Spectral characteristics of dissolved organic carbon derived from biomass-pyrogenic smoke (SDOC) in the aqueous environment and its solubilization effect on hydrophobic organic pollutants

Mobility of biochar-derived dissolved organic matter and its effects on sulfamerazine transport through saturated soil porous media

Dissolved organic matter (DOM) released from biochar may impact antibiotic mobility and environmental fate in subsurface environments. Here, DOM samples derived from biochars (BDOM) generated by pyrolyzing corn straw at 300, 450, and 600 °C were employed to elucidate the mobility characteristics of these organic substances and their influences on the transport of sulfamerazine (SMZ, a typical sulfonamide antibiotic) in soil porous media. The results demonstrated that BDOM produced at a lower pyrolysis temperature exhibited greater mobility owing to the weaker hydrophobic and H-bonding interactions between BDOM and soil particles. Additionally and importantly, BDOM facilitated the promotion of SMZ mobility owing to the increased electrostatic repulsion between SMZ- forms and soil grains, the steric hindrance effect induced by the deposition of organic matter, and the competitive retention between SMZ molecules and BDOM. Meanwhile, the promotion effects of BDOM enhanced with improving pyrolysis temperature owing to the promoted deposition of organic matter on soil surfaces and the strengthened electrostatic repulsion. Moreover, the facilitated effects of BDOM on SMZ mobility declined as the solution pH values were raised from 5.0 to 9.0 or the flow rate increased from 0.18 to 0.51 cm min-1. This trend was due to decreased deposition competition and the steric effect caused by decreased retention of BDOM on soil particles. Furthermore, the cation-bridging effect emerged as an important mechanism contributing to the promotion effects of BDOM when the solution contained divalent cations (Cu2+ or Ca2+). Moreover, a two-site non-equilibrium model was used to interpret the controlling mechanisms for the effects of BDOM on the transport of SMZ. Findings from this work highlight that biochar-derived dissolved organic matter can remarkably affect the environmental behaviors of antibiotics in aquatic environments.

The heterogenous molecular characteristics of biomass-pyrogenic smoke dissolved organic matters (BPS-DOMs) binding with PAHs: Novel insights from combined analysis of FT-ICR MS and fluorescence variation

Biomass-pyrogenic smoke dissolved organic matter (BPS-DOM) can co-deposit with polycyclic aromatic hydrocarbons (PAHs), thereby altering their environmental behavior and fate in surface environments. However, the heterogeneous molecular characteristics of BPS-DOM binding with PAHs remain unclear. This study systematically elucidates the binding characteristics of PAHs (phenanthrene and pyrene), with various molecular compositions in BPS-DOM, utilizing FT-ICR MS and fluorescence variation analysis. CHO compounds in BPS-DOM, characterized by high aromaticity and abundant CO bonds, significantly enhance PAHs binding by promoting π-π electron donor-acceptor interactions. In contrast, CHON compounds with higher aliphaticity inhibit pyrene binding by competing for binding sites on BPS-DOM. Furthermore, the binding sequence of different fluorescent molecules follows the order of CHO→CHOS→CHON for phenanthrene and CHO→CHON→CHOS for pyrene. This was primarily due to the larger conjugated aromatic structures of CHO compounds, which provide stronger π-π interaction sites for PAHs binding. The difference in binding sequences between phenanthrene and pyrene is primarily attributed to phenanthrene's reliance on π-π electron donor-acceptor interactions induced by -SO and -N = O, while pyrene binding depended on π-π interactions driven by larger conjugated aromatic structures. These results provide an important theoretical foundation for further understanding the molecular-level interactions between BPS-DOM and PAHs.

