1. laws of physics;
(1) Gravity separation method: Gravity separation method is a typical primary treatment method, which uses the density difference between oil and water and the incompatibility between oil and water to realize the separation of oil droplets, suspended solids and water in static or flowing state, mainly using Stoke formula. In the oil droplet floating stage, the accelerated floating time is very short, and the oil droplet floats at a constant speed, which is regarded as the terminal speed of oil droplet floating.
(2) Mechanical separation method: Although the grease trap method is relatively simple, it occupies a large area. In order to overcome this shortcoming, mechanical separation equipment can be used to make oily wastewater form local vortex and zigzag collision in the separation equipment, or narrow channels can be used to capture and coalesce fine oil droplets, increase the particle size of oil droplets and reduce the residence time, thus achieving better separation effect.
(3) Centrifugal separation method: Centrifugal separation method uses the centrifugal force generated by rapid rotation to make the water with high density flow outward along the annular path, and the oil with low density is thrown into the inner ring to form large oil beads for floating separation. The separation efficiency increases with the increase of rotating speed. If an ultra-high speed centrifuge is used, emulsified oil in water can be separated.
2. Physical and chemical methods;
(1) Coagulation+dissolved air flotation method: firstly, the coagulant in water is put into water, which is hydrolyzed on the one hand and polymerized on the other hand to form macromolecular polymer. Under the action of electrostatic force, van der Waals force, hydrogen bond and ligand, oil droplets are adsorbed, flocculated and bridged to form coarse alum flower, which makes large-scale oil droplets come out of water. At the same time, some low molecular coagulants also have electrostatic neutralization effect, which makes the electricity of oil droplet colloid disappear and further promotes the oil droplets to get close to each other and condense. Then a large number of microbubbles (10~ 120 micron) are released into the water, and the tiny oil droplets dispersed in the water are adhered to the microbubbles by surface tension, so that the buoyancy of the bubbles increases and floats, thus achieving the purpose of separation.
(2) Adsorption method: Adsorption method uses porous adsorbent to physically adsorb (van der Waals force), chemically adsorb (chemical bond force) or exchange adsorb (electrostatic force) the oil dissolved in wastewater to realize oil-water separation. Commonly used adsorbents include activated carbon, activated clay, magnetic sand, slag, fiber, polymer and adsorption resin.
3. Biochemical method; Part of the oil is absorbed by microorganisms as nutrients, converted into organic components or propagated into new microorganisms, and the rest is decomposed into simple inorganic or organic substances by biological oxidation, such as CO2, N2, CH4, etc. So as to purify the wastewater.
4. Electrochemical method; The essence of electrochemical purification of wastewater is to directly or indirectly remove pollutants from water by electrolysis, or to convert toxic substances into non-toxic and low-toxic substances.