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This study investigated the treatment and biomethane recovery performance of a high-biomass submerged anaerobic membrane bioreactor (HBSAnMBR) treating abattoir wastewater in six operational phases (Phases 1 – 6) at an organic loading rate (OLR) range of 1.05 – 7 kg-COD/m3/d. The HBSAnMBR system demonstrated a biomethane recovery of 75.5 ± 2.0% and COD removal efficiency of 98.8 ± 0.71% during the most sustainable operational phase at an OLR of 4 kg-COD/m3/d. Volatile fatty acids (VFAs) such as acetic, propanoic, isobutyric, and valeric acids significantly correlated with OLR and biomethane production, while butyric and isovaleric acid concentrations were unaffected. The biomethane recovery performance of the HBSAnMBR system correlated positively with microbial community dynamics in different operational phases. The functional analysis of the microbiome indicated that Pseudomonas and Anaerolineaceae played a significant role in the hydrolysis and fermentation of complex organic matter, which led to the production of VFAs and other intermediate products. Methanothrix were observed to utilize acetate for acetoclastic methanogenesis at OLR 4 kg-COD/m3/d, producing the highest biomethane. On the contrary, the acetoclastic methanogenesis was replaced by hydrogenotrophic methanogenesis by Methanolinea and Methanospirillum at OLR above OLR 4 kg-COD/m3/d, leading to a decline in biomethane production. [Display omitted] • The anaerobic membrane bioreactor produced CH 4 (>75.5%) at OLR 4 kg-COD/m3/d. • An excellent COD removal (>95%) was achieved during the stable operation. • Methanothrix soehngenii was the dominant Archaea in the methanogenic population. • Anaerolineaceae and Pseudomonas were syntrophic with methanogens to recover CH 4. • Acetoclastic methanogenesis is replaced by Hydrogenotrophic methanogenesis at high OLRs. [ABSTRACT FROM AUTHOR]

Conventional treatments for nutrient removal in wastewater are shifting to Anaerobic Membrane Bioreactors, which produce a high-quality effluent with minimum sludge production. The effluent resulting contains high nitrogen and phosphorus load that can be eliminated by microalgae culture. The aim of this study is to evaluate the ammonium and phosphorus removal rate of different microalgae species in the effluent of an anaerobic treatment. For that, 4 different microalgae species have been tested (Chlamydomonas reinhardtii, Scenedesmus obliquus, Chlorella vulgaris and Monoraphidium braunii) in batch monoculture and mixed conditions. Results indicate that all species are able to eliminate both P and N in the medium with high removal rates. However, a slight interspecies competition may boost these removal rates and productivity values ensuring, the success of the process. [ABSTRACT FROM AUTHOR]

Highlights • SFDM resistance in an S-AnSFDMBR was dynamically analyzed for the first time. • Fast SFDM formation and sustainable low-resistance high-flux operation were achieved. • Increasingly more compact SFDMs were resulted from more small particles and eEPS. • The stability of SFDM filtration was mainly controlled by its specific resistance. • The main mechanisms governing SFDM specific resistance changed with time. Abstract This study attempts to provide an improved fundamental understanding of the self-forming dynamic membrane (SFDM) filtration process in submerged anaerobic bioreactors. Excellent system performances were achieved in terms of high COD removal efficiency (∼ 90%), fast formation/reformation of SFDM (<1 h), and sustainable low-resistance (3.92 × 1010 m−1) high-flux (10–30 L/m2·h) filtration. A typical flux-variation profile consisted of an initial abruptly fast decrease followed by a gradually slow reduction, corresponding to the formation and sustainable operation period, respectively. The increase of SFDM resistance in formation period was attributable to the fast deposition of large particles on coarse-pore support materials. After SFDM formation, the subsequent increase of SFDM resistance was controlled more by the increase of specific resistance, which was firstly mainly resulted from the increasing accumulation of small particles with higher hydrophobicity and the external deposition of eEPS but later most attributable to the increase of internal release of eEPS. [ABSTRACT FROM AUTHOR]

Typically, anaerobic membrane bioreactors are operated at an organic loading rate (OLR) less than 10 kg chemical oxygen demand (COD)/m3 d. This paper discusses the development and performance of a high-rate submerged anaerobic membrane bioreactor (SAnMBR) for a high-strength synthetic industrial wastewater treatment. An OLR as high as 41 kg COD/m3 d was achieved with excellent COD removal efficiency (>99%). The membrane was operated at constant fluxes (9.4–9.9 ± 0.5 L/m2 h) and the change in trans-membrane pressure (TMP) was monitored to characterize the membrane performance. The results showed a low TMP (<5 kPa) under steady-state operation with only biogas sparging and relaxation as control strategy for over 300 days, implying no significant fouling was developed. Inorganic fouling was the dominant fouling mechanism occurred at the end of the study. The results suggest that the newly developed SAnMBR configuration can treat high-strength wastewater at lower capital expenditure while still providing superior effluent quality for water reuse or system closure. [ABSTRACT FROM PUBLISHER]

