Characteristic Regions of the Fluorescence Excitation-Emission Matrix (EEM) To Identify Hydrophobic/Hydrophilic Contents of Organic Matter in Membrane Bioreactors

An intelligent system for precise management of coagulants in sludge conditioning: Inspired by the exploratory behavior in primates using senses

Coagulation conditioning is a key step for sludge dewatering, while the control of optimal coagulant dosing is still a challenge. This study proposes an intelligent system for the precise management of coagulants (IISPMC) in sludge conditioning. This system was assembled using an electrical impedance spectroscopy (EIS)-based sensor and a decision-making model to conduct the self-perception, decision-making, execution, and dosage optimization in sludge conditioning through a feedback-driven exploratory trial process, conceptually inspired by structured exploration behavior observed in primates. Using the optimal dosage obtained by the traditional manual jar test as the reference, the accuracy and repeatability of the IISPMC were investigated. The robustness under different perturbed conditions, reliability, and generalizability of the IISPMC were further assessed. Moreover, the long-term operational capability and the feasibility of the application in the scaled-up conditioning were also discussed. The results showed that the intelligent system achieved statistical median accuracy and repeatability of approximately 5 %, good reliability with a 5 g/kg resolution (R2 > 0.94 in validation tests) in determining the optimal coagulant dosage, and strong robustness under sludge conductivity and concentration perturbed conditions. In addition, the performance of the IISPMC was validated across different sludge sources, including activated sludge, dredged sediment, and algal sludge, as well as different coagulants, exhibiting solid generalizability. The system also demonstrated stable continuous operation over 40 batches, which is equivalent to the number of continuous operation batches of a small-sized treatment plant over approximately half a month. Furthermore, even after scaling up the conditioning tank, the IISPMC maintained stable performance. These findings highlight the potential of the IISPMC for practical applications in sludge conditioning.

Spatial heterogeneity of EPS-mediated microplastic aggregation in phycosphere shapes polymer-specific Trojan horse effects

The pervasive contamination of aquatic ecosystems by microplastics represented a critical environmental challenge. While algal-bacterial symbiosis systems demonstrated potential for microplastic aggregation via extracellular polymeric substances (EPS), prior studies have focused on temporal dynamics rather than spatial heterogeneity in phycosphere. This study systematically investigated the adsorption mechanisms of Polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE) and polystyrene (PS) across stratified EPS fractions, tightly bound (TB-EPS), loosely bound (LB-EPS), and soluble (S-EPS), in phycosphere. Combining controlled aggregation assays with multimodal characterization, we revealed a hierarchical spatial framework governing EPS-microplastic interactions. Adsorption efficiency governed by polymer-specific interfacial energies and EPS organic composition. EPS at distinct hierarchical levels exhibited material-specific adsorption preferences for microplastics. PVC and PET demonstrated higher affinities for hydrocarbon components, while PE and PS were preferentially captured through interactions with polysaccharides and amide I groups, respectively. The adsorption and aggregation behaviors between EPS and microplastics in the phycosphere promoted eco-corona formation and induced the Trojan horse effect. However, the energy barrier of interaction forces and EPS spatial configurations jointly governed the hierarchical stabilization of polymer-specific microplastics. PVC and PET primarily colonized the outermost S-EPS layer, PS preferentially accumulated in the intermediate LB-EPS layer, and PE penetrated into the innermost TB-EPS layer. These findings addressed a key knowledge gap by delineating the ecological niche-specific distribution of EPS-microplastic binding, offering novel insights for optimizing bioremediation strategies and informing regulatory measures targeting particulate plastic pollution in hydrologic systems.

Polarity and fluorescent fractions of manure dissolved organic matter could affect differently the adsorption and desorption of antibiotics in soils

The impacts of manure dissolved organic matter (DOM) on the adsorption and desorption of veterinary antibiotics in soils have not been fully explored. In this study, the effects of pig manure (PM) DOM and its hydrophilic and hydrophobic fractions on antibiotic adsorption and subsequent desorption in three topsoils of bamboo stands under different fertilization conditions (control, with heavy manure application, and with heavy manure application suspended) were examined by batch experiments, with the aid of excitation-emission matrix fluorescence spectroscopy, Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy. The addition of 100 mg-C L-1 PM DOM was found to increase the adsorption (in terms of the Freundlich affinity coefficient (Kf)) of florfenicol by 71.27%-132.23% but decrease the adsorption of doxycycline, enrofloxacin, and sulfamethazine by 41.67%-94.78%, 98.09%-99.99%, and 22.93%-67.20%, respectively. These effects resulted mainly from the increases in solution pH by PM DOM addition and preferential adsorption of PM DOM's protein-like fraction to the soils. Effects of hydrophilic and hydrophobic fractions of PM DOM were antibiotic and soil specific, except the increases in adsorption Kf of florfenicol in all tested soils. Among the four antibiotics, sulfamethazine exhibited the lowest Kf values in the soils with PM DOM addition during both the adsorption and desorption processes, implying that sulfamethazine may be the most leachable antibiotic in the field. The results of this study indicate that it is essential to consider the varying effects of the aromaticity and hydrophobicity of manure DOM in assessing the leaching risk of veterinary antibiotics in manured soils.

Extreme Rainfall Amplified the Stimulatory Effects of Soil Carbon Availability on N2O Emissions

Ongoing climate change is predicted to increase the frequency and intensity of extreme rainfall, which will dramatically alter soil nitrous oxide (N2O) emissions, especially changes in soil organic carbon (SOC) due to anthropogenic management. However, our ability to predict this effect is limited owing to a dearth of research. Therefore, we selected two croplands in Northeast China with the same quantity but contrasting availability of SOC to explore the in situ dynamics of N2O fluxes and N-cycling microbes through 2-year field experiment and N2O production pathways by laboratory 15N-tracing experiment. In a normal rainfall year, the croplands with high (HCA) and low (LCA) SOC availability emitted 0.66 and 0.25 kg N2O-N ha-1 without N-fertilization and 2.03 and 1.51 kg N2O-N ha-1 with N-fertilization, respectively. In a record-breaking wet year, multiple heavy rainfall events caused water supersaturation in the low-lying HCA cropland over 2 months. Consequently, the background N2O emissions increased by 508% compared with the normal rainfall year, and the N-induced N2O emission factor increased from 0.77% to 2.24%. Soil dissolved organic carbon (DOC) was identified as the primary driver of larger N2O fluxes from HCA cropland which facilitated denitrification by fueling nirS- and nirK-denitrifiers metabolism. Furthermore, a greater N substrate supply via a faster mineralization-nitrification coupling process promoted the contribution of autotrophic nitrification to N2O in HCA cropland. The N2O pulses from HCA soils during the waterlogging period were derived from stimulated denitrification, which dominated N2O production (> 90%). Simultaneously, C availability enhanced and nitrate was produced via archaeal nitrification, leading to an increased nirS/nosZII ratio that fostered N2O production through incomplete denitrification. Overall, our findings highlight the importance of avoiding the amendment of exogenous organic materials with high C lability, particularly under climate extremes, to eliminate the potential positive feedback of SOC management on climate change by inducing N2O emissions.

Novel Sodium Carbonate Activation for Manufacturing Sludge-Based Biochar and Assessment of Its Organic Adsorption Property in Treating Wool Scouring Wastewater

Under the concept of green and low-carbon development, efficient and environmentally friendly biochar preparation methods have attracted much attention. This study assessed a novel sodium carbonate activator combined with acid modification for sludge-based biochar (SB) production and its adsorption of organics in wool scouring wastewater. Under 600 °C, the optimal carbonization temperature, the residual weight percentage of biochar carbonized material increases from 27% to 73% after Na2CO3 activation compared to ZnCl2 activation. Compared to HCl-modified ZnCl2-activated biochar (Zn-Cl-SB), HCl-H2SO4-modified Na2CO3-activated biochar (Na-Cl/S-SB) had a specific surface area of 509.3 m2/g, and the average mesopore size was 7.896 nm, with micropore volume and specific surface area increasing by 83.3% and 79.8%, respectively. Meanwhile, the C-O oxygen-containing functional groups and pyrrole nitrogen-containing functional groups were significantly increased. Na-Cl/S-SB exhibited an excellent adsorption performance for organic matter in wool scouring wastewater, with a maximum adsorption capacity of 168.3 mg/g. Furthermore, the adsorption process followed the pseudo-second-order kinetic model. Three-dimensional fluorescence spectrum analysis showed that Na-Cl/S-SB had a strong adsorption capacity for aromatic protein analogs, proteins containing benzene rings, and dissolved microbial by-products in wool scouring wastewater. This study will serve as a guideline for the green synthesis of SB while improving its ability to adsorb pollutants.

