Extracellular Polymeric Substances Layer Research Articles

Molecular mechanisms of iron nanominerals formation in fungal extracellular polymeric substances (EPS) layers during fungus-mineral interactions

Extracellular polymeric substances (EPS), which envelop on fungal hyphae surface, interact strongly with minerals and play a crucial role in the formation of nanoscale minerals during biomineralization in nature environments. However, it remains poorly understood about the molecular mechanisms of nanominerals (i.e., iron nanominerals) formation in fungal EPS halos during fungus-mineral interactions. This process is vital because fungi typically grow attached to various mineral surfaces in nature. According to the changes of thickness of the fungal cell and EPS layers during the Trichoderma guizhouense NJAU 4742 and hematite cultivation experiments, we found that fungal biomineralization could trigger the formation of EPS layers. Fe-dominated nanominerals, aromatic C (283-286.1 eV), alkyl C (287.6-288.3 eV), and carboxylic C (288.4-289.1 eV) were the dominant chemical groups on the EPS layers, as determined by nanoscale secondary ion mass spectrometry (NanoSIMS), high-resolution transmission electron microscope (HRTEM), and carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Further, evidence from Fe K-edge X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) spectra indicated that oxygen vacancy (OV) was formed on the Fe-dominated nanomineral surface during fungus-mineral interactions, which played an important role in catalyzing H2O2 decomposition and HO∗ production. Taken together, the intrinsic peroxidase-like activity by reactive oxygen species (ROS) could modulate the Fe-dominated nanominerals formation in EPS layers to newly form a physical barrier between the cell and the external environments around hyphae, providing novel insights into the effects of ROS-mediated fungal-mineral interactions on fungal nutrient recycling, attenuation of contaminants, and biological control in nature environments.

Sludge bound-EPS solubilization enhance CH4 bioconversion and membrane fouling mitigation in electrochemical anaerobic membrane bioreactor: Insights from continuous operation and interpretable machine learning algorithms

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days’ operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/Lreactor/d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/Lreactor/d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPSPS and S-EPSPN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR.

Earthworm gut digestion drives the transfer behavior of antibiotic resistance genes in layers of extracellular polymeric substances during vermicomposting of dewatered sludge

Gut digestion by earthworms (GDE) is a crucial step in vermicomposting, affecting the fate of antibiotic resistance genes (ARGs) in vermicompost sludge. The extracellular polymeric substance (EPS) matrix of sludge is an important space for ARG transfer. However, the effect of GDE on EPS-associated ARGs remains unclear. Therefore, this study explored the role of GDE in driving the transfer of ARGs within different EPS layers in sludge. For this, the changes in intracellular ARGs and EPS-associated ARGs in sludge were analyzed after 5 days of the GDE process. The results showed that after the GDE process, both nitrate and dissolved organic carbon significantly increased in all EPS layers of sludge, while the proteins and polysaccharides only enhanced in soluble and loosely bound EPS of sludge. In addition, a 7.0% decrease in bacterial diversity was recorded after the GDE process, with a functional bacterial community structure emerging. Moreover, the absolute abundance of total ARGs and mobile genetic elements decreased by 90.71% and 61.83%, respectively, after the GDE process. Intracellular ARGs decreased by 92.1%, while EPS-associated ARGs increased by 4.9%, indicative of intracellular ARG translocation into the EPS during the GDE process. Notably, the ARGs exhibited significant enrichment in both the soluble and loosely bound EPS, whereas they were reduced in the tightly bound EPS. The structural equation modeling revealed that the GDE process effectively mitigated the ARG dissemination risk by modulating both the EPS structure and microenvironment, with the organic structure representing a primary factor influencing ARGs in the EPS.

