SUVA254 Values Research Articles

Applying fluorescence and 2D-correlation spectroscopy to elucidate changes in the chemical composition of DOM from soils with different vegetation types

ABSTRACT To understand the decomposition of the dissolved organic matter (DOM), four different soils (from grassland, spruce forest, oak forest, and agricultural land) were incubated at 15 °C, and the DOM changes were monitored using UV-Vis, synchronized fluorescence and 2D-correlation spectroscopy. The DOM fraction of the agricultural and grassland soils showed a significant increase in both SUVA values in the middle of the incubation ranging from an initial 3–5 L mg−1 m−1 to 40–50 L mg−1 m−1. Synchronous fluorescence spectroscopy revealed that at the beginning of incubation, on day 3, there was an increase in the proportion of low molecular-weight, readily biodegradable compounds (PLF, protein-like fluorescence), while from day 8 onwards, microbial degradation generated a large number of medium-molecular-weight molecules (MHLF, microbial humus-like fluorescence). At further sampling dates, the proportion of compounds of microbial origin decreased systematically, due to a decrease in microbial activity caused by the lack of substrate. 2D-correlation measurements revealed further details of the changes in the quality of DOM, revealing two distinct patterns in the DOM dynamics of the soils, the sequence MHLF→PLF being observed for grassland and arable land and PLF→HLF for forest soils, probably due to the different N supplies of the soils.

Stemflow dissolved organic matter in mixed temperate forests: temporal and interspecific variation of optical indices and development of a stemflow-specific PARAFAC model

Stemflow is a conduit for the transport of canopy-derived dissolved organic matter (DOM) to the forest floor. This study examined the character of stemflow DOM for four tree species over four phenophases (leafless, emergence, leafed, and senescence for deciduous species and leafed-winter, emergence, leafed- spring/summer, and senescence for coniferous species) occurring in temperate forests; namely, Betula lenta L. (sweet birch), Fagus grandifolia Ehrh. (American beech), Liriodendron tulipifera L. (yellow poplar), and Pinus rigida Mill. (pitch pine). American beech exhibited the lowest average specific UV absorbance at 254 nm (SUVA254) values, while yellow poplar displayed the highest values. SUVA254 values were largest in senescence and smallest in emergence. The spectral slope ratio was lower for pitch pine than the deciduous tree species. Humification index (HIX) values decreased across all species during the emergence phenophase. The developed and validated stemflow-specific four-component parallel factor analysis (PARAFAC) model demonstrated the combined influence of interspecific and temporal fluctuations on the composition of humic and protein-like substances within stemflow. By separating and examining stemflow DOM independent of throughfall, our study provides fresh insights into the spatiotemporal dynamics of stemflow inputs to near-trunk soils that may inform hot spots and hot moments theories.

Investigation of the Distribution and Binding Affinity of Copper to Size-Fractioned Dissolved Organic Matter (DOM) in a Constructed Wetland

This study investigated the distribution and binding affinity of dissolved copper (Cu) and organic carbon (OC) in size-fractioned dissolved organic matter (DOM) in a constructed wetland (CW). Two sites were studied: one at the inflow (P-1) and one within the wetland (P-2). The DOMs (<0.45 μm) were separated into six size fractions using a cross-flow ultrafiltration system. In the wetland (P-2), the concentrations of dissolved organic carbon (DOC) increased while the concentrations of Cu decreased. The high molecular weight fraction (1 kDa–0.45 μm, HMW) contained most of the OC mass (57.4–71.2% averages). On the other hand, Cu was almost equally distributed in HMW and low molecular weight fractions (<1 kDa, LMW) with mean HMW percentages of 50.3–51.3%. The mean Cu binding affinity to DOM ratios (CuBADOM) was 74.9 ± 24.0 μmol/g-C at site P-1 and 17.3 ± 2.6 μmol/g-C at site P-2. The CuBADOM ratios were decreased in wetlands of bulk and size-fractioned DOM (p < 0.001 to p = 0.073). The SUVA254 values for bulk DOM solution were 2.54 ± 0.15 and 1.68 ± 0.18 L/mg-C/m, and humidification index (HIX) values were 1.74 ± 0.16 and 2.09 ± 0.19 for sites P-1 and P-2, respectively. Optical indicators suggested that the wetland process decreased aromaticity but increased the humification degree of DOM. Furthermore, the CuBADOM ratios positively correlated with SUVA254 and HIX within the constructed wetland DOM but not in the influent DOM. Understanding the Cu distribution and binding affinity to size-fractioned DOM makes it possible to develop strategies to mitigate the potential effects of copper pollution in wetlands.

