Changes In Extracellular Polymeric Substances Research Articles

Response of Anaerobic Granular Sludge Reactor to Plant Polyphenol Stress: Floc Disintegration and Microbial Inhibition

Plant polyphenols are potential inhibitors for the anaerobic treatment of wastewater from the wood processing, pharmaceutical, and leather industries. Tannic acid (TA) was selected as a model compound to assess the inhibitory effect of plant polyphenols in simulated wastewater in this study. The influences of TA on methanogenic activity, sludge morphology, and the microbial community were investigated under glucose and sodium acetate as carbon substrates, respectively. The results show that a threshold concentration of TA above 1500 mg·L−1 that triggers significant methanogenesis depression and volatile fatty acids (VFAs) accumulation. In addition, granules might be weakened by TA addition, reflected in changes in extracellular polymeric substances (EPS) within the granules and an increase in floc in the effluent. The anaerobic granular sludge (AnGS) fed with sodium acetate was more sensitive than the presence of glucose as the substrate when facing the challenge of TA. The concentration of the mcrA gene in granular sludge decreased markedly in response to TA stress, providing direct evidence that a high concentration of TA caused the inhibition of specific gene expressions. This study provides details about the adverse impacts of TA stress on methane production, the microbial community, and granule integrity, deepening our understanding of the anaerobic treatment of plant polyphenols contained in wastewater.

Molecular spectra and docking simulations investigated the binding mechanisms of tetracycline onto E. coli extracellular polymeric substances

Extracellular polymeric substances (EPS), which were an important fraction of natural organic matter (NOM), played an important role in various environmental processes. However, the heterogeneity, complexity, and dynamics of EPS make their interactions with antibiotics elusive. Using advanced multispectral technology, this study examined how EPS interacts with different concentrations of tetracycline (TC) in the soil system. Our results demonstrated that protein-like (C1), fulvic-like (C2), and humic-like (C3) fractions were identified from EPS. Two-dimensional synchronous correlation spectroscopy (2D–SF–COS) indicated that the protein-like fraction gave faster responses than the fulvic-like fraction during the TC binding process. The sequence of structural changes in EPS due to TC binding was revealed by two-dimensional Fourier Transformation Infrared correlation spectroscopy (2D–FTIR–COS) as follows: 1550 > 1660 > 1395 > 1240 > 1087 cm−1. It is noteworthy that the sensitivity of the amide group to TC has been preserved, with its intensity gradually increasing to become the primary binding site for TC. The integration of hetero-2DCOS maps with moving window 2D correlation spectroscopy (MW2DCOS) provided a unique insight into understanding the correlation between EPS fractions and functional groups during the TC binding process. Moreover, molecular docking (MD) discovered that the extracellular proteins would provide plenty of binding sites with TC through salt bridges, hydrogen bonds, and π-π base-stacking forces. With these results, systematic investigations of the dynamic changes in EPS components under different concentrations of antibiotic exposure demonstrated the advanced capabilities of multispectral technology in examining intricate interactions with EPS in the soil environment.

Deep dewatering of municipal sludge by combining alternating electric field electro-osmosis and nano-CaO2 oxidation

To improve the effect of traditional electroosmotic sludge dewatering, combining alternating electric field electro-osmosis and nano-calcium peroxide (CaO2) oxidation, a homemade vertical electro-osmosis dewatering device was employed in this work to study the effects of different parameter on the dewatering of primary dewatered sludge from municipal sewage treatment facilities with a moisture content of around 85%. The sludge water content (Wr) was used as an indicator, and concentration of extracellular polymeric substances (EPS) in the dewatered sludge was measured, and its structure was analyzed to investigate the effect of EPS changes on sludge dewatering.The response surface method was used to optimize the parameters. Wr decreased to 36.23 % at a CaO2 amount of 14.79 mg·g−1 dry sludge, a time ratio of 7.98:1, and a voltage gradient of 19.71 V·cm−1. Analysis of zeta potential and infrared characterization indicates that under acidic circumstances, CaO2 reacts more positively with water to produce hydrogen peroxide, and EPS is more easily destabilized and degraded, due to this, the problem of unequal water content in the cathode and anode sludge cakes is also solved. During the sludge dewatering process, the synergistic effect of alternating electric field and calcium peroxide together destroys the cell structure and EPS of sludge, especially the tightly bound EPS (TB-EPS), enabling the migration of substances and the formation of loosely bound EPS (LB-EPS), slime EPS (S-EPS), or filtrate, which can improve the sludge dewaterability.

