Identification of biofoulant of membrane bioreactors in soluble microbial products

Determination of Sustainable Critical Flux through a Long-Term Membrane Resistance Model

A long-term membrane resistance model (LMR) was established to determine the sustainable critical flux, which developed and simulated polymer film fouling successfully in a lab-scale membrane bioreactor (MBR) in this study. The total polymer film fouling resistance in the model was decomposed into the individual components of pore fouling resistance, sludge cake accumulation and cake layer compression resistance. The model effectively simulated the fouling phenomenon in the MBR at different fluxes. Considering the influence of temperature, the model was calibrated by temperature coefficient τ, and a good result was achieved to simulate the polymer film fouling at 25 and 15 °C. The relationship between flux and operation time was simulated and discussed through the model. The results indicated that there was an exponential correlation between flux and operation time, and the exponential curve could be divided into two parts. By fitting the two parts to two straight lines, respectively, the intersection of the two straight lines was regarded as the sustainable critical flux value. The sustainable critical flux obtained in this study was just 67% of the critical flux. The model in this study was proven to be in good agreement with the measurements under different fluxes and different temperatures. In addition, the sustainable critical flux was first proposed and calculated in this study, and it was shown that the model could be used to predict the sustainable operation time and sustainable critical flux, which provide more practical information for designing MBRs. This study is applicable to polymer films used in a wide variety of applications, and it is helpful for maintaining the long-term stable operation of polymer film modules and improving the efficiency of polymer film modules.

Two strategies of stubborn biofouling strains surviving from NaClO membrane cleaning: EPS shielding and/or quorum sensing

The declined performance of repeated chemically-enhanced-backwashing (CEB) seriously hampered the sustainable operation of membrane bioreactor (MBR) in long-term, and could be partially attributed to the strengthened anti-cleaning properties of residual stubborn microbes. Although plenty of research has been done towards either the model strains or the whole post-CEB microbial community, little was known about the resisting behavior of practical stubborn strains when confronting oxidative stresses induced by NaClO. Hence, this study isolated 21 strains from samples in a large-scale MBR plant with routine CEB treatment. To unravel how they survive and affect membrane fouling, their anti-oxidation ability, fouling potential and quorum sensing (QS) effect before and after NaClO stimuli were evaluated. The composition and molecular weight distribution of extracellular polymeric substance (EPS) were also investigated to understand their roles during the anti-CEB process. It was found that typical stubborn strains tended to secrete more EPS as protective shields, where polysaccharides (especially the ones >1 kDa) made major contribution. However, sometimes EPS could not well resist the stimuli, with consequent low survival rate and high intracellular ROS level. Under such circumstances, stubborn strains would rather choose to be sensitive with surged QS level and quick population regrowth to maintain vitality under the oxidative stresses. Both strategies aggravated biofouling and eventually enhanced the anti-cleaning properties of biofilm.

Using excitation-emission matrix fluorescence to evaluate the performance of water treatment plants for dissolved organic matter removal

This study is aimed at assessing the performance of water treatment plants (both wastewater and drinking water treatment plants) for dissolved organic matter (DOM) removal using excitation-emission matrix fluorescence (EEMF) as the monitoring technique. The influent from the wastewater treatment plant (WWTP) of Burgos (Spain) is characterized from the presence of protein-like peaks (T1 and T2) and humic-like peaks (A and C), T2 and A showing the highest fluorescence intensity. The percentages of total removal in the effluent were in the following order: peak T1 (65%) > peak A (45%) > peak C (34%) > peak T2 (26%). The humic-like peaks were the most removed at the primary sedimentation stage, whereas peak T1 was by far the most removed in the biological reactor. Protein-like peaks T1 and T2 experienced a slight increase in the final effluent in comparison to their fluorescence at the previous stage (the exit of the biological reactor), an increase that can be explained by the release of SMP (soluble microbial products) from the biomass in the secondary clarifier. A poor correlation was obtained between peak T2 fluorescence and COD, BOD (r² = 0.34-0.38). The natural water from the Úzquiza reservoir in Burgos (Spain) is characterized by the only presence of humic substances: a majority peak A (fulvic-like) and a weak peak C (humic-like). The whole fluorescent DOM was removed by coagulation-flocculation but a low fluorescence peak T2 appeared at the final stage, coming from protein-like SMPs released by the biomass attached to the filters.

