Effect Of Extracellular Polymeric Substances Research Articles

New insights into uranium biomineralization mediated by Pseudomonas sp. WG2-6 in the presence of organic phosphorus: Promoting effect of extracellular polymeric substance and formation of U-P nanominerals

Microbial biomineralization significantly affects the uranium (U) behavior in the environment. However, the mechanism of microbial biomineralization of U is still not fully understood. In this study, a dominant bacterium (Pseudomonas sp. WG2–6) was isolated from U tail mining area. Abiotic precipitation tests demonstrated that U biomineralization was entirely attributed to the mediation of Pseudomonas sp. WG2–6 when the concentration ratio of exogenous β-glycerophosphate (SGP) to U was 10:1. Pseudomonas sp. WG2–6 exhibited strong immobilization ability towards U (97.59 %) according to batch experiments, and acylamide, carbonyls, and phosphate groups were the main functional groups that interacted with U. Besides, U mainly existed in the form of amorphous U-P complexes after biomineralization by Pseudomonas WG2–6, which could be converted into crystalline nano-minerals H2(UO2)2(PO4)2·8H2O in the presence of SGP. In particular, the formation and structural composition changes of extracellular polymeric substance (EPS) as well as the decrease in U4f binding energy were observed during the U biomineralization process of Pseudomonas sp. WG2–6 in the presence of SGP, indicating that EPS provided the nucleation site for the formation of stable biomineralized products. This work provides new insight into the mechanism of U microbial biomineralization and a theoretical basis for the remediation of U contaminated environments through microbial biomineralization.

The role elucidating of EPS in thermal hydrolysis and nitrogen conversion of sewage sludge during hydrothermal carbonization process, and its effect on hydrochar's properties

Hydrothermal carbonization (HTC) was conducted to observe the effect of extracellular polymeric substances (EPS) structure on the nitrogen migration mechanism during the HTC process. The denitrification efficiency of activated sewage sludge (ASS) decreases with an increase in EPS stripping intensity. Loosely and tightly bound extracellular polymers diminish the denitrification effectiveness by inhibiting the hydrolysis of nitrogen-containing organic compounds and protecting the cell structure, respectively. Intracellular nucleic acids and proteins generate stable N-containing species, such as heterocyclic-N and quaternary-N, which are unfavorable for deep denitrification. In general, nitrogen removal is more effective outside the cell than inside. Deep destruction of EPS eliminated a considerable number of N-containing components, and the N/C value of hydrochar at 180 °C without cell membrane protection was 0.06, which dropped to half that of ASS (0.11). This study revealed the influence of EPS structure on nitrogen migration in hydrothermal environment and provided significant insights for the preparation of clean solid fuels.

The effect of extracellular polymeric substances on the distribution and transmission of antibiotic resistance genes treating antibiotic wastewater via microbial electrolysis cells

Microbial electrolysis cells (MEC) have emerged as a prominent technology for the treatment of antibiotics-containing wastewater in recent years. However, there remains a dearth of comprehensive exploration regarding the influence of extracellular polymers substances (EPS) on the distribution and transmission of antibiotic resistance genes (ARGs) in MEC. In this study, we quantified the distribution of ARGs in MEC by Fluorescence quantitative polymerase chain reaction and explored with emphasis on impact of EPS component on ARGs transmission at under different concentrations of roxithromycin. Results showed that the absolute abundance of ARGs in the electrode biofilm was 1–2 orders of magnitude higher than that in the anolyte. Specifically, EPS-associated ARGs accounted for 2.31%–11.18% of ARGs in electrode biofilm. The presence of elevated roxithromycin concentration led to electroactive microorganisms (Geobacter and Geothrix) as potential hosts of ARGs. In addition, both protein and polysaccharide content in the electrode biofilm increased with increasing roxithromycin concentration and showed positive correlations with EPS-associated ARGs. Fluorescence quenching experiments further elucidated that tryptophan and tyrosine residues in EPS could bind to ARGs effectively, contributing the hindering the ARGs transmission between hosts. Therefore, increased EPS content within electrode biofilm could reduce the concentration of ARGs present in anolyte while also influencing ARGs distribution throughout MEC. This study provides valuable insights into the distribution of ARGs in MEC systems and the role of EPS in regulating ARGs migration.