Effects of successional sulfadiazine exposure on biofilm in moving bed biofilm reactor: Secretion of extracellular polymeric substances, community activity and functional gene expression

The effects of sulfadiazine (SDZ) on responses of biofilm in a moving bed biofilm reactor were explored with emphasis on the changes in extracellular polymeric substances (EPS) and functional genes. It was found that 3 to 10 mg/L SDZ reduced the protein (PN) and polysaccharide (PS) contents of EPS by 28.7%-55.1% and 33.3%-61.4%, respectively. The EPS maintained high ratio of PN to PS (10.3–15.1), and the major functional groups within EPS remained unaffected to SDZ. Bioinformatics analysis showed that SDZ significantly altered the community activity such as increased expression of s_Alcaligenes faecali. Totally, the biofilm held high SDZ removal rates, which were ascribed to the self-protection by secreted EPS, and genes levels upregulation of antibiotic resistance and transporter protein. Collectively, this study provides more details on the biofilm community exposure to an antibiotic and highlights the role of EPS and functional genes in antibiotic removal.

Antimicrobial and antibiofilm effects of total flavonoids from Potentilla kleiniana Wight et Arn on Pseudomonas aeruginosa and its potential application to stainless steel surfaces

Pseudomonas aeruginosa (P. aeruginosa) contamination poses challenges to the food industry. Total flavonoids of Potentilla Kleiniana Wight et Arn (TFP) are poorly understood for their antibiofilm effects against P. aeruginosa. Therefore, the inhibitory effects of TFP against planktonic cells were determined by agar diffusion, microtiter plate and time-kill curve assays. The mechanism of inhibition is evaluated by changes in membrane (potential, permeability and damage), cell motility and virulence factors production. Morphological changes were verified by transmission electron microscopy (TEM). A modified microtiter-plate assay determined its inhibitory effects against biofilm cells. The inhibitory mechanism was studied by changes in extracellular polymeric substances (EPS) and cell surface hydrophobicity. These inhibition effects were verified by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Finally, TFP was applied to stainless steel surfaces to evaluate its potential application in food production. TFP damaged P. aeruginosa cell membrane integrity, inhibited bacterial motility, virulence factors, surface hydrophobicity and colony counting on stainless steel. These results provide evidence for the utilization of TFP as a novel natural bioactive preservative in food processing.

Unraveling membrane fouling in anoxic/oxic membrane bioreactors treating anaerobically digested piggery wastewater

Anaerobically digested piggery wastewater (ADPW) draws increasing attention due to the high nitrogen and carbon level. In this study, four parallel lab-scale anoxic-oxic membrane bioreactors were applied to treat ADPW with the hydraulic retention time (HRT) of 75, 60, 45 and 30 h, respectively. Reactor performance and membrane fouling mechanisms also have been systematically evaluated. The results demonstrated a decline in chemical oxygen demand and total nitrogen biodegradation (from 65.8 ± 2.5% and 62.2 ± 5.5% to 38.6 ± 3.6% and 26.2 ± 5.7%, respectively) and a rise in membrane resistance (from 37.34 × 1012 m−1 to 51.69 × 1012 m−1) as the HRT decreased. The decline of HRT didn’t affect the functional group types of cake layer extracellular polymeric substances (EPS) and tightly bound EPS (TB-EPS) of activated sludge, but led to the increased concentrations of protein (PN) and polysaccharide (PS) in loosely bound EPS (LB-EPS) and soluble microbial products (SMP) of activated sludge and a decreased PN/PS ratio in SMP. These changes in SMP and EPS accelerated the formation of cake layer and aggravated the membrane fouling. Proteobacteria and Bacteroidetes were the predominant phyla on membrane surface. The abundant Proteobacteria in the reactor with longer HRTs was beneficial to mitigate membrane fouling while the relative abundance of Bacteroidetes remained stable in all reactors. The enrichment of Thauera was the primary reason for membrane fouling at genus level in the reactors. This study provides scientific insights on the practical application of membrane bioreactors in terms of membrane fouling control.

