Exploring the fate and oxidation behaviors of different organic constituents in landfill leachate upon Fenton oxidation processes using EEM-PARAFAC and 2D-COS-FTIR

Application of FTIR two-dimensional correlation spectroscopy (2D-COS) analysis in characterizing environmental behaviors of microplastics: A systematic review

Microplastics (MPs) are ubiquitous in the environment, continuously undergo aging processes and release toxic chemical substances. Understanding the environmental behaviors of MPs is critical to accurately evaluate their long-term ecological risk. Generalized two-dimensional correlation spectroscopy (2D-COS) is a powerful tool for MPs studies, which can dig more comprehensive information hiding in the conventional one-dimensional spectra, such as infrared (IR) and Raman spectra. The recent applications of 2D-COS in analyzing the behaviors and fates of MPs in the environment, including their aging processes, and interactions with natural organic matter (NOM) or other chemical substances, were summarized systematically. The main requirements and limitations of current approaches for exploring these processes are discussed, and the corresponding strategies to address these limitations and drawbacks are proposed as well. Finally, new trends of 2D-COS are prospected for analyzing the properties and behaviors of MPs in both natural and artificial environmental processes.

Utilization of microbial fuel cells as a dual approach for landfill leachate treatment and power production: a review

Landfill leachate, which is a complicated organic sewage water, presents substantial dangers to human health and the environment if not properly handled. Electrochemical technology has arisen as a promising strategy for effectively mitigating contaminants in landfill leachate. In this comprehensive review, we explore various theoretical and practical aspects of methods for treating landfill leachate. This exploration includes examining their performance, mechanisms, applications, associated challenges, existing issues, and potential strategies for enhancement, particularly in terms of cost-effectiveness. In addition, this critique provides a comparative investigation between these treatment approaches and the utilization of diverse kinds of microbial fuel cells (MFCs) in terms of their effectiveness in treating landfill leachate and generating power. The examination of these technologies also extends to their use in diverse global contexts, providing insights into operational parameters and regional variations. This extensive assessment serves the primary goal of assisting researchers in understanding the optimal methods for treating landfill leachate and comparing them to different types of MFCs. It offers a valuable resource for the large-scale design and implementation of processes that ensure both the safe treatment of landfill leachate and the generation of electricity. The review not only provides an overview of the current state of landfill leachate treatment but also identifies key challenges and sets the stage for future research directions, ultimately contributing to more sustainable and effective solutions in the management of this critical environmental issue.

Natural and anthropogenic dissolved organic matter in landfill leachate: Composition, transformation, and their coexistence characteristics

A large number of natural and anthropogenic wastes were landfilled, and dissolved organic matter (DOM) were formed during landfill. However, the composition, transformation, and coexistence characteristics of natural and anthropogenic DOM in leachate remain unclear. Fourier transform ion cyclotron resonance mass spectrometry, size exclusion chromatography, gas chromatography coupled with mass spectrometry, and three-dimensional excitation-emission matrix spectrum were employed to clarify comprehensively the abovementioned question. The results showed that natural DOM in young leachate constituted mainly straight-chain organic acids, protein substances, and building blocks of humic substances (BB). Straight-chain organic acids vanished in old leachates, and the concentration of protein substances and BB decreased from 44% to 26% and from 47% to 12%, respectively, while CHON and CHONS were degraded to CHO and CHOS during the process. As to anthropogenic DOM, its types and relative content in leachate increased during landfill, and aromatic acids, terpenes, halogenated organics, indoles, and phenols became the main organic components in old leachate. Compared to natural DOM, anthropogenic DOM was degraded slowly and accumulated in leachate, and some of the natural DOM facilitated the dechlorination of dichlorinated organic compounds. This study demonstrates that landfill led to an increase in humic substances and halogenated organic compounds in old leachate, which was intensified with concentrated leachate recirculation.

New insights into the effect of pyrolysis temperature on the spectroscopy properties of dissolved organic matter in manure-based biochar

Dissolved organic matter (DOM) derived from biochar takes a crucial role in transport and bioavailability toward contaminants; hence, it is undeniable that a thorough analysis of its properties is important. So far, the effect of pyrolysis temperature on the functional groups, components, and evolutionary sequence of manure-based biochar DOM has not been adequately investigated. Here, DOM was released from two typical livestock manures (cow and pig) at five pyrolysis temperatures (300 ~ 700°C), and it was explored in depth with the aid of moving window 2D correlation spectroscopy (MW-2D-COS) and heterogeneous 2D correlation spectroscopy (hetero-2D-COS). The results demonstrated that the concentration, aromaticity, and hydrophobicity of DOM were greater at high temperatures, and more DOM was liberated from cow manure-based biochar at identical temperature. Protein-like compounds dominated at high temperatures. The pyrolysis temperatures of final configuration transformation points of the fulvic acid-like component and the aromatic ring C=C in DOM were 400°C and 500°C, respectively. Moreover, Fourier transform infrared spectroscopy combined with two-dimensional correlation analysis indicated that the functional group evolution of DOM depends on the pyrolysis temperature and feedstock type. The study provides a new perspective on manure management and environmental applications of biochar.

Spectroscopic insights into the binding characteristics of heavy metals to dissolved organic matter in landfill leachate

Landfill leachate is produced in the process of sanitary landfilling, which contains significant amounts of dissolved organic matter (DOM) and heavy metal contaminants. Insights into the interactions between heavy metals and DOM in landfill leachate are beneficial for the understanding of heavy metal fates and optimization of landfill leachate treatment. In this work, the coherent structural changes of landfill leachate DOM during binding with various heavy metals were explored through the integration of molecular spectroscopic methods with chemometrics and statistic correlation analyses. The results indicate that protein substances, phenolic and discrete carboxyl groups in landfill leachate DOM were involved in the complexation with heavy metals, resulting in the formation of conjugated macromolecules/aggregates with high aromaticity and molecular weight/size. The fluorescent protein-like, fulvic acid-like, and humic-like fractions in DOM were engaged in the interaction, which were closely related to phenolic-like and carboxylic-like structure. Compared to membrane concentrates DOM, raw leachate DOM exhibited a higher binding affinity to heavy metals (especially for Cu2+, whilst the weakest was Cd2+). The integrated approach provides useful information in elucidating the binding processes of metals with landfill leachate DOM, including site heterogeneity, binding strength and functional group sequences.

Gas-liquid contact evaporation of concentrate leachate from disk-tube reverse osmosis treatment in waste incineration plant

In order to utilize waste heat such as exhaust steam and hot air passing through air preheater in the waste incineration plant to heat air used for evaporating leachate concentrate (LC) by gas-liquid contact evaporation technology, hot air of 600 °C, 450 °C and 250 °C was used to evaporate LC in a laboratory-scale evaporator to obtain purified condensate used for supplying water for circulating cooling water system. The influence of pH, hot air temperature and evaporation rate on COD and NH3-N in condensate were investigated to identify the optimum operation of this technology. The results showed that COD concentration in condensate obviously decreased with increase in hot air temperature. Higher hot air temperature led to higher initial evaporation temperature, and evaporation rate of water was significantly greater than that of small molecular organic matter with lower boiling point than water with increasing hot air temperature. Reduction in contents of phenol, ketone and benzene was responsible for COD decreasing in condensate. COD in condensate decreased with increase in pH, as the amount of volatile organic matter such as fatty acids escaped from LC to condensate decreased. The pH had little influence on the DOM in condensate according to EEM spectra analysis. Evaporation rate had little influence on COD in the condensate water. NH3-N concentrations in condensate in all experimental groups were far away from the limit value (10 mg/L) in the water quality standard. Under the premise of meeting water quality standard, the lowest temperature (450 °C) of hot air was selected to save energy and use lower grade waste heat. Therefore, the optimum condition was 450 °C of hot air, pH = 7 of LC and CF = 10. At this condition, molecular weight of DOM in the condensate was smaller and humification degree and aromaticity of DOM were lower according to UV-visible absorption spectrum analysis.

