Pilot-scale Submerged Membrane Bioreactor Research Articles

Enhanced Removal of Organic Pollutants and Reactive Dye in Polyethersulfone Submerged Membrane Bioreactor (PES-SMBR) for Textile Wastewater

The present investigation was carried out to assess the operation of a pilot-scale submerged membrane bioreactor (SMBR) for the treatment of reactive dye and textile wastewater. The operation of SMBR model was conducted by using a polyethersulfone (PES) hollow fibre membrane with continuous flow mode at different HRTs at 8, 6 and 4 h, for 90 days. During the entire operation, the average permeate flux, TMP, F/M ratio and OLR was found to be 19 (L/m²/h), 2.6 (psi), 0.10 (g BOD/(g MLSS•d) and 0.89 (kg BOD/m³.d), respectively. The variations in the permeate flux, TMP, F/M ratio and OLR have not adversely effects on the operation of the SMBR model. Throughout the entire operation, despite the TP, TDS and conductivity, the high amount of COD (82%), BOD (86%), NO3-N (79%), TSS (98%), turbidity (97%) and colour (79%), removal was achieved. The permeate flux was declined by membrane fouling and it was recovered by chemical cleaning as well as regular backwashing during the entire operation. The results obtained from the study concluded that the hollow fibre ultrafiltration polyethersulfone (PES) membrane shows good performance while treating textile wastewater along with reactive dye solution.

Design and testing of a pilot-scale submerged membrane bioreactor (MBR) for textile wastewater treatment

The objective of this paper is to deal with the design of a pilot-scale submerged membrane bioreactor (MBR) and a short-term functionality test to be performed with textile wastewater. The design calculations were done based on the design parameters analysed from local textile wastewater and typical values of activated sludge kinetic coefficients. Other process parameters like bioreactor volume (tank size), hydraulic residence time (HRT), biomass loading (F/M ratio), oxygen demand, etc., were calculated depending on the real textile wastewater characteristics. Taking the design basis into consideration, a pilot-scale MBR was constructed equipped with LabVIEW programme- and sensors-controlled computer system. Based on the theoretical calculations, the hydraulic volume of the MBR reactor was around 56.6 L with flat sheet membranes (3 sheets, with 25 cm × 25 cm dimensions of each sheet) with HRT of 16.9 h. Finally, performance tests for 6 weeks were carried out in a local (Darmstadt, Germany) laundry textile wastewater to test the functionality of MBR pilot plant. Under the operating conditions of 250 mbar suction pressure and 12 g/L of MLSS, the COD removal efficiency was around 90% for 800–3500 mg/L inlet COD fed to the membrane bioreactor.

Treatment of cake shop wastewater by pilot-scale Submerged Membrane Bioreactor (SMBR)

In this work, the treatment of cake shop wastewater using Submerged Membrane Bioreactor (SMBR) on pilot-scale has been studied. The commercial hollow fiber membrane was used with a total surface area of 0.609 m2. The experiment was set up with three different conditions as follows: model 1 - the SMBR system used suspended activated sludge; model 2 – the SMBR system was combined with the substrate inside; model 3 – the SMBR system was added with PAC (Poly Aluminium Chloride) excluding substrate. Effects of organic loading rates (OLR) were investigated to assess the performance of each model. The results showed that the optimal OLR of model 1 achieved at 11 kgCOD/m3.day and COD, TN, TP removal efficiencies were 97.93%, 71.04% and 79.04%, respectively. The optimal OLR of model 2 was 13.3 kgCOD/m3.day and the COD, TN, TP removal efficiencies were 98.04%, 82.35% and 84.59%, respectively. 11 kgCOD/m3.day was optimal OLR for model 3 with COD, TN, TP removal efficiencies 98.10%, 73.35% and 84.70%, respectively. Trans-membrane pressure (TMP) of the whole operation was in range of 20 to 55.5 CmHg and flux values were observed in the range of 35.86 to 333.24 L/m2.h. Depending on discharge requirements, an approximate processing model for cake shop wastewater treatment is chosen.

