Extracellular Polymeric Substances Content Research Articles

Will the removal of carbon, nitrogen and mixed disinfectants occur simultaneously: The key role of heterotrophic nitrification-aerobic denitrification strain

The capacity and mechanism of heterotrophic nitrification-aerobic denitrification (HNAD) strain (H1) to remove carbon, nitrogen, disinfectants chloroxylenol (PCMX) and benzethonium chloride (BEC) were investigated in this study. PCMX was removed via metabolism and chemical oxygen demand co-metabolism process. BEC was eliminated through bacterial adsorption, which greatly inhibited the removal of other pollutants. Carbon source optimization tests revealed that glucose was the optimal carbon source for co-removal of pollutants under mixed disinfectants circumstances (PCMX + BEC). Comparing the groups without (G1) and with disinfectants (G2), the content of extracellular polymeric substances was higher, and hydrophobicity was enhanced under the hazardous conditions of G2. All the nitrogen metabolism functional genes in G2 were up-regulated, and the electron transport system activity was also improved. At the same time, G2 had lower reactive oxygen species content, which reduced the probability of resistance genes dissemination, but the abundance of most quantified resistance genes was elevated in G2. Toxicity assessment assays found a dramatic reduction in the virulence of G2’s effluent compared with the mixed disinfentants. The results confirmed that H1 strain could be used to treat the disinfectant-containing wastewater, which may aid in the application of HNAD process.

Asymmetric Flow Field-Flow Fractionation for Comprehensive Characterization of Hetero-aggregates made of nano-Silver and Extracellular Polymeric Substances

The present study explores the capability of asymmetrical flow field-flow fractionation (AF4) coupled online with diode array (DAD), fluorescence detectors (FLD), multi-angle light scattering (MALS) and dynamic light scattering (DLS) to characterize silver nanoparticles (nAg) hetero-aggregates formed with diatoms derived extracellular polymeric substances (EPS). The content of EPS varied from 10.5 to 105 mgC L-1 and nAg were dispersed at 4 mg L-1 in a freshwater medium. Good recoveries (∼ 76.9 ± 8.4%) of nAg-EPS were obtained from AF4-DAD signals, but an anomalous elution was observed as EPS concentration increased: AF4 retention times decreased despite average gyration radii measured by MALS for nAg-EPS increased (from 16 nm to 24 nm), which suggests a change in the aggregation state, as evaluated by UV-Vis scans obtained from DAD. A regular Brownian relaxation of nAg-EPS was proven for each EPS concentration using these 2 detectors. The comparison of on-line and batch DLS measurements validated in addition, that no (dis)aggregation occurs upon injections. After a thorough comparison with classical AF4 using standards, the frit-inlet-AF4 was used. Slightly higher recovery (79.6±4.6 %) was obtained but similar deviation of nAg-EPS elution occurred, excluding the implication of membrane differential fouling of nAg-EPS /conditioning effects of EPS. The investigation of physico-chemical parameters controlling the Brownian relaxation of nAg-EPS suggests the influence of nAg-EPS structure and EPS loading. This study demonstrates the suitable use of AF4 coupled to multiple detectors to probe-out eco-corona formation and characterize polydisperse systems containing NPs, EPS and their hetero-aggregates in freshwaters, even under a non-ideal size-fractionation scenario.

Synchronous bioremediation of vanadium(V) and chromium(VI) using straw in a continuous-flow reactor

Vanadium (V) and chromium (Cr) are key resources widely used in industrial production. However, mining causes V(V) and Cr(VI) contamination in groundwater, posing health and environmental risks. Straw is an important byproduct and considered waste, however, it could be a solid carbon source. Therefore, the feasibility of V(V) and Cr(VI) bioremediation in groundwater was determined using straw as the carbon source in this study. A continuous-flow reactor able to resist fluctuations in pollutant concentrations in groundwater was constructed. V(V) and Cr(VI) were completely removed (100%, 10-34 d) in the reactor, and the maximum Cr(VI) removal rate from effluent was 1.19 mg/(L·h) (34-64 d). After long-term reactor operation (114 d), the V(V) and Cr(VI) removal rates reached almost 100%. Moreover, the formation of humus and tryptophan contributed to V(V) and Cr(VI) bioremediation. The extracellular polymeric substance content increased from 108.28 to 113.98 mg/g VSS, and combined with V(V) and Cr(VI) to reduce their concentrations. Moreover, functional microbes associated with heavy metal removal (Bacillus and Pseudobacteroides) and straw decomposition (Paludibacter) were found. The findings of this study offer empirical evidence that support the utilization of straw for mitigating composite heavy metal pollution, thereby laying a foundation for its practical engineering applications.

