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.

中文翻译：

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混合强度和持续时间对厌氧消化池中沼气生产的影响：综述。

本文是对厌氧消化池中混合气对沼气生产率影响的重要评估。混合在确定厌氧消化过程的效率中起着重要作用。这篇综述分析了在各种混合强度下以及在消化过程的不同阶段中混合的其他影响（对微生物群落，甲烷含量和挥发性脂肪酸的影响）。就产生的沼气的质量和数量而言，间歇性混合（间隔混合）似乎是优选的，并且导致与大规模沼气生产相关的较低的功率消耗和维护成本。优选的混合时间（间隔时间）和强度取决于蒸煮器和叶轮的几何形状。得出的结论是，对浆体流变学的研究对于混合设备的设计，蒸煮器的形状和尺寸以及管道输送系统的设计至关重要，这有助于最大程度地减少初始投资和运营成本。因此，本文重点研究确定混合效力的参数，例如粘度，总固体含量和蒸煮器设计。比较和审查了各种研究人员关于流变特性的经验数据。因此，应特别注意混合的速度，混合时间和叶轮几何形状的优化，尤其是在消化过程的不同阶段（水解，产酸，产乙酸和产甲烷）。最后，会指导读者阅读有关优化，未来研究方向以及厌氧消化池混合操作故障排除的大量出版物。这项研究将有助于提高与沼气厂的混合效率。亮点剪切速率对厌氧消化过程的不同阶段的影响。甲烷含量随混合速度的变化而变化。当总固体含量较高时，混合效果显着。间歇混合是与连续搅拌相比，蒸煮器和混合器的几何形状对于评估蒸煮器的混合至关重要。