Deciphering retention effect of extracellular polymeric substances to typical heavy metals and their interaction with key inner enzymes of Candidatus Kuenenia

This study employed spectroscopy, metagenomics, and molecular simulation to investigate the inhibitory effects of Cd(II) and Cu(II) on the anammox system, examining both intracellular and extracellular effects. At concentrations of 5 mg/L, Cd(II) and Cu(II) significantly reduced nitrogen removal efficiency by 41.46 % and 62.03 %, respectively. Additionally, elevated metal concentrations were correlated with decreased extracellular polymeric substances (EPS), thereby reducing their capacity to absorb heavy metals, particularly Cu(II), which decreased from 76.47 % to 14.67 %. Spectral analysis revealed alterations in the secondary structures of EPS induced by Cd(II) and Cu(II), decreasing the ratio of extracellular protein α-helix to (β-sheet + random coil), which resulted in looser extracellular protein configurations. The results of the metagenomics study showed that the abundance of Candidatus Kuenenia and its genes encoding nitrogen removal-related enzymes was reduced. The abundance of hzs-γ was reduced by 35.09 % at a concentration of 5 mg/L Cu(II). Conversely, genes associated with metal efflux enzymes, like czcR, increased by 54.86 % at 2 mg/L Cd(II). Molecular docking revealed robust bindings of Cd(II) to HZS-α (−342.299 ± 218.165 kJ/mol) and Cu(II) to HZS-γ (−880.934 ± 55.526 kJ/mol). This study elucidated the inhibitory mechanisms of Cd(II) and Cu(II) on the anammox system, providing insights into the resistance of anammox bacteria to heavy metals.

The effect of extracellular polymeric substances on MICP solidifying rare earth slags and stabilizing Th and U.

Microbially induced carbonate precipitation (MICP) has been used to cure rare earth slags (RES) containing radionuclides (e.g. Th and U) and heavy metals with favorable results. However, the role of microbial extracellular polymeric substances (EPS) in MICP curing RES remains unclear. In this study, the EPS of Lysinibacillus sphaericus K-1 was extracted for the experiments of adsorption, inducing calcium carbonate (CaCO3) precipitation and curing of RES. The role of EPS in in MICP curing RES and stabilizing radionuclides and heavy metals was analyzed by evaluating the concentration and morphological distribution of radionuclides and heavy metals, and the compressive strength of the cured body. The results indicate that the adsorption efficiencies of EPS for Th (IV), U (VI), Cu2+, Pb2+, Zn2+, and Cd2+ were 44.83%, 45.83%, 53.7%, 61.3%, 42.1%, and 77.85%, respectively. The addition of EPS solution resulted in the formation of nanoscale spherical particles on the microorganism surface, which could act as an accumulating skeleton to facilitate the formation of CaCO3. After adding 20 mL of EPS solution during the curing process (Treat group), the maximum unconfined compressive strength (UCS) of the cured body reached 1.922 MPa, which was 12.13% higher than the CK group. The contents of exchangeable Th (IV) and U (VI) in the cured bodies of the Treat group decreased by 3.35% and 4.93%, respectively, compared with the CK group. Therefore, EPS enhances the effect of MICP curing RES and reduces the potential environmental problems that may be caused by radionuclides and heavy metals during the long-term sequestration of RES.

Effect of extracellular polymeric substances on the colony size and morphological changes of Microcystis.

