Conventional Membrane Bioreactor Research Articles

Applicability of osmotic bioreactor using potassium pyrophosphate as draw solution combined with reverse osmosis for removal of pharmaceuticals and production of high quality reused water

Osmotic membrane bioreactor (OMBR) has emerged as an alternative to the conventional membrane bioreactor (MBR) to precede reverse osmosis (RO) for wastewater treatment and reuse. However, it has not been fully demonstrated yet that technical improvements that may be obtained by OMBR-RO, when compared to MBR-RO, will be sufficient to support its application beyond laboratory scale. Therefore, this work addressed some key challenges to provide a general evaluation of the applicability of OMBR-RO for water reuse, focusing on the analysis of the combined process. Potassium pyrophosphate (K4P2O7) proved to be a promising draw solute to mitigate the prevalent problem of high reverse salt flux in OMBR, as the solute permeability obtained (0.05 LMH) is lower than those previously reported in literature using sodium chloride. The use of OMBR before RO allowed maintaining constant RO permeate flux. In terms of reused water quality (i.e. RO permeate), OMBR-RO process provided water of better quality: the concentrations of nitrite, nitrate, sulfamethoxazole, carbamazepine and diclofenac were 4, 10, 74, 6 and 4 times lower, respectively, in this process when compared to an MBR-RO. The only exception as 17-α-ethinylestradiol, whose concentration was higher in reused water obtained by OMBR-RO. The improvement in water quality for almost all PhACs and operational advantages due to double membrane barrier can support OMBR-RO implementation, particularly when very high removal of PhACs and nutrients is critical for the reuse option.

Improved two-reactor system with sulfonated membranes in wastewater treatment

The ion exchange membrane bioreactor with two-reactor system has gained attention because it has been known to be beneficial to the simultaneous removal of organic and nitrogen. However, this system has a disadvantage for accumulation of nitrate in nitrification due to low diffusivity of nitrate through a cation exchange membrane. To resolve this problem, this study proposed a unique membrane bioreactor system bounded sulfonate membrane to be applied for simultaneous removal of organic and nitrogen in wastewater. The unique membrane bioreactor system consists of two reactors called reactors A and B. The reactor A was maintained in anoxic condition while the reactor B was operated in aerobic condition during the operation period. In ammonium migration experiment, the ammonium migration rates were determined by measuring ammonium concentrations in reactor A. As a result of the measurement, the maximum mass fluxes at the initial ammonia levels of 500, 1000, 1500, and 2000 mg N/L resulted in 1.03, 2.06, 2.98, and 3.87 mg/m2• s, respectively. Those high fluxes indicated that the unique membrane bioreactor exhibited high ion diffusivity. The mass fluxes of ammonia nitrogen in this system were strongly correlated to the initial concentrations of ammonia. The nitrate produced in the reactor B by biological nitrification was effectively migrated to the reactor A, and then the migrated nitrate in the reactor A was converted to nitrogen gas by denitrifying bacteria. As a result, almost complete nitrogen removal efficiency was achieved as 99% in the batch system. Further interestingly, no severe nitrate accumulation problem was observed in reactor B in the unique membrane bioreactor, although such a problem commonly exists in the conventional cation exchange membrane bioreactor system. It is expected that this unique membrane system can be operated with low operation costs and high removal efficiencies of ammonia nitrogen.

Innovative encapsulated self-forming dynamic bio-membrane bioreactor (ESFDMBR) for efficient wastewater treatment and fouling control

