A small amount of fresh oil can then be added to create an oil-in-water emulsion so that the cells will stick to the oil droplets. In a water-in-oil emulsion, cells associate with the water droplets. The bacteria usually partition to the oil-water interface and move with the discontinuous phase into a two-phase emulsion. Another approach is to separate two immiscible liquids of varying densities by using a settling tank, where the liquid mixture is given enough residence time for them to form two layers, which are then drained (U.S. The phases are usually separated by liquid–liquid hydroclones. Unfortunately, a tight emulsion is usually formed, and it must be broken in order to recover the desulfurized oil, recycle the cells, and separate the byproducts. The explanation for this is that Rhodococcus “drinks from the oil” whereas Pseudomonas “drinks from the water” ( Monticello, 2000).Įffective oil-cell-water contact and mixing is essential for good mass transfer. On the other hand, when dealing with Pseudomonas systems, the cells remain suspended in the aqueous phase. When a cell-water-oil suspension is allowed to settle, the bacteria are found to be associated with oil droplets at the interface, and the aqueous phase remains clear. In an oil-water system, these bacteria adhere to the oil-water interface.

Similar limitations are observed when dsz genes are cloned into Pseudomonas hosts. A Pseudomonas system with naphthalene dioxygenase-like ring cleavage enzymes has been used to show that the transfer of DBT from the oil to the water phase and then from the water to the cells can limit the rate of DBT metabolism. Mass-transfer issues strongly influence the process design.

Oil in water emulsion