This study investigated the physical, mechanical, and microstructural properties of bagasse compost to optimize its densification into durable pellets for agricultural applications. Bagasse compost was initially subjected to hammer milling across various moisture contents (8-16% wet basis) and screen sizes (1-4 mm). Results showed that specific grinding energy increased exponentially with moisture content and decreased with larger screen sizes, ranging from 11 to 750 kJ/kg. Particle size distributions were characterized, revealing broader distributions with coarser screens. Pellets were subsequently produced using a closed-die hydraulic press under controlled pressures (50-150 MPa), moisture contents (8-20%), and particle sizes (1-4 mm). Compaction energy, fracture resistance, and pellet density were modeled using Response Surface Methodology. Increasing pressure significantly enhanced compaction energy, fracture resistance, and pellet density. Higher moisture content generally reduced compaction energy but improved fracture resistance, while pellet density exhibited an initial increase followed by a decrease. Particle size had a less pronounced effect on compaction energy and density but positively influenced fracture resistance. Microstructural analysis via Scanning Electron Microscopy (SEM) revealed more open fiber bundles and cracks in compost compared to raw bagasse, indicative of structural changes. X-Ray Diffraction (XRD) analysis showed an increased crystallinity index in compost due to the degradation of amorphous regions (hemicellulose and lignin), with crystalline cellulose remaining stable. Differential Scanning Calorimetry (DSC) identified the compost's average glass transition temperature at 89.7 °C, highlighting the importance of temperature control during densification to preserve beneficial microorganisms. Fourier Transform Infrared (FTIR) spectroscopy confirmed significant chemical changes, particularly the degradation of hemicellulose. These findings offer crucial insights for optimizing bagasse compost pelletization for sustainable and efficient utilization.

Food and agro-industrial waste, exceeding 1.3 billion tons annually, represents both a significant environmental burden and an untapped resource. Hydrothermal carbonization (HTC) has emerged as a promising thermochemical pathway for converting wet biomass into hydrochar and nutrient-rich process water, offering reduced greenhouse gas emissions compared to conventional disposal methods. However, the sustainability of HTC remains insufficiently characterized across environmental, economic, and digital dimensions. This study presents a comprehensive framework that integrates life cycle assessment (LCA), techno-economic analysis (TEA), and machine learning (ML) for HTC systems. Published LCA studies are synthesized to highlight greenhouse gas mitigation potentials and environmental hotspots, while TEA investigations are examined to identify cost drivers, investment risks, and market barriers. The emerging role of ML is critically analyzed, with emphasis on its ability to predict HTC performance, mitigate data scarcity, and support real-time process optimization. An integrative framework is proposed to bridge LCA, TEA, and ML, enabling multi-objective decision-making and policyrelevant evaluation. By aligning HTC deployment with circular economy principles and the United Nations Sustainable Development Goals, this framework advances the methodological foundation of HTC sustainability assessment. Finally, key research gaps are identified, providing a decision-grade basis for the sustainable scale-up of HTC systems.

Food wastage has significant repercussions, such as hindering efforts to combat hunger, contributing to unsustainable resource exploitation, and accounting for approximately half of the greenhouse gas emissions from the entire agri-food system. Converting food waste (FW) into valuable resources and energy provides significant environmental, social, and economic benefits, which are crucial for establishing a circular bioeconomy. Traditional methods of FW valorization, such as landfilling, incineration, and anaerobic digestion, have advanced, with current research and policies increasingly focusing on more sophisticated techniques like hydrothermal carbonization (HTC). HTC involves carbonizing wet biomass at high temperatures and pressures to produce hydrochar, a solid phase, and a nutrient-rich liquid phase. Transforming food waste into useful products like biochar, syngas, and nutrient recovery (e.g., phosphates from waste) addresses the role of HTC in supporting the circular economy and emphasizes the shift from waste disposal to resource recovery. This state-of-the-art review explores how HTC can be integrated with other technologies such as anaerobic digestion, aiming to optimize energy and material recovery with improved properties. The latest advancements in the optimization of HTC process variables, catalytic enhancements, and downstream applications are discussed. Besides, by highlighting the latest life cycle assessments and techno-economic analyses, the economic viability, scalability, and environmental benefits of HTC integration are assessed. Presenting emerging research on novel conversion pathways and potential synergies between HTC and other industries (e.g., agriculture, energy storage) would highlight how the field is evolving to create more versatile uses for HTC byproducts.