Effective treatment of leachate concentrate from waste incineration plant by combination of coagulation and direct contact evaporation

In order to verify that coagulation as pre-treatment can reduce the temperature of the hot air used for direct contact evaporating the leachate concentrate (LC) and low-grade waste heat such as exhaust steam in the waste incineration plant can be used to evaporate the LC. The supernatants after coagulation using polymerized ferrous sulfate (PFS), polymeric-aluminum (PAC), polymeric silicate aluminum ferric (PSAF) and poly-aluminum ferric chloride (PAFC) as coagulants were further treated in a lab-scale direct contact evaporation system. The results showed that the best performance with removal efficiencies of COD and NH3-N of 58.70% and 29.09% was achieved after coagulation when PAFC dosage = 15 g/L, PAM dosage = 30 mg/L and initial pH of supernatant = 6. After coagulation, a large amount of the fulvic-like acid and aromatic heterocyclic compounds were removed and the degree of complexity and aromaticity of organics decreased. After direct contact evaporation, using PAFC as coagulant still was the best selection due to its lowest concentrations of COD and NH3-N (22 mg/L and 1.02 mg/L) in the condensate produced by this two-stage treatment when initial pH of supernatant was 6 during evaporation and the condensate produced by this two-stage treatment met the water quality standard for using as supplying water for circulating cooling water system when temperature of hot air used for heating LC was at low temperature (250 °C). The fulvic-like acid and aromatic heterocyclic compounds in the condensate continuously reduced. Phenol, adamantane, 1-isocyanato, phthalic anhydrid, tri(2-chloroethyl) phosphat, Heptadecane, 2-methyl, ginsenol and Octadecane, 2-methyl- in the condensate obviously decreased. The effect of four coagulants as pretreatment on reducing the temperature of hot air used for evaporating LC was ranked as PAFC > PFS > PAC > PSAF. PSAF was not recommended due to the large amount of NH3-N produced when using PSAF to treat the LC.

Combination of coagulation, Fe0/H2O2 and ultra-high lime aluminium processes for the treatment of residual pollutants in biologically-treated landfill leachate

Refractory substances (humus) and salts (chloride (Cl-) and sulphate (SO42-) ions) remain in the biotreated landfill leachate treatment, and it is necessary to carry out further treatments by a suitable method before discharge. In this study, the effect and operational mechanism of a combination of the coagulation Fe0/H2O2 and ultra-high lime aluminium (UHLA) processes for the treatment of refractory organic substances and salts in the leachate effluent of a semi-aerobic aged refuse biofilter (SAARB) were investigated. The results showed that polyferric sulphate is a relatively efficient coagulant comparing to FeCl3, Al2(SO)4, and polyaluminium chloride. The Fe0/H2O2 process further removed refractory organics from wastewater, achieving 49.8% of total organic carbon removed. Further treatment by the UHLA process was carried. The results demonstrated that the amount of precipitant, reaction duration, and temperature had a significant impact on the Cl- and SO42- removals. After three treatments, the cumulative SO42- and Cl- removal efficiencies were 98% and 80%, respectively. The SO42- and Cl- were removed in the form of precipitates such as UHLA, specific components of which included calcium alumina, Fremy's salt of calcium, aluminium chloride, and calcium hydroxide. Overall, the UV254, CN, Cl-, and SO42- removal efficiencies from the SAARB effluent were 94.08%, 98.73%, 79.96%, and 98.44%, respectively, for the combined coagulation Fe0/H2O2 and UHLA processes. Therefore, the combined processes could effectively remove residual pollutants in the biologically-treated landfill leachate, and the study provides a useful reference for the removal of refractory organic matter and salts in landfill leachate.HighlightsCoagulation-Fe0/H2O2-UHLA process is effective to SAARB effluent treatment.Refractory organics are substantially degraded by the coagulation-Fenton-like stage.Both Cl- and SO42- in SAARB effluent are greatly removed by UHLA process.

Revealing How Polyvinyl Chloride Microplastic Physicochemically Affect the Anaerobic Digestion of Waste Activated Sludge

Recent studies have shown that the microplastics in waste activated sludge (WAS) can directly reduce the microbial activity and influence the performance of anaerobic digestion. Unfortunately, few studies paid attention on the interactions between WAS and MPs, since MPs could impact the contact between sludge flocs and microorganisms. We found that PVC-MP changed the interfacial energy properties of the WAS surface and affected methane production. Low concentration (40 mg/L) of PVC-MP changed the water affinity and greatly reduced the energy barrier of interfacial reaction. Simultaneously, WAS surface charge characteristics changed with increasing MPs concentration, which made the sludge difficult to contact with microorganisms. The change process of WAS surface functional groups also indicated that PVC-MP first cover the sludge surface to prevent from being utilized by microorganisms, and then affect the surface protein structure before toxic substances leaching. Our study provides new insights into how MPs affect anaerobic digestion.

Humic acid recovery from stabilized leachate: Characterization and interference with chemical oxygen demand-colour removal

Heterogeneous combinations of organic compounds (humic acid (HA) and fulvic acid) are the prime factor for the high concentration of colour and chemical oxygen demand (COD) in semi-aerobic stabilized landfill leachate. These organics are less biodegradable and cause a severe threat to environmental elements. Microfiltration and centrifugation processes were applied in this study to investigate the HA removal from stabilized leachate samples and its corresponding interference with COD and colour. The three-stage extraction process recovered a maximum of 1412 ± 2.5 mg/L (Pulau Burung landfill site (PBLS) leachate), 1510 ± 1.5 mg/L (Alor Pongsu landfill site (APLS leachate) at pH 1.5 and 1371 ± 2.5 mg/L (PBLS) and 1451 ± 1.5 mg/L (APLS) of HA (about 42% of the total COD concentration) at pH 2.5, which eventually indicates the process efficiency. Comparative characteristics analysis of recovered HA by scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy, and Fourier transform infrared significantly indicate the existence of identical elements in the recovered HA compared with the previous studies. The higher reduction (around 37%) in ultraviolet (UV) absorbance values (UV254 and UV280) in the final effluent indicates the elimination of aromaticity and conjugated double-bond compounds from leachate. Moreover, 36 and 39% COD and 39 and 44% colour removal exhibit substantial interference.

Impact of different classification schemes on discrimination of proteins with noise-contaminated spectra using laboratory-measured fluorescence data

Biological agents are important to detect and identify with respect to environmental contamination and public health. Noise contamination in fluorescent spectra is one of the contributors to the uncertainties of identification. In order to investigate the noise-tolerant capability provided by laboratory-measured excitation-emission matrix (EEM) fluorescence spectra that are used as a database, fluorescence properties of four proteinaceous biotoxin samples and ten harmless protein samples were characterized by EEM fluorescence spectra, and the predicting performance of models trained by laboratory-measured fluorescence data was tested and verified from validation data with noise-contaminated spectra. By means of peak signal of noise (PSNR) as an indicator of noise levels, the potential impact of noise contaminations on the characterization and discrimination of these samples was evaluated quantitatively. Different classification schemes utilizing multivariate analysis techniques of Principal Component Analysis (PCA), Random Forest (RF), and Multi-layer Perceptron (MPL) coupled with feature descriptors of differential transform (DT), Fourier transform (FT) and wavelet transform (WT) were conducted under different PSNR values. We systematically analyzed the performance of classification schemes by the case study at 20 PSNR and by statistical analysis from 1-100 PSNR. The results show that the spectral features with EEM-WT decreased the demanding number of input variables while retaining high performances in sample classification. The spectral features with EEM-FT presented the worst performance although having the largest number of features. The distributions of feature importance and contribution were found sensitive to noise contaminations. The classification scheme of PCA prior to MPL with EEM-WT as input presented an improvement in lower PSNR. These results indicate that robust features extracted by corresponding techniques are critical to enhancing the spectral differentiation capabilities among these samples and play an important role in eliminating the noise effect. The study of classification schemes for discriminating protein samples with noise-contaminated spectra presents tremendous potential for future developments in the rapid detection and identification of proteinaceous biotoxins based on three-dimensional fluorescence spectrometry.

