MEMBRANE BIOREACTOR FOULING: MECHANISMS, IMPACTS, AND CONTROL TECHNIQUES

Membrane bioreactors (MBRs) for wastewater treatment show great potentials in the sustainable development of urban environments. However, fouling of membranes remains the largest challenge of MBR technology. Dissolved extracellular polymeric substances (EPS) are often assumed be the main foulant in MBRs. However, single bacterial cells are often erroneously measured as EPS in traditional spectrophotometric analysis of EPS in activated sludge, so we hypothesized that single cells in many cases could be the true foulants in MBRs for wastewater treatment. To study this, raw MBR sludge and sludge supernatant with varying concentrations of planktonic cells were filtered on microfiltration (MF) membranes, and we found a direct correlation between the cell count and rate of flux decline. Addition of planktonic cells to fresh MBR sludge dramatically increased the flux decline. The identity of the most abundant planktonic cells in a full-scale MBR water resource recovery facility was determined by DNA fingerprinting. Many of these genera are known to be abundant in influent wastewater suggesting that the influent bacterial cells may have a direct effect on the fouling propensity in MBR systems. This new knowledge may lead to new anti-fouling strategies targeting incoming planktonic bacteria from the wastewater feed. PRACTITIONER POINTS: Planktonic cells constituted up to 60% of the total protein content of "soluble extracellular polymeric substances" in membrane bioreactor sludge. Planktonic cells are hidden under a surrogate concentration of extracellular polymeric substances which is often associated with fouling. Membrane fouling rate is directly proportional to amount of free planktonic cells suspended in sludge. Several influent bacterial genera are enriched in the water phase of membrane bioreactor sludge. Removing these may mitigate fouling.

A review of modeling bioprocesses in membrane bioreactors (MBR) with emphasis on membrane fouling predictions

Relation between EPS adherence, viscoelastic properties, and MBR operation: Biofouling study with QCM-D

Recently, enzymatic quorum quenching has proven its potential as an innovative approach for biofouling control in the membrane bioreactor (MBR) for advanced wastewater treatment. However, practical issues on the cost and stability of enzymes are yet to be solved, which requires more effective quorum quenching methods. In this study, a novel quorum quenching strategy, interspecies quorum quenching by bacterial cell, was elaborated and proved to be efficient and economically feasible biofouling control in MBR. A recombinant Escherichia coli which producing N-acyl homoserine lactonase or quorum quenching Rhodococcus sp. isolated from a real MBR plant was encapsulated inside the lumen of microporous hollow fiber membrane, respectively. The porous membrane containing these functional bacteria (i.e., "microbial-vessel") was put into the submerged MBR to alleviate biofouling on the surface of filtration membrane. The effect of biofouling inhibition by the microbial-vessel was evaluated over 80 days of MBR operation. Successful control of biofouling in a laboratory scale MBR suggests that the biofouling control through the interspecies quorum quenching could be expanded to the plant scale of MBR and various environmental engineering systems with economic feasibility.

Membrane bioreactors (MBRs), in which membranes are applied to biological wastewater treatment for biomass separation, provide many advantages over conventional treatment. However, membrane fouling in MBRs restricts their widespread application because it reduces productivity and increases maintenance and operating costs. Recently much research and development has taken place to investigate, model, and control membrane fouling processes. However, unified and well-structured theories on membrane fouling are not currently available because of the complexity of the biomass matrix, which is highly heterogeneous and includes living microorganisms. Membrane fouling in MBR systems can be reversible (i.e., removable by physical washing) or irreversible (removable by chemical cleaning only), and can take place on the membrane surface or into the membrane pores. Although establishing a general model to describe membrane fouling in such a process is made extremely difficult by the inherent heterogeneity of the syste...