Surface blooms of colony-forming Microcystis are increasingly occurring in aquatic ecosystems on a global scale. Recent studies have found that the Microcystis colonial morphology is a crucial factor in the occurrence, persistence, and dominance of Microcystis blooms, yet the mechanism driving its morphological dynamics has remained unknown. This study conducted a laboratory experiment to test the effect of extracellular polymeric substances on the morphological dynamics of Microcystis. Ultrasound was used to disaggregate colonies, isolating the cells and of the Microcystis suspension. The single cells were then re-cultured under three homologous EPS concentrations: group CK, group Low, and group High. The size, morphology, and EPS [including tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS), bound polysaccharides (B-polysaccharides), and bound proteins (B-proteins)] changes of colonies were closely monitored over a period of 2 months. It was observed that colonies were rapidly formed in group CK, with median colony size (D50) reaching 183 µm on day 12. The proportion of colonies with a size of 150-500 µm increased from 1% to more than 50%. Colony formation was also observed in both groups Low and High, but their D50 increased at a slower rate and remained around 130 µm after day 17. Colonies with a size of 50-150 µm account for more than 50%. Groups CK and Low successively recovered the initial Microcystis morphology, which is a ring structure formed of several small colonies with a D50 of 130 µm. During the recovery of the colony morphology, the EPS per cell increased and then decreased, with TB-EPS and B-polysaccharides constituting the primary components. The results suggest that colony formation transitioned from adhesion driven to being division driven over time. It is suggested that the homologous EPS released into the ambient environment due to the disaggregation of the colony is a chemical cue that can affect the formation of a colony. This plays an important but largely ignored role in the dynamics of Microcystis and surface blooms.

Magnetic silk fibroin nanospheres loaded with amphiphilic polypeptides and antibiotics for biofilm eradication.

The eradication of established biofilms is a highly challenging task, due to the protective barrier effect of extracellular polymeric substances (EPS) and the presence of persister cells. Both increased drug permeability and elimination of persister cells are essential for the eradication of biofilms. Here, magnetic silk fibroin nanospheres loaded with antibiotics and host defense peptide (HDP) mimics (MPSN/S@P) were developed to demonstrate a new strategy for biofilm eradication. As an HDP mimic, an amphiphilic polypeptide containing 90% L-lysine and 10% L-valine (Lys90Val10) was selected for loading onto magnetic silk fibroin nanospheres via electrostatic interactions. Lys90Val10 exhibited excellent antibacterial activities against both planktonic and persister cells of Staphylococcus aureus (S. aureus). As a representative of the hydrophobic drug, spiramycin (SPM) was conveniently embedded into the β-sheet domain during the self-assembly process of silk fibroin. The sustained release of SPM during biofilm eradication enhanced the antibacterial efficacy of MPSN/S@P. The antibacterial test demonstrated that the extract from the MPSN/S@P suspension can kill both planktonic and persister cells of S. aureus, as well as inhibiting biofilm formation. Importantly, with the assistance of magnetic guidance and photothermal effects derived from Fe3O4 nanoparticles (Fe3O4 NPs), over 92% of bacteria in the biofilm were killed by MPSN/S@P, indicating the successful eradication of mature biofilms. The simple preparation method, integration of photothermal and magnetic responsiveness, and persister cell killing functions of MPSN/S@P provide an accessible strategy and illustrative paradigm for efficient biofilm eradication.

Influence of extracellular polymeric substances on arsenic bioaccumulation and biotransformation in biofilms

It is well recognized that biofilms can biosorb and biotransform heavy metals in aquatic environments. However, the effects of extracellular polymeric substance (EPS) on inorganic arsenic (As) bioaccumulation and biotransformation in biofilms are still unrevealed and need to be investigated. In order to explore the above scientific issues, the As accumulation and speciation in EPS-containing or EPS-free biofilms and growth medium under As(V)/As(III) exposure conditions were measured. After the removal of EPS, the amount of As uptake (Asup) and As adsorption (Asad) in biofilms were significantly reduced, no matter whether exposed to As(V) or As(III). FTIR analysis further suggested that the interaction between these functional groups with As was limited after the removal of EPS. In the EPS-containing biofilms, the Asad was mainly As(V) with low toxicity. However, after the removal of EPS, the Asad was mainly As(III) with high fluidity, and no methylated As was found. Moreover, the removal of EPS inhibited As(III) oxidation and methylation by biofilms, resulting in the decrease of As(V) and methylated As in the growth medium. The findings of this study emphasized the essential impact of EPS on the biosorption and biotransformation of As in biofilms. This study provides a unique understanding of the role of biofilms in As biogeochemical cycle, and water quality purification function in water environments.

