Abstract Municipal sewage treatment has become an energy-intensive sector associated with substantial CO2 emissions and waste activated sludge (WAS) generation. Chain elongation (CE), as a promising carbon resource recovery route, enables the conversion of sludge-derived short-chain fatty acids into medium-chain fatty acids (MCFAs). This study developed a microbial electrolysis system (MES) to couple CO2 utilization with caproate production from prefermented WAS, while chloroform and 2-bromoethanesulfonic acid were applied to regulate methanogenesis and homoacetogenesis. CO2 promoted caproate synthesis only under closed-circuit conditions, indicating that its positive role depended on electrochemical electron supply rather than simple substrate addition. The closed-circuit MES with chloroform and CO2 addition achieved the highest caproate concentration, yield, and selectivity, reaching 3092.9 ± 73.1 mg COD/L, 0.66 g COD/g COD, and 58.06%. Compared with 2-bromoethanesulfonic acid, chloroform more effectively inhibited homoacetogens, thereby reducing the diversion of CO2 and H2 toward acetate accumulation and redirecting carbon and reducing equivalents toward caproate formation. Electrochemical analyses confirmed enhanced cathodic biofilm activity, as indicated by the lowest charge transfer resistance of 2.401 Ω. Microbial and functional pathway analyses revealed the enrichment of electroactive and chain-elongating bacteria and the high abundance of key genes involved in the Wood-Ljungdahl pathway, acetyl-CoA generation, fatty acid biosynthesis, and reverse β-oxidation. These findings provide a low-carbon strategy for synergistic CO2 utilization and high-value WAS upgrading.
Abstract Duckweed-based wastewater treatment systems have attracted increasing attention for sustainable water pollution control, yet predictive tools to optimize their operation under real-world conditions remain limited. Here, we develop and validate a temperature- and nutrient-dependent kinetic model for the duckweed species Wolffia angusta, integrating nutrient limitation (Monod model), temperature dependence (Arrhenius model) and internal nutrient reserve dynamics. The model was parametrized and validated through laboratory-scale batch experiments (20–30 °C), in small cylindrical plastic vessels, under varying phosphorus and nitrogen supplies, including nutrient-limiting scenarios. Temperature predominantly drives biomass production, with optimal growth observed at 25–30 °C (maximum relative growth rate of 0.427 d–1), while nutrient availability more strongly governs biological nutrient uptake and removal efficiency. Maximum nutrient removal rates reached 6.85 mg N L–1 d–1 and 1.85 mg P L–1 d–1 under nutrient-replete conditions. Biomass accumulation increases at the higher end of optimum temperature values, but specific nitrogen uptake rates decrease, indicating metabolic constraints. Model calibration markedly improved predictive accuracy (R2 > 0.9; RPD > 2), even under nutrient-limited conditions. The model was applied to simulate a duckweed-based pond systems to polish the effluent from a hybrid anaerobic baffled reactor (HyABR) processing domestic wastewater under tropical conditions (Indonesia). Beyond predicting effluent nutrient concentrations, the model was used as a process design tool to optimize system configuration to meet local effluent discharge consents. Simulations showed that increasing the number of duckweed ponds in series reduces total hydraulic retention time and total land area while lowering per-pond productivity, with an optimal configuration of two to three ponds balancing treatment performance and resource recovery. This work advances the mechanistic understanding of Wolffia’s growth and nutrient uptake, and delivers a practical, transferable modeling framework for design and optimization of duckweed-based nutrient control units for decentralised wastewater treatment, particularly in tropical regions. The approach represents a significant step toward integrating nature-based systems into circular, sustainable water management strategies.
