A combined treatment process,consisting of modified iron-carbon micro-electrolysis coupled with hydrolytic acidification and followed by an anoxic/oxic(A/O)biological system,was developed and evaluated to address the complex composition and low biodegradability of textile dyeing wastewater.Granular iron-carbon micro-electrolysis media were prepared using zero-valent iron(ZVI),activated carbon,and kaolin as the main raw materials.In an aqueous environment,the media formed a relatively stable micro-electrolysis system,in which ZVI acted as the anode,while activated carbon served as the cathode and adsorption carrier.Through the synergistic effects of electrochemical reactions and adsorption,the transformation and degradation of refractory organic pollutants were enhanced,thereby improving the pretreatment performance during the hydrolytic acidification stage.The incorporation of activated carbon and kaolin effectively mitigated the aggregation and surface passivation of ZVI during operation and contributed to the structural stability of the micro-electrolysis media.Based on these findings,the iron-carbon micro-electrolysis media were further modified with metallic manganese and applied in the hydrolytic acidification reactor to regulate microbial metabolic processes and carbon conversion pathways.Continuous-flow experiments were conducted to investigate organic matter transformation characteristics,volatile fatty acid(VFA)production,and greenhouse gas emissions during the hydrolytic acidification stage.The results indicated that the introduction of manganese maintained high pollutant degradation efficiency while simultaneously reducing greenhouse gas emissions during the hydrolytic acidification stage.When the modified micro-electrolysis media were employed,the concentration of VFAs in the hydrolytic acidification effluent reached 348.34 mg COD/L,providing a readily biodegradable carbon source for subsequent biological treatment.Under the same operating conditions,the methane emission flux from the hydrolytic acidification reactor was measured at 21.32 g·m-2·d-1.During long-term continuous operation of the combined micro-electrolysis/hydrolytic acidification/anoxic/oxic process,the system exhibited stable performance and effective pollutant removal.The removal efficiencies for COD and NH4+-N reached 94.8%and 74.4%,respectively,while the color removal efficiency was 65%.These results indicate that the combined process can effectively enhance dyeing wastewater treatment performance and reduce greenhouse gas emissions during the anaerobic pretreatment stage.However,certain limitations should be considered for practical engineering applications.Although simulated dyeing wastewater was used in this study,actual dyeing wastewater typically exhibits substantial fluctuations in water quality,which may affect pollutant removal efficiency and operational stability.In addition,the potential release of Mn2+from manganese-modified micro-electrolysis media during long-term operation of the hydrolytic acidification reactor has not been fully clarified,and its possible impact on process performance requires further investigation under more complex influent conditions and extended operational periods.
Residual disinfectants in aquatic environments may influence the dissemination of antibiotic resistance genes(ARGs)by affecting horizontal gene transfer among microorganisms.The phenolic disinfectant p-chloro-m-xylenol(PCMX)has been widely used and is frequently detected in municipal wastewater and surface waters at concentrations ranging from ng/L to μg/L.However,its potential effects on plasmid-mediated ARG dissemination remain insufficiently understood.This study investigated the influence of PCMX on the conjugative transfer of ARGs and explored the underlying mechanisms involved.An intergeneric conjugation model was established using Escherichia coli CHS56 carrying plasmid RP4-8 as the donor strain and Pseudomonas sp.TS44 as the recipient strain.The effects of PCMX on conjugative transfer were evaluated across a concentration range of 0.1-10,000.0 μg/L.Conjugation experiments were combined with reactive oxygen species(ROS)detection,cell membrane permeability measurements,and transcriptomic analysis to investigate the physiological responses and molecular mechanisms associated with PCMX exposure.The results demonstrated that PCMX promoted plasmid-mediated conjugative transfer within an environmentally relevant concentration range.Specifically,at concentrations between 0.1 and 100.0 μg/L,PCMX enhanced the transfer frequency of plasmid RP4-8 between the donor and recipient strains,reaching a peak conjugation frequency of 7.22×10-6 at 10 μg/L PCMX.When the concentration increased to 1,000-10,000 μg/L,the conjugation frequency declined,which may be attributed to the inhibitory effects of high PCMX concentrations on bacterial growth and cellular activity.Flow cytometry analysis using DCF-DA staining indicated that PCMX exposure increased intracellular ROS levels in the donor strain E.coli CHS56 at 100 and 10,000 μg/L.In contrast,no significant ROS variation was detected in the recipient strain Pseudomonas sp.TS44.The addition of the ROS scavenger N-acetylcysteine(NAC)significantly reduced intracellular ROS levels in the donor strain but did not markedly decrease the conjugation frequency,suggesting that oxidative stress was not the dominant driver for the enhancement of plasmid transfer under PCMX exposure.Membrane permeability analysis revealed that PCMX exposure altered the integrity and permeability of bacterial cell membranes,particularly in the recipient strain.Increased membrane permeability likely facilitated physical contact between donor and recipient cells,thereby promoting plasmid transfer.Transcriptomic analysis further showed that PCMX exposure significantly affected the global gene expression profiles of both strains.Multiple genes associated with membrane transport and transmembrane processes were differentially expressed.Notably,a glycerol uptake facilitator gene involved in membrane transport was significantly upregulated,indicating enhanced transmembrane transport activity under PCMX stress.Overall,these results suggest that PCMX enhancea plasmid-mediated ARG conjugative transfer primarily by altering cell membrane permeability and transmembrane transport processes rather than through ROS-mediated oxidative stress.Considering that PCMX cannot be completely removed during conventional wastewater treatment,residual PCMX may persist in biological treatment units containing dense microbial communities,thereby increasing the potential risk of ARG dissemination.These findings provide experimental evidence for evaluating the ecological risks of disinfectant residues in wastewater treatment systems and aquatic environments.