Insights into the effect of extracellular polymeric substances on anaerobic digestion foaming: From perspectives of composition, hydrophobicity, and functional groups

Foaming is a common issue limiting the efficient and stable operation of food waste anaerobic digesters, and extracellular polymeric substances (EPSs) have been identified as key contributors to the foaming process. To further elucidate the influence mechanism of EPSs on foaming, batch tests were performed under various conditions, including different total solid contents, substrate-to-inoculum ratios, stirring frequencies, and substrate compositions, to induce the production of EPSs with different characteristics. The contributions of EPS composition and hydrophilic and hydrophobic characteristics to the foam formation and foam stabilization processes were analyzed. Hydrophobic EPSs were the main contributor to foam formation (with a correlation coefficient [r] of 0.56 and p < 0.01), while hydrophilic EPSs increased the contribution of hydrophobic EPS by increasing sludge viscosity (r = 0.65, p < 0.01). For foam stabilization, hydrophobic proteins (r = 0.61, p < 0.01) and humic substances (HU) (r = 0.77, p < 0.01) were the main contributors. The former increased foam stability by reducing surface tension (r = 0.63, p < 0.01), while the latter contained functional groups such as amino, hydroxyl, and ether that might enhance the viscosity of the apparent molecular layer of the liquid film, thereby inhibiting foam breakup. Considering that the hydrophobicity of proteins was significantly correlated with the ratio of α-helix to (β-sheet + random coil) in their secondary structure (r = 0.80, p < 0.01), and that HU contributed to foam stabilization owing to the hydration of functional groups, disrupting the secondary structure of proteins and the hydration of HU might contribute to defoaming.

Pitting corrosion behavior and mechanism of 316L stainless steel induced by marine fungal extracellular polymeric substances

In this study, effect of extracellular polymeric substances (EPS) secreted by fungus Aspergillus terreus on the pitting corrosion of 316L stainless steels (SS) was deeply investigated by electrochemical measurements and surface analysis. Results demonstrated that adsorption of EPS can change surface wettability of 316L SS leading to a much more hydrophilic steel–water interface. EPS not only accelerates uniform corrosion but enhances pitting corrosion of 316L SS. EPS can promote the formation of metastable pitting corrosion and the subsequent growth of corrosion pits. The density of corrosion pits (>2 µm) reach (5.6 ± 0.5)× 103 pits/cm2 when EPS is 400 mg/L.

Effect of extracellular polymeric substances on Dolichospermum aggregation during temperature rise

Effect of extracellular polymeric substances on Dolichospermum aggregation during temperature rise

Effect of EPS production on the performance of membrane-based biofilm reactors

This study explored the effect of extracellular polymeric substance (EPS) production on the performance of membrane-based biofilm reactors. Changing EPS production was induced by eliminating one of the main EPS polysaccharides, i.e., Pel. The studies were carried out using a pure culture of either Pseudomonas aeruginosa or an isogenic P. aeruginosa mutant that was unable to produce the Pel polysaccharide. The biofilm cell density for both strains was compared to confirm the Pel deletion mutant decreased overall EPS production in a bioreactor system. When the Pel-deficient mutant was grown as a biofilm, its cell density, i.e., ratio of cells/(cells+EPS), was 74 % higher than the wild type, showing EPS production was reduced by eliminating pel production. The growth kinetics were determined for both strains. The Pel-deficient mutant had a maximum specific growth rate (μ^) that was 14% higher than the wild type. Next, the effects of EPS reduction on reactor performance were assessed for a membrane aerated biofilm reactor (MABR) and a membrane bioreactor (MBR). For the MABR, the organic removal with the Pel-deficient mutant was around 8% higher than for the wild type. For the MBR, the time to reach the fouling threshold was 65 % greater for the Pel-deficient mutant than for the wild type. These results suggest that amount of EPS production can have significant effects on bacterial growth kinetics and bacterial cell density, which in turn can affect the performance of the membrane-based biofilm reactors. In both cases, lower EPS production correlated with more efficient treatment processes.

