Structure Of Extracellular Polymeric Substances Research Articles

Role of extracellular polymeric substances in anaerobic granular sludge: Assessing dewaterability during Fe(II)-peroxydisulfate conditioning and granulation processes

In this study, Fe(II) activated peroxydisulfate (PDS) conditioning and sludge granulation were conducted to investigate the dewaterability of anaerobic granular sludge (AGS). After Fe(II)-PDS conditioning, the dewaterability of three AGS from different sources was enhanced. The specific resistance to filtration (SRF) reduction rates were achieved (98.30% ± 0.19%, 99.51% ± 0.17% and 96.47% ± 1.25%, respectively) under the optimal Fe(II) and PDS additions; And the optimal reductions of capillary suction time (CST) were 93.49% ± 2.49%, 95.33% ± 0.02% and 88.04% ± 2.95%, respectively. The mechanism of improving AGS dewaterability by Fe(II)-PDS conditioning was proposed. The radical SO4⋅−/OH⋅ destroyed the structure of extracellular polymeric substances (EPS) layers and microbial cells, resulting in the bound water released from AGS. Thereafter, the generated Fe(III) facilitated the sludge re-flocculation and decreased the electrostatic repulsion. During a 132-day granulation, the CST value showed a positive correlation with protein (S-EPS), polysaccharide and zeta potential, and a negative correlation with protein (LB-EPS), protein (TB-EPS), particle size and VSS. Collectively, the protein was the primary component in AGS and showed a strong correlation with dewaterability. The variations of protein in TB-EPS during the conditioning and the granulation were consistent with the changes of sludge dewaterability.

Evaluation of the combined effect of sodium persulfate and thermal hydrolysis on sludge dewatering performance.

This innovative study makes use of a thermal hydrolysis process (THP) and the conditioner sodium persulfate (SPS) to improve the dewaterability of sewage sludge. The best-operating conditions were optimized using response surface methodology (RSM): 100mg/g of dry solids (DS) of SPS, 101min of reaction time of THP, and a temperature of 200°C. Distribution of extracellular polymeric substances (EPS), zeta potential, bound water, and solid characters were analyzed to reveal the mechanisms involved in the dewatering process. These results indicate that the sewage sludge after treatment (SPS combined with THP) had a superior dewaterability. The specific resistance to filtration (SRF) under the best conditions was 0.51 × 1011m/kg, decreasing by 91.65% compared to the raw sludge (RS) (6.11 × 1011m/kg). This mechanism could be explained as follows: (1) Aromaticity and hydrophobicity of sludge cake after SPS + THP treatment was increased; (2) sludge flocs were re-flocculated by charge neutralization, giving rise to a loose and porous structure; (3) the structure of extracellular polymeric substances and cells was destroyed, and the bound water was released. Overall, the conditioning by combination of SPS and THP is an effective mean to improve sewage sludge dewaterability. Graphical abstract.

A new method for removal of nitrogen in sewage sludge-derived hydrochar with hydrotalcite as the catalyst

The high content of nitrogen in hydrochar produced from hydrothermal carbonization (HTC) of sewage sludge (SS) leads to serious NOx pollution when the hydrochar is used as a solid fuel. Mg-Ga layered double hydroxides (LDHs), Mg-Al LDHs and their calcined samples (layered double oxides, LDO) were prepared. The LDHs and LDO all can notably promote the removal of nitrogen element, in which organic-N was transferred to NH4+-N to cause increasing pH value. Mg-Al LDO showed the highest efficiency for the removal of nitrogen among the catalysts. The thermal decomposition of the N-organic matter with acidic sites in catalyst was the key step to release NH3. The key role of basic sites in Mg-Al LDO was that it can effectively destroy the cell wall and extracellular polymeric substances structure. The lipid-like substance did not participate in the carbonization reaction, but they can be absorbed by the hydrochar. Partial SS floc directly transformed to hydrochar according to “solid-solid” reaction. The reaction pathways of remove nitrogen were proposed.

Inactivation of Pseudomonas aeruginosa Biofilms by 405-Nanometer-Light-Emitting Diode Illumination.

