Molecular Insights into the Transformation of Dissolved Organic Matter in Landfill Leachate Concentrate during Biodegradation and Coagulation Processes Using ESI FT-ICR MS

Sequential hydrothermal liquefaction of lignocellulose-rich livestock manure: A new perspective on enhancing the production and quality of low-phenolic biocrude

The treatment and valorization of bulk livestock manure rich in lignocellulose demand efficient processing techniques. Hydrothermal liquefaction (HTL) has emerged as a promising approach for waste-to-energy conversion, effectively transforming lignocellulosic biomass into renewable biocrude. However, the advances in the utilization of HTL-derived biocrude have been hindered by its poor oil quality due to several factors including high phenolic compound content. This study focuses on enhancing the production and quality of low-phenolic biocrude via a sequential HTL process. The results revealed that sequential HTL achieved a high biocrude yield of 59.9%, with a concurrent reduction in phenolic content to 4.2%. This represents an 84.2% decrease in phenolic content compared to biocrude derived from direct HTL (280 ℃), achieving a tradeoff between biocrude yield and quality. Notably, GC-MS revealed that the biocrude produced through sequential HTL was enriched with fatty acids and esters accounting for 80.5%, contributing to the production of hydrocarbon fuels. Additionally, FT-ICR MS revealed that sequential HTL enhanced the biocrude quality and encouraged the production of light fuels. The petroleum fractionation analysis further revealed that sequential HTL-derived biocrude was more desirable in the downstream petroleum refining industry. The model compounds experiments revealed that phenols were likely to to be transferred to the oil phase at relatively high temperatures. Overall, it is the first study to elucidate the phenols removal mechanism and quality improvement of biocrude through the sequential HTL, demonstrating its potential for sustainable disposal and valorization of waste lignocellulosic biomass, and contributing to the development of renewable energy.

A molecular transformation study on the humus soil biomaterial promoting effects on the humification process in an anaerobic digestate composting system

Biopolymers with different biodegradability result in the asynchronous production of humus precursors during anaerobic digestate composting, which hinders humus formation. This study aimed to improve the humification process of digestate composting with Humus Soil Biomaterial (HSB) as ameliorant, and unveiled corresponding humification mechanisms. Results indicated that HSB containing pumice stone, phenolics, and native microbes promoted the humification process of digestate composting and contributed to higher aromaticity and humification degree. HSB provided additional phenolics as aromatic skeleton to polymerize with amine-N to rapidly form humic substances, which avoided the adverse effects of lignin rate-limiting decomposition on humification process while reducing mineralization of amine-N precursors. Pumice stone and native microbes in HSB improved microbial composition by increasing microbial abundance and diversity, respectively, which strengthened the interactions between microorganisms and organics to accelerate humus formation and composting maturity. This study proposed a novel rapid humification option for the resourceful treatment of anaerobic digestate.

Integrating dual-stage gas permeable membranes and humic acid recovery to optimize fenton oxidation of landfill leachate: Insights into full-process performance and DOM molecular-level transformation

This research introduces an innovative full-process treatment technology that integrates dual-stage gas permeable membranes (GPM) and humic acid (HA) recovery to enhance Fenton oxidation of landfill leachate (LFL). In terms of full-process performance, this integrated approach (LFL-GPM-HA (Fenton)) synergistically combines LFL concentration, ammonia recovery, HA recovery, purified water reclamation, and efficient Fenton oxidation, thereby achieving holistic minimization, detoxification, and resource recovery of LFL. Specifically, under the conditions of low-intensity aeration and a temperature gradient of 65-55-25 °C, the GPM achieved an ammonia recovery rate exceeding 96 %, while the LFL was concentrated by a factor of 4.72 within 12 h. During HA recovery at pH 2, the HA yield from the concentrated LFL reached 3.68 g/L, representing an 88.72 % increase compared to the raw LFL. Due to the significant consumption of bicarbonate alkalinity during the GPM process, the required dosage of H₂SO₄ per gram of HA recovered was reduced by 86.72 %. Under different dimensionless oxidant dosages, the LFL-GPM-HA (Fenton) demonstrated a significant improvement in COD removal efficiency compared to standalone Fenton oxidation. In terms of dissolved organic matter (DOM) molecular-level transformation, ESI FT-ICR-MS analysis showed a significant enhancement in the removal of CHOS and CHONS in LFL-GPM-HA (Fenton), with a concurrent reduction in the produced sulfurous byproducts. Additionally, the LFL-GPM-HA (Fenton) notably increased the frequency of decarboxylation, desulfurization, and dealkylation reactions. In terms of operational stability and economic feasibility, this integrated system demonstrates excellent long-term stability and robust membrane fouling-cleaning recovery properties, achieving LFL treatment at a cost of approximately 12.142 $/m³, which is significantly more cost-effective than conventional full-process advanced treatment technologies (20-30 $/m³). In conclusion, the findings offer a pathway for developing more efficient and cost-effective strategies for LFL management.

The nanoscale explanation of metal cations differences in enhancing the Fe(III) coagulation performance

Coagulation is a widely applied and important process for water treatment, and the development of improved coagulation reagents continues to be a practical objective. However, mechanisms guiding the development of composite coagulants remain insufficiently understood. In addressing this deficiency, this study has investigated the enhancement of conventional Fe(III) coagulation by composite coagulants that incorporate an additional metal salt (Me: Ca²⁺, Al³⁺, Ti⁴⁺, Zr⁴⁺), focusing on the mechanistic roles that Me constituents play in Fe-based coagulation. The effectiveness of composite coagulants was assessed through floc size and the removal of organics and phosphates. Results demonstrated that Me constituents enhance coagulation performances to varying extents, with Al³⁺ and Zr⁴⁺ showing the most significant improvements. FT-ICR MS analysis at the molecular scale reveals that additional Me facilitates the removal of humic acid, hydrophobic macromolecules, and highly aromatic organics containing polycarboxyl and secondary carbon structures. EXAFS results indicate that co-hydrolysis of Fe³⁺ with Me disrupts the formation of conventional ferrihydrite at the nanoscale of flocs and promotes the development of Fe-phosphate clusters. Me effectively reduces the corner- and edge-sharing coordination between FeO₆ octahedra within clusters, resulting in a more dispersed arrangement of FeO₆ polymers with available binding sites for the PO4 tetrahedron. The shortened Fe-P bond indicates that Me promotes a more compact link between FeO₆ octahedra and PO₄ tetrahedra. By revealing how cations in composite coagulants change the nanoscale structure of Fe flocs to affect macroscopic coagulation, this study enhances the understanding of metal ion interactions during co-hydrolysis and co-precipitation in natural systems.

Unraveling the roles of algal extracellular and intracellular organic matters in photosensitized degradation of tetracycline: Insights from triplet excited algal organic matters

The rapid growth of algae has significantly increased algae-derived organic matter (AOM) in surface water, and AOM has been shown to play an important role in the photosensitized degradation of emerging contaminants under natural sunlight. This study investigated the photosensitized degradation of tetracycline (TC) by different AOM, i.e. extracellular organic matter (EOM) and intracellular organic matter (IOM) obtained from Anabaena sp. and Scenedesmus quadricauda, with the focus on the role of the triplet excited states of AOM (3AOM*). Results showed that EOM achieved superior photosensitized degradation of TC (up to 73.2 %), which was 1.24-1.44 times higher than that by IOM (up to 57.4 %), mainly due to the higher content of photosensitive groups and cream-like substances in EOM, and the lower content of protein-like substances. It was further revealed that the 3AOM* contributed to 61.76 %-65.59 % of the photosensitized degradation of TC by enhancing demethylation, deamination, and ring-opening reactions, facilitating further conversion of TC to low-molecular-weight compounds while reducing toxic intermediates. This study unravels the essential role of algal EOM- and IOM-derived 3AOM* in photosensitized degradation of TC, offering new perspectives on antibiotic degradation in high-algal water environments.

Insight into the characterization of dissolved organic matter in shallow lakes with different trophic states and their net photo-generation capacity of reactive oxygen species

Reactive oxygen species (ROS) are ubiquitous in the aquatic environment, and they are closely related to several biogeochemical processes. Dissolved organic matter (DOM) is one of the main photosensitizers involved in the formation of ROS and it also serves as a sink for ROS by involving in scavenging, quenching, and antioxidant reactions. The net effect of these processes depends on the concentration, source, and composition of the DOM. Current studies have mainly focused on the steady-state concentration of reactive oxygen species ([ROS]ss) produced by the total DOM in lakes with different trophic states and ignored the net photo-generation capacity of ROS ([ROS]DOM, the net steady concentration of ROS generated per unit mass of DOM), leading to a vague understanding of the photochemical properties of DOM in aquatic systems, especially in shallow lakes with different trophic states. In this study, the optical composition of DOM was determined with optical characterization, such as specific UV-Vis and excitation-emission matrices with fluorescence regional integration (FRI-EEMs), and its molecular characteristics were analyzed by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results revealed that DOM in lakes with different trophic states had mixed endogenous and exogenous characteristics, accompanied by an increasing trend in endogenous characteristics with the increasing trophic state of lakes. Spectroscopic probes were used to detect the steady-state concentration of ROS and further calculate the [ROS]DOM, such as [3DOM*]DOM, [•OH]DOM, [1O2]DOM and [O2.-]DOM. The results indicated that the [ROS]DOM in lakes with light-eutrophic states was significantly higher than that in lakes with moderate-eutrophic and hyper-eutrophic states, which indicated that the DOM in lower trophic state lakes has a higher net photo-generation capacity of ROS. Pearson analysis results showed that [3DOM*]DOM, [•OH]DOM, [1O2]DOM and [O2.-]DOM had a significant positive correlation with lignin/CRAMs-like, aromatic, and tannin compounds, as well as the fluorescence components, fulvic- and humic-like substances and the UV-Vis indicator: SUVA254 revealed that DOM with higher humification and aromaticity had a higher net photo-generation capacity of ROS in different trophic state lakes. In addition, the molecular uniqueness of the DOM was dominated by lignin/CRAMs-like and aromatic compounds, which were positively correlated with [ROS]DOM, in the following order: [3DOM*]DOM > [•OH]DOM > [1O2]DOM > [O2.-]DOM. This study emphasizes the importance of focusing on the source, composition, and net photo-generation capacity of ROS by DOM, which would help evaluate the photochemical potential and other behaviors of DOM in lakes with different trophic states and provide guidance for the risk assessment of DOM input from different sources.