This study deals with the treatment of high suspended solids raw tannery wastewater using flat sheet Submerged Anaerobic Membrane (0.4 μm) Bioreactor (SAMBR) acclimatized with hypersaline anaerobic seed sludge for recovering biogas. The treatability of SAMBR achieved higher COD removal efficiency (90%) and biogas yield (0.160 L.g −1 COD removed ) coincided with high r 2 values between permeate flux and TSS (0.95), biogas and COD removed (0.96). The acidification of hypersaline influent wastewater by biogas mixing with high CO 2 , achieved quadruplet benefit of gas liquid and solid separation, in-situ pH and NH 3 control, in-situ CH 4 enrichment, and prevention of membrane fouling. The initial high VFA became stable as time elapsed reveals the hydrolysing ability of particulate COD into soluble COD and into biogas, confirms the suitability of SAMBR for high suspended solids tannery wastewater. [ABSTRACT FROM AUTHOR]

This study examined the effects of Fe 2+ and its bioavailability for controlling VFAs during organic shock loads in batch reactors and a submerged anaerobic membrane bioreactor (SAMBR). When seed grown under Fe-sufficient conditions (7.95 ± 0.05 mg Fe/g-TSS), an organic shock resulted in leaching of Fe from the residual to organically bound and soluble forms. Under Fe-deficient seed conditions (0.1 ± 0.002 mg Fe/g TSS), Fe 2+ supplementation (3.34 mg Fe 2+ /g-TSS) with acetate resulted in a 2.1–3.9 fold increase in the rate of methane production, while with propionate it increased by 1.2–1.5 fold compared to non-Fe 2+ supplemented reactors. Precipitation of Fe 2+ as sulphides and organically bound Fe were bioavailable to methanogens for acetate assimilation. The results confirmed that the transitory/long term limitations of Fe play a significant role in controlling the degradation of VFAs during organic shock loads due to their varying physical/chemical states, and bioavailability. [ABSTRACT FROM AUTHOR]

This paper focuses on the treatment of leachate from the organic fraction of municipal solid waste (OFMSW) in a submerged anaerobic membrane bioreactor (SAMBR). Operation of the SAMBR for this type of high strength wastewater was shown to be feasible at 5 days hydraulic retention time (HRT), 10 L min −1 (LPM) biogas sparging rate and membrane fluxes in the range of 3–7 L m −2 hr −1 (LMH). Under these conditions, more than 90% COD removal was achieved during 4 months of operation without chemical cleaning the membrane. When the sparging rate was reduced to 2 LPM, the transmembrane pressure increased dramatically and the bulk soluble COD concentration increased due to a thicker fouling layer, while permeate soluble COD remained constant. Permeate soluble COD concentration increased by 20% when the sparging rate increased to 10 LPM. [ABSTRACT FROM AUTHOR]

A novel design for a pilot scale anaerobic submerged membrane bioreactor (AnSMBR) equipped with an ultrafiltration unit, treating municipal wastewater at 18 ± 2 °C, and inoculated with a mesophilic inoculum without acclimation, was implemented and evaluated over 3 years of stable operation. The AnSMBR operated with a volumetric loading rate between 1.6 to 2.0 kg COD/m 3 UASB d, 12.8 to 14.2 h hydraulic retention time, and reached a tCOD removal efficiency of around 90%. Biosolid production was between 0.05 and 0.083 g VS/g COD removed . Dissolved methane oversaturation in the effluent was observed, reaching average values of 19.1 ± 0.84 mg CH 4 /L. The permeate flow rate ranged from 10 to 14 L/m 2 h with trans-membrane pressure (TMP) values of 400–550 mbar, using cycles of 30 s backwash, 7.5 min filtration, and continuous biogas sparging (9–16 m/h). During the three years of continuous operation, the membrane was not physically or chemically cleaned. [ABSTRACT FROM AUTHOR]