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

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

Water extractable carbon and nitrogen across vegetated and non-vegetated coastal habitats

Many coastal ecosystems have a high carbon (C) and nitrogen (N) accumulation capacity. Extractable C and N have been shown to be useful indicators to assess changes in soil C and N in terrestrial systems but have not been widely used in coastal habitats. Here, we quantified cold and hot water extractable organic C (cweC, hweC) and N (cweN, hweN) and determined specific ultraviolet absorbance (SUVA254) to evaluate how water extractable C and N concentration and chemistry change along the transition from mangrove (vegetated) to tidal flat (non-vegetated) and with sediment depth. Sediment cores (20 cm depth) were collected along transects in a muddy (29–46 % clay + silt, Snells Beach) and sandy (8–11% clay + silt, Hobson Bay) estuary in the Auckland region, New Zealand. Cold water exactable C and N concentrations were similar in the muddy and sandy estuary (7–173 μg C g−1 soil; 1–32 μg N g−1 soil). However, cweC and cweN made up a larger proportion of sediment C and N concentration at the sandy estuary. The hweC and hweN concentrations were significantly higher in the muddy (240–2440 μg C g−1 soil; 25–244 μg N g−1 soil) than sandy estuary (50–960 μg C g−1 soil; 6–119 μg N g−1 soil) suggesting a higher release of C and N from the muddy estuary with organic matter rich sediments. Habitat had a strong effect at both sites with extractable C and N concentrations being higher in mangroves compared to tidal flat. The C:N ratios and SUVA254 values of cweC tended to be lower than hweC across all habitats in both estuaries, suggesting a higher proportion of algal-derived organic matter and a lower proportion of aromatic molecules. Our findings demonstrate that water extractable C and N provide valuable insights into the quality and drivers of C and N in coastal habitats.

Analyzing photodegradation of dissolved organic matter in different water bodies: river, lake, and pond

DOM is an important part of water ecosystems worldwide and provides a specific footprint to water bodies. A photochemical reactor and UV/Vis-spectrophotometer were used to treat and characterize water samples from Lake Xuanwu, Qinhuai River, and a pond. Comparing the absorbance, DOC concentration, and SUVA254 values of the water samples shows that UV radiation could degrade aromatics contents in water, and the process is most pronounced in the pond water samples compared to the other two. The results of this study could provide a reference to other studies regarding the hydrosphere in Nanjing and be helpful to future projects in the protection of the Xuanwu Lake and Qinhuai River in Nanjing.

Insight into enhanced photogeneration mechanism of reactive intermediates from dissolved black carbon by co-pyrolysis of plastics and biomass

The dissolved black carbon (DBC) derived from co-pyrolysis of plastic and biomass be released into aquatic environment. DBC was an important photoactive constituent, however, the photochemical activity of DBC from the co-pyrolysis plastic and biomass remains unclear. Herein three popular plastic wastes (polystyrene, PS; polylactic acid, PLA; plastic mulch film, PMF) and pine needle biomass prepared co-pyrolysis biochar, and effects of co-pyrolysis plastics on DBC’s photogeneration ability of reactive intermediates, affecting pollutant photodegradation, were investigated. In comparison to individual DBC, the mixed DBC from co-pyrolysis biochar had a lower molecular weight and more oxygen-containing groups. Quantum yields of singlet oxygen (1O2) and triplet state DBC (3DBC*) from mixed DBC were higher, especially PMF-DBC since its lower aromaticity and molecular weight connected with its higher E2/E3 and lower SUVA254 values. Steady-state photochemical experiment demonstrated 3DBC* formation rates for mixed DBC were lower than individual DBC, while the second-order reaction rate constants of 3DBC* with 2,4,6-trimethylphenol for mixed DBC were higher than that of individual DBC. Quenching experiment by sorbic acid to distinguish high/low-energy triplets revealed that contributions of low-energy triplets to 3DBC* and 1O2 generation decreased relative to individual DBC, indicating the transformation of reductive groups to oxidative groups, which was supported by the phototransformation kinetics. Quantum yields of 3DBC* and 1O2 were positively linear correlations with E2/E3 using twenty DBC samples. These findings are helpful in understanding DBC’s photochemical activity from co-pyrolysis of plastics and biomass, especially in aquatic environments adjacent to soil amended by biochar.