Simultaneous removal of hardness and organic matter from oilfield-produced water by microbially induced calcite precipitation

Oilfield-produced water (PW), the largest by-product of petroleum extraction, presents significant treatment challenges due to high concentrations of total dissolved solids, heavy metals, and organic compounds. In this study, a ureolytic bacterium Staphylococcus succinus J3, with efficient petroleum degradation and microbially induced calcite precipitation (MICP) capabilities, was screened for simultaneous removal of hardness ions and organic pollutants from PW. Strain J3 showed excellent removal of Ca2+ (95 %), organic contaminants (62 %), and heavy metals (100 % for As and Mn, 94 % for Cu, 71 % for Ba) in high salinity PW under low nutrient conditions. Mechanistic analysis revealed that the bacteria removed organic pollutants through biodegradation, and the biominerals generated by MICP further accelerated the removal of organic contaminants through adsorption. Meanwhile, molecular characterization via FT-ICR MS demonstrated the conversion of large organic molecules into smaller, less toxic compounds, facilitating the downstream treatment of PW. Furthermore, the ammonium by-product (NH4-N) from urea hydrolysis was efficiently recovered (83.73 %) as ammonium sulfate for agricultural production through Donnan dialysis (DD). This research presents a promising new approach for the pre-treatment of high-hardness organic wastewater and provides molecular-level insights into the mechanisms of organic matter removal, thus supporting the advancement and optimization of PW recycling technology.

Pre-treatment of excess sludge with sulfide-containing wastewater for composite electron donor formation to enhance denitrification

Utilizing the fermentation liquor of excess sludge (ES) for the denitrification process represents an effective strategy for the valorization of ES and achieving environmentally friendly denitrification. However, ES fermentation technologies require significant energy or chemical product inputs. The present study proposes a novel method utilizing sulfide-containing wastewater to pretreat ES for generating dissolved organic matter (DOM), with sulfides and DOM collectively forming a composite electron donor (S-ES-DOM). The introduction of S-ES-DOM enables the establishment of integrated autotrophic and heterotrophic denitrification (IAHD) process, achieving 100 % denitrification efficiency. Molecular analysis identified an increase in biodegradable components within S-ES-DOM, which were effectively utilized during the IAHD process. The functional genes associated with nitrate-sulfide-organic carbon metabolism and electron transfer exhibited upregulation. The mixotrophic microbial community enables flexible adoption of multiple metabolic pathways. This strategy simultaneously achieves low-cost ES valorization and low-carbon nitrate/sulfide removal through integrated nitrogen-sulfur-carbon metabolism.

Microbial processes dominate DOM degradation in alpine karst lakes over photochemical effects

Karst lakes, known as major inorganic carbon sinks, have recently been recognized as stable reservoirs of organic carbon. However, the mechanisms governing organic carbon stability in these systems remain poorly understood. In particular, the role of dissolved organic matter (DOM) degradation in shaping DOM composition and stability through photochemical and microbial pathways has not been well characterized. By combining fluorescence spectroscopy and FT-ICR-MS with microbial high-throughput sequencing, we conducted a controlled experiment on water- and sediment-derived DOM from a Jiuzhaigou karst lake, employing light-only, microbe-only, and combined treatments. While photochemical processes contribute to changes in DOM properties, microbial activity primarily dominates DOM degradation under photo-biological conditions. Specifically, photochemical processes primarily degraded aromatic compounds into aliphatic forms, resulting in reduced O/C ratios and increased H/C ratios. In contrast, microorganisms preferentially degraded compounds with low O/C and high H/C ratios. Notably, DOM containing nitrogen and sulfur exhibited higher biological reactivity, whereas CHO compounds were more likely to contribute to recalcitrant DOM pools. Furthermore, high-molecular-weight DOM restricted microbial diversity, whereas DOM with high O/C ratios facilitated more complex microbial networks. This study provides insights into the stability of water and sediment DOM and the mechanisms driving its degradation, offering a deeper understanding of C cycling in karst ecosystems.

Fate of dissolved organic matter in thermal hydrolysis pretreatment aided autothermal thermophilic aerobic digestion of high solid sludge

Thermal hydrolysis pretreatment (THP) combined with autothermal thermophilic aerobic digestion (ATAD) process is a novel technology to achieve rapid stabilization of high solid sludge. In this study, the molecular transformation pathway of dissolved organic matter (DOM) during THP-ATAD process was analyzed by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS). The findings indicated that the removal of volatile solids from sludge containing 15% total solids achieved a rate of 40.3% following 6 d of ATAD treatment, facilitated by the conducive biodegradation environment established during the THP stage. Specifically, THP removed 24.22% of the O/C compounds and produced 45.66% of reduced organic matter. ATAD process effectively harnessed these reduced compounds from the THP stage, leading to the mineralization of organic matter through deamination and oxidation reactions, which was reflected by a 59.84-fold increase in the humification index. This work provides in-depth mechanistic insights into the transformation of organic matter during high solid sludge stabilization.

Built-in electric field of Ag2Se thermoelectric effect activated persulfate for humic acid decomposition in water: Molecular transformation mechanism

Water temperature fluctuations directly impact pollutant decomposition processes in wastewater. Thermoelectric effect is considered an alternative to utilize these temperature variations for pollution control. In this study, a system for persulfate (PS) activation by Ag2Se thermoelectric catalyst under water temperature gradients (Ag₂Se/ΔT/PS) was developed for humic acid (HA) degradation in water. The experimental results showed that the Ag2Se/ΔT/PS system achieved a 90.7 % HA removal efficiency, outperforming both PS/ΔT (PS with temperature gradients) and Ag2Se/ΔT systems. Thermoelectric simulations indicated that Ag2Se generated an electric field under temperature variations, with higher current density at surface pores where polarized charges efficiently activated PS. Density functional theory calculations revealed that the thermoelectric effect of Ag2Se lowered the energy barriers for PS activation and ·SO4- generation. Different from ·OH-led decomposition of HA in the Ag₂Se/ΔT system, ·SO4- and ·OH dominated HA decomposition in the Ag₂Se/ΔT/PS system, and ¹O₂ also contributed this process. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that oxidation, decarboxylation, and sulfidation were the primary pathways driving HA degradation, leading to decreases in CHO-containing compounds and formation of S-rich byproducts. These findings highlighted the potential of thermoelectric catalysts in advancing water treatment technologies.

Exploring the chemical behaviors of dissolved organic matter to thermal hydrolysis temperature at the molecular level and its fate in anaerobic membrane bioreactor

Thermal hydrolysis pretreatment (THP) coupled with anaerobic membrane bioreactor (AnMBR) to enhance biomass bioconversion and methane production is a promising biotechnology. Herein, we shed light on the effects of THP temperature on molecular structure changes of dissolved organic matter of sewage sludge and food waste and its underlying mechanisms on hydrolysis, and methane bioconversion. The optimal THP condition was 160 °C, with a 1.87-times increase in soluble chemical oxygen demand (6.35 ± 0.09 g/L). FT-ICR MS indicated most of the compounds were biodegradable after 160 °C THP treatment, which had low aromatic or polarity, corresponding to protein/amino sugars and unsaturated hydrocarbon regions. Side reactions, like Maillard reaction and caramelization, induced the production of recalcitrant formulas with high hydrophobic and aromatic structure content (lower O/C and H/C values). These recalcitrant formulas attributed to carboxylic-rich alicyclic molecules (CRAM) exhibited poor biodegradability. For homologous DOMs sharing the same Kendrick mass defect (KMD), compounds exhibiting lower nominal oxidation state of carbon (NOSC), higher H/C ratios, and lower O/C ratios tend to exhibit greater biodegradability. Microbial analysis revealed that samples after THP pretreatment showed enhanced enrichment of both organic matter-degrading bacteria (e.g., Prolixibacteraceae, Anaerolineae and SJA-15) and methanogenic archaea (e.g., Methanosaeta, Methanobacterium, and Candidatus Methanofastidiosum) during the AD process. leading to a synergistic effect among microorganisms (such as Anaerolineae and Methanosaeta). Our findings highlight the interactive mechanism among molecular-level DOMs composition, microbial community succession, and AnMBR's performance, which provides a basis for an in-depth understanding of the THP strategy on anaerobic digestion.