Physicochemical methods for biofilm removal allow for control of biofilm retention time in a high rate MBBR

ABSTRACT Controlling biofilm retention time in moving bed biofilm reactor (MBBR) and maintaining its performance for A-stage carbon redirection requires a reliable method to use as side stream biocarriers treatment. This paper investigates biofilm detachment and residual biofilm activity under multiple physicochemical treatment scenarios aiming to provide an applicable technique for control of biofilm retention time. Different mixing intensities (i.e. 30–120 rpm), filling fractions (i.e. 20%–100%), and pH (i.e. 2–12) were evaluated. Two continuously operating MBBRs were subjected to pH shocks of 2 and 12 to evaluate the impact of residual acidic or alkaline compounds on performance. The highest solids detachment (i.e. 70 ± 5%) was found in alkaline conditions and independent of mixing intensity and filling fraction. Biofilm detachment test revealed that alkaline shock produced higher detachment levels in a longer exposure time when compared to acidic conditions. The kinetic tests revealed 60% and 90% of the residual biofilm activity was lost at pH 12 and 2. The continuously operating MBBRs subjected to pH shocks of 2 and 12 demonstrated a 50% loss of soluble COD removal capability within one hydraulic retention time. Extracellular polymeric substances changes in its structure and surface properties influencing the degree of biofilm detachment and its solubilization properties leading to differences in biofilm resilience. The findings have shown that by applying a side stream alkali treatment it could be possible to control biofilm retention time ensuring its detachment up to 70% and a reduced impact on the residual biofilm activity returning to the reactor.

Response of Activated Sludge to Long-Term Nanosilver Input and Changes in Extracellular Polymeric Substances (EPS)

This study investigates the response of activated sludge to continuous nanosilver (AgNPs) input in a large concentration range. In addition to substrate removal, changes taking place in the different fractions of Extracellular Polymeric Substances (EPS), namely, very loosely bound-EPS (VLB-EPS), loosely bound-EPS (LB-EPS), and tightly bound-EPS (TB-EPS), as well as the protein and carbohydrate content of each fraction were examined. At relatively low AgNP concentrations (5 mg/L), production of loosely bound fractions became higher. At AgNP ≥ 12 mg/L, also TB-EPS production was promoted. Seemingly, bacteria were protected from inhibitory effects by regulation of EPS production. Moreover, new proteins emerged in EPS. Respiration tests indicated no effect on substrate removal even at high AgNP concentrations because the nanomaterial lost its effectiveness upon continuous aeration. In WWTPs, AgNP concentrations are normally below 0.8 mg/L. Therefore, no negative impact on substrate removal and no visible changes in EPS production would be expected.

Calcium ions affect sludge digestion performance via changing extracellular polymeric substances in anaerobic bioreactor