Contrasting optical properties of dissolved organic matter between oceanic regions near the Getz and Dotson ice shelves in the Amundsen Sea, West Antarctica

The Amundsen Sea, located in West Antarctica, is experiencing rapid melting due to the intrusion of Circumpolar Deep Water, which is causing ice sheet thinning and basal melting. The resulting changes can affect the biogeochemical cycle of dissolved organic matter (DOM) by supplying iron from sea ice and/or glacier, thereby influencing primary production and ocean circulation. Therefore, it is crucial to understand the dynamics of the DOM in this region. In this study, our primary focus was to examine the optical properties of DOM in the oceanic regions adjacent to the West Getz Ice Shelf (WGIS) and the Dotson Ice Shelf (DIS). Significant differences in DOM optical properties, including the chromophoric DOM (CDOM) absorption coefficient at 350 nm (a350), spectral slope coefficient (S275–295), and specific UV absorbance at 254 nm (SUVA254), were observed between the WGIS and DIS regions (t-test, p < 0.05). Notably, the WGIS regions exhibited high a350 values. Additionally, the S275–295 and SUVA254 values, which serve as indices of molecular weight, indicated that the DOM pool in the WGIS regions was dominated by high molecular weight compounds with a substantial proportion of aromatic compounds. In contrast, the low values of a350 and SUVA254 along with the high S275–295 values in the DIS region suggested the dominance of low molecular weight CDOM associated with compounds of lower aromaticity. Furthermore, significant negative correlations were found between biomass of Phaeocystis antarctica (P. antarctica) and phosphate (PO4) in the WGIS regions (r2 = 0.82, p < 0.01 for WGIS 1 and r2 = 0.73, p < 0.01 for WGIS 2). However, no significant relationship was observed in the DIS region. These findings suggest that the high value and molecular weight of a350, extending from the surface layer to the deep layer, in the WGIS regions were associated with autochthonous sources, primarily driven by the colony-forming bloom of P. antarctica. These findings demonstrate that the quantity and quality of DOM in the Amundsen Sea are strongly affected by bloom conditions. The results emphasize that a combination of physical and biological processes interacts in complex ways to determine the characteristics of DOM in the Amundsen Sea.

Organo-mineral associations and size-fractionated colloidal organic carbon dynamics in a redox-controlled wetland

The formation of organo-mineral associations serves as a crucial mechanism for stabilizing soil organic matter, particularly for determining the fate of soil organic carbon (OC) in redox dynamic wetlands characterized by high C content. Despite its importance, few studies have assessed the retention, transformation, and transport of colloids (1–1000 nm) and colloidal OC (COC) in those environments. This leaves a crucial knowledge gap concerning the quantities of colloids and COC and their molecular compositions, especially considering the significant role of metabolically active depressional wetlands that may play as biogeochemical hotspots for C cycling. To address this gap, we conducted a study in a Delmarva Bay depressional wetland located in Blackbird State Forest, Delaware, USA. We established a transect encompassing upland (U), transition (T), and wetland (W) zones based on seasonal hydrologic conditions. We installed piezometers at 50 cm, 100 cm, and 200 cm depths within each zone and collected pore-water samples from 11/2017 to 05/2019. We then fractionated these samples into dissolved (<2.3 nm), natural nanoparticle (NNP, 2.3–100 nm), fine colloid (100–450 nm), and particulate (450–1000 nm) fractions via sequential centrifugation and ultrafiltration, and quantified their concentration and molecular composition. We observed variations in the concentration and molecular composition of soil COC both vertically at different soil depths and horizontally along a redox gradient from the U-T-W transect. The sum of the NNP and fine colloid fractions accounted for 47±20% of the operationally defined “dissolved” (<450 nm) fraction. Isotope ratio mass spectrometry and X-ray photoelectron spectroscopy analyses further revealed that the NNP fraction is more enriched in heavier δ13C isotope and oxidized carbonyl/carboxyl C functional groups (C=O, p<0.05) with significantly higher surficial atomic percentages of C (p<0.01), N (p<0.01), and Mg:Al ratios (p<0.05), and lower atomic percentages of Al (p<0.01) and Si (p<0.01) compared to the larger particles. The formation of cation bridges and/or hydrogen bonds between carboxylic OC and phyllosilicate minerals likely dominated the mineral-OC association in the NNP fraction. The higher surface C enrichment in the particulate fraction compared to the NNP fraction suggests a patchy distribution of more plant-derived OC through organo-organic interactions in the larger fractions. Along the transect, Zone U exhibited significant enrichment of heavier δ13C isotope and lower SUVA values than the Zones T and W indicating inefficient decomposition and dissociation of SOM from minerals due to the reductive dissolution of Fe and Al oxides under anoxic conditions. Furthermore, an increase in low molecular weight microbial metabolites with reduced aromatic OC content was observed at deeper depths in Zones U and T. Our study provides new insights into the concentration and molecular composition of size-fractionated COC, highlighting the need to separately consider the NNP and fine colloid fractions from the operationally defined “dissolved” phase. This is crucial for assessing the biogeochemical cycling of OC in redox-active wetlands, a pressing need amidst the growing concerns about the impacts of climate change.