Novel ellipsoid-like granules exhibit enhanced anammox performance compared to sphere-like granules

Anammox granular sludge (AnGS) serves as an important platform for cost-effective nitrogen removal from wastewater. Different to the traditionally sphere-like granules, a novel type of AnGS in a unique ellipsoid-like shape was obtained through enhancing shear force. The ellipsoid-like AnGS significantly exhibited a smaller aspect ratio (-25.1 %) and granular size (-11.8 %), compared to traditional sphere-like AnGS (p < 0.01). Comprehensive comparisons showed that ellipsoid-like AnGS possessed a significantly higher extracellular polymeric substances (EPS) content and strength, as well as an enhanced mass transfer and a higher viable bacteria proportion due to the larger substrate permeable zone (p < 0.01). Additionally, the anammox bacterial abundance (Candidatus Kuenenia) was 12.2 % higher in ellipsoid-like AnGS than in sphere-like AnGS. All these characteristics of ellipsoid-like AnGS jointly increased the specific anammox activity by 29.0 % and nitrogen removal capacity by 22.6 %, compared to sphere-like AnGS. Further fluid field simulation suggested the enhanced flow shear on the side surface of AnGS likely drove the formation of ellipsoid-like AnGS. The higher shear force on the side surface led to an increase of EPS content (especially hydrophobic protein) and elastic modulus, thus constraining lateral expansion. This study sheds light on impacts of granular shape, an overlooked morphological factor, on anammox performance. The ellipsoid-like AnGS presented herein also offers a unique and promising aggregate to enhance anammox performance.

Enhancement of livestock wastewater treatment by a novel wooden-modified biocarrier

Intensive livestock wastewater poses threat to ecosystem. A novel wooden-modified biocarrier was applied in this study to enhance the livestock wastewater treatment in anoxic-aerobic systems. Compared to the ordinary polyethylene (PE) biocarrier, the novel wooden-modified biocarrier improved the biomass owing to its rough surface and porous side wall, and had better nitrogen removal ability. The biomass of wooden-modified biocarrier was 6.3 ± 1.1 and 36.4 ± 17.0 times that of PE biocarrier in anoxic and aerobic condition, respectively. The removal rates of ammonia nitrogen and total nitrogen of this novel biocarrier on specific biofilm's aera eventually stabilized at 0.64 ± 0.10 and 0.94 ± 0.21 g N/m2/d, respectively. Notably, this wooden-modified biocarrier was conducive to increase nitrogen removal by simultaneous nitrification and denitrification to some extent. The biofilm on novel modified biocarrier had higher extracellular polymeric substances (EPS) contents than activated sludge (AS), and the proportions of polysaccharides (PS) in EPS from biocarrier were more than those from AS. Compared to PE biocarrier and AS, the wooden-modified biocarriers enhanced the enrichment of nitrifying and denitrifying bacteria, and promoted the membrane transport and aerobic nitrogen metabolism. This study confirmed the superiority of wooden-modified biocarrier and provided reference for the treatment of high concentration sewage in full-scale project.

Temporal enrichment of comammox Nitrospira and Ca. Nitrosocosmicus in a coastal plastisphere.

