Effect of organic loading rate on organic matter and foulant characteristics in membrane bio-reactor

Effect of organic loading rates on the performance of membrane bioreactor for wastewater treatment behaviours, fouling, and economic cost

Although submerged membrane bioreactor (MBR) are widely used in treating municipal wastewater and recovery of potential resources, membrane operational parameters and membrane fouling control remain debated issues. In this study, the treatment of municipal wastewater by MBR at high-biomass sludge (MLSS (g/L) ranging from 5.4 g/L to 16.1 g/L) was assessed at an organic loading rates (OLRs) ranging from 0.86 to 3.7 kg COD/m3d. The correlation between trans-membrane pressure and total fouling resistance was thoroughly investigated in this study. According to the findings, greater OLRs of 0.86 to 3.7 kg COD/m3d caused a decrease in COD, BOD, and NH4-N removal efficiency, and higher OLRs of 3.7 kg COD/m3d resulted in a higher increase in total fouling resistance (Rt). The economic study of using the MBR system proved that for a designed flow rate of 20 m3/d, the payback period from using the treated wastewater will be 7.98 years, which confirms the economic benefits of using this MBR for treating municipal wastewater. In general, understanding the challenges facing the efficiency of MBR would improve its performance and, consequently, the sustainability of wastewater reclamation.

The potential of microalgae Dunaliella salina to treat shrimp pond wastewater in a PAN/GO membrane bioreactor

Graphene has attracted a significant amount of attention because to its excellent mechanical, electrical, thermal, and optical characteristics. In this work, a membrane bioreactor with hollow fibre PAN/GO nanocomposite was studied for the treatment of Persian Gulf shrimp pond wastewater. Dunaliella salina microalgae have been used for better treatment and the formation of sludge mass in a shorter period of treatment in the MBR system. Additionally, GO nanoparticles were used in order to improve the hydrophilicity of the membranes. Various tests, such as Pure water permeate (PWP), X-ray diffraction spectroscopy (XRD), Atomic force microscopy (AFM), Dynamic light scattering (DLS), Contact angle (CA), Scanning electronic microscopy (SEM), Fourier transform infrared substances (FTIR) were used to characterize the synthesized membranes. To evaluate the treated wastewater, several factors were evaluated, including: TP, TN, TSS, NTU, BOD, COD, EC. The contact angle was reduced by the inclusion of GO nanoparticles from 53.8° for PAN-0 to 45.4° for PAN-3. The results of FTIR analysis confirmed the synthesis of GO and showed the formation of different deposits as fouling on the surface of the prepared membranes after MBR process. Also, the removal percentage of COD and BOD₅ was over 90% for membranes with graphene oxide nanoparticles. The turbidity for all fabricated membranes were removed ∼98%. Also, very little fouling occurred in the membranes constructed with GO membranes and the maximum concentration of GO let to maximum performance regarding to the high potential of fouling control. In addition, the growth of Microalgae Dunaliella salina with shrimp wastewater was observed successfully. In conclusion, the finding of this work not only proposed a promising solution for controlling fouling in an MBR but also resulted in a benefit product, i.e. microalgae Dunaliella salina.

An increase in sludge loading rate induces gel fouling in membrane bioreactors treating real sewage

The main objective of this study was to investigate the cause of gel fouling in membrane bioreactors (MBRs) treating real sewage in terms of soluble microbial products (SMPs) and microbial aspects. Two anoxic/oxic-MBRs were operated as the control reactor (S1) and the sludge loading rate increased reactor (S2). The reactors were operated under low-temperature around 11 °C conditions. Membrane permeability substantially decreased in S2, and gel layer biofilm was formed on membrane surface. In contrast, the permeability of S1 gradually decreased and cake layer formed. When gel fouling occurred, the protein and polysaccharide of SMP in S2 were 47 and 23 mg L^-1, which were significantly lower than those recorded in S1 accounted for 118 and 68 mg L^-1, respectively. Furthermore, the total organic carbon concentration of SMPs was 24 mg L^-1, which was lower than the influent in S2, accounted for 62 mg L^-1. Finally, Campylobacteraceae which exists in sewage and uncultured OD1, dominated the gel layer biofilm in S2, unlike the cake layer biofilm in S1. These results indicated that the gel layer biofilm might be composed of influent substances, demonstrating the importance of influent decomposition in MBR for gel fouling mitigation.