Ethanol has the largest-volume production among the biotechnological products. Worldwide production of ethanol has increased almost three times during the last 15 years. Even though the technology for industrial ethanol production is quite mature, efforts have been made in order to enhance the production yield and productivity as well as decrease the production costs. The knowledge of commercial-scale cultivation and utilization of yeasts for ethanol production as well as the advances achieved in strain and process development can shed light on the way of higher alcohol development. In this chapter, the technologies for enhanced ethanol production, for example, process design challenges and engineering microorganisms, are discussed.

Microwave and ultrasound techniques were utilized on walnut green husk (WGH) to extract valuable phenolic compounds and enhance the residual biomass's susceptibility to hydrolysis for subsequent ethanol production. The aim was to optimize process variables in order to achieve an integrated biorefinery with the zero-waste-base standpoint. For microwave-assisted extraction (MAE), four-time levels (0.5, 1.0, 2.0, and 5 min) and power settings (300, 450, 600, and 800 W) were tested. Ultrasound-assisted extraction (UAE) was conducted at a frequency of 28 kHz and power of 100 W over varying time intervals (2, 6, 10, 14, 18, and 22 min). Generally, higher power settings and longer extraction times produced higher contents. Specifically, the maximum total phenolic content (TPC) (220.13 mg GAE/g-DW), total flavonoid content (TFC) (63.21 mg catechin/g-DW), and DPPH scavenging activity (86.13 %) were achieved using the highest power and longest extraction time for MAE. Similarly, the longest UAE time resulted in the highest TPC (214.32 mg GAE/g-DW), highest TFC (58.44 mg catechin/g-DW), and DPPH scavenging activity (76.15 %). Moreover, increased microwave power and longer extraction times favored glucose and ethanol yields, with maximum yields of 55.30 % and 36.67 %, respectively, obtained at 800 W for 5 min. For UAE, the highest glucose and ethanol yields (52.33 % and 34.16 %, respectively) were obtained at 22 min. Conversely, lower extraction times and power settings for microwave, as well as shorter ultrasound times, were beneficial for lignin removal. The application of MAE and UAE in the WGH biorefinery process enhanced the extraction of phenolics and improved biomass hydrolysis, leading to more efficient, sustainable, and economically viable production of biofuels and bioproducts.

The cost associated with raw materials for biodiesel production is the most determinant factor in final biodiesel price and therefore non-edible, easily available, and inexpensive feedstocks are envisaged. Pistacia atlantica mutica (PAM) is oil-rich and abundantly available biomass in Iran's jungles that can be considered as a promising energy crop for biodiesel production. Its seeds contained 30% of high quality oil. The fatty acid profile of PAM oil is rich in 16-18 carbon chains, close to those of petrol-diesel oil. The effects of ultrasound-assisted process variables on the biodiesel yield from PAM oil were investigated. A rotatable central composite design (RCCD) was used to optimize the operating parameters, i.e. amplitude, molar ratio, and reaction time, affecting the reaction yield. Accordingly, amplitude and pulse had a positive impact on the methyl ester content. Besides, the interaction of molar ratio and time became significant (p = 0.01). The optimum values of 64% for amplitude, 7.1 methanol to oil molar ratio, and 387 s were predicted by the model. The corresponding yield of 92.9% was obtained which is quite close to the experimental value, i.e. 92.3%. The properties of PAM methyl ester met the requirements of the ASTM D6751 biodiesel standard.