Abstract Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative, and toxic contaminants characterized by highly stable fluorinated alkyl chains. Due to their chemical resilience, PFAS are frequently detected in both influents and effluents of conventional wastewater treatment plants, where they undergo minimal to no removal. Electrooxidation offers a promising, chemical-free approach for PFAS remediation, but it typically relies on expensive, high-performance electrodes such as boron-doped diamond (BDD) or titanium-based materials, limiting scalability and practical deployment. This study establishes the use of low-cost, unmodified, flexible graphite sheet electrodes as anodes for the electrochemical degradation of perfluorooctanoic acid (PFOA). The degradation efficiency was assessed under varying conditions, including initial PFOA concentrations (5–1,000 μg·L–1), current densities (2.5–12.5 mA.cm–2), pH (3–9), electrolyte concentrations (0–0.05 M NaCl), and the presence of reactive radical species. Under optimized conditions (0.05 M NaCl, 10 mA.cm–2, pH ≈ 6), ∼99% PFOA degradation was achieved within 90 min at an initial concentration of 10 μg·L–1, with a corresponding energy consumption of 16.09 kWh.m–3 per order. Hydroxyl radicals and chlorine-based reactive species were identified as key contributors to the degradation mechanism. However, degradation efficiency was inhibited in the presence of a complex wastewater matrix, consistent with the known limitations of radical-mediated processes. Liquid chromatography–mass spectrometry (LC-MS) analysis of the 90 min sample revealed the formation of intermediate degradation products, including shorter-chain perfluoroalkyl carboxylic acids such as perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), and perfluorobutanoic acid (PFBA). Overall, the electrochemical oxidation approach demonstrated in this study offers a promising, economically attractive alternative for the degradation of PFAS in contaminated groundwater and wastewater.
Abstract Cross-feeding, defined as the exchange of metabolites within the microbiome, plays a critical role in the promotion of bacterial activity and growth. Marine anammox bacteria (MAB) possess natural advantages for the treatment of marine wastewater (MW). Herein, the folate-mediated cross-feeding mechanism in MAB-based microbiome was first elucidated under salt stress. The total nitrogen removal rate notably reached 5.2 kg/(m3·d) at the optimal exogenous folate concentration (1.1 mg/L). The stoichiometric ratios of marine anammox (ΔNO2––N/ΔNH4+–N = 1.30, ΔNO3––N/ΔNH4+–N = 0.24) ultimately stabilized around the theoretical values with exogenous folate addition. Besides, exogenous folate markedly enriched the relative abundance of MAB, achieving a remarkable 4.4-fold increase. A metabolic interaction network was elucidated among MAB and their symbionts. Based on metagenomic analysis, bacteria affiliated with Pseudomonadota and Bacteroidota possessed the genetic potential to supply folate for MAB, which is involved in the Wood–Ljungdahl pathway for CO2 fixation in anammox. In resource exchange, MAB secreted extracellular public goods to them. However, with exogenous folate addition, this resource exchange was substantially weakened. MAB reduced the secretion of extracellular public goods for resource exchange and reallocated more energy toward cellular growth during the metabolic exchange interactions. This weakened cross-feeding interaction was further supported by a marked decrease in extracellular protein concentration. This work deepened the understanding of folate-mediated cross-feeding between MAB and symbiotic bacteria and provided a promising strategy to improve the nitrogen removal through MAB in MW treatment.
Abstract Medium-chain fatty acids (MCFAs) production from organic waste via microbial chain elongation (CE) technology represents a pivotal way toward high-value resource recovery. However, real organic wastes generally have complex composition, which results in intricate interspecies interactions in microbial consortium and affects MCFAs yield and process stability. Enhancing microbial cooperation and limiting competition constitute promising strategies for directing carbon flux and reducing equivalents toward the chain elongation pathway. This review provides insights into microbial interactions within real waste-fed chain elongation systems and summarizes key impact factors and recent research advances concerning the regulatory strategies for microbial cooperation. Interspecies interactions can be affected by organic waste compositions, microbial electron transfer pathways, environmental conditions, and quorum-sensing communication systems. Major optimization strategies were systematically introduced including the exogenous additions of signal molecules, supplementation of electron-transfer-mediated materials, and an advanced approach of synthetic microbial consortia. The current review aims to provide theoretical and technical support for enhancing the efficiency of MCFAs’ production from real organic wastes.
