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

Effects of elevated atmospheric carbon dioxide to Microcystis aeruginosa under different forms of phosphorus sources

Human activities have led to an increase in atmospheric carbon dioxide (CO2) concentration, which can enhance the flux of CO2 from air to water, thus impacting algal growth. Phosphorus (P) is a key factor influencing the formation of cyanobacteria blooms. Nutrient utilization is closely related to carbon (C) metabolism, but the effects of elevated CO2 on microalgae under different P sources are rarely studied. In this study, we investigated the growth and physiological and biochemical responses of Microcystis aeruginosa (M. aeruginosa) under ambient (400 ppm) and elevated (550 ppm) CO2 levels in P-free, dissolved inorganic P (DIP, 1 mg P/L), and dissolved organic P (DOP, 1 mg P/L) groups. The bioavailability of DIP to M. aeruginosa was greater than that of DOP, and elevated CO2 increased both the uptake of DIP and DOP. Elevated CO2 promoted the growth (increasing by 9.0%-14.2%), photosynthesis, and CO2 fixation of M. aeruginosa under different P sources (P-free, DIP, DOP), and increased total microcystin-LR content (increasing by 5.4%-12.6%), which increased the risk of microcystin-LR release into the environment. Furthermore, elevated CO2 aggravated the stress effect of DOP, leading to an increase in protein content and proportion of humic acid substances in the extracellular polymeric substances. Our study provides a theoretical basis for understanding the impact of elevated CO2 on cyanobacteria bloom under different P sources, and provides a new insight for the control of eutrophic waters under the background of climate change.

Variability of the optical signatures of dissolved organic matter in soils of different mangrove stands (Ouvéa, New Caledonia)

Mangrove ecosystems are known to play a key role in the global carbon cycle, due to their productivity and their ability for carbon sequestration both in the biomass and in the soil. In the latter, various geochemical processes lead to the production of dissolved organic matter (DOM) that can be exported through tidal pumping and then constitute an important source of organic carbon for adjacent ecosystems. DOM characteristics, and their variabilities, within mangrove soils depend on several factors, including the mangrove species, yet these variations and their origin still need to be precisely constrained. This study examined DOM sources in soils of a carbonate atoll mangrove (Ouvéa, New Caledonia), focusing on two tree species, Rhizophora apiculata and Bruguiera gymnorhiza, at different growth stages. We analysed porewater properties and DOM optical characteristics through spectroscopic and EEM-PARAFAC methods. Our results indicate distinct TOC and DOC concentrations across species, with mature B. gymnorhiza soils showing the highest TOC content (~ 30%) but the lowest DOC content (32 mg L-1). These differences seem not to be directly related to site physicochemical conditions (redox, pH, salinity) but may rather reflect differences in DOM sources and production, notably due to different symbiotic relationships with mycorrhizal fungi, which influence microbial activity and organic matter diagenesis. DOM absorbance patterns also varied significantly between species: Beneath R. apiculata, DOM had higher protein-like and fulvic-like fluorescence, indicating fresher organic matter, while beneath B. gymnorhiza, especially in mature stands, DOM was more humified, suggesting older OM because of a possible long-term accumulation due to the basin-like morphology of this site.

Unraveling the interaction of dissolved organic matter and microorganisms with internal phosphorus cycling in the floodplain lake ecosystem

Internal nutrient cycling, especially phosphorus (P), is of great influence in lake eutrophication. Dissolved organic matter (DOM) and microorganisms are ubiquitous in the sediments and closely associated with P-cycling. However, the underlying interactions of DOM, microorganisms and P in floodplain lake area with different hydrological characteristics remain scarce. This study evaluated the P and DOM properties, P functional genes and microbial community ranging from channel to stagnant to grass area (CA, SA, GA) in a floodplain lake, respectively. The results showed that sediments dissolved organic carbon (DOC) and total P (TP) gradually decreased from GA to SA to CA. Organic P (64.44%) and Fe-bound P (34.86%) were primary bioavailable P fractions in three areas. Water Chl-a, DO, DOC and fulvic-like C1 component were essential driving factors affecting the distribution of P in sediments (p < 0.05). Microbial diversity, community structure and P-cycling function were significantly different in three areas and closely associated with sediment P and DOM (p < 0.05). The co-occurrence network analysis revealed that the interconnection of microbial communities, DOM components and P fractions decreased from CA (node: 123, edge: 1399) to SA (node: 122, edge: 667) to GA (node: 119, edge: 521). Sediment microbial communities enhanced P cycling via mineralizing organic P and dissolving inorganic P (Ca-P) in CA and coupling DOM mineralization and Fe-P dissolution in SA, while sediment in GA owned the significant potential of P and DOM storage and the abundant P-cycling genes. This finding provides further understanding that underlying mechanisms of internal P-cycling in floodplain lake ecosystem.

Impact of physicochemical and microbial drivers on the formation of disinfection by-products in drinking water distribution systems: A multivariate Bayesian network modeling approach

The formation of disinfection byproducts (DBPs) in drinking water distribution systems (DWDS) is significantly affected by numerous factors, including physicochemical water properties, microbial community composition and structure, and the characteristics of organic DBP precursors. However, the codependence of various factors remains unclear, particularly the contribution of microbial-derived organics to DBP formation, which has been inadequately explored. Herein, we present a Bayesian network modeling framework incorporating a Bayesian-based microbial source tracking method and excitation-emission fluorescence spectroscopy-parallel factor analysis to capture the critical drivers influencing DBP formation and explore their interactions. The results showed that the planktonic and suspended particle-associated bacteria in tap water mainly originated from bacteria in the treated water. Protein- and tryptophan-like fluorescence components were identified, illustrating their contribution to DBP formation cannot be ignored. The microbial abundance of Actinobacteria, Bacilli, and Bacteroidia is significantly related to the formation of trihalomethanes, haloacetic acids, and N-nitrosamines. These findings highlight the necessity for prioritizing management policies to control biofilm formation and minimize DBP formation in DWDSs.

Unveiling the role of stratified extracellular polymeric substances in membrane-based microalgae harvesting: Thermodynamic and computational insights

Membrane separation technology has emerged as a highly energy-efficient method for microalgae enrichment and harvesting in wastewater treatment. However, membrane fouling caused by algal cells and stratified extracellular polymeric substances (EPS) remains a critical barrier to its industrial-scale application. This study meticulously investigates the micro process of algae-derived pollutants stacking to the membrane surface affected by stratified EPS. The fouling process resulting from algal cell particle deposition and cake layer formation are clearly simulated using a semi-coupled computational method of Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) for the first time. The results reveal that the hydrophilic component and spatial network structure of soluble EPS (S-EPS) effectively impede the algae-membrane adhesion, and enable the algal cake layer exhibit "dynamic membrane" characteristic to enhance the organic matter retention. In contrast, bound EPS (B-EPS) with higher protein content exhibits a stronger fouling potential and adhesion tendency of algal cells. The influence of stratified EPS on the variation of thermodynamic interaction with contact scale in the sphere-plane/sphere-sphere model is inventively conducted. Based on different algal cell filtration modes, a sequential increase in the eigenvalue n was observed by delaminating EPS layer by layer, indicative of a more severe membrane pore blockage. The semi-coupled CFD-DEM method provides a quantitative analysis of the deposition process, offering spatial resolution and force analysis for algal-derived pollutants. Additionally, we propose a novel calculation method to reverse the deposition process based on the particle stress, providing a valuable reference for simulating membrane-based microalgae harvesting under the influence of stratified EPS.

Implications of the different submerged extent of typical sandbars to local DOM and SDOM during the pre-flood season in the middle reaches of Yangtze River

In large rivers, sandbar evolution is mainly driven by changes in discharge, flow velocity, and sediment concentration in the water, which can shape the implications of local dissolved organic matter (DOM) and sediment dissolved organic matter (SDOM). After the completion of the Three Gorges Dam (TGD), the water level in the middle reaches of the Yangtze River changes rapidly during the year, and the submerged extent of the Yangtze River sandbars are significantly affected by the change in water level, so that when the water level rises to the defense level or higher, the sandbars may be completely submerged. As a result, different submerged extent such as periodically and long-term have occurred on the typical sandbars. However, the extent to which the submersion of typical sandbars affects the source, composition and content of regional DOM/SDOM in large rivers remains unclear. This study was conducted in the middle reaches of the Yangtze River, the characteristics, sources, and influencing factors of DOM were studied using methods such as three-dimensional fluorescence spectrum (EEMS) and parallel factor analysis (PARAFAC) to ascertain the response mechanisms of DOM/SDOM distribution patterns in different submerged extents of the Sanba Sandbar (SBS) and Wugui Sandbar (WGS). The results indicated that the source and component characteristics of DOM/SDOM from different submerged extents in typical sandbars exhibited some differences and similarities. The sediment conditions of the local sandbars, physicochemical parameters of the water, and human activities jointly controlled the DOM/SDOM characteristics of the local sandbars. The DOM of long-term submerged sandbars is generated by mixed endogenous and exogenous inputs; its fractions are more complex, and protein-like proteins are the main components; however, periodically submerged sandbars are dominated by inputs from terrestrial sources, and DOM is relatively more strongly humified, hydrophobic, and aromatic. Sediment dissolved organic matter (SDOM) is an important organic component in sediments, which has an important impact on the ecological environment of the water, the material cycle and the migration of pollutants. The endogenous characteristics of SDOM of sandbars with different submerged extents are evident, mostly in the form of land-source inputs; SDOM is similarly dominated by protein-like humus with a relatively high percentage on periodically submerged sandbars. However, the SDOM component of long-term submerged sandbars is more complex than that of periodically submerged sandbars, and SDOM has more hydrophobic and aromatic properties. This study is the first to analyze the DOM and SDOM of typical sandbars in the middle reaches of the Yangtze River, offering new insights into the characteristics and influencing factors of DOM and SDOM in this region, as well as its distribution in large rivers.