In this study, batch tests were conducted with and without the addition of calcium ions to clarify the interaction between calcium ions and extracellular polymeric substances (EPS). The maximum degradation rates of EPS and chemical oxygen demand (COD) in the reactor with the addition of Ca2+ reached 58.26, 67.19, 69.35 mg∙g−1 mixed liquor suspended solids (MLSS) and 89.70%, 94.04%, 91.70%, respectively, and were higher than those in the control reactor. The results showed that Ca2+ (1000–2000 mg∙L−1) significantly promoted the secretion of EPS and improved sludge digestion performance during the process of anaerobic digestion. In addition, Ca2+ changed the functional groups of EPS and the microstructure of granular sludge compared with the control reactor. The concentrations of EPS in the reactor with added Ca2+ were positively correlated with the COD degradation rate, with coefficients of determination of 0.88, 0.91, and 0.98 in reactors R1, R2, and R3, respectively, which suggests that EPS can affect the bioactivity of anaerobic granular sludge (AnGS), and particularly the degradation of organics. The results were reaffirmed by analyzing volatile fatty acids (VFAs) and cytochrome c (c-Cyts). There was no obvious relationship between the EPS content and COD degradation rate in the control reactor (R2 = 0.63), which indicates that Ca2+ may be an important factor in attaining the above results. Therefore, we speculate that Ca2+ caused changes in EPS, as the concentration of EPS increased and the COD degradation rate increased (and vice versa), which affected the digestion performance of AnGS.

Spatiotemporal Organization of Biofilm Matrix Revealed by Confocal Raman Mapping Integrated with Non-negative Matrix Factorization Analysis.

Biofilms are microbial aggregates of microorganisms surrounded by a hydrogel-like matrix formed by extracellular polymeric substances (EPS). The formation of biofilms is intrinsically complex, from the attachment of microbial cells to the dispersion of the biofilm. Meanwhile, the three-dimensional framework built up by EPS changes with time and protects the microorganisms against environmental stress. Simultaneously acquiring chemical and structural information within the biofilm matrix is vital for the cognition and regulation of biofilms, yet it remains a great challenge due to the sample complexity and the limited approaches. In this study, confocal Raman microscopy and non-negative matrix factorization (NMF) analysis were combined to investigate spatiotemporal organization of Escherichia coli biofilms during development at molecular-level detail. The alternating non-negative least-squares (ANLS) approach was incorporated with the sequential coordinate-wise descent (SCD) algorithm to realize the NMF analysis for the large-scale hyperspectral data set. As a result, three components, including bacteria, protein, and polyhydroxybutyrate (PHB), were successfully resolved from the spectra of E. coli biofilm. Furthermore, the structural changes of biofilms could be visualized and quantified by their abundances derived from the NMF analysis, which might be related to the nutrient and oxygen gradient and physiological functions. This methodology provides a comprehensive understanding of the chemical constituents and their spatiotemporal distribution within the biofilm matrix. Furthermore, it also shows great potential for the analysis of unknown and complex biological samples with 3D Raman mapping.

Investigating trivalent chromium biosorption-driven extracellular polymeric substances changes of Synechocystis sp. PCC 7806 by parallel factor analysis (PARAFAC) analysis

In this study, experiments were conducted to investigate the biosorption effect of the cyanobacteria Synechocystis sp. PCC 7806 on trivalent chromium (Cr (III)) and the fate of extracellular polymeric substances (EPS) during the biosorption process. Results indicated that Synechocystis sp. PCC 7806 could effectively adsorb Cr (III) but this adsorption capacity was inhibited by high amount Cr (III). The biosorption process decreased the growth rate of Synechocystis sp. PCC 7806. Furthermore, the characteristics of Synechocystis sp. PCC 7806 EPS were evaluated by parallel factor analysis (PARAFAC) combined with fluorescence excitation–emission matrices (EEMs). The results showed that there were four main components of EPS in Synechocystis sp. PCC 7806. It indicated that the fluorescent characterization of EPS was obvious affected by adsorption process of Cr (III). The tryptophan-like substances, amino acid substances and fulvic acids-like substances largely participated in the binding and biosorption of Cr (III).

