Mechano-Enzymatic Deconstruction with a New Enzymatic Cocktail to Enhance Enzymatic Hydrolysis and Bioethanol Fermentation of Two Macroalgae Species

The aim of this study was to explore the efficiency of a mechano-enzymatic deconstruction of two macroalgae species for sugars and bioethanol production, by using a new enzymatic cocktail (Haliatase) and two types of milling modes (vibro-ball: VBM and centrifugal milling: CM). By increasing the enzymatic concentration from 3.4 to 30 g/L, the total sugars released after 72 h of hydrolysis increased (from 6.7 to 13.1 g/100 g TS and from 7.95 to 10.8 g/100 g TS for the green algae U. lactuca and the red algae G. sesquipedale, respectively). Conversely, total sugars released from G. sesquipedale increased (up to 126% and 129% after VBM and CM, respectively). The best bioethanol yield (6 g_eth/100 g TS) was reached after 72 h of fermentation of U. lactuca and no increase was obtained after centrifugal milling. The latter led to an enhancement of the ethanol yield of G. sesquipedale (from 2 to 4 g/100 g TS).

A review on the biomass pretreatment and inhibitor removal methods as key-steps towards efficient macroalgae-based biohydrogen production

(Red, green and brown) macroalgal biomass is a propitious candidate towards covenant alternative energy resources to be converted into biofuels i.e. hydrogen. The application of macroalgae for hydrogen fermentation (promising route in advancing the biohydrogen generation process) could be accomplished by the transformation of carbohydrates, which is a topic receiving broad attention in recent years. This article overviews the variety of marine algal biomass available in the coastal system, followed by the analyses of their pretreatment methods, inhibitor formation and possible detoxification, which are key-aspects to achieve subsequent H₂ fermentation in a proper way.

Combined De-Algination Process as a Fractionation Strategy for Valorization of Brown Macroalga Saccharina japonica

A combined process, de-algination followed by enzymatic saccharification, was designed to produce alginate and glucose from Saccharina japonica consecutively. The process conditions of de-algination were optimized separately for each stage of acidification and alkaline extraction. Collectively, the de-algination yield was 70.1% under the following optimized conditions: 2.4 wt% of Na2CO3, 70 °C, and 100 min with the acidified S. japonica immersed in a 0.5 wt% H2SO4 solution for 2 h at room temperature. The glucan content in the de-alginated S. japonica increased to 38.0%, which was approximately fivefold higher than that of the raw S. japonica. The enzymatic hydrolysis of the de-alginated S. japonica almost completed in 9 h, affording 5.2 g (96.8% of glucan digestibility) of glucose at a de-alginated S. japonica loading of 14.2 g.

Ethanol production from brown seaweed using non-conventional yeasts

The use of macroalgae (seaweed) as a potential source of biofuels has attracted considerable worldwide interest. Since brown algae, especially the giant kelp, grow very rapidly and contain considerable amounts of polysaccharides, coupled with low lignin content, they represent attractive candidates for bioconversion to ethanol through yeast fermentation processes. In the current study, powdered dried seaweeds (Ascophylum nodosum and Laminaria digitata) were pre-treated with dilute sulphuric acid and hydrolysed with commercially available enzymes to liberate fermentable sugars. Higher sugar concentrations were obtained from L. digitata compared with A. nodosum with glucose and rhamnose being the predominant sugars, respectively, liberated from these seaweeds. Fermentation of the resultant seaweed sugars was performed using two non-conventional yeast strains: Scheffersomyces (Pichia) stipitis and Kluyveromyces marxianus based on their abilities to utilise a wide range of sugars. Although the yields of ethanol were quite low (at around 6 g/L), macroalgal ethanol production was slightly higher using K. marxianus compared with S. stipitis. The results obtained demonstrate the feasibility of obtaining ethanol from brown algae using relatively straightforward bioprocess technology, together with non-conventional yeasts. Conversion efficiency of these non-conventional yeasts could be maximised by operating the fermentation process based on the physiological requirements of the yeasts.