Plastic marine debris is known to harbor a unique microbiome (termed the "plastisphere") that can be important in marine biogeochemical cycles. However, the temporal dynamics in the plastisphere and their implications for marine biogeochemistry remain poorly understood. Here, we characterized the temporal dynamics of nitrifying communities in the plastisphere of plastic ropes exposed to a mangrove intertidal zone. The 39-month colonization experiment revealed that the relative abundances of Nitrospira and Candidatus Nitrosocosmicus representatives increased over time according to 16S rRNA gene amplicon sequencing analysis. The relative abundances of amoA genes in metagenomes implied that comammox Nitrospira were the dominant ammonia oxidizers in the plastisphere, and their dominance increased over time. The relative abundances of two metagenome-assembled genomes of comammox Nitrospira also increased with time and positively correlated with extracellular polymeric substances content of the plastisphere but negatively correlated with NH4+ concentration in seawater, indicating the long-term succession of these two parameters significantly influenced the ammonia-oxidizing community in the coastal plastisphere. At the end of the colonization experiment, the plastisphere exhibited high nitrification activity, leading to the release of N2O (2.52ng N2O N g-1) in a 3-day nitrification experiment. The predicted relative contribution of comammox Nitrospira to N2O production (17.9%) was higher than that of ammonia-oxidizing bacteria (4.8%) but lower than that of ammonia-oxidizing archaea (21.4%). These results provide evidence that from a long-term perspective, some coastal plastispheres will become dominated by comammox Nitrospira and thereby act as hotspots of ammonia oxidation and N2O production.

Higher biodegradation rate of atrazine by Paenarthrobacter sp. KN0901 with P-doped hydrochar: The important role of biofilm regulated by autoinducer-2 regulated quorum sensing during the degradation process

The presence of atrazine residue in runoff from agricultural areas poses a significant risk to the ecosystem. This study aimed to develop microorganism-material systems using the atrazine-degrading strain Paenarthrobacter sp. KN0901 and P-doped hydrochar to effectively remove atrazine residues from aquatic environments. The atrazine degradation rate increased by 22.6 % with the addition of P-doped hydrochar after three days of incubation at 15 °C. Autoinducer-2 activity increased from 100 % to 116.7 % with P-doped hydrochar addition, indicating improved quorum sensing compared to free microorganisms. The extracellular polymeric substance content was significantly higher in the PHC groups compared to the blank groups, suggesting enhanced biofilm formation. Quorum sensing was inhibited by the use of nitazoxanide and sodium nitroprusside, leading to decreased atrazine degradation. In contrast, the presence of glucose and S-adenosyl methionine enhanced the rate of atrazine degradation due to elevated quorum sensing. These results suggested that P-doped hydrochar enhanced strain KN0901′s ability to assemble, increasing quorum sensing and accelerating atrazine degradation. Additionally, P-doped hydrochar promoted atrazine degradation by strain KN0901 under various conditions by enhancing quorum sensing. This work offers a new perspective on developing and using bioremediation techniques to remediate atrazine-contaminated environments under diverse conditions.

Sludge size affects sorption of organic micropollutants in full-scale aerobic granular sludge systems

Aerobic granular sludge (AGS) is gaining popularity as an alternative to activated sludge for wastewater treatment. However, little information is available on AGS regarding the removal of organic micropollutants (OMPs) through sorption. In this study, the sorption behavior of 24 OMPs at environmentally relevant concentrations (1 μg/L) was investigated in six sludge fractions of varying sizes (>4 mm, 2–4 mm, 1–2 mm, 0.6–1 mm, 0.2–0.6 mm, and <0.2 mm) from a full-scale AGS reactor using batch experiments. Sorption was significant (removal efficiency >40 %) for 10 OMPs, including 4 zwitterionic and 6 positively charged pharmaceuticals, indicating the importance of electrostatic interaction for OMP sorption in AGS systems. Larger granules exhibited a higher sorption coefficient and capacity than smaller AGS fractions, probably due to increased extracellular polymeric substance content for larger granules. Equilibrium OMP sorption was only reached after 72 h in granules larger than 2 mm, indicating an effect of longer diffusion distance for OMPs into larger granules. Additionally, compared to activated sludge, AGS demonstrates a similar or even slightly higher sorption capacity for 10 OMPs at 1 μg/L. Overall, this study is the first to investigate the sorption behavior of six AGS size fractions for OMPs at environmentally relevant concentrations (1 μg/L) and propose the possible roles of different-sized sludge in OMP sorption in the full-scale AGS reactor.

