Search Results (62)

Deoxygenation in marine ecosystems has received increasing attention. The variation of dissolved organic matter (DOM) during deoxygenation has been investigated in hypoxic and anoxic waters in coastal seas and open oceans. In the present study, the dynamics of DOM were investigated during summertime deoxygenation in the bottom water of the shallow coastal Bohai Sea, China. Dissolved organic carbon (DOC), chromophoric and humic-like fluorescent DOM (CDOM and FDOM) gradually increased in the bottom water during summer, which was mainly induced by biological activities in the water column and/or the surface sediment. The estimated net accumulation rates of DOC, CDOM and humic-like FDOM from June to early August in the bottom water were 0.11 ± 0.04 µmol L⁻¹ d⁻¹, 0.002 ± 0.0002 m⁻¹ d⁻¹ and 0.0004 ± 0.0001 R.U. d⁻¹, respectively. Moreover, the ratio of DOC to CO₂ accumulations was 0.08 in this duration in the bottom water. Compared with DOM in the bottom water prior to deoxygenation, the newly accumulated DOC contained more CDOM and humic-like FDOM that are considered to be microbially refractory. Full article

Parent material is a fundamental determinant of soil pedogenesis, yet its specific role in regulating the molecular composition and vertical evolution of dissolved organic matter (DOM) in paddy soils remains poorly understood. The primary objective of this study was to elucidate how distinct parent materials and soil depths interact to shape DOM chemodiversity. This study investigated 14 paddy soil samples from the plow horizon (Ap, 0–20 cm) and subsoil horizon (Br, 20–50 cm) paddy soils derived from seven parent materials (plate shale: PS, quaternary red clay: QRC, granite: GR, Alluvial Sediment: AS, limestone: LS, sandy gravel: SG, and purple soil: PR). For each composite sample, DOM extraction and subsequent optical characterizations were performed in triplicate (n = 3 analytical replicates). The analysis of soil physicochemical properties was integrated with ultraviolet-visible (UV-Vis) absorption and excitation-emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC). Our results revealed that parent material significantly dictated the soil chemical microenvironments, with LS, SG, and PR maintaining alkaline profiles, whereas others exhibited distinct surface acidity. Consequently, this microenvironmental heterogeneity profoundly influenced DOM characteristics. While DOM generally shifted towards higher molecular weight and increased aromaticity with depth, its evolutionary trajectory was highly dependent on the parent material. For instance, SG soils preserved a strong autochthonous signature in Ap, whereas GR soils exhibited the highest humification degree. Furthermore, PARAFAC analysis identified a dominant refractory humic-like component (C1 and C2) alongside a highly variable labile protein-like component (C3, 15–40%). Correlation and principal component analyses (PCA) further demonstrated that soil depth and parent material jointly drive DOM evolution, wherein soil organic matter (SOM) abundance showed strong positive associations with total nitrogen (TN), total phosphorus (TP), and available arsenic. These findings underscore that parent material properties are critical variables for understanding soil carbon cycling and managing heavy metal risks in paddy ecosystems. Full article

The circular valorization of biomass for sustainable energy recovery is a strategic priority in the transition toward low-carbon systems. In the last decade, anaerobic digestion (AD) has emerged as an efficient technology to produce an energetic vector to replace natural gas with biomethane and reduce waste; however, the hydrolysis of refractory fractions remains the main rate-limiting step. This study investigates an innovative electro-assisted pretreatment of biomass to promote the first rate-limiting hydrolysis step of refractory compounds in biomethane production. Lignocellulosic residues are employed not only as feedstock for the AD process but also as substrates in electrohydrolysis (EH) pretreatment using an Ir-Ta mixed metal oxide (MMO) anode coupled with advanced biomass-derived carbon felt cathodes. Two cathodes were functionalized with Phragmites Australis (PhA) hydrochars, untreated (PA) and KOH-activated (PA-KOH), to enhance the in situ generation of reactive oxygen species (ROS). Brassica napus (Bn) was chosen as the other biomass selected as a feedstock of AD, and was subjected to EH at varying energy inputs (500–5000 kJ kg⁻¹), evaluating structural and biochemical shifts. The results demonstrate that EH effectively modifies the biomass matrix; the PA-KOH-CF cathode exhibited good selectivity to degrade lignocellulosic structures, but higher biomethane production was achieved at 2500 kJ·kg⁻¹ TS using PA-CF, reaching an increase of 52% compared with untreated samples. Kinetic analysis of the biomethane potential was performed using the modified Gompertz model. The model accurately captured the asymmetric sigmoidal transitions of methane production with different electrode configurations, and finally, energy balance assessment identified 2500 kJ·kg⁻¹ TS as the optimal operational threshold. These findings suggest that an excess of applied energy is critical to the availability of soluble organic matter and the presence of refractory compounds that reduce efficiency. This electro-assisted approach offers a robust strategy for intensifying AD, aligning with circular bioenergy objectives. Full article