Ethanol, as a neat chemical or gasoline blend, is the most consumed liquid biofuel for transportation purposes. At present, ethanol is industrially produced from sugar- and starch-based substrates, and ethanol production from lignocelluloses and algae is envisaged over the future. An industrial ethanol-producing microorganism, Saccharomyces cerevisiae, is well-known for ethanol production. However, some Zygomycetes and Ascomycetes species have emerged as ethanol producers. The advantages of using these fungi are high ethanol yield, titer and productivity, high tolerance to inhibitory chemicals in the fermentation broth, and having valuable fungal biomass as a by-product of fermentation. In addition, filamentous fungi may facilitate the production of n-butanol, as an advanced biofuel, from waste materials through different approaches. In this chapter, the production of ethanol by filamentous fungi and the potential roles of fungi in n-butanol production are discussed.

Hydrothermal pretreatment at different solid loading was performed on biogenic municipal solid waste BMSW, and the effects of solid loading on enzymatic hydrolysis and ethanol production were compared. The pretreatment was performed at 160 °C for 30 min at solid/liquid ratio (w/w) of 1:10, 1:7, and 1:5, and the liquid and solid fraction were simultaneously hydrolyzed and fermented to ethanol without detoxification and sterilization. Solubilization of starch and partial solubilization of hemicelluloses occurred during the hydrothermal pretreatment; while, glucan fractions mostly remained in the solid part. Pretreatment considerably enhanced ethanol production, and increasing solid loading from 1:10 to 1:5 was in favor of ethanol production from liquor and against ethanol production from solid fraction. Maximum 300 g/kg-BMSW was obtained from the sample pretreated at 1:10 solid loading. However, when solid loading increased from 1:10 to 1:5, considerably higher ethanol concentration was achieved, favoring lower energy consumption for ethanol recovery. Successful fermentation with Mucor indicus could help the process economy by producing a highly valuable biomass used for the production of a number of industrial products, e.g., superabsorbents. The impact of solid loading was strongly critical on BMSW fractionation to liquid and solid parts as well as final ethanol concentration.

Efficient release of fermentable sugars from the complex biomass structure such as second-generation or third-generation feedstocks by an appropriate enzymatic hydrolysis needs a prior biomass fractionation. This process facilitates the exposure of more cellulose and hemicelluloses for enzymatic hydrolysis. This review focused on 'green fractionation' of biomass by applying the principles of green chemistry for bioethanol production. Besides, the recent technological achievements in applying these principles for the fractionation have been discussed. For green fractionation, energy delivery systems are referred to as microwave and ultrasound. Besides, green cellulose solvents, biomass-derived solvents, and supercritical carbon dioxide play an important role in green biomass fractionations. Furthermore, ball milling and biological treatment are significantly considered in this regard. These novel technologies are superior processes than conventional fractionation techniques in terms of energy and mostly environmental point of view.

The effects of switching morphology and replacing supplementary nutrients with fungal extract (5 and 10 g/L) on the production of major metabolites and chitosan by Mucor rouxii were investigated. This approach was supposed to promote sustainability of the fermentation process and improve its economic feasibility. Different fungal morphologies, i.e., purely filamentous (PF), purely yeast-like (PY), mostly filamentous (MF), and mostly yeast-like (MY), were evaluated. The highest ethanol yields were obtained from the media supplemented with 10 g/L fungal extract for all morphologies, while adding nutrient salts did not make any improvements in these yields, except a slight decrease in the fermentation time. Except for PF morphology, the replacement of yeast extract favored the biomass production yields. Moreover, the alkali insoluble material (AIM) yields were higher as a result of the replacement for most cases. Furthermore, the replacement resulted in increased glucosamine and decreased N-acetyl-glucosamine content of AIM for almost all the morphologies. AIM yields of at least 0.25 g/g-glucose and maximum chitin/chitosan yield of 0.78 g/g-AIM were obtained from the solids remaining after autolysis process, which were higher than that obtained from the raw biomass. The maximum yield of 0.135 g/g-AIM purified chitosan with intact molecular weight was obtained from the biomass with PF morphology supplemented with 10 g/L fungal extract plus nutrients.

