Extracellular Polymeric Substances Extraction Research Articles

The feasibility and applicability of sequential extraction of high value-added biogenic materials from sewage sludge

ABSTRACT The sequential extraction routes of biogenic materials from sewage sludge (SS) were investigated. Physical methods (ultrasound, heating) and chemical methods (sodium hydroxide, sodium carbonate) were used to extract extracellular polymeric substances (EPS) and alginate-like extracellular polymers (ALEs) from SS. The residues after extraction were further subjected to physical methods (heating) and chemical methods (sulfuric acid, sodium hydroxide) for protein extraction. A comparison was made between sequential extraction routes and direct extraction of biomaterials from sludge in terms of extraction quantity, material properties, and applicability. The results showed that sequential extraction of biomaterials is feasible. The highest extraction quantities were obtained when using sodium carbonate for EPS and ALE extraction and sodium hydroxide for protein, reaching 449.80 mg/gVSS, 109.78 mg/gVSS, and 5447.08 mg/L, respectively. Sequential extraction procedures facilitate the extraction of biomaterials. Finally, suitable extraction methods for different application scenarios were analyzed.

Differentiation and quantification of extracellular polymeric substances from microalgae and bacteria in the mixed culture

Extracellular polymeric substances (EPS) play significant roles in the formation, function, and interactions of microalgal-bacteria consortia. Understanding the key roles of EPS depends on reliable extraction and quantification methods, but differentiating of EPS from microalgae versus bacteria is challenging. In this work, cation exchange resin (CER) and thermal treatments were applied for total EPS extraction from microalgal-bacteria mixed culture (MBMC), flow cytometry combined with SYTOX Green staining was applied to evaluate cell disruption during EPS extraction, and auto-fluorescence-based cell sorting (AFCS) was used to separate microalgae and bacteria in the MBMC. Thermal extraction achieved much higher EPS yield than CER, but higher temperature and longer time reduced cell activity and disrupted the cells. The highest EPS yield with minimal loss of cell activity and cell disruption was achieved using thermal extraction at 55℃ for 30 min, and this protocol gave good results for MBMC with different microalgae:bacteria (M:B) mass ratios. AFCS combined with thermal treatment achieved the most-efficient biomass differentiation and low EPS loss (<4.5 %) for the entire range of M:B ratios. EPS concentrations in bacteria were larger than in microalgae: 42.8 ± 0.4 mg COD/g TSS versus 9.19 ± 0.38 mg COD/g TSS. These findings document sensitive and accurate methods to extract and quantify EPS from microalgal-bacteria aggregates.

Extracellular Polymeric Substance Composition Effects on Biosorption for Primary Carbon Diversion

This paper characterizes the composition of extracellular polymeric substances (EPSs) in different types of activated sludge (AS) processes and analyzes the biosorption of soluble organics when waste AS (WAS) is mixed with raw wastewater for primary carbon diversion. The fraction of AS organics identified as EPSs was 26% in a membrane bioreactor (MBR), 54% in conventional AS (CAS), and 51% in a trickling filter/solids contact (TF/SC) process. EPSs were found to be approximately 15% carbohydrates, 40% proteins, 40% humics, and 5% uronics in CAS and MBR AS. Biosorption was not correlated to the organic portion (VSS) of the WAS; however, statistically significant correlations were found for the total amount of EPSs (for TF/SC and CAS) and the protein fraction (for TF/SC and MBR) in the VSS. EPSs from different types of AS biosorbed the same amount of soluble organics, removing 1.43 ± 0.15 (n = 16) mg of soluble chemical oxygen demand (sCOD), and 1.20 ± 0.18 (n = 16) mg of truly soluble COD (ffCOD), per mg of cation exchange resin (CER) total extracted EPSs. Utilizing multiple extraction methods in series (CER–base–sulfide) increased EPS extraction yields by nearly 100% relative to CER alone and indicated different EPS fractionization for CAS (a smaller fraction of carbohydrates and a larger fraction of humics).