The mechanism of alkali to inhibit the organics polymerization in improving the biodegradability of wastewater treated by heat/peroxydisulfate

High-temperature wastewaters can themselves activate peroxydisulfate (PDS) to remove aromatic contaminants via polymerization. This, however, may result in an insufficient carbon source for denitrification during biochemical treatment, and the formed polymers, without a proper reuse method, will be costly to handle as hazardous waste. This study demonstrates that the addition of NaOH can suppress the polymerization of aromatic contaminants, which is observed not only in simulated wastewater but also in actual coking wastewater (ACW). Taking phenol as an example, the formation of phenoxy radical (PhO•) through the reaction between SO4•- and phenol is the crucial step for phenol polymerization. The addition of NaOH can convert sulfate radicals (SO4•-) to hydroxyl radicals (HO•), and simultaneously, HO• can quickly consume PhO•. Both processes contribute to the inhibition of phenol polymerization. After treatment with heat/NaOH/PDS, the biodegradability of ACW is significantly enhanced with a relatively low carbon source loss (around 16%). Moreover, Fourier transform-ion cyclotron resonance mass spectrometry analysis indicates that the transformation of polyphenols to highly unsaturated and phenolic compounds is beneficial for the biodegradability improvement of ACW. Therefore, the NaOH/PDS system is an effective way to utilize waste heat and enhance the biodegradability of wastewater.

Molecular-level insights of microplastic-derived soluble organic matter and heavy metal interactions in different environmental occurrences through EEM-PARAFAC and FT-ICR MS

The interactions between microplastic-derived dissolved organic matter (MPs-DOM) and heavy metals (Cu, Pb, and Cd) regulate the complex environmental transport behavior of pollutants in terrestrial and aquatic environments. In this study, fluorescence excited emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) and electrospray ionization coupled Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) were employed to investigate the complexation mechanism of MPs-DOM with heavy metals, as well as the effects of different environmental occurrences of MPs-DOM on the transport behaviors of heavy metals in saturated porous medium. The findings demonstrated that MPs-DOM, particularly humic-like substances containing aromatic structures and various oxygen functional groups, could form stable complexes with heavy metals. This interaction significantly altered the transport capacity of Pb and Cu in saturated porous media. It is noteworthy that MPs-DOM in the free and deposited states in the environment may have markedly disparate effects on heavy metal transport. MPs-DOM in the free state may facilitate the co-migration of heavy metal ions in porous media, thereby enhancing the mobility of heavy metals. In contrast, sedimentary-state MPs-DOM can retain heavy metals in porous media and inhibit their migration through complexation with them.

Molecular composition of hydroxyl radical-resistant organics in municipal solid waste leachate

Although hydroxyl radicals (•OH) degrade organic pollutants nonselectively, their mineralization rate during the treatment of waste leachate biological treatment effluent (BTL) using Fenton or Fenton-like systems is not high, and the reason is unknown. In this study, we investigated three typical Fenton-like systems that act on dissolved organic matter (DOM) in BTL. We analyzed the molecular composition of DOM resistant to •OH, using ultrahigh resolution mass spectrometry. We find that DOM resistant to •OH is more oxidized, less unsaturated/aromatic, has higher molecular weights, and contains more unsaturated oxygen-containing functional groups than does DOM reactive to •OH. Resistant-DOM is further categorized into DOM derived by the action of •OH (DOMderived) and DOM initially present (DOMintrinsic), whose quantities account for approximately 20 % and 80 %, respectively. The DOMderived is gradually removed under extended reaction time, while DOMintrinsic is relatively unreactive with •OH and is always present in the treated effluent. Based on the molecular composition of resistant-DOM, we propose a method to increase the mineralization rate (up to 95 % TOC removal with only 5 mM persulfate). This study provides direct evidence for the first time that the presence of resistant-DOM (mainly stemming from DOMintrinsic) in BTL is an important reason for the unideal mineralization rate in the advanced treatment of Fenton or Fenton-like systems.

Deciphering the link between particulate organic matter molecular composition and lake eutrophication by FT-ICR MS analysis

Eutrophication has emerged as a significant environmental problem for global lakes. As an essential carrier of nutrients, particulate organic matter (POM) plays a vital role in the eutrophication process of these aquatic systems. In this study, POM from seven lakes with different trophic states in the middle and lower reaches of the Yangtze River (China) was characterized using carbon and nitrogen stable isotopes and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The aim was to elucidate the relationship between the source and molecular composition of POM during the eutrophication process of lakes. The results indicated that POM was mainly composed of autochthonous (62.7%) and allochthonous (37.3%) sources, with the contribution from autochthonous sources being more pronounced across the different sources. The POM formulas mainly consisted of the subclasses CHO, CHON, CHOP, CHOS, and CHONS. Notably, CHOP formulas had the highest proportion of labile formula compounds, according for 51.56%. The unsaturation, aromaticity, and oxidation of unique POM formulas gradually decreased with increasing trophic states. A significant positive correlation was observed between CHOP and the percentage of labile compounds (MLBL%) in unique POM formulas. The relative abundance of lipid and protein compounds of unique POM formulas showed a positive correlation with lake trophic states, which indicated that with the increase of lake trophic states, the content of autochthonous POM gradually increased. Herein, we inferred that with the intensification of lake eutrophication, the autochthonous POM increased, which was accompanied by a further increase of labile P-containing compounds in POM, thus leading to the increasing eutrophication process of lakes in the form of positive feedback. Overall, this investigation of POM at the molecular level illustrates the deep-rooted mechanism of frequent lake eutrophication. This is of great significance in understanding the fate of POM and effectively controlling lake eutrophication.

Transformation of dissolved organic matter in membrane-concentrated landfill leachate during Cu-Fenton-biological treatment

Membrane-concentrated landfill leachate (MCLL) is a highly concentrated and recalcitrant wastewater with remarkably low biodegradability. In this study, a multi-stage Cu-Fenton oxidation coupled with biological process was proposed for MCLL treatment. Importantly, Fourier transform ion cyclotron resonance mass spectrometry was employed to unveil the molecular transformation of dissolved organic matter (DOM) in MCLL during this integrated treatment process. The multi-stage Cu-Fenton process exhibited a high capacity to remove CHON compounds, resulting in a decrease in their relative abundance from 43% to 28%. Conversely, CHOS compounds displayed an increased relative abundance. For compound classes, the relative abundance of aliphatic/protein groups increased from 11% to 20%, whereas lignin/CRAM-like structures decreased from 36% to 12%, resulting significant improvement of the effluent biodegradability. The recalcitrant species during the multi-stage Cu-Fenton process were 300-400 Da lignin/carboxylic rich alicyclic molecules and tannins with high O/C ratios, which were effectively degraded by the subsequent biological treatment, particularly for the higher molecular weight organic fractions. This work provides new insights into the transformation characteristics of DOM in MCLL at a molecular level and offers technical guidance for the treatment of this refractory organic wastewater.

Identifying the Molecular Signatures of Organic Matter Leached from Land-Applied Biosolids via 21 T FT-ICR Mass Spectrometry

Intensification of wastewater treatment residual (i.e., biosolid) applications to watersheds can alter the amount and composition of organic matter (OM) mobilized into waterways. To identify novel tracers of biosolids, characterization of biosolids and their impacts on OM composition in recipient ecosystems is required. Here, water-soluble OM was leached from surface soils from Florida pastures with differing levels of biosolid amendment and an adjacent control site. The biosolid endmember was further constrained by extracting water-soluble OM from biosolids sourced from four Florida wastewater treatment facilities. Nontargeted analysis of organic molecules by negative-ion electrospray ionization 21 T Fourier transform ion cyclotron resonance mass spectrometry examined the molecular composition of soil and biosolid leachates and identified molecular formulas unique to these biosolids and biosolid amended soils. Overall, biosolids leachates were enriched in aliphatic (+16.3% relative abundance) and heteroatomic (+42.5% RA) formulas and depleted in aromatic formulas (-33.5% RA) compared to soil leachates. A subset of 297 molecular formulas were present only in biosolids and amended soil leachates (i.e., not present in control soil leachates), the vast majority of which contained nitrogen (66%) or sulfur (27%). The identification of these molecular formulas is a key step in identifying novel tracers of biosolids movement through impacted watersheds.