Azolla filiculoides is an aquatic fern native to tropical regions, and because of its unique composition, it was subjected to integrated biorefineries for biochemicals and bioenergy production. The compositional analysis showed that its raw biomass contained 41.4% carbohydrates, comprising galactan, glucan, and arabinan, 12% lignin, and 10.3% inorganic matter. Lipids, proteins, and phenolic compounds were extracted from the biomass and analyzed by different methods to enhance extraction yield and estimate their nutritional values. The residues remained after the (sequential) extraction of the major biochemicals was subjected to biogas production. A maximum lipid yield of 18.1% was obtained from the biomass, which was rich in palmitic acid and eicosapentaenoic acid (EPA). EPA, an omega-3 fatty acid with wide applications as a food supplement, accounted for 39.8% of total fatty acids, corresponding to 72 mg/g biomass. Two protein extraction methods, i.e., ultrasound-assisted water followed by sodium hydroxide extraction and sequential extraction by hot trichloroacetic acid, were applied. Using the first method at the optimum conditions, up to 24.4% protein was obtained, while a maximum 11.9% water-soluble protein was isolated by applying ultrasound-assisted extraction. In the amino acid profile of the fern protein, glutamic acid was the most abundant component with 20.5%, followed by threonine. Up to 37.9% of total amino acids were composed of essential amino acids that showed a high nutritional value of the fern protein. The total phenolic content of 27.2 mg gallic acid equivalent per 100 g of biomass was obtained. In the HPLC analysis, chlorogenic acid, luteolin, caffeic acid, and tannic acid were detected in which caffeic acid had the highest concentration of 18.5 mg/100 g raw material. Tannic acid removal was the most effective pretreatment for enhanced biomethane production. A maximum cumulative methane yield of 250.1 mL/g-VS was obtained from tannic acid-free biomass, which was 12% higher than that of the raw biomass. (C) 2020 Elsevier Ltd. All rights reserved.

Waste wheat bread was hydrolyzed using amylolytic enzymes and dilute hydrochloric acid, and the effects of process variables on glucose yield, aflatoxin fate, and ethanol production were studied. Dilute acid hydrolysis was performed with a full factorial experimental design with three levels for acid concentration, i.e., 0.32%, 1%, and 2% (v/v), and three levels for hydrolysis time, i.e., 0, 10, and 20 min at 121 °C. For enzymatic hydrolysis, the samples were first liquefied, and the saccharification of liquefied samples was performed via a rotatable central composite design with two levels of 10 and 48 h for time and two levels of 100 and 150 g/L for substrate loading. The highest glucose yield of 69.8% was obtained from the experiment with acid concentration of 1% and hydrolysis time of 20 min. The maximum glucose yield of 93% was obtained in enzymatic hydrolysis at 55 h and 125 g/L substrate loading. The general linear model was used to model the glucose yields obtained in dilute acid hydrolysis, while the results of enzymatic hydrolysis were best fit to the quadratic model. In the optimized condition for dilute acid and enzymatic hydrolysis, aflatoxin B1 was completely removed by dilute acid hydrolysis, and amylolytic enzymes enabled to remove up to 75% aflatoxin B1. The highest glucose obtained during dilute acid and enzymatic hydrolysis yielded a maximum of 86.9% and 83.0% of theoretical ethanol, respectively, corresponding to 248 and 313 g ethanol per kilogram dry bread residues.

A number of Ascomycetes and Zygomycetes fungi produce ethanol through fermentation. Among them, some are oleaginous and capable of accumulating substantial amounts of intracellular lipids, which can be extracted and derivatized to biodiesel. Cellulolytic enzymes production is another important feature of the contribution of fungi to the second-generation biofuels production. This chapter first presents an introduction to the physiology and growth of fungi and basic considerations in designing the bioprocesses in which fungi are used for fuels application. Subsequently, the bioprocess design for first, second, and third generation bioethanol production and integrated approaches for bioethanol, biodiesel, and enzymatic hydrolysis of lignocelluloses are reviewed and discussed. Selection criteria for bioreactor type in the fermentation process and the enzymatic hydrolysis of lignocellulosic substrates are also included in this chapter.