Cake layer reformation rates on self forming dynamic membranes and performance comparison with microfiltration membranes

Dynamic membranes (DMs) keep on attracting attention progressively as an alternative to conventional membranes because they can be operated with relatively higher fluxes and lower fouling rates. However, there are many factors affecting the performance of DMs, such as DM pore size, structure, and operating conditions. In this study, mainly focused on the investigation of cake formation rates both in initial formation and reformation rates after physical/chemical cleaning. In this context, it has been evaluated the performances of DMs with different pore sizes (171 μm, 90 μm, and 30 μm) and different structures under the same conditions and compared their performances with microfiltration (MF) membranes (0.45 μm and 0.22 μm) in a single reactor. In the study, the effects of different fluxes (15-, 20-, 25 L/m²·h (LMH), SAD_m (1-, 0.8-, 0.5 m³-air /m²·h) and F/M (0.095, 0.125, 0.19 g-COD/g-MLSS·day) conditions on the treatment and filtration performance of DMs were investigated. High COD (>95%) and turbidity (<10 NTU) removals were obtained in this study. In particular, the 30 μm DM (0.65 ± 0.47 NTU) produced quite close effluent turbidity compared to MFs (0.12 ± 0.05 NTU). Low SAD_m and high F/M values resulted in increased effluent COD concentrations and turbidity values. By decreasing the SAD_m, the cake formation rate and the fouling rate increased, which showed that there is a definite relationship between the cake formation rates and the fouling rates. Additionally, considering all the results, the most stable operation was obtained in the 30 μm DM, although it has been occurred the least fouling in the 90 μm membrane in the study. This study, focused on cake reformation rates, attempts to show that DMs can be used as an alternative to MBRs. Especially, when taking into account the results of the reformation rate of 30 μm DM (6.09 NTU/h) and other high filterability features.

Alternating current-enhanced carbon nanotubes hollow fiber membranes for membrane fouling control in novel membrane bioreactors

A novel electro-assisted membrane bioreactor (EMBR) was built up with alternating current (AC) voltage applying on carbon nanotubes hollow fiber membranes (CNTs-HFMs) as the basic separation unit (AC-EMBR). Herein, a combination effect of electrostatic repulsion, electrochemical oxidation and translational motion behaviors was used to mitigate membrane fouling with +1.0 V for 1 min and -1.2 V for 1 min repeatedly applying on CNTs-HFMs. During the 73-day operation, the CNTs-HFMs in AC-EMBR exhibited a superior antifouling capability with a lower average fouling rate of 0.017 bar/d comparing to control groups, which were 0.021 bar/d in EMBR with CNTs-HFMs as cathode (C-EMBR), 0.025 bar/d in EMBR with CNTs-HFMs as anode (A-EMBR) and 0.029 bar/d in MBR without voltage, respectively. The AC potential led pollutants to loosely attach on membranes, which reduced irreversible fouling as well as reduced unrecoverable fouling levels. Bound extracellular polymeric substances (EPS) concentration in biomass of AC-EMBR was lower than those in the other reactors, which also contributed to suppressing membrane fouling. Meanwhile, an excellent effluent quality was obtained in AC-EMBR with COD removal rate higher than 96% and effluent NH₄⁺-N concentration lower than 2 mg/L. Microbial community diversity has been promoted by AC electric field according to the microbial community analysis. The results of this study suggested the effectiveness of utilizing AC for membrane fouling mitigation and wastewater treatment in MBR systems.

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.