Molecular characteristics of dissolved organic phosphorus in watershed runoff: Coupled influences of land use and precipitation

Land use and precipitation are two major factors affecting phosphorus (P) pollution of watershed runoff. However, molecular characterization of dissolved organic phosphorus (DOP) in runoff under the joint influences of land use and precipitation remains limited. This study used Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to study the molecular characteristics of DOP in a typical P-polluted watershed with spatially variable land use and precipitation. The results showed that low precipitation and intense human activity, including phosphate mining and associated industries, resulted in the accumulation of aliphatic DOP compounds in the upper reaches, characterized by low aromaticity and low biological stability. Higher precipitation and widespread agriculture in the middle and lower reaches resulted in highly unsaturated DOP compounds with high biological stability constituting a higher proportion, compared to in the upper reaches. While, under similar precipitation, more aliphatic DOP compounds characterized by lower aromaticity and higher saturation were enriched in the lower reaches due to more influence from urban runoff relative to the middle reaches. Photochemical and/or microbial processes did result in changes in the characteristics of DOP compounds during runoff processes due to the prevalence of low molecular weight and low O/C bioavailable aliphatic DOP molecules in the upper reaches, which were increasingly transformed into refractory compounds from the upper to middle reaches. The results of this study can increase the understanding of the joint impacts of land use and precipitation on DOP compounds in watershed runoff.

Molecular-Level Insights into Recalcitrant Ozonation Products from Effluent Organic Matter

Wastewater ozonation is commonly employed to enhance the subsequent biodegradation of effluent organic matter (EfOM) and contaminants of concern. However, there is evidence suggesting the formation of recalcitrant ozonation products (OPs) from EfOM. To investigate the biodegradability of OPs we conducted batch biodegradation experiments using wastewater effluent ozonated with mass-labeled (18O) ozone. Molecular level analysis of EfOM was performed using reversed-phase liquid chromatography coupled with Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR MS) after 3 and 28 days in batch bioreactors. The use of mass labeling allowed for the unambiguous detection of OPs, with 2933 labeled OP features identified in the ozonated EfOM. Furthermore, employing polarity separation with LC facilitated the investigation of reactivity among different OP isomers. Overall, OPs exhibited a comparable proportion of recalcitrant and bioproduced molecular formulas when compared to the remaining EfOM, with 12% of OPs classified as recalcitrant and 17% bioproduced, indicating that OPs themselves are not inherently biodegradable. Additionally, recalcitrant OPs were found to be more polar based on the O/C ratios and retention time, in comparison to biodegradable OPs. Approximately one-third of the OP isomers displayed variations in their biodegradability, suggesting that studying the degradability of ozonated EfOM at the molecular formula level is heavily influenced by structural differences. Here, we offer unique insight into the biological transformation of EfOM after ozonation using labeled ozone and LC-FT-ICR MS analysis.

Response and roles of algal organic matter under copper stress: Spectral and mass spectrometry analysis

Eutrophication leads to various environmental issues, including pollution caused by the production of algal organic matter (AOM). Algae typically respond to environmental changes (e.g., light, temperature, copper [Cu(II)] concentration and pH) by regulating the production and release of different substances, thereby causing unpredictable effects on water quality. We explored the characteristics of AOM and the response mechanisms of algae under Cu(II) stress in the study, using fluorescence spectrum and high-resolution mass spectrometry (HRMS) analysis. The growth of Microcystis aeruginosa was inhibited under Cu(II) stress which was irreversible at Cu(II) concentration ≥ 2 μmol/L. Tryptophan- and humic-like fluorophores were important constituents of extracellular organic matter (EOM), and their contents increased with the addition of Cu(II), indicating that Cu(II) stimulates the production of tryptophan- and humic-like compounds. In addition, fulvic acid-like compounds in EOM were the main components binding to Cu(II) and were overproduced by algae under Cu(II) stress. It was found by HRMS at the molecular level that the formula numbers of EOM generally increased over inhibition time. Under 1 μmol/L Cu(II) stress, nitrogenous compounds (CHON formulae) were the primary AOM, accounting for 37.3-52.0 %. In addition, algae release a large amount of condensed aromatic structures to balance Cu(II) stress. This study provides a molecular-level analysis to explain the variation trends and response mechanisms of algae under various Cu(II) concentrations. The research methods are helpful for utilizing multiple advanced analysis methods to study algae growth and AOM release.

Photochemical behavior of extracellular polymeric substances in intimately coupled TiO2 photocatalysis and biodegradation system

Photosensitization of extracellular polymeric substances (EPS) in aqueous environments is significant for pollutants degradation, but the synergistic effects in intimately coupled photocatalysis and biodegradation (ICPB) remain unknown. In this study, the pivotal role of EPS photosensitization in the degradation of 17β-estradiol 3-sulfate (E2-3S) was investigated in ICPB. Protein and polysaccharide contents in loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) increased by 16.6, 9.15 and 9.2, 2.2 times compared with R1 (biofilm with light without photocatalyst) and R2 (biofilm with photocatalyst without light), respectively. During irradiation tests, more reactive species were generated in LB-EPS, and achieving 99.8 % degradation efficiency of E2-3S; tryptophan-like protein in EPS firstly to be converted, while the tyrosine-like protein underwent greater conversion; furthermore, hydrophilic molecules with O/C < 0.45 in EPS decreased and unsaturated molecules with H/C = 0.7-1.5 and O/C = 0-0.1 increased. This study reveals the photosensitization reaction of EPS in ICPB, which provides new insights for pollutants degradation.

Lignocellulose biodegradation to humic substances in cow manure-straw composting: Characterization of dissolved organic matter and microbial community succession

Composting, a sustainable practice, facilitates the biodegradation of organic waste, notably lignocellulosic biomass, into value-added humic substances. Despite its potential, the application of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to characterize dissolved organic matter (DOM) for assessing the changes in maturity during cow manure-straw composting is underexplored. Furthermore, the link between these changes, microbial community succession, and the biochemical pathways of humus formation is seldom investigated. This study leveraged ESI FT-ICR MS and metagenomic analysis to elucidate the molecular changes in DOM, identified key microbes in humus formation, and traced the humus formation pathway during composting. The results highlighted the crucial role of microorganisms such as Thermobifida, Luteimonas, Ascomycota, and Chloroflexi in accelerating the breakdown and transformation of plant biopolymers. Large molecular nitrogen compounds from cow manure-straw were converted into unsaturated, aromatic oxygen compounds, which resemble humic substances in their chemical properties. The ESI FT-ICR MS data revealed that humus formation occurred through a series of reactions, including protein deamination, lignin delignification, and decarbonylation. This research offered new light on strategies to enhance the stabilization and humification of cow manure-straw composting, contributing to more effective composting processes.

Unraveling the role of anthropogenic and hydrologic drivers with respect to the optical and molecular properties of dissolved organic matter and organic phosphorus in a P-contaminated river

Anthropogenic and hydrological drivers are key factors influencing the fate of dissolved organic matter (DOM) and dissolved organic phosphorus (DOP) in river runoff. However, how anthropogenic disturbances and hydrological conditions jointly affect the composition and characteristics of DOM and DOP in river runoff remains unclear. This study used fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and the stable water isotopes to interpret the chemical composition and properties of DOM and DOP as well as their linkages to anthropogenic disturbances and hydrological conditions in a typical P-contaminated tributary to the central Yangtze River. The results show in the wet season, the average abundance of humic-like components in DOM exceeded 60 %, while the average abundance of tryptophan-like components in DOM exceeded 50 % in the dry season. During the dry season, hydrological conditions had a greater impact on highly unsaturated DOM compounds compared to anthropogenic disturbances because a decrease in precipitation reduced the transport of terrestrial DOM into aquatic systems and increased water retention time in the river, promoting the production of unsaturated compounds from photochemistry. The effects of the two factors were similar in the wet season because active agricultural activities and intense precipitation jointly facilitated the entry of exogenous humics into the runoff, leading to the similar relative abundance of highly unsaturated DOM compounds associated with both factors. Anthropogenic disturbances had a greater impact on aliphatic DOM and DOP than hydrological conditions, which was associated with intense human activities in the watershed, such as phosphate mining, agricultural cultivation, and domestic sewage discharge. This study provides new knowledge about the composition, properties and underlying mechanisms of DOM and DOP in the P-contaminated watershed runoff.

Chemodiversity of dissolved organic matter and its association with the bacterial community at a zinc smelting slag site after 10 years of direct revegetation

Dissolved organic matter (DOM) plays a critical role in driving the development of biogeochemical functions in revegetated metal smelting slag sites, laying a fundamental basis for their sustainable rehabilitation. However, the DOM composition at the molecular level and its interaction with the microbial community in such sites undergoing long-term direct revegetation remain poorly understood. This study investigated the chemodiversity of DOM and its association with the bacterial community in the rhizosphere and non-rhizosphere slags of four plant species (Arundo donax, Broussonetia papyrifera, Cryptomeria fortunei, and Robinia pseudoacacia) planted at a zinc smelting slag site for 10 years. The results indicated that the relative abundance of lipids decreased from 18 % to 5 %, while the relative abundance of tannins and lignins/CRAM-like substances increased from 4 % to 10 % and from 44 % to 64 % in the revegetated slags, respectively. The chemical stability of the organic matter in the rhizosphere slag increased due to the retention of recalcitrant DOM components, such as lignins, aromatics, and tannins. As the diversity and relative abundance of the bacterial community increased, particularly within the Proteobacteria, there was better utilization of recalcitrant components (e.g., lignins/CRAM-like compounds), but this utilization was not invariable. In addition, potential preference associations between specific bacterial OTUs and DOM molecules were observed, possibly stimulated by heavy metal bioavailability. Network analysis revealed complex connectivity and strong interactions between the bacterial community and DOM molecules. These specific interactions between DOM molecules and the bacterial community enable adaptation to the harsh conditions of the slag environment. Overall, these findings provide novel insights into the transformation of DOM chemodiversity at the molecular level at a zinc smelting slag sites undergoing long-term revegetation. This knowledge could serve as a crucial foundation for developing direct revegetation strategies for the sustainable rehabilitation of metal smelting slag sites.