Self‐diagnosis of model suitability for continuous measurements of stream‐dissolved organic carbon derived from in situ UV–visible spectroscopy

AbstractApplication of high‐frequency monitoring of dissolved organic carbon (DOC) is difficult in instances where training datasets are challenging to develop (e.g., remote locations) and the relationship between optical features and DOC concentration changes due to environmental or landscape shifts (e.g., climate or land‐use change). We developed and compared three partial least squares (PLS) models using in situ water level measurements, conductivity, and UV–Vis spectral attenuation to predict DOC. Two site‐specific models were developed using data from a hillslope‐dominated forest or a low‐relief wetland‐pond‐dominated stream catchment. The third model, using data from both sites, exhibited the best performance (DOC range = 4–15.5 mg C L−1, mean = 8.38 mg C L−1, training RMSE = 0.34 mg C L−1, internal validation RMSE = 0.50 mg C L−1, external validation RMSE = 2.43 mg C L−1). We further demonstrate using PLS model statistics to monitor performance and elucidate when and how models should be updated. These statistics, Hotelling's T2 and squared prediction errors, are useful consistency checks for the predictions made and detect underlying inconsistencies that, if undetected, can reduce the robustness of DOC prediction. For example, via the T2 statistic, we identified the summer–autumn transition as a period when DOC composition differed from what was represented in the training dataset. We also determined that elevated SUVA254 values contributed to the overall bias observed in predictions made during the subsequent year as part of the external validation. This enabled the application of a bias correction that reduced the RMSE from 2.43 to 0.89 mg C L−1. The method presented here could be applied to future monitoring programs enabling model updates to monitor DOC fluxes accurately from optical datasets (e.g., attenuance or fluorescence) in the face of developing datasets in remote locations or environmental change. Implementation of this approach may also identify possible regime shifts or landscape and hydrologic change associated with climate and other environmental changes relevant to terrestrial to aquatic fluxes.

Heat-induced changes in soil water-extractable organic matter characterized using fluorescence and FTIR spectroscopies coupled with dimensionality reduction methods

