Development of a fluorescence EEM-PARAFAC model for potable water reuse monitoring: Implications for inter-component protein-fulvic-humic interactions

Recycling C and N from biogas slurry and wastewater of hydrothermal carbonization to rice-paddy systems: Enhanced soil dissolved C and N retention

This study explores a sustainable agricultural approach by mixing biogas slurry (BS) with hydrothermal carbonization aqueous phase (HCAP) to recycle carbon and nitrogen to rice-paddy system. Over two years, the effects of combining swine-derived BS with vegetable-derived HCAP as an alternative for synthesized nitrogen fertilizer in a rice-paddy system were evaluated. Four nitrogen substitution rates were tested: 0 % (control group, CKU), 50 % (low nitrogen substitution rate, BSVL), 75 % (medium nitrogen substitution rate, BSVM), and 100 % (high nitrogen substitution rate, BSVH). Results demonstrated combined application of BS and HCAP significantly improved soil dissolved organic matter (DOM) and total nitrogen content by 28.5-82.5 % and 5.8-7.2 %, respectively, with positive correlations to the increase in nitrogen substitution rate (P < 0.05). The DOM components revealed substantial increases in microbial by-product-like and fulvic acid-like substances in the soil, by 0.6-2.0 folds and 2.8-10.3 folds, respectively. Ammonia volatilization was significantly reduced by 15.6-46.3 % and 2.2-12.6 % across two years, correlating with pH and ammonium levels in floodwater (P < 0.05). Additionally, substituting chemical nitrogen fertilizer with BS and HCAP maintained grain nitrogen content without compromising rice nitrogen uptake. The results of structural equation model indicate that substituting nitrogen with BS and HCAP enhanced the recycling of carbon and nitrogen in paddy soil by improving soil DOM and total nitrogen accumulation. Overall, this study presents a viable strategy for recycling carbon and nitrogen from BS and HCAP into paddy soil, thereby substituting chemical fertilizers and enhancing soil fertility.

Using fluorescence spectroscopy of DOM as an indicator of human-derived pollution: a case study in the Chongqing-Three Gorges section of the Yangtze River

Dissolved organic matter (DOM) is a crucial component of aquatic environments and is shaped by both natural and anthropogenic factors. In this study, we screened optical indicators associated with human-derived pollution by combining the fluorescence spectroscopy with source identification analysis. Three distinct components were identified: one microbial-like component (C1) and two terrestrial-like components (C2 and C3). Overall, the water quality was good, with autochthonous DOM dominating the composition, accounting for 66%-69% of the total DOM. In cluster and redundancy analyses, C2 showed a strong correlation with dichloromethane and petroleum substances, suggesting a strong correlation to gas extraction industry. While C3 was closely associated with linear alkylbenzene sulfonate, a commonly used anionic surfactant, as well as nutrients, indicating a connection to domestic wastewater discharges. This study provides a screening strategy for optical indicators which allows tracing the source of human-derived pollution in a rapid and economic way.

Ceramic membrane fouling caused by recycling biological activated carbon filter backwash water: Effective backwash with ozone micro-nano bubbles

The widespread use of ceramic membranes in wastewater recycling is still hampered by membrane fouling problems. Frequent chemical cleaning increases operating and maintenance costs. This work proposes ozone micro-nano-bubble (O3-MNB) backwash as a new backwashing method to control the ceramic membrane fouling. Activated carbon filter backwash water (ACFBW) was used as feed water for the ceramic membrane and the effect of O3-MNB backwash was compared with tap water backwash, air-micro-nano-bubble (Air-MNB) backwash and ozone water backwash. The results of the flux tests showed that the irreversible fouling resistance (RFi) for the O3-MNB backwash was only 4.8 %, 10.0 % and 23.3 % of the RFi for the tap water backwash, Air-MNB backwash and O3 water backwash, respectively. The results of the SEM and CLSM analyses demonstrated that the combination of ozone with MNB for backwashing was an effective method for the removal of viable cells and majority of proteins and polysaccharides from the surface of the ceramic membrane. However, the application of ozone also led to the release of microbial DNA, which increased its binding to Al₂O₃ on the ceramic membrane. Furthermore, the increased ozone concentration transported by the MNB could promote the generation of a large number of hydroxyl radicals (•OH) due to the effect of Al₂O₃, which potentially enhanced the oxidation of macromolecular contaminants in the pores. At the same time, the electrostatic repulsion and hydrophobic action provided by the MNB improved the efficacy of peeling off the filter cake layer when cleaning the membrane pores. Consequently, this study demonstrated the effectiveness of O3-MNB backwash in the long-term operation of ceramic membranes and provided insights into the fundamental mechanism by which this process controlled the membrane fouling.