Biofilm formation by Pseudomonas aeruginosa contributes to its survival on surfaces and represents a major clinical threat because of the increased tolerance of biofilms to disinfecting agents. This study aimed to investigate the efficacy of 405-nm light-emitting diode (LED) illumination in eliminating P. aeruginosa biofilms formed on stainless steel coupons under different temperatures. Time-dependent killing assays using planktonic and biofilm cells were used to determine the antimicrobial and antibiofilm activities of LED illumination. We also evaluated the effects of LED illumination on the disinfectant susceptibility, biofilm structure, extracellular polymeric substance (EPS) structure and composition, and biofilm-related gene expression of P. aeruginosa biofilm cells. Results showed that the abundance of planktonic P. aeruginosa cells was reduced by 0.88, 0.53, and 0.85 log CFU/ml following LED treatment for 2 h compared with untreated controls at 4, 10, and 25°C, respectively. For cells in biofilms, significant reductions (1.73, 1.59, and 1.68 log CFU/cm2) were observed following LED illumination for 2 h at 4, 10, and 25°C, respectively. Moreover, illuminated P. aeruginosa biofilm cells were more sensitive to benzalkonium chloride or chlorhexidine than untreated cells. Scanning electron microscopy and confocal laser scanning microscopic observation indicated that both the biofilm structure and EPS structure were disrupted by LED illumination. Further, reverse transcription-quantitative PCR revealed that LED illumination downregulated the transcription of several genes associated with biofilm formation. These findings suggest that LED illumination has the potential to be developed as an alternative method for prevention and control of P. aeruginosa biofilm contamination.IMPORTANCEPseudomonas aeruginosa can form biofilms on medical implants, industrial equipment, and domestic surfaces, contributing to high morbidity and mortality rates. This study examined the antibiofilm activity of 405-nm light-emitting diode (LED) illumination against mature biofilms formed on stainless steel coupons. We found that the disinfectant susceptibility, biofilm structure, and extracellular polymeric substance structure and composition were disrupted by LED illumination. We then investigated the transcription of several critical P. aeruginosa biofilm-related genes and analyzed the effect of illumination temperature on the above characteristics. Our results confirmed that LED illumination could be developed into an effective and safe method to counter P. aeruginosa biofilm contamination. Further research will be focused on the efficacy and application of LED illumination for elimination of complicated biofilms in the environment.

Understanding the role of extracellular polymeric substances in the rheological properties of aerobic granular sludge

The gel-properties of aerobic granular sludge could sustain the mechanical strength and stability of granules during the operation of wastewater treatment. The contributing extracellular polymeric substances to the gel strength of aerobic granular sludge were verified from the perspective of rheological properties in this study. Moreover, the correlations between the molecular structure and gel properties of extracellular polymeric substances were established by analyzing rheological properties and spectrum results of extracellular polymeric substances extracted by various extraction methods. The results indicated that protein and polysaccharide were indispensable to maintain the cross-linking structure of extracellular polymeric substances. The gel strength of extracellular polymeric substances was positively correlated with the amount of α-helix of natural protein and intermolecular hydrogen bond between each component. The cation exchange resin method which retained the relatively higher ratio of α-helix of natural protein and intermolecular hydrogen bond could better preserve the gel properties of the original aerobic granular sludge. This study could provide a theoretical reference for the cultivation of aerobic granular sludge and the optimization of operating conditions of the reactor.

Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic, anoxic and oxic conditions

Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al3+ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al3+ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al3+. The highest removal efficiency of total phosphorus (TP) was achieved at an Al3+ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al3+ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al3+. At the Al3+ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al3+ concentrations ( 10 mg/L) weakened microbial activity. Higher Al3+ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO43−.

Effect of Ca2+ on the Nitrification Activity and the Flocculation and Sedimentation Performances of the Activated Sludge

Ca2+ is an important microbial growth factor that can affect the activity, flocculation, and sedimentation of activated sludge. In order to study the roles of Ca2+ in the activated sludge system, the activity changes of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were analyzed using the specific oxygen uptake rates (SOURAOB and SOURNOB). The changes in composition and structure of extracellular polymeric substances (EPS) were analyzed using Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation emission fluorescence spectroscopy (3D-EEM). The effects of Ca2+on the nitrification activity and microbial metabolites were investigated. The results showed that when the Ca2+concentration increased from 0.45 mmol·L-1 to 3 mmol·L-1, SOURAOB and SOURNOB increased from 6.3 mg·(g·h)-1 to 10.4 mg·(g·h)-1 and from 2.3 mg·(g·h)-1 to 3.7 mg·(g·h)-1, respectively. The EPS concentrations increased from 68 mg·g-1 to 93 mg·g-1, and the flocculation ability (FA) of the sludge was improved. When the Ca2+ concentration was higher than 3 mmol·L-1, SOURAOB and SOURNOBboth decreased. The FA was maintained at about 30%, and the particle size of the sludge continued to increase. Based on FTIR analysis, the main components of EPS were always amino, amide Ⅰ, and carboxyl with an increase in Ca2+ concentration. Based on EEM analysis, the composition of loosely-bound (LB)-EPS did not change, and humic acid substances appeared in the tightly-bound (TB)-EPS at low nitrification rates. Low concentrations of Ca2+ promoted nitrification activity and flocculation of the sludge. However, high concentrations of Ca2+ led to a decline in the sludge nitrification activity.

