Biological and electrochemical valorisation of lignocellulosic wastes from pulp & paper industry to give new generation biodiesel and aromatic compounds

Technical lignin and cellulosic wastepaper represent the main side-streams of the existing industrial-scale biorefineries and paper industry. The valorisation of these renewable and low- or negative-value feedstocks is a strategic approach to enhance the biorefinery and paper industry sustainability. Lignin represents a promising source of aromatic compounds, while cellulosic wastepaper is a high-quality source of sugars which can be converted into several added-value bioproducts, such as biofuels, biochemicals and biomaterials. In this perspective, in the present work, the electrochemical valorisation of lignin to give aromatics was performed [1], whereas in the case of wastepaper, a direct enzymatic hydrolysis was optimised to simultaneously produce glucose and xylose which were then fermented by oleaginous yeasts to produce new generation biodiesel [2]. In particular, the soda technical lignin Protobind™ 1000 (P1000) was adopted as starting material. It is produced on an industrial scale by the company GreenValue (Switzerland), starting from a mix of wheat straw and sarkanda grass, after an alkaline extraction with sodium hydroxide. In order to improve the lignin exploitation to added-value aromatic compounds, a mild chemical conversion route based on electrochemistry was investigated [1]. Under the optimal reaction conditions (NiOOH electrode, pH 14, lignin 20 g/L, 0.4 V), the electro-oxidative depolymerisation of lignin by electrolysis was performed in a divided cell. The main products were sinapic acid, vanillin, vanillic acid, and acetovanillone. The obtained preliminary results demonstrated the potential feasibility of this innovative electrochemical route for lignin valorisation for the production of bio-aromatic chemicals. The wastepaper derived from the converting process for the production of tissue paper products by different local companies in Lucca (Italy). The waste cellulosic powder is produced in the converting section, where the paper coil is unrolled and the sheet is subjected to mechanical operations to give the final commercial product. This cellulosic waste is not suitable to be recycled within the same papermaking process. For this reason, it is typically recovered by aspiration and sent to the landfill. Regarding the exploitation of wastepaper, an innovative two-step process for the conversion of waste tissue paper to single cell oil (SCO) was optimised. SCO represents an outstanding alternative to both fossil sources and vegetable oils for the production of biodiesel. Hydrolysates containing glucose and xylose were produced by enzymatic hydrolysis of the untreated waste. Under the optimised reaction conditions (Cellic® CTec2 25 FPU/g glucan, 48 h, biomass loading 20 g/L), the yield of 95 mol% was reached for both glucose and xylose. The undetoxified hydrolysate was adopted as substrate for a batch-mode fermentation by the oleaginous yeast Lipomyces starkeyi. Lipid yield, lipid content for single cell, oil production and maximum oil productivity were 20.2 wt%, 37 wt%, 3.7 g/L and 2.0 g/L/d, respectively. This new generation oil, obtained from a negative value industrial waste, represents a promising platform chemical for the production of biodiesel, biosurfactants, animal feed and biobased plastics

Microwave-assisted FeCl3-catalysed production of glucose from giant reed and cardoon cellulose fraction and its fermentation to new generation oil by oleaginous yeasts

The replacement of fossil fuels and materials with biofuels and bioproducts is a crucial current global goal. Biorefining of lignocellulosic biomass generates pentose and hexose sugars which can be converted into several added-value bio-based compounds. Among biofuels, biodiesel is one of the most promising renewable energy sources since it does not require new technology and engines for its use. Traditional biodiesel is produced on the industrial scale starting from vegetable oils obtained from oleaginous crops, such as palm oil, rapeseed oil and sunflower oil. However, most of the oleaginous plant species are food crops, determining the ethical debate on the right use of these renewable resources and the competition between the energy industry and food chain. An innovative and promising solution is represented by single cell oil (SCO) produced from oleaginous yeasts. This new generation oil, if obtained from low or negative value industrial waste, represents a promising platform chemical for the production of biodiesel, biosurfactants, animal feed and biobased plastics [1]. This study investigated the microwave-assisted FeCl3-catalysed hydrolysis of giant reed (Arundo donax L.) and defatted cardoon (Cynara cardunculus L.) cellulose fractions to give glucose. Giant reed is a promising energy crops able to grow on marginal lands, while cardoon stalks are the crop residue in the production of vegetable oil. A preliminary acid pretreatment was adopted for giant reed [2], while steam-explosion pretreatment was performed on cardoon [3], both allowing a significant removal of xylan fractions. Under different reactions conditions, the microwave-assisted FeCl3-catalysed hydrolysis converted the two pretreated feedstocks into glucose-rich hydrolysates which were employed as fermentation medium for the production of SCO by the oleaginous yeast Lipomyces starkeyi DSM 70296. For giant reed, the low production of furanic compounds enabled the direct fermentation of undetoxified hydrolysates, while for cardoon the furfural removal was necessary before the fermentation step. After hydrolysis, for both hydrolysates the fermentation provided promising lipid yields (~14 wt%) and oil content (~25 wt%). Figure 1 shows the process layout of the implemented third-generation biorefinery scheme. The SCO appears a valid candidate for the production of new generation biodiesel with good oxidative stability and cold flow properties. Moreover, it resulted very similar to palm and rapeseed oils, usually employed as a renewable source for the production of traditional biodiesel

