New mathematical models of biomass viability and membrane fouling in a membrane bioreactor

University of Technology, Sydney. Faculty of Engineering and Information Technology.The optimized performance of a membrane bioreactor (MBR) for wastewater treatment depends not only on the biomass viability but also on the dynamic effects of biomass properties on membrane fouling. This research developed new conceptual mathematical models of biomass viability and fouling using biomass parameters and operational parameters of an MBR. It also presents, as outcomes, new simple and practical models for tracking biomass viability and fouling of an MBR system. The proposed models can be used to track instability in the operation of an MBR, and consequently, measures can be taken to act against instability in the oxygen uptake and for fouling control. The proposed conceptual models include parameters such as the specific oxygen uptake rate (SOUR) of microorganisms, the soluble or colloidal chemical oxygen demand (COD) of effluent along with the mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) concentrations. The COD parameters of the models represent soluble microbial product (SMP) or bound extra-polymeric substances (bEPS) present within an MBR, offering the possibility of developing practical models with these easily measurable parameters. The experimental study investigated the effects of biomass parameters on SOUR in a lab-scale sponge submerged MBR (SSMBR) system. Statistical analyses of experimental results indicate that bEPS, SMP, MLSS and MLVSS had significant effects on SOUR and their relative influence on SOUR was EPS>bEPS>SMP>MLVSS/MLSS. The EPS is considered as a lumped parameter of SMP and bEPS. The progressive change of SMP and bEPS within the bioreactor consistently maintained a negative exponential correlation with SOUR, and two independent models of biomass viability were developed based on correlations among these parameters. Both the model simulations for biomass viability agreed well with experimental values of the SSMBR system. The simplified model of membrane fouling considered cake formation on the membrane and its pore blocking as the major processes of fouling. In the model, MLSS is used as a lumped parameter to describe the cake layer formation including the biofilm whereas SMP is assumed as the key contributor to pore fouling. The combined effects of aeration and backwash on detachment of membrane foulants, and new exponential coefficients are included to better describe the exponential increase of transmembrane pressure (TMP). With practical assumptions of these major processes, the new model successfully simulated the fouling phenomena with fairly accurate predictions of the rise of TMP for the operations of two lab-scale submerged MBR systems

Opportunities and Challenges in Developing Nuclear Security in Africa

Those involved in nuclear security recognize that regions of significant instability in Africa have an impact on the safety and security of the continent\u27s nuclear material and un-enriched uranium; however, some countries outside of continental Africa have taken counterproductive approaches to this issue. Despite challenges, the nuclear security community continues to develop and apply appropriate levels of nuclear security where needed. The community also takes every opportunity to make significant contributions to the global discourse on nuclear security culture

A review towards finding a simplified approach for modelling the kinetics of the soluble microbial products (SMP) in an integrated mathematical model of membrane bioreactor (MBR)

Soluble microbial products (SMPs) tend to accumulate in the membrane bioreactor (MBR) systems as a consequence of high membrane rejection and apparently low biodegradability within the wastewater treatment system. The extension of the activated sludge models (ASMs) with SMPs, therefore, has received crucial importance in recent days, particularly considering their potential use as indicators of the membrane fouling propensity. This paper presents a critical review of the formation and degradation kinetics of SMP subdivisions that have so far been used for the mathematical modelling of MBR. The paper identified a simplified approach to incorporate the kinetics of the SMP formation and degradation in the general mathematical models of MBR. It suggested that the inclusion of only four additional linear differential equations in the ASM1-SMP integrated mathematical model could simulate well the effluent quality and membrane fouling prediction. The model would also serve as a useful tool in optimizing operation conditions for better treatability and fouling control. © 2013 Elsevier Ltd

Enhanced biological phosphorus removal and its modeling for the activated sludge and membrane bioreactor processes

A modified activated sludge process (ASP) for enhanced biological phosphorus removal (EBPR) needs to sustain stable performance for wastewater treatment to avoid eutrophication in the aquatic environment. Unfortunately, the overall efficiency of the EBPR in ASPs and membrane bioreactors (MBRs) is frequently hindered by different operational/system constraints. Moreover, although phosphorus removal data from several wastewater treatment systems are available, a comprehensive mathematical model of the process is still lacking. This paper presents a critical review that highlights the core issues of the biological phosphorus removal in ASPs and MBRs while discussing the inhibitory process requirements for other nutrients' removal. This mini review also successfully provided an assessment of the available models for predicting phosphorus removal in both ASP and MBR systems. The advantages and limitations of the existing models were discussed together with the inclusion of few guidelines for their improvement. © 2013 Elsevier Ltd

New proposed conceptual mathematical models for biomass viability and membrane fouling of membrane bioreactor

The production and accumulation of soluble microbial products (SMP), extracellular polymeric substances (EPS) and colloidal inert compounds within a membrane bioreactor (MBR) may greatly affect the biomass viability and subsequently the permeability of the membrane. This paper aims at presenting new mathematical models of biomass viability and membrane fouling that has been conceptually developed through establishing links between these biomass parameters and operating parameters of the MBR. The proposed models can be used to predict the biomass viability and membrane fouling at any state of operation of MBR. Meanwhile, easily measurable parameters of the proposed model can also serve to estimate SMP/EPS concentration in the supernatant of MBR without the tedious and expensive measurement. © 2013 Elsevier Ltd

