Membrane fouling mechanism of biofilm-membrane bioreactor (BF-MBR): Pore blocking model and membrane cleaning

Comparison of single and mixed microalgae in microalgae-bacteria MB-MBR:From efficiency of wastewater treatment, bioactivity and membrane fouling

In this study, two microalgae-bacterial moving bed membrane bioreactors (MB-MBRs) were constructed for co-culture of L1 (Scenedesmus obliquus) and L2 (Chlorella pyrenoidosa and Scenedesmus obliquus) with activated sludge. Nutrient removal efficiency, biological activity and membrane fouling of two microalgae-bacterial MB-MBRs were evaluated. Both reactors demonstrated robust performance, with L2 exhibiting superior functionality. near-complete ammonia nitrogen removal (99.33 ± 1.11 %), total organic carbon (TOC) removal of 73.72 ± 4.83 %, chemical oxygen demand (COD) removal of 92.93 ± 3.23 %, and dehydrogenase activity (DHA) peaked at 10 μg TF/(mL·h). L2 sludge flocs displayed a more compact circular morphology compared to those of L1. It was found that proteins in the extracellular polymeric substance (EPS) were the key to initial biofilm attachment, while polysaccharides facilitated biofilm maturation. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy demonstrated that tryptophan and aromatic proteins played critical roles in biofilm formation and membrane fouling. According to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, ΔGAB was the main factor influencing membrane fouling. These results demonstrate that hybrid microalgae-bacterial systems with biofilm carriers synergistically enhance wastewater treatment efficiency, increase biological activity, and alleviate membrane fouling, offering a sustainable strategy for wastewater treatment.

Effect of micro-granular activated carbon on bacteriophage MS2 removal and fouling control in flat-plate MBR

Pathogenic microorganisms pose a severe risk to the aquatic environment and human health. Membrane bioreactors (MBRs) have attracted much attention due to their simultaneous biological treatment and virus retention, but membrane fouling is the main obstacle. This study explored the effect of micro-granular activated carbon (μGAC) on bacteriophage MS2 removal efficiency and membrane fouling in a flat-plate MBR. The results showed that the μGAC addition with a particle size of 180-300 μm improved the removal of MS2 (LRVMBR of 4.77 log) and enhanced the removal of COD and ammonia nitrogen. The μGAC integrated MBR (μGAC-MBR) exhibited a higher MS2 retention rate by the membrane filter layers with an average LVRMem of 2.03 log compared to that of a control reactor (C-MBR) of 1.89 log. Meanwhile, the total membrane filter layer resistance of μGAC-MBR was significantly lower than that of C-MBR, particularly in terms of cake layer resistance and organic pore-blocking exclusion. The μGAC addition slightly reduced MS2 adsorption by the activated sludge while significantly altering the extracellular polymeric substances (EPS) profiles. The fluorescent components in the bound EPS and PN/PS ratio of the activated sludge were reduced. We found that μGAC enhanced membrane surface roughness and hydrophilicity. Notably, the μGAC significantly influenced the quorum sensing (QS) systems, reducing the abundance and synthesis of AHL-related genes. The synthase luxI in the AHL-QS system was reduced by 93.21% in μGAC-MBR. The AHL-QS system is closely related to biofilm formation, and the total EPS of the surface filer layer of μGAC-MBR decreased by 57.73%, and PN in LB-EPS and TB-EPS decreased by 91.33% and 54.44% compared with C-MBR, indicating a significant reduction in biofilm formation. This study exhibited a new perspective on promoting MS2 removal with the synergistic effect of alleviating fouling in the MBR process.

Modeling MBR fouling: A critical review analysis towards establishing a framework for good modeling practices

This study critically analyses filtration process modeling in membrane bioreactor (MBR) technology. More specifically, the variety of approaches and assumptions considered within a curated selection of resistance-in-series (RIS) filtration models found in the literature is critically assessed. Aimed to move towards good filtration process modeling practices, the basis for establishing a unified framework rooted in the fundamentals of membrane fouling is defined in this work, considering fouling classifications, process dynamics, and underlying processes used by different authors for elucidating membrane fouling phenomena. Systematically analyzing these factors should be considered as a basic step for efficiently comparing the performance of different models. This involves a detailed examination of the processes applied within each model and their interplay with the involved resistances and fouling types. A lack of homogeneity in RIS-based filtration modeling has been observed. To address this, basic guidelines towards good modeling practices are proposed aimed at balancing model accuracy and complexity. Specifically, seven model processes, six resistances, and three subgroups for types of fouling, further divided into four or five categories are proposed to guide the selection of processes and state variables in the model structure. Hence, this study facilitates the understanding of different approaches to be used during the modeling exercise of membrane filtration processes within the MBR field, not only to enhance the comprehensibility of available filtration models, but also to help the comparison, implementation, and adaptation of available models and the comprehensive development of new ones.