Cutaneotrichosporon oleaginosus: A Versatile Whole-Cell Biocatalyst for the Production of Single-Cell Oil from Agro-Industrial Wastes

Cutaneotrichosporon oleaginosus is an oleaginous yeast with several favourable qualities: It is fast growing, accumulates high amounts of lipids and has a very broad substrate spectrum. Its resistance to hydrolysis by-products makes it a promising biocatalyst for custom tailored microbial oils. C. oleaginosus can accumulate up to 60 wt.% of its biomass as lipids. This species is able to grow by using several compounds as a substrate, such as acetic acid, biodiesel-derived glycerol, N-acetylglucosamine, lignocellulosic hydrolysates, wastepaper and other agro-industrial wastes. This review is focused on state-of-the-art innovative and sustainable biorefinery schemes involving this promising yeast and second- and third-generation biomasses. Moreover, this review offers a comprehensive and updated summary of process strategies, biomass pretreatments and fermentation conditions for enhancing lipid production by C. oleaginosus as a whole-cell biocatalyst. Finally, an overview of the main industrial applications of single-cell oil is reported together with future perspectives

Single cell oil production from undetoxified Arundo donax L. hydrolysate by Cutaneotrichosporon curvatus

The use of low-cost substrates represents one key issue to make single cell oil production sustainable. Among low-input crops, Arundo donax L. is a perennial herbaceous rhizomatous grass containing both C5 and C6 carbohydrates. The scope of the present work was to investigate and optimize the production of lipids by the oleaginous yeast Cutaneotrichosporon curvatus from undetoxified lignocellulosic hydrolysates of steam-pretreated A. donax. The growth of C. curvatus was first optimized in synthetic media, similar in terms of sugar concentration to hydrolysates, by applying the response surface methodology (RSM) analysis. Then the bioconversion of undetoxified hydrolysates was investigated. A fed-batch process for the fermentation of A. donax hydrolysates was finally implemented in a 2-L bioreactor. Under optimized conditions, the total lipid content was 64% of the dry cell weight and the lipid yield was 63% of the theoretical. The fatty acid profile of C. curvatus triglycerides contained 27% palmitic acid, 33% oleic acid and 32% linoleic acid. These results proved the potential of lipid production from A. donax, which is particularly important for their consideration as substitutes for vegetable oils in many applications such as biodiesel or bioplastics

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMFsynthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions

Sustainable Valorisation and Efficient Downstream Processing of Giant Reed by High-Pressure Carbon Dioxide Pretreatment

This work investigated the catalytic high-pressure CO2 pretreatment of giant reed. CO2 is a renewable resource; its use does not generate chemical wastes and it can be easily removed and recycled. The effect of the addition of low concentrations of FeCl3 (0.16 wt%) and PEG 400 (1.0 wt%) on the hemicellulose hydrolysis to xylose and xylo-oligosaccharides (XOS) is reported for the first time. Under the optimised pretreatment conditions, the xylan conversion of 82 mol% and xylose and XOS yields of 43 and 20 mol% were achieved, respectively. The solid residues obtained from different pretreatments were used as the substrate for the enzymatic hydrolysis to give glucose. The total glucose yield achieved under the optimised two-step process was 67.8 mol% with respect to the glucan units in the biomass. The results demonstrated that PEG-assisted FeCl3-catalysed scCO(2) pretreatment can produce xylose- or XOS-rich hydrolysates and improve the enzymatic hydrolysis of biomass

The case of study of hazelnut shells biorefinery: Synthesis of active carbons from the hydrochar recovered downstream of levulinic acid production