Evaluating the efficacy of microalgal-bacterial granular sludge system in lake water remediation.

The microalgal-bacterial granular sludge (MBGS) process is attracting attention as a green wastewater treatment technology. However, research on the application of MBGS in lake water remediation is limited. Thus, this experiment investigated the feasibility and the efficacy of the MBGS process for the treatment of natural lake water in a continuous-flow tubular reactor. The averageremoval efficiencies of COD, NH4+-N, NO3--N, NO2--N, TN, PO43--P, TP, and turbidity by MBGS system in the day/night cycles were 50.10/61.39%, 63.52/75.23%, 43.37/73.57%, 90.72/93.48%, 78.30/80.02%, 71.13/74.62%, 65.08/70.57%, 92.32/89.84%, respectively. As the experiment progressed, the total chlorophyll content in MBGS decreased as the granule size increased, while the extracellular polymeric substances content increased, suggesting that thelake water contributed to bacterial growth and favored the stability of MBGS. Moreover, the eukaryotic microorganisms were dominated by Chlorophyta and Rotifera, and prokaryotic microorganisms were dominated by Proteobacteria in MBGS. By promoting the decomposition of various organic compounds in the lake water and inhibiting sludge expansion, these microorganisms helpthe MBGS system tomaintain excellent granular characteristics and performance. Overall, the MBGS system proved to be a feasible option for the remediation of natural lake waters.

Mechanism of membrane fouling mitigation by microalgae biofilm formation for low C/N mariculture wastewater treatment: EPS characteristics, composition and interfacial interaction energy

Membrane fouling is considered one of the main limitations of membrane bioreactor (MBR) in wastewater treatment applications, including low C/N aquaculture wastewater. Although much research has focused on the integration of MBR with bacterial biofilm, there has been limited exploration into the mitigation mechanism of membrane fouling by microalgae biofilm. In this study, extracellular polymeric substances (EPS) before and after the formation of microalgae biofilm were compared, leading to the conclusion that the microalgae biofilm formation could reduce membrane fouling potential of EPS, thereby mitigating membrane fouling. EPS content and fluorescence components analysis indicated that microalgae biofilm formation could effectively reduce protein to polysaccharide ratios (PN/PS) of three types of EPS (soluble EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS)), lowering the membrane fouling potential associated with protein substances, especially tryptophan-like protein. Moreover, the analysis of molecular weight (MW) suggested that microalgae biofilm could considerably decrease the MW of both S-EPS and LB-EPS, thus mitigating the influence of high MW substances on membrane fouling. Meanwhile, the precise composition of EPS revealed a reduction in hydrophobic alkanes and recalcitrant aromatics, which often lead to membrane fouling. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further highlighted that microalgae biofilm weakened the interfacial interaction energy between the three EPS and membrane to mitigate membrane fouling. Therefore, this study provides a comprehensive elucidation of how microalgae biofilm formation mitigates membrane fouling, offering theoretical support for utilizing microalgae biofilm MBR in treating low C/N mariculture wastewater.

Ferrous-driven efficient removal of nitrate and various heavy metals by Zoogloea sp. ZP7 under oligotrophic conditions: Kinetics and heavy metal stress responses

