An experimental investigation is reported of the flocculation of bentonite and Alcaligenes eutrophus in a batch oscillatory baffled flocculator (OBF), where fluid mixing is achieved by eddies that are generated when fluid passes through a set of equally spaced stationary orifice baffles. Periodically formed vortices can be controlled by a combination of operational and geometrical parameters, such as, oscillation frequency, oscillation amplitude, baffle diameter and baffle spacing. The effect of oscillation frequency and amplitude in the OBF on the percentage of flocculation of both bentonite and Alcaligenes eutrophus was examined, the hoc sizes at Various operational conditions observed and the strain rates in the OBF measured using a digital particle image velocimetry (DPIV) technique. The results show that the oscillation amplitude is the dominant factor in influencing the percentage of flocculation. The measured strain rate was linked with the percentage of flocculation per ppm polymer dose and the results compared with those obtained in conventional stirred tank flocculators.