The effect of temperature on fouling in anaerobic membrane bioreactor: SMP- and EPS-membrane interactions

Biofouling is the main challenge in the operation of anaerobic membrane bioreactors (AnMBRs). Biofouling strongly depends on temperature; therefore, we hypothesize that the interactions and viscoelastic properties of soluble microbial products (SMP) and extracellular polymeric substances (EPS) vary with temperature, consequently influencing membrane permeability. This study compares the performance of an AnMBR operated at a similar permeate flux at two temperatures. The transmembrane pressure (TMP) rose rapidly after 5 ± 2 days at 25 °C but only after 18 ± 2 days at 35 °C, although the reactor's biological performance was similar at both temperatures, in terms of the efficiency of dissolved organic carbon removal and biogas composition, which were obtained by changing the hydraulic retention time. Using confocal laser scanning microscopy (CLSM), a higher biofilm amount was detected at 25 °C than at 35 °C, while quartz crystal microbalance with dissipation (QCM-D) showed a more adhesive, but less viscous and elastic EPS layer. In situ optical coherence tomography (OCT) of an ultra-filtration membrane, fed with the mixed liquor suspended solids (MLSS) at the two temperatures, revealed that while a higher rate of TMP increase was obtained at 25 °C, the attachment of biomass from MLSS was markedly less. Increased EPS adhesion to the membrane can accelerate TMP increase during the operation of both the AnMBR and the OCT filtration cell. EPS's reduced viscoelasticity at 25 °C suggests reduced floc integrity and possible increased EPS penetration into the membrane pores. Analysis of the structures of the microbial communities constituting the AnMBR flocs and membrane biofilms reveals temperature's effects on microbial richness, diversity, and abundance, which likely influence the observed EPS properties and consequent AnMBR fouling.

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L−1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

Pivotal role of intracellular oxidation by HOCl in simultaneously removing antibiotic resistance genes and enhancing dewaterability during conditioning of sewage sludge using Fe2+/Ca(ClO)2

Pre-acidification has been shown to be crucial in attenuating antibiotic resistance genes (ARGs) during the conditioning of sewage sludge. However, it is of great significance to develop alternative conditioning approaches that can effectively eliminate sludge-borne ARGs without relying on pre-acidification. This is due to the high investment costs and operational complexities associated with sludge pre-acidification. In this study, the effects of Fe2+/Ca(ClO)2 conditioning treatment on the enhancement of sludge dewaterability and the removal of ARGs were compared with other conditioning technologies. The dose effect and the associated mechanisms were also investigated. The findings revealed that Fe2+/Ca(ClO)2 conditioning treatment had the highest potential, even surpassing Fenton treatment with pre-acidification, in terms of eliminating the total ARGs. Moreover, the effectiveness of the treatment was found to be dose-dependent. This study also identified that the •OH radical reacted with extracellular polymeric substance (EPS) and extracellular ARGs, and the HOCl, the production of which was positively correlated with the dose of Fe2+/Ca(ClO)2, could infiltrate the EPS layer and diffuse into the cell of sludge flocs, inducing the oxidation of intracellular ARGs. Furthermore, this study observed a significant decrease in the predicted hosts of ARGs and MGEs in sludge conditioned with Fe2+/Ca(ClO)2, accompanied by a significant downregulation of metabolic pathways associated with ARG propagation, thereby contributing to the attenuation of sludge-borne ARGs. Based on these findings, it can be concluded that Fe2+/Ca(ClO)2 conditioning treatment holds great potential for the removal of sludge-borne ARGs while also enhancing sludge dewaterability, which mainly relies on the intracellular oxidation by HOCl.

Migration and morphological transformation patterns of heavy metals on sludge cells and extracellular polymeric substances (EPS) under the influence of different treatments.

