Filtration characteristics of activated sludge in hybrid membrane bioreactor with porous suspended carriers (HMBR)

The suspended carriers were efficient in controlling membrane fouling in hybrid membrane bioreactor with porous suspended carriers (HMBR). The purpose of this study consisted in investigating the effect of suspended carriers on the sludge suspension, especially the filterability of sludge suspension. The filterability of sludge suspension in HMBR and general membrane bioreactor (MBR) were investigated and compared in parallel conditions by dead-end filtration for better evaluating the influence of suspended carriers on the sludge suspension. Several aspects of sludge suspension such as filtration resistance, specific cake resistance and particle size were discussed. During long-term operation the filtration resistances rose gradually in the early stage (about 100 days) and then increased rapidly, but there was a slight difference between MBR and HMBR with the prolongation of operation time. The granulometric analysis revealed that the mean particle size of sludge suspension of HMBR decreased more sharply than that of MBR, because the fluidized carriers in HMBR would impose shear stresses on sludge flocs and induce the destruction of the network of sludge zoogloea. Dead-end filtration experiments indicated that the resistance-increasing rates of three portions of sludge suspension were in the order of supernatant > dissolved organics > microbial flocs. In order to further understand the filterability of sludge suspension, the specific cake resistance (α or α.C) of sludge suspension and supernatant in HMBR and MBR were determined. During long-term operation the α and α.C increased with operation time. These results revealed that the suspended carriers in HMBR had appreciably negative effect on the biological characteristics and filterability of the sludge suspension, but they were efficient in controlling membrane fouling during continuous operation of HMBR.     

Effects of the sludge reduction system in MBR on the membrane permeability

For the sludge volume reduction, gravity thickening and mechanical thickening processes have been mainly applied. However, these processes usually cause several problems such as large footprint, low thickening efficiency, etc. To solve these problems, a sludge reduction system using submerged membrane in a reactor with excess sludge from a biological nutrient removal (BNR) system was investigated. Both lab and pilot scale experiments for sludge reduction were carried out. The hydraulic retention time (HRT) was in a range of 4.5-6.7 days during the experimental period. A flat-sheet membrane with a mean pore size of 0.08 µm was used and operated at a flux range of 7-20 L/m²·h.During the experimental period, concentrations of BOD and SS were maintained less than 8 mg/L, 3 mg/L, respectively, which indicated the high quality of treated wastewater. While extracellular polymeric substances (EPS) were lowest at a coagulant concentration of 15 ppm, soluble microbial product (SMP) concentrations did not have any correlation with coagulant concentrations. The critical flux was observed in a range of 18-24 L/m²·h.These results suggested that the sludge reduction system using membrane bioreactor (MBR) could be applied as one of suitable processes to overcome problems of conventional processes such as gravity and mechanical thickening.     

MLSS concentration: Still a poorly understood parameter in MBR filterability

In this paper Membrane Bioreactor (MBR) activated sludge is obtained from full scale MBRs and submitted to cross-flow filtration using always the same membrane and operational conditions. Samples are diluted in order to create suspensions with different Mixed Liquor Suspended Solids (MLSS) concentrations. MLSS values varied between 3.6 and 18.3 g/L. Contrary to literature results filterability did not present a continuous increase with decreasing MLSS concentrations. Activated sludge with MLSS concentration exceeding 10 g/L originated dilution samples with worse filterability. The dilution caused an increase of particles in the range 10 to 20 μm and a decrease in the range 30 to 100 μm. The activated sludge samples had non- Newtonian viscosity and Soluble Microbial Products (SMP) concentrations varied between 60 and 11 mg/L. Activated sludge samples with MLSS concentrations exceeding 10 g/L are entrapping particles smaller than 20 μm in the activated sludge bulk that therefore are not contributing to the increase of resistance on the membrane. Activated sludge samples with lower MLSS concentrations do not show the capability to entrap particles. These different behaviours suggest that are optimal MLSS concentration ranges for MBR operation.     

