Fluorescence excitation-emission matrix regional integration to quantify spectra for dissolved organic matter

Characterization of atmospheric humic-like substances (HULIS) at a high elevation in North China: Abundance, molecular composition and optical properties

The optical absorption of large molecular compounds HULIS (humic-like substances) can significantly impact the aerosol light absorption and radiative forcing, influencing cloud condensation nuclei formation and thus the climate and atmospheric environment. This study collected aerosol (PM2.5) samples from the summit of Mount Tai in North China to investigate the concentration, molecular composition, and optical properties of HULIS. The average concentration of HULIS in the PM2.5 in this study was 1.26 ± 0.54 µg/m3, comprising for 56 % of the water-soluble organic carbon (WSOC), with levels lower than urban areas but higher than other mountainous regions. Mass spectrometry revealed that CHO and CHON components, with high aromaticity and phenolic groups, are major contributors to absorption and fluorescence. These results indicate that HULIS is mainly composed of lignin and proteins/amino sugars, derived from combustion and secondary formation, and possesses a high light absorption capacity (with MAE365 (mass absorption efficiency) and AAE (Ångström exponent) indices of 0.62 m2/g and 4.99, respectively). Parallel factor analysis identified three fluorescence components of HULIS, with proportions of 60.8 % for less oxygen humic-like substances, 21.0 % for high oxygen humic-like substances, and 18.2 % for protein-like substances. Our study highlights the significance of the light-absorbing capacity and secondary formation of HULIS at Mount Tai, laying the groundwork for investigation into the climate effects, formation mechanisms, and sources of HULIS generation.

Heterogeneous microstructure induces floatation in high-rate anammox granules

The floatation of anammox granules can be a serious challenge in practical wastewater treatment, as it can deteriorate reactor performance and cause bacterial loss. To deepen the understanding of floatation mechanism, in this study, both the floating (F-AnGS) and settling anammox granules (S-AnGS) from a high-rate anammox reactor were comparatively investigated. F-AnGS demonstrated 1.6 times higher specific anammox activity compared to S-AnGS, but only 65 % of produced gas could be successfully released, as quantified by anaerobic respirometry. In addition to the overall EPS accumulation, F-AnGS exhibited a heterogeneous microstructure distinct from that of S-AnGS, as revealed by 3D X-ray microscopic imaging at the single granule level. The heterogeneous distribution of EPS, which can form a dense surface layer, was the main cause for granule floatation. The heterogeneous microstructure of F-AnGS can reduce the distance between microorganisms and enhance the metabolic interaction between anammox bacteria and heterotrophs. The abundance of community members did not have a significant variation, but the functional genes related to anammox and partial denitrification pathway were significantly increased, indicating the enhanced nitrite loop in F-AnGS. This study proposed new structural insights into mechanism of anammox granule floatation, suggesting the appropriate activity control of granule-based anammox process.

Effects of chromophoric dissolved organic matter on the optical properties of different fluorescent probes

The new detection technology represented by fluorescent probe is an effective supplement to the traditional instrument analysis of environmental pollutants. However, background interference is an inevitable obstacle in the fluorescent analysis of complex samples. Dissolved organic matter (DOM) in water is widespread and significantly affects the performance of fluorescent probes in pollutants detection. In this work, the impact of DOM on the performance of fluorescent probes were investigated under different conditions. Firstly, three-dimensional fluorescence spectroscopy of local lake was performed to identify the composition of organic matter in water. The types of chromophoric DOM in local lake mainly include humic acids and tryptophan, and its concentrations varied over time and across different regions. Then, three fluorescent probes with different fluorescence emission were selected to investigate the interaction between DOM (humic acids, tryptophan, and fulvic acid as the interfering substances) and fluorescent groups. The experimental results demonstrated that humic acid significantly reduced the signal intensity of fluorescent probes through mechanisms such as inner filter effects and fluorescence resonance energy transfer. In contrast, tryptophan and fulvic acid had relatively minor impacts. More importantly, the altered pH and ions of the environmental water did not significantly alter the interference of DOM on fluorescent probe. To further verify the influence of chromophoric DOM on fluorescent probes in real water, the water treatment under UV irradiation with H2O2 was used for the preparation of simulated water samples. The influence of DOM on fluorescent probes in real water samples was also similar to that in buffer. These results suggested that the chromophoric DOM can effectively affect the spectral properties of different fluorescent probes, and greatly interfere with the sensitivity and accuracy of fluorescence detection. This work help to understand the interference mechanisms of DOM in water, and are significant for improving the accuracy of fluorescent probes in water quality monitoring applications.

Biodegradation of sulfadiazine in anaerobic co-digestion of swine manure and food waste

This study explored the feasibility of employing the AcoD process for the removal of antibiotics and examined the impact of antibiotics on system performance. Sulfadiazine (SDZ), a prevalent broad-spectrum sulfonamide antibiotic in veterinary medicine, was selected as the model compound. Results showed that with the presence of SDZ at a concentration of 450 mg/kg total solids, the cumulative methane yield demonstrated a substantial decline of 79.2 % compared to the control group. The specific removal rate of SDZ was 47.5 % at 450 mg SDZ/kg total solids, surpassing those observed in traditional mono-anaerobic treatment processes. The elimination of SDZ by the AcoD system was predominantly ascribed to biodegradation. Within the AcoD system, cytochrome P450 enzyme (CYP450) served as the crucial enzyme in the biodegradation of SDZ. From a molecular point of view, the main interaction sites of SDZ with CYP450 enzyme were located as Thr258, Glu257, Pro428, Ala254, and Val318. Six transformation products were identified in the biodegradation process. Community diversity revealed that the predominant genera, Syntrophomonadaceae, Acinetobacter, AUTHM297, and Anaerolineaceae, were enriched in the AcoD process, which probably contributed to SDZ removal. In summary, the AcoD system may possess sufficient robustness to transform SDZ antibiotic.

Effect of perfluorooctanoic acid on denitrifying phosphorus removal system under short-term stress

Perfluorooctanoic acid (PFOA), a novel contaminant, is extensively found in aquatic environments. However, the capability of the denitrifying phosphorus removal process to treat PFOA-containing wastewater, as well as its response mechanisms, are unclear. This study used batch experiments to assess the short-term impact of PFOA on denitrifying phosphorus removal systems. During a single cycle, the addition of PFOA predominantly enhanced phosphate removal in the system mainly by the anaerobic phosphorus release pathway, but had no substantial effect on nitrogen removal. COD removal efficiency has a substantial positive correlation with C6-HSL and C8-HSL concentrations. As the PFOA concentration increased, the ROS concentration and enzyme activity also increased, while the PN/PS ratio decreased, causing the sludge to become looser. At the beginning of the second cycle, the impact of PFOA on phosphorus removal efficiency shifted from promotion to inhibition. These findings shed fresh light on the influence of PFOA on the denitrifying phosphorus removal mechanism, potentially furthering its use in the treatment of fluoride-containing wastewater.

Diatomaceous organic matter is overlooked but forms disinfection byproducts of high cytotoxicity during chlorination

Diatomaceous organic matter (DAOM) has the potential to be the main precursor of disinfection byproducts (DBPs) in multiple drinking water sources during diatom blooms. However, characterization of DAOM and subsequent formation of chlorination DBPs, especially at the molecular level, have rarely been studied, let alone the links between DAOM chemodiversity and DBPs' cytotoxicity. Herein three types of DAOM derived from Cyclotella meneghiniana, Synedra ulna, and Fragilaria nanana - which are common species during diatom blooms in drinking water sources - were selected. Cyanobacterial organic matter (CAOM) that originated from the common bloom-forming cyanobacterium Microcystis aeruginosa was also selected to thoroughly compare the differences. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) revealed that DAOM contained more lipids, while the content of proteins in CAOM was higher. Compared with CAOM, DAOM had fewer molecules with CHON formulas, but more with CHO formulas, lower molecular weight, fewer aromatic and unsaturated compounds, and higher hydrogen saturation. High-molecular-weight DBPs (more than two carbon atoms) made up the majority of DBPs (67.7-78.7 %). DAOM generated more high-molecular-weight carbonaceous DBPs, but CAOM formed more macromolecular nitrogenous DBPs after chlorination. Chlorination of DAOM mainly occurred through chlorine substitution, and the proportion of precursors associated with substitution reactions in DAOM was larger than that in CAOM. Furthermore, the cytotoxicity of chlorinated DAOM was obviously higher than that of CAOM at the same algal density (about 2.3-3.1 times). This study provides new insights into the formation of DBPs, especially the unknown macromolecular DBPs, and the potential cytotoxicity of DBPs during chlorination of DAOM-containing water.