Wastewater treatment in a pilot-scale submerged membrane bioreactor: study of hydrodynamics under constant operating pressure

Abstract A pilot-scale Submerged Membrane Bioreactor provided with PEI hollow fiber membranes was operated under constant pressure mode in order to evaluate the effects of hydrodynamic conditions on the process performance, such as air flow rate, module packing density and aeration configuration. For the three different air flow rates studied (2, 5 and 8 L/min), results showed a limit value for this parameter, in which above this value a better performance will not be obtained and can even be worse. The air flow rate of 5 L/min presented the best performance, followed by 8 and 2 L/min. The module packing density was studied for two diameters (0.75 and 1 inch); the best result was observed for the larger diameter module, because lower packing density causes more space between fibers, increasing the aeration homogeneity inside de fiber bundle. Both aeration geometric tested showed similar permeate fluxes, indicating they did not affect the process performance. For all hydrodynamic conditions, the removal of TOC and COD was 96% and 93%, respectively.

Incorporating Submerged MBR in Conventional Activated Sludge Process for Municipal Wastewater Treatment: A Feasibility and Performance Assessment

A pilot-scale submerged membrane bioreactor (MBR) was incorporated in a conventional activated sludge (CAS) process for more than 100 days in order to assess the feasibility and performance on the municipal wastewater treatment. After a stabilization period of 50 days, the MBR unit was operated under various temperatures (21 ± 4°C), mixed liquor suspended solids (MLSS) concentrations (14000 ± 1800 mg L-1 ), and different aeration intensities (3 to 6 m3 h-1). No significant deterioration in membrane flux was observed while operating with high biomass concentration. From the results, the removal of total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus (TP) were enhanced using MBR. However, due to some limiting operational conditions, the total nitrogen (TN) removal was less efficient in MBR than in CAS. The MBR unit was 100% effective in removing E. coli and enterococcus, as well as noroviruses and adenovirus, making it more efficient than CAS. Also, the removal of most of the trace organic compounds (TrOCs) including personal care products, pharmaceuticals, steroid hormones and perfluorinated compounds were enhanced after the incorporation of MBR to CAS, as well as for many heavy metals in MBR.

Physical cleaning initiation controlled by transmembrane pressure set-point in a submerged membrane bioreactor

The application of physical cleaning methods such as backflushing or relaxation is an essential part of the operation mode in submerged membrane bioreactors (SMBRs) applied to wastewater treatment. However, the strategy usually applied for pre-set fixed value of the cleaning frequency involves a loss of water production. This paper deals with the validity of a control system for cleaning initiation by monitoring transmembrane pressure using both physical cleaning methods. To evaluate the effect of the key operational parameter (transmembrane pressure set-point, TMPsp) on membrane fouling and process productivity, sludge samples from a pilot-scale SMBR were filtered under different filtrate flux values (J=20–40lh−1m−2) in bench filtration unit. From this study, it was found that this system automatically adjusts the cleaning frequency as a function of the membrane fouling which results in an increase in the net permeate produced. Cleaning efficiency, described in terms of residual fouling resistance, and the cake fouling rate can be significantly affected by the value of TMPsp selected and the cleaning method performed. A maximal net permeate flux can be achieved when backflushing is used, a filtrate flux above the threshold value of 30lh−1m−2 is imposed and intermediate TMPsp values are applied.

A pilot investigation into membrane bioreactor using mesh filter for treating low-strength municipal wastewater

A pilot-scale submerged membrane bioreactor (MBR) using nylon mesh as filter was investigated for treatment of low-strength municipal wastewater (average influent COD=145.7±59.9mg/L). During the operation, biomass was effectively retained by the nylon mesh with biofilm attached, and a low effluent turbidity of below 2NTU was obtained. The average COD and NH4+-N removal efficiencies reached 86.3% and 98.1%, respectively, at a hydraulic retention time of 5h. A sludge concentration of 4.15±0.15g/L was maintained in the system without excess sludge discharge, attributed to the prolonged solid retention time and low organic loading rate. The low sludge concentration was also beneficial for mitigating the filter fouling. Thus, this mesh filter MBR provides a low-cost, efficient and simple approach to treat municipal wastewater, and shows a high potential for application in rural and sparsely populated areas.

