In this work, liquid flow pattern and mixing time in a biogas digester with side entering mixer were investigated experimentally using flow visualization technique and electrical conductivity variation technique, respectively. The impellers used were 4- and 6-bladed inclined blade fan turbine having 3 and 4 cm in diameter. It was concluded that the liquid flow in the biogas digester with side entering inclined blade turbine are characterized by macro-instability flow patterns, that is a large-scale low-frequency flow phenomena. The flow consists of a set of the organized unstable motions differing in both time and scale domains over several orders of magnitude. The macro-instability is characterized by space and time scales considerably exceeding the scales of current turbulent. Flow rate of discharge stream from the impeller region increase with increasing the number of impeller blades for constant impeller rotational speed and the same impeller diameter. Flow rate of discharge stream increase with
increasing impeller rotational speed for the same impeller.The mixing performance of biogas digester in term of mixing time for achieving almost homogenous mixture was affect by impeller rotational speed and number of impeller blades.