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Purpose: Effects of aeration on distribution and release potential of organic phosphorus in sediments are of great significance. The aim of this study was to investigate effects of fine bubble aeration at the sediment‒water interface on species distributions of organic phosphorus and related microbial activities in the sediments from Nanfei River, a seriously polluted urban river in Hefei City, Anhui Province, China. Materials and methods: A simulation experiment with a precision oxygen distribution system with fine bubble was applied and the sediments in system were taken out at intervals to test various indicators, mainly including the contents of phosphorus, species distribution of organic phosphorus, microbial biomass (MBC), and alkaline phosphatase activity (APA), as well as the number of phosphate solubilizing bacteria. Results: The results showed that the content of dissolved organic carbon (DOC) increased in the sediments, along with the decrease of pH and the significant increase of oxidation–reduction potential (ORP). The content of total phosphorus and inorganic phosphorus in the surface sediments generally presented a downward trend when the content of organic phosphorus increased first and then decreased during aeration. The variation trends of liable organic phosphorus and moderately labile organic phosphorus were similar to organic phosphorus, while the content of non-labile organic phosphorus was slightly decreased. In addition, the MBC and APA increased. The number of organic phosphorus mineralizing bacteria (OPB) increased while that of inorganic phosphorus solubilizing bacteria (IPB) decreased, and the number of OPB was significantly correlated to APA, which corresponds to the mineralization mechanism of organic phosphorus. Conclusions: There were two stages of phosphorus transformation in the surface sediments during the aeration treatment: the stabilization of inorganic phosphorus in the early stage and the mineralization of organic phosphorus latterly, which means an increased risk of phosphorus release into the water in the late stage. Therefore, the fine bubble aeration treatment at the sediment‒water interface applied to controlling the internal pollution of water bodies should be considered, especially focusing on the strict control of the aeration time. Overall, the present study can provide scientific guidance for in situ remediation of heavily polluted sediments. [ABSTRACT FROM AUTHOR]

Abstract Wastewater effluent makes up an increasingly large percentage of surface water supplies, but the impacts of discharge of effluent organic matter (EfOM) on receiving riverine and lacustrine dissolved organic matter (DOM) is still largely unknown. In the present study, we investigated variations of DOM quantity and quality along wastewater treatment plants (WWTPs)-river-lake continuum during drought periods, and made a tentative discussion on its implications for watershed environmental management. We used dissolved organic carbon (DOC) concentrations, UV absorption coefficients and excitation-emission-matrixs (EEMs) fluorescence spectroscopy combined with fluorescence regional integration (FRI) to characterize EfOM and riverine and lacustrine DOM along WWTPs-river-Chaohu Lake continuum. Our results showed that changes in DOM quantity and quality in receiving waterbodies were related to EfOM discharged from WWTPs and external input of DOM along inflowing river. Specifically, we found that the ratio of protein-like/humic-like notably decreased (P < 0.05), and %humic-like increased (P < 0.01) along WWTPs-river-lake continuum. Furthermore, the recent autochthonous contribution index (BIX) and the humification index (HIX) values showed that these variations of DOM composition were attributed to microbial degradations in receiving waterbodies. We concluded that the changes of DOM quantity and quality along WWTPs-river-lake continuum had important implications for DOM behaviors, and offered some novel ideas for watershed environmental management. Graphical abstract Image 1 Highlights • EEM-FRI technique could monitor the variations of DOM quantity and quality along water path way. • The protein-like significantly decreased along WWTPs-river-lake continuum, while the fulvic acid-like notably increased. • DOM composition varied along WWTPs-river-lake continuum, and resulted in altering its properties and environmental behaviors. • Quantity and quality of discharged DOM should be taken into account for watershed environmental management. [ABSTRACT FROM AUTHOR]