Analysis of dissolved organic matter characteristics in pharmaceutical wastewater via spectroscopy combined with Fourier-transform ion cyclotron resonance mass spectrometry

Studying the changes in organic matter and characteristic pollutants during the treatment of penicillin-containing pharmaceutical wastewater, which can be reflected by changes in dissolved organic matter (DOM), is crucial for improving the effectiveness of wastewater treatment units and systems. Herein, water quality indicators, spectroscopic methods, and Fourier-transform ion cyclotron resonance mass spectrometry were utilized to characterize the general molecular compositions and specific molecular changes in DOM during the treatment of typical penicillin-containing pharmaceutical wastewater, including in each of the influent, physicochemical treatment, biological treatment, oxidation treatment, and effluent stages. The influent exhibited a high organic matter content (concentration of dissolved organic carbon >10,000 mg·L-1), its DOM mainly contained protein- and lignin-like substances composed of CHON and CHONS molecules, and the relative intensity (RI) of penicillin was extremely high (RI = 0.220). Compared with the influent, the abundance of CHON and CHONS molecules detected after physicochemical treatment decreased by 70.3 % and 62.5 %, respectively, and the RI of penicillin decreased by 85.5 %. Biological treatment caused substantial changes in DOM components through oxidation, dealkylation, and denitrification reactions, accounting for 36.8 %, 28.9 %, and 14.8 % of the total identified reactions, respectively. Additionally, lignin-like substances were generated in large quantities, the overall humification level significantly increased, and the RI value increased for the penicillin intermediate, 6-aminopenicillanic acid (6-APA). Oxidation treatment effectively removed phosphorus-containing substances and some lignin-like substances produced by biological treatment; however, it was not effective in removing characteristic pollutants such as 6-APA. Such characteristic substances continued to be present in the effluent, and the DOM mainly contained protein- and humus-like substances, accounting for 30.8 % and 47.3 %, respectively. The study findings reveal the changes in organic matter and characteristic pollutants during the treatment of penicillin-containing wastewater from the perspective of the general molecular composition and specific molecular changes in DOM, providing support for further exploration of wastewater treatment mechanisms and improvements in treatment unit efficiency.

Enhanced coagulation for removal of dissolved organic nitrogen in water: A review

Wastewater treatment plants (WWTPs) meeting strict nutrient discharge regulations typically effectively remove inorganic nitrogen, leaving dissolved organic nitrogen (DON) as the main component of total nitrogen in the effluent. DON in treated effluent from both WWTPs and drinking water treatment plants (DWTPs) has the potential to induce eutrophication and contribute to the formation of nitrogenous disinfection byproducts (N-DBP). While numerous studies have investigated DON in different water sources, a limited number of studies have focused on its removal through enhanced coagulation. The variable removal efficiencies of dissolved organic carbon (DOC) and DON in treatment processes highlight the need for comprehensive research on enhanced coagulation for DON removal. Enhanced coagulation is a viable option for DON removal, but underlying mechanisms and influencing factors are still being actively researched. The effectiveness of enhanced coagulation depends on DON characteristics and coagulant properties, but knowledge gaps remain regarding their influence on treatment. DON is a complex mixture of compounds, with only a small fraction identified, such as proteins, degraded amino acids, urea, chelating agents, humic substances, and soluble microbial products. Understanding molecular-level characteristics of DON is crucial for identifying unknown compounds and understanding its fate and transformation during treatment processes. This review identifies knowledge gaps regarding enhanced coagulation process for DON removal, including the role of coagulant aids, novel coagulants, and pretreatment options. It discusses DON characteristics, removal mechanisms, and molecular-level transformation of DON during enhanced coagulation. Addressing these gaps can lead to process optimization, promote efficient DON removal, and facilitate safe water production.

Insights into the photoreactivity mechanisms of micro-sized rubber particles with different structure: The crucial role of reactive oxygen species and released dissolved organic matter

Micro-sized rubber particles (MRPs), as a significant component of tire wear particles (TWPs), increasingly garnered attention due to the potential ecological risks. However, the impact of photoaging of MRPs and the characteristics of the dissolved organic matter (DOM) derived from MRPs on the photoreactivity of co-existing pollutants is remain unclear. To bridge this knowledge gap, this study selected MRPs with different structure including butadiene rubber (BR), styrene butadiene rubber (SBR) and nitrile butadiene rubber (NBR) and took tetracycline (TC) as the target pollutant to firstly study potential effects of structural characteristics and active components of MRPs on TC photodegradation process under simulated sunlight irradiation. The results indicated that BR, NBR and SBR enhanced TC photodegradation to varying extents, with SBR having the most pronounced effect. This effect was attributed mainly to the high electron transport capacity and the generation of more triple excited DOM (3DOM*) of SBR, thereby producing more active species (•OH and 1O2) and significantly promoting TC photodegradation. Additionally, the unsaturated bonds and aromatic groups in MRPs-DOM was identified as another crucial factor influencing their photoreactivity. This study will provide a new perspective for understanding the potential ecological effects between MRPs and co-existing pollutants in the natural environment.

Feasibility of intimately coupled CaO-catalytic-ozonation and bio-contact oxidation reactor for heavy metal and color removal and deep mineralization of refractory organics in actual coking wastewater

Considering the challenges for both single and traditional two-stage treatments, advanced oxidation and biodegradation, in the treatment of actual coking wastewater, an intimately coupled catalytic ozonation and biodegradation (ICOB) reactor was developed. In this study, ICOB treatment significantly enhanced the removal of Cu2+, Fe3+, and color by 39 %, 45 %, and 52 %, respectively, outperforming biodegradation. Catalytic ozonation effectively breaking down unsaturated organic substances and high-molecular-weight dissolved organic matter into smaller, more biodegradable molecules. Compared with biodegradation, the ICOB system significantly increased the abundances of Pseudomonas, Sphingopyxis, and Brevundimonas by ∼ 96 %, ∼67 %, and ∼ 85 %, respectively. These microorganisms, possessing genes for degrading phenol, aromatic compounds, polycyclic aromatics, and sulfur metabolism, further enhanced the mineralization of intermediates. Consequently, the ICOB system outperformed biodegradation and catalytic ozonation treatments, exhibiting chemical oxygen demand removal rate of ∼ 58 % and toxicity reduction of ∼ 47 %. Overall, the ICOB treatment showcases promise for practical engineering applications in coking wastewater treatment.

Refractory COD removal from bio-treated paper wastewater using powdered activated coke adsorption technology with ozonation regeneration: Performance and molecular insights

The present study employed powdered activated coke (PAC) for the adsorptive removal of refractory COD from the bio-treated paper wastewater (BTPW). The adsorption reached equilibrium after 3 h, resulting in a decrease in the COD concentration from 98.9 mg L-1 in BTPW to 42.6 mg L-1 when utilizing a PAC dosage of 5 g L-1. The dominant fractions of dissolved organic matter in BTPW were hydrophilic acids (HIA), hydrophilic neutrals (HIN), and hydrophobic acids (HOA), accounting for 48.8%, 34.2%, and 17.0% of the total dissolved organic carbon, respectively. Three fractions were all predominantly composed of humic/fulvic acid-like substances, while the HOA fraction exhibited highest susceptibility to adsorption by PAC, followed by the HIA and HIN fractions. FT-ICR MS data revealed PAC preferentially adsorbed the unsaturated and oxygen-rich substances containing more carboxyl groups. Additionally, the spent PAC was regenerated through ozonation and subsequently utilized in the adsorption cycles. The regeneration was successfully conducted under an ozone concentration of 1 mg L-1 for a duration of 10 min, and the regeneration efficiency remained about 87.0% even after undergoing five-cycle of adsorption-regeneration. The findings of this study demonstrate that PAC adsorption is a viable and efficacious treatment technology for efficiently removing refractory COD from BTPW.

Molecular-level insights into dissolved organic matter and its variations of the full-scale processes in a typical petrochemical wastewater treatment plant

Petrochemical wastewater (PCWW) treatment poses challenges due to its unique and complex dissolved organic matter (DOM) composition, originating from various industrial processes. Despite the addition of advanced treatment units in PCWW treatment plants to meet discharge standards, the mechanisms of molecular-level sights into DOM reactivity of the upgraded full-scale processes including multiple biological treatments and advanced treatment remain unclear. Herein, we employ water quality indexes, spectra, molecular weight (MW) distribution, and Fourier transform ion cyclotron resonance mass spectrometry to systematically characterize DOM in a typical PCWW treatment plant including influent, micro-oxygen hydrolysis acidification (MOHA), anaerobic/oxic (AO), and micro-flocculation sand filtration-catalytic ozonation (MFSF-CO). Influent DOM is dominated by tryptophan-like and soluble microbial products with MW fractions 〈 1 kDa and 〉 100 kDa, and CHO with lignin and aliphatic/protein structures. MOHA effectively degrades macromolecular CHO (10.86 %) and CHON (5.24 %) compounds via deamination and nitrogen reduction, while AO removes CHOS compounds with MW < 10 kDa by desulfurization, revealing distinct DOM conversion mechanisms. MFSF-CO transforms unsaturated components to less aromatic and more saturated DOM through oxygen addition reactions and shows high CHOS and CHONS reactivity via desulfurization and deamination reactions, respectively. Moreover, the correlation among multiple parameters suggests UV254 combined with AImod as a simple monitoring indicator of DOM to access the chemical composition. The study provides molecular-level insights into DOM for the contribution to the improvement and optimization of the upgraded processes in PCWW.

