• Energy Research

Fusarium oxysporum is a filamentous fungus which has attracted a lot of scientific interest not only due to its ability to produce a variety of lignocellulolytic enzymes, but also because it is able to ferment both hexoses and pentoses to ethanol. Although this fungus has been studied a lot as a cell factory, regarding applications for the production of bioethanol and other high added value products, no systematic study has been performed concerning its ethanol tolerance levels.In aerobic conditions it was shown that both the biomass production and the specific growth rate were affected by the presence of ethanol. The maximum allowable ethanol concentration, above which cells could not grow, was predicted to be 72 g/L. Under limited aeration conditions the ethanol-producing capability of the cells was completely inhibited at 50 g/L ethanol. The lignocellulolytic enzymatic activities were affected to a lesser extent by the presence of ethanol, while the ethanol inhibitory effect appears to be more severe at elevated temperatures. Moreover, when the produced ethanol was partially removed from the broth, it led to an increase in fermenting ability of the fungus up to 22.5%. The addition of F. oxysporum's system was shown to increase the fermentation of pretreated wheat straw by 11%, in co-fermentation with Saccharomyces cerevisiae.The assessment of ethanol tolerance levels of F. oxysporum on aerobic growth, on lignocellulolytic activities and on fermentative performance confirmed its biotechnological potential for the production of bioethanol. The cellulolytic and xylanolytic enzymes of this fungus could be exploited within the biorefinery concept as their ethanol resistance is similar to that of the commercial enzymes broadly used in large scale fermentations and therefore, may substantially contribute to a rational design of a bioconversion process involving F. oxysporum. The SSCF experiments on liquefied wheat straw rich in hemicellulose indicated that the contribution of the metabolic system of F. oxysporum in a co-fermentation with S. cerevisiae may play a secondary role.

The ability of sweet sorghum to be utilized as feedstock for ethanol production at high initial dry material concentration was investigated. Sweet sorghum, after being dried, was liquefacted employing commercial cellulase solution Celluclast® 1.5L, in order submerged fermentation to be permitted under high-solids concentrations. The presence of a separate enzymatic liquefaction step at 350 kg m−3 initial DM enhanced both ethanol production and productivity by 29.76% and 250%, respectively. Response surface methodology, based on the central composite design was applied to explore the combined effect of liquefaction duration and enzyme loading in order liquefaction conditions to be optimized. When the optimum conditions were tested using an enzyme load of 8.32 FPU g−1 of dry material for 8.6 h at 50 °C, high productivity (3.0 kg m−3 h−1) and final ethanol production (62.5 kg m−3) were achieved.

Biomass fractionation, as an alternative to biomass pretreatment, has gained increasing research attention over the past few years as it provides separate streams of cellulose, hemicellulose, and lignin. These streams can be used separately and can provide a solution for improving the economics of emerging biorefinery technologies. The sugar streams are commonly used in microbial conversions, whereas during recent years lignin has been recognized as a valuable compound as it is the only renewable and abundant source of aromatic chemicals. Successfully converting lignin into valuable chemicals and products is key in achieving both environmental and economic sustainability of future biorefineries. In this work, lignin retrieved from beechwood sawdust delignification pretreatment via an organosolv process was depolymerized with thermal and catalytic pyrolysis. ZSM-5 commercial catalyst was used in situ to upgrade the lignin bio-oil vapors. Lignins retrieved from different modes of organosolv pretreatment were tested in order to evaluate the effect that upstream pretreatment has on the lignin fraction. Both thermal and catalytic pyrolysis yielded oils rich in phenols and aromatic hydrocarbons. Use of ZSM-5 catalyst assisted in overall deoxygenation of the bio-oils and enhanced aromatic hydrocarbons production. The oxygen content of the bio-oils was reduced at the expense of their yield. Organosolv lignins were successfully depolymerized towards phenols and aromatic hydrocarbons via thermal and catalytic pyrolysis. Hence, lignin pyrolysis can be an effective manner for lignin upgrading towards high added value products.

AbstractThe urgent need to reduce CO2 emissions has motivated the development of CO2 capture and utilization technologies. An emerging application is CO2 transformation into storage chemicals for clean energy carriers. Formic acid (FA), a valuable product of CO2 reduction, is an excellent hydrogen carrier. CO2 conversion to FA, followed by H2 release from FA, are conventionally chemically catalyzed. Biocatalysts offer a highly specific and less energy‐intensive alternative. CO2 conversion to formate is catalyzed by formate dehydrogenase (FDH), which usually requires a cofactor to function. Several FDHs have been incorporated in bioelectrochemical systems where formate is produced by the biocathode and the cofactor is electrochemically regenerated. H2 production from formate is also catalyzed by several microorganisms possessing either formate hydrogenlyase or hydrogen‐dependent CO2 reductase complexes. Combination of these two processes can lead to a CO2‐recycling cycle for H2 production, storage, and release with potentially lower environmental impact than conventional methods.

Fusarium oxysporum F3 alone or in mixed culture with Saccharomyces cerevisiae F12 were used to ferment carbohydrates of wet exploded pre-treated wheat straw (PWS) directly to ethanol. Both microorganisms were first grown aerobically to produce cell mass and thereafter fermented PWS to ethanol under anaerobic conditions. During fermentation, soluble and insoluble carbohydrates were hydrolysed by the lignocellulolytic system of F. oxysporum. Mixed substrate fermentation using PWS and corn cobs (CC) in the ratio 1:2 was used to obtain an enzyme mixture with high cellulolytic and hemicellulolytic activities. Under these conditions, activities as high as 34300, 9100, 326, 24, 169, 27 and 254 U dm(-3) of xylanase, endoglucanase, beta-glucosidase, arabinofuranosidase, avicelase, feruloyl esterase and acetyl esterase, respectively, were obtained. The replacement of the enzyme production phase of F. oxysporum by the addition of commercially available enzymes Celluclast (R) 1.5 L FG and Novozym (R) 188 in 3:1 ratio for the treatment of PWS, resulted in a 3-fold increase in the volumetric ethanol productivity without increasing the ethanol production significantly. By direct bioconversion of 110 kg m(-3) dry matter of PWS, ethanol concentration (4.9 kg m(-3)) and yield (40 g kg(-1) of PWS) were similarly obtained by F. oxysporum and the mixed culture, while productivity rates as high as 34 g m(-3) h(-1) and 108 g m(-3) h(-1) were obtained by F. oxysporum and the mixed culture, respectively.