Performance of a flat-sheet submerged membrane bioreactor during long-term treatment of municipal wastewater

A pilot-scale submerged membrane bioreactor (SMBR) with anoxic and oxic tanks was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. A fl at type membrane with a pore size of 0.038 μm and having a total surface area of 3.60 m2 was used in the experiments. During the operation, MLSS concentration in aeration (oxic) tank of SMBR was maintained at about 5–7 g/l. Influent and effluent pH in the SMBR also changed between 7.3–8.4. Raw wastewater with average chemical oxygen demand (COD): total nitrogen (TN) ratio of 12:2 was treated at various temperatures (10–30 °C) over an interval of about 160 d. When average influent nutrient mass ratio (COD:TN:TP) was 100:8.2:1.2 and BOD5:COD ratio was 0.5, removal efficiencies of COD, BOD5, TSS, TN and TP were 99.1%, 99.3%, 99.4%, 43.4% and 68.2%, respectively. Nitrification occurred in the aerobic reactor with NH4 +–N removal efficiency ranging from 88.7 to 99.7% averaging at 97.8%. Nitrog...

Critical flux and chemical cleaning-in-place during the long-term operation of a pilot-scale submerged membrane bioreactor for municipal wastewater treatment

The critical flux and chemical cleaning-in-place (CIP) in a long-term operation of a pilot-scale submerged membrane bioreactor for municipal wastewater treatment were investigated. Steady filtration under high flux (30 L/(m2 h)) was successfully achieved due to effective membrane fouling control by sub-critical flux operation and chemical CIP with sodium hypochlorite (NaClO) in both trans-membrane pressure (TMP) controlling mode (cleaning with high concentration NaClO of 2000–3000 mg/L in terms of effective chorine was performed when TMP rose to 15 kPa) and time controlling mode (cleanings were performed weekly and monthly respectively with low concentration NaClO (500–1000 mg/L) and high concentration NaClO (3000 mg/L)). Microscopic analysis on membrane fibers before and after high concentration NaClO was also conducted. Images of scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that NaClO CIP could effectively remove gel layer, the dominant fouling under sub-critical flux operation. Porosity measurements indicated that NaClO CIP could partially remove pore blockage fouling. The analyses from fourier transform infrared spectrometry (FTIR) with attenuated total reflectance accessory (ATR) and energy dispersive spectrometer (EDS) demonstrated that protein-like macromolecular organics and inorganics were the important components of the fouling layer. The analysis of effluent quality before and after NaClO CIP showed no obvious effect on effluent quality.

Effect of intermittent aeration on the treatment performance in a submerged membrane bioreactor

In order to improve removal for nitrogen in a pilot-scale submerged membrane bioreactor (SMBR), intermittent aeration was conducted, and the effect on the treatment performance under four kinds of operation condition (run 1, continuous aeration; run 2, 60/60 min aeration on/off time; run 3, 60/90 min aeration on/off time; run 4, 60/75 min aeration on/off time) was evaluated. The results showed that depending on the specific on/off of the aeration time ratio, removal efficiency of nitrogen could be improved significantly, and the removal rates of total nitrogen (TN) under different operation conditions were 28.0%, 59.5%, 66.8% and 70.7%, respectively. There were no obvious differences for removal rates for CODCr and ammonia among different operation conditions. In general, intermittent aeration could be used as a feasible way to improve treatment performance for nitrogen in the SMBR.

Impact of Temperature Seasonal Change on Sludge Characteristics and Membrane Fouling in a Submerged Membrane Bioreactor

Effects of temperature seasonal change on sludge characteristics and membrane fouling in a pilot-scale submerged membrane bioreactor (MBR) were studied. Results showed that bound extracellular polymeric substances (EPS), soluble chemical oxygen demand (SCOD), polysaccharides, and proteins in the supernatants all increased under low temperature operation. The increase of diluted sludge volume index (DSVI) and capillary suction time (CST) indicated that the settling and dewatering ability of mixed liquors deteriorated. It was also found that the increase of EPS, polysaccharides, and proteins led to the increase of biopolymers attached to membrane surfaces and in turn caused severe membrane fouling.