The impediment of sludge resource utilization stems from the presence of heavy metals within the sludge matrix. To optimize heavy metal removal techniques from undried sludge, it is essential to study the distribution of heavy metals in the sludge flocs structure and the changes in morphology in the sludge cells after different treatments. In this study, the sludge was subjected to chemical treatments using citric acid (CA), EDTA, and saponin, as well as electrokinetic treatment at 2 V/cm. The distribution and migration of Cu, Ni, and Zn in sludge flocs after various treatment methods were analyzed. The heavy metals were found to migrate from intracellular to extracellular polymeric substances (EPS) without causing extensive sludge cell lysis. They gradually diffused outward with the dispersion of the EPS layer. The migration efficiency of the three heavy metals in the sludge flocs was Zn, Ni, and Cu. This was mainly related to the initial distribution and morphology of the heavy metals. Under the influence of chemicals and an electric field, the acid-soluble and reducible heavy metals in the cells partially migrated to the EPS, while the stable heavy metals transformed into an unstable state. Furthermore, the order of chemical reagents in terms of their effect on the migration efficiency of heavy metals was CA > EDTA > Saponin, owing to the varying binding strengths of heavy metals and their impact on the degree of loosening of the EPS. Especially after CA treatment a greater proportion of Cu, Ni, and Zn were transferred from the cells to the EPS. The acidification effect near the anode during electrokinetic treatment intensifies the migration of heavy metals. This study provides basic research for subsequent engineering optimization aimed at removing heavy metals from sludge.

Assessment of extracellular polymeric substances production and antioxidant defences in periphytic communities exposed to effluent contaminants.

Periphyton is frequently used in the evaluation of the ecological status of aquatic ecosystems using diatoms as a proxy. However, periphyton has a particularity, the production of extracellular polymeric substances (EPS), which might play a protective role against exposure to harmful environmental contaminants. Effluents originating in wastewater treatment plants (WWTPs) constitute some of the most complex mixtures of contaminants, to which aquatic ecosystems are frequently exposed, often containing tens to hundreds of different chemicals. In such challenging scenarios, a putative protective role of EPS may obscure the bioindicator value of diatoms. To address this problem, we sampled periphyton upstream and downstream of the effluent outfall from three different WWTPs, quantifying EPS production and simultaneously evaluating general stress responses in the community (protein and sugar content, photosynthetic pigments, antioxidant enzyme activity and oxidative damage). By combining these endpoints with a characterization of the sediments of the riverine systems receiving the effluents made in a previous study (metals, polycyclic aromatic hydrocarbons, pharmaceuticals and personal care products), we aimed to elucidate whether effluent contaminants trigger negative effects, which may be mitigated by EPS layers protecting the communities. Our results indicated that under a comparatively milder contamination burden, EPS production is enhanced in samples collected downstream of the effluent outfall; under a higher contamination burden, EPS production is hampered. Stress-coping mechanisms were activated by environmental contaminants, including the antioxidant defense, particularly through catalase and superoxide dismutase activity. The findings support the generally assumed protective effect of EPS, but also suggest that EPS production depends on the contamination burden and that protective effects should be in place under specific scenarios of, for example, relatively low contamination levels. Overall, the integrative approach used in this study contributes to a better understanding of the complex interplay of interactions between effluent-driven contamination and thriving periphytic communities inhabiting recipient waterways, including evolved protection mechanisms.

Enhancement of sewer sediment control and disruption of adhesive gelatinous sediment structure using low-dose calcium peroxide

Large quantities of sediments in urban sewer systems pose significant risk of pipe clogging and corrosion. Owing to their gel-like structure, sewer sediments have strong resistance to hydraulic shear stress. This study proposed a novel approach to weaken the erosion resistance of sewer sediments by destroying viscous gel-like biopolymers in sediments with low doses of calcium peroxide (CaO2). After treatment with 10–50 mg g−1 TS of CaO2, the critical erosion shear stress was significantly reduced by 25.7%–59.9%. The sediment aggregates gradually disintegrated into small diameter particles with increasing CaO2 dosage. Further analysis showed that the strong oxidizing and alkaline environment induced by CaO2 treatment led to cell lysis and changes in the composition and property of extracellular polymeric substances (EPS). After CaO2 treatment, aromatic proteins and humic acid-like substances associated with adhesion translocated from the inner EPS layers to outer layers while being disintegrated into small organic molecules. Concomitantly, CaO2 treatment disrupted the main functional groups (–OH, COO−, C–N, CO, and CN) in inner EPS layers, thus weakening EPS adhesion. Analysis of protein secondary structure and zeta potential reflected the reduced aggregation capacity of sediment microorganisms and loosening of sediment structure after CaO2 treatment. Thus, CaO2 treatment facilitated fragmentation and disaggregation of the gelatinous structure of sewer sediments. Such green strategy decreased the cost of sewer sediment disposal by 42.10–68.95% when compared to water flushing, and it would improve the self-cleaning capacity of sewer system and efficiency of dredging equipment.