Cellulose solvent-based fractionation technologies can prove to be economical to enhance lignocellulosic biomass microbial conversion to fuels and chemicals.

Mucoralean fungi are suitable microorganisms for the sustainable production of food, fodder, and fuels from inexpensive natural resources. Ethanol-producing Mucorales are particularly advantageous for second-generation ethanol production in comparison to the conventional ethanolic yeasts and bacteria. They are able to ferment a wide range of sugars to a range of valuable products, while they are typically resistance against the inhibitors available in different substrates, including untreated lignocellulosic hydrolysates. In addition to a high ethanol yield, the fungi produce several commercially valuable by-products, including chitosan, microbial oil (mainly polyunsaturated fatty acids), and protein. Moreover, the fungal extracts can replace the expensive nutrients required in fermentation. Besides, their morphologies can be altered from filamentous to yeast like and are adjustable based on the process requirement. The focus of this review is on applying Mucorales in producing ethanol and the biomass by-products thereof.

Anaerobic mono- and co-digestion of two municipal sludge wastes (A and C), grease trap waste (B), and meat processing waste (D) were investigated under mesophilic temperature conditions by biochemical methane potential (BMP) assays and kinetic modeling. Wastes ratios in the mixtures were systematically selected based on Simplex Lattice mixture design, and statistical analyses were performed to elucidate possible synergetic and antagonistic effects of wastes interactions on the kinetics and ultimate methane potentials of wastes co-digestion. The mixture of 1/8A + 1/8B + 1/8C + 5/8D (VS basis) showed the highest COD and VS removals of 35.0% and 33.8%, respectively. Substrates B and D with 980 and 641 mL/g-VS methane yields, respectively, had the highest BMP. However, with reaction rate constants of 0.047 and 0.070 d(-1), their methane production was very slow. It was observed that diluting these organic-rich but complex substrates with readily soluble wastes (A and C) enhanced their biogas production rate markedly. Statistical analysis showed that the interactions among the substrates in co-digestion did not have a significant impact on the ultimate cumulative methane yields. Nevertheless, these interactions proved to have synergic and antagonistic effects on the reaction rates, leading to accelerated or hindered methane production rates. As a result, while the methane yield of wastes co-digestion could be predicted by proportional summation of methane yields obtained in mono-digestions of these waste fractions, such linear regressions were unable to provide a good estimation of the rate constants. Quadratic equations, however, were found to estimate the rate constants of the co-digestion process with good accuracy.

In a novel valorization approach for simultaneous pectin extraction and pretreatment (SPEP) of citrus waste (CW) by dilute nitric acid and ethanol, almost all of the CW was converted to bio-derived chemicals in a single-step process at a low/moderate temperature. The SPEP was performed at different temperatures (70 °C and 80 °C), pH (1.8, 3.0, and 4.3), and extraction times (2 h and 3 h) with a full factorial design. The maximum pectin yield of 45.5% was obtained at pH 1.8, 80 °C, and 2 h. The pectin yields at pH 1.8 were much higher than at pH 4.3 and 3. Also, the degree of methyl-esterification at pH 1.8 was higher than 50%, whereas at the higher pH, low methoxyl pectins were extracted. The treated CW obtained after the SPEP, free from limonene, was subjected to separate cellulolytic enzymatic hydrolysis and ethanolic fermentation. The glucose yields in the enzymatic hydrolysates were higher for the CW treated at pH 1.8. The fermentation of the enzymatic hydrolysates by Mucor indicus resulted in fungal biomass yields in the range of 355 to 687 mg per g of consumed sugars. The optimum conditions for obtaining the maximum SPEP yield (glucose + pectin (g) / raw material (g))*100) were pH 1.8, 80 °C, and 2 h, which resulted in a yield of 58.7% (g/g CW).

