Resource recovery from lignocellulosic wastes via biological technologies: Advancements and prospects

Harnessing of Sunflower Stalks by Hydrolysis and Fermentation with Hansenula polymorpha to Produce Biofuels

A sequential valorization process of sunflower stalks was carried out using nitric acid (0.1-2 mol dm-3) as a hydrolytic agent and fermenting the hydrolysate of higher sugar concentration in the presence of the non-conventional yeast Hansenula polymorpha. Values reached for ethanol yield (0.25 g g-1) and xylitol yield (0.14 g g-1) were higher than those achieved after pretreatment with other acids in previous studies. The effect of acid treatment with nitric, phosphoric, and sulfuric acids on the separated solid fractions was evaluated to determine its potential use as solid biofuel by FTIR and SEM determinations. A significant loss of lignin and hemicellulose was found in the solid treated with nitric acid, while a higher HHV was obtained when pretreated with phosphoric acid (19.16 MJ kg-1) and sulfuric acid (19.12 MJ kg-1). A subsequent enzymatic hydrolysis of acid-pretreated solids showed that the nitric acid pretreatment increased the availability of glucose from the cellulose fraction to a greater extent than the other two acids, by reducing the hemicellulose fraction to 0.7% and the lignin fraction to 2.5%. This study shows that pretreatment of biomass with nitric acid leads to better fermentation results to obtain biofuels such as ethanol, which could be further increased by additional enzymatic hydrolysis, while pretreatment with the other two acids generates better solid fuels.

Optimizing fungal treatment of lignocellulosic agro-industrial by-products to enhance their nutritional value

This study delves into the dynamic interaction between various fungal strains, substrates, and treatment durations to optimize the nutritional value of these by-products. Six fungi, including Penicillium chrysogenum, Fusarium sp., Fusarium oxysporum, Fusarium solani, Penicillium crustosum, and Cosmospora viridescens, were evaluated across three substrates: wheat straw (WS), cedar sawdust (CW), and olive pomace (OP) over treatment periods of 4, 8, and 12 weeks. The study discerned profound impacts of these fungi across multiple parameters, including cellulose variation (C.var), lignin variation (L.var), and in vitro true digestibility variation (IVTD.var). Our results demonstrated that the various fungi had a significant effect on all parameters (p < .001). Noteworthy, F. oxysporum and F. solani emerged as exemplars, displaying notable lignin degradation, cellulose liberation, and IVTD enhancement. Importantly, P. crustosum demonstrated substantial cellulose degradation, exhibiting optimal efficacy in just 4 weeks for all substrates. Notably, F. sp. excelled, yielding favorable results when treating WS. P. chrysogenum achieved optimal outcomes with 8-week treatment for WS. Both Fusarium sp. and P. chrysogenum exhibited slight cellulose release, with remarkable reduction of WS lignin compared to other substrates. Especially, WS and OP displayed superior digestibility enhancements relative to CW. It should be noted that the treatment duration further shaped these outcomes, as prolonged treatment (12 weeks) fostered greater benefits in lignin degradation and digestibility, albeit with concomitant cellulose degradation. These findings underscore the intricate balance between fungal strains, substrates, and treatment durations in optimizing the nutritional value of lignocellulosic agro-industrial by-products. The outcomes of this study lead to the enhancement in the overall value of by-products, promoting sustainable livestock feed and advancing agricultural sustainability.

Tailored microbial consortium producing hydrolytic enzyme cocktail for maximum saccharification of wheat straw

The potential of hydrolytic enzyme cocktail obtained from designed bacterial consortium WSh-1 comprising Bacillus subtilis CRN 16, Paenibacillus dendritiformis CRN 18, Niallia circulans CRN 24, Serratia marscens CRN 29, and Streptomyces sp. CRN 30, was investigated for maximum saccharification. Activity was further enhanced to 1.01 U/ml from 0.82 U/ml by supplementing growth medium with biotin and cellobiose as a cofactor and inducer. Through kinetic analysis, the enzyme cocktail showed a high wheat straw affinity with Michaelis-Menten constant (Km) of 0.68 µmol/L and a deconstruction rate (Vmax) of 4.5 U/ml/min. The statistical optimization of critical parameters increased saccharification to 89 %. The optimized process in a 5-L lab-scale bioreactor yielded 501 mg/g of reducing sugar from NaOH-pretreated wheat straw. Lastly, genomic insights revealed unique abundant oligosaccharide deconstruction enzymes with the most diverse CAZyme profile. The consortium-mediated enzyme cocktails offer broader versatility with efficiency for the economical and sustainable valorization of lignocellulosic waste.