Dewatering performance of sewage sludge under pretreatment with modified corn-core powder

The water retained inside the sludge flocs is the bottleneck for the dehydration of sewage sludge, which hindered the following treatment. In this study, corn core powder was modified (MCCP) using sodium hydroxide (NaOH) and cationic surfactant cetyltrimethylammonium bromide (CTMAB) to break the structure of extracellular polymeric substances (EPS) and cell membrane for enhancing the dewaterability of sewage sludge. The dewatering performance, the properties of the treated sludge, the composition and distribution of EPS were investigated to discuss the dewatering mechanism of sludge. Adding 20% DS (mass of dry solids in sludge) of MCCP reduced the moisture content (MC) and the specific resistance of filtration (SRF) of the sludge by 40% and 55%, respectively. Then, correlation analyses were performed between dewatering indices of sludge and sludge properties. A multiple linear regression model was established which indicated the relationship between MC and the key factors reflecting sludge dewaterability, demonstrating that larger particle size of sludge flocs and more total dissolved solids in filtrate may be propitious to reduce content of bound water in sludge.

Anode potentials regulate Geobacter biofilms: New insights from the composition and spatial structure of extracellular polymeric substances

The extracellular electron transfer (EET) efficiency in bioelectrochemical systems has been proven to be dependent on anode potentials. To explore the underlying mechanism, previous studies have mainly focused on EET conduit and bacterial biomass but rarely concerned with the role of extracellular polymeric substances (EPS) surrounding electroactive cells. In this study, the response of Geobacter biofilms to anode potentials was investigated with a special emphasis on the mechanistic role of EPS. The electrochemical activities and cell viabilities of Geobacter soli biofilms were simultaneously attenuated at 0.4 and 0.6 V compared to −0.2 and 0 V. It was found that the biofilms (especially the biofilm region closer to electrode surface) grown at −0.2 and 0 V produced relatively more extracellular redox-active proteins and less extracellular polysaccharides, which conferred higher electron accepting/donating capacities to EPS and consequently facilitated EET. Meanwhile, electrically nonconductive extracellular polysaccharide-dominated interior layers were formed in the biofilms grown at 0.4 and 0.6 V, which limited direct EET but might serve as physical barriers for protecting cells in these biofilms from the increasing stress by poised electrodes. These results demonstrated that the production of EPS under different anode potentials might be finely regulated by cells to keep balance between EET efficiency and cell-protection. This study provides a new insight to investigate the Geobacter biofilms coping with various environments, and is useful for optimizing electrochemical activity of anode biofilms.

Effect of NaCl Salinity on Extracellular Polymeric Substances and Bioflocculation of Anoxic Sludge in A2/O Process

In order to improve the biological removal efficiency of nitrogen and phosphorus and bioflocculation performance of salt-containing wastewater, the effect of NaCl salinity on the efficiency of denitrification and phosphorus removal in the anoxic zone of an A2/O process was investigated. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition and structure of extracellular polymeric substances (EPS) in activated sludge of the anoxic zone, to discern the effect of salinity on bioflocculation. Results showed that when NaCl salinity was 0-5 g·L-1, flocculation ability (FA) in A2/O anoxic zone was about 44% and the sludge particle size was 45.5 μm. EPS content increased from 52.3 mg·L-1 to 62 mg·L-1 and protein (PN)/polysaccharide (PS) remained at 2.1. When NaCl salinity increased from 10 g·L-1 to 40 g·L-1, bioflocculation of sludge significantly decreased. FA decreased from 40% to 22% and sludge particle size decreased from 43.7 μm to 32.1 μm. EPS content increased from 76.5 mg·L-1 to 101.0 mg·L-1 and PN/PS decreased from 1.5 to 1.3. Based on FTIR analysis, with increase in salinity, the main components of EPS were always amino, amideⅠ, and carboxyl. Based on XPS analysis, increasing salinity led to charge transfer of some groups (such as C, O, and N groups) during the interaction between EPS and Na+, but its form did not change.

Fusimonas intestini gen. nov., sp. nov., a novel intestinal bacterium of the family Lachnospiraceae associated with diabetes in mice

Our previous study shows that an anaerobic intestinal bacterium strain AJ110941P contributes to type 2 diabetes development in mice. Here we phylogenetically and physiologically characterized this unique mouse gut bacterium. The 16S rRNA gene analysis revealed that the strain belongs to the family Lachnospiraceae but shows low sequence similarities ( < 92.5%) to valid species, and rather formed a distinct cluster with uncultured mouse gut bacteria clones. In metagenomic database survey, the 16S sequence of AJ110941P also matched with mouse gut-derived datasets (56% of total datasets) with > 99% similarity, suggesting that AJ110941P-related bacteria mainly reside in mouse digestive tracts. Strain AJ110941P shared common physiological traits (e.g., Gram-positive, anaerobic, mesophilic, and fermentative growth with carbohydrates) with relative species of the Lachnospiraceae. Notably, the biofilm-forming capacity was found in both AJ110941P and relative species. However, AJ110941P possessed far more strong ability to produce biofilm than relative species and formed unique structure of extracellular polymeric substances. Furthermore, AJ110941P cells are markedly long fusiform-shaped rods (9.0–62.5 µm) with multiple flagella that have never been observed in any other Lachnospiraceae members. Based on the phenotypic and phylogenetic features, we propose a new genus and species, Fusimonas intestini gen. nov., sp. nov. for strain AJ110941P (FERM BP-11443).