Hydrothermal carbonization (HTC) has emerged as a promising technique for food waste treatment. However, food waste is composed of complex components, including refractory proteins and polysaccharides, which lead to low efficiency and high costs during the HTC process. Enhancing the decomposition of food waste while enabling efficient nutrient recovery remains a significant challenge for the widespread application of HTC in food waste management. This study introduces deep eutectic solvents (DESs) to enhance treatment efficiency during the HTC of food waste. A comprehensive characterization of the resulting hydrochar and aqueous phase was conducted, and the effect of DES addition on the migration and speciation of phosphorus and nitrogen species during HTC was investigated. The results indicated that the addition of DESs promoted the decomposition of food waste, reducing the hydrochar yield from 22.6% to 20.2% and decreasing the volatile matter content in the hydrochar from 86.63% to 71.60% at 200 °C. Additionally, DESs significantly lowered the nitrogen content in the hydrochar from 5.99% to 3.77%. By disrupting the hydrogen-bonding networks in proteins and polysaccharides, DESs facilitated the dissolution of organic matter into the aqueous phase. Furthermore, with DES addition, 5.06 mg of phosphorus species was enriched in the hydrochar, compared to only 1.78 mg in the control group without DESs. This study provides a sustainable strategy for the efficient treatment of food waste while simultaneously enabling the effective recovery of valuable nutrients. Full article

In cold-region lakes, high organic matter concentrations with low bioavailability are common, yet the underlying causes and stabilisation mechanisms remain unclear. This study conducted a 60-day microbial treatment experiment in Hulun Lake using algae (DOMa), grass (DOMg), and manure (DOMm) as DOM sources. Fourier transform ion cyclotron resonance mass spectrometry and 16S rRNA analysis were employed to characterise DOM composition and bacterial communities. The bioavailability of DOMa, DOMg, and DOMm was 86.1%, 84.08%, and 70.9%, respectively. Differences in degradation cycles were mainly associated with the slowly biodegradable fraction; the half-lives of DOMa, DOMg, and DOMm were 49.51 days, 77.02 days, and 198.04 days, respectively. At the molecular level, proteins and lipids were rapidly utilised by microorganisms, leading to the generation of lignin, condensed aromatic hydrocarbons, and tannins, with many new molecules falling within the carboxylic acid-rich alicyclic molecule (CRAM) region. The overall community succession patterns of different DOM sources were highly similar, with initial DOM composition differences leading to variations in microbial communities during intermediate degradation stages (5~10 days). Moreover, microbiological processes facilitated the convergence of DOM source compositions and the accumulation of refractory organic matter. It is hypothesised that the regional climatic characteristics of the freeze–thaw cycle exacerbate organic matter accumulation by compressing the “effective degradation time”. These findings elucidate the causes of high organic matter and low bioavailability in cold-region lakes. Full article

This study explores the application of a cobalt–manganese oxide catalyst supported on coal gangue (CoMnOx@CG) for peroxymonosulfate (PMS) activation to degrade phenol in coal chemical wastewater (CCW). The synthesized CoMnOx@CG catalyst demonstrated remarkable catalytic activity, achieving above 90% phenol removal within 10 min at pH 9 and 11. More importantly, the catalyst exhibited excellent stability and reusability, maintaining over 85% phenol removal efficiency after four consecutive cycles and cobalt leaching below 100 μg/L. Quenching experiments and electron paramagnetic resonance (EPR) analyses revealed that singlet oxygen (¹O₂), sulfate radicals (SO₄·⁻), and hydroxyl radicals (·OH) contributed to the degradation process. When treating actual CCW, the system significantly reduced both phenol and fluorescent dissolved organic matter, demonstrating its effectiveness for complex wastewater matrices. CoMnOx@CG provides a sustainable and practical solution for alkaline refractory wastewater remediation. Full article

