Methods for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production

Abstract

This invention relates to the field of wastewater treatment technology, specifically a method for recovering phenol and ammonia from phenol and ammonia wastewater generated during semi-coke production. The method involves adding a required amount of alkali to the phenol and ammonia wastewater and then feeding it into a deammoniation tower for deammoniation. The resulting phenol-containing ammonia water is adsorbed and purified to obtain pure ammonia water. Solid sodium sulfate is added to the deammoniation liquid to obtain a salt solution. Phenol is precipitated through salting out, followed by phase separation. The remaining solution is fed into a resin adsorption column for phenol adsorption, yielding adsorbed and dephenolized effluent. The resulting regenerated liquid is sent to a distillation tower to recover methanol or ethanol, with crude phenol obtained from the bottom of the distillation tower. The adsorbed and dephenolized effluent is then fed into a catalytic oxidation unit to obtain catalytically oxidized effluent that meets emission standards. This invention employs low-temperature salting out and adsorption dephenolization technology. The adsorption resin is regenerated using low-boiling-point solvents such as methanol and ethanol, significantly reducing investment costs and energy consumption. Furthermore, it can recover high-purity ammonia water and crude phenol, while achieving a COD of less than 50 mg / L in the discharged effluent.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and is a method for recovering phenol and ammonia from phenol and ammonia wastewater generated during the production of semi-coke. Background Technology

[0002] Semi-coke (half-coke) wastewater is a complex, highly toxic, and difficult-to-degrade coal chemical wastewater, and its treatment is a global challenge. The phenol-ammonia wastewater obtained from the semi-coke production process is complex in composition, with high levels of ammonia nitrogen and COD. The COD is mainly caused by phenolic substances, with total phenol content reaching 4000 mg / L to 6000 mg / L and COD reaching 40000 g / L to 70000 mg / L. For example, the phenol-ammonia wastewater from a certain company's semi-coke production is dark purple, with a COD of 46360 mg / L, total phenols of 4387.5 mg / L, ammonia nitrogen of 1144.5 mg / L, oil of 1535.4 mg / L, and conductivity of 13.21 mS / cm.

[0003] Chinese invention patent CN202111507258.7 discloses a method for treating semi-coke wastewater using a pre-oxidation oil and phenol removal-electro-Fenton technology. By adding reducing iron powder to the pre-oxidation unit, organic matter such as oils and phenols is initially reduced and oxidized. This, combined with the acid precipitation unit, causes the organic matter to precipitate in the form of suspended solids, thus enhancing the removal of organic matter and oils. In the electro-Fenton unit, the reducing iron powder generates ferrous ions, which, together with hydrogen peroxide, form a Fenton reagent to further remove organic matter from the wastewater.

[0004] Chinese invention patent application number CN113912237A discloses a treatment process for heavily polluted semi-coke wastewater, including the following steps: (1): the wastewater is pretreated by removing oil and filtering, and then a demulsifier is added to the wastewater while continuously stirring; (2): the wastewater treated in step (1) is subjected to ammonia stripping, and then the pH of the wastewater is adjusted to neutral and a photosensitizer is added; (3): the wastewater is pre-oxidized under light conditions, the wastewater is filtered, and then super-oxidized under light conditions, with the addition of a photosensitizer and hydrogen peroxide; (4): the wastewater is neutralized and then filtered to obtain clean water. The above three patents directly oxidize or biodegrade phenolic substances in the wastewater, without recovering phenols.

[0005] Chinese invention patent CN113772870A discloses a short-process treatment method for semi-coke wastewater. (1) Pretreatment: The semi-coke wastewater is allowed to settle naturally until the floating oil rises and the sediment sinks. The top floating oil is collected, the bottom sediment is discharged, and the pretreated wastewater is discharged. (2) Stripping distillation: The pretreated wastewater is stripped in a distillation tower. The pretreated wastewater and steam come into countercurrent contact to conduct mass and heat transfer, resulting in a gas phase and residual liquid. (3) Ammonium bicarbonate recovery: The gas phase obtained in step (2) is fed into an ammonia recovery tank and condensed to form ammonium bicarbonate crystal slurry. The ammonium bicarbonate crystal slurry is then separated to obtain ammonium bicarbonate crystals and light component concentrate. (4) Evaporation concentration: The residual liquid in step (2) is evaporated and concentrated to obtain evaporation condensate and concentrate. (5) Membrane separation: The evaporation condensate obtained in step (4) is separated by membrane to obtain membrane permeate and membrane concentrate. The membrane permeate is discharged or reused. The membrane concentrate and the residual liquid in step (2) are mixed and evaporated and concentrated again.