Molecular foundations for shear-induced dynamics of natural organic matter

The overall objective of the present work was to quantify how shear, coupled with varying salt concentration, affected the particle size distribution and relaxation/aggregation behavior for various organic sources of nonliving natural organic matter (NNOM) in surface water. NNOM has been implicated as a conditioning agent leading to the formation of biofilms such as algae. NNOM is also a responsible in surface waters for facilitated transport of a variety of anthropogenic pollutants. These are NNOM surface-related phenomena, yet the variable surface area and surface composition of NNOM, which can change dependent on shear rate, is not discussed in the literature. NNOM polymer-like dynamics can interact with stream water velocity differences to determine the process and result of aggregation. The fundamental role of post-shear NNOM molecular structure and dynamic aggregation (self-assembly) is examined here alongside fresh (hydrological) versus mined (terrestrial) NNOM. Shear rate can be seen as a change in the velocities of streamlines in hydrology. In this early work, the response to shear rate for three types of NNOM was measured using a stress-controlled rheometer under varying conditions of ionic strength. Samples were studied for rheological response after a variety of pre-shear conditions, and data then coupled with surface composition data from previously reported fluorescence studies. Interestingly, a size class of 5 μm aggregates disappeared when Aldrich humic acid samples were treated with 0.3 M Ca2+. Evidence is also presented that the environmental samples flocculated at shear rates up to 400 s-1, rather than exhibiting particle breakup, with implications for reducing NNOM surface area. Dynamic response of different NNOM sources was not the same, some sources showing evidence of self-assembly. The molecular response to shear may play an important role in understanding the surface area and composition of NNOM responsible for facilitated transport of pollutants and initiation of biofilms.

Analysis of small three-dimensional fluorescence spectroscopy dataset using migration learning an example of phenol concentration prediction in wastewater

Three-dimensional fluorescence spectroscopy has been widely used to detect organic pollutants in water. However, the amount of data required for three-dimensional fluorescence spectroscopy analysis is relatively large, and the time cost of sample collection is high. The amount of data has become an unavoidable limitation of spectral analysis. This study takes the detection of phenol in industrial discharge wastewater as an example and proposes a transfer learning method for small fluorescence spectroscopy datasets. First, fluorescence spectra are generated by splitting them into linear combinations of positively and negatively distributed spectra. Then, based on the idea of transfer learning, the generated fluorescence spectra are used to train a task-specific pre-trained model, which is then transferred to the collected spectral dataset. Experimental results show that the prediction performance of the transfer learning method is improved by 50.08 % compared with that obtained by directly training the model using a small amount of spectral data. In addition, when the spectral data remains unchanged, the accuracy of the model can be improved to a certain extent by increasing the amount of spectral data used for pre-training. The transfer learning method proposed in this study further improves the prediction accuracy when data is limited, and the results of verification in real environments are also satisfactory. It provides a feasible solution to the problem of data limitations in three-dimensional fluorescence spectroscopy.

Fluorescence spectrometric analysis for diagnosing compositional variations in effluent organic matter by chlorination and ozonation

Analyzing the reactivity of organic matter to oxidants such as chlorination and ozonation is crucial for evaluating the effectiveness of water treatment systems and their potential impacts on environmental safety and human health. This study explored the changes in organic substances, specifically bovine serum albumin (BSA), humic acid sodium salt (HA), and effluent organic matter (EfOM) from a wastewater treatment facility during chlorination and ozonation. Four spectrometric techniques were employed: ultraviolet absorbance at 254 nm (UVA254), fluorescent excitation-emission matrix (EEM), synchronous fluorescence two-dimensional correlation spectroscopy (SF-2DCOS), and EEM-parallel factor integrated 2DCOS (EEM-PARAFAC-2DCOS). The findings revealed that ozone possesses superior oxidizing properties compared to chlorine, as evidenced by UVA254 and EEM analyses, resulting in more diverse structural modifications in EfOM. SF-2DCOS and EEM-PARAFAC-2DCOS provided comprehensive details on the direction and sequence of these changes, with EEM-PARAFAC-2DCOS delivering clear and intuitive insights. Protein-like and fulvic-like substances were susceptible to chlorination and ozonation, exhibiting different reaction sequences with each oxidant. Furthermore, variations in protein-like and humic-like components in actual EfOM samples may not align precisely with those in model substances, emphasizing the importance of considering specific organic matter variations in real EfOM samples compared to model substances. This research offered a deeper understanding of the reactivity and transformation of organic matter in wastewater treatment processes through simple and rapid spectroscopic methods, potentially improving the management and mitigation of undesired byproducts.

Magnetic biochar enhanced microbial electrolysis cell with anaerobic digestion for complex organic matter degradation in landfill leachate

Combining microbial electrolytic cells with anaerobic digestion (MEC-AD) was considered as an important method for enhancing complex organic matter degradation. However, the magnetic biochar (MBC) addition would be an effective approach for enhancing biodegradation in MEC-AD. By designing orthogonal experiments, the optimal parameters of MBC-enhanced MEC-AD system for landfill leachate treatment were determined. The results indicated that the optimal conditions were identified as HRT of 72 h, electrode spacing of 2.5 cm, and applied voltage of 0.8 V. Under these conditions, the COD removal efficiency reached a maximum of 54.7 %. Additionally, the UV-vis, 3D-EEM, and GC-MS indicated the macromolecules 13-Docosenamide (Z), Bis(2-ethylhexyl) benzene-1,4-dicarboxylate and bis(2-ethylhexyl) phthalate were degraded. 13-Docosenamide (Z) was almost completely removed under the conditions of 0.8 V applied voltage, 2.5 cm electrode spacing and 24 h HRT, with a removal efficiency of 99.91 %. Significant differences were observed in the microbial core genera among the MEC-AD systems. The core genera in the anodic and cathodic biofilms were primarily fermentative and electroactive bacteria, including Soehngenia (2.2 % - 32.1 %, 3.2 % - 26.4 %) and Desulfomicrobium (1.1 % - 10.2 %, 2.0 % - 29.3 %). Fermentative bacteria, norank_f__Bacteroidetes_vadinHA17, established cooperative relationships with electroactive bacteria Acinetobacter. The enrichment of electrochemically active bacteria optimized microbial interactions, thereby synergistically enhancing the biotransformation of complex organic matter in landfill leachate.