With the rapid advancement of industrialization and urbanization,high-risk pollutants—including antibiotics,endocrine-disrupting compounds,polycyclic aromatic hydrocarbons,pesticides,and synthetic dyes—are now recognized as persistent contaminants in aquatic environments.These contaminants are characterized by high toxicity,environmental persistence,bioaccumulation potential,and resistance to conventional treatment processes,thereby posing long-term risks to ecological and human health.Traditional physicochemical methods often suffer from high energy consumption,limited selectivity,incomplete mineralization,and the risk of secondary pollution,underscoring the urgent need for efficient and sustainable alternatives.Laccase,a multicopper oxidase that utilizes molecular oxygen as the terminal electron acceptor,has emerged as a promising green biocatalyst due to its broad substrate spectrum,mild operating conditions,and low environmental impact.It can directly oxidize phenolic and aromatic amine compounds and,in the presence of low-molecular-weight mediators,expand its catalytic scope to non-phenolic and high-redox-potential pollutants.However,the practical application of free laccase is hindered by poor operational stability,rapid deactivation,and limited reusability in complex wastewater systems.Immobilization is widely employed to overcome these limitations by anchoring enzymes onto or within solid supports,thereby enhancing structural stability,improving resistance to environmental fluctuations,and enabling enzyme recovery and reuse.In parallel,genetic engineering strategies have been developed to improve enzyme yield,catalytic efficiency,and environmental adaptability.These two approaches are increasingly integrated to construct robust biocatalytic systems.This review systematically summarizes recent advances in immobilized laccase systems for the degradation of high-risk pollutants.Major immobilization strategies,including adsorption,covalent bonding,entrapment,cross-linked enzyme aggregates(CLEAs),and composite immobilization,are comparatively analyzed in terms of their mechanisms,carrier materials,operational performance,and pollutant specificity.Among these,composite immobilization has demonstrated superior performance by coupling adsorption-driven enrichment with catalytic degradation,often achieving removal efficiencies exceeding 90%along with enhanced operational stability.Furthermore,the integration of immobilization with genetically engineered laccase-producing microorganisms is highlighted.Particularly,immobilized whole-cell systems and carrier-attached biofilms enable continuous enzyme expression,prolonged catalytic activity,and improved adaptability to dynamic wastewater environments.In practical applications,immobilized laccase systems exhibit strong tolerance to complex matrices and maintain high degradation efficiencies in mixed-contaminant systems,such as pharmaceutical-dye and phenol-antibiotic wastewaters.Notably,advanced carriers,including magnetic nanomaterials and biochar-based composites,further enhance stability under extreme conditions,such as alkaline pH,high salinity,and temperature fluctuations.Overall,immobilized laccase systems show significant potential for treating dye wastewater,pharmaceutical effluents,municipal secondary effluents,and phenol-containing industrial wastewater.Future research should focus on developing novel biodegradable composite carriers,optimizing immobilization strategies to minimize activity loss,validating these systems at a large scale in real wastewater,and comprehensively evaluating long-term stability and cost-effectiveness.These efforts will facilitate the practical implementation of laccase-based biocatalytic technologies in sustainable environmental remediation.
With the continuous accumulation of refractory organic pollutants and antibiotics in aquatic environments,the development of efficient and sustainable water treatment technologies has become an important research focus in the field of environmental catalysis.Among emerging advanced oxidation technologies,piezocatalysis has attracted increasing attention because it can directly convert ubiquitous mechanical energy into chemical energy for reactive oxygen species(ROS)generation without requiring external light irradiation or additional oxidants.However,conventional piezocatalytic materials generally suffer from several intrinsic limitations,including weak piezoelectric polarization,rapid recombination of charge carriers,insufficient active sites,and sluggish interfacial reaction kinetics,which severely restrict their practical catalytic efficiency.Although heterojunction engineering is widely considered an effective strategy to improve charge separation,constructing highly efficient piezoelectric heterojunction systems with directional charge-transfer pathways and strong redox capability remains a major challenge.To address these issues,BiOCl/g-C3N4(BOC/CN)composites were successfully synthesized via a hydrothermal route,rationally constructing a tightly coupled Z-scheme heterojunction through interfacial engineering.The phase structure,morphology,interfacial characteristics,charge-transfer behavior,and piezocatalytic performance of the composites were systematically investigated.The results demonstrate that BOC nanosheets are uniformly anchored onto the CN surface,forming an intimate heterointerface that effectively promotes interfacial charge migration and spatial charge separation.More importantly,the Z-scheme charge-transfer pathway preserves the strong oxidation capability of valence-band holes in BOC and the high reduction capability of conduction-band electrons in CN,thereby significantly enhancing ROS generation efficiency under ultrasonic stimulation.Benefiting from the synergy between piezoelectric polarization and interfacial charge redistribution,the BOC/CN composite exhibits remarkably enhanced piezocatalytic activity toward tetracycline(TC)degradation.Under ultrasonic vibration,its degradation rate reaches 0.189 min-1,which is 11.8 and 5.7 times higher than that of pure CN and BOC,respectively.Radical trapping experiments confirmed that holes(h+),hydroxyl radicals(·OH),and superoxide radicals(·O-2)synergistically dominated the degradation process.In addition,BOC/CN displays excellent performance in piezocatalytic H2O2 synthesis,achieving a generation rate of 280 μmol·L-1·h-1,which is significantly higher than those of pure BOC and CN(both close to 20 μmol·L-1·h-1).This enhanced H2O2 production is mainly attributed to the efficient two-electron oxygen reduction pathway enabled by the Z-scheme heterojunction and piezo-induced charge separation.This work deepens the understanding of piezoelectric Z-scheme interfacial mechanisms and provides a promising strategy for designing highly efficient piezocatalysts for environmental remediation and sustainable energy conversion.
The escalating challenges of rapid industrialization and increasingly stringent environmental regulations have placed immense pressure on existing wastewater treatment plants (WWTPs), particularly those within industrial parks. These facilities often face the dual imperative of expanding their treatment capacity to accommodate rising influent volumes and simultaneously upgrading their processes to meet higher effluent quality standards, all while constrained by limited physical space. To address these critical issues, this study comprehensively evaluated an in-situ upgrading strategy for a WWTP in a major industrial park in Nanjing, China. The technical approach integrated a Moving Bed Biofilm Reactor (MBBR) into the traditional Anaerobic-Anoxic-Oxic (AAO) system to assess its feasibility and efficacy for significant capacity expansion and achieving Class Ⅳ surface water standards. The results demonstrated a rapid and successful system start-up, with a mature and stable biofilm layer established on the MBBR carriers within 30 days during favorable summer temperatures. Under a demanding hydraulic loading rate of 150% of the original design capacity (corresponding to an influent flow rate of 1.5 m3/h), the hybrid system exhibited exceptional resilience. During the warm season, the treated effluent consistently met all Class Ⅳ surface water quality standards. While low temperatures during the cold season exerted inhibitory effects on microbial activity, the MBBR-enhanced process demonstrated remarkable robustness: the average effluent chemical oxygen demand (COD) concentration only slightly exceeded the Class Ⅳ limit (30.87 ± 2.54 mg/L), whereas ammonia, total nitrogen, and total phosphorus concentrations all comfortably satisfied the stringent requirements. This outcome confirms that the MBBR-enhanced process effectively achieved the dual goals of in-situ capacity expansion and substantial effluent quality improvement for the complex industrial park wastewater. Analysis of the microbial community structure revealed a pronounced seasonal shift in community composition and assembly. During the warm season, the biofilm community exhibited significantly higher α-diversity, with a notable enrichment of various thermophilic heterotrophic bacteria. Conversely, the microbial community shifted dramatically in the cold season, with a clear enrichment of cold-tolerant microorganisms. Notably, the significant proliferation of the genus Nitrospira was crucial for sustaining effective nitrification under low-temperature conditions. The assembly of the microbial community in the warm season was predominantly governed by deterministic processes. In contrast, community assembly during the cold season shifted towards a greater influence of stochastic processes. Concurrently, microbial network analysis indicated that the interspecies interaction network became simplified in winter and spring, likely enhancing overall community resilience and stability. In conclusion, this study offers a robust and scalable solution applicable to WWTPs worldwide that are facing similar challenges of expansion and stringent effluent quality improvement.