Riparian wetlands play important roles in the enhancement of water quality by controlling nonpoint source pollution and protecting aquatic ecosystems. In the present study, we surveyed and identified vegetation types in riparian wetlands, evaluated how vegetation types influence spatial patterns of water-extracted soil organic matter (WSOM) from riparian wetland, and probed the impacts of riparian fluorescent WSOM on fluorescent dissolved organic matter (FDOM) and water trophic states in river ecosystems. We used absorption and excitation-emission-matrix (EEM) fluorescence spectroscopy to characterize the optical properties of riparian WSOM and riverine DOM from Chongming Island, China, the largest alluvial plain island in the world. Our results showed that fifty-eight spermatophytes in riparian wetland were clustered into five vegetation types, including warm coniferous forest (WCF), deciduous broad leaf forest (DBF), evergreen broad leaf forest (EBF), aquatic plants (AP) and herbaceous plants (HP). Absorption spectra revealed the effects of vegetation types on riparian chromophoric WSOM quantity. Although no difference in water-extracted soil organic carbon (WSOC) contents was observed, deciduous broad leaf forest (DBF) and evergreen broad leaf forest (EBF) fed more fluorescent WSOM quantity than did the other vegetation (AP, HP and WCF), and deciduous broad leaf forest (DBF) and aquatic plants (AP) provided more humic-like (RC.1 and RC.2) and fulvic-like (RC.3) substances into riparian wetland ( P < 0.05 or P < 0.01). In addition, we noted that humic-like and protein-like substances (RC.4) transported from riparian wetland into a river water body, and riverine terrestrial-originated components (FC.1 and FC.2) were significantly related to the four riparian fluorescent WSOM components ( P < 0.05). Furthermore, the riverine trophic state was significantly higher when the fluvial DOM and its component quantity increased ( P < 0.05). We concluded that riparian wetland can control the quantity and quality of riparian WSOM and reshaped riverine DOM compositions and riverine water quality with important management implications. [ABSTRACT FROM AUTHOR]

Riparian wetland controls the transfer of terrestrial dissolved organic matter (DOM) to surface water bodies. However, the effects of land use on riparian soil DOM quality and its contribution to aquatic environment are largely unknown. In this study, the amount and composition of water-extracted soil organic matter (WSOM) in riparian wetlands were determined to evaluate the effect of land uses on spatial patterns of WSOM and streamwater quality on Chongming Island, China. The fluorescent properties of WSOM and fluvial DOM were analyzed using EEM spectra-combining PARAFAC model and accurate MS and MS/MS identification. Our findings showed no differences in the riparian WSOC contents between land use types (agricultural land, natural wetland, commercial land and industrial land). However, the fluorescent WSOM and its humic-like (Comp.1 and Comp.2) and microbial degradation (Comp.4) components significantly varied under different land uses ( P < 0.05). Overall, the fluorescent WSOM quantities and its components (Comp.1, Comp.2 and Comp.4) were present at markedly lower concentrations for agricultural land use relative to the other three land uses. The same distribution pattern was observed for carbonyl compounds and fatty acids in the riparian WSOM molecules ( P < 0.05), but the distribution patterns of the lipids were different between the four land uses ( P < 0.05). Industrial land could result in the input of more organic matter into the riparian wetland. Our results showed that fluvial Comp.1 and Comp.2 were significantly correlated with WSOM Comp.2 and WSOM Comp.4 ( P < 0.05). We also observed that the fluvial trophic status was significantly higher when the fluvial DOM components increased ( P < 0.05). These results indicated that land uses can alter the composition of riparian WSOM, reshape fluvial DOM compositions and significantly affect fluvial water quality. [ABSTRACT FROM AUTHOR]

Dissolved effluent organic matter (dEfOM) from wastewater treatment plants (WWTPs) is bound to encounter photo- and bio-degradation as discharged into the receiving water body. However, the comprehensive variations of dEfOM by photo- and bio-degradation are not well unveiled because of its compositional heterogeneity. In this work, dissolved organic carbon (DOC) concentrations, UV–Vis and fluorescent spectra combined with fluorescence regional integration (FRI) analysis were used to investigate the changes in bulk dEfOM and its fluorescent components during photo- and bio-degradation processes in the receiving water body. Results showed that 48.49%–69.62% of the discharged dEfOM was decomposed by ultra violet (UV)-irradiation and indigenous microbes, while the others (33%–45%) were recalcitrant and stable in the receiving water body. Specifically, the photo- and bio-degradation of chromophoric, fluorescent dEfOM and its components were found to follow the single or double exponential kinetic model, and the differences in photo- and bio-degradability of each components shifted its composition. Furthermore, results of bio-degradation after UV-irradiated dEfOM indicated that there was overlapping of photo- and bio-degradable fractions in dEfOM, and photoreactions could improve the self-production of natural organic matter in the receiving water body. These results could improve the understanding the fate of discharged dEfOM in the receiving water body, and we proposed some cost-effective strategies for discharging WWTPs effluent. Image 1 • 66.90% ± 1.34% of the discharged dEfOM could be decomposed by UV-irradiation and indigenous microbes in receiving water body. • UV-irradiation played a major roles in decomposing dEfOM after discharged into receiving water body. • The double exponential kinetic model was better suited to describe the photo- and bio-degradation processes of dEfOM. • Photochemistry reactions would improve bio-degradability of dEfOM for indigenous microbes. [ABSTRACT FROM AUTHOR]