Unveiling the mechanisms of ultrasonic radiation-induced free radical stress on algal communities: Insights into growth inhibition, photosynthetic disruption, and antioxidant defense responses

Algal blooms pose a significant threat to global environmental health, compromising water quality and public safety. Ultrasonic radiation has emerged as a promising, eco-friendly strategy for controlling these blooms, but the underlying mechanisms remain unclearly understood. This study investigated the effects of ultrasonic radiation on the growth, photosynthetic performance, and antioxidant defense systems of an algal mixture over a 5-day period. Analysis techniques, including scanning electron microscopy (SEM), excitation-emission matrix (EEM) analysis, and transcriptomic profiling, were employed to elucidate the multifaceted responses of algal cells to ultrasonic treatment. Ultrasonic radiation induced significant free radical generation, primarily hydroxyl radicals (·OH), which played a critical role in cellular damage. Within 24 h, treatment led to a 50% reduction in algal cell counts, a 30% decline in chlorophyll-a levels, and a 25% decrease in photosynthetic efficiency. Phycocyanin, a vital pigment for cyanobacteria, exhibited heightened sensitivity to a single ultrasonic treatment, while subsequent treatments showed no additional reduction, suggesting that Microcystis aeruginosa is particularly susceptible to the ultrasonic damage. EEM analysis revealed significant changes in the fluorescence intensity of extracellular organic matter (EOM) and intracellular organic matter (IOM) peaks, indicative of oxidative stress and metabolic disruption. Transcriptomic analysis of Microcystis aeruginosa revealed a profound reprogramming of gene expression in response to sonication. Stress response genes, particularly those involved in antioxidant defense, were upregulated, while photosynthesis-related genes were downregulated. Our research indicates that short-term ultrasonic radiation has a long-term stress effect on algal cells, and this might be able to prevent the tendency of cyanobacteria blooms.

Deciphering the inhibitory mechanisms of polystyrene microplastics on thermophilic methanogens from the insights of microbial metabolite profiling and metagenomic analyses

Due to the utilization of food packaging bags, a substantial amount of polystyrene microplastics (PS MPs) are introduced into the food waste (FW) treatment system during the pre-treatment process, potentially impacting the subsequent biochemical treatment system. In order to investigate the mechanism by which PS MPs affect anaerobic methanogenesis metabolism in thermophilic condition, this study analyzed the characteristics of methanogenesis in thermophilic anaerobic digestion (AD) of FW under different concentrations of PS MPs (100 μm, 10-200 mg/L). The results revealed a negative correlation between PS MPs concentration and methane (CH4) yield from FW. When the concentration of PS MPs reached 200 mg/L, CH4 yield decreased by 47.8 %. Further mechanistic investigations revealed that while the presence of PS MPs at lower concentrations could alleviate its adverse impact on methanogenesis by enhancing EPS content, the accumulation of reactive oxygen species (ROS) persisted with increasing PS MPs concentration, thereby inhibiting the activities of key enzymes involved in solubilization and acidification metabolisms (e.g., acetate kinase and F420). Metagenomics analysis indicated that the presence of PS MPs down-regulate abundance of genes for quorum sensing and CH4 metabolism pathways. These findings not only unveil potential detrimental effects of PS MPs on AD systems but also provide novel insights into comprehending and controlling the impact of MPs pollution on environmental preservation and energy recovery processes.

Performance of ultrafiltration-ozonation for municipal wastewater reclamation under rainstorm conditions: Impacts of DOM surge on micropollutant removal and associated risks

This study investigated the impacts of rainstorms on the performance of a combined ultrafiltration (UF)-ozonation (O3) process for micropollutant removal and risk mitigation during municipal wastewater reclamation. Results reveal that the rainstorm triggered a substantial surge in dissolved organic matter (DOM) in secondary effluent, primarily composed of protein-like substances and terrestrial humus. Meanwhile, 12 commonly detected pharmaceuticals and personal care products (PPCPs) were found at concentrations slightly lower than in normal weather, ranging from 5.0 to 545.0 ng L-1. Following the rainstorm, the overall removals of PPCPs spanned a wide range of 14.8 %-77.7 %, where a significantly lower retention of high molecular-weight pollutants (e.g., ≥ 400 Da) was observed for UF. For the ozonation unit, the removals remained comparable, while the relative contribution of radical oxidation increased. This shift was related to the enhanced generation of HO• and/or other reactive species, driven by the enrichment of unsaturated proteins (originating from upstream sludge loss) as precursors. Higher concentrations of disinfection by-products (DBPs), reaching up to 1372.5 μg L-1, were observed in chlorinated effluents after the rainstorm, ascribing to the elevated content of terrestrial humus persisting through the treatments. While the risks associated with PPCPs were negligible, the formed DBPs posed considerable risks to human health (with cancer risk at 10-5) and aquatic ecosystem (with risk quotient up to 13.6), particularly post ozonation. These findings highlight the role of rainstorm-fueled DOM in reclaimed water quality and provide insights into ensuring reclaimed water safety under different weather conditions.

Flow condition mitigates the inhibition of high concentration Cu2+ on the sulfate reduction performance of microbial electrolysis cell

Microbial electrolysis cells (MECs) are promising for treating acidic mine drainage (AMD) containing high concentrations of sulfates and heavy metals. However, the performance of MEC cathodic biofilms is influenced not only by high heavy metals concentrations but also by hydrodynamic mixing conditions. Yet, there is a lack of precise assessment on the impact of hydrodynamic mixing conditions on MEC treating sulfate-laden wastewater under high heavy metal stress, and the defense mechanisms of MECs remain unclear. This study investigated the effects of different hydrodynamic conditions (EG, flow condition; CG, stationary condition) on the performance of MECs treating sulfate wastewater under high heavy metal stress, delving into microbial activity, community composition, electrochemical performance, and microbial defense capabilities against heavy metals. The results indicated that under heavy metal stress, microbial cells underwent severe deformation and death, with the assimilatory sulfate reduction pathway severely impaired, leading to a decline in MEC performance, and the reduction rate of CG group was finally reduced to 14.47%. In contrast, under flow conditions, the EG group exhibited increased extracellular polymeric substances (EPS) composition, enhanced biofilm community diversity, and elevated levels of copper resistance genes, significantly mitigating the inhibitory effects of Cu2+ on microorganisms, ultimately maintaining a performance of 47.18%. Ultimately, Cu2+ in the system was removed through bioprecipitation and biosorption, forming CuS and Cu(OH)2. This work provides critical insights for scaling up MEC technology to address co-contamination challenges in acid mine drainage remediation, particularly for environments with hydrodynamic mixing conditions and elevated heavy metal concentrations.

Insights into a Novel and Efficient Microbial Nest System for Treating Pig Farm Wastewater

A microbial nest system (MNS) represents a novel and efficient approach to treating solid-liquid mixtures from pig farming instead of the conventional method, which separates the solid and liquid at first using centrifugation before treating the solid and liquid. However, the key environmental factors influencing the efficiency of this system and the microbial structure are still not clear. This study aimed to elucidate the changes in an MNS considering physicochemical properties, spectral analysis, and correlations between microbial community structures and environmental factors during the treatment. The results showed that the MNS underwent three temperature stages during the treatment process of piggery slurry: a warming period, a high-temperature period, and a cooling period. In the high-temperature period, the most abundant bacterium was Bacillus, with a relative abundance of 22.16%, and Chaetomium dominated the fungal community with a relative abundance of 11.40%. Moreover, the moisture content, pH value, and electrical conductivity (EC) exhibited an increasing trend, whereas the carbon-to-nitrogen (C/N) ratio and the ratio of ammonia nitrogen to nitrate nitrogen (NH4+-N/NO3--N) showed a decreasing trend. The accumulation of humic acid and fulvic acid suggested that the humification process of organic matter was occurring. The moisture content and C/N ratio were identified as crucial factors influencing the bacterial and fungal community structures, respectively. This study provides a theoretical basis for enhancing the efficiency of piggery slurry treatment using an MNS and rational optimisation of the associated processes.

Tracking Changes in Organic-Copper Speciation during Wastewater Treatment Using LC-ICPMS-ESIMS

Wastewater is a significant source of copper to freshwater environments, which can severely harm aquatic life. The bioavailability and toxicity of copper in water are influenced by its complexation with dissolved organic matter (DOM). Speciation models, like the biotic ligand model (BLM) that guides Cu regulations, assume DOM is dominated by humic substances. Research suggests that anthropogenic compounds in wastewater discharge may be important copper binding ligands, although their identities remain largely unknown. To address this knowledge gap, we identified and quantified organic copper species isolated from 24 h composite wastewater samples by solid phase extraction (SPE) using liquid chromatography (LC) with inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization mass spectrometry (ESIMS). Analyses of samples across different stages of treatment revealed the net removal of Cu (73%) and DOC (66%). LC-ICPMS showed that certain complexes were selectively removed, while others evaded removal or were generated during treatment. Relatively hydrophobic complexes decreased in abundance from the initial to the secondary treatment stage. In contrast, more hydrophilic organic Cu complexes, likely formed during treatment, showed a significant increase from the secondary to the tertiary stage. The molecular mass and formula of seven discrete chromatographically resolved complexes were identified by LC-Orbitrap MS. Six were detected only in wastewater, and one was detected in all the wastewater and river samples. Identification of these compounds provides additional evidence for the formation of new copper-binding ligands during treatment and confirms the presence of nitrogen- and sulfur-containing compounds with copper-chelating properties in the wastewater. These findings demonstrate the utility of LCMS approaches for identifying and quantifying distinct organic-copper species in wastewater, as well as tracking their changes and removal during the treatment process.