Fluorescent dissolved organic matter variations in a submerged membrane bioreactor under different sludge retention times

Abstract A pilot-scale submerged membrane bioreactor (MBR) for the treatment of real municipal wastewater was operated in this study under various sludge retention time (SRT) in order to verify the correlations of fluorescent dissolved organic matter (DOM) with membrane fouling. The fluorescent DOM determined by three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy and the trans-membrane pressure (TMP) under different SRT operation were investigated, and the correlations between them were analyzed. The results showed that the variations of fluorescent DOM (Peaks B and C) in the sludge supernatants correlated well with the variations of EEM spectra signal of bound extracellular polymeric substances (EPS) even though they were different in nature, i.e., the bound EPS were found to be more non-biodegradable than DOM. The fluorescent intensity (FI) variations of Peaks A and B in the EEM spectra of DOM were closely related to the TMP increase rate (membrane fouling) in the MBR, suggesting that they might be used to monitor the DOM variations and to indicate MBR performance. Through the EEM spectra analysis, it was confirmed in this work that the DOM in the sludge supernatants was not only originated from the bound EPS but also from the influent wastewater.

Relationships of activated sludge characteristics to fouling rate and critical flux in membrane bioreactors for wastewater treatment

The objectives of this study were to examine the effects of activated sludge characteristics on fouling rate (FR), and to discern whether there is a correlation between FR and critical flux. The activated sludge samples were collected from pilot scale submerged membrane bioreactor plants operated under different process conditions. Their characteristics were assessed by analyzing mixed liquor suspended solids, mixed liquor volatile suspended solids, time to filter, diluted sludge volume index, colloidal total organic carbon, and bound and soluble extracellular polymeric substances including carbohydrate, proteins and humic substances. The fouling potential of these samples was measured in terms of FR and critical flux. Results confirmed that colloidal particles were key constituents responsible for short-term fouling. The soluble carbohydrates were identified as the most important soluble extracellular polymeric substances component responsible for short-term fouling potential. Furthermore, an excellent correlation was observed between critical flux and FR suggesting that the colloidal total organic carbon measurement could be used to predict not only critical flux but also FR.

Reduction of membrane fouling by simultaneous upward and downward air sparging in a pilot-scale submerged membrane bioreactor treating municipal wastewater

A vertically oriented hollow fiber membrane module equipped with a downward aerator as well as an upward aerator for the simultaneous upward and downward air sparging was evaluated in a pilot-scale bioreactor. The operation was divided into three consecutive phases based on different membrane air sparging configurations: the simultaneous upward and downward air sparging (Phase 1), the single upward air sparging (Phase 2), and the simultaneous upward and downward air sparging (Phase 3). Although the SMBR operation, process performances including particulate matters, organic matters, and nutrients removals were stable, the membrane fouling characteristics were significantly different for the different air sparging configurations. The parameters such as the trans-membrane pressure increasing rate, the permeability decreasing rate, the irreversible membrane fouling rate, and the fouling resistance increased when the air sparging configuration was changed from the simultaneous upward and downward mode to the single upward mode (i.e., Phase 1→Phase 2), while the parameters decreased when the air sparging configuration was switched from the single upward mode to the simultaneous upward and downward mode (i.e., Phase 2→Phase 3). Taken together the results strongly support the effectiveness of the simultaneous upward and downward membrane air sparging in reducing membrane fouling.

