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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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Two experimental studies evaluated the effect of aerobic and membrane aeration changes on sludge properties, biological nutrient removal and filtration processes in a pilot plant membrane bioreactor. The optimal operating conditions were found at an aerobic dissolved oxygen set-point (DO) of 0.5 mg O2 L(-1) and a membrane specific aeration demand (SADm) of 1 m h(-1), where membrane aeration can be used for nitrification. Under these conditions, a total flow reduction of 42% was achieved (75% energy reduction) without compromising nutrient removal efficiencies, maintaining sludge characteristics and controlled filtration. Below these optimal operating conditions, the nutrient removal efficiency was reduced, increasing 20% for soluble microbial products, 14% for capillarity suction time and reducing a 15% for filterability. Below this DO set-point, fouling increased with a transmembrane pressure 75% higher. SADm below 1 m h(-1) doubled the values of transmembrane pressure, without recovery after achieving the initial conditions., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In start-up periods low MLSS concentration may lead to fouling phenomena and uncommon frequency of chemical cleanings using membrane bioreactors. A knowledge-based control module for the optimisation of start-up procedures in membrane bioreactors is presented and validated in this paper. The main objective of the control module is to accelerate the growth of MLSS and the achievement of the design flux while minimising the fouling phenomenon during start-up periods. The module was validated in a pilot-scale membrane bioreactor with the University of Cape Town configuration and submerged flat sheet microfiltration membranes. The knowledge of the control system was represented as a decision tree before being implemented. A fully satisfactory start-up, both for the filtration and the biological phase, was obtained in 20 days, saving time and preserving the membrane integrity., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The impact of removable and irremovable fouling on the retention of viral and bacterial indicators by the submerged microfiltration membrane in an MBR pilot plant was evaluated. Escherichia coli, sulphite-reducing Clostridium spores, somatic coliphages and F-specific RNA bacteriophages were used as indicators. The membrane demonstrated almost complete removal of E. coli and sulphite-reducing Clostridium spores. However, there was no correlation with membrane fouling. The phage removal varied in accordance with the irremovable fouling, rising from 2.6 to 5.6 log(10) units as the irremovable fouling increased (measured by the change in the transmembrane pressure). In contrast, removable fouling did not have any effect on the retention of viruses by the membrane. These results indicate that irremovable membrane fouling may affect the removal efficiency of MBRs and, therefore, their capacity to ensure the required microbiological standards for the permeate achieved., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Although there is not a complete agreement on the causes of foaming in anaerobic digestion, experts and operators do have valuable empirical knowledge of key factors. Based on this knowledge, a model for calculating the risk of foaming in anaerobic digestion systems due to microbiological causes has been developed. Organic loading rate, variation in organic loading rate, and the presence of filamentous microorganisms in the activated sludge system, used as a feed source for the digester, have been selected as the inputs of a knowledge-based model designed to provide as output the risk of foaming in an anaerobic digester. The performance of the model is demonstrated by means of a case study using the IWA Benchmark Simulation Model No. 2 as a framework, where risk of foaming is used as a new evaluation criterion. The simulated results of an open-loop configuration and two closed-loop control strategies illustrate the usefulness of this knowledge-based approach as a means of estimating the risk of foaming in anaerobic digestion., ((c) 2010 Elsevier Ltd. All rights reserved.)

The performance of an MBR pilot plant for biological nutrient removal was evaluated during 210days of operation. The set point values for the internal recycles were determined in advance with the use of an optimisation spreadsheet based on the ASM2d model to optimise the simultaneous removal of C, N and P. The biological nutrient removal (BNR) efficiencies were high from the start of operation with COD and N removal efficiencies of 92+/-6% and 89+/-7, respectively. During the course of the experiment P removal efficiencies increased and finally a P-removal efficiency of 92% was achieved. The activity of poly-phosphate accumulating organisms (PAOs) and denitrifying poly-phosphate accumulating organisms (DPAOs) increased and the specific phosphate accumulation rates after 150days of operation amounted to 13.6mgPg(-1)VSSh(-1) and 5.6mgPg(-1)VSSh(-1), for PAOs and DPAOs, respectively., (Copyright 2010 Elsevier Ltd. All rights reserved.)