Where should Fenton go for the degradation of refractory organic contaminants in wastewater?

Fenton process has become a research hotspot due to the nonselective and efficient degradation of dissolved organic matter (DOM) by ·OH. However, there are still many challenges and bottlenecks for conventional Fenton (CF). This study provides the first comprehensive insight into the mechanisms of DOM degradation by the Fenton process, including the various subcategories of humic substances, emerging trace contaminants, including persistent organic pollutants, endocrine disrupting chemicals, and pharmaceuticals and personal care products, and the interference of humus and low molecular weight organic acids on the removal of trace contaminants. In addition, a statistical comparison of the economics of CF and three types of Fenton-like technologies (Photo-Fenton, Electro-Fenton, and Ultrasonic-Fenton) is conducted based on existing studies, which can be used as a reference for engineering applications. Moreover, a brief overview of the categories and characteristics of heterogeneous Fenton, which have been extensively studied in recent years, and a comparison of their catalysts are presented. In the end, the paper advances a possible future research direction.

Molecular-level characterization of natural organic matter in the reactive electrochemical ceramic membrane system for drinking water treatment using FT-ICR MS

Applications of electrochemical advanced oxidation processes are rising in drinking water treatment for effective mitigation of refractory organic compounds. This study explored the fate of natural organic matter (NOM) (lake water and standard NOM (SRNOM solution)) at molecular-level in the reactive electrochemical membrane (REM) system utilizing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Fluorescence spectroscopy showed above 90 % removal of the humic-like component in both lake water and SRNOM solution in 10 min of REM operation compared to 70-80 % removal of the fulvic-like component after 30 min. REM-based treatment effectively eliminated (>70 %) the disinfection byproduct precursors. The lake water, sharing ~70 % of similar compounds with SRNOM, displayed a different propensity toward electrochemical oxidation, and its finished water was characterized with relatively lower double-bond equivalent (DBE), nominal oxidation state of carbon (NOSC), and aromaticity compared to that of SRNOM. The chloride ions in the water matrix of lake water impacted the electrochemical oxidation and generated significantly different transformation products than SRNOM solution. The heteroatoms (N and S) containing compounds (CHON and CHOS) were preferentially degraded in lake water; however, CHOS compounds were removed fewer in SRNOM. The electrosorption and electrochemical oxidation on the REM surface were the significant contributors for NOM removal. The newly formed compounds were mostly retained on the REM surface and fewer were released in finished water. This study is believed to help understand the fate of NOM in real source drinking water during electrochemical treatment.

Influence of dissolved organic matter and heavy metals on the utilization of soil-like material mined from different types of MSW landfills

Soil-like material (SLM) mined from municipal solid waste (MSW) landfills can be used as nursery cultivation soil, landfill cover, and as a building material. However, SLM utilization is restrained by heavy metal (HM) contents whose speciation and migration are influenced by their dissolved organic matter (DOM) content. Therefore, the properties of aged refuse and the correlation between DOM and HM forms were studied using samples from different types of MSW landfills. The dominant components of aged refuse were SLM (18.80%-83.51%) and plastics (11.17%-65.51%). The moisture, organic matter, and pH ranged from 29.55% to 57.92%, 15.70%-57.68%, and 7.84-8.51, respectively. The Zn content was highest (455.48-1379.27 mg/kg) in the SLM, followed by Cu (96.29-428.90 mg/kg), Cr (49.10-236.21 mg/kg), Pb (53.52-222.71 mg/kg), and Ni (20.92-39.10 mg/kg). The SLM cannot be used for agriculture because the HM contamination exceeds the multiple of 0.07-7.99. Zinc in the acid-soluble state and reducible state had the highest mobility in SLM. However, Cu and Pb, mainly in the oxidizable state, and Cr and Ni, in the oxidizable and residual states, were relatively stable. In the sanitary and simple MSW landfills, the average proportion of protein-like materials decreased from 84.44% to 82.61% and from 65.58% to 55.94%, respectively, as the landfill depth increased. Both the acid-soluble and oxidizable HM states and all forms of Zn in the SLM were significantly positively correlated with tyrosine-like materials (r = 0.58*-0.87**). Protein-like materials may enhance the mobility of HMs.

Regional-scale investigation of the molecular weight distribution and metal-binding behavior of dissolved organic matter from a shallow macrophytic lake using multispectral techniques

In this work, based on excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-FARAFAC) and two-dimensional correlation analysis of synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy, and combination of two spectra (2D-SF-COS, 2D-FTIR-COS, and Hetero-2D-COS), the characteristics and metal-binding behaviors of DOM in Dongping Lake were explored for molecular weight (MW), fluorescence components, and functional groups. The results showed that the entire lake was governed by protein-like materials with low MW(< 1 kDa). The complexation occurred preferentially in protein-like materials for bulk DOM after adding copper (Cu²⁺) and lead (Pb²⁺), which were changed by fractionation for MW. The active points were aliphatic C－OH for DOM-Cu and phenol －OH or polysaccharide for DOM-Pb from 2D-FTIR-COS. The protein-like components possessed higher LogK than humic-like component during binding to Cu²⁺ or Pb²⁺. Moreover, the complexing affinities of DOM-Cu (LogK_Cu: 3.26 ± 0.87-4.04 ± 0.49) were higher than those of DOM-Pb (LogK_Pb: 2.66 ± 0.52-3.78 ± 0.36). On a spatial scale, high LogK_Cu and LogK_Pb were found in the center and entrance of the lake, respectively. Humic-like component C2 in the LMW fraction possessed a stronger binding capacity with Cu²⁺. This study affords new insights into the migration and conversion of HMs in lakes.

Biochar-seeded struvite precipitation for simultaneous nutrient recovery and chemical oxygen demand removal in leachate: From laboratory to pilot scale

Refuse transfer station (RTS) leachate treatment call for efficient methods to increase nutrient recovery (NH4+−N and PO43−−P) and chemical oxygen demand (COD) removal. In this study, the effects of various operational factors (seeding dose, pH, initial NH4+-N concentration, and reaction time) on biochar-seeded struvite precipitation were investigated at laboratory and pilot scales. Mealworm frass biochar (MFB) and corn stover biochar (CSB) were used as seeding materials to compare with traditional seed struvite. The maximum NH4+−N and PO43−−P recover efficiency of the MFB-seeded process reached 85.4 and 97.5%, higher than non-seeded (78.5 and 88.0%) and CSB-seeded (80.5 and 92.0%) processes and close to the struvite-seeded (84.5 and 95.1%) process. The MFB-seeded process also exhibited higher COD removal capacity (46.4%) compared to CSB-seeded (35.9%) and struvite-seeded (31.2%) processes and increased the average particle size of the struvite product from 33.7 to 70.2 μm for better sustained release. XRD, FT-IR, and SEM confirmed the orthorhombic crystal structure with organic matter attached to the struvite product. A pilot-scale test was further carried out in a custom-designed stirred tank reactor (20 L). In the pilot-scale test, the MFB-seeded process still spectacularly recovered 77.9% of NH4+−N and 96.1% of PO43−−P with 42.1% COD removal, which was slightly lower than the laboratory test due to insufficient and uniform agitation. On the whole, MFB-seeded struvite precipitation is considered to be a promising pretreatment method for rural RTS leachate.

