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Global energy demand is increased with the rapidly growing population; and it is fulfilled by fossil fuels. However, it also contributes to the greenhouse gas effect in the ...environment. In recent years, the rapid consumption of fossil fuels has resulted in its depletion, which raised the questions concerning the environment safety. The lignocellulosic biomass has emerged as an alternative solution for these problems. The lignocellulosic biomass is abundantly present on the earth, which can be transformed into bioethanol and/or biochemical products after some suitable pre-treatment methods include physical, chemical and biological methods. But these approaches have certain limitations as they are expensive and inconvenient. These limitations have been overcome by developing a new alternative novel, cost-effective, efficient and eco-friendly method i.e. nanotechnology which offers promising solution to the existing pre-treatment methods. In this review, various conventional pre-treatment methods and evolving nanobiotechnological routes in lignocellulosic pretreatment methods are critically discussed.
Agricultural residues could become feedstocks for biobased products as they are renewable, carbon neutral, and do not compete with food. In India, > 130 MT rice straw is available annually for ...alternate uses. Exploiting this abundant biomass for biochemical production will pave way for bio-based economy. Rice straw is highly recalcitrant due to lignin-carbohydrate complex and high ash. For production of value added products, the cellulose fraction is very important and also lignin can be used. However, for overall economic efficiency, it is imperative to separate and recover these fractions maximally from biomass and convert them into high value products at high titers and efficiency. Biomass has to be deconstructed to access these fractions. An improvised pretreatment with sodium hydroxide (NaOH) coupled with acidified water wash enabled high retrieval of cellulose and lignin. More than 80% of cellulose present in raw rice straw was recovered in pretreated solids and lignin (> 65%) recovered from acidification of alkali prehydrolysates/wash waters. Enzymatic hydrolysis of solids with commercial cellulases resulted in 80–100% glucan conversion at 6% and 3% loading respectively yielding ~ 5.5% and 3.3% sugar syrups which can be fermented to value added chemicals.
Saccharomyces cerevisiae
LN fermented hydrolysates with 77–97% efficiency producing 0.508 gg
−1
and 0.403 gg
−1
ethanol within 24 h consuming all glucose while xylose was unutilized. Material calculations showed that this process converted 63% of cellulose present in rice straw to ethanol potentially yielding 135 L ethanol and ~ 100 Kg lignin per ton of rice straw with limited water use.
Cost effective bioethanol production from biomass requires complete utilization of mixed sugars and their efficient fermentation to ethanol. The fermenting strain should be capable of hexose and ...pentose utilization and tolerant to inhibitory byproducts of pretreatment. While, metabolic engineering strategies on Saccharomyces have yielded laboratory strains capable of mix sugar fermentation, hardly a few approaches have realized in industrial strains. Therefore, bioprospecting non-conventional native yeasts for efficient utilization of carbohydrate component of the biomass is imperative. In the present study, the fermentation efficiency of naturally pentose utilising yeasts such as Pichia stipitis NCIM3498, Pichia stipitis NCIM3497, Candida tropicalis Y6 and Rhodotorula glutinis Y1 was assessed on alkali pretreated rice straw hydrolysates, synthetic sugar/mixture and in presence of inhibitors. Highest fermentation efficiency (57.30%) on hydrolysate within 24 h was observed in P. stipitis NCIM3497 while P. stipitis NCIM3498 and C. tropicalis Y6 showed 53.03 and 46.51% respectively. On 2% glucose, fermentation efficiency was 64.77%–86.96% for Pichia and Candida strains, complete sugar depletion with 8.87 g L−1 highest ethanol production. On mixed sugars, highest fermentation efficiency was 87.35%. Pichia and Candida strains were tolerant to furfural and produced ethanol. Acetic acid and formic acid inhibited growth, sugar consumption and no ethanol detected.