Optimization of the bicinchoninic acid assay for quantifying carbohydrates of soil extracellular polymeric substances

Background and aimsThe bicinchoninic acid (BCA) method was not yet applied on soil extracts of extracellular polymeric substances (EPS) to quantify polysaccharides, although this might be possible by introducing a cleavage step to produce monosaccharides. A pre-extraction with CaCl2 to remove interfering substances is usually performed before extracting EPS. The main objective of this study was to optimize the BCA assay for total carbohydrates quantification by applying a hydrolysis step to the EPS extracts, while also testing carbohydrate contents of CaCl2 pre-extracts.MethodsTotal carbohydrates were quantified with BCA in EPS extracts of three soils, after hydrolysis with H2SO4, using two acid concentrations (0.75 and 1.0 M), three hydrolysis temperatures (100, 120 and 130 °C), and five hydrolysis times (10, 30, 50, 70, and 90 min). EPS were extracted with the cation exchange resin (CER) method adapted to soils. Two versions of pre-extraction with CaCl2 were tested twice consecutively.ResultsMore carbohydrates were measured after hydrolysis with 0.75 M H2SO4 at below 100 °C and after 10 min for all soils. Decreasing values were seen after longer reaction times and higher temperatures. CaCl2 extracted no or negligible amounts of carbohydrates from the soil.ConclusionThe pre-extraction step can be done without in most cases. The BCA assay is free of toxicity and easily performed, while also tolerant to interferences from most compounds in EPS extracts. These characteristics highlight the potential of this method for a rapid quantification of carbohydrates in studies of extractable polymers in several areas of soil biogeochemistry.

Enhanced short-chain fatty acids production from anaerobic fermentation of secondary sludge by lignosulfonate addition: Towards circular economy

This study is the first to unveil the potential of lignosulfonate as an additive in the production of short-chain fatty acids (SCFAs) from anaerobic fermentation of secondary sludge. Batch-scale tests were performed to assess SCFAs production and distribution with lignosulfonate addition of 20–80 mg/g volatile solids (VS), along with potential mechanisms and phytotoxicity. The results showed that lignosulfonate addition improved the SCFAs production and the ratio of acetic acid, while shortening the fermentation time required. The maximum SCFAs production (185.0 ± 1.0 mg COD/g VS) and acetic acid ratio (51.4 ± 0.6%) were achieved with 60 mg lignosulfonate/g VS at 4 d of fermentation time, outperforming the control (93.1 ± 2.7 mg COD/g VS, 44.4 ± 1.8%). Lignosulfonate addition decreased the zeta potential between sludge particles by 19.9%–45.1%, and increased the extractable extracellular polymeric substances matrix by 1.45–2.33 times, compared to the control group. Furthermore, lignosulfonate addition effectively promoted the solubilization, hydrolysis, and acidification processes by up to 116.0%, 58.8%, and 47.6%, respectively. The seed germination index of Chinese cabbage and lettuce using fermented sludge residues increased by up to 486 ± 29% and 158 ± 13%, respectively. These findings suggest that lignosulfonate addition is a sustainable method for SCFAs recovery from sludge, benefiting sludge agricultural reuse, and contributing to the circular economy.

Nanobiopolymer: Potential Applications in Bioremediation of Cadmium Contaminated Water

Nanobiopolymer nanotechnology, bacterial extracellular polymeric substances (EPS), has been used markedly for various water treatments.EPS has polysaccharides, proteins, and lipids, which have functional groups such as amino, sulfhydryl, carboxylic, and phosphate groups that allow binding to metal ions. The accumulation of the metal ions onto the EPS bacterial cell walls is used widely in the bioremediation of cadmium and other metals. This study objectives were extracting EPSs from the bacterium Bacillus subtilis 168 Cd2 and investigating their cadmium adsorption in bead column reactors after being immobilized with calcium alginate. For comparison with the bacterium's role, B. subtilis 168 Cd2 was used before EPS extraction and immobilized with calcium alginate, as well as a comparison with the use of calcium alginate. Cadmium adsorption from solution onto calcium alginate beads with untreated B. subtilis 168 Cd2 and EPS-free B. subtilis 168 Cd2 and under different pH (4.00, 7.00, and 7.50) were studied. The percentages of adsorption onto untreated B. subtilis 168 Cd2 and EPS-free B. subtilis 168 Cd2 were determined and were 89% and 77%, respectively. The adsorption of these were reduced when the pH increased. Scanning electron microscopy (SEM) confirmed the changes in the morphology of the adsorbents, and X-ray fluorescence (XRF) spectrometry analysis recorded the cumulative concentrations of cadmium in the adsorbents after the cadmium adsorption process. EPS in untreated B. subtilis 168 Cd2 significantly enhanced cadmium adsorption percentages. The fewer carboxyl and phosphate groups in EPS-free B. subtilis 168 Cd2 decreased cadmium adsorption. The results obtained in this study are of fundamental significance for applying nano biopolymers nanotechnology environmental biotechnology and bioremediation.