Multi-laser nanoparticle tracking analysis (NTA): A unique method to visualize dynamic (shear) and dynamic (Brownian motion) light scattering and quantify nonliving natural organic matter (NNOM) in environmental water

Application of simultaneous multi-laser nanoparticle tracking analysis (NTA) to environmental water samples to investigate nonliving natural organic matter (NNOM) is introduced as an innovative method for observing particles directly in their native media. Multi-laser NTA results of particle visualization, particle number concentration, and particle size distribution elucidated particle dynamics in low and high total dissolved solids (TDS) aqueous environmental samples. A pond water sample and concentrate from a reverse osmosis (RO) treatment process (Stage 1) had 1.3 × 108 and 5.62 × 1019 particles/mL, respectively, (at time = 0) after filtration at 0.45 μm. Beyond the traditional applications for this instrument, this research presents novel evidence-based investigations that probe the existence of supramolecular structures in environmental waters during turbulence or quiescence. The pond water sample exhibited time-dependent aggregation as the volume distribution shifted to greater diameter during quiescence, compared to turbulence. Disaggregation (increased numbers of particles over time) was noted in the >250 nm to <600 nm region, and aggregation of >450 nm particles was also noted in the quiescent RO concentrate sample, indicative of depletion of small particles to form larger ones. Multi-laser NTA and dynamic light scattering (DLS) capabilities were compared and contrasted. DLS and NTA are different (complementary) particle sizing techniques. DLS yielded more information about the physical hydrogel in the NNOM hierarchy whereas multi-laser NTA better characterized meta-chemical and chemical hydrogel characteristics. Operationalization of innovation-moving from fundamental investigations to application-is supported by implementing novel analytical instrumentation as we address issues involving climate change, drought, and the scarcity of potable water. Multi-laser NTA can be used as a tool to study and optimize complex water and wastewater treatment processes. Questions about water treatment efficiencies, membrane fouling, assistance of pollutant transport, and carbon capture cycles affected by NNOM will benefit from insights from multi-laser NTA.

Molecular-level insights into dissolved organic matter and its variations of the full-scale processes in a typical petrochemical wastewater treatment plant

Petrochemical wastewater (PCWW) treatment poses challenges due to its unique and complex dissolved organic matter (DOM) composition, originating from various industrial processes. Despite the addition of advanced treatment units in PCWW treatment plants to meet discharge standards, the mechanisms of molecular-level sights into DOM reactivity of the upgraded full-scale processes including multiple biological treatments and advanced treatment remain unclear. Herein, we employ water quality indexes, spectra, molecular weight (MW) distribution, and Fourier transform ion cyclotron resonance mass spectrometry to systematically characterize DOM in a typical PCWW treatment plant including influent, micro-oxygen hydrolysis acidification (MOHA), anaerobic/oxic (AO), and micro-flocculation sand filtration-catalytic ozonation (MFSF-CO). Influent DOM is dominated by tryptophan-like and soluble microbial products with MW fractions 〈 1 kDa and 〉 100 kDa, and CHO with lignin and aliphatic/protein structures. MOHA effectively degrades macromolecular CHO (10.86 %) and CHON (5.24 %) compounds via deamination and nitrogen reduction, while AO removes CHOS compounds with MW < 10 kDa by desulfurization, revealing distinct DOM conversion mechanisms. MFSF-CO transforms unsaturated components to less aromatic and more saturated DOM through oxygen addition reactions and shows high CHOS and CHONS reactivity via desulfurization and deamination reactions, respectively. Moreover, the correlation among multiple parameters suggests UV254 combined with AImod as a simple monitoring indicator of DOM to access the chemical composition. The study provides molecular-level insights into DOM for the contribution to the improvement and optimization of the upgraded processes in PCWW.

Molecular-weight dependent promotion and competition effects of natural organic matter on dissolved black carbon removal by coagulation

Dissolved black carbon (DBC) is the ubiquitous component of dissolved organic matter pools with the high reactivity for disinfection byproducts formation. However, it is unknown that the influence of molecular weight (MW) of natural organic matter (NOM) on the DBC removal from potable water sources. Therefore, it was studied that the DBC removal by coagulation in the presence of the NOM with various molecular weights. The DBC removal was promoted due to the presence of NOM and the promotion degree decreased with decreasing MW of NOM. Furthermore, the removal ratio of humic-like component increased as the MW of NOM decreased, suggesting that the competition between DBC and NOM increased with decreasing MW. The functional groups after coagulation were the same with that before coagulation as the MW of NOM varied, suggesting that the molecular structure was not the key factor of influencing the DBC removal. This study will give the deep insight into the prediction of the DBC removal ratio by coagulation based on the MW of NOM in water sources.

