Studies of Mixing Systems in Anaerobic Digesters using CFD and the Future Applications of Nanotechnologies
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REVIEW
Studies of Mixing Systems in Anaerobic Digesters using CFD and the Future Applications of Nanotechnologies Grazia Leonzio1 Received: 4 May 2019 / Accepted: 23 September 2019 © Springer Nature B.V. 2019
Abstract 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. Graphic Abstract
Keywords Anaerobic digesters · Nanoparticles · Computational fluid-dynamics · Mixing · Biogas production Extended author information available on the last page of the article
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Statement of Novelty The work is timely for a review, because a similar work is not present in literature. It is an interesting research study that would provide bases for future research regarding anaerobic digestions, showing what is already done. Nanotechnology is suggested as an important aspect to improve the efficiency of anaerobic digesters.
Introduction The anaerobic digestion allows the degradation of organic matter by micro-organisms that not require oxygen and is the most developed technology for the treatment of sludge, from wastewater treatment plants. The process produces a gas stream, called the biogas mainly constituted by methane and carbon dioxide. The current line of research is aimed at maximizing the recovery of energy and therefore the produced biogas is sent into a cogeneration or tri-generation system: the electrical energy produced by these systems can be recovered for the operation of the same biogas plant. In particular, the system consumes electricity for mixing, that has an important role inside the anaerobic digestion process. The consumes of electricity for mixing are reported in literature. Regarding to this, Kissel et al. [1] report that in ten pilot plants the consumed electricity for mixing inside an anaerobic digester is equal to 25% of a
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