Importance of inner-sphere P-O-Fe bonds in natural and synthetic mineral-organic associations

Sorption of organic molecules on mineral surfaces can occur through several binding mechanisms of varying strength. Here, we investigated the importance of inner-sphere P-O-Fe bonds in synthetic and natural mineral-organic associations. Natural organic matter such as water extracted soil organic matter (WESOM) and extracellular polymeric substances (EPS) from liquid bacterial cultures were adsorbed to goethite and examined by FTIR spectroscopy and P K-edge NEXAFS spectroscopy. Natural particles from a Bg soil horizon (Gleysol) were subjected to X-ray fluorescence (XRF) mapping, NanoSIMS imaging, and NEXAFS spectro-microscopy at the P K-edge. Inner-sphere P-O-Fe bonds were identified for both, adsorbed EPS extracts and adsorbed WESOMs. Characteristic infrared peaks for P-O-Fe stretching vibrations are present but cannot unambiguously be interpreted due to possible interferences with mono- and polysaccharides. For the Bg horizon, P was only found on Fe oxides, covering the entire surface at different concentrations, but not on clay minerals. Linear combination fitting of NEXAFS spectra indicates that this adsorbed P is mainly a mixture of orthophosphate and organic P compounds. By combining atomic force microscopy (AFM) images with STXM-generated C and Fe distribution maps, we show that the Fe oxide surfaces were fully coated with organic matter. In contrast, clay minerals revealed a much lower C signal. The C NEXAFS spectra taken on the Fe oxides had a substantial contribution of carboxylic C, aliphatic C, and O-alkyl C, which is a composition clearly different from pure adsorbed EPS or aromatic-rich lignin-derived compounds. Our data show that inner-sphere P-O-Fe bonds are important for the association of Fe oxides with soil organic matter. In the Bg horizon, carboxyl groups and orthophosphate compete with the organic P compounds for adsorption sites.

Integrated resource recovery from aerobic granular sludge plants

The study evaluated the combined phosphorus, nitrogen, methane, and extracellular polymeric substances (EPS) recovery from aerobic granular sludge (AGS) wastewater treatment plants. About 30% of sludge organics are recovered as EPS and 25–30% as methane (≈260 ml methane/g VS) by integrating alkaline anaerobic digestion (AD). It was shown that 20% of excess sludge total phosphorus (TP) ends in the EPS. Further, 20–30% ends in an acidic liquid waste stream (≈600 mg PO4-P/L), and 15% in the AD centrate (≈800 mg PO4-P/L) as ortho-phosphates in both streams and is recoverable via chemical precipitation. 30% of sludge total nitrogen (TN) is recovered as organic nitrogen in the EPS. Ammonium recovery from the alkaline high-temperature liquid stream is attractive, but it is not feasible for existing large-scale technologies because of low ammonium concentration. However, ammonium concentration in the AD centrate was calculated to be 2600 mg NH4-N/L and ≈20% of TN, making it feasible for recovery. The methodology used in this study consisted of three main steps. The first step was to develop a laboratory protocol mimicking demonstration-scale EPS extraction conditions. The second step was to establish mass balances over the EPS extraction process on laboratory and demonstration scales within a full-scale AGS WWTP. Finally, the feasibility of resource recovery was evaluated based on concentrations, loads, and integration of existing technologies for resource recovery.