Abstract Conventional anaerobic ammonium oxidation (anammox) relies on nitrite (NO2–) as the electron acceptor for ammonium (NH4+) oxidation. However, NO2– is often insufficient in ammonium-rich wastewater, necessitating complex pretreatment to meet the stoichiometric NH4+: NO2– ratio of 1:1.32. Recent studies suggest that anammox bacteria (AnAOB) can perform extracellular electron transfer (EET), indicating a possible route to reduce NO2– demand. However, how to achieve efficient and stable EET under nitrite-deficient conditions remains unclear. Here, an electrochemical anammox membrane bioreactor equipped with conductive membranes (Amx-EMBR) was developed to couple AnAOB enrichment with EET-assisted nitrogen removal. By promoting the dense AnAOB accumulation on the anode, the efficiency of electron transfer from AnAOB to the anode was significantly enhanced, thereby enabling the system to realize EET-associated NO2– oxidation. With influent concentrations of 250 mg/L NH4+ and 150 mg/L NO2–, the reactor achieved a total nitrogen removal efficiency of approximately 90%, corresponding to a 32.8% increase compared with the nonelectrified reactor. 15N-labeling, riboflavin, and hydroxylamine (NH2OH) interference experiments confirmed the occurrence of an EET-driven nitrogen removal pathway. Meanwhile, metagenomic analysis further supported the genetic potential for electrode-dependent NH4+ oxidation and extracellular electron transfer. Furthermore, the reactor exhibited reduced membrane fouling during long-term operation. This study demonstrates an effective strategy for enhancing nitrogen removal under nitrite-deficient conditions, breaking through the strict stoichiometric constraints of conventional anammox with respect to the influent ammonium-to-nitrite ratio.
Abstract Agriculture is the leading anthropogenic source of nitrous oxide (N2O), which is the third most important anthropogenic greenhouse gas and also a critical ozone-depleting substance. Mitigation efforts are constrained by poorly known spatiotemporal heterogeneities and underlying biogeochemical complexities in its emissions. Herein is described the development, testing and validation, and field deployment of an open-path N2O sensor for a small unmanned aerial vehicle (UAV). The open-path configuration of the sensor allows for a low mass (2.7 kg), low power consumption (7 W), high-frequency sampling response (10 Hz), and compact size (38 cm mirror separation). An interband cascade laser (ICL) at 4.542 μm is coupled to a Herriott cell with an optical path length of 21.81 m. Measurement precision of 0.1 parts per billion by volume (ppbv) at 10 Hz is exhibited with drift within 0.2 ppbv at time intervals from 1 s up to 1 h. The measurements were intercompared (r = 0.99) with a commercial closed-path sensor. Field testing took place by constant-altitude mapping flights over an agricultural field during a controlled release experiment. While the sensor is designed for a UAV, its physical and performance attributes make it readily adaptable to autonomous ground vehicles or portable and hand-held N2O sensing.
Abstract It has been demonstrated that the abatement of micropollutants in drinking water by biological activated carbon (BAC) filters with aged media deteriorates due to the decreased porosity and aerobic metabolism in dense biofilm. In this study, micro- and nanobubbles (MNBs) were introduced to the influent of young and aged BAC filters to potentially enhance the removal of micropollutants with various functional groups. Results showed that intermittent MNB introduction could enhance biodegradable micropollutant abatement in aged BAC filters. MNB introduction could yield a ∼10–70% relative increase in removal efficiencies of biodegradable micropollutants in 15-year BAC filters. Meanwhile, the cytotoxicity reduction in BAC filters was elevated from <60% to ∼80% due to the formation of less cytotoxic transformation products, as evidenced by mass spectrometry combined with a machine learning tool. Intermittent MNB introduction could induce localized reshaping of dense biofilm architecture, resulting in recovered pore structures in biofilm, which were pivotal for convective mass transfer. Correspondingly, abundances of Bacteroidota, Chloroflexota, and Acidobacteriota associated with aerobic metabolism of organic substances could be elevated in aged biofilm. However, continuous MNB introduction severely damaged biofilm integrity. The findings of this study support intermittent MNB introduction as a new approach to restore dense biofilm in aged BAC filters, resulting in enhanced biodegradation of micropollutants.