The photo-redox of chromium regulated by microplastics (MPs) and MPs-derived dissolved organic matter (MPs-DOM) and the CO2 emission of MPs-DOM

Microplastics (MPs) and chromium (Cr) are common pollutants in wastewater treatment plants, where ultraviolet disinfection processes may degrade MPs and photooxidize Cr(III) into more hazardous Cr(VI). In this study, the effects of MPs on the phototransformation of coexisting Cr, as well as the role and ecological effects of MPs-derived dissolved organic matter (MPs-DOM), were investigated. The photooxidation of MPs and Cr(III) was radical-driven reaction. The addition of MPs inhibited the photooxidation of Cr(III) and induced the photoreduction of Cr(VI) through surface adsorption. Both MPs and MPs-DOM generated comparable ROS at different irradiation moments, which can affect the photodegradation of MPs and MPs-DOM, as well as the phototransformation of Cr. The 56-day incubation showed a higher mineralization ratio of MPs-DOMs than riverine humic acid, indicating the vital contribution of MPs-DOMs to carbon emissions. In general, MPs-DOM lowered microbial abundance and diversity compared to the original inoculum. Bacterial and fungal succession was affected by both MPs-DOM and the original inoculum, with polyvinyl chloride-derived DOM possessing a stronger filtration impact on microbial communities than the other three MPs-DOMs. In this study, a win-win solution for Cr(VI) reduction and MPs treatment through photoirradiation was proposed, and the potential significant role of MPs-DOM in the transformation of coexisting contaminants, the carbon cycle, and microbial succession was highlighted.

The evolution of calcified anaerobic granular sludge bed informs the deep insight into its agglomeration process

Calcium-induced agglomeration of anaerobic granular sludge bed (AGSB) has become a critical factor in performance decline of calcified anaerobic reactors. However, the agglomeration process of AGSB and the underlying mechanisms remain unclear and elusive. This study delved into the evolution of calcified AGSB, and four typical states of normal AGSB (Nor-AGSB), calcified dispersed AGSB (Dis-AGSB), calcified dimeric AGSB (Dim-AGSB), and calcified polymeric AGSB (Pol-AGSB) were characterized. It was found that the minimum transport velocity of Dis-AGSB was 3.14-3.79 times higher than that of Nor-AGSB, and surpassed both the superficial velocity and the bubble-induced wake velocity. This led to the sedimentation of AGS at the bottom of reactor, resulting in stable contacts with each other. Solid fillers between AGS, namely cement, were observed within Dim-AGSB and Pol-AGSB, and could be classified as tightly- and loosely- bonded cement (T- and L-cement). Further analysis revealed that T-cement was rich in extracellular polymeric substances and intertwining pili/flagella, serving as the primary driving force for robust inter-AGS adhesion. While the L-cement was primarily in the form of calcite precipitation, and blocked the convective mass transfer pathways in Pol-AGSB, leading to the decreased convective mass transfer capacity. The critical distance between calcite and AGS was further revealed as 5.33 nm to form stable initial adhesion. Consequently, the agglomeration mechanism involving the evolution of AGSB was proposed as calcium-induced sedimentation, calcium-induced adhesion, and calcium-induced stasis in order. This study is expected to offer deep insight into the calcium-induced agglomeration especially from the overlooked perspective of AGSB, and provides feasible control strategies to manage the pressing calcification issues in engineering applications.

The binding effects and mechanisms of dissolved organic matter (DOM) on the fate of mercury in sludge anaerobic digestion combined with thermal hydrolysis

Dissolved organic matter (DOM) plays an important role in regulating the fate of mercury (Hg), e.g., mobility, bioavailability, and toxicity. Clarifying the role of DOM in binding Hg in the treatment processes of sewage sludge is important for relieving Hg contamination risks in land applications. However, the impacts of DOM on Hg binding in sewage sludge are still unclear. In this study, we investigated the evolution of Hg and its speciation in full-scale sludge anaerobic digestion (AD) with thermal hydrolysis. The role of DOM in binding Hg(II) was further analyzed. The results showed that AD with thermal hydrolysis led to an increase in the Hg content in the sludge (from 3.72 ± 0.47 mg/kg to 10.75 ± 0.16 mg/kg) but a decrease in Hg mobility (the mercury sulfide fraction increased from 60.56 % to 79.78 %). Further adsorption experiments revealed that at equivalent DOM concentrations, DOM with a low molecular weight (MW<1 kDa) in activated sludge, DOM with a medium molecular weight (1 kDa 5 kDa) in both anaerobically digested sludge and conditioned sludge showed high binding amounts of Hg(II), with 1372.54, 535.28, 942.09 and 801.51 mg Hg/g DOM, respectively. Parallel factor analysis (PARAFAC) and fluorescence quotient (FQ) results showed that tryptophan-like and tyrosine-like substances had high binding affinities for Hg(II). Furthermore, X-ray photoelectron spectroscopy (XPS) indicated that the reduced organic sulfur contained in the DOM was potentially bound to Hg through the interactions of Hg-S and Hg-O. These results indicated that DOM may play special roles in regulating Hg speciation. The association between DOM and Hg(II), such as the significant positive correlation (p < 0.05) between the dissolution rate of Hg(II) and release of tryptophan-like substances during thermal hydrolysis, suggested the potential way for removing Hg from sludge.

Magnetite alleviating calcification of anaerobic granular sludge (AnGS): Electron transfer enhancement and ion competition

Calcification accompanied by deactivation of anaerobic granular sludge (AnGS) is a continuing challenge for high calcium wastewater treatment. The interaction between Ca2+ and extracellular polymeric substances (EPS) is a precondition for this problem. In this study, magnetite for activity recovery and calcification alleviation simultaneously of AnGS under high calcium stress was investigated. The results showed that, in the presence of magnetite, the relative biogas production increased by 13.2 % with the higher activities of key enzymes involved in methanogenesis. Methanosarcina turned into the dominant methanogens, and syntrophic bacteria such as Chloroflexi, Synergistota were enriched, which indicated the enhancement of electron transfer by magnetite, supported by an 18 % increase of the electron transfer system (ETS) activity. Further characterizations of AnGS suggested that the granule calcification was alleviated with a final decrease of 13-40 % calcium content of AnGS with particle size of 1-2.5 mm. Besides, calcium was partially substituted by iron in the EPS, and the secretion of EPS especially proteins decreased. Batch tests demonstrated the competition between Fe2+ dissolved from magnetite and Ca2+, which interfered the interaction between Ca2+ and EPS, so the granule calcification was prevented. Therefore, magnetite played a pluripotent role in the alleviation of granule calcification and deactivation in situ via (1) enhancing electron transfer, and (2) blocking the complex between Ca2+ and EPS. This study provides a novel insight into the application of conductive metal materials in biological wastewater treatment systems suffering from high calcium attack.

Photochemical behaviors of sludge extracellular polymeric substances from bio-treated effluents towards antibiotic degradation: Distinguish the main photosensitive active component and its environmental implication

Activated sludge extracellular polymeric substances (ASEPSs) comprise most dissolved organic matters (DOMs) in the tail water. However, the understanding of the link between the photolysis of antibiotic and the photo-reactivity/photo-persistence of ASEPS components is limited. This study first investigated the photochemical behaviors of ASEPS's components (humic acids (HA), hydrophobic substances (HOS) and hydrophilic substances (HIS)) separated from municipal sludge's EPS (M-EPS) and nitrification sludge's EPS (N-EPS) in the photolysis of sulfadiazine (SDZ). The results showed that 60% of SDZ was removed by the M-EPS, but the effect in the separated components was weakened, and only 24% - 39% was degraded. However, 58% of SDZ was cleaned by HOS in N-EPS, which was 23% higher than full N-EPS. M-EPS components had lower steady-state concentrations of triplet intermediates (3EPS*), hydroxyl radicals (·OH) and singlet oxygen (1O2) than M-EPS, but N-EPS components had the highest concentrations (5.96 ×10-15, 8.44 ×10-18, 4.56 ×10-13 M, respectively). The changes of CO, C-O and O-CO groups in HA and HOS potentially correspond to reactive specie's generation. These groups change little in HIS, which may make it have radiation resistance. HCO-3 and NO-3 decreased the indirect photolysis of SDZ, and its by-product N-(2-Pyrimidinyl)1,4-benzenediamine presents high environmental risk.