Sensitive and Accurate Differentiation of Extracellular Polymeric Substance Hydrolysis Using Flow Cytometry during Biofilm Extracellular Polymeric Substance Extraction

Extracellular polymeric substances (EPS) affect the formation, properties, and function of biofilms. Understanding the roles of EPS in biofilm-related processes depends on reliable extraction and evaluation methods. However, differentiating true EPS from intracellular organic polymers released by cell lysis has proven to be difficult during EPS extraction. In this study, thermal and cation exchange resin (CER) treatments were used to extract biofilm EPS. SYTOX Green (SG) dye was used to stain nucleic acid (NA), and the enhanced fluorescence signal (FS) from the NA-SG complex was sensitively recorded by flow cytometry (FC). Results showed that thermal extraction could achieve effective EPS release, but a higher temperature and longer time caused a significant cell activity decline, protein denaturation, and cell lysis. In contrast, CER extraction had no effects on cell activity and organics denaturation, and it only caused minor cell lysis at a high CER dose. Combining all the results indicates that CER extraction using 70 g-CER/g-VSS for 2 h provided reliable and efficient extraction of biofilm EPS: high EPS extraction efficiency with minimal EPS denaturation, cell lysis, and loss of cell activity. FC combined with SG staining should be applicable for evaluating the effectiveness of EPS extraction from any microbial aggregates.

A comparative study of the accumulation and detoxification of copper and zinc in Chlamydomonas reinhardtii: The role of extracellular polymeric substances

Extracellular polymeric substances (EPS) form an interface between microalgae and the surrounding water environment. Copper (Cu) and zinc (Zn) are essential micronutrients but may negatively affect microbial growth when their concentrations reach toxic thresholds. However, how EPS affect the accumulation and resistance of Cu and Zn in microalgae remains largely unknown. Here, we investigated EPS production upon Cu/Zn exposure and compared the tolerance strategies to the two metals by Chlamydomonas reinhardtii with and without EPS. Microalgal EPS synthesis was induced by Cu/Zn treatments, and the functional groups of polysaccharides and proteins were involved in complexation with metal ions. The extraction of EPS aggravated the toxicity and reduced the removal of metals from solution, but the effect was more pronounced for Cu than for Zn. Copper bound on the cell surface accounted for 54.6 ± 2.0 % of the Cu accumulated by C. reinhardtii, whose EPS components strongly correlated with Cu adsorption. In contrast, 74.3 ± 3.0 % of accumulated Zn was absorbed in cells, and glutathione synthesis was significantly induced. Redundancy and linear correlation analyses showed that the polysaccharide, protein and DNA contents in EPS were significantly correlated with Cu accumulation, absorption and adsorption but not with Zn. Data fitted to a Michaelis–Menten model further showed that the EPS-intact cells had higher binding capacity for Cu2+ but not for Zn2+. These differential impacts of EPS on Cu/Zn sorption and detoxification contribute to a more comprehensive understanding of the roles of microalgal EPS in the biogeochemical cycle of metals.

Extracting extracellular polymeric substances from fungi in contrasts: from quantity to quality

Many fungi are able to produce extracellular polymeric substances (EPS) for environmental, food, and industrial applications. This study evaluated the extraction (in vivo) of EPS from Rhodotorula mucilaginosa, a typical yeast with abundant EPS. Three extracting methods were set, i.e., heating, addition of NaCl during heating, and cation exchange resin (CER). The abundance of extracted proteins and polysaccharides showed evident contrasts (elevatedto ~ 600 and 1700 mg/L, respectively) after heating at 70 °C in water. Although the higher temperature will increase the extracted abundance of EPS, the leakage of DNA would be enhanced due to cell rupture. The addition of NaCl further promoted the efficiency of extraction, either for proteins (from ~ 550 to ~ 650 mg/L) or polysaccharides (from ~ 1700 to ~ 2010 mg/L). Moreover, the biochemical results showed that the extracted abundance of EPS via heating was dramatically higher than that via CER. Additionally, DNA leakage in the CER treatment (2.0 g/g DW) was significantly higher (up to > 6 mg/L) than that under heating at 70 °C (< 2 mg/L). Furthermore, the three-dimensional excitation-emission matrix spectra showed two characteristic peaks of emission/excitation wavelength at 280/300 and 280/350, suggesting the relative high diversity of organic matters in EPS after heating treatments. Finally, a fluctuation of polysaccharide abundance in EPS at 500-1500 mg/L Pb2+ level was elucidated by the extraction based on heating treatment. This study hence confirmed that the heating method might be recommended for extraction of EPS from fungi in vivo KEY POINTS: • 3D-EEM results indicated that heating could extract more EPS compared with CER. • Heating treatments showed lower DNA leakage from fungi than CER treatments. • Addition of NaCl promoted the detachment of EPS from fungal cells in vivo.