Integration of moving bed biofilm reactor and gravity-driven membrane bioreactor for decentralized domestic wastewater treatment: Efficiency and mechanistic insights

This study investigated the coupling of a moving bed biofilm reactor (MBBR) with a gravity-driven membrane bioreactor (GDMBR) for the long-term treatment of decentralized domestic wastewater. The results indicated that the introduction of MBBR significantly improved the stable flux of GDMBR (by 8 % - 22 %) and enhanced its resistance to the shock loading of influent quality. Such improvements were attributed to the reduction in extracellular polymeric substances (EPS) (by 30 % - 46 %), positive modifications to the membrane biofilm, and improvements in microbial richness and community composition. Compared to GDMBR control, the start-up period of MBBR-GDMBR systems was reduced by 6-15 days, owing to the beneficial effects of MBBR-derived microorganisms, which promoted microbial evolution within the GDMBR membrane biofilm, thereby accelerating the stabilization of filtration performance. Overall, this study provides valuable insights into shortening the start-up period of the GDMBR process, enhancing its resistance to external shock loads, and improving flux levels.

Valorizing Hydrothermal liquefaction aqueous phase via nanofiltration: Enhancing biocrude production from algal biomass

The hydrothermal liquefaction aqueous phase (HTL-AP), a nutrient- and carbon-rich waste byproduct of the HTL process, can be recirculated to enhance biocrude production efficiency. To avoid dilution of the HTL feedstock and reduced fuel quality associated with recirculating untreated HTL-AP, this study investigated nanofiltration to concentrate organic compounds and separate nutrients from HTL-AP of three algal biomass sources: an algal wastewater treatment system and two from harmful algal blooms in lakes. Up to 99 % of the organics were recovered in the concentrated HTL-AP (retentate), and significant increases in both permeate flux and permeation of nitrogenous compounds were achieved by increasing HTL-AP temperature to 45 °C and pH to 11. Recirculating the concentrated HTL-AP increased biocrude yield by 70 %-116 % and reduced biocrude nitrogen content by up to 12 %. The carbon and energy capture in the biocrude also increased by 66 % and 68 %, respectively.

Insights into in-situ free nitrous acid induced extracellular polymeric substances changes and membrane fouling mitigation in a nitritation membrane bioreactor

This study investigated the effectiveness of free nitrous acid (FNA) on mitigating membrane fouling, with the associated mechanisms, in two nitritation membrane bioreactors (MBRs) operated with Nitrosomonas-enriched culture. Results showed that FNA stress, regulated by pH and nitrite concentration, maintained a low-level fouling as opposed to the control MBR where trans-membrane pressure (TMP) exceeded 30 kPa. Compared to the control MBR, production of biofilm in the FNA stressed MBR was reduced by 68.1% in terms of mass and 78.2% in terms of thickness. Suspended biomass and biofilm extracellular polymeric substances (EPS) characterized by liquid chromatography (LC-OCD-OND) indicated FNA stress reduced the amount of low molecular weight neutrals and hydrophobic dissolved organic carbon. These components would have had high fouling potential. Excitation emission matrix (EEM) fluorescence contours indicated that exposure to FNA stimulated the production of tyrosine-like proteins but reduced those of SMP like and humic acid-like substances. This could have affected the adhesion between bacteria and membrane and so contributed to the reduced biofilm and fouling. X-ray photoelectron spectroscopy (XPS) analysis revealed marked differences in intensities of the main functionalities in the EPS for both sludge and biofilm, due to the oxidative effect of FNA, e.g. FNA stress resulted in more aliphatic C-OH, amines and amides while the control had more C=O, amino acids and amino sugars. This study showed that in-situ generated FNA could be employed to mitigate membrane fouling effectively via its biocidal and oxidative effect.

The bidirectional matter transfer in adsorption-promoted photocatalytic ozonation system derived by triazine nanosheets-heptazine nanotubes homojunction composite biochar

Heterogeneous catalytic ozonation (HCO) process is an efficiency and eco-friendly solution to the growing challenge of water purification, yet is challenging by O3 utilization, pollutants selectivity, and matter transfer resistance. Herein, adsorption-promoted photocatalytic ozonation (HCO/POAP) system was constructed derived by triazine nanosheets-heptazine nanotubes homojunction carbon nitride composite Enteromorpha prolifera derived biochar (CNTh-St/EpC) to provide a targeted solution for the refractory organic pollutants treatment. In the HCO/POAP system, the adsorption sites predominantly reside on EpC, while the catalytic sites are primarily located on CN. The construction of efficient transport channels is facilitated by the induction of triazine structures from amorphous C, N compounds along the edges of heptazine. This leads to the independent yet closely interconnected process of inward transfer of pollutants and outward transfer of active species, confining reactions to a bidirectional transfer channel. This strategic confinement significantly amplifies the performance of HCO/POAP system. Specifically, the removal rates are 80 % for TC and 94 % for PNP in 30 min with almost entirely harmless or non-toxic degradation products, and mark a 56 % and 77 % enhancement over O3 system, respectively. Moreover, the HCO/POAP system demonstrates exceptional efficacy in treating dissolved organic matter, chemical oxygen demand (COD), and ultraviolet absorbance at 254 nm (UV254) in diverse actual wastewater. This study highlights the potential of HCO/POAP process in efficient water purification, and provides mechanistic insights into the bidirectional matter transfer during the contaminants remove.

Self-assembly of algal-bacterial granules induced by bacterial N-acyl-homoserine lactone variation in response to high-strength pyridine

Algal-bacterial granules (ABGs) system represents a promising technology for organic wastewater treatment due to its high settleability, efficient oxygen transfer, and low-energy consumption. However, the secretion of extracellular polymeric substances (EPS) in algae, which played a key role in self-assembly of ABGs, would be inhibited by concentrated organic wastewater. This study proposed a novel strategy for developing ABGs by inducing bacterial N-acyl-homoserine lactone (AHL) variation through high-strength pyridine application. Results showed that bacterial long-chain AHL concentrations significantly increased in response to high-strength pyridine at 550 mg L-1, inducing the secretion of algal extracellular aromatic proteins and facilitating ABGs construction. The ABGs system achieved over 99 % pyridine removal efficiency and 82 % settleability. Moreover, the proportions of β-sheet and α-helix structures in the extracellular aromatic proteins of ABGs increased, while the random coil structures decreased. This shift in protein structure lowered the surface free energy and energy barriers, which in turn enhanced the surface hydrophobicity and promoted cell adhesion. Furthermore, based on metatranscriptomic analysis, the mechanism for AHL-regulated physiological and behavioral responses between algae and bacteria in ABGs was proposed. This study provides an economically feasible approach to develop efficient and sustainable ABGs systems for industrial wastewater treatment.

Overcoming challenges in the analysis of short-chain per- and polyfluoroalkyl substances in raw landfill leachates: Clean-up method optimization and interference identification

Municipal solid waste (MSW) landfill leachate is an important emission hotspot for per- and polyfluoroalkyl substances (PFASs) in the water environment. However, quantifying short-chain PFASs in raw landfill leachate is challenging due to severe matrix effects that occur during liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. To overcome this obstacle, an enhanced clean-up method was developed for the accurate determination of short-chain PFASs in raw landfill leachate. This method involved comparing various graphitized carbon black (GCB) adsorbents and purification sequences. The results showed that the GCB cartridge exhibited optimal purification efficiency when applied directly to raw leachate samples. It achieved recoveries for all 6 short-chain PFASs ranging from 85 % to 113 %, with RSDs ≤ 7.2 %. In particular, perfluorobutanoic acid (PFBA) and perfluoropentanoic acid (PFPeA) were most effectively separated from interfering co-extracts during chromatographic analysis, as compared to other purification strategies. Humic acid-like substances were characterized as the main components causing interference. By applying the modified method, the total concentrations of the 6 short-chain PFAS targets were found to range from 10.7 to 22.7 µg/L, representing 33.0-93.7 % of total PFASs detected. This study presents an effective approach to the extraction of short-chain PFASs from complex environmental matrices, which is important for the comprehensive determination of PFAS profiles in raw landfill leachate.

Alkaline-thermal synergistic activation of persulfate for sawdust hour-level humification to prepare fulvic-like-acid fertilizer

Sawdust is a by-product of wood processing and it was rapidly humified with K2S2O8 under alkaline-thermal synergistic activation to produce a fulvic-like-acid (FLA) organic fertilizer (SFOF) in this study. The optimum conditions were K2S2O8: KOH mass ratio of 1:2 and 150°C, meanwhile FLA yield could reach 180.3 mg/g in 2 h. The carboxylation, Maillard reaction, and aromatization processes occurred during sawdust humification. And then, SFOF was mixed with attapulgite and modified starch binder to get an organic fertilizer (SAM), and coated with amino silicone oil (ASO) to create a slow-release granule (SAM@ASO). The release mechanism of FLA from SAM@ASO was consistent with Ritger-Peppas release kinetics. SAM@ASO, with high biosafety, could promote water spinach growth and remediate acidic soil (pH from 4.9 to 6.3). This method offers a promising approach for sawdust utilization and a novel FLA-based organic fertilizer for acidic soil remediation.