Abstract Soil contamination by Cd and Pb poses significant risks to ecological security and human health. Herein, a series of modified biochar (AMBC) were synthesized from Astragalus membranaceus residues, and subsequently employed as carriers of Atlantibacter hermannii XJ08 to construct biochar-microbe composites for soil remediation. Among the tested materials, brown sugar-modified AMBC (BS-AMBC) showed the highest microbial loading capacity (9.2 × 107 CFU·g–1) and superior Cd and Pb adsorption performance. The BS-AMBC@A. hermannii XJ08 composite effectively reduced DTPA-extractable Cd and Pb concentrations to 0.26 mg·kg–1 and 68 mg·kg–1, respectively. Notably, > 56% of labile fractions (water-soluble/acid-soluble) were transformed into stable oxidizable and residual forms, indicating persistent metal immobilization. In addition, the composite significantly improved soil quality, increasing soil organic matter, cation exchange capacity, and available nitrogen/phosphorus/potassium to 22.3 g·kg–1, 30.4 cmol·kg–1, and 122/44.0/235 mg·kg–1, respectively. Urease, phosphatase, and dehydrogenase activities were markedly elevated by 243%, 527%, and 685%, respectively. Microbial community analysis further revealed the enrichment of functional taxa (e.g., Cytobacillus) associated with heavy metal immobilization, alongside the regulation of key metabolic pathways involved in biogeochemical cycling. This study demonstrates a sustainable approach for valorizing medicinal plant residues into high-performance biochar-microbe composites, offering an effective strategy for the ecological restoration of multimetal contaminated soils.
Abstract Iron-reduction coupled with anaerobic ammonium oxidation (Feammox) often coexists with multiple Fe–N transformation pathways, such as nitrate-dependent Fe (II) oxidation (NDFO). However, an imbalance between iron supply and consumption across these pathways impedes the establishment of a stable Feammox-based process. Here, we established an Fe–O dual-driven strategy using an Fe2O3-integrated membrane-aerated biofilm reactor (MABR) to sustain Feammox activity. Results demonstrated that the pump-free diffusive aeration mode effectively attenuated the interfacial oxygen concentration, while the integrated Fe2O3 enhanced the oxygen transfer rate (OTR) by 26.87% via physicochemical retention and biological regulation. This concerted mechanism restricted oxygen penetration depth, thereby broadening the colonization niche for anaerobes. Cryosectioning-16S rRNA sequencing combined with microelectrode analysis confirmed this spatial reorganization: Feammox bacteria migrated to the middle-outer regions, and NDFO bacteria were enriched across all layers, whereas nitrifiers were confined to the inner biofilm. This stratified architecture promoted O2-driven Fe (II) oxidation and nitrification-derived nitrate generation, effectively regenerating the Fe (III) pool for a stable Fe–N–O cycle. Consequently, the system achieved a nitrogen removal rate of 0.67 g N m–2 d–1 with 68.15% N2 selectivity. These findings deepen our understanding of microbial interactions within biofilms and advance Feammox-based nitrogen removal in wastewater treatment.
Abstract This study introduces a novel, rapid, and sustainable biorefinery approach for lignocellulosic biomass valorization, employing a natural deep eutectic solvent (NADES) system composed of betaine hydrochloride and lactic acid (15:85 w/w). Within just 4 min of microwave-assisted treatment, this green solvent system enables efficient extraction of structurally pristine lignin, preserving its native architecture and unlocking its remarkable multifunctionality. The extracted lignin exhibits exceptional properties, including >95% UV shielding efficiency (transmittance < 5% in the 280–400 nm range at 0.5 mg/mL), strong antioxidant activity (69.7% DPPH inhibition at just 50 μg/mL), and potent antimicrobial effects, especially antifungal inhibition zones surpassing those of standard agents by over 75%. Simultaneously, the holocellulose-rich residue was successfully converted into bioethanol via fed-batch simultaneous saccharification and fermentation, achieving an impressive 82% of the theoretical yield. This integrated process is not only time- and solvent-efficient but also entirely free from toxic chemicals, aligning perfectly with the principles of green chemistry and circular bioeconomy. Altogether, this work positions betaine hydrochloride/lactic acid–based NADES as a transformative green solvent for holistic biomass valorization, offering a promising pathway toward sustainable production of advanced biofuels and high-value functional bioproducts.