Influence of organic matters on the adsorption-desorption of 1,2-dichloroethane on soil in water and model saturated aquifer

1,2-Dichloroethane (1,2-DCA) is a typical organic chlorinated compound largely utilized in chemical manufacturing and industrial production and also a common pollutant in organically contaminated sites. The adsorption of 1,2-DCA on soil grains significantly influences its environmental fate and removal process. This study investigated the influence of fulvic acid (FA) and humic acid (HA) on the adsorption-desorption of 1,2-DCA in solid-liquid interfaces in water or constructed porous media. Experimental findings demonstrated the influence of organic matter on the adsorption of 1,2-DCA at the solid-water interface. 1,2-DCA adsorption increased in the FA or HA-treated soils when organic matter was present on the solid surfaces. The 1,2-DCA adsorption in the mixture of FA and HA was slightly lower than that in single organic acids, depending on the binding of FA and HA to the soil grains/colloids. Basic conditions reduced the adsorption of 1,2-DCA on soils, whereas acidic conditions enhanced adsorption due to the increased interactions via adsorption sites and hydrogen bonds. Conversely, the presence of organic matter in solutions (liquid phase in constructed porous media) will reduce the adsorption of 1,2-DCA on solid surfaces and increase the transport in the model aquifer. The combination of FA, HA, and rhamnolipids is helpful for the removal of 1,2-DCA from solid surfaces. Additionally, because of the enhanced desorption, the risk of 1,2-DCA contamination in groundwater can be increased when the organic matter or surfactant is present in the liquid phase if the eluent is not collected. This study helps to better understand the cooperative interaction of soil organic matter and chlorinated hydrocarbons at solid-water interfaces and the environmental fate and potential removal strategies of chlorinated hydrocarbons in contaminated sites.

In-situ sewer sediment self-cleaning by plant ash-driven hydrolysis: Impairing adhesion and hydraulic erosion resistance from gelatinous biopolymer molecule deconstruction

The gelatinous structure and adhesion of sediments induced strong hydraulic erosion resistance and bottom siltation, which brought about serious challenges in sewer management. The in-situ sediment self-cleaning technology with low energy and labor consumption has become urgent demand. This study proposed an innovative plant ash-triggered molecule hydrolysis strategy for driving sewer sediment self-cleaning. Plant ash treatment at the optimal dosage of 0.10 g/g SS promoted molecular deconstruction and dissolution of aromatic proteins (tryptophan-like and tyrosine-like proteins), humic acids (fulvic acid-like and humic acid-like substances) and carbohydrates with secondary structure deflocculation (α-helix to β-turn), meanwhile numerous microbial cells were lysed, contributing to linkage breakage in extracellular polymeric substance (EPS). The gelatinous EPS disruption and outward migration with cohesion reduction were achievable. Sediment adhesion was vulnerable to EPS structural damage, which was degenerated by 91.14 %. Correspondingly, the sediment matrix structure was observably disintegrated into dispersive and small fragments, with increased surface electronegativity and eliminated adhesive bio-agglomeration. Thereby, the sensitivity of sediments to hydraulic erosion was greatly improved. In this case, substantial organic and inorganic sediment particles were solubilized and downstream transported by gravity sewage flow. Such plant ash-triggered hydrolysis provided a sustainable strategy for sediment self-cleaning in "waste control by waste" pattern, which improved sediment floating by 7.25-9.57 times. Considerable economic benefits of 35.56-123.46 CNY/(sewer meter length) were obtained compared with traditional mechanical flushing approaches. The findings might provide theoretical and engineering inspirations for solving sewer sediment issues.

Spatial and seasonal controls on dissolved organic matter composition in shallow aquifers under the rapidly developing city of Patna, India

The distribution and composition of dissolved organic matter (DOM) affects numerous (bio)geochemical processes in environmental matrices including groundwater. This study reports the spatial and seasonal controls on the distribution of groundwater DOM under the rapidly developing city of Patna, Bihar (India). Major DOM constituents were determined from river and groundwater samples taken in both pre- and post-monsoon seasons in 2019, using excitation-emission matrix (EEM) fluorescence spectroscopy. We compared aqueous fluorescent DOM (fDOM) composition to satellite-derived land use data across the field area, testing the hypothesis that the composition of groundwater DOM, and particularly the components associated with surface-derived ingress, may be controlled, in part, by land use. In the pre-monsoon season, the prominence of tryptophan-like components likely generated from recent biological activity overwhelmed the humic-like and tyrosine-like fluorescence signals. Evidence from fluorescence data suggest groundwater in the post-monsoon season is composed of predominantly i) plant-derived matter and ii) anthropogenically influenced DOM (e.g. tryptophan-like components). Organic tracers, as well as Eh and Cl-, suggest monsoonal events mobilise surface-derived material from the unsaturated zone, causing dissolved organic carbon (DOC) of more microbial nature to infiltrate to >100 m depth. A correlation between higher protein:humic-like fluorescence and lower vegetation index (NDVI), determined from satellite-based land use data, in the post-monsoon season, indicates the ingression of wastewater-derived OM in groundwater under the urban area. Attenuated protein:humic-like fluorescence in groundwater close to the river points towards the mixing of groundwater and river water. This ingress of surface-derived OM is plausibly exacerbated by intensive groundwater pumping under these areas. Our approach to link the composition of aqueous organics with land use could easily be adapted for similar hydrogeochemical settings to determine the factors controlling groundwater DOM composition in various contexts.