Comparison of different process strategies for bioethanol production from Eucheuma cottonii: An economic study

The aim of this work was to evaluate the efficacy of red macroalgae Eucheuma cottonii (EC) as feedstock for third-generation bioethanol production. Dowex (TM) Dr-G8 was explored as a potential solid catalyst to hydrolyzed carbohydrates from EC or macroalgae extract (ME) and pretreatment of macroalgae cellulosic residue (MCR), to fermentable sugars prior to fermentation process. The highest total sugars were produced at 98.7 g/L when 16% of the ME was treated under the optimum conditions of solid acid hydrolysis (8% (w/v) Dowex (TM) Dr-G8, 120°C, 1h) and 2% pretreated MCR (P-MCR) treated by enzymatic hydrolysis (pH 4.8, 50°C, 30 h). A two-stream process resulted in 11.6g/L of bioethanol from the fermentation of ME hydrolysates and 11.7 g/L from prehydrolysis and simultaneous saccharification and fermentation of P-MCR. The fixed price of bioethanol obtained from the EC is competitive with that obtained from other feedstocks.

Direct bioconversion of brown algae into ethanol by thermophilic bacterium Defluviitalea phaphyphila

BACKGROUND

Brown algae are promising feedstocks for biofuel production with inherent advantages of no structural lignin, high growth rate, and no competition for land and fresh water. However, it is difficult for one microorganism to convert all components of brown algae with different oxidoreduction potentials to ethanol. Defluviitalea phaphyphila Alg1 is the first characterized thermophilic bacterium capable of direct utilization of brown algae.

RESULTS

Defluviitalea phaphyphila Alg1 can simultaneously utilize mannitol, glucose, and alginate to produce ethanol, and high ethanol yields of 0.47 g/g-mannitol, 0.44 g/g-glucose, and 0.3 g/g-alginate were obtained. A rational redox balance system under obligate anaerobic condition in fermenting brown algae was revealed in D. phaphyphila Alg1 through genome and redox analysis. The excess reducing equivalents produced from mannitol metabolism were equilibrated by oxidizing forces from alginate assimilation. Furthermore, D. phaphyphila Alg1 can directly utilize unpretreated kelp powder, and 10 g/L of ethanol was accumulated within 72 h with an ethanol yield of 0.25 g/g-kelp. Microscopic observation further demonstrated the deconstruction process of brown algae cell by D. phaphyphila Alg1.

CONCLUSIONS

The integrated biomass deconstruction system of D. phaphyphila Alg1, as well as its high ethanol yield, provided us an excellent alternative for brown algae bioconversion at elevated temperature.

Integrated bioethanol and protein production from brown seaweed Laminaria digitata

A wild-growing glucose-rich (i.e. 56.7% glucose content) brown seaweed species Laminaria digitata, collected from the North Coast of Denmark in August 2012, was used as the feedstock for an integrated bioethanol and protein production. Glutamic acid and aspartic acid are the two most abundant amino acids in the algal protein, both with proportional content of 10% in crude protein. Only minor pretreatment of milling was used on the biomass to facilitate the subsequent enzymatic hydrolysis and fermentation. The Separate Hydrolysis and Fermentation (SHF) resulted in obviously higher ethanol yield than the Simultaneous Saccharification and Fermentation (SSF). High conversion rate at maximum of 84.1% glucose recovery by enzymatic hydrolysis and overall ethanol yield at maximum of 77.7% theoretical were achieved. Protein content in the solid residues after fermentation was enriched by 2.7 fold, with similar distributions of amino acids, due to the hydrolysis of polymers in the seaweed cell wall matrix.

Comparison of industrially viable pretreatments to enhance soybean straw biodegradability

This study explores acid and alkaline pretreatments in order to enhance soybean straw biodegradability. The effects of sulfuric acid and sodium hydroxide for different pretreatment times at 30°C and 121°C on biomass dissolution and the subsequent enzymatic hydrolysis were investigated. The highest total conversion to reducing sugars of 93.9% was attained when soybean straw was pretreated with acid (4% H2SO4, 121°C, 1 h) and subsequently subjected to the enzymatic process. However, conversion of 86.5%, were reached only with the hydrolysis of the pretreated residue using mild conditions, (0.5% NaOH, 30°C, 48 h), involving the reduction cost of the process. In addition to this, this result was dramatically decreased when pectinase was removed from the enzyme cocktail. It has been also demonstrated that the reduction of the enzyme loading to less than half allowed obtaining about 96% of the reducing sugars attained with the highest enzyme dose.

