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

Effects of Ca2+ and Mg2+ on Cu binding in hydrophilic and hydrophobic dissolved organic matter fractions extracted from agricultural soil

Dissolved organic matter (DOM) has significant effects on soil copper (Cu) bioavailability. However, little is known about Cu interactions and major cation binding toward hydrophilic and hydrophobic DOM components extracted from soil solutions. In this study, we investigated the influence of major cations (Ca2+/Mg2+) on Cu complexing characteristics on different hydrophilic and hydrophobic DOM fractions using absorbance spectroscopy at different Cu2+ concentrations in the absence/presence of Ca2+/Mg2+. Different compositional hydrophobic and hydrophilic DOM fraction proportions occurred at three agricultural soil sites, with the hydrophobic acid (HOA) fraction accounting for the highest proportion. The addition of Cu2+ generated distinct ultraviolet (UV) bands/peaks (processed by differential linear and differential logarithmic transformation) of three hydrophilic DOM fractions, whereas Cu2+ induced less and weak specific peaks in the differential spectra and differential logarithmic of the HOA fractions, indicating hydrophilic DOM fractions tend to have a higher density of Cu2+ complexation sites. In the presence of either Ca2+/Mg2+, increased depression caused by Cu2+ binding on different DOM fractions was observed with increasing 10, 100, and 1000 μM Ca2+/Mg2+ levels, with more significant variations in peaks/banks for hydrophilic base (HIB) and HOA fractions, and less for hydrophilic acid (HIA) and hydrophilic neutral (HIN) fractions. In our study, the spectral parameters ΔS225-275 and ΔS275-325 were successfully used to quantify Cu amounts bonded to HIA and HIB, respectively. They exhibited strong linear relationships with correlation coefficients (R2) of 0.96 for HIA and 0.87 for HIB, respectively. Furthermore, Mg2+ exhibited stronger competition with Cu for HIA and HIB binding sites when compared with Ca2+.

The structural transformation reversibility of biogas slurry derived dissolved organic matter and its binding properties with norfloxacin under temperature fluctuation

The widespread use of biogas slurry could potentially raise the environmental risk of antibiotics. Dissolved organic matter (DOM), as the most active part of biogas slurry, was able to interact with antibiotics and play a crucial role in the structure and function of soil and aquatic ecosystems. The recent shifts in global climate patterns have garnered significant attention due to their substantial impact on temperature, thereby exerting a direct influence on the characteristics of DOM and subsequently on the environmental behavior of antibiotics. However, there is limited research concerning the impact of temperature on the binding of DOM and antibiotics. Thus, this study aimed to explore the temperature-dependent structural transformation and driving factors of biogas slurry-derived DOM (BSDOM). Additionally, the binding characteristics between BSDOM and the commonly used antibiotic norfloxacin (NOR) at different temperatures were studied by using multi spectroscopic methods and two-dimensional correlation spectroscopy (2D-COS) analysis. The results suggested that the temperature-dependent structural transformation of BSDOM was reversible, with a slight lag in the transition temperature under cooling (13 °C for heating and 17 °C for cooling). Heating promoted the conversion of protein-like to humic-like substances while cooling favored the decomposition of humic-like substances. BSDOM and NOR were static quenching, with oxygen-containing functional groups such as C-O and -OH playing an important role. Temperature influenced the order of binding, the activity of the protein fraction, and its associated functional groups. At temperatures of 25 °C and 40 °C, the fluorescent components were observed to exhibit consistent binding preferences, whereby the humic-like component demonstrated a greater affinity for NOR compared to the protein-like component. However, the functional group binding order exhibited an opposite trend. At 10 °C, a new protein-like component appeared and bound preferentially to NOR, when no C-O stretch corresponding to the amide was observed. The finding will contribute to a comprehensive understanding of the interaction mechanisms between DOM and antibiotics under climate change, as well as providing a theoretical basis to reduce the environmental risks of biogas slurry and antibiotics.