The mechanism of extracellular polymeric substances in the formation of activated sludge flocs

In this study, activated sludge (AS) presented high aggregation ability of 56.9% to form flocs. To elucidate the effects of extracellular polymeric substances (EPS) on the AS flocs formation, four EPS fractions, including soluble EPS (S-EPS), loosely bound EPS (LB-EPS), ionic tightly bound EPS (ionic TB-EPS) and hydrophobic tightly bound EPS (hydrophobic TB-EPS), were extracted and characterized. The ionic TB-EPS were the largest fraction, accounting for 51.3% of the total EPS. By extracting EPS fractions, it was shown that ionic TB-EPS followed by hydrophobic TB-EPS played positive contribution to the formation of AS flocs, while both S-EPS and LB-EPS had negative effects. Furthermore, chemical reagents (Urea, SDS and EDTA) assays, zeta potential and spectroscopic assays were conducted to explore the role of hydrogen bonds, electrostatic interaction and hydrophobic interaction in the formation of AS flocs. The result showed that ionic TB-EPS contained sufficient cation-binding sites, such as -OH and CO-O- groups, and promoted AS aggregation through ion bridging. Hydrophobic TB-EPS contained hydrophobic groups and promoted AS aggregation through hydrophobic action. A high proportion of uronic acids resulted in high surface negative charge, which might be the reason that LB-EPS and S-EPS inhibited AS aggregation through electrostatic repulsion. From the perspective of molecule structure, the proteins in ionic TB-EPS had a loose structure, which fully exposed the inner cation-binding sites. This might be the critical reason why ion bridging acted as the main force for the formation of AS flocs. This study provided a new sight for the extraction of EPS fractions and expanded the understanding of EPS in the formation of AS flocs.

Synergistic effect of extracellular polymeric substances and carbon layer on electron utilization of Fe@C during anaerobic treatment of refractory wastewater

Nano zero-valent iron (NZVI) has been widely used to improve refractory wastewater treatment. However, the rapid dissolution of NZVI causes a waste of resources and an unstable bioaugmentation. Herein, to verify the essential role of slow release of NZVI on biological systems, a core-shell structured Fe@C composite was developed to demonstrate the long-term feasibility of Fe@C for enhancing azo dye biodegradation in comparison to a mixture of NZVI and carbon powder (Fe+C). The 150 days of long-term reactor operation showed that, although both Fe@C and Fe+C enhanced azo dye degradation, the former achieved a better performance than the latter. The strengthening effect of Fe@C was also more durable and stable than Fe+C. It may be due to the fact that the carbon layer of Fe@C could interact with extracellular polymeric substances (EPS) through physical adsorption and chemical bonding to form a stable buffer to regulate NZVI dissolution. The buffer layer could not only regulate the attack of H+ on NZVI to reduce its dissolution rate but also complex released Fe2+ and neutralize OH− to alleviate the passivation layer formed on the NZVI surface. Moreover, microbial community analysis indicated that both Fe@C and Fe+C increased the abundance of fermentative bacteria (e.g., Bacteroidetes_vadinHA17, Propionicicella) and methanogens (e.g., Methanobacterium), but only Fe@C promoted the growth of azo dye degraders (e.g., Clostridium, Geobacter). Metatranscriptomic analysis further revealed that only Fe@C could substantially stimulate the expression of azoreductase and redox mediator (e.g., riboflavin, ubiquinone) biosynthesis involved in the extracellular degradation of azo dye. This work provides novel insights into the bioaugmentation of Fe@C for refractory wastewater treatment.

Role of extracellular polymeric substances in the aggregation and biological response of micro(nano)plastics with different functional groups and sizes

In this work, the effects of extracellular polymeric substances (EPS) on the aggregation and biological responses of different micro(nano)plastics (MNPs, <1000 µm) were investigated. EPS increased the colloidal stability of PS MPs in NaCl or CaCl2. For the three PS NPs (PS-NH2, PS-COOH, and PS-naked), EPS also enhanced their colloidal stabilities in the presence of NaCl. However, the effect of CaCl2 on the colloidal stabilities of PS NPs in the presence of EPS depended on their surface functional groups. In CaCl2, both Derjaguin-Landau-Verwey-Overbeek theory and molecular bridging explained the interaction between MNPs (both NPs and MPs) and EPS. Laser Direct Infrared and scanning electron microscope imaging showed that opalescent EPS corona formed on PS MPs via intermolecular-bridging by Ca2+, and the critical coagulation concentrations (70 mM in NaCl, 1.5 mM in CaCl2) in EPS were much lower than that for PS NPs (1000 mM for NaCl; 65 mM for CaCl2). PS-NH2 NPs showed the highest increase in the growth of bacteria (Bacillus subtilis), followed by PS MPs and PS-naked NPs, while PS-COOH NPs had no significant effect. Biological response of PS NPs was unaffected by EPS, while EPS further enhanced the positive effects of PS MPs on bacterial growth.