Dissolved organic matter mediates the interactions between bacterial community and heavy metal fractionation in contaminated coal mine soils

Heavy metal (HM) contamination in coal mine soils disrupts local bacterial networks, leading to prolonged soil deterioration. Dissolved organic matter (DOM), a crucial soil component, actively modulates both bacterial metabolism and HM mobilization. Despite its significance, our understanding of the complex interactions among bacterial communities, soil chemical and DOM properties, and HM fractionation remains limited. In this study, DOM and bacterial communities from three contaminated mines with varying HM levels and soil properties were analyzed using optical methods and high-throughput sequencing technique. Our results revealed pH and DOM composition, especially the ratio of recalcitrant to labile substances, as key environmental drivers of HM mobilization. Moreover, the composition of bacterial community, particularly the keystone and abundant species, exhibits pronounced site-specificity and HM-dependency. Distinct characteristic genera that are pertinent to HM tolerance/mobility were identified across three mines. Specifically, in Zibo (ZB) soils, Rhodococcus, Acinetobacter, and Pseudomonas significantly regulated the fractionation of Pb, Cu, Se, and Hg possibly via protein-like exudates releasing. In Zaozhuang (ZZ) soils, relationships were recognized between Reyranella, oxides associated Pb, and soil cation exchange capacity. Paenibacillus and Fictibacillus contributed to Se mobilization/tolerance in Linyi (LY) soils. Based on these field findings, two mechanisms were identified for how DOM mediates interactions between HM fractionation and bacterial communities. First, metal-resistant bacteria can produce labile DOM compounds, modifying HM fractionation and reducing metal bioavailability, as observed in ZB soils. Second, humic substances in DOM promoted the development of cohesive bacterial networks featuring metal-resistant keystone bacteria, thereby enhancing community resistance to metal contamination, as evidenced in LY and ZZ soils. Overall, this study provides field evidence elucidating the multilateral interactions among bacterial communities, soil chemical and DOM properties, and HM fractionation, underscoring the significant role of DOM in connecting soil bacterial activity and HM mobilization.

Tuning pH to motivate chain reaction of iron release with extracellular polymeric substances formation for long lasting Fe0-driven autotrophic denitrification

Although zero-valent iron (Fe0)-driven autotrophic denitrification (ADN) is free of external carbon source during nitrogen removal, Fe0 surface passivation restricted the nitrogen removal capacity of Fe0-driven ADN. Tuning influent pH can boost Fe0 corrosion, thereby improving Fe0-driven ADN. It is imperative to find the pH balance between Fe0 corrosion and autotrophic denitrifying bacteria growth. Herein, by altering pH over a wide range of 5.0-9.0 in batch operation, it was confirmed that the optimal pH of 6.0 maintained Fe0 corrosion and denitrifying bacteria growth simultaneously. The maximum total nitrogen (TN) removal efficiency of 87.0 % was accomplished at the influent pH of 6.0 in batch operation. Furthermore, the TN removal efficiency in continuous flow operation reached as high as 84.8 % when the influent pH was 6.0 and hydraulic retention time was 24 h. Meanwhile, the released Fe2+ and Fe3+ from Fe0 corrosion significantly promoted the formation of extracellular polymeric substances (EPS). EPS facilitated the electron transfer between Fe0 and nitrate (NO3--N), consequently promoting nitrogen removal. The genera of Thauera and Defluviimonas were dominant denitrifiers in batch operation, while Ellin6067 prevailed in continuous flow operation, utilizing EPS as carbon source. The microbial community exhibits a certain disparity between batch and continuous flow operation modes. However, the similar nitrogen removal pathway maintained a stable denitrification efficiency in both batch and continuous flow reactors. Modulating influent pH to bolster Fe0-driven ADN was a promising and handy strategy in actual application.

Exploration of ammonia stripping coupled adsorption-membrane filtration process for treating kitchen waste biogas slurry

The potential contamination of biogas slurry generated from the anaerobic digestion of kitchen waste (KW) poses a considerable challenge to its safe and effective utilization as a fertilizer. To tackle this problem, a novel route termed "AS-BC" was developed, integrating ammonia stripping (AS), biochar adsorption, and ceramic membrane filtration (CMF) for comprehensive pollutant mitigation. A stepwise optimization was carried out, comparing biochar adsorption investigation, the AS process, and the combined AS + CMF process. Results indicated that the AS process possessed the maximum total ammonia nitrogen (TAN) removal of 86.21% at an airflow rate of 40 L/min. The combined AS and CMF process with 0.1 μm membrane had best performance for total phosphorus (TP) with removal efficiencies of 80.45%-87.98%. Under the optimal biochar addition condition of 5 g/L with a particle size of 0.25-0.85 μm, the adsorption pretreatment effectively removed 0.41 g/g of soluble chemical oxygen demand (SCOD), prevented nutrient loss, and substantially enhanced pollutant removal efficiency in the subsequent CMF process. Compared to other routes, the route AS-BC achieved higher total nitrogen (TN), TAN, TP, and SCOD removal efficiency of 91.42%, 91.49%, 89.54%, and 76.34% from the raw biogas slurry, respectively. Moreover, the route AS-BC demonstrated its cost-effectiveness in producing nutrient-rich concentrated slurry suitable for use as fertilizer. The route AS-BC was proved to comprehensively remove various indicators from the KW biogas slurry while generating economically reuse by-products during the membrane filtration process. This study offers valuable insights into the trade-offs between AS performance enhancement and pollutant mitigation, pinpointing essential routes for future research and practical improvements.

Enhanced removal of perfluorooctanoic acid and perfluorooctane sulphonic acid by direct current in iron-based constructed wetlands

Iron minerals have been used for the treatment of PFOA and PFOS in constructed wetlands (CWs). Electron transfer that mediated by iron cycling is the primary mechanism for the removal of PFOA and PFOS. To further improve the electron transfer and enhance treatment efficiency of PFOA and PFOS, direct current with different voltages was applied in iron-based CWs. The results show that PFOA and PFOS removal efficiencies reached 63.2 ± 2.3 % and 57.5 ± 2.2 % at the voltage of 0.3 V, and further improved by 2.7 % and 3.5 % after the voltage increased to 0.8 V. The Cyt C that involved in electron transfer was increased to 174.9 ± 5.2 nmol/L in the cathode of voltage-added CWs. The contents of fulvic-like acids (18.2 %) and humic-like acids (9.5 %) materials that contribute to electron transfer were also 4.1 % and 2.6 % higher than that without direct current. The abundance of Geobacter that involved in electron transfer, PFOA and PFOS removal, was highly enriched in the application of direct current. Moreover, microbial pathways associated with PFOA and PFOS removal such as carbohydrate metabolism (sucrose metabolism), energy metabolism (oxidative phosphorylation), and membrane transfer (bacterial secretion system) were up-regulated. In general, the application of direct current showed excellent removal performance of PFAS through the enhanced electron transfer in iron minerals-based CWs.

Response characteristics of the microbial community, metabolic pathways, and anti-resistance genes under high nitrate and sulfamethoxazole stress in a fluidized sulfur autotrophic denitrification process

The adaptability and microbial response mechanism of a sulfur autotrophic denitrification (SADN) biofilm under high nitrate (NO3--N) and sulfamethoxazole (SMX) stress through long-term operation of a fluidized bioreactor was evaluated. The SADN biofilm adapted to nitrate contents of up to 150 mg/L, and at 1 mg/L SMX, the nitrogen removal efficiency and SMX removal efficiency were as high as 85 % and 64 %, respectively. Microbial adaptation was driven by upregulated secretion of acyl-homoserine lactone (AHL) signal molecules, specifically 3OC6-HSL and 3OC8-HSL, which stabilized at concentrations of 575.7 ng/L and 579.9 ng/L, respectively. These molecules dynamically regulated the composition of extracellular polymeric substances, with total EPS content increasing from 113.37 mg/gVSS in the initial phase to 456.85 mg/gVSS under early SMX exposure, ensuring biofilm structural integrity. Under prolonged SMX stress, Simplicispira emerged as a key genus with a relative abundance of 21.20 %, utilizing apoptotic autotrophic denitrifiers and EPS metabolites as carbon sources for heterotrophic denitrification. This genus harbored critical nitrate reductase genes, including NarG, which accounted for 28.5 % of total functional gene abundance. In addition, SMX stress reduced the abundance of total anti-resistance genes (ARGs), with resistance mechanisms dominated by antibiotic efflux pumps, with the contribution increased from 63 % to 67 %. The relevance of this pump continuously increased, which hindered binding of SMX to cells and effectively reduced its toxicity. The results of this study provide scientific evidence for the application of SADN technology in a high-nitrate and antibiotically stressed environment. The results can further guide practical operations and provide technical support for increasing denitrification efficiency and antibiotic removal capacity in the SADN process.

Emerging applications of fluorescence excitation-emission matrix with machine learning for water quality monitoring: A systematic review

Fluorescence excitation-emission matrix (FEEM) spectroscopy is increasingly utilized in water quality monitoring due to its rapid, sensitive, and non-destructive measurement capabilities. The integration of machine learning (ML) techniques with FEEM offers a powerful approach to enhance data interpretation and improve monitoring efficiency. This review systematically examines the application of ML-FEEM in urban water systems across three primary tasks of ML: classification, regression, and pattern recognition. Contributed by the effectiveness of ML in nonlinear and high dimensional data analysis, ML-FEEM achieved superior accuracy and efficiency in pollutant qualification and quantification. The fluorescence features extracted through ML are more representative and hold potential for generating new FEEM samples. Additionally, the rich visualization capabilities of ML-FEEM facilitate the exploration of the migration and transformation of dissolved organic matter in water. This review underscores the importance of leveraging the latest ML advancements to uncover hidden information within FEEM data, and advocates for the use of pattern recognition methods, represented by self-organizing map, to further elucidate the behavior of pollutants in aquatic environments. Despite notable advancements, several issues require careful consideration, including the portable or online setups for FEEM collection, the standardized pretreatment processes for FEEM analysis, and the smart feedback of long-term FEEM governance.