Molecular insight into biomass-burning smoke water-soluble organic matter binding with Cd(II): Comprehensive analysis from fluorescence EEM-PARAFAC, FT-ICR-MS and two-dimensional correlation spectroscopy

The deposition of biomass-burning smoke water-soluble organic matter (BBS-WSOM) significantly affects the environmental behavior of heavy metals in aqueous environments. However, the interactions between BBS-WSOM and heavy metals at the molecular level remain unknown. This study combined FT-ICR-MS, fluorescence spectrum, FTIR, and two-dimensional correlation spectroscopy to anatomize the molecular characteristics of BBS-WSOM binding with Cd(II). The results show that CHO and CHOP compounds were responsible for the fluorescence response of BBS-WSOM at Ex: 225 nm and 275 nm/Em: 325 nm, and abundant proteins or CHON compounds were responsible for the fluorescence response of BBS-WSOM at Ex: 225-250 nm/Em: 350-450 nm and Ex: 300-350 nm/Em: 350-450 nm, which was very different from the fluorescence molecules in natural organic matters. Fluorescence change after Cd(II) addition indicated that CHOP and CHOS compounds enhanced BBS-WSOM binding with Cd(II). Differently, the CHON compounds could weaken the binding of other compounds with Cd(II). Different compounds binding with Cd(II) generally followed the order: CHON/CHOS compounds>CHOP compounds>CHO compounds, and the chemical groups binding with Cd(II) generally followed the prioritization: -COO-> -NH/SO>P = O/P-O>aromatic ring>CO>C-OH of phenol/alcohol>C-O-C. This study provides a profound insight into the interaction between BBS-WSOM and Cd(II) at the molecular level.

Binding characters of biomass burning smoke-derived dissolved organic matter with Cu(II) in aqueous environment: Roles of functional groups and organic components

The environmental effect of biomass burning smoke-derived dissolved organic matter (BBS-DOM) has attracted growing attention due to the increasing wildfire globally. BBS-DOM eventually deposits on the water and soil environments, thus altering the environmental behaviors of pollutants (e.g., heavy metals) in the surface environments of the wildfire region. However, presently, the binding characters between heavy metals and BBS-DOM remains unknown. In this study, alfalfa, pinewood, and corn straw were burned at 300 °C and 600 °C to produce BBS-DOMs and their binding characters with Cu(II) were investigated using fluorescence excitation-emission matrix spectra coupled with parallel factor (EEM-PARAFAC), synchronous fluorescence spectra combined with two-dimensional correlation spectroscopy (2D-SFS-COS) and FTIR combined with two-dimensional correlation spectroscopy (2D-FTIR-COS). The fluorescence quenching/enhancing results after Cu(II) addition suggested that the binding capacities with Cu(II) of various organic components in BBS-DOMs followed an order of polyphenols-like matters (Ex/Em: 220 nm/310 nm) > aromatic protein-like matters (Ex/Em: 275 nm/310 nm) ≈ small humic-like matters (Ex/Em: 300 nm/380 nm) > large humic-like matters (Ex/Em: 330 nm/410 nm). Interestingly, the quenching effect of Cu(II) addition on the fluorescence intensities of polyphenols-like matters and humic-like matters decreased with their increasing abundances, which possibly depended on the proportion of organic ligands of these components. Furthermore, 2D-FTIR-COS demonstrated that the binding sequence of different functional groups followed deprotonated -COOH→deprotonated phenol-OH→-C]O of aldehydes, ketones, and lactones/aromatic rings/-NH→C-O-C/C-OH of ethers and alcohols. Another novelty was that Cu(II) binding could increase the molecular size and humification of BBS-DOMs, due to the bridge effect of Cu(II). This work provides an importantly theoretical basis for deeply understanding the mechanism of BBS-DOM binding with Cu(II) at the molecular level, which is a key for reasonably predicting the multimedia-crossing effects of BBS-DOM and the environmental behavior of heavy metals in the wildfire region.

