The wastewater containing phenolic substances has a wide range of sources and is harmful. Coking plants, gas plants and gas generating stations produce a large amount of phenol-containing wastewater, the phenol concentration is 1000 ~ 3000mg/L, and it also contains pollutants such as oil, suspended solids, sulfide, ammonia nitrogen and cyanide. Petroleum refineries, shale refineries, wood preservation plants, wood retorting plants and various industries that use phenol as raw material or synthesize phenol, such as resin, synthetic fiber, dye, medicine, perfume, pesticide, explosive, glass fiber, paint, disinfectant, flotation agent, chemical reagent and other industrial production processes, will produce phenol-containing wastewater with different quantities and properties.
If phenol-containing wastewater is discharged into water without treatment, it will endanger the reproduction and survival of aquatic organisms. When the water contains 0. 1 ~ 0.2 mg/L of phenol, the fish will smell of phenol. The phenol content of 1mg/L will affect the spawning and migration of fish. When the phenol content is 5 ~ 10mg/L, a large number of fish will die. Drinking water contains phenol, which will affect human health. Even if the concentration of phenol is only 0.002 mg/L, disinfection with chlorine will produce chlorophenol smell. Crops irrigated with high concentration phenol-containing wastewater will wither and die.
Many water bodies in the world are polluted by phenol-containing wastewater, such as Mississippi River, Rhine River, Volga River and Songhua River. Preventing phenol-containing wastewater from polluting the environment has aroused widespread concern. As early as the 1930s, Britain and the Soviet Union began to study the treatment technology of phenol-containing wastewater, and China started in the 1950s. Some countries have established structures to treat phenol-containing wastewater, and carried out various research work extensively. There are two basic ways to solve the problem of phenol wastewater. One is to transform the process to reduce the phenol concentration in wastewater, or to recycle wastewater to reduce emissions. For example, after some domestic gas stations adopt closed-circuit circulation system, the pollution of phenol to rivers is eliminated; The Soviet Union mixed phenol-containing wastewater from coking plant with other industrial cooling circulating water systems; Dow Chemical Company of the United States combines the production of phenol and chlor-alkali into a "closed production circle" without discharging wastewater. The second is the recycling of wastewater. Phenol is an important chemical raw material. Extracting phenol from wastewater is an important source of phenol. The Federal Republic of Germany recovers 654.38+00000 tons of phenol from phenol-containing wastewater from coking plants and gas plants every year.
High-concentration phenol-containing wastewater (phenol is greater than 1000 mg/L) is generally recovered first and then treated harmlessly.
In the past, the methods of recovering phenol from wastewater mainly included:
Extraction is widely used because of its high phenol removal efficiency and wide source of extractant. There are dozens of extraction dephenolization devices in operation in China. About one-third of coking plants in the United States and one-quarter of coking plants in Poland use solvent extraction to remove phenol. Commonly used extractants are benzene, heavy benzene, butyl acetate and light oil. The equipment of pulsed sieve plate extraction tower is not very complicated, and the dephenolization efficiency is generally 93 ~ 97%, which is widely used in China. Fig. 2 is the flow chart of extraction dephenolization and biological treatment of phenol-containing wastewater from a natural gas plant in China. The high-concentration ammonia distillation waste liquid (containing 2500 ~ 3000mg/L phenol) produced by this factory is sent to the pulse extraction tower after degreasing, precipitation and cooling. The effluent after dephenolization (containing phenol 100 ~ 150mg/L) enters the intermediate tank, which is mixed with low-concentration phenol-containing final cooling wastewater and pumped into the aeration tank, and the wastewater at the inlet of the tank. Phenol in the extractant combines with alkali liquor in the alkali washing tower to form sodium phenolate, which enters the sodium phenolate tank for sodium removal and phenol recovery. The extractant is washed with alkali, regenerated and recycled.
Centrifugal extractor is a kind of equipment with high extraction efficiency, small volume and low solvent consumption, and the dephenolization rate can reach 99%. The United States, Japan, Germany and the United States have been used in production.
The steam dephenolization method adopts the earlier dephenolization method, which is simple to operate and suitable for treating wastewater containing volatile phenol. The essence of this method lies in boiling the mixture of phenol and steam. Phenol in water is converted into steam to purify wastewater, and then the steam containing phenol is washed with alkali liquor to recover phenol. The dephenolization rate is about 80%. Some factories in the United States use this method to treat tar extraction and p-cumene phenol production wastewater, and the dephenolization efficiency reaches 97%. The method does not use organic solvent, and the recovered phenol has good quality, large water treatment capacity and simple operation; However, only volatile phenol can be recovered, and the consumption of steam is large, the dephenolization tower is huge, and the concentration of residual phenol in wastewater is high.