Transformation of organic carbon through medium pressure (polychromatic) UV disinfection of wastewater effluent during wet weather events

An observed decrease in total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations following wastewater disinfection with medium pressure (MP, polychromatic) ultraviolet (UV) irradiation during wet weather flows is investigated. When antecedent rainfall in the previous 7-days was >2 in (5 cm), TOC and DOC concentrations decreased dramatically following MP-UV disinfection. Organic carbon surrogate measurements of biological oxygen demand (BOD), TOC, DOC, turbidity, UVA - 254 nm, SUVA (specific UVA), scanning UV-Visible spectra (200-600 nm), fluorescence excitation-emission matrix (EEM) spectra, and light scattering data are presented for wastewater resource recovery facility (WRRF) influent, secondary effluent (pre-UV-disinfection), and MP-UV-disinfected (final effluent) samples. TOC and DOC in wastewater influent and secondary effluent (i.e., pre-UV disinfection) correlated with antecedent rainfall conditions. The percent TOC and DOC removal through secondary treatment (i.e., from influent to effluent pre-UV) and the percent TOC and DOC removal through MP-UV disinfection (i.e., from effluent pre-UV to effluent post-UV) were compared and the latter approached 90 % through MP-UV disinfection during high antecedent rainfall conditions. Spectroscopy (UV, visible, or fluorescence) was performed on samples after filtration through 0.45 μm filters, i.e., the operationally defined DOC fraction of aquatic carbon. Scanning UV-visible spectra indicated transformation of an unidentified wastewater component into light-scattering entities regardless of antecedent rainfall conditions. The types of organic carbon (diagenetic, biogenic, or anthropogenic) and the significance of wet weather are discussed. An organic carbon contribution via infiltration and inflow was attributed as a source-of-interest in this research.

A tailored and rapid approach for ozonation catalyst design

Catalytic ozonation is widely employed in advanced wastewater treatment owing to its high mineralization of refractory organics. The key to high mineralization is the compatibility between catalyst formulation and wastewater quality. Machine learning can greatly improve experimental efficiency, while fluorescence data can provide additional wastewater quality information on the composition and concentration of organics, which is conducive to optimizing catalyst formulation. In this study, machine learning combined with fluorescence spectroscopy was applied to develop ozonation catalysts (Mn/γ-Al₂O₃ catalyst was used as an example). Based on the data collected from 52 different catalysts, a machine-learning model was established to predict catalyst performance. The correlation coefficient between the experimental and model-predicted values was 0.9659, demonstrating the robustness and good generalization ability of the model. The range of the catalyst formulations was preliminarily screened by fluorescence spectroscopy. When the wastewater was dominated by tryptophan-like and soluble microbial products, the impregnation concentration and time of Mn(NO₃)₂ were less than 0.3 mol L^-1 and 10 h, respectively. Furthermore, the optimized Mn/γ-Al₂O₃ formulation obtained by the model was impregnation with 0.155 mol L^-1 Mn(NO₃)₂ solution for 8.5 h and calcination at 600 °C for 3.5 h. The model-predicted and experimental values for total organic carbon removal were 54.48% and 53.96%, respectively. Finally, the improved catalytic performance was attributed to the synergistic effect of oxidation (•OH and ¹O₂) and the Mn/γ-Al₂O₃ catalyst. This study provides a rapid approach to catalyst design based on the characteristics of wastewater quality using machine learning combined with fluorescence spectroscopy.

Coupled effects of sedimentary iron oxides and organic matter on geogenic phosphorus mobilization in alluvial-lacustrine aquifers

The organic matter (OM) biodegradation and reductive dissolution of iron oxides have been acknowledged as key factors in the release of geogenic phosphorus (P) to groundwater. However, the coupled effects of natural OM with iron oxides on the mobilization of geogenic P remain unclear. Groundwater with high and low P concentrations has been observed in two boreholes in the alluvial-lacustrine aquifer system of the Central Yangtze River Basin. Sediment samples from these boreholes were examined for their P and Fe species as well as their OM properties. The results show that sediments from borehole S1 with high P levels contain more bioavailable P, particularly iron oxide bound P (Fe-P) and organic P (OP) than those from borehole S2 with low P levels. Regarding borehole S2, Fe-P and OP show positive correlations with total organic carbon as well as amorphous iron oxides (Fe_OX1), which indicate the presence of Fe-OM-P ternary complexes, further evidenced by FTIR results. In a reducing environment, the protein-like component (C3) and terrestrial humic-like component (C2) will biodegrade. In the process of C3 biodegradation, Fe_OX1 will act as electron acceptors and then undergo reductive dissolution. In the process of C2 biodegradation, Fe_OX1 and crystalline iron oxides (Fe_OX2) will act as electron acceptors. Fe_OX2 will also act as conduits in the microbial utilization pathway. However, the formation of stable P-Fe-OM ternary complexes will inhibit the reductive dissolution of iron oxides and OM biodegradation, thus inhibiting the mobilization of P. This study provides new insights into the enrichment and mobilization of P in alluvial-lacustrine aquifer systems.

