Effect of particle size, moisture content, and supplements on selective pretreatment of cotton stalks by Daedalea flavida and enzymatic saccharification

Effect of substrate size reduction and periodic nutrient supplementation on biological wood oxidation

Biological wood oxidation (BWO) is a composting heat recovery system tailored for woody lignocellulose valorization, with the potential to generate sustainable and low-temperature heat. This study investigated the effects of feedstock particle sizing and periodic nutrient supplementation (PNS) on microbial activity and wood decomposition during BWO. Birch wood was processed into sawdust (<5 mm) and cubes of various diameters (5, 10, and 15 mm), incubated in batch-mode BWO reactors for 88 days, and periodically supplemented with a nutrient medium. Sawdust-BWO outperformed cubes-BWO and demonstrated greater sensitivity to PNS, exhibiting in total 207% higher cumulative oxygen consumption, 50%∼ higher nitrogen utilization efficiency, 217% higher wood dry matter (DM) loss, and 101% higher total carbohydrates removal. The use of human urine as a nutrient source, combined with sawdust and PNS, further enhanced the BWO performance and resulted in an unprecedented 34.2% DM loss and 45.5% total carbohydrate removal over a 60-day incubation period. As revealed by an overall energy balance analysis, the process of grinding wood cubes into sawdust consumes around 55-72 kWh/t DM of additional electricity but results in a potentially 10-fold increase in heat output (680.6-719.5 kWh/t DM). Hence, combining fine grinding of wood with PNS emerges as an effective and energy-efficient strategy to elevate the performance and heat generation potential of BWO.

Enhanced ethanol production using hydrophobic resin detoxified Pine forest litter hydrolysate and integrated fermentation process development supplementing molasses

Globally escalating ethanol demand necessitates the use of hybrid technologies integrating first- and second-generation biofuel feedstocks for achieving the futuristic targets of gasoline replacement with bioethanol. In present study, an optimized two-step sequential pre-treatment (first dilute alkali, then dilute acid) of Pine forest litter (PFL) was developed. Furthermore, the saccharification of pre-treated PFL was optimized through Response Surface Methodology using Box-Behnken Design, wherein 0.558 g/g of reducing sugar was released under the optimized conditions (12.5% w/v of biomass loading, 10 FPU/g of PFL enzyme loading, 0.15% v/v Tween-80 and 48 h incubation time). Moreover, during hydrolysate fermentation using Saccharomyces cerevisiae NCIM 3288 strain, 22.51 ± 1.02 g/L ethanol was produced. Remarkably, hydrophobic resin (XAD-4) treatment of PFL hydrolysate, significantly removed inhibitors (Furfural, 5-hydroxymethylfurfural and phenolics) and increased ethanol production to 27.38 ± 1.18 g/L. Furthermore, during fermentation of molasses supplemented PFL hydrolysate (total initial sugar: 100 ± 3.27 g/L), a maximum of 46.02 ± 2.08 g/L ethanol was produced with 0.482 g/g yield and 1.92 g/l/h productivity. These findings indicated that the integration of molasses to lignocellulosic hydrolysate, would be a promising hybrid technology for industrial ethanol production within existing bio-refinery infrastructure.

Wheat bran as an efficient agro-process waste for enhanced yellow laccase production by Lentinus tigrinus SSB_W2 and its application in anthraquinone dye degradation

Lentinus tigrinus SSB_W2, isolated from Mahabaleshwar in the Western Ghats of Maharashtra, India, was employed to enhance laccase production in solid-state fermentation (SSF). The spectral analysis indicated that the laccase produced by L. tigrinus is a typical yellow laccase, exhibiting no absorption at 600 nm. Notably, this yellow laccase demonstrated exceptional catalytic activity, as confirmed by electrochemical analysis. Four agricultural processing wastes were evaluated as substrates for SSF, and the results showed that L. tigrinus effectively utilized wheat bran. Initial testing by one-factor-at-a-time method showed 3.79-fold increase in yellow laccase production, which subsequently increased to 6.51-fold after Plackett-Burman design. Moreover, employing response surface methodology resulted in 11.87-fold increase (108,472 IU gds-1) in laccase production. The utilization of yellow laccase for the biotransformation of various textile dyes was investigated, and it exhibited the highest degradation efficiency toward Reactive blue 4, a recalcitrant anthraquinone dye, with a rate of 18.36 mg L-1 h-1, for an initial concentration of 1000 mg L-1.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03881-9.

