Studies of Mixing Systems in Anaerobic Digesters using CFD and the Future Applications of Nanotechnologies

Anaerobic digesters are extensively used for the treatment of wastewaters. The impact of nanoparticles, such as silver, zinc oxide, titanium dioxide, and copper oxide within the wastewater treatment systems is recently discussed in the literature. Furthermore, in some cases, different conclusions are drawn from studies investigating the impacts of nanoparticles on the microbial activity, during the anaerobic digestion. For a detailed analysis of this system, a computational fluid-dynamic analysis can be used. In fact, the fluid-dynamic analysis is generally used to evaluate the mixing of anaerobic digesters and different mixing systems can be used: mechanical pumping, mechanical agitation, recirculation of biogas or slurry, pneumatic mixing. An important parameter to evaluate mixing inside digesters is the uniformity index. In general, fermenters for bio-hydrogen production, anaerobic digesters with perfect mixing, photo-bioreactors, bio-film reactors are studied by fluid-dynamic analysis, as shown with the reported literature work of this review. However, more studies should be developed regarding the application of nanotechnologies in anaerobic digesters to evaluate the heat and mass transfer during mixing, using the computational fluid-dynamics analysis. This can be an important research for the next future.