Extraction and application of extracellular polymeric substances from fungi.

Extracellular polymeric substances (EPS) are extracellular metabolites of microorganisms, highly associated with microbial function, adaptation, and growth. The main compounds in EPS have been revealed to be proteins, polysaccharides, nucleic acids, humic substances, lipids, etc. EPS are not only biomass, but also a biogenic material. EPS have high specific surface, abundant functional groups, and excellent degradability. In addition, they are more extensible to the environment than the microbial cells themselves, which exhibits their huge advantages. Therefore, they have been applied in many fields, such as the environment, ecosystem, basic commodities, and medicine. However, the functions of EPS highly depend on the suitable extraction process, as different extraction methods have different effects on their composition, structure, and function. There are many types of EPS extraction methods, in which physical and chemical methods have been widely utilized. This review summarizes the extraction methods and applications of EPS. In addition, it considers some important gaps in current knowledge, and indicates perspectives of EPS for their future study.

Extraction of extracellular polymeric substances (EPS) from indigenous bacteria of rare earth tailings and application to removal of thorium ions (Th4+).

Thorium, as an important radioactive element, is widely present in nature, and its accompanying environmental pollution is also serious. Extracellular polymeric substances (EPS) are commonly found on the surface of microbial bodies and have strong adsorption capacity for metal ions. In this study, four methods were used to extract EPS from indigenous bacteria of rare earth tailings and to determine the best extraction method. The extracted EPS was applied to treat Th4+, and the changes in functional groups and composition of EPS were investigated. The results showed that the ultrasonic method was more efficient than other methods. The best removal efficiency was observed at pH 3.5, Th4+ concentration of 20 mg/L, and EPS dosage of 30 mL at 25 °C. After 9 h, the adsorption process reached equilibrium with a maximum removal efficiency of 75.93% and a maximum theoretical adsorption capacity of 25.96 mg/g. The Th4+ removal process was consistent with the Langmuir and Freundlich adsorption isotherms and the kinetic data were consistent with the pseudo-second-order kinetic model, which is mainly based on chemisorption. Amide I and amide II of proteins, C-H from aliphatic, as well as O-H and C = O from carboxylic acid play important roles in the adsorption process.

Characterising soil extracellular polymeric substances (EPS) by application of spectral-chemometrics and deconstruction of the extraction process

Extracellular polymeric substances (EPS) exuded by microbes are found in diverse habitats, including soil. The quantification and characterization of EPS are essential prerequisites for understanding the ecological functions of extracellular products in soil. However, few studies have conducted in-depth profiling of soil EPS extraction steps and chemical characteristics. Here we examine the C and N contents, biopolymer contents, and optical properties of EPS involving three soil pre-treatment methods (moist soil, moist soil pre-incubated, and air-dried soil pre-incubated) and simultaneously track the compositional changes during the two-step extraction process (extract with CaCl2 in Step 1 and phosphate buffer solution (PBS) with cation exchange resin (CER) in Step 2). The optical properties of soil EPS are investigated using ultraviolet-visible adsorption (UV–Vis), excitation-emission-matrix fluorescence (EEM), and fourier transform infrared (FTIR) spectroscopy coupled with multivariate analytical methods such as parallel factor analysis (PARAFAC), principal component analysis (PCA), and correlation analysis. Results show that Step 2 releases significantly more dissolved organic carbon and biopolymers (polysaccharides, proteins, and uronic acids) from soils. UV–Vis and EEM spectroscopy suggest that the fractions extracted in Step 2 exhibit higher mean aromaticity, molecular weight, and humification degree than those extracted in Step 1. When using the standard method to extract EPS from moist aggregates (Step 2), EPS has a distinct fluorescence profile, rich in tryptophan- and tyrosine-like signals. Reassuringly, the fluorescence-profiles found in pre-extracts (Step 1) are very different - except where i) aggregates have an experimental drying step added, and ii) pure water is used as a pre-extractant. Drying of aggregates is thus problematic, and the use of pure water as an alternative pre-extractant is not advisable. Soil treatments have significant effects on the qualities of the various extracts which are detected by both the FTIR-PCA and EEM-PCA analyses. EEM fluorescence profiles of EPS suggest that both tryptophan-like and tyrosine-like substances are key components of the EPS extracted from all soils regardless of pretreatment. Our findings indicate that chemical characterization of soil EPS combined with spectral-chemometric approaches can be applied to identify and characterise the extracellular responses of soil microbes and thus help reveal the ecological functions of extracellular products in soils.