Microbiome and antibiotic resistome in bioelectrochemical toilets for onsite treatment of fecal sludge

Effective management of fecal sludge (FS) is essential for preventing environmental and public health risks. Developing safe and efficient FS treatment technology is crucial for reducing the health risks of onsite sanitation systems. In this study, bioelectrochemical toilets (BETs) were developed to treat FS onsite. Compared with the open-circuit BETs (OC-BETs), BETs exhibited higher removal efficiencies for total organic carbon, total nitrogen, and total phosphorus. Specifically, the enhancements in removal efficiencies were 18.82 ± 1.73 %, 7.28 ± 0.32 %, and 11.41 ± 0.05 % for urine, and 19.28 ± 4.08 %, 21.65 ± 1.23 %, and 24.68 ± 0.95 % for feces, respectively. Microbiome analysis indicated that the dominant populations were affiliated with electroactive bacteria (Desulfuromonas and Pseudomonas) in the electrode biofilm of BETs. The species co-occurrence network showed that the electrode biofilm microbiome in BETs had more complex correlations than that in OC-BETs, suggesting that a weak electrical current enhanced the microbiome stability. The relative abundance of antibiotic resistance genes in BETs and OC-BETs reduced by 59.85 ± 1.32 % and 53.01 ± 2.81 % compared with the initial FS, respectively. These findings indicate that BETs are an alternative system for enhancing onsite treatment of fecal sludge and provide a theoretical foundation for the implementation of BETs.

Biochar-derived organic carbon promoting the dehydrochlorination of 1,1,2,2-tetrachloroethane and its molecular size effects: Synergies of dipole-dipole and conjugate bases

The environmental effects of biochar-derived organic carbon (BDOC) have attracted increasing attention. Nevertheless, it is unknown how BDOC might affect the natural attenuation of widely distributed chloroalkanes (e.g., 1,1,2,2-tetrachloroethane (TeCA)) in aqueous environments. We firstly observed that the kinetic constants (ke) of TeCA dehydrochlorination in the presence of BDOC samples or their different molecular size fractions (<1 kDa, 1∼10 kDa, and >10 kDa) ranged from 9.16×103 to 26.63×103 M-1h-1, which was significantly greater than the ke (3.53×103 M-1h-1) of TeCA dehydrochlorination in the aqueous solution at pH 8.0, indicating that BDOC samples and their different molecular size fractions all could promote TeCA dehydrochlorination. For a given BDOC sample, the kinetic constants (ke) of TeCA dehydrochlorination in the initial pH 9.0 solution was 2∼3 times greater than that in the initial pH 8.0 solution due to more formation of conjugate bases. Interestingly, their DOC concentration normalized kinetic constants (ke/[DOC]) were negatively correlated with SUVA254, and positively correlated with A220/A254 and the abundance of aromatic protein-like/polyphenol-like matters. A novel mechanism was proposed that the CH dipole of BDOC aliphatic structure first bound with the CCl dipole of TeCA to capture the TeCA molecule, then the conjugate bases (-NH-/-NH2 and deprotonated phenol-OH of BDOC) could attack the H atom attached to the β-C atom of bound TeCA, causing a CCl bond breaking and the trichloroethylene formation. Furthermore, a fraction of >1 kDa had significantly greater ke/[DOC] values of TeCA dehydrochlorination than the fraction of <1 kDa because >1 kDa fraction had higher aliphiticity (more dipole-dipole sites) as well as more N-containing species and aromatic protein-like/polyphenol-like matters (more conjugate bases). The results are helpful for profoundly understanding the BDOC-mediated natural attenuation and fate change of chloroalkanes in the environment.

Fractionation of biomass-burning smoke-derived dissolved organic matters on the surface of clay minerals: Variations of molecular properties and components