Abstract Sulfidated nano zerovalent iron (S-nZVI) shows promise for Cr(VI) remediation, yet the influence of coexisting organic acid (OAs) structures on Cr(VI) reduction by S-nZVI with different sulfur contents remains unclear. Herein, polysulfide (Sx2–) precursors induced Fe0 oxidation to produce high-sulfur Sx2–@nZVI with 9-fold higher sulfidation efficiency than monosulfide-derived S2–@nZVI. Sx2–@nZVI exhibited superior Cr(VI) reduction due to the reduced interfacial resistance and increased FexSy serving as secondary electron donors. OAs enhanced Cr(VI) reduction via proton supply and complexation-induced depassivation. Elongated alkyl chains suppressed OA ionization, increasing H+ availability and promoting direct electron donation from iron (poly)sulfides. In contrast, numerous hydroxyl (−OH) groups reduced H+ availability but strengthened complexation, mitigating the surface passivation. However, strong complexation of –OH increased the negative surface potential of Fe(III/II)-OA complexes, intensifying electrostatic repulsion with S2–/Sx2– and HCrO4–/CrO42–, which suppressed Fe(II) regeneration and Fe(II)-OA electron transfer to Cr(VI). OAs with weaker-complexing alkyl chains exhibited the opposite effect and effectively suppressed Fe/Cr leaching. Consequently, long alkyl chains with high H+ capacity and low complexation favor high-sulfur Sx2–@nZVI for Cr(VI) removal, while α-OH groups with strong complexation and extra electron-donating function govern low-sulfur S2–@nZVI performance. These findings provide mechanistic guidance for S-nZVI design and OA selection in Cr(VI) remediation.
Abstract Arsenic (As) contamination in drinking water is a major health concern. This study investigated As(III) and As(V) removal by continuous flow-through iron electrocoagulation (EC) under varying iron doses and water chemistry conditions. Effective arsenic removal (>90% of 100 μg/L) was achieved with a low iron dose of 5 mg/L and a short EC reactor residence time of 11 s that was followed by flocculation and settling. Removal was primarily through adsorption of As(III) and As(V) to the EC-generated Fe(III) oxyhydroxide solids ferrihydrite and lepidocrocite. For influents containing As(III), oxidation of As(III) to As(V) also occurred. The removal processes occurred in both the EC reactor and downstream treatment. EC-generated reactive solids with high surface area and adsorption capacity provided better arsenic removal than with preformed adsorbents. The removed arsenic remained largely immobile in the EC-generated solids. The extent of arsenic removal was generally similar across pH 6 to 8. Phosphate (1 mg/L as P) inhibited the removal of both arsenic species. Dissolved silica (20 mg/L as SiO2) suppressed As(III) removal but had little effect on the amount of As(V) removed. In addition to thermodynamic effects on adsorption equilibria, pH and co-occurring phosphate and silica influenced removal rates by affecting iron oxidation, nucleation, and aggregation kinetics. The results integrate mechanistic understanding with treatment performance, providing insight relevant to both fundamental research and the application of EC in water treatment.
Abstract Hierarchically structured bioderived materials with integrated interfacial functionalities offer new opportunities for advanced water purification, yet coupling redox activity with selective adsorption in macroscopic scaffolds remains challenging. Herein, we engineer a multifunctional wood-based adsorbent by integrating polydopamine (PDA) and polyethylenimine (PEI) within a delignified wood (DW) framework, enabling synergistic control over surface chemistry and transport pathways. Delignification generates an interconnected porous architecture that facilitates mass transfer, while conformal PDA deposition and PEI grafting introduce redox-active catechol groups and high-density amine functionalities, yielding a pH-responsive, positively charged interface (ζ of +28 mV). Detailed mechanistic analysis was conducted only for hexavalent chromium (CrVI), whereas AsV, NiII, and dyes were examined as proof-of-concept contaminants. Their interactions with PEI/PDA-W were interpreted based on the observed adsorption trends. The resulting material exhibits coupled adsorption–reduction behavior toward CrVI, achieving ∼95% removal under acidic conditions, with spectroscopic evidence confirming partial in situ reduction to CrIII mediated by PDA redox chemistry. Adsorption follows Langmuir-type behavior (qm = 23.3 mg/g) and pseudo-second-order kinetics, indicating surface-controlled interactions on energetically uniform sites. Beyond chromium, the system demonstrates mechanism-dependent selectivity toward coexisting contaminants: arsenate removal is governed by electrostatic interactions and pH-dependent speciation, whereas nickel uptake is dominated by coordination with amine/catechol ligands. Dye adsorption further reveals structure-sensitive behavior, where π–π and hydrophobic interactions enable near-complete removal of aromatic cationic dyes, while weakly interacting species exhibit limited uptake. This work establishes a design strategy for integrating redox functionality and multivalent interfacial interactions within a hierarchical wood scaffold, providing a versatile platform for selective and multimodal water purification.