Precise regulation of UV/H2O2 processes: •OH generation/reaction and DOM transformation as the main free radical scavenger

The widespread application of UV/H2O2 is limited by the empirical operational practices, which can lead to excessive energy, chemical input and the generation of uncontrollable by-products. This study presents a precise regulation approach based on the characteristics of free radical generation/reaction and the chemical transformation of organics, assessed through a pilot experiment. The findings indicated that increasing H2O2 dosage was more effective than increasing UV dose in enhancing •OH generation and pollutant removal. As the H2O2 dosage and UV dose increased, the relative influence of water quality on pollutant removal gradually diminished. Dissolved organic matter (DOM) in the water quality background accounted for the largest proportion of •OH scavenging (76.4 %) and the most complex component. Moreover, changes in operating conditions were accompanied by the uncontrollable production of low-molecular-weight (LMW) DOM. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed the chemical transformation of LMW DOM at the molecular level. Higher H₂O₂ dosages triggered more extensive oxidative degradation, resulting in more complex effluent compositions. Considering treatment efficiency, energy consumption, and effluent product composition, H₂O₂ dosages of 5-10 mg/L and UV doses of 350-450 mJ/cm² were identified as optimal. This research contributes to the efficient purification of organic micropollutants in water using UV/H2O2 technology with low energy consumption, minimal chemical input, and relatively controllable by-products.

Insight into the characterization of dissolved organic matter in shallow lakes with different trophic states and their net photo-generation capacity of reactive oxygen species

Reactive oxygen species (ROS) are ubiquitous in the aquatic environment, and they are closely related to several biogeochemical processes. Dissolved organic matter (DOM) is one of the main photosensitizers involved in the formation of ROS and it also serves as a sink for ROS by involving in scavenging, quenching, and antioxidant reactions. The net effect of these processes depends on the concentration, source, and composition of the DOM. Current studies have mainly focused on the steady-state concentration of reactive oxygen species ([ROS]ss) produced by the total DOM in lakes with different trophic states and ignored the net photo-generation capacity of ROS ([ROS]DOM, the net steady concentration of ROS generated per unit mass of DOM), leading to a vague understanding of the photochemical properties of DOM in aquatic systems, especially in shallow lakes with different trophic states. In this study, the optical composition of DOM was determined with optical characterization, such as specific UV-Vis and excitation-emission matrices with fluorescence regional integration (FRI-EEMs), and its molecular characteristics were analyzed by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results revealed that DOM in lakes with different trophic states had mixed endogenous and exogenous characteristics, accompanied by an increasing trend in endogenous characteristics with the increasing trophic state of lakes. Spectroscopic probes were used to detect the steady-state concentration of ROS and further calculate the [ROS]DOM, such as [3DOM*]DOM, [•OH]DOM, [1O2]DOM and [O2.-]DOM. The results indicated that the [ROS]DOM in lakes with light-eutrophic states was significantly higher than that in lakes with moderate-eutrophic and hyper-eutrophic states, which indicated that the DOM in lower trophic state lakes has a higher net photo-generation capacity of ROS. Pearson analysis results showed that [3DOM*]DOM, [•OH]DOM, [1O2]DOM and [O2.-]DOM had a significant positive correlation with lignin/CRAMs-like, aromatic, and tannin compounds, as well as the fluorescence components, fulvic- and humic-like substances and the UV-Vis indicator: SUVA254 revealed that DOM with higher humification and aromaticity had a higher net photo-generation capacity of ROS in different trophic state lakes. In addition, the molecular uniqueness of the DOM was dominated by lignin/CRAMs-like and aromatic compounds, which were positively correlated with [ROS]DOM, in the following order: [3DOM*]DOM > [•OH]DOM > [1O2]DOM > [O2.-]DOM. This study emphasizes the importance of focusing on the source, composition, and net photo-generation capacity of ROS by DOM, which would help evaluate the photochemical potential and other behaviors of DOM in lakes with different trophic states and provide guidance for the risk assessment of DOM input from different sources.

Comparison of single and mixed microalgae in microalgae-bacteria MB-MBR:From efficiency of wastewater treatment, bioactivity and membrane fouling

In this study, two microalgae-bacterial moving bed membrane bioreactors (MB-MBRs) were constructed for co-culture of L1 (Scenedesmus obliquus) and L2 (Chlorella pyrenoidosa and Scenedesmus obliquus) with activated sludge. Nutrient removal efficiency, biological activity and membrane fouling of two microalgae-bacterial MB-MBRs were evaluated. Both reactors demonstrated robust performance, with L2 exhibiting superior functionality. near-complete ammonia nitrogen removal (99.33 ± 1.11 %), total organic carbon (TOC) removal of 73.72 ± 4.83 %, chemical oxygen demand (COD) removal of 92.93 ± 3.23 %, and dehydrogenase activity (DHA) peaked at 10 μg TF/(mL·h). L2 sludge flocs displayed a more compact circular morphology compared to those of L1. It was found that proteins in the extracellular polymeric substance (EPS) were the key to initial biofilm attachment, while polysaccharides facilitated biofilm maturation. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy demonstrated that tryptophan and aromatic proteins played critical roles in biofilm formation and membrane fouling. According to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, ΔGAB was the main factor influencing membrane fouling. These results demonstrate that hybrid microalgae-bacterial systems with biofilm carriers synergistically enhance wastewater treatment efficiency, increase biological activity, and alleviate membrane fouling, offering a sustainable strategy for wastewater treatment.

Fate, characteristics, and potential threat of microplastics in sludge under various dewatering treatments

Microplastics (MPs), an emerging environmental pollutant, have been found in wastewater sludge with increasing frequency. Their occurrence, surface properties, and adsorption characteristics may be altered during various sludge dewatering processes. This study explored and compared the performance of four types of sludge dewatering processes (FeCl3 + CaO, Fe2+ + H2O2 + CaO, Fe2+ + peroxymonosulfate (PMS) + CaO, and Fe2+ + CaO2 + CaO) in improving sludge dewaterability, the fate and characteristics of MPs during treatments, and their effect on the adsorption of heavy metals by aged MPs. Results showed that iron-based advanced oxidation processes (Fe-AOPs) indicated superior performance in improving sludge dewaterability compared to conventional FeCl3 + CaO treatment, as evidenced by the water content of sludge cakes being reduced to below 54.0 % (w/t) in Fe-AOPs. Fe2+ + PMS + CaO and FeCl3 + CaO effectively reduced MPs concentrations in both dewatered sludge and filtrate, thereby mitigating potential environmental risks. The potential risk associated with heavy metal adsorption onto treated MPs was greater for Fe2+ + PMS + CaO than for FeCl3 + CaO. In summary, Fe2+ + PMS + CaO offered a feasible method for sludge dewatering and MPs removal, particularly suited to sludge with low heavy metal concentrations. FeCl3 + CaO treatment effectively mitigated co-toxicity between heavy metals and MPs, proving more suitable for sludge with high heavy metal content. This study offers new insights into the selection of appropriate sludge treatments regarding MPs.

Effect of carbon source on the migration and transformation of sulfate and rare earth elements in wastewater by sulfate-reducing anaerobic digestion

The rare earth extraction wastewater containing trace amounts of rare earth elements (REE3+), posed significant environmental risks and complicated recovery efforts. Sulfate-reduced anaerobic digestion (SRAD) offered promising treatment for the wastewater. However, the influence of carbon source on the collaborative transformation of sulfate and REE3+ within SRAD remained inadequately explored. Thus, this study explored the transformation of sulfate and REE3+ under different carbon source conditions. The results demonstrated that, despite the advantage of ethanol in electron donation, it was less effective than a mixed carbon source in removing REE3+. This was attributed to several factors: (1) Mixed carbon sources not only enhances the production of S2- but also promotes the stable forms of REE3+ through preferential formation of organically bound fraction/residual fraction coordination complexes; (2) Microorganisms cultivated with mixed carbon sources secreted more tryptophan-like proteins capable of adsorbing REE3+; and (3) CO-SRB (complete oxidizers-sulfate-reducing bacteria) enriched by mixed carbon sources exhibited stronger adaptability to REE3+ and more robust interspecies interactions. Moreover, the COD/SO42- ratio of 1.5 was found to be optimal, achieving approximately 90 % removal of REE3+ and 69.38 ± 4.63 % removal of SO42-. This study provides theoretical guidance for carbon source dosing strategies aimed at the simultaneous removal of sulfate and REE3+ from rare earth wastewater.