Enhanced hydrolysis of Macrocystis pyrifera by integrated hydroxyl radicals and hot water pretreatment

Integrated hydroxyl radicals and hot water pretreatment (IHRHW) was employed in the bioconversion of the brown macroalgae Macrocystis pyrifera (M. pyrifera) in this study. The optimum experimental pretreatment condition (100°C, 30 min, 11.9 mM FeSO4) and the predicted optimum pretreatment condition (113.95°C, 29.1 min, 12.75 mM FeSO4) were identified using a central composite design method. All glucan and xylan were recovered as monosaccharides or polysaccharides without a fermentation inhibitor (e.g., hydroxymethyl furfural and furfural). The IHRHW-treated macroalgae digestibility reached 88.1% under the optimum experimental condition, whereas that under the predicted optimum condition reached 92.1%. The value was approximately threefold higher than those obtained with untreated M. pyrifera. Carbohydrate recovery and enzymatic hydrolysis can be significantly enhanced by the new economic hydroxyl radicals and hot water pretreatment.

Enhanced enzymatic hydrolysis and ethanol production from cashew apple bagasse pretreated with alkaline hydrogen peroxide

The effect of combinations and ratios between different enzymes has been investigated in order to assess the optimal conditions for hydrolysis of cashew apple bagasse pretreated with alkaline hydrogen peroxide (the solids named CAB-AHP). The separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes were evaluated in the ethanol production. The enzymatic hydrolysis conducted with cellulase complex and β-glucosidase in a ratio of 0.61:0.39, enzyme loading of 30FPU/g(CAB-AHP) and 66CBU/g(CAB-AHP), respectively, using 4% cellulose from CAB-AHP, turned out to be the most effective conditions, with glucose and xylose yields of 511.68 mg/g(CAB-AHP) and 237.8 mg/g(CAB-AHP), respectively. Fermentation of the pure hydrolysate by Kluyveromyces marxianus ATCC 36907 led to an ethanol yield of 61.8kg/ton(CAB), corresponding to 15 g/L ethanol and productivity of 3.75 g/( Lh). The ethanol production obtained for SSF process using K. marxianus ATCC 36907 was 18 g/L corresponding to 80% yield and 74.2kg/ton(CAB).

Hydroxyl radical-aided thermal pretreatment of algal biomass for enhanced biodegradability

BACKGROUND

Algal biomass, known as a potential feedstock for biofuel production, has cell wall structures that differ from terrestrial biomass. The existing methods for processing algae are limited to conventional pretreatments for terrestrial biomass.

RESULTS

In this study, we investigated a novel hydroxyl radical-aided approach for pretreating different types of algal biomass. In this process, hydroxyl radicals formed by a Fenton system were employed in combination with heating to alter the crystalline structure and hydrogen bonds of cellulose in the algal biomass. FeSO4 and H2O2 at low concentrations were employed to initiate the formation of hydroxyl radicals. This method releases trapped polysaccharides in algal cell walls and converts them into fermentable sugars. The effects of temperature, time, and hydroxyl radical concentration were analyzed. The optimal pretreatment condition [100 °C, 30 min, and 5.3 mM H2O2 (determined FeSO4 concentration of 11.9 mM)] was identified using a central composite design. Complete (100 %) carbohydrate recovery was achieved with some algal biomass without formation of inhibitors such as hydroxymethylfurfural and furfural as by-products. Both microalgal and macroalgal biomasses showed higher enzymatic digestibility of cellulose conversion (>80 %) after the milder pretreatment condition.

CONCLUSION

Hydroxyl radical-aided thermal pretreatment was used as a novel method to convert the carbohydrates in the algal cell wall into simple sugars. Overall, this method increased the amount of glucose released from the algal biomass. Overall, enhanced algal biomass digestibility was demonstrated with the proposed pretreatment process. The new pretreatment requires low concentration of chemical solvents and milder temperature conditions, which can prevent the toxic and corrosive effects that typically result from conventional pretreatments. Our data showed that the advantages of the new pretreatment include higher carbohydrate recovery, no inhibitor production, and lower energy consumption. The new pretreatment development mimicking natural system could be useful for biochemical conversion of algal biomass to fuels and chemicals.