Organic pollutants variation and antifouling enhancement with attapulgite clay addition in MBR treating micro-polluted surface water

Membrane bioreactors (MBR) are a promising method for wastewater treatment that combines microbial degradation with membrane separation. MBRs offer efficient and sustainable wastewater treatment by combining biological processes with membrane filtration, providing high-quality effluents for reuse. The advantages of MBRs, such as their compact design, reduced sludge production, and water recycling potential, make them increasingly significant in addressing global water scarcity and pollution challenges. Nevertheless, the issue of biofouling persists as a notable obstacle, primarily caused by the interplay of bacteria, membrane surfaces, and the release of extracellular polymeric substances (EPS). Integrating photocatalysts into MBR membranes offers a new method to reduce fouling. This study provides a comprehensive overview of current research on the membrane modification using photocatalysts in MBR systems, focusing on the existing challenges and prospects in this field. Despite these potential advantages, research on improving MBR membrane performance through photocatalysis is sparse. To ensure the sustainability of this technology, it is essential to consider important factors, such as reactor configuration, kinetics, fouling processes, economic feasibility, and scaling issues

Micro-granular sludge driven by powder carrier in membrane bioreactor: highly-efficient N & P removal and membrane fouling alleviation.

Recent developments in biofouling control in membrane bioreactors for domestic wastewater treatment

Membrane biofouling impedes wide application of membrane bioreactor (MBR) for wastewater treatment. Recently, quorum sensing (QS) mechanisms are accounted for one of major mechanisms in biofouling of MBRs. In this study, vanillin was applied to investigate reduction of biofouling in MBRs. MBR sludge was analyzed to contain QS signal molecules by cross-feeding biosensor assay and HPLC. In addition, the inhibitory activity of vanillin against bacterial quorum sensing was verified using an indicator strain CV026. The vanillin doses greater than 125 mg/L to 100 mL of MBR sludge showed 25% reduction of biofilm formed on the membrane surfaces. Two MBRs, i.e., a typical MBR as a control and an MBR with vanillin, were operated. The TMP increases of the control MBR were more rapid compared to those of the MBR with the vanillin dose of 250 mg/L. The treatment efficiencies of the two MBRs on organic removal and MLSS were maintained relatively constant. Extracellular polymeric substance concentrations measured at the end of the MBR operation were 173 mg/g biocake for the control MBR and 119 mg/g biocake for the MBR with vanillin. Vanillin shows great potential as an anti-biofouling agent for MBRs without any interference on microbial activity for wastewater treatment.

Effect of polypropylene microplastics on the performance of membrane bioreactors in wastewater treatment.

Despite continuous developments in the field of MBR technology, membrane fouling together with the associated energy demand and related costs issues remain major challenges. The efficiency of the filtration process in an MBR is governed by the activated sludge filterability, which is still limitedly understood and is determined by the interactions between the biomass, the wastewater and the applied process conditions. The purpose of this thesis is to increase understanding of the factors impacting activated sludge filterability during full-scale membrane bioreactor (MBR) operation. The overall research goal was to determine conditions for enhanced and efficient operation of the MBR technology. The research work included both extended on-site measurements and operational data analysis. Filterability of the activated sludge was experimentally determined in full- and pilot-scale MBRs treating both municipal and industrial wastewater. Subsequently, the most influential parameters influencing activated sludge filterability were determined. In addition, the design, operational and performance data were collected from the selected full-scale MBR plants and analysed in respect to plant functioning, i.e., operation, energy efficiency and operational costs. Therefore, the research links activated sludge filterability assessment and full-scale MBR functioning, i.e., design options, operation, performance and energy efficiency. Overall, it can be concluded that good filterability of the activated sludge is indispensable for efficient and optimal operation of an MBR. Operation with poor sludge filterability will be associated with a cost penalty due to sub-optimal filtration conditions. Wastewater composition and temperature are important influencing parameters with respect to filterability. MBR plant layout and membrane configuration influence overall MBR functioning and should be chosen carefully. The energy efficiency of an MBR is driven by the hydraulic utilization of the membranes and can be improved by implementation of flow equalization, new aeration strategies and adjusting operational settings to the incoming flow.

Membrane bioreactor (MBR) is credible and promising technology methods for industrial wastewater treatment and recycle it to use in different applications. Today MBR has many domestic and industrial applications and it is popular among the types of conventional treatment methods. The main drawback in the operation of MBR is membrane fouling, that drive to the decrease in permeate flux so need some technique to clean the membrane. In spite of more than a decade of significant advances in improvement of fouling reduction technique, various physical and mechanical methods are still necessary to be improved to limit the membrane fouling problems. In this review, the advantages and disadvantages of membrane bioreactor, fundamental of membrane fouling that is affected by some factors and methods of controlling membrane fouling were discussed.

Effect of filamentous bacteria on membrane fouling in submerged membrane bioreactor

Peak flux performance and microbial removal by selected membrane bioreactor systems