Ligninolytic characteristics of Pleurotus ostreatus cultivated in cotton stalk media

Biodelignification is widely regarded as a low-efficiency process because it is usually slow and difficult to control. To improve its efficiency and understand its mechanism, the present study analyzed the delignification characteristics of Pleurotus ostreatus grown on a cotton stalk medium. The results demonstrated that all strains of P. ostreatus can selectively degrade the cotton stalk lignin. When cultured in a cotton stalk medium for 60 days, P. ostreatus degraded lignin primarily during its mycelium growth with up to 54.04% lignin degradation and produced laccase and manganese dependent peroxidase with high activity levels at the peaks of 70.17 U/ml and 62.39 U/ml, respectively, but no detectable lignin peroxidase. The results of nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy analyses of significant changes in lignin structure revealed that syringyl (S) lignin units were more degraded than guaiacyl (G) lignin units, with a significantly elevated G/S ratio. The Gas Chromatography-Mass Spectrometer analysis of low-molecular-weight compounds revealed that the delignification resulted in the formation of alcohols, organic acids, benzodiazepines, and alkanes. Identified benzodiazepines implied the degradation of G and S units of lignin. These findings will help to improve the efficiency of biodelignification and expand our understanding of its mechanism.

Biodelignification of lignocellulose using ligninolytic enzymes from white-rot fungi

Lignocellulose is the most abundant biomass available on earth, including wood and agricultural wastes such as rice straw, corn cobs, and oil palm empty bunches. The biopolymer content in lignocellulose has a great potential as feedstock for producing industrial raw materials such as glucose, sorbitol, xylose, xylitol, and other pharmaceutical excipients. Currently, scientists and governments agree that the enzymatic delignification method is an environmentally friendly green method to be applied. This review attempts to explain the proper preparation of the enzymes laccase, lignin peroxidase, and manganese peroxidase, as well as the important factors influencing their activity. The recent applications of the enzymes for detoxification of hazardous substances, proper enzyme immobilization technique, and future prospect combination with DESs extraction of lignin are also discussed.

Isolation, identification and optimization of enhanced production of laccase from Galactomyces geotrichum under solid-state fermentation

Laccases are a group of oxidases that catalyze the oxidation of a wide range of electron rich substrates like phenolic compounds, lignin and aromatic amines. They are of interest because of their potential to be used in environmental and industrial applications. In this research, potent laccase producer fungi were screened and isolated from olive mill wastewater (OMW). One of the 23 isolated fungi was identified as Galactomyces geotrichum based on 18S rDNA sequence analysis that detected good laccase activity. Produced laccase had a molecular weight of 55 kDa that was confirmed by zymogram analysis. This is the first report about the optimization of laccase Production by G. geotrichum under solid-state fermentation. The optimization was made by the Taguchi design of experiments (DOE) methodology. An orthogonal array (L25) was designed using Minitab 19 software to study four effective process factors in five levels for laccase production. The optimum condition derived was; moisture content (80%), fermentation time (14 day), CuSO₄⋅5H₂O as the inducer (300 μM), glucose as a co-substrate (5 g/L). Maximum laccase activity of 52.86 (U/g of dry substrate) was obtained using optimum fermentation condition. This study aimed to better understand the laccase producing microorganisms in OMW and take them to OMW treatment that is rich in phenolic compounds.