Enhancing the hydrolysis of microbial macromolecules by supplementing exogenous hydrolases may improve membrane performance via structural disruptions of fouling layers and alterations to sludge characteristics. This was investigated by short batch filtration (<1 h) and 30-day extended filtration experiments using laboratory-scale anaerobic membrane bioreactors. Crude hydrolases were either dispersed directly into the reactor, or immobilized onto microfiltration membranes. Under constant flux operation, dispersed enzymes consistently moderated increases in transmembrane pressures (TMPs) compared to the control setup. Immobilized hydrolases appeared effective in the short filtration test, but in the extended experiment, the pseudo-stable TMP was not significantly lower compared to the control TMP. With dispersed enzymes, the average TMP was almost 30% lower than the control value. This was associated with a 33% reduction in the protein content of the bulk extracellular polymeric substances, and a 45% reduction in the membrane cake density. Immobilized enzymes limited cake formation to a similar extent through hydrolysis at the base of the cake, but this was negated by the increase in gel resistance attributed to the hydrophobic attraction between the immobilization layer and proteinaceous hydrolysis products. Even as the dispersed hydrolases exhibited greater effectiveness under the conditions studied, there is scope for further enhancement in both approaches. [ABSTRACT FROM AUTHOR]

An anaerobic membrane bioreactor (AnMBR) is a biological treatment process which uses a membrane for solidliquid separation in wastewater treatment. The present research studied the application of a lab-scale vacuum-driven submerged anaerobic membrane bioreactor (SAnMBR) with polypropylene hollow fiber membranes in treating synthetic acidified wastewater. The reactor with a working volume of 6.75 to 7 L was operated at mesophilic temperature (35±1 °C) for 120 days. The area of the polypropylene membrane module was 0.1 m2. The reactor was fed with synthetic wastewater of volatile fatty acids (VFAs) in the range of COD between 1000 to 6000 mg/L. Organic loading rate increased from 0.4437 to 4.45 kg/m3/day during the operation period. Average COD removal was 96.33% at a HRT of 1.5 days. Maximum COD removal was 99.6% at a HRT of 4.5 days, and at which influent COD of 6000 mg/L was reduced to 17.11 mg/L. The average of fluxes in this bioreactor was 6.3086 L/m2.h. Turbidity of the effluent was often less than 5 NTU. TSS and VSS of the effluent were very low, and constituted only a small part of total solids (TS). The results of this research showed that a submerged anaerobic hollow fiber membrane bioreactor (SAnMBR) is effective in treating wastewaters with low to middle concentration of organic materials. Also low amounts of suspended solids in the effluent made this bioreactor very suitable for treating industrial wastewaters with high amounts of suspended solids. [ABSTRACT FROM AUTHOR]

This work studies the use of a well-known and spread activated sludge system (UCT configuration) to treat the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) treating domestic wastewater. Ammonia, phosphate, dissolved methane and sulphide concentrations in the SAnMBR effluent were around 55 mg NH4–N L−1, 7 mg PO4 –P L−1, 30 mg non-methane biodegradable COD L−1, and 105 mg S 2− L−1 respectively. The results showed a nitrification inhibition caused by the presence of sulphur compounds at any of the solids retention time (SRT) studied (15, 20 and 25 days). This inhibition could be overcome increasing the hydraulic retention time (HRT) from 13 to 26 h. Among the sulphur compounds, sulphide was identified as the substance which caused the nitrification inhibition. When the nitrification was well established, removal rates of nitrogen and phosphorus of 56% and 45% were reached respectively. The sulphide present in the influent was completely oxidised to sulphate, contributing this oxidation to the denitrification process. Moreover, the presence of methanotrophic bacteria, detected by FISH technique, could also contribute to the denitrification. [ABSTRACT FROM AUTHOR]

In this study, the aim was to assess the impact of different membrane modules such as cylinder-shaped, funnel-shaped, and U-shaped on the membrane fouling behavior in a laboratory-scale submerged anaerobic membrane bioreactor (AnSMBR) treating the synthetic wastewater for over 124 days. A series of analysis, including soluble microbial products (SMP), extracellular polymeric substances (EPSs), scanning electron microscopy, energy dispersive X-ray spectroscopy, particle size distribution, and filtration resistances, was performed by considering all membrane modules. The results showed that difference between COD and TOC removals was negligible in membrane modules designed at different forms. However, the priority of the membrane modules in terms of providing high permeate fluxes was found to be cylinder-shaped > funnel-shaped > U-shaped bundle. Both SMP and EPS within cake formed on the fibers in the cylinder-shaped module were lower than those in the U-shaped and funnel-shaped modules. The particles in the U-shaped module were smaller than those in other modules while they were coarse in the cylinder-shaped module. The results demonstrate that cylinder-shaped module was the most suitable module of hollow fiber to control the membrane fouling in a AnSMBR. [ABSTRACT FROM PUBLISHER]

Abstract: The aim of this study was the long-term validation of a model capable of reproducing the filtration process occurring in a submerged anaerobic membrane bioreactor (SAnMBR) system. The proposed model was validated using data obtained from a SAnMBR demonstration plant fitted with industrial-scale hollow-fibre membranes. The validation was carried out using both lightly and heavily fouled membranes operating at different bulk concentrations, gas sparging intensities and transmembrane fluxes. Across a broad spectrum of operating conditions, the model correctly forecast the respective experimental data in the long term. The simulation results revealed the importance of controlling irreversible fouling in order to ensure sustainable long-term membrane performance. [Copyright &y& Elsevier]