Low-molecular weight organic acids can enhance the microbial reduction of iron oxide nanoparticles and pollutants by improving electrons transfer

The combined application of dissimilatory iron-reducing bacteria (DIRB) and Fe(III) nanoparticles has garnered widespread interest in the contaminants transformation and removal. The efficiency of this composite system relies on the extracellular electron transfer (EET) process between DIRB and Fe(III) nanoparticles. While modifications to Fe(III) nanoparticles have demonstrated improvements in EET, enhancing DIRB activity also shows potential for further EET enhancement, meriting further investigation. In this study, we demonstrated that the addition of low-molecular organic acids (LMWOAs) (oxalate, pyruvate, malate, citrate, or fumarate) can improve the reduction of Fe2O3 nanoparticles by Geobacter sulfurreducens PCA through three pathways: increasing intracellular electron production, enhancing the reductive activity of extracellular metabolites, and improving the electron-donating capacity of extracellular polymeric substances. The maximum reduction of Fe2O3 nanoparticles reached up to 72 %. Our results further showed that LMWOAs significantly boosted the removal rate and ratio of Cr(VI) and hexachlorobenzene (HCB) by accelerating the EET process. Following the introduction of LMWOAs, the maximum reduction ratio of Cr(VI) reached 98 ± 0.05 % within 24 h, while the degradation efficiency of HCB reached 92 ± 0.06 % within 9 h. Overall, our study provided a precise mechanism of the role of LMWOAs on the EET process and a new strategy for reductive bioremediation of pollutants.

Effects of different natural organic matter on catalytic properties of green rust: Mechanism and environmental significance

Natural organic matter (NOM) has an important impact on the environmental behaviors of iron minerals, such as green rust (GR), however, NOM with different types and concentrations on these phenomena and mechanisms are still limited. This study explored effects of two common NOM (humic acid (HA) and fulvic acid (FA)) on the physicochemical properties of GR as well as the catalytic degradation of Bisphenol F (BPF). Results indicated that both HA and FA had a critical impact on the mineralization process and catalytic performance of GR, and the impact was concentration-dependent. High concentration of NOM inhibited the GR crystallization, accompanied by changing the surface structure from lamellar to porous, while reducing the degradation efficiency of BPF. Low concentration of NOM modified the morphology of GR into a petal-like shape, which increased surface oxygen vacancies and charge transfer, more importantly, facilitated the reduction of Fe(III) in GR. As a result, the production of reactive oxygen species, such as hydroxyl radicals (•OH), superoxide anions (O2•-), and singlet oxygen (1O2) was increased. O2•- and •OH were identified as the primary ROS for enhancing the degradation of BPF. Humic-like substances and tyrosine of NOM played an important role in promoting the reduction of Fe(III).

Enhancement separation selectivity of mineral ions and perfluorinated and polyfluoroalkyl substances by nanofiltration membrane through hydrogel-assisted interfacial polymerization

The presence of perfluorinated and polyfluoroalkyl substances (PFAS) in drinking water is a critical concern for water safety and public health. Nanofiltration (NF) membranes have emerged promising technology for the elimination of trace organic contaminants from drinking water, but many previous studies have sacrificed the retention of vital mineral ions in human body in pursuit of efficient removal of PFAS. In this study, hydrogel-assisted interfacial polymerization (IP) strategy was designed to enhance the selectivity of mineral ions over PFAS, optimized pore size and surface characteristics of polyamide layers were obtained by IP process assisted by hydrogel formed by chitosan and glutaraldehyde. This approach facilitated the fabrication of NF membranes with a thinner active layer, enlarged pore size, and a more negatively charged surface. The optimized modified membrane exhibited a remarkable improvement in water permeance (16 LMH/bar, over 200 % than the control membrane) and maintained high rejection rates (>90 %) for PFAS with molecular weights ranging from 214 to 514 Da, while significantly reducing the rejection of Ca2+ and Mg2+ ions (<20 %). Density functional theory calculations revealed that all membranes exhibited reduced adsorption energies for PFAS. The treatment of natural surface water indicated the superior rejection selectivity of the modified membrane for mineral ions over natural organic matter, the average gap value of inorganic ions and natural organic matter in modified membranes was 4.6, while the average gap in commercial membranes was 1.6, improved by 2.6 times in selectivity compared to existing commercial membranes. This study offers valuable insights into the targeted enhancement of mineral ions/PFAS selectivity in NF membranes, thereby paving the way of more efficient and sustainable water treatment processes.

Unraveling the roles of algal extracellular and intracellular organic matters in photosensitized degradation of tetracycline: Insights from triplet excited algal organic matters

The rapid growth of algae has significantly increased algae-derived organic matter (AOM) in surface water, and AOM has been shown to play an important role in the photosensitized degradation of emerging contaminants under natural sunlight. This study investigated the photosensitized degradation of tetracycline (TC) by different AOM, i.e. extracellular organic matter (EOM) and intracellular organic matter (IOM) obtained from Anabaena sp. and Scenedesmus quadricauda, with the focus on the role of the triplet excited states of AOM (3AOM*). Results showed that EOM achieved superior photosensitized degradation of TC (up to 73.2 %), which was 1.24-1.44 times higher than that by IOM (up to 57.4 %), mainly due to the higher content of photosensitive groups and cream-like substances in EOM, and the lower content of protein-like substances. It was further revealed that the 3AOM* contributed to 61.76 %-65.59 % of the photosensitized degradation of TC by enhancing demethylation, deamination, and ring-opening reactions, facilitating further conversion of TC to low-molecular-weight compounds while reducing toxic intermediates. This study unravels the essential role of algal EOM- and IOM-derived 3AOM* in photosensitized degradation of TC, offering new perspectives on antibiotic degradation in high-algal water environments.

Changes in the spectroscopic response of soil organic matters by PBAT microplastics regulated the Cd adsorption behaviors in different soils

Contamination of microplastics (MPs) and heavy metals occurs frequently in terrestrial ecosystems, but their interactions remain unclear. A 60-day incubation experiment was conducted to study the behaviors of cadmium (Cd) in polybutylene adipate terephthalate (PBAT) MPs-contaminated soils, with different doses (1, 10%) and sizes (150-300 and 75-150 μm). Soil chemical properties, including the three-dimensional fluorescence of dissolved organic matter (DOM) and microbial diversity in both farmland and woodland soils were analyzed. Results showed that soil properties, especially the components and fluorescence characteristics of DOM varied with soil types and PBAT properties. Higher soil chemical properties and microbial diversity were found in woodland soils. The soluble microbial by-product substances and humic acid-like substance were dominated in soil DOM, while the proportions of fulvic/humic-acid like substances and soil humification decreased with the addition of 10% PBAT. Soil microbial diversity increased with doses of PBAT, but not sensitive to the sizes of PBAT. The adsorption capacity of Cd decreased with the addition of PBAT, especially in the 10% and 75-150 μm PBAT treatments. Both Langmuir and Freundlich models fitted well with the adsorption isotherms of Cd. Multiple correlation analyses showed that low molecular weight fractions, humus index of DOM and soil microbial diversity such as Shannon, Simpson, and Pielou all positively correlated with the adsorption behaviors of Cd in PBAT-contaminated soils. Biodegradable MPs can change soil quality and promote the release of soil Cd, which deserves further research attention.

The role of Lysinibacillus fusiformis S01 in cadmium removal from water and immobilization in soil

Cadmium pollution is widespread in water and soil worldwide. Microbial remediation is an effective method for removing heavy metals. This study explored the cadmium remediation mechanism and efficiency of Lysinibacillus fusiformis S01. The removal process includes extracellular adsorption, intracellular accumulation, biomineralization, extracellular polymer sequestration, and binding to cell surface functional groups. In an aqueous solution with a 20 % v/v bacterial dosage, 71.22 % of 10 mg/L Cd2 + was removed within 7 days, with a dissolution rate below 3 % after 15 days. A sequencing batch reactor (V=1 L) was done with an initial concentration of 5 mg/L Cd2+ and only 200 mL of bacterial solution, over 2-day cycles, achieving an 80 % removal rate with a stable pH of around 8.30. In artificially contaminated soil experiments, 76.96 % of exchangeable cadmium was passivated in low concentration soil (3.504 mg/kg), while the passivation rate was 66.43 % in high concentration soil (9.324 mg/kg) after 7 days, with 5 mL of bacterial solution added to every 30 g of soil at 30°C. In actual contaminated soil (8.190 mg/kg), it was reduced from 22.75 % to about 14 % after 28 days. The high-throughput sequencing of the soil experiments revealed that L. fusiformis S01 became the dominant strain (from 0.01 % to 5.10 %), increasing diversity (Shannon index from 2.94 to 3.41 and Simpson index from 0.15 to 0.08) and reducing harmful organisms. The study demonstrates the potential of L. fusiformis S01 for cadmium pollution remediation.