Biological treatment of lignocellulosic biomass by Curvularia lunata for biogas production

In the present study, biological treatment of lignocellulosic biomass has been performed by employing Curvularia lunata. Optimization of treatment conditions was performed by using response surface methodology to reduce the duration of treatment time. Three factors were studied at three severity levels: temperature - 28, 32, 36 °C; moisture content - 65, 75, 85%; treatment time - 14, 28, 42 days. Released reducing sugars were considered as the output response as the disruption of lignin barrier by biological treatment should increase the quantity of free reducing sugar. Impact of different combinations of factors (at varying severity levels) on output response was studied to attain the optimized conditions: 32 °C, 23 days and 65% moisture. Predicted outcomes were aligned with the experimental results (R2 = 0.93). After treating at optimized conditions, wheat and pearl millet straw were subjected to anaerobic digestion and showcased 19 and 28% increase in biogas production respectively as compared to the untreated straws.

Fungal Laccase Production from Lignocellulosic Agricultural Wastes by Solid-State Fermentation: A Review

Laccases are copper-containing oxidase enzymes found in many fungi. They have received increasing research attention because of their broad substrate specificity and applicability in industrial processes, such as pulp delignification, textile bleaching, phenolic removal, and biosensors. In comparison with traditional submerged fermentation (SF), solid-state fermentation (SSF) is a simpler technique for laccase production and has many advantages, including higher productivity, efficiency, and enzyme stability as well as reduced production costs and environmental pollution. Here, we review recent advances in laccase production technology, with focus on the following areas: (i) Characteristics and advantages of lignocellulosic agricultural wastes used as SSF substrates of laccase production, including detailed suggestions for the selection of lignocellulosic agricultural wastes; (ii) Comparison of fungal laccase production from lignocellulosic substrates by either SSF or SF; (iii) Fungal performance and strain screening in laccase production from lignocellulosic agricultural wastes by SSF; (iv) Applications of laccase production under SSF; and (v) Suggestions and avenues for future studies of laccase production by fungal SSF with lignocellulosic materials and its applications.

Biological Pretreatment of Oil Palm Empty Fruit Bunch by Schizophyllum commune ENN1 without Washing and Nutrient Addition

Washing and drying are common steps for oil palm empty fruit bunch (OPEFB) preparation prior to pretreatment. However, the mass balance of OPEFB preparation proved a major loss of OPEFB during the washing and drying steps. An indigenous fungus, Schizophyllum commune ENN1 was used for delignification of unwashed OPEFB in biological pretreatment without nutrient addition. S. commune ENN1 achieved a maximum lignin removal of 53.8% after 14 days of biological pretreatment of unwashed OPEFB. S. commune ENN1 was able to grow on unwashed OPEFB during biological pretreatment at 55% of moisture content and 5% of oil residue. The highest amount of reducing sugars obtained from OPEFB pretreated by S. commune ENN1 was 230.4 ± 0.19 mg/g with 54% of hydrolysis yield at 96 h. In comparison, the sugar yield of OPEFB pretreated by Phanerochaete chrysosporium was 101.2 ± 0.04 mg/g. This study showed that S. commune ENN1 was feasible to remove lignin of OPEFB through biological pretreatment for enzymatic saccharification without washing and addition of nutrients.

Simultaneous laccase production and transformation of bisphenol-A and triclosan using Trametes versicolor