New and practical mathematical model of membrane fouling in an aerobic submerged membrane bioreactor

© 2017 Elsevier Ltd This study aimed to develop a practical semi-empirical mathematical model of membrane fouling that accounts for cake formation on the membrane and its pore blocking as the major processes of membrane fouling. In the developed model, the concentration of mixed liquor suspended solid is used as a lumped parameter to describe the formation of cake layer including the biofilm. The new model considers the combined effect of aeration and backwash on the foulants’ detachment from the membrane. New exponential coefficients are also included in the model to describe the exponential increase of transmembrane pressure that typically occurs after the initial stage of an MBR operation. The model was validated using experimental data obtained from a lab-scale aerobic sponge-submerged membrane bioreactor (MBR), and the simulation of the model agreed well with the experimental findings

Membrane fouling reduction and improvement of sludge characteristics by bioflocculant addition in submerged membrane bioreactor

© 2015 Elsevier B.V. All rights reserved. The effectiveness of a green bioflocculant (Gemfloc®) on enhanced performance of a submerged membrane bioreactor (SMBR) was evaluated in terms of membrane fouling reduction and sludge characterization. Two MBRs were operated parallelly in this study, namely conventional MBR (CMBR) and MBR with Gemfloc® addition (MBR-G). Results showed mitigated membrane fouling through Gemfloc® addition in terms of cake layer formation and pore blocking. When compared to the CMBR, in spite of more extracellular polymeric substances (EPS) presented in activated sludge, the MBR-G demonstrated less soluble microbial products (SMP), larger sludge flocs, higher zeta potential and greater relative hydrophobicity of sludge flocs, which decreased cake layer resistance and pore blocking resistance. The reduced cake layer resistance in the MBR-G could be also ascribed to less growth of suspended biomass, lower sludge viscosity, as well as less EPS, SMP and biopolymer clusters in the cake layer. In addition, a modified resistance-in-series model was employed by considering SMP and mixed liquor suspended solids. The simulated results implied that the model could predict the influence of sludge characteristics on membrane fouling behavior of the SMBR

Effect of MXene Loaded on g-C3N4 Photocatalyst for the Photocatalytic Degradation of Methylene Blue

This is the final version. Available on open access from MDPI via the DOI in this recordPhotocatalytic degradation is one of the environmentally friendly methods used in treat-ing dye wastewater. In this study, a series of MXene/g-C3N4 heterostructure photocatalysts with different loading amounts of MXene (1, 4, 8, and 12 wt.%) were successfully synthesized via the wet impregnation method and their photocatalytic activity was evaluated via the degradation of methylene blue under visible-light irradiation. As such, the 1 wt.% MXene/g-C3N4 heterostructure photocatalyst achieved a high degradation of methylene blue compared to the pure g-C3N4 under visible-light illumination of 180 min. This significant improvement was attributed to the intimate interfacial contact, evidently from the FESEM analysis, which allows the smooth photocharge carriers to transport between g-C3N4 and MXene. Additionally, the larger BET surface area demonstrated by the 1 wt.% MXene/g-C3N4 heterostructure allowed this sample to have higher adsorption of dye molecules and provided a higher number of reactive sites, which was beneficial for the enhancement of the photocatalytic activity. Nevertheless, it was found that the excessive loading of MXene can substantially impede photocatalytic activity. This was attributed to the decrease in the active sites, as well as the weakened crystallinity of the MXene/g-C3N4 heterostructure photocatalyst, evident from the FTIR and XRD analysis. All in all, this study has shown the potential of the MXene/g-C3N4 photocatalyst as a promising photocatalyst for highly efficient wastewater treatment applications.Chemical Engineering Department of Universiti Teknologi PETRONASCentre of Innovative Nanostructures and Nanodevices (COINN

How do Graphene Composite Surfaces Affect the Development and Structure of Marine Cyanobacterial Biofilms?

The progress of nanotechnology has prompted the development of novel marine antifouling coatings. In this study, the influence of a pristine graphene nanoplatelet (GNP)-modified surface in cyanobacterial biofilm formation was evaluated over a long-term assay using an in vitro platform which mimics the hydrodynamic conditions that prevail in real marine environments. Surface characterization by Optical Profilometry and Scanning Electron Microscopy has shown that the main difference between GNP incorporated into a commercially used epoxy resin (GNP composite) and both control surfaces (glass and epoxy resin) was related to roughness and topography, where the GNP composite had a roughness value about 1000 times higher than control surfaces. The results showed that, after 7 weeks, the GNP composite reduced the biofilm wet weight (by 44%), biofilm thickness (by 54%), biovolume (by 82%), and surface coverage (by 64%) of cyanobacterial biofilms compared to the epoxy resin. Likewise, the GNP-modified surface delayed cyanobacterial biofilm development, modulated biofilm structure to a less porous arrangement over time, and showed a higher antifouling effect at the biofilm maturation stage. Overall, this nanocomposite seems to have the potential to be used as a long-term antifouling material in marine applications. Moreover, this multifactorial study was crucial to understanding the interactions between surface properties and cyanobacterial biofilm development and architecture over time