What happens when an emulsion is centrifuged
How does the emulsion breakdown work?
Behind the term emulsification there are different processes that are used in the Wastewater treatment be applied. Emulsions are mixtures of liquids that are not soluble in one another. In order to produce a stable emulsion, emulsifiers are required. If the liquids are to be separated from each other again, emulsion splitting is used.
Emulsions in everyday life and in industry
The best known emulsion is milk. It consists mainly of water and fat. The emulsifier in milk is called casein. It ensures that the fat droplets remain distributed in the milk. The oldest method of emulsion separation is buttering. The casein casings, which enclose the small fat droplets and prevent them from clumping together, are destroyed by mechanical forces. Larger and larger lumps of fat form. What remains is buttermilk. The best known method of producing emulsions is washing. Removing greasy contaminants is difficult with water alone. With soap as an emulsifier, it is child's play. What remains is wastewater in the form of an emulsion. The water treatment takes place in sewage treatment plants by splitting emulsions. In metalworking, emulsions are used as cooling lubricants. The cooling effect of the water and the lubricating effect of the oil enable the material to be machined. This results in large amounts of emulsified wastewater. In order to recover the water from this, the emulsion has to be broken down.
Overview of the methods of emulsification
Emulsion splitting is possible by a variety of methods. It succeeds in a mechanical, thermal, chemical, electrochemical and biological way. Which method is optimal depends on the specific mode of action of the existing emulsifiers and on the other components of the emulsion.
The mechanical methods of emulsion breakdown include centrifugation and ultrafiltration. With these methods, mechanical forces cancel the effect of the emulsifiers in the emulsions.
During centrifugation, the centrifugal force affects the density differences between the components of the emulsion. On a large scale, this process is carried out in separators. While a centrifuge has to be loaded and emptied alternately, separators enable continuous operation.
Ultrafiltration is based on high pressure with which the water is pressed through a membrane. Organic substances with large molecules are retained by the membrane. This procedure can only be used with emulsions that are compatible with the membranes.
Distillation and adsorption are used as thermal processes for splitting the emulsions.
During the distillation, the water is evaporated and recovered as condensate. Despite different boiling points, part of the emulsified liquid always evaporates with the water. The part of the oil that gets into the condensate with the steam is then removed in mechanical separators. Water needs a lot of heat to evaporate. The heat is released again when it condenses. In vacuum evaporation, the heat of condensation is recovered for evaporation. This is possible through different pressures in the two sub-processes, which cause boiling temperatures that differ from one another.
During adsorption, organic compounds from an emulsion attach to solids such as activated carbon. This process requires low temperatures. Therefore it is assigned to the thermal process. Two methods are used in adsorption. In one case, activated carbon or special oil binders are mixed into the emulsion in comminuted form and then separated off together with the organic material. The other option is to let the emulsion seep through an apparatus filled with the adsorbent that holds back the oil.
Chemical emulsification uses release agents that combine with the emulsifiers and the emulsified components or dissolve them. Strong acids or special organic release agents are used. The acids destroy the emulsifiers. Then the oil pots clump together. This process is known as coagulation or coalescence. Oil and water form their own phases, which are separated from each other in separators.
This process has the disadvantage that the water has to be neutralized again. This produces large amounts of sludge.
Special organic release agents, which are called demulsifiers or emulsion breakers in technical jargon, prevent the effect of the emulsifiers by forming chemical compounds with them or by dissolving the emulsified substances. The new compounds or solutions float up and form a cohesive layer on the surface of the liquid. Floating is often aided and accelerated by additives called flotation agents.
Many emulsifiers work on the basis of electrical charges. In these cases an emulsion can be split with the help of an electric field. The electric field is generated by electrodes that have a DC voltage applied to them and are immersed in the liquid. The substances with the opposite charge accumulate on the electrodes. Separate phases are formed by coagulation or coalescence and are separated from one another.
The basis for biological emulsion splitting processes are specially cultivated microorganisms that feed on the emulsified substances. The microorganisms are added to the emulsions. Under optimal conditions, the microorganisms grow and multiply. In settling basins they collect as biomass on the bottom and form what is known as activated sludge. The prerequisite for this method is that the emulsions do not contain any biocides that are unhealthy for microorganisms. Forms of biological emulsion splitting are often used in water treatment in sewage treatment plants.
Water treatment in the emulsion splitting plant
Emulsion splitting plants are often part of the technical equipment for treating wastewater. A distinction is made between decentralized and centralized wastewater treatment. Decentralized emulsion splitting plants are operated by companies that want to reduce their waste volume and reclaim service water. The large quantities of wastewater that are collected by disposal companies in the individual companies or that arise in sewage treatment plants are treated in central systems.
Decentralized emulsion splitting plants
A decentralized emulsion breaker is a compact system that consists of a unit for emulsion breakdown and a unit for separation of the lighter phase. In these plants, mainly thermal and chemical emulsion separation are implemented. For thermal cleavage, the market has vacuum evaporators with throughputs from a few liters to a few cubic meters per hour. Similar orders of magnitude are also offered for chemical systems that work with a demulsifier. Downstream of the emulsion splitting there are separators in which the liquids separate into two phases. One phase contains organic compounds, the other water.
Central emulsion splitting plants
In central water treatment plants, the emulsion splitting plant is integrated into a system of stores for liquids, facilities for energy supply, settling basins and components for control and regulation. The processing of large quantities of liquids is energetically more efficient than decentralized treatment.
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