Cadmium-Induced Responses and Tolerance Mechanisms of Aerobic Methanotrophs in Rice Paddy Soils

Paddy fields are major sources of atmospheric methane and are at risk of cadmium (Cd) contamination. Aerobic methanotrophs, which serve as biological methane sinks, play a key role in methane cycling, but their responses to Cd stress remain poorly understood. Here, we examined the relationship between Cd pollution levels and aerobic methane oxidation potential in paddy soils. We evaluated methanotrophic enrichments under Cd exposure, applied metagenomic sequencing to identify functional microbes, and investigated Cd tolerance mechanisms in pure culture. Aerobic methane oxidation rates were positively correlated with Cd levels in paddy soils from South China, with Methylocystis and Methylomonas emerging as dominant genera possessing diverse Cd tolerance genes. Notably, interspecific differences in Cd tolerance were observed among methanotrophic strains. The faster-growing Methylomonas sp., endowed with more robust antioxidant defenses and extracellular polymeric substances synthesis genes, exhibited Cd resistance through markedly enhanced loosely bound extracellular polymeric substances production, in contrast to the Cd-sensitive Methylobacter sp. Gene knockout experiments confirmed the essential roles of glutathione synthase, glutathione peroxidase, and exosortase in exopolysaccharide extrusion for Cd detoxification. These findings advance our understanding of the methane cycle in Cd-contaminated rice paddies and suggest potential strategies to mitigate methane emissions while addressing Cd detoxification.

Effects of polylactic acid microplastics on dissolved organic matter across soil types: Insights into molecular composition

Increasing evidence has highlighted the effects of biodegradable microplastics (MPs) on soil organic matter (SOM), but the role of soil type and incubation time remains unclear. This study investigated the effects of polylactic acid microplastics (PLA-MPs) on the amount and molecular composition of dissolved organic matter (DOM) across three paddy soil types (Ferralsol, Alfisol, and Mollisol) and incubation times, revealing soil-specific patterns in DOM transformation: PLA-MPs reduced DOM content in Ferralsol and Alfisol by 29.3-68.2 mg/kg and 27.3-30.9 mg/kg, respectively, but initially increased it in Mollisol (30 d: 220.9 mg/kg; 60 d: 622.0 mg/kg). Molecular analyses revealed a decrease in DOM component diversity at both 30 and 180 d, potentially due to PLA-MPs stimulating microbial activity and accelerating native SOM decomposition. PLA-MPs promoted the formation of CHO (containing carbon (C), hydrogen (H), and oxygen (O)) compounds, whereas microbes selectively decomposed CHONS (containing C, H, O, nitrogen (N), and sulfur (S)) compounds to meet C and N demands, particularly in Ferralsol and Alfisol. This study enhances the understanding of biodegradable MPs' impact on SOM, emphasizing the role of soil properties.

Electrochemical enhancement of the accumulation of photosensitive components in anoxygenic phototrophic bacteria extracellular: A new insight into the preparation of degradable microbial photosensitizer for water treatment

Extracellular polymeric substances (EPS) are promising biomaterials for environmental remediation, but their application is hindered by low production efficiency and limited pollutant degradation capacity. In this study, photosynthetic electron extraction enabled Rhodopseudomonas palustris (R. palustris) to efficiently produce EPS enriched with functionalized components. The enhanced EPS (0.2V-EPS), produced from electrically domesticated R. palustris, achieved an 82 % degradation rate of sulfamethoxazole (SMX) within 10 hours, an 18 % improvement compared to EPS produced under open-circuit conditions (OP-EPS). Mechanistic analysis revealed that photosynthetic electron extraction enriched EPS with photosensitive molecules, including tryptophan, humic acid, fulvic acid, which significantly promoted the generation of reactive species. The primary reactive species identified were triplet-excited EPS (³EPS*), ¹O₂, and •OH, with ¹O₂ as the dominant contributor to SMX degradation. The steady-state concentration of ³EPS*, ¹O₂, and •OH increased by 73 %, 34 % and 16 %, respectively, compared to the control. Structural modifications of 0.2V-EPS, including increased hydrophilicity, electronegativity, and aromaticity, enhance its physicochemical properties, thereby facilitating interactions with pollutants. Furthermore, an 88 % reduction in biofilm polysaccharides diminished free radical scavenging activity, promoting the generation of reactive species. This study provides a sustainable strategy for enhancing EPS functionality and offers insights into the metabolic regulation of microorganisms for pollutant degradation.

The irreversible transformation of the molecular structure of humic acid during pH change and its effects on the formation of disinfection by-products

Humic acid (HA) is an important component of natural organic matter, and understanding the nature and environmental behavior of HA is essential for advancing water treatment technologies and environmental remediation strategies. This study investigated the structural differences of HA at various pH values and whether the structure is reversible (whether the structure is similar when HA at different pH values is adjusted back to neutral compared to the original pH 7) by optical characteristics, hydrodynamic volume, fluorescence, infrared and circular dichroism spectroscopy. After adjustment back to neutral, from prior exposure to different pH values (2-12), the results showed an irreversible behavior of HA. For acidified HA restoring neutrality, the TOC and UV254 values decreased by 12.2 % and 11.2 %, respectively, and the formation of haloacetic acids (HAAs) and trihalomethanes (THMs) decreased by 24.1 % and 31.5 %, respectively. These changes were attributed to the protonation of oxygenated groups, the weakening of hydrogen bonding, resulting in the formation of aggregates by HA molecules and hydrophilic and hydrophobic structural changes. For alkalized HA restoring neutrality, the TOC increased by 10.7 %, and the formation of HAAs and THMs increased by 16.1 % and 26.2 %, respectively. These changes were attributed to the increase of electronegativity following deprotonation of HA functional groups, molecular swelling caused by increased molecular repulsion, and twisting of the secondary structure. This study provides new insights regarding the effect of changes in pH conditions on the structure and reactivity of HA, which are important for future approaches to the removal of HA and management of disinfection by-products (DBPs) formation in water treatment.

Calcium-modified siderite-driven optimization of sulfur autotrophic denitrification systems: Synergistic nitrogen/phosphorus removal and multidimensional mechanism insights

Sulfur autotrophic denitrification (SAD) is a promising technology for secondary treatment. However, existing methods struggle with coordinating sulfur oxidation-acidification, limiting efficient nitrogen and phosphorus removal from medium to high- strength wastewater. This study proposes a calcium-modified siderite-sulfur autotrophic denitrification (SCAD) process. Through long-term (90 d) continuous-flow comparisons of SAD, sulfur-siderite denitrification, and SCAD, the study evaluates SCAD's advantages in N/P removal, sulfate suppression, and pH buffering. The Fe2+/Ca2+ slow-release properties of Siderite-Ca stabilize pH and enhance denitrification. Phosphorus removal occurred via Fe-P and Hydroxyapatite precipitates. Microbial community analysis reveals that increased biomass, alongside the functional co-enrichment of Thiobacillus, Sulfurimona, and Ferritrophicum, drives enhanced pollutant removal. The Fe2+/S0 co-electron donor mechanism upregulates key denitrification (narG, nirK) and sulfur oxidation (sqr) genes. This study establishes SCAD as a novel strategy for concurrent nitrogen-phosphorus elimination with pH stability, while elucidating microbial community evolution and contaminant degradation mechanisms.

Optimizing extraction conditions to enhance the humification and soil remediation potential of compost-derived dissolved organic matter

Compost tea (CT), primarily composed of dissolved organic matter derived from compost, is widely used in various environmental and agricultural applications. Nevertheless, limited information is available regarding how extraction parameters influence the quality of CT and its efficacy in soil remediation. In this study, a multi-factor orthogonal design L16 (43) was employed to investigate the effects of compost-to-water ratio (CWR), extraction time (ET), and aeration pattern (AP) on nutrient extraction and humification of CT, aiming to optimize the extraction conditions. Results showed that N, P2O5, and K2O extraction efficiencies in all treatments ranged from 10 to 25 %, 10-20 %, and 50-85 %, respectively. The comprehensive humification score was in the range of 1.27-1.60. Among the three parameters, ET showed the most significant influence on CT quality. The optimal treatment for nutrient extraction was T15 (CWR 1:60, ET 48 h, and stirring), while T17 (CWR 1:30, ET 48 h, and aeration) exhibited superior performance on humification. Furthermore, the total Cd removal efficiency of T17 was 83.64 % after multiple washing cycles, which was attributed to an increased number of hydroxyl, carboxyl, and carbonyl functional groups that provided additional binding sites for Cd.

Exploring relationships among landfill leachate parameters through multivariate analysis for monitoring purposes

Elucidating the properties of landfill leachate and the relationships among leachate parameters is crucial for efforts to determine appropriate landfill leachate monitoring activity and management strategies. This study investigated the physical, chemical and optical parameters of leachate in an old Japanese landfill over a 13-month period. The parameters were explored based on their relationships with the maximum fluorescence (Fmax) of three components (microbial humic-like C1, terrestrial humic-like C2 and protein-like C3) deconvoluted from excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis. Dissolved organic carbon (DOC), chemical oxygen demand (COD), Cl- and SO42- concentrations and pH ranged from 2.6 to 38.2 mg C L-1, 9 to 324 mg L-1, 14 to 972 mg L-1, 26 to 1554 mg L-1 and 6.9 to 11.6, respectively. Linear regression analysis suggested that the Fmax values of C2 and C3 represented DOC, whereas the Fmax value of C2 alone could serve as a COD indicator. Hierarchical cluster analysis and principal component analysis were employed to successfully categorise leachate samples based on their locations. Higher dissolved organic matter levels were observed in leachate within the old disposal area, whereas elevated levels of inorganic components such as SO42- and Cl- were found in leachate collected from the extended disposal area and at a treatment facility. Statistical analysis provides crucial tools for assessing and managing various areas of a landfill, supporting targeted and effective waste management strategies.