A comprehensive review on BPA degradation by heterogeneous Fenton-like processes

Synthetic organic pollutants emanating continuously in the ecosystem have become a global concern because of their toxicity and persistent nature. Bisphenol A (BPA) is one such pollutant which threatens public health and safety. It is a monomer used in manufacturing plastics, polycarbonate resins, epoxy resins and is a well-recognised endocrine disruptor mimicking estrogen. BPA leaches into food and beverages stored in containers causing contamination issues. Its widespread exposure and potential toxicity is an environmental health concern. In this review, a systematic investigation has been carried out on the heterogeneous catalysts used for Fenton-like processes for BPA degradation. The Fenton-like reaction is one such reaction that is used for wastewater remediation purposes. The reaction advances through the generation of powerful oxidizing radicals like •OH and SO₄^•- in the presence of a suitable catalyst. The application of various Fenton catalysts, with their distinguished morphological characteristics, oxidizing properties, toxicity analysis, and the present state of the art of BPA degradation by these catalysts, have been documented in the current work. This review also highlights a few challenges and prospects for analysing degradation products of landfill leachate.

New insights into the transformation of effluent organic matter during Fe(II)-assisted advanced oxidation processes: Parallel factor analysis coupled with self-organizing maps

The negative effects of effluent organic matter (EfOM) on receiving aquatic environments and advanced treatment facilities pose significant concerns. However, the effective removal of EfOM is challenging due to its chemically complex nature and its refractory characteristics. In this study, two Fe(II)-assisted oxidation processes including UV/Fe(II)/H₂O₂ and UV/Fe(II)/persulfate (UV/Fe(II)/PS) were investigated to promote EfOM reduction. Fe(II) was essential for promoting EfOM degradation. The mineralization rate of EfOM increased from 7 to 29% with 2 mM Fe(II) addition in the UV/H₂O₂ process and to 23% with 0.8 mM Fe(II) addition in the UV/PS process. A preliminary experiment was conducted to obtain the optimal molar ratio of oxidant to Fe(II) for practical applications based on different indicators. The form of Fe(III) prevalent at different pH values strongly affected Fe(II)/Fe(III) cycling, thus determining the progress of EfOM degradation. A machine learning approach consisting of parallel factor analysis coupled with self-organizing maps (PARAFAC-SOM) was employed with fluorescence spectra to visualize the degradation behavior of EfOM in the different reaction systems. Four components (i.e., two humic-like substances, one fulvic acid, and one tryptophan-like substance) were eventually identified, and their reductions reached more than 62% during the Fe(II)-assisted oxidation processes. The degradation orders for each component in the different oxidation processes were initially evaluated by SOM analysis with F_max percentage data. The degradation behavior of EfOM in the UV/Fe(II)/H₂O₂ and UV/Fe(II)/PS systems exhibited different trends based on the best matching unit map and component planes. The humic-like component was more refractory than the other three components in both oxidation processes. The microbial humic-like and high-molecular-weight fulvic acid substances showed higher reactivity with SO·₄^- than with ·OH, while the tryptophan-like substance was more reactive in the UV/Fe(II)/H₂O₂ system than in the UV/Fe(II)/PS system. The outcomes of this study provide new insights into the degradation behavior of EfOM, promoting the development of advanced wastewater treatments.

Fenton pre-oxidation of natural organic matter in drinking water treatment through the application of iron nails

This study investigated for the first time the efficiency of an advanced oxidation process (AOP) zero valent iron/hydrogen peroxide (ZVI/H₂O₂) employing iron nails for the removal of Natural Organic Matter (NOM) from natural water of Regent's Park lake, London, UK. The low cost of nails and their easy separation from the water after the treatment make this AOP attractive for water utilities in low- and middle-income countries. The process was investigated as a pre-oxidation step for drinking water treatment. Results showed that UV254 removal in the natural water was lower than that of simulated water containing commercial humic acid (HA), indicating a matrix effect. Statistical analysis confirmed the maximum removal of dissolved organic carbon (DOC) in natural water depends on the initial pH (best at 4.5) and H₂O₂ dosage (best at 100% excess of stoichiometric dosage). DOC and UV254 removals under this operational condition were 51% and 89%, respectively. Molecular weight (MW) and specific UV absorbance (SUVA254) were significantly reduced to 74% and 78%, respectively. Formation of Chloroform THM in natural water sample after the ZVI/H₂O₂ process (initial pH 4.5) was below the limit for drinking water, and 48% less than the THM formation in the same water not subjected to pre-oxidation. Characterization of oxidation products on the iron-nail-ZVI surface after the ZVI/H₂O₂ treatment by SEM, XRD, and XPS identified the formation of magnetite and lepidocrocite. Results suggest that the investigated ZVI/H₂O₂ process is a promising technology for removing NOM and reducing THM formation during drinking water treatment.

Insights into the minimization of excess sludge production in micro-aerobic reactors coupled with a membrane bioreactor: Characteristics of extracellular polymeric substances

The production of excess sludge by the activated sludge system of wastewater treatment plants is a problem. In this study, the EPS characteristics on production and degradation were investigated in the real-scale food processing wastewater treatment system (i.e., a micro-aerobic reactor coupled with a membrane bioreactor (MAR-MBR)) with a treatment capacity of 150 t d^-1, which could cater for the low production of excess sludge (i.e., 9 t·a^-1; 76% moisture content). The total organic carbon concentrations in the different EPS fractions were in the following order: soluble EPS (S-EPS) < loosely bound EPS (LB-EPS) < tightly bound EPS (TB-EPS). Although the components (e.g., protein and humic acid-like substances) of each EPS fraction changed significantly throughout the MAR-MBR process owing to the low production of excess sludge, the degrees of change in S-EPS, LB-EPS, and TB-EPS were significantly different from the corresponding change in their relative molecular weights. Furthermore, the microbial community composition was beneficial for the release and degradation of EPS, and the regulation of gene functions via the MAR-MBR enhanced this process.

The molecular differences of young and mature landfill leachates: Molecular composition, chemical property, and structural characteristic

Landfill leachate is a highly contaminated and complex organic wastewater. It can be categorized into young (YL) and mature leachate (ML) based on the landfill age, with significant differences in the composition of organic matter, resulting from the significant differences in humification degree. To compare the organic composition of YL and ML, ESI FT-ICR MS was applied to systematically investigate their molecular composition, chemical properties, and structural characteristics. The molecular weight of YL organics was lower than that of ML organics. In addition, O/C and H/C distributions of YL and ML organics were significantly different. YL mainly consisted of CHO compounds and aliphatic compounds. ML mainly consisted of CHON compounds and high oxygen highly unsaturated and phenolic compounds. The unsaturation degree of YL organics was expressed by carbon double bond equivalents ((DBE-C)/C = -0.0336) and was not significantly different from that of ML (-0.0241), but nominal oxidation state of carbon (NOSC = -0.8010) and aromaticity (AI_mod = 0.1254) of YL were significantly lower than of ML (NOSC = -0.0692; AI_mod = 0.2464). In addition, YL and ML organics were rich in functional groups, but the YL organics contained more straight-chain structures. The ML organics contained fewer straight-chain structures, a larger number of benzene-ring structures, and more oxygen-containing functional groups. The more complex structural properties of ML organics may be the result of the transformation of YL organics after a long series of reactions, including electrocyclization, decarboxylation, and hydrogen abstraction reactions, which eventually increased the humification degree of leachate organic matter.

Applying synchronous fluorescence spectroscopy conjunct second derivative and two-dimensional correlation to analyze the interactions of copper (II) with dissolved organic matter from an urbanized river

Heavy metal speciation and distribution is significantly influenced by dissolved organic matter (DOM) exhibited in ecosystems, particularly in urbanized rivers. Synchronous fluorescence spectroscopy (SFS) conjunct second derivative and two-dimensional correlation spectroscopy (2D-COS) was devoted to characterizing interactions of DOM-copper (II). Three typical water samples were collected from Baitapu River. Only protein-like fluorescence (PLF) and fulvic-like (FLF) were identified from the SFS. Stability constant (log K) values of PLF complexes with copper (II) varied from 4.277 to 5.833, and proportion of binding fluorescent materials (f) were 0.054-2.640. The log K values of FLF complexes with copper (II) varied from 3.996 to 4.243, while the f values were 0.001-0.036. Obviously, PLF had much stronger complexing capacity than FLF. There were four obvious peaks in the principal component analysis and second derivative fluorescence spectroscopy (SDFS), i.e., tyrosine-like (TYLF), tryptophan-like (TRLF), microbial humus-like (MHLF) and FLF. The log K values of TYLF and TRLF complexes were 4.899-5.907 and 4.598-5.831, respectively, which were similar to those from PLF. The log K values of MHLF complexes varied from 4.311 to 5.760, and the f values were 0.261-8.688. The log K values of FLF complexes were ranged from 4.598 to 5.831, which were higher than those deduced from the SFS. Interestingly, by the SDSF, PLF was divided into TYLF and TRLF, which increased the parameters values from DOM-copper (II) complexes. 2D-SFS-COS revealed that the TRLF was more susceptive response to copper (II) appended than TYLF, MHLF, and FLF. Moreover, TYLF and TRLF could priorly interact with copper (II). The SDSF conjunct 2D-COS could be effective approaches for insight into the complexing heterogeneity of DOM with copper (II). The study could present a support to preventing heavy metals and organic pollution in urbanized rivers.