Elaboration of Thermally Performing Polyurethane Foams, Based on Biopolyols, with Thermal Insulating Applications

In this work, biobased rigid polyurethane foams (PUFs) were developed with the aim of achieving thermal and fireproofing properties that can compete with those of the commercially available products. First, the synthesis of a biopolyol from a wood residue by means of a scaled-up process with suitable yield and reaction conditions was carried out. This biopolyol was able to substitute completely the synthetic polyols that are typically employed within a polyurethane formulation. Different formulations were developed to assess the effect of two flame retardants, namely, polyhedral oligomeric silsesquioxane (POSS) and amino polyphosphate (APP), in terms of their thermal properties and degradation and their fireproofing mechanism. The structure and the thermal degradation of the different formulations was evaluated via Fourier Transformed Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Likewise, the performance of the different PUF formulations was studied and compared to that of an industrial PUF. From these results, it can be highlighted that the addition of the flame retardants into the formulation showed an improvement in the results of the UL-94 vertical burning test and the LOI. Moreover, the fireproofing performance of the biobased formulations was comparable to that of the industrial one. In addition to that, it can be remarked that the biobased formulations displayed an excellent performance as thermal insulators (0.02371-0.02149 W·m-1·K-1), which was even slightly higher than that of the industrial one.

Optimization of biogas production from straw wastes by different pretreatments: Progress, challenges, and prospects

Lignocellulosic biomass (LCB) presents a promising feedstock for carbon management due to enormous potential for achieving carbon neutrality and delivering substantial environmental and economic benefit. Bioenergy derived from LCB accounts for about 10.3 % of the global total energy supply. The generation of bioenergy through anaerobic digestion (AD) in combination with carbon capture and storage, particularly for methane production, provides a cost-effective solution to mitigate greenhouse gas emissions, while concurrently facilitating bioenergy production and the recovery of high-value products during LCB conversion. However, the inherent recalcitrant polymer crystal structure of lignocellulose impedes the accessibility of anaerobic bacteria, necessitating lignocellulosic residue pretreatment before AD or microbial chain elongation. This paper seeks to explore recent advances in pretreatment methods for LCB biogas production, including pulsed electric field (PEF), electron beam irradiation (EBI), freezing-thawing pretreatment, microaerobic pretreatment, and nanomaterials-based pretreatment, and provide a comprehensive overview of the performance, benefits, and drawbacks of the traditional and improved treatment methods. In particular, physical-chemical pretreatment emerges as a flexible and effective option for methane production from straw wastes. The burgeoning field of nanomaterials has provoked progress in the development of artificial enzyme mimetics and enzyme immobilization techniques, compensating for the intrinsic defect of natural enzyme. However, various complex factors, such as economic effectiveness, environmental impact, and operational feasibility, influence the implementation of LCB pretreatment processes. Techno-economic analysis (TEA), life cycle assessment (LCA), and artificial intelligence technologies provide efficient means for evaluating and selecting pretreatment methods. This paper addresses current issues and development priorities for the achievement of the appropriate and sustainable utilization of LCB in light of evolving economic and environmentally friendly social development demands, thereby providing theoretical basis and technical guidance for improving LCB biogas production of AD systems.

Lignocellulosic biorefineries: A multiscale approach for resource exploitation

Biomass can become the source for chemicals towards a sustainable production system. However, the challenges it presents such as the variety of species, their widespread and sparse availability, and the expensive transportation claims for an integrated approach to design the novel production system. Multiscale approaches have not been properly extended to biorefineryes design and deployment, due to the comprehensive experimental and modelling work they require. A systems perspective provides the systematic framework to analyze the availability and composition of raw materials across regions, how that affects process design, the portfolio of products that can be obtained by evaluating the strong link between the biomass features and the process design. The use of lignocellulosic materials requires for a multidisciplinary work, that must lead to new process engineers with technical competences in biology, biotechnology but also process engineering, mathematics, computer science and social sciences towards a sustainable process/chemical industry.

Lactic acid bacteria as a tool for biovanillin production: A review

Vanilla is the most commonly used natural flavoring agent in industries like food, flavoring, medicine, and fragrance. Vanillin can be obtained naturally, chemically, or through a biotechnological process. However, the yield from vanilla pods is low and does not meet market demand, and the use of vanillin produced by chemical synthesis is restricted in the food and pharmaceutical industries. As a result, the biotechnological process is the most efficient and cost-effective method for producing vanillin with consumer-demanding properties while also supporting industrial applications. Toxin-free biovanillin production, based on renewable sources such as industrial wastes or by-products, is a promising approach. In addition, only natural-labeled vanillin is approved for use in the food industry. Accordingly, this review focuses on biovanillin production from lactic acid bacteria (LAB), which is generally recognized as safe (GRAS), and the cost-cutting efforts that are utilized to improve the efficiency of biotransformation of inexpensive and readily available sources. LABs can utilize agro-wastes rich in ferulic acid to produce ferulic acid, which is then employed in vanillin production via fermentation, and various efforts have been applied to enhance the vanillin titer. However, different designs, such as response surface methods, using immobilized cells or pure enzymes for the spontaneous release of vanillin, are strongly advised.