Climate and Environmental Variables Drive Stream Biofilm Bacterial and Fungal Diversity on Tropical Mountainsides

High mountain freshwater systems are particularly sensitive to the impacts of global warming and relevant environmental changes. Microorganisms contribute substantially to biogeochemical processes, yet their distribution patterns and driving mechanism in alpine streams remain understudied. Here, we examined the bacterial and fungal community compositions in stream biofilm along the elevational gradient of 745-1874 m on Mt. Kilimanjaro and explored their alpha and beta diversity patterns and the underlying environmental drivers. We found that the species richness and evenness monotonically increased towards higher elevations for bacteria, while were non-significant for fungi. However, both bacterial and fungal communities showed consistent elevational distance-decay relationships, i.e., the dissimilarity of assemblage composition increased with greater elevational differences. Bacterial alpha diversity patterns were mainly affected by chemical variables such as total nitrogen and phosphorus, while fungi were affected by physical variables such as riparian shading and stream width. Notably, climatic variables such as mean annual temperature strongly affected the elevational succession of bacterial and fungal community compositions. Our study is the first exploration of microbial biodiversity and their underlying driving mechanisms for stream ecosystems in tropical alpine regions. Our findings provide insights on the response patterns of tropical aquatic microbial community composition and diversity under climate change.

Photochemical behavior of dissolved organic matter derived from Alternanthera philoxeroides hydrochar: Insights from molecular transformation and photochemically reactive intermediates

Hydrochar-derived dissolved organic matter (HDOM) enters aquatic ecosystems through soil leaching and surface runoff following the application of hydrochar. However, the photochemical behavior of HDOM remains unclear. The photo-transformation of HDOM was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), multiple spectroscopy methods, high-performance liquid chromatography, and combining synchronous fluorescence and Fourier-transform infrared spectroscopy with two-dimensional correlation spectroscopy. The results showed that with the increase of carbonization temperature, amide II in protein-like substances were observed to be preferentially photolyzed, and the protein-like substances were more sensitive to low irradiation time, while the duration time of the photochemical behavior of amide II and aliphatic C-H were more persistent. FT-ICR MS results showed that N and S-containing molecules, including lignins and lipids were more sensitive to ultraviolet irradiation. Furthermore, the photo-transformation of HDOMs was accompanied by the generation of triple excited state dissolved organic matter and singlet oxygen. Our findings will be beneficial for understanding the mechanisms of photo-transformation of HDOM and for predicting the possible behaviors of hydrochar produced at different temperatures before large-scale application.

The telltale fluorescence fingerprints of sewer flows for interpreting the low influent concentration in wastewater treatment plant

Low degradability of wastewater treatment plant (WWTP) influents negatively affects its ability to effectively remove pollutants through wastewater treatment processes. Proactive assessment of urban sewer system performance is highly valued in the selection of targeted countermeasures for this occurrence. In this study, a fluorescence spectrum interpretation approach was developed to identify the causes of low biodegradability of WWTP influent by using parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) of excitation-emission matrix spectroscopy. Statistical analysis was also used to further interpret the PARAFAC- and FRI-derived data. The urban sewer catchment served by a WWTP in Wuhan City, China, was used as the test site to demonstrate the effectiveness of this approach. The results showed that electronics manufacturing industrial wastewater and groundwater input into the urban sewer would significantly decrease the biodegradability of the WWTP influents, and these sources were characterized by much lower fluorescence peak intensities, especially for protein-like substances, including tryptophan-like T and tyrosine-like B1 and B2. The potential conversion of high freshness T into low freshness B2 within the sewer may also contribute to this undesirable scenario. The ratio of peak T to peak B2 and the ratio of the FRI fraction of region I to that of region II can be used together to determine the predominance of industrial wastewater and groundwater. T/B2 < 1.3 indicates the entry of industrial wastewater or groundwater into urban sewers, and I/II > 0.5 further confirms the input of industrial wastewater. Accordingly, the low biodegradability of the WWTP influents in our study site is mostly due to the inflow of industrial wastewater rather than groundwater infiltration into the urban sewers. Therefore, actions should be focused on the surveillance of industrial wastewater rather than widespread sewer inspection and repairs. In this way, this methodology is cost-effective in aiding targeted countermeasures to improve the urban sewer system performance.