[0006] Chinese invention patent CN111646620B discloses a method and apparatus for treating semi-coke wastewater. The method involves adjusting the pH of the semi-coke wastewater using an acidification device, allowing it to stand to achieve gravity oil removal and separation and recovery, and then allowing the wastewater to enter a stripping tower in two separate streams, one hot and one cold, from the top and upper-middle sections of the deacidification tower to remove acidic gases from the wastewater and sending it to a tail gas treatment device. The deacidification kettle liquid is then subjected to countercurrent extraction with an extractant, and the extract phase is separated by distillation to recover the extractant and obtain crude phenol product. The raffinate phase is then subjected to a solvent stripping tower to recover the solvent, and the effluent is subjected to an ammonia stripping tower to remove ammonia nitrogen from the water to produce concentrated ammonia water.

[0007] Chinese invention patent CN113860625A discloses a semi-coke wastewater treatment process based on electrochemical catalytic oxidation. In step one, the semi-coke wastewater is subjected to oil-water separation treatment. In step two, the phenol in the semi-coke wastewater is condensed and flocculated to form phenol sludge, thereby achieving phenol removal. In step three, an oil sludge discharge system is formed. In step four, the semi-coke wastewater is subjected to a combination of electrochemical catalytic oxidation and photocatalysis treatment, which enables the pollutants in the wastewater to be removed rapidly, effectively enhancing the degradation and purification effect of the semi-coke wastewater.

[0008] Therefore, the most widely used technology for treating phenol and ammonia wastewater from semi-coke production is the ammonia stripping + extraction phenol removal process. This involves pre-treating the wastewater with oil separation and air flotation to remove oil, followed by acid removal, and then ammonia stripping to remove most of the ammonia nitrogen and recover ammonia water. After ammonia removal, the wastewater is then used for phenol removal via extraction. Commonly used extractants include carbon tetrachloride, chloroform, cyclohexane, benzene, xylene, and ketone organic solvents such as methyl isobutyl ketone. Carbon tetrachloride, chloroform, and benzene are highly toxic and are generally used less frequently. The phenol extract phase is back-extracted with alkaline solution to obtain sodium phenolate, or directly distilled to obtain crude phenol. The organic solvents recovered from back-extraction or distillation are returned to the extraction process. The remaining phenol extraction liquid is sent to subsequent biochemical units and ozone catalytic oxidation units for further COD removal. The advantages of this process are that ammonia in the wastewater can be recovered as ammonia water, phenol can be recovered as crude phenol, and the final effluent can meet treatment standards. The disadvantages are: (1) The process includes deacidification, deammoniation, extraction dephenolization, biochemical treatment, and catalytic oxidation units. The process flow is long and the equipment investment is high, especially the investment in the extraction dephenolization tower and the biochemical unit. (2) Low volatile organic compounds in the wastewater will enter the ammonia water during deammoniation. The ammonia water has poor purity and needs further purification. (3) Due to the solubility of the extractant, the phenol extraction residue carries the extractant and has a high COD. The extractant needs to be recovered by distillation, which further increases the cost. (4) The sodium phenolate obtained by the phenol extraction phase back extraction needs to be further acidified to obtain crude phenol. When the extractant is recovered by evaporation of the phenol extraction phase, the extractant such as methyl isobutyl ketone has a high boiling point and the evaporation energy consumption is high. Summary of the Invention

[0009] This invention provides a method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production, overcoming the shortcomings of the prior art. It can effectively solve the problems of high energy consumption in recovering solvents or extractants, difficulty in purifying phenol and ammonia-containing water, and high COD in effluent from existing treatments of phenol and ammonia wastewater from semi-coke production.