Stratified structure of membrane clogs observed in full scale cross-flow tubular ultrafiltration (UF) system: Fouling characterization and a proposed two-stage formation mechanism

Membrane fouling remains a significant challenge in wastewater treatment, hindering both efficiency and lifespan. This study reports a distinct phenomenon of stratified membrane clogging observed in a full-scale cross-flow tubular ultrafiltration (UF) system treating sludge anaerobic digestion (AD) reject water. The distinct stratified structure, comprising inner and outer layers within the cake layer, has not been previously described. This research involved characterizing the filtration performance, analyzing membrane clog composition, and proposing a two-stage formation mechanism for the stratified clogs. It was revealed that higher inorganic and lower organic content in the outer layer compared to the inner layer. Acid and alkali treatments demonstrated the effectiveness of combined cleaning strategies. A mathematical model was developed to determine the critical conditions for stratified clog formation, influenced by membrane flux and cross-flow velocity (CFV). It is proposed that outer layer forms through long-term selective deposition, while the inner layer results from short-term dewatering within limited tubular space. High CFV (>2.5 m/s) prevents inner layer formation. Critical conditions for stratification occur at a flux of 18 L/m2/h with a CFV of 0.1 m/s or 65 L/m2/h with a CFV of 0.35 m/s. This study contributes a novel understanding of stratified membrane clogging, proposing a two-stage formation mechanism and identifying critical conditions, which provides insights for effective fouling control strategies and maintenance of operational efficiency for membrane systems.

Unveiling the impacts of salts on halotolerant bacteria during filtration: A new perspective on membrane biofouling formation in MBR treating high-saline organic wastewater

In recent decades, membrane bioreactor (MBR) has been prevalently employed to treat high-saline organic wastewater, where the halotolerant microorganisms should be intensively utilized. However, limited works were devoted to investigating the biofouling characteristics from the perspective of the relationship between halotolerant bacteria and salts. This work filled the knowledge gap by exploring the biofouling formation mechanisms affected by high salinity. The results showed that the amount of negative charge on halotolerant bacteria surface was significantly reduced by high content of NaCl, probably leading to the obvious cell agglomeration. Despite the normal proliferation, the halotolerant bacteria still produced substantial EPS triggered by high salinity. Compared with the case of control without salt addition, the enhanced biofouling development was observed under high-saline conditions, with the fouling mechanism dramatically transformed from cake filtration to intermediate blocking. It was inferred that the halotolerant bacteria initially adhered on membrane created an extra filter layer, which contributed to the subsequent NaCl retention, resulting in the simultaneous occurrences of pore blockage and cake layer formation because of NaCl deposition both on membrane pores as well as on biofilm layer. Under high-saline environment, remarkable salt crystallization occurred on the biofilm layer, with more protein secreted by the attached halotolerant bacteria. Consequently, the potential mechanisms for the enhanced biofouling formation influenced by high salinity were proposed, which should provide new insights and enlightenments on fouling control strategies for MBR operation when treating high-saline organic wastewater.

Employing Atomic Force Microscopy (AFM) for Microscale Investigation of Interfaces and Interactions in Membrane Fouling Processes: New Perspectives and Prospects

Membrane fouling presents a significant challenge in the treatment of wastewater. Several detection methods have been used to interpret membrane fouling processes. Compared with other analysis and detection methods, atomic force microscopy (AFM) is widely used because of its advantages in liquid-phase in situ 3D imaging, ability to measure interactive forces, and mild testing conditions. Although AFM has been widely used in the study of membrane fouling, the current literature has not fully explored its potential. This review aims to uncover and provide a new perspective on the application of AFM technology in future studies on membrane fouling. Initially, a rigorous review was conducted on the morphology, roughness, and interaction forces of AFM in situ characterization of membranes and foulants. Then, the application of AFM in the process of changing membrane fouling factors was reviewed based on its in situ measurement capability, and it was found that changes in ionic conditions, pH, voltage, and even time can cause changes in membrane fouling morphology and forces. Existing membrane fouling models are then discussed, and the role of AFM in predicting and testing these models is presented. Finally, the potential of the improved AFM techniques to be applied in the field of membrane fouling has been underestimated. In this paper, we have fully elucidated the potentials of the improved AFM techniques to be applied in the process of membrane fouling, and we have presented the current challenges and the directions for the future development in an attempt to provide new insights into this field.

Identification of performance and cost in a new backwash method to clean the UF membrane: backwashing with low dosage of NaClO

Ultrafiltration (UF) is widely used in wastewater reclamation treatments. Conventional backwashing is usually performed at regular time intervals (10-120 min) with permeate and without the addition of chemicals. Chemical enhanced backwashing (CEB) is usually applied after 70-90 filtration cycles with added chemicals. These cleaning methods cause membrane fouling and require costly chemicals. Instead of conventional backwashing, we propose herein a new backwashing method involving backwashing the effluent with low doses of sodium hypochlorite (NaClO) named as BELN. The performance and cost of UF backwashing were investigated with Beijing wastewater reclamation treatment. The results showed that the transmembrane pressure (TMP) increased from 33.2 to 48.2 kPa during hydraulic backwashing after 80 filtration cycles but increased from 33.3 to 39.3 kPa during backwashing with a low NaClO content of 20 mg/L. It was also noticed that the hydraulic-irreversible fouling index decreased from 5.58 × 10-3 m2/L to 3.58 × 10-3 m2/L with the new method. According to the three-dimensional fluorescence excitation-emission (3D-EEM), the response increased from 11.9 to 15.2% with BELN. Protein-like material was identified as the main component causing membrane fouling by blocking the membrane pores. The results indicated that the low dosage of NaClO effectively stripped the fouling layer. Finally, based on an economic evaluation, the capacity of the UF process was increased from 76,959 to 109,133 m3/d with the new method. The amount of NaClO consumed for Beijing wastewater reclamation treatment was similarly compared with the conventional backwashing in per year under BELN. The new method has good potential for application.

