Phenolic wastewater pretreatment system and process

Abstract

The invention belongs to the technical field of wastewater treatment in the petrochemical industry, and particularly relates to a pretreatment system and process for phenolic wastewater. The phenol-containing wastewater pretreatment system comprises a water inlet pipeline, a coagulation zone, a flocculation zone, a sedimentation zone and a water outlet tank which are sequentially communicated in the wastewater flowing direction, and the water outlet tank is communicated with the coagulation zone through a backflow pipeline; the water inlet pipeline is provided with a first chromaticity online detector for monitoring a water inlet chromaticity value, and the water outlet tank is provided with a second chromaticity online detector for monitoring a water outlet chromaticity value; the first chromaticity online detector and the second chromaticity online detector are both connected with the DCS remote control system, and the DCS remote control system adjusts the reflux ratio of the reflux pipeline according to the monitored water inlet chromaticity value and the monitored water outlet chromaticity value. The treatment system and process have a good treatment effect on phenolic wastewater in the petrochemical industry, the removal rate of heavy components such as sewage suspended solids and asphaltene in the wastewater can reach 95% or above, and the removal rate of COD can reach 10% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment in the petrochemical industry, and specifically relates to a pretreatment system and process for phenol-containing wastewater. Background Art

[0002] The composition of wastewater in the petrochemical industry is relatively complex, including a large number of phenolic substances such as phenol, cresol, xylenol, asphaltene, benzene, toluene, xylene and other organic matter, as well as inorganic salts, heavy metal ions, etc. This type of phenol-containing wastewater has a wide range of pollution and is highly harmful, causing serious harm to humans, water bodies, fish and crops.

[0003] The steam dephenolization method is an earlier dephenolization method with simple operation and is suitable for treating wastewater containing mainly volatile phenol. The essence of this method is that the phenol and water vapor form an azeotropic mixture. The phenol in the water is transferred into the steam to purify the wastewater, and then the phenol-containing steam is washed with alkali solution to recover the phenol. The dephenolization rate is about 80%. Some factories in the United States use this method to treat wastewater from tar extraction, p-isopropylbenzene-phenol production, etc., and have achieved a dephenolization efficiency of 97%. This method does not use organic solvents, has good quality of recovered phenol, treats a large amount of water, and is relatively simple to operate; the current conventional process is that the phenol-containing wastewater first enters the storage tank for static sedimentation to remove slag, the middle and upper layer liquid enters the oil-water separator for further separation, and the separated light components enter the steam dephenolization device. There are multi-stage filtration devices in the process flow to remove slag;

[0004] The current problems of this process are as follows: ① During the treatment process, the static sedimentation and slag removal in the storage tank, the slag removal in the oil-water separator, the basket filter, and the membrane tube filter have poor filtering effects, and there are still certain insolubles and asphaltene residues, which makes the heat exchanger, steam dephenolization tower and other devices very easy to clog and frequently overhauled, seriously affecting the purification of phenol-containing wastewater. ② The ammonia nitrogen and COD content of the steam dephenolization device influent is too high (ammonia nitrogen is about 10,000 mg / L, COD is about 100,000 mg / L, oil content is about 1500 mg / L, and chromaticity is about 10,000), and the removal effect is not good. As a result, after the subsequent combined process of deacidification and deammoniation, extraction and oil removal, and recovery of residual extractant in the water, the effluent COD is still about 10,000 mg / L, resulting in high COD indicators in the subsequent biochemical wastewater treatment influent, and high treatment costs.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a pretreatment system and process for phenol-containing wastewater to solve the problems of easy blockage of the device, high effluent COD index, poor treatment effect, high cost, etc. in the existing treatment process.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A pretreatment system for phenol-containing wastewater, comprising an inlet pipeline, a coagulation zone, a flocculation zone, a sludge sedimentation zone and an outlet tank which are sequentially connected along the flow direction of the wastewater, wherein the outlet tank is connected to the coagulation zone through a return pipeline; a first online chromaticity detector for monitoring the chromaticity value of the inlet water is arranged on the inlet pipeline, and a second online chromaticity detector for the chromaticity value of the outlet water is arranged on the outlet tank; the first online chromaticity detector and the second online chromaticity detector are both connected to a DCS remote control system, and the DCS remote control system adjusts the reflux ratio of the return pipeline according to the monitored chromaticity value of the inlet water and the chromaticity value of the outlet water.

