Municipal solid waste (MSW) poses a major challenge due to its increased heterogeneity and complex chemical composition. Derived from varied household and industrial streams, MSW contains a broad mix of organic and inorganic materials with highly diverse chemical structures and reactivities. Grasping this chemical complexity is critical for developing efficient and sustainable waste valorization and recovery pathways. Yet, the highly variable nature of MSW means that its behavior in bioconversion processes like hydrothermal liquefaction (HTL) is still not well understood, resulting in difficulties in achieving consistent operation and predictable product quality. However, the existing HTL literature is highly fragmented, with most studies examining isolated fractions such as food waste, plastics, or lignocellulosic materials rather than real mixed MSW. As a result, a unified reaction-network framework integrating all MSW fractions is still lacking. While recent studies suggest synergistic interactions between plastics and food or paper fractions that affects product distribution, solvolysis, radical recombination, and liquefaction efficiency, these cross-fraction interactions remain largely unexplored and represent an emerging research frontier. This review therefore examines the detailed chemical composition of MSW and the fundamental chemical processes governing its conversion via HTL. Emphasis is placed on the interplay between key organic components, their intrinsic properties, and their transformation pathways under hydrothermal conditions. Key technical barriers limiting efficient MSW HTL are systematically analyzed from a structural chemistry perspective. By synthesizing existing literature and identifying knowledge gaps, this review proposes actionable directions to accelerate the development and deployment of HTL for efficient MSW valorization.

The global waste crisis is a significant concern driven by urbanization and economic expansion. Untreated waste poses major environmental, economic, and societal challenges, especially affecting agriculture and industry. Addressing this crisis necessitates innovative waste management strategies and sustainable practices to mitigate the impending waste burden on ecosystems and societies worldwide. Recent advancements in biofuels and biochemicals intensified research into the conversion of biogenic waste into bio-carboxylic acid/volatile fatty acids (VFAs), driven by the dual imperatives of sustainable waste management and renewable resource development. This study presents a comparative analysis of three waste streams: cheese whey from the cheese-making industry, lignocellulosic brewery spent grains (BSG), and agricultural by-products like wheat straw (WS) assessing their efficacy in carboxylic acid production by mixed culture fermentation. Each substrate produced a diverse array of carboxylic acids, including acetic, propionic, butyric, valeric, iso-valeric, and caproic acids exhibiting unique fermentation efficiencies in carboxylic acid production. The experimental results reveal distinct fermentation efficiencies, the highest concentration of short-chain carboxylic acids (SCCA) production of 11.84 gCOD per L from CW, alongside a medium-chain carboxylic acid (MCCA) production of 3.95 gCOD per L. Notably, despite the lignocellulosic composition of the substrates, both BSG and WS demonstrated substantial and competitive yields of SCCA and MCCA. Specifically, BSG produced 10.68 gCOD per L of SCCA and 3.54 gCOD per L of MCCA, while WS yielded 11.51 gCOD per L of SCCA and 3.84 gCOD per L of MCCA. These findings highlight the viability of lignocellulosic substrates for carboxylic acid production, suggesting significant opportunities for enhancing bioprocessing strategies in biochemical and industrial applications. Taxonomic analysis of microbial communities showed a significant predominance of Firmicutes, Bacteroidota, and Actinobacteriota. The Clostridiaceae family exhibited dominance across all reactors, with respective abundances of 82.72%, 27.67%, and 61.29%. The BSG uniquely showcased an enrichment of Lactobacillaceae (23.86%), Ruminococcaceae (7.72%), and Prevotellaceae (3.24%). Key genera contributing to carboxylic acid production included Clostridium sensu stricto 1, Romboutsia, and Enterococcus. This diversity highlights the influence of substrate composition on microbial community structure, highlighting the intricate relationships between substrate nature and microbial metabolites suggesting that strategic substrate selection could optimize fermentation efficiency and enhance product yield.

Biofouling remains a critical challenge across marine, medical, and industrial sectors, driving the need for sustainable and eco-friendly antifouling coatings. Biomass-based materials, including lignin, tannins, betaines, polysaccharides, and proteins, have emerged as promising candidates due to their biocompatibility, biodegradability, and diverse antifouling mechanisms. These materials inhibit biofouling through mechanisms such as hydration layer formation, surface charge repulsion, hydrophobic foul-release, and biocidal effects, offering effective resistance to protein adsorption, bacterial attachment, and biofilm formation. This review provides a comprehensive overview of recent advancements in biomass-based antifouling coatings, focusing on their antifouling mechanisms, synthesis methods, and applications. Key challenges concerning mechanical durability and scalability are explored, along with potential approaches to enhance the development of sustainable antifouling technologies.