The treatment of refractory nitrogenous organic matter in industrial wastewater management poses challenges in the removal of organic matter and nitrogen. To address these issues, this study utilized a novel composite hydrodynamic cavitator, mainly consisting of spiral pipes and a step drain, which could generate cavitation twice per pass at the throat of the spiral pipe and the step drain of the cavitation cavity, thereby distinguishing it from other existing cavitators that produce cavitation only once per pass. The composite hydrodynamic cavitator, optimized using ANSYS 19.2 simulation software, offers significant advantages in energy utilization and mass transfer efficiency. Moreover, it generates a high concentration of hydroxyl free radicals, which are crucial for organic matter degradation. Batch experiments demonstrated the effective treatment of 4-aminophenol. Within 120 min, 4-aminophenol degradation efficiency reached 74.7% and total nitrogen concentration decreased slightly from 1.28 mg/L to 1.06 mg/L, while ammonia nitrogen concentration initially increased before decreasing from its peak value of 0.82 mg/L to 0.77 mg/L. During the cavitation treatment of 4-aminophenol, intermediate products, such as benzoquinone, were generated. Under the strong oxidizing action of hydroxyl radicals, nitrogen undergoes deamination to form ammonium ions, which were likely removed predominantly as nitrogen gas. The experimental results are anticipated to establish a foundation for the application of hydrodynamic cavitation technology in the treatment of refractory organic wastewater degradation and to support denitrification processes. Full article

This study investigated the degradation efficacy, kinetics, and mechanism of the ozone (O₃) process and two enhanced O₃ processes (O₃/peroxymonosulfate (O₃/PMS) and O₃/peroxymonosulfate/iron molybdates/biochar composite (O₃/PMS/FeMoBC)), especially the O₃/PMS/FeMoBC process, for the degradation of tetracycline (TC) in water. An FeMoBC sample was synthesized by the impregnation–pyrolysis method. The XRD results showed that the material loaded on BC was an iron molybdates composite, in which Fe₂Mo₃O₈ and FeMoO₄ accounted for 26.3% and 73.7% of the composite, respectively. The experiments showed that, for the O₃/PMS/FeMoBC process, the optimum conditions were obtained at pH 6.8 ± 0.1, an initial concentration of TC of 0.03 mM, an FeMoBC dosage set at 200 mg/L, a gaseous O₃ concentration set at 3.6 mg/L, and a PMS concentration set at 30 μM. Under these reaction conditions, the degradation rate of TC in 8 min and 14 min reached 94.3% and 98.6%, respectively, and the TC could be reduced below the detection limit (10 μg/L) after 20 min of reaction. After recycling for five times, the degradation rate of TC could still reach about 40%. The introduction of FeMoBC into the O₃/PMS system significantly improved the TC degradation efficacy and resistance to inorganic anion interference. Meanwhile, it enhanced the generation of hydroxyl radicals (^•OH) and sulfate radicals (SO₄^•−), thus improving the oxidizing efficiency of TC in water. Material characterization analysis showed that FeMoBC has a well-developed porous structure and abundant active sites, which is beneficial for the degradation of pollutants. The reaction mechanism of the O₃/PMS/FeMoBC system was speculated by the EPR technique and quenching experiments. The results showed that FeMoBC efficiently catalyzed the O₃/PMS process to generate a variety of reactive oxygen species, leading to the efficient degradation of TC. There are four active oxidants in O₃/PMS/FeMoBC system, namely ^•OH, SO₄^•−, ¹O₂, and •O₂⁻. The order of their contribution importance was ^•OH, ¹O₂, SO₄^•−, and •O₂⁻. This study provides an effective technological pathway for the removal of refractory organic matter in the aquatic environment. Full article

