Oily water treatment in a multistage tower operated under a novel induced pre-saturation process in the presence of a biosurfactant as collector

Abstract

The increase in water-oil separation efficiency as a function of biosurfactant in a novel process of a continuous induced pre-saturation tower (IPST) with stages was described. The pre-saturation of the effluent in a new IPST prior to its entrance in each stage enabled enhancing the effect of the biosurfactant on the flocculation of oil droplets due to the close contact with the air during the formation of microbubbles inside a centrifuge pump. This change of a conventional dissolved-air flotation device enabled each stage to serve as a final flocculation chamber and flotation separator. The initial flocculation step occurred nearly entirely within the centrifugation pump adapted for the generation of microbubbles. Experimental tests in a bench-scale prototype of an IPST enabled drafting two operation diagrams based on the absence and presence of the biosurfactant produced by the bacterium Pseudomonas cepacia CCT 6659. We used an effluent composed of water and semi-synthetic motor oil at 500 ± 13 mg L−1. The oil removal efficiency was estimated with the aid of Damköhler numbers applied under the analogy of considering the IPST to be a set of perfect-mixture tanks in series. To quantify the increase in efficiency achieved with the addition of the biosurfactant, we identified the kinetic laws corresponding to the addition and non-addition of the biosurfactant. The addition of the biosurfactant led to an increase in the oil removal rate in the IPST from 92.5 % to 97.0 %.

Keywords

• Oily water
• Biosurfactant
• Liquid-liquid separation
• Operation diagram
• Bench prototype