Artificial neural network implementation for dissolved organic carbon quantification using fluorescence intensity as a predictor in wastewater treatment plants

Although spectroscopic methods provide a fast and cost-effective means of monitoring dissolved organic carbon (DOC) in natural and engineered water systems, the prediction accuracy of these methods is limited by the complex relationship between optical properties and DOC concentration. In this study, we developed DOC prediction models using multiple linear/log-linear regression and feedforward artificial neural network (ANN) and investigated the effectiveness of spectroscopic properties, such as fluorescence intensity and UV absorption at 254 nm (UV₂₅₄), as predictors. Optimum predictors were identified based on correlation analysis to construct models using single and multiple predictors. We compared the peak-picking and parallel factor analysis (PARAFAC) methods for selecting appropriate fluorescence wavelengths. Both methods had similar prediction capability (p-values >0.05), suggesting PARAFAC was not necessary for choosing fluorescence predictors. Fluorescence peak T was identified as a more accurate predictor than UV₂₅₄. Combining UV₂₅₄ and multiple fluorescence peak intensities as predictors further improved the prediction capability of the models. The ANN models outperformed the linear/log-linear regression models with multiple predictors, achieving higher prediction accuracy (peak-picking: R² = 0.8978, RMSE = 0.3105 mg/L; PARAFAC: R² = 0.9079, RMSE = 0.2989 mg/L). These findings suggest the potential to develop a real-time DOC concentration sensor based on optical properties using an ANN for signal processing.

Spectroscopic fingerprints profiling the polysaccharide/protein/humic architecture of stratified extracellular polymeric substances (EPS) in activated sludge

Extracellular polymeric substances (EPS), with a stratified structure including tightly-bound EPS (TB-EPS), loosely-bound EPS (LB-EPS), and soluble EPS (S-EPS) surrounding the microbial cells, are known to vitally affect the physicochemical and biological functions of activated sludge in wastewater treatment. Polysaccharides (PS), proteins (PN), and humic acids (HA) are key components of EPS but their roles in constructing the multi-layer architecture are still unclear. This study explored the EPS characteristics in relation to the components using spectroscopic fingerprinting techniques. Ultraviolet-visible (UV-vis) spectra demonstrated stark difference between TB-EPS and other EPS. Fluorescence excitation-emission matrix (FEEM) and apparent quantum yield revealed further detailed differences. Fluorescence quotient analysis highlighted the dominance of TB-EPS, LB-EPS, and S-EPS in the excitation/emission wavelength (Ex/Em) region of Em = 350-400 nm, Em > 400 nm, and low-Stokes shift band (Em - Ex < 25 nm), respectively. Wavelength-wise prediction of the FEEM intensity was achieved through multiple linear regression against the chemical composition and variance partitioning analysis witnessed binary interactions of PS×HA and PS×PN in S-EPS, PN×HA and PS×PN in LB-EPS, and ternary interaction of PS×PN×HA in TB-EPS as well as the wavelength-specific fluorescence responses of these interactions. Further, X-ray photoelectron spectroscopy, infrared spectra, and circular dichroism spectra corroborated the differences in primary, secondary, and tertiary structures across the EPS layers. Ultrahigh-performance liquid chromatography-mass spectrometry detected molecular fragments confirming the multi-component hybridization among PS, PN, and HA. This study demonstrates a spectroscopic approach to sensitively fingerprint the fine structure of EPS, which has the potential for rapid monitoring of EPS and related sludge properties in wastewater treatment systems.

Mitigation of ultrafiltration membrane fouling by a simulated sunlight-peroxymonosulfate system with the assistance of irradiated NOM

Oxidation pretreatments prior to ultrafiltration are hindered by the need for energy input and sludge disposal. Herein, a simulated sunlight-induced natural organic matter (NOM) for peroxymonosulfate (PMS) activation was used as pretreatment to alleviate ultrafiltration membrane fouling caused by NOM itself in the Songhua River water. When light intensity was over 100 mW/cm², the pretreatment removed NOM effectively, characterized with UV₂₅₄, dissolved organic carbon (DOC) and maximum fluorescent intensity (F_max), and improved filtration flux. At 200 mW/cm² light intensity and 0.5 mM PMS, 57.5% of UV₂₅₄ and 18.5% of DOC were removed, and humic-like fluorescent component was degraded by 84%-94% while ∼60% for protein-like substance. Membrane flux was increased by 94%, and reversible and irreversible fouling resistances were reduced by 62.4% and 51.9%, respectively. Both total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) were moderately correlated with the DOC, whereas they prominently correlated with the UV₂₅₄ and the F_maxs of all fluorescence components, which could be served as key indicators to predict and control membrane fouling. Mathematical modeling showed that the pretreatment alleviated the fouling in the membrane pores and cake layer. The simulated sunlight-induced NOM (³NOM* and e_aq^¯) could activate PMS to form active species, which enabled to oxidize high molecular weight (MW) substances and mineralize low MW compounds in NOM as well as hinder their linking with inorganic cations, thereby reducing organic and inorganic membrane fouling simultaneously. This study may provide a new strategy for decentralized potable water treatment, especially in a single household or community.