Effects of extracellular polymeric substances on the aggregation of Aphanizomenon flos-aquae under increasing temperature.

Aphanizomenon flos-aquae (A. flos-aquae) blooms are serious environmental and ecological problems. Extracellular polymeric substances (EPSs) are among the most important indicators for the growth and aggregation of A. flos-aquae. In this study, the secretion of the EPS matrix under temperature rise (7–37°C) was investigated and the role of this matrix in A. flos-aquae aggregation was quantified. First, when the temperature increased, the aggregation ratio increased from 41.85 to 91.04%. Meanwhile, we found that when soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs), and tightly bound EPSs (TB-EPSs) were removed successively, the aggregation ratio decreased from 69.29 to 67.45%, 61.47%, and 41.14%, respectively. Second, the content of polysaccharides in the EPS matrix was higher than the content of proteins under temperature change. The polysaccharide in TB-EPSs was closely related to the aggregation ability of A. flos-aquae (P < 0.01). Third, PARAFAC analysis detected two humic-like substances and one protein-like substance in EPSs. Furthermore, Fourier transforms infrared spectroscopy (FTIR) showed that with increasing temperature, the polysaccharide-related functional groups increased, and the absolute value of the zeta potential decreased. In conclusion, these results indicated that a large number of polysaccharides in TB-EPSs were secreted under increasing temperature, and the polysaccharide-related functional groups increased correspondingly, which reduced the electrostatic repulsion between algal cells, leading to the destruction of the stability of the dispersion system, and then the occurrence of aggregation. This helps us to understand the process of filamentous cyanobacterial aggregation in lakes.

A novel treatment for amelioration of sludge dewaterability using green starch-grafted flocculant and realized mechanism

To clarify the effect of extracellular polymeric substances (EPS), protein and hydrophilic substances on the dewatering efficiency during starch-grafted flocculant (SBF) conditioning, a green and cost-saving SBF was synthesized. Dewatering performance of sludge, secondary structure of protein, change of hydrophobic substances and removal of bound water were investigated. Results showed that after SBF conditioning, filter cake moisture content and specific resistance to filtration decreased from 75.63 % and 2.31 × 1012 m/kg to 66.76 % and 5.68 × 1011 m/kg, respectively. SBF neutralized the negative charges from the sludge system, promoting the increase of sludge flocs size and EPS decomposition, decreasing the compressibility of sludge and constructing a channel for water release. Moreover, the secondary structures of protein were changed through the interaction between SBF and the oxygen-containing functional groups in EPS, resulting in the reduction of hydrophilic substances and the increase of hydrophobic substances, which increased the hydrophobicity of molecules and thus improved the dewatering capacity of sludge. Meanwhile, the construction of sludge skeleton channels, charge neutralization, hydrophobic association effect were the primary mechanisms of SBF conditioning sludge dewatering. Additionally, SBF has an excellent economy as a sludge conditioner. This paper provided a new ideal for starch-based flocculants for improving the dewatering capacity of sludge treatment.

Elucidating the role of extracellular polymeric substances (EPS) in dewaterability of fecal sludge from onsite sanitation systems, and changes during anaerobic storage.