The use of biomass in the energy landscape has aroused great interest because of the diversity of high-value-added products that can be obtained. Among them, carbon materials stand out for properties such as their high chemical and thermal stability, large specific surface area, and possibility of modifying their surface properties by introducing heteroatoms, which make them ideal candidates for countless applications. The present review addresses to some of the representative works related to the preparation of advanced carbon materials prepared from biomass residues for applications of environmental interest, such as environmental remediation, catalytic processes, and energy-related devices.
Abstract Although converting carbonaceous components in sewage sludge into value-added esters via pyrolysis presents significant resource recovery potential, the complex temperature-dependent interconversion and the limited molecular resolution of conventional analytical techniques have impeded mechanistic elucidation and selective regulation. Here, an integrated approach combining Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), paired mass distance (PMD) network analysis, interpretable machine learning, and density functional theory (DFT) calculations was employed to elucidate the transformation network of organooxygen species (OOSs) during sludge pyrolysis and enabled the proposal of a cascade pathway governing ester enrichment. Esters, unsaturated acids, saturated acids, and peptides/amides accounted for over 95.7% of total OOSs. Ester content decreased at 300–400 °C and regenerated at 400–500 °C, consistent with hydrolysis-esterification interconversion, defining a highly reactive temperature window. Within this interval, dominant interconversion pathways of peptides/amides ⇌ acids ⇌ esters were proposed, suggesting a cascade transformation pathway of peptides/amides → unsaturated acids → saturated acids → esters. The process yielded an additional net benefit of 164.6–474.6 CNY/t over conventional sludge disposal, with a carbon mitigation potential of 776.7 kg CO2e/t. These findings provide a molecular-scale basis for engineering-directed process optimization of pyrolysis systems targeting selective ester production from organic solid wastes.
Abstract While coal-fired power plants are being phased out, waste-to-energy (WTE) facilities remain important during the clean energy transition, providing both waste management and energy recovery. This study presents a mild, modular process that integrates zinc recovery with CO2 mineralization from WTE fly ash (FA). Feedstock characterization showed high Ca (25 wt·%) and Zn (1.2 wt·%) contents. A two-step leaching strategy, DI water washing followed by mild acid leaching (pH 3, HNO3), effectively partitioned Ca and Zn into distinct streams, increasing the Ca/Zn ratio from 20 in raw ash to 223.6 in the water-soluble fraction and 13.6 in the acid-soluble fraction. Electrochemical recovery from the acidic leachate achieved 99% Zn2+ removal under ambient conditions, yielding a cathodic deposit with an estimated Zn content of 58 wt·% that may serve as an intermediate feedstock for further refining. Subsequent carbonation of the Ca-rich stream yielded CaCO3 with 77 wt·% purity and 99.5% Ca removal efficiency. Integration of Zn recovery with CO2 mineralization enables simultaneous valorization of metals and carbonates within a single workflow, minimizing cross-contamination and maintaining compatibility with existing WTE plant infrastructure. The process operates without highly acidic leaching conditions, elevated temperatures, or complex chemical separation steps, supporting scalability to continuous-flow or staged reactor configurations. By coupling resource recovery with carbon sequestration, this approach offers a pathway toward net-negative emissions when paired with CO2 captured from WTE flue gas. The results highlight the potential for WTE FA valorization to contribute to circular-economy objectives and carbon reduction targets through the production of value-added products from an underutilized waste stream.