Maintaining microbial diversity mitigates membrane fouling of an anoxic/oxic membrane bioreactor under starvation condition

The aim of this study was to evaluate the contribution of dissolved organic carbon (DOC) and microbial community dynamics to membrane fouling development in membrane bioreactor (MBR). We operated laboratory-scale anoxic/oxic-MBRs under prolonged starvation conditions in different seasons and the dynamics and diversity of the microbial communities were investigated. Although fouled-MBRs showed DOC accumulation in the activated sludge (AS), the fouling-mitigated MBR suggested that dissolved oxygen was consumed and DOC of the sludge supernatant was degraded. 16S rRNA genes analysis of AS in the MBRs revealed that Chitinophagaceae and Candidatus Promineofilum specifically increased in the fouling-mitigated MBR, suggesting that they played important roles in membrane fouling mitigation; high microbial diversity in the reactor also contributed to fouling mitigation. In the fouled reactor, enrichment of Xanthomonadaceae might be related to fouling causing substances formation leading to membrane fouling development; lower microbial diversity also contributed to fouling development in the fouled MBR.

Diversity of Acyl Homoserine Lactone Molecules in Anaerobic Membrane Bioreactors Treating Sewage at Psychrophilic Temperatures

This study explores the types of acyl homoserine lactone (AHL) and their concentrations in different compartments of different conventional anaerobic bioreactors: (i) an upflow anaerobic membrane bioreactor (UAnMBR, biofilm/mixed liquor (sludge)); (ii) an anaerobic membrane bioreactor (AnMBR, biofilm/mixed liquor (sludge)); and (iii) an upflow sludge blanket (UASB, sludge only), all operating at 15 °C. Ten types of the AHL, namely C4-HSL, 3-oxo-C4-HSL, C6-HSL, 3-oxo-C6-HSL, C8-HSL, 3-oxo-C8-HSL, C10-HSL, 3-oxo-C10-HSL, C12-HSL, and 3-oxo-C12-HSL, which were investigated in this study, were found in UAnMBR and UASB, whilst only six of them (C4-HSL, 3-oxo-C4-HSL, C8-HSL, C10-HSL, 3-oxo-C10-HSL, and C12-HSL) were found in AnMBR. Concentrations of total AHL were generally higher in the biofilm than the sludge for both membrane bioreactors trialed. C10-HSL was the predominant AHL found in all reactors (biofilm and sludge) followed by C4-HSL and C8-HSL. Overall, the UAnMBR biofilm and sludge had 10-fold higher concentrations of AHL compared to the AnMBR. C10-HSL was only correlated with bacteria (p < 0.05), whilst other types of AHL were correlated with both bacteria and archaea. This study improves our understanding of AHL-mediated Quorum Sensing (QS) in the biofilms/sludge of UAnMBR and AnMBR, and provides new information that could contribute to the development of quorum quenching anti-fouling strategies in such systems.

Investigation of the short-term effects of extracellular polymeric substance accumulation with different backwashing strategies in an anaerobic self-forming dynamic membrane bioreactor

The optimum operation strategy for a side-stream external anaerobic self-forming dynamic membrane bioreactor (AnSFDMBR) was investigated by coupling such a system with an up-flow anaerobic sludge blanket reactor. Time-based backwashing with different intervals and transmembrane pressure (TMP)-based backwashing were compared as the operation strategies of the AnSFDMBR. The system performance, extracellular polymeric substance (EPS) accumulation in the dynamic layer and on the membrane mesh of the AnSFDMBR, and the physical properties of the dynamic layer were closely monitored. Both operation strategies achieved stable operation with effluent turbidity less than 5 nephelometric turbidity units with a slowly increasing TMP. However, with the time-based backwashing strategy, the EPS accumulation rate in the dynamic layer was more than 20 times higher than that on the mesh, indicating that frequent backwashing might have a negative impact on the AnSFDMBR. The impacts of EPS accumulation on the membrane mesh were negligible considering the small amount of EPS residual and the large pore size of the mesh. On the contrary, the EPS accumulation in the dynamic layer changed the layer's physical properties and further impacted on the performance of the AnSFDMBR. The accumulation of polysaccharides in the dynamic layer was the main reason for the layer's compactness, which was negatively correlated with the specific surface area and further led to the TMP increase. The polysaccharides in the dynamic layer-to-sludge ratio increased to around 1.6 with only 5 days of time-base operation. With TMP-based operation, it took more than 10 days for polysaccharides in the dynamic layer-to-sludge ratio reaching 1.6. The low TMP increase rate, high effluent quality, and slow EPS accumulation with TMP-based backwashing indicated TMP-based operation is applicable in the studied AnSFDMBR. Nevertheless, the correlation between TMP and the accumulation of polysaccharides should be further investigated to find the optimum TMP for backwashing.