Improved dewaterability of anaerobically digested sludge and compositional changes in extracellular polymeric substances by indigenous persulfate activation

In this study, an indigenous activation of persulfate by iron-bearing minerals was examined using peroxymonosulfate (PMS) and peroxydisulfate (PDS) for the dewaterability and extracellular polymeric substances (EPS) composition of anaerobically digested sludge (ADS). Iron minerals originally present in the ADS seemed to operate as an initiator of the persulfate activation, which was indicated by an increase in the total dissolved iron in the supernatant. The PMS showed higher performance in improving the ADS dewaterability compared to the PDS, with more reduction in the average microbial flocs size. The extracted EPS consisted of three different fluorescent components of tryptophan-like (C1), humic-like (C2), and fulvic-like (C3) components. In the tightly bound (TB)-EPS, two humic-like components (C2 and C3), which were resistant to degradation, exhibited a strong linkage with dewaterability; whereas, in both the PMS and the PDS systems, the C1 was preferentially degraded by the radical-based oxidation, with a greater extent for the PMS-based treatments. The results showed that prior to the actual EPS degradation, the produced radicals were initially involved in cell disruption. The SEC results during the oxidation clearly demonstrated the degradation of a large-sized biopolymer fraction, followed by the production of relatively small sized molecules. They also revealed in the TB-EPS a close association between the ADS dewaterability and the degradation of humic substances.

Characterization of changes in extracellular polymeric substances and heavy metal speciation of waste activated sludge during typical oxidation solubilization processes

Biopolymer solubilization is considered to be the rate-limiting stage of anaerobic digestion of waste activated sludge (WAS). Oxidation processes have been proven to be effective in disrupting sludge flocs and causing solubilization of the solid biopolymers. In this study, WAS was treated by NaNO2 or H2O2 oxidation at pH of 2. The changes in extracellular polymeric substances properties and the speciation of heavy metals were investigated. The results revealed that both NaNO2 and H2O2 treatments were effective in solubilizing organics in WAS, while the conversion of biopolymers in the two treatment processes was different. Free nitrous acid destroyed the gel network structure of EPS, and organic materials were released from the solid phase to the supernatant. Indigenous peroxidase catalyzed H2O2 to produce hydroxyl radicals which caused significant solubilization of biopolymers, and the protein-like substances were further degraded into micro-molecule polypeptides or amino acids at high dosages of H2O2. During the oxidation processes, Zn, Cd and Cu, with excellent mobility, tended to migrate to the supernatant, and thus were easy to remove through the liquid–solid separation process. Ni and As showed moderate migration ability, of which the residual fraction tended to transform into reducible and soluble fractions. With poor mobility, Cr and Pb mainly existed in the forms of residual and oxidizable fractions, which were difficult to dissolve and remove from WAS. Both NaNO2 and H2O2 treatment resulted in the enhancement of sludge solubilization efficiency and heavy metal mobility in WAS, but different heavy metals showed distinct migration and transformation behaviors.

Changes in extracellular polymeric substances (EPS) content and composition in aerobic granule size-fractions during reactor cycles at different organic loads

This study aimed to systematically investigate the effect of organic loading on granule diameters, and on the composition of extracellular polymeric substances (EPS) in granules in various size-fractions at the beginning and end of the cycle of granular sludge sequencing batch reactor (GSBR). The organic loadings were 0.78 kg COD/(m3·d) (GSBR1), 1.16 kg COD/(m3·d) (GSBR2) and 1.53 kg COD/(m3·d) (GSBR3). Granules with a diameter of 0.5–1 mm had the most stable EPS content and composition. The smallest granules had the largest amount of bound EPS. The amount of loosely-bound EPS increased as granule diameters decreased; it was lowest in the famine phase at end of the cycle. The proteins/polysaccharides ratio decreased below 1 only in soluble EPS in the famine period. In GSBR1, granules with a diameter <0.5 mm predominated, and the increase in soluble EPS at end of the cycle was most substantial resulting in the lowest COD removal.

