What are the water treatment chemicals? Let’s take a comprehensive look at the role of each type of water treatment chemical in water treatment processes

Thread Content

This post was last edited by LQ198619 on 2019-2-20 at 19:32. Chemical agents necessary for the treatment process are used, and through their application, the water can be brought to specified quality standards. Its primary effects include controlling the formation of scale and sludge, reducing foam, minimizing erosion of materials in contact with water, removing suspended solids and toxic substances from water, deodorizing and decoloring it, as well as softening the water quality. Currently, due to the sharp increase in water consumption by countries around the world, various environmental protection regulations (such as water purification laws) have been enacted one after another, with increasingly strict requirements; as a result, there has been rapid development in various efficient water treatment chemicals. In our country, against the backdrop of an increasingly severe water capital crisis, the production capacity of water treatment chemicals is very low and their quality cannot be guaranteed; therefore, it is urgent to accelerate the development of the industry related to water treatment chemicals as an environmental protection material. Water treatment chemicals include flocculants, corrosion inhibitors, scale inhibitors, biocides, dispersants, cleaners, pre-film agents, defoamers, decolorizers, chelating agents, oxygen scavengers, and ion exchange resins, etc. This article will provide a systematic introduction to flocculants and biocides. Water treatment chemicals in our country began to receive attention and develop gradually only after the introduction of large-scale fertilizer production facilities in the 1970s ； Since then, a series of water treatment agents have been independently developed. The main types of water treatment agents in our country include scale inhibitors, corrosion inhibitors, biocides and algaecides, inorganic coagulants, and organic flocculants. Water treatment chemicals can generally be divided into three main categories: 1. Chemicals for sewage treatment; 2. Chemicals for industrial circulating water treatment; 3. Oil-water separators. Commonly used water treatment chemicals include scale inhibitors, corrosion inhibitors, biocides (water treatment disinfectants), cleaners, sludge dispersants, flocculants, coagulants, dispersants, etc. Sodium hexametaphosphate is also a type of water treatment chemical. IV. Green water treatment agent PASP – polyaspartic acid. Water treatment agents, water quality testing agents, water quality testing instruments. Features of this new water treatment agent: 1. Fast reaction speed; it takes only half an hour to a few hours to treat ordinary industrial wastewater. 2. It has a wide range of effects on organic pollutants, and exhibits excellent degradation capabilities even for those organic substances that are difficult to degrade. 3. It features a simple process, low investment costs, a long service life, easy operation and maintenance, excellent treatment results, and requires less microelectrolytic reactant during treatment. 4. After microelectrolytic treatment, native ferrous or ferric ions are formed in the water; these ions have a better coagulation effect than conventional coagulants. There is no need to add additional coagulants such as iron salts, resulting in a high COD removal rate without causing any secondary pollution to the water. 5. It has excellent coagulation properties, enabling effective removal of color and COD, thereby greatly improving the biodegradability of wastewater. 6. This method can achieve phosphorus removal through chemical precipitation, and it can also remove heavy metals via reduction. 7. Analyze the opportunities facing the development of water treatment chemicals in China, and describe the current application status of environmentally friendly water treatment chemicals. It is believed that, on the solid foundation of continuous innovation in coagulation theory, water treatment chemicals will develop rapidly in the direction of green water treatment chemicals, multi-component composite water treatment chemicals, as well as new types of efficient water treatment chemicals such as nanomaterials and microbial flocculants. Features: A natural mineral wastewater treatment agent that is a new type of product made from composite aluminum silicate non-metallic minerals as the main raw materials, through specific technical processes; it differs fundamentally from chemically synthesized water treatment agents. Its states are slurry and powder. It has an acidic nature, with a pH value of 3–4. The specific gravity of the slurry is 1.5–1.6, while that of the powder is 1.2–1.3. Color is gray to dark gray. Natural mineral wastewater treatment agents possess five properties: adsorption, ion exchange, catalytic cracking, chemical transformation, and physiological facilitation. Advantages of application: (1) The most important advantage is its ability to treat various types of hard-to-treat wastewater, especially toxic wastewater ； (2) Can remove a small amount of floating debris ； (3) The flocculation and precipitation occur rapidly; the sediment has a low moisture content, high density, and good dewatering properties, making it easy to treat by pressure filtration ； (4) The wastewater treatment facilities and processes are simple and easy to operate, which greatly reduces the one-time investment required for project construction; at the same time, the operating costs are also low ； (5) The sludge generated from wastewater treatment acts as a synergistic additive in agricultural fertilizers, as this mineral material is originally a potent fertilizer additive. Thereby completely eliminating secondary pollution. In the water treatment industry, not only are various water treatment devices widely used, but water treatment chemicals also make significant contributions to different industries. Water treatment chemicals include corrosion and scale inhibitors, flocculants, reducing agents, disinfectants, catalysts, cleaners, etc.; each of these chemicals has its own function and characteristics. Flocculant properties: The molecular formula of the flocculant is +CH2-CHn; it belongs to linear polymer compounds, with a molecular weight ranging from 4 million to 20 million. Flocculants enable the efficient mixed microbial community with flocculation and degradation capabilities, isolated from urban domestic wastewater, to treat this wastewater, ensuring that the removal rates of COD and BOD in the wastewater reach 100%. Corrosion and scale inhibition properties: As the name implies, corrosion and scale inhibitors are water treatment chemicals used to prevent scaling and corrosion in equipment that uses circulating water, such as boilers. This agent is composed of alkaline substances and organic compounds, with a corrosion inhibitor added to prevent corrosion of the heated surfaces. The alkaline substances in the chemicals react, through chemical reactions within the boiler, with calcium and magnesium salts present in the water to form sludge. This sludge settles and is then removed from the boiler via the drainage system, thereby reducing the concentration of calcium and magnesium ions in the water and preventing scale formation inside the boiler. Detergent property: A detergent is a volatile solvent that can dissolve penetrants, and it is used to remove excess penetrant from the surface of the part being inspected. Some cleaning agents are specifically designed to remove metal hydroxides, calcium carbonate, and other similar deposits that adhere to the surfaces of polyamide, polysulfone, and film-based components. Before using the cleaning agent, check the cleaning tank, pipelines, and safety filter, as well as install new filter elements. Fungicides: From their name, it’s clear what their function is. Fungicides are agents primarily used to eliminate harmful bacteria such as bacteria and microorganisms. Internationally, it is generally used as a general term for agents used to prevent and treat various pathogenic microorganisms. Biocides do not pose the same risks to the system as chemicals such as bromine, iodine, peroxides, or peracetic acid. Common techniques 1. Sterilization and disinfection: Water disinfection methods can be divided into chemical and physical types. Physical disinfection methods include heating, ultraviolet light, ultrasound, and others ； Chemical methods include chlorination, ozone treatment, heavy metal ion methods, and other oxidant methods. 2. Magnetization: The treatment of water utilizing the effects of magnetic fields is known as magnetic treatment of water. 3. Precision filtration technology: Micro-porous filter elements and membranes made from special materials utilize their uniform pore size to trap particles, bacteria, and other contaminants in water, preventing them from passing through the filter elements or membranes and thus removing them. Precision filtration can filter out particles and bacteria at the micron (μm) or nanometer (nm) level. It is also widely used in the advanced treatment of water. 4. Ultrafiltration technology: Ultrafiltration is a membrane separation technique. It is a technology in which, under certain pressure (ranging from 0.07 to 0.7 Mpa, with a maximum of 1.05 Mpa), water flows over the membrane surface; water and dissolved salts, along with other electrolytes in the form of tiny particles, can pass through the ultrafiltration membrane, while particles with larger molecular weights and colloidal substances are blocked by the membrane, thereby allowing certain particles in the water to be separated. The pore size of an ultrafiltration membrane is determined through retention tests using substances of a specific molecular weight, and it is expressed as a numerical value corresponding to that molecular weight. 