Removal of Chemically Emulsified Oil

This treatment sequence requires a reaction tank and a pH adjustment tank. The salts and polymers that break the emulsions are added to the tank by means of metering pumps and mixed with mechanical mixers, or injected in line prior to the tank and the pump, using the pump as the mixer. Metals can be removed in the second tank. The final polishing step again consists of a tank filled with organoclay. Activated carbon use is optional.

Either of these systems depends on a final polishing step with organoclay to allow zero discharge and recycling of the wastewater. Wastewater treatment costs range around $0.5-0.10/gallon, which is considerably cheaper than hauling it away, particularly if the wastewater is hauled over long distances. There are no liabilities such as those involved with hauling wastewater and the potential of spills due to accidents. Zero discharge and recycling implies near zero dealings with local water authorities.

Techniques For Splitting Oily Emulsions

The design of oil/water separators is based on Stoke’s Law, the lighter oil droplets impact on the slant ribs of the media, coagulate, and rise to the surface. The principle of air flotation is that oil droplets will adhere to air and gas bubbles and rise to the surface of the tank. Chemically emulsified oil can be removed by heating the water from 150-220 degrees F, which can become expensive. Evaporators remove the water and leave the oil behind. This is expensive and results in difficult clean ups of the elements of the evaporator. The addition of salts, polymers, bentonite powders and pH adjustment are the most difficult, but also most successful method of breaking emulsions and removing the oil.

When chemical treatment is applied, prior bench testing is required. The first step is addition of an inorganic salt, such as magnesium or aluminum sulfate, which may be sufficient to break emulsions, or de-emulsify the oil, if sodium soaps are the emulsifier. If that is not successful, a cationic coagulant may be added. The purpose is to neutralize the charges on the oil droplet caused by the emulsifier, ie. drive the zeta potential towards zero. If this step is not successful, the pH may have to be adjusted downward to 3.5 with sulfuric acid, which results in the break up of the surfactant. Coagulants and flocculants may then be added to remove the oil. This step is followed by passing the water through a bed of organoclay to remove the last traces of oil (polymers are not economical below 30 ppm), adjustment of the pH to 5 or higher, and a pass through an activated carbon bed. Now the water can be reused.

Breaking emulsions and getting the right pH will increase performance. pH can be used to increase capacity. When the absorbate is neutral (no ionic charge) it will fit into the long hydrocarbon chains in the Quat and the micro pores in carbon. The closer you get the absorbate to its saturation concentration the better it will adsorb. For example, benzoic acid is soluble at 1-2 grams ,but benzoate ionic form is 50 grams soluble per liter of water.