Molecular-level transformations of dissolved black carbon in UV-based advanced oxidation processes

Dissolved black carbon (DBC) released from biochar, is an essential group in the dissolved organic matter (DOM) pool and is widely distributed in aquatic environments. In various advanced oxidation processes (AOPs), DBC exhibits enhanced free radical scavenging compared to typical DOM, attributed to its smaller molecular weight and more compacted aromatic structure; however, the molecular-level transformations of DBC in different AOPs, such as UV/H2O2, UV/PDS, and UV/Chlorine, remain unclear. This study employed a DBC derived from wheat biochar for experimentation. Characterization involved ultraviolet-visible (UV-Vis) spectroscopy and fluorescence excitation-emission-matrix (EEM) spectroscopy, revealing the transformation of DBC through diminished SUVA254 values and reduced intensity of three-dimensional fluorescence peaks. Further insights into the transformation were gained through Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). After each UV-AOP treatment, a conspicuous augmentation in the oxygen content of DBC was observed. The detailed oxygenation processes were elucidated through mass difference analysis, based on 23 types of typical reactions. Results indicated that oxygenation reactions were most frequently detected in all three UV-AOP treatments. Specifically, the hydroxylation (+O) predominated in UV/H2O2, while the di-hydroxylation (+2O) prevailed in UV/PDS. UV/Chlorine treatments commonly exhibited tri-hydroxylation (+3O), with the identification of 1194 Cl-BPs of unknown structures. This study contributes to a comprehensive understanding of the molecular transformations of DBC induced by various free radicals in different UV-AOP processes, leading to a better understanding of the different fates of DBC in UV-AOP processes. In addition, the identification of DBC as a precursor of by-products will also contribute to the understanding of how to inhibit the generation of by-products.

Natural Attenuation of Groundwater Uranium in Post-Neutral-Mining Sites Evidenced from Multiple Isotopes and Dissolved Organic Matter

Although natural attenuation is an economic remediation strategy for uranium (U) contamination, the role of organic molecules in driving U natural attenuation in postmining aquifers is not well-understood. Groundwaters were sampled to investigate the chemical, isotopic, and dissolved organic matter (DOM) compositions and their relationships to U natural attenuation from production wells and postmining wells in a typical U deposit (the Qianjiadian U deposit) mined by neutral in situ leaching. Results showed that Fe(II) concentrations and δ34SSO4 and δ18OSO4 values increased, but U concentrations decreased significantly from production wells to postmining wells, indicating that Fe(III) reduction and sulfate reduction were the predominant processes contributing to U natural attenuation. Microbial humic-like and protein-like components mediated the reduction of Fe(III) and sulfate, respectively. Organic molecules with H/C > 1.5 were conducive to microbe-mediated reduction of Fe(III) and sulfate and facilitated the natural attenuation of dissolved U. The average U attenuation rate was -1.07 mg/L/yr, with which the U-contaminated groundwater would be naturally attenuated in approximately 11.2 years. The study highlights the specific organic molecules regulating the natural attenuation of groundwater U via the reduction of Fe(III) and sulfate.

Mechanisms of conjugative transfer of antibiotic resistance genes induced by extracellular polymeric substances: Insights into molecular diversities and electron transfer properties

Dissemination of antibiotic resistance genes (ARGs) has become a critical threat to public health. Activated sludge, rich in extracellular polymeric substances (EPS), is an important pool of ARGs. In this study, mechanisms of conjugation transfer of ARGs induced by EPS, including tightly bound EPS (TBEPS), soluble EPS (SEPS), and loosely bound EPS (LBEPS), were explored in terms of molecular diversities and electron transfer properties of EPS. Conjugation transfer frequency was increased by 9.98-folds (SEPS), 4.21-folds (LBEPS), and 15.75-folds (TBEPS) versus the control, respectively. Conjugation-related core genes involving SOS responses (9 genes), membrane permeability (18 genes), intercellular contact (17 genes), and energy metabolism pathways (13 genes) were all upregulated, especially in the presence of TBEPS. Carbohydrates and aliphatic substances in SEPS and LBEPS were contributors to ARG transfer, via influencing reactive oxygen species (ROS) formation (SEPS) and ROS and adenosine triphosphate (ATP) production (LBEPS). TBEPS had the highest redox potential and greatest lability and facilitated electron transfer and alternated respiration between cells, thus promoting ARG transfer by producing ATP. Generally, the chemical molecular characteristics and redox properties of EPS facilitated ARG transfer mainly by influencing lipid peroxidation and ATP, respectively.

Co-hydrothermal carbonization of municipal sludge and agricultural waste to reduce plant growth inhibition by aqueous phase products: Molecular level analysis of organic matter

The organic matter molecular mechanism by which combined hydrothermal carbonization (co-HTC) of municipal sludge (MS) and agricultural wastes (rice husk, spent mushroom substrate, and wheat straw) reduces the inhibitory effects of aqueous phase (AP) products on pak choi (Brassica campestris L.) growth compared to HTC of MS alone is not clear. Fourier-transform ion cyclotron resonance mass spectrometry was used to characterize the differences in organic matter at the molecular level between AP from MS HTC alone (AP-MS) and AP from co-HTC of MS and agricultural waste (co-Aps). The results showed that N-bearing molecules of AP-MS and co-Aps account for 70.6 % and 54.2 %-64.1 % of all molecules, respectively. Lignins were present in the highest proportion (56.3 %-78.5 %) in all APs, followed by proteins and lipids. The dry weight of co-APs hydroponically grown pak choi was 31.6 %-47.6 % higher than that of the AP-MS. Molecules that were poorly saturated and with low aromaticity were preferentially consumed during hydroponic treatment. Molecules present before and after hydroponics were defined as resistant molecules; molecules present before hydroponics but absent after hydroponics were defined as removed molecules; and molecules absent before hydroponics but present after hydroponics were defined as produced molecules. Large lignin molecules were broken down into more unsaturated molecules, but lignins were the most commonly resistant, removed, and produced molecules. Correlation analysis revealed that N- or S-bearing molecules were phytotoxic in the AP. Tannins positively influenced the growth of pak choi. These results provide new insights into potential implementation strategies for liquid fertilizers produced from AP arising from HTC of MS and agricultural wastes.

Interfacial interactions between minerals and organic matter: Mechanisms and characterizations

Minerals and organic matter are essential components of soil, with minerals acting as the "bone" and organic matter as the "skin". The interfacial interactions between minerals and organic matter result in changes in their chemical composition, structure, functional groups, and physical properties, possessing a significant impact on soil properties, functions, and biogeochemical cycles. Understanding the interfacial interactions of minerals and organic matter is imperative to advance soil remediation technologies and carbon targets. Consequently, there is a growing interest in the physicochemical identification of the interfacial interactions between minerals and organic matter in the academic community. This review provides an overview of the mechanisms underlying these interactions, including adsorption, co-precipitation, occlusion, redox, catalysis and dissolution. Moreover, it surveys various methods and techniques employed to characterize the mineral-organic matter interactions. Specifically, the up-to-date spectroscopic techniques for chemical information and advanced microscopy techniques for physical information are highlighted. The advantages and limitations of each method are also discussed. Finally, we outline future research directions for interfacial interactions and suggests areas for improvement and development of characterization techniques to better understand the mechanisms of mineral-organic matter interactions.

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

Landfill leachate a potential challenge towards sustainable environmental management

The increasing amount of waste globally has led to a rise in the use of landfills, causing more pollutants to be released through landfill leachate. This leachate is a harmful mix formed from various types of waste at a specific site, and careful disposal is crucial to prevent harm to the environment. Understanding the physical and chemical properties, age differences, and types of landfills is essential to grasp how landfill leachate behaves in the environment. The use of Sustainable Development Goals (SDGs) in managing leachate is noticeable, as applying these goals directly is crucial in reducing the negative effects of landfill leachate. This detailed review explores the origin of landfill leachate, its characteristics, global classification by age, composition analysis, consequences of mismanagement, and the important role of SDGs in achieving sustainable landfill leachate management. The aim is to provide a perspective on the various aspects of landfill leachate, covering its origin, key features, global distribution, environmental impacts from poor management, and importance of SDGs which can guide for sustainable mitigation within a concise framework.