Extraction, characterization, and anticancer potential of extracellular polymeric substances from marine actinobacteria of Streptomyces species.

To check the ability of the anticancer activity, the extracted extracellular polymeric substances (EPS) from marine actinobacteria were done. Potential of the anticancer activity of EPS which was extracted from marine actinobacteria of Streptomyces species through an assay called MTT. Marine actinobacterial isolation, identification and micromorphology of the strain, and biochemical analysis were performed (Shirling and Gottlieb, 1966). The production of EPS from marine actinobacteria was quantified(P. Sivaperumal et al., 2018). Carbohydrate content in the EPS was quantified, and MCF-7 cell proliferation was done using an MTT assay. EPS-producing marine Streptomyces was isolated and identified. The production of EPS and their protein, carbohydrate, lipid, and other parameters were estimated. Further, the EPS showed more than 50% of inhibition after 72 h using the MTT assay in the MCF-7 cancer cell line. The present study exhibited that EPS from marine Streptomyces species has significant anticancer activity.

Influence of salt addition to stimulating biopolymers production in aerobic granular sludge systems

The influence of salt addition to stimulating biopolymers production in aerobic granular sludge (AGS) systems was evaluated. The control systems (R1: acetate and R2: propionate) initially obtained less accumulation of mixed liquor volatile suspended solids (MLVSS), indicating that the osmotic pressure in the salt-supplemented systems (R3: acetate and R4: propionate) contributed to biomass growth. However, the salt-supplemented systems collapsed between days 110 and 130 of operation. R3 and R4 showed better performance regarding nutrients removal due to the greater abundance of nitrifying and denitrifying bacteria and phosphate-accumulating organisms. Salt also contributed to the higher production of biopolymers such as alginate-like exopolymers (ALE) per gram of volatile suspended solids (VSS) (R1: 397 mgALE∙gVSS−1, R2: 140 mgALE∙gVSS−1, R3: 483 mgALE∙gVSS−1, R4: 311 mgALE∙gVSS−1). Amino acids like tyrosine and tryptophan were better identified in extracellular polymeric substances extract from salt-operated reactors. This study brings important results in the context of resource recovery by treating saline effluents.

Surface biomineralization of uranium onto Shewanella putrefaciens with or without extracellular polymeric substances

The influence of extracellular polymeric substances (EPS) on the interaction between uranium [U(VI)] and Shewanella putrefaciens (S. putrefaciens), especially the U(VI) biomineralization process occurring on whole cells and cell components of S. putrefaciens was investigated in this study. The removal efficiency of U(VI) by S. putrefaciens was decreased by 22% after extraction of EPS. Proteins were identified as the main components of EPS by EEM analysis and were determined to play a major role in the biosorption of uranium. SEM-EDS results showed that U(VI) was distributed around the whole cell as 500-nanometer schistose structures, which consisted primarily of U and P. However, similar uranium lamellar crystal were wrapped only on the surface of EPS-free S. putrefaciens cells. FTIR and XPS analysis indicated that phosphorus- and nitrogen-containing groups played important roles in complexing U (VI). XRD and U LIII-edge EXAFS analyses demonstrated that the schistose structure consisted of hydrogen uranyl phosphate [H2(UO2)2(PO4)2•8H2O]. Our study provides new insight into the mechanisms of induced uranium crystallization by EPS and cell wall membranes of living bacterial cells under aerobic conditions.