Structural Analysis and Dewatering Characteristics of Waste Sludge from WWTP MBR

Abstract

A pilot‐scale UF membrane bioreactor (MBR) of 1 m³/day capacity was set up in an industrial wastewater treatment plant to evaluate its performance. This study mainly focused on testing the dewaterability and structural analysis of MBR sludge. MBR had 14% reduction of excess sludge production in relative to the conventional activated sludge process (CAS sludge). For dewatering, MBR sludge had comparable dewaterability with the CAS sludge but required nearly 20% less flocculant to reach the highest filterability χ and lowest specific filtration resistance (SRF). This could reduce the cost for running the dewatering facilities and final disposal. Meanwhile the chemical and morphological analyses on MBR sludge exhibited lower EPS (exocellular polymeric substances) content, slightly smaller flocs and more compact morphology. Additionally, to estimate the appropriate polyelectrolyte dose prior to dewatering, we measured the hysteresis loop area of the sludge rheogram (shear stress vs. shear rate) using a co‐axial cylinder viscometer. For both sludges, the area dramatically increased at some critical flocculant dosage and then plateaued off. The critical dosage, though not optimal, still led to an acceptable dewatering performance for the sludge.     

Biological modelling of MBR and impact of primary sedimentation

Within the AMEDEUS European project, a work package is dedicated to biological modelling of Membrane Bioreactors (MBR) processes as well as the impact of a pre-treatment by primary sedimentation on sludge production, sludge characteristics and permeate quality. The supposed interest of this pre-treatment is to decrease sludge production and to improve oxygen transfer by decreasing sludge concentration.Two MBR pilots were operated side by side under the same operating conditions, one fed by screened (1 mm screen) raw municipal wastewater and the other by primary settled raw municipal wastewater. This side by side operation allows a true comparison of the performances and model calibration. In average, screened water was observed to contain 30% more solids than settled water. In this study, the sludge age was fixed at 40 days and then modified to 15 days to calibrate the model on a broad range of operating conditions in order to validate and identify the biological activated sludge model (ASM) limits.With a sludge retention time (SRT) of 15 days, sludge production is less important in the pilot fed by settled water because of better bio-accessibility behaviour of settled water. In comparison with ASM1 default parameter values, calibrated parameters are quite different concerning nitrification and denitrification because of an improvement of oxygen transfer induced by lower floc size distribution (K_OA = 0.25-0.3 g O₂/m³, K_OH = 0.1 g O₂/m³). With a SRT of 40 days, model calibration is not validated and the pilot fed with screened water has a sludge production reduction that is less important than the one of the pilot fed by settled water where accumulation of inert organic matter is observed.     

Effect of an electro phosphorous removal process on phosphorous removal and membrane permeability in a pilot-scale MBR

The pilot membrane bioreactor (MBR) was equipped with an electro-coagulation process for phosphorous removal (EPR process). The effect of the EPR process on nutrient removal and membrane permeability was investigated in this study.Experiments were carried out for about 5 months with the pilot MBR that treated wastewater at a capacity of 50 m³/day. And the MBR used two different materials of the plate type membrane: polyvinylidene fluoride (PVDF) and polyethersulfone (PES). Phosphorous ion released from the anaerobic settling tank was coagulated by electrochemical reaction with aluminum ion discharged from aluminum plate electrodes in the EPR tank. The phosphate (PO₄³⁻-P) removal efficiency and the total phosphorous (TP) removal efficiency by electro-coagulation were 89.2% and 79.9%, respectively. Results of particle size distribution (PSD) analysis showed that the particle sizes of flocs were mostly in the range of 50-150 μm, and the membrane resistance decreased significantly in the MBR as the EPR proceeded. Consequently, this study showed that the EPR process was useful for reducing trans-membrane pressure (TMP) and for removal of phosphorous in the MBR, which was operated in long sludge retention time (SRT) conditions.     

Filterability of activated sludge in membrane bioreactors

The filterability of activated sludge is an important factor for the economical operation of membrane bioreactors (MBR). In the literature mainly investigations on sludge dewaterability in respect to further disposal are published. In this study, a procedure for determining filterability in a crossflow test cell is introduced. Its features are: no increase in sludge concentration during batch trials, crossflow conditions, and little impact on the sludge structure. The activated sludge filterability is given as the ratio of permeate flux after 40 min of operation to clear water flux. Sludge samples of eight different MBR and one conventional wastewater treatment plant (wwtp) have been examined and compared. Contrary to the literature, no impact of suspended solids (SS) concentration, sludge viscosity, or extractable extracellular polymer substances (EPS) concentration on the filterability was found. Instead, the composition of the liquid phase was found to effect most the filterability of activated sludge, a major influence being the concentration of suspended EPS: the higher the suspended EPS concentration, the lower the filtration index. Suspended EPS concentration increases with high mechanical stress in the MBR and high F/M ratios, if the treated wastewater contains considerable amounts of proteins or polysaccharides.     