Unraveling the characteristics of dissolved organic matter removed by aluminum species based on FT-ICR MS analysis

Given the complexity of dissolved organic matter (DOM) and its interactions with coagulant chemicals, the mechanisms of DOM removal by aluminum (Al) coagulants remains a significant unknown. In this study, six test waters containing DOM with molecular weight (MW, <1 kDa, 1-10 kDa and >10 kDa) and hydrophobicity (hydrophilic, transphilic and hydrophobic) were prepared and coagulated with Al0, Al13 and Al30. The molecular-level characteristics of DOM molecules that were removed or resistant to removal by Al species were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that at the molecular level, saturated and reduced tannins and lignin-like compounds containing abundant carboxyl groups exhibited higher coagulation efficiency. Unsaturated and oxidized lipids, protein-like, and carbohydrates compounds were relatively resistant to Al coagulation due to their higher polarity and lower content of carboxyl groups. Al13 removed molecules across a wider range of molecular weights than Al0 and Al30, thus the DOC removal efficiency of Al13 was the highest. This study furthers the understanding of interactions between Al species and DOM, and provides scientific insights on the operation of water treatment plants to improve control of DOM.

Anaerobic digestion of process water from hydrothermal treatment processes: a review of inhibitors and detoxification approaches

Integrating hydrothermal treatment processes and anaerobic digestion (AD) is promising for maximizing resource recovery from biomass and organic waste. The process water generated during hydrothermal treatment contains high concentrations of organic matter, which can be converted into biogas using AD. However, process water also contains various compounds that inhibit the AD process. Fingerprinting these inhibitors and identifying suitable mitigation strategies and detoxification methods is necessary to optimize the integration of these two technologies. By examining the existing literature, we were able to: (1) compare the methane yields and organics removal efficiency during AD of various hydrothermal treatment process water; (2) catalog the main AD inhibitors found in hydrothermal treatment process water; (3) identify recalcitrant components limiting AD performance; and (4) evaluate approaches to detoxify specific inhibitors and degrade recalcitrant components. Common inhibitors in process water are organic acids (at high concentrations), total ammonia nitrogen (TAN), oxygenated organics, and N-heterocyclic compounds. Feedstock composition is the primary determinant of organic acid and TAN formation (carbohydrates-rich and protein-rich feedstocks, respectively). In contrast, processing conditions (e.g., temperature, pressure, reaction duration) influence the formation extent of oxygenated organics and N-heterocyclic compounds. Struvite precipitation and zeolite adsorption are the most widely used approaches to eliminate TAN inhibition. In contrast, powdered and granular activated carbon and ozonation are the preferred methods to remove toxic substances before AD treatment. Currently, ozonation is the most effective approach to reduce the toxicity and recalcitrance of N and O-heterocyclic compounds during AD. Microaeration methods, which disrupt the AD microbiome less than ozone, might be more practical for nitrifying TAN and degrading recalcitrant compounds, but further research in this area is necessary.

Bioinspired stormwater control measure for the enhanced removal of truly dissolved polycyclic aromatic hydrocarbons and heavy metals from urban runoff

Stormwater harvesting (SWH) addresses the UN's Sustainable Development Goals (SDGs). Conventional stormwater control measures (SCMs) effectively remove particulate and colloidal contaminants from urban runoff; however, they fail to retain dissolved contaminants, particularly substances of concern like polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs), thereby hindering the SWH applicability. Here, inspired by protein folding in nature, we reported a novel biomimetic SCM for the efficient removal of dissolved PAHs and HMs from urban runoff. Lab-scale tests were conducted together with a more mechanistic investigation on how the contaminants were removed. By integrating hydrophobic organic chains with low-cost hydrophilic flocculant matrixes, our biomimetic flocculants achieved a 1.4-9.5 times removal of all detected dissolved PAHs and HMs, while enhancing the removal of a wide-spectrum of particulate and colloidal contaminants, compared to existing SCMs. Ecotoxicity, as indicated by newborn Daphnia magna as experimental organisms, was reduced from "acute toxicity" of the original runoff sample (toxic unit of ∼2.6) to "non-toxicity" (toxic unit < 0.4) of the treated water. The improved performance is attributed to the protein-folding-like features of the bioinspired flocculants providing: (i) stronger binding to PAHs (via hydrophobic association) and HMs (via coordination), and (ii) the ability of spontaneous aggregation. The bio-inspired approach in this work holds strong promise as an alternative or supplementary component in SCM systems, and is expected to contribute to sustainable water management practices in relation to SDGs.

Molecular transformation of dissolved organic matter in manganese ore-mediated constructed wetlands for fresh leachate treatment

The organic matter (OM) and nitrogen in Fresh leachate (FL) from waste compression sites pose environmental and health risks. Even though the constructed wetland (CW) can efficiently remove these pollutants, the molecular-level transformations of dissolved OM (DOM) in FL remain uncertain. This study reports the molecular dynamics of DOM and nitrogen removal during FL treatment in CWs. Two lab-scale vertical-flow CW systems were employed: one using only sand as substrates (act as a control, CW-C) and the other employing an equal mixture of manganese ore powder and sand (experimental, CW-M). Over 488 days of operation, CW-M exhibited significantly higher removal rates for chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and dissolved organic matter (represented by dissolved organic carbon, DOC) at 98.2 ± 2.5%, 99.2 ± 1.4%, and 97.9 ± 1.9%, respectively, in contrast to CW-C (92.8 ± 6.8%, 77.1 ± 28.1%, and 74.7 ± 9.5%). The three-dimensional fluorescence excitation-emission matrix (3D-EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses unveiled that the influent DOM was predominantly composed of readily biodegradable protein-like substances with high carbon content and low unsaturation. Throughout treatment, it led to the degradation of low O/C and high H/C compounds, resulting in the formation of DOM with higher unsaturation and aromaticity, resembling humic-like substances. CW-M showcased a distinct DOM composition, characterized by lower carbon content yet higher unsaturation and aromaticity than CW-C. The study also identified the presence of Gammaproteobacteria, reported as Mn-oxidizing bacteria with significantly higher abundance in the upper and middle layers of CW-M, facilitating manganese cycling and improving DOM removal. Key pathways contributing to DOM removal encompassed adsorption, catalytic oxidation by manganese oxides, and microbial degradation. This study offers novel insights into DOM transformation and removal from FL during CW treatment, which will facilitate better design and enhanced performance.

Dissolved organic nitrogen is a key to improving the biological treatment potential of landfill leachate

Biological treatment is one of the most promising efficient, low-carbon and affordable approaches for the treatment of recalcitrantly degradable wastewater, such as landfill leachate. However, even the macroscopic molecular level analysis of dissolved organic matter (DOM) is limiting to the enhancement of biological treatment efficacy, and there is an urgent need for deeper exploration of DOM to gain insights into the key constraining substances. In the present study targeting at piercing leachate organic at molecular level, nitrogen-containing dissolved organic matter (DOMN) was identified to be the bottleneck that govern the biotreatment potential. The conclusion was made based on two series of experiments that compared the same anoxic-aerobic membrane bioreactor process (A process) operated stably at different regions, and compared with C process that coupling A process with a circulation aeration membrane bioreactor to improve aeration efficiency. The results confirmed that the relative abundance of DOMN was absolutely dominant among the three categories of DOM in all biologically treated samples, contributing to 60.36 %-65.81 % in removed-DOM, 60.33 %-70.95 % in refractory-DOM and 63.14 %-71.36 % in derived-DOM. Specifically, the high latitude A process had much lower DOMN removal rate than the low latitude A process (p < 0.05) and much higher refractory and derivatization rates than the low latitude A process (p < 0.05). DOM had similar results. No statistically significant differences were observed in the proportion of the three categories of DOM (DOMN), the elements composition, and the subcategory composition of the C process compared to the A process, in which the DOM (DOMN) derivation rate of NEC1-C (31.92 % and 33.41 %) was much higher than that of NEC1-A (20.88 % and 22.19 %). However, the AIwa and AImodwa of the derived-DOM (DOMN) were significantly higher in the C process than in the A process, which implied that excessive aeration did not enhance the biological treatment potential of the A process, but instead led to the proliferation of microorganisms and the secretion of extracellular polymer substances, which resulted in the derivation of more complex compounds. The results of the correlation analysis indicated that there were some regional differences in the molecular information of DOMN driven by climate temperature. In addition, it was worth mentioning that the nominal oxidation state of carbon (NOSCwa) of derived-DOMN in different regions of A process was noticeably higher than the corresponding DOM (p < 0.0001), implying that the derived-DOMN were still highly biodegradable, in other words, there was still great room for improving the biological treatment potential of landfill leachate. The present study provided a deeper insight and analysis of landfill leachate at the molecular level (DOMN) through multiple practical engineering cases, with a view to providing a theoretical basis for efficient optimization of biological treatment.

Phage lysate can regulate the humification process of composting

Phages play a crucial role in orchestrating top-down control within microbial communities, influencing the dynamics of the composting process. Despite this, the impact of phage-induced thermophilic bacterial lysis on humification remains ambiguous. This study investigates the effects of phage lysate, derived explicitly from Geobacillus subterraneus, on simulated composting, employing ultrahigh-resolution mass spectrometry and 16S rRNA sequencing techniques. The results show the significant role of phage lysate in expediting humus formation over 40 days. Notably, the rapid transformation of protein-like precursors released from phage-induced lysis of the host bacterium resulted in a 14.8 % increase in the proportion of lignins/CRAM-like molecules. Furthermore, the phage lysate orchestrated a succession in bacterial communities, leading to the enrichment of core microbes, exemplified by the prevalence of Geobacillus. Through network analysis, it was revealed that these enriched microbes exhibit a capacity to convert protein and lignin into essential building blocks such as amino acids and phenols. Subsequently, these components were polymerized into humus, aligning with the phenol-protein theory. These findings enhance our understanding of the intricate microbial interactions during composting and provide a scientific foundation for developing engineering-ready composting humification regulation technologies.

