A review of practical tools for rapid monitoring of membrane bioreactors

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.

Integrated membrane bioreactors modelling: A review on new comprehensive modelling framework

Integrated Membrane Bioreactor (MBR) models, combination of biological and physical models, have been representing powerful tools for the accomplishment of high environmental sustainability. This paper, produced by the International Water Association (IWA) Task Group on Membrane Modelling and Control, reviews the state-of-the-art, identifying gaps for future researches, and proposes a new integrated MBR modelling framework. In particular, the framework aims to guide researchers and managers in pursuing good performances of MBRs in terms of effluent quality, operating costs (such as membrane fouling, energy consumption due to aeration) and mitigation of greenhouse gas emissions.

Cultivation of aerobic granular sludge for the treatment of food-processing wastewater and the impact on membrane filtration properties

A laboratory-scale sequencing batch reactor was operated for approximately 300 days, divided into four periods based on the feeding strategy, to develop stable aerobic granular sludge (AGS) while treating chocolate processing wastewater. Application of a prolonged mixed anaerobic feeding was not sufficient to develop AGS and reach stable reactor performance. Through the application of a partially non-mixed and a partially mixed feeding strategy, the reactor performance was increased and stable AGS formation was established characterized by low diluted sludge volume index (D)SVI DSVI_10,30) values of 78 ± 27 mL·g^-1 and 52 ± 17 mL·g^-1, respectively, and a capillary suction time/mixed liquor suspended solids value of 0.9 sec·(g·L^-1)^-1. The membrane bioreactor (MBR) filtration tests showed a reduction of the fouling rate (FR) and an increase of the sustainable flux (SF_0.5) for AGS compared to flocs treating the same industrial wastewater. The SF_0.5 (FR > 0.5 mbar·min^-1) for the flocs was 10 L·(m²·h)^-1 while for AGS the SF_0.5 is higher than 45 L·(m²·h)^-1 because the FR did not exceed 0.1 mbar·min^-1. Additionally, the AGS showed reduced irreversible fouling tendencies due to pore blocking. Our results underline the need for an increased substrate gradient during anaerobic feeding for the development and long-term maintenance of AGS under minimum wash-out conditions. The AGS-MBR filtration performance also shows strong advantages compared to a floccular MBR system due to a high increase of the SF_0.5 and reduced reversible and irreversible fouling.

Removal of sulfadiazine from simulated industrial wastewater by a membrane bioreactor and ozonation

Ozonation can be used as a polishing treatment for degrading low-concentration pharmaceutical compounds recalcitrant to biological treatment, when large amounts of biodegradable organics have been previously removed by biological processes. Nevertheless, a systematic investigation has not yet been carried out for the coupled MBR + O₃ process through an experimental design approach. Thereby, the purpose of this study is to evaluate the performance of different processes (membrane bioreactor-MBR, ozonation; and integrated MBR + O₃) for removing the antibiotic sulfadiazine (SDZ) from a synthetic wastewater matrix of industrial interest. The MBR behavior was monitored over seven months for different parameters (pH, temperature, permeate flow, transmembrane pressure, biological oxygen demand-BOD₅, chemical oxygen demand-COD, total organic carbon-TOC, solids, and SDZ concentration). Additionally, the amount of SDZ sorbed onto the sludge was characterized, an issue which is scarcely addressed in most research works. Ozonation experiments were conducted in batch mode in a 2-L glass reactor provided with openings for gas flow. For the MBR + O₃ process, the effects of gas flow rate (0.1-1.5 L min^-1) and inlet ozone concentration (4-12 mg L^-1) on SDZ removal from the MBR permeate were systematically assessed using a Doehlert experimental design and response surface methodology. The results indicated that the MBR system showed good performance regarding organic matter removal efficiency, evaluated in terms of BOD₅ (91.5%), COD (93.1%) and TOC (96.3%). In contrast, SDZ was partially removed (33%) by the MBR; in that case, the results indicated that the antibiotic was moderately removed with the sludge and partially biodegraded. In turn, the MBR + O₃ system showed excellent performance for removing SDZ (100%), TOC (97%), BOD₅ (94%) and COD (97%). The statistical analysis confirmed that the influence of ozone gas flow rate upon the SDZ removal rate was more important than that exhibited by inlet ozone concentration. Therefore, coupling MBR and ozone can be considered a promising alternative for point source treatment of antibiotic production wastewater.

Multi-year diagnosis of unpredictable fouling occurrences in a full-scale membrane bioreactor

The membrane bioreactor (MBR) at the Traverse City Regional Wastewater Treatment Plant has experienced sudden and unpredictable periods of substantial permeability decline since 2011. Early observations detected irregularly-shaped Gram-positive bacteria that correlated with plant upsets. Use of biomolecular techniques, such as DNA sequencing of laboratory isolates and the mixed liquor microbial community, and fluorescent in situ hybridization, identified the dispersed organisms as members of the genus Staphylococcus. However, Staphylococcus species were consistently present during normal operation and therefore were more likely to be an indicator of the upset, not the cause. The results suggest that these microorganisms are responding to specific influent wastewater constituents. We chemically analysed seven mixed liquor samples from periods of permeability decline in 2017 and 2018, and four samples from a period of normal operation. During upset conditions, the total carbohydrate content exceeded that of normal operation by 40%. Additionally, mixed liquor calcium concentrations were 65% above normal during the upset in 2017. It is hypothesized and supported through multivariate statistical analysis and estimation of specific resistance to filtration values that a calcium-intermediated polymer bridging mechanism with extracellular polymeric substance constituents is a major contributor to fouling and permeability disruptions in the Traverse City MBR.

