Oil-in-water emulsion breaking marine bacteria for demulsifying oily wastewater

Oily wastewater is a large waste stream produced by a number of industries. This wastewater often forms stable oil-in-water (O/W) emulsion. These emulsions require demulsification in order to effectively treat the water prior to release. Although biological demulsification of O/W emulsion has advantages over traditional approaches, its development is at a preliminary stage with few demulsifying bacteria reported and a need for effective screening methods for such bacteria. In this study, thirty-seven marine O/W emulsion demulsifying bacterial strains belonging to 5 genera and 15 species were reported. Cell hydrophobicity and interfacial activity played key roles in the emulsion breaking. One of the highly effective demulsifying bacteria, Halomonas venusta strain N3-2A was identified and characterized. Both its extracellular biosurfactant and cell surface contributed to demulsification resulting in breaking of 92.5% of the emulsion within 24 h. A high throughput and effective screening strategy targeting O/W emulsion breaking bacteria using oil spreading test coupled with cell hydrophobicity test was proposed. In addition, the 37 demulsifying bacteria showed a certain degree of species/genus specific patterns of surface activity and cell hydrophobicity. The reported bacteria and the screening strategy have promising potential for the biological demulsification of O/W emulsions and oily wastewater treatment.