The concept of a novel living encapsulated self-forming dynamic bio-membranes (ESFDM) for an innovative wastewater treatment in membrane bioreactor (MBR) is presented in the current study. The active filtering membrane is encapsulated, and thus stabilized, between two support meshes with pore in micrometer size. The combination of activated sludge, the ESFDM and the cake layer formed external to the filtering module contributed to the treatment of municipal wastewater. COD concentration reductions (average value of 95.55 ± 1.44%) by ESFDM bioreactor (ESFDMBR) were comparable to those obtained with a previously reported membrane bioreactor (MBR), where a conventional membrane was studied under the same operating conditions. The ESFDMBR, compared to the conventional MBR, obtained higher reductions of NH3-N, NO3–N and PO43–P concentrations. Increased removals of nitrogen-containing nutrients were ascribed to anoxic conditions reached in the ESFDM layer protected from the aeration by the external cake layer. Rate of increase of transmembrane pressure (TMP) per day in the ESFDMBR (0.03 kPa/day) was lower than the value obtained in the previously reported conventional MBR (8.08 kPa/day). Lower concentrations of fouling precursors in combination with the effective filtration capacity of the porous living ESFDM resulted in the reduction of the fouling rate. Analysis of microbiological community revealed that the microbial community structures in the mixed liquor and ESFDM were different. The ESFDM layer promoted growth of bacteria as indicated by the higher total cell count and higher microbial diversity compared to those observed in the mixed liquor.

Effective leachate treatment by a pilot-scale submerged electro-membrane bioreactor.

Most landfill leachates contain organic compounds that cannot be easily separated by conventional biological processes. Recently, integration of membrane bioreactors and electro-oxidation has been proposed as a suitable option for the treatment and separation of organic and inorganic contaminants in leachate. Therefore, in the present study, the performance of submerged electro-membrane bioreactor (SEMBR) along with a conventional membrane bioreactor (MBR) on a pilot scale was evaluated for the treatment of leachate. Both bioreactors were used to compare treatment efficiency under the same conditions. The removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), phosphate (PO43--P), color, UV254, and metals were investigated. The results showed that applying electric current to the MBR could approximately increase the COD removal efficiency from 94 to 98.5%; PO43--P removal from 70 to 99%; NH3+-N removal from 91 to 99%; UV254 removal from 80 to 96%; and heavy metals removal from 40 to 95%. Humic acid removal efficiency as another indicator of humic substances was increased from 75% in the MBR to 96% in the SEMBR process. The results also showed that the effluent can be introduced into the wastewater treatment plant for further treatment. The SEMBR process achieved a minimization of fouling of membranes compared to conventional MBR. The consumption of the energy and electrode was in accordance with the previous results, and the required energy of 1.57 kWh/m3 of wastewater was calculated. The sludge volume index (SVI) in SEMBR (105 ml/g) was better than MBR (135 ml/g) due to the electrokinetic effect on the production of denser flocs. Based on the results, it can be concluded that the application of electric current can improve the performance of MBR in removing PO43-, NH4+, and membrane fouling.

Use of combined UASB + eMBR treatment for removal of emerging micropollutants and reduction of fouling

Abstract This study employs a novel combined pilot plant consisting of an anaerobic reactor followed by a membrane electrochemical bioreactor (eMBR) to treat domestic water containing selected contaminants of emerging concern (CECs) [ibuprofen (IB), carbamazepine (CBZ), diclofenac (DCF) and 17α-ethinylestradiol (EE2)]. The first phase operated as a conventional membrane bioreactor to achieve the removal of organic matter [chemical oxygen demand (COD)], the CECs and phosphorus. A removal rate of 96.3% for COD, 94.5% for IB, 37.1% for CBZ, 87.1% for DCF and 96% for EE2 was obtained. In the three subsequent phases, current density (CD) of 5, 10 and 15 A/m2 was applied successively in the eMBR with the aim of investigating the effects on the removal of the former components and the fouling of the membrane. After the application of 5 and 10 A/m2 CD, the removal rate of COD decreased. Regarding phosphorus, a CD of 5 A/m2 was enough to achieve the rate of 97% and the membrane fouling suffered a substantial reduction too. Finally, the experimental results were subject to statistical analysis using the Kruskal–Wallis and Wilcoxon tests to validate the influence of each CD.

Exploration on Optimized Control Way of D-Amino Acid for Efficiently Mitigating Membrane Biofouling of Membrane Bioreactor.