[0009] Furthermore, the coagulation zone includes a coagulation zone A and a coagulation zone B which are interconnected; the coagulation zone A is respectively connected to the water inlet pipeline and the return pipeline, and the coagulation zone B is connected to the flocculation zone; the coagulation zone A is provided with a demulsifier addition pipeline, and the coagulation zone B is provided with a coagulant addition pipeline.

[0010] Furthermore, a first flow meter for monitoring the inlet flow is provided on the water inlet pipeline, and a second flow meter for monitoring the return flow is provided on the return pipeline; the first flow meter and the second flow meter are both connected to the DCS remote control system, and the DCS remote control system adjusts the inlet flow and the return flow through the first flow meter and the second flow meter.

[0011] In addition, the present invention also provides a pretreatment process for phenol-containing wastewater, which adopts the pretreatment system according to any one of claims 1 to 3, and comprises the following steps:

[0012] S1. Conducting online color detection on the influent of phenol-containing wastewater;

[0013] S2, after the phenol-containing wastewater is treated in the coagulation zone, flocculation zone and sludge sedimentation zone in sequence, the effluent part is returned to the coagulation zone to dilute the influent, and the chromaticity of the effluent is tested online to ensure that the chromaticity value of the effluent is less than 4000;

[0014] S3, substituting the inlet water chromaticity value and the outlet water chromaticity value into formula (1) to calculate the K value; when the outlet water chromaticity value is ≥4000, adjusting the reflux ratio to be greater than the K value, and the outlet water enters the subsequent treatment after reaching the standard;

[0015] K = (inlet water chromaticity value - 6000) ÷ (6000 - outlet water chromaticity value) formula (1).

[0016] Furthermore, after adjusting the reflux ratio to be greater than the K value, the chromaticity value of the outlet water is ≤4000.

[0017] Furthermore, part of the effluent is returned to the coagulation area to dilute the influent, and the chromaticity of the diluted wastewater = chromaticity of the influent ÷ dilution multiple.

[0018] Further, the reflux ratio is adjusted to be less than 5.

[0019] Furthermore, the coagulation treatment process includes: adding a demulsifier in the coagulation zone A to demulsify the wastewater to reduce the viscosity of the oil; then sending it to the coagulation zone B, adding a coagulant, and coagulating the wastewater.

[0020] Furthermore, in the coagulation zone A, the demulsification time is 6 to 10 minutes; in the coagulation zone B, the coagulation time is 6 to 10 minutes.

[0021] Furthermore, the flocculation time is 10 to 15 minutes.

[0022] Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects:

[0023] (1) The pretreatment system and process of phenol-containing wastewater of the present invention has a good treatment effect on phenol-containing wastewater in the petrochemical industry. The removal rate of heavy components such as sewage suspended matter and asphaltene in the wastewater can reach more than 95%, which can avoid the blockage of subsequent towers, heat exchangers and other equipment. The COD removal rate can reach more than 10%, and some difficult-to-degrade COD is removed, which is beneficial to subsequent biochemical treatment.

[0024] (2) The pretreatment process of phenol-containing wastewater of the present invention automatically controls the appropriate influent dilution ratio (automatic control of reflux ratio) through the DCS remote control system, achieving a better treatment effect. In addition, part of the reagent still exists in the effluent and is refluxed to the coagulation area for recycling, which can reduce the dosage of the reagent and reduce the operating cost.