Biomass burning (e.g., wildfire) frequently occurs globally, inevitably produces abundant biomass-burning smoke-derived dissolved organic matters (BBS-DOMs) which eventually deposits on the surface environment. The adsorption and fractionation of BBS-DOMs on clays inevitably alter their biogeochemical process and environmental behaviors in the surface environment. It is therefore important to clarify the adsorption and fractionation of BBS-DOM on clay surfaces. This study found that the fractionation of BBS-DOMs on clays (montmorillonite and kaolinite) were controlled by their functional groups, aromaticity, molecular size and organic components. The spectral indexes (SUVA254 and S275-295) of BBS-DOMs in solution after clays adsorption suggested that with the increasing DOC concentration, the primary interaction between BBS-DOMs and clays changed from hydrogen bond to hydrophobic/pore filling effects, and the adsorption ratio of the large molecules increased, which were very different from natural fulvic acid. Furthermore, various BBS-DOMs and fulvic acid had different component fractionation behaviors during clay adsorption, because they had different abundances of protein-like matters (hydrogen bond donors), pyridine-N/pyrimidine-N (positive charge doners of electrostatic interaction), and fulvic-like matters (hydrophobic interaction and pore filling effect). Additionally, the increasing pH weakened the adsorption of bulk BBS-DOMs and enhanced the adsorption ratio of aromatic matters and smaller BBS-DOM molecules. Meanwhile, at a higher pH, the adsorption ratio of protein-like matters increased, while the adsorption ratio of humic- and fulvic-like matters decreased. The result was ascribed to the enhanced hydrogen bond between protein-like matters and clays as well as the enhanced electrostatic repulsion between humic-/fulvic-like matters and clays. This study is helpful for deeply understanding the multimedia-crossing environmental behavior of BBS-DOMs in the surface environment.

Effect of pyrolysis temperature and molecular weight on characterization of biochar derived dissolved organic matter from invasive plant and binding behavior with the selected pharmaceuticals

A comprehensive understanding of the characteristics of biochar released-dissolved organic matter (BDOM) derived from an invasive plant and its impact on the binding behavior of pharmaceuticals is essential for the application of biochar, yet has received less attention. In this study, the binding behavior of BDOM pyrolyzed at 300-700 °C with sulfathiazole, acetaminophen, chloramphenicol (CAP), and carbamazepine (CMZ) was investigated based on a multi-analytical approach. Generally, the pyrolysis temperature exhibited a more significant impact on the spectral properties of BDOM and pharmaceutical binding behavior than those of the molecular weight. With increased pyrolysis temperature, the dissolved organic carbon decreased while the proportion of the protein-like substance increased. The highest binding capacity towards the drugs was observed for the BDOM pyrolyzed at 500 °C with the molecular weight larger than 0.3 kDa. Moreover, the protein-like substance exhibited higher susceptive and released preferentially during the dialysis process and also showed more sensitivity and bound precedingly with the pharmaceuticals. The active binding points were the aliphatic C-OH, amide II N-H, carboxyl CO, and phenolic-OH on the tryptophan-like substance. Furthermore, the binding affinity of the BDOM pyrolyzed at 500 °C was relatively high with the stability constant (logKM) of 4.51 ± 0.52.

Molecular-level insights into the temperature-dependent formation dynamics and mechanism of water-soluble dissolved organic carbon derived from biomass pyrolysis smoke

Water soluble organic carbon (WSOC) derived from biomass pyrolytic smoke is deposited through atmospheric aerosols, negatively affecting aquatic ecological quality and safety. However, the temperature-dependent molecular diversity and dynamic formation of smoke-derived WSOC remain poorly understood in water. Herein, we explored the molecular-level formation mechanism of pyrolytic smoke-derived WSOC in water to explain the evolution, heterogeneous correlations, and sequential responses of molecules and functional groups to increasing pyrolysis temperature. Two-dimensional correlation spectroscopy was used to innovatively establish the characteristic correlations between spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry. Temperature-dependent formation of WSOC exhibited diversity in absorbance/fluorescent components, unique/common molecules, and their chemical parameters, showing the simultaneous formation and degradation reactions. The common WSOC molecules with lower and higher degrees of oxidation showed significant positive and negative correlations with the fluorescent components, respectively. The primary sequential response of WSOC molecules to increasing pyrolysis temperature (lignin-like molecules → unsaturated hydrocarbons, condensed aromatic molecules → lipid-like/aliphatic-/peptide-like molecules) corresponded to the temperature response of functional groups (carboxylic/alcoholic → polysaccharides → aromatics/amides/phenolic/aliphatic groups), demonstrating well synergistic relationships between them. These novel findings will contribute to the comprehensive understanding and assessments of potential environmental behavior or risks of WSOC in aquatic ecosystems.