Nitrogenous organics in sewage sludge: New insights into bottlenecks of anaerobic transformation

As the most crucial carrier of carbon and nitrogen in sludge, nitrogenous organics, are essential in governing the efficiency of sludge anaerobic digestion (AD). An in-depth understanding of the anti-degradation mechanism of nitrogenous organics in sludge at various occurrence states is needed. This study classified nitrogenous organics in sludge into extracellular nitrogenous organics (e-NO) and intracellular nitrogenous organics (i-NO). Further, it identified the hindrances of anaerobic degradation of e-NO and i-NO in sludge by comparing the structural and AD performance differences between sludge and other nitrogen source substrates (food waste, straw, chicken manure, soybean, and beef). Experimentally, soybean and beef (with excellent e-NO degradation rates) and chicken manure (with excellent i-ON degradation efficiency) were further compared. We found that the relative abundance of peptidase genes in sludge was generally lower than in soybean and beef. Also, the pyruvate (a volatile fatty acid precursor) metabolism of some amino acids (Gly, Ala, Phe) with high content was inactive. Refractory hydrolysis and incomplete fermentation of nitrogenous organics in sludge are the main reasons for the low e-ON degradation rate. Further experiments showed that the anaerobic degradation rate of i-NO in the sludge was lower than that of e-NO. However, the former was significantly enhanced by extracellular polymeric substances (EPS) removal. Thus, the distribution and structure of EPS in the sludge were compared with that found in the chicken manure. We observed that the proportion of tightly bound EPS (TB-EPS) in sludge was higher, and the refractory glycoconjugates were mainly distributed in TB-EPS. Meanwhile, organic-bound Fe was higher in the sludge EPS. These results indicate that the difficulties of anaerobic degradation of i-NO arise from a tight EPS layer protecting the cell body. Future studies may consider combining enhanced hydrolysis methods (i.e., additional enzymes) and cell-breaking pretreatment techniques to facilitate the degradation of nitrogenous organics in sludge. In addition, refractory amino acids can also be studied to produce functionalized organic matter (such as humic substances) for high-value applications.

Insight into the roles of soluble, loosely bound and tightly bound extracellular polymeric substances produced by Enterobacter sp. in the Cd2+ and Pb2+ biosorption process: Characterization and mechanism

Extracellular polymeric substances (EPSs) are macromolecular polymers formed by metabolic secretion, and they have great potential for removing heavy metal (HM) ions from the aquatic phase. In this study, the contributions of soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs) and tightly bound EPSs (TB-EPSs) secreted by Enterobacter sp. to Cd2+ and Pb2+ adsorption were analyzed. The results indicated that in a solution containing both Cd2+ and Pb2+, pH= 6.0 was best suited for the adsorption process, and adsorption equilibrium was reached in approximately 120 min. Moreover, the mechanism for adsorption of Cd2+ and Pb2+ by the different layers of EPSs involved spontaneous chemical processes. However, Cd2+ adsorption by the three layers of the EPSs was an exothermic process (∆H0 <0), but Pb2+ adsorption by the three layers of the EPSs was an endothermic process (∆H0 >0). The variations in zeta potentials indicated that ion exchange occurred during Cd2+ and Pb2+ adsorption. FT-IR, XPS and 3D-EEM analyses indicated that the functional groups of the EPSs involved in adsorption were mainly the CO, C-O and C-O-C groups of the polysaccharides; furthermore, fulvic acid-like substances, humic-like substances and tyrosine-like proteins played important roles in the adsorption of Cd2+ and Pb2+ by the different EPS layers.