Synergistic effects of ozonation pretreatment and trace phosphate on water quality health risk and microbial stability in simulated drinking water distribution systems

The proliferation and chlorine resistance of pathogenic bacteria in drinking water distribution systems (DWDSs) pose a serious threat to human health. In this study, the synergistic effects of ozonation pretreatment and trace phosphate on water quality health risk and microbial stability were investigated in the small-scale DWDSs simulated by biofilms annular reactors with cast iron coupons. The results indicated that ozonation of drinking water containing trace phosphate was equivalent to increasing microbial carbon and phosphorus sources, further leading to the rapid proliferation of opportunistic pathogens (OPs) in subsequent DWDSs. Under the influent condition of ozonation pretreatment and 0.6 mg/L phosphate, the gene copy numbers of living Legionella spp., Mycobacterium spp., and Acanthamoeba spp. reached up to 1.50 × 104, 1.21 × 104, and 2.29 × 104 gene copies/mL, respectively. The extracellular polymeric substances from suspended biofilms in DWDSs exhibited higher content, molecular weight, and flocculating efficiency, contributing to the improvement of microbial chlorine resistance. Meanwhile, more Fe3O4 appeared in the corrosion products, which enhanced the extracellular electron transfer via cytochrome c and weakened the electrostatic repulsion between corrosion products and microbes in DWDSs. Finally, more active OP growth and microbial metabolic activity occurred in DWDSs. This study revealed that ozonation pretreatment and trace phosphate, as a green technology and an inconspicuous nutrient, respectively, can trigger significant microbial health risks in subsequent DWDSs. Therefore, the phosphate in drinking water should be more strictly restricted when ozonation technology is used in waterworks, especially without a biofiltration treatment process.

Characteristics concerning the evolution of dissolved organic matter and dynamics of bacterial community during continuous thermophilic composting of oxytetracycline fermentation residue

Continuous thermophilic composting (CTC) is a potential technique to recycle oxytetracycline fermentation residue (OFR) with the extremely high level of antibiotics but is still not explored. To investigate the efficiency of CTC on treating OFR, the differences between this technique and conventional composting in the evolution of dissolved organic matter and dynamics of bacterial community were compared. The higher degradation efficiency of oxytetracycline (OTC) was obtained in CTC than conventional composting. The transformation of organic matter occurred faster and the maturity degree of compost product was higher in CTC than conventional composting. Compared with conventional composting, CTC increased the bacterial diversity and screened some functional microorganisms related to OTC degradation and organic matter transformation. The results indicate that CTC is a precise strategy for efficiently recycling OFR as soil amendment.

Unraveling stress responses of microalgal-bacterial granular sludge when treating ciprofloxacin-laden wastewater

Unraveling the potential of microalgal-bacterial granular sludge (MBGS) technology for sustainable treatment of ciprofloxacin (CIP)-laden wastewater and mitigation of antibiotic resistance genes (ARGs) remains limited. This study evaluated the performance of bacterial granular sludge (BGS) and MBGS systems in terms of nutrient and CIP removal, granular stability, and ARG attenuation under long-term exposure to CIP for the first time. While both systems achieved effective pollutant removal at low CIP concentrations (0.1 and 0.5 mg/L), MBGS demonstrated superior resilience and efficiency under high CIP loads (10 mg/L). Notably, MBGS improved phosphorus removal by 32.71 %, achieved a 70.42 μg/(g-SS)/d greater CIP removal and maintained structural integrity, unlike BGS, which disintegrated under oxidative stress. The microalgae species (Pseudoneochloris and Chlamydopodium) could effectively resist various concentrations of CIP. Additionally, the relative abundance of ARGs in MBGS was 30.91 % lower than that in BGS, suggesting that microalgae in MBGS system could reduce ARG production. Overall, these findings improve our understanding of the role of microalgae in enhancing CIP remediation and controlling ARG propagation in MBGS systems.

Valorization of food waste to biofertilizer and carbon source for denitrification with assistance of plant ash and biochar toward zero solid discharge

This study developed a novel strategy for food waste (FW) valorization through incorporating plant ash and biochar into enzymatic hydrolysis of FW. After 12-h hydrolysis of FW with fungal mash, the solid and soluble products were separated and harvested as solid biofertilizer and carbon source for denitrification respectively. Soluble COD produced from plant ash and biochar mediated FW hydrolysis could reach approximately 170 g/L on average, which showed a specific denitrification rate of 26.23-31.33 mg N/g MLVSS/h higher than that with commercial glucose (i.e. 25.92 mg N/g MLVSS/h). The applicability of solid biofertilizers produced from plant ash- or biochar-assisted hydrolysis of FW was evidenced by the higher germination rate of 138-166 % against that without exogeneous additives (122 %). It is expected that the proposed approach can offer an effective solution for upgrading FW into value-added products, while realizing a complete resource recycle with no wastes discharged.

Long-term effects of food waste on erosion resistance and production of methane and sulfide in sewer sediments: New insights into extracellular polymeric substances and genetic response mechanisms

Discharge of food waste (FW) into sewer systems causes environmental issues, such as sewer blockage and odour problems. This study investigated the long-term effects of FW addition on sediment properties, microbial communities, and metabolic pathways using laboratory-scale reactors for 160-day incubation. The addition of 2 g/L FW increased the critical erosion shear stress of sediments by 40.63% and reduced their self-cleaning capacity by 39.46%. This was attributed to the fact that FW discharge increased extracellular polymeric substances (EPS) in sediments by 82.94%, especially aromatic protein with high hydrophobicity and high content of intermolecular hydrogen bonds, which was supported by the increased genes encoding aminoacyl-tRNA biosynthesis. The denser biofilm on the sediment surface hindered oxygen transfer to deeper sediment zones, and lowered oxidation-reduction potential below -400 mV. Microbial and metagenomic analysis revealed an enrichment of methanogenic archaea (e.g., Methanothrix) and sulfate-reducing bacteria (e.g., Desulforhabdus), along with increased genes for dissimilatory sulfate reduction and methanogenesis pathways of acetate and CO2/H2. These microbial and metabolic shifts led to a 95.49% and 34.99% increase methane and sulfide production in the FW-2 group. Overall, the negative effects of FW discharge into sewers emphasizes the need for more rational policies to manage this issue.

Exploring the co-occurrence of microplastics, DOM and DBPs inside PVC pipes undergoing chlorination by correlation analysis and unsupervised learning

Drinking water distribution systems face a multifaceted emerging concern, including in situ microplastic (MP) generation, chemical leaching from plastic pipes, and the formation of disinfection by-products (DBPs). This study investigated the co-release of MPs and chemical leachates from polyvinyl chloride (PVC) pipes exposed to different chlorine concentrations on a lab scale, as well as the subsequent formation of DBP. Results highlighted significant evidence of PVC-derived dissolved organic matter (PVC-DOM) and microplastic (PVC-MP) leaching at higher chlorine concentrations. However, at chlorine residuals of 1 ppm, natural organic matter (NOM) retained its importance, with minimal release of PVC-DOM and PVC-MP from plastic pipes. Correlation analysis highlights the critical role of DOM, including both NOM and PVC-DOM, as a key intermediary between MPs and DBPs. This is evidenced by the strongest observed correlations within the DOM group and its significant associations with both MPs and DBPs. Conversely, the limited direct connections between MPs and DBPs further underscore the importance of DOM as the key link between these two targets. Using unsupervised learning techniques, including clustering and dimensionality reduction, further elucidated the influence of DOM in controlling the data patterns, enabling robust interpretation of complex datasets, and providing valuable insights. This study contributes to advancing understanding of the co-occurrence and behaviors of MP, DOM, and DBP within drinking water distribution systems, as well as propelling the associated risk in this intricate scenario.

Enhanced leachate concentrate degradation across variable pH ranges using Cu@ATP-CTS Fenton-like catalysts for H₂O₂ activation

Landfill leachate nanofiltration concentrates (LLNC) contain complex organic pollutants that are difficult to treat. This study developed a copper-doped attapulgite-chitosan composite catalyst (Cu@ATP-CTS) for efficient LLNC degradation in a Fenton-like system. The incorporation of attapulgite extended the effective pH range of Fenton reactions from 2 to 8, overcoming traditional limitations. Optimized via response surface methodology, the catalyst achieved 89.02% UV254 removal, 73.86% COD removal, and 77.24% TOC removal within 115 min under optimal conditions. Copper played a crucial role in H₂O₂ activation, cycling between Cu0, Cu+, and Cu2+ to generate hydroxyl radicals (·OH), the key species driving pollutant degradation. The Cu@ATP-CTS catalyst also demonstrated strong stability and reusability over five cycles. This study provides a robust and sustainable method for LLNC treatment, offering significant potential for application in landfill leachate and wastewater management.

Performance of four thermophilic bacteria for primary sludge hydrolysis: Sludge disintegration and hydrolase activities

Thermophilic bacteria (TB) pretreatment is an efficient and environmentally friendly way for accelerating sludge hydrolysis. In this study, a complete comparison of the hydrolysis performance of Bacillus sp. AT07-1 (X1), Parageobacillus toebii X2 (X2), Geobacillus kaustophilus X3 (X3) and Parageobacillus toebii R-35642 (X4) was performed. Results indicated that pretreatment with four strains promoted the release of organic matter in extracellular polymeric substance and the disintegration of sludge structure, causing the increase of soluble substances. The total percent fluorescence response of tyrosine-like and soluble microbial by-products in dissolved organic matter increased to 64.8% after pretreatment with strain X4. Moreover, pretreatment with strain X4 resulted in the highest relative activities of α-glucosidase (1.4) and protease (2.0). Engineering implication and economic analysis verified that TB pretreatment has the potential for economic benefits and industrial applications. This study demonstrated that strain X4 exhibited the highest hydrolysis efficiency, providing a new strategy for accelerating primary sludge hydrolysis.