Plugging problems observed in severe hydrocracking of vacuum residue

Carbons deposited on the filter after the reactor of hydrocracking (US-Sludge) and in the heat exchanger (DS-Sludge) in a commercial H-Oil process were analyzed through the elemental analysis, XRD, SEM, optical microscope, ¹³C-NMR and Raman spectroscopy to elucidate their formation mechanism. Heat treatment of sludge and oil products recovered from the commercial process was performed at 698 K of a reaction temperature. XRD showed the presence of Fe_1−xS, NaCl, and CaSO₄ as well as carbon (2Θ = 26.6°) in US-Sludge. The carbon showed medium and fine mosaic textures surrounding the isotropic grains. DS-Sludge showed mixed texture of domain and flow surrounding the fine mosaic grains. The sludge consisted of stacked carbon flakes with a number of pores on the surface. EDX showed dominant presence of NaCl and CaO particles in the mosaic region. Heat treatment of asphaltene in the product mixed with US-Sludge gave the same appearance to that of DS-Sludge. US- and DS-Sludge are concluded to be formed through the respective carbon formation in the reactor and to be separated on the filter and on the heat exchanger surface, respectively. The carbon particles produced in the reactor collect contaminant Fe_1−xS and CaSO₄ particles to form the agglomerate where the growth and coalescence of the anisotropic spheres are very restricted to form the fine mosaic texture as observed in the US-Sludge. In contrast, the carbonization of the major precipitated heavy aromatic component leads to the domain or flow anisotropic texture through rather free growth and coalescence of anisotropic spheres on the surface of the heat exchanger wall. Although some parts of precipitated component together with US-Sludge give mosaic texture through the restricted growth and coalescence of anisotropic sphere by the presence of reactive fine solids.     

Wastewater filtration performance of multilayer glassy microporous filters

The glassy composition (quartz, clinoptilolite and frit glass mixture) provides a filter having glassy pore wall microstructure and thus enables easily cleaning through the filter recovery by back flushing. The filter was obtained as multilayer compaction by one step slip cast-processing where a cylindrical filter, consisting of filtration layer on granular assemblies with specific interlayer was shaped by a fine particle migration phenomenon. The multilayer compaction has low resistance to liquid flow and thus the filter great potential to use for wastewater filtration. It is known that high capacity filtration also requires correct pore size/interval with respect to filtered particles. In this study, a wastewater overflow from marble factory (0.035 wt.% of solid with a size distribution of 0.58-1.46 μm) was filtered by different pore sizes of the glassy filters (pore size intervals: 0.4-10 μm, 0.2-4 μm, 0.1-1.5 μm and 0.04-2 μm) and significantly different filtering capacities was obtained; the irreversible fouling capacities were determined between 2.9 and 8.5 m³ of filtrate per m² of the filter area through the filtration produced 5 min intervals. The filtration pressure was 5 bar and backflushing was achieved at 1 bar. The high filterability (8.1 m³/m² in 5 min) with high filtrate clarity (∼0.5 nephelometric turbidity units) could be obtained using finer pore sized filters. The large size filter was seriously clogged during the filtration.     

Dynamic in-series resistance modeling and analysis of a submerged membrane bioreactor using a novel filtration mode

This study is focused on the physical filtration characteristics of a flatsheet membrane bioreactor (MBR) operated under a novel filtration mode. The objective of this research was to demonstrate the possibility of running an MBR with high MLSS concentration for prolonged periods without frequent blocking of the membranes. Current MBR designs, mostly dictated by the manufacturers, have restrictions on the level of MLSS due to fouling. It has been observed that this restraint can be eliminated by applying high shear rates for better removal of cake layer from membrane surface. A pilot scale MBR was setup at the inlet works of a domestic sewage treatment plant. The system was dynamically modeled and calibrated for flux, hydraulic permeability, transmembrane pressure using the in-series resistance model. Resistance components were experimentally determined and compared against the results of dynamic simulations. Intrinsic membrane resistance (R_m) and fouling resistance (R_f) were the major components contributing to total resistance with fractions of 69% (R_m/R_t) and 30% (R_f/R_t) respectively. It was found that cake resistance did not have major impact on the total resistance which was linked to the high aeration intensity. Proposed model was validated by experiments which indicated its potential use on other MBR systems.     