Exploring the potential of iTRAQ proteomics for tracking the transformation of extracellular proteins from enzyme-disintegrated waste activated sludge

To characterize the transformation of extracellular proteins extracted from raw and enzyme-disintegrated waste activated sludge (WAS), extracts of extracellular polymeric substances (EPS) were subject to isobaric tags for relative and absolute quantitation (iTRAQ) proteomics analysis. 209 proteins were identified and categorized into three Gene Ontology classifications: “cellular components”, “molecular function”, and “biological processes”. Most identified proteins originated from intracellular components, organelles, or cytoplasm, suggesting that cell decline and lysis represent the main sources of extracellular proteins in WAS. The major protein functions comprised “transporter binding activity”, “macromolecule metabolic process”, and “biosynthesis enzyme catalytic activity”. In total, 15 proteins categorized as “membrane part” and “biological adhesion” and 10 as “organelle” were down- or up-regulated, respectively, implying that the enzyme-disintegration mainly induced WAS floc-structure disintegration via membrane structure and corresponding biological adhesion disruption. The proteomics study will provide valuable clues to better understand EPS changes associated with enzymatic treatment at molecular levels.

Temporal changes in extracellular polymeric substances on hydrophobic and hydrophilic membrane surfaces in a submerged membrane bioreactor

Membrane surface hydrophilic modification has always been considered to mitigating biofouling in membrane bioreactors (MBRs). Four hollow-fiber ultrafiltration membranes (pore sizes ∼0.1 μm) differing only in hydrophobic or hydrophilic surface characteristics were operated at a permeate flux of 10 L/m2 h in the same lab-scale MBR fed with synthetic wastewater. In addition, identical membrane modules without permeate production (0 L/m2 h) were operated in the same lab-scale MBR. Membrane modules were autopsied after 1, 10, 20 and 30 days of MBR operation, and total extracellular polymeric substances (EPS) accumulated on the membranes were extracted and characterized in detail using several analytical tools, including conventional colorimetric tests (Lowry and Dubois), liquid chromatography with organic carbon detection (LC-OCD), fluorescence excitation - emission matrices (FEEM), fourier transform infrared (FTIR) and confocal laser scanning microscope (CLSM). The transmembrane pressure (TMP) quickly stabilized with higher values for the hydrophobic membranes than hydrophilic ones. The sulfonated polysulfone (SPSU) membrane had the highest negatively charged membrane surface, accumulated the least amount of foulants and displayed the lowest TMP. The same type of organic foulants developed with time on the four membranes and the composition of biopolymers shifted from protein dominance at early stages of filtration (day 1) towards polysaccharides dominance during later stages of MBR filtration. Nonmetric multidimensional scaling of LC-OCD data showed that biofilm samples clustered according to the sampling event (time) regardless of the membrane surface chemistry (hydrophobic or hydrophilic) or operating mode (with or without permeate flux). These results suggest that EPS composition may not be the dominant parameter for evaluating membrane performance and possibly other parameters such as biofilm thickness, porosity, compactness and structure should be considered in future studies for evaluating the development and impact of biofouling on membrane performance.

Production of protein‐ and carbohydrate‐EPS in activated sludge reactors operated at different carbon to nitrogen ratios

AbstractBACKGROUNDThis study aimed to clarify how a variation in the carbon to nitrogen (C/N) ratio in influent wastewater affects the production and composition of extracellular polymeric substances (EPS) in activated sludge. In the literature such a comparative analysis is rarely presented, most studies on EPS focus on simultaneous organic carbon removal and nitrification whereas little attention is paid to the case of low organic load or separate‐stage nitrification.RESULTSAmong the very loosely bound, loosely bound and tightly bound EPS fractions, tightly bound EPS prevailed in semi‐continuously fed batch activated sludge reactors that were fed at a C/N ratio of 10, 5 and 0, respectively. The C/N ratio had no clear effect on total EPS production, however it changed the proportion of proteins and carbohydrates. In each sludge proteins constituted the dominant part of EPS, but the EPS of the nitrifying sludge (C/N = 0), had a definitely higher protein content. As evidenced by HPSEC fingerprints, in all EPS fractions most proteins had MWs ≤16 kDa. Depending on the C/N ratio in a reactor, high MW proteins in EPS shifted from tightly bound fractions to others.CONCLUSIONThe study is among the few that highlight how the protein and carbohydrate content in EPS changes at different C/N ratios. Since wastewater composition in a treatment system affects the chemical composition of EPS, each sludge might have different responses to uptake of xenobiotics such as metals. Further, this difference in composition might affect sludge settling, dewatering and membrane fouling. © 2014 Society of Chemical Industry