Abstract The degradation of perfluorooctanoic acid (PFOA) remained challenging due to the extraordinary stability of its carbon–fluorine bonds, which were resistant to conventional photocatalytic processes. In this work, a metal–organic framework (MOF), MIL-125-NH2, was grown in situ on reduced graphene oxide (rGO) to form nanocomposites (RMGs), enabling rapid PFOA degradation via an integrated dual-redox pathway without the addition of sacrificial agents. Under UV irradiation, the RMG composite achieved an 80.2% degradation of PFOA (20 mg L–1) within 4 h, corresponding to an apparent rate constant of 0.405 h–1, and exhibited competitive degradation productivity among reported photocatalytic systems operating without external oxidants or sacrificial agents. PFOA degradation exhibited pronounced pH dependence with the RMG composite delivering optimal performance at pH 5. Moreover, the RMG catalyst showed excellent stability and reusability. In natural water matrices, the RMG composite achieved approximately 70% PFOA degradation within 10 h. The MOF/rGO heterojunction promoted directional charge separation, enabling photogenerated holes to trigger carbon–carbon bond cleavage and stepwise shortening of perfluorinated intermediates, while electrons were efficiently transferred to PFOA to induce hydrogen–fluorine atom exchange. Overall, this study highlights the pivotal role of synergistic redox integration in enabling efficient PFOA remediation in aqueous systems.
Abstract Plastics entering composting systems are frequently found as fragments in finished compost, yet the mechanisms controlling their degradation and persistence remain unclear. In this study, food waste amended with virgin, 30-day UV-weathered, and 30-day sunlight-weathered polyethylene (PE) and poly(methyl methacrylate) (PMMA) microbeads was treated under aerobic and hyperthermophilic composting conditions. PE showed increased surface oxidation after both composting conditions, with the carbonyl index increasing from 3.6–16.6 in virgin to 12.2–25.1 in UV-weathered and 15.0–21.3 in sunlight-weathered beads. This oxidation corresponded with a decreased C/O ratio due to the formation of carbonyl and ester/carboxyl groups. Composting increased crack density on PE surfaces without altering molecular weight, indicating surface-limited degradation. In contrast, PMMA showed a 44–71% decrease in molecular weight after weathering, but no additional molecular weight reduction occurred during composting of weathered PMMA beads. After exposure to both composting conditions, PMMA showed increased thermal stability, whereas PE showed decreased thermal stability. Degradation rates were 6.2–19.5 μm yr–1 for PE and 5.9–33.9 μm yr–1 for PMMA, with estimated degradation times of 8.6–26.9 and 5.8–41.9 years, respectively. A field study showed that surface oxidation and crack density of PE, PP, PS, and PET correlated with compost maturity, likely due to prolonged exposure to dynamic composting conditions. These findings reveal plastic degradation pathways in compost and enable the prediction of their long-term environmental fate.
Abstract Wet oxidation denitrification of flue gas enables ultralow NOx emissions and is increasingly adopted at coal-fired power plants. However, the process discharges wastewater enriched in nitrate and sulfate with minimal heavy metals. Conventional limestone and magnesium hydroxide treatments reliably remove sulfate but are ineffective for nitrate control. To bridge this gap, we propose a catalytic approach that selectively targets high nitrate while concurrently removing sulfate and trace metals. Waste heat from the plant is recovered to heat the wastewater, after which ferrous oxalate is dosed. This initiates a catalytic cycle among oxalate, Fe2+, and nitrate, generating Fe3+ in situ while consuming H+. The resulting pH rise triggers a secondary crystallization–precipitation sequence wherein Fe3+ precipitates sulfate as jarosite, coprecipitating trace Cu and Cr and releasing H+ back into the wastewater. Under optimized conditions at 95 °C, nitrate was reduced by 98% to 1.1 g/L and sulfate fell below the detection limit, allowing the treated wastewater to be directly reused in the wet oxidation process for flue gas purification. This approach uses simple equipment under atmospheric conditions and offers adaptive operational strategies for water recycling and sustainable wastewater management in coal-fired power plants.