Influence of sludge organic matter on elimination of polycyclic aromatic hydrocarbons (PAHs) from waste activated sludge by ozonation: Controversy over aromatic compounds

Ozonation has been widely used as a viable advanced oxidation process (AOP) for elimination of PAHs in waste activated sludge through effective sludge disintegration and abatement of organic pollutants. However, sludge organic matter (SOM) influences PAHs degradation during ozone treatment is still rarely understood. In this study, we investigated such an influence with the aid of solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy and the corresponding two-dimensional correlation analysis (2D-COS) strategy. The results showed that the degradation of SOM macromolecules in the order of aromatic substances > aliphatic carbon > α carbon > amides groups > O-alkyl upon ozone treatment. Moreover, the PAHs removal efficiency was positively correlated with the aromaticity of sludge (R² = 0.84-0.98), while negative associated with its aliphaticity (R² = 0.81-0.95). Lastly, humic acid (HA) was used as a proxy of aromatic SOM to further explore their interaction with PAHs in sludge matrix. The results revealed that freely dissolved (HA-D) and suspended particulates (HA-S) imposed distinctively different influence on ozone-based PAHs degradation. The HA-S facilitated the elimination of PAHs by 7.95 ± 0.11%, while those HA-D reduced the removal efficiency by 16.70 ± 0.13%.

Characterization and treatment of landfill leachate: A review

Landfill leachate is a complicated organic wastewater generated in the sanitary landfilling process. Landfill leachate must be appropriately disposed to avoid ecotoxicity and environmental damage. An in depth understanding of the physiochemical characteristics and environmental behaviors of landfill leachate is essential for its effective treatment. In this study, recent advances on the properties of landfill leachate, its characterization methods and treatment techniques are critically reviewed. Specifically, the up-to-date spectroscopic techniques for landfill leachate characterization and advanced oxidation treatment techniques are highlighted. Moreover, the drawbacks and challenges of current techniques for landfill leachate characterization and treatment are discussed, along with the future perspectives in the development of characterization and treatment approaches for landfill leachate.

A year-long cyclic pattern of dissolved organic matter in the tap water of a metropolitan city revealed by fluorescence spectroscopy

Delivering drinking water with stable quality in metropolitan cities is a big challenge. This study investigated the year-long dynamics of dissolved organic matter (DOM) in the tap water and source water of a metropolitan city in southern China using fluorescence spectroscopy. The DOM detected in the tap water, and source water of Shenzhen city was season and location-dependent. A year-long cyclic trend of DOM was found with predominate protein-like fluorescence in the dry season compared to the humic-like enriched DOM in the wet season. A general DOM pattern was estimated by measuring the shift in dominant fluorescence regions on the excitation-emission matrix (EEM). The difference in fluorescent DOM (FDOM) composition (in terms of the ratio of protein-like to humic-like fluorescence) was above 200% between wet and dry seasons. The taps associated with reservoirs receiving water from the eastern tributary of Dongjiang River showed significant changes in protein-like contents than the taps with source water originating from the western part of the river. This study highlights the importance of optimizing drinking water treatment plants' operational conditions after considering seasonal changes and source water characteristics.

Facile Bioself-Assembled Crystals in Plants Promote Photosynthesis and Salt Stress Resistance

Salty soil is a global problem that has adverse effects on plants. We demonstrate that bioself-assembled molybdenum-sulfur (Mo-S) crystals formed by the foliar application of MoCl₅ and cysteine augment the photosynthesis of plants treated with 200 mM salt for 7 days by promoting Ca²⁺ signal transduction and free radical scavenging. Reductions in glutathione and phytochelatins were attributed to the biosynthesized Mo-S crystals. Plants embedded with the Mo-S crystals and exposed to salty soil exhibited carbon assimilation rates, photosynthesis rates (Fv/Fm), and electron transport rates (ETRs) that were increased by 40%, 63-173%, and 50-78%, respectively, compared with those of plants without Mo-S crystals. Increased compatible osmolyte levels and decreased levels of oxidative damage, stomatal conductance (0.63-0.42 mmol m² s^-1), and transpiration (22.9-15.3 mmol m² s^-1), free radical scavenging, and calcium-dependent protein kinase, and Ca²⁺ signaling pathway activation were evidenced by transcriptomics and metabolomics. The bioself-assembled crystals originating from ions provide a method for protecting plant development under adverse conditions.

Advances in the characterization and monitoring of natural organic matter using spectroscopic approaches

Natural organic matter (NOM) is ubiquitous in environment and plays a fundamental role in the geochemical cycling of elements. It is involved in a wide range of environmental processes and can significantly affect the environmental fates of exogenous contaminants. Understanding the properties and environmental behaviors of NOM is critical to advance water treatment technologies and environmental remediation strategies. NOM is composed of characteristic light-absorbing/emitting functional groups, which are the "identification card" of NOM and susceptive to ambient physiochemical changes. These groups and their variations can be captured through optical sensing. Therefore, spectroscopic techniques are elegant tools to track the sources, features, and environmental behaviors of NOM. In this work, the most recent advances in molecular spectroscopic techniques, including UV-Vis, fluorescence, infrared, and Raman spectroscopy, for the characterization, measurement, and monitoring of NOM are reviewed, and the state-of-the-art innovations are highlighted. Furthermore, the limitations of current spectroscopic approaches for the exploration of NOM-related environmental processesand how these weaknesses/drawbacks can be addressed are explored. Finally, suggestions and directions are proposed to advance the development of spectroscopic methods in analyzing and elucidating the properties and behaviors of NOM in natural and engineered environments.

Exploration of nanocellulose washing agent for the green remediation of phenanthrene-contaminated soil

Polycyclic aromatic hydrocarbons are hazardous contaminants existing ubiquitously in polluted soil. In this study, using nanocellulose (CNC) fluid as an eco-friendly agent was proposed for the first time in the remediation of phenanthrene (PHE) contaminated soil. The effects of environmental factors on the mobilization of PHE in soil by CNC nanofluid was investigated using factorial analysis. The results showed that temperature and ionic strength had a significant influence on PHE removal, which were associated with the viscosity and zeta potential change in the nanofluid. The analysis based on two-dimensional correlation spectroscopy integrated with FTIR and synchrotron-based XRF imaging revealed that metals and minerals in soil played important roles in PHE detachment. The hydroxyl groups on CNC bonded with Fe-O, Si-O, and Mn-O in soil as time went on, and eventually achieved PHE mobilization through the interruption of PHE/SOM-metal/mineral linkages. The complexation and transport of PHE/SOM-metals/minerals from soil particles to the aqueous phase could be the primary PHE removal mechanism. Besides, the biotoxicity study displayed a detoxification effect of CNC nanofluid on PHE contaminants in soil. This study offers new insight into a cost-effective and biodegradable nanocellulose washing agent, which can be a good alternative to the available site remediation options.