Performance of modified hollow fiber membrane silver nanoparticles-zeolites Na-Y/PVDF composite used in membrane bioreactor for industrial wastewater treatment

Membrane bioreactor (MBR) deteriorates due to fouling on the membrane pores, which can reduce the membrane performance. To reduce membrane fouling, the addition of inorganic filler can enhance the antifouling properties. This study investigates two different membrane preparation by thermally induced phase separation (TIPS) and dip coating methods to modify hollow fiber membrane with Silver Nanoparticles (AgNPs)-Zeolites used in MBR for industrial wastewater treatment. Performance was evaluated by analyzing the flux of water and wastewater, rejection, water content, and antifouling properties. Characterization result represented the synthesized silver nanoparticles had similar diffraction peak with commercial AgNPs, then the micrograph of AgNPs and zeolites addition membrane showed that the inorganic material had an octahedral shape representing zeolite crystal and irregular shape representing AgNPs. The addition of zeolites and AgNPs resulted in satisfying performance, increased flux, rejection, and antifouling properties.

Biological processes modelling for MBR systems: A review of the state-of-the-art focusing on SMP and EPS

A mathematical correlation between biomass kinetic and membrane fouling can improve the understanding and spread of Membrane Bioreactor (MBR) technology, especially in solving the membrane fouling issues. On this behalf, this paper, produced by the International Water Association (IWA) Task Group on Membrane modelling and control, reviews the current state-of-the-art regarding the modelling of kinetic processes of biomass, focusing on modelling production and utilization of soluble microbial products (SMP) and extracellular polymeric substances (EPS). The key findings of this work show that the new conceptual approaches focus on the role of different bacterial groups in the formation and degradation of SMP/EPS. Even though several studies have been published regarding SMP modelling, there still needs to be more information due to the highly complicated SMP nature to facilitate the accurate modelling of membrane fouling. The EPS group has seldom been addressed in the literature, probably due to the knowledge deficiency concerning the triggers for production and degradation pathways in MBR systems, which require further efforts. Finally, the successful model applications showed that proper estimation of SMP and EPS by modelling approaches could optimise membrane fouling, which can influence the MBR energy consumption, operating costs, and greenhouse gas emissions.

Understanding Protein and Polysaccharide Fouling with Silicon Dioxide and Aluminum Oxide in Low-Pressure Membranes

Humic, protein, and polysaccharide substances have been recognized as significant types of foulants in membrane systems. Despite the remarkable amount of research that has been performed on the interaction of these foulants, particularly humic and polysaccharide substances, with inorganic colloids in RO systems, little attention has been paid to the fouling and cleaning behavior of proteins with inorganic colloids in UF membranes. This research examined the fouling and cleaning behavior of bovine serum albumin (BSA) and sodium alginate (SA) with silicon dioxide (SiO₂) and α-aluminum oxide (Al₂O₃) in individual and combined solutions during dead-end UF filtration. The results showed that the presence of SiO₂ or Al₂O₃ in water alone did not cause significant fouling or a flux decline in the UF system. However, the combination of BSA and SA with inorganics was observed to have a synergistic effect on membrane fouling, in which the combined foulants caused higher irreversibility than individual foulants. Analysis of blocking laws demonstrated that the fouling mechanism shifted from cake filtration to complete pore blocking when the combined organics and inorganics were present in water, which resulted in higher BSA and SA fouling irreversibility. The results suggest that membrane backwash needs to be carefully designed and adjusted for better control of BSA and SA fouling with SiO₂ and Al₂O₃.

The Application of Polyethersulfone Ultrafiltration Membranes for Separation of Car Wash Wastewaters: Experiments and Modelling

The wastewater generated as a result of car washes is considered a new source of water. However, recovered water must meet the required quality criteria for reuse. For this purpose, the ultrafiltration (UF) process can be successfully used. The main aim of the present work was to investigate the influence of the membrane's molecular weight cut-off (MWCO) on the UF performance in terms of the fouling phenomenon and retention degree of car wash wastewater. Moreover, for a better understanding of the fouling mechanisms, Hermia's model was used. The experimental studies were conducted with the use of two polyethersulfone (PES) membranes (MWCO of 10 kDa and 100 kDa). It has been noted that the used membranes provided a high-quality permeate and excellent turbidity removal, up to 99%. Moreover, it has been noted that the MWCO membrane has a significant impact on the fouling mechanism. Generally, a much greater intensity of fouling for the membrane with MWCO of 100 kDa was observed. Results obtained in the present study showed that both real wastewaters and the clean solutions used for washing cars cause the fouling phenomenon. It has been proven that rinsing the membranes with water is not sufficient to recover the initial membrane's performance. Hence, periodic chemical cleaning of the membranes was required. Fitting the experimental data to Hermia's model allowed us to indicate that membranes with MWCO of 100 kDa are more prone to intermediate blocking. To sum up, the findings suggest that for the UF of the car wash wastewater, the use of membranes with MWCO equal to 10 kDa is recommended.

Generalization and Expansion of the Hermia Model for a Better Understanding of Membrane Fouling

One of the most broadly used models for membrane fouling is the Hermia model (HM), which separates this phenomenon into four blocking mechanisms, each with an associated parameter n. The original model is given by an Ordinary Differential Equation (ODE) dependent on n. This ODE is solved only for these four values of n, which limits the effectiveness of the model when adjusted to experimental data. This paper aims extend the original Hermia model to new values of n by slightly increasing the complexity of the HM while keeping it as simple as possible. The extended Hermia model (EHM) is given by a power law for any n ≠ 2 and by an exponential function at n = 2. Analytical expressions for the fouling layer thickness and the accumulated volume are also obtained. To better test the model, we perform model fitting of the EHM and compare its performance to the original four pore-blocking mechanisms in six micro- and ultrafiltration examples. In all examples, the EHM performs consistently better than the four original pore-blocking mechanisms. Changes in the blocking mechanisms concerning transmembrane pressure (TMP), crossflow rate (CFR), crossflow velocity (CFV), membrane composition, and pretreatments are also discussed.