Multispecies biofilms on reverse osmosis membrane dictate the function and characteristics of the bacterial communities rather than their structure

The main reason for the deterioration of membrane operation during water purification processes is biofouling, which has therefore been extensively studied. Biofouling was shown to reduce membrane performance reflected by permeate flux decline, reduced selectivity, membrane biodegradation, and consequently, an increase in energy consumption. Studies of biofouling focused on the identification of the assembled microbial communities, the excretion of extracellular polymeric substances (EPS), and their combined role in reduced membrane performance and lifetime. However, the link between the structure and function of biofouling communities has not been elucidated to date. Here, we provide a novel insight, suggesting that bacterial functions rather than composition control biofouling traits on reverse osmosis (RO) membranes. We studied the potential activity of RO biofilms at metatranscriptome resolution, accompanied by the morphology and function of the biofouling layer over time, including microscopy and EPS composition, adhesion, and viscoelastic properties. To that end, we cultivated natural multispecies biofilms in RO membranes under treated wastewater flow and extracted RNA to study their taxonomies and gene expression profiles. Concomitantly, the biofilm structure was visualized using both scanning electron microscopy and laser scanning confocal microscopy. We also used quartz crystal microbalance with dissipation to characterize the affinity of EPS to membrane-mimetic sensors and evaluated the viscoelasticity of the Ex-Situ EPS layer formed on the sensor. Our results showed that different active bacterial taxa across five taxonomic classes were assembled on the RO membrane, while the composition shifted between 48 and 96 h. However, regardless of the composition, the maturation of the biofilm resulted in the expression of similar gene families tightly associated with the temporal kinetics of the EPS composition, adhesion, and viscoelasticity. Our findings highlight the temporal selection of specific microbial functions rather than composition, featuring the adhesion kinetics and viscoelastic properties of the RO biofilm.

Promoting vivianite recovery: Crucial role of tightly-bound extracellular polymeric substances

Vivianite is an important bio-induced product of dissimilated iron reduction (DIR), which exists widely in activated sludge and digested sludge of wastewater treatment plants (WWTPs). Extracellular polymeric substances (EPS) surrounding dissimilatory iron-reducing bacteria (DIRB) were reported to be transient media for microbial extracellular electron transfer (EET) and DIR. However, what happens when a layer of EPS envelops microbial cells during vivianite recovery? This study tried to assess the relationship between iron reduction and electron transfer by stripping EPS layer-by-layer, then clarified the delamination of different EPS layers on the performance of vivianite recovery. After stripping total EPS (PC-EPS batches) of DIRB, the Fe (III) reduction efficiencies (RFe), Fe (III) reduction rate (VFe), and vivianite formation efficiency (RV) decreased by 33%, 37%, and 30%, respectively. Tightly bound-EPS (TB-EPS) was confirmed to play a crucial role in vivianite formation, which contributed 28–51% to vivianite recovery and 34–55% to iron reduction. Electronic shuttle substances were contained in TB-EPS, which enhanced the EET rate and efficiency between cells and Fe (III). The polysaccharide content of TB-EPS was positively related to adhesiveness between cells and mineral, as well as the iron reduction efficiency. Furthermore, redox proteins (PpcA, OmcB) were embedded in EPS, which shortened the distance of electron hopping to across the EPS layer and further accelerated vivianite recovery from wastewater. Long-term operation of anaerobic reactors confirmed that TB-EPS played critical roles in bio-induced vivianite formation.

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

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

Malodorous volatile organic compounds (MVOCs) formation after dewatering of wastewater sludge: Correlation with the extracellular polymeric substances (EPS) and microbial communities