Characteristics of organic matter removed from highly saline mature landfill leachate by an emergency disk tube-reverse osmosis treatment system

Some sanitary landfills in China are required to treat aging landfill leachate that is highly saline. In this study, the effectiveness of an emergency disk tube-reverse osmosis (DTRO) treatment system for such a refractory mature landfill leachate was evaluated. A molecular-level analysis was then applied to reveal the changes of the characteristics of leachate organic matter (OM). The DTRO system achieved >83% water recovery rate, reduced the electrical conductivity of effluent to 0.15-0.22 ms/cm, and reduced carbonaceous and nitrogenous pollutants to a level suitable for discharge. Furthermore, the vast majority of salts (e.g., chloride and sulfate ions), as well as refractory OM (e.g., humic- and fulvic-like substances), were effectively removed. The DTRO system can effectively remove a large number of macromolecular dissolved organic compounds with carbon number >23, as well as highly unsaturated compounds with DBE >12. Additionally, > 80% of the molecules assigned to the dissolved OM (DOM) were removed; even CHONS compounds with complex molecular structures were completely removed. The constitution of DOM in the DTRO effluent was simple, mainly comprising anti-sludge agents (e.g., small molecule alcohol and alkyl benzene sulfonic acid, etc.). However, the DOM in the resulting membrane concentrates was very similar to that in raw landfill leachate and the concentration was much higher. Therefore, an effective and feasible method should be developed to treat DTRO membrane concentrates because they pose high environmental risk.

Enhanced darkening effect from the interaction of MnO2 and oxygen on the component evolution of amino-phenolic humic-like substances

Humification is greatly enhanced by metallic oxides in nature, and the related products are critical to various environmental processes. However, little is known about the interaction between metallic oxides and oxygen in promoting the oxidative polymerization of small organic molecules during the humification process. The synthesis of humic-like acids (HLAs) with MnO₂ was performed in the presence and absence of oxygen, and the influence of oxygen and MnO₂ on the composition evolution of amino-phenolic HLAs was illustrated. The results of ultraviolet-visible (UV-Vis) spectra of reaction mixtures associated with two-dimensional correlation spectroscopy (2D-COS) combined with the XPS spectra of N 1s content changes in HLAs demonstrated that MnO₂ induced pyrrole-type nitrogen formation and enhanced darkening. Furthermore, MnO₂ mainly acted as a catalyst, and oxygen activated the regeneration of MnO₂ by oxidizing free manganese ions, thus substantially promoting the formation and accumulation of HLAs, whereas it decreased the reaction rate of HLAs formation. Moreover, carbon dioxide release was found during the process of the formation of fulvic-like acids (FLAs), and the reaction was oxygen-independent. Additionally, the formation and transformation of products without MnO₂ do not obey kinetics equations, whereas the darkening reaction with MnO₂ followed the pseudo-second-order and pseudo-zero-order kinetics equations. These findings provide new insights into the behaviours and fate of the oxygen-mediated humification process and related reaction products.

Transformation mechanisms of refractory organic matter in mature landfill leachate treated using an Fe0-participated O3/H2O2 process

An Fe⁰-participated O₃/H₂O₂ (Fe⁰-O₃/H₂O₂) process was applied to remove refractory organic matter (OM) in semi-aerobic aged refuse biofilter (SAARB) leachate arising from treating mature landfill leachate. The degradation and transformation characteristics of refractory OM were revealed at molecular level. Removal efficiencies of aromatic substances were 63.55% by the Fe⁰-O₃/H₂O₂ process (much higher than in other single or binary processes), and fulvic- and humic-like substances were more effectively degraded by this process than by other treatments. According to Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), 6645 categories of OM in SAARB leachate were identified. Although there was little difference in number of OM categories after treatment using the single-O₃ and Fe⁰-O₃/H₂O₂ processes, Fe⁰-O₃/H₂O₂ process can better reduce OM relative abundance. It is noteworthy that the Fe⁰-O₃/H₂O₂ process more effectively degraded CHONS compounds than the single-O₃ process, while also producing more CHO compounds having higher bio-availability. The enhanced degradation efficiency of the Fe⁰-O₃/H₂O₂ process were attributed to the formation of the Fenton process initiated by leached Fe²⁺ and H₂O₂. The heterogeneous catalytic effect from iron (hydro) oxides for O₃/H₂O₂ also increased the treatment capacity of the Fe⁰-O₃/H₂O₂ process, resulting in better total organic carbon removal. The Fe⁰-O₃/H₂O₂ process is an efficient method for removing refractory OM in SAARB leachate.

Molecular-level insights into the transformation mechanism for refractory organics in landfill leachate when using a combined semi-aerobic aged refuse biofilter and chemical oxidation process

Landfill leachate contains high concentrations of complex organic matter (OM) that can severely impact the ecological environment. If landfill leachate is to be treated using a combined "biological + advanced treatment" process, the molecular information of OM must be investigated to optimize the operation parameters of the combined process and maximize the removal of organic pollutants. This study applied ultra-high resolution mass spectroscopy to investigate the degradation and transformation characteristics of refractory OM in mature landfill leachate at the molecular level (m/z = 150-800) during biological treatment (i.e., semi-aerobic aged refuse biofilter, SAARB) and subsequent chemical oxidation (i.e., the Fenton process and ozonation). After SAARB treatment, the polycyclic aromatics (aromatic index, AI > 0.66) and polyphenol (0.66 ≥ AI > 0.50) contents increased, and the highly unsaturated phenolic compounds (AI ≤ 0.50 and H/C < 1.5), which have a high bioavailability, were mostly removed. Compared with raw leachate, SAARB effluent (i.e., SAARB leachate) contained fewer organics with short carbon chains, more organics with long carbon chains, an elevated condensation degree for organics and, thus, a considerably reduced biodegradability. Although both the Fenton and ozonation processes could remove many of the polycyclic aromatics and polyphenols, ozone produced considerable amounts of aliphatic compounds with high bioavailability. Compared to ozonation, the Fenton process utilized the hydroxyl radical to non-selectively react with OM and produced better mineralization results.

Molecular investigation into the transformation of dissolved organic matter in mature landfill leachate during treatment in a combined membrane bioreactor-reverse osmosis process

This study investigated the effectiveness of a combined membrane bioreactor (MBR) and reverse osmosis (RO) process for treating leachate produced by a large-scale anaerobic landfill. The MBR process had limited treatment efficiency for removing organic pollutants, but when combined with RO, the integrated system completely removed macromolecular compounds (i.e., humic- and fulvic-like substances) and produced effluent that satisfied the applicable discharge standard. The landfill leachate contained many types of DOM that had high molecular weight and were highly unsaturated. Although the MBR process removed some DOM that had a relatively low saturated degree (mainly aliphatic compounds (2.0 ≥ H/C ≥ 1.5) with relatively high bioavailability), many bio-refractory compounds were not removed. The RO system greatly reduced the content of residual DOM in MBR effluent and was effective for removing heteroatom DOM, especially polycyclic aromatics (AI > 0.66) and polyphenols (0.66 ≥ AI > 0.50). The effluent from the combined process of MBR and RO treatment mainly contained a small number of aliphatic compounds and phenolic compounds (AI ≤ 0.50 and H/C < 1.5) that had higher bioavailability than DOM in the raw leachate and posed little environmental risk.

Degradation characteristics of dissolved organic matter in nanofiltration concentrated landfill leachate during electrocatalytic oxidation

Nanofiltration concentrated landfill leachate (NCLL) is produced during the integration process of biodegradation and nanofiltration, containing a large amount of recalcitrant dissolved organic matter (DOM). In this work, electrocatalytic oxidation technology was employed to degrade DOM in NCLL and spectroscopic technology was applied to explore the structural changes. The results showed that under the optimal experimental condition (pH = 2.0, NaCl concentration = 0.7%, Fe₂(SO₄)₃ concentration = 0.8%, the retention time = 6 h), the removal rates of COD, TOC, and UV₂₅₄ were 99.0%, 57.4%, 99.3% respectively. Ultraviolet-Visible (UV-Vis) spectral analysis showed that aromatic CC can be effectively degraded by electrocatalytic oxidation, resulting in decreases of aromaticity and molecular weight in NCLL. Two fluorescent components (terrestrial humic-like substances and fulvic-like substances) were identified in NCLL by parallel factor analysis, which can be effectively removed by electrocatalytic oxidation with removal rates of 99.9% and 90.5%, respectively. In addition, through two-dimensional correlation spectroscopic analysis, the sequence of structural changes of the DOM in NCLL was confirmed: unsaturated double bonds → fulvic-like components/aromatic structures → terrestrial humic-like components. These spectral characterization techniques can provide a deep understanding of the degradation pathways of DOM and provide new insights for the treatment of NCLL.