Molecular insights into the bonding mechanisms between selenium and dissolved organic matter

Natural organic matter (NOM) plays a critical role in the mobilization and bioavailability of metals and metalloids in the aquatic environment. Selenium (Se), an environmental contaminant of aquatic systems, has drawn increasing attention over the years. While Se is a vital micronutrient to human beings, animals and plants, excess Se intake may pose serious long-term risks. However, the interaction between Se and dissolved organic matter (DOM) remains relatively unexplored, especially the reaction mechanisms and interactions of specific NOM components of certain molecular weight and the corresponding functional group change. Herein, we report an investigation on the interactions between Se and DOM by focusing on the mass distribution profile change of operationally defined molecular weight fractions of humic acid (HA) and fulvic acid (FA). The results showed that across all molecular weights studied, HA fractions were more prone to enhanced aggregation upon introduction of Se into the system. For FA, the presence of Se species results in aggregation, dissociation, and redox reactions with the first two being the major mechanisms. Total organic carbon analysis (TOC), UV-vis spectroscopy (UV-vis), and Orbitrap MS data showed that [10, 30] kDa MW fraction had the largest aromatic decrease (CRAM-like, lignin-like and tannin-like) upon addition of SeO2 via dissociation as the dominant mechanism. Fourier transform infrared spectroscopy (FT-IR) revealed that Se based bridging or chelation of functional groups from individual DOM components through hydrogen bonding in the form of SeO⋯H and possibly Se⋯H and/or attractive electrostatic interactions lead to aggregated DOM1⋯Se⋯DOM2. It was concluded from two-dimensional correlation analyses of excitation emission matrix (EEM) and FT-IR that the preferred Se-binding follows lipid ➔ peptide ➔ tannin ➔ aromatic functionalities. These results provide new understanding of Se interactions with various NOM components in aquatic environments and provide insight for Se assessing health risk and/or treatment of Se contaminated water.

Arsenic biogeochemical cycling association with basin-scale dynamics of microbial functionality and organic matter molecular composition

Geogenic arsenic (As)-contaminated groundwater is a sustaining global health concern that is tightly constrained by multiple interrelated biogeochemical processes. However, a complete spectrum of the biogeochemical network of high-As groundwater remains to be established, concurrently neglecting systematic zonation of groundwater biogeochemistry on the regional scale. We uncovered the geomicrobial interaction network governing As biogeochemical pathways by merging in-field hydrogeochemical monitoring, metagenomic analyses, and ultrahigh resolution mass spectrometry (FT-ICR MS) characterization of dissolved organic matter. In oxidizing to weakly reducing environments, the nitrate-reduction and sulfate-reduction encoding genes (narGHI, sat) inhibited the dissolution of As-bearing iron minerals, leading to lower As levels in groundwater. In settings from weakly to moderately reducing, high abundances of sulfate-reduction and iron-transport encoding genes boosted iron mineral dissolution and consequent As release. As it evolved to strongly reducing stage, elevated abundance of methane cycle-related genes (fae, fwd, fmd) further enhanced As mobilization in part by triggering the formation of gaseous methylarsenic. During redox cycling of N, S, Fe, C and As in groundwater, As migration to groundwater and immobilization in mineral particles are geochemically constrained by basin-scale dynamics of microbial functionality and DOM molecular composition. The study constructs a theoretical model to summarize new perspectives on the biogeochemical network of As cycling.

Treatment of landfill leachate by coagulation: A review

Landfill leachate is a seriously polluted and hazardous liquid, which contains a high concentration of refractory organics, ammonia nitrogen, heavy metals, inorganic salts, and various suspended solids. The favorable disposal of landfill leachate has always been a hot and challenging issue in wastewater treatment. As one of the best available technologies for landfill leachate disposal, coagulation has been studied extensively. However, there is an absence of a systematic review regarding coagulation in landfill leachate treatment. In this paper, a review focusing on the characteristics, mechanisms, and application of coagulation in landfill leachate treatment was provided. Different coagulants and factors influencing the coagulation effect were synthetically summarized. The performance of coagulation coupled with other processes and their complementary advantages were elucidated. Additionally, the economic analysis conducted in this study suggests the cost-effectiveness of the coagulation process. Based on previous studies, challenges and perspectives met by landfill leachate coagulation treatment were also put forward. Overall, this review will provide a reference for the coagulation treatment of landfill leachate and promote the development of efficient and eco-friendly leachate treatment technology.

Enhanced landfill leachate treatment performance by adsorption-assisted membrane distillation

Membrane fouling and high-strength membrane concentrate production are two limitations of membrane distillation (MD) for landfill leachate treatment. In this study, activated carbon- and biochar-based adsorption processes were integrated into a conventional MD system to overcome these limitations. The organic matter fractionations of the leachate were thoroughly investigated during the treatment. Membrane-reversible and irreversible foulants differed remarkably from the inlet leachate in the non-assisted MD system. Specifically, reversible foulants were characterized by a high abundance of humic-like fluorescent components, high-molecular-weight humic-size constituents, peptides, and unsaturated compounds. In contrast, irreversible foulants were enriched with fulvic-like fluorescent components, low-molecular-weight neutrals, unsaturated compounds, and polyphenols. The adsorption-based pre-treatment effectively removed foulant precursors from landfill leachate, with a relatively higher (20%) adsorption performance for specific biochar used in this study than for activated carbon. Compared with the non-assisted MD system, the biochar-assisted MD system showed improved performance, achieving 40% overall membrane flux recovery, 42% higher filtration fluxes, and 53% lower concentrate production. In addition, a 15% higher removal of irreversible foulants was observed as compared to the reversible foulants, which can potentially increase the membrane lifespan. This study demonstrates the effectiveness of an adsorption-assisted MD system supported by increased filtration, membrane fouling alleviation, and low-strength leachate concentrate generation.

Deciphering fluorescent and molecular fingerprint of dissolved organic matter leached from microplastics in water

Despite extensive research into the presence and behavior of microplastics (MPs) in the environment, limited attention has been given to the investigation of the characteristics of dissolved organic matter (DOM) that leaches from MPs (MPs-DOM). Herein, two frequently encountered plastic particles in aquatic environments, specifically polyethylene terephthalate (PET)- and polyethylene (PE)-MPs, were subjected to leaching in the aquatic settings for seven days, both in the absence of light and under UV irradiation. Measurements of dissolved organic carbon (DOC) indicated that UV exposure enhanced the liberation of DOM from PET-MPs, while PE-MPs did not exhibit such leaching. After UV treatment for seven days, the DOM released from PET-MPs increased by 25 times, while that from PE-MPs remained almost unchanged. Then, the molecular diversity and the evolving formation of DOM originating from different MPs were comprehensively analyzed with fluorescence excitation-emission matrix (EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Specifically, both PET- and PE-DOM exhibited three fluorescence signatures, with the predominant C1 (tryptophan-like) component showing a decline in PET-DOM and a rise in PE-DOM during aging. The FT-ICR-MS analysis unveiled that PET-DOM grew more recalcitrant under UV exposure, while PE-DOM became increasingly labile. In brief, UV irradiation influences MPs-DOM release and transformation differently, depending on the plastic composition. This highlights the significance of exploring MPs-DOM transformation in securing environmental safety.

Wastewater from natural gas Cansolv desulfurization process: Comprehensive characterization and effective removal of organic compounds

The wastewater generated by the solvent amine desulfurization process in natural gas purification plants is characterized by its recalcitrant organic compounds and high salinity. Without effective treatment, it has the potential to inflict severe environmental harm. The composition of organic matter, however, exerts a profound influence on the outcomes of oxidation processes. To rectify the limitations associated with indiscriminate oxidation that yields suboptimal results, this investigation meticulously performed a molecular-level analysis of organic matter. Based on the organic matter composition in the influent, this study compared the treatment efficacy of three oxidation processes and determined O3/H2O2-Fenton as the optimal joint approach. After O3/H2O2 oxidation, long-chain unsaturated organic compounds (C > 40,DBE > 20) underwent degradation into short-chain aldehydes and low-molecular-weight fatty acids, with priority given to reactions involving CC, CO, and OH over CH reactions. Subsequent Fenton oxidation effectively removed the refractory organics (CHOS, CHONS) and significantly reduced the diversity of organic matter (from 7730 to 4237). The carboxylation, demethylation, and dehydrogenation reactions further facilitated the removal of recalcitrant organic compounds. In light of these findings, this study substantiates that the conversion of extended-chain unsaturated compounds into abbreviated-chain saturated compounds within the system through O3/H2O2 oxidation significantly enhances the subsequent efficacy of Fenton oxidation in organic matter removal. These insights offer valuable perspectives for the efficient remediation of analogous high-salinity organic wastewater scenarios.