Membrane Bioreactors: A Promising Approach to Enhanced Enzymatic Hydrolysis of Cellulose

The depletion of fossil fuel resources and the negative impact of their use on the climate have resulted in the need for alternative sources of clean, sustainable energy. One available alternative, bioethanol, is a potential substitute for, or additive to, petroleum-derived gasoline. In the lignocellulose-to-bioethanol process, the cellulose hydrolysis step represents a major hurdle that hinders commercialization. To achieve economical production of bioethanol from lignocellulosic materials, the rate and yield of the enzymatic hydrolysis of cellulose, which is preferred over other chemically catalyzed processes, must be enhanced. To achieve this, product inhibition and enzyme loss, which are two major challenges, must be overcome. The implementation of membranes, which can permeate molecules selectively based on their size, offers a solution to this problem. Membrane bioreactors (MBRs) can enhance enzymatic hydrolysis yields and lower costs by retaining enzymes for repeated usage while permeating the products. This paper presents a critical discussion of the use of MBRs as a promising approach to the enhanced enzymatic hydrolysis of cellulosic materials. Various MBR configurations and factors that affect their performance are presented.

Polyaniline derived carbon membrane and its in-situ membrane fouling mitigation performance in MBR based on metal-free electro-Fenton

An electro-enhanced membrane bioreactor (EMBR) was constructed with polyaniline-based carbon (PAC) separation membrane as the membrane-electrode, which could realize the in-situ electro-generation and activation of H₂O₂ to ·OH depending on the graphitic and pyridinic N as active sites without metal catalyst. After the continuous operation of the bioreactor for 74 days, approximately 77.41% irreversible membrane fouling occurred on the electrochemically enhanced membrane, which was less than that on the control membrane (85.96%). The ·OH oxidation combined with electrostatic barrier formed by -1.0 V enhanced PAC membrane suppressed the extracellular polymeric substances deposition on membrane. After operation, the strength of total cell, proteins, β-polysaccharides and α-polysaccharides on the membrane without bias were 5.17, 4.32, 9.65 and 16.31, respectively. In EMBR, the corresponding strength were 2.03, 3.35, 2.15 and 6.73. After calculation, the unblocked pores accounted for 35.3% and 78.5% of the total membrane surface in MBR and EMBR, respectively, indicating the fouling was alleviated obviously. Meanwhile, the EMBR owned a satisfactory wastewater treatment effect with average effluent chemical oxygen demand and NH₄⁺-N around 18.98 mg/L and 0.68 mg/L. The successful implementation of this strategy achieved a green and metal-free method for ·OH production with electrochemical effect for membrane fouling control in MBR.

Pilot Scale Application of a Ceramic Membrane Bioreactor for Treating High-Salinity Oil Production Wastewater

The offshore oil extraction process generates copious amounts of high-salinity oil-bearing wastewater; at present, treating such wastewater in an efficient and low-consumption manner is a major challenge. In this study, a flat ceramic membrane bioreactor (C−MBR) process combining aerobic microbial treatment technology and ceramic membrane filtration technology was used to treat oil-bearing wastewater. The pilot test results demonstrated the remarkable performance of the combined sequential batch reactor (SBR) and C-MBR process, wherein the chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺−N) removal rates reached 93% and 98.9%, respectively. Microbial analysis indicated that the symbiosis between Marinobacterium, Marinobacter, and Nitrosomonas might have contributed to simultaneously removing NH₄⁺−N and reducing COD, and the increased enrichment of Nitrosomonas significantly improved the nitrogen removal efficiency. Cleaning ceramic membranes with NaClO solution reduces membrane contamination and membrane cleaning frequency. The combined SBR and C−MBR process is an economical and feasible solution for treating high-salinity oil-bearing wastewater. Based on the pilot application study, the capital expenditure for operating the full-scale combined SBR and C−MBR process was estimated to be 251,717 USD/year, and the unit wastewater treatment cost was 0.21 USD/m³, which saved 62.5% of the energy cost compared to the conventional MBR process.

Investigation and evaluation of membrane fouling in a microbial fuel cell-membrane bioreactor systems (MFC-MBR)

Two membrane bioreactors with and without adding an electric circuit (named as MFC-MBR and C-MBR, respectively) were established to investigate the effects of micro-electric field on membrane fouling. With the aeration rate of 1.5 L/min, the synergistic effect of aeration and micro-electric field was the best in reducing membrane fouling and COD in treatment of a simulated phenol wastewater. Compared with C-MBR, the running time of MFC-MBR was extended for 16 days. Scanning electron microscope (SEM) and energy-dispersive X-ray detector (SEM-EDX) demonstrated that less foulants were attached to the membrane and the attachment was loosend in MFC-MBR. The decreased absolute value of zeta potential indicated repulsion among the negatively-charged sludge particles was reduced and flocculation of the sludge was improved, which alleviated the membrane fouling. The soluble microbial products (SMP) and loosely-bound extracellular polymeric substances (LB-EPS) were also decreased in MFC-MBR. It was found that migration and neutralization of the negatively-charged particles, and degradation of microorganisms contributed to the alleviation of membrane fouling. Moreover, the decreases of carbohydrates in LB-EPS led to higher protein/carbohydrates (PN/PS) ratio, which was a key parameter for alleviating membrane fouling. Meanwhile, the increase of tightly bound extracellular polymeric substances (TB-EPS) could also slow down membrane fouling. Because TB-EPS can be used as a binder to strengthen the flocculation of sludge particles.