Dissolution of lignocelluloses in N-methylmorpholine-N-oxide (NMMO or NMO) at moderate conditions, e.g., 120 °C for 3 h under atmospheric pressure, and regeneration with water, is among the most effective nonderivatization pretreatment for the improvement of enzymatic hydrolysis and ethanol production. The effects of the pretreatment on two different types of wood, hardwood elm and softwood pine, were compared via physicochemical structural analyses, i.e., FTIR, XRD, SEM, TGA, and enzyme adsorption techniques, to relate their properties to the extent of enzymatic conversion. After the pretreatment, cellulose was highly recovered and characterized to be mainly cellulose II and amorphous cellulose, with lower cellulose crystallinity index, higher thermal stability, and more favorable surface features for hydrolysis, compared to native woods. Moreover, the strength of enzyme binding onto the lignocelluloses, which was directly related to the enzymatic hydrolysis rate, increased by 57% and 164% for pinewood and elmwood, respectively. The highest total reducing sugars yield for untreated pinewood was 9.8% (74 mg/g-substrate) and improved to 58.5% (330 mg/g-substrate) after the pretreatment, whereas the corresponding values for elmwood were 14.7% (104 mg/g-substrate) vs. 51.4% (274 mg/g-substrate). Furthermore, maximum ethanol theoretical yields of 63.5 and 41.4% were obtained from pinewood and elmwood by Saccharomyces cerevisiae and Mucor indicus, respectively.

The recent advances and future perspectives in the complete valorization of citrus processing waste (CPW), a by-product of citrus processing industries, are presented in this review paper. First, the importance of valorization of CPW to develop a bio-economy and to reduce its negative environmental impacts is assessed. A brief survey of applications of native/modified CPW for nanoparticle, bio-sorbent, and biofertilizer production is presented. As the core part of the valorization scheme and regarding the environmental aspects, the perspectives for the application of CPW are via green extraction techniques, e.g., microwave- and ultrasound-assisted extractions, and biochemical processes. Furthermore, green extraction and biochemical techniques result in processes' intensification toward integrated biorefinery models. The superiority of green extraction techniques over traditional techniques, challenges for implementation, and the valuable extracts obtained by these methods as well as a summary of their analytical techniques are discussed. The challenges of bioconversion of CPW to biofuels and fermentative products and strategies to overcome them are later presented. Finally, a literature review on using the concept of green chemistry for the integrated biorefinery of CPW and its engineering challenges is presented and a biorefinery scheme is proposed accordingly.

The potential of two zygomycetes fungi, Mucor indicus and Rhizopus oryzae, in assimilating citrus waste free sugars (CWFS) and producing fungal chitosan, oil, and protein as well as ethanol was investigated. Extraction of free sugars from citrus waste can reduce its environmental impact by decreasing the possibility of wild microorganisms growth and formation of bad odors, a typical problem facing the citrus industries. A total sugar concentration of 25.1 g/L was obtained by water extraction of citrus waste at room temperature, used for fungal cultivation in shake flasks and airlift bioreactor with no additional nutrients. In shake flasks cultivations, the fungi were only able to assimilate glucose, while fructose remained almost intact. In contrast, the cultivation of M. indicus and R. oryzae in the four-liter airlift bioreactor resulted in the consumption of almost all sugars and production of 250 and 280 g fungal biomass per kg of consumed sugar, respectively. These biomasses correspondingly contained 40% and 51% protein and 9.8% and 4.4% oil. Furthermore, the fungal cell walls, obtained after removing the alkali soluble fraction of the fungi, contained 0.61 and 0.69 g chitin and chitosan per g of cell wall for M. indicus and R. oryzae, respectively. Moreover, the maximum ethanol yield of 36% and 18% was obtained from M. indicus and R. oryzae, respectively. Furthermore, that M. indicus grew as clump mycelia in the airlift bioreactor, while R. oryzae formed spherical suspended pellets, is a promising feature towards industrialization of the process.