Measuring the soil-microbial interface: Extraction of extracellular polymeric substances (EPS) from soil biofilms

Many soil microbes exist in biofilms. These biofilms are typified by variable quantities of extracellular polymeric substances (EPS: predominantly polysaccharides, glycoconjugates, and proteins) and the embedded microbial cells. A method to measure soil-EPS (the biofilm exclusive of microbial cells) has not yet been described. The present work investigates the potential of five extraction methods to estimate changes in soil-EPS content. A rationale for selection of appropriate EPS extraction and methodology is discussed, including the crucial consideration of both intracellular and extracellular contamination.EPS was developed in situ by provision of labile C (glycerol) to the microbial biomass of a moist soil and then applying desiccation stress. Only two out of the five extraction methods showed statistically significant increases in polysaccharide production responding to substrate addition. Humified organic matter, estimated by its humic acid equivalent (HAE) was used to indicate the degree of extracellular contamination, and/or creation of humic artefacts – both of which affect detection of changes in EPS. The HAE concentration was very high when applying original and modified methods designed to extract glomalin related soil protein (GRSP). Extraction methods involving heating with dilute sulphuric acid appeared to overestimate EPS-polysaccharide. Using microbial ATP as an indicator of cell-lysis, confidence could only be ascribed to EPS extraction with cation exchange resin. Using this method, the expected increases in EPS-polysaccharide were clearly apparent. The HAE/protein ratios of EPS extracts were also lowest with cation exchange – indicating this method did not cause excessive contamination from humified soil organic matter or create related artefacts.

Operational experience with a seasonally operated full-scale membrane bioreactor plant

A seasonally operated full-scale membrane bioreactor plant (flat sheet, 0.03μm) treating municipal wastewater from a recreation facility was monitored for 2years. In particular, membrane bioreactor operation characteristics and development and changes in extracellular polymeric substances and soluble microbial product concentrations were observed, which were both dependent on volume and quality of incoming wastewater. Microbiological effluent quality, nutrient removal efficiency and activated sludge characteristics were analysed on a regular basis. Correlations between activated sludge quality, extracellular polymeric substance and soluble microbial product concentrations were identified. Pathogen related changes in effluent quality during plant operation were also observed. Nutrient removal efficiency was very good, despite fluctuations in influent flow.

Impact of magnesium on membrane fouling in membrane bioreactors

The characteristics of membrane fouling were compared in submerged membrane bioreactors at three Mg:Ca molar ratios (1:5, 1:1, and 5:1), constant calcium concentration of around 1.7 mM and a solids retention time (SRT) of 15 d. Permeability, extracellular polymeric substances (EPS), soluble microbial products (SMP), Ca 2+ and Mg 2+ concentrations were measured regularly in the reactors to investigate the cause of membrane fouling. Molecular weight fractionation and relative hydrophobicity of EPS and SMP were also measured. In terms of membrane fouling rate, no differences were observed between Mg:Ca ratios of 1:5 and 1:1. The increase in the EPS and the concomitant decrease in SMP concentrations, both as protein and carbohydrates, due to divalent cation binding and enhanced bioflocculation were not significant enough to change the membrane permeability. More hydrophobic EPS was formed due to lower divalent cations at the low Mg:Ca ratio, resulting in higher EPS deposition on the membrane surface and membrane fouling. Comparison of the reactors with Mg:Ca ratios of 5:1 and 1:5 showed that the fouling rate is lower in the reactor with the higher Mg:Ca ratio. The introduction of magnesium at the higher Mg:Ca ratios proved that magnesium is beneficial in reducing membrane fouling due to changes in EPS and SMP characteristics as well as molecular weights.