Seaweed plays a critical role in marine carbon sequestration due to its high release rate of organic matter. However, the impacts of Porphyra cultivation on the concentration and composition of dissolved, particulate and sedimentary organic matter (DOM, POM and SOM) in coastal cultivation zones remain unclear. Herein, we investigated the optical properties of DOM, POM and SOM along a transect from the subtropical Chi River to the adjacent Porphyra cultivation zone in Dayu Bay (southeast China) during the late cultivation stage. The results revealed that all types of organic matter in coastal cultivation zones were predominantly characterized by highly autochthonous sources, contrasting sharply with the allochthonous, terrestrial sources observed at freshwater sites. The estuarine mixing model and principal component analysis further indicated that the organic matter dynamics in the coastal zone are primarily controlled by Porphyra cultivation, with relatively limited contributions from riverine inputs, coastal sediment and porewater sources. Porphyra cultivation leads to significant additions of protein-like components in the coastal water and sediment. Microbial degradation incubations of DOM and POM further demonstrated that Porphyra cultivation promotes the in situ production of humic-like components (peak M) in coastal water. DOM exhibited a higher microbial transformation efficiency into refractory components than POM, suggesting a more substantial role of DOM in coastal carbon sequestration. Our findings underscore the potential of Porphyra cultivation to enhance the carbon sequestration of coastal ecosystems. Full article

A brackish water front, where river water meets seawater, is a hotspot for biogeochemical processes. In this study, we examined the quantity and composition of dissolved organic matter (DOM) over a 24 h tidal cycle at a brackish water front near the Yangtze River estuary. Utilizing elemental analysis, fluorescence and ultraviolet spectroscopy, and ultra-high-resolution mass spectrometry, we observed rapid fluctuations in DOM throughout the tidal cycle. The dissolved organic carbon (DOC) and total nitrogen (TN) concentrations ranged from 0.70 to 1.5 mg/L and 0.43 to 0.94 mg/L, respectively. Water samples during low tide exhibited a higher fractional abundance of CHON (17.2 ± 0.1% vs. 14.6 ± 0.4%), CHOS (14.6 ± 4.5% vs. 9.1 ± 3.1%), and CHONS (1.6 ± 0.5% vs. 0.5 ± 0.3%) formulas, and a higher aromatization and average molecular weight, which is consistent with a stronger terrestrial influence. In contrast, at high tide, the water samples contained a greater abundance of CHO compounds (75.7 ± 3.8% vs. 66.5 ± 4.1%), a humic-like fluorescent C1 component, and carboxyl-rich alicyclic molecules (CRAMs), indicating a greater release of refractory DOM from resuspended sediments. However, variations in the DOC concentrations and several optical spectral parameters did not correlate with the changes in the salinity and tidal height. The results of the principal component analysis revealed different controls on specific fractions of DOM that are related to variable DOM sources or biogeochemical processes. The complexity of DOM dynamics underscores the necessity of elucidating DOM compositions at varying levels to enhance our understanding of carbon cycling in estuarine and coastal ecosystems. Full article

The single-atom catalyst (SAC) activated persulfate process has emerged as a highly efficient technology for eliminating refractory organic compounds in aqueous environments. This review delves into the intricacies of utilizing SACs for the effective removal of various contaminants in water. The common supports and the preparation procedures of SACs are summarized at first. The synthesis methods of SACs (i.e., wet chemical method, one-pot hydrothermal method, and high-temperature pyrolysis method) are also described. Then, a comprehensive overview of the diverse reaction mechanisms in SAC-activated persulfate systems is presented, including a radical oxidation process via sulfate or hydroxyl radicals and superoxide radicals, or a nonradical process via single oxygen, surface active complex, and high-valent metal-oxo species oxidation. The impact of key factors such as peroxides concentration, SAC dosage, reaction pH, inorganic anions, organic matter, operando stability, and real water is also delved. The removal of various pollutants (i.e., azo dyes, phenolic compounds, pharmaceuticals, and bacteria) by this process is further summarized. Finally, the challenges and perspectives in the field of water treatment utilizing SACs are discussed. Full article

Magnetic CuFe₂O₄ was prepared with the modified sol–gel method and used for enhanced peroxymonosulfate (PMS) activation and ofloxacin (OFL) degradation. The OFL could almost degrade within 30 min at a catalyst dosage of 0.66 g/L, PMS concentration of 0.38 mM, and initial pH of 6.53 without adjustment, using response surface methodology (RSM) with Box-Behnken design (BBD). In the CuFe₂O₄/PMS system, the coexisting substances, including CO₃²⁻, NO₃⁻, SO₄²⁻, Cl⁻ and humic acid, have little effect on the OFL degradation. The system also performs well in actual water, such as tap water and surface water (Mei Lake), indicating the excellent anti-interference ability of the system. The cyclic transformation between Cu(II)/Cu(I) and Fe(III)/Fe(II) triggers the generation of active radicals including SO₄^•−, •OH, •O₂⁻ and ¹O₂. The OFL degradation pathway, mainly involving the dehydrogenation, deamination, hydroxylation, decarboxylation and carboxylation processes, was proposed using mass spectroscopy. Moreover, the toxicity assessment indicated that the end intermediates are environmentally friendly. This study is about how the CuFe₂O₄/PMS system performs well in PMS activation for refractory organic matter removal in wastewater. Full article