Physical properties and Extracellular Polymeric Substances pattern of aerobic granular sludge treating hypersaline wastewater

The modification of the physical properties of aerobic granular sludge treating fish-canning wastewater is discussed in this paper. The structure and composition of the Extracellular Polymeric Substances (EPSs) were analyzed at different salinity levels and related to granules stability. Results outlined that the total EPSs content increased with salinity, despite the EPSs increment was not proportional to the salt concentration. Moreover, the EPSs structure was significantly modified by salinity, leading to a gradual increase of the not-bound EPSs fraction, which was close to the 50% of the total EPSs content at 75gNaClL−1. The increasing salt concentration modified also the EPSs composition, causing the gradual reduction of protein content resulting in a decrease of granule hydrophobicity. The results pointed out that the granules stability significantly reduced above 50gNaClL−1, suggesting the existence of a salinity threshold above which granules stability is compromised.

Effects of d-amino acids and norspermidine on the disassembly of large, old-aged microbial aggregates

The increasing threat of microbial aggregates in many fields highlights the need to develop methods to promote their disassembly. This study investigated the coupled effects of d-tyrosine (d-Tyr) and norspermidine on the disassembly of a type of old-aged (more than 6 months), large (about 900 μm) microbial aggregate formed by mixed culture. Results showed that d-Tyr and norspermidine acting together effectively triggered the disassembly of microbial aggregates, with disassembly ratio enhanced by 30–164% compared to the control at the concentration of 50–500 μM of d-Tyr and norspermidine. d-Tyr and norspermidine reduced the content of extracellular protein and polysaccharide in microbial aggregates and altered the matrix structure of extracellular polymeric substances as confirmed by a confocal laser scanning microscope. The microbial aggregates lost stability after treatment with d-Tyr and norspermidine as could be seen from the increase in surface negative charge and decrease in cell hydrophobicity. Fourier transform infrared spectroscopy analysis revealed that norspermidine could directly interact with polysaccharide and caused the disappearance of an IR band at 1152 cm−1 that may be correlated with the functional group C–O–C. Overall, the combined application of d-amino acids and norspermidine offers an effective approach to disassemble large and resistant microbial aggregates.

Effect of Cathodic Biofilm on the Performance of Air-Cathode Single Chamber Microbial Fuel Cells

Biofilm formation is inevitable in a bioelectrochemical system in which microorganisms act as a sole biocatalyst. Cathodic biofilm (CBF) works as a double-edged sword in the performance of the air-cathode microbial fuel cells (MFCs). Proton and oxygen crossover through the CBF are limited by the robust structure of extracellular polymeric substances, composition of available constituents and environmental condition from which the biofilm is formed. The MFC performance in terms of power, current and coulombic efficiency is influenced by the nature and origin of CBF. Development of CBF from different ecological environment while keeping the same anode inoculums, contributes additional charge transfer resistance to the total internal resistance, with increase in coulombic efficiency at the expense of power reduction. This study demonstrates that MFC operation conditions need to be optimized on the choice of initial inoculum medium that leads to the biofilm formation on the air cathode.

Combined use of confocal laser scanning microscopy (CLSM) and Raman microscopy (RM): Investigations on EPS – Matrix

Confocal laser scanning microscopy (CLSM) was applied in combination with Raman microscopy (RM) for the characterization of heterotrophic biofilms. Compared to CLSM, RM allows for a deeper insight into the chemical structure of extracellular polymeric substances (EPS) of the biofilm matrix. A low load of glucose (2 g m −2 d −1) was applied as substrate to ensure small growth rates of the heterotrophic biofilm. To investigate the influence of hydrodynamic conditions on the chemical composition of EPS, a three funnel flow system was used, wherein biofilms were grown at Reynolds numbers of 1000, 2500 and 4000, respectively. 31 and 92 days after inoculation with activated sludge supernatant RM was applied as an additional technique to standard CLSM measurements for a more detailed analysis of the biofilm matrix. Polysaccharide-related Raman bands are in good agreement with the lectin binding analysis from CLSM. For the older biofilm, lectin binding analysis showed no change in the composition of EPS, whereas Raman spectra pointed out a change of EPS composition from predominantly polysaccharides to predominantly (glyco) proteins. For the applied substrate condition no significant influence of the Reynolds number on the chemical properties was observed.