Influence of filtration conditions on membrane fouling and scouring aeration effectiveness in submerged membrane bioreactors to treat municipal wastewater

Membrane fouling and scouring aeration effectiveness were studied using three large pilot-scale submerged membrane bioreactors (MBRs) operated at a series of permeate fluxes, scouring aeration intensities and cyclic aeration frequencies to treat municipal wastewater. The results showed that when operated at the sustainable conditions, the MBRs had a stable reversible fouling resistance. At unsustainable conditions, the reversible fouling resistance increased exponentially as filtration progressed. For each of above two cases, the fouling ratios newly defined by Eqs. (7) and (8) were calculated from the transmembrane pressure increases to compare the relative reversible fouling rates. With the range of sustainable filtration conditions, the fouling ratios at the same reference scouring aeration intensity were found to be proportional to permeate flux. Similarly, the fouling ratios calculated with the same reference permeate flux decreased exponentially with increasing scouring aeration intensity. Moreover, the effects of scouring aeration intensity and permeate flux on the fouling ratios were found to be independent of one another. As a result, an empirical relationship was derived to relate the stable reversible fouling resistance to sustainable permeate fluxes and scouring aeration intensities. Its application was demonstrated by constructing transmembrane pressure contours overlaid with scouring aeration effectiveness contours to aid in the selection of optimal MBR filtration conditions.

Microbial community structure and dynamics in a pilot-scale submerged membrane bioreactor aerobically treating domestic wastewater under real operation conditions

A pilot scale submerged ultra-filtration membrane bioreactor (MBR) was used for the aerobic treatment of domestic wastewater over 9 months of year 2006 (28th March to 21st December). The MBR was installed at a municipal wastewater facility (EMASAGRA, Granada, Spain) and was fed with real wastewater. The experimental work was divided in 4 stages run under different sets of operation conditions. Operation parameters (total and volatile suspended solids, dissolved oxygen concentration) and environmental variables (temperature, pH, COD and BOD 5 of influent water) were daily monitored. In all the experiments conducted, the MBR generated an effluent of optimal quality complying with the requirements of the European Law (91/271/CEE 1991). A cultivation-independent approach (polymerase chain reaction-temperature gradient gel electrophoresis, PCR-TGGE) was used to analyze changes in the structure of the bacterial communities in the sludge. Cluster analysis of TGGE profiles demonstrated significant differences in community structure related to variations of the operation parameters and environmental factors. Canonical correspondence analysis (CCA) suggested that temperature, hydraulic retention time and concentration of volatile suspended solids were the factors mostly influencing community structure. 23 prominent TGGE bands were successfully reamplified and sequenced, allowing gaining insight into the identities of predominantly present bacterial populations in the sludge. Retrieved partial 16S-rRNA gene sequences were mostly related to the α-Proteobacteria, β-Proteobacteria and γ-Proteobacteria classes. The community established in the MBR in each of the four stages of operation significantly differed in species composition and the sludge generated displayed dissimilar rates of mineralization, but these differences did not influence the performance of the bioreactor (quality of the permeate). These data indicate that the flexibility of the bacterial community in the sludge and its ability to get adapted to environmental changes play an important role for the stable performance of MBRs.

Extracellular polymeric substances (EPS) properties and their effects on membrane fouling in a submerged membrane bioreactor

A pilot-scale submerged membrane bioreactor (MBR) for real municipal wastewater treatment was operated for over one year in order to investigate extracellular polymeric substances (EPS) properties and their role in membrane fouling. The components and properties of bound EPS were examined by the evaluation of mean oxidation state (MOS) of organic carbons, Fourier transform infrared (FT-IR) spectroscopy, three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy, and gel filtration chromatography (GFC), etc. Test results showed that MOS of organic carbons in the bound EPS was ranging from −0.14 to −0.51, and major components could be assessed as proteins and carbohydrates. FT-IR analysis confirmed the presence of proteins and carbohydrates in the bound EPS. The organic substances with fluorescence characteristics in the bound EPS were identified as proteins, visible humic acid-like substances and fulvic acid-like substances by EEM technology. GFC analysis demonstrated that EPS had part of higher MW molecules and a broader MW distribution than the influent wastewater. It was also found that a high shear stress imposed on mixed liquor could result in the release of EPS, which would in turn influence membrane fouling in MBRs. Bound EPS solution was observed to have a stronger potential of fouling than mixed liquor. During long-term operation of the MBR, bound EPS demonstrated positive correlations with membrane fouling while temperature was verified as a negative factor affecting EPS concentration. Compared to tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) showed more significant correlations with membrane fouling. This critical investigation would contribute towards a better understanding of the behavior, composition and fouling potential of EPS in MBR operation.