Chemical activation of cotton fibers with varied regents induces distinct morphology of activated carbon and adsorption capacity of methylene blue

Some biomasses like cotton contain natural fibrous structures. This is a desirable structural feature for exposure of adsorption sites on cotton-derived activated carbon (AC). This was verified herein by conducting activation of cotton with ZnCl2, H3PO4, K2C2O4, or KOH, probing whether structural transformation during activation could be confined inside a cotton fiber. The results indicated that ZnCl2 showed the highest capability for generating pores (1432.8 m2·g-1), especially mesopores (> 50 %). This resulted from its highest activity for catalyzing the aromatization reactions associated with deoxygenation during the activation (C/O of 13.1 versus C/O of ca. 3.6 for counterparts). The intensive cracking from the potassium activators interfered with aromatization, retaining more oxygen but diminished pore development (ca. 1000 m2·g-1), especially mesopores (< 7 %). Furthermore, ZnCl2 catalyzed condensation of intermediates bearing CO and C-O-C, but KOH or K2C2O4 could not. ZnCl2 activation retained the fibrous structure of resulting activated carbon but induced the merge of fiber with the help of the formed reactive carbon cation, while H3PO4 led to the full deformation of fibers. Reactive "fiber intermediates" could also form in activation with KOH but not with K2C2O4, as K2C2O4 only catalyzed the transformation of inner structures. This work supports cotton pretreatment and chemical activation as a promising technique for creating porous AC with high adsorption capacity.

Enhanced pharmaceutical removal from building wastewater by the novel integrated system of anaerobic baffled biofilm-membrane bioreactor and UV/O3: Microbial community, occurrence of bio-intermediates and post-treatment

This research aimed to develop the novel integrated system of anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) (with and without microaeration) and UV/O3 for removal of target pharmaceuticals (ciprofloxacin (CIP), caffeine (CAF), sulfamethoxazole (SMX) and diclofenac (DCF)) from building wastewater. The investigation was performed to elucidate how microaeration affected the removal performances, degradation kinetics and pathways of bio-intermediates of the AnBB-MBR. Two AnBB-MBR reactors - R1: AnBB-MBR (without microaeration) and R2: AnBB-MBR with microaeration at 0.93 LO2/LFeed - were operated at the same hydraulic retention time (HRT) of 30 h. The UV/O3 was selected as the post-treatment system. While UV alone slightly removed CIP without the removal of other compounds. After 150 min of the UV/O3, the R1 with UV/O3 achieved 97.31-100% removal efficiency of targeted pharmaceuticals and increased to 99.47-100% with the R2 integrated with UV/O3. The obtained pseudo-first order kinetic rate constants of the UV/O3 in treating the permeate of R1 were 0.0235, 0.004, 0.0423 and 0.097 min-1 for CIP, CAF, SMX and DCF, respectively. Whereas the obtained pseudo-first order kinetic rate constants of the UV/O3 in treating the permeate of R2 were 0.021, 0.0338, 0.0511 and 0.0527 min-1 for CIP, CAF, SMX and DCF, respectively. For the major microorganisms involved in targeted pharmaceutical removal in the R2 under microaerobic conditions included ammonia oxidizing bacteria (AOB) and methanotrophs, while Bacillus, Longilinea, Clostridium and Lactivibrio were possibly responsible for pharmaceutical removal in the R1 under anaerobic conditions. The differences of bio-intermediates between anaerobic and microaerobic conditions were exclusively identified. In addition, the integration of AnBB-MBR with microaeration and UV/O3 was more effective in removing a wide variety of bio-intermediates than the case of the integrated system without microaeration. Therefore, the integrated system of AnBB-MBR with microaeration and UV/O3 can be a promising technology for pharmaceutical removal from building wastewater.

Deciphering the key role of biofilm and mechanisms in high-strength nitrogen removal within the anammox coupled partial S0-driven autotrophic denitrification system

Anammox coupled partial S0-driven autotrophic denitrification (PS0AD) technology represents an innovative approach for removing nitrogen from wastewater. The research highlighted the crucial role of biofilm on sulfur particles in the nitrogen removal process. Further analysis revealed that sulfur-oxidizing bacteria (SOB) are primarily distributed in the inner layer of the biofilm, while anammox bacteria (AnAOB) are relatively evenly distributed in inner and outer layers, with Thiobacillus and Candidatus Brocadia being the dominant species, respectively. Except for anammox and PS0AD processes, 15N isotope labeling tests determined that sulfur reshaped nitrogen metabolism pathways, providing solid evidence for the occurrence of sulfammox process. SOB and AnAOB collaborate in nitrogen and sulfur conversion, with SOB-drived PS0AD processes reducing nitrate to nitrite for AnAOB to remove ammonia. Conversely, the nitrate produced from anammox process can be reused by SOB. Metagenomic analyses verified that SOB drove the PS0AD process through encoding soxBYZ gene, while AnAOB might play an important role in simultaneously driving the anammox and sulfammox processes. These findings underscore the importance of biofilm and clarify the nitrogen-sulfur cycle mechanisms within the coupled system.

Toxicity assessment of wastewater using a battery of bioassays in two textile wastewater treatment plants from a large industrial park in Guangxi, Southwest China

Textile effluents are important sources of pollutants in aquatic environments. The textile industry in China has been relocating from developed to less developed regions, yet the potential environmental impact of textile effluents remains unclear. Here, we investigated the acute toxicity of wastewater collected from different processing units of two textile wastewater treatment plants (WWTPs) in a large industrial park in Guangxi province (Southwest China), using whole effluent toxicity testing. Moreover, we explored the relationships between the toxicity of wastewater and its characteristics, including physicochemical parameters, heavy metals, fluorescence intensity, and non-persistent and persistent organic pollutants. Untreated textile effluents were highly toxic to all test organisms, with toxic units reaching 42.9 for lux-modified bacteria, 14.0 for green algae, 10.1 for duckweed, and 17.3 for zebrafish embryos. Their toxicity was reduced significantly but not removed completely, following treatment processes that included coagulation, anaerobic-aerobic process, Fenton oxidation process, chlorine disinfection and wetland treatment systems. In the wetland effluent, both toxicity and physicochemical parameters met the textile effluent discharge standards in China and other countries. The toxicity of wastewater was associated with various characteristics, such as chemical oxygen demand (COD), fluorescence intensity related to fulvic acid-like materials, 4-nonylphenol, bisphenol A, bis(2-ethylhexyl) phthalate, perfluorobutane sulfonic acid, and acenaphthene. These results suggest the effectiveness of the investigated WWTPs in treating textile effluents concerning both physicochemical parameters and acute toxicity. The present study highlights the importance of integrating ecotoxicological data alongside chemical data to enhance the risk assessment and evaluation of the environmental safety of effluent discharges.

Characteristics of airborne particles emitted from typical indoor combustion sources

Combustion is an important source of indoor emissions, and exposure to combustion emissions not only concerns the quality of life of individuals but also directly affects the overall health level of society. To date, very few studies have examined the size-resolved emission characteristics of airborne particulate matter (PM) emitted from indoor sources. The study examined PM emissions from the specified combustion sources. PM concentrations and emission factors for metals and polycyclic aromatic hydrocarbons (PAHs) were analyzed under identical burning durations. Particle size distributions were determined, and dissolved organic matter (DOM) components were characterized using fluorescence spectroscopy. Health risk assessments were conducted to identify major carcinogenic risks among the emitted components. The results revealed distinct trends in PM concentrations and emission factors among the combustion sources, with cigarettes exhibiting the highest levels followed by mosquito coils and candles. The peak diameters of PM number concentration were found to be 68.5 nm for mosquito coils, 105.5 nm for cigarettes, and 201.7 nm for candles. Fine fraction (PM0.056-3.2) had significantly higher emission factors than coarse fraction (PM3.2-18), with the highest emission factor observed within the particle range of 0.18-0.32 μm. DOM from burning mosquito coils and cigarettes comprised two primary components: a protein-like (C1) and a humus-like (C2) fluorescent component. Health risk assessments indicated that chromium and benzo[a]pyrene posed the greatest carcinogenic risks among metals and PAHs in typical indoor combustion environments. Our results were primarily helpful to determine the characteristics of the PM from combustion emissions and also significant to ensure public health protection, especially for people who usually spend time indoors.