Deciphering DOM-metal binding using EEM-PARAFAC: Mechanisms, challenges, and perspectives

Dissolved organic matter (DOM) is a pivotal component of the biogeochemical cycles and can combine with metal ions through chelation or complexation. Understanding this process is crucial for tracing metal solubility, mobility, and bioavailability. Fluorescence excitation emission matrix (EEM) and parallel factor analysis (PARAFAC) has emerged as a popular tool in deciphering DOM-metal interactions. In this review, we primarily discuss the advantages of EEM-PARAFAC compared with other algorithms and its main limitations in studying DOM-metal binding, including restrictions in spectral considerations, mathematical assumptions, and experimental procedures, as well as how to overcome these constraints and shortcomings. We summarize the principles of EEM to uncover DOM-metal association, including why fluorescence gets quenched and some potential mechanisms that affect the accuracy of fluorescence quenching. Lastly, we review some significant and innovative research, including the application of 2D-COS in DOM-metal binding analysis, hoping to provide a fresh perspective for possible future hotspots of study. We argue the expansion of EEM applications to a broader range of areas related to natural organic matter. This extension would facilitate our exploration of the mobility and fate of metals in the environment.

Rainwater extracting characteristics and its potential impact on DBPs generation: A case study

Frequent extreme precipitation events due to global warming can lead to large amounts of pollutants entering source water bodies via surface runoff and wet deposition, thus posing a threat to water supply security. In order to better understand the source characteristics and leaching mechanisms of rainwater dissolved organic matter (DOM), as well as its disinfection by-products formation potential (DBPsFP) during disinfection processes, rainwater samples were collected and extracting experiments were conducted. Three components were identified in rainwater through Parallel factor (PARAFAC) analysis, which were microbial humic-like component C1 (63.1 %), protein (tryptophan-like) component C2 (28.9 %), marine or terrestrial humic-like component C3 (8.1 %). The average molecular weight of rainwater fractions was ordered: hydrophobic neutral (HON) < hydrophobic bases (HOB) < hydrophobic acidic (HOA) < hydrophilic (HIS). The HOA and HON fractions of rainwater were the dominant precursors of trihalomethanes (THMs), while the rainwater HON fraction and hydrophilic fraction were the main precursor of haloacetic acids (HAAs) and trihloroacetonitrile (TCAN), respectively. Subsoil extracts had a higher concentration of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) than topsoil extracts. Partial least squares path modeling (PLS-PM) demonstrated that the extraction temperature was the dominant factor affecting the abundance of DOM in the topsoil extracts (R2 = 0.28), while the extraction time accounted more for the abundance of fluorescence substance and physicochemical indices in the subsoil extracts (R2 = 0.23 and 0.32, respectively). These results provide key information for controlling the impacts of global warming, in particular the risk of water sources being heavily contaminated by request rainfalls.

UV/persulfate processes for the removal of total organic carbon from coagulation-treated industrial wastewaters

Sulfate radical-based oxidation processes were investigated to understand the relationship between persulfate (PS) consumption and total organic carbon (TOC) removal from industrial wastewater under various PS concentrations. First, the degradation and mineralization of Bisphenol A (BPA) (initial concentration: 11 mg/L) were investigated in ultraviolet (UV)/PS systems. Complete degradation was achieved within 30 min of UV irradiation, and 41%-72% TOC removal was achieved at PS concentrations of 200 and 400 mg/L. The consumed concentration of S2O82- and generated concentration of SO42- increased gradually to similar levels. The ratio of the PS consumption to TOC removal based on the mass concentration (mg/L) was 14.5 and 23.2 at 180 min for 200 and 400 mg/L of S2O82-, respectively. Three types of coagulation-treated industrial wastewater from metal-processing, food-processing, and adhesive-producing plants were obtained, and TOC removal was analyzed using the same UV/PS systems (initial TOC concentration: 100 mg/L). The TOC removal rates ranged from 16.9% to 94.4% after 180 min of UV irradiation at PS concentrations of 1,000, 2,000, 4,000, and 8,000 mg S2O82-/L. Despite the higher TOC removal at higher PS concentrations, the PS activation efficiency decreased significantly as the PS concentration increased. Only approximately 30%-40% activation efficiency was achieved at a PS concentration of 8,000 mg/L. In this study, the ratio of PS consumption to TOC removal ranged from 20.6 to 43.9.

Investigating the different transformations of tetracycline using birnessite under different reaction conditions and various humic acids

Prior studies have successfully used manganese oxides to facilitate the transformation of tetracycline in aqueous solution. To further understand the kinetic and the transformation pathway of tetracycline via birnessite (δ-MnO2) under different conditions, experiments were conducted at pH levels of 3, 6, and 9 in the presence or absence of Aldrich humic acid (ADHA). Tetracycline removal followed the pseudo-second-order reaction model in all investigated cases, and the removal efficiency (g mg-1 h -1) followed the following trend: pH 3 (0.45/0.27) > pH 6 (0.036/0.087) > pH 9 (0.036/0.103) in the absence/presence of ADHA. Liquid chromatography-mass spectrometry/mass spectrometry results identified five main transformation products at m/z 495, 477, 493, 459, and 415, produced by the transformation reactions, including hydration, oxidation, desaturation, and oxy reduction. Notably, in the presence of ADHA at pH 3, products with higher toxicity secondary (m/z 477 and 495) were reduced, while less toxicity products (m/z 459 and 415) were enhanced. The experiments utilizing tetracycline and δ-MnO2 with varied humic acids (HA) revealed that HA with high polar organic carbon groups, such as O-alkyl, exhibited higher removal efficiency at pH 6. This research offers the first comprehensive insights into the pathway transformations of tetracycline via δ-MnO2 under different pH conditions and HA types. For further understanding, future work should investigate the binding of HA, TTC, and/or Mn2+ and the oxidation capacity of MnO2 after the reaction to clarify Mn2+ elution mechanisms.

Synergetic effect on fouling alleviating of membrane distillation in urine resource recovery by thermally activated peroxydisulfate pretreatment

Given that the spontaneous precipitation of minerals caused by urea hydrolysis and abundant organic compounds, membrane fouling became a major obstacle for urine recovery by membrane distillation (MD). Herein, this study developed a combined system (TAP-MD) by integrating thermally activated peroxydisulfate (TAP) and MD process to inhibit membrane fouling and improve separation efficiency. Based on the TAP-MD system, the separation performance was improved significantly, improving nutrient recovery efficiency and quality of reclaimed water. More than 80% of water could be recovered from urine, and about 94.13% of total ammonia nitrogen (TAN), 99.02% of total nitrogen (TN), 100% of total phosphate (TP), and 100% of K+ were rejected. The mechanism for alleviating urine-induced fouling was systematically and intensively studied. With TAP pretreatment, the TAN concentration of pretreated urine was kept at a low level steadily and the pH was at neutral or weakly acidic. Hence, inorganic scaling represented by carbonate and phosphate precipitates were significantly inhibited by creating unfavorable solvent environment for crystallization with TAP pretreatment. Additionally, aromatic proteins were found as the main organic foulants. According to the secondary structure of protein, the proteins were degraded by the cleavage of peptide bonds by TAP pretreatment. Meanwhile, the hydrophilicity of protein increased, which reduced the hydrophobic interaction of protein and membrane surface and thus alleviated protein-induced membrane fouling. This study revealed the inorganic and organic foulants in urine that caused membrane fouling and demonstrated the mechanism of membrane fouling alleviation by TAP-MD system. The experimental results will be instrumental in better understanding the mechanisms of membrane fouling induced by urine and optimize MD process for resource recovery from urine.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL₁/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL₂/ST-DNF), and an ozonation contact reactor (O₃). The FL₁/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL₂/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Fluorescence-based indicators predict the performance of conventional drinking water treatment processes: Evaluation based on the changes in the compositions of dissolved organic matter