As the importance of fecal sludge management (FSM) is increasingly being realized, the need for adequately designed and functioning fecal sludge (FS) treatment plants is also increasing. Research to fill this gap is only emerging and dewatering is a key challenge for developing sustainable treatment solutions. This study evaluated the effect of extracellular polymeric substances (EPS) on dewaterability of FS, and how EPS and dewaterability change during anaerobic storage (as a proxy for time in onsite containment). EPS was extracted from FS and activated sludge using Na2CO3 and sonication and added to sludge samples to determine the effect on dewaterability. The results confirmed that an increase in EPS had a direct impact of decreasing FS dewaterability (as capillary suction time). In this context, we evaluated FS degradation during anaerobic storage, the effect of anaerobic storage time on EPS, EPS fractions and particle size distribution, and the effect of variations in these factors on FS dewaterability. Variations in EPS, EPS fraction and particle size distribution during anaerobic storage were less than expected and average VS reduction of 20% was recorded over 7 weeks. Although anaerobic digestion was verified (biogas production), the results indicate that kinetics of degradation of FS is different from wastewater sludges. Comparatively, EPS fractions in FS were 70 – 75% lower and with higher fractions of humic-like substances than wastewater sludges. Although EPS significantly affects FS dewaterability, anaerobic storage time is not a predictor of dewaterability.

Impact of the Salt Concentration and Biophysical Cohesion on the Settling Behavior of Bentonites

The flocculation behavior of clay minerals in aquatic environments is an important process in estuarine and riverine dynamics, where strong gradients in salinity can locally occur. Various contradicting observations have been reported in the literature on the impact of salt concentration on the settling process of cohesive sediments. To address this issue in a systematic manner, we investigate the settling behavior of clay minerals as a function of the salt concentration of the ambient water. Specifically, we focus on montmorillonite as a prototype clay mineral with a high cation exchange capacity (CEC). To this end, we study suspensions of Wyoming bentonite (Volclay SPV) as a very important constituent for many constructional and industrial purposes. We perform an experimental campaign to study the settling behavior of moderately turbid montmorillonite concentrations in monovalent salt solutions with different salinities (sodium chloride) to represent different environments ranging from deionized to ocean water, respectively. The subsequent settling process was monitored by taking pictures by a camera in regular time intervals over a total observation time up to 48 h. In addition, a modified hydrometer analysis is conducted to determine the grain size distribution (in terms of an equivalent diameter) of the flocculated clay suspension in salt water. Despite the rather high cation exchange capacity of the investigated clay (CEC=88.1), our results show that the settling speed drastically increases within a range of 0.6–1.0 PSU and stays approximately constant for higher salinities. This critical salt concentration is defined here as the critical coagulation concentration (CCC) and lies well below the salinity of natural open water bodies. The hydrometer analysis revealed that 60% of the agglomerates exceed the equivalent grain size of 20 μm. Finally, the findings of this study are supplemented with experiments studying the effect of Extracellular Polymeric Substances (EPS) on the flocculation behavior of bentonite in salt water. Our results demonstrate that salinity is the original trigger for flocculation, whereas EPS allows for even larger floc size but it does not play a significant role for the settling processes of bentonite in estuarine environments.

Insight into nitrogen removal performance of anaerobic ammonia oxidation in two reactors: Comparison based on the aspects of extracellular polymeric substances and microbial community

Anaerobic ammonium oxidation (Anammox) is expected to play a promising role in treating low C/N ratio wastewater. In this study, nitrogen removal performance and the effects of extracellular polymeric substances (EPS) on anammox activity were investigated in two different reactors, followed by analysis of 16S rRNA high-throughput sequencing. A sequencing batch reactor (SBR) and an up-flow anammox sludge blanket reactor (UASB) operated for 133 days, with total nitrogen removal efficiencies of 82.09 ± 4.76% and 87.91 ± 2.59% in the phase 3, respectively. The EPS concentration in UASB was about 1.6 times higher than that in SBR. Also, in the batch tests, especially the anammox-EPS of UASB (AU-EPS) additions contributed to better nitrogen removal capability for anammox bacteria (AnAOB). The relative abundance of AnAOB in UASB was observed to reach 19.68% in the end, accounting for a relatively high degree in the whole community. In SBR, the effluent NH4+-N concentration increased when increasing the substrate concentration, followed by the decrease of the relative abundance of AnAOB. Thus, the different feeding strategies would lead to different granulation styles, further influencing the activity and stability of anammox system. This research aims to get a better understanding of the different mechanisms associated with AnAOB enrichment strategies.