For the treatment technology of oil-bearing industrial sewage, domestic and foreign research institutions have been unremitting in-depth research and discussion, summed up its technical route is to remove a large number of oil in the water while taking into account the removal of organic matter, suspended matter, soap, acid and alkali, sulfide, ammonia nitrogen and so on.
So the treatment methods are physical separation, chemical removal and biological degradation.
In the 1970s, the removal of suspended emulsified oil in water by air flotation has been widely used in various countries. At the same time, combined with biological methods, the oil content in water can be reduced to 10 ~ 20mg / L, and the organic matter can reach the allowable level of discharge.
The seasonality of cooking oil processing is very strong, and the longest time of production in a year is four months.
Treatment of oil wastewater
In the UK, anaerobic contact process is used to treat edible oil wastewater. The average BOD5 concentration of wastewater in the production period is 30000mg / L. after anaerobic treatment, the removal rate of BOD5 reaches 99%, and the effluent is directly discharged into the water body.
Due to the success of anaerobic treatment, the UK has proposed that all wastewater from edible oil industry should be treated by anaerobic treatment.
In Japan, dissolved air flotation is used to treat oil-bearing wastewater from oil and fat plants. In Japan, electric flocculation was also developed to treat emulsified oil wastewater.
In the 1990s, people began to use bioflocculant to treat oil and water, use ultrasonic to separate emulsion, and use lipophilic material to absorb oil.
In recent years, membrane infiltration has become more popular. The membrane is made into plate, tube and hollow fiber.
The United States has also developed a dynamic membrane, which is used in porous materials and water treatment. The treatment of oily wastewater is often a combination of many methods.
At present, gravity separation, centrifugal separation, solvent extraction, air flotation, biochemical, chemical and dialysis methods are widely used in the United States, Britain, Japan and other countries.
Common processes in China:
From the analysis of the treatment process commonly used in foreign countries, we can see that the general research direction is: the developed countries are mainly committed to the secondary and tertiary treatment; while China is inclined to the primary and secondary treatment, the tertiary treatment is rarely used, only as a supplementary measure in special circumstances.
Therefore, we often choose the process to make full use of environmental purification to save the cost of advanced treatment.
At present, the research level of oily water treatment in China is consistent with that in developed countries. What is missing is the improvement of water treatment process in small and medium-sized oil plants. At present, some large cities in China, such as Beijing, Shanghai, Wuhan, Guangzhou, Zhuhai and other places, have oil wastewater treatment projects, and many of them have been put into operation, with good results.
Basic technological process of oil wastewater treatment
The waste water from cooking oil production and refining workshop can be biodegraded after neutralization. Generally, the oil is recovered first and then discharged into the urban sewer system or water body after treatment. For oil containing wastewater, the commonly used process is oil separation to remove suspended oil, followed by air flotation to remove emulsified oil, and finally biochemical removal of dissolved oil and most of organic matter. After these steps, the sewage usually reaches the discharge standard.
In the conventional treatment process, the pre-treatment part is usually composed of grid(Johnson screen grid), oil separator, regulating tank and air flotation tank. The main purpose of this part is to remove the grease in the water.
As the oil in sewage is basically acid oil mixed with soap foot and phospholipid, which has poor solubility, especially when the water temperature is low, the oil is semi-solid, and the effect of direct air flotation treatment is poor, so it is an effective method to take necessary measures in the oil separator at this time.
For example, adding demulsifier in the water or changing the solubility of sewage oil through the adjustment of value, so as to facilitate oil separation and removal.
Biochemical treatment section is the key to ensure that the sewage treatment meets the discharge standard. At present, anaerobic and aerobic or two processes can be used in series for biochemical treatment process.
Due to the difference of oil processing technology and raw materials, the concentration of organic matter in the influent water after pretreatment is quite different. Generally, anaerobic treatment is more reasonable for the wastewater discharged in the chemical refining process, while aerobic treatment is appropriate for the wastewater treatment in the physical refining process.
As the effluent after anaerobic treatment generally can not meet the discharge requirements, it is usually connected to aerobic treatment after anaerobic treatment.
Up flow anaerobic sludge bed (UASB), anaerobic filter bed and anaerobic composite bed are widely used in the anaerobic treatment process, and the medium temperature digestion mode is generally adopted.
Although anaerobic technology has great advantages in the treatment of high concentration organic wastewater, it also has some disadvantages, such as long start-up time, high management level of operation and management, especially for small-scale industrial wastewater treatment projects. In addition, due to the small project, it produces less biogas, which can not be used and is difficult to dispose In the treatment of oil wastewater, the adoption of anaerobic process should also be considered comprehensively.