This study investigated the treatability of dissolved organic matter (DOM) by the selected lab-scale drinking water treatment processes using fluorescence excitation-emission matrix (EEM) analysis. The fluorescence ratio Peak 3/Peak 2 was established from well-defined fluorescence peak intensity of humic-like components (Ex/Em: 225 nm/425 nm) and protein-like components (Ex/Em: 230 nm/345 nm). Peak 3/Peak 2 predicted the aromatic characteristics of DOM and their origins in the different natural surface water feeding the different drinking water treatment plants. The drinking water treatment processes confirmed the treatability of DOM using Peak 3/Peak 2 and was well-confirmed by specific UV₂₆₀ absorbance relative to dissolved organic carbon (DOC) (SUVA) and fluorescence-based indices. Peak 3/Peak 2 was demonstrated to have a strong correlation with SUVA and DOC removal for the water after treatment by coagulation, adsorption, and chlorination. Compared to the humification index and fluorescence index, Peak 3/Peak 2 is better for indicating the DOM composition in terms of treatability. These findings can broaden the use of fluorescence spectroscopy in water treatment applications, by developing the fluorescence ratio to evaluate the performance of drinking water treatment plants.

Ultrasound-assisted H2O2 directional-modification of powdered activated carbon for the enhanced adsorption of secondary effluent organic matter from printing and dyeing processes

The physicochemical properties of powdered activated carbon (PAC) are important factors affecting its adsorption performance, which is also related to the characteristics of target organic pollutants. In this study, the key indicators affecting the adsorption performance of PAC were identified, and the physicochemical properties of PACs were modified by hydrogen peroxide and/or ultrasound in a targeted manner to improve the adsorption performance. The results indicated the adsorption properties of printing and dyeing secondary effluent organic matter (EfOM) in terms of COD_cr and UV absorbance at 254 nm (UV₂₅₄) positively correlated with mesoporous volume, average pore size and acid group content of PAC. After modification, the mesoporous volume and average pore size of PAC increased, and the number of acidic groups increased, thus enhancing the adsorption efficiency. EfOM removal characteristics showed that PAC preferentially adsorbed unsaturated bonds or aromatic compounds, tryptophan-like proteins, soluble microbial metabolites and low molecular weight fractions below 1 kDa. In addition, the relative contents of specific surface area, pore volume and oxygen-containing functional groups (O-CO, C-OH, CO/O-C-O) of PAC decreased after adsorption, indicating that EfOM adsorption was a physical and chemical process, including pore filling, hydrophobic interaction and chemical bond force interaction. In general, PACs with larger mesoporous volume, average pore size and abundant acid groups possessed good adsorption performance towards EfOM.

Cupric ions inducing dynamic hormesis in duckweed systems for swine wastewater treatment: Quantification, modelling and mechanisms

Hormesis has attracted close attention of environmental and toxicological communities over the past decades. Most studies focused on the hormesis induced by stressors in the aspect of their biotoxicity to organisms, while little research was conducted on hormesis in the aspect of biological wastewater treatment process. In this study, removal of NH₄⁺-N and Cu²⁺ by S. polyrrhiza under long-term Cu²⁺ exposure at environmentally relevant concentrations in swine wastewater was investigated. Removal efficiencies of NH₄⁺-N by duckweeds at 0.0, 0.1, 0.5, 1.0, 2.0 and 4.0 mg/L Cu²⁺ were 81.6 %, 83.7 %, 89.4 %, 74.9 %, 61.8 % and 45.1 % on day 28, however, during the initial period of cultivation (0-4 days), such hormetic effect was not observed, indicating time-dependent feature of hormesis in NH₄⁺-N removal. The modified logistic growth model was applied to describe long-term hormesis induced by Cu²⁺ on NH₄⁺-N removal and it suggested that the optimal copper exposure for ammonium removal was 0.48 mg/L. More importantly, it was found that previous exposure to low doses of Cu²⁺ (0-1 mg/L) could enhance NH₄⁺-N removal performance under the second exposure. Cu²⁺ above 1 mg/L could switch copper bioaccumulation pattern from the Langmiur-irreversible type to reversible one, indicating risk of secondary pollution. Six components including freshly-produced humic-like substances, lignin, fulvic acid-protein complex, free amino acid-like substances, tyrosine-like substance and soluble amino acid-like substances in duckweeds were detected by parallel factor (PARAFAC) model detected. Principle component analysis (PCA) conducted on PARAFAC components suggested that enhanced synthesis of protein and growth factors intracellularly at low dose stimulation improved ammonia uptake from the environment. This study provided a novel strategy to improve treatment performance of duckweeds for copper contaminated wastewater and helped understand biochemical responses and their roles in evolutionary adaptive strategies to stresses.

Treatment of sewage sludge hydrothermal carbonization aqueous phase by Fe(II)/CaO2 system: Oxidation behaviors and mechanism of organic compounds

The Fe(II)/CaO₂ system with a stable oxidant and a low-cost homogeneous activating agent has been considered as a prospective process for the disposal of wastewater. The system was constructed to treat sewage sludge hydrothermal carbonization aqueous phase (HTC-AP) in this study. As the hydrothermal temperature increased, the organics in the HTC-AP were first decomposed and then cyclized, while the Maillard reaction occurs throughout the stage. The oxidation efficiency of the Fe(II)/CaO₂ system was related to the composition of organics in HTC-AP, and the removal of dissolved organic carbon (DOC) by the system was 38.56 % in the HTC-AP obtained by hydrothermal treatment at 220 °C. Redundancy analysis showed that the low molecular weight organics, hydrophobic acids, and hydrophobic neutral components were beneficial to DOC removal, while Maillard products and cyclization products were hard to be oxidized to CO₂ and H₂O. The CN functional group of the protein facilitated DOC removal, and some organics in HTC-AP were oxidized to acids and phenols. The energy input to remove DOC in Fe(II)/CaO₂ system was 27.74 MJ per kg carbon. This study provides a low-energy consumption Fe(II)/CaO₂ system for the post-treatment of HTC-APs and explores the applicability of the system.

New insight into soluble extracellular metabolites during sludge bulking process based on excitation-emission matrix spectroscopy and ultrahigh-performance liquid chromatography-mass spectrometry

Soluble extracellular metabolites (SEM) produced by microorganisms might significantly change during sludge bulking, which is a major operational problem caused by the excessive growth of filamentous bacteria. However, knowledge remains limited about the dynamics and potential role of SEM in the bulking of sludge. In this study, filamentous bulking was simulated in a laboratory-scale reactor and changes to SEM characteristics during the bulking process were investigated using excitation-emission matrix spectroscopy and ultrahigh-performance liquid chromatography-mass spectrometry. SEM components changed significantly at different phases of sludge bulking. Changes in SEM were closely correlated with the structure of the bacterial community. Based on the EEM profiles, significant increases in fulvic acid-like and humic acid-like substances in SEM were observed with the development of filamentous bulking. The degree of humification in SEM showed a clear increasing trend. Untargeted extracellular metabolomic analysis showed that the intensity of berberine and isorhamnetin in SEM increased significantly during the bulking phase, which might synergistically facilitate the development of filamentous bulking.