Hazelnut processing industry generates significant waste streams, in particular cuticles and shells. Extractives are the main components of the cuticle fraction (~36 wt%), mainly including polyphenols and fatty acids, which can be advantageously employed in the pharmaceutical and cosmetic industry. Focusing on the shell fraction, this represents ~50 % of the total nut weight. Differently from cuticles, shells are rich in recalcitrant lignin (~38 wt%), in addition to cellulose and hemicellulose (each component accounting for ~23 wt%). Up to now, this waste, which is preponderantly produced in Italy and Turkey, is mostly underutilized, being limitedly used as a boiler fuel for domestic heating and for landscaping. On the other hand, both these fractions of hazelnut shells can be successfully valorized and, in agreement with the objectives of the project PRIN 2020 LEVANTE “LEvulinic acid Valorization through Advanced Novel Technologies” (2020CZCJN7), we have proposed a new cascade approach, converting its cellulosic fraction into levulinic acid (∼9-12 wt%), recovering as final waste an abundant carbonaceous hydrochar (∼45 wt%), mainly composed of aromatic (from lignin) and furanic (from degradation of C5/C6 sugars) units. In the LEVANTE project, this hydrochar was activated by pyrolysis and chemical treatments (H3PO4, ZnCl2, KOH, NaOH), and the synthesized new active carbons (ACs) have been properly characterized (ultimate and proximate analysis, FT-IR, surface properties and SEM microscopy). This preliminary screening allowed us to select the KOH-AC as the most interesting one, as further confirmed by the highest CO2 adsorption capacity (~90 mg/g), due to its well-developed microporous texture. This new AC was also effective for the removal of the bulkier methylene blue (complete removal, corresponding to ~250 mg/g). This proposed integrated approach makes possible to fully exploit the hazelnut shell feedstock, smartly closing the biorefinery cycle of the hazelnut wastes, in a circular economy perspective. In addition, the selective fractionation of soluble C5 and C6 sugars of shell fraction is currently under investigation and this will enable us to obtain an hydrochar with a less-degraded lignin fraction, thus moving towards progressively more sustainable hydrothermal and activation reaction conditions. The authors are grateful to Italian “Ministero dell'Istruzione dell'Università e della Ricerca” for the financial support provided through the stated PRIN 2020 LEVANTE project

New exploitation strategies of the by-products deriving from the hazelnut supply chain

Hazelnut processing industry generates significant waste streams, in particular cuticles and shells. Extractives are the main components of the cuticle fraction (~36 wt%), mainly including polyphenols and fatty acids, which can be advantageously used in the pharmaceutical and cosmetic industry. Focusing on the shell fraction, this represents ~50 % of the total nut weight (about 273 thousand metric tons, based on the 2021-2022 worldwide data on hazelnut production). Differently from cuticles, shells are rich in recalcitrant lignin (~38 wt%), in addition to cellulose and hemicellulose (each component accounting for ~23 wt%). Up to now, this waste, which is preponderantly produced in Italy and Turkey, is mostly underutilized, being limitedly used as a boiler fuel for domestic heating and for landscaping. On the other hand, these both fractions of hazelnut shells can be successfully valorized and, in this perspective, we have proposed a new cascade approach, converting its cellulosic fraction into levulinic acid (∼9-12 wt%), and recovering an abundant carbonaceous hydrochar as the final waste (∼45 wt%), mainly composed of aromatic and furanic units. In this work, the exploitation of this waste biomass-derived hydrochar for environmental applications has been investigated, after its pyrolysis and chemical activation treatments (H3PO4, ZnCl2, KOH, NaOH). The synthesized new active carbons (ACs) have been properly characterized and used as adsorbents for CO2 and methylene blue removal. This proposed integrated approach makes possible to fully exploit the hazelnut shell feedstock, smartly closing the biorefinery cycle of the hazelnut wastes, in a sustainable and circular perspective

Catalytic hydrogenation of crude hexanoic acid, easily obtained by anaerobic fermentation of grape pomace

The transition from fossil resources to renewable ones represents an urgent need. Biomasses are promising feedstocks, potentially exploitable through novel bio-catalytic processes, such as acidogenic fermentation to carboxylic acids, which can be further converted into more value-added bio-products through cascade chemical approaches, such as hydrogenation to corresponding alcohols/esters. In this work, the optimization of the hydrogenation of commercial hexanoic acid to 1-hexanol and hexyl hexanoate was first investigated. For this purpose, 5 wt% Re/C resulted active and selective towards 1-hexanol production. The same catalyst was further tested for the hydrogenation of crude hexanoic acid, obtained by fermentation of red and white grape pomaces. Hydrogenation of these crude hexanoic acid mixtures confirmed the promising performances of 5 wt% Re/C, achieving the complete substrate conversion with a prevailing selectivity to 1-hexanol (~58 mol%), rather than to hexyl hexanoate (~30 mol%). Moreover, the use of an acid support, such as Al2O3, markedly shifted the selectivity towards hexyl hexanoate (~51 mol%). This observation was further demonstrated by testing physical mixtures of 5 wt% Re/C and different amounts of acidic niobium phosphate. Based on these promising results, exploitation of grape pomace for 1-hexanol/hexyl hexanoate production, to use as bio-fuels or bio-solvents, represents a smart possibility