Draft genome sequence of Microbulbifer elongatus strain HZ11, a brown seaweed-degrading bacterium with potential ability to produce bioethanol from alginate

Microbulbifer elongatus strain HZ11, was a new strain of M. elongates DSM 6810(T), which has the ability to degrade brown seaweeds such as Laminaria japonica into single cell detritus particles. Here we report a high quality draft genome of M. elongatus strain HZ11, which comprises 4,223,108bp in 9 contigs with the G+C content of 56.70%. A total of 3293 protein-coding sequences were predicted, including nine alginate lyases (EC 4.2.2.3), five agarases (EC 3.2.1.81), 2-dehydro-3-deoxygluconate kinase (EC 2.7.1.45) and all enzymes involved in the Entner-Doudoroff pathway. Our results suggest that strain HZ11 has the potential ability to produce bioethanol from alginate with moderate genetic modification, which may significantly increase the yield of bioethanol from brown seaweed and the utilization rate of brown seaweeds.

Augmented digestion of lignocellulose by steam explosion, acid and alkaline pretreatment methods: a review

Lignocellulosic materials can be explored as one of the sustainable substrates for bioethanol production through microbial intervention as they are abundant, cheap and renewable. But at the same time, their recalcitrant structure makes the conversion process more cumbersome owing to their chemical composition which adversely affects the efficiency of bioethanol production. Therefore, the technical approaches to overcome recalcitrance of biomass feedstock has been developed to remove the barriers with the help of pretreatment methods which make cellulose more accessible to the hydrolytic enzymes, secreted by the microorganisms, for its conversion to glucose. Pretreatment of lignocellulosic biomass in cost effective manner is a major challenge to bioethanol technology research and development. Hence, in this review, we have discussed various aspects of three commonly used pretreatment methods, viz., steam explosion, acid and alkaline, applied on various lignocellulosic biomasses to augment their digestibility alongwith the challenges associated with their processing.

Simultaneous saccharification and fermentation of cassava to succinic acid by Escherichia coli NZN111

In this study, the production of succinic acid from cassava starch and raw cassava instead of glucose by Escherichia coli NZN111 was investigated. During the two-stage fermentation, simultaneous saccharification and fermentation (SSF) was applied in the anaerobic stage. The results showed that both the productivity and specific productivity in the process conducted at 40°C were higher than those in the cultivation conducted at 37°C. The yield of succinic acid based on the amount of added starch reached the highest level 0.86 g/g and cassava starch was almost totally hydrolyzed in the SSF process. With the improved cell density, 127.13 g/L of succinic acid was obtained. When the liquefied crude cassava powder was used directly in SSF, 106.17 g/L of succinic acid was formed. The result showed that crude cassava powder could be another cheap raw material for succinic acid formation.

Pretreatment of macroalgae for volatile fatty acid production

In this study, a novel method was proposed for the biological pretreatment of macroalgae (Laminaria japonica, Pachymeniopsis elliptica, and Enteromorpha crinita) for production of volatile fatty acid (VFA) by anaerobic fermentation. The amount of VFA produced from 40 g/L of L. japonica increased from 8.3 g/L (control) to 15.6 g/L when it was biologically pretreated with Vibrio harveyi. The biological treatment of L. japonica with Vibrio spp. was most effective likely due to the alginate lyase activity of Vibrio spp. However, a considerable effect was also observed after biological pretreatment of P. elliptica and E. crinita, which are red and green algae, respectively. Alkaline pretreatment of 40 g/L of L. japonica with 0.5 N NaOH resulted in an increase of VFA production to 12.2 g/L. These results indicate that VFA production from macroalgae can be significantly enhanced using the proposed biological pretreatments.

Pretreatment of the macroalgae Chaetomorpha linum for the production of bioethanol--comparison of five pretreatment technologies

A qualified estimate for pretreatment of the macroalgae Chaetomorpha linum for ethanol production was given, based on the experience of pretreatment of land-based biomass. C. linum was subjected to hydrothermal pretreatment (HTT), wet oxidation (WO), steam explosion (STEX), plasma-assisted pretreatment (PAP) and ball milling (BM), to determine effects of the pretreatment methods on the conversion of C. linum into ethanol by simultaneous saccharification and fermentation (SSF). WO and BM showed the highest ethanol yield of 44 g ethanol/100g glucan, which was close to the theoretical ethanol yield of 57 g ethanol/100g glucan. A 64% higher ethanol yield, based on raw material, was reached after pretreatment with WO and BM compared with unpretreated C. linum, however 50% of the biomass was lost during WO. Results indicated that the right combination of pretreatment and marine macroalgae, containing high amounts of glucan and cleaned from salts, enhanced the ethanol yield significantly.