Highlights: [•] A two-stage AnMBR was designed for the treatment of sugarcane vinasse. [•] Intermittent feeding was found to be effective to acclimate the microorganisms. [•] COD and DOC removals efficiencies were 96.9±0.7% and 95.0±1.1%, respectively. [•] Membrane filtration resistance was found to be predominantly removable. [•] SMP protein and EPS protein were correlated to membrane filtration resistance. [ABSTRACT FROM AUTHOR]

Abstract: A demonstration plant with two commercial HF ultrafiltration membrane modules (PURON®, Koch Membrane Systems, PUR-PSH31) was operated with urban wastewater. The effect of the main operating variables on membrane performance at sub-critical and supra-critical filtration conditions was tested. The physical operating variables that affected membrane performance most were gas sparging intensity and back-flush (BF) frequency. Indeed, low gas sparging intensities (around 0.23 Nm3 h−1 m−2) and low BF frequencies (30-s back-flush for every 10 basic filtration–relaxation cycles) were enough to enable membranes to be operated sub-critically even when levels of mixed liquor total solids were high (up to 25 g L−1). On the other hand, significant gas sparging intensities and BF frequencies were required in order to maintain long-term operating at supra-critical filtration conditions. After operating for more than two years at sub-critical conditions (transmembrane flux between 9 and 13.3 LMH at gas sparging intensities of around 0.23 Nm3 h−1 m−2 and MLTS levels from around 10–30 g L−1) no significant irreversible/irrecoverable fouling problems were detected (membrane permeability remained above 100 LMH bar−1 and total filtration resistance remained below 1013 m−1), therefore no chemical cleaning was conducted. Membrane performance was similar to the aerobic HF membranes operated in full-scale MBR plants. [Copyright &y& Elsevier]

Abstract: Effects of wastewater and mixed liquor characteristics on membrane fouling in both a submerged anaerobic membrane bioreactor and a thermophilic submerged aerobic membrane bioreactor were studied with four types of industrial wastewaters. Significant differences in particle size distribution, colloidal content, the protein to polysaccharide ratio, and soluble compounds molecular weight distribution were observed among the four types of wastewaters and mixed liquors. Differences in wastewater and mixed liquor characteristics were correlated to the changes in membrane filtration behavior in both systems. The colloidal content in feed and mixed liquor plays a dominant role and is more important than the quantity of total suspended solids in controlling membrane fouling. The ratio of proteins to polysaccharides is more important than the total quantity of soluble organic substances in controlling membrane fouling. A full characterization of feed and mixed liquor may be used as a tool to predict membrane performance. [Copyright &y& Elsevier]

This study investigated the removal of nitrogen and phosphorus from the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) by means of a lab-scale photobioreactor in which algae biomass was cultured in a semi-continuous mode for a period of 42 days. Solids retention time was 2 days and a stable pH value in the system was maintained by adding CO 2 . Nitrogen and phosphorus concentrations in the SAnMBR effluent fluctuated according to the operating performance of the bioreactor and the properties of its actual wastewater load. Despite these variations, the anaerobic effluent proved to be a suitable growth medium for microalgae (mean biomass productivity was 234 mg l −1 d −1 ), achieving a nutrient removal efficiency of 67.2% for ammonium (NH 4 + –N) and 97.8% for phosphate (PO 4 −3 –P). When conditions were optimum, excellent water quality with very low ammonium and phosphate concentrations was obtained. [ABSTRACT FROM AUTHOR]

The main aim of this work was to study the influence of the mixed liquor total solids (MLTS) concentration on membrane permeability (K20) in a submerged anaerobic membrane bioreactor (SAnMBR) pilot plant, which is equipped with industrial hollow-fibre membranes and treats urban wastewater. This pilot plant was operated at 33 WC and 70 days of SRT. Two different transmembrane fluxes (13.3 and 10 LMH) were tested with a gas sparging intensity of 0.23 Nm3 m-2 h-1 (measured as Specific Gas Demand referred to membrane area). A linear dependence of K20 on MLTS concentration was observed within a range of MLTS concentration from 13 to 32 g L-1 and J20 of 10 LMH. K20 was maintained at sustainable values (about 100 LMH bar-1) even at high MLTS concentrations (up to 20 g L-1). In addition, several short-tests were carried out when the membranes were operated at high MLTS concentrations in order to assess the effect of the physical cleaning strategies (relaxation and back-flush) on membrane performance. It was observed that, with the applied gas sparging intensity, the duration of the relaxation stage did not critically affect the membrane performance. On the other hand, the required back-flush frequency was considerably affected by the MLTS concentration. [ABSTRACT FROM AUTHOR]