Carbamazepine removal from wastewater and the degradation mechanism in a submerged forward osmotic membrane bioreactor

A submerged forward osmotic membrane bioreactor (FOMBR) was used to reveal the removal and degradation mechanism of carbamazepine (CBZ) from wastewater. The results showed that the removal mechanism consisted of the rejection of the forward osmotic (FO) membrane and biodegradation of the activated sludge. The removal efficiencies of COD, NH₄⁺-N, and CBZ by the FOMBR were approximately 94.77%-97.45%, 93.56%-99.28%, and 88.20%-94.45%, respectively. Moreover, the COD and NH₄⁺-N removal efficiencies were positively correlated with the increased CBZ concentrations. The results of the soluble microbial products (SMP) and extracellular polymeric substances (EPS) tests illustrated that the membrane fouling potential of EPS may be higher than that of SMP. According to the identified 14 degradation products, oxidation, hydroxylation, and decarboxylation were defined as the primary CBZ degradation mechanism. In addition, the RNA results showed that Delftia could be the characteristic bacteria in the CBZ degradation process.

Considering a membrane bioreactor for the treatment of vegetable oil refinery wastewaters at industrially relevant organic loading rates

The present study aims to shed more light on the use of membrane bioreactors (MBRs) for the treatment of vegetable oil refinery wastewaters (VORWs). A MBR was operated for 157 days in which it was fed with real VORW of varying composition at a range of organic loading rates (0.20 ± 0.05-3.79 ± 0.29 kg COD m^-3 day^-1). The hitherto unconsidered fate of VORW constituents through the biological process was followed using gas chromatography/mass spectrometry analysis. This analysis revealed that only 19% of the identified feed constituents remained in the MBR effluent whereas ten new compounds were formed. Linear correlation analysis attributed the effluent residual COD to soluble microbial products (SMP) and non-readily biodegradable recalcitrant oily compounds. Trend of change of MLSS, mixed liquor viscosity and SMP with increasing OLR suggested that when MBR is operated under industrial conditions for the VORW treatment, the mixed liquor fouling propensity potentially increases with increasing OLR in the range studied.

Impact of hydraulic retention time and organic matter concentration on side-stream aerobic granular membrane bioreactor

This study investigated the effect of hydraulic retention time (HRT) and chemical oxygen demand (COD) concentration on membrane fouling in aerobic granular membrane bioreactor (AGMBR) in a systematic approach. Changes in HRT (7, 10, and 15 h) and COD (500, 1000 and 1500 mg/L) were applied in five operational phases, to determine the most significant parameters to control membrane fouling for enhanced AGMBR performance. Membrane permeability loss was dramatically intensified with increase in HRT from 7.5 to 15 h and COD from 500 to 1000 mg/L. The highest polysaccharide content of loosely bound EPS (0.41 mg PS/mg VSS) and soluble microbial products (SMPs) (27 mg PS/L) occurred alongside poor AGMBR performance. Variations in membrane fouling were accompanied with considerable changes in Flavobacterium, Thauera and Paracoccus populations. Analysis of variance (ANOVA) demonstrated that HRT and interaction between HRT and COD were the most significant parameters in controlling membrane fouling.

Linking process performances and core microbial community structures in anaerobic membrane bioreactor with rotatory disk (ARMBR) system fed with high-strength food waste recycling wastewater

This study first evaluated the process performances and microbial community structures of anaerobic rotary membrane bioreactor (ARMBR) fed with food waste recycling wastewater (FRW). Three identical ARMBRs were operated under different organic loading rate (OLR) conditions (1.5, 3.0, and 6.0 kg COD m^-3 d^-1) after the same start-up periods. The start-up performances and archaeal community structures differed among the ARMBRs, probably due to the sudden OLR shock. After the start-up, bio-methane was stably produced until the end of the operational period, with all of the ARMBRs showing >95% COD removal efficiency. Methanosaeta spp. was the predominant methanogen; diverse hydrogenotrophic methanogens co-existed. Bacteroidetes-like bacteria and Candidatus Cloacamonas acted as major fermentative bacteria producing acetate or hydrogen for the growth of methanogens. The results suggest that our ARMBR system can be a promising option to manage high-strength organic wastewater such as FRW.

