The basic principle of using oil separation tanks and sedimentation tanks to treat wastewater is the same, both of which achieve separation by utilizing the different densities of suspended solids and water in wastewater. The structure of the oil separation tank is mostly of the horizontal flow type. The oily wastewater enters the rectangular oil separation tank through the water distribution tank, flows slowly along the horizontal direction, and the oil rises to the surface during the flow. It is pushed into the dehydration tank by the oil collection pipe or the oil scraper set on the tank surface. The heavy oil and other impurities that settle in the oil separation tank accumulate in the sludge hopper at the bottom of the tank and enter the sludge pipe through the sludge discharge pipe.

 

The oil separation tank is often built with reinforced concrete, or with bricks and stones on a rectangular plane. It is divided into 2-4 compartments along the direction of water flow, and the width of each compartment generally does not exceed 6 meters, in order to distribute water evenly. The effective water depth does not exceed 2 meters, and the length of the oil separation tank is generally more than 4 times the width of each grid. Oil separators often use chain type oil scrapers and mud scrapers to remove floating oil and bottom sludge, respectively. Generally, a set of oil scraper and mud scraper are installed in each compartment, with a sludge hopper. If a baffle is added in the middle of each grid, and oil scrapers and sludge scrapers are installed on both sides of the baffle, and sludge hoppers are installed, it is called a two-stage oil separation tank, which can improve the oil removal efficiency, but with more equipment, energy consumption will increase. If several inclined plates are added to the oil separation tank, the oil removal efficiency can also be improved, but the construction investment is relatively high. In cold regions, to prevent oil from solidifying in winter, a steam pipe can be installed at the bottom of the oil collection pipe for heating. Oil separators generally need to be covered and steam pipes should be installed under the cover to provide insulation, prevent fires and oil volatilization, and prevent dust and sand from entering

 

The proportion of oil in wastewater is generally smaller than that of water, and it exists in three states:

 

① Suspended state: The oil particles are relatively large, with a diameter of 0.1 millimeters or more, floating on the water surface and easy to separate from the water. In the petroleum industry, these types of oil products account for approximately 60-80% of the oil content in wastewater.

 

② Emulsification state: The dispersed particle size of the oil product is small, and the diameter of the oil droplets is below 0.1 millimeters. It is in an emulsified state and is not easy to float and separate from the water. This type of oil product accounts for approximately 10-15% of the oil content in wastewater.

 

③ Dissolution state: Petroleum has extremely low solubility in water, and the oil soluble in water accounts for 0.2-0.5% of the oil content in wastewater

 

design basis

 

1. The oily wastewater from canteens and restaurants should be discharged into the sewage pipeline only after passing through the oil removal device.

 

2. The sewage flow rate should be calculated based on the design second flow rate.

 

3. The flow rate of sewage containing edible oil in the pool shall not exceed 0.005m/s.

 

4. The residence time of sewage containing edible oil in the pool water is 2-10 minutes.