Water extractable organic matter (WEOM) is a very mobile and reactive soil OM fraction, critical in the translocation of carbon (C) from soils to other environmental compartments. Transformations of WEOM due to soil heating can have implications not only at a local scale, but in places far away from the location of the event. However, their accurate characterization is costly when analyzing a large number of samples. The objectives of this work were to identify common patterns for the changes in WEOM caused by the heating of various soil types using a combination of spectroscopic and dimensionality reduction techniques. Six soils from Spain, Kenya and Israel were collected at depths 0–10 cm and analysed before and after heating in air to temperatures of 300 and 600 °C. Fluorescence EEMs were measured in soil–water extracts containing WEOM, and decomposed using parallel factor (PARAFAC) analysis. The FTIR spectra were measured in freeze-dried extracts and further analysed using non-negative matrix factorization (NMF). Total organic C and SUVA254 values of the extracts experienced changes with the heating treatments that were soil dependant. Four PARAFAC and three NMF components were sufficient to characterize WEOM changes in all soils, which showed common thermal transformation patterns irrespective of their origin and properties. Thermal transformation of fluorescent WEOM led to the increase in the proportion of a component with an emission maximum at Ex 300/Em 392 nm, and to a lower extent one with the emission maximum at Ex 300/Em 426 nm. Concomitantly, the proportion of components with emission maxima at longer excitation wavelengths was reduced. These changes occurred at the lowest heating temperature and were maintained at 600 °C, and they seem to indicate a depletion of fluorescent components more conjugated, bigger in size, and an enrichment in smaller ones. The NMF components obtained from FTIR spectra showed an increase of the proportion of compounds with CO bonds, more oxidized. No correlations were found between the components obtained with each method, thus indicating that the information obtained from the fluorescence EEMs-PARAFAC analysis and the NMF decomposition of FTIR spectra is complementary. It can be concluded that there is a common pattern of WEOM changes induced by thermal soil transformations irrespective of the origin and properties of the soils studied, and that the combination of different spectroscopic techniques coupled with dimensionality reduction methods can be used as a simple and low-cost method to fingerprint changes in WEOM composition, in general, and those caused by soil heating, in particular.

Conversion of polyphenolic polymers in aerobic biochemical treatment

Polyphenols are organic substances commonly involved in a wide variety of industrial processes. They are prone to polymerize with other organic chemicals during production and subsequent wastewater treatment section, which yields various persistent and recalcitrant organic chemicals. To better understand the behavior of polyphenolic polymers in wastewater treatment processes and the effect on the biodegradability of wastewater, we explored the conversion of polyphenolic polymers during aerobic biochemical treatment and their relationship with extracellular polymeric substances (EPS). The CODCr (chemical oxygen consumption measured using potassium dichromate) removal efficiency of the polyphenolic polymers with high concentration was only 29.66% with CODCr of 437.5 mg/L, which was far from the wastewater discharge standard (60–100 mg/L, first class standard of GB 8978–1996). In the activated sludge system with stabilized organic matter as the substrate, the effluent had the highest degree of humification with the maximum SUVA value of 6.87 L/(mg∙m). The polyphenolic polymers caused a component variation in EPS, further affecting wastewater's humification degree and degradability. In particular, the content of humic acid-like substances in loose bound EPS (LB-EPS) was up to 4 times more than control, indicating higher aromatization and humification degree and of the waste. On the contrary, the content of polysaccharides in LB-EPS decreased by about 46.2–87.7% in treatments with different concentration of polyphenolic polymer. The high-concentration polyphenol polymers somehow stimulated the microbial production like proteins and humic-like substances. The direct conversion of polyphenol polymers also contributed to the increased humification of wastewater.

Partial ozonation enhanced the content and aromatization of humic substances in activated sludge through chemical and microbial effects

Influences of partial ozonation on characteristics of humic substances (HS) in activated sludge (AS) was systematically investigated. It was firstly found that partial ozonation not only reduced sludge production, but also increased content and aromatization of HS in AS. The total extractable carbon of HS (TEC) in AS subjected to partial ozonation (i.e., an increasing O3 dosage, from 25 to 125 mg O3/g VS) considerably increased, from 138.7 ± 2.4 mg/L (SBR-25) to 151.6 ± 2.7 mg/L (SBR-125), which were 1.01–1.10 times the TEC of the control (SBR-0). In which the organic carbon of fulvic acids (FAC) and humic acids (HAC) increased from 30.9 ± 4.8 and 106.3 ± 4.6 mg/L (SBR-0) to 34.7 ± 1.3 and 116.9 ± 1.4 mg/L (SBR-125), respectively. SUVA254 values of both FA and HA in SBR-25∼SBR-125 were greater than their values in SBR-0. Mechanisms were clarified from chemical and microbial perspectives. During O3 treatment, organic nitrogenous substances and aliphatic compounds in HA were more mineralized and fused by O3; FA were more formed from soluble proteins and polysaccharides than mineralized. Consequently, HA content in AS was reduced with enhanced aromaticity, while FA content was increased with maintained aromaticity after O3 treatment. Then, after the ozonated AS was returned to SBR systems, the enhanced microorganism-led formation of HA in SBR from more accessible FA played a dominating role in the final increased TEC. Enhanced relative abundance (RA) of genera Lactococcus and Thauera after partial ozonation was possibly responsible for the increased RA of K00615 (tktA) and K00873 (pyk), promoting production of intermediates including phosphoenolpyruvate and erythrose-4-phosphate (initial metabolites for shikimate pathway) from glucose, enhancing HA formation related with shikimate pathway, and finally increasing the content and aromatization of HS. The results could guide researchers on improving sludge management by decreasing sludge production yield and enhancing sludge utilization potential through partial ozonation during wastewater treatment.

