Agro-food industrial processes produce a large amount of residues, most of which are organic. One of the possible solutions for the treatment of these residues is anaerobic digestion in bioreactors. A novel 18-L bioreactor for treating waste water was designed based on pneumatic agitation and semispherical baffles. Flow patterns were visualized using the particle tracer technique. Circulation times were measured with the particle tracer and the thermal technique, while mixing times were measured using the thermal technique. Newtonian fluid and two non-Newtonian fluids were used to simulate the operational conditions. The results showed that the change from Newtonian to non-Newtonian properties reduces mixed zones and increases circulation and mixing times. Circulation time was similar when evaluated with the thermal and the tracer particle methods. It was possible to predict dimensionless mixing time (theta(m)) using an equivalent Froude number (Fr-eq).