[0010] One of the technical solutions of this invention is achieved through the following measures: A method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production, comprising the following steps: First, adding the required amount of alkali to the phenol and ammonia wastewater to adjust the pH value, and then sending it to a deammoniation tower for deammoniation. Phenol-containing ammonia water is obtained at the top of the deammoniation tower, and deammoniation-treated liquid is obtained at the bottom of the deammoniation tower; Second, sending the phenol-containing ammonia water to a resin adsorption column for adsorption and impurity removal to obtain pure ammonia water; Third, adding solid sodium sulfate to the deammoniation-treated liquid to obtain a salt solution, adjusting the concentration of the salt solution, and precipitating the phenol in the solution through salting out, followed by phase separation to obtain crude phenol and the remaining solution; Fourth, sending the remaining solution to a resin adsorption column for adsorption and dephenolization to obtain adsorbed and dephenolized effluent. At the same time, the resin after adsorption breakthrough is regenerated with methanol or ethanol, and the obtained regenerated liquid is sent to a distillation tower to recover methanol or ethanol. Crude phenol is obtained at the bottom of the distillation tower; Fifth, sending the adsorbed and dephenolized effluent to a catalytic oxidation unit to remove COD after catalytic oxidation to obtain catalytic oxidation effluent that meets emission standards.

[0011] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions:

[0012] The main pollutants in the aforementioned phenol-ammonia wastewater are ammonia nitrogen, phenol, and oil. The total phenol content exceeds 4000 mg / L, the ammonia nitrogen content is greater than 1000 mg / L, and the oil content is greater than 1000 mg / L.

[0013] In the first step above, the pH value of the phenol-ammonia wastewater is adjusted to be greater than 12, and the ammonia nitrogen in the deammoniation solution is less than 10 mg / L.

[0014] In the first step above, when ammonia removal is carried out in the ammonia removal tower, the temperature at the top of the tower is 95°C to 100°C and the temperature at the bottom of the tower is 105°C to 110°C.

[0015] In the second step above, the resin in the resin adsorption column is a polystyrene skeleton resin, and the resulting pure ammonia water has a COD of less than 100 mg / L.

[0016] In the third step above, the concentration of the obtained salt solution is 150 g / L to 200 g / L, the pH value of the salt solution is 6 to 7, and the temperature of the remaining solution is 2℃ to 10℃.

[0017] In the third step above, the total phenol concentration in the remaining solution is less than 80 mg / L, and the COD concentration is less than 1000 mg / L.

[0018] In the fourth step above, the resin in the adsorption column is a polyacrylate framework resin, and the total phenol content in the adsorbed phenol-desorbed water is less than 1 mg / L, and the COD is less than 200 mg / L.

[0019] In the fifth step above, the catalytic oxidation method is ozone catalytic oxidation or ultraviolet light catalytic oxidation, and the COD of the catalytically oxidized water is less than 50 mg / L.

[0020] The present invention has the following beneficial technical effects:

[0021] (1) By utilizing the salting-out effect of salt on phenols, the salt concentration, pH, and temperature of the wastewater are controlled, and most of the phenols in the wastewater are precipitated to obtain crude phenol products. The wastewater after phenol precipitation is further adsorbed with polyacrylate resin, and the COD of the wastewater can be reduced to below 200 mg / L. The combination of low-temperature salting-out and adsorption-based phenol removal replaces extraction-based phenol removal and biochemical operations, greatly reducing investment. Low-boiling-point methanol or ethanol replaces traditional high-boiling-point extractants, and the energy consumption for distillation recovery of solvents or extractants is greatly reduced.

[0022] (2) Ammonia water containing organic matter is adsorbed and purified by polystyrene skeleton resin. The COD of the effluent is less than 100 mg / L. The resin is regenerated with methanol or ethanol, which solves the problem of purifying phenol-containing ammonia water.

[0023] (3) Ammonia and phenol in wastewater were recovered, and the final effluent COD was less than 50 mg / L. Detailed Implementation

[0024] This invention is not limited to the following embodiments; specific implementation methods can be determined based on the technical solution of this invention and actual circumstances. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art.