The present work investigates the suitability of pretreated corn stover (CS) to serve as feedstock for high gravity (HG) ethanol production at solids-content of 24wt%. Steam explosion, with and without the addition of H2SO4, and organosolv pretreated CS samples underwent a liquefaction/saccharification step followed by simultaneous saccharification and fermentation (SSF). Maximum ethanol concentration of ca. 76g/L (78.3% ethanol yield) was obtained from steam exploded CS (SECS) with 0.2% H2SO4. Organosolv pretreated CS (OCS) also resulted in high ethanol concentration of ca. 65g/L (62.3% ethanol yield). Moreover, methane production through anaerobic digestion (AD) was conducted from fermentation residues and resulted in maximum methane yields of ca. 120 and 69mL/g volatile solids (VS) for SECS and OCS samples, respectively. The results indicated that the implementation of a liquefaction/saccharification step before SSF employing a liquefaction reactor seemed to handle HG conditions adequately.

Olive mill wastewater (OMWW) is a major problem in olive oil - producing countries, due to its high organic load and concentration in phenols that are toxic for marine life, plants and soil microorganisms. In the present study, two mushroom species were tested in regard to their OMWW's oxidative capacity, Pleurotus citrinopileatus LGAM 28684 and Irpex lacteus LGAM 238. OMWW (25% v/v) degradation was investigated for several culture conditions, namely pH, agitation speed, nitrogen-based supplements and their concentration. The selected values were pH 6, agitation rate 150 rpm, 30 g L-1 corn steep liquor as nitrogen source for P. citrinopileatus and 20 g L-1 diammonium tartrate for I. lacteus. The two strains performed well in cultures supplemented with OMWW, generating very high titers of oxidative enzymes and achieving more than 90% color and phenols reduction within a 24 days cultivation period. In addition, the amount of glucans present in the fungal biomass was assessed. Hence, P. citrinopileatus and I. lacteus appear as potent degraders of OMWW with the ability to use the effluent as a substrate for the production of biotechnologically important enzymes and valuable fungal glucans.

The importance of expanding our knowledge on microorganisms derived from extreme environments stems from the development of novel and sustainable technologies for our health, food, and environment. Microalgae and cyanobacteria represent a group of diverse microorganisms that inhabit a wide range of environments, are capable of oxygenic photosynthesis, and form a thick microbial mat even at extreme environments. Studies of thermophilic microorganisms have shown a considerable biotechnological potential due to their optimum growth and metabolisms at high temperatures (≥50 °C), which is supported by their thermostable enzymes. Microalgal and cyanobacterial communities present in high-temperature ecosystems account for a large part of the total ecosystem biomass and productivity, and can be exploited to generate several value-added products of agricultural, pharmaceutical, nutraceutical, and industrial relevance. This review provides an overview on the current status of biotechnological applications of thermophilic microalgae and cyanobacteria, with an outlook on the challenges and future prospects.

The negative impact of fossil fuels and the increased demand for renewable energy sources has led to the use of novel raw material sources. Lignocellulosic biomass could serve as a possible raw material for anaerobic digestion and production of biogas. This work is aimed at using forest biomass, both softwood (spruce) and hardwood (birch), as a raw material for anaerobic digestion. We examined the effect of different operational conditions for the organosolv pretreatment (ethanol content, duration of treatment, and addition of acid catalyst) on the methane yield. In addition, we investigated the effect of addition of cellulolytic enzymes during the digestion. We found that inclusion of an acid catalyst during organosolv pretreatment improved the yields from spruce, but it did not affect the yields from birch. Shorter duration of treatment was advantageous with both materials. Methane yields from spruce were higher with lower ethanol content whereas higher ethanol content was more beneficial for birch. The highest yields obtained were 185 mL CH4/g VS from spruce and 259.9 mL CH4/g VS from birch. Addition of cellulolytic enzymes improved these yields to 266.6 mL CH4/g VS and 284.2 mL CH4/g VS, respectively.

Single cell oils (SCOs) are considered potential raw material for the production of biodiesel. Rhodosporidium sp. and Lipomyces sp. are good candidates for SCO production. Lipid extractability differs according to yeast species and literature on the most suitable method for each oleaginous yeast species is scarce. This work aimed to investigate the efficiency of the most cited strategies for extracting lipids from intact and pretreated cells of Rhodosporidium toruloides and Lipomyces starkeyi. Lipid extractions were conducted using hexane or combinations of chloroform and methanol. The Folch method resulted in the highest lipid yields for both yeasts (42% for R. toruloides and 48% for L. starkeyi). Also, this method eliminates the cell pretreatment step. The Bligh and Dyer method underestimated the lipid content in the tested strains (25% for R. toruloides and 34% for L. starkeyi). Lipid extractability increased after acid pretreatment for the Pedersen, hexane, and Bligh and Dyer methods. For R. toruloides unexpected fatty acid methyl esters (FAME) composition were found for some lipid extraction strategies tested. Therefore, this work provides useful information for analytical and process development aiming at biodiesel production from the SCO of these two yeast species.