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Oilfield wastewater treatment is an important part of oil production process. This article describes the characteristics of oilfield wastewater, and introduced details about the current oilfield wastewater treatment technology and its advantages and disadvantages. It also analyzes the developing trend of oilfield wastewater treatment technology. Oilfield wastewater is complex liquid mixture, whose main ingredients are water, oil, soluble gases, suspended solids, electrolytes, bacteria and various oilfield chemical additives. Oilfield wastewater containins oil, and direct discharge will cause oil pollution; Acidic gas or salts in oilfield wastewater will accelerate corrosion of pipelines and equipments; Suspended solids in oilfield wastewater can block the formation; industrial bacteria in oilfield wastewater makes pipeline corrosion, pipes blocks, and deterioration of water quality. The rational use of oil field wastewater treatment technology is critical.
1. Oilfield Wastewater Treatment Methods
According to principles, oilfield wastewater treatment methods can be divided into physical, chemical, physico-chemical and biological.
(1) Physical method of gravity sedimentation: The basic principle of gravity sedimentation is to take advantage of the density difference between oil and water in the oil oilfield wastewater. The mixture of oil and water will move relatively in the gravitational field, and ultimately achieve the separation of oil and water. Gravity settling equipment is gravity settling tank and can be used for pre-treatment of oilfield wastewater.
Coarse-grained method: coarse-grained means coarse materials makes the diameter of oil bead in oilfield wastewater become bigger while the wastewater pass the chemical control tank. Coarse graining method is mainly used before gravity sedimentation.
Filtration method: The filter method is to remove solid impurities in wastewater by using porous medium, which is commonly used in the last paragraph of the wastewater treatment. Oilfield wastewater treatment filters are included gravity filter and pressure filter. Pressure filter is current widely used in China
(2) Chemical flocculation method: chemical flocculation method means the colloidal suspensions in oilfield wastewater react with electrostatic adsorption or bridging under the action of flocculants. By that way, the flocculating constituents can be removed. Flocculation process is widely used in major oil fields as a pretreatment technique, generally in conjunction with the flotation method.
Chemical conversion: chemical conversion method is to make the inorganic and organic chemicals dissolved in the oilfield chemicals convert to poisoning or non toxic by using chemical agents. The resulting material is stable and easy to separate from the wastewater. The method comprises of ozone treatment method, neutralization treatment, electrolysis treatment, photochemical catalysis, oxidation method. Chemical conversion method D is often used as the chemical conversion pretreatment method and also can be used in combination with other methods.
(3) physical chemical adsorption: adsorption method is the use of molecular attraction or bond strength to make the porous solid adsorbent surface enrichment, so as to achieve the purpose of oilfield wastewater separation of dissolved oil and other organic pollutants. Adsorption method commonly used in their treatment of oilfield wastewater.
Flotation: flotation method (also known as air flotation method) is to pass bubbles into the wastewater by making use of hydrophobic propertyof the granules in the wastewater.After that, contaminants of the wastewater will adhered on the bubbles. The density of the bond is less than water. With bubbles floating, contaminants floats to the surface of the water and forming a three-phase foam layer comprising of bubbles, water and contaminant. By collecting bubbles, we can separate contaminants and water. Flotation method widely used, often in combination with the use of flocculation process.
(4) Biological method is to deal with the oilfield water by using microbial to metabolize organics to inorganics. Depending on the type of microorganisms, it can be divided into aerobic and anaerobic method, including activated sludge method, biofilm method, oxidation pond method and, BAF method. .
2. Developing trend of oilfield wastewater treatment technology
Future trend of oilfield wastewater treatment technologies focused on the following four areas:
First, there are more and more researches on efficient wastewater treatment process, such as joint usage of a variety of methods, giving full play to the advantages of each processing to improve the efficiency of oilfield wastewater treatments;
The second is to strengthen researches on small-scale wastewater treatment equipments, such as jet flotation machine, dynamic hydrocyclone and so on;
Third is to develop new oilfield wastewater treatment chemicals, such as the multi-functional development of the spectrum;
The fourth is to strengthen the researches on mechanism of oilfield wastewater oil and developments of new technologies.
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