Membrane fouling in aerobic granular sludge (AGS)-membrane bioreactor (MBR): Effect of AGS size

The main goal of the current study was to investigate the membrane fouling mechanism of aerobic granular sludge (AGS) with various AGS sizes. In this regard, AGSs were sieved into 6 levels: 0∼0.5, 0.5∼0.7, 0.7∼1, 1∼1.2, 1.2∼1.7 mm and larger than 1.7 mm, then filtrated by a small dead-end filtration cell. Interestingly, there appeared a critical AGS size (1∼1.2 mm) for membrane fouling. Above 1.2 mm, flux increased and fouling reduced with size, due to the loose cake layer and high permeability caused by larger AGS. Below 1 mm, for smaller AGS, higher flux and lower fouling appeared, because less extracellular polymeric substance (EPS) formed and adhered onto AGS foulants. In the critical size, membrane fouling was serious to the most extent, on account of the dual role of the compact structure of cake fouling layer and the adhesion of EPS. Moreover, this critical AGS size also possessed the highest cake layer, pore blocking and irreversible fouling, which generally existed in various operational conditions. Besides, the results of SEM, AFM, hydrophilicity and ATR-FTIR also proved that the existence of the maximum membrane fouling at the critical AGS size. This study provides a deep understanding of the membrane fouling mechanisms of AGS in membrane filtration and is beneficial for developing a new membrane fouling mitigation strategy by terms of regulating AGS size.

Influence of polyelectrolyte architecture on the electrokinetics and dewaterability of industrial membrane bioreactor activated sludge

Improvement of sludge dewaterability is greatly hindered by the presence of large amounts of interstitial water molecules trapped in the sludge as a result of strong hydrophilic characteristics. This study has investigated the influence of six different polyacrylamide (PAM) flocculants with different molecular architecture (linear, slightly and highly branched), charge density (CD) and molecular weight (MW) on the electro-kinetics and dewatering of highly stable industrial membrane bioreactor (MBR) sludge. The impact of PAM on flocculation is manifested in the supernatant turbidity, particle zeta potential, sludge capillary suction time (CST), floc size and settleability. Turbidity removal and reduction in zeta potential are used to identify the optimum polymer dose. An optimum dose of 70 mg.L^-1 has been determined for linear PAM of 40% CD. However, a highly-branched PAM, with the same CD, has shown an optimum value of 30 mg.L^-1. In all cases, a turbidity removal of more than 99% and CST reduction of 51-64% is attained; the linear PAMs have resulted in the highest CST reduction. Higher PAM doses have resulted in larger flocs and the maximum particle size is observed at the saturation point. The reduction in sludge volume relates with the floc size and PAM dose. For sludge conditioning and dewaterability, highly branched PAM with low MW has shown superior performance over linear high MW PAM. Enhancement of flocculation and dewatering is correlated with the surface charge neutralization and bridging mechanisms.

Carbon nanostructures for advanced nanocomposite mixed matrix membranes: a comprehensive overview

The highly progressive membrane separation technology challenges conventional separation processes such as ion exchange, distillation, precipitation, solvent extraction, and adsorption. The integration of many desired properties such as low energy consumption, high removal efficiency, affordable costs, suitable selectivity, acceptable productivity, ease of scale-up, and being environmentally friendly have made the membranes capable of being replaced with other separation technologies. Combination of membrane technology and nanoscience has revolutionized the nano-engineered materials, e.g. nanocomposites applied in advanced membrane processes. Polymer composites containing carbon nanostructures are promising choices for membrane fabrication owing to their enhanced chemistry, morphology, electromagnetic properties, and physicochemical stability. Carbon nanostructures such as carbon nanotubes (CNTs), nano graphene oxides (NGOs), and fullerenes are among the most popular nanofillers that have been successfully applied in modification of polymer membranes. Literature review shows that there is no comprehensive overview reporting the modification of mixed matrix membranes (MMMs) using carbon nanofibers, nano-activated carbons, and carbon nanospheres. The present overview focuses on the applications of carbon nanostructures mainly CNTs and NGOs in the modification of MMMs and emphasizes on the application of CNTs and NGO particles.

Effects of electrochemical processes application on the modification of mixed liquor characteristics of an electro-membrane bioreactor (e-MBR)

This study evaluated the effects of electrochemical processes on the mixed liquor characteristics of an electro-membrane bioreactor (e-MBR) applied to municipal wastewater treatment. A laboratory-scale e-MBR was assessed under two experimental runs: without the electric field (run I) and with electric field, controlled by the application of an electric current set in 10.0 A m^-2 under intermittent exposure mode of 6 minutes ON/18 minutes OFF (run II). The electric field caused approximately 55% removal of both soluble microbial products (SMP) and extracellular polymeric substances (EPS), whereas the proteins/carbohydrates ratio in EPS was increased from 1.9 in the run I to 2.9 in run II, leading to an increment of flocs' hydrophobicity. Additionally, the sludge floc size average value was reduced from 42.2 μm in run I to 24.6 μm in run II, which led to a significant enhancement in the sludge settleability. As a result, the membrane fouling rate was always less than 3.80 mbar d^-1 in run II, whereas in run I these values reached up to 34.7 mbar d^-1. These results demonstrated that the electrochemical processes enhanced the mixed liquor filterability. Therefore, their implementation represents a great alternative to improve the operational stability of membrane bioreactors.