Electrocatalytic ozonation (ECO) has emerged as a prominent research hotspot in water treatment, owing to its rapid reaction kinetics, high efficiency in organic mineralization, and relatively low operational costs. This review systematically summarizes recent advances in ECO technology, focusing on the following aspects: (1) classification of operational modes, including electrocatalysis followed by ozonation, ozonation followed by electrocatalysis, and integrated electrocatalysis-ozone systems; (2) key influencing factors, with an emphasis on anode materials (e.g., nickel-antimony co-doped tin oxide, graphite felt, and activated carbon fiber), cathode materials (e.g., carbon-polytetrafluoroethylene composites and iron-nitrogen co-doped carbon nanotubes), and operational parameters such as current density, ozone concentration, and solution pH; and (3) application scenarios, highlighting performance evaluations in complex aqueous matrices including antibiotic wastewater, dyeing wastewater, and landfill leachate. Regarding mechanisms, this review analyzes the generation and roles of reactive oxygen species (ROS) in ECO systems, particularly the formation pathways of hydroxyl radicals (·OH), synergistic effects, and their contributions to pollutant degradation. Using typical contaminants such as phenol and ibuprofen as model compounds, it analyzes the oxidation intermediates, bond cleavage patterns, and final mineralization in detail. Additionally, the formation of chlorate and other by-products during the treatment of chloride-containing wastewater is addressed. Despite its potential, ECO technology faces challenges in practical implementation, including the long-term stability and versatility of electrode materials under complex water conditions, as well as the intricate interactions of multiple ROS that complicate reaction pathways. Finally, this review outlines future research directions, such as the development of advanced electrode materials, artificial intelligence (AI)-assisted process optimization, integration with other technologies, and a comprehensive life cycle assessments (LCA) covering environmental and economic aspects. By consolidating recent research and mechanistic insights, this review aims to provide technical support for the large-scale application of ECO technology in water treatment engineering.
Antibiotic resistance pollution has become a major threat to public health and ecological security, and wastewater treatment plants (WWTPs) are widely recognized as important reservoirs and emission sources of antibiotic resistance genes (ARGs). To quantify the environmental dissemination risk of wastewater-borne resistomes, we integrated and reanalyzed 81 metagenomic samples from 29 WWTPs in 11 countries, encompassing influent, effluent, and paired upstream and downstream receiving river samples. These publicly available datasets span approximately the last decade and cover eight representative biological treatment configurations. In total, 1,794 ARG subtypes affiliated with 27 ARG types were detected. Influent samples exhibited significantly higher ARG abundance (mean: 2.16 copies/cell) and diversity (mean: 556 subtypes) than effluent and river samples. Even after full-scale wastewater treatment, effluents retained a mean abundance of 0.65 copies/cell and a mean of 295 ARG subtypes, indicating incomplete elimination of wastewater-derived resistomes. Compared with upstream river water, downstream sites showed mean increases of 39.5% in ARG abundance and 11.3% in ARG diversity. To move beyond descriptive resistome profiling, we applied a structured, comprehensive risk assessment framework based on MetaCompare (v2.0). This framework integrates three dimensions of ARG-related risk: occurrence features, mobility potential, and host pathogenicity. The results showed that the overall resistome risk score of downstream receiving waters increased by an average of 35%, indicating that wastewater discharge elevates ARG loads and amplifies their potential ecological and health relevance. Building on this risk-oriented analysis, we identified 23 wastewater-derived ARGs posing dissemination risks according to their occurrence, persistence, and downstream proliferation characteristics. Collectively, these high-risk subtypes accounted for 22.6% of the total ARG abundance in downstream waters. Among them, qacH, mexW, and oqxB displayed particularly strong environmental proliferation potential, whereas APH(6)-Id, aadA, sul1, and sul2 warrant special concern as they are also classified as clinically important high-risk ARGs. Marked differences were observed among treatment processes. The anaerobic-anoxic-oxic (AAO), oxidation ditch (OD), and sequencing batch reactor (SBR) processes removed more than 80% of the wastewater-derived ARGs with dissemination risk, whereas the cyclic activated sludge system (CASS) and membrane bioreactor (MBR) processes showed selective enrichment effects for several subtypes. A plausible explanation is that the fluctuating redox and substrate conditions in the CASS, coupled with the high biomass density, prolonged sludge retention time, biofilm- or membrane-associated microbial aggregation, and residual extracellular DNA in the MBR, create favorable niches for the persistence, horizontal transfer, or selective enrichment of certain ARGs. Overall, the environmental dissemination risk framework established here, the identification of representative wastewater-derived high-risk ARGs, and the evaluation of process-specific removal spectra provide a solid scientific foundation for mechanistic studies and the development of targeted mitigation strategies against antibiotic resistance pollution.