Abstract: A submerged anaerobic MBR demonstration plant with two commercial hollow-fibre ultrafiltration systems (PURON®, Koch Membrane Systems, PUR-PSH31) was operated using municipal wastewater at high levels of mixed liquor total solids (MLTS) (above 22gL−1). A modified flux-step method was applied to assess the critical flux (JC ) at different gas sparging intensities. The results showed a linear dependency between JC and the specific gas demand per unit of membrane area (SGDm). JC ranged from 12 to 19LMH at SGDm values of between 0.17 and 0.5Nm3 h−1 m−2, which are quite low in comparison to aerobic MBR. Long-term trials showed that the membranes operated steadily at fluxes close to the estimated JC , which validates the JC obtained by this method. After operating the membrane for almost 2years at sub-critical levels, no irreversible fouling problems were detected, and therefore, no chemical cleaning was conducted. [Copyright &y& Elsevier]

This study investigated the evolution of archaeal and bacterial populations of two submerged anaerobic membrane bioreactors (SAMBRs) operating at a mean solids residence time of 30 (SAMBR30) and 300 days (SAMBR300) at mesophilic and psychrophilic temperatures. SAMBRs were fed with leachate produced in a hydrolytic reactor (HR) treating the organic fraction of municipal solid waste. The archaeal fingerprint using denaturing gradient gel electrophoresis showed different populations in the first and second stage of the two-stage anaerobic process. A build up of volatile fatty acids (VFAs) was observed at 20°C in SAMBR30; whereas in SAMBR300, the VFAs only built up at 10°C. The dominant bacterial species in the HR belonged to Prevotella and Thauera, whereas the dominant ones in SAMBR300 belonged to Sphingobacteriales, Anaerovorax, Spirochaetaceae, Hydrogenophaga, Ralstonia, Prevotella, and Smithella. Low bacterial diversity in SAMBR30 compared with SAMBR300 resulted in a persistently high soluble chemical oxygen demand (>2 g/L) in the bulk reactor due to an insufficient residence time for bacteria to carry out the degradation of recalcitrant chemical oxygen demand found in the leachate. [ABSTRACT FROM AUTHOR]

In this study, various methods were compared to reduce the Chemical Oxygen Demand (COD) content of stabilised leachate from a Submerged Anaerobic Membrane Bioreactor (SAMBR). It was found that Powdered Activated Carbon (PAC) resulted in greater COD removals (84 %) than Granular Activated Carbon (GAC-80 %), an ultrafiltration membrane of 1kDa (75 %), coagulation-flocculation with FeCl3 and polyelectrolyte (45 %), FeCl3 alone (32 %), and polymeric adsorbents such as XAD7HP (46 %) and XAD4 (32 %). Results obtained on the <1 kDa fraction showed that PAC and GAC had a similar adsorption efficiency of about 60 % COD removal, followed by XAD7HP (48 %), XAD4 (27 %) and then FeCl3 (23 %). The post-treatment sequence UF+GAC would result in a final effluent with less than 100 mg COD/L. Size Exclusion Chromatography (SEC) revealed that the extent of adsorption of low MW compounds onto PAC was limited due to low MW hydrophilic compounds, whereas the kinetics of PAC adsorption depended mainly on the adsorption of high MW aromatics. [ABSTRACT FROM PUBLISHER]

Abstract: A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) was operated for 106days for municipal secondary wastewater treatment. COD removal efficiency of approximately 90% with methane yield rate of 0.26 LCH4/gCODremoval was achieved. The results of laboratory-scale experiment served to full-scale SAnMBR design. Cost analysis of the full-scale SAnMBR system showed that membrane costs and gas scouring energy accounted for the largest fraction of total life cycle capital costs and operational costs, respectively. The operational costs can be totally offset by the benefits from biogas recovery. Sensitive analysis showed that membrane parameters including flux, price and lifetime play decisive roles in determining the total life cycle costs of the SAnMBR. The study demonstrated the technical feasibility as well as economic feasibility of SAnMBR treating municipal wastewater, providing that the membrane performance was significantly improved or membrane price significantly decreased. [Copyright &y& Elsevier]

Abstract: Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping pressate were studied for 416days. The results showed that the SAnMBR system were highly resilient to temperature variations in terms of chemical oxygen demand (COD) removal. The residual COD in treated effluent was slightly higher at 55°C than that at 37 and 45°C. There were no significant changes in biogas production rate and biogas composition. However, temperature shocks resulted in an increase in biogas production temporarily. The SAnMBR could tolerate the 5 and 10°C temperature shocks at 37°C and the temperature variations from 37 to 45°C. The temperature shock of 5 and 10°C at 45°C led to slight and significant disturbance of the performance, respectively. Temperature affected the richness and diversity of microbial populations. [Copyright &y& Elsevier]