Biochar improved the solubility of triclocarban in aqueous environment: Insight into the role of biochar-derived dissolved organic carbon

Biochar as an effective adsorbent can be used for the removal of triclocarban from wastewater. Biochar-derived dissolved organic carbon (BC-DOC) is an important carbonaceous component of biochar, nonetheless, its role in the interaction between biochar and triclocarban remains little known. Hence, in this study, sixteen biochars derived from pine sawdust and corn straw with different physico-chemical properties were produced in nitrogen-flow and air-limited atmospheres at 300-750 °C, and investigated the effect of BC-DOC on the interaction between biochar and triclocarban. Biochar of 600∼750 °C with low polarity, high aromaticity, and high porosity presented an adsorption effect on triclocarban owing to less BC-DOC release as well as the strong π-π, hydrophobic, and pore filling interactions between biochar and triclocarban. In contrast and intriguingly, biochar of 300∼450 °C with low aromaticity and high polarity exhibited a significant solubilization effect rather than adsorption effect on triclocarban in aqueous solution. The maximum solubilization content of triclocarban in biochar-added solution reached approximately 3 times its solubility in biochar-free solution. This is mainly because the solubilization effect of BC-DOC surpassed the adsorption effect of biochar though the BC-DOC only accounted for 0.01-1.5 % of bulk biochar mass. Furthermore, the high solubilization content of triclocarban induced by biochar was dependent on the properties of BC-DOC as well as the increasing BC-DOC content. BC-DOC with higher aromaticity, larger molecular size, higher polarity, and more humic-like matters had a greater promoting effect on the water-solubility of triclocarban. This study highlights that biochar may promote the solubility of some organic pollutants (e.g., triclocarban) in aqueous environment and enhance their potential risk.

Water-soluble organic carbon (WSOC) from vegetation fire and its differences from WSOC in natural media: Spectral comparison and self-organizing maps (SOM) classification

Vegetation fire frequently occurs globally and produces two types of water-soluble organic carbon (WSOC) including black carbon WSOC (BC-WSOC) and smoke-WSOC, they will eventually enter the surface environment (soil and water) and participate in the eco-environmental processes on the earth surface. Exploring the unique features of BC-WSOC and smoke-WSOC is critical and fundamental for understanding their eco-environmental effects. Presently, their differences from the natural WSOC of soil and water remain unknown. This study produced various BC-WSOC and smoke-WSOC by simulating vegetation fire and used UV-vis, fluorescent EEM-PARAFAC, and fluorescent EEM-SOM to analyze their different features from natural WSOC of soil and water. The results showed that the maximum yield of smoke-WSOC reached about 6600 folds that of BC-WSOC after a vegetation fire event. The increasing burning temperature decreased the yield, molecular weight, polarity, and protein-like matters abundance of BC-WSOC and increased the aromaticity of BC-WSOC, but presented a negligible effect on the features of smoke-WSOC. Furthermore, compared with natural WSOC, BC-WSOC had a greater aromaticity, smaller molecular weight, and more humic-like matters, while smoke-WSOC had a lower aromaticity, smaller molecular size, higher polarity, and more protein-like matters. EEM-SOM analysis indicated that the ratio between the fluorescence intensity at Ex/Em: 275 nm/320 nm and the sum fluorescence intensity at Ex/Em: 275 nm/412 nm and Ex/Em: 310 nm/420 nm could effectively differentiate WSOC of different sources, following the order of smoke-WSOC (0.64-11.38) > water-WSOC and soil-WSOC (0.06-0.76) > BC-WSOC (0.0016-0.04). Hence, BC-WSOC and smoke-WSOC possibly directly alter the quantity, properties, and organic compositions of WSOC in soil and water. Owing to smoke-WSOC having far greater yield and bigger difference from natural WSOC than BC-WSOC, the eco-environmental effect of smoke-WSOC deposition should be given more attention after a vegetation fire.