Investigation of hydrolysis acidification process during anaerobic treatment of coal gasification wastewater (CGW): Evolution of dissolved organic matter and biotoxicity

Coal gasification wastewater (CGW) contains several types of aromatic pollutants, which impart high biotoxicity and reduce the quality of anaerobic treatment. Two types of hydrolysis acidification processes, namely microaerobic hybrid reactor (HA-1) and upflow anaerobic sludge blanket reactor (HA-2), were developed for pre-treatment before the anaerobic treatment. The changes in the dissolved organic matter and biotoxicity were investigated to comprehensively understand the degradation process. The results showed that HA-2 coupled with an anaerobic reactor achieved a 12.3% and 13.4% higher removal efficiency for chemical oxygen demand and total phenols, respectively, compared with the coupled process with HA-1. Furthermore, HA-2 could transform macromolecules into small molecules more efficiently and produce fewer intermediates. The coupled process with HA-2 preferentially removed complex aromatic substances with absorption wavelengths of 285 and 254 nm, according to the sequential orders interpreted from two-dimensional correlation spectroscopy. In addition, the results of fluorescence excitation-emission-matrix with regional integration analysis revealed that the contents of typical cyclic compounds in CGW, such as phenolic, heterocyclic, and polycyclic aromatic compounds were remarkably reduced by HA-2. In addition, HA-2 reduced the toxic unit value of CGW by 67.5% and increased the resazurin dehydrogenase activity of the sludge by 37.5% during CGW treatment, thus improving the biotoxicity removal and biodegradability. However, the coupled process with HA-2 did not significantly affect the "indirect estrogenic activity" of CGW. A Pearson correlation analysis indicated that spectral indicators, such as UV₂₅₄ and Φ_T,n, presented a high positive correlation with the reduction of acute toxicity and organics.

Comparison of copper binding properties of DOM derived from fresh and pyrolyzed biomaterials: Insights from multi-spectroscopic investigation

The binding of dissolved organic matter (DOM) with metals affects the latter's biogeochemical processing in the environment. This study used multi-spectroscopic analyses to compare the heterogeneities of the Cu(II) binding properties of DOM derived from fresh and pyrolyzed biomaterials. The results showed that the DOM derived from fresh macrophyte (MDOM) and their corresponding biochar (BDOM) consisted mostly of protein-like and humic-like substances, respectively. The stability constant (log K_M) of protein-like matter in the MDOM was 5.27, and the values of humic-like components in the BDOM were 4.32-5.15. Compared with the MDOM, the BDOM exhibited lower affinities and active binding sites for Cu(II). In addition, the BDOM contents decreased after pyrolysis. Therefore, the pyrolysis of fresh biomaterials into biochar is a promising method for reducing the potential migration risk posed by Cu(II) due to the MDOM being a positive carrier for Cu(II) contamination. Polysaccharide was the only functional group that participated in the binding of Cu(II) in both MDOM and BDOM. Aliphatic groups and amides associated with protein-like matter were responsible for the Cu(II) binding to MDOM, whereas phenolic and aromatic groups mainly participated in the complexation of BDOM-Cu(II). The CO group of amide I in the MDOM, and polysaccharide in the BDOM, showed the fastest response to Cu(II). This study was helpful for elucidating the effects of fresh and pyrolyzed biomaterials (biochars) on the environmental behavior of Cu(II) at the molecular level.

Synergistically coupling membrane electrochemical reactor with Fenton process to enhance landfill leachate treatment

Landfill leachate is challenging to treat due to its complex composition. Advanced oxidation processes such as Fenton process can be effective to treat leachate. Herein, a previously developed membrane electrochemical reactor (MER) was coupled with Fenton oxidation through providing synergistic benefits with the low solution pH, reduced organics, and ammonia removal/recovery. This two-stage coupled system reduced the leachate COD by 88%, much higher than that from the standalone Fenton process treating raw leachate. In addition, the usage of chemical reagents has been greatly reduced. At a dimensionless oxidant dose of 1.0, the coupled MER-Fenton system reduced the consumption of both FeSO₄⋅7H₂O and H₂O₂ by 39%, H₂SO₄ by 100%, and NaOH by 55%. Consequently, the sludge production was reduced by 51% in weight and 12% in volume. Despite electricity consumption by the MER, the coupled system cost $4.76 per m³ leachate less than the standalone Fenton treatment. More notably, direct Fenton oxidation removed only 21% of ammonia; in comparison the MER-Fenton system removed ammonia by 98% with the possibility for recovery at a rate of 30.6-55.2 kg N m^-3 reactor d^-1. Those results demonstrate that coupling MER with Fenton process could mitigate some inherent drawbacks of Fenton oxidation such as ineffective ammonia removal, high acid and chemical reagents dose requirements, and a large amount of sludge generation. This system may be moved towards practical applications by addressing a few challenges such as using renewable energy to power MER.

Study on the source of magnetic properties of three novel boratopolyoxovanadates via two-dimensional infrared correlation spectroscopy

Three novel polyoxovanadoborates namely [V₁₂B₁₈O₄₆(OH)₁₄(H₂O)_0.75]·20.5H₂O 1, Na₂[V₁₂B₁₈O₄₈(OH)₁₂(H₂O)_0.5]·26.5H₂O 2 and Cd_0.5{[Na(H₂O)₂]2[Na(H₂O)]₂[Na(H₂O)₃]2V₁₂B₁₈O₅₃(OH)₇(H₂O)_0.5}·11H₂O 3 have been hydrothermally synthesized and structurally characterized. The boratopolyoxovanadate cage [V₁₂B₁₈O₆₀] backbones in 1-3 are constructed by the combination of two hexameric oxovanadate units [V₆O₉] and one puckered [B₁₈O₄₂] ring via sharing O atoms. All three compounds were obtained under alkaline conditions, and the cluster anions were all [V₁₂B₁₈O₆₀]. But the cations were different, it is inferred that the protonation of the three compound cluster ions is different, respectively [V₁₂B₁₈O₄₆(OH)₁₄(H₂O)_0.75] in 1, [V₁₂B₁₈O₄₈(OH)₁₂(H₂O)_0.5]^2- in 2 and [V₁₂B₁₈O₅₃(OH)₇(H₂O)_0.5]^7- in 3. The V oxidation states ratio of V^IV to V^V were 2:1 confirmed by valence bond calculation and XPS. We studied the magnetic properties of three compounds by two methods: The variable temperature magnetic susceptibility and the 2D IR COS under magnetic perturbation. From the 2D IR COS under magnetic perturbation map, it is showed that all three: (1) the presence of V^IV. (2) Certain quasi-aromaticity from B₃O₃ six-membered ring. (3) The difference of protonation and the charge of the cluster anions. This work enriches the theory of two-dimensional correlation spectroscopy and also provides a new approach to the study of magnetic materials.

