Progress in sewage treatment technology of the hot

Progress in oil refining wastewater treatment technology

with the rapid development of petrochemical industry, the discharge of oil refining wastewater has increased year by year. The main pollutants of refinery sewage are oil, solid suspended solids, dissolved organic compounds and bacteria, and some may even contain elements toxic to human body, such as arsenic and chromium. If directly discharged into the environment, it will cause great harm to environmental ecology and human health

1 current situation of domestic oil refining sewage treatment

1.1 characteristics of oil refining sewage

oil refining sewage is a heterogeneous system integrating suspended oil, emulsified oil, dissolved organic matter and salt. The main pollutants include petroleum, COD, BOD, sulfide, volatile phenol, suspended matter and ammonia nitrogen, Suspended solids and salts come from the electric desalting process. Oil and sulfide, phenol, cyanide dissolved in sewage are related to the crude oil processing process

1.2 treatment status of oil refining sewage

oil refining sewage treatment technology is divided into primary treatment, secondary treatment and tertiary treatment according to the degree of treatment. The methods used in the primary treatment include gravity sedimentation method, flotation method, etc; The secondary treatment methods mainly include coagulation method, biochemical method, etc.; the tertiary treatment methods include adsorption method, membrane separation method, etc. Refinery wastewater can generally meet the discharge standard after secondary treatment. Few domestic enterprises use tertiary treatment, while many foreign refinery wastewater generally use tertiary or advanced treatment process

2 the special committee for the treatment of oil refining wastewater also maintains good communication with relevant industry organizations at home and abroad for data processing methods and research progress

in recent years, oil refining wastewater treatment technology has developed rapidly, and the commonly used treatment methods are as follows

2.1 gravity sedimentation method

gravity optimization method is based on the density difference between oil and water. Under the action of gravity, the oil-water mixture will be separated automatically after a certain time. Gravity sedimentation method is one of the most common and simple oil removal methods, which can remove oil with a particle size of 100 μ M above the oil slick removal is particularly effective, generally used as a pretreatment operation unit for oil-water separation. Reasonable hydraulic design and sewage retention time are two important factors affecting the efficiency of oil removal. The longer the retention time, the better the treatment effect. The characteristic of gravity sedimentation method is that it can accept oily sewage of any concentration and remove a large amount of dirty oil

the main equipment for gravity sedimentation oil removal includes vertical oil removal tank, inclined plate oil separation tank and coarse grain oil removal tank

2.2 filtration method

filtration method is to remove the suspended solids, oil and other harmful substances in the sewage by passing the oil refining sewage through the device with holes or through the filter layer composed of a certain granular medium, using its interception, screening, inertial collision and other functions. The filtration method has the advantages of simple equipment, convenient operation and low investment cost. However, with the increase of operation time, the pressure drop gradually increases, and 5. Impact speed: 2.5m/s. Backwash frequently to ensure normal operation

2.3 membrane separation innovative technology separation method

membrane separation method uses the selective permeability of the membrane to separate and purify. It uses microporous membrane to intercept oil beads and surface active impurities, which is mainly used to remove emulsified oil and some dissolved oil. Emulsified oil is in a stable state, and it is difficult to separate it by physical or chemical methods. At this time, membrane separation method can achieve good results. Membrane separation method has the advantages of no demulsification, direct oil-water separation, no oily sludge, simple process flow, good treatment effect and so on, but the treatment capacity is small, which is not suitable for large-scale sewage treatment, and the filter is easy to be blocked and the operation cost is high. Current research tends to combine various membrane treatment methods or other methods, such as ultrafiltration and microfiltration to separate oil refining wastewater, membrane separation and electrochemical methods, and ozone oxidation is also used as the pretreatment of ultrafiltration, so as to prolong the service life of ultrafiltration

five membrane separation technologies commonly used in refinery wastewater treatment are reverse osmosis (RO), ultrafiltration (UF), microfiltration (MF), electrodialysis (ED) and nanofiltration (NF). The key of separation technology lies in the choice of membrane. Membrane materials include organic membrane and inorganic membrane. Common organic membranes include cellulose acetate membrane, polysulfone membrane, polypropylene membrane, etc. common inorganic membranes include ceramic membrane alumina, cobalt oxide, titanium oxide, etc

2.4 flotation method

flotation method is to introduce air or other gases into the water to produce fine bubbles, so that some fine suspended oil beads and solid particles in the water adhere to the bubbles, so that the buoyancy increases and floats to the water surface with the bubbles to form scum (oily foam layer), and then use appropriate oil removal equipment to remove the oil. It is mainly used to treat dispersed oil, emulsified oil and fine suspended solids that are difficult to be removed by gravity separation in oily wastewater

according to the different ways of generating bubbles, flotation methods can be divided into pressurized dissolved air flotation, impeller flotation, aeration flotation, induced air flotation and electrolytic flotation, among which pressurized dissolved air flotation is the most widely used. In order to improve the flotation effect, inorganic or organic polymer flocculants can be added to the wastewater, that is, flocculation flotation method, which will also improve the effect of oil-water separation