Mechanistic insights into electric field-enhanced methanation of lignite via microbial metabolic pathway optimization

This study investigates the mechanistic insights into the enhancement of methane production from low-rank coal (lignite) through the application of electric fields. Experimental results demonstrate that an optimal electric field intensity of 1.6 V/cm significantly accelerates methane production, achieving a cumulative yield of 98.9 mL CH4/g lignite, which is 3.2 times higher than the control without an electric field (31.1 mL/g). Detailed analysis reveals that electric fields facilitate direct interspecies electron transfer, enriching electroactive microorganisms such as Coprothermobacter and Fermentibacteraceae. The abundance of these electroactive bacteria increased by up to 50 % at 1.6 V/cm, leading to improved degradation of complex organic substrates and optimized metabolic pathways. Metabolic pathways related to lactate and acetic acid production, precursors for methane, were found to be more abundant under electric field conditions. These findings offer new mechanistic insights into the role of electric fields in optimizing microbial pathways for low-rank coal methanation.

Investigating the impact of organic matter on Vibrio parahaemolyticus inactivation in aquaculture water by UV-LED system

Ultraviolet (UV) irradiation becomes a promising technology in inactivating pathogenic microbes, but the compositional change of organics and its consequence of inactivation need further study in raw water during UV light-emitting diode (UV-LED) irradiation. Herein, the bench-scale study aimed at evaluating the effect of organic fractions isolated from shrimp-farming water on the inactivation efficiency of Vibrio parahaemolyticus using UV-LED process at wavelengths of 265 nm, 280 nm, and combined wavelengths. The lowest required UV fluence (4.06 mJ/cm2) for 3-log inactivation was attained with UV-LED 280 nm. After UV irradiation the changes in elemental compositions of organic compounds, based on H/C and O/C ratios, were small. This is probably due to low UV exposure and UV resistant structure of organic constituents, predominantly lipid-like compounds. Contrarily, fluorescent spectroscopic analysis that showed degradation of protein-like substances by UV irradiation. In addition, the significant declines in the number of chemical formulas in organic compounds were identified through non-target screening using orbitrap mass spectrometry, suggesting degradation and amalgamation into new compounds. The presence of organic compounds did not profoundly affect inactivation efficiency at applying a minimum required fluence or greater. This study highlights the potential of UV-LED irradiation, particularly at 280 nm, for efficient inactivation of V. parahaemolyticus and subsequent molecular structure alteration of organic matter after UV irradiation.

Novel knowledge for identifying point pollution sources in watershed environmental management

Identifying point pollution sources (PPSs) is essential for enforcing penalties against illegal discharge behaviours that violate acceptable water quality (WQ) standards. However, there are existing knowledge gaps in understanding the association between the pollutants in water bodies and the pollutants emitted by PPSs, as well as how to utilize the knowledge to identify PPSs in water pollution accidents. This study developed a novel framework for identifying PPSs based on the conventional chemical pollutants and matrix calculations model (CCI-MCM). A two-step statistical analysis and correlation analysis extracted pollutant information in sewage wastewater from 256,025 PPSs and further developed the similarity matrix of industrial sewage wastewater indicators (SM-ISWI) and the correlation matrix of industrial sewage wastewater indicators (CM-ISWI). The SM-ISWI and CM-ISWI comprised 820 and 7790 pollution units, which could distinguish 41 industries and further identify the PPSs in these industries. Single factor index analysis and Pearson correlation analysis developed the WQ concentration matrix (WQ-CM) and WQ concentration correlation matrix (WQ-CCM), highlighting concentration anomalies of conventional chemical pollutants in natural water bodies and supply data for matrix calculation model to identify PPSs. The matrix calculation model with the Zf, Zc and Zf-c scores indicated the relative probability of each PPS responsible for the water pollution. Four publicly reported water pollution incidents in China were selected as case studies to validate the effectiveness of the CCI-MCM in PPSs identification. The TE values in four case areas ranged from 25.0 % to 53.9 %, demonstrating a practical enhancement in identifying PPSs relative to random sampling identifying PPSs methods. The proposed CCI-MCM method provided specialized knowledge in understanding the association between the pollutants in water bodies and the pollutants emitted by PPSs, as well as how to utilize the knowledge to identify PPSs in water pollution accidents.

Chemical activation of willow with co-presence of FeCl3 tailors pore structure of activated carbon for enhanced adsorption of phenol and tetracycline

FeCl3 is a Lewis acid catalyzing condensation reaction, which might be beneficial for enhancing mass yield of activated carbon (AC) if used as a co-activator. Herein, this was verified by conducting activation of willow with various activators (ZnCl2, K2C2O4, H3PO4) in the presence/absence of FeCl3. The results indicated that FeCl3 competed with acid-catalyzed reactions induced by ZnCl2 or H3PO4, interfering aromatization and diminishing AC yields (from 40.8 % to 37.0 % with ZnCl2). In the activation with K2C2O4 + FeCl3, In-situ IR measurement showed that FeCl3 catalyzed polymerization reactions, but polymeric products were not stable and were further cracked with K2C2O4, reducing AC yield drastically from 27.6 % to 7.1 %. The co-presence of FeCl3 in the activation reduced overall specific surface area (1201.6 versus 1127.2 m2 g-1 for K2C2O4) by merging of micropores to form a higher percentage of mesopores (i.e. 2.0 % to 17.1 % for K2C2O4, and 9.2 % to 41.4 % for H3PO4). This pore restructuring significantly enhanced tetracycline adsorption (99.9 % removal for AC- K2C2O4 + FeCl3 versus 61.1 % for AC-K2C2O4 alone), while compromising phenol adsorption (48.7 % versus 96.1 %) due to reduced micropore availability. The reduced specific surface area was also attributed to the retention of inorganics by solid phase reactions between FeCl3 and K2C2O4 or H3PO4. Additionally, the presence of FeCl3 resulted in more fragmented surface of ACs generated from all activators.

Fluoride-induced stress shapes partial denitrification granules to sustain microbial metabolism

The presence of fluoride ions (F-) in nitrogen-rich wastewater from photovoltaic and semiconductor industries introduces a significant challenge to biological treatment processes, particularly for the innovative partial denitrification (PD) process, which supplies nitrite for anaerobic ammonium oxidation (Anammox). This study provides the first comprehensive and systematic investigation of the effects of F- stress on the granule-based PD process through batch tests and long-term operation. Results indicate that PD activity remains resilient to F- shock up to 1.5 g/L but is markedly impaired at concentrations of 2.0-3.0 g/L, despite maintaining a nitrate-to-nitrite transformation ratio (NTR) of approximately 80 %. Under long-term F- stress at 0.5 g/L, NTR gradually reduces to 50 %, but subsequently recovers to and maintains at 70 %. The increased secretion of loosely bound extracellular polymeric substances and proteins likely enhances the resistance of PD granules to F- stress, though excessive amounts degrade their settling properties. F--induced microbial community succession shapes a predominance of medium granules (1.0 < d < 2.0 mm of 60.2 %) by enhancing aggregation of smaller granules and disintegration of larger ones. This enhances the mechanical strength and microbial activity of PD granules, aiding in resistance to F- stress to sustain microbial metabolism. Thauera is selectively enriched under long-term F- stress, with upregulated nirBDS genes contributing to the reduced NTR. Additionally, increased electron metabolism activity and a robust antioxidative response help to maintain higher microbial metabolic activity, mitigating F--induced oxidative stress. These findings advance our understanding of the resilience and adaptability of the PD process under F- stress, providing critical insights for optimizing biological wastewater treatment systems in challenging environments.