5. Ozone: It is a gas that appears blue at room temperature and has a distinctive fishy odor; its molecular formula is O3. Ozone is an allotrope of oxygen; at room temperature it decomposes on its own into oxygen atoms, and individual oxygen atoms possess extremely strong oxidizing properties. Ozone causes oxidation and denaturation of proteins in bacteria, fungi, and other microorganisms, rendering electrolytes ineffective. It can kill bacterial vegetative forms and spores, viruses, fungi, etc., and can also destroy botulinum toxin. Ozone can eliminate and kill toxic substances and bacteria present in air, water, and food; it also removes unpleasant odors. Therefore, it is widely used in various processes such as disinfection and sterilization during food production. During the disinfection and sterilization process, ozone produces only non-toxic oxides; any excess ozone is eventually reduced to oxygen, leaving no residues on the items being disinfected. Therefore, it can be used directly for the disinfection and sterilization of food. 6. Ion exchange: Ion exchange refers to the charge-neutralizing reaction that occurs between ions in water and ions on the ion exchange resin. The reaction process of ion exchange can be illustrated using the exchange reaction between H+-type cation exchange resin HR and Na+ in water: HR + Na+ → Na+ + H+. As can be seen from this equation, in the ion exchange reaction, the cations in water (such as Na+) are transferred to the resin, while an exchangeable H+ on the ion exchange resin moves into the water. The process of Na transferring from water to the resin is an ion exchange process. The process by which H on the resin is exchanged into water is called the desorption process. Therefore, as a result of the free and displacement processes, Na and H swap positions; this change is known as ion exchange. 7. Ultraviolet rays: When a mercury lamp is turned on, it emits ultraviolet rays with wavelengths ranging from 1400nm to 4900nm (1nm = 10-10m). Such rays can penetrate the cell walls of bacteria, killing microorganisms and thus achieving disinfection and sterilization. Ultraviolet light with a wavelength of around 2600 nm is most effective. Ultraviolet disinfection is mainly used for treating small volumes of drinking water. Its characteristics are: strong killing ability and short contact time ； The equipment is simple, easy to operate and manage; the treated water is colorless, odorless, and poses no risk of poisoning ； It will not increase chloride ions as occurs when using chlorine for disinfection. 8. Adsorption water purification technology: This mainly refers to the adsorption technology utilizing substances with adsorption capabilities, such as activated carbon. Here is a brief introduction to some of the characteristics of activated carbon: It is widely used in the purification, dehydrogenation, oil removal, and deodorization of water used in domestic drinking water, the food industry, the chemical industry, power generation, and other sectors. Typically, it can remove 63%-86% of colloidal substances ； About 50% iron ； As well as 47%-60% organic matter. Common chemicals: Polyaluminum chloride. Polyaluminum chloride is an inorganic polymer coagulant; it is an inorganic polymer water treatment agent with a high molecular weight and high charge, formed due to the bridging effect of hydroxide ions and the polymerization of polyvalent anions. Features: 1. Fast flocculent formation, good activity, and excellent filtration performance. 2. No alkaline additives are required; even if it deliquesces, its effectiveness remains unchanged. 3. It can adapt to a wide range of pH values, has strong adaptability, and is widely applicable. 4. The treated water contains less salt. 5. It can remove the contamination of water caused by heavy metals and radioactive substances. 6. High content of active ingredients, making it easy to store and transport. The flocculating effect of poly(chloro)aluminate is as follows: a) strong electro-neutralization of colloidal substances in water. b. The excellent bridging adsorption effect of the hydrolysis products on suspended solids in water. c. Selective adsorption of soluble substances. Polyaluminum chloride is an inorganic polymer coagulant; it is an inorganic polymer water treatment agent with a high molecular weight and high charge, produced as a result of the bridging effect of hydroxide ions and the polymerization of polyvalent anions. Its characteristics are primarily determined by the working principle of pressure atomizers, which gives this drying system its own unique features. Since the products obtained by pressure spray drying are porous granular or hollow particulate in nature, pressure spray drying is employed for anionic polyacrylamide primarily to produce granular products. The resulting granular products exhibit excellent dust-proof and flow properties. Uses: 1. Urban water supply and drainage purification: river water, reservoir water, groundwater. ⒉Purification of industrial feedwater. ⒊Urban sewage treatment. ⒋Recovery of useful substances from industrial