Water treatment necessitates the sustainable use of natural resources. This paper focuses on the characterization of three oxidic lithological materials (OLMs) with the aim of utilizing them to prepare calcined adsorbent substrates for ionic adsorption. The three materials have pH levels of 7.66, 4.63, and 6.57, respectively, and organic matter contents less than 0.5%. All of the materials are sandy loam or loamy sand. Their electric conductivities (0.18, 0.07, and 0.23 dS/m) show low levels of salinity and solubility. Their CEC (13.40, 13.77, and 6.76 cmol(+)kg) values are low, similar to those of amphoteric oxides and kaolin clays. Their aluminum contents range from 7% up to 12%, their iron contents range from 3% up to 7%, their titanium contents range from 0.3% to 0.63%, and their manganese contents range from 0.007% up to 0.033%. The amphoteric oxides of these metals are responsible for their ionic adsorption reactions due to their variable charge surfaces. Their zirconium concentrations range from 100 to 600 mg/g, giving these materials the refractory properties necessary for the preparation of calcined adsorbent substrates. Our XRD analysis shows they share a common mineralogical composition, with quartz as the principal component, as well as albite, which leads to their thermal properties and mechanical resistance against abrasion. The TDA and IR spectra show the presence of kaolinite, which is lost during thermal treatments. The results show that the OLMs might have potential as raw materials to prepare calcined adsorbent substrates for further applications and as granular media in the sustainable treatment of both natural water and wastewater. Full article

Over the past few decades, peroxymonosulfate (PMS)-driven advanced oxidation processes (AOPs) have garnered substantial interest in the field of organic decontamination. The copper (Cu)/PMS system is intriguing due to its diverse activation pathways and has been extensively employed for the clearance of refractory organic pollutants in water. This article is designed to offer a comprehensive overview of the latest trends in Cu-based catalysts such as single-metal and mixed-metal catalysts aimed at treating recalcitrant pollutants, highlighting PMS activation. Subsequently, investigative methodologies for assessing PMS activation with copper-based catalysts are reviewed and summarized. Then, the implications of pH, PMS and catalytic agent concentrations, anions, and natural organic matter are also addressed. The combination of Cu-based catalyst/PMS systems with other advanced oxidation technologies is also discussed. Following that, the degradation mechanisms in the Cu-based catalyst-activated PMS system are considered and synopsized. Lastly, potential future research avenues are proposed to enhance the technology and offer support for developing of economically viable materials based on copper for activating PMS. Full article

This study focuses on understanding the association of rare earth elements (REE; lanthanides + yttrium + scandium) with organic matter from the Middle Devonian black shales of the Appalachian Basin. Developing a better understanding of the role of organic matter (OM) and thermal maturity in REE partitioning may help improve current geochemical models of REE enrichment in a wide range of black shales. We studied relationships between whole rock REE content and total organic carbon (TOC) and compared the correlations with a suite of global oil shales that contain TOC as high as 60 wt.%. The sequential leaching of the Appalachian shale samples was conducted to evaluate the REE content associated with carbonates, Fe–Mn oxyhydroxides, sulfides, and organics. Finally, the residue from the leaching experiment was analyzed to assess the mineralogical changes and REE extraction efficiency. Our results show that heavier REE (HREE) have a positive correlation with TOC in our Appalachian core samples. However, data from the global oil shales display an opposite trend. We propose that although TOC controls REE enrichment, thermal maturation likely plays a critical role in HREE partitioning into refractory organic phases, such as pyrobitumen. The REE inventory from a core in the Appalachian Basin shows that (1) the total REE ranges between 180 and 270 ppm and the OM-rich samples tend to contain more REE than the calcareous shales; (2) there is a relatively higher abundance of middle REE (MREE) to HREE than lighter REE (LREE); (3) there is a disproportionate increase in Y and Tb with TOC likely due to the rocks being over-mature; and (4) the REE extraction demonstrates that although the OM has higher HREE concentration, the organic leachates contain more LREE, suggesting it is more challenging to extract HREE from OM than using traditional leaching techniques. Full article