Electrokinetic extraction of surfactants and heavy metals from sewage sludge

Waste management represents a quite serious problem involving aspects of remediation technologies and potential re-utilization in different fields of human activities. Of course, wastes generated in industrial activities deserve more attention because of the nature and amount of xenobiotic components, often difficult to be eliminated. However, also ordinary wastes of urban origin are drawing more and more attention, depending on the concentration of noxious substances like surfactants and some heavy metal, which may eventually require expensive disposal. In the present paper, a research has been carried out on the application of electrokinetic treatments for the abatement of the above xenobiotic components from sewage sludge generated in urban wastewater treatment plants. Experiments were carried out on a laboratory scale, in a 250 mm × 50 mm × 100 mm cell, using 250-300 g of sludge for each test and current densities between 2.4 and 5.7 mA cm⁻². As a general result, quite significant abatements of heavy-metal ions and surfactants were achieved, with relatively low energy consumption.     

High-pressure sorption isotherms and sorption kinetics of CH4 and CO2 on coals

Using a manometric experimental setup, high-pressure sorption measurements with CH₄ and CO₂ were performed on three Chinese coal samples of different rank (VR_r = 0.53%, 1.20%, and 3.86%). The experiments were conducted at 35, 45, and 55 °C with pressures up to 25 MPa on the 0.354-1 mm particle fraction in the dry state. The objective of this study was to explore the accuracy and reproducibility of the manometric method in the pressure and temperature range relevant for potential coalbed methane (CBM) and CO₂-enhanced CBM (CO₂-ECBM) activities (P > 8 MPa, T > 35 °C). Maximum experimental errors were estimated using the Gauss error propagation theorem, and reproducibility tests of the high-pressure sorption measurements for CH₄ and CO₂ were performed. Further, the experimental data presented here was used to explicitly study the CO₂ sorption behaviour of Chinese coal samples in the elevated pressure range (up to 25 MPa) and the effects of temperature on supercritical CO₂ sorption isotherms.The experiments provided characteristic excess sorption isotherms which, in the case of CO₂ exhibit a maximum around the critical pressure and then decline and level out towards a constant value. The results of these manometric tests are consistent with those of previous gravimetric sorption studies and corroborate a crossover of the 35, 45, and 55 °C CO₂ excess sorption isotherms in the high-pressure range. The measurement range could be extended, however, to significantly higher pressures. The excess sorption isotherms tend to converge, indicating that the temperature dependence of CO₂ excess sorption on coals at high-pressures (>20 MPa) becomes marginal. Further, all CO₂ high-pressure isotherms measured in this study were approximated by a three-parameter excess sorption function with special consideration of the density ratio of the “free” phase and the sorbed phase. This function provided a good representation of the experimental data.The maximum excess sorption capacity of the three coal samples for methane ranged from 0.8 to 1.6 mmol/g (dry, ash-free) and increased from medium volatile bituminous to subbituminous to anthracite. The medium volatile bituminous coal also exhibited the lowest overall excess sorption capacity for CO₂. However, the subbituminous coal was found to have the highest CO₂ sorption capacity of the three samples. The mass fraction of adsorbed substance as a function of time recorded during the first pressure step was used to analyze the kinetics of CH₄ and CO₂ sorption on the coal samples. CO₂ sorption proceeds more rapidly than CH₄ sorption on the anthracite and the medium volatile bituminous coal. For the subbituminous coal, methane sorption is initially faster, but during the final stage of the measurement CO₂ sorption approaches the equilibrium value more rapidly than methane.     

Prefiltration of wastewater effluent: Effects on foulants and performance during dead end ultrafiltration

An important trend in the development of ultrafiltration (UF) of wastewater effluent is the integration of pretreatment to improve the performance of membranes. In this paper the results of a study on the effect of three prefiltration techniques (multimedia filtration, granulated activated carbon filtration and biological activated carbon filtration) on foulants and performance of UF are presented. The objectives of the study are: (1) to establish the different effect of three prefiltration configurations on performance of UF and foulants of wastewater effluent and (2), to determine in which particle size range the most particles or colloidals are removed after the three prefiltration configurations.From all of the filters, the biological granulated activated carbon filter (BGAC) presented the highest increase of filterability. During this study, the specific ultrafiltration resistance (SUR) value of the filtrate is always below 5 · 10¹² m^− 2 independent on the incoming SUR value. From all the foulants especially the proteins and humic substances are removed by granulated activated carbon filter (GAC) and BGAC. BGAC is the only prefiltration technique that shows significant removal of the fraction between 0.1 µm and 0.2 µm.     