Investigating spectroscopic and copper binding characteristics of dissolved organic matter in wastewater using EEMs with two-dimensional Savitzky-Golay second-order differentiation-PARAFAC

Dissolved organic matter (DOM) in wastewater interacts with heavy metal particles in aquatic environments, which changes their dynamics and bioavailability. For quantifying the DOM, an excitation-emission matrix (EEM) paired alongside parallel factor analysis (PARAFAC) is typically employed. However, a drawback of PARAFAC has been revealed in recent studies, i.e., the rise of overlapping spectra or wavelength shifts in fluorescent components. Here, traditional EEM-PARAFAC and, for the first time, two-dimensional Savitzky-Golay second-order differential-PARAFAC (2D-SG-2nd-df-PARAFAC) were used to study the DOM-heavy metal binding. The samples from four treatment units of a wastewater treatment plant, i.e., influent, anaerobic, aerobic, and effluent, underwent the process of fluorescence titration with Cu2+. Four components were separated with dominant peaks in regions I, II, and III (proteins and fulvic acid-like) through PARAFAC and 2D-SG-2nd-df-PARAFAC. A single peak was observed in region V (humic acid-like) by PARAFAC. In addition, Cu2+-DOM complexation indicated clear differences in DOM compositions. The binding strength increased between Cu2+ and fulvic acid-like components in contrast to protein-like components from influent to the effluent, and increasing fluorescence intensity with the addition of Cu2+ in the effluent indicated changes in their structural composition. Moreover, when comparing both methods, the 2D-SG-2nd-df-PARAFAC provided the components without peak shifts and better fitting for Cu2+-DOM complexation model, demonstrating it to be a more reliable technique compared to only traditional PARAFAC for DOM characterization and quantifying metal-DOM in wastewater.

Sustainable exploitation and safe utilization of biochar: Multiphase characterization and potential hazard analysis

Pyrolysis temperature determines the multiphase (solid and dissolved) structure of biochar (BC). In this study, the temperature-dependent evolution of characteristics and potential hazards of three crop (cotton, alfalfa, and wheat) residue BC were systematically investigated. The results showed that pyrolysis temperature significantly affected the elemental composition and morphology of BC. A higher pyrolysis temperature led to a higher aromatization and graphitization degree of BC. A numerical relationship between pyrolysis temperature and BC surface properties (functional groups, carbonization degree) was established. Pyrolysis temperature controlled the content, composition, and functional group evolution of BC-derived dissolved organic matter. Although the amount of potentially toxic elements (PTEs) in BC was concentrated after pyrolysis, the potentially risk of PTEs significantly decreased. The spin concentration of persistent free radicals in BC prepared at 500 °C was the highest. These findings will hopefully offer comprehensive guidance for sustainable utilization of crop straw and fit-for-purpose exploitation of BC.

Hyperbranched polyethyleneimine-functionalised chitosan aerogel for highly efficient removal of melanoidins from wastewater

Melanoidins are hazardous dark-coloured substances contained in molasses-based distillery wastewater. Adsorption is an effective approach to eliminate melanoidins from wastewater. However, melanoidin adsorption capacities of available adsorbents are unsatisfactory, which seriously limits their practical application. A hyperbranched polyethyleneimine-functionalised chitosan aerogel (HPCA) was fabricated as an effective adsorbent for melanoidin scavenging. HPCA demonstrated superior melanoidin adsorption efficiency because of its high specific surface area, abundant amino functional groups, and high hydrophilicity. Melanoidin removal rate of HPCA was 94.95%, which remained at 91.45% after 5 cycles. Notably, using the Langmuir isothermal model, the maximum melanoidin adsorption capacity of HPCA was determined to be 868.36 mg/g, surpassing those of most of previously reported adsorbents. Toxicity experiments indicated that HPCA can be considered a safe adsorbent with excellent biocompatibility that hardly threatens aquatic organisms. The efficient melanoidin removal of HPCA was attributed to electrostatic attraction, H-bonding, and van der Waals force. However, the adsorption might be predominantly controlled by electrovalent interaction between protonated amino groups of HPCA and carboxyl/carboxylate groups of melanoidins. Two novel models, namely, external diffusion resistance-internal diffusion resistance mixed model and adsorption on active site model, were employed to describe the dynamic mass transfer characteristics of melanoidin adsorption by HPCA.