[0025] (3) The phenol-containing wastewater pretreatment system of the present invention is simple to operate, has a short treatment time, a large amount of treated water, a small footprint, a low construction cost, and a high degree of automation, thereby achieving the purpose of saving costs and extending the service life of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0027] Figure 1 The figure is a flow chart of the pretreatment system of phenol-containing wastewater of the present invention;

[0028] Explanation of the reference numerals: 1. water inlet pipeline; 2. coagulation zone; 21. coagulation zone A; 22. coagulation zone B; 3. flocculation zone; 4. sludge sedimentation zone; 5. water outlet tank; 6. return pipeline; 11. first online colorimetric detector; 51. second online colorimetric detector; 110. first flow meter; 610. second flow meter.

[0029] Figure 2It is a linear graph showing that the chromaticity of phenol-containing wastewater is proportional to the concentration of heavy substances in the phenol-containing wastewater;

[0030] Figure 3 This is a comparison chart of the phenol-containing wastewater before and after treatment in Example 1. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0032] In the description of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, they can be fixed connections or detachable connections; they can be directly connected or indirectly connected through intermediate components. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] According to a first aspect of the present invention, Figure 1 As shown, a pretreatment system for phenol-containing wastewater is provided, comprising an inlet pipeline 1, a coagulation zone 2, a flocculation zone 3, a sludge sedimentation zone 4 and an outlet tank 5 which are sequentially connected along the flow direction of the wastewater, and the outlet tank 5 is connected to the coagulation zone 2 through a return pipeline 6; a first online chromaticity detector 11 for monitoring the chromaticity value of the inlet water is provided on the inlet pipeline 1, and a second online chromaticity detector 51 for the chromaticity value of the outlet water is provided on the outlet tank 5; the first online chromaticity detector 11 and the second online chromaticity detector 51 are both connected to a DCS remote control system, and the DCS remote control system adjusts the reflux ratio of the return pipeline according to the monitored chromaticity value of the inlet water and the chromaticity value of the outlet water.

[0034] Direct coagulation and sedimentation of phenol-containing wastewater will lead to a large proportion of sludge, difficulty in sedimentation, poor liquid fluidity, easy clogging, etc., and because the sedimentation tank is a non-closed device, the raw water is highly volatile and has a high odor toxicity, making it difficult for personnel to perform daily maintenance and operation. Therefore, this method uses the influent to mix with part of the effluent backflow, dilutes the influent in a certain proportion, and then performs coagulation and sedimentation, wherein a first flowmeter 110 for monitoring the influent flow is provided on the influent pipeline 1, and a second flowmeter 610 for monitoring the reflux flow is provided on the reflux pipeline 6; the first flowmeter 110 and the second flowmeter 610 are both connected to the DCS remote control system, and the DCS remote control system adjusts the influent flow and reflux flow through the first flowmeter 110 and the second flowmeter 610. The influent flow and reflux flow are set to proportional control, that is, the reflux ratio is automatically controlled, and the reflux ratio is automatically controlled by the influent and effluent chromaticity setting logic control, and the entire process is automatically controlled through the DCS remote control system, which improves the processing efficiency and reduces the cost.

[0035] In the above-mentioned pretreatment system for phenol-containing wastewater, as a preferred embodiment, the coagulation zone 2 specifically includes a coagulation zone A 21 and a coagulation zone B 22 that are connected in the same manner. The coagulation zone A 21 is connected to the inlet pipeline 1 and the return pipeline 6 respectively, and the coagulation zone B 22 is connected to the flocculation zone 3. The inlet water and the return liquid are mixed in the coagulation zone A 21, and the coagulation zone A 21 is provided with a demulsifier addition pipeline. The demulsifier addition amount is automatically controlled according to the inlet water volume, which is used to break the internal balance of the phenol-containing wastewater and help the subsequent precipitation; when the machine is just started, since the circulating water does not contain any demulsifier, the demulsifier dosage is relatively large at the start-up. After stable operation, part of the demulsifier is precipitated, and part of the demulsifier is still present in the effluent, which is returned to the flocculation zone for recycling, which can reduce the dosage of the agent and save operating costs.