Feasibility of Sludge Ozonation for Stabilization and Conditioning

A pilot-scale sludge treatment plant was built to investigate the feasibility of ozonation processes for waste activated sludge treatment. Ozonation of wastewater sludge resulted in mass reduction by mineralization as well as by supernatant and filtrate recycle. Another advantage of sludge ozonation is a significant improvement of settleability and dewaterability. Experimental results showed that mass reduction of 70% and volume reduction of 85% compared with the control sludge was achieved through the sludge ozonation at a dose of 0.5?gO₃/gDS. It is also interesting to note that the filterability deteriorates up to ozone dose of 0.2?gO₃/gDS and then improves considerably at a higher ozone dose. The filterability could be improved by chemical conditioning even at a low ozone dose. The economic feasibility by cost analysis reveals that ozonation processes can be more economical than other alternative processes for sludge treatment and disposal at small-sized wastewater treatment plants.     

Decolorization and COD reduction of disperse and reactive dyes wastewater using chemical-coagulation followed by sequential batch reactor (SBR) process

This paper summarizes the results of disperse and reactive dyes wastewater treatment processes aiming at the destruction of the wastewater's color and chemical oxygen demand (COD) reduction by means of coagulation/flocculation (CF) followed by sequential batch reactor (SBR) process. The color removal efficiency of magnesium chloride aided with lime [MgCl₂/CaO] was compared with that of alum [Al₂ (SO₄)₃] and lime [Cao]. The experimental results showed that treatment with lime alone (600 mg/l) at pH value of 11.7 proved to be very effective. Color removal reached 100% and COD was reduced by 50%. Treatment with magnesium chloride aided with lime at pH value of 11 removed color completely and reduced the COD value by 40%. However, lime or lime in combination with magnesium chloride produced high amounts of sludge (1.84 kg/m³ for lime & 1.71 kg/m³ for MgCl₂ aided with lime). Also, the pH of the treated effluent was around 11 and needs correction prior to discharge into sewer network. The use of 200 mg/l alum without pH adjustment removed 78.9% of the color. To improve the effectiveness of alum, the cationic polymer namely cytec was used as a coagulant aid. This significantly increased color removal from 78.9 up to 94% and COD reduction was around 44%. Moreover, sludge production was only 0.36 kg/m³. Chemically pre-treated effluent was subjected to SBR process at an HRT of 5.0 h. Residual COD_total, total biochemical oxygen demand (BOD_{5 total}) and total suspended solids (TSS) in the final effluent were 78 ± 7.7; 28 ± 4.2 and 17 ± 4.2 mg/l, corresponding to the removal efficiency of 68.2; 76.3 and 61.4% respectively. Furthermore, almost complete removal of COD_particulate and BOD_5particulate has been achieved.     

A comparative study of tertiary membrane filtration of industrial wastewater treated in a granular and a flocculent sludge SBR

Membrane fouling has been identified by many researchers as an inconvenience for the industrial application of membranes in wastewater treatment plants. Membrane fouling decreases permeability and therefore permeates flow, increasing costs. Although fouling is the result of complex phenomena not completely known, it can be said that fouling takes place by the presence of three different kinds of compounds in the water: suspended solids, colloids and solutes. In this sense, the characteristics of the suspended solid aggregates might be an important aspect in order to diminish the impact of suspended solids on membrane fouling. The main objective of this study was to compare the operation of two similar tertiary membrane filtration units treating the effluent of two different SBRs, respectively: A granular sludge SBR (GSBR) and a membrane flocculent sludge SBR system, at laboratory scale. Two PVDF microfiltration membrane modules were used for tertiary filtration of the effluent treated in the SBRs. Both reactors were used for treating the wastewater generated in a factory of the fish freezing sector. COD of the wastewater was between 700 and 1100 mg/L, total nitrogen concentration was between 110 and 180 mg N/L and total phosphorus ranged around 110 mg P/L. The chemical characteristics of both permeates were similar. Moreover, the presence of either granules or flocs in the tertiary membrane filtration systems did not have an appreciable impact on the membrane filtration. Nevertheless, it was observed that the operation of the membrane on the flocculent system tends to be more instable, showing a major tendency to achieve critical flux.     