Stringent nitrogen discharge standards necessitate advanced treatment technologies for secondary effluent from municipal wastewater treatment plants(WWTPs).Conventional heterotrophic denitrification faces limitations,such as dependence on organic carbon and potential emissions of nitrous oxide(N2O),a potent greenhouse gas.To address these challenges,this study established and systematically evaluated a novel staged denitrification system integrating sulfur autotrophic and heterotrophic processes.The effects of two coupling configurations—sulfur autotrophic followed by heterotrophic(R1)versus heterotrophic followed by sulfur autotrophic(R2)—were investigated in terms of overall nitrogen removal efficiency,N2O emission dynamics,and the underlying electron distribution patterns within the microbial consortia.The results demonstrated that the R1 configuration exhibited superior nitrogen removal performance.In the initial sulfur autotrophic stage,high nitrate removal efficiency(>75%)was achieved,accompanied by consistent nitrite accumulation(6-8 mg/L),indicating incomplete denitrification.This intermediate was subsequently utilized in the downstream heterotrophic stage,facilitating the near-complete removal of residual nitrogen substrates.Consequently,the R1 system produced a final effluent with a remarkably low total nitrogen(TN)concentration of 4-5 mg/L and a TN removal efficiency of 75.5%.In contrast,the R2 system,starting with heterotrophic denitrification,demonstrated negligible accumulation of denitrification intermediates but achieved a lower overall TN removal efficiency.Critically,the R1 configuration yielded a significantly lower N2O emission factor(0.12%of the removed TN)compared to the R2 system(0.64%),highlighting its environmental advantage in mitigating greenhouse gas emissions.To elucidate the mechanistic basis for these performance differences,targeted batch experiments were conducted to quantify electron flux distribution among key denitrifying enzymes.The results indicated that in the sulfur autotrophic stage of R1,electrons were preferentially channeled towards nitrate reductase(NAR),accounting for 45.36%of the total electron flux.Conversely,in the subsequent heterotrophic stage,a substantially larger proportion of electrons was allocated to the downstream enzymes nitrite reductase(NIR),nitric oxide reductase(NOR),and nitrous oxide reductase(NOS).This electron allocation pattern in the heterotrophic phase likely promoted the efficient reduction and removal of N2O,contributing to the lower emissions observed in the R1 system.Microbial community analysis revealed structural similarities between the systems,with the sulfur autotrophic stage dominated by the genus Thiobacillus(54.25%-69.00%),renowned for its sulfur-oxidizing denitrification capability.The heterotrophic stages were primarily colonized by members of the family Burkholderiaceae(15.82%-24.21%)and the genus Thauera(5.87%-16.45%).This study provides compelling evidence that the staged system,particularly with autotrophy preceding heterotrophy(R1),is a highly effective and sustainable strategy.It simultaneously achieves advanced nitrogen removal and significantly reduces N2O emissions,offering a promising solution for enhancing the environmental sustainability of municipal WWTPs.
With the rapid development of the integrated circuit (IC) industry, organic wastewater generated during manufacturing has garnered significant attention. This wastewater is characterized by its complex composition, high toxicity and poor biodegradability. The safe disposal and resource recovery of such organic wastewater are of great significance for the sustainable development of the IC industry. However, a comprehensive literature review discussing resource and energy recovery alongside advanced detoxification of organic wastewater in the IC industry is still lacking. This paper systematically reviews the main sources and physichemical properties of IC organic wastewater, and analyzes the occurrence of bulk organic pollutants (e.g., tetramethylammonium hydroxide, N-methylpyrrolidone, isopropanol) and trace emerging contaminants (e.g., per- and polyfluoroalkyl substances, PFAS). On this basis, the current research status of IC organic wastewater treatment is evaluated from three perspectives: resource recovery, energy conversion, and advanced detoxification. For high concentration single-component organic waste liquid/wastewater, priority is given to the direct recovery or downgraded utilization of high-purity components. For medium-to-high concentration organic wastewater, methane production through anaerobic digestion represents an important pathway for resource utilization. For the advanced treatment of low-concentration wastewater and effluent after biological treatment, an advanced detoxification strategy integrating separation-enrichment and destructive mineralization is recommended. The advantages, disadvantages, and applicability of various technologies are systematically compared from three dimensions: application scope (e.g., removal rate, mineralization degree), economic feasibility (e.g., energy consumption, operational cost), and engineering applicability (e.g., maturity, scalability for real IC wastewater). In addition, this paper explores current challenges in IC organic wastewater treatment, including insufficient systematic validation under real wastewater conditions and the absence of dedicated techno-economic assessments. Finally, future development trends regarding intelligent technology, integrated processes, and life-cycle pollution control are outlined, providing theoretical references and technical support for the efficient and green treatment of IC organic wastewater.
Per-and polyfluoroalkyl substances(PFAS)are of significant environmental concern due to their exceptional chemical stability and bioaccumulation potential,posing serious threats to ecosystems and human health.The extraordinary strength of C-F bonds renders PFAS recalcitrant to conventional water treatment technologies,which typically fail to achieve complete degradation or mineralization.Therefore,developing efficient and targeted removal techniques has become a major challenge in environmental science.Iron-based materials,owing to their natural abundance,environmental compatibility,and strong redox activity associated with multiple valence states,have shown great promise for PFAS degradation.This review systematically summarizes recent advances in PFAS degradation using iron-based systems,with a focus on material properties and reaction mechanisms.Iron-based systems are categorized into homogeneous iron species(Fe2+/Fe3+ions)and heterogeneous materials,including zero-valent iron(ZVI),iron-bearing minerals,multimetallic iron composites,and supported iron materials.Their physicochemical properties,affinity for PFAS,and catalytic reactivity are comprehensively evaluated.Structural design and active-site engineering are critical for enhancing catalytic performance.Compared with conventional ZVI,which suffers from limited reactivity,novel iron-based nanocomposites—such as those modified with graphene or encapsulated in nitrogen-doped graphene-like structures—can achieve defluorination efficiencies of 50%-100%.Regarding degradation mechanisms,iron-based materials facilitate PFAS transformation via multiple pathways:(i)reductive processes,including direct electron transfer from ZVI,as well as reactions with hydrated electrons or atomic hydrogen radicals;(ii)oxidative processes driven by hydroxyl and sulfate radicals that target head groups and C-F bonds,along with the ligand-to-metal charge transfer(LMCT)mechanism enabling photoinduced electron transfer;(iii)redox synergy,in which reductive defluorination or chain-shortening lowers the reaction barrier and promotes subsequent radical oxidation;and(iv)iron-based material-microbial synergy,where iron-based materials mediate extracellular electron transfer and act in concert with microbial surface reductive activity.Among these pathways,reductive degradation is currently the most effective approach for deep defluorination of long-chain PFAS,while the LMCT mechanism offers unique advantages in photocatalytic oxidation by lowering energy barriers.Despite the remarkable potential of iron-based materials,their practical application faces several challenges.Short-chain PFAS,due to their weak hydrophobicity and low adsorption affinity,exhibit significantly lower degradation efficiencies than their long-chain counterparts and tend to accumulate as recalcitrant intermediates,complicating complete mineralization.Additional challenges include iron leaching,surface passivation,and interference from complex water matrices.Future research should focus on developing iron-based composites with enhanced stability and reactivity,advancing pilot-scale and field applications to evaluate economic and technical feasibility,and exploring the coupling of iron-based materials with renewable energy sources for sustainable operation.This review aims to provide a theoretical foundation for the rational design of iron-based materials and their application in PFAS pollution control.