[0036] The demulsifier used in the present invention is a conventional demulsifier, i.e., a surfactant that can destroy an emulsion. Demulsifiers mainly destroy emulsions by partially replacing the effect of stabilizing the membrane, and can also be used to reduce the viscosity of oily substances, making them less prone to clogging; preferably, the demulsifier in the present invention uses a conventional reverse demulsifier, the ratio of hydrophilic groups to hydrophobic groups in its molecular structure is biased towards hydrophobicity, and the molecules are relatively stable in the oil phase, but can be adsorbed on the surface of oil droplets in the water phase, forming a structure of "hydrophilic groups facing the oil droplets and hydrophobic groups facing outwards", thereby destroying the interaction between the oil droplets and the oil phase, and separating the oil droplets from the oil phase. Its main function is to reduce the tension of the oil-water interface, making the originally stable emulsified system unstable, and promoting the aggregation, merging and separation of the oil droplets from the water phase.

[0037] A coagulant addition pipeline is provided in coagulation zone B 22, and the addition amount is automatically controlled according to the water inflow. In practice, it is found that iron salts will combine with organic matter in sewage and become ineffective. Therefore, aluminum salts are selected as coagulants in this method to make the insoluble matter and asphaltene in the raw water clump into flocs.

[0038] The wastewater after coagulation treatment enters the flocculation tank 3, in which a guide tube is arranged, and the flocculant addition pipe extends to the bottom of the guide tube. The wastewater after flocculation reaction flows into the sludge sedimentation area 4 from the inclined wall push flow tank. The sedimentation area is an inclined tube sedimentation area. The flocs are precipitated under the action of the inclined tube and are collected by the sludge collecting bucket in the center of the sedimentation area.

[0039] According to the second aspect of the present invention, in order to further understand the pretreatment system of phenol-containing wastewater of the present invention, the present invention also provides a pretreatment process of phenol-containing wastewater, comprising the following steps:

[0040] Step 1: Performing online colorimetric detection on the influent of the phenol-containing wastewater by using a first online colorimetric detector 11;

[0041] Step 2: After the phenol-containing wastewater is treated in the coagulation zone 2, the flocculation zone 3 and the sludge sedimentation zone 4 in sequence, the effluent part is returned to the coagulation zone 2 through the reflux line 6 to dilute the influent water, and the effluent is tested for chromaticity online by the second chromaticity online detector 51 to ensure that the chromaticity value of the effluent is less than 4000;

[0042] Step 3: Substitute the real-time inlet water chromaticity value and outlet water chromaticity value monitored by the first online chromaticity detector 11 and the first online chromaticity detector 51 into formula (1) to calculate the K value; when the outlet water chromaticity value is ≥4000, adjust the reflux ratio to be greater than the K value, and enter the subsequent treatment after the outlet water meets the standard;

[0043] K = (inlet water chromaticity value - 6000) ÷ (6000 - outlet water chromaticity value) formula (1).

[0044] The pretreatment process of phenol-containing wastewater of the present invention achieves better treatment effect by automatically controlling the appropriate influent dilution ratio (i.e., automatic control of the reflux ratio), and part of the reagent still exists in the effluent and is refluxed to the coagulation zone for recycling, which can reduce the dosage of the reagent and reduce the operating cost.

[0045] The reflux ratio is mainly affected by two aspects: ① The difficulty of treating phenol-containing wastewater: Since the treated wastewater is often in a fluctuating state, when there are more heavy substances in the wastewater, the treatment is difficult and the required dilution ratio is high, and vice versa. The content of heavy substances (asphaltene and some insoluble matter) can be characterized by the chromaticity of the influent; ② The treatment effect of the current operating conditions: It is affected by the current dosage, quality of the reagents and the actual treatment effect under the environment. The better the treatment effect, the higher the removal rate of heavy substances, and vice versa. The actual treatment effect can be characterized by the chromaticity of the effluent.