Comparative characterisation of forest litter on sod-podzolic soils of Forest Experimental Dacha in RSAU–MAA named after K.A. Timiryazev

Forest litter under linden and pine forests was studied at the Forest Experimental Dacha of the RSAU–MAA named after K.A. Timiryazev. Despite significant differences in physical and chemical parameters between the litter formed under the conditions of different forest communities, the properties of sod-podzolic soils formed under both vegetation types are quite similar. The litter under linden forest has higher ash content, it is less acidic and contains almost 2 times more exchangeable bases, the content of hydrogen and nitrogen is higher by 0.82 wt% and 0.66 wt%, respectively. The litter of linden and pine forests, according to the atomic ratios H : C, C : N and the degree of oxidation, are equal to 1.82, 30.3, -0.92 and 1.64, 45.7, -0.71, respectively; the litter of linden forests differs from litter of pine forests in the higher content of aliphatic, nitrogen-rich, reduced organic compounds. In the litter of linden forests concentration coefficients of phosphorus and magnesium 1.2 times higher; of carbon, potassium and aluminium – 1.3 times higher; of calcium – 1.4 times higher; of nitrogen – 1.8 times higher, and of silicon – 3 times higher, than in the litter of pine trees. However, the concentration factor of manganese in the pine forest litter is 1.9 times higher compared to the litter of linden. According to the results of UV spectroscopy, water-soluble organic matter of pine forest litter, unlike water-soluble organic matter of linden forest litter, is more enriched by components of aromatic origin. This is evidenced by higher values of SUVA254 and lower values of coefficients E2/E3 and E4/E6.

Characteristics of dissolved organic matter in two alternative water sources: A comparative study between reclaimed water and stormwater

Reclaimed water and stormwater are two important alternative water sources to mitigate water resource shortage. They can be reused by discharging into drinking water sources. Due to different sources, characteristics of dissolved organic matter (DOM, a precursor of disinfection by-products, DBPs) present in reclaimed water and stormwater would be different. This study selected reclaimed water to compare with stormwater (including both stormwater runoff and rainwater) by investigating their DOM characteristics, including concentrations, aromaticity, molecular weight, hydrophobicity/hydrophilicity, composition and DBPs formation potential. The results showed that reclaimed water had higher dissolved organic carbon (DOC) concentrations (6.02–10.8 mg/L) than stormwater (3.62–5.48 mg/L) while SUVA254 values of stormwater runoff (1.92–2.53 L/(mg-C·m)) were higher than reclaimed water (1.11–1.24 L/(mg-C·m)). Additionally, reclaimed water is more hydrophobic while stormwater runoff and rainwater are more hydrophilic. Although all water types included the highest fraction of DOM with molecular weight <1 kDa (43.0 %–77.5 %), reclaimed water primarily contained soluble microbial products (SMPs)-like and humic acid-like substances while stormwater runoff primarily contained humic acid-like DOM. In terms of DBPs, reclaimed water showed relatively higher formation potential than stormwater runoff while rainwater had the lowest DBPs formation potential. These results can contribute to effective water resource management. Particularly, when reclaimed water or/and stormwater are discharged into drinking water sources, these outcomes can help on efficient drinking water treatment.