Malodorous volatile organic compounds (MVOCs) are often the key odorants in determining sludge odor character and odor impact. However, the emission characterization and generation mechanisms of MVOCs from various dewatered sludge have not been sufficiently understood partly due to the diverse and complex composition and low concentration of odorants. In this study, waste activated sludge (WAS) was collected to examine the variation of MVOC emission from sludge after different dewatering treatment in lab-scale trials. The MVOCs were measured using the electronic nose (eNose), headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC–MS). The results showed that centrifugation treatment promoted the generation of various odorous volatiles. The identified key odorants included dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), geosmin, and p-cresol according to their odor activity values (OAVs). The effects of the enhanced dewatering on volatile production were greater than thickening, however, the key odorants of dewatered sludge using gravity thickening varied more greatly than sludges from centrifuge thickening. The distribution of extracellular polymeric substances (EPS) and variation of microbial community showed correlations with the production of key odorants. Tryptophan-like substances in the inner layer of EPS (LB-EPS and TB-EPS) were better correlated with the key odorants. The bound EPS released by centrifugation may play the role of precursor for odorous microbial volatiles. According to the predicted functions of differential microbial genera, Desulfobulbus (Desulfobacterota), Gordonia (Actinobacteriota), and Hyphomicrobium (Proteobacteria) were associated with the production of DMS, DMDS, and DMTS, while Gordonia and Hyphomicrobium were related to p-cresol production.

Insights into the resistance of different extracellular polymeric substance (EPS) layers to the fermentation environment in sludge anaerobic digestion

• EPS layer delamination had great promotion for the methane production. • The semi-rigid structure of sludge flocs was damaged after EPS layer delamination. • EPS layer delamination reduced metal contents and the apparent activation energy. Extracellular polymeric substance (EPS) is key in maintaining microbial cell stability and agglomeration in sludge, which may play as a protective layer for cells. This study tried to assess the digestive performances of sludge after delamination of different EPS layers, aiming to understand the resistance of different EPS layers to the external environment. Results indicated that, after EPS layer delamination, the cumulative methane yield in anaerobic digestion (AD) was improved from 148.8 to 199.9 mL/g COD. The total methane yield for the EPS layers and EPS extracted sludge increased by 32.2% compared to the raw sludge. Moreover, with the delamination of EPS layers, the apparent activation energy (AAE) of the sludge samples decreased, and the interactions between metals and organic substances were destroyed, resulting in lower energy barrier in organic solubilization. Additionally, the treatment changed the distribution of organic substances in sludge, and the residual organic substances presented higher theoretical methane production (TMP). Therefore, both the hydrolytic efficiency and the conversion efficiency of organic substances to methane in AD were improved. By understanding the resistance effects of different EPS layers to the fermentation environment, this study will help us develop more targeted methods in sludge pretreatment for improving its digestive performance.

Unraveling pH Effects on Ultrafiltration Membrane Fouling by Extracellular Polymeric Substances: Adsorption and Conformation Analyzed with Localized Surface Plasmon Resonance.

Extracellular polymeric substances (EPSs) can conform and orient on the surface according to the applied aquatic conditions. While pH elevation usually removes EPSs from membranes, small changes in pH can change the adsorbed EPS conformation and orientation, resulting in a decrease in membrane permeability. Accordingly, EPS layers were tested with localized surface plasmon resonance (LSPR) sensing and quartz crystal microbalance with dissipation monitoring (QCM-D) using a hybrid sensor. A novel membrane-mimetic hybrid QCM-D-LSPR sensor was designed to indicate both "dry" mass and mechanical load ("wet" mass) of the adsorbed EPS. The effect of pH on the EPS layer's viscoelastic properties and hydrated thickness analyzed by QCM-D corroborates with the shift in EPS areal concentration, ΓS, and the associated EPS conformation, analyzed by LSPR. As pH elevates, the processes of (i) elevation in EPS layer's thickness (QCM-D) and (ii) decrease in the EPS areal density, ΓS (LSPR), provide a clear indication for changes in EPS conformation, which decrease the effective ultrafiltration (UF) membrane pore diameter. This decrease in the pore diameter together with the increase in surface hydrophobicity elevates UF membrane hydraulic resistance.