Metabolomic interpretation of bacterial and fungal contribution to per- and polyfluoroalkyl substances interface migration in waterlogged paddy fields

Per- and polyfluoroalkyl substances (PFAS) are widely distributed in paddy soils, and their multi-phase partitioning in soil fractions was proved to be strongly interact with soil microbial community composition and functions. Despite this, soil bacterial and fungal metabolic molecular effects on PFAS water-soil interface migration in waterlogged paddy fields still remain unclear. This study integrated soil untargeted metabolomics with microbial amplicon sequencing to elucidate soil metabolic modulations of 15 PFAS interface release. Inhibition of bacterial and fungal metabolic activity both significantly altered PFAS cross-media translocation (p < 0.05). Gemmatimonadota, Desulfobacterota, Acidobacteriota, Actinobacteriota, and Bacteroidota were vital bacterial taxa affecting PFAS transport, while Basidiobolomycota and Chytridiomycota were vital fungal taxa. Fungi regulated PFAS migration more (R2 = 0.379-0.526) than bacteria (R2 = 0.021-0.030) due to the higher metabolic stability of stochastic-dominated fungi than deterministic-dominated bacteria. At the water-soil interface, the amino acid-like dissolved organic matter (Tyrosine and Tryptophan) contributed most (48.5-58.6 %) to the PFAS multiphase distribution. Untargeted metabolomics further clarified that fungal amino acid-like metabolites, including Phosphoenolpyruvate and Methionine, were key triggers stimulating Tyrosine and Tryptophan biosynthesis (p < 0.001), which were vital in modulating PFAS interface translocation (p < 0.001). These results provide novel insights into soil microbial metabolites' participation in PFAS water-soil interface migration, benefiting PFAS pollution control and agricultural security risk assessment in waterlogged paddy ecosystems.

Trace organic compounds and photosensitizing activity in Salvadoran surface and tap water sources: A first look

Despite their potential risks to human health and the environment at ng/L to μg/L concentrations, there has been relatively little effort to measure trace organic compounds (TOrCs) in surface waters of Central America. The concentrations of eighteen TOrCs detected at eleven surface water sites in the Lempa River basin of El Salvador and four sources of drinking water for the cities of San Salvador, Antiguo Cuscatlán, Soyapango, and Santa Tecla are reported here. All samples were analyzed via liquid chromatography with tandem mass spectrometry (LC-MS/MS). Detected TOrCs in surface water included sixteen compounds. Maximum concentrations of 23 μg/L, 6 μg/L, and 2 μg/L were measured for sulfamethoxazole, sucralose, and bisphenol A, respectively. In tap water, a total of fourteen species were found, with peak concentrations of 17 μg/L for sulfamethoxazole, 640 ng/L for bisphenol A, and 224 ng/L for tris(chloropropyl) phosphate (TCPP). To assess potential mechanisms of TOrCs attenuation in surface waters, samples were irradiated with UVA light (315-400 nm) for 12 h in the presence of furfuryl alcohol (FFA) to establish singlet oxygen (1O2) formation. All the samples exhibited photosensitizing activity upon irradiation, resulting in 1O2 concentrations of the order of 10-14 M. To our knowledge, this is the first study that reports the quantification of TOrCs presence and the possible natural attenuation routes in Salvadoran surface and tap water sources.

Iron(II/III) Alters the Relative Roles of the Microbial Byproduct and Humic Acid during Chromium(VI) Reduction and Fixation by Soil-Dissolved Organic Matter

Though reduction of hexavalent chromium (Cr(VI)) to Cr(III) by dissolved organic matter (DOM) is critical for the remediation of polluted soils, the effects of DOM chemodiversity and underlying mechanisms are not fully elucidated yet. Here, Cr(VI) reduction and immobilization mediated by microbial byproduct (MBP)- and humic acid (HA)-like components in (hot) water-soluble organic matter (WSOM), (H)WSOM, from four soil samples in tropical and subtropical regions of China were investigated. It demonstrates that Cr(VI) reduction capacity decreases in the order WSOM > HWSOM and MBP-enriched DOM > HA-enriched DOM due to the higher contents of low molecular weight saturated compounds and CHO molecules in the former. The presence of Fe(II/III) selectively coprecipitates with high molecular weight components (e.g., tannins, lignin, and CHON-rich compounds) to form ferrihydrite and greatly inhibits Cr(VI) transformation and fixation in MBP-enriched DOM but enhances that in HA-enriched DOM. This is probably owing to the combined effects of (1) the increase of DOM electron-donating capacity and Fe(II) generation during the reactions of HA with Fe(II) and Fe(III), respectively; (2) the enrichment of phenolic and carboxyl groups, aromatic compounds, and carbon defects on ferrihydrite surfaces; and (3) the acceleration of HA decomposition and MBP mineralization by hydroxyl radicals. These findings enhance our understanding of the chemodiversity of soil DOM, the complex interactions between Cr(VI), DOM, and Fe(II/III), and can help design remediation strategies for contaminated environments.

Screening of Bacteria Promoting Carbon Fixation in Chlorella vulgaris Under High Concentration CO2 Stress

The cooperation between microalgae and bacteria can enhance the carbon fixation efficiency of microalgae. In this study, a microalgae-bacteria coexistence system under high-concentration CO2 stress was constructed, and the bacterial community structure of the entire system was analyzed using the 16S rDNA technique. Microbacterium sp., Bacillus sp., and Aeromonas sp. were screened and demonstrated to promote carbon fixation in Chlorella vulgaris HL 01 (C. vulgaris HL 01). Among them, the Aeromonas sp. + C. vulgaris HL 01 experimental group exhibited the most significant effect, with an increase of about 24% in the final biomass yield and a daily carbon fixation efficiency increase of about 245% (day 7) compared to the control group. Continuous cultivation of microalgae and bacterial symbiosis showed that bacteria could utilize the compounds secreted by microalgae for growth and could produce nutrients to maintain the vitality of microalgae. Detection of extracellular organic compounds of microorganisms in the culture broth by excitation-emission matrix spectral analysis revealed that bacteria utilized the aromatic proteinaceous compounds and others secreted by C. vulgaris HL 01 and produced new extracellular organic compounds required by C. vulgaris HL 01. The metabolic organic substances in the liquids of the experimental groups and the control group were analyzed by liquid chromatography-mass spectrometry, and it was found that 31 unique organic substances of C. vulgaris HL 01 were utilized by bacteria, and 136 new organic substances were produced. These differential compounds were mainly organic acids and their derivatives, benzene compounds, and organic heterocyclic compounds, etc. These results fully demonstrate that the carbon fixation ability and persistence of C. vulgaris HL 01 are improved through material exchange between microalgae and bacteria. This study establishes a method to screen carbon-fixing symbiotic bacteria and verifies that microalgae and bacteria can significantly improve the carbon fixation efficiency of microalgae for high-concentration CO2 through material exchange, providing a foundation for further research of microalgae-bacterial carbon fixation.

Insight into the evolution of phosphorous conversion, microbial community and functional gene expression during anaerobic co-digestion of food waste and excess sludge with spicy substances exposure

Garlic and chili are widely used as food flavoring agents in food cooking, therefore might be accumulated in large amounts in food waste (FW). The effects of garlic and chili on the dissolution, hydrolysis, acidification and methanation in an anaerobic co-digestion system were investigated during the combined co-digestion of FW and excess sludge (ES). Additionally, the transformation of phosphorus form and microbial metabolism changes during the process were analyzed. The results showed the addition of garlic and chili promoted the release of protein in the soluble chemical oxygen demand. Secondly, the addition of garlic and chili up-regulated the relative abundances of key coding genes pstS, pstA, pstB and pstC. The relative abundances of the pstS and pstC genes increased by 0.0113% and 0.0021%, respectively, when 10 g garlic was added compared with no garlic. Furthermore, with respect to phosphorus conversion, the addition of garlic inhibited the conversion of solid phosphorus to gaseous phosphorus, whereas the addition of chili had the opposite effect. Meanwhile, garlic and chili inhibited the expression of key coding genes in phosphofructokinase. This work provides new insights into the phosphorus conversion and microbial metabolism in the process of anaerobic co-digestion of FW and ES under the influence of spicy substances.

The role of sulfidated zero-valent iron in enhancing anaerobic digestion of waste activated sludge

Zero-valent iron (ZVI) has been confirmed in enhancing methane production by improving interspecies electron transfer during anaerobic digestion (AD) of waste activated sludge (WAS). In this study, we suppose that sulfidated zero-valent iron (S-ZVI), a semiconductor material, has better property of electron transfer in AD process. Based on two-phase anaerobic digestion process, nitrite and S-ZVI were used separately for improving acidogenic phase and methanogenic phase of anaerobic sludge digestion. Based on XRD and XPS, Fe(Ⅱ)-O and Fe(Ⅲ)-O were substituted by Fe(Ⅱ)-S and Fe(Ⅲ)-S after ZVI sulfidation, which increased the electric conductivity of S-ZVI. Nyquist plot and Tafel corrosion curve showed that the sulfidation treatment can reduce impedance of electronic transmission. The results showed that the addition of S-ZVI increased methane production by 24.22% compared with ZVI alone. The addition of S-ZVI increased the relative abundance of Actinobacteria in R3(Raw + S-ZVI) and R6(NO2- + S-ZVI), enhancing the activity of microbial in anaerobic sludge digestion. The relative abundance of Acidobacteriota, Synergistota, WPS-2, Firmicutes, Caldisericota, and Gampylobactenota have changed markedly, and facilitated the activity of acidogenic microbes to produce more biodegradable organic matter, further boosting methane production. The findings of in-situ formation of S-ZVI in R5 anaerobic digestion saves the economic cost of S-ZVI preparation, which will be helpful for the extensive application of this technology.