Transport of dissolved organic matters derived from biomass-pyrogenic smoke (SDOMs) and their effects on mobility of heavy metal ions in saturated porous media

Biomass-pyrogenic smoke-derived dissolved organic matter (SDOMs) percolating into the underground environment profoundly impacts the transport and fate of environmental pollutants in groundwater systems. Herein, SDOMs were produced by pyrolyzing wheat straw at 300-900 °C to explore their transport properties and effects on Cu²⁺ mobility in quartz sand porous media. The results indicated that SDOMs exhibited high mobility in saturated sand. Meanwhile, the mobility of SDOMs was enhanced at a higher pyrolysis temperature due to the decrease in their molecular sizes and the declined H-bonding interactions between SDOM molecules and sand grains. Furthermore, the transport of SDOMs was elevated as pH values were raised from 5.0 to 9.0, which resulted from the strengthened electrostatic repulsion between SDOMs and quartz sand particles. More importantly, SDOMs could facilitate Cu²⁺ transport in the quartz sand, which stemmed from forming soluble Cu-SDOM complexes. Intriguingly, the promotional function of SDOMs for the mobility of Cu²⁺ was strongly dependent on the pyrolysis temperature. Generally, SDOMs generated at higher temperatures exhibited superior effects. The phenomenon was mainly due to the differences in the Cu-binding capacities of various SDOMs (e.g., cation-π attractive interactions). Our findings highlight that the high-mobility SDOM can considerably affect heavy metal ions' environmental fate and transport.

Pyrolysis Atmospheres and Temperatures Co-Mediated Spectral Variations of Biochar-Derived Dissolved Organic Carbon: Quantitative Prediction and Self-Organizing Maps Analysis

Biochar-derived dissolved organic carbon (BDOC), as a highly activated carbonaceous fraction of biochar, significantly affects the environmental effect of biochar. This study systematically investigated the differences in the properties of BDOC produced at 300-750 °C in three atmosphere types (including N₂ and CO₂ flows and air limitation) as well as their quantitative relationship with biochar properties. The results showed that BDOC in biochar pyrolyzed in air limitation (0.19-2.88 mg/g) was more than that pyrolyzed in N₂ (0.06-1.63 mg/g) and CO₂ flows (0.07-1.74 mg/g) at 450-750 °C. The aliphaticity, humification, molecular weight, and polarity of BDOC strongly depended on the atmosphere types as well as the pyrolysis temperatures. BDOC produced in air limitation contained more humic-like substances (0.65-0.89) and less fulvic-like substances (0.11-0.35) than that produced in N₂ and CO₂ flows. The multiple linear regression of the exponential form of biochar properties (H and O contents, H/C and (O+N)/C) could be used to quantitatively predict the bulk content and organic component contents of BDOC. Additionally, self-organizing maps could effectively visualize the categories of fluorescence intensity and components of BDOC from different pyrolysis atmospheres and temperatures. This study highlights that pyrolysis atmosphere types are a crucial factor controlling the BDOC properties, and some characteristics of BDOC can be quantitatively evaluated based on the properties of biochar.