The thorny issue of membrane biofouling in membrane bioreactors (MBR) calls for new effective control measures. Herein, D-amino acid (DAA) was employed to mediate MBR membrane biofouling by inhibiting biofilm information and disintegrating formed biofilm. Different DAA control ways involving membrane property, DAA-adding timing, and DAA-control mode were explored through experiments and the multiple linear regression model and the response surface methodology. The optimized DAA control ways were acquired, involving DAA used as an active agent, and the DAA-adding timing of 4 h cultured before running, as well as both hydrophilic and hydrophobic membrane, resulting in an approximately 40.24% decrease in the membrane biofouling rate in comparison with the conventional MBR. DAA is an efficient membrane biofouling mediating approach for MBR under optimized control ways combination and a facile solution for solving membrane biofouling in actual membrane systems.

Comparison between novel vibrating ceramic MBR and conventional air-sparging MBR for domestic wastewater treatment: Performance, fouling control and energy consumption

Two crucial themes emerge from the growing application of MBRs treating domestic wastewater so far: fouling control and energy demand. The significance of in-situ shear-enhanced methods for fouling control in MBRs has been widely acknowledged with air sparging over decades. However, it is still a challenge to develop energy-efficient ways to replace energy-intensive air sparging for effective fouling control during long-term real domestic wastewater treatment. A novel vibrating flat-sheet ceramic MBR (VMBR) was established for investigating the effects of different shear rates on treatment performance, fouling control and specific energy demand compared with air-sparging MBR (ASMBR). Three levels of shear rates with vibration speed of 120, 80, and 40 RPM in the VMBR, versus specific aeration rate of 1.5, 1.0 and 0.5 LPM in the ASMBR were examined as high-, middle- and low-shear phases. Results showed that the VMBR removed over 78.35% TOC, 89.89% COD and 99.9% NH4-N over three phases, and retarded initial increases in transmembrane pressure to control membrane fouling effectively with average fouling rate around 2.31 kPa/d, 3.59 kPa/d and 10.15 kPa/d, almost 70% lower than the ASMBR in Phase 1, 2 and 3, respectively. Particle size distribution of mixed liquor revealed that colloids and biopolymer clusters were significantly reduced in the VMBR showing less propensity for foulant formation. DOM characteristics further indicated that lower production of polysaccharides and protein (by approximately half in Phases 1 and 2) of SMP and EPS in the VMBR generated lower biopolymer content, promoting better fouling mitigation and enhanced dewaterability compared to the ASMBR. Moreover, the VMBR showed superior energy efficiency for fouling control and could save 51.7% to 78.5% energy of the ASMBR under similar-shear condition. The combination of excellent treatment performance, fouling control and energy efficiency from the VMBR makes this an attractive strategy for future improvement of MBR designs in full-scale application with the potential to replace conventional ASMBR.

Gravity-Driven Membrane Reactor for Decentralized Wastewater Treatment: Effect of Reactor Configuration and Cleaning Protocol.

In this study, three gravity-driven membrane (GDM) reactors with flat sheet membrane modules and various biocarriers (synthetic fibers, lava stones, and sands) were operated for municipal wastewater treatment. The effects of water head, periodically cleaning protocol, and operation temperature on the GDM reactor performance were illustrated in terms of membrane performance and water quality. The results indicated that: (1) the cake layer fouling was predominant (>~85%), regardless of reactor configuration and operation conditions; (2) under lower water head, variable water head benefited in achieving higher permeate fluxes due to effective relaxation of the compacted cake layers; (3) the short-term chemical cleaning (30–60 min per 3–4 days) improved membrane performance, especially when additional physical shear force was implemented; (4) the lower temperature had negligible effect on the GDM reactors packed with Icelandic lava stones and sands. Furthermore, the wastewater treatment costs of the three GDM reactors were estimated, ranging between 0.31 and 0.37 EUR/m3, which was greatly lower than that of conventional membrane bioreactors under lower population scenarios. This sheds light on the technical and economic feasibility of biocarrier-facilitated GDM systems for decentralized wastewater treatment in Iceland.