Transformation of Agro-Waste into Value-Added Bioproducts and Bioactive Compounds: Micro/Nano Formulations and Application in the Agri-Food-Pharma Sector

The agricultural sector generates a significant amount of waste, the majority of which is not productively used and is becoming a danger to both world health and the environment. Because of the promising relevance of agro-residues in the agri-food-pharma sectors, various bioproducts and novel biologically active molecules are produced through valorization techniques. Valorization of agro-wastes involves physical, chemical, and biological, including green, pretreatment methods. Bioactives and bioproducts development from agro-wastes has been widely researched in recent years. Nanocapsules are now used to increase the efficacy of bioactive molecules in food applications. This review addresses various agri-waste valorization methods, value-added bioproducts, the recovery of bioactive compounds, and their uses. Moreover, it also covers the present status of bioactive micro- and nanoencapsulation strategies and their applications.

Recovery of value-added products from biowaste: A review

This review provides an update on the state-of-the art technologies for the valorization of solid waste and its mechanism to generate various bio-products. The organic content of these wastes can be easily utilized by the microbes and produce value-added compounds. Microbial fermentation techniques can be utilized for developing waste biorefinery processes. The utilization of lignocellulosic and plastics wastes for the generation of carbon sources for microbial utilization after pre-processing steps will make the process a multi-product biorefinery. The C1 and C2 gases generated from different industries could also be utilized by various microbes, and this will help to control global warming. The review seeks to expand expertise about the potential application through several perspectives, factors influencing remediation, issues, and prospects.

Sugarcane Bagasse-Based Ethanol Production and Utilization of Its Vinasse for Xylitol Production as an Approach in Integrated Biorefinery

Biorefinery of sugarcane bagasse into ethanol and xylitol was investigated in this study. Ethanol fermentation of sugarcane bagasse hydrolysate was carried out by Saccharomyces cerevisiae. After ethanol distillation, the vinasse containing xylose was used to produce xylitol through fermentation by Candida guilliermondii TISTR 5068. During the ethanol fermentation, it was not necessary to supplement a nitrogen source to the hydrolysate. Approximately 50 g/L of bioethanol was produced after 36 h of fermentation. The vinasse was successfully used to produce xylitol. Supplementing the vinasse with 1 g/L of yeast extract improved xylitol production 1.4-fold. Cultivating the yeast with 10% controlled dissolved oxygen resulted in the best xylitol production and yields of 10.2 ± 1.12 g/L and 0.74 ± 0.04 g/g after 60 h fermentation. Supplementing the vinasse with low fraction of molasses to improve xylitol production did not yield a positive result. The supplementation caused decreases of up to 34% in xylitol production rate, 24% in concentration, and 24% in yield.

Variations in lignin monomer contents and stable hydrogen isotope ratios in methoxy groups during the biodegradation of garden biomass

Lignin, a highly polymerized organic component of plant cells, is one of the most difficult aromatic substances to degrade. Selective biodegradation under mild conditions is a promising method, but the dynamic variations in lignin monomers during the biodegradation of lignocellulose are not fully understood. In this study, we evaluated the differences in lignin degradation under different microbial inoculation based on the lignin monomer content, monomer ratio, and stable hydrogen isotope ratio of lignin methoxy groups (δ2HLM). The weight loss during degradation and the net loss of lignocellulosic components improved dramatically with fungal inoculation. Syringyl monolignol (S-lignin), which contains two methoxy groups, was more difficult to degrade than guaiacyl (G-lignin), which contains only one methoxy group. The co-culture of Pseudomonas mandelii and Aspergillus fumigatus produced the greatest decrease in the G/S ratio, but δ2HLM values did not differ significantly among the three biodegradation experiments, although the enrichment was done within the fungal inoculation. The fluctuation of δ2HLM values during the initial phase of biodegradation may be related to the loss of pectic polysaccharides (another methoxy donor), which mainly originate from fallen leaves. Overall, the relative δ2HLM signals were preserved despite decreasing G/S ratios in the three degradation systems. Nevertheless, some details of lignin δ2HLM as a biomarker for biogeochemical cycles need to be explored further.

A critical review for advances on industrialization of immobilized cell Bioreactors: Economic evaluation on cellulose hydrolysis for PHB production

Advances such as cell-on-cell immobilization, multi-stage fixed bed tower (MFBT) bioreactor, promotional effect on fermentation, extremely low temperature fermentation, freeze dried immobilized cells in two-layer fermentation, non-engineered cell factories, and those of recent papers are demonstrated. Studies for possible industrialization of ICB, considering production capacity, low temperatures fermentations, added value products and bulk chemical production are studied. Immobilized cell bioreactors (ICB) using cellulose nano-biotechnology and engineered cells are reported. The development of a novel ICB with recent advances on high added value products and conceptual research areas for industrialization of ICB is proposed. The isolation of engineered flocculant cells leads to a single tank ICB. The concept of cell factories without GMO is a new research area. The conceptual development of multi-stage fixed bed tower membrane (MFBTM) ICB is discussed. Finally, feasible process design and technoeconomic analysis of cellulose hydrolysis using ICB are studied for polyhydroxybutyrate (PHB) production.