Extracellular polymers substances towards the toxicity effect of Microcystis flos-aquae under subjected to nanoplastic stress

The widespread presence of nanoplastics in aquatic ecosystems and their harmful effects on algae have garnered significant attention. However, little is known about the mechanisms of extracellular polymeric substances (EPS) derived from algae in response to nanoplastic stress. This study investigated the impact of EPS on the toxicity of polyvinyl chloride (PVC, 537 nm) and polymethyl methacrylate (PMMA, 485 nm) nanoplastics on Microcystis flos-aquae (MFa)under nanoplastic stress. The results revealed that EPS removal reduced algal biomass. PVC nanoplastics (250 mg L-1) caused biomass inhibition of -16.87% before and -9.82% after EPS removal. PMMA nanoparticles exhibited a more significant inhibition of growth and chlorophyll synthesis compared to PVC. After EPS removal, algal cells gradually recovered their maximum quantum yield of photosystem II and exhibited increased superoxide dismutase (SOD) enzyme activity, suggesting a self-regulation mechanism. Nanoplastic stress elevated EPS protein and polysaccharide levels, with maxima of 12.38 mg L-1 at 50 mg L-1 PVC and 17.24 mg L-1 at 100 mg L-1 PMMA. At the same time, the polysaccharide content in nanoplastics was significantly higher than that of proteins, with the maximum value being 2.82 times that of proteins. Fourier-transform infrared spectroscopy (FTIR) and excitation-emission matrix (EEM) analyses showed that aldehyde functional groups on the surface of algal cells were oxidized into carboxylic acids by both types of nanoparticles. Exposure to different nanoplastics increased humic-like substances in tightly bound EPS (TB-EPS), indicating that EPS dynamically adjusts to reduce nanoplastic toxicity by enhancing viscosity and algal aggregation. These results demonstrate that EPS mitigates the direct contact between algal cells and nanoplastics by increasing viscosity and promoting algal self-aggregation, thereby reducing the toxicity of nanoplastics to algae. This phenomenon is consistent across various stress conditions, providing valuable insights into the self-protection mechanisms of microalgae against nanoplastic stress.

Electro-enhanced mass transfer boosting photocatalysis towards ionized organic pollutants

Removing antibiotics from wastewater in an efficient and sustainable way is a great challenge. Herein, we developed an electro-enhanced photocatalysis system. It was found that a positively-charged organic molecule (tetracycline) could be attracted by the negatively-polarized electrode, thus leading to enhanced mass transfer and improved removal rate.

Efficient sulfur accumulation in biological desulfurisation and denitrification induced by microbial and chemical interactions

Efficient accumulation of sulfur from simultaneous desulfurisation denitrification process can achieve high economic and environmental benefits. This work aims to study the effect of product accumulation on elemental sulfur production and understand its potential mechanism. The addition of the intermediate product thiosulfate and the final product sulfate during the reaction led to an increase in the production of biological elemental sulfur (S bio 0 ). The effect is mainly reflected in the efficient accumulation effect of S bio 0 at high sulfide loads. When the sulfide feed water load was 300 mg/L, the S bio 0 production reached 65.94 mg/L in 24 h with the addition of 30 mg/L thiosulfate and 20 mg/L sulfate, which was 3.11 times higher than that of the control group. The addition of sulfate increased the content of aromatic protein I and aromatic protein II, and accelerated the propagation of Thiobacillus denitrificans, whose viable bacterial amount was 1.12-2.98 times higher than that of the control group. On the one hand, low-dose sulfate induced Thiobacillus denitrificans to participate in the sulfur-producing reaction (S 2 - →S bio 0 ) more quickly by accelerating the propagation of the strains in the pre-reaction stage. On the other hand, the addition of sulfate shifted the overall reaction equilibrium to the left and inhibited the formation of thiosulfate, thus accelerating the accumulation of S bio 0 in the whole reaction stage. This study would provide guidance for artificially promoting efficient sulfur accumulation in desulfurisation denitrification treatments.Highlights The S bio 0 production reached 65.94 mg/L in 24 h at high sulfide load.20 mg/L sulfate induced the rapid propagation of Thiobacillus denitrificans.Thiobacillus denitrificans were involved early in the sulfur-producing reaction.Inhibition of thiosulfate formation indirectly promoted sulfur accumulation.

Exploring the interaction between quorum sensing and sludge physical properties in Anammox systems

Quorum sensing(QS) is a crucial aspect of Anammox(anaerobic ammonium oxidation) technology operation. Given the difficulty of accumulating Anammox bacteria, the favorable characteristics of sludge are vital for optimizing the stable operation of Anammox systems. Therefore, it is essential to study the interaction between QS and the physical properties of sludge in the Anammox process. In this study, the extended Derjaguin-Landau-Verwey-Overbeek(XDLVO) theory and rheological properties were used to determine the physical characteristics of different Anammox sludges, subsequently the relationship between these properties and signaling molecules, microorganisms and extracellular polymeric substances(EPS) was analyzed. The results indicated that certain physical properties, such as elasticity, sludge aggregation capability, and hydrophobicity, were significantly correlated with specific signaling molecules. Additionally, the dynamic changes in microbial community structure were one of the main causes of changes in the levels of signaling molecules, which stimulated the nitrogen removal performance and also affected the properties of the sludge.

Electro-activation of peroxymonosulfate by novel Co3O4/sludge biochar cathode for sulfamethoxazole removal: cobalt-mediated synergistic effect and mechanism

Sludge biochar (SBC) has emerged as a value-added solid waste-derived catalyst for peroxymonosulfate-based advanced oxidation processes (PMS-AOPs). This study developed a cobalt oxide-modified SBC composite electrode supported on nickel foam (Co/SBC@NF), establishing an electro-enhanced Co/SBC@NF-PMS system (E-Co/SBC@NF-PMS) for efficient sulfamethoxazole (SMX) degradation. The integrated system synergistically combined electrochemical activation with heterogeneous catalysis to optimize PMS utilization. Under relatively low PMS concentration (0.15 mM) and current density (5 mA/cm2), the E-Co/SBC@NF-PMS system demonstrated enhanced degradation efficiency (kobs = 0.0870 min-1), exhibiting a 4.7-fold and 9.3-fold improvement over the Co/SBC@NF-PMS (kobs = 0.0186 min-1) and E-Co/SBC@NF (kobs = 0.0094 min-1) systems, respectively, and the synergistic coefficient was 3.11. Reactive species quenching tests and density functional theory calculations revealed that electrochemical, radical, and non-radical oxidation were the combined attack mechanisms for SMX removal. Cobalt species served as dual-functional mediators, facilitating both electrochemical redox cycling for radical generation and the formation of C=O on the SBC surface for non-radical processes of PMS activation. This study promoted the resource utilization of sludge and provided a novel strategy for aquatic ecosystem remediation by synergistically enhancing PMS activation.

Synergistic oxidation and coagulation of raw water by novel Fe(II)/sulfite process: A comparative study with peroxydisulfate and peroxymonosulfate

Latest findings demonstrate that the oxidative Fe(II)/sulfite (Fe(II)/S(IV)) process can rapidly generate iron particles, holding potential for coagulation while simultaneously removing emerging contaminants. Herein, we first report the synergistic oxidation-coagulation treatment of RW by Fe(II)/S(IV) process, and compare with traditional Fe-based coagulation (FeSO4, Fe2(SO4)3), Fe(II)/PDS and Fe(II)/PMS processes. Results revealed that the Fe(II)/S(IV) process outperformed traditional Fe-based coagulants, Fe(II)/PDS and Fe(II)/PMS in removing turbidity, UV254, and DOC. For emerging contaminants removal from RW, Fe(II)/PMS showed the highest efficiency, followed by Fe(II)/PDS, while Fe(II)/S(IV) was slightly less effective, it still demonstrated a significant improvement (40 %∼65 %) over traditional coagulation processes. Moreover, the Fe(II)/S(IV) process is the most effective in reducing DBPs formation (56 %∼86 %). Although Fe(II)/PDS and Fe(II)/PMS also significantly reduce DBPs formation, their high oxidation potential at low pH generated toxic N-DBPs. Mechanistic analysis indicated that the Fe(II)/S(IV) process was most effective in removing humic substances and biopolymers. Its moderate oxidation preserved macromolecular structures, enhancing coagulation. And the hydrolysis of S(IV) generates OH⁻, promoting electrostatic neutralization and floc enlargement. Cost analysis revealed that the Fe(II)/S(IV) process is significantly more economical, with costs only 1/60 of Fe(II)/PMS. These results highlight the Fe(II)/S(IV) process as a promising and cost-effective approach to advanced water treatment.

Spotlight on the long-term effects of micro/nanoplastics exposure on Spirulina platensis: Algal cells, extracellular polymeric substances, and phycocyanin

Spirulina platensis (SP) provides humans with proteins and natural pigments. The effects of micro/nanoplastics (MNPs) on SP are of great interest. We focused on the effects of high concentrations (100-300 mg/L) of polystyrene MNPs on SP for 50 days. MNPs caused growth retardation, a decrease in peak concentration of algal cells, the emergence of surface cracks and pores, and stimulated the secretion of extracellular polymeric substances that promoted heterogeneous aggregation of SP. During the first 35 days, there were significant differences between the exposure groups in the phycocyanin concentration, yield and purity and the ratio of phycocyanin to phycobiliprotein, with the higher MNPs concentration resulting in lower values, whereas on day 50 there were no statistically significant differences in any of these metrics between the control or exposure groups. This study enriches the knowledge about the long-term effects of MNPs on SP for microalgae culture and food industry.