With rapid urbanization and the continuous expansion of urban water infrastructure, pollution source identification in pipe networks has become a critical task for water environment management, risk control, and emergency response. Contamination events in drainage and water distribution networks are often hidden, transient, and uncertain, where locations, release times, durations, and intensities are usually unknown. Furthermore, available monitoring points are frequently limited, and sensor data often suffer from noise or missing values, which renders pollutant source tracing a typical inverse problem. Numerical inversion methods provide an effective framework to reconstruct source information from hydraulic, water-quality, and monitoring data. This review summarizes recent research progress on numerical inversion methods for pollutant source identification in urban pipe networks. Four major categories of methods are discussed: mechanistic model-based optimization, probabilistic methods, data assimilation, and surrogate model-based methods. Mechanistic model-based optimization methods employ hydraulic and water-quality transport models as forward simulators to estimate source parameters by minimizing the discrepancies between simulated and observed responses. While providing strong physical interpretability and quantitative source information, they usually require repeated forward simulations, incurring high computational costs in large-scale networks. Probabilistic methods describe source parameters using probability distributions. They are capable of quantifying uncertainty and are well-suited for inverse problems characterized by measurement errors and non-unique solutions, though their performance heavily depends on prior information, likelihood functions, and sampling efficiency. Data assimilation methods combine model predictions with real-time or quasi-real-time observations to dynamically update system states and source parameters, making them highly effective for online tracking despite their dependency on reliable sensor configurations. Surrogate model-based methods utilize machine learning or deep learning to approximate source-response relationships, significantly enhancing computational efficiency for rapid identification in large-scale networks. However, their accuracy remains constrained by the quality of training samples, and their physical interpretability requires further enhancement. In summary, these methods exhibit distinct trade-offs in physical interpretability, computational efficiency, uncertainty quantification, and real-time applicability. Mechanistic models are ideal for high-confidence offline analysis; probabilistic methods excel in risk-based decision-making; data assimilation supports online dynamic tracking; and surrogate models are best suited for rapid screening and early warning. Future research should focus on integrating mechanistic models with data-driven approaches, advancing the application of deep learning and graph neural networks, developing real-time online source identification systems, and enhancing robustness across diverse network topologies and pollution scenarios. These advancements will provide stronger technical support for precise pollutant tracing, contaminant control, and informed decision-making in urban pipe networks.
Facing the dual challenges of the sustainable disposal of harvested cyanobacteria from eutrophic water bodies and the lack of bioavailable carbon for denitrification in sewage treatment plants with a low C/N ratio influent,this study aimed to develop and evaluate an integrated process for converting cyanobacterial biomass into an efficient liquid carbon source,thereby providing a synergistic solution for both waste valorization and enhanced nitrogen removal.To achieve this,cyanobacteria collected from Taihu Lake in China were first subjected to thermo-alkaline pretreatment to disrupt the cell walls.This was followed by mesophilic anaerobic fermentation to produce a volatile fatty acid(VFA)-rich fermentation broth.Due to the high ammonium nitrogen content,the broth was subsequently treated via vacuum thermal stripping,and the effects of pH,temperature,and stripping time on ammonia removal were systematically optimized.Finally,the denitrification performance of the de-ammoniated broth was assessed in both batch experiments and a continuous-flow reactor with activated sludge.The influences of the C/N ratio and pH were investigated,and the broth was compared with sodium acetate and glucose.Nitrogen species were monitored,and the denitrification potential(PDN)was calculated.The broth produced by anaerobic fermentation contained 15,582.00 mg/L of VFAs,with acetate accounting for 72.94%.The optimized vacuum thermal stripping process achieved 93.77%NH4+-N removal at pH 10.5,53 ℃,and 40 min,increasing the C/N ratio from 11.25 to 70.59,thus making the broth a suitable carbon source.Denitrification tests revealed that a C/N ratio of 6 and a pH of 7 were optimal,achieving 99.46%nitrate removal.Notably,the maximum nitrite accumulation was significantly lower than that observed in the sodium acetate system.The PDN value for the cyanobacteria broth(0.192 g N/g COD)exceeded that of sodium acetate(0.176 g N/g COD)and glucose(0.150 g N/g COD).Operation of the continuous-flow reactor indicated that when the carbon source in the fermentation broth had a C/N ratio≥5,the average nitrate removal efficiency remained stable at over 98.61%,and the average total nitrogen removal efficiency exceeded 82%,demonstrating stable and efficient denitrification performance.In conclusion,this study demonstrated that cyanobacterial biomass can be efficiently converted into a promising external carbon source for sewage denitrification through a sequential process comprising thermo-alkaline pretreatment,anaerobic fermentation,and vacuum thermal stripping.The fermentation broth exhibited better denitrification performance than commercial carbon sources like glucose and showed an advantage over sodium acetate in terms of lower nitrite accumulation and higher intrinsic carbon efficiency(PDN).This verifies the technical feasibility and effectiveness of the proposed strategy,offering a sustainable solution for both algal waste mitigation and enhanced nitrogen removal in sewage treatment.Moreover,this circular strategy transforms environmental waste into a valuable resource,potentially reducing the carbon footprint associated with both algal disposal and synthetic carbon production.The complex components in the broth appeared to promote more stable denitrification kinetics with reduced accumulation of intermediates compared to pure compounds,suggesting operational benefits for improved process stability.
