The anaerobic fermentation process has achieved growing importance in practice in recent years. Anaerobic fermentation is especially valuable because its end product is methane, a renewable energy source. While the use of renewable energy sources has accelerated substantially in recent years, their potential has not yet been sufficiently exploited. This is especially true for biogas technology. Biogas is created in a multistage process in which different microorganisms use the energy stored in carbohydrates, fats, and proteins for their metabolism. In order to produce biogas, any organic substrate that is microbiologically accessible can be used. The microbiological process in itself is extremely complex and still requires substantial research in order to be fully understood. Technical facilities for the production of biogas are thus generally scaled in a purely empirical manner. The efficiency of the process, therefore, corresponds to the optimum only in the rarest cases. An optimal production of biogas, as well as a stable plant operation requires detailed knowledge of the biochemical processes in the fermenter. The use of mathematical models can help to achieve the necessary deeper understanding of the process. This paper reviews both the history of model development and current state of the art in modeling anaerobic digestion processes.
The diffusion of charged nanoparticles at an aqueous/air interface is not invariant under a charge reversal of the particles. Negatively charged particles slow down with the ionic strength of the aqueous phase, while positively charged particles speed up. The diffusion constant of the particles reflects their immersion into the aqueous/air interface. We argue that the opposing behavior of oppositely charged particles is proof that the immersion depth of the particles scales with the contrast in electric surface potential of the particle to the electric surface potential of the air/water interface, not with the particle’s charge density. We therefore propose to incorporate the potential drop across the air/water interface into theories of electrodipping.
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