Insights into leachate reduction in landfill with different ventilation Rates: Balance of Water, waste physicochemical Properties, and microbial community

Ventilation is an efficient approach employed for accelerating stabilization and reducing aftercare of landfill, but its effect on leachate reduction is still elusive. To fill this knowledge gap, five lab-scale landfill reactors with different ventilation rates were established in this study. Suitable ventilation (e.g. 0.25-0.5 L·min^-1·kg^-1 dry solid of waste (DS)) was beneficial to promoting the stabilization of landfill, which effectively accelerated the degradation of organic matter and reduced water content of landfilled waste. Based on the mass balance of water, the dominant input water was initial water of landfilled waste (more than 94 %), which was partially converted to leachate and evaporated water. Ventilation enhanced the intensity of biochemical reactions heat to increase evaporated water content from 0 to 0.29 t/t DS while reducing the leachate generation significantly from 0.69 to 0.49 t/t DS with the increase of ventilation rate. Besides, the hydrophilic substances, such as humic acid-like substances, in landfilled waste increased, and the surface of the landfilled waste converted from smooth to rough. The reduction of the bound water content has a significant correlation with the degradation of organic matter content (p less than 0.05), which reduced the water-holding capacity of waste. Actinobacteriota and Firmicutes were the key bacterial phyla in the degradation of organic matter to promote bio-heat and evaporation of water, thus reducing leachate production under suitable ventilation conditions. Carbohydrates and amino acids were the main energy metabolism sources of bacteria during the landfill process. This study deepens our understanding of the leachate reduction mechanism in the micro-aerobic landfill.

A new process to further remove dissolved organic matter and disinfection by-product formation potential during drinking water treatment

Biological activated carbon (BAC) will produce soluble microbial products (SMPs), which affect effluent quality. To clarify the mechanism by which BAC affects effluent water quality, the processes of a drinking water plant in Jiangsu Province were investigated. It was found that during the O₃-BAC process, although ozonation could remove dissolved organic matter (DOC) to a certain extent, the DOC increased from 4.44 to 4.47 mg/L after BAC. Dissolved organic matter (DOM) in effluent from different processes was divided into five fractions based on hydrophilicity and hydrophobicity by resin fractionation. Through fluorescence excitation-emission matrix (EEM) spectroscopy combined with DOC analysis, it was found that SMPs are mainly included in transitional hydrophilic neutral (TPIN) fraction, which was the main cause of the DOC increase. Therefore, a new combined process was designed to remove TPIN effectively by coagulation after biological treatment, and found that coagulation had a good removal rate (13.2%) on TPIN. The trihalomethane formation potential (THMFP) of TPIN could be reduced effectively by 44.9% after coagulation. Compared with the old process, the new combined process had a higher removal rate (14.2-30.0%) of DOC, as well as a greater reduction of THMFP (29.0-78.6%) and haloacetic acid formation potential (HAAFP) (46.4-75.3%). This study aims to reveal the mechanism by which SMPs affect effluent water quality and exacerbate health risks, and to propose a solution to provide theoretical support for the design and optimization of drinking water treatment processes.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5-6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of -0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

Oxygen availability regulates the quality of soil dissolved organic matter by mediating microbial metabolism and iron oxidation

Dissolved organic matter (DOM) plays a vital role in biogeochemical processes and in determining the responses of soil organic matter (SOM) to global change. Although the quantity of soil DOM has been inventoried across diverse spatio-temporal scales, the underlying mechanisms accounting for variability in DOM dynamics remain unclear especially in upland ecosystems. Here, a gradient of SOM storage across 12 croplands in northeast China was used to understand links between DOM dynamics, microbial metabolism, and abiotic conditions. We assessed the composition, biodegradability, and key biodegradable components of DOM. In addition, SOM and mineral-associated organic matter (MAOM) composition, soil enzyme activities, oxygen availability, soil texture, and iron (Fe), Fe-bound organic matter, and nutrient concentrations were quantified to clarify the drivers of DOM quality (composition and biodegradability). The proportion of biodegradable DOM increased exponentially with decreasing initial DOM concentration due to larger fractions of depolymerized DOM that was rich in small-molecular phenols and proteinaceous components. Unexpectedly, the composition of DOM was decoupled from that of SOM or MAOM, but significantly related to enzymatic properties. These results indicate that microbial metabolism exhibited a dominant role in DOM generation. As DOM concentration declined, increased soil oxygen availability regulated DOM composition and enhanced its biodegradability mainly through mediating microbial metabolism and Fe oxidation. The oxygen-induced oxidation of Fe(II) to Fe(III) removed complex DOM compounds with large molecular weight. Moreover, increased oxygen availability stimulated oxidase-catalyzed depolymerization of aromatic substances, and promoted production of protein-like DOM components due to lower enzymatic C/N acquisition ratio. As global changes in temperature and moisture will have large impacts on soil oxygen availability, the role of oxygen in regulating DOM dynamics highlights the importance of integrating soil oxygen supply with microbial metabolism and Fe redox status to improve model predictions of soil carbon under climate change.

Landfill leachate treatment by graphite engineered anaerobic membrane bioreactor: Performance enhancement and membrane fouling mitigation

Low efficiency of anaerobic digestion and membrane fouling, treating landfill leachate, are big barriers in the application of anaerobic membrane bioreactor (AnMBR). Anaerobic digestion enhancement and membrane fouling mitigation of AnMBR with graphite addition, treating landfill leachate, were investigated in this study. The effect of graphite on organics removal, biogas production, methane content in biogas, membrane fouling, microbial responses and foulant compositions were analyzed. With the graphite addition, chemical oxygen demand (COD) removal of 78% was achieved for influent COD concentration of 3000 mg/l, which was significantly higher than the stage without graphite addition (65%) for influent COD concentration of 2000 mg/l. Similarly, methane content in biogas with graphite addition was 56%, while without graphite addition it was 46%. These digestion improvements were due to the promotion of organics degradation, facilitated by direct interspecies electron transfer (DIET) mechanism via graphite addition in AnMBR. The graphite addition prolonged membrane cleaning cycle from 13 days to 30 days. Protein content in loosely bound extracellular polymeric substance (LB-EPS) was the main fouling agent, which decreased with the graphite addition. The main mechanism behind membrane fouling mitigation was the protein content reduction in LB-EPS, which was biodegraded by Trichococcus being increased in relative abundance with the graphite addition. Furthermore, abundance of Denitratisoma decreased in anaerobic sludge and its accumulation reduced on membrane surface, subsequently membrane fouling was mitigated. Overall, graphite addition in AnMBR is a potential eco-innovative approach that efficiently removes pollutants from landfill leachate, enhances biogas quality and mitigates membrane fouling.

Process water recirculation for catalytic hydrothermal carbonization of anaerobic digestate: Water-Energy-Nutrient Nexus

The process water (PW) from acid-catalyzed hydrothermal carbonization (HTC) is still an environmental burden due to the enriched organics, nutrients, and salts. This study proposed a novel strategy to valorize food waste digestate into multifunctional hydrochar by recirculating the PW in the HCl-catalyzed HTC process. The produced multifunctional hydrochar could be utilized as a high-quality solid fuel with HHV of 27.9 MJ kg^-1 (hydrochar without PW recirculation) and a slow-release fertilizer by converting the complex Ca and P compounds from the food waste digestate into a Ca-P deposit (hydroxyapatite) with more than a 93 % P recovery rate (hydrochar with PW recirculation). Adding fresh HCl in the HTC PW recirculation system only displayed a marginal catalytic impact on the hydrochar properties after two cycles of recirculation. This study demonstrated the importance of inherent Ca in the feedstocks and the dual role of HCl in the HTC with PW recirculation.

Enhanced degradation mechanism of tetracycline by MnO2 with the presence of organic acids

In this study, we constructed MnO₂/organic acid (OA) systems using MnO₂ colloid, the most reactive phase of Mn(IV), and two kinds of OA (oxalic acid and l-tartaric acid). We investigated the effect of OA on tetracycline (TC) degradation by MnO₂. The results show that both OA obviously accelerate TC degradation by MnO₂. Mn(III) formed during the reaction lead to the acceleration. Mn(III)-oxalate complex formed in oxalic acid system resulted in the lower degradation efficiency than that in l-tartaric acid system. The acceleration of oxalic acid was decreased when the concentration was more than 75 μM, and even completely disappeared with the concentration of 500 μM, owning to the fact that excess oxalic acid decreased the pH and some MnO₂ was fast reduced to Mn²⁺ by oxalic acid and unable to react with TC. The impact of pH on TC degradation resulted from the influences of H⁺ on MnO₂ redox potentials and TC deprotonation. And acidic conditions accelerated TC degradation. The addition of Mg²⁺, Ca²⁺, Fe³⁺ and Zn²⁺ exhibited an inhibitory effect in both systems for their occupying reactive sites on MnO₂ surface and blocking the access of TC to MnO₂. Similar intermediates in the two systems were detected, indicating a similar TC degradation mechanism including a series of reactions like dehydration, hydroxylation and oxidation. The MnO₂/OA system provides an efficient treatment of TC in wastewater. And it is also noticeable that MnO₂/OA system should also have an important effect on the fate of pollutants in environment, from our results.