[0046] For phenol-containing wastewater in petrochemical industry, when the chromaticity of raw water is 10000, the raw water is diluted to test the chromaticity. Through the test, it is known that the chromaticity of the diluted wastewater = the chromaticity of raw water ÷ the dilution factor, that is, the chromaticity of phenol-containing wastewater is proportional to the concentration of heavy substances in the phenol-containing wastewater. The linear relationship between the two is shown in the attached figure. Figure 2 As shown; Assuming that the raw water concentration is 1, the test results are shown in Table 1 below:

[0047] Table 1

[0048] Dilution multiple concentration Detection of color 10 0.1 993 5 0.2 2022 4 0.25 2561 3 0.33 3297 2 0.5 5031 1 1.0 10000

[0049] The physical and chemical properties of the treated effluent are similar to those of the influent. The mixing of the chromaticity of the influent and effluent is a mixing of concentrations, and the actual chromaticity after mixing is also the same. That is, the chromaticity after mixing = (influent flow × influent chromaticity + return flow × effluent chromaticity) ÷ (influent flow + return flow);

[0050] Reflux ratio = reflux flow rate ÷ inlet flow rate;

[0051] From this we can see that the chromaticity after mixing = (inlet water chromaticity + reflux ratio × outlet water chromaticity) ÷ (reflux ratio + 1).

[0052] A lot of practice has proved that the demulsification effect is better when the chromaticity of the mixed inlet water and return water is below 6000. When the chromaticity is greater than 6000, the demulsifier does not work and the difficulty of water treatment increases. Therefore, the operation requirement is set as: the chromaticity of the mixed inlet water and return water is less than 6000, that is, the return ratio is greater than (inlet water chromaticity value - 6000) ÷ (6000 - outlet water chromaticity value).

[0053] Considering experience and cost, the reflow ratio should not be too large. If it is too large, it will exceed the water design load. The reflow ratio should be adjusted to <5, that is: (inlet water chromaticity - 6000) ÷ (6000 - outlet water chromaticity) < reflow ratio < 5.

[0054] If the calculated (inlet water chromaticity - 6000) ÷ (6000 - outlet water chromaticity) is greater than 5, it is considered an abnormal situation and the reflux ratio automatic control needs to be disabled and recirculated water needs to be added to dilute the inlet water. After the system stabilizes, the reflux ratio automatic control can be put back into use.

[0055] When the system is just started, there is no effluent water, so there is no reflux water. Therefore, the incoming water is first diluted with circulating water. The chromaticity of the circulating water can be basically considered to be 0. Therefore, after mixing and dilution, it can basically meet the requirement of 6000 chromaticity of the incoming water. Since the chromaticity of the incoming water is about 10,000, the circulating water can be operated at a lower reflux ratio when diluting. Based on experience, the reflux ratio is initially set at 3. Under this condition, the chromaticity of the outlet water is very low, at 1000-2000, and there is no need to use the reflux ratio automatic control; when the outlet water tank reaches a certain liquid level, the outlet water can be used as the reflux dilution liquid. In the initial stage, the circulating water still accounts for a large proportion. When the reflux ratio is 3, it can still be used. Meet the requirement of effluent chromaticity < 4000; as the circulating water is gradually discharged, when the effluent chromaticity reaches 4000, the automatic control can be used, and the reflux ratio will be gradually increased to maintain the effluent chromaticity at 4000; the effluent chromaticity is controlled within 4000, and the impurities (asphaltene and some insoluble matter) are basically removed: after the influence of the final circulating water is completely eliminated, the system reaches a steady state and the reflux ratio reaches a stable value; during stable operation, as the influent water quality fluctuates, the reflux ratio is adjusted accordingly, that is, when the water quality is good, the reflux ratio is low, saving operating costs, and when the water quality is poor, the reflux ratio is high, and the treatment needs are met through automatic control of the reflux ratio.

[0056] In the above-mentioned pretreatment process, as a preferred embodiment, the coagulation treatment process includes: adding a demulsifier in the coagulation zone A 21 to demulsify the wastewater to reduce the viscosity of the oil; then sending it to the coagulation zone B 22, adding a coagulant, and coagulating the wastewater.

[0057] In the above-mentioned pretreatment process, as a preferred embodiment, in the coagulation zone A 21, the demulsification time is 6 to 10 minutes (for example, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes); in the coagulation zone B 22, the coagulation time is 6 to 10 minutes (for example, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes).