[0025] The present invention will be further described below with reference to embodiments:

[0026] Example 1: The method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production is carried out according to the following steps: First, add the required amount of alkali to the phenol and ammonia wastewater to adjust the pH value, and then send it to a deammoniation tower for deammoniation. Phenol-containing ammonia water is obtained at the top of the deammoniation tower, and deammoniation-treated liquid is obtained at the bottom of the deammoniation tower; Second, send the phenol-containing ammonia water to a resin adsorption column for adsorption and impurity removal to obtain pure ammonia water; Third, add solid sodium sulfate to the deammoniation-treated liquid to obtain a salt solution, adjust the concentration of the salt solution, and precipitate the phenol in the solution through salting out, and then perform phase separation to obtain crude phenol and the remaining solution; Fourth, send the remaining solution to a resin adsorption column for adsorption and dephenolization to obtain adsorbed and dephenolized effluent. At the same time, the resin after adsorption breakthrough is regenerated with methanol or ethanol, and the obtained regenerated liquid is sent to a distillation tower to recover methanol or ethanol. Crude phenol is obtained at the bottom of the distillation tower; Fifth, send the adsorbed and dephenolized effluent to a catalytic oxidation unit to remove COD after catalytic oxidation to obtain catalytic oxidation effluent that meets emission standards.

[0027] Example 2: As an optimization of the above example, the main pollutants in the phenol-ammonia wastewater are ammonia nitrogen, phenol, and oil, wherein the total phenol content exceeds 4000 mg / L, the ammonia nitrogen content is greater than 1000 mg / L, and the oil content is greater than 1000 mg / L.

[0028] Example 3: As an optimization of the above example, in the first step, the pH value of the phenol-ammonia wastewater is adjusted to be greater than 12, and the ammonia nitrogen in the deammoniation liquid is less than 10 mg / L.

[0029] Example 4: As an optimization of the above example, in the first step, when ammonia removal is carried out in the ammonia removal tower, the top temperature of the ammonia removal tower is 95°C to 100°C and the bottom temperature is 105°C to 110°C.

[0030] Example 5: As an optimization of the above example, in the second step, the resin in the resin adsorption column is a polystyrene skeleton resin, and the COD of the obtained pure ammonia water is less than 100 mg / L.

[0031] Example 6: As an optimization of the above example, in the third step, the concentration of the obtained salt solution is 150 g / L to 200 g / L, the pH value of the salt solution is 6 to 7, and the temperature of the remaining solution is 2°C to 10°C.

[0032] Example 7: As an optimization of the above example, in the third step, the total phenol in the remaining solution is less than 80 mg / L and the COD is less than 1000 mg / L.

[0033] Example 8: As an optimization of the above example, in the fourth step, the resin in the adsorption column is a polyacrylate backbone resin, and the total phenol in the adsorbed phenol-desorbed water is less than 1 mg / L and the COD is less than 200 mg / L.

[0034] Example 9: As an optimization of the above example, in the fifth step, the catalytic oxidation method is ozone catalytic oxidation or ultraviolet photocatalytic oxidation, and the COD of the catalytically oxidized water is less than 50 mg / L.

[0035] Example 10: A semi-coke production enterprise had wastewater with a pH of 8.40, COD of 46360 mg / L, total phenols of 4387.5 mg / L, ammonia nitrogen of 1144.5 mg / L, oil of 1535.4 mg / L, and conductivity of 13.21 mS / cm.

[0036] (1) Sodium hydroxide is added to the wastewater to adjust the pH to be greater than 12, and then the wastewater enters the deammoniation tower for deammoniation. The temperature at the top of the tower is 95℃ to 100℃, and the temperature at the bottom of the tower is 105℃ to 110℃. The ammonia nitrogen in the effluent (after deammoniation) at the bottom of the tower is less than 10 mg / L.

[0037] (2) The ammonia water containing phenol (low-boiling point component) obtained at the top of the column enters the adsorption column for adsorption and impurity removal, and pure ammonia water with COD less than 100 mg / L is obtained. The adsorption column is filled with polystyrene framework resin. The resin after adsorption breakthrough is regenerated with methanol, and the regenerated liquid is sent to the subsequent distillation unit to recover methanol;

[0038] (3) After deammoniation, solid sodium sulfate was added to adjust the salt concentration to 150 g / L, the pH of the solution was controlled to 6, and the temperature of the solution was controlled to 10 °C. Under the action of salting out, the phenol in the solution precipitated out. After phase separation, crude phenol was obtained, and the total phenol in the remaining solution was 50 mg / L, and the COD was 625 mg / L.