Radical-dominated advanced oxidation processes often suffer from low selectivity and inefficient oxidant utilization in water treatment.In this work,the quasi-pyrolysis regulation of NiFe-BDC at 400 ℃ successfully transformed the sulfamethoxazole(SMX)degradation pathway during peroxymonosulfate(PMS)activation from a radical-driven process to a nonradical-dominated one,aiming to improve PMS utilization and achieve selective oxidation under environmentally relevant conditions.Specifically,SMX degradation and PMS decomposition were quantified by high-performance liquid chromatography(HPLC)and UV-Vis spectrophotometry.The temperature-dependent structural evolution of NiFe-BDC was characterized by SEM,TGA,XRD,FTIR,and Raman spectroscopy.Electron paramagnetic resonance(EPR)and quenching experiments were conducted to identify the dominant types of reactive oxygen species,while XPS combined with correlation analysis elucidated the electronic interactions between oxygen vacancies(OV)and Ni active sites.HPLC-MS was employed to determine the degradation intermediates and pathways,while the environmental stability was evaluated through ion interference,recyclability,and inductively coupled plasma(ICP)-based leaching tests.The NiFe-BDC-400/PMS process achieved 99.5%SMX removal with a PMS utilization efficiency of 8.49%,far exceeding that of pristine NiFe-BDC/PMS(SMX removal:26.1%,PMS efficiency:3.27%).Structural characterizations demonstrated that quasi-pyrolysis at 400 ℃ partially preserved the carbon framework while exposing abundant Ni and Fe sites,leading to the in-situ formation of uniformly dispersed NiO/NiFe2O4 nanoparticles on the carbon matrix.This configuration enhanced both the accessibility of active sites and the efficiency of charge transfer.Mechanistic investigations revealed that both OV and NIII species acted as the key active sites for singlet oxygen(1O2)generation.OV activated O2 to produce O2•-,contributing approximately one-third of the total 1O2,whereas inner-sphere complexation between NiIII and PMS produced SO5•-intermediates responsible for the remaining two-thirds.Moreover,OV facilitated charge transfer and induced the NiII→NiIII transformation,enriching high-valence NiIII centers and establishing intrinsic electronic coupling between the two active sites.This synergistic interaction enhanced 1O2 formation,which mediated the selective SMX degradation pathway.LC-MS identified nitro-substituted intermediates as the main degradation products,typically associated with 1O2-dominated pathways.The catalyst maintained high activity in the presence of common anions and humic acid,with the Ni leaching concentration remaining below 0.5 mg/L after three cycles,meeting the Chinese Class V water discharge standard.Overall,this study demonstrates that quasi-pyrolysis effectively regulates active sites and electron-transfer channels in NiFe-BDC,enabling a stable and selective nonradical oxidation pathway with high PMS utilization efficiency.Furthermore,the formation of NiFe2O4 nanoparticles endowed the catalyst with magnetic properties that facilitated recovery and reuse.These results highlight the need for further investigation into how OV density and electronic coupling quantitatively influence 1O2 generation.Future work may explore controlled defect engineering and heteroatom modulation to optimize the balance between stability and selectivity.The present findings provide mechanistic insights and a methodological reference for developing recyclable,OV-rich catalysts for sustainable pollutant removal and related environmental redox processes.
Recirculating aquaculture systems (RAS) have emerged as a key driver for the green upgrading of the aquaculture industry amid the global shift toward intensification and ecological sustainability. However, the widespread application of RAS still faces challenges such as the limited removal of characteristic pollutants (e.g., high-concentration inorganic nitrogen and trace organic compounds) and high operational energy consumption. From a systems engineering perspective, this review comprehensively discusses the coupling mechanisms and targeted regulation strategies of core water treatment units in RAS. For biological nitrogen removal, we evaluate autotrophic nitrogen removal pathways (e.g., Feammox) that potentially break through the efficiency bottlenecks of conventional nitrification-denitrification. Although these novel pathways demonstrate promising energy savings (up to a 44.7% reduction compared to complete nitrification-denitrification), their practical application remains largely at the laboratory scale, with unresolved challenges in reactor stability and process control under real aquaculture conditions. In addition, to address current difficulties in controlling biofilm thickness within existing processes, we propose that future optimizations should focus on achieving targeted enrichment of microbial communities and steady-state maintenance through filler modification and fluid shear stress regulation. Regarding pathogenic risk control, conventional chemical disinfection and antibiotics lack selectivity, thereby disturbing the system's ecology and exacerbating antimicrobial resistance. Cost-effective and environmentally friendly options like performic acid are therefore gaining attention. In contrast, precision technologies such as quorum quenching and gene silencing are theoretically attractive but face significant engineering challenges including activity maintenance and scaling costs in the near term. For multiphase separation, conventional mechanical micro-screens fail to intercept fine particles smaller than 30 μm, leading to excessive organic accumulation. Microbubble-driven dissolved air flotation offers a highly efficient alternative to overcome this physical interception limit, significantly reducing the biochemical oxygen demand on downstream biofilters. Meanwhile, advanced oxidation processes (AOPs), such as ozone and photoelectrocatalysis, effectively degrade refractory dissolved organics and trace antibiotics; however, they introduce an operational trade-off where excessive oxidation substantially increases energy demands and risks inducing the horizontal transfer of antibiotic resistance genes (ARGs). Thus, balancing oxidation dosages for both ecological safety and energy efficiency remains paramount. Looking forward, we outline the development trajectories of RAS toward system integration and digital operation and maintenance. We propose that under the Water-Energy-Food nexus framework, concrete pathways for technology implementation include: (i) hydrodynamic optimization assisted by computational fluid dynamics to reduce hydraulic energy consumption; (ii) artificial intelligence-enabled predictive water quality control to achieve feedforward regulation rather than lagged responses; (iii) the integration of renewable energy sources (e.g., solar and wind) to power electrolytic oxygen supply and temperature control, thereby lowering operational costs; and (iv) digital twin technologies that integrate real-time sensor data with mechanistic models for flow field reconstruction and early warning. Collectively, these cross-disciplinary innovations are driving the transformation of aquaculture models toward the deep fusion of data-driven and mechanistic approaches. This review aims to provide theoretical and technological support for achieving a low-carbon transition in aquaculture and the full-process steady-state operation of RAS.
Landfill leachate,a highly contaminated wastewater,poses significant threats to surrounding ecosystems if not properly treated.The biochemical-dual membrane process,typically consisting of a two-stage anoxic/oxic(A/O)membrane bioreactor(MBR)followed by nanofiltration(NF)and reverse osmosis(RO),has become a mainstream technology for leachate treatment in China due to its high efficiency and stable effluent quality.However,challenges such as high energy consumption and secondary concentrate pollution call for a comprehensive diagnostic approach beyond conventional indicator evaluations.To systematically assess operational efficiency and identify energy-saving potential,this study established a dual-perspective framework integrating material flow and energy consumption analyses.Focusing on a full-scale"two-stage A/O-MBR-NF-RO"process in an environmental park in South China,detailed carbon(C),nitrogen(N),and phosphorus(P)mass balance models were developed alongside an energy consumption structure model based on long-term monitoring and full-process sampling.The results indicated that the removal efficiencies of COD,total nitrogen(TN),and total phosphorus(TP)in the biological treatment unit reached 83.31%,84.11%,and 93.10%,respectively.The subsequent NF-RO system intercepted over 95%of the residual pollutants,ensuring that the final effluent consistently met discharge standards.Material balance analysis revealed that the balance rates for C and P exceeded 96%,demonstrating high data reliability;however,nitrogen exhibited a material loss of approximately 10%,primarily attributed to incomplete nitrification-denitrification caused by dissolved oxygen(DO)interference in the anoxic zones under a high reflux ratio.The specific electrical energy consumption for treating the leachate was 40.44 kWh/m3.Energy structure analysis showed that energy consumption in the biological treatment unit accounted for 53.37%of the total,primarily driven by aeration and mixing for biochemical reactions.In contrast,energy consumption in the advanced treatment unit constituted 93.75%of its subsystem's input,which was mainly consumed by the phase transfer of pollutants.Both units exhibited high energy intensity and low energy utilization efficiency.Based on these findings,targeted improvement strategies with quantitative metrics were proposed,including optimizing the nitrification recycle ratio from 1500%to 800%-1000%and maintaining the DO concentration in the anoxic zone below 0.2 mg/L.Furthermore,the partial integration of an energy-efficient Anammox-based process was recommended.Quantitative predictions indicated that implementing these measures could increase TN removal efficiency to 88%-90%,reduce the energy consumption of recycle pumps by approximately 30%,decrease aeration energy demand by about 60%,and eliminate the need for external carbon sources,ultimately achieving a 20%-30%reduction in the overall energy consumption of the biochemical unit.This study provides a scientific foundation for refined operational control and energy-saving retrofits in landfill leachate treatment plants.
