Institute of Energy Engineering and Chemical Machinery, University of Miskolc, Miskolc, Hungary.
Crit Rev Biotechnol. 2020 Jun;40(4):508-521. doi: 10.1080/07388551.2020.1731413. Epub 2020 Mar 30.
This paper is a critical evaluation of the effect of mixing on biogas production rates in an anaerobic digester. Mixing plays a prominent role in determining the efficiency of the anaerobic digestion process. This review analyzes the miscellaneous effects of mixing (on the microbial community, methane content and volatile fatty acids) at various mixing intensities and during different stages of the digestion process. Intermittent mixing (mixing at intervals) seems preferable in terms of the quality and quantity of biogas produced, and results in lower power consumption and maintenance costs associated with large-scale biogas production. Preferable mixing time (the length at intervals) and the intensity depends on the geometry of the digester and impeller.The conclusion is drawn that the study of the slurry rheology is very crucial in the designing of the mixing equipment, the shape and size of the digester, and the pipe transport system which can assist in minimizing the initial investment and operational costs. Accordingly, this paper focuses on the parameters which determine the potency of mixing, such as viscosity, total solid content and digester design. Empirical data demonstrated by various researchers regarding rheological characteristics is compared and reviewed. Consequently, close attention should be paid toward the optimization of mixing in terms of its speed, mixing time and impeller geometry, especially during different stages of the digestion process (hydrolysis, acidogenesis, acetogenesis and methanogenesis). Finally, readers will be guided to the extensive publications regarding optimization, directions of future research, and troubleshooting of the mixing operation in an anaerobic digester. This investigation will help to improve mixing efficiency with biogas plants.HighlightsEffect of shear rate on different stages of an anaerobic digestion process.Methane content varies with the variation in mixing speeds.Mixing effect is significant when the total solid content is higher.Intermittent mixing is favorable when compared to continuous mixing.The geometry of the digester and mixer is essential to evaluate digester mixing.
本文对搅拌对厌氧消化器中沼气产生速率的影响进行了批判性评估。搅拌在确定厌氧消化过程的效率方面起着重要作用。本综述分析了在不同搅拌强度和消化过程不同阶段下搅拌（对微生物群落、甲烷含量和挥发性脂肪酸）的各种影响。间歇搅拌（间隔搅拌）在沼气的产量和质量方面似乎更优，并且与大规模沼气生产相关的能耗和维护成本更低。优选的搅拌时间（间隔长度）和强度取决于消化器和叶轮的几何形状。结论是，在混合设备的设计、消化器的形状和尺寸以及可以帮助最小化初始投资和运营成本的管道输送系统中，研究浆料流变性非常关键。因此，本文重点介绍了决定混合能力的参数，例如粘度、总固体含量和消化器设计。比较和回顾了不同研究人员提供的关于流变特性的经验数据。因此，应特别注意优化搅拌的速度、搅拌时间和叶轮几何形状，特别是在消化过程的不同阶段（水解、产酸、产乙酸和产甲烷）。最后，读者将了解到有关优化、未来研究方向以及厌氧消化器中混合操作故障排除的广泛出版物。这项研究将有助于提高沼气厂的混合效率。
要点
搅拌对厌氧消化过程不同阶段的影响。
甲烷含量随搅拌速度的变化而变化。
当总固体含量较高时，混合效果显著。
与连续搅拌相比，间歇搅拌更有利。
消化器和搅拌器的几何形状对于评估消化器混合至关重要。