PVDF membranes modified with diblock copolymer PEO-b-PMMA as additive: Effects of copolymer and barrier pore size on filtration performance and fouling in a membrane bioreactor

In the present work, filtration performance and fouling behavior of four poly(vinylidene difluoride) (PVDF) membranes with different composition and molecular weight cut-off (MWCO) were investigated in a lab-scale submerged membrane bioreactor (MBR) system, treating real pharmaceutical wastewater. Poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymer or FeCl2 or the combination of PEO-b-PMMA and FeCl2 were used as special additives during membrane formation. A 30-day filtration experiment was performed using four membranes in the same aeration tank simultaneously, and filtration performance of the membranes was investigated over the entire filtration period. Fouling parameters were calculated for all membranes and the TMP-step method was used to determine the critical flux of the membranes. Formed cake layers onto the surface of the membranes at the end of each filtration run were collected and extracellular polymeric substances (EPSs), excitation and emission matrix (EEM) fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy analyses were performed for the cake layers. Collected cake layers after EPSs extraction were dried and their masses were measured to estimate anti-biofilm formation potential of the membranes. Obtained results revealed that incorporation of the PEO-b-PMMA diblock copolymer into the PVDF membrane accompany with FeCl2 salt which tailors the MWCO and prevents the increment of the pore size improves membrane performance and reduces its fouling propensity, in a way that membrane with smaller MWCO containing copolymer revealed lower flux decline, higher critical flux, higher flux recovery ratio (FRR) and lower biofilm mass per area. Moreover, EPS and EEM analyses revealed that membrane surface chemistry has considerable effect on the composition of the cake layers. Finally, chemical oxygen demand (COD) removal efficiency proved that MWCO does not have obvious effect on effluents’ quality. The present study confirms the importance of the surface chemistry and MWCO on fouling behavior of the membranes in the MBR system and reveals that the addition of the PEO-b-PMMA diblock copolymer to the PVDF membrane improves antifouling property of the membrane considerably.

Effect of extracellular polymeric substances removal and re-addition on the denitrification performance of activated sludge: Carbon source metabolism, electron transfer and enzyme activity

Extracellular polymeric substances (EPS) play an important role in the metabolic activities of activated sludge. The effect of EPS removal (pellet group) and re-addition (pellet + EPS group) on the denitrification of activated sludge were analyzed in this study. The results indicated that EPS removal deteriorated the denitrification performance of the activated sludge. The denitrification rates in the pellet group with EPS extraction degrees of 7.77%, 12.37%, 35.89%, and 100% were only 82.6%, 75.7%, 64.1%, and 26.9%, respectively, of the control group. However, the denitrification rate of the pellet increased by 19–34% by re-adding the extracted EPS. Moreover, when the EPS extraction degree was 7.77%, the denitrification rate of the pellet + EPS group was 10.4% higher than that of the control group. The EPS contain many redox mediators. The electron transport system activity (ETSA) and key enzymes in biological denitrification were improved by re-adding EPS. The ETSA in the pellet + EPS group were 1.66-fold that in control group. The pellet + EPS group had a lower reaction activation energy, which was 42.9% lower with that of the control group. In addition, EPS re-addition promoted the activities of enzymes related to glycolysis by 9.60–18.08%, and nicotinamide adenine dinucleotide yield increased by 6.5%, which enhanced the denitrification rate of activated sludge. This study provides a novel method to enhance the denitrification performance of activated sludge by in situ appropriate desorption of EPS as endogenous redox mediator.

Effects of alkaline solvents and heating temperatures on the solubilization and degradation of gel-forming Extracellular Polymeric Substances (EPS) extracted from aerobic granular sludge

The effects of solvents and heating temperatures on the recovery and degradation of gel-forming EPS (Extracellular Polymeric Substances) extracted from aerobic granular sludge were investigated. Sodium hydroxide has allowed a better EPS solubilization compared to sodium carbonate (711.3 ± 38 and 408.4 ± 4 mg VS /g VS respectively) but the capacity to precipitate gel-forming EPS at acidic pH was higher in sodium carbonate (22% compared to 6% in sodium hydroxide at 80 °C). Increasing the temperature from 20 °C to 80 °C during EPS solubilization has multiplied the amount of solubilized matter by 4 in sodium carbonate and 2.2 in sodium hydroxide. Similar biochemical composition but different molecular weight profiles were observed for the two solubilized EPS extracts, evidencing partial degradation of the polymers in sodium hydroxide. Furthermore, coupling molecular weight analysis and precipitation yield measurement revealed that the lower precipitation of sodium hydroxide solubilized EPS is related to the size reduction due to degradation. Altogether these results help to guide towards a unified protocol for the extraction of gel-forming EPS.