The main purpose of this study was to demonstrate a novel, sustainable flotation process for the selective extraction of chalcopyrite from sulfide ores containing pyrite as the primary gangue mineral. This process is based on the partial replacement of fossil-based potassium amyl xanthate (PAX) collectors with bio-based, biodegradable, and non-toxic organosolv lignin particles (OLP). In the rougher stages, the addition of OLP increased copper recovery by almost 20 %, while improving selectivity; concentrate grades increased from 7.1 % to 12.2–12.4 %. In the cleaner stages, copper recovery (86.2–89.0 %) was approximately twice that achieved using PAX alone (41.9 %). Consequently, the proposed process enabled a 70–80 % reduction in PAX dosage while enhancing flotation performance. Furthermore, the total elimination of lime was possible, as the OLP maintained high selectivity even at a lower pH of 8.6. The results indicate that OLP modifies the flotation response of sulfide minerals, enhancing chalcopyrite recovery while suppressing pyrite flotation, likely through selective surface interactions and changes in surface charge under mildly alkaline conditions.

This study demonstrates a green method to produce low-density cellulose using organosolv pretreated pulp, which also yields high-purity fractions of hemicelluloses and lignin that can be processed further to obtain different chemicals. A base-catalyzed organosolv pretreatment was employed on Norway spruce woodchips to release the cellulose fibrils, which were used to make low-density (20 kg/m3) porous foams (98%). Sodium hydroxide was used as a catalyst, ranging from 0.25 to 1.5 M. The fibers obtained from these pretreatment conditions were characterized and correlated to the foam formation and properties. Furthermore, the samples were compared to foams made from commercially available unbleached and bleached sulfite pulp. A simple production technique was employed by rapidly agitating cellulose pulp with surfactant and additives to induce air into the system. The cellulose fibers arranged around the bubbles and formed a 3-D network upon drying. The lignin content and fiber aspect ratio of the organosolv fibers showed a positive correlation to the foam formation and stability. The foams presented good mechanical resistance (75%), and this property was tuned by the additives. High moisture adsorption tendency and comparably slower scavenging of antioxidant molecules were hypothesized to be due to the position of lignin in the interiors of the cell wall; these properties make the organosolv foams interesting for bioactive packaging applications. 

The production of biogas through anaerobic digestion (AD) of organic-renewable feedstocks is recognized as a viable solution within the renewable energy sector. Biogas typically contains a methane concentration ranging from 60 to 70%, presenting a significant opportunity for energy generation. However, the co-generated carbon dioxide (CO2), which constitutes approximately 30–40% of biogas, poses challenges to overall energy efficiency, thus necessitating the implementation of purification methods to enhance methane concentrations. It is noteworthy that the production of one ton of biomethane results in the generation of approximately two tons of biogenic CO2. This reality opens avenues for carbon capture, storage, and valorization strategies. The biogas industry is beginning to recognize CO2 not merely as a byproduct to be discarded, but as a valuable resource for the synthesis of biomethane, chemicals, fuels, and even building materials. There is a growing interest in utilizing biogenic CO2 as a climate-friendly feedstock, with “bio-Carbon Capture and Utilization” (bio-CCU) practices facilitating the development of sustainable fuels, chemicals, and materials. The article extends to various methods of valorization for biogenic CO2, providing an analysis of techniques for separating and upgrading CO2 derived from biogas. This assessment encompasses both physical and biological methodologies within the carbon capture, utilization, and storage (CCUS) framework. The article further demonstrates both in-situ and ex-situ processes, including biological methodologies that employ microorganisms for CO2 conversion, as well as thermo-physicochemical processes that transform CO2 into biobased products. Additionally, the article demonstrates the economic and environmental advantages associated with the strategic utilization of biogenic CO2. Repurposing this resource is vital for achieving sustainability goals, particularly in renewable energy sectors, where it can significantly enhance energy efficiency and reduce waste. Finally, the article emphasizes the importance of these practices in climate change mitigation, advocating for a circular economy that prioritizes carbon reuse over atmospheric emissions, thus contributing to the advancement of a sustainable future.