Monitoring dissolved organic matter in wastewater and drinking water treatments using spectroscopic analysis and ultra-high resolution mass spectrometry

Dissolved organic matter (DOM) plays a critical role in determining the quality of wastewater and the safety of drinking water. This is the first review to compare two types of popular DOM monitoring techniques, including absorption spectroscopy and fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) vs. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), for the applications in wastewater and drinking water treatments. The optical techniques provide a series of indices for tracking the quantity and quality of chromophoric and fluorescent DOM, while FT-ICR-MS is capable of identifying thousands of DOM compounds in wastewater and drinking water at the molecule level. Both types of monitoring techniques are increasingly used in studying DOM in wastewater and drinking water treatments. They provide valuable insights into the variability of DOM composition in wastewater and drinking water. The complexity and diversity of DOM highlight the challenges for effective water treatments. Different effects of various treatment processes on DOM are also assessed, which indicates that the information on DOM composition and its removal is key to optimize the treatment processes. Considering notable progress in advanced treatment processes and novel materials for removing DOM, it is important to continuously utilize these powerful monitoring tools for assessing the responses of different DOM constituents to a series of treatment processes, which can achieve an effective removal of DOM and the quality of treated water.

Functional Determinants of Extracellular Polymeric Substances in Membrane Biofouling: Experimental Evidence from Pure-Cultured Sludge Bacteria

The aim of this work was to better understand the roles of extracellular polymeric substances (EPS) in membrane biofouling at the single-strain level. In the present study, a total of 23 bacterial strains were isolated from a sludge sample. The EPS extracted from pure-cultured bacteria were assessed for their fouling potentials and were simultaneously analyzed using Fourier transform infrared spectroscopy (FTIR). Further, the impact of calcium on the chemical composition of EPS and membrane fouling behavior was investigated in a strain-dependent manner. The EPS of the 23 bacterial strains exhibited different IR features for protein and polysaccharide regions. In addition, an α-1,4-glycosidic linkage (920 cm-1) and amide II (1,550 cm-1) correlated very well with the fouling potentials of all pure-cultured bacteria. In contrast to low-fouling strains, medium- and high-fouling strains exhibited two distinct peaks at 1,020 cm-1 (uronic acids) and 1,250 cm-1 (O-acetyl), which accelerate membrane fouling given their gelling capacities. In the presence of calcium, the fouling potential of a high-fouling strain (Bacillus sp. strain JSB10) was profoundly reduced (P < 0.0005) due to the binding activity of an α-1,4-glycosidic linkage and amide II with calcium. However, the impact of calcium on a low-fouling strain (Vagococcus sp. strain JSB21) was insignificant. Two-dimensional FTIR correlation spectroscopic (2D-FTIR-COS) analysis further revealed that the susceptibilities of functional groups to calcium largely relied on the composition and abundance of the above-described functional groups in EPS. These findings suggest that bacterial strains with different fouling potentials exhibit varied responses to calcium.IMPORTANCE Membrane biofouling is one of the main challenges for the operation of membrane-based processes used for water and wastewater treatment. This study revealed the functional determinants of EPS in membrane biofouling of 23 bacterial strains isolated from a full-scale membrane bioreactor (MBR) plant. We found that an α-1,4-glycosidic bond, amide II, and uronic acids of EPS significantly correlated with the fouling potentials of bacteria. The roles of these EPS groups in membrane fouling were impacted by calcium resulting from EPS-calcium interactions. In addition, our results also demonstrated that any perturbations in the sludge bacterial community in MBRs can lead to varied filtration potentials of the bulk liquor.

Influence of Feed Composition on the Monomeric Structure of Free Bacterial Extracellular Polysaccharides in Anaerobic Digestion

Six 5.0-L fill-and-draw batch reactors were used with different feed compositions containing a range of carbohydrates (glucose, sucrose, fructose) and nitrogen sources (urea, NH₄Cl) at various concentrations to investigate free extracellular polysaccharide (EPS) production during anaerobic digestion (AD). This work analyzed not only their monosaccharide components, but also their specific linkage patterns and the change associated with different chemical nature in carbon substrates or nitrogen sources; all of these parameters can have profound biological consequences, and were correlated to macronutrients present in the feed. It is believed that feed composition is a major factor which determines the physicochemical characteristics of the free EPS. Our findings also suggest that the differences associated with the digestion of various carbon substrates and/or nitrogen sources could alter monomeric saccharide composition and concentrations of the free EPS. Such insights demonstrate that previous studies on feed C/N ratios tended to overestimate EPS production, while variations in the chemical nature of the nitrogen source were overlooked. Our results also link the physiochemical properties of free EPS with underlying biofouling mechanisms, and demonstrate that membrane fouling is to some extent dependent upon the prevailing nutritional environment and feed composition.