Enhancement of nitrogen removal by supplementing fluidized-carriers into the aerobic tank in a full-scale A2/O system

Fluidized-carriers were supplemented into the aerobic tank of a full-scale wastewater treatment plant (WWTP) using an anaerobic/anoxic/aerobic (A²/O) system to improve the nitrogen removal efficiency in effluents. The effects of carrier supplementation on denitrification ability and the bacterial community structures were investigated over 10 months. The results showed that the average effluent concentration of total nitrogen (TN) was maintained at 9.46 ± 1.14 mg/L, which was lower than 15.17 ± 2.00 mg/L in the effluent without carrier supplementation, indicating that adding fluidized-carriers into the aerobic tank contributed to nitrogen removal efficiency. A thick biofilm was formed after 4 months, which provided a good anoxic-aerobic microenvironment to the microbes. Illumina sequencing analysis showed a higher bacterial diversity in the biofilm. The relative abundance of nitrifying bacteria, denitrifying bacteria, and aerobic denitrifying bacteria in the biofilms was 13.68-39%, 11.56-12.17%, and 9.76-12.50%, respectively, which was beneficial for nitrogen removal in the system. The most prevalent genera were Nitrospira, Bacillus, Thauera, Hyphomicrobium, Acinetobacter, Zoogloea, Pseudomonas, and Paracoccus, which can metabolize nitrogenous or aromatic compounds and were the major functional bacterial genera, suggesting that these organisms play key roles in biodegradation processes in the carrier-added A²/O wastewater treatment system.

Strategy for Flux Enhancement in Biofilm Ceramic Membrane Bioreactor Applying Prepolymerized and Non-Prepolymerized Inorganic Coagulants

Considering new legislative and economic restrictions caused by the water crisis, this work focuses on a more efficient wastewater treatment process, which combines biological treatment in a moving bed biofilm system with a membrane bioreactor (BF-MBR) and coagulation, particularly addressing fouling alleviation in the separation stage. The study justifies the positive impact of coagulant dosing in BF-MBR regarding membrane flux and fouling rate. Statistical techniques connect the results of coagulation and membrane separation experiments with properties of mixed liquor, obtained after biotreatment in the representative pilot plant and characteristics of prepolymerized and non-prepolymerized inorganic coagulants. Research results substantiate the need for a pH-controlled coagulation of mixed liquor in BF-MBR depending on coagulant type, which influences charge, hydrophobicity and size of flocs and organic content of the system. It is suggested, that the adsorption/charge neutralization mechanism dominates in flux enhancement in BF-MBR, giving the best results in the case of prepolymerized aluminium coagulants. Together with high quality of permeate, the application of prepolymerized aluminium chloride of medium basicity entails a tenfold increase in filtration time of the membrane separation cycle and increases net membrane flux by 30–56%. The results of the study are practically significant for the development of an automated control system for BF-MBR, optimizing treatment rates together with membrane separation efficiency.

Pilot-scale study to investigate the impact of rotating belt filter upstream of a MBR for nitrogen removal

The goal of this study was to investigate what kind of impact the removal of particulate organic matter with 33μm rotating belt filter (RBF) (as a primary treatment) will have on the membrane bioreactor (MBR) performance. Two small MBR pilot plants were operated in parallel, where one train treated 2mm screened municipal wastewater (Train A) and the other train treated wastewater that had passed through a RBF with a 33μm filter cloth (Train B). The RBF was operated without a filter mat on the belt. About one third of the organic matter was removed by the fine mesh filter. The assessment of the overall performance showed that the two pilot plants achieved approximately the same removal efficiencies with regard to total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus and total nitrogen. It was also observed that the system with 33μm RBF as a primary treatment produced more sludge, which could be used for biogas production, and required about 30% less aeration downstream. Transmembrane pressure was significantly lower for the train receiving 33μm primary treated wastewater compared to the control receiving 2mm screened wastewater.