Activated carbon adsorption is a widely used adsorption method. The United States and Britain use this method to recover phenol from wastewater from chemical plants with relatively simple water quality and pesticide plant. Activated carbon adsorption was used to treat the wastewater from bicester Agricultural Chemical Company. The phenol content decreased from 800 mg/L to 8 mg/L, and the dephenolization rate was 99%. As a highly purified equipment for refinery wastewater, activated carbon filter has been used in Changling Refinery in China and Dongfanghong Refinery in Beijing. It is quite common to treat phenol-containing wastewater from coking plant with cheap adsorbent slag in Czechoslovakia, and the phenol removal efficiency can reach 75%. The recovery of phenol from phenol-containing wastewater by macroporous adsorption resin in the United States is successful.
In ion exchange method, the best effect of removing phenol with ion exchanger is the adsorption of regenerated phenol with weakly basic anion exchange resin. As early as 1950s, German * * and China used weakly basic anion exchange resin to recover a large amount of phenol from the wastewater of gas plants and coking plants. Sulfonated coal filter is widely used in pharmaceutical industry in China, and the adsorption efficiency of sulfonated coal in Shanghai Sixth Pharmaceutical Factory can reach over 98%.
Chemical precipitation method is to separate and recover phenol from wastewater by adding chemicals, such as further evaporating and concentrating wastewater containing high concentration of phenol and formaldehyde in resin factory to concentrate phenol and formaldehyde into phenolic resin; Phenols and fatty acids in peat gas station wastewater are converted into calcium salts by calcium oxide, and then further recovered.
Phenol-containing wastewater with low biological concentration and no recycling value, or wastewater containing tens to hundreds of milligrams of phenol per liter after recycling, needs to be purified and discharged or reused. Commonly used purification treatment methods are: ① Activated sludge process: good treatment effect and low cost. With the development of activated sludge biological research, the improvement of activated sludge culture technology, especially the domestication and application of high-efficiency phenol-breaking strains, and the emergence of new high-efficiency devices, this method has become the main method to treat various phenol-containing wastewater. The removal rate of phenol can reach 95 ~ 99%. ② Biological filter method: it has strong adaptability to load change and simple operation and management. In recent years, plastic filter, tower biological filter and biological rotary table have appeared, which have overcome the shortcomings of large area and low treatment efficiency of ordinary filters and have been applied to the treatment of phenol-containing wastewater in coking plants, gas plants and chemical fiber plants. ③ Oxidation pond method: purification by natural biological action. In the United States, it is widely used to treat phenol-containing wastewater from refineries and coking plants. This method has low treatment cost, but it occupies a large area. If the land conditions are available, it can be considered.
In recent years, with the development of electric power industry, especially the vigorous development of hydropower and nuclear power in modern times, the cost of electric energy has been reduced, which has opened up a good prospect for the application of electrochemistry in wastewater treatment.
Electrochemical methods for wastewater treatment include electrolysis (oxidation or reduction), electric capture, electrocoagulation and electrodialysis. Electrochemical methods have been used to treat electroplating wastewater, chemical wastewater, dye wastewater, papermaking wastewater, leather wastewater, biochemical wastewater and pharmaceutical wastewater. And is used for electrochemical synthesis of water treatment agent.
The electrolytic flocculation experiment of treating organic wastewater by electrolytic flocculation method takes graphite as cathode, stainless steel, aluminum plate and iron plate as anode respectively. It is found that the effect of using aluminum electrode is good. The cell voltage is 10V, current density is 12.5/Am2, electrolysis time is 12 h, raw water COD is 2458 mg/L, BOD is 5355.80 mg/L, and TP is 77. TN is 37.59 mg/L, suspended matter is 670 mg/ L, and chromaticity is 160. After electrocoagulation, the removal rates of suspended solids, COD, BOD5, tp and TN were 100%, 94.62%, 90.83%, 100% and 77.76% respectively.
Indirect oxidation method of sewage treatment Indirect oxidation method is to generate chemically active substances with strong oxidation properties in the process of anode reaction, and then use these substances to decompose refractory substances. Chlorine and hypochlorous acid can be used as oxidation mediators of organic compounds, and the weaker the reduction potential, the better the oxidation mediator effect. Indirect oxidation has been verified in the oxidation process of benzene, phenol, oil and chloride. After precipitation, extraction and separation, the wastewater from the production of p-nitrophenol from nitrochlorobenzene still contains hundreds of milligrams of phenol and a lot of sodium chloride per liter. Chlorine and hypochlorite can be produced by electrolytic oxidation of organic matter in wastewater. After oxidation, the tail liquid still contains hypochlorite, which is mixed with raw water for further oxidation, and the dephenolization rate reaches 99%.
In addition, the electrochemical degradation of coking wastewater containing phenol can be used for reference:
Abstract: Using Ti/ir2o 3/Ruo 2 as anode and C-PTFE gas diffusion electrode as cathode, simulated coking wastewater containing phenol was degraded. The optimum operating conditions were obtained by orthogonal experiment. The effects of phenol concentration, current density, electrolyte concentration and pH value on phenol removal rate were investigated. Kinetic analysis of electrochemical degradation of phenol proved that the reaction was a first-order kinetic reaction. Keywords: orthogonal experiment; Coking wastewater; Degradation treatment; Electrochemical method; phenol
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