Denitrification in surface water is affected by its oligotrophic characteristics and heavy metal pollution. In this study, a heterotrophic denitrifying bacterium Zoogloea resiniphila ZP7, which can utilize ferrous (Fe2+) as an additional electron donor under oligotrophic conditions, was isolated. Strain ZP7 achieved a 98.5 % nitrate (NO3−-N) removal efficiency (NRE) within 12 h using sodium acetate as carbon sources, with a Fe2+ concentration of 10.0 mg L−1, pH of 7.0, carbon to nitrogen ratio of 2.0, and NO3−-N concentration of 5.01 mg L−1, and no nitrite residue was observed. The denitrification performance and the removing ability of heavy metal by strain ZP7 were studied when exposed to copper (Cu2+), zinc (Zn2+), and cadmium (Cd2+) alone or in combination. When 1.0 mg L−1 Cu2+, Zn2+, and Cd2+ were added simultaneously, the strain ZP7 could achieve 91.3 % NRE in 14 h, and the removal efficiencies of Cu2+, Zn2+, and Cd2+ were 68.1, 89.2, and 83.5 %, respectively. The results of fluorescence region integration showed that the response of strain ZP7 to different heavy metal system stresses was different. Moreover, the changes in the content of extracellular polymeric substances (EPS) and humic acids indicated that they contributed to the enhancement of the resistance of strain ZP7 to heavy metals. Various characterization results showed that EPS and bio‑iron oxides were beneficial to remove heavy metals. In future studies, strain ZP7 can be considered to be immobilized in biomaterials to treat contaminated oligotrophic water bodies to explore its application prospects in actual contaminated water bodies.

Synchronous reinforcement azo dyes decolorization and anaerobic granular sludge stability by Fe, N co-modified biochar: enhancement based on extracellular electron transfer

Anaerobic digestion (AD) treatment of azo dyes wastewater often suffers from low decolorization efficiency and poor stability of anaerobic granular sludge (AnGS). In this study, iron and nitrogen co-modified biochar (FNC) was synthesized based on the secondary calcination method, and the feasibility of this material for enhanced AD treatment of azo dye wastewater and its mechanism were investigated. FNC not only formed richer conducting functional groups, but also generated Fe2+/Fe3+ redox pairs. The decolorization efficiency of Congo red and AD properties (e.g., methane production) were enhanced by FNC. After adding FNC, the content of extracellular polymeric substances (EPS) and the ratio of proteins remained stable under the impact of Congo red, which greatly protected the internal microbial community. This was mainly contributed to the excellent electrochemical properties of FNC, which strengthened the microbial extracellular electron transfer and realized the coupled mechanism of action: On the one hand, an electron transfer bridge between decolorizing bacteria and dyes was constructed to achieve rapid decolorization of azo dyes and mitigate the impact on methanogenic bacteria; On the other hand, the stability of AnGS was enhanced based on enhanced extracellular polymeric substances secretion, microbial community and direct interspecies electron transfer (DIET) process. This study provides a new idea for enhanced AD treatment of azo dyes wastewater.

Treatment of domestic wastewater and extracellular polymeric substance accumulation in siphon-type composite vertical subsurface flow constructed wetland.

In this study, the siphon-type composite vertical flow constructed wetland (Sc-VSsFCW) was constructed with anthracite and shale ceramsite chosen as the substrate bed materials. During the 90-day experiment, typical pollutant removal effects of wastewater and extracellular polymeric substance (EPS) accumulation were investigated. Meanwhile, X-ray diffraction and scanning electron microscopy were used to examine the phase composition and surface morphology to analyze adsorptive property. Additionally, we evaluated the impact of siphon effluent on clogging and depolymerization by measuring the EPS components' evolution within the system. The findings reveal that both the anthracite and shale ceramsite systems exhibit impressive removal efficiencies for total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP), chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), and nitrate nitrogen (NO3 --N). However, as the experiment progressed, TP removal rates in both systems gradually declined because of the saturation of adsorption sites on the substrate surfaces. Although the dissolved oxygen (DO) levels remained relatively stable throughout the experiment, pH exhibited distinct patterns, suggesting that the anthracite system relies primarily on chemical adsorption, whereas the shale ceramsite system predominantly utilizes physical adsorption. After an initial period of fluctuation, the permeability coefficient and porosity of the system gradually stabilized, and the protein and polysaccharide contents in both systems exhibited a downward trend. The study underscores that anthracite and shale ceramsite have good effectiveness in pollutant removal as substrate materials. Overall, the hydraulic conditions of the double repeated oxygen coupling siphon in the Sc-VSsFCW system contribute to enhanced re-oxygenation capacity and permeability coefficient during operation. The changes in EPS content indicate that the siphon effluent exerts a certain depolymerization effect on the EPS within the system, thereby mitigating the risk of biological clogging to a certain extent. PRACTITIONER POINTS: The system can still maintain good pollutant treatment effect in long-term operation. The re-oxygenation method of the system can achieve efficient and long-term re-oxygenation effect. The siphon effluent has a certain improvement effect on the permeability coefficient and porosity, but it cannot effectively inhibit the occurrence of clogging. The EPS content did not change significantly during the operation of the system, and there was a risk of biological clogging.