Insights into the role of concentration polarization on the membrane fouling and cleaning during the aerobic granular sludge filtration process

The aerobic granular sludge (AGS) effectively mitigates the membrane fouling of a membrane bioreactor. However, the role and effects of the concentration polarization (CP), induced during the AGS filtration process on the membrane fouling and membrane cleaning efficiency, remain unclear. In the present study, the AGS resulted in a higher CP proportion (>50%) and a lower CP resistance (<3 × 10¹² m^-1), compared with the flocculent sludge, owing to the synergistic effect of the hydraulic shear and AGS scouring development, which improved the AGS in suspension and also minimized its deposition on the membrane. High-frequency interactions (contact and collision) between the AGS and membrane enhanced the CP resistance by returning more granular sludge from the cake layer to the CP, which proportionally increased the fouling resistance. Based on the correlation of CP and fouling resistance, the CP resistance was divided into 3 categories: high-intensity (2.76 × 10¹² m^-1), medium-intensity (1.74 × 10¹² m^-1), and low-intensity (0.62 × 10¹² m^-1). At the high-intensity CP, most membrane pores were "sealed" (complete pore blocking [R² > 0.9015]) and the pore blocking condition was the most serious (K-value = 0.0622 s^-1), while the membrane surface became denser and rougher. As a result, the permeability loss after the long-term filtration increased. In the chemical cleaning investigation, the alkaline detergents yielded an enhanced membrane cleaning efficiency to recover permeability. By reducing the CP, the membrane cleaning efficiency was marginally improved. The present study reveals the quantitative role of CP and offers insights into the mechanisms that govern membrane fouling in a membrane bioreactor.

Biodegradation performance and anti-fouling mechanism of an ICME/electro-biocarriers-MBR system in livestock wastewater (antibiotic-containing) treatment

Livestock wastewater is an important reservoir of antibiotic resistance genes (ARGs) and antibiotic residues. Membrane fouling is one of the most challenging problems confining the operation and application of membrane bioreactor (MBR). In this work, a novel iron-carbon micro-electrolysis (ICME)/electro-biocarriers-MBR system was established to explore the performance of pollutant removal and anti-fouling for an actual livestock wastewater. A light-weight porous ceramsite (bulk density 0.98 g/cm³) was used as the MBR biocarriers. The electrons generated from iron corrosion in the ICME tank traveled through external wires to the stainless steel membrane modules of MBR and the protons were transferred from the MBR tank to the ICME tank through a salt bridge, thus producing a spontaneous electric field. Under the optimized conditions, the system exhibited chemical oxygen demand removal of 76.0%, total suspended solids removal of 100%, antibiotic removal of 86.4%, NH₄⁺-N removal of 91.1%, and ARGs reduction of 6-8 orders of magnitude. The quality of the final effluent can reach the national Class I-A discharge criteria. Adding ceramsite could not only effectively improve biodegradation performance but also alleviate membrane fouling through the migration and enrichment of microbial flora to the ceramsite. The self-generated electric field had no significant improvement effect on pollutant removal, but exhibited good anti-membrane fouling behavior which could be ascribed to (i) oxidization of membrane foulants by the electrochemical products (such as H₂O₂ and •OH radicals), and (ii) electrostatic repulsion of negatively charged foulants and bacterial cells. The bacterial community structure and diversity were studied using high-throughput pyrosequencing, and the results demonstrated the roles of electric field and biocarriers in enrichment of anti-fouling communities and repulsion of biofouling-creating communities.

Role of nano-Fe3O4 particle on improving membrane bioreactor (MBR) performance: Alleviating membrane fouling and microbial mechanism

This study would investigate the effect of nano-Fe3O4 particles on the performance of membrane bioreactor (MBR), including membrane fouling, membrane rejection and microbial community. It can effectively alleviate membrane fouling and improve the effluent quality in MBR by bio-effect rather than nanoparticle adsorption. The lowest membrane fouling resistance was achieved at R4-MBR (sludge and membrane surface with nano-Fe3O4), which decreased by 46.08%. Meanwhile, R3-MBR (sludge with nano-Fe3O4) had the lowest concentration of COD in effluent which was below 20 mg/L in the stable phase of MBR operation. After applying nano-Fe3O4, the content of extracellular polymeric substances (EPS) and soluble microbial products (SMP) were both reduced with a lower molecular weight. From the microbial community analysis, the abundance of Proteobacteria increased from 25.06 to 45.11% at the phylum level in R3-MBR. It contributed to removing organic substances in MBRs. Moreover, the nano-Fe3O4 restricted Bacteroidetes growth, especially in R4-MBR, leading to a more excellent performance of membrane flux. Besides, the applied nano-Fe3O4 promoted the abundance of Quorum Quenching (QQ) microorganism, and declined the percentage of Quorum Sensing (QS) bacteria. Then, a lower content of N-Acyl-l-Homoserine Lactones (AHLs) in containing nano-Fe3O4 sludge. That was also prone to control membrane fouling. Overall, this study indicates the nano-Fe3O4 particle is appropriate for elevating MBR performance, such as membrane fouling and effluent quality, by bio-effect.

