1 centrifugal separation method
Centrifugal separation method is to make the container containing oily wastewater high-speed rotation, the formation of centrifugal force field, due to the solid particles, oil beads and wastewater density is different, subject to different centrifugal force, to achieve the removal of solid particles from the wastewater, oil beads of the method. Commonly used equipment is hydrocyclone separator.
2 flotation method
Flotation method, also known as air flotation, is a water treatment technology that is being studied in depth at home and abroad and constantly promoted. The method is in the water through the air or other gases to produce fine bubbles, so that some of the small suspended oil beads in the water and solid particles attached to the bubbles, with the bubbles together with the formation of slag on the surface of the water (oil-containing foam layer), and then use the appropriate skimmer to skim off the oil. This method is mainly used to deal with the grease trap treatment of dispersed oil, emulsified oil and fine suspended solids remaining in the water after treatment with a particle size of 10 to 60 μm, and the quality concentration of oil in the effluent can be reduced to 20-30 mg/ L. The oil concentration in the effluent can be reduced to 20-30 mg/ L. The oil concentration in the effluent can be reduced to 20-30 mg/ L. According to the different ways of generating bubbles, air flotation is divided into pressurized air flotation, air flotation, electrolytic air flotation, etc., which is the most widely used pressurized dissolved air flotation method.
3 biological oxidation
Bio-oxidation method is to use microbial biochemistry to purify wastewater is a method. Oil is a hydrocarbon organic matter, you can use microbial metabolism and other life activities to decompose it into carbon dioxide and water. The organic matter in oily wastewater is mostly in dissolved and emulsified state, and the BOD5 is high, which is favorable for biological oxidation. For wastewater with oil concentration below 30-50 mg/ L and other biodegradable harmful substances, biochemical treatment is commonly used, mainly for removing dissolved oil in wastewater. Common biochemical treatment methods for oily wastewater include activated sludge method, biological filtration method, biological turntable method and so on. Activated sludge method has good treatment effect and is mainly used to treat wastewater with high requirements and stable water quality. Compared with the activated sludge method, biofilm method, biofilm attached to the surface of the filler carrier, so that the slow reproduction rate of microorganisms can also exist, thus constituting a stable ecosystem. However, since the amount of microorganisms attached to the carrier surface is difficult to control, it is less flexible in operation and has a limited volumetric load.
4 gravity separation method
Gravity separation is a typical primary treatment method, is the use of oil and water density difference and oil and water insolubility, in the static or flow state to achieve the separation of oil beads, suspended solids and water. Dispersed in the water under the action of buoyancy oil beads slowly floating, stratification, oil beads floating speed depends on the size of the oil beads particles, oil and water density difference, flow state and viscosity of the fluid. 2 filtration method
Filtration method is the wastewater through the device with holes or through the filter layer composed of some kind of granular media, the use of its retention, sieving, inertial collision and other effects of the wastewater in the suspended solids and oil and other harmful substances can be removed. There are three commonly used filtration methods: layered filtration, membrane filtration and fiber media filtration. Membrane filtration method is also known as membrane separation method[5] , is the use of microporous membranes to retain oil beads and surfactants, mainly used to remove emulsified oil and some dissolved oil. Membrane includes ultrafiltration membrane, reverse osmosis membrane and mixed filtration membrane. Membrane materials include organic and inorganic membranes, common organic membranes are acetate membranes, polysulfone membranes, polypropylene membranes, etc., commonly used inorganic membranes are ceramic membranes, alumina, cobalt oxide, titanium oxide and so on. Emulsified oil is in a stable state, it is difficult to separate it by physical or chemical methods. With the rapid development of membrane science, membrane process to deal with emulsified oil wastewater has been gradually accepted and applied in industry.
5 chemical method
Chemical method, also known as the pharmaceutical method, is the addition of chemicals by the chemical action of the pollutants in the wastewater into harmless substances, so that the wastewater is purified in a way. Commonly used chemical methods are neutralization, precipitation, coagulation, redox and so on. Coagulation is mainly used for oily wastewater. Coagulation method is to add a certain proportion of flocculant to the oily wastewater, after hydrolysis in the water to form positively charged gel groups and negatively charged emulsified oil to produce electric neutralization, oil particles aggregation, particle size, and at the same time to generate flocs adsorption of small oil droplets, and then through the settlement or flotation method to achieve the separation of oil and water. Common flocculants are polymerized aluminum chloride (PAC), ferric chloride, aluminum sulfate, ferrous sulfate and other inorganic flocculants and acrylamide, polyacrylamide (PAM) and other organic polymer flocculants, different flocculants with different dosage and pH value of the applicable range. This method is suitable for emulsified oil droplets and other fine suspended matter which can not be separated by gravity settling.
6 adsorption method
Adsorption method is the use of oleophilic materials, adsorption of dissolved oil and other dissolved organic matter in wastewater. The most commonly used oil-absorbing material is activated carbon, which can adsorb dispersed oil, emulsified oil and dissolved oil in wastewater. Due to the limited adsorption capacity of activated carbon (for oil is generally 30-80 mg/ g), high cost, regeneration difficulties, generally only used as the last stage of multi-stage treatment of oily wastewater, the effluent quality concentration of oil can be reduced to 0.1-0.2 mg/ L. In 1976, Hunan Changling Oil Refinery in the wastewater treatment of the depth of the treatment of the use of activated carbon adsorption. The development of new adsorbents at home and abroad has also achieved some useful results. It has been found that flake graphite can adsorb heavy oil released by oil spill from offshore tankers and can be easily separated from water. Adsorption resin is a new type of organic adsorbent material developed in recent years, with good adsorption performance, easy regeneration, and the trend of gradually replacing activated carbon.