Pb0 flue gas biosorption in denitrifying MBfR: Characteristics and binding ability of extracellular polymeric substances

Pb⁰ in flue gas which is ubiquitous in the environment, poses a certain threat to human and ecology, but the study on EPS-dependent stabilization of lead to remove Pb⁰ from flue gas remains insufficient. In this investigation, the characteristics and heavy metals-binding ability of four EPS fractions were evaluated. The EPS were extracted from denitrifying membrane biofilm reactor (MBfR) and divided into slime EPS (S-EPS), loosely-bound EPS (LB-EPS), tightly-bound EPS (TB-EPS) and EPS in circulating flow (Y-EPS). The S, LB, TB-EPS related to Pb stabilization on biofilm need more attention. Compared to Pb-S-EPS (0.013 mg g^-1) and Pb-LB-EPS (0.13 mg g^-1), the Pb-TB-EPS (0.26 mg g^-1) was mainly stable form of vapor Pb⁰, since TB-EPS's higher content (30.67-82.44 mg g^-1 VSS), proteins (13.47-36.32 mg g^-1 VSS) and polysaccharides (9.37-32.48 mg g^-1 VSS) concentration. Particularly, proteins related ligands were more effective in S, LB, TB-EPS dependent adsorption of Pb, complexing with hydrophobic acid ligands further strengthened in TB-EPS adsorption. The Pb-EPS complex formed via binding with functional groups (such as O-H, N-H, C-H and CC) on EPS, also facilitated by loose structure of proteins. This study enlightens the researchers on the bio-treatment and EPS-dependent biosorption of Pb⁰ in flue gas in denitrifying MBfR.

Dissociation and removal of alkali and alkaline earth metals from sewage sludge flocs during separate and assisted thermal hydrolysis

High levels of alkali and alkaline earth metals (AAEM, including K, Na, Ca, and Mg) in sludge needs to be removed in pretreatment process for alleviating adverse effects on subsequent disposal. Theoretically, the liquid environment provided by the pretreatment technology of thermal hydrolysis (TH) is the ideal condition for the dissolution of AAEM. Therefore, this work quantified AAEM removal efficiency of TH and carbonaceous skeleton (CSkel) assisted TH that we previously proposed for sludge dewatering. Then the mechanism of AAEM dissociating from sludge was explored through the new perspective of biological structure evolution and chemical species transformation. The results showed that all of the AAEM in raw sludge was trapped in extracellular polymer substances (EPS) and cells. Only the water-soluble K/Na in EPS could be released by TH to the supernatant, the residual K/Na in EPS was organically linked with humic matters that were generated through the degradation of proteins. Water/NH₄Ac-soluble K/Na in cells still stayed inside with a more stable form of HCl-soluble after TH. Fortunately, with the assistance of CSkel, this part of K/Na could be leached out due to organic acids derived from hemicellulose decomposition. In such a case, the removal efficiency of K/Na was elevated to 55.5% and 72.5%, respectively. Unlike K/Na, nearly all the Ca/Mg in EPS were transferred to cell residuals during TH. They were combined with the bio-phosphorus in cell residuals as the form of HCl-soluble Ca/Mg-P precipitates, rather than carbonates, sulfates or other compounds. This precipitation reaction was also moderately suppressed in CSkel-assisted TH with low pH, then 7.7% and 34.1% of Ca/Mg were taken away by filtrate. This means that appropriately raising the reaction temperature and adding CSkel with high hemicellulose/cellulose contents can promote the removal of AAEM in sludge during TH process.

Quantification of organic fluorophores in absorbing media by solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy of modeled mixtures containing bovine serum albumin (BSA) and colorants

Solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy is beneficial for investigating the characteristics of natural organic matter (NOM) in the solid phase without extraction procedures. However, inner filter effect (IFE) due to the presence of dark components in samples can make it difficult to quantify the fluorophore concentration. To establish a new method to determine unknown concentrations of a fluorescent material in a sample containing various absorbing materials by SPF spectroscopy, modeled mixtures containing bovine serum albumin (BSA) and colorants at different ratios were examined. Fluorescence intensities of BSA against various concentrations afforded different saturation curves for different colorants in the mixtures, suggesting that it is difficult to use the SPF intensity for quantifying the concentration of fluorescent samples in which IFE has occurred, because one cannot obtain a single calibration curve that does not depend on the absorbing medium that it is mixed in. However, products of the fluorescence intensity and Kubelka-Munk (KM) function at the excitation wavelength were proportional to the first order of BSA weight concentrations, regardless of the colorant type. By using this trend as a calibration curve, it may be possible to quantify the amount of BSA from its SPF-EEM spectrum. In this study, the KM function was obtained using an ultraviolet-visible (UV-Vis) spectrometer with an integrating sphere. To reduce the labor and equipment cost of UV-Vis spectroscopy, a substrate of the KM function also was obtained from the Rayleigh scattering in an SPF-EEM spectrum, which could be used as a parameter for calibration curves that quantify the BSA concentration. Although further studies are required, this study proposed that the product of the SPF intensity and KM function at the excitation wavelength can be partially used for an empirical formula to quantify a variety of fluorescent materials mechanically mixed with various absorbing materials.