Treatment of landfill leachate evaporation concentrate by a modified electro-Fenton method

Landfill leachate evaporation concentrate (LLEC) is difficult to treat due to its complex pollutant composition, which involves large amount of organic matter and inorganic salts such as scaling ions. Because of its high conductivity and high chloride-ion content, this study employed the modified electro-Fenton method with a self-developed iron-loaded cathode to treat LLEC wastewater. The operating variables were optimized according to the response surface methodology where the chemical oxygen demand (COD) removal efficiency was considered as the response based on single-factor experiments. A second-order polynomial regression model was obtained, and an application experiment revealed that it could be applied to determine LLEC treatment conditions. The removal rates of COD and colour were 100% and 99.8%, respectively, under the optimal operating conditions of an initial pH of 6, electrode spacing of 1 cm and applied voltage of 9 V. Three-dimensional fluorescence spectroscopy demonstrated that the humic acid and fulvic acid pollutants were almost completely removed. Scanning electron microscopy and energy dispersive spectroscopy analysis showed that the iron catalyst was loaded in activated carbon pores and exhibited almost no consumption during the reaction, which effectively solved the problem of iron sludge precipitation caused by electro-Fenton oxidation technology. The atomic distribution in the crystal was also analyzed by X-ray diffraction. The specific energy consumption of electrochemical oxidation was 0.498 Wh·mg^-1 COD. The results indicate that the modified electro-Fenton technique with the proposed novel cathode is an effective method for treating LLEC.

Comprehensive chemical characterization of dissolved organic matter in typical point-source refinery wastewaters

In petroleum refineries, the electric desalting, distillation, and stripping processes could generate large amounts of wastewaters that contain toxic substances. In this study, eight wastewater samples were collected from the three typical refining processes for comprehensive chemical characterization of the dissolved organic matter (DOM) using excitation emission matrix fluorescence spectroscopy, gas chromatography-mass spectrometry, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that protein-like components and benzene were ubiquitous in all these wastewaters. Oxygen-containing volatile organic compounds had higher contents in crude distillation and stripping wastewater than those in electric desalting wastewater. Among the three refinery processes, molecular composition of DOM in the stripping wastewater had the highest complexity. The O_x and O_xS_y class species assigned from the negative-ion electrospray ionization FT-ICR MS were dominant in all wastewaters. The O_xS₂ class species which were effectively removed during stripping treatment had highest relative abundance in stripping influent. These results are instructive to guide the development of "divide and conquer" and would improve the treatment and management of refinery wastewater streams.

A review on fluorescence spectroscopic analysis of water and wastewater

In recent years, the application of fluorescence spectroscopy has been widely recognized in water environment studies. The sensitiveness, simplicity, and efficiency of fluorescence spectroscopy are proved to be a promising tool for effective monitoring of water and wastewater. The fluorescence excitation-emission matrix (EEMs) and synchronous fluorescence spectra have been widely used analysis techniques of fluorescence measurement. The presence of organic matter in water and wastewater defines the degree and type of pollution in water. The application of fluorescence spectroscopy to characterize dissolved organic matter (DOM) has made the water quality assessment simple and easy. With the recent advances in this technology, components of DOM are identified by employing parallel factor analysis (PARAFAC), a mathematical trilinear data modeling with EEMs. The majority of wastewater studies indicated that the fluorescence peak of EX/EM at 275 nm/340 nm is referred to tryptophan region (Peak T1). However, some researchers identified another fluorescence peak in the region of EX/EM at 225-237 nm/340-381 nm, which described the tryptophan region and labeled it as Peak T2. Generally, peak T is a protein-like component in the water sample, where T1 and T2 signals were derived from the <0.20μm fraction of pollution. Therefore, a more advanced approach, such as an online fluorescence spectrofluorometer, can be used for the online monitoring of water. The results of various waters studied by fluorescence spectroscopy indicate that changes in peak T intensity could be used for real-time wastewater quality assessment and process control of wastewater treatment works. Finally, due to its effective use in water quality assessment, the fluorescence technique is proved to be a surrogate online monitoring tool and early warning equipment.

Mechanisms by which different polar fractions of dissolved organic matter affect sorption of the herbicide MCPA in ferralsol

Exogenous dissolved organic matter (DOM) modifies the sorption of 4-chloro-2-methylphenoxyacetic acid (MCPA, a polar herbicide) in soil. However, how the chemodiversity and diverse fractions of DOM affect MCPA sorption is still unknown. Here, DOM was extracted from compost and rice straw; the structure-activity correlations between DOM chemodiversity and their effects on MCPA sorption were investigated by redundancy analysis. Moreover, the mechanism involved was explored by spectroscopic techniques, microbeam and modeling. DOM mainly affected MCPA sorption by altering soil surface properties and MCPA complexed form. Hydrophobic neutral (HON) and acid insoluble matter (AIM) were the fractions of DOM that most inhibited MCPA sorption through soil pore blockage, and were related to the humic-like substances with high aromaticity and large molecular weight. The hydrophobic acid fraction (HOA) only showed an intermediate inhibition on the sorption, although the largest competitive sorption occurred. This was because HOA contained abundant aromatic acid and polar groups with moderate polarity. Thus, the reduced effect caused by competitive sorption was partly compensated by the greatest co-sorption by HOA. The hydrophilic matter (HIM) had the weakest inhibition on MCPA sorption, because this fraction was rich in simple sugars, poly- and oligosaccharides, but lacked aryl groups. The results will aid in the risk assessments and prevention of MCPA in DOM-introduced soil.

New insight into quinones triggered ferrate in-situ synthesized polynuclear Fe-hydroxyl complex for enhancing interfacial adsorption in highly efficient removal of natural organic matter

In this study, the effects of quinone on the formation of in-situ synthesized polynuclear Fe-hydroxide (PnFe-H) from ferrate activation and enhanced degradation of organics were investigated by in-situ UV linear differential absorbance spectra for the first time. Results indicated benzoquinone (BQ) efficiently activated ferrate for the flocculation of humic acid (HA) that the flocculation reactions rate constants in Fe(VI)-0.1 mM BQ was 3.3 times as much as the blank. Interestingly, quenching studies suggested PnFe-H derived from the high-valence iron species which were the active components by BQ activation, was proved the vital factor for removing of HA. According to the analysis of interaction energy, BQ promoted FeOH²⁺ converted to Fe(OH)₂⁺ and Fe₂(OH)₂⁴⁺ which weakened the polar property and increased hydrophobicity of compounds, further benefited for adsorption with lower Lifshitz-van del Waals (LW) and Lewis acid-base (AB) interfacial energy between PnFe-H-contaminant compounds. However, excessive BQ reduced freshly particulate Fe(III) to Fe(II), weakened the PnFe-H flocculation performance which retarded the transformation of iron species. In addition, the effects of HA concentration were also studied due to the existent of functional quinone-like moieties. The contribution of PnFe-H flocculation removal on the total removal (Re_flocculation/Re_total) improved from 2.6% to 17.09% with Fe(VI)/HA from 0.1 to 1.12. Fe(VI) sufficient oxidized electron-rich moieties and decreased the aromaticity due to π bond was broken, further cooperated with PnFe-H captured small fragment particles by sweep flocculation that Fe(VI) self-accelerating decay produced more Fe(III). The research elucidated a new insight into of ferrate activation by quinone which could expand our knowledge of activation pathway, further regulate the relationship between oxidation and flocculation for enhancing organic and colloidal particle removal in practical application.

