Chemical refining

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Chemical purification is much more complex than the physical method, and in this process, chemical coagulation and electrical coagulation are used. In this method, which mentions chlorine and ozone as the main reaction materials, purification is done with the help of ion exchange and pH adjustment. Chemicals prevent the reproduction of bacteria in water and purify the water. This method is not highly recommended due to the production of sludge at the end of the process, which is toxic and very expensive. During this process, a variety of materials and chemical reactions are used to treat wastewater, especially industrial wastewater.
Colloidal particles, fats and oils in wastewater and industrial and sanitary effluents are not able to settle on the floor of the treatment plant due to their high electrical load. The only way to purify these heavy particles is by using chemical methods to reduce the concentration and weight of these particles as much as possible. When these electric charges lose their weight, they are able to connect to each other, creating a clot-like layer on the pool floor or on the floating surface of the sewer. In the final stage, with the help of oil skimmer, this layer can be collected.
In general, chemical treatment includes the removal of strong organic matter, the removal of heavy metals, the removal of BOD, the control of the odor of wastewater, and the control of the pH of wastewater. The most important applications of chemical wastewater treatment methods are precipitation, coagulation and oxidation. Unlike physical and biological methods of wastewater treatment, this method leads to an increase in effluent TDS, which can be problematic in units after the chemical treatment unit.
The method of collecting and coagulating the particles in the effluent is different according to their type and the flocculant package can be used. The basis of these packages is by injection of polyelectrolyte or polyacrylamide and the type of material and powder used in it and are classified into two types of cationic and anionic.
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Chemical precipitation is the most common method for removing soluble metals from industrial wastewater containing metals that affect the quality of the effluent. This reaction is completely dependent on the pH and how this process works depends on the type of metal present, the concentration of the metal and the type of reagent used. This method is used in order to have a clear effluent and better quality of chemicals for sedimentation and sedimentation of suspended solids. Substances such as phosphorus, heavy metals such as copper, mercury, nickel, barium and cyanium and zinc can be removed by this method. There are many reactions to this method, some of which we will mention. They include the reactions of alum, lime, ferrous sulfate and lime, and ferric chloride.
This method also starts with three modes of reaction. Pre-precipitation, simultaneous precipitation and post-precipitation are the steps of this chemical method. It should be noted that in the precipitation process, water sometimes reacts with the particles in the wastewater. Since the particles in wastewater are divided into two groups, hydrophilic and hydrophobic, and among these, hydrophilic particles have a high tendency to react with water.
Coagulation
The purpose of coagulation and flocculation is the use of coagulants in the separation of colloidal and soluble particles from wastewater that has a negative electric charge. Using these materials, small colloidal particles become clots and large particles that settle due to the force of weight. These colloidal particles, fats and oils in wastewater and industrial and sanitary effluents can not be solved by biological treatment and the only way to treat them is to get help from chemical treatment methods.
In this method, the electric charge of the particles is reduced as much as possible by using coagulants. It should be noted that aluminum and iron salts are often used as coagulants. At this point, the colloidal particles, which have lost their electrical charge, bind together to form a clot-like layer. These layers either settle to the bottom of the pool or float on the surface of the sewer and can be collected with the help of an oil skimmer.
This chemical process involves the destabilization of wastewater particles. The type and amount of coagulant used can be determined by jar testing. The most important coagulants in wastewater are polymers and polyelectrolytes, sulfates and aluminum hydrates. Adding coagulants to wastewater doubles to three to three times the amount of sludge obtained in sedimentation pools, and naturally increases the volume of sludge digestion sources and the amount of gas produced.
Chemical oxidation
This method is also used in water and wastewater treatment, which adds a kind of pure oxygen compounds to water or wastewater. Oxidation reactions are among the most important reactions in the process of chemical wastewater treatment. These substances help to eliminate organic pollutants by creating hydroxyl radicals in water. Municipal wastewater treatment plants use aerobic bacteria to stabilize and separate the materials in the wastewater. Chemical oxidation is done in both classical and advanced methods. It is also used to destroy drugs such as antibiotics or cytostatic drugs that may be found in water.