Urban sewage pipelines are significant sources of greenhouse gas (GHG) emissions. However, the mechanisms underlying GHG production and release at the sediment-water interface, particularly in real-world sewage networks characterized by highly variable water quality, remain under-researched. This study aimed to clarify the dynamic patterns and driving mechanisms of these processes. From November to December 2024, sediment and overlying water samples were collected from representative sewage pipelines in Shenzhen. To systematically investigate the physicochemical and microbial processes at the sediment-water interface, a comprehensive approach was adopted, incorporating water quality analysis, headspace gas chromatography measurements of dissolved GHGs (CH4, CO2, N2O), 16S rRNA gene amplicon sequencing, and quantitative PCR. The results indicated that the dissolved CH4 concentration did not respond immediately to changes in water quality, but exhibited significant metabolic lag effects, demonstrating that CH4 production and release at the sediment-water interface follow a delayed response to environmental changes. In contrast, dissolved CO2 generation showed distinct patterns: in the overlying water, CO2 was positively correlated with several water quality indicators, such as chemical oxygen demand (COD), volatile fatty acids (VFAs), and nitrogen compounds, suggesting that its source is linked to various microbial and biochemical processes. In the sediment, CO2 was primarily associated with COD and VFAs, indicating production mainly through fermentation. N2O was detected only in pipeline sections with relatively higher dissolved oxygen (DO) levels, confirming that DO is a critical environmental factor governing the types of GHGs produced. Microbial analysis further highlighted that organic load is a central factor driving the differentiation of microbial community structure and the distribution of carbon metabolism pathways. High-organic-load conditions favored the enrichment of microbial communities specializing in the degradation of large organic molecules, with representative genera such as Syntrophorhabdus, leading to increased carbon flow toward CO2 production. Under moderate-organic-load conditions, microbial communities that utilize small-molecule substrates, including genera like Lactivibrio, became more abundant. These communities showed a significant positive correlation with the abundance of the methane-producing gene mcrA-1, which is associated with increased CH4 emissions in the overlying water. Microbial communities appeared to regulate the balance of CH4 and CO2 emissions through a "synergy-competition steady-state" mechanism, a dynamic regulation influenced by both the type and amount of organic matter present in the system. Finally, daily dynamic monitoring of GHG emission fluxes further confirmed that microbial community function plays a crucial role in regulating the timing and magnitude of GHG emissions.
Emerging biological contaminants(e.g.,pathogenic bacteria,antibiotic-resistant bacteria[ARB],antibiotic resistance genes[ARGs],and viruses)pose significant threats to ecosystems and public health due to their environmental persistence and potential for human infection.Unlike conventional chemical pollutants,these biological agents can replicate and transfer genetic information,rendering their control considerably more challenging.Wastewater treatment systems serve as major sinks and sources of these contaminants,necessitating a systematic evaluation of their removal efficiency and underlying mechanisms.This review systematically summarizes the performance of typical wastewater treatment processes in removing these emerging biological contaminants.Conventional secondary biological processes(e.g.,oxidation ditches and anaerobic/anoxic/oxic[A/A/O]systems)can achieve 2-5 log reduction of microorganisms through biodegradation and sludge adsorption;however,residual resistance genes and viruses remain detectable in the effluent.Membrane separation technologies effectively retain resistant bacteria and intracellular ARGs,but exhibit limited removal efficiency for extracellular ARGs and small viruses(e.g.,adenoviruses and noroviruses).Mechanistically,membrane separation relies primarily on physical retention without inactivating genetic material,whereas advanced oxidation processes(AOPs)generate reactive oxygen species(e.g.,hydroxyl radicals)that attack DNA structures,leading to cleavage and loss of gene function.Consequently,AOPs(e.g.,electro-Fenton and UV/O3)can achieve 5-7 log inactivation of pathogens and ARB,a 2-8 log degradation of ARGs,and a 2-4 log reduction of viruses,albeit with high operational costs and limited stability.The unique challenges posed by emerging biological contaminants stem from their proliferative capacity,low infectious doses,and the risk of horizontal gene transfer.Removal efficiency is governed by multiple factors,including water quality characteristics(e.g.,organic loading and ammonia nitrogen)and operational conditions(e.g.,temperature,pH,and hydraulic retention time).Additionally,coexisting pollutants such as antibiotics and heavy metals exert selective pressures,promoting the maintenance and dissemination of resistance through synergistic effects.Future research should prioritize establishing control lists for high-risk contaminants(e.g.,mobile ARGs,carbapenem resistance genes,and persistent viruses),developing synergistic multi-barrier strategies,and advancing smart,online monitoring technologies.Promising directions include online biosensors and soft sensors for real-time data acquisition,machine learning-based early-warning models,and digital twin-based adaptive control to dynamically optimize operation against influent fluctuations and shifting selective pressure.Overall,these advances will provide scientific support for the precise management of emerging biological contaminants in wastewater infrastructure.