Abstract: The aim of this study was to assess the effect of several operational variables on both biological and separation process performance in a submerged anaerobic membrane bioreactor pilot plant that treats urban wastewater. The pilot plant is equipped with two industrial hollow-fibre ultrafiltration membrane modules (PURON® Koch Membrane Systems, 30m2 of filtration surface each). It was operated under mesophilic conditions (at 33°C), 70days of SRT, and variable HRT ranging from 20 to 6h. The effects of the influent COD/SO4–S ratio (ranging from 2 to 12) and the MLTS concentration (ranging from 6 to 22gL−1) were also analysed. The main performance results were about 87% of COD removal, effluent VFA below 20mgL−1 and biogas methane concentrations over 55% v/v. Methane yield was strongly affected by the influent COD/SO4–S ratio. No irreversible fouling problems were detected, even for MLTS concentrations above 22gL−1. [Copyright &y& Elsevier]

Considering the membrane fouling problem in submerged anaerobic membrane bioreactors, a set of submerged double-shaft rotary anaerobic membrane bioreactor (SDRAnMBR) was constructed by applying a double-shaft rotary module to submerged anaerobic bioreactor, and the theoretic analysis of the characteristics of hydraulics dynamics in SDRAnMBR has been performed. The membrane fouling performance for treatment of synthetic brewery wastewater was investigated by SDRAnMBR. The results of a theoretical analysis showed that the effects of homogenization, interleaving oscillation and three-phase rotating flow were produced within SDRAnMBR. Owing to their synergistic effect, the characteristics of shear, turbulence, oscillation and mass transfer within rotating fluid were enhanced so that the concentration polarization was reduced and permeate flux increased. The experiment results showed that SDRAnMBR had good anti-contamination performance and could maximize the reduction and control of the membrane fouling, proving the theoretic analysis on the characteristics of hydraulics dynamics in SDRAnMBR. [ABSTRACT FROM AUTHOR]

Abstract: A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) was used for thermomechanical pulping whitewater treatment. Sludge cake formation on membrane surfaces was identified as the dominant mechanism of membrane fouling. The spatial distribution of physical, chemical and microbiological structure of cake layers was characterized by various analytical techniques, including micro-tome slicing technique, confocal laser scanning microscopy (CLSM), conventional optical microscopy (COM), scanning electron microscopy (SEM)-energy-dispersive X-ray analyzer (EDX), particle size distribution (PSD) analysis, Fourier transform infrared (FTIR) spectroscopy, extraction and chemical analysis of extracellular polymeric substances (EPS), and polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). The results showed that the areal porosity decreased from the top layer to the bottom layer. Smaller flocs had a higher tendency to accumulate on membrane surfaces but the consolidation of cake sludge in the bottom layers resulted in larger flocs as compared to the fresh cake sludge formed on the top layers. There was an increase in the bound EPS density (mgEPS/cm3 wet sludge) and a decrease in the ratio of proteins to polysaccharides in bound EPS from the top to bottom layers. PCR-DGGE study showed that there were significant differences in microbial community population density along the cake layer depth. Through the CLSM and COM images, cake layer was found to have a loose outer surface when compared with the cake bottom. The results provide a new insight in cake layer structure and suggest that structures change significantly from the top layer to the bottom layer. [Copyright &y& Elsevier]

Abstract: A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping whitewater was operated for over 7months to investigate and compare the characteristics of cake sludge and bulk sludge during stable state operation period. Serial analysis showed that cake sludge had a smaller particle size distribution (PSD), much higher specific filtration resistance (1.34×1014 m/kg), 1.5 times higher bound EPS and significantly different microbial community as compared with bulk sludge. Further analysis indicated that small flocs, bound EPS and inorganic materials play important role in cake formation process. The formed cake layer was found to have a heterogeneous structure. The results obtained in this study indicated that cake formation process started from attachment of small flocs and/or specific bacterial clusters which colonize the surface of the membrane and provide enhanced conditions that allow for cake formation to progress. [ABSTRACT FROM AUTHOR]

Characteristics of different fractions (small flocs vs. large flocs) of sludge flocs from a submerged anaerobic membrane bioreactor treating thermomechanical pulping (TMP) whitewater were determined using various analytic techniques, including extraction and chemical analysis of extracellular polymeric substances (EPS), particle size analyzer, and polymer chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). The results showed that the fraction of smaller flocs contained a higher level of bound EPS and had a higher fractal dimension as compared to the fraction of larger flocs. PCR-DGGE analysis indicated that there were significant differences in microbial community between the fraction of smaller flocs and large flocs. The microbial community of the smaller flocs was similar to that of the sludge cake layers, indicating the pioneering role of the microbial community in smaller flocs in membrane fouling. These findings provide a new insight in the difference of membrane fouling potential between smaller flocs and larger flocs fraction. [ABSTRACT FROM AUTHOR]