Optimization of biological nutrient removal in a pilot plant UCT-MBR treating municipal wastewater during start-up

This study shows that an MBR pilot plant with UCT configuration is able to obtain high nutrient removal efficiency already during start-up. The biological nutrient removal (BNR) efficiencies significantly increased towards the end of the experimental run, achieving a COD removal efficiency exceeding 94% and N removal efficiency in the range of 89 to 93%. P removal efficiencies in the range of 80 to 92% have been obtained. During the experimental period (4 months) the evolution of the activity of polyphosphate-accumulating organisms, obtained from P_release and P_uptake rates, showed a small increase in the activity of polyphosphate-accumulating organisms (PAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs). The specific phosphate accumulation at the end of the experimental run amounted to 8.0 mg P g^− 1VSS h^− 1 and 3.29 mg P g^− 1VSS h^− 1, for the PAOs and DPAOs respectively. Moreover, the DPAOs activity increased faster than PAOs activity, i.e. from 0.36 to 0.41 of phosphate uptake rate (PUR) ratio.     

Reduction of high content of free fatty acid in sludge palm oil via acid catalyst for biodiesel production

In this study, sulphuric acid (H₂SO₄) was used in the pretreatment of sludge palm oil for biodiesel production by an esterification process, followed by the basic catalyzed transesterification process. The purpose of the pretreatment process was to reduce the free fatty acids (FFA) content from high content FFA (> 23%) of sludge palm oil (SPO) to a minimum level for biodiesel production (> 2%). An acid catalyzed esterification process was carried out to evaluate the low content of FFA in the treated SPO with the effects of other parameters such as molar ratio of methanol to SPO (6:1-14:1), temperature (40-80 °C), reaction time (30-120 min) and stirrer speed (200-800 rpm). The results showed that the FFA of SPO was reduced from 23.2% to less than 2% FFA using 0.75% wt/wt of sulphuric acid with the molar ratio of methanol to oil of 8:1 for 60 min reaction time at 60 °C. The results on the transesterification with esterified SPO showed that the yield (ester) of biodiesel was 83.72% with the process conditions of molar ratio of methanol to SPO 10:1, reaction temperature 60 °C, reaction time 60 min, stirrer speed 400 rpm and KOH 1% (wt/wt). The biodiesel produced from the SPO was favorable as compared to the EN 14214 and ASTM D 6751 standard.     

Sulphur retention during co-combustion of coal and sewage sludge

The aim of this work is the study of the S retention in ashes from combustion of three bituminous coals and a sewage sludge, processed with lime from an urban wastewater treatment plant, that uses FeCl₃ as a coagulant. The effect of the sludge addition during co-combustion of sludge-coal blends in the proportions 10 and 50 wt% of sludge is analysed. The combustion was carried out in an electric furnace at different temperatures (800, 900, and 1100 °C).The results have confirmed that sludge addition to coal enhances S retention at any temperature due to the high CaO contents of the sludge and the formation of CaSO₄. However, the addition of FeCl₃ may be prejudicial, since it produces Na and K volatilisation during co-combustion. Moreover, the presence of Fe₂O₃ from FeCl₃ can reduce the amount of retained sulphur due to its reaction with CaO to produce calcium ferrite. Another element with a similar effect to Fe is Si, since it forms larnite (2CaO·SiO₂) in coal-sludge blends with high Si and Ca contents. Lineal relationships have been found between S retention and the above oxide contents.     

Filterability in a submerged anaerobic membrane bioreactor

Studies on anaerobic membrane bioreactor (AMBR) show high variability about filterability. Therefore, in this study, a laboratory-scale submerged AMBR (SAMBR) was operated with the aim of identifying operational conditions and sludge characteristics that influence the membrane flux. Short-term experiments applying the flux-step method resulted in values of the critical flux (Jc) variable depending on the operational condition applied in the SAMBR. The application of different parameters for the identification of Jc gave comparable results. Although the plant was operated applying different operational conditions, a rapid membrane fouling was usually observed. The applicable fluxes were between 2 and 5 L/(m² h) depending on operational conditions. Therefore, the results confirm the much lower sludge filterability in anaerobic than aerobic MBRs. Multiple regression analysis showed that the supernatant composition plays the most important role in membrane fouling.