Understanding Partial Denitrification-hydroxyapatite (PD-HAP) coupled granules to enhance process stability and phosphorus removal by investigating the size effect of granules

The innovative Partial Denitrification-hydroxyapatite (PD-HAP) coupled granule offers a promising biotechnology for supplying nitrite to Anammox while simultaneously removing phosphorus. This study systematically examined the characteristics, biomass activity, and microbial community of PD-HAP granules of various sizes to enhance system stability and phosphorus removal efficiency. The results showed that larger granules had higher inorganic mineral and extracellular polymeric substances (EPS) content. These factors contributed to their denser structure, smoother surfaces, and better settling velocities compared to smaller granules. In contrast, smaller granules exhibited higher denitrification activity due to their greater biomass content and more efficient mass transfer. Calcium and phosphorus were identified as the primary inorganic constituents, mainly in the form of HAP, and were especially abundant in larger granules. Granules larger than 3.0 mm demonstrated a higher capacity for phosphorus removal. This was due to their significantly greater tightly bound EPS (T-EPS) content, which led to increased HAP and phosphorus levels. All granule sizes maintained a nitrate-to-nitrite transformation ratio (NTR) above 80 %, primarily due to the dominance of Flavobacterium (65.8 %-74.9 %). Although larger granules had lower denitrification activity, they still achieved an excellent NTR (above 85 %). They also showed superior settling velocity (174.9 m/h) and stronger phosphorus removal capacity (54.1 mg/g SS) compared to smaller granules. Maintaining a dominant proportion of granules larger than 3.0 mm could be an effective strategy to enhance both system stability and phosphorus removal. This study provides valuable insights into the PD-HAP coupled granular process, promoting efficient nitrite production and effective phosphorus removal.

Carbon capture characteristics and mechanisms of municipal wastewater treatment using coagulation-enhanced HRCS system

This study optimized coagulation in HRCS systems for municipal wastewater treatment, investigating coagulant dosage effects on carbon capture and microbial communities. Real wastewater testing in coagulation-enhanced HRCS (CE-HRCS) systems further revealed carbon capture efficiency and microbial mechanisms, enhancing resource utilization. The results demonstrated that with a coagulant dosage of 20 mg/L, the combined proportion of Proteobacteria and Bacteroidetes, the pivotal bacteria for carbon capture, exceeded 90 %. This dosage achieved a maximum sludge extracellular polymeric substance (EPS) content of 150 mg/g VSS and a carbon capture efficiency of 83 %. Upon transitioning to real municipal wastewater, while the chemical oxygen demand (COD) removal rate slightly dipped to approximately 80 %, the carbon capture rate remained robust at 63 ± 2 %, down from 70 %. The EPS content stabilized at 138 ± 2 mg/g VSS, indicating a satisfactory carbon capture efficiency for practical municipal wastewater treatment. Moreover, the microbial population in the CE-HRCS system exhibited an increase in species richness and diversity. Although the proportion of Proteobacteria declined from 83 % to 62 %, the presence of Firmicutes and Bacteroidota increased, with carbon degradation-related functional bacteria continuing to dominate. This study offers valuable insights and new guidance for enhancing carbon capture from municipal wastewater using CE-HRCS technology.