Powdered activated carbon addition for fouling control in anaerobic membrane bioreactor

The effect of powdered activated carbon (PAC) addition to a conventional anaerobic membrane bioreactor (AnMBR) on removal performance and membrane fouling was explored in this study. The optimal one-off PAC dose could increase average chemical oxygen demand (COD) and total organic carbon (TOC) removal rates up to 15.7% and 15.6%, respectively. The PAC addition exhibited not only lower TMP increase rate, but also reduced soluble microbial product (SMP) and extracellular polymeric substances (EPS). Higher protein to polysaccharide ratio of SMP and higher zeta potential in AnMBR with PAC could enhance hydrophobicity and flocculation ability, thereby effectively alleviating membrane fouling. Lower total membrane resistance and pore blocking resistance indicated that PAC addition could prevent both severe pore blocking and irreversible fouling, due to the lower polysaccharide level in SMP of the cake layer. Moreover, PAC addition facilitated the decrease in fouling-related bacteria such as Cloacibacterium and Paludibacter.

Wastewater treatment and fouling control in an electro algae-activated sludge membrane bioreactor

The effect of addition of algae to activated sludge as active biomass in membrane bioreactors (MBRs) and electro-MBRs (e-MBRs) for wastewater remediation was examined in this study. The performances of Algae-Activated Sludge Membrane Bioreactor (AAS-MBR) and electro Algae-Activated Sludge Membrane Bioreactor (e-AAS-MBR) were compared to those observed in conventional MBR and e-MBR, which were previously reported and utilized activated sludge as biomass. The effect of application of electric field was also examined by the comparison of performances of e-AAS-MBR and AAS-MBR. Similar chemical oxygen demand (COD) reduction efficiencies of AAS-MBR, e-AAS-MBR, MBR, and e-MBR (98.35 ± 0.35%, 99.12 ± 0.08%, 97.70 ± 1.10%, and 98.10 ± 1.70%, respectively) were observed. The effect of the algae-activated sludge system was significantly higher in the nutrient removals. Ammoniacal nitrogen (NH3−N) removal efficiencies of AAS-MBR and e-AAS-MBR were higher by 43.89% and 26.61% than in the conventional MBR and e-MBR, respectively. Phosphate phosphorous (PO43−-P) removals were also higher in AAS-MBR and e-AAS-MBR by 6.43% and 2.66% than those in conventional MBR and e-MBR. Membrane fouling rates in AAS-MBR and e-AAS-MBR were lower by 57.30% and 61.95% than in MBR and e-MBR, respectively. Lower concentrations of fouling substances were also observed in the reactors containing algae-activated sludge biomass. Results revealed that addition of algae improved nutrient removal and membrane fouling mitigation. The study also highlighted that the application of electric field in the e-AAS-MBR enhanced organic contaminants and nutrients removal, and fouling rate reduction.

고율하수처리를 위한 생물막여과와 분리막 연계시스템 구성

Compared with the conventional MBR, granular sludge MBR due to the reactor compact design, outstanding settleability, and the ability of granules to withstand high organic loading rate has emerged with strong potential to overcome membrane fouling. The objective of this study is to configure an high-rate system using granular sludge sequencing batch reactor (GSSBR) and granular media filter (GMF) using sand and granular activated carbon (GAC)) coupled with membrane for enhancing membrane filtration performance and reducing membrane fouling in treating wastewater. As a result, GSSBR/GMF/MF configured system achieved higher efficiency than GSSBR-MBR and GSSBR/MF systems in reducing total organic carbon (TOC), total nitrogen (T-N) and total phosphorus (T-P), respectively. For transmembrane pressure (TMP), the GSSBR/GMP/MF developed much lower than that of GSSBR-MBR. In particular, the GSSBR/sand filter/MF system achieved lower TMP build-up than that of the GSSBR/GAC filter/MF system The above results indicate the GSSBR-MF coupled with GMF is more effective than conventional MBR using activated sludge in mitigating membrane fouling. The food/microorganism (F/M) ratio in the GSSBR and the biofilm growth in the GMF play an important role to reduce contaminants and TMP build-up.