As the emerging contaminants, the behavior and fate of microplastics (MPs) were highly related to the interactions with surrounding organic matters. However, information on the effects of molecular sizes of organic matters on the interaction is still lacking. In this study, the bulk algal-derived organic matter (AOM) samples were obtained and further fractionated into high molecular weight (HMW-, 1kDa-0.45 μm) and low molecular weight (LMW-, < 1 kDa) fractions. The interaction between MPs [polyethylene (PE) and polystyrene (PS)] and these MW-fractionated AOMs were characterized by dissolved organic carbon, fluorescence and absorbance spectroscopy, and fourier transform infrared (FTIR) analysis. Results showed that presence of AOM could effectively inhibit the release of additives from MPs. Further analysis found that the inhibition extents decreased in the order of HMW- > bulk > LMW-AOM. The absorbance and fluorescence spectroscopy showed that aromatic protein-like substances in HMW fraction exhibited higher adsorption affinity to MPs than the bulk and LMW counterparts. The strong sorption of aromatic substances may offer more binding sites for additives to inhibit the release of organic substances. Moreover, two dimensional FTIR correlation spectroscopy revealed that the HMW non-aromatic substances were preferentially adsorbed onto PS, which led to an enhanced adsorption capacity to additives by forming H-bonding. Therefore, the MW- and component-dependent heterogeneities of AOM samples must be fully considered in evaluating the environmental behavior of MPs. [ABSTRACT FROM AUTHOR]

The behavior and composition of hydrochar-based dissolved organic matter (DOM) would affect the efficiency of copper (Cu) removal from wastewater through adsorption. In this study, the reed was hydrolyzed in the presence of feedwater with and without ZnCl 2 , FeCl 3 , and SnCl 4 to produce pristine hydrochars (PHCs), which were named H 2 O-HC, ZnCl 2 -HC, FeCl 3 -HC, and SnCl 4 -HC. After removal of DOM, washed hydrochars (WHCs) were obtained, labelled as W–H 2 O-HC, W-ZnCl 2 -HC, W-FeCl 3 -HC, and W-SnCl 4 -HC. The release dynamics of DOM from PHCs were analyzed, and the adsorption behaviors of Cu2+ on both PHCs and WHCs were investigated. The results showed that chloride-modifications were beneficial for the porosity, specific surface area (SSA), and functional groups of WHCs. Meanwhile, the quantity of hydrochar-based DOM was significantly affected by chloride-modifications. In particular, the relative contents of Ar–P and Fa-L in the DOM released from hydrochars varied with time and modification. Furthermore, the Qe of Cu2+ adsorption on WHCs followed the order of W-SnCl 4 -HC > W-FeCl 3 -HC > W-ZnCl 2 -HC > W–H 2 O-HC at 15 °C. Compared to PHCs, the adsorption capacity of Cu2+ on WHCs was improved by 7.15–119.77% at the temperature of 35 °C. Simultaneously, the adsorption capacity of Cu2+ in WHCs showed a significant correlation with the SSA via physical adsorption (P < 0.05). Moreover, XPS analysis revealed that Cu2+ adsorption also occurred via complexation and chelation through newly formed Cu–O group between W-SnCl 4 -HC and Cu2+. Notably, the increase of Cu2+ adsorption in WHCs was significantly correlated with the release of Fa-L and Ar–P from PHCs (P < 0.05). This study found that the content and composition of hydrochar-based DOM could be a major driving factor for Cu2+ adsorption. [Display omitted] • The adsorption performance of chlorides-modified hydrochars for Cu2+ was studied. • The Q e of Cu2+ adsorption followed the order of W-SnCl 4 -HC > W-FeCl 3 -HC > W-ZnCl 2 -HC > W–H 2 O-HC at 15 °C. • Cu2+ removal efficiency of hydrochars was improved significantly by removing DOM. • Due to complexation, DOM should not be overlooked in the adsorption of Cu2+ on hydrochars. [ABSTRACT FROM AUTHOR]