Urea promotes alkaline anaerobic fermentation of waste activated sludge for hydrogen production

Hydrogen production from waste activated sludge (WAS) represents a promising pathway for sustainable energy generation. This study explores the impact of urea on enhancing hydrogen production during alkaline fermentation of WAS, with the aim of reducing alkali use. Experimental results revealed that treating WAS with 90 mg/g VSS urea at a constant pH of 9.5, followed by anaerobic fermentation for 10 days, yielded 24.57 mL/g VSS of hydrogen, which is 1.42 times higher than the fermentation at constant pH 9.5 without urea. Additionally, urea exposure reduced NaOH consumption by 40.74 % and 15.79 % at constant pH 10 and 9.5, respectively, achieving a cost-effective hydrogen production at 9.16 USD/m3 H2. The observed reduction in NaOH consumption is attributed to free ammonia from urea decomposition, which acts as an NH3/NH4+ buffer. Mechanistic analysis suggests that urea disrupts hydrogen bonds within proteins, enriching hydrogen-producing microbes while inhibiting hydrogen-consuming ones, thereby promoting hydrogen production.

High-Spin States of Manganese(III) Enable Robust Cold-Adapted Activity of MnO2 Nanozymes

Developing novel cold-adapted nanozymes and elucidating their mechanisms of action remains a great challenge. Inspired by natural oxidases that utilize high-spin and high-valent metal-oxygen intermediates to achieve high efficiency at low temperatures, in this study, a series of MnOx nanomaterials with varied valence and spin states are synthesized. The activity assay revealed that the oxygen vacancy-engineered ε-MnO2 nanozyme displayed excellent cold-adapted oxidase-like properties, and no observable activity loss is observed in the temperature range of -20 to 45 °C. The superior performance is attributed to the high-spin Mn(III)-O species coupled with its induced Jahn-Teller effect, which facilitates the dissociation and activation of oxygen at low temperatures. As a proof of concept, an excellent cold-adapted δ-MnO2 nanozyme can be obtained using Mn3O4 as the precursor by regulating the spin state of Mn(III). Moreover, a novel and effective degradation strategy for corn stalk at low temperature is built based on the robust cold-adapted oxidase-like activity of ε-MnO2. These results not only provide new insights for the rational design of cold-adapted nanozymes but also broaden the application of nanozymes in low-temperature industrial processes.

Re-granulation and performance of anaerobically digested bacterial and algal-bacterial aerobic granular sludge

Effective treatment and sustainable waste sludge management are critical challenges for future biorefinery wastewater treatment plants (WWTPs). This study investigated the feasibility of re-granulating anaerobically digested bacterial and algal-bacterial aerobic granular sludge (AGS) for sustaining the continuous operation of the AGS-based WWTPs due to the requirement of long-term operation for granulation of flocculent activated sludge. Rapid re-granulation was achieved within 12 and 6 days respectively from digested bacterial AGS and algal-bacterial AGS, demonstrating their high stability and settleability even after anaerobic digestion (AD). The re-granulated bacterial AGS system exhibited >90% dissolved organic carbon (DOC) removal, probably attributed to its greater microbial diversity and richness and elevated extracellular polymeric substances (EPS) secretion. The re-granulated algal-bacterial AGS system featured enhanced functional adaptability. It showed a lower average effluent dissolved total carbon concentration (∼100 mg/L) and high total inorganic nitrogen removal (>89%) in addition to > 56% maximum total phosphorus removal. Morphological observations revealed that some granules retained their compact structure and cores after AD, providing a niche for their re-granulation. Aromatic proteins and fulvic acid-like organics were the critical promoters for AGS regranulation. Notable shifts in microbial community structure, particularly the increase in abundance of photosynthetic bacteria such as Erythromicrobium, Leptolyngbya, and Rhodobacter, played an essential role in enhancing the overall performance of the re-granulated algal-bacterial AGS. By validating the system's effectiveness and exploring the factors governing re-granulation, this study proposes a viable strategy for advancing the sustainability of AGS-based WWTPs and promoting circular bioeconomy practices.

Hydrothermal pretreatment of food waste enhances performance of anaerobic co-digestion with sludge

Food waste (FW) presents a significant opportunity for renewable energy production through anaerobic digestion (AD) when subjected to appropriate treatment. This study investigates the impact of thermal hydrolysis pretreatment (THP) on FW at varying temperature levels (90 °C, 120 °C, and 140 °C) prior to mesophilic anaerobic co-digestion with sewage sludge (SS). Results demonstrate enhanced FW hydrolysis at 120 °C, leading to a cumulative methane yield of 324.39 ± 4.5 mL/gVSadd, representing a 41.75% increase over untreated FW (228.83 ± 1.13 mL/gVSadd). Shifts in microbial communities, particularly Methanosarcina, Methanobactrium, and Methanobrevibacter, support efficient methanogenesis. Co-digestion of FW pretreated at 120 °C yields maximum energy production of 11.48 MJ/t, a 49.47% improvement compared to untreated processes. The economic analysis underscores the profitability of co-digestion with FW pretreated at 120 °C. These findings highlight the potential for enhanced methane production and energy conversion efficiency with hydrothermally pretreated FW and SS co-digestion.

Catalytic ozone oxidation of chemical RO membrane concentrate wastewater by a Cu-Ce@γ-Al2O3 ozone catalyst

A Cu-Ce@γ-Al₂O₃ catalyst was developed for the efficient treatment of chemical reverse osmosis (RO) membrane concentrate wastewater. The working conditions and reaction mechanisms of Cu-Ce@γ-Al₂O₃ catalytic ozonation were systematically investigated, and its application in the catalytic ozonation of chemical RO membrane concentrate wastewater was explored. The catalyst was comprehensively characterized using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), and Fourier-transform infrared (FTIR) spectroscopy, revealing its microstructure, elemental composition, and crystal structure. The optimal reaction conditions were identified as follows: ozone dosage of 8 mg/L/min, initial pH of 9.0, catalyst filling ratio of 10%, and a reactor height-to-diameter ratio of 5:1. Under these conditions, the catalytic ozonation achieved a chemical oxygen demand (COD) removal rate of 63.4%. Free-radical quenching experiments confirmed that hydroxyl radicals (·OH) played a dominant role in the catalytic ozonation system. Kinetic analysis revealed that the catalytic ozonation of chemical RO membrane concentrate wastewater with Cu-Ce@γ-Al₂O₃ followed second-order kinetics. The degradation mechanisms of organic matter in the wastewater were further analyzed using ultraviolet-visible (UV-Vis) spectroscopy and three-dimensional fluorescence spectroscopy. Additionally, a weighted rank sum ratio (WRSR) evaluation model was developed to provide a comprehensive assessment of the process performance. PRACTITIONER POINTS: Cu-Ce@γ-Al2O3 catalysts with excellent catalytic performance were prepared. Efficient catalytic ozonation of chemical RO membrane concentrate with high salinity was realized. Degradation mechanism of organic pollutants by catalytic ozonation is clarified. Evaluation model for catalytic ozonation of chemical RO membrane concentrate was established.

Ultraviolet-enhanced Fe0-activated H2O2 process for the removal of refractory organic matter from landfill leachate: Performance and mechanism

The Fenton-like process, utilizing zero-valent iron (Fe0) and hydrogen peroxide (H2O2), is employed to degrade refractory organic matter in membrane bioreactor (MBR) effluent derived from landfill leachate. However, the rate-limiting Fe2+/Fe3+ redox step diminishes treatment efficacy and generates substantial iron sludge. This study elucidates the mechanism by which ultraviolet (UV) irradiation augments the Fe0/H2O2 process for the removal of refractory organic matter in MBR effluent. The results show that the UV- enhanced H2O2 process effectively disrupts the aromatic structure of organic compounds, reducing molecular weight, degree of polymerization, and humification. Compared with the Fe0/H2O2 process, the removal efficiency of UV254, color number, and total organic carbon in the effluent treated by the UV/Fe0/H2O2 process increased by 24.16%, 14.62%, and 57.46%, respectively. Concurrently, the generation of iron sludge was reduced by 21.6%. This enhancement is primarily attributed to UV's ability to intensify the Fe2+/Fe3+ redox cycle and expedite the surface corrosion of Fe0, yielding more iron oxides. This accelerates the decomposition of H2O2, generating a higher quantity of •OH through both homogeneous and heterogeneous Fenton-like reactions. The refractory organic matter is removed through the oxidation by •OH, as well as the adsorption and precipitation facilitated by iron-based colloids. PRACTITIONER POINTS: UV promotes Fe0/H2O2 process to degrade refractory organic matter in MBR effluent. UV promotes Fe0 to dissolve more Fe2+ and the redox cycle of Fe2+ and Fe3+. The dosage of H2O2 or Fe0 influences the treatment effect of the process.

Regulation of desiccation-immersion cycle on the rate and fate of dissolved organic carbon release by Ulva pertusa

Macroalgae widely distribute in intertidal zones, one of blue carbon organisms. However, the regulatory mechanisms of tide on the carbon sequestration of macroalgae are still unclear. This study explored the effects of desiccation-rewetting cycles induced by tide on dissolved organic carbon (DOC) release from Ulva pertusa, which is prevalent from high to low tidal zones. Results showed that during desiccation stage, the DOC release of U. pertusa varied with desiccation levels, releasing 0.082, 0.22, and 0.35 mg g-1 FW at 0%, 40%, and 80% water loss, respectively, DOC accumulated on the surface of U. pertusa at a rate of about 0.52 mg g-1 FW h-1. Following 4 h of rewetting, DOC released surges to 0.99, 2.51, and 2.10 mg g-1 FW h-1. Using a stable isotope (13C) tracer method, we found that most DOC released by U. pertusa come from early fixed carbon. At 40% water loss, partial DOC stemmed from newly fixed carbon. DOC composition varied with desiccation level, affecting its bioavailability. After 16 days of degradation, DOC concentrations from U. pertusa at 0%, 40%, and 80% desiccation were 1.99, 3.22, and 2.54 mg g-1 FW, respectively. The 80% water loss showed the highest degradation rate, while the non-water-loss treatment group had the most potential to form refractory DOC. This study underlines the complex relationship between tide and the dynamics of DOC release in U. pertusa, highlighting their role in coastal carbon cycling.