Combining biofilm and membrane flocculation to enhance simultaneous nutrients removal and membrane fouling reduction

The stability and processing capacity of membrane bioreactor can be improved with long sludge retention time. However, phosphorus removal will be markedly reduced under long sludge retention time and membrane fouling will be aggravated. Adding aluminum (Al) salt is a common way to achieve chemical phosphorus removal and membrane fouling reduction. But, accumulated Al will cause the decline of metabolic activity of activated sludge. In this study, biofilm-membrane flocculation reactor was proposed to enhance simultaneous nutrients removal and membrane fouling reduction. It showed that the removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP) in biofilm-membrane flocculation reactor were 95.7%, 96.7%, 87.4%, and 97.2%, respectively. Compared with the control group, accumulated Al increased extracellular polymeric substances (EPS) secretion by 1.9%-35.4%, biofilm biomass by 12.4%-26.1%, and the activities of ammonia oxidation bacteria (AOB) and nitrite oxidation bacteria (NOB) in the biofilm increased by 42.9% and 65.9%, respectively. The relative abundance of Nitrospira, Dechloromonas, and Terrimonas in the biofilm increased by 1.78%, 3.01%, and 2.88%, respectively, which was conducive to facilitating the nitrification. Therefore, biofilm-membrane flocculation reactor is a promising way for enhancing simultaneous nutrients removal and membrane fouling reduction.

Sequencing Batch Integrated Fixed-Film Activated Sludge Membrane Process for Treatment of Tapioca Processing Wastewater

Tapioca processing industries are very popular in the rural community to produce a variety of foods as the end products. Due to their small scales and scattered locations, they require robust modular systems to operate at low capacity with minimum supervision. This study explores the application of a novel sequencing batch-integrated fixed-film activated sludge membrane (SB-IFASM) process to treat tapioca processing wastewater for reuse purposes. The SB-IFASM employed a gravity-driven system and utilizes biofilm to enhance biodegradation without requiring membrane cleaning. The SB-IFASM utilizes the biofilm as a secondary biodegradation stage to enhance the permeate quality applicable for reuse. A lab-scale SB-IFASM was developed, preliminarily assessed, and used to treat synthetic tapioca processing industry wastewater. The results of short-term filtration tests showed the significant impact of hydrostatic pressure on membrane compaction and instant cake layer formation. Increasing the pressure from 2.2 to 10 kPa lowered the permeability of clean water and activated sludge from 720 to 425 and from 110 to 50 L/m²·h bar, respectively. The unsteady-state operation of the SB-IFASM showed the prominent role of the bio-cake in removing the organics reaching the permeate quality suitable for reuse. High COD removals of 63-98% demonstrated the prominence contribution of the biofilm in enhancing biological performance and ultimate COD removals of >93% make it very attractive for application in small-scale tapioca processing industries. However, the biological ecosystem was unstable, as shown by foaming that deteriorated permeability and was detrimental to the organic removal. Further developments are still required, particularly to address the biological stability and low permeability.

A New Polyvinylidene Fluoride Membrane Synthesized by Integrating of Powdered Activated Carbon for Treatment of Stabilized Leachate

Stabilized landfill leachate contains a wide variety of highly concentrated non-biodegradable organics, which are extremely toxic to the environment. Though numerous techniques have been developed for leachate treatment, advanced membrane filtration is one of the most environmentally friendly methods to purify wastewater effectively. In the current study, a novel polymeric membrane was produced by integrating powdered activated carbon (PAC) on polyvinylidene fluoride (PVDF) to synthesize a thin membrane using the phase inversion method. The membrane design was optimized using response surface methodology (RSM). The fabricated membrane was effectively applied for the filtration of stabilized leachate using a cross-flow ring (CFR) test. The findings suggested that the filtration properties of fabricated membrane were effectively enhanced through the incorporation of PAC. The optimum removal efficiencies by the fabricated membrane (14.9 wt.% PVDF, 1.0 wt.% PAC) were 35.34, 48.71, and 22.00% for COD, colour and NH3-N, respectively. Water flux and transmembrane pressure were also enhanced by the incorporated PAC and recorded 61.0 L/m2·h and 0.67 bar, respectively, under the conditions of the optimum removal efficiency. Moreover, the performance of fabricated membranes in terms of pollutant removal, pure water permeation, and different morphological characteristics were systematically analyzed. Despite the limited achievement, which might be improved by the addition of a hydrophilic additive, the study offers an efficient way to fabricate PVDF-PAC membrane and to optimize its treatability through the RSM tool.

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.