Comparing the performance of the conventional and fixed-bed membrane bioreactors for treating municipal wastewater.

Membrane bioreactor (MBR) is relatively a new technology in wastewater treatment. It can efficiently remove soluble and suspended organics. However, it may constantly encounter bio-fouling and cannot efficiently remove nutrient pollutants. These two deficiencies have motivated researchers to upgrade the design and operation of conventional MBR (CMBR). This study evaluates the performance of hybrid fixed bed MBR (FBMBR) treating real domestic wastewater in different operational conditions. It also compares the experimental results of FBMBR with the CMBR. For this purpose, two identical reactors are constructed as CMBR and FBMBR. Each module contains the net volume of 140L and is operated continuously in two aerobic (DO > 4mg/L) and anoxic (DO < 1mg/L) conditions with average organic loading rates (OLRs) of 0.58, 0.71 and 1.55 kgCOD/m3d. The pore sizes of flat sheet membranes are 0.2-0.8μm with total surface area of 1.4m2 per module. The experimental results revealed that the removal efficiencies of BOD, COD and TSS are above 95 % in both CMBR and FBMBR in all operating conditions. However, fouling occurs with lower rates in FBMBR. The growing rate of transmembrane pressure (TMP) in aerobic condition is 1.7mBar/day in CMBR, while it reduces to 1.2mBar/day for FBMBR in solid retention time (SRT) of 75 days and OLR of 0.58 and 0.71 kgCOD/m3d. In anoxic condition with SRT of 100 days and OLR of 1.55 kgCOD/m3d, the TMP in FBMBR is 59 % of CMBR. In addition, total nitrogen (TN) removal is between 12 % (aerobic) and 27 % (anoxic) in CMBR, while it is between 25 % (aerobic) and 49 % (anoxic) in FBMBR. Total phosphorous (TP) removal also ranges between 50 and 66 % in CMBR, while it is between 51 and 86 % in FBMBR. Consequently, using hybrid systems of FBMBR can reduce membrane fouling rate and improve nutrient removal efficiency in comparison with CMBR. This approach can reinforce the biological treatment efficiency and preserve permeate quality in higher OLRs or in lower DO level.

Coupling of Immobilized Photosynthetic Bacteria with a Graphene Oxides/PSF Composite Membrane for Textile Wastewater Treatment: Biodegradation Performance and Membrane Anti-Fouling Behavior.

The membrane bioreactor (MBR), as one of the promising technologies, has been widely applied for treatments of wastewater. However, serious membrane fouling and low microbial activity have been reported as major problems hindering the development of the MBR. To overcome these drawbacks, we intend to improve the MBR process in the view of membrane surface modification and efficient granular bacteria cultivation. In the present study, immobilized photosynthetic bacteria integration with graphene oxide (GO)/polysulfone (PSF) composite membrane separation (IPMBR) was first applied for textile wastewater treatment. Due to the high activity of immobilized cells, the IPMBR system exhibited higher efficiency on the removal of color, ammonia–nitrogen, and chemical oxygen demand than the conventional MBR system. In comparison with a pure PSF membrane, GO/PSF composite membrane presented the higher hydrophilicity (water contact angles of 62.9°) and more attractive permeability (178.5 L/m2h) by reducing the adhesion of hydrophobic foulants. During the whole operation, the immobilized photobioreactor exhibited approximately seven times higher membrane permeability that that of the conventional MBR. Meanwhile, the effect of the structure and character of immobilized photosynthetic bacteria on the membrane fouling reduction was investigated in detail. The change of extracellular polymeric substance concentration, settleability and particle size of flocs was very beneficial to alleviate membrane fouling. As a result, this research will open a new avenue for developing efficient and anti-fouling MBR technology in the future.