Spectroscopic and Molecular Characterization of Water Soluble Organic Matter from Sediments in the Macrophyte-dominated and Algae-dominated Zones of Taihu Lake

Macrophyte- and algae-dominated lakes (zones) are the two typical states of shallow lakes, where the source and composition of organic matter are distinct. The burial of organic matter (OM) in the sediment supports the role of lakes as carbon sinks. However, organic matter in the sediments could be further processed, influencing the carbon cycle. The post-burial metabolism of the sedimentary OM relates closely to its composition. However, information on the differences in composition remains limited, especially the molecular composition of organic matter from sediments in the macrophyte-dominated and algae-dominated lakes. In this study, sediments were collected from the macrophyte-dominated and algae-dominated zones of Taihu Lake (East Taihu Lake and Meiliang Bay, respectively), and the active pool of sedimentary OM (water soluble organic matter, WSOM) was extracted and purified. The composition of the WSOM was characterized in detail via absorption spectroscopy, fluorescent spectroscopy, infrared spectroscopy, and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The optical index of E2:E3 showed that the molecular size of WSOM in the macrophyte-dominated zone (M-WSOM) was slightly larger than that in the algae-dominated zone (A-WSOM). Consistently, the intensity-weighted molecular weights were identified as 388.9 and 379.9, respectively, via FT-ICR MS analysis. M-WSOM was more humified than A-WSOM, as evidenced by the SUVA254 and HIX values. The FT-ICR MS results showed that the relative abundance of the condensed aromatic substance and the aromatics were 6.3% (intensity-weighted) and 7.7% for M-WSOM and 1.1% and 4.4% for A-WSOM, respectively. The excitation-emission matrix fluorescence-parallel factor analysis (EEM-PARAFAC) suggested that the protein-like component was more in A-WSOM than that in M-WSOM, and the FT-ICR MS results showed that the intensity-weighted relative abundances of peptides were 35.6% and 15.6% for A-WSOM and M-WSOM, respectively. The FT-ICR MS results further showed that the heteroatom-containing molecules were abundant in the sedimentary WSOM, i.e., 82.9% and 91.7% for M-WSOM and A-WSOM, respectively. The nitrogen-containing molecules dominated, contributing to 53.5% and 78.5% of M-WSOM and A-WSOM, respectively. There were 30.4% and 41.4% phosphorus-containing molecules in M-WSOM and A-WSOM, respectively. The phosphorus-containing molecules in M-WSOM were mainly aliphatics and highly unsaturated structures with low oxygen, whereas those in A-WSOM were mainly peptides. This study elucidated the detailed molecular composition of WSOM in the macrophyte-dominated and algae-dominated zones of Taihu Lake, which aids understanding of the carbon, nitrogen, and phosphorus biogeochemical cycles in lakes.

Effect of adsorption and coagulation pretreatment sequence on ultrafiltration membrane fouling: Process study and targeted prediction

A novel combined pretreatment strategy, where the hydrophobicity of feedwater is reduced and the morphology of flocs is optimized by varying the sequence of powdered activated carbon (PAC) adsorption and coagulation, is applied to alleviate membrane fouling. To explore the effects of pretreatment sequence and the role of PAC on the membrane fouling, the combined pretreatments of adsorption followed by coagulation (A-C) and coagulation followed by adsorption (C-A) are investigated with various PAC dosages (10, 20, and 50 mg/L). The results reveal that since PAC directly participates in the growth of flocs as the core during A-C pretreatment, the A-C pretreatment is more conducive than the C-A pretreatment to form flocs with a larger size, higher strength, and smaller fractal dimension. Thus, the flocs can accumulate into a porous cake layer to improve the membrane permeability and fouling reversibility. Moreover, the irreversible fouling is highly linearly correlated SUVA values in the early ultrafiltration cycles (R2SUVA = 0.9536) and with the floc strength in the late cycles (R2Strength = 0.9348–0.9763). This finding can be used to make a targeted diagnosis of irreversible fouling in different cycles, providing valuable guidance for prolonging the service life of ultrafiltration membranes.