3DEEM spectroscopy analysis to assess the EPS composition in different carriers in HMBR systems

A hybrid membrane bioreactor (HMBR) with biological band carriers (Reactor A) and an HMBR with suspended honeycomb carriers (Reactor B) were conducted in parallel to investigate the effects of different carriers on extracellular polymeric substances (EPS). Composition and concentration of EPS were examined by three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra and parallel factor analysis (PARAFAC). 3DEEM spectra demonstrated that the main organic substances of the EPS in two reactors were protein-like, humic acid-like and fulvic acid-like substances. The fluorescence intensity (FI) indicated that the protein-like composition was dominant in EPS, and its intensity in reactor B was stronger than that in A (392.94 > 250.25). Results of the FI identified from the 3DEEM by PARAFAC showed that the EPS in two reactors included two humic acid-like compositions C1 (230, 320/406 nm), C2 (250, 360/440 nm) and one protein-like C4 (230, 280/340 nm), while C3 was fulvic acid-like (220/429 nm) and protein-like (230/357 nm) in reactor A and B, respectively. The proportion and FI of protein-like substances in reactor B were higher than that in A. Consequently, it was concluded that reactor A could control the membrane fouling effectively, compared with reactor B.

Colorimetric measurement of carbohydrates in biological wastewater treatment systems: A critical evaluation

Four laboratory preparations and three commercially available assay kits were tested on the same carbohydrate samples with the addition of 14 different interfering solutes typically found in wastewater treatment plants. This work shows that a wide variety of solutes can interfere with these assays. In addition, a comparative study on the use of these assays with different carbohydrate samples was also carried out, and the metachromatic response was clearly influenced by variation in sample composition. The carbohydrate content in the supernatant of a submerged anaerobic membrane bioreactor (SAMBR) was also measured using these assays, and the amount in the different supernatant samples, with and without a standard addition of glucose to the samples, showed substantial differences. We concluded that the carbohydrates present in wastewater measured using these colorimetric methods could be seriously under- or over-estimated. A new analytical method needs to be developed in order to better understand the biological transformations occurring in anaerobic digestion that leads to the production of soluble microbial products (SMPs) and extracellular polymeric substance (EPS).

Mitigated membrane fouling of anammox membrane bioreactor by microbiological immobilization

In this study, membrane fouling behavior of anammox MBR with or without carriers made by magnetic porous carbon microspheres was investigated. The results show that Trans Membrane Pressure was an order of magnitude lower after 50days due to use of carriers, which did not directly contact with membrane surface. Scanning Electron Microscope analysis indicates that abundance of anammox bacteria formed biofilm on membrane surface. Fourier transform infrared spectroscopy combined with amino acids contents analysis for membrane surface deposition show that metabolite released by anammox bacteria contains more hydrophobic groups than hydrophilic, which was considered as important reason for its abundant existence on hydrophobic membrane surface. Microbiological immobilization not only reduces biological membrane fouling, but also mitigates organic fouling including organic matter containing COO, hydrophobic groups (CH3, CH2 and CH etc), as well as inorganic deposition. Our finding provides an effective method for mitigating MBR membrane fouling in anammox process.

Recent developments in anaerobic membrane reactors

Anaerobic membrane reactors (AnMBRs) have recently evolved from aerobic MBRs, with the membrane either external or submerged within the reactor, and can achieve high COD removals (~98%) at hydraulic retention times (HRTs) as low as 3 h. Since membranes stop biomass being washed out, they can enhance performance with inhibitory substrates, at psychrophilic/thermophilic temperatures, and enable nitrogen removal via Anammox. Fouling is important, but addition of activated carbon or resins/precipitants can remove soluble microbial products (SMPs)/colloids and enhance flux. Due to their low energy use and solids production, and solids free effluent, they can enhance nutrient and water recycling. Nevertheless, more work is needed to: compare fouling between aerobic and anaerobic systems; determine how reactor operation influences fouling; evaluate the effect of different additives on membrane fouling; determine whether nitrogen removal can be incorporated into AnMBRs; recover methane solubility from low temperatures effluents; and, establish sound mass and energy balances.