New age micro-pollutants, bisphenol-A (BPA) and triclosan (TCA), known for their carcinogenic effects in living organisms can effectively be removed from water using laccase from Trametes versicolor. Laccase was produced from T. versicolor JSRK13 in both submerged and solid-state fermentation (SmF and SSF) conditions. In SmF, T. versicolor JSRK13 gave the maximum production of laccase on the 10th day with an activity of 22 U mL^- 1, whereas, in SSF 185 U g^- 1 of the enzyme was produced on the 17th day. Maximum production of laccase was observed with Parthenium as substrate. Parthenium, with a particle size of 3-5 mm having 60% moisture was found to be a suitable substrate for laccase production and simultaneous transformation (LPST) of BPA in a synergistic manner. A one-step concentration using 85% ammonium sulphate followed by dialysis was sufficient to give 6.7-fold purification of laccase from the crude culture filtrate. Transformation of BPA was achieved in both SmF and SSF conditions along with the production of laccase, whereas TCA was degraded with free enzyme only. Above 90% of BPA (55-5 mg L^- 1) was degraded using the LPST strategy with HBT acting as a mediator in the reaction. LPST strategy did not work for TCA as it completely inhibits the growth of T. versicolor JSRK13. TCA was degraded up to 75% (1.5-0.375 mg L^- 1) by the free enzyme. Our study of simultaneous laccase production and transformation proved to be efficacious in case of BPA. The results indicate that industrial and sewage wastewater containing BPA can potentially be treated with T. versicolor JSRK13 laccase. The described strategy can further be used to develop a bioprocess which can work both on solid and liquid wastes containing BPA.

Lignin-Degrading Abilities of Novel Autochthonous Fungal Isolates Trametes hirsuta F13 and Stereum gausapatum F28

The aim of this research is to isolate and identify fungi with high lignin-degrading abilities that are autochthonous to southern Serbian region. Two novel fungal isolates identified as Trametes hirsuta F13 and Stereum gausapatum F28 were selected to assess their ligninolytic enzyme activities and the efficiency of lignin removal from beech wood sawdust. Obtained results show that both isolates are good sources of industrially valuable enzymes with a potential for application in various biotechnological and industrial processes. Both isolates showed laccase, manganese-dependent peroxidase, and versatile peroxidase activities, while only S. gausapatum F28 had lignin peroxidase activity. This is the first record of the ability of S. gausapatum species to produce lignin peroxidase. T. hirsuta F13 showed higher laccase activity than S. gausapatum F28, while S. gausapatum F28 had higher manganese peroxidase activity. Also, T. hirsuta F13 exhibited much higher laccase activity under submerged cultivation conditions than solid-state cultivation conditions, which is rare for fungi. This is important for industrial processes since the submerged fermentation is a dominant technique in industry. The test of the efficiency of lignin removal showed that both isolates are efficient lignin decomposers. After five weeks of incubation on beech wood sawdust, the total lignin losses were 33.84% with T. hirsuta F13 and 28.8% with S. gausapatum F28.

Fungal pretreatment of sweet sorghum bagasse with supplements: improvement in lignin degradation, selectivity and enzymatic saccharification

Sweet sorghum bagasse (SSB) from food processing and agricultural industry has attracted the attention for uses in production of biofuel, enzymes and other products. The alteration in lignocellulolytic enzymes by use of supplements in fungal pretreatment of SSB to achieve higher lignin degradation, selectivity value and enzymatic hydrolysis to fermentable sugar was studied. Fungal strain Coriolus versicolor was selected for pretreatment due to high ligninolytic and low cellulolytic enzyme production resulting in high lignin degradation and selectivity value. SSB was pretreated with supplements of veratryl alcohol, syringic acid, catechol, gallic acid, vanillin, guaiacol, CuSO₄ and MnSO₄. The best results were obtained with CuSO₄, gallic acid and syringic acid supplements. CuSO₄ increased the activities of laccase (4.9-fold) and polyphenol oxidase (1.9-fold); gallic acid increased laccase (3.5-fold) and manganese peroxidase (2.5-fold); and syringic acid increased laccase (5.6-fold), lignin peroxidase (13-fold) and arylalcohol oxidase (2.8-fold) resulting in enhanced lignin degradations and selectivity values than the control. Reduced cellulolytic enzyme activities resulted in high cellulose recovery. Enzymatic hydrolysis of pretreated SSB yielded higher sugar due to degradation of lignin and reduced the crystallinity of cellulose. The study showed that supplements could be used to improve the pretreatment process. The results were confirmed by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric/differential thermogravimetric analysis of SSB.