Drying Technology
With the rapid improvement of China's market economy, all industries have achieved very rapid development, and standards and quality of life of urban residents have also been significantly improved, but at the same time, the ecological environment has damaged severely by various pollution.
Water pollution is a complex subject with many pollution sources, and in our country's water pollution treatment work, the treatment of oily sewage is a very difficult task. We should fully analyze the sources of oily sewage and its hazards to clarify the working process of oily sewage treatment, so as to formulate scientific and reasonable treatment countermeasures.
Sources and Hazards of Oily Sewage
1. Source of Oily Sewage
The sources of oily sewage in our country are very extensive. Oily sewage is generated in the process of steel refining, industrial production, oil extraction, pesticide and food processing and production, and these oily pollutants mainly exist in four forms, they are dissolved oil, dispersed oil, slick oil and emulsified oil.
1.1 In petrochemical industry, oily wastewater will be generated at almost any stage from the initial mining to the final transportation and consumption. With the rapid development of science and technology, tertiary oil recovery technology has also been widely used, which improves the oil displacement effect, but also makes the composition of the oily sewage more complicated.
1.2 In chemical and pharmaceutical projects, During the manufacturing process, a large amount of water and lubricating oil are used in the stages of raw material reaction, product separation and raw material pretreatment, so a large amount of high-concentration oily wastewater will be produced then.
1.3 In metal smelting industry, when process smelting metals, whether it is materials or equipment in contact with oil, we all need to cool, clean and lubricate them, and the lubricating oil may also directly contact with it, so oily sewage will be formed.
1.4 In food processing and production, the oily sewage is generated during equipment cleaning and machine lubrication.
2. Hazard Analysis of Oily Sewage
2.1 Oily sewage pollutes drinking water sources. If our daily drinking water source is contaminated by oily sewage, not only humans and animals will be infected, but it may even cause food poisoning, which is very harmful. In addition, oily sewage also contains a certain amount of carcinogens, so it will increase the incidence of cancer in areas contaminated by oily sewage;
2.2 Oily sewage is discharged into rivers and lakes. The density of oily sewage is lower than that of normal pure water. So once the oily sewage is discharged into rivers and lakes, it will adhere to the surface of the water, and the atmosphere and water gas cannot be exchanged normally. The oxygen content in the water decline constantly, then aquatic plants cannot grow normally, the quality of the water body is seriously affected, and the utilization value of water resources is greatly reduced;
2.3 If oily sewage is used as irrigation water to irrigate the soil, then the oil stains will be deposited on the surface of the crops, the soil cannot effectively exchange with the outside air, and the metabolism of the soil will slow down, which will affect the normal growth of the plant, and even lead to the death of crops, if oily crops are eaten by humans, it will be harmful to our health.
Process Procedure of Oily Sewage Treatment
Normally, in our process of treating sewage containing sewage, the process flow is to first separate oil and water from the oily sewage, and then further remove the oil and water by coagulation or floating. At this time, we should add PAM and PAC quantitatively to ensure the full occurrence of flocculation reaction and coagulation reaction. This process can avoid the occurrence of oil clogging of the treatment device, and at the same time, the oil removal performance of each device can also be fully utilized.
When the oily sewage enters the high-efficiency combined air flotation, a large amount of SS and oil have been removed. At this time, we should first measure the water quality. If the water quality is still not up to the standard, then we should use activated carbon filter tank or quartz sand filter tank to filter it to ensure that it meets the quality standards before it can be discharged.
The main purpose of our first oil-water separation is to reduce the degree of emulsification of oily sewage. If it is oily sewage with a high freezing point and large particle size, then there should be heat preservation and heating equipment during treatment. If it is oily sewage with a small oil-water specific gravity difference, a filter device should be used.
When selecting the material of the processing device, we should fully consider the temperature parameter. When the high-efficiency combined air-floating scum is discharged into the sludge storage tank, it is driven by the pneumatic diaphragm pump to the chamber filter press for filtering and dewatering, and finally it is transported for treatment.
Key Technical Methods for Oily Wastewater Treatment
Coagulation
This method is mainly aimed at the separation of tiny suspended oil particles and colloidal oil particles in oily sewage. First of all, we should add a certain amount of chemicals to the oily sewage to make a sufficient chemical reaction, and then it will gradually condense into a floc or a relatively stable mixture; after that, we will add the coagulant to the sewage, so that the gelatinous oil particles in the sewage are no longer negatively charged, but are electric Neutral, flocculent polymers or stable mixtures will sink slowly. In the actual treatment process, we often use coagulants such as ferric chloride, basic alumina, aluminum sulfate and ferrous sulfate, and accelerated clarification tanks are usually used as structures.
Filtering Method
The filtration method means that the particulate matter in the oily sewage is intercepted under the action of the filter membrane, so that the oil and water are separated to achieve the ideal purification effect. In general, the filtration method should be the next-level treatment method of the coagulation method and the floating method. After the formation of a polymer or a stable mixture, the filtration method can be used to remove the colloidal oil stains in the sewage. With this treatment method, the oil content of the finished oily sewage does not exceed 10mg/l, and the pressure filter and the ordinary fast filter are usually regarded as structures. The management process using the filtration method is somewhat difficult, and hot water backwashing or reverse air aeration operation should be performed, otherwise the problem of filter material clogging is prone to occur.
Air Floatation
This method is mainly used in the work of removing emulsified oil and smaller oil particles in oily sewage. The oil content of oily sewage treated by this method does not exceed 30mg/l. Its working principle is: first irrigate the oily sewage Into a certain amount of air, a large number of bubbles will appear in the sewage, and the bubbles will also float up. At this time, an uneven system composed of bubbles, water and oil is formed. The bubbles will be closer to the density of the oil. Combined and gradually moving upwards, the effect of oil-water separation is achieved. According to the different ways of generating bubbles, we can divide the floating method into the following types:
1. Dissolved Air Floatation: This method realizes oil-water separation by separating bubbles from saturated oily sewage, adding oily sewage and air to the dissolved air tank and increasing the pressure gradually to ensure that the air is well dissolved In the sewage, the dissolution time is about 4 minutes. After that, the sewage is sent to the floating tank. When the air is suddenly decompressed, many small bubbles will appear. The bubbles and oil particles will float together. The biggest advantage of this method is the sewage and the air can be fully integrated;
2. Air Flotation: The working principle of this method is to cut the air dissolved in water. Commonly used equipment such as impeller air flotation, water pump suction pipe air flotation, diffuser aeration flotation and jet air flotation, etc. The method is easy to operate and manage, and the energy consumption is reduced, but the breakage degree of bubble cannot be accurately controlled, and the effect of floating may be affected;
3. Electric Floatation: This method is also called electrolytic condensation air floatation method. Its working principle is to install a positive and negative electrode in the oily sewage, so that under the action of direct current, electrolysis will occur and the cathode will also produce bubbles. The oil particles will also gradually combine with the bubbles and float upward, and finally realize the oil-water separation of the oily sewage.
The treatment of oily sewage is a complex system engineering. We should analyze the source and hazards of oily sewage in detail, continuously optimize the treatment process of oily sewage, and adopt the key treatment technology of oily sewage scientifically to make more progress in oily sewage processing work.