Ultra low-pressure filtration system for energy efficient microalgae filtration

Microalgae-based products have gained growing interest leading to an increase in large-scale cultivation. However, the high energy associated with microalgae harvesting becomes one of the bottlenecks. This study evaluated an energy-efficient microalga harvesting via ultra-low-pressure membrane (ULPM) filtration (<20 kPa) in combination with aeration. ULPM offered various benefits especially in terms of reducing the energy consumption due to it operated under low transmembrane pressure (TMP). High TMP often associated with high pumping energy hence would increase the amount of energy consumed. In addition, membrane with high TMP would severely affect by membrane compaction. Results showed that membrane compaction leads to up to 66 % clean water permeability loss when increasing the TMP from 2.5 to 19 kPa. The Chlorella vulgaris broth permeabilities decreased from 1660 and 1250 to 296 and 251 L/m²hrbar for corresponding TMPs for system with and without aeration, respectively. However, it was found that membrane fouling was more vulnerable at low TMP due to poor foulant scouring from a low crossflow velocity in which up to 56 % of permeability losses were observed. Membrane fouling is the biggest drawback of membrane system as it would reduce the membrane performance. In this study, aeration was introduced as membrane fouling control to scour-off the foulant from membrane surface and pores. In terms of energy consumption, it was observed that the specific energy consumption for the ULPM were very low of up to 4.4 × 10^-3 kWh/m³. Overall, combination of low TMP with aeration offers lowest energy input.

Treatment of Wastewater from a Food and Beverage Industry Using Conventional Wastewater Treatment Integrated with Membrane Bioreactor System: A Pilot-Scale Case Study

This study compares the performance of the Hollow Fiber (HF) and Flat Sheet (FS) types of membrane bioreactors (MBRs) for the treatment of food and beverage (F&B) industry wastewater in a pilot-scale study of a wastewater treatment plant (WWTP). HF and FS membrane configurations were evaluated at two different Mixed Liquor Suspended Solid (MLSS) levels: 6000 mg/L and 12,000 mg/L. The performance of each configuration was evaluated in terms of Chemical Oxygen Demand (COD) and Total Suspended Solid (TSS) removals for effluent quality measurement. The transmembrane pressure (TMP), flux rate, and silt density index (SDI) were monitored and calculated for membrane fouling assessment. The results show that the rejection rates of COD and TSS for HF and FS membrane types were more than 84% for the two different MLSS levels. During the study, the HF membrane recorded 0.3 bar transmembrane pressure, which complies with the recommended range (i.e., two to three times of chemical cleaning). On the other hand, the FS membrane operates without chemical cleaning, and the TMP value was below the recommended range at 0.2 bar. It was found that the flux values recorded for both the HF and FS systems were within the recommended range of 40 L/m²/h. Analysis of SDI revealed that the calculated index ranged between 1 and 2.38 and was within the allowable limit of 3. Both types of MBR consistently achieved an 80% to 95% rejection rate of COD and TSS. Effluent quality measurement of treated F&B wastewater in this pilot-scale study using a WWTP integrated with an MBR indicated a good achievement with compliance with the Malaysia industrial effluent discharge standards.

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 140 L and is operated continuously in two aerobic (DO > 4 mg/L) and anoxic (DO < 1 mg/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 0.2-0.8 μm 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.

Effect and mechanism of reduced membrane bioreactor fouling by powdered activated carbon

Powered Activated Carbon - Membrane Bioreactors (PAC-MBRs) have been used with good results for slightly polluted water treatment. Our batch experiments showed that the transmembrane pressure of a PAC-MBR was 25% less than that of a MBR in one period of test, which indicated that PAC did help control the fouling in MBRs. Based on this observation, several mechanisms of membrane fouling of MBRs and PAC-MBRs were investigated to have some insight into how PAC brought a positive impact. The total resistances decreased by 60% and different resistances were redistributed after adding PAC. The dominant one changed from filtration resistance to cake resistance. These smaller cake resistances resulted from the PAC because, showing in the scanning electron microscopy pictures, it made the cake layer looser and rougher than that on a normal membrane. Meanwhile, the analysis of the membrane eluent showed that the addition of PAC changed the microbial species and its metabolites on the membrane and effectively reduced the adsorption of hydrophilic organic molecules on the membrane surface. Additionally, PAC prevented polypeptide compounds from being trapped inside the pores of membranes, so the cake on the PAC-MBR contaminated membrane surface was easier to scrape off. In the test of cleaning methods, alkaline cleaning removed the most organics from contaminated membranes to restore membrane performance.

A statistical approach for modelling the physical process of bacterial attachment to abiotic surfaces

A statistical approach using a polynomial linear model in combination with a probability distribution model was developed to mathematically represent the process of bacterial attachment and study its mechanism. The linear deterministic model was built based on data from experiments investigating bacterial and substratum surface physico-chemical factors as predictors of attachment. The prediction results were applied to a normal-approximated binomial distribution model to probabilistically predict attachment. The experimental protocol used mixtures of Streptococcus salivarius and Escherichia coli, and mixtures of porous poly(butyl methacrylate-co-ethyl dimethacrylate) and aluminum sec-butoxide coatings, at varying ratios, to allow bacterial attachment to substratum surfaces across a range of physico-chemical properties (including the surface hydrophobicity of bacterial cells and the substratum, the surface charge of the cells and the substratum, the substratum surface roughness and cell size). The model was tested using data from independent experiments. The model indicated that hydrophobic interaction was the most important predictor while reciprocal interactions existed between some of the factors. More importantly, the model established a range for each factor within which the resultant attachment is unpredictable. This model, however, considers bacterial cells as colloidal particles and accounts only for the essential physico-chemical attributes of the bacterial cells and substratum surfaces. It is therefore limited by a lack of consideration of biological and environmental factors. This makes the model applicable only to specific environments and potentially provides a direction to future modelling for different environments.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Bio-inspired anchoring of amino-functionalized multi-wall carbon nanotubes (N-MWCNTs) onto PES membrane using polydopamine for oily wastewater treatment