wastewater and waste residues, promotion of the sedimentation of coal powder in coal washing wastewater, and recovery of starch in the starch manufacturing industry. ⒌Treatment of various industrial wastewater types: printing and dyeing wastewater, leather wastewater, fluoride-containing wastewater, heavy metal wastewater, oily wastewater, papermaking wastewater, coal washing wastewater, mine wastewater, brewing wastewater, metallurgical wastewater, meat processing wastewater, and sewage treatment. ⒍Paper sizing ⒎ Refining of sugar solutions ⒏ Casting and molding ⒐ Wrinkle prevention for fabrics ⒑ Catalyst carriers ⒒ Pharmaceutical refining ⒓ Accelerating cement setting ⒔ Raw materials for cosmetics. Polyferric sulfate appears as a light-yellow, amorphous powdery solid that is highly soluble in water. A 10% (by weight) aqueous solution of it is a red-brown, transparent liquid; it is also hygroscopic. Ferrous sulfate polymer is widely used in the purification of drinking water, industrial water, various industrial wastewater, municipal sewage, and sludge dewatering. Application features: Compared with other inorganic flocculants, polyferric sulfate has the following characteristics: 1. A new type of high-quality, highly efficient inorganic polymer flocculant based on iron salts ； 2. Excellent mixing properties, dense floccules, and fast settling speed ； 3. It offers excellent water purification performance; the water quality is good, free from harmful substances such as aluminum, chlorine, and heavy metal ions, and there is no transfer of iron ions into the water phase. It is non-toxic, harmless, and safe to use ； 4. It exhibits significant effects in removing turbidity, decolorizing, removing oil, dehydrating, sterilizing, deodorizing, eliminating algae, as well as reducing COD, BOD, and heavy metal ions in water ； 5. It can adapt to a wide pH range of 4–11, with the optimal pH range being 6–9. The pH value and total alkalinity of the raw water after purification change little, resulting in low corrosivity to the treatment equipment ； 6. It exhibits significant purification effects on slightly polluted water, water containing algae, as well as water with low turbidity and low temperature; its performance is particularly excellent when purifying water with high turbidity ； 7. Low dosage required, low cost; treatment expenses can be reduced by 20%-50%. Characteristics in the treatment of oily wastewater: Coagulation technology is widely used in the treatment of oily wastewater due to its strong adaptability, as well as its ability to remove emulsified oil and dissolved oil, along with certain complex polymeric organic substances that are difficult to biodegrade. The commonly used flocculants can be mainly divided into three categories: inorganic flocculants, organic flocculants, and composite flocculants. Among inorganic polymeric flocculants, inorganic flocculants with lower molecular weights such as polyaluminum chloride and polyferric sulfate exhibit good treatment effects; they are inexpensive, require less dosage, and are efficient, which leads to their widespread use. Polyacrylamide: Polyacrylamide (PAM) is a water-soluble polymer that is insoluble in most organic solvents. It possesses excellent flocculating properties and can reduce the frictional resistance between liquids. Based on their ionic characteristics, it can be classified into four types: non-ionic, anionic, cationic, and amphoteric. Mechanism of action 1) Flocculation mechanism: When PAM is used for flocculation, it is related to the surface properties of the substances to be flocculated, particularly their zeta potential, viscosity, turbidity, and the pH of the suspension. The zeta potential on the particle surface is what prevents particles from aggregating. Adding PAM with opposite surface charge can reduce this zeta potential, thereby promoting aggregation. 2) Adsorption and bridging: The PAM molecular chains become fixed on the surfaces of different particles, forming polymer bridges between the particles, thereby causing the particles to aggregate and settle. 3) Surface adsorption: Various adsorptions of particles onto the polar groups on PAM molecules. 4) Reinforcing effect: The PAM molecular chains bind the dispersed phase together through various mechanical, physical, and chemical mechanisms, forming a network that thereby provides a reinforcing effect. Application areas: 1. Used as a retention agent and reinforcing agent in the papermaking process. 2. Used as a coagulant aid, flocculant, and sludge dewatering agent in water treatment. 3. Used as a dewatering agent and oil displacement agent in oil drilling and production. 4. PAM is also widely used in thickening, stabilizing colloids, reducing drag, bonding, film formation, biomedical materials, and other applications. Tar dehydrator: Simple and fast dehydration, saving steam and costs! The moisture content can be reduced from 30 to below 1. Coking wastewater COD remover A909 reduces the COD in coking wastewater by 200–500 ppm