Plastic waste, especially from packaging, poses major recycling challenges due to the presence of mixed polymers, which often result in inconsistent blends that are unsuitable for reuse in food-grade applications. Chemical recycling, particularly alkaline hydrolysis, offers a promising solution in the case of chemically reactive polymers, such as polyesters, with poly(ethylene terephthalate) (PET) being one of the dominant plastics suitable for both mechanical and chemical recycling. Mechanical recycling is currently used for the largest part of PET recycling, due to the fact that turning the polymer back into its monomeric building blocks requires catalysts, elevated temperatures, or prolonged reaction times. This study presents a recently developed Heated High-Ethanol Alkaline Aqueous (HHeAA) process that enables efficient, catalyst-free PET hydrolysis under milder conditions. Nearly complete hydrolysis was achieved within just 20 min at 90 °C using a loading of 0.624 g of NaOH/g of PET. The process was successfully scaled up with commercial PET bottles, achieving full hydrolysis while significantly reducing the liquid-to-solid ratio from 20 to just 5 L/kg. These results highlight the industrial potential of the HHeAA method as a more sustainable and energy-efficient alternative for PET recycling and chemical reuse and in turn reduced environmental impact.

Conventional food packaging materials are mainly derived from petroleum-based plastics, contributing significantly to environmental degradation, waste accumulation and resource depletion. Although several biodegradable alternatives have been investigated, a comprehensive understanding of microbial-derived biopolymers and their potential for sustainable food-packaging applications remains limited. Therefore, this review focuses on the physicochemical characteristics, production processes, and functional performance of key microbial-derived polymers used in sustainable food packaging. Bacterial cellulose, polylactic acid (PLA), polyhydroxyalkanoates (PHAs), fungal mycelium, chitosan, alginate, agar, and xanthan gum are among the important biopolymers that are systematically discussed in this review. Advanced fabrication approaches such as microbial fermentation, electrospinning, and 3D printing are also examined for their role in enhancing material functionality and application potential.

The reviewed studies indicate that these biopolymers exhibited high biodegradability, mechanical strength, barrier properties, and antibacterial activity, contributing to improved food quality and shelf-life. However, challenges related to scale-up, cost competitiveness, material consistency, and regulatory approval remain significant obstacles to commercialization. In conclusion, further interdisciplinary research is required to address challenges related to production scalability, cost-effectiveness, and regulatory acceptance.

The growing demand for sustainable bioresources has given prominence to lignocellulosic biomass as a possible alternative. Halophytes offer a specific advantage in this context, because they can grow on non-arable land with minimal freshwater requirements. To our knowledge, this is the first study to integrate organosolv fractionation to either Soxhlet extraction (SLE) or subcritical water extraction, (SWE) at 140 °C, as pretreatment strategies, into a single sequential process applied to halophyte biomass allowing the recovery of bioactive molecules from halophyte biomass. The spent fibers underwent organosolv fractionation under varied process conditions (180–200 °C, 15–60 min, 40–60% v/v ethanol) and were subsequently evaluated for bioenergy production via anaerobic digestion. Organosolv fractionation generates separate lignin and hemicellulose streams, which can be further converted into value-added products. Either extraction methodology effectively facilitated subsequent biomass fractionation. SLE-pretreated fibers attained > 96.4% hemicellulose removal in 87.5% of the tested conditions and 78.1% delignification. SWE-pretreated fibers exhibited slightly lower hemicellulose removal at higher (60% v/v) ethanol content and 69.3% delignification. Crucially, SWE fibers demonstrated superior bioenergy potential, achieving a methane yield of 336 mL-CH₄/gVS, and complete saccharification in 62.5% of tested conditions. Our findings highlight the potential of synergistic pretreatment strategies in an integrated biorefinery approach, which valorizes halophytes as a sustainable feedstock for bio-based applications.

The goal of torrefaction is to transform lignocellulosic biomass into a solid product with better characteristics than raw biomass. Torrefaction is especially helpful when converting biomass into a final energy carrier via thermochemical processes like gasification and direct combustion. However, even though torrefied biomass has demonstrated advantageous quality, the prevailing torrefaction methods are not yet considered sufficiently advanced to overcome certain operational difficulties such as finding the proper balance between salient independent variables like temperature, reaction time and particle size; hence, much of the torrefied products obtained exhibit inconsistent properties. The technique also lacks the ability to efficiently handle a wide range of biomass feedstocks and exhibits scale-up issues that could be linked to poor temperature control and non-uniform heat distribution. Many of the existing torrefaction systems have been developed and validated for use in the processing of wood-based materials. Studies performed with non-woody materials yielded unsatisfactory results due to their inclination to ignite and carbonize readily during torrefaction. This review, therefore, presents a status overview of torrefaction technology and discusses the limitations of the technique from a reactor design perspective, as well as identifies system-level research that could potentially help to address the technology’s constraints. The basic principles of torrefaction and the mechanisms that affect the quality of torrefied products, including key process variables and kinetics are also discussed. Other expounded aspects include reactor design concepts, process monitoring and control, and specific technological barriers thought to hamper the technology’s attempt to achieve commercial success.