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The anaerobic digestion of wastewater treatment sludge (WAS) produces a "green" biogas while reducing the amount of residual sludge. To increase the yield of biogas, several individual or combined pre-treatment methods of WAS can be used. These pre-treatment methods substantially reduce the amount of volatile suspended solids (VSSs) and their associated total chemical oxygen demand (TCOD). Pre-treating the sludge will increase the methane yield by 15 to 30%. Although the individual methods have been dealt with in research and large-scale operations, the combined (hybrid) methods have not previously been reviewed. Here, different hybrid treatment methods are reviewed, including (1) thermochemical hydrolysis pre-treatment, using an alkaline or acid addition to enhance solubilization of the sludge cells and increase biogas production; (2) alkaline and high-pressure homogenizer pre-treatment, combining a chemical and mechanical treatment; (3) alkaline and ultrasound pre-treatment, capable of solubilizing organic sludge compounds by different mechanisms, such as the fast and effective ultrasound disruption of cells and the increasing effect of the alkaline (NaOH) treatment; (4) combined alkaline and microwave pre-treatment, which enhances sludge solubilization by at least 20% in comparison with the performance of each separate process; (5) microwave (MW) and peroxidation pre-treatment of WAS suspended solids (SSs), which are quickly (<5 min) disintegrated by MW irradiation at 80 °C; (6) ultrasound and peroxidation pre-treatment, with ozone and peroxides as powerful oxidizing agents; and (7) pulsed electric field (PEF) pretreatment. All literature findings are assessed, discussing relevant operation conditions and the results achieved. [ABSTRACT FROM AUTHOR]

The optimization of integrated membrane bioreactors (MBRs) models is of paramount importance in view of reducing the costs, greenhouse gas emissions or enhancing the water quality. 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 control and optimization of integrated MBR models. Whether aerobic or anaerobic, such modelling allows the consideration of specific functioning conditions and optimization problems together with the estimation and monitoring of Performance Index (PIs). This paper reviews the diversity of those problems criteria used in performance assessment. Dividing issues that can be addressed either off-line or online, it is shown that integrated models have attained an important degree of maturity. Several recommendations for mainstreaming the optimization of MBRs using such integrated models. The key findings of this work show that there is room for improving and optimizing the functioning of MBRs using integrated modelling and that this integrated modelling approach is necessary to link functioning conditions together with PI estimation and monitoring., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)