Spectral characteristics coupled with self-organizing maps analysis on different molecular size-fractionated water-soluble organic carbon from biochar

Biochar-derived water-soluble organic carbon (BWSOC) plays important roles in the environmental effect of biochar. The environmental behavior and fate of BWSOC are closely related to its size distribution and chemical components. However, the molecular size-dependent BWSOC components and properties remain little known. To evaluate molecular size-dependent BWSOC characteristics, BWSOC samples were prepared by pyrolyzing biomasses in air-limitation and N₂-flow atmospheres at 300-600 °C and fractionated through a series of membranes with different pore sizes including 0.7 μm, 0.45 μm, 100 kDa, 10 kDa, 3 kDa, and 1 kDa. In all BWSOCs, <1 kDa and 0.45-0.7 μm fractions had the maximum abundance (mean: 40.6 %) and the minimum abundance (mean: 4.4 %), respectively. The spectral characteristics of BWSOC including polarity index, spectral slope, and humification index varied significantly with molecular size. The fluorescence excitation-emission matrix parallel factor (EEM-PARAFAC) analysis indicated that BWSOC was mainly composed of three organic components (humic-like, fulvic-like, and aromatic protein/polyphenol-like substances). Humic-like and fulvic-like substances mainly existed in <1 kDa fraction, while aromatic protein/polyphenol-like substances mainly existed in medium-size fractions (3 kDa-0.45 μm). The different locations of <1 kDa, 1 kDa-0.45 μm, and 0.45-0.7 μm fractions in EEM and PARAFAC self-organizing maps indicated self-organizing maps could effectively distinguish 0.45-0.7 μm, 1 kDa-0.45 μm, and < 1 kDa fractions via the variations of fluorescence intensity and organic components. Additionally, the distribution ratio of different molecular size fractions as well as the abundances of organic components in different molecular size fractions were strongly controlled by pyrolysis atmospheres (air-limitation and N₂-flow). This study systematically clarified the organic components and properties of different molecular size fractions in BWSOC, and the results are helpful to understand the possible environmental behavior and fate of BWSOC.

Mobility of water-soluble aerosol organic matters (WSAOMs) and their effects on soil colloid-mediated transport of heavy metal ions in saturated porous media

Water-soluble aerosol organic matters (WSAOMs) produced by biomass pyrolysis/burning can penetrate subsurface environment, and are anticipated to have a profound effect on the fate of contaminants in aquatic ecosystems. Herein, WSAOMs derived from corn straw (CS-WSAOMs) and pinewood sawdust (PW-WSAOMs) pyrolysis at 300-900 °C were utilized to investigate their mobility characteristics and impacts on the transport of heavy metal ions (i.e., Cd²⁺) in saturated quartz sand with or without soil colloids. This study clearly demonstrated that WSAOMs in subsurface systems exhibited high mobility, which increased as WSAOMs molecular sizes decreased and hydrogen-bond interactions between WSAOMs and sand grains declined. WSAOMs significantly improved heavy metal (i.e., Cd²⁺) and soil colloid-mediated Cd²⁺ mobility in the porous media, which stemmed from the increased binding affinities of colloids toward metal ions and the high mobility of WSAOMs. Interestingly, in terms of the mobility and colloid-facilitated transport of Cd²⁺, WSAOMs from higher pyrolysis temperatures exhibited enhanced effects; meanwhile, the PW-WSAOMs demonstrated stronger effects than the CS-WSAOMs. The trends were mainly attributed to the differences in the metal-binding affinities (e.g., cation-π interactions) and transport abilities of WSAOMs, as well as diverse Cd²⁺ adsorption capacities of colloids induced by various WSAOMs.

Water quality and periphyton functional response to input of dissolved manure-derived hydrochars (DHCs)