Sustainability assessment of wastewater treatment techniques in urban areas of Iraq using multi-criteria decision analysis (MCDA)

Abstract Sustainable development is based on environmental, social, economic, and technical dimensions. In this study, the sustainability of wastewater treatment techniques in urban areas of Iraq was assessed using a multi-criteria decision analysis (MCDA)/the weighted sum model (WSM). The analysis was performed on 13 operating wastewater treatment plants in 10 provinces, Iraq, using a questionnaire sheet with the assistance of 52 specialists in the Ministry of Municipalities and Public Works, Iraq. Four types of wastewater treatment techniques (Conventional Treatment, Oxidation Ditches, Aeration Lagoons, and membrane bio-reactor (MBR)) were assessed. The environmental, social, economic, and technical dimensions were represented by 11, 5, 7, and 4 indicators, respectively. The main results of this study indicate that the sustainability of MBR recorded the highest total importance; the order of the total importance from the highest to the lowest was: MBR &amp;gt; Oxidation Ditches &amp;gt; Aeration Lagoons &amp;gt; Conventional Treatment. The environmental dimension proved its dominance in the four studied treatment techniques' sustainability as it recorded the maximum contribution to sustainability. While the technical dimension recorded the least contribution to sustainability, the order from the highest to the lowest was: Environmental Dimension &amp;gt; Economic Dimension &amp;gt; Social Dimension &amp;gt; Technical Dimension.

Electroconductive moving bed membrane bioreactor (EcMB-MBR) for single-step decentralized wastewater treatment: Performance, mechanisms, and cost

Membrane bioreactor (MBR) is an advantageous technology for wastewater treatment. However, efficient nutrient removal and membrane fouling mitigation remain major challenges in its applications. In this study, an electroconductive moving bed membrane bioreactor (EcMB-MBR) was proposed for simultaneous removal of organics and nutrients from domestic wastewater. The EcMB-MBR was composed of a submerged MBR, filled with electrodes and free-floating conductive media. Conductive media were introduced to reduce energy consumption in an electrochemical MBR, to improve nitrogen removal, and to mitigate membrane fouling. The results showed that COD, total nitrogen, and total phosphorus removal was up to 97.1 ± 1.4%, 88.8 ± 4.2%, and 99.0 ± 0.9%, respectively, in comparison with those of 93.4 ± 1.5%, 65.2 ± 5.3%, and 20.4 ± 11.3% in a conventional submerged MBR. Meanwhile, a total membrane resistance reduction of 26.7% was obtained in the EcMB-MBR. The optimized operating condition was determined at an intermittent electricity exposure time of 10 min-ON/10 min-OFF, and a direct current density of 15 A/m2. The interactions between electric current and conductive media were explored to understand the working mechanism in this proposed system. The conductive media reduced 21% of the electrical resistivity in the mixed liquor at a selected packing density of 0.20 (v/v). The combination of electrochemical process and conductive media specially enhanced the reduction of nitrate-nitrogen (NO3−-N) through hybrid bio-electrochemical denitrification processes. These mechanisms involved with electrochemically assisted autotrophic denitrification by autotrophic denitrifying bacteria. As a result, 5.2% of NO3−-N remained in the effluent of EcMB-MBR in comparison with that of 29.5% in the MBR. Membrane fouling was minimized via both mechanical scouring and electrochemical decomposition/precipitation of organic/particulate foulants. Furthermore, a preliminary cost analysis indicated that an additional operating cost of 0.081 USD/m3, accounting for 10 – 30% increment of the operating cost of a conventional MBR, was needed to enhance the nitrogen and phosphorus removal correspondingly in the EcMB-MBR.

Aerobic granular sludge (AGS) scouring to mitigate membrane fouling: Performance, hydrodynamic mechanism and contribution quantification model