Effect of cations on aerobic granulation for sidestream treatment

Aerobic granular sludge (AGS) represents an aggregate of sludge formed through the self-immobilization of microorganisms under aerobic conditions. It is currently under scrutiny for its potential as a technology to reduce carbon emissions and promote sustainability. The practicality of AGS stems from its ability to encourage granule formation and enhance structural stability. In this study, a total of five cations (K+, Ca2+, Mg2+, Al3+, Fe3+) were introduced to facilitate stable structuring and the formation of granules for treating high-strength wastewater, such as side-stream treatment. As a result of the experiment, the loosely bound extracellular polymeric substances (LB-EPS) content in the cation-enhanced sludge witnessed a significant increase, leading to elevated total EPS content under all experimental conditions. Furthermore, the protein (PN)/polysaccharide (PS) ratio, a pivotal component of EPS influencing AGS's hydrophobicity and structural stability, exhibited a collective increase, with Mg2+ reaching the highest value of 1.7. The relationship between relative hydrophobicity and the PN/PS ratio was found to strongly impact sludge adhesion, with noteworthy results observed particularly for Mg2+, Al3+, and Fe3+. The viability of attached cells reached 96.8 %, the highest recorded in the case of Mg2+. In the context of treating high-strength wastewater, Mg2+ emerged as the optimal cation for accelerating AGS formation and enhancing structural stability.

Tracking the transformation of extracellular polymeric substances during the ultraviolet/peracetic acid disinfection process: Emphasizing on molecular-level analysis and overlooked mechanisms

In this study, the transformation mechanisms of extracellular polymeric substances (EPS) during ultraviolet/peracetic acid (UV/PAA) disinfection were elucidated based on multiple molecular-level analyses. After UV/PAA disinfection, the contents of soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were reduced by 70.47 %, 57.05 % and 47.46 %, respectively. Fluorescence excitation-emission matrix-parallel factor and Fourier transform ion cyclotron resonance mass spectrometry analyses showed that during UV/PAA disinfection, EPS was transformed from the state characterized by high aromaticity, low saturation and low oxidation to the one with reduced aromaticity, increased saturation and higher oxidation. Specifically, sulfur-containing molecules (CHOS, CHONS, etc.) in EPS were converted into highly saturated and oxidized species (such as CHO), with the aromaticity index (AImod) decreasing by up to 53.84 %. Molecular characteristics analyses further indicated that saturation degree, oxidation state of carbon and molecular weight exhibited the most significant changes in S-EPS, LB-EPS and TB-EPS, respectively. Additionally, mechanistic analysis revealed that oxygen addition reaction was the predominant reaction for S-EPS (+O) and TB-EPS (+3O) (accounting for 31.78 % and 36.47 %, respectively), while the dealkylation was the main reaction for LB-EPS (29.73 %). The results were consistent with functional groups sequential responses analyzed by Fourier transform infrared and two-dimensional correlation spectroscopy, and were further verified by density functional theory calculations. Most reactions were thermodynamically feasible, with reaction sites predominantly located at functional groups such as CO, CO, CN and aromatic rings. Moreover, metabolomics analysis suggested that changes in metabolites in raw secondary effluent during UV/PAA disinfection were strongly correlated with EPS transformation. Our study not only provides a strong basis for understanding EPS transformation during UV/PAA disinfection at molecular-level but also offers valuable insights for the application this promising disinfection process.

Sulfamethoxazole exposure shifts partial denitrification to complete denitrification: Reactor performance and microbial community