Influence of thermal air oxidation on the chemical composition and uranium binding property of intrinsic dissolved organic matter from biochar

In this work, uranium (U(VI)) binding characteristics of the intrinsic dissolved organic matters (DOM) from the biochars prepared under thermal air oxidation (TAO) and non-TAO conditions were studied using synchronous fluorescence spectra (SFS) and Fourier transform infrared (FTIR) in conjunction with the general two-dimensional correlation spectroscopy (2D-COS), heterospectral 2D-COS and moving-window (MW) 2D-COS. The chemical compositions of the intrinsic DOMs from biochars with/without TAO were investigated by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that the preferential binding of U(VI) to functional groups followed the order: 937 (carboxyl γ_C-OH), 981 (carboxyl γ_C-OH), 1511 (aromatic v_C = C), 1108 (esters or ethers v_C-O), 1282 (esters or carboxyl v_C-O), 1698 (saturated carboxylic acid or ketone v_C = O) cm^-1 for biochar DOM after TAO (OB600), and 937 (carboxyl γ_C-OH), 1484 (lipids δ_C-H or phenolic v_C-O), 1201 (esters or carboxyl v_C-O), 1112 (esters or ethers v_C-O), 1706 (saturated aldehyde, carboxylic acid or ketone v_C = O), 1060 (phenolic, esters or ethers v_C-O), 1014 (phenolic, esters or ethers v_C-O) cm^-1 for the pristine biochar (B600). Fulvic-like substances at 375 nm in the biochar DOM showed a preferential binding with U(VI) after TAO, while humic-like substances played a more critical role in the U(VI) complexation with biochar DOM obtained from non-TAO condition. The results also indicated that TAO increased the content of fluorescent DOM and the chemical stability of DOM-U(VI) complexes. The FT-ICR MS results showed an increase in the relative abundance of protein-like, carbohydrates-like, tannins-like, unsaturated hydrocarbons, and condensed aromatic structure and a decrease in the relative abundance of lipid-like and lignin-like after TAO. Consequently, although biochar after TAO had a much poorer content of intrinsic DOM, its intrinsic DOM showed a much higher capacity in U(VI) precipitation. Therefore, the TAO substantially changed the chemical composition, binding property and environmental behavior of intrinsic DOM from biochar.

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS): Part III. Versatile applications

In this review, the comprehensive summary of two-dimensional correlation spectroscopy (2D-COS) for the last two years is covered. The remarkable applications of 2D-COS in diverse fields using many types of probes and perturbations for the last two years are highlighted. IR spectroscopy is still the most popular probe in 2D-COS during the last two years. Applications in fluorescence and Raman spectroscopy are also very popularly used. In the external perturbations applied in 2D-COS, variations in concentration, pH, and relative compositions are dramatically increased during the last two years. Temperature is still the most used effect, but it is slightly decreased compared to two years ago. 2D-COS has been applied to diverse systems, such as environments, natural products, polymers, food, proteins and peptides, solutions, mixtures, nano materials, pharmaceuticals, and others. Especially, biological and environmental applications have significantly emerged. This survey review paper shows that 2D-COS is an actively evolving and expanding field.

Overlooked mechanism of Pb immobilization on montmorillonite mediated by dissolved organic matter in manure compost

In this study, three kinds of dissolved organic matter (DOM) derived from fresh chicken manure (FDOM), immature compost (IDOM) and mature compost (MDOM) were employed to compare their effects on Pb adsorption onto montmorillonite (MMT). The potential mechanism was revealed by characterization of mineral structure and calculation of interface force. The results demonstrated that the adsorption capacity (q_max) of Pb onto MMT was decreased by 14.3% and 29.8% in the presence of FDOM and IDOM, respectively, while increased by 44.4% in the presence of MDOM, resulting from the release or co-adsorption of DOM-Pb complexes. Parallel factor (PARAFAC) further indicated that Pb mainly bound to protein-like substances in FDOM and IDOM, and fulvic-like in MDOM. The X-ray diffraction (XRD) analysis proved that MDOM-Pb complex had a stronger ability to enter into the interlayer of MMT. The van der Waals force dominated the adsorption of FDOM-Pb and IDOM-Pb, while ligand exchange was involved in the case of MDOM-Pb. This study provided a comprehensive insight into the geochemical behavior of livestock manure and its compost as well as their interactions with heavy metal and soil mineral.

