Coal chemical industry tail water treatment technology
Today, with the vigorous development of coal chemical industry, coal chemical tail water treatment has become a key link that cannot be ignored in the industry. Coal chemical industry is a process that uses coal as raw material and converts it into various chemical products through chemical processing. The tail water produced in this process contains a large number of complex pollutants. If it is directly discharged without proper treatment, it will cause serious harm to the environment. damage, threatening ecological balance and human health.
1. Characteristics and hazards of tail water from coal chemical industry
(1) Features
Complex and diverse components: Coal chemical industry tailwater contains a variety of organic matter, inorganic matter and heavy metals. Among them, organic substances include refractory substances such as phenols, polycyclic aromatic hydrocarbons, and nitrogen-containing heterocyclic compounds; inorganic substances include ammonia nitrogen, sulfates, nitrates, etc. These substances are intertwined, making the treatment of tailwater extremely difficult. For example, phenolic substances are toxic and chemically stable, and are not easily decomposed by conventional methods.
High salinity: In the coal chemical production process, due to process requirements, a large amount of salt substances will be introduced, resulting in a significant increase in tail water salinity. The high-salinity environment not only inhibits microorganisms during biological treatment, but may also cause problems such as corrosion and scaling of equipment during the treatment process, increasing treatment costs and difficulty in equipment maintenance.
Large fluctuations in water quality and quantity: The complexity and intermittency of the coal chemical production process cause large fluctuations in the water quality and quantity of the tail water. At different production stages, the concentration and types of pollutants in the tail water will change, and the water volume will also vary due to adjustments in production load. This kind of fluctuation brings huge challenges to the stable operation of the tail water treatment system, requiring the treatment process to have strong adaptability and flexibility.
(2) Harm
Impact on the water environment: If coal chemical industry tailwater is directly discharged into natural water bodies, a large number of pollutants in it will cause the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of the water body to rise sharply, causing water body hypoxia and triggering Aquatic life dies. The toxicity of phenolic substances can directly harm the nervous system and respiratory system of aquatic organisms. Polycyclic aromatic hydrocarbons and other organic substances have the “three effects” of carcinogenesis, teratogenesis, and mutagenesis, which will destroy the balance and stability of aquatic ecosystems and affect aquatic life. Plant reproduction and survival.
Harm to the soil environment: Long-term discharge of untreated or substandard treated coal chemical tailwater will increase the salt content in the soil, leading to soil salinization. At the same time, heavy metals and organic pollutants in tailwater will accumulate in the soil, changing the physical and chemical properties of the soil, reducing soil fertility, affecting the growth and quality of crops, and passing through the food chain, ultimately threatening human health.
Pollution to groundwater: Coal chemical industry tailwater may enter underground aquifers through infiltration, contaminating groundwater. Once groundwater is contaminated, it is extremely difficult to repair because groundwater flows slowly and has weak self-purification capabilities. Contaminated groundwater may threaten drinking water sources in surrounding areas and cause health problems for residents, such as an increase in the incidence of cancer and neurological diseases.
2. Coal chemical tail water treatment technology
(1) Physical processing technology
Sedimentation and filtration: Sedimentation uses gravity to make suspended particles in the tail water naturally settle to the bottom, removing larger suspended particles such as sand, coal powder, etc. Filtration uses filter materials (such as quartz sand, activated carbon, filters, etc.) to further intercept fine solid particles and improve the clarity of the tail water. In some coal chemical companies, a primary sedimentation tank will be set up for preliminary sedimentation, and then sand filtration or membrane filtration will be used for depth filtration to effectively reduce the suspended matter content in the tail water.
Adsorption method: Adsorption technology uses adsorbents (such as activated carbon, resin, etc.) to adsorb and remove organic matter, heavy metals and other pollutants in tail water. Activated carbon has a large specific surface area and rich pore structure, and can adsorb a variety of organic pollutants such as phenols and polycyclic aromatic hydrocarbons. For example, in a coal chemical tailwater treatment project, a powdered activated carbon dosing device is used to evenly add activated carbon powder into the tailwater. After sufficient mixing and a certain residence time, the organic pollutants in the tailwater are adsorbed by the activated carbon. Thereby reducing the COD and chroma of the tail water.
(2) Chemical treatment technology
Coagulation and sedimentation: By adding coagulants (such as polyaluminum chloride, polyacrylamide, etc.) to the tail water, the tiny particles and colloidal substances in the water are coagulated and flocculated to form larger flocs, which are then sedimented or filtered. Remove. Coagulants neutralize the charge of colloidal particles, causing them to destabilize and bind to each other. For example, polyaluminum chloride is hydrolyzed in water to form aluminum hydroxide colloid, which can adsorb and capture suspended impurities and some organic matter in the tail water. After precipitation, it can effectively reduce the turbidity and part of the organic matter content in the tail water.
Advanced oxidation technology: including ozone oxidation, Fenton oxidation, etc. Ozone oxidation uses the strong oxidizing property of ozone to oxidize and decompose organic matter in tail water into small molecular substances or carbon dioxide and water. Ozone can directly attack the double bonds, aromatic rings and other structures of organic matter, causing reactions such as ring opening and chain scission. Fenton oxidation uses a combination of ferrous ions and hydrogen peroxide to generate hydroxyl radicals (OH). Hydroxy radicals have extremely high oxidation potential and can non-selectively oxidize various organic matter in tail water, which is difficult to degrade. Organic matter has better treatment effect. For example, when treating coal chemical tailwater containing phenols, Fenton oxidation process can achieve a high removal rate of phenolic substances.
Chemical denitrification technology: For ammonia nitrogen in tail water, chemical precipitation method, breakpoint chlorination method, etc. can be used. The chemical precipitation method is to add magnesium salt and phosphate to the tail water, so that ammonia nitrogen reacts with magnesium ions and phosphate ions to form ammonium magnesium phosphate and precipitate for removal. The breakpoint chlorination method is to add a sufficient amount of chlorine to the tail water containing ammonia nitrogen so that the ammonia nitrogen is oxidized into nitrogen and removed. For example, in some coal chemical enterprises, when the concentration of ammonia nitrogen in the tail water is high and there are strict requirements for total nitrogen removal, a process combining chemical precipitation and biological denitrification is used to remove most of the ammonia nitrogen through chemical precipitation first, and then use Biological treatment further removes remaining nitrogen.