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•Pichia stipitis, Candida tropicalis, Rhodotorula glutinis grew on straw hydrolysate.•P. stipitis NCIM3498 consumed >90% sugars producing 8.8 gL-1 ethanol on hydrolysate.•C. tropicalis Y6 used 57% sugars producing 2.84 gL-1 ethanol on straw hydrolysate.•P. stipitis NCIM3498 produced ∼4% ethanol in optimized synthetic mixed sugar medium.•Yeast strains were tolerant to furfural but inhibited by formic and acetic acid.
Lignocellulose based processes consist of technology platforms for production of materials and products for developing a bio-based, sustainable economy. Production of sugar streams and ethanol from ...cellulose is a mature technology, and its deployment results in increased lignin availability. Although lignin is used for low-value applications, its high-value utilization needs to be explored and developed. The aromatic intermediates from lignin can be transformed into high-value products. The unique structural/chemical properties of lignin offer possibilities for valorization, which can be achieved through thermochemical or biological transformation platforms, each route having its pros and cons. Lignin degrading oragnisms hold promise for biovalorization. In this work, different categories of organisms (fungi and bacteria) capable of degrading lignin, possessing unique repertoires of enzymes have been discussed. Under natural niches consortium of organisms decay lignin as a single organism does not possess all the activities. The constraints in biological processing can be addressed by using a combination of processes for lignin depolymerization to aromatic intermediates, followed by their conversion to target products. The recent devised metabolic engineering strategies to tackle these challenges are reviewed. Ultimately, the success of biorefineries will be dictated by the technical feasibility of bioconversions, robustness of engineered organisms, and their ability to produce the desired products in high titers with relatively high purity, scalability, and overall economics.
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•Lignin, a byproduct from biorefineries, still underutilized.•High value application entailed depolymerization.•Chemical/catalytic/biological platforms for depolymerization entail challenges.•Biological valorization through ligninolytic organisms and enzymes has potential.•Metabolic engineering to get robust organisms and pure products in high titer.
Rice straw, an abundant agro-residue, is available for energy production. In many parts of Asian countries, it is burnt on fields causing harm to the environment. Rice straw contains lignin, ...cellulose, hemicelluloses, and silicates making it recalcitrant. Pretreatment processes disintegrate lignin-carbohydrate matrix for efficient bioconversion of polysaccharides to fermentable sugars. A good number of physical, biological and chemical processes have been tried but degradation of polysaccharides and subsequent fermentation is still a challenge. Alkaline pretreatment causes effective delignification and swelling of biomass. The present study was performed on alkaline pretreatment of rice straw with 1% NaOH by autoclaving for 30 min at 121 °C at 10% solid loading. It was extracted with water to remove lignins, solids separated by filtrations and washed again to neutralize the pH. Water washing also led to removal of phenolic inhibitors. High (63%) glucan enrichment was obtained with concomitant lignin loss. Dry matter loss was around 50%. Enzymatic saccharification of the pretreated solids at 5 and 10% with Accellerase® 1500 for 24 h at 50 °C gave saccharification efficiency 76 and ~ 50% respectively. Hydrolysates containing 18 and 23 gL
−1
sugars, supplemented with minimal salts, yeast extract, fermented by
S. cerevisiae
LN for 24 h yielded ~ 2 and 4 gL
−1
ethanol with fermentation efficiency 55–66%. Thus, NaOH pretreatment is a cost effective option for ethanol production from rice straw. Lignin removed in prehydrolysates can be recovered by acidification.
Azolla is often considered an invasive weed because of the rapid colonization on water surfaces. It is a free-floating aquatic fern, known for its N fixing potential, short doubling time, and ...bioremediation potential. It has several applications as green manure, N bio fertilizer, cattle, chicken, and fish feed supplements because of its high protein content. It can grow on wastewater improving its quality. Azolla biomass thus produced can be utilized for energy production. It has been used for the production of biogas. Recently, its bio-oil potential has been studied. Azolla biomass has been used for biodiesel, biogas, and biohydrogen production. The exploitation of Azolla biomass as feedstock for bioenergy needs critical evaluation.