Emissions of atmospheric pollutants such as methane(CH4),hydrogen sulfide(H2S),ammonia(NH3),and volatile organic compounds(VOCs)from wet waste treatment plants pose serious environmental and health risks.Conventional monitoring methods,which rely on fixed stations or manual sampling,often face challenges such as limited spatial coverage,delayed data collection,and operational safety hazards.To address these limitations,this study developed a gas monitoring system utilizing a multi-parameter sensor integrated with an unmanned aerial vehicle(UAV).Field monitoring was conducted at a wet waste treatment plant in Shanghai to assess pollutant distribution,vertical concentration gradients,and correlations with environmental factors across different functional areas.The results revealed that CH4 concentrations were significantly higher than those of other gases,reaching up to 1860 μg/m3 throughout the plant,making CH4 the primary contributor to the total emission load.In contrast,H2S and NH3 exhibited distinct point-source characteristics,with high concentrations closely associated with specific processing stages,including the kitchen waste workshop,the catering waste workshop,the drying workshop,and the unloading hall.Although VOC concentrations were relatively low,their complex composition presented potential environmental risks.Vertical profile monitoring showed that CH4 maintained high concentrations at all heights(1800-1900 μg/m3);NH3 tended to accumulate in the upper sections of the facility,while H2S concentrations gradually increased with height.Conversely,VOCs exhibited a relatively homogeneous vertical distribution across the plant.These diffusion trends suggest that NH3 could intensify odor pollution,while VOCs may enhance ozone formation and the generation of secondary organic aerosols.Correlation analysis indicated that humidity and air pressure were key environmental factors influencing the release and dispersion of these gases.Among these factors,humidity demonstrated the most significant influence on NH3 and VOC levels,suggesting its critical role in determining their atmospheric residence time and transport behavior.This study demonstrates the effectiveness of UAV-based sensing for detecting pollutant gases in complex industrial settings.By enabling precise monitoring and real-time data acquisition,this approach improves environmental risk assessment and supports the creation of targeted pollution control strategies for wet waste treatment plants.Our findings confirm that UAV-mounted systems provide significant advantages over conventional methods,specifically in terms of expanded spatial coverage and enhanced operational safety.Overall,this study highlights the transformative potential of UAV technology in environmental monitoring,offering critical insights for air quality management and evidence-based policymaking in waste treatment sectors.
With the continuous development of industries such as integrated circuits,wind power,and nuclear energy,the accumulation of spent thermosetting resin-based composites has emerged as an increasingly pressing environmental issue.Pyrolysis represents a promising technology for the resource recovery and value-added utilization of these wastes.To elucidate the pyrolysis characteristics of such wastes,this study systematically investigated the thermal decomposition behavior of spent ion-exchange resins based on a styrene-divinylbenzene backbone functionalized with sodium sulfonate groups.In addition,artificial intelligence models were developed to predict key pyrolysis parameters across different types of thermosetting resin-based composite wastes.The mass-loss behavior and heat flow evolution during pyrolysis were analyzed using thermogravimetry-differential scanning calorimetry(TG-DSC).The composition and distribution of gaseous and liquid products were further characterized by thermogravimetry-mass spectrometry(TG-MS)and pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS).The results indicate that the cleavage of the styrene-divinylbenzene crosslinked backbone occurred predominantly between 415 and 505 ℃.During this stage,the major pyrolysis products were styrene,ethylbenzene,and toluene—high-value chemicals that accounted for approximately 77%of the detected products at 455 ℃.At temperatures above 581 ℃,CH4,H2,and CO2 became the dominant gaseous products,forming combustible gases with potential for energy recovery,while a char yield of approximately 45%was observed.An increase in heating rate led to a higher temperature corresponding to the maximum mass-loss rate,a broader temperature range for backbone cleavage,and a higher overall mass-loss rate.These changes collectively influenced the temperature window and yield of volatile products as well as the amount of residual char.Therefore,the heating rate is a key process parameter for the efficient recovery of gas,liquid,and char products from spent ion-exchange resins.Furthermore,regression models and artificial neural network(ANN)models were developed by integrating experimental results from this study with literature data on various thermosetting resin-based wastes.Based on feature importance analysis using the F-test,these models were trained using the proximate and ultimate analyses of spent resins to predict their pyrolysis parameters,including onset temperature,temperature of maximum mass-loss rate,termination temperature,and overall weight loss.Among all modeling approaches,the ANN trained using the Levenberg-Marquardt algorithm exhibited the best predictive performance,achieving a coefficient of determination(R2)of 0.99 and a mean squared error of 0.0007.In future research,emphasis should be placed on improving the purity of gaseous and liquid products,enhancing the performance of char materials,expanding the experimental database,and employing more advanced machine learning techniques.These efforts will further improve the generalization and predictive accuracy of models,thereby providing more reliable guidance for optimizing pyrolysis processes toward the efficient synergistic recovery of gas,liquid,and char products from thermosetting resin-based composite wastes.
Biomass sorption-enhanced steam reforming is a promising route for the efficient conversion of biomass into H2-rich syngas by improving H2 selectivity and yield.This study investigates the design and performance of CaO-based hybrid materials for the sorption-enhanced steam reforming(SESR)of pine sawdust for H2 production.The hybrid materials were synthesized by incorporating different proportions of polymorphic Ca2SiO4 into CaO via a hydrothermal method followed by carbon-template removal.A homogeneous precursor solution containing Ni,Ca,and Si species was transferred into a 50 mL autoclave and subjected to hydrothermal treatment at 200 ℃ for 36 h.The obtained samples were then dried and calcined in air by heating to 800 ℃ at a rate of 5 ℃·min-1,followed by a holding period of 2 h.After carbon-template removal,hollow-shell sorbents were obtained.The CO2 sorption capacity and cyclic stability of the undoped sorbents were evaluated,and 10 wt.%Ni was subsequently introduced into the optimized sample.The results indicate that Ca2SiO4 loading significantly affects the balance between CO2 uptake and cyclic stability.Among the tested sorbents,the sample containing 10 wt.%Ca2SiO4 exhibited the best overall performance,achieving the highest cumulative CO2 uptake over 10 cycles while maintaining relatively high CaO utilization.Structural characterization revealed that the stabilization effect of Ca2SiO4 arises both from the dilution of the active phase and from its role as a spatially distributed inert framework between CaO grains.The results from X-ray diffraction(XRD),Brunauer-Emmett-Teller(BET)surface area analysis,and scanning electron microscopy with energy-dispersive X-ray spectroscopy(SEM-EDS)consistently suggest that Ca2SiO4 was uniformly dispersed within the hollow shell.This distribution physically separated adjacent CaO particles,restricted grain growth during repeated carbonation and calcination,and helped preserve pore volume and accessible surface area.Consequently,this microstructural stabilization effectively suppressed sintering and delayed the loss of fast-reaction sites.Furthermore,Ni incorporation reduced the CaO crystallite size and improved the utilization of active CaO while preserving the hollow-shell morphology.Upon further doping with 10 wt.%Ni,both H2 production and purity were significantly enhanced compared with those of the undoped sorbents.After 10 carbonation cycles,the Ni10Ca9Si1-HS sorbent maintained a H2 yield of 1.80 mmol/(gbm·gmat·min),representing only a 4.32%decrease from the initial value of 1.88 mmol/(gbm·gmat·min).Meanwhile,the H2 purity decreased slightly from 71.50%to 67.63%,demonstrating excellent cyclic stability.This study demonstrates that morphological control and the use of polymorphic stabilizers are crucial for improving the cyclic stability of catalyst-sorbent hybrid materials for sustainable H2 production from biomass,providing guidance for the structural design of highly efficient CaO-based hybrid materials.
