Owing to increasingly stringent effluent quality requirements, intensifications of the conventional activated sludge process (ASP) are required. Due to high biomass concentrations employed, higher metabolic rates and better nutrient removal are possible in membrane bioreactors (MBRs). Decoupling of hydraulic and solids residence times offers additional possibilities for process design and optimisation. Recently, unconventional concepts like post-denitrification and enhanced biological phosphorus removal in MBRs have emerged. The objective of this paper is to present current knowledge on nutrients removal in MBRs and trends in process optimisation in comparison with conventional ASP.

Biogas production is a relevant component in renewable energy systems. The paper addresses modeling approaches from an energy system, as well as from a process optimization, point of view. Model approaches of biogas production show different levels of detail. They can be classified as white, gray, and black box, or bottom-up and top-down approaches. On the one hand, biogas modeling can supply dynamic information on the anaerobic digestion process, e.g., to predict biogas yields or to optimize the anaerobic digestion process. These models are characterized by a bottom-up approach with different levels of detail: the comprehensive ADM1 (white box), simplifications and abstractions of AD models (gray box), or highly simplified process descriptions (black box). On the other hand, biogas production is included in energy system models. These models usually supply aggregated information on regional biogas potentials and greenhouse gas emissions. They are characterized by a top-down approach with a low level of detail. Most energy system models reported in literature are based on black box approaches. Considering the strengths and weaknesses of the integration of detailed and deeply investigated process models in energy system models reveals the opportunity to develop dynamic and fluctuating business models of biogas usage.