Laccase production by Coriolopsis caperata RCK2011 under solid state fermentation was optimized following Taguchi design of experiment. An orthogonal array layout of L18 (2(1) × 3(7)) was constructed ...using Qualitek-4 software with eight most influensive factors on laccase production. At individual level pH contributed higher influence, whereas, corn steep liquor (CSL) accounted for more than 50% of the severity index with biotin and KH2PO4 at the interactive level. The optimum conditions derived were; temperature 30°C, pH 5.0, wheat bran 5.0 g, inoculum size 0.5 ml (fungal cell mass = 0.015 g dry wt.), biotin 0.5% w/v, KH2PO4 0.013% w/v, CSL 0.1% v/v and 0.5 mM xylidine as an inducer. The validation experiments using optimized conditions confirmed an improvement in enzyme production by 58.01%. The laccase production to the level of 1623.55 Ugds(-1) indicates that the fungus C. caperata RCK2011 has the commercial potential for laccase.
•Sugarcane bagasse was biologically treated with 3 white-rot fungi.•Shorter incubation resulted in higher H/L ratio.•Myco-substrate showed significant improvement in sugar release on ...hydrolysis.•Saccharification of lignocellulosic biomass by cellulase from brown-rot fungus.
The sugarcane bagasse was biologically pretreated with three white-rot fungi; Pleurotus florida, Coriolopsis caperata RCK 2011 and Ganoderma sp. rckk-02, individually under solid-state fermentation. P. florida, C. caperata RCK 2011 and Ganoderma sp. rckk-02 degraded lignin up to 7.91, 5.48 and 5.58%, respectively. The lignocellulolytic enzymes produced by these fungi were also monitored during solid state fermentation of sugarcane bagasse. The fungal fermented sugarcane bagasse when hydrolyzed with crude cellulases from brown-rot fungus, Fomitopsis sp. RCK2010, released comparatively 1.5–2.4 fold higher sugars than in case of untreated sugarcane bagasse. The study demonstrated that white-rot fungal pretreatment improved the amenability of plant material for enzymatic hydrolysis.
Uncinula necator and Botrytis cinerea are the most destructive pathogens of the grapevine in Tunisia and elsewhere. We used two strains of Bacillus subtilis group, B27 and B29 to control powdery ...mildew and the grey mold disease of the grapevine. Green house experiments showed that B29 and B27 strains of the bacteria efficiently reduced the severity of powdery mildew up to 50% and 60%, respectively. Further, they decreased Botrytis cinerea development on grape leaf by 77% and 99%, respectively. The mode of action has been shown to be chitinolytic. These two bacteria showed significant production of total proteins discharged into the culture medium. Determination of some chitinolytic enzymes revealed the involvement of N-acetyl glucosaminidase (Nagase), the chitin-1,4-chitobiosidase (Biase) and endochitinase in degrading the mycelium of B. cinerea.
► Selective lignin degradation using a new fungal isolate i.e. Ganoderma sp. rckk02. ► Higher lignin degradation in shorter time span providing higher nutrition. ► Fermented feed had higher crude ...protein, digestibility and metabolizable energy. ► In vivo trial showed high feed intake, nutrient digestibility and N balance in goat.
Solid state fermentation (SSF) of wheat straw with Ganoderma sp. rckk02 was carried out for 15days for improving its digestibility and nutrients. Fungal growth caused a significant (P<0.05) decrease in acid detergent fiber (ADF), neutral detergent fiber (NDF), hemicellulose, lignin and cellulose content till 15th day. In vitro gas production (IVGP) test revealed that 10th day fermented feed possessed higher metabolizable energy (ME: 4.87MJ/kg), in vitro organic matter digestibility (OMD: 334g/kg) and short chain fatty acids (SCFAs: 1.82mmol/g Dry Matter). The fermented feed was also evaluated in vivo in goats fed with either untreated wheat straw (T1) or fungal treated straw (T2). Dry matter intake (DMI), digestible crude protein (DCP), total digestible nutrients (TDN) and nitrogen (N) intake were found significantly (P<0.05) increased in T2 group. The study shows that fermentation of wheat straw with Ganoderma sp. rckk02 holds potential in improving its nutritive value.
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