[0058] Optionally, the flocculation time is 10 to 15 min (e.g., 10 min, 11 min, 12 min, 13 min, 14 min, 15 min).

[0059] The present invention will be described in detail below in conjunction with embodiments of the present invention, and each example is provided by way of explanation of the present invention without limiting the present invention. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as a part of an embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present invention includes such modifications and variations within the scope of the appended claims and their equivalents.

[0060] In the embodiments of the present invention, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0061] Example 1

[0062] This embodiment provides a pretreatment process for phenol-containing wastewater. The experimental object is a phenol-containing wastewater from a company in Shaanxi Province. The COD of the wastewater is about 100,000 mg / L and the chromaticity is about 11,000. The water is dark brown and very turbid. At the beginning of the operation, the reflux dilution is performed by 5 times, that is, the reflux ratio is 4. At the beginning of the operation, the chromaticity control dilution ratio (reflux ratio automatic control) is not used because the chromaticity of the circulating water is low.

[0063] In the first part of the coagulation zone, the dosage of demulsifier is 50 mg / L, and the rapid stirring is 8 minutes; in the second part of the coagulation zone, the dosage of coagulant PAC is 100 mg / L, and the rapid stirring is 8 minutes; the dosage of PAM in the flocculation zone is 3 mg / L, and the slow stirring time is 12 minutes; in the sedimentation zone, the mud and water are separated rapidly, the clear water flows upward, and enters the water outlet tank through the inclined pipe separation and the water collection tank, and the sludge sinks downward, and the sludge is concentrated by the thickening scraper and then discharged;

[0064] When the liquid level in the outlet pipe rises to 30%, the circulating water pipeline is closed, and the outlet water replaces the circulating water as the diluent. When the liquid level rises to 50%, the outlet water is discharged to control the liquid level at 30-50%. As the outlet water gradually flows back, the outlet water chromaticity gradually increases. When it rises to 4000, the chromaticity reflux ratio is automatically controlled. As the influence of the circulating water decreases, the reflux ratio gradually increases to maintain the outlet water chromaticity at 4000. After it stabilizes, the reflux ratio is 4.3.

[0065] After stable operation, part of the demulsifier is precipitated, and part of the demulsifier is still present in the effluent and returned to the flocculation area for recycling. The demulsifier dosage is adjusted to 30 mg / L.

[0066] The final effluent COD is 89300mg / L, and the COD removal rate is 10.7%. With the removal of difficult-to-treat heavy substances, the effluent COD is about 4000mg / L after subsequent combined treatment of deacidification and deammoniation, extraction and oil removal, and recovery of residual extractant in water, meeting the subsequent biochemical sewage treatment influent standards. Figure 3 The changes in the appearance of phenol-containing wastewater before and after treatment. The device used to need to be shut down for maintenance every two months. After changing to this method, it has been running stably for 6 months without any abnormal blockage.

[0067] Comparative Example 1

[0068] The conventional process was used for treatment, and the experimental object was the same as that in Example 1. Demulsifier was added, that is, the storage tank was allowed to settle → oil-water separator → multi-stage filter, and a reaction tank was set in front of the storage tank, demulsifier was added to the tank, and the mixture was stirred for reaction. During the operation, the treatment effect was the same as that of the old process, and frequent maintenance and clearing were required.

[0069] Comparative Example 2

[0070] This comparative example provides a pretreatment process for phenol-containing wastewater, and the remaining step parameters are the same as those in Example 1, except that no demulsifier is added. During operation, the COD removal rate is low, and circulating water needs to be frequently added for dilution, resulting in high operating costs.

[0071] Comparative Example 3

[0072] This comparative example provides a pretreatment process for phenol-containing wastewater, and the remaining step parameters are the same as those in Example 1, except that the effluent is not refluxed and the influent is not diluted. During operation, the odor is strong, and it is difficult for personnel to operate. In addition, due to the poor fluidity of the liquid, the agitators in the coagulation zone and flocculation zone are severely coked, the precipitation effect is poor, and it cannot be operated.