Formation of distinct soluble microbial products by activated sludge: kinetic analysis and quantitative determination

Soluble microbial products (SMP) released by microorganisms in bioreactors are classified into two distinct groups according to their different chemical and degradation kinetics: utilization-associated products (UAP) and biomass-associated products (BAP). SMP are responsible for effluent chemical oxygen demand or for membrane fouling of membrane bioreactor. Here an effective and convenient approach, other than the complicated chemical methods or complex models, is developed to quantify the formation of UAP and BAP together with their kinetics in activated sludge process. In this approach, an integrated substrate utilization equation is developed and used to determine UAP and their production kinetics. On the basis of total SMP measurements, BAP formation is determined with an integrated BAP formation equation. The fraction of substrate electrons diverted to UAP, and the content of BAP derived from biomass can then be calculated. Dynamic quantification data are obtained for UAP and BAP separately and conveniently. The obtained kinetic parameters are found to be reasonable as they are generally bounded and comparable to the literature values. The validity of this approach is confirmed by independent SMP production tests in six different activated sludge systems, which demonstrates its applicability in a wide range of engineered system regarding SMP production. This work provides a widely applied approach to determine the formation of UAP and BAP conveniently, which may offer engineers with basis to optimize bioreactor operation to avoid a high effluent soluble organics from SMP or SMP-based membrane fouling in membrane bioreactors.

Characterization of the size-fractionated biomacromolecules: tracking their role and fate in a membrane bioreactor

This article presents a study aimed at the fractionation and characterization of what is thought to be one of the most complex organic mixtures produced by activated sludge: biomacromolecules (BMM). Photometric quantification combined with excitation-emission matrix (EEM) fluorescence spectroscopy and nuclear magnetic resonance (NMR) measurements were used to characterize BMM in a membrane bioreactor (MBR) from a chemical perspective. Overall, the BMM in sludge supernatant were mainly present in three fractions: colloidal BMM (BMMc, >0.45 μm), biopolymeric BMM (BMMb, 0.45 μm-100 kDa) and low molecular weight (MW) fraction (<5 kDa). The analysis of fluorescence regional integration (FRI) showed that the organics in membrane permeate and those in the low-MW fraction of sludge supernatant were of similar chemical composition. The characterization by NMR suggested that the BMMc fraction had similar carbon content of proteins and polysaccharides. In contrast, the BMMb and the low-MW BMM were proved to be carbonaceous and aromatics, respectively. Moreover, because of the high MW and gelling property, polysaccharides were found to have a high potential to accumulate on the membranes. In addition, the lipids present in the BMMb of the sludge supernatant were demonstrated to be another important foulant due to their large size. Our results also indicated that aromatic proteins had a higher fouling propensity than tryptophan proteins though they were of similar size nature. This work could be useful for better understanding of the chemical nature of BMMs in MBRs.

Linking microbial community structure to membrane biofouling associated with varying dissolved oxygen concentrations

In order to elucidate how dissolved oxygen (DO) concentration influenced the generation of extracellular polymeric substance (EPS) and soluble microbial products (SMP) in mixed liquor and biocake, 16S rDNA fingerprinting analyses were performed to investigate the variation of the microbial community in an aerobic membrane bioreactor (MBR). The function of microbial community structure was proved to be ultimately responsible for biofouling. Obvious microbial community succession from the subphylum of Betaproteobacteria to Deltaproteobacteria was observed in biocake. High concentration of EPS in biocake under the low DO concentration (0.5 mg L(-1)) caused severe biofouling. The correlation coefficient of membrane fouling rate with EPS content in biocake (0.9941-0.9964) was much higher than that in mixed liquor (0.6689-0.8004).