This study elucidated the influence on a partial denitrification (PD) system under 0–1 mg/L sulfamethoxazole (SMX) stress in a sequencing batch reactor. The results showed that the nitrite accumulation rate (NAR) significantly (P ≤ 0.01) decreased from 68.68 ± 9.00% to 49.05 ± 11.68%, while the total nitrogen removal efficiency significantly (P ≤ 0.001) increased from 23.19 ± 4.42% to 31.36 ± 2.73% in presence of SMX. The results indicated that SMX exposure switched the PD process to complete denitrification through the deterioration of the nitrite accumulation and the promotion of further nitrite reduction. The SMX removal loading rate increased from 0.21 ± 0.04 to 5.03 ± 0.77 mg-SMX/(g-MLVSS·d) with the extended reactor operation under SMX stress. Low SMX concentration exposure increased extracellular polymeric substances (EPS) content from 107.69 ± 20.78 mg/g-MLVSS (0.05 mg-SMX/L) to 123.64 ± 9.66 mg/g-MLVSS (0.5 mg-SMX/L), while EPS secretion was inhibited under high SMX concentration exposure (i.e., 1 mg-SMX/L). Moreover, SMX exposure promoted the synthesis of aromatic protein-like compounds and changed the functional groups as revealed by EEM and FTIR analysis. Additionally, SMX exposure significantly shifted the microbial community structures at both phylum and genus levels. Particularly, the abundance of Thauera, i.e., functional bacteria related to PD, considerably decreased from 41.69% to 11.62% after SMX exposure, whereas the abundances of Denitratisoma and SM1A02 significantly rose under different SMX concentrations. These outcomes hinted that the addition of SMX resulted in the shifting of partial denitrification to complete denitrification.

Regulatory roles of extracellular polymeric substances in uranium reduction via extracellular electron transfer by Desulfovibrio vulgaris UR1

The pathway of reducing U(VI) to insoluble U(IV) using electroactive bacteria has become an effective and promising approach to address uranium-contaminated water caused by human activities. However, knowledge regarding the roles of extracellular polymeric substances (EPS) in the uranium reduction process involving in extracellular electron transfer (EET) mechanisms is limited. Here, this study isolated a novel U(VI)-reducing strain, Desulfovibrio vulgaris UR1, with a high uranium removal capacity of 2.75 mM/(g dry cell). Based on a reliable EPS extraction method (45 °C heating), manipulation of EPS in D. vulgaris UR1 suspensions (removal or addition of EPS) highlighted its critical role in facilitating uranium reduction efficiency. On the second day, U(VI) removal rates varied significantly across systems with different EPS contents: 60.8% in the EPS-added system, 48.5% in the pristine system, and 22.2% in the EPS-removed system. Characterization of biogenic solids confirmed the reduction of U(VI) by D. vulgaris UR1, and the main products were uraninite and UO2 (2.88–4.32 nm in diameter). As EPS formed a permeable barrier, these nanoparticles were primarily immobilized within the EPS in EPS-retained/EPS-added cells, and within the periplasm in EPS-removed cells. Multiple electroactive substances, such as tyrosine/tryptophan aromatic compounds, flavins, and quinone-like substances, were identified in EPS, which might be the reason for enhancement of uranium reduction via providing more electron shuttles. Furthermore, proteomics revealed that a large number of proteins in EPS were enriched in the subcategories of catalytic activity and electron transfer activity. Among these, iron-sulfur proteins, such as hydroxylamine reductase (P31101), pyruvate: ferredoxin oxidoreductase (A0A0H3A501), and sulfite reductase (P45574), played the most critical role in regulating EET in D. vulgaris UR1. This work highlighted the importance of EPS in the uranium reduction by D. vulgaris UR1, indicating that EPS functioned as both a reducing agent and a permeation barrier for access to heavy metal uranium.

Role of diffusible signal factor in regulating aerobic granular sludge formation under temperature shocks

Signal-molecule-mediated strategies are proposed for aerobic granular sludge (AGS), but the regulatory mechanisms behind AGS formation are largely unexplored. In this study, two sequence batch reactors (SBRs) were operated to investigate the regulation of diffusible signal factor (DSF) in AGS formation. DSF secretion in Reactor 2 (R2: 10 °C→25 °C) decreased by 15 % compared to Reactor 1 (R1: 25 °C→10 °C), correlating with a 26 % increase in extracellular polymeric substance (EPS) concentration, resulting in a 63 % acceleration of the granulation process. After temperature shocks in R2, DSF concentration increased by 70 %, while EPS concentration decreased by 47 %. Batch tests confirmed that DSF inhibited EPS secretion. Combined 16S rRNA analysis and machine learning identified key bacteria responsible for secreting EPS and signal molecule. The decrease in the abundances of these bacteria reduced EPS production. These findings on DSF regulation of EPS secretion provide an in-depth understanding of enhanced AGS granulation.