Abstract: A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) was operated for over 160 days to assess the potential to treat kraft pulp mill evaporator condensate. Cake formation was identified as a dominant feature contributing to the deterioration of membrane performance. The influence of various operational parameters and sludge properties on sludge cake formation rate (CFR) was investigated. These included biogas sparging and permeate flow rates, as well as mixed liquor suspended solids (MLSS), soluble chemical oxygen demand (CODs) in the mixed liquor, and particle size distribution (PSD) and fractal dimension (D f) of particles. CFR was highly dependent on biogas sparging rate and permeate flow rate, and less dependent on MLSS. CODs, PSD and D f were found to significantly influence the CFR. Confocal laser scanning microscopic (CLSM) imaging and chemical analyses of extracellular polymeric substances (EPS) indicated that EPS was involved in sludge cake formation. Characterization of the sludge cake layers, when compared to the bulk sludge, indicated that smaller flocs and EPS preferentially accumulated in the sludge cake. The identification of factors including biogas sparging rate, permeate flow rate, CODs, EPS, PSD, and D f that impact the cake formation process provides a basis for selecting operating conditions to manage fouling in an SAnMBR. [Copyright &y& Elsevier]

Abstract: The effects of elevated pH shocks on the performance and membrane fouling of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping (TMP) whitewater was studied over a 120-day period. Changes in chemical oxygen demand (COD) removal, biogas production, sludge and cake layer properties, and their correlations to membrane fouling – before and after pH shocks – were systematically studied using various analytical tools. The results showed that a pH 8.0 shock had a minor impact, while pH 9.1 and 10.0 shocks exerted significant long-lasting negative impacts on COD removal, biogas production and membrane filtration performance of the SAnMBR. When the normal pH (7.0) was resumed, it took approximately 1, 6, and 30 days for the performance to recover for pH 8.0, 9.1 and 10.0 shocks, respectively. The elevated pH shocks induced the dispersion of sludge flocs and resulted in the accumulation of colloids and solutes or biopolymers in the sludge suspension, and thus deteriorated membrane performance. Statistical analysis showed that the ratio of proteins (PN) to polysaccharides (PS) in extracellular polymeric substances (EPS) had a strongly negative effect on the membrane fouling rate. There were smaller size particles deposited on the membrane surface and a more compact and denser cake layer was formed after being exposed to an alkaline shock at pH 10, resulting in higher membrane fouling rates. [Copyright &y& Elsevier]

The feasibility of using a thermophilic submerged anaerobic membrane bioreactor (SAnMBR) for kraft evaporator condensate treatment was studied at 55 ± 1°C over 6.5 months. Under tested organic loading rate of 1-7 kgCOD/m³ day, a soluble COD removal efficiency of 85-97% was obtained. The methane production rate was 0.35 ± 0.1 L methane/gCOD and the produced biogas was of excellent fuel quality with 80-90% methane. A higher membrane fouling rate was related to the presence of a larger portion of fine colloidal particles (1-10μm). The thermophilic SAnMBR was sensitive to the presence of toxic compounds in feed and unexpected pH probe failure (leading to a higher pH). Feed toxic shock caused sludge deflocculation and thus deteriorated membrane performance. Operating the reactor as a conventional anaerobic reactor to waste some of the fine flocs in treated effluent during the start-up process was an effective strategy to reduce membrane fouling. The experimental results from this study indicate that treatment of kraft evaporator condensate is feasible in terms of COD removal and biogas production using thermophilic SAnMBRs but pre-treatment may be needed to remove toxic sulfur compounds and membrane fouling caused by the large portion of fine particles may be a challenge. [ABSTRACT FROM AUTHOR]