Dissolved organic matter (DOM) plays a critical role in the global carbon cycle and provides food and energy for aquatic organisms. Recently, hydrochar, as a solid carbonaceous substance derived from hydrothermal carbonization, has been increasingly used as a soil amendment. Upon entering the soil, dissolved components (DHCs) were released from hydrochar as exogenous DOM, finally entering the aquatic ecosystems by runoff, which participates in environmental geochemical processes. However, relevant reports revealing the response of the aquatic ecosystem to the input of DHCs remain insufficiently elucidated. For the first time, the fundamental features of DHCs and their influence on water quality and aquatic biological function were investigated in this study. DHCs at 260 °C (DHC260) had lower yields, a greater [C/N], worse biodegradability, and larger humic acid relative amounts than did DHCs at 180 °C (DHC180). The DHC structural alterations in periphyton-incubated aquatic ecosystems suggested that protein substances were more easily degraded or assimilated by periphyton, especially for DHC180, with rates of decrease of 34.5-63.5%. The increased chemical oxygen demand (COD) degradation in the DHC260 treatments was most likely due to humic acid substances with higher COD equivalents. Furthermore, DHC260 caused phosphorus to accumulate in periphyton, reducing aquatic phosphorus concentration. Notably, the abundances of Flavobacteria and Cyanobacteria associated with water blooms increased 12.7-25.5- and 1.3-8.3-fold, respectively; consequently, the promotional impact of DHCs on algal blooms should be considered. This result extends the nonnegligible role of DHCs in aquatic ecosystems and underlines the need to regulate the hydrochar application process.

Spectral characteristics of dissolved organic carbon (DOC) derived from biomass pyrolysis: Biochar-derived DOC versus smoke-derived DOC, and their differences from natural DOC

Biochar-derived dissolved organic carbon (BDOC) and smoke-derived dissolved organic carbon (SDOC) are two different biomass-pyrogenic DOCs. They inevitably enter soil and water, then potentially pose different impacts on the chemistry of these media. This study systemically investigated the emissions and spectral characteristics of BDOC and SDOC as well as their differences from natural DOC. The results showed that the emission of SDOC was 1-3 orders of magnitude greater than that of BDOC after biomass pyrolysis. UV-vis spectra indicated that BDOC had higher aromaticity and molecular weight as well as lower polarity than SDOC. The two-dimensional correlation infrared spectrum (2D-PCIS) matrix indicated that BDOC contained more chemical groups with stronger temperature-dependence than SDOC. Fluorescence EEM-PARAFAC analysis showed that BDOC was dominated by macromolecular humic-like substances, while SDOC was primarily composed of small molecules of aromatic protein/polyphenols-like compounds. The fluorescence indicators including humification index (HIX) (0.08-0.76) and biological index (BIX) (1.18-1.72) of SDOC were significantly different from those of BDOC (HIX: 1.64-12.68, and BIX: 0.17-1.62). The higher BIX and more small molecules of aromatic protein/polyphenols-like compounds indicated SDOC had potentially higher bioavailability and turnover rate in the environment than BDOC. Furthermore, the UV-vis spectral indicator (S_275-295) and fluorescence spectral indicators (HIX, and BIX) of BDOC were equivalent to those of natural DOC, whereas these indicators of SDOC were significantly different from those of natural DOC. This study demonstrated that BDOC and SDOC had significantly different components and properties and they might present different environmental behaviors and effects.

Surface Activity and Aggregation Behavior of Polyhydroxylated Fullerenes in Aqueous Solutions

Polyhydroxylated fullerene (PHF) surface activity and aggregation behavior at the air-water interface were examined using surface tension and resonance-enhanced second harmonic generation (SHG). Surface tension data showed that PHFs are surface active with a limiting surface excess corresponding to 130 Ų/molecule in aqueous (Millipore water) solutions. Increasing the solution-phase ionic strength (through the addition of NaCl) reduces the PHF surface excess. Conductivity measurements show that PHFs carry a single charge, presumably negative. Surface-specific SHG experiments show a small but measurable fixed wavelength, nonlinear response from solutions having surface excess coverages as low as ∼400 Ų/molecule. The SHG response of PHF solutions in the low-concentration limit shows unexpected behavior, implying that at bulk concentrations below 0.06 mg/mL, PHF monomers adsorb to the surface and interfere destructively with the intrinsic nonlinear susceptibility of the aqueous/vapor interface, leading to a ∼75% reduction in the SH signal. Above a PHF concentration of 0.0.06 mg/mL, the SH signal begins to rise in the Millipore and 50 mM NaCl solutions but remains very low in the 500 mM NaCl solutions. From this behavior, we infer that an increased nonlinear optical response is due to adsorbed aggregates.