Impact of magnesium ions on lysozyme-triggered disintegration and solubilization of waste activated sludge

Lysozyme can efficiently accelerate solubilization and hydrolysis of waste activated sludge (WAS) for anerobic digestion. However, the effect of lysozyme was easily to be inhibited by metal ions in WAS. The impact of magnesium ions (Mg2+) on lysozyme catalyze WAS disintegration was investigated in this study. The effect of lysozyme on WAS hydrolysis could be hindered by Mg2+. Relatively high concentrations (>50 mg/L) of Mg2+ in sludge significantly reduced the release of soluble polysaccharides and proteins from WAS, while sulfate ions or chloride ions caused no such effect. Proteins were difficult to be extracted from extracellular polymeric substances (EPS) of WAS in the presence of Mg2+ (>10 mg/L) due to the divalent cation bridging (DCB) behavior, while the extraction of polysaccharides was not significantly affected. The polysaccharides and proteins in the inner EPS layer were transferred to the outer layer during the lysozyme treatment, and total quantities of both components maintained constantly. At least 23.1% lysozymes were trapped in the liquid phase of 100 mg Mg2+/L in the first hour. Mg2+ could significantly affect the transfer of lysozyme from liquid phase to the inner layer of sludge. Mg2+ neutralized the negative surface charge of the sludge particles, which hindered the absorption of positively charged lysozyme molecules by sludge flocs from the liquid phase. The proteins of TB-EPS had higher ratios of α-helixes and tighter structures than those in LB-EPS, which could impede the lysozyme transfer to the cell wall.

Ebselen’s Potential to Inhibit Planktonic and Biofilm Growth of Neisseria mucosa

Background: Antibiotic resistance of various bacterial communities remains a global burden in the healthcare industry. Biofilm formation is one of the resistance mechanisms acquired by bacterial communities in order to reverse the action of antibiotics. There is an urgent need for the discovery of novel antimicrobials and novel approaches to tackle this problem. However, it is very expensive and challenging to develop new antibiotics. Drug repurposing is an efficient strategy which reduces time and cost associated with drug discovery. Objective: In the current study, anti-microbial and antibiofilm potential of an organoselenium clinical molecule Ebselen against Neisseria mucosa has been elucidated. Methods: Ebselen Antibacterial studies include Minimum Inhibitory Concentration (MIC), growthkill, Colony Forming Unit (CFU) assays and intracellular Reactive Oxygen Species (ROS) accumulation studies. Antibiofilm studies included inhibition, eradication and cell surface hydrophobicity assays, quantification of Extracellular Polymeric Substance (EPS) and eDNA and for anti-quorum sensing activity, protease and urease enzyme activities were elucidated. Results: Ebselen showed efficient bactericidal activity as indicated by its low MIC values, bacterial growth inhibition over time and its ability to prevent clonal propagation in this bacterium. Increased accumulation of ROS in Ebselen treated cells indicates radical mediated induction of bacterial death. Interestingly, Ebselen inhibited and distorted matured biofilms by degrading the eDNA component of the EPS layer. Ebselen also attenuated quorum-sensing pathway as indicated by decreased urease and protease enzyme activities. Conclusion: Taken together, these results paved the way to repurpose Ebselen as a potential drug target to curb Neisseria mucosa infections.

Adsorptive removal of gallium from aqueous solution onto biogenic elemental tellurium nanoparticles

This study investigated the adsorption of gallium onto chemical and biogenic elemental tellurium nanoparticles. Biogenic elemental tellurium nanoparticles (BioTeNPs) were found to be a good adsorbent for the removal and recovery of gallium from aqueous solution with an adsorption capacity of 74 mg of Ga3+ per g BioTeNPs. The adsorption mechanism followed pseudo second order kinetics (R2 = 0.999) and the experimental data fitted the monolayer adsorption theory-based Langmuir model. BioTeNPs had a size of 5.30–86.1 nm, a negative zeta potential (–32 mV) and were coated with a layer of extracellular polymeric substances (EPS). Further, a high desorption efficiency of 99% from Ga3+ adsorbed onto the BioTeNPs was achieved using oxalic acid (0.1 M) as eluent. This study proposes a novel removal and recovery method for Ga3+ by adsorption on BioTeNPs produced in bioreactors treating tellurium oxyanion rich wastewaters.