Engineering of an MBR supernatant fouling layer by fine particles addition: a possible way to control cake compressibility

For membrane bioreactors (MBR) applied to wastewater treatment membrane fouling is still the prevalent issue. The main limiting phenomena related to fouling is a sudden jump of the transmembrane pressure (TMP) often attributed to the collapse of the fouling layer. Among existing techniques to avoid or to delay this collapse, the addition of active particles membrane fouling reducers (polymer, resins, powdered activated carbon (PAC), zeolithe...) showed promising results. Thus the main objective of this work is to determine if fouling can be reduced by inclusion of inert particles (500 nm and inert compared to other fouling reducers) and which is the impact on filtration performances of the structuring of the fouling. Those particles were chosen for their different surface properties and their capability to form well structured layer. Results, obtained at constant pressure in dead end mode, show that the presence of particles changes foulant deposition and induces non-compressible fouling (in the range of 0.5-1 bar) and higher rejection values compared to filtration done on supernatant alone. Indeed dead end filtration tests show that whatever interactions between biofluid and particles, the addition of particles leads to better filtration performances (in terms of rejection, and fouling layer compressibility). Moreover results confirm the important role played by macromolecular compounds, during supernatant filtration, creating highly compressible and reversible fouling. In conclusion, this study done at lab-scale suggests the potential benefit to engineer fouling structure to control or to delay the collapse of the fouling layer. Finally this study offers the opportunities to enlarge the choice of membrane fouling reducers by taking into consideration their ability to form more consistent fouling (i.e. rigid, structured fouling).

Preparation of solid acid catalyst from glucose-starch mixture for biodiesel production

The aim of this work is to study the catalyst prepared by glucose-starch mixture. Assessment experiments showed that solid acid behaved the highest esterification activity when glucose and corn powder were mixed at ratio of 1:1, carbonized at 400°C for 75 min and sulfonated with concentrated H(2)SO(4) (98%) at 150°C for 5 h. The catalyst was characterized by acid activity measurement, XPS, TEM and FT-IR. The results indicated that solid acid composed of CS(0.073)O(0.541) has both Lewis acid sites and Bronsted acid sites caused by SO(3)H and COOH. The conversions of oleic acid esterification and triolein transesterification are 96% and 60%, respectively. Catalyst for biodiesel production from waste cottonseed oil containing high free fatty acid (FFA 55.2 wt.%) afforded the methyl ester yield of about 90% after 12h. The catalyst deactivated gradually after recycles usage, but it could be regenerated by H(2)SO(4) treatment.

Effects of microbial degradation of biofoulants on microfiltration membrane performance in a membrane bioreactor

In membrane bioreactors (MBRs) for wastewater treatment, membrane fouling, particularly biofouling caused by soluble microbial products (SMP), is a nuisance problem causing decreases in permeation flux. In a previous study, we identified primary biofoulants of microfiltration (MF) membranes in SMP as polysaccharides containing uronic acids that undergo inter- and intramolecular ionic cross-linking by polyvalent cations, forming a gelatinous mass that clogs membrane pores. In the present study, we therefore attempted to isolate biofoulant-degrading microorganisms from activated sludge on a polygalacturonic acid-overlaid agar medium and evaluate their efficiency for preventing biofouling of MF membranes. Among the isolates, the fungal strain HO1 identified as Phialemonium curvatum degraded 30% of polysaccharides containing uronic acids into smaller molecules in a SMP solution containing a high concentration of saccharides after 30 days of cultivation. Microfiltration tests using a laboratory-scale submerged MBR indicated that the filtration resistance of this degraded SMP solution was lower than that of the control SMP solution without fungal inoculation. Importantly, accumulation of gelatinous mass on the membrane responsible for biofouling was avoided in the SMP solution augmented with P. curvatum HO1 during the microfiltration test. This is the first report to describe a new method for avoiding biofouling of MBRs by microbial degradation of primary biofoulants.

Fate of proteins and carbohydrates in membrane bioreactor operated at high sludge age

The paper evaluated the fate of proteins and carbohydrates in the course of substrate removal by membrane bioreactor (MBR), which was used for the biological treatment of black and grey water components of a controlled decentralized residential area. The MBRs were operated at a high sludge age of 60 days to better observe the magnitude of soluble residual products. Both groups were detected in the raw wastewater and represented 15% of the soluble chemical oxygen demand (COD) content for black water and 9% for grey water. Corresponding ratios in the process effluent were significantly increased to 70% and 24% respectively, indicating that both proteins and carbohydrates were likely to be generated as residual soluble microbial products. Residual soluble organics accumulated in the reactor at much higher levels as compared to the effluent due to cake filtration occurring on the surface of the membrane, entrapping fractions larger than 4-8 nm for proteins, and around 14 nm for carbohydrates. Mass balance showed that proteins and carbohydrates accumulated in the reactor were partially removed due to longer retention and possible acclimation of the biomass. The observed removal rate was much lower for carbohydrates compared with proteins.