[0039] (4) The remaining solution obtained from the phase separation enters the adsorption and phenol removal process for adsorption and phenol removal. The adsorption resin is a polyacrylate framework resin, and the total phenol in the adsorbed water is less than 1 mg / L and the COD is less than 200 mg / L. After adsorption breakthrough, the resin is regenerated with methanol, and the regenerated liquid is sent to the distillation unit to recover methanol. Crude phenol is obtained from the bottom of the distillation column.

[0040] (5) The effluent from the adsorption and phenol removal process enters the catalytic oxidation unit for further COD removal. The oxidation process uses ozone catalytic oxidation, and the COD of the effluent from the oxidation process is less than 50 mg / L, which meets the emission standards.

[0041] Example 11: A semi-coke production enterprise had wastewater with a pH of 8.99, COD of 52060 mg / L, total phenols of 5214.1 mg / L, ammonia nitrogen of 3230 mg / L, oil of 1655.5 mg / L, and conductivity of 14.88 mS / cm.

[0042] (1) Sodium hydroxide is added to the phenol-ammonia wastewater to adjust the pH to be greater than 12, and then the wastewater enters the ammonia removal tower for ammonia removal. The temperature at the top of the tower is 95℃ to 100℃, and the temperature at the bottom of the tower is 105℃ to 110℃. The ammonia nitrogen in the effluent (after ammonia removal) at the bottom of the tower is less than 10 mg / L.

[0043] (2) The ammonia water containing phenol (low boiling point component) obtained at the top of the column enters the adsorption column for adsorption and impurity removal, and pure ammonia water with COD < 100 mg / L is obtained. The adsorption column is filled with polystyrene framework resin. The resin after adsorption breakthrough is regenerated with ethanol, and the regenerated liquid is sent to the subsequent distillation unit to recover ethanol;

[0044] (3) After deammoniation, solid sodium sulfate was added to adjust the salt concentration to 200 g / L, the pH of the solution was controlled to 7, and the temperature of the solution was controlled to 2℃. Under the action of salting out, the phenol in the solution precipitated out. After phase separation, crude phenol was obtained, and the total phenol in the remaining solution was 62 mg / L, and the COD was less than 752 mg / L.

[0045] (4) The remaining solution obtained from the phase separation enters the adsorption and dephenolization process for adsorption and dephenolization. The adsorption resin is a polyacrylate framework resin, and the total phenol in the adsorbed water is less than 1 mg / L and the COD is less than 200 mg / L. After adsorption breakthrough, the resin is regenerated with ethanol, and the regenerated liquid is sent to the distillation unit to recover ethanol. Crude phenol is obtained from the bottom of the distillation column.

[0046] (5) The effluent from the adsorption and phenol removal process enters the catalytic oxidation unit for further COD removal. The oxidation process can be ozone catalytic oxidation or ultraviolet photocatalysis. The COD of the effluent from the oxidation process is less than 50 mg / L, which meets the discharge standards.

[0047] Example 12: A semi-coke production enterprise had wastewater with a pH of 9.12, COD of 42740 mg / L, total phenols of 4159.2 mg / L, ammonia nitrogen of 2851.5 mg / L, oil of 1415.5 mg / L, and conductivity of 13.62 mS / cm.

[0048] (1) Sodium hydroxide is added to the wastewater to adjust the pH to be greater than 12, and then the wastewater enters the deammoniation tower for deammoniation. The temperature at the top of the tower is 95℃ to 100℃, and the temperature at the bottom of the tower is 105℃ to 110℃. The ammonia nitrogen in the effluent (after deammoniation) at the bottom of the tower is less than 10 mg / L.

