Cheese whey (CW), a major by-product of the dairy industry, is characterized by high organic load and large production volumes, creating significant environmental and management challenges. Conventional biological treatments such as anaerobic digestion (AD) and dark fermentation (DF) enable partial resource recovery, but their efficiency is often limited by process instability, intermediate accumulation, and weak metabolic cooperation within mixed microbial communities. In this context, extracellular electron transfer (EET) has emerged as a promising approach to enhance microbial interactions and process performance. This review explores current CW valorization strategies, focusing on the role of EET in regulating metabolic pathways, shaping microbial community dynamics, and improving system efficiency. DF, AD, and bioelectrochemical systems are discussed as the main valorization routes, with particular attention to electrically conductive materials (ECM) and electrochemical strategies that stimulate direct interspecies electron transfer (DIET), improve redox balance, and promote the production of hydrogen, methane, and other value-added compounds. EET-based strategies can also reshape microbial community dynamics by promoting electroactive and syntrophic interactions and enhancing lactate conversion and carbon/electron flux distribution. Overall, integrating EET with microbial community control could significantly advance sustainable CW valorization within a circular bioeconomy framework.
Per- and polyfluoroalkyl substances (PFAS) are synthetic chemical compounds used widely in industrial and consumer products. The exceptional stability of terminal perfluoroalkyl acids (PFAAs)—including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS)—stems from strong carbon–fluorine bonds, which render these compounds highly resistant to environmental degradation. Polyfluoroalkyl precursors, by contrast, retain at least one non-fluorinated carbon and are capable of undergoing stepwise environmental transformation, ultimately yielding the same persistent PFAAs as terminal products. This longevity has led to widespread contamination of surface waters, groundwater, soils, and drinking water globally. In 2024, the U.S. EPA established enforceable standards for six PFAS, with limits as low as 4 ng/L for PFOA and PFOS, reflecting health concerns at trace concentrations. Legacy compounds continue to persist despite regulatory phase-outs. Short-chain alternatives and polyfluoroalkyl precursors transform into stable perfluoroalkyl acids, sustaining environmental burdens. We examine PFAS chemistry, environmental fate, and management technologies across the product life cycle-from manufacturing to disposal. Transport through interconnected environmental compartments receives particular attention, with soils and sediments functioning as long-term secondary sources. Toxicity in aquatic organisms and human health implications are reviewed, with emphasis on chronic low-dose exposure and mixture effects. Analytical approaches span targeted methods, suspect screening, and fluorine mass-balance techniques. Management technologies are evaluated with a distinction between separation and destruction processes, including verification requirements. Knowledge gaps in emerging PFAS, precursor transformation, and analytical harmonization point toward the need for improved monitoring and risk-reduction strategies. Key conclusions of this synthesis are: (a) soils and sediments act as long-term PFAS reservoirs introducing multi-year lags between emission controls and exposure reductions; (b) targeted analytical methods capture only a fraction of total organofluorine burden, requiring tiered frameworks combining TOP assay and fluorine mass-balance metrics; (c) human exposure is inherently mixture-driven and demands compound-group rather than substance-by-substance risk assessment; and (d) treatment technologies must demonstrate verified destruction rather than mere phase transfer of PFAS.
Per- and polyfluoroalkyl substances (PFAS) have emerged as persistent contaminants of significant concern due to widespread use. The vadose zone plays a critical role in PFAS fate and transport, as a temporary reservoir, trapping PFAS, and a conduit to groundwater. This paper reviews the current status and future challenges in detecting, predicting fate, and remediating PFAS in the vadose zone. The paper first evaluates detection technologies, highlighting sensitivity and reliability across environmental matrices and remaining challenges (i.e., emerging PFAS, the lack of real-time in-situ monitoring). PFAS fate and transport are then examined within the vadose zone, where interfacial processes and environmental conditions significantly affect PFAS mobility. Critical gaps in transport modeling are identified, emphasizing the need for long-term field data and system-specific studies. Furthermore, current and emerging technologies (e.g., novel materials) for remediation are assessed for their potential to enhance PFAS removal. Treatment effectiveness varies based on PFAS chain length, environmental conditions, treatment duration, and scalability. Challenges in translating laboratory success to field applications, maintaining long-term performance, managing treatment residuals, and meeting regulatory targets are also discussed. The novelty of this review is grounded in deciphering PFAS interfacial dynamics in the vadose zone and the potential of machine learning and deep learning to overcome knowledge gaps and challenges caused by the complex interfacial interactions. Bridging pore-scale retention and field-scale predictability can help optimize detection, transport modeling, and remediation. This framework redefines the unsaturated subsurface as a contaminant reservoir, providing a predictive roadmap for managing this persistent groundwater contamination source.
Malting and brewery wastewaters present environmental and economic challenges to the brewing industry due to their high organic loads and variable nutrient content, with chemical oxygen demand (COD) values ranging from 328 to 4500 mg/L and 910 to 8926 mg/L, respectively. Conventional treatment methods are limited by high energy consumption, sludge generation, and most importantly, a lack of resource valorisation. This review critically examines the role of extracellular polymeric substances (EPS) as key functional enablers in microalgae-based treatment of these effluents. Microalgal EPS enhance pollutant removal through biosorption mechanisms, facilitate biomass harvesting via natural self-flocculation, and represent valuable bioproducts with applications in the food, pharmaceutical, and environmental sectors. Integrating these functions within a circular biorefinery framework offers a holistic strategy that shifts traditional linear treatment methods toward circular resource utilisation pathways. Key technical and economic barriers to implementation are also identified in this review, including process scale-up, low-energy EPS extraction, and market development for EPS products.
The global coffee industry generates millions of tons of biomass residues annually, including pulp, husk, silverskin, and spent coffee grounds (SCG). These residues are often underutilized or discarded, despite being rich in bioactive compounds, dietary fiber, and carbonaceous materials. Their underutilization represents a missed opportunity for sustainable valorization and resource efficiency. This review synthesizes recent advances in chemical, biochemical, and thermochemical approaches for coffee residue valorization. Unlike prior reviews that typically address a single residue type or application domain, this work makes three integrative contributions: it covers the full spectrum of waste streams-pulp, husk, silverskin, and SCG-across the entire processing chain; it bridges agricultural valorization and nanotechnological/material-based applications within a unified evaluative framework; and it embeds these assessments within system-level considerations including cascading biorefinery design, life cycle assessment, techno-economic analysis, and digital optimization. Green extraction techniques, biotransformation processes, and advanced materials processing are critically evaluated across these dimensions. Coffee residues can be effectively converted into functional ingredients, biostimulants, bioplastics, and carbon-based nanomaterials, but the environmental and economic ranking of competing valorization routes is highly sensitive to feedstock moisture, transport logistics, product portfolio diversification, and grid carbon intensity. Cascading biorefinery models can achieve over 85