Fouling Development in A/O-MBR under Low Organic Loading Condition and Identification of Key Bacteria for Biofilm Formations

Membrane fouling in membrane bioreactors (MBR) remains a major issue and knowledge of microbes associated with biofilm formation might facilitate the control of this phenomenon, Thus, an anoxic/oxic membrane bioreactor (A/O-MBR) was operated under an extremely low organic loading rate (0.002 kg-COD·m⁻³·day⁻¹) to induce membrane fouling and the major biofilm-forming bacteria were identified. After operation under extremely low organic loading condition, the reactor showed accumulation of total nitrogen and phosphorus along with biofilm development on the membrane surface. Thus, membrane fouling induced by microbial cell lysis was considered to have occurred. Although no major changes were observed in the microbial community structure of the activated sludge in the MBR before and after membrane fouling, uncultured bacteria were specifically increased in the biofilm. Therefore, bacteria belonging to candidate phyla including TM6, OD1 and Gammaproteobacteria could be important biofilm-forming bacteria.

Effects of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor for municipal wastewater treatment

This study aimed to evaluate the impact of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor (SAAMB-AnGMBR) in municipal wastewater treatment. The results showed that organic removal efficiencies were above 94% at all C/N conditions. Nutrient removal was over 91% at C/N ratio of 100/5 but was negatively affected when decreasing C/N ratio to 100/10. At lower C/N ratio (100/10), more noticeable membrane fouling was caused by aggravated cake formation and pore clogging, and accumulation of extracellular polymeric substances (EPS) in the mixed liquor and sludge cake as a result of deteriorated granular quality. Foulant analysis suggested significant difference existed in the foulant organic compositions under different C/N ratios, and humic substances were dominant when the fastest fouling rate was observed. The performance of the hybrid system was found to recover when gradually increasing C/N ratio from 100/10 to 100/5.

Dynamic changes of dissolved organic matter in membrane bioreactors at different organic loading rates: Evidence from spectroscopic and chromatographic methods

Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) and size exclusion chromatography (SEC) were utilized to explore the dynamics in extracellular polymeric substances (EPS), soluble microbial products (SMP), and effluent for the membrane bioreactors at two different organic loading rates (OLRs). Combination of three different fluorescent components explained the compositional changes of dissolved organic matter. The lower OLR resulted in a higher production of tryptophan-like component (C1) in EPS, while the opposite trends were found for the other two components (humic-like C2 and tyrosine-like C3), signifying the role of C1 in the endogenous condition. Larger sized molecules were more greatly produced in EPS at the lower OLR. Meanwhile, all the size fractions of SMP were more abundant at the higher OLR particular for the early phase of the operation. Irrespective of the OLR, the higher degrees of the membrane retention were found for relatively large sized and protein-like molecules.

Single-stage versus two-stage anaerobic fluidized bed bioreactors in treating municipal wastewater: Performance, foulant characteristics, and microbial community

This study examined the receptive performance, membrane foulant characteristics, and microbial community in the single-stage and two-stage anaerobic fluidized membrane bioreactor (AFMBR) treating settled raw municipal wastewater with the aims to explore fouling mechanisms and microbial community structure in both systems. Both AFMBRs exhibited comparable organic removal efficiency and membrane performances. In the single-stage AFMBR, less soluble organic substances were removed through biosorption by GAC and biodegradation than those in the two-stage AFMBR. Compared to the two-stage AFMBR, the formation of cake layer was the main cause of the observed membrane fouling in the single-stage AFMBR at the same employed flux. The accumulation rate of the biopolymers was linearly correlated with the membrane fouling rate. In the chemical-cleaned foulants, humic acid-like substances and silicon were identified as the predominant organic and inorganic fouants respectively. As such, the fluidized GAC particles might not be effective in removing these substances from the membrane surfaces. High-throughout pyrosequencing analysis further revealed that beta-Proteobacteria were predominant members in both AFMBRs, which contributed to the development of biofilms on the fluidized GAC and membrane surfaces. However, it was also noted that the abundance of the identified dominant in the membrane surface-associated biofilm seemed to be related to the permeate flux and reactor configuration.

Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling

The membrane bioreactor (MBR) has emerged as an efficient compact technology for municipal and industrial wastewater treatment. The major drawback impeding wider application of MBRs is membrane fouling, which significantly reduces membrane performance and lifespan, resulting in a significant increase in maintenance and operating costs. Finding sustainable membrane fouling mitigation strategies in MBRs has been one of the main concerns over the last two decades. This paper provides an overview of membrane fouling and studies conducted to identify mitigating strategies for fouling in MBRs. Classes of foulants, including biofoulants, organic foulants and inorganic foulants, as well as factors influencing membrane fouling are outlined. Recent research attempts on fouling control, including addition of coagulants and adsorbents, combination of aerobic granulation with MBRs, introduction of granular materials with air scouring in the MBR tank, and quorum quenching are presented. The addition of coagulants and adsorbents shows a significant membrane fouling reduction, but further research is needed to establish optimum dosages of the various coagulants/adsorbents. Similarly, the integration of aerobic granulation with MBRs, which targets biofoulants and organic foulants, shows outstanding filtration performance and a significant reduction in fouling rate, as well as excellent nutrients removal. However, further research is needed on the enhancement of long-term granule integrity. Quorum quenching also offers a strong potential for fouling control, but pilot-scale testing is required to explore the feasibility of full-scale application.

A submerged membrane bioreactor with pendulum type oscillation (PTO) for oily wastewater treatment: membrane permeability and fouling control

In this study, a novel submerged membrane bioreactor (SMBR) with pendulum type oscillation (PTO) hollow fiber membrane modules was developed to treat oily wastewater and control the problem of membrane fouling. To assess the potential of PTO membrane modules, the effect of oscillation orientation and frequency on membrane permeability was investigated in detail. The forces exerted on sludge flocs in the oscillating SMBR were analyzed to evaluate the impact of membrane oscillating on the cake layer resistance reduction. Results showed that the optimized PTO SMBR system exhibited 11 times higher membrane permeability and better fouling controllability than the conventional MBR system. By hydrodynamic analysis, it was found that the cooperative effect of bubble-induced turbulence and membrane oscillation in PTO SMBR system generated strong shear stress at liquid-membrane interface in vertical and horizontal direction and effectively hindered the particles from depositing on membrane surface.

Salt stress in a membrane bioreactor: dynamics of sludge properties, membrane fouling and remediation through powdered activated carbon dosing

Membrane bioreactors are a well-established technology for wastewater treatment. However, their efficiency is adversely impacted by membrane fouling, primarily inciting very conservative operations of installations that makes them less appealing from an economic perspective. This fouling propensity of the activated sludge is closely related to system disturbances. Therefore, improved insight into the impact of fouling is crucial towards increased membrane performance. In this work, the disturbance of a salt shock was investigated with respect to sludge composition and filterability in two parallel lab-scale membrane bioreactors. Several key sludge parameters (soluble microbial products, sludge-bound extracellular polymeric substances, supramicron particle size distributions (PSD), submicron particle concentrations) were intensively monitored prior to, during, and after a disturbance to investigate its impact as well as the potential governing mechanism. Upon salt addition, the supramicron PSD immediately shifted to smaller floc sizes, and the total fouling rate increased. Following a certain delay, an increase in submicron particles, supernatant proteins, and polysaccharides was observed as well as an increase in the irreversible membrane fouling rate. Recovery from the disturbance was evidenced with a simultaneous decrease in the above mentioned quantities. A similar experiment introducing powdered activated carbon (PAC) addition used for remediation resulted in either no or less significant changes in the above mentioned quantities, signifying its potential as a mitigation strategy.