[0073] Comparative Example 4

[0074] This comparative example provides a pretreatment process for phenol-containing wastewater, and the remaining step parameters are the same as those in Example 1, except that: the chromaticity reflux ratio is not automatically controlled, but the reflux ratio is fixed at 4. During the operation, the chromaticity of the effluent fluctuates continuously. When the water quality is good, the chromaticity of the effluent is low. When the water quality is poor, it cannot be adjusted in time, which easily leads to blockage of the back end.

[0075] The relevant indicators and operating conditions of the effluent water quality of Example 1 and Comparative Examples 1-4 are shown in Table 2:

[0076] Table 2

[0077]

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pretreatment system for phenol-containing wastewater, characterized in that: It includes an inlet pipeline, a coagulation zone, a flocculation zone, a sludge sedimentation zone and an outlet tank which are sequentially connected along the flow direction of the wastewater, and the outlet tank is connected to the coagulation zone through a return pipeline; the inlet pipeline is provided with a first online chromaticity detector for monitoring the chromaticity value of the inlet water, and the outlet tank is provided with a second online chromaticity detector for the chromaticity value of the outlet water; the first online chromaticity detector and the second online chromaticity detector are both connected to a DCS remote control system, and the DCS remote control system adjusts the reflux ratio of the return pipeline according to the monitored inlet chromaticity value and outlet chromaticity value.

2. The pretreatment system according to claim 1, characterized in that: The coagulation zone includes a coagulation zone A and a coagulation zone B which are interconnected; the coagulation zone A is respectively connected to a water inlet pipeline and a return pipeline, and the coagulation zone B is connected to a flocculation zone; the coagulation zone A is provided with a demulsifier addition pipeline, and the coagulation zone B is provided with a coagulant addition pipeline.

3. The pretreatment system according to claim 1, characterized in that: The water inlet pipeline is provided with a first flow meter for monitoring the water inlet flow, and the return pipeline is provided with a second flow meter for monitoring the return flow; the first flow meter and the second flow meter are both connected to the DCS remote control system, and the DCS remote control system adjusts the water inlet flow and the return flow through the first flow meter and the second flow meter.

4. A pretreatment process for phenol-containing wastewater, characterized in that: The pretreatment system according to any one of claims 1 to 3 is used, comprising the following steps: S1. Conducting online color detection on the influent of phenol-containing wastewater; S2, after the phenol-containing wastewater is treated in the coagulation zone, flocculation zone and sludge sedimentation zone in sequence, the effluent part is returned to the coagulation zone to dilute the influent, and the chromaticity of the effluent is tested online to ensure that the chromaticity value of the effluent is less than 4000; S3, substituting the inlet water chromaticity value and the outlet water chromaticity value into formula (1) to calculate the K value; when the outlet water chromaticity value is ≥4000, adjusting the reflux ratio to be greater than the K value, and the outlet water enters the subsequent treatment after reaching the standard; K = (inlet water chromaticity value - 6000) ÷ (6000 - outlet water chromaticity value) formula (1).

5. The pretreatment process according to claim 4, characterized in that: After adjusting the reflux ratio to be greater than the K value, the chromaticity value of the outlet water is ≤4000.

6. The pretreatment process according to claim 4, characterized in that: Part of the effluent flows back to the coagulation area to dilute the influent. The chromaticity of the diluted wastewater = chromaticity of the influent ÷ dilution multiple.

7. The pretreatment process according to claim 4, characterized in that: Adjust the reflux ratio to <5.

8. The pretreatment process according to claim 4, characterized in that: The coagulation treatment process includes: adding demulsifier in coagulation zone A to demulsify the wastewater to reduce the viscosity of the oily matter; then sending it to coagulation zone B to add coagulant to coagulate the wastewater.

9. The pretreatment process according to claim 7, characterized in that: In coagulation zone A, the demulsification time is 6 to 10 minutes; in coagulation zone B, the coagulation time is 6 to 10 minutes.

10. The pretreatment process according to claim 4, characterized in that: The flocculation time is 10 to 15 minutes.

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