Characterising the interactions between Cu(II) and fulvic acid subcomponents using differential fluorescence spectroscopy combined with parallel factor analysis

Fulvic acid (FA) consists of various organic compounds that interact with metals in the aquatic environment. Interactions between subcomponents (FA3, FA5, FA7, FA9 and FA13) of FA and Cu(II) were investigated using fluorescence quenching titration by coupling differential fluorescence spectroscopy (DFS) and parallel factor analysis (PARAFAC). The material fluorescence intensities derived from FA subcomponents decreased with Cu(II) concentration increase, and stronger quenching was experienced at low Cu(II) concentrations. Humic-like materials of FA3 and protein-like materials of FA9 have relatively higher presence of carboxylic groups with greater molecular polarity, and preferential interaction of Cu(II) occurs. Fluorescence DFSs can be successfully broken down into five components as follows: fulvic-like components of a major compound containing carboxylic-like and phenolic-like groups, fulvic-like components of a major compound containing groups of other components, humic-like components of a major compound containing carboxylic-like and phenolic-like groups, humic-like components of a major compound containing carboxylic-like groups, and protein-like components. The fulvic-like components of a major compound containing carboxylic-like and phenolic-like groups exhibited stronger quenching with Cu(II) in five FA subcomponents. Static quenching is the dominant mechanism for the binding of Cu(II) by the FA subcomponent. The log K of quenching constants fitted using the modified Ryan-Weber equation (R2 = 0.9368-0.9985) ranged from 4.32 to 6.14 for five components derived from FA subcomponents. Subcomponents that were eluted earlier exhibited stronger binding affinity with Cu(II).

Spectroscopic characterization of dissolved organic matter from macroalgae Ulva pertusa decomposition and its binding behaviors with Cu(II)

Dissolved organic matter (DOM) from macroalgae is regarded a crucial source of autochthonous DOM in coastal ocean. In the present study, the characteristics of DOM from the macroalgae Ulva pertusa decomposition (U. pertusa-DOM) and its binding behaviors with Cu(II) using multiple spectroscopic techniques and chemometric analyses. The labile U. pertusa-DOM could be consumed and transformed by microorganisms. The absorption spectroscopic descriptors indicate that the hydrophobicity, aromaticity, and molecular weight of the U. pertusa-DOM increase during the 27-day incubation period. Fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis suggests that the relative abundance of the protein-like component (C1) (96.10-84.96%) sequentially decreases, whereas the humic-like components (C2) (2.16-9.73%) and (C3) (1.75-5.31%) in the U. pertusa-DOM increase with the U. pertusa decomposition. The Cu(II) binding properties of the U. pertusa-DOM are dependent on the decomposition time. The order of the conditional stability constant (logK_M) is C2 > C1 > C3. The complexation capacity (f) of C1 is higher than those of C2 and C3 at a specific time. Synchronous fluorescence spectroscopy coupled with two-dimensional correlation spectroscopy reveals that the microbial degradation could accelerate the Cu(II) binding to humic-like fractions in the U. pertusa-DOM. These findings will help us better understand the biogeochemical behaviors of macroalgal DOM and heavy metal in coastal ecosystems.

Insight into interactions of heavy metals with livestock manure compost-derived dissolved organic matter using EEM-PARAFAC and 2D-FTIR-COS analyses

Dissolved organic matter (DOM), as the most active ingredient in compost, directly determines the speciation and environmental behavior of HMs. Here, the binding properties of DOM derived from chicken-manure compost (CHM), cow-manure compost (COM) and pig-manure compost (PIM) with HMs were explored by analyses of Fluorescence excitation-emission matrix parallel factor (EEM-PARAFAC) and two-dimensional correlation Fourier transform infrared spectroscopy (2D-FTIR-COS). Results showed that the binding characteristics vary with origin of DOM and type of HMs. The fulvic-like component dominated the transformation of HMs speciation, and CHM-DOM had higher affinity with HMs and greater risk causing pollution due to its higher aromaticity, molecular weight and distribution of fluorescent components. Moreover, Cu(II) can efficiently bind to DOM with the stability constants (log k_M) ranging from 4.53 to 5.38, followed by Pb(II) (3.34-3.57), whereas Cd(II) can hardly bind to DOM. The amide and polysaccharide were the predominant sites for HMs binding in CHM-DOM, and polysaccharide and phenolic in COM-DOM, while phenolic and amide in PIM-DOM, respectively. Although the proportion of protein-like components and non-fluorescent polysaccharides in DOM were low, their role in HMs binding should not be ignored. In brief, the environmental risk caused by livestock manure compost may originate from interactions between DOM and HMs.