Aerobic granular sludge (AGS) has been proven to have a low fouling potential in membrane bioreactor (MBR). Nevertheless, AGS scouring effect on mitigating membrane fouling remains poorly investigated. The main objective of this study is to examine AGS-MBR performance, to reveal the AGS scouring mechanism and quantify its contribution rate to membrane fouling mitigation, from the views of theory and experiment. Above all, AGS-MBR exhibited a low fouling rate ((transmembrane pressure (TMP) kept below 20 kPa) without membrane cleaning and a higher removal of organics and nutrients than conventional MBR during 80 days’ sludge granulation process. Then, flocculent sludge (FS) with various AGS ratios was applied to simulate the sludge granulation phase. When AGS ratio increased from 0% to 100%, the permeate flux gradually elevated from 40.0 L m−2h−1 to 92.9 L m−2h−1, and fouling resistance decreased from 9.0 × 10−12m−1 to 3.9 × 10−12m−1 benefiting from the loose structure and high porosity of AGS fouling layer. Meanwhile, the scouring effect produced by AGS on the membrane fouling mitigation was investigated. Based on the momentum conservation, a new hydrodynamic model was developed to explain the scouring mechanism of AGS. The scouring stress, proportional to the total amount of AGS depositing on the membrane surface, effectively reinforced the collision between AGS and FS, and reduced their deposition on the membrane surface by friction with the membrane; thus it was further conducive to membrane fouling mitigation. Moreover, a novel contribution quantification model was proposed for analyzing the contribution rate of AGS scouring effect to mitigate membrane fouling. AGS scouring possessed a significant contribution rate (39.9%) for fouling mitigation, compared with AGS structure (50.3%) and hydraulic stress (9.7%). In final, this study provides an in-depth understanding to mitigate the MBR membrane fouling by the unique advantages of sludge granulation.

Evaluating the effect of air flow rate on hybrid and conventional membrane bioreactors: Implications on performance, microbial activity and membrane fouling

This study addressed the impact of air flow rate on the performance, membrane fouling behaviour and microbial community of a sequencing batch conventional membrane bioreactor (SB-MBR) and a sequencing batch hybrid membrane bioreactor (SB-HMBR) with carrier media for biofilm growth. Two different scenarios were evaluated: high (6.4 L min−1) and low (1.6 L min−1) air flow rates, associated with high (4.5 mg L−1) and low (1.5 mg L−1) dissolved oxygen (DO) concentrations and specific aeration demand per membrane area (SADm) of 0.426 and 0.106 m3 m−2 h−1, respectively. Both reactors were subjected to alternating non-aerated and aerated conditions for organic matter (as chemical oxygen demand - COD), nitrogen and phosphate removal from a municipal wastewater. From the bacterial community analysis, the key players in nutrient removal processes were assessed. The results showed that COD removal efficiencies were above 95% in both MBRs, regardless of the aeration intensity, while complete ammonium removal was observed at the higher DO. However, nitrifying activity was adversely affected under low DO levels. High nitrification levels were re-established faster in the hybrid MBR, thanks to the presence of biofilm, where nitrifying activity was favoured and the bacterial community profile did not exhibit substantial changes upon DO reduction. A higher denitrification potential was found for the carrier-based MBR, resulting in lower effluent nitrate concentrations. Regarding phosphorus removal, a slight improvement was observed in the SB-HMBR at reduced DO, while in the SB-MBR it remained practically constant. Moreover, the specific phosphate uptake rate exhibited a significant increase, especially in the hybrid MBR, reaching 44.6 mgP gVSS−1 h−1. At lower aeration rate, however, worse filterability and higher membrane fouling rates were observed, especially in the conventional MBR. Overall, the results demonstrated that the hybrid MBR better withstood the reduced air flow rate and DO as compared to the conventional counterpart.

Performance evaluation of conventional membrane bioreactor and moving bed membrane bioreactor for synthetic textile wastewater treatment

In this study, conventional membrane bioreactor (MBR) and moving bed-membrane bioreactor (MB-MBR) processes were compared in synthetic textile wastewater treatment. For this purpose, the bioreactors were operated as a conventional MBR, an MB-MBR with a biocarrier filling ratio of 20 % and an MB-MBR with a biocarrier filling ratio of 10 %, respectively. In the conventional MBR operation, 93.1 % chemical oxygen demand (COD) and 87.1 % color (Reactive Red 390) removal efficiencies were obtained. In both MB-MBR operations, almost equal COD and color removal efficiencies were found as 98.5 % and 89.5 %, respectively. Moreover, offline physical and chemical membrane cleaning processes were applied every other day and every 15 days throughout the conventional MBR operation, respectively, while no physical or chemical membrane cleaning was required during both MB-MBR operations. Furthermore, lower polysaccharide concentrations of extracellular polymeric substances (EPS) and floc sizes of sludge and higher zeta potential of sludge were determined in MB-MBR. Considering the obtained results, it may be stated that the MB-MBR process is an attractive treatment technology for reducing membrane fouling propensity for treatment of textile wastewater.

