A treater for separating oil from water in an emulsion uses vertical coalescing vanes extending through the oil portion into the water portion. The vanes are made of a conductive material, and are electrically grounded in the produced water, and may be coated or partially coated to promote de-watering. Water droplets coalescing on the faces of the vanes are transported down the vane into the water portion and are removed from the system. In a further embodiment, the vanes extend above the oil portion into the gas portion to facilitate removal of gas entrained in the oil. In another embodiment, at least some of the coalescing vanes are rotatable, allowing external control of the flow of fluid through the treater.