[0049] (2) The ammonia water containing phenol (low-boiling point component) obtained at the top of the column enters the adsorption column for adsorption and impurity removal, and pure ammonia water with COD less than 100 mg / L is obtained. The adsorption column is filled with polystyrene framework resin. The resin after adsorption breakthrough is regenerated with methanol, and the regenerated liquid is sent to the subsequent distillation unit to recover methanol;

[0050] (3) After deammoniation, solid sodium sulfate was added to adjust the salt concentration to 175 g / L, the pH of the solution was controlled to 6.5, and the temperature of the solution was controlled to 7℃. Under the action of salting out, the phenol in the solution precipitated out. After phase separation, crude phenol was obtained, and the total phenol in the remaining solution was 49 mg / L, and the COD was 537 mg / L.

[0051] (4) The remaining solution obtained from the phase separation enters the adsorption and phenol removal process for adsorption and phenol removal. The adsorption resin is a polyacrylate framework resin, and the total phenol in the adsorbed water is less than 1 mg / L and the COD is less than 200 mg / L. After adsorption breakthrough, the resin is regenerated with methanol, and the regenerated liquid is sent to the distillation unit to recover methanol. Crude phenol is obtained from the bottom of the distillation column.

[0052] (5) The effluent from the adsorption and phenol removal process enters the catalytic oxidation unit for further COD removal. The oxidation process uses ozone catalytic oxidation, and the COD of the effluent from the oxidation process is less than 50 mg / L, which meets the emission standards.

[0053] In summary, this invention employs low-temperature salting-out and adsorption-based phenol removal technologies. The adsorption resin is regenerated using low-boiling-point solvents such as methanol and ethanol, which not only significantly reduces investment costs and energy consumption but also allows for the recovery of high-purity ammonia and crude phenol. Simultaneously, the COD of the discharged effluent is less than 50 mg / L.

[0054] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production, characterized in that... The following steps are followed: First, add the required amount of alkali to the phenol-ammonia wastewater to adjust its pH value, then feed it into a deammoniation tower for deammoniation. Phenol-ammonia-containing water is obtained at the top of the tower, and deammoniation-treated liquid is obtained at the bottom. The main pollutants in the phenol-ammonia wastewater are ammonia nitrogen, phenol, and oil. The total phenol content exceeds 4000 mg / L, ammonia nitrogen is greater than 1000 mg / L, and oil content is greater than 1000 mg / L. During deammoniation in the deammoniation tower, the top temperature is 95℃ to 100℃, and the bottom temperature is 105℃ to 110℃. Second, feed the phenol-ammonia-containing water into a resin adsorption column for adsorption and impurity removal to obtain pure ammonia water. The resin in the adsorption column is a polystyrene skeleton resin. The obtained pure ammonia water has a COD of less than 100 mg / L. Third, add solid... Sodium sulfate is used to obtain a salt solution. The concentration of the salt solution is adjusted, and phenol in the solution is precipitated through salting out. Then, phase separation is performed to obtain crude phenol and a residual solution. The total phenol content of the residual solution is less than 80 mg / L, and the COD is less than 1000 mg / L. In the fourth step, the residual solution is sent to a resin adsorption column for phenol adsorption and removal, resulting in phenol-removed effluent. At the same time, the resin after adsorption breakthrough is regenerated with methanol or ethanol. The regenerated liquid is sent to a distillation column to recover methanol or ethanol. Crude phenol is obtained from the bottom of the distillation column. The resin in the adsorption column is a polyacrylate framework resin. The total phenol content of the phenol-removed effluent is less than 1 mg / L, and the COD is less than 200 mg / L. In the fifth step, the phenol-removed effluent is sent to a catalytic oxidation unit. After catalytic oxidation, the COD is removed, resulting in catalytic oxidation effluent that meets emission standards.

2. The method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production according to claim 1, characterized in that... In the first step, the pH value of the phenol-ammonia wastewater is adjusted to be greater than 12, and the ammonia nitrogen in the deammoniation solution is less than 10 mg / L.

3. The method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production according to claim 1 or 2, characterized in that... In the third step, the concentration of the obtained salt solution is 150 g / L to 200 g / L, the pH value of the salt solution is 6 to 7, and the temperature of the remaining solution is 2℃ to 10℃.

4. The method for recovering phenol and ammonia from phenol and ammonia wastewater in semi-coke production according to claim 3, characterized in that... In the fifth step, the catalytic oxidation method is ozone catalytic oxidation or ultraviolet light catalytic oxidation, and the COD of the effluent from the catalytic oxidation is less than 50 mg / L.