Uncover the secret of granule calcification and deactivation in up-flow anaerobic sludge bed (UASB) reactor with long-term exposure to high calcium

Calcification of anaerobic granular sludge causing the decrease of microbial activity has been focused for several decades, but the mechanism of calcification and deactivation of calcified granule are still lacking. In this study, the calcification process of anaerobic granular sludge was analyzed in the UASB reactor with long-term exposure to a high calcium level of 2 gCa²⁺L^-1. Greyish-white calcified granules with larger size and density first appeared at the bottom of sludge bed. Characterization of granular surface demonstrated that calcified granules had smaller specific surface area and pore volume with the disappearing channels in granules visualized over calcification. The coverage of calcite on granular surface with a thickness of 500-600 µm was observed by a microscope, which is responsible for the blockage of channels for substrate diffusion and transport. The evaluation of mass transfer showed that the 'effectiveness factor' η of calcified granules was higher than 1.23, proving the existence of mass transfer resistance. Furthermore, the interactions between calcium and extracellular polymeric substances (EPS) revealed the possible mechanism of calcite location at the outer layer of anaerobic granular sludge: The bulk calcite directly binds the EPS such as humic acids via charging functional groups, and bulk CO₃^2- could react easily with Ca²⁺ bound to EPS according to thermodynamic analysis.

Characteristics of DOM in 14 AAO processes of municipal wastewater treatment plants

The characteristics of dissolved organic matter (DOM) such as chemical composition, molecular weight (MW) distribution and hydrophobic/hydrophilic distribution can affect wastewater treatment efficiency, effluent quality and ecological risk. Fluorescence spectroscopy could provide a quick estimate of DOM characteristics during the monitoring of wastewater treatment plants (WWTPs). In this study, the characteristic and quantitative correlation of DOM from 14 anaerobic-anoxic-oxic (AAO) processes of WWTPs located in different provinces (municipalities) of China were investigated. The results showed that DOM of MW <1 kDa was the largest group of DOM in influent and secondary effluent, and DOM removal increased as the MW increased. Hydrophilic (HPI) fraction and hydrophobic acid (HPO-A) comprised the major portion of DOM in influent and secondary effluent and exhibited the lowest rate of removal. In addition, DOM concentrations in the northern provinces were higher than in the southern provinces, which were related to the water quality, economy and population. There were positive correlations between specific fluorescence intensity (SFI) and the MW <1 kDa, 1-5 kDa and <10 kDa fractions. The smaller the molecular weight, the better the correlation. Strong positive correlations between regional fluorescence proportion (f_i) and HPI were found. SFI and f_i may be explored as potential indicators of the MW fractions and the hydrophobic/hydrophilic distribution of DOM in AAO processes WWTPs.

Removal of CX3R-type disinfection by-product precursors from rainwater with conventional drinking water treatment processes

In addition to surface water and groundwater, rainwater is used as an important drinking water source in many parts of the world, especially in areas with serious water pollution or insufficient water resources. Conventional drinking water treatment technologies can remove dissolved organic matter and therefore reduce the formation of disinfection by-products (DBPs) during subsequent disinfection using surface water or groundwater as drinking water sources. However, little information has been known about the effect of conventional water treatment processes on DBP formation when rainwater is used as drinking water source. This study evaluated CX₃R-type DBP precursors removal from rainwater by conventional drinking water treatments and the corresponding decrease of CX₃R-type DBP (trihalomethanes (THMs), haloaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs)) formation and toxicity during the subsequent chlor(am)ination. The result showed that both sand filtration (SF) and activated carbon filtration (GAC) were able to remove DBP precursors and GAC outperformed SF, but no DBP precursors removal was observed during coagulation-sedimentation treatment. Among all treatments, SF + GAC was the most effective for DBP precursors removal, with removal efficiencies of 64.2% DOC, 98% DON and 76.6% UV₂₅₄. Correspondingly, both SF and GAC decreased the formation of THMs, HALs, HANs and HAMs, and GAC performed better than SF. The combination of SF and GAC, especially SF + GAC, greatly decreased DBP formation, with average reduction of 79.2% and 85% during chlorination and chloramination respectively. After different treatments, the comprehensive toxicity risk of CX₃R-type DBPs was all reduced, among which GAC + SF exhibited superior performance. Generally, the main contribution of integrated toxicity was HANs during chlor(am)ination. The formation potential of THMs, HALs, HANs and HAMs and the corresponding integrated toxicity were greater during chlorination than that during chloramination. Therefore, the combination of GAC and chloramination was promising in mitigating the comprehensive toxicity risk of THMs, HALs, HANs and HAMs for rainwater.

Denitrification strategies of strain YSF15 in response to carbon scarcity: Based on organic nitrogen, soluble microbial products and extracellular polymeric substances

This paper aims to determine the denitrification strategies of strain YSF15 in carbon scarcity condition from novel view of organic nitrogen, soluble microbial products (SMP) and extracellular polymeric substances (EPS). The batch tests demonstrated that strain YSF15 could achieve complete denitrification at C/N of 3.0. The conversion ratio of nitrogen gas accounted for 89.03%, 85.29% and 82.95% among total nitrogen in C/N systems from 3.0 to 5.0, respectively, indicating denitrification instead of assimilation was the major contribution to nitrogen removal. C/N could affect composition and content of organic nitrogen, SMP and EPS. The biodegradability of EPS was better than SMP, whereas polysaccharide (PS) likely correlated with nitrogen removal, predating the protein (PN). These results implied high biodegradability of EPS and more electron donors for denitrification both improved denitrification capacity of strain YSF15, which revealed the potential contribution of bacterium with production of biodegradable SMP or EPS in biological treatment process.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Relationship between fluorescence excitation-emission matrix properties and the relative degree of DOM hydrophobicity in wastewater treatment effluents

Excitation-emission matrix (EEM) fluorescence spectroscopy is a powerful tool for the characterization of dissolved organic matter (DOM) in wastewater systems. It is of particular value if its utility could be extended by connecting the spectral features to hydrophobicity, one of the fundamental physicochemical properties of DOM. In this study, we employed a DAX-8 resin column to fractionate the hydrophobic/philic components of DOM and determine the relative degree of hydrophobicity by adjusting the critical retention factor (k'_cr, the ratio of treated water sample volume to column volume). A higher k'_cr would result in a higher hydrophobicity of the column effluent. At different k'_cr values (5, 10, 25, 50, 100, and 200), the EEM characteristics of the obtained DOM components were inspected, including overall properties (average fluorescence per total organic carbon and UV absorbance), regional properties (fluorescence regional integration (FRI) and its secondary parameters), and energy-related properties (energy level of the excited states, Stokes shift for relaxation of the excited states, and fluorescence lifetime). In case studies of a wastewater membrane bioreactor and an oxidation ditch, plenty of the EEM properties varied significantly with logk'_cr (r > 0.9, p < 0.05). The average fluorescence per UV absorbance (reflecting quantum yield), fluorescence proportion at Stokes shift ≥ 1.1 μm^-1, and some secondary FRI parameters presented the best linear fitting with logk'_cr, suggesting a smooth variation of the π-conjugated structures with the relative degree of DOM hydrophobicity. This may help to further understand the relationship between EEM fingerprints and DOM hydrophobicity.

Characteristic of dissolved organic matter polar fractions with variable sources by spectrum technologies: Chemical properties and interaction with phenoxy herbicide

Dissolved organic matter (DOM) is ubiquitous with high biological and chemical activity. The large intake of DOM from compost, plant residues or soil can modify the behaviors of agrochemicals. Phenoxy herbicide is the third widely used herbicide around the world with both aromaticity and polarity. However, how the diverse fractions of DOM interacting with phenoxy herbicide and the underlying mechanisms remain unknown. Thus, it is crucial to investigate the heterogeneous chemical properties of DOM fractions from variable sources and explore the interactive mechanisms. In this study, polar DOM derived from compost, rice straw and soil were fractionated, and the chemical properties of fractions were analyzed by spectrum technology and the complex interaction with phenoxy herbicide was assessed by infrared spectroscopy. Results showed that hydrophobic acid (HOA) was the largest component (49.6%) in compost DOM, while hydrophilic matter (HIM) was the main component in the polar DOM from rice straw and soil. The 4-chloro-2-methylphenoxyac etic acid (MCPA) as one representative of phenoxy herbicides was used in our study, and the results showed the interaction between different DOM fractions and MCPA was heterogeneous. HOA containing abundant fulvic-like component and polar groups resulted a greatly complex interaction with MCPA mainly via hydrophobic force, ligand exchange and hydrogen bonding. Hydrophobic neutral fraction and acid-insoluble matter showed a medium interaction with MCPA as a result of enrichment with the high aromatic humic-like molecules. Inversely, no significant interaction between HIM and MCPA was observed. Our research revealed that the aromatic framework associated with polar groups in DOM dominated the interaction with phenoxy herbicide, which might affect the bioavailability, toxicity, and mobility of phenoxy herbicide.