Elimination of UV-quenching substances from MBR- and SAARB-treated mature landfill leachates in an ozonation process: A comparative study

Ultraviolet-quenching substances (UVQS), recently identified pollutants in landfill leachate, can interfere with ultraviolet disinfection when landfill leachate is co-treated with municipal sewage. This study investigated the elimination of UVQS in mature landfill leachates through a membrane bioreactor (MBR) and a semi-aerobic aged refuse biofilter (SAARB). Humus (i.e., fulvic and humic acids) was the main component of organic matter in both MBR- and SAARB-treated landfill leachates, while there was a more stable chemical structure of humus in the MBR-treated leachate. The concentration of UVQS in MBR-treated mature landfill leachate was higher than that of SAARB-treated leachate. Ozonation can degrade UVQS effectively, especially for landfill leachate containing a high concentration UVQS (i.e., MBR-treated landfill leachate). However, a large accumulation of small molecule acid might be caused by ozonation for highly concentrated UVQS in landfill leachate, leading to the delayed degradation of total organic carbon. Moreover, ozonation degraded both fulvic acid and humic acid; and degraded humic acid more effectively. For instance, 88.0% removal (MBR-CP2) and 96.0% removal (SAARB-CP2) of humic acid was higher than those (83.3% for MBR-CP1 and 92.3% for SAARB-CP1) of fulvic acid. The destruction of UV-quenching functional groups of organics (such as CC) by ozone was the main UVQS degradation mechanism of ozonation applied to MBR- and SAARB-treated landfill leachates. Therefore, the ozonation process can efficiently decrease UV absorption intensity in both MBR- and SAARB-treated landfill leachates.

Using EEM-PARAFAC to probe NF membrane fouling potential of stabilized landfill leachate pretreated by various options

Pretreatment processes substantially modify the organic composition of landfill leachate, which affect the fouling behavior in the post-treatment of membrane filtration. In this study, the changes in the chemical composition of stabilized landfill leachate upon various pretreatments, which encompassed coagulation/flocculation (C/F), ion exchange resins (MIEX), granular activated carbon (GAC) adsorption, and their combinations, were tracked via excitation emission matrix - parallel factor analysis (EEM-PARAFAC), and the membrane fouling potentials were assessed in the subsequent processes of nanofiltration (NF). Fluorescence components, fulvic-like (C1), protein-like (C2), and humic-like (C3), were identified and validated using EEM-PARAFAC. MIEX and C/F pretreatments were not effective to remove C1 and C2, which were associated with relatively small sized and hydrophilic molecules. GAC adsorption did not show any preference with the removal towards different components. These differences in the chemical heterogeneity among the variously pretreated leachates led to the discrepancies in membrane fluxes at a similar leachate concentration. The result also signified the importance of probing the chemical composition of pretreated leachate for the optimization of the post membrane filtration. The sum of C2 and C3 in the pretreated leachate showed a good correlation with reversible membrane fouling resistance (r = 0.93; p < 0.05), while C1 was highly correlated with irreversible membrane resistance (r = 0.872; P < 0.05). These findings provided a new insight into the applicability of fluorescence spectroscopy for tracking the changes in the membrane fouling potential of stabilized landfill leachate after various pretreatments.

Formation of disinfection byproducts during Fenton's oxidation of chloride-rich landfill leachate

Because of the production of chlorine species in leachate during Fenton's oxidation, harmful disinfection byproducts (DBP) can be formed but this has not been well studied before. Herein, we have investigated five classes of DBP: trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, and halonitromethanes during Fenton's oxidation of landfill leachates. The results show that the DBP concentration increased with the increase of [H₂O₂]: [Cl^-] ratio due to the increased concentration of chlorine species. The highest total DBP concentration was 4860 μg L^-1 at [H₂O₂]: [Cl^-] = 4.0 and the lowest was 84 μg L^-1 at [H₂O₂]: [Cl^-] = 0.25. Both the DBP concentration and DBP toxicity increased with the increase of the [H₂O₂]: [Fe²⁺] ratio, because of the increased concentration and lifetime of the chlorine species. Most of the DBP were formed during the first minute of the reaction and stayed stable up to 3 h, indicating that DBP may not be preferred targets of hydroxyl radicals in the presence of a large amount of organics. In most cases, trihalomethanes dominated the DBP concentration, while haloacetonitriles dominated the total additive toxicity. This study has provided important implications to understand DBP formation during Fenton's oxidation.

Elucidating the structural variation of membrane concentrated landfill leachate during Fenton oxidation process using spectroscopic analyses

Membrane concentrated landfill leachate (MCLL) contains large amounts of recalcitrant organic matter that cause potential hazards to the environment. Knowledge on the compositional variation of MCLL during treatment is important for a better understanding on the degradation pathway of organic pollutants. In this work, the structural change of MCLL during Fenton oxidation process was examined using spectroscopic techniques. The removal rates of COD, TOC and UV₂₅₄ reached 78.9 ± 1.3%, 70.2 ± 1.4% and 90.64 ± 1.6%, respectively, under the optimal condition (i.e., dosage of H₂O₂ = 9.0 mL/200 mL, H₂O₂/Fe(II) molar ratio = 3.0, pH = 3.0, time = 40 min). Spectral analyses suggested that aromatic/CC structure and CO bonds in MCLL can be successfully destroyed by Fenton oxidation, resulting in a decrease in molecular weight. One fulvic-like and one humic-like components were identified in MCLL, both of which can be removed by Fenton treatment. In addition, two-dimensional correlation spectroscopic analyses suggested the oxidative changes of MCLL structure in the order of fulvic-like component/unsaturated conjugated bond > aromatic structure > humic-like component. The results may provide a new insight to the understanding on the structure variation of MCLL during treatment, which is beneficial for the design of cost-effective treatment strategies.

Targeted removal of organic foulants in landfill leachate in forward osmosis system integrated with biochar/activated carbon treatment

Forward osmosis (FO) has been adopted to treat complex wastewater such as landfill leachate due to its high rejection of organics. In this study, the in-line adsorptive process using biochar (BC) or powdered activated carbon (PAC) was applied to a cross flow FO system to enhance the mitigation of the FO membrane fouling from landfill leachate. The changes in the leachate composition along the treatments were tracked by excitation emission matrix-parallel factor analysis (EEM-PARAFAC) to identify tryptophan-like (C1), fulvic-like (C2), and humic-like (C3) components. After a single operation of FO, the C1 was found to be the main constituent responsible for membrane fouling irrespective of varying operation conditions regarding draw solute concentrations and flow rates. Both sorbents (i.e., BC and PAC) exhibited the preferential removal behavior towards C1 > C2 > C3, which was well supported by their individual adsorption isotherm model parameters. The addition of in-line adsorption treatment to FO resulted in substantial improvements in the filtered volume (>57%) and the flux recovery (>80%) compared to the single FO operation. Without chemical cleaning of membrane, the flux was fully recovered at a dose of 10 g/L BC or 0.3 g/L of PAC. A significant and negative correlation was found between the flux recovery and the C1 of the feed leachate or the corresponding spectral peak intensity (p < 0.05) for the integrated FO system, suggesting the potential of using on-line fluorescence monitoring for the performance of the integrated system in terms of fouling mitigation. This study provided a new insight into the effectiveness of BC or PAC adsorption as the in-line integration with an FO system for the targeted removal of FO membrane foulants in landfill leachate.

Systematic discovery about NIR spectral assignment from chemical structural property to natural chemical compounds

Spectra-structure interrelationship is still the weakness of NIR spectral assignment. In this paper, a comprehensive investigation from chemical structural property to natural chemical compounds was carried out for NIR spectral assignment. Surprisingly, we discovered that NIR absorption frequency of the skeleton structure with sp² hybridization is higher than one with sp³ hybridization. Specifically, substituent was another vital factor to be explored, the first theory discovery demonstrated that the absorption intensity of methyl substituted benzene at 2330 nm has a linear relationship with the number of substituted methyl C-H. The greater the number of electrons given to the substituents, the larger the displacement distance of absorption bands is. In addition, the steric hindrance caused by the substituent could regularly reduce the intensity of NIR absorption bands. Furthermore, the characteristic bands and group attribution of 29 natural chemical compounds from 4 types have been systematic assigned. These meaningful discoveries provide guidance for NIR spectral assignment from chemical structural property to natural chemical compounds.