Molecular characterization of nitrogen-containing organic compounds in fractionated atmospheric humic-like substances (HULIS) and its relationship with optical properties

Diverse nitrogen-containing organics are important components of humic-like substances (HULIS) in the atmosphere. In this study, organic components in particulate matter (PM) samples representing multiple sources were separated by successive solvent fractionation, which were then analyzed by mass spectrometric and optical instruments. The CHON compounds were eluted and clustered into the Low-polar, Medium-polar, and High-polar fractions, and discrepancies of the polar-fractions were particularly reflected by molecular descriptors such as aromaticity, oxygen content and molecular weight. In addition, the results from the light-absorbing parameters (i.e., MAE365 and SUVA254) underscored the importance of the Low-polar and High-polar fractions on optical absorption properties. The Low-polar fraction accounted for 40% of the cumulative SUVA254 values, suggesting significant content of ultraviolet-absorbing organics. The High-polar fraction contributed 52% of the cumulative MAE365 values, indicating abundant light absorption capacity and efficiency. Significant improvements were made on statistical analysis of multidimensional data by a combination of the molecular descriptors and optical parameters. Molecular structures, including condensed aromatic, lignin-like, and aliphatic compounds observed in distinct electrospray ionization modes, were found as main contributors to the light absorption capacity and the abundances of fluorophores in individual polar-fractions. Differential contributions of molecular characteristics on types and abundances of fluorophores were further found among the samples of multiple sources. Conclusions obtained from this successive solvent fractionation experiment could promote development of the pretreatment method for exploring the potential light-absorbing organics, which also provide insights into the emission sources of organics that are related to specific light absorption and fluorescence properties.

Component structure and characteristic analysis of cyanobacterial organic matters.

The characteristic analysis of cyanobacterial organic matters is an important premise of cyanobacterial organic pollution control. This paper investigated the component structure characteristics of algal organic matters (AOM) secreted and released by cyanobacteria in laboratory culture and actual Taihu Lake environment by spectroscopic quantitative and qualitative methods. Results showed that the secretion amount of AOM was mainly 4-6 μg COD/106 cells during the growth period of Microcystis aeruginosa, and the content ratio of extracellular organic matters (EOM) to intracellular organic matters (IOM) gradually increased from 0.83 in adaptation and logarithmic period to 3.33 in stable and decay period. The secretion of IOM showed a decrease trend, which indicated the decrease of its synthesis or the gradual infiltration and loss caused by cell membrane damage. From the component characteristics, the EOM had lower SUVA value and higher proportion of small molecular substances with molecular weight <3 kDa, indicating its more difficult to separate from water than IOM. Compared with the laboratory culture environment, the actual Taihu Lake resulted in more obvious characteristic heterogeneity of cyanobacteria EOM and IOM.

Effects of Feedstock Material and Pyrolysis Temperature on Dissolved Organic Matter in Biochars

The aim of this study was to investigate the effects of feedstock material and pyrolysis temperature on the content and spectral properties of dissolved organic matter(DOM) in biochars. Biochars were produced from the pyrolysis of rice straw and Cunninghamia lanceolata litter at three temperatures(350, 500, and 650℃). The results showed that the pH values of the two biochars with pyrolysis temperature increases were improved from 8.10 and 6.56 to 10.53 and 8.23, respectively. The pyrolysis temperature had no significant effect on the total C content of biochar, but the feedstock material and their interaction had significant effects on the total C content of the biochar(P<0.05). The dissolved organic carbon(DOC) content of the two types of biochar first decreased and then increased with increasing pyrolysis temperature, and the content of DOC of the biochar derived from rice straw was significantly higher than that from Cunninghamia lanceolata litter under the same temperature(P<0.05). The feedstock material had no significant effect on the SUVA254 value of DOM, but temperature and its interactive effect with the feedstock material had a significant effect on the SUVA254 values(P<0.05). Maximum DOC SUVA254 values occurred at 500℃ in the two types of biochar, indicating the highest degree of aromatization. Three-dimensional fluorescence spectra showed that the DOM components of the two types of biochar were dominated by fulvic acid-like and humic acid-like material, which had different responses to pyrolysis temperature. FTIR spectra suggested that the DOM of the biochars had absorption peaks at similar positions, in five regions, and the stretching vibration of aliphatic C-H gradually weakened with an increase in pyrolysis temperature. Therefore, the biochars produced at higher pyrolysis temperatures(500℃ and 650℃) had lower DOC contents but a higher aromatization degree and humification degree, and were more stable, compared to the biochars produced at a lower pyrolysis temperature(350℃).