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■ What is a coagulant? A coagulant is a cationic polymer with a relatively low molecular weight. In water, negatively charged colloidal particles float while repelling each other, but the positive action of the coagulant cancels out this repulsive force, allowing intermolecular forces (Van der Waals forces) to create small aggregates (microflocs). ■ What does a flocculant do? A flocculant is a chemical used to aggregate substances dispersed in water. The colloidal particles contained in raw water can be removed more easily by using filtration or sedimentation, as the small flocs created by the coagulant are further gathered by the flocculant into larger sizes. ■ How do the two chemicals work together? The coagulant neutralizes the charges of the repelling colloidal particles to form small flocs, while the flocculant, which is a chain-like polymer, entangles these flocs together, allowing them to grow into larger clumps. The negative charges are neutralized by the positive forces, and they are connected like strings to increase in size. Please feel free to consult us first.

■What are inorganic coagulants? Inorganic coagulants are coagulants that do not contain carbon, used to neutralize the surface charge of fine impurities in water and to form flocs (clumps of impurities). They are broadly classified into aluminum-based and iron-based, with polyaluminum chloride (PAC) and ferric chloride being well-known examples. ■What is different about polymer coagulants? Unlike inorganic coagulants, polymer coagulants do not form new flocs; instead, chain-like polymers are added to entangle and bridge the existing flocs, promoting their aggregation. They are also referred to as "coagulation aids" because they support the function of inorganic coagulants. ■Why use a combination of the two types? In wastewater treatment, it is common to first create fine flocs using inorganic coagulants and then to aggregate them using polymer coagulants in a two-step process. The settling velocity of flocs increases proportionally to the square of their particle size, making sedimentation separation easier as they become larger. Please feel free to consult us.

■What does a polymer coagulant do? A polymer coagulant is a chemical that causes "secondary aggregation." It adheres fine flocs created by adding inorganic coagulants like PAC together using a "glue" effect, forming larger "coarse flocs." Coarse flocs settle quickly in water, allowing for rapid separation of impurities and water, making them essential for wastewater treatment. ■Why are inorganic coagulants alone insufficient? The fine flocs produced by inorganic coagulants (primary aggregation) are still light and difficult to settle. The long chain-like molecules of polymer coagulants connect multiple fine particles and flocs, allowing them to grow into larger, heavier flocs. ■What types of polymer coagulants are there? Polymer coagulants, also known as polymers, are classified into three categories based on their ionic nature: anionic (negative), cationic (positive), and nonionic (no charge). Generally, cationic types tend to be suitable for organic sludge, anionic types for inorganic sludge, and nonionic types are used across a wide range of water qualities. ■Which polymer coagulant should I choose? The appropriate type varies depending on the characteristics of the raw water, pH, and the combination with inorganic coagulants. Please feel free to consult us first.

■What are the characteristics of anionic polymer coagulants? They have a large molecular weight of 10 million to 20 million and exhibit excellent coagulation effects with a small amount of usage. However, due to significant changes in effectiveness with pH, they are used in neutral to alkaline industrial wastewater. It is common practice to first neutralize the negatively charged suspended solids in wastewater with positively charged inorganic coagulants before treating them with anionic polymer coagulants. ■What are the characteristics of nonionic polymer coagulants? Although their molecular weight is slightly smaller than that of anionic coagulants, they are characterized by their ability to maintain effectiveness even in acidic conditions. Therefore, they are used for the purification of acidic to neutral industrial wastewater. ■What are the characteristics of cationic polymer coagulants? They are primarily used to promote the dewatering of sludge generated from urban sewage or industrial wastewater. By neutralizing the suspended solids in negatively charged sludge, they create aggregates that drain well, allowing for efficient dewatering of the sludge. ■What are amphoteric polymer coagulants? These are types that possess both positive and negative charges within the molecule. For sludge that contains a high amount of organic matter, where cationic coagulants alone do not provide sufficient dewatering effects, the combined use of inorganic coagulants and amphoteric polymer coagulants can enhance effectiveness. Please feel free to consult us first.

■ Why does poor coagulation occur? The causes of poor coagulation at water treatment plants can include insufficient injection of coagulants, inappropriate pH and alkalinity levels, equipment malfunctions, clogged pipes, and a sudden increase in coagulation inhibitors, among various other factors. Alkalinity is a different indicator from pH and indicates the ability of water to neutralize acids. ■ Why is pH important? The amount of coagulant added varies depending on the type, concentration, and pH of the raw water. If the pH is too high or too low, sufficient effectiveness cannot be achieved, so each coagulant has an "effective pH range" in which it performs optimally. pH adjustment is a crucial operation for effective coagulation and sedimentation. ■ What happens when poor coagulation occurs? If flocs are not formed properly, sedimentation will not proceed effectively, leading to an increase in the turbidity of treated water, which affects the efficiency of subsequent treatment processes. ■ How can poor coagulation be prevented? It is important to conduct regular inspections of dosing equipment, maintain piping, and thoroughly manage the pH and alkalinity of the raw water. It is also effective to confirm the optimal dosing amount and pH in advance through jar tests. Please feel free to consult us first.