Submerged anaerobic membrane bioreactor (SAnMBR) technology was studied for kraft evaporator condensate treatment at 37 ± 1°C over a period of 9 months. Under tested organic loading rates of 1-24 kg COD/m3/day, a chemical oxygen demand (COD) removal efficiency of 93-99% was achieved with a methane production rate of 0.35 ± 0.05 L methane/g COD removed and a methane content of 80-90% in produced biogas. Bubbling of recycled biogas was effective for in-situ membrane cleaning, depending on the biogas sparging rate used. The membrane critical flux increased and the membrane fouling rate decreased with an increase in the biogas sparging rate. The scanning electron microscopy images showed membrane pore clogging was not significant and sludge cake formation on the membrane surface was the dominant mechanism of membrane fouling. The results suggest that the SAnMBR is a promising technology for energy recovery from kraft evaporator condensate. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the performance of two submerged anaerobic membrane bioreactors (SAMBRs) operating at a mean solids residence time (SRT) of 30 (SAMBR30) and 300 days (SAMBR300) at mesophilic and psychrophilic temperatures. At 35°C results showed that SAMBR30 and 300 could achieve 95% soluble chemical oxygen demand (SCOD) removal at 1.5 and 1.1 days HRT, respectively, whereas at 20°C only SAMBR300 could maintain the same performance. Low temperatures were associated with higher bulk SCOD concentrations, which contributed to reducing the flux, but this was partly reversible once the SCOD was degraded. The utilization rate of compounds was affected differently by the drop in temperature with the concentration of some recalcitrants increasing, while for others such as bisphenol A it decreased when the temperature was decreased. Among the recalcitrants detected in SAMBR30 at 20°C there were not only long chain fatty acids such as undecanoic acid and dodecanoic acid, but also long chain alkanes such as tetracosane and heneicosane that could not be hydrolyzed at 20°C. In SAMBR300 these alkanes and acids only appeared at 10°C, whereas at 20°C complex compounds such as phenol, 2-chloro-4-(1,1-dimethylethyl), 6-tert-butyl-2,4-dimethylphenol, benzophenone, and n-butyl benzenesulfonamide were found. [Copyright &y& Elsevier]

Abstract: Sulfate reduction in salt rich wastewaters (50gNaClL−1 and 1gMgCl2·6H2OL−1; conductivity 60–70mScm−1) was investigated in a 6L submerged anaerobic membrane bioreactor (SAMBaR) and inoculated solely with the halotolerant sulfate reducing bacterium Desulfobacter halotolerans. The SAMBaR was fed with acetate and ethanol at organic loading rates up to 14gCODL−1 day−1 in excess of sulfate (COD/SO4 2− of 0.5) and operated at pH 7.2±0.2 and a hydraulic retention time (HRT) from 8 to 36h. A sulfate reduction rate up to 6.6gSO4 2− L−1 day−1 was achieved in the SAMBaR operating at a flux of 17.1Lm−2 h−1, which resulted in a HRT of 9h including the backflow of permeate used for backflushing. The fairly constant very high specific sulfate reduction rate of 5.5gSO4 2− gVSS−1 day−1 showed that the performance of the SAMBaR was limited by the low amount of biomass (0.85gVSSL−1) present in the reactor at the end of the experiment. It was shown that sulfate reducing submerged anaerobic membrane bioreactors can be operated over extended periods of time without chemical cleaning of the membranes at a certain fixed flux if this flux is substantially below the nominal critical flux determined experimentally (18–21Lm−2 h−1). Intermittent operation as well as backflush of the membranes were shown to slow the fouling in the membranes. Frequent backflush (e.g. 1min each 10min) is the suggested operational strategy to minimize fouling in anaerobic MBRs. [Copyright &y& Elsevier]

Anaerobic membrane bioreactor (AnMBR) has been applied as a promising technology for treating a variety of industrial wastewaters. Nevertheless, the potential of AnMBR for methanolic wastewater treatment is still not well recognized. In this study, a lab-scale AnMBR fed with low-strength methanolic wastewater was operated for 166 days with stepwise decreased HRT, and the roles of colloidal particles and soluble biopolymers in membrane fouling behaviors were elucidated comprehensively. The results showed that AnMBR showed the desirable performance and process stability with total chemical oxygen demand removal of 89.8 ± 1.1% and the highest methane production rate of 5.49 L/L-reactor/d at organic loading rate of 20.00 g-COD/L-reactor/d and hydraulic retention time of 18 h. The serious membrane fouling was observed after a period of operation at low HRT or high OLR due to the production of colloidal particles and the liberation of soluble biopolymers. Decreased particle size, and increased adhesion forces of gel-like flocs caused by the secretion of hydrophobic protein-bearing biopolymers accelerated the deposition of foulants and the formation of cake layer, inducing the easily mitigated membrane fouling. Further observations proved that the main bioconversion pathway of methanolic wastewater to biomethane was methylotrophic methanogenesis, followed by acetotrophic/hydrogenotrophic processes. Collectively, although the membrane fouling cannot be eliminated, this research confirmed the technical feasibility of AnMBR for methanolic wastewater treatment in real-world applications. Image 1 • Anaerobic membrane bioreactor was used for methanolic wastewater treatment.. • The highest methane production of 5.49 L-CH 4 /L/d was obtained at HRT 18 h. • Colloidal organics blocked membrane pores, causing severe fouling. • Methanomethylovorans was the main degrader of methanol. [ABSTRACT FROM AUTHOR]