Effect of substrate concentration on sulfamethoxazole wastewater treatment by osmotic microbial fuel cell: Insight into operational efficiency, dynamic changes of membrane fouling and microbial response

To solve the problems of antibiotic pollution, water resources and energy shortage, an osmotic microbial fuel cell (OsMFC) was adopted innovatively to treat antibiotic wastewater containing sulfamethoxazole (SMX), and achieved SMX removal, water production and electricity generation. Substrate concentration was one of the key factors affecting the performances of OsMFC, but there were few relevant studies This study explored the effect of substrate concentration on system performances, clarified the dynamic changes of membrane fouling under different substrate concentrations, and further revealed the response of microbial communities. The results showed that the stable removal efficiency of SMX exceeded 98.8 % due to the efficient interception of forward osmosis (FO) membrane. Compared with the 1.0 g/L NaAc system, the SMX degradation efficiency and maximum output voltage in the 2.0 g/L NaAc system were only increased by 3.9 % and 6.3 %, respectively. However, the initial water flux decreased by 30.1 % in the 7th cycle due to more serious FO membrane fouling. In addition, there were significant differences in the dynamic formation process of FO membrane fouling. Higher substrate concentration increased the relative abundance of Desulfobacterota and Geobacter. Functional prediction analysis showed that increasing substrate concentration promoted carbohydrate metabolism pathways and relative abundance of sulfur respiration functional groups, thereby improving COD and SMX removal rates. However, the biosynthesis of other secondary metabolites was significantly improved, resulting in increased contents of EPS and SMP, which aggravated membrane fouling. Overall, the system performed better when the substrate concentration was 1.0 g/L. This study would provide certain guidance for the performance optimization and membrane fouling mitigation of OsMFC, thereby promoting its practical application in antibiotic wastewater treatment.

Novel mixotrophic denitrification biofilter for efficient nitrate removal using dual electron donors of polycaprolactone and thiosulfate

A novel mixotrophic denitrification biofilter for nitrate removal using polycaprolactone and thiosulfate (MD-PT) as electron donors was investigated. MD-PT achieved high nitrate removal efficiency of approximately 99.8 %. The nitrate removal rates of MD-PT reached 1820 g N/m3/d, which was 304 g N/m3/d higher than that of autotrophic denitrification biofilter using thiosulfate (AD-T). Autotrophic and heterotrophic denitrification pathways in MD-PT were responsible for 67.6-94.5 % and 4.7-32.4 % of the nitrate removal, respectively. The production of SO42- in MD-PT was lower than that in AD-T, and the effluent pH was maintained at approximately 7.3 without acid-base neutralization. The abundance of key genes involved in carbon, nitrogen, and sulfur transformation was enhanced, which improved the nitrate removal of MD-PT. Alicycliphilus and Simplicispira related to organic compounds degradation were enriched after the addition of polycaprolactone. This research provided new insights into mixotrophic denitrification systems.

Biodegradation-assisted removal of sulfur-based odor compounds in rural drinking water using durable chitosan/polyvinyl alcohol biochar aerogels

Rural drinking water often suffers from unpleasant odors like dimethyl sulfide (DMDS) and dimethyl trisulfide (DMTS) due to poor raw water quality and limited treatment options. This study introduces durable chitosan/polyvinyl alcohol (PVA) biochar aerogels-supported bioflims in ultrafiltration (BAB-UF) reactors, where the incorporation of PVA significantly enhances structural integrity, biodegradation resistance, and functional lifespan, providing an efficient, sustainable solution for removing odorous compounds from rural water. Experimental results showed the enhanced chitosan/PVA porous biochar aerogels (CPPCA) displayed excellent biocapacity and structural stability. After 63 days of continuous operation, the degradation rate of biochar aerogels with 0.2 wt% PVA (CP2PCA) was only 8.2 %. The one-step membrane reactors utilizing PVA-enhanced aerogels achieved removal efficiencies for DMDS/DMTS pollutants of up to 98.4 %, surpassing systems without PVA. These findings indicate the potential for improved aerogels in rural drinking water treatment, providing a viable solution for effective and low-maintenance water purification.

Algal classification and Chlorophyll-a concentration determination using convolutional neural networks and three-dimensional fluorescence data matrices

In recent years, the frequency of harmful algal blooms has increased, leading to the release of large quantities of toxins and compounds that cause unpleasant odors and tastes, significantly compromising drinking water quality. Chlorophyll-a (Chl-a) is commonly used as a proxy for algal biomass. However, current methods for measuring Chl-a concentration face challenges in accurately quantifying algae by categories and effectively adapting to natural aquatic environments. This study combined convolutional neural networks (CNNs) and three-dimensional fluorescence data matrices to address these challenges. The algal classification model achieved over 99.5% accuracy in identifying thirteen types of algal samples, with class activation maps showing that the model primarily focused on algal pigment regions. In determining Chl-a concentrations of each algal species in mixed algae solutions (Microcystis aeruginosa, Cyclotella, and Chlorella), the Chl-a models demonstrated Mean Absolute Percentage Errors (MAPEs) ranging from 6.55% to 10.56% in the ultrapure water background, 11.57%-14.12% in the Qingcaosha Reservoir raw water background, and 21.46%-123.37% in the Lake Taihu raw water background. After calibration, the models were significantly improved, achieving MAPEs ranging from 11.86% to 14.18% in the Lake Taihu raw water background. Discrepancies in determination performance indicated that the intensity and locations of characteristic algal pigment fluorescence peaks greatly influenced the Chl-a models' accuracy. This research introduces a novel approach for algal classification and Chl-a concentration determination in water bodies, with significant potential for practical applications.

Removal pathways and mechanism of NO by Tetradesmus obliquus PF3 culture-based DeNOx system

Microalgae-based DeNOx technology, as an emerging approach for flue gas denitrification, is suitable for the deep treatment of NOx at medium to low concentrations. To address the ambiguity surrounding the removal pathways and mechanisms in the development of microalgae DeNOx technology, the pathways and mechanisms of NO removal within a microalgae cultivation system was investigated. By investigating the gas-liquid and liquid-solid nitrogen transfer pathways facilitated by algal cells, algal cells were found to play a pivotal role in NO removal by the T. obliquus PF3 cultivation system. Microalgae cells enhance NO transfer across gas-liquid phases via extracellular substance secretion, exogenous iron reduction, NO adsorption, and NO molecular absorption. During this process, NO is transformed in the liquid phase into molecular NO, ionic nitrate, and nitrite, as well as organically complexed NO. The soluble extracellular substances of T. obliquus PF3 are primarily composed of humic-like acids and fulvic-like acids, while bound extracellular substances are dominated by tryptophan and tryptophan-like proteins, both of which possess reductive properties conducive to iron reduction and NO adsorption/complexation. By employing ATP hydrolysis inhibitor HgCl2 and analyzing nitrogen balance in the system, It was revealed that the primary NO removal pathway involves NO dissolution and oxidation within the algal culture broth, with ionic nitrogen being the predominant form assimilated and utilized by algal cells from the solution. This study clarifies the NO removal pathways and mechanisms within the microalgae cultivation system, thereby providing a theoretical foundation for the advancement and process design of microalgae-based DeNOx technology.

Chlorine disinfectant significantly changed microfauna habitat, community structure, and colonization mode in wastewater treatment plants

During the coronavirus disease 2019 epidemic, excessive chlorine disinfectants have been used to block the spread of severe acute respiratory syndrome-coronavirus 2, resulting in large amounts of residual disinfectants entering wastewater treatment plants (WWTPs) through sewage systems. So far, no relevant research has been conducted on the impact of chlorine disinfectants on microfauna, an important microbial component in activated sludge treatment systems. This study comprehensively investigated the changes in microfauna habitat, community structure, and colonization mode under the chlorine stress by combining the full-scale WWTP survey and laboratory-scale sequencing batch reactor experiments. The results showed that chlorine disinfectants significantly changed the community structure of microfauna, including decrease in sedentary ciliates and increase in free-living ciliates, amoebas, and flagellates. Besides the disinfection effect of chlorine disinfectants, the microfauna community was also influenced by changes in habitat and bacterial community. The loose structure and excessive extracellular polymeric substance (EPS) of activated sludge caused by chlorination would impact the colonization of sedentary ciliates, while it was conducive to the survival of free-living ciliates due to their predation on EPS as the nutrients. Bacteria in the activated sludge had strong interactions with protozoa, and their changes under chlorine stress directly affected the protozoan community and even indirectly affected the micro-metazoa community through the food chain.

IMPORTANCE

This study revealed that chlorine disinfectant significantly changed microfauna habitat, community structure, and colonization mode in wastewater treatment plants during the coronavirus disease 2019 pandemic. Chlorine disinfectant could destroy the structure and stability of sludge flocs, reduce the abundance of beneficial microfauna in activated sludge, and even affect the colonization of sedentary ciliates on sludge. In addition, chlorine disinfectants might induce environmental and ecological risks related to microfauna, such as elevated suspended solids and release of bacteria and microfauna in the effluents.