Impact of ozone treatment on dissolved organic matter in land-based recirculating aquaculture systems studied by Fourier transform ion cyclotron resonance mass spectrometry

In land-based recirculating aquaculture systems (RAS), the accumulation of dissolved organic matter (DOM) can have detrimental effects on water quality impacting the system performance, microbial community, and consequently fish health and welfare. Ozone is used in the RAS water treatment process to improve water quality and remove DOM. However, little is known about the molecular composition of DOM in RAS and its transformation when exposed to ozone. In this study, we performed a detailed molecular characterization of DOM in RAS and explored its transformation induced by ozonation of RAS waters. Ultra-high resolution (UHR) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) was used to characterize the DOM matrix of RAS waters (pump-sump and tanks) and to evaluate its transformation by ozonation. The analysis of DOM extracted from makeup water and feed samples allowed for the determination of DOM sources in RAS prior to ozonation. The CHO and unsaturated group of compounds were the most abundant class found in water samples. On the contrary, the DOM from feed samples was unique and consisted mainly of CHO, CHON and unsaturated group of compounds. After the ozonation of RAS waters, humic-like and unsaturated compounds [positive oxygen subtracted double bond equivalent per carbon (DBE-O)/C)] were decomposed, particularly the CHO-DOM that contained fewer -CH₂- features. Fulvic-like compounds and several hundred saturated compounds [negative (DBE-O)/C)] were formed post ozonation, particularly the CHON and CHONS group of compounds that were associated with fish diets, makeup waters and transformation products from the ozonation of the RAS waters. This study showed that the high accuracy of the ultra-high resolution FTICR MS can be applied to characterize and monitor the changes of DOM at a molecular level in RAS waters. To our knowledge, this is the first study where FTICR MS was incorporated for the characterization of DOM and its sources in RAS.

Challenges in quantifying and characterizing dissolved organic carbon: Sampling, isolation, storage, and analysis

Despite the advancements in analytical techniques, there are still great challenges and difficulties in accurately and effectively quantifying and characterizing dissolved organic carbon (DOC) in environmental samples. The objectives of this review paper are (a) to understand the roles and variability of DOC along the water continuum; (b) to identify the constraints, inconsistences, limitations, and artifacts in DOC characterization; and (c) to provide recommendations and remarks to improve the analytical accuracy. For the first objective, we summarize the four ecological and engineering roles of DOC along the water continuum from source water to municipal utility, including nutrients and energy sources, controlling the fates of micropollutants, buffering capacity, and treatability and precursors of disinfection byproducts. We also discuss three major challenges in DOC analysis, including spatial and temporal variations, degradability and stability, and unknown structures and formulas. For the second objective, we review the procedures and steps in DOC analysis, including sampling in diverse environmental matrices, isolation of DOC fraction, storage and preservation techniques, and analyses on bulk chemical characteristics. We list and discuss the available options and evaluate the advantages and disadvantages of each choice. Last, we provide recommendations and remarks for each stage: sampling, isolation, storage, and analysis.

Drinking water aromaticity and treatability is predicted by dissolved organic matter fluorescence

Samples from fifty-five surface water resources and twenty-five drinking water treatment plants in Europe, Africa, Asia, and USA were used to analyse the fluorescence composition of global surface waters and predict aromaticity and treatability from fluorescence excitation emission matrices. Nine underlying fluorescence components were identified in the dataset using parallel factor analysis (PARAFAC) and differences in aromaticity and treatability could be predicted from ratios between components H_ii (λ_ex/λ_em= 395/521), H_iii (λ_ex/λ_em= 330/404), P_i, (λ_ex/λ_em=290/365) and P_ii (λ_ex/λ_em= 275/302). Component H_ii tracked humic acids of primarily plant origin, H_iii tracked weathered/oxidised humics and the "building block" fraction measured by LC-OCD, while P_i and P_ii tracked amino acids in the "low molecular weight neutrals" LC-OCD fraction. Ratios between PARAFAC components predicted DOC removal at lab scale for French rivers in standardized tests involving coagulation, powdered activated carbon (PAC), chlorination, ion exchange (IEX), and ozonation, alone and in combination. The ratio H_ii/H_iii, for convenience named "PARIX" standing for "PARAFAC index", predicted SUVA according to a simple relationship: SUVA = 4.0 x PARIX (RMSEp=0.55) Lmg^-1m^-1. These results expand the utility of fluorescence spectroscopy in water treatment applications, by demonstrating the existence of previously unknown relationships between fluorescence composition, aromaticity and treatability that appear to hold across diverse surface waters at various stages of drinking water treatment.

Comparison of Pretreatment Methods for Salinity Gradient Power Generation Using Reverse Electrodialysis (RED) Systems

With the increasing concern about climate change and the energy crisis, the use of reverse electrodialysis (RED) to utilize salinity gradient power (SGP) has drawn attention as one of the promising renewable energy sources. However, one of the critical issues in RED processes is membrane fouling and channel blockage, which lead to a decrease in the power density. Thus, this study aims to improve our understanding of SGP generation by using RED by investigating the effect of pretreatment on the RED performance. Experiments were conducted by using a laboratory-scale experimental setup for RED. The low-salinity and high-salinity feed solutions were brackish water reverse osmosis (BWRO) brine from a wastewater reclamation plant, and a NaCl solution simulating seawater desalination brine. Several pretreatments were applied to the RED process, such as cartridge filter (CF), microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), activated filter media (AFM), and granular activated carbon (GAC). The results indicate that the open-circuit voltage (OCV) and the power density were similar, except for in the NF pretreatment, which removed the dissolved ions to increase the net SGP. However, the pressure in the RED stack was significantly affected by the pretreatment types. The excitation–emission matrix (EEM) fluorescence spectroscopy and the parallel factor analysis (PARAFAC) quantified the organic compounds that are related to the stack pressure. These results suggest that the removal of both colloidal and organic matters by pretreatments is crucial for improving the RED performance by reducing the pressure that is increased in the RED stack.