Extracellular polymeric substances in indigenous microalgal-bacterial consortia: advances in characterization techniques and emerging applications

Extracellular polymeric substances (EPS) synthesized by indigenous microalgal-bacterial consortia (IMBC) play multifunctional roles in enhancing wastewater treatment efficiency, nutrient sequestration, and ecological system stability. This comprehensive review critically evaluates state-of-the-art analytical methods for characterizing EPS composition, physicochemical properties, and functional dynamics, including colorimetry, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). While these methods provide critical insights into EPS structure-function relationships, challenges persist in resolving spatial heterogeneity, real-time secretion dynamics, and molecular-scale interactions within complex IMBC systems. Emerging technologies such as expansion microscopy (ExM), electrochemical impedance spectroscopy (EIS), and integrated multi-omics approaches are highlighted as transformative tools for in situ EPS profiling, offering nanoscale resolution and temporal precision. By synthesizing these innovations, this review proposes a multidisciplinary framework to decode EPS-mediated microbial symbiosis, optimize IMBC performance, and advance applications in sustainable bioremediation, bioenergy, and circular resource recovery.

Preparation and ecological risk assessment of porous sewage sludge substrate for ecological restoration

Mining activities often bring great pressure to the surrounding ecological environment, so it is necessary to carry out ecological restoration in mining areas. In this study, a constructed technosol (denoted SAS) for ecological restoration was prepared with municipal sludge as main materials, and its properties and ecological risk was assessed. The results showed that the optimal conditions for preparation were as follows: raw material ratio of 0.04, water-cement ratio of 0.01, aluminum powder dosage of 0.03%, curing temperature of 40 ℃, curing time of 24 h. The solidification of cement contributed to the connection path between the sludge particles, and the bubbles generated by aluminum powder further formed the microscopic pore structure. Heavy metals chemical species analysis concluded that As, Cd and Pb were immobilized, while Cu and Ni were tended to be activated, assessment result indicated low risk level. The transformation of macromolecular organic matter into humus was beneficial to improve the structure and biological activity, and the pot experiment result also displayed the low toxicity to plants. This work enriched the research system of ecological restoration in mining areas and provides a new strategy for the recycling of municipal sludge.

Structural diversity and environmental impacts of Cladophora mats in a large plateau brackish lake

Filamentous algal blooms (or algal mats) are increasingly recognized as a growing threat to clear lakes worldwide, particularly in the context of climate change and lake eutrophication. Nevertheless, knowledge about filamentous algal mats and their environmental consequences is still limited. In this study, we investigated the structural characteristics and environmental impact of filamentous algae (Cladophora) mats in the brackish water of Qinghai Lake on the Tibetan Plateau. Our results classify the development of Cladophora blooms into three distinct stages: the attachment stage (May to July), the floating stage (August to September), and the decomposition stage (October to November), corresponding to attached, floating, and decaying mats, respectively. The attached mats consist of single layer, while the floating and decaying mats exhibit more complex structures, with two-layer and three-layer formations, respectively. Each layer displays distinct physiological states in the vertical direction, highlighting their structural diversity. The layered structure enables Cladophora mats to better adapt to environmental changes, ensuring long-term stability in the lake ecosystem through the synergistic effects of upper-layer protection, middle-layer growth, and bottom-layer decomposition. Notably, the water surrounding the decaying mats showed significantly elevated concentrations of nitrogen, phosphorus, and dissolved organic matter. Partial Least Squares Path Modeling analysis further revealed that Cladophora mats have a substantial influence on dissolved organic carbon and fluorescent dissolved organic matter, with path coefficients of 0.84 and 0.65, respectively. These findings significantly enhance our understanding of the dynamics of filamentous algal blooms and their environmental impacts, and are crucial for the conservation of lakes with high water quality.

Specialized genera and niche partitioning promote the biosynthesis of short-chain fatty acids in anaerobic cofermentation of sewage sludge and protein-rich waste

Elucidating the relationships among various microorganisms and their reactions to environmental fluctuations, such as dissolved organic matter (DOM), remains a key objective in the anaerobic cofermentation (ACF) of sewage sludge (SS) and protein-rich waste (PRW); however, this topic is inadequately understood. In this study, the microbial traits associated with the biosynthesis of short-chain fatty acids (SCFAs) were investigated in the ACF of SS in conjunction with four distinct PRWs (pupa, fishmeal, maize gluten, and soybean meal). Compared with those in the SS-only reactor, the first-order rate constants for biosolid dissolution in the SS/PRW reactors were increased by 1.9-4.0-fold. Pupa performed best among the four PRWs in the ACF process, with the solubilization rate increasing from 9.4% (SS-only reactor) to 33.5%. The copious and readily biodegradable DOM created a unique niche for functional microbes, leading to reframing of the microfloral structure. Specialized genera, such as Holophaga, Alistipes, and Geothrix, were responsible for SCFA biosynthesis in the SS/pupa reactor. The highly differentiated, low-redundancy microecosystem constructed in the SS/pupa reactor contributed to the independent functioning of the hydrolyzers and acidogens, resulting in an SCFA yield that was 6.9-fold greater than that in the SS-only reactor. In addition, the ACF of SS/pupa resulted in the genes encoding the NiFe hydrogenase and Wood-Ljungdahl pathway being intact, which promoted the synthesis of SCFAs, especially acetate. These findings offer new insights into the microbiological mechanisms that augment SCFA generation by the ACF of SS/PRW in terms of microorganism fate, metabolic network relationships, and microecosystem niche.

A novel gravity-driven fixed-bed ceramic membrane filtration (GDFBCM) with critical PAC-MnOx-ceramsite filters for simultaneously removing hazardous manganese and ammonia from groundwater

Groundwater is widely threatened by hazardous manganese and ammonia. In present study, a novel gravity-driven fixed-bed ceramic membrane filtration (GDFBCM) with critical PAC-MnOx-ceramsite filters was built to address these issues. Static ceramsite filters in GDCM significantly increased membrane flux from 11 L/m2·h to 18 L/m2·h on the 50th day of filtration. Their synergistic effects with aerated fluidization further reduced membrane fouling by 29 %. Ammonia removal was improved from 62 % to 78 % by ceramsite filters after accelerating nitrification and denitrification by stimulating Nitrospira and Nitrosomonas. Metabolite secretion, ATP level, bacteria abundance and microorganism community analysis evidenced that ceramsite filters acted as immobilization carriers to stimulate Mn-oxidizing bacteria (e.g. Pseudomonas and Hyphomicrobium) for greater biological oxidation of dissolved manganese. According to FTIR, XRD, XPS spectra and SEM-EDS mapping, the facilitated formation of two-dimensional sheet-like birnessite on ceramsite filters established a virtuous cycle for continuous manganese removal. These processes further benefited from the increased hydraulic retention time by denser membranes. The excellent resistance to suddenly increasing pollution loading confirmed the outstanding applicability of GDFBCM. Energy consumption analysis also indicated that GDFBCM was an energy-saving system for groundwater treatment with the specific energy consumption of less than 4 × 10-3 kWh/m3.

Compositions of suspended particulates in typical urban river of Shanghai, China and its significance for ecological restoration

Although the water quality of urban rivers in Shanghai, China has been improved significantly in the past decades, their transparency is still unsatisfactory. To clarify the turbidity and its possible mechanisms, the characteristics of suspended particulate matters (SPM) are analyzed carefully, which reveals that suspended microbes dominate the component in urban rivers with high turbidity. Based on the principal component analysis and random forest analysis, nutrients and organic pollutants is revealed to promote the turbidity by promoting the growth of suspended algae and microbes. Furthermore, high-throughput sequencing is used to analyze the microbes in bulk water of urban rivers and iris rhizosphere of ecological floating bed. It reveals that there are significant differences between the microbial communities in bulk water and iris rhizosphere, suggesting that microbes immobilized in iris roots are not derived from bulk water. The metabolic function enrichment analysis based on PICRUSt shows that rhizosphere microbes mainly concentrate on the metabolism of plant secretions, while suspended microbes in bulk water mainly concentrate on the metabolism of pollutants. Since microbial diversity, metabolic richness, and interactions of rhizosphere microbes are much higher than those microbes in bulk water, it suggests that rhizosphere microbes may reduce suspended microbes in water via their competitive effects, thus purify pollutants and reduce turbidity in bulk water (improve transparency). These findings reveal the theoretical basis of water ecological restoration, thus might be helpful to technological innovation in the ecological restoration of urban rivers with high turbidity.

Spatial assessment of drinking water flavor in China: Revealing regional disparities and underlying drivers

Drinking water flavor, a critical water quality metric, exhibits substantial regional variations across China, influenced by local geology and chemistry. Despite growing consumer concerns about water flavor, a spatial assessment of the determinants of water flavor in China has been notably lacking. This study bridges this gap by conducting a spatially comprehensive analysis of 78 tap water samples throughout China. A reliable flavor evaluation method, alongside advanced statistical techniques, including correlation analysis, principal component analysis (PCA), and spatial autocorrelation analysis, were applied to identify the drivers behind regional flavor differences. The findings reveal four predominant types of flavor variations attributed to distinct organic and inorganic factors. The spatial distribution patterns of key parameters impacting flavor were clarified by Moran's I statistic. Notably, the South-to-North Water Diversion Project is highlighted for its role in enhancing water flavor by modifying the chemical composition of water in recipient regions. Dissolved organic carbon (DOC), trihalomethanes (THMs), and the fluorescence index (ΦIV,n) are identified as non-negligible supplementary indicators of water flavor. The research highlights the need for region-specific strategies to enhance the flavor of drinking water nationwide.