Effects of mixing energy on the sedimentation of vegetable oil spills by clay

Abstract

The effects of clay dose and mixing energy on the efficiency of vegetable oil sedimentation by clay are investigated. The sedimentation efficiency increased with increasing clay dose to a maximum of about 80% of added oil. The maximum sedimentation efficiency was achieved at a lower clay dose, and the sedimentation efficiency was greater for a given clay dose when the oil was present as a thick oil film rather than as a thinner film. Sedimentation efficiency was relatively constant for mixing energies less than about 0.01 m2 s−3 (0.01 W kg−1) but decreased dramatically at higher energy dissipation rates. Mixing energy may not be an important factor in determining the effectiveness of this response alternative because energy dissipation rates in natural surface water bodies under most typical conditions are less than 0.01 m2 s−3. The effects of oil film thickness and mixing energy on the efficiency of vegetable oil sedimentation suggests that vegetable oil–mineral aggregates (VOMA) form through a different mechanism to that of petroleum oil–mineral aggregates (OMA). One consequence of the different formation mechanisms is that VOMA are much larger than petroleum OMA.