Determination of Saccharides in Environments Using a Sulfuric Acid-Fluorescence Approach

Accurate, rapid, and reliable quantification of saccharides is essential for understanding their behaviors and roles in environmental processes. However, the conventional colorimetric method for saccharide quantification fails to discriminate between fructose and glucose, resulting in the misestimation of total saccharides. To solve this problem, a fluorescence approach, that is, parallel factor framework-linear regression analysis, was developed in this work to quantify the specific fluorescence signatures of the fluorescent products generated from the reaction between saccharides and sulfuric acid. The fluorescent derivatives of saccharides were recognized and the simultaneous quantification of glucose and fructose was achieved with a detection limit of 2.9 μg/mL and 1.3 μg/mL, respectively. Furthermore, 200 μg/mL of the treated sorbitol and gluconic acid only, respectively, equaled to 6 μg/mL and 3 μg/mL of the treated glucose, indicating their negligible interference for the saccharide quantification using this method. In addition, the feasibility and robustness of this method in environmental applications were validated with the recovery tests using spiked real water samples. This fluorescence-based approach offers a new tool to monitor saccharides in complex environments.

Biological performance and fouling mitigation in the biochar-amended anaerobic membrane bioreactor (AnMBR) treating pharmaceutical wastewater

Anaerobic membrane bioreactor (AnMBR) is an advanced technology in treating pharmaceutical wastewater, but the membrane fouling limits its development. In this study, the biochar with adsorption capacity of biopolymers was added in AnMBR to investigate its potential in treating pharmaceutical wastewater and alleviating membrane fouling. In the biochar-amended AnMBR, adsorbable organic halogen (AOX) was removed effectively, and more COD was biotransformed into CH₄. Membrane fouling mitigation was achieved in the third stage with a 56% decrease of average transmembrane pressure difference (TMP) rising rate. The predominant culprit, proteins of extracellular polymeric substance (EPS-proteins) in sludge mixture and cake layer, was reduced significantly. Particularly, the proportion of micromolecular (0.1-0.15 kDa) EPS-proteins in cake layer was 1.5-folds that of the control group. The important bio-foulant genus Arcobacter aggregating on the membrane had less and almost half the relative abundance (16.5%) than that of the control group (30.7%).

Membrane autopsy deciphering keystone microorganisms stubborn against online NaOCl cleaning in a full-scale MBR

The knowledge about membrane biofouling evolution in full-scale membrane bioreactor (MBR) applications is quite lacking, notwithstanding a few lab-scale investigations. For the first time, this study elaborated the effect of online NaOCl cleaning on the dynamic development of membrane biofilm microbiota during long-term operation of a large-scale MBR for municipal wastewater treatment (40,000 m³/d). Four times of membrane autopsies were conducted during 160 days operation to scrutinize the microbial community and concomitant organic foulants. The transmembrane pressure difference (TMP) development revealed limited effect of 30 min online NaOCl cleaning on long-term biofouling removal. NaOCl not only altered the structure of biofilm communities but also increased the richness and evenness on early fouling stages. Meanwhile, network analysis revealed the keystone taxa f_Comamonadaceae that played key roles in stabilizing community structure and developing anti-cleaning and irreversible fouling propensity of the biofilm. NaOCl cleaning also impacted the evolving of keystone taxa by intensifying the competition between the dominated taxa f_Moraxellaceae and other species during early fouling stages. Furthermore, the succession of the biofilm microbiota synchronously accelerated the TMP increase and the accumulation of organic foulants including polysaccharides, aromatic proteins and soluble microbial products during biofilm maturation. These identified key stubborn foulants shed light on limitations of current online NaOCl cleaning and provide guidance to optimize the efficiency of online chemical cleaning protocols in full-scale MBR operations.

Stokes Shift and Specific Fluorescence as Potential Indicators of Organic Matter Hydrophobicity and Molecular Weight in Membrane Bioreactors

Hydrophobicity and molecular weight (MW) are two fundamental properties of dissolved organic matter (DOM) in wastewater treatment systems. This study proposes fluorescence Stokes shift and specific fluorescence intensity (SFI) as novel indicators of hydrophobicity and MW. These indicators originate from the energy gap and photon efficiency of the fluorescence process and can be readily extracted from a fluorescence excitation-emission matrix (EEM). The statistical linkages between these indicators and hydrophobicity/MW were explored through investigation of DOM across 10 full-scale membrane bioreactors treating municipal wastewater. Stokes shift was found to exhibit a general rule among the hydrophobicity components in the order of hydrophilic substances (HIS) < hydrophobic acids (HOA) < hydrophobic bases (HOB). The Stokes shift of 1.2 μm^-1 is a critical border, above which the relative fluorescence correlated significantly with the HOA-related content (Pearson's r = 0.8). With regard to MW distribution (<1, 1-10, 10-100, and >100 kDa), SFI was found to be the most sensitive to the change of MW of <1 kDa proportion, especially at the excitation/emission wavelengths of 200-320/310-550 nm (r > 0.9). Hydrophobicity-related π conjugation and MW-dependent light exposure might be responsible for the correlations. These fluorescence indicators may be useful for convenient monitoring of DOM in wastewater treatment systems.

Characterization of fluorescence foulants on ultrafiltration membrane using front-face excitation-emission matrix (FF-EEM) spectroscopy: Fouling evolution and mechanism analysis

The understanding of fouling behavior and mechanism is critical for fouling control in membrane processes. This study adopted a novel fluorescence front-face excitation-emission matrix (FF-EEM) approach to characterize the fluorescence foulants deposited on membrane surface. Methods for quantifying protein and humic substances deposited on ultrafiltration (UF) membrane were established. Foulants deposited on the membrane surface during the UF of model foulants (bovine serum albumin (BSA) and humic acids (HA)) and wastewater effluent organic matter (EfOM) were quantified using the FF-EEM and liquid EEM coupled with mass balance calculation. The foulants mass data obtained by FF-EEM were further used to analyze fouling mechanism involved in UF. The FF-EEM based method was more accurate than the liquid EEM based method, as the problems associated with liquid EEM based method (such as the error propagation in the mass balance calculation and the ineffectiveness of inner filter correction) were avoided in FF-EEM based method. The fouling resistance did not correlate well with the amount of foulants, as the major fouling mechanism instead of the mass of foulants mainly determined the extent of fouling. This work demonstrated FF-EEM could be a powerful tool for investigating fouling evolution and fouling mechanism in UF process.

The power of fluorescence excitation–emission matrix (EEM) spectroscopy in the identification and characterization of complex mixtures of fluorescent silver clusters

Silver and gold clusters have received a lot of recent attention for their use in biomedical imaging. However, crude solutions of clusters are often complex mixtures, leading to discrepancies in their identification and characterization; important factors in determining their utility in biological applications. In the present study, silver clusters were separated for analysis using reverse-phase high performance liquid chromatography, which has previously been implemented in the efficient separation of gold clusters. Using fluorescence excitation–emission matrix (EEM) spectroscopy, we have demonstrated that a certain family of glutathione-protected silver clusters, previously thought to be one optically distinct species, is better described as a complex mixture of at least three distinct silver cluster species, each possessing unique optical properties. Based on these findings, EEM spectroscopy can be implemented as a powerful technique for determining the purity of complex mixtures, especially when other techniques, including mass spectrometry, fail to provide adequate characterization of a given material.

EEM spectroscopy can be implemented as a powerful technique for determining the purity of complex mixtures, especially when other techniques, including mass spectrometry, fail to provide adequate characterization of a given material.