Distribution and transformation of molecular weight of organic matters in membrane bioreactor and conventional activated sludge process

The distribution and transformation of molecular weight (MW) of organic matters in a pilot-scale submerged membrane bioreactor (MBR) and a conventional activated sludge (CAS) process was studied in order to better understand organic pollutant behaviours and removal mechanisms in the two processes. Gel filtration chromatography (GFC) images of the CAS process showed that the influent wastewater had relatively large MW molecules and a narrow MW distribution while the dissolved organic matters (DOM) in the anaerobic, anoxic, oxic basins and the effluent water demonstrated a broad MW distribution. MW distribution in the MBR system illustrated that the organic matters with high MW molecules were degraded into relatively low MW organic substances, whereas DOM in the oxic basin had a little part of high MW molecules produced by microorganisms during the metabolism of substrates. There is a lack of those high MW molecules in the effluent water due to the retention of the macromolecules by the membrane. Test results also showed that in both the CAS process and the MBR the majority of molecules in the influent wastewater with MW between 100 kDa and 500 kDa were mainly transformed into the molecules with MW between 10 kDa and 100 kDa.

Effects of various backwash scenarios on membrane fouling in a membrane bioreactor

The main objective of this work was to determine the impact of various backwash scenarios on fouling in a pilot-scale submerged membrane bioreactor (MBR) aerobically treating domestic wastewater. A total of seven different backwash scenarios were tested. The degree of membrane fouling was determined employing the flux-step method and using the resistance-in-series model for each backwash scenario. Fouling rates and total membrane resistances generally decreased with more frequent backwashing; decreasing of filtration duration improved fouling control. A higher rate of fouling was observed above critical flux for all scenarios. As the backwashing scenarios approached “no-backwash-continuous filtration”, permeabilities deviated more from linearity indicating a higher degree of fouling. At a flux of 20 L/m 2-h, fouled membrane resistance was reduced by 1.63-fold with 9 min 45 s of filtration followed by 15 s of backwash compared to continuous filtration. The negative impacts of filtration duration on total membrane resistances were more pronounced than the positive impacts of backwash duration, i.e., as the ratio of filtration/backwash duration increased resistances also increased linearly ( R 2: 0.96). The strong correlation found among this ratio and the total membrane resistance suggests that the use of this ratio may be an effective tool in the optimization of fouling control in submerged MBRs employing routine backwashing. Scenarios 4 (9 min 55 s of filtration followed by 5 s of backwash) and 5 (9 min 45 s of filtration followed by 15 s of backwash) were found to be optimum based on fouling control and net daily volume of permeate production. The reversible fouling caused mainly by pore blocking and cake layer was effectively removed by these filtration/backwash scenarios as long as the operating flux was less than the critical flux.

Membrane fouling in a pilot-scale submerged membrane bioreactor operated under various conditions

The main objective of this work was to determine the impacts of various operational conditions and biomass characteristics on membrane fouling in a pilot-scale, submerged membrane bioreactor (MBR). Fouling behavior was studied at five different mixed liquor suspended solids (MLSS) concentrations and four different aeration velocities at each MLSS concentration. Concentrations of both protein and carbohydrate fractions of extracellular polymeric substances (EPS) and soluble microbial products (SMP) increased with increasing MLSS concentrations. The distribution of particle sizes shifted toward smaller particles and mean particle size decreased as the MLSS concentrations increased. Carbohydrate fractions of both EPS and SMP contributed to fouling more than protein fractions. The impact of flux on fouling rate was small as long as the operating flux was less than critical flux, a trend found independent of MLSS concentration. Aeration velocity exhibited positive impacts on fouling control at all MLSS concentrations; however, the degree of this impact decreased significantly with increasing MLSS concentrations. Increasing MLSS concentration significantly decreased permeability values and increased fouling rates at each flux tested, a trend consistent for all aeration velocities. It was concluded that membrane fouling was affected by a combination of factors including operating flux (beyond the critical flux), MLSS concentration (thus the concentrations of both carbohydrate and protein fractions of EPS) and aeration intensity.