An absolute analysis was brought on the outcome of fusing the biogas production in an anaerobic digester by targeting the impeller geometry and mixing modes. Agitation, the most prominent factor, undeviatingly determines the consequences of an anaerobic digester operated at higher solid content. The sustainability of homogeneity of substrate for solid liquid phase and the uniformity of microbial community hinge on agitation in an anaerobic digester. In spite of having clash of views on mixing intensity and sort of mixer usage multifaceted studies have been directed rendering worthful results. This survey assesses the hydrodynamic factors which regulates the effects of mixing such as the particle flow pattern, the stagnant zones, the liquid velocities and shear stress. The efficiency of mixing can be determined in terms of homogeneity of slurry, reduction of dead volume, power consumption by mixers and formation of floating layers. Besides this, the consequences of mixing on microbial community, pH value, methane content, and viscosity having multifarious pros and cons are represented. The chief attention is on optimization of various mixing parameters like intensity of mixing, time of mixing, type of mixer used so that a smooth agitation takes place without having negative effects on an anaerobic digestion process at different stages (hydrolysis, acidogenesis, acetogenesis and methanogenesis). The scale-up of industrial mixing processes should be prime stand point for optimization of existing mixing paraphernalia. (C) 2019 Elsevier Ltd. All rights reserved.