The major problem that limits the utilization of PES membranes in treatment of oily wastewater is the drastic irreversible membrane fouling due to the attachment of oil droplets onto the membrane surface. The goal of this study was to develop a novel, fast and facile post-functionalization of polydopamine (PDA) coated membranes using pre-synthesized nanoparticles for fabrication of novel organic-inorganic hybrid recoverable membranes with high hydrophilicity and underwater oleophobicity. Here, bio-inspired technique was studied because the membrane technology could separate small oil droplets (even <10 µm) with high performance if faced little fouling phenomena during the treatment process. The amino-functionalized multi-wall carbon nanotubes (N-MWCNTs) were anchored onto the PDA coated PES membranes. The membranes characteristics, with specific focus on surface morphology and wettability were investigated. The newly developed PES/PDA/N-MWCNTs membranes showed an enhanced flux (~1086%) compared to the unmodified PES membrane. This enhancement was attributed to the high hydrophilic and underwater oleophobic properties, which were found to alleviate the effect of fouling. The total fouling ratio (R_t) of the PES/PDA/N-MWCNTs membrane was 22.35%, which was far lower than that of the unmodified PES membrane (98.38%). Meanwhile, most of the fouling was reversible for the former with the remaining (irreversible fouling) of 18.08%. It was concluded that cake filtration is the dominant fouling mechanism of the PES/PDA/N-MWCNTs membranes due to their average pore diameter. The modified membranes showed high oil rejection (>99%) so that the obtained clean water with oil concentration lower than 5 ppm met the wastewater discharge standard recommendations. Also, evaluation of the PES/PDA/N-MWCNT membrane in cross-flow filtration showed its antifouling properties in the long-term application (16 h).

Hysteresis effect on backwashing process in a submerged hollow fiber membrane bioreactor (MBR) applied to membrane fouling mitigation

Hysteresis effect on backwashing in a submerged MBR was investigated with dead-end hollow fiber membranes. The out-of-step changes in TMP and flux is the real hysteresis effect which is common but easily overlooked. Methods of visualization and ultrasonic spectrum analysis were implemented. The results showed that fouling layer is just the culprit of hysteresis effect. Fouling level and fiber length were determined as two key factors that affect hysteresis effect by data and model derivation. Moreover, a hysteresis evaluation index "τ_bw" is proposed to quantify the result of TMP vs time. The relationship between influence factors and "τ_bw" is interactive. A linear relationship between fouling level and "τ_bw" was found as well as an extreme value between fiber length and "τ_bw". A lower fouling level (lower backwashing flow) and optimal backwashing duration will be helpful for an effective backwashing no matter for membrane fouling control or energy cost reduce.

Current Advances in Biofouling Mitigation in Membranes for Water Treatment: An Overview

Membranes, as the primary tool in membrane separation techniques, tend to suffer external deposition of pollutants and microorganisms depending on the nature of the treating solutions. Such issues are well recognized as biofouling and is identified as the major drawback of pressure-driven membrane processes due to the influence of the separation performance of such membrane-based technologies. Herein, the aim of this review paper is to elucidate and discuss new insights on the ongoing development works at facing the biofouling phenomenon in membranes. This paper also provides an overview of the main strategies proposed by “membranologists” to improve the fouling resistance in membranes. Special attention has been paid to the fundamentals on membrane fouling as well as the relevant results in the framework of mitigating the issue. By analyzing the literature data and state-of-the-art, the concluding remarks and future trends in the field are given as well.

Enhanced removal of copper by electroflocculation and electroreduction in a novel bioelectrochemical system assisted microelectrolysis

The idea is immensely attractive if copper ions can be completely removed in wastewater. In this study, a novel bioelectrochemical system assisted microelectrolysis was developed for the enhanced removal of copper. One abandoned aluminium was used as anode and graphite/activated carbon as biological anode, and a bifunctional catalytic conductive membrane as cathode. Under the combined action of electroreduction and electroflocculation, copper ions directly pumped into the cathode chamber were efficiently treated, and organic matter was synchronously removed (Copper ions >99.9%, TOC >98.2%, COD >97.9%, NH₄⁺-N >94.5% and TP >94.9%). The reactions of primary batteries and microelectrolysis in anode chamber significantly enhanced the self-production capacity of BES (maximum power density of 2250 mW m^-3 at current density 10.65 mA m^-2, maximum cell voltage of 1.4 V). The results confirmed the application potential of bioelectrochemical system assisted microelectrolysis for the removal of copper.

Chemical Enhancement for Retrofitting Moving Bed Biofilm and Integrated Fixed Film Activated Sludge Systems into Membrane Bioreactors

Positive effects of retrofitting MBBR and IFAS systems into MBRs can be exploited by introducing chemical enhancement applying coagulants in the membrane separation step. The current study reports basic principles of chemical enhancement with aluminium sulphate coagulant in biofilm-MBR (Bf-MBR) based on results of total recycle tests performed at different dosages of the chemical enhancer and properties characterization of filtrates, supernatants and sediments. It demonstrates a possibility to achieve lower membrane fouling rates with dosing of aluminium sulphate coagulant into MBBR and IFAS mixed liquors by extending operational cycles by 20 and 80 time respectively as well as increasing operating permeability of membrane separation by 1.3 times for IFAS. It has been found that charge neutralization is the dominating mechanism of aluminium sulphate action as a chemical enhancer in Bf-MBR, however, properties of the membrane surface influencing charge repulsion of foulants should be considered together with the secondary ability of the coagulant to improve consolidation of sediments.