■Where do flocs originate? Flocs are formed as clumps of sediment collected by coagulants within a series of equipment that includes the "coagulant injection system," "chemical mixing tank," "floc formation tank," and "sedimentation tank" at a water treatment facility. ■Does floc have another face? The term floc can also refer to a collection of cotton-like microorganisms contained in activated sludge (one of the methods for water purification). The activated sludge process is a treatment method that breaks down organic matter in wastewater using the power of microorganisms, which proliferate and form clumps (flocs) that are separated from the treated water through sedimentation. ■What does a coagulation test involve? In actual practice, a "coagulation test" is conducted by stirring and allowing to stand in multiple beakers while varying the dosage of chemicals and pH conditions, in order to find the conditions under which the turbidity of the supernatant liquid is lowest. The formation of large, easily settling flocs and the clarity of the supernatant liquid are indicators of a good condition. Please feel free to consult us first.

■What is ferric chloride? It is an inorganic coagulant used in the electronics industry for processes such as etching. It is a strongly acidic and corrosive chemical with a basicity of 0, which causes the pH to drop rapidly when added to water, making neutralization with an alkaline agent essential. While it is effective for deodorization and decolorization, a drawback is that it can easily corrode pipes and equipment. ■What is polysilicic acid iron? Polysilicic acid iron, also known as polyferric, has a basicity of about 10-20% and is less corrosive compared to ferric chloride, leading to its increasing use as an inorganic coagulant. ■What is quicklime? Quicklime (calcium hydroxide) is well-known as an inorganic coagulant other than iron and aluminum-based ones. Unlike other inorganic coagulants that exhibit acidity, quicklime shows strong alkalinity. ■How can it coagulate despite being alkaline? Many coagulants are acidic and coagulate by neutralizing negatively charged debris in water with positive ions. Quicklime also produces calcium ions with a positive charge when dissolved in water, allowing it to exhibit coagulation effects despite being alkaline. It is often used as a neutralizing agent. These inorganic coagulants are selected based on the desired effects and the corrosion resistance of the equipment. Please feel free to consult us first.

■What is the "basicity" of inorganic coagulants? Many inorganic coagulants are acidic chemicals, which lower the pH when added to water. The measure of how resistant the pH is to lowering is referred to as "basicity." It is determined by the ratio of hydroxyl groups (OH) to aluminum contained in the coagulant; coagulants with lower basicity tend to lower the pH more easily, while those with higher basicity are less likely to do so. ■What is polyaluminum chloride (PAC)? PAC is a representative inorganic coagulant used in drinking water, with a basicity of 50%. Compared to other inorganic coagulants, it is characterized by being less likely to lower the pH, resulting in less need for pH adjustment after addition. ■What is aluminum sulfate? Aluminum sulfate (alum) is another representative inorganic coagulant alongside PAC. It has a basicity of 0%, making it more likely to lower the pH than PAC. It is effective in removing suspended solids (SS) and is used in general wastewater treatment. The flocs produced are small and light. ■Which one should you choose? If you want to minimize pH adjustment, choose PAC; if you prioritize the removal of suspended solids, consider aluminum sulfate. You can select based on your objectives, water quality, and cost. Please feel free to consult with us first.

■What is floc? Floc refers to a mass of particles formed by the precipitation of chemicals added as coagulants in water treatment. This floc exhibits coagulation reactions against suspended solids, organic matter, bacteria, and coloring components in the water, resulting in purification effects. ■Why do they stick together when coagulants are added? Debris in water typically has a negatively charged surface, which causes it to repel each other and makes it difficult to stick together. By adding coagulants, this repulsion is neutralized, allowing the debris to clump together into larger masses, making them heavier and easier to settle. ■What happens to the floc afterward? The large floc that has grown is separated through sedimentation in a settling tank, as well as removed from the water through flotation separation and filtration. Coagulants include inorganic coagulants that neutralize charges and gather fine particles, and polymer coagulants that further bridge and grow these into larger floc, which are used in stages. ■How is coagulation treatment utilized? Coagulation treatment is a fundamental technology widely used in various water treatment settings, such as wastewater treatment and drinking water treatment. It is important to adjust the type and amount of coagulant based on the type and concentration of contaminants. Please feel free to consult with us first.