Activated sludge filterability improvement by nitrifying bacteria abundance regulation in an adsorption membrane bioreactor (Ad-MBR)

Autotrophic nitrifying bacteria have its intrinsic properties including low EPS production, dense colonial structure and slow-growth rate, favoring the sludge filterability improvement. An adsorption-MBR (Ad-MBR) was developed to enrich nitrifier abundance in the MBR chamber by inlet C/N regulation, and its possible positive effect on sludge filterability and underlying mechanisms were investigated. By DNA extraction, PCR amplification and Illumina high-throughput pyrosequencing, the abundance of nitrifying bacteria was accurately quantified. More than 8.29% nitrifier abundance was achieved in Ad-MBR sludge, which was above three times of that in conventional MBR. Regulated C/N ratio and thereafter nitrifier abundance enrichment improved sludge filterability by altering sludge mixture and its supernatant properties, reflected by a good sludge settleability, a low supernatant viscosity and turbidity, a low supernatant organic substances concentration, and a small amount of strong hydrophobic fractional components, thus to profoundly improve sludge filterability and decelerate membrane fouling.

Effect of PAC dosage in a pilot-scale PAC-MBR treating micro-polluted surface water

To address the water scarcity issue and advance the traditional drinking water treatment technique, a powdered activated carbon-amended membrane bioreactor (PAC-MBR) is proposed for micro-polluted surface water treatment. A pilot-scale study was carried out by initially dosing different amounts of PAC into the MBR. Comparative results showed that 2g/L performed the best among 0, 1, 2 and 3g/L PAC-MBR regarding organic matter and ammonia removal as well as membrane flux sustainability. 1g/L PAC-MBR exhibited a marginal improvement in pollutant removal compared to the non-PAC system. The accumulation of organic matter in the bulk mixture of 3g/L PAC-MBR led to poorer organic removal and severer membrane fouling. Molecular weight distribution of the bulk liquid in 2g/L PAC-MBR revealed the synergistic effects of PAC adsorption/biodegradation and membrane rejection on organic matter removal. Additionally, a lower amount of soluble extracellular polymer substances in the bulk can be secured in 21 days operation.

Impact of food to microorganism (F/M) ratio and colloidal chemical oxygen demand on nitrification performance of a full-scale membrane bioreactor treating thin film transistor liquid crystal display wastewater

This study investigated impact of food to microorganism (F/M) ratio and colloidal chemical oxygen demand (COD) on nitrification performance in one full-scale membrane bioreactor (MBR) treating monoethanolamine (MEA)/dimethyl sulfoxide (DMSO)-containing thin film transistor liquid crystal display (TFT-LCD) wastewater. Poor nitrification was observed under high organic loading and high colloidal COD conditions, suggesting that high F/M ratio and colloidal COD situations should be avoided to minimize their negative impacts on nitrification. According to the nonmetric multidimensional scaling (NMS) statistical analyses on terminal restriction fragment length polymorphism (T-RFLP) results of ammonia monooxygenase (amoA) gene, the occurrence of Nitrosomonas oligotropha-like ammonia oxidizing bacteria (AOB) was positively related to successful nitrification in the MBR systems, while Nitrosomonas europaea-like AOB was positively linked to nitrification rate, which can be attributed to the high influent total nitrogen condition. Furthermore, Nitrobacter- and Nitrospira-like nitrite oxidizing bacteria (NOB) were both abundant in the MBR systems, but the continuously low nitrite environment is likely to promote the growth of Nitrospira-like NOB.

Aerobic SMBR/reverse osmosis system enhanced by Fenton oxidation for advanced treatment of old municipal landfill leachate

A novel combined process of Fenton oxidation, submerged membrane bioreactor (SMBR) and reverse osmosis (RO) was applied as an appropriate option for old municipal landfill leachate treatment. Fenton process was designed to intensively solve the problem of non-biodegradable organic pollutant removal and low biodegradability of leachate, although the removal of ammonia-nitrogen was similar to 10%. After SMBR treatment, it not only presented a higher removal efficiency of organics, but also exhibited high ammonia-nitrogen removal of 80% on average. The variation of extracellular polymeric substance (EPS) content, zeta potential, and particle size of flocs after Fenton effluent continually fed in SMBR was found to be benefit for alleviating membrane fouling. Finally, three kinds of RO membranes (RE, CPA, and BW) were applied to treat SMBR effluents and successfully met wastewater re-utilization requirement. Compared with simple RO process, the troublesome membrane fouling can be effectively reduced in the combined process.