Osmotic membrane bioreactor (OMBR) in refinery wastewater treatment: The impact of a draw solute with lower diffusivity in the process performance

The present work considered an osmotic membrane bioreactor (OMBR) for the treatment of a complex and recalcitrant refinery wastewater. Magnesium chloride (MgCl2) was employed as draw solution (DS) to minimize the effects of salinity build up within the mixed liquor (ML). The flux decrease was mainly attributed to the salinity build up. Due to the higher contaminant retention time compared to conventional membrane bioreactor or hybrids UF-OMBRs, the recalcitrant compounds started to be degraded. Moreover, the reverse flux of magnesium favored a higher granulation of the sludge, which in turn enhanced nitrification and denitrification processes. The increase in fouling resistance was attributed to deposits formation, as showed in SEM micrographs and EDX spectra, and the pore blockage by low molecular weight compounds originated by the biological degradation. The increase in salinity (maximum ~10 g/L) lead to a higher production of SMP and EPS protein-like substances, which have lower effect in fouling propensity. Furthermore, even though the ML volatile suspended solids (MLVSS) and ML suspended solids (MLSS) decreased, the mean MLVSS/MLSS ratio was 0.75 ± 0.15, which shows that the salinity build up did not degrade the biological activity. In this sense, when the OMBR is operated with MgCl2 as DS, the permeate shows good physical–chemical quality due to increased contaminants retention time, demonstrating that the system can be used even for applications that demands elevated physical–chemical quality.

Impacts of bio-carriers on the characteristics of soluble microbial products in a hybrid membrane bioreactor for treating mariculture wastewater

To gain greater insights into impacts of bio-carriers on the fate and characteristics of soluble microbial products (SMPs) for mariculture wastewater treatment, the hybrid membrane bioreactor (HMBR) and conventional membrane bioreactor (CMBR) were investigated. Both protein and polysaccharide exhibited lower level in HMBR (8.95 ± 0.28 mg/L and 20.49 ± 1.3 mg/L for anoxic stage, 5.16 ± 0.22 mg/L and 17.85 ± 0.92 mg/L for aerobic stage) than CMBR (14.6 ± 0.68 mg/L and 28.3 ± 2.99 mg/L for anoxic stage, 10.53 ± 0.68 and 26.04 ± 3.15 mg/L for aerobic stage). Three-dimensional fluorescence excitation emission matrix (EEM) revealed bio-carriers reduced the production of aromatic protein-like components in anoxic and aerobic supernatant and caused a blue-shift of soluble microbial product in aerobic stage. Molecular weight (Mw) distribution indicated that bio-carriers ameliorated the excretion of biopolymer (Mw > 500 kDa) in anoxic supernatant and intermediate Mw fractions (20–500 kDa) in aerobic supernatant. Moreover, little changes were observed in SMPs with Mw < 3 kDa down the whole treatment process of both systems. Gas chromatography-mass spectrometry (GC–MS) demonstrated that the major SMPs were long-chain alkanes and aromatics in all units of both systems and fewer aromatics were detected in HMBR. For anoxic stage, more peaks were identified in the HMBR (138) than CMBR (115), while for aerobic stage, more compounds were observed in the CMBR (94) than HMBR (70). Over 50% of the compounds in the anoxic supernatant for the HMBR were the same as in the CMBR. And 27 compounds were the same in aerobic supernatant for the HMBR and CMBR. Fewer compounds in the HMBR effluent (52) was observed, compared to CMBR effluent (80). Approximately 25.7% of compounds in the aerobic stage of the HMBR were rejected by membrane, while this value decreased to 14.9% in the CMBR.