A method and apparatus for treating petrochemical wastewater

Abstract

The present application relates to a kind of method and device for treating petrochemical wastewater, and petrochemical wastewater is sequentially subjected to pretreatment unit, biochemical unit and phosphorus removal precipitation unit after oil removal, wherein pretreatment unit adopts softening-coagulation-sedimentation treatment, so that calcium hardness is 60-200mg / L;Biochemical unit adopts A2O pool-cyclone-MBR pool treatment, A2O pool effluent enters cyclone, and underflow port discharge of cyclone enters MBR pool, and separated sludge returns A pool, and water production enters phosphorus removal precipitation unit treatment.The method of the present application avoids the problem of MBR membrane pollution, improves the phosphorus removal effect, and at the same time improves the treatment effect of COD, ammonia nitrogen and total nitrogen.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water pollution treatment, and particularly relates to a method and device for treating petrochemical wastewater. BACKGROUND

[0002] The petrochemical industry is an important part of China's economic and social development, but it is also one of the industries that have a greater impact on the environment. A large amount of wastewater is generated in the production process of petrochemical products. These wastewaters usually contain a large amount of petroleum, long-chain hydrocarbons, organic acids, alcohols, aromatic compounds and other difficult-to-degrade organic matter, and also contain inorganic matter such as sulfides, cyanides, nitrogen and phosphorus that are harmful to the environment. At the same time, the wastewater has the characteristics of high salinity and large water quality fluctuations. With the promulgation of the new pollutant discharge standard for the petrochemical industry (GB 31571-2015), the emission limits of pollutants such as COD, ammonia nitrogen, total nitrogen and total phosphorus in wastewater have been further improved. Therefore, for most petrochemical wastewater treatment plants, the original wastewater treatment process has been unable to meet the new emission standards.

[0003] Solid / Liquid Separation Membrane Bioreactor (SLSMBR) is a water treatment technology that uses membrane separation process to replace the secondary sedimentation tank in the traditional activated sludge process. It has the advantages of improving solid-liquid separation efficiency, improving biological concentration, realizing complete separation of hydraulic retention time and sludge age, being conducive to the retention and growth of nitrogen-fixing bacteria, nitrifying bacteria and difficult-to-degrade organic matter decomposing bacteria, reducing land occupation, resisting impact, being easy to transform from traditional biochemical units, etc. The Anaerobic-Anoxic-Oxic (A2O) process is one of the most widely used wastewater treatment processes at present. Therefore, the A2O-MBR process is becoming mature and is gradually being applied to wastewater treatment in various industries. However, the A2O-MBR process still has the problems of limited phosphorus removal capacity and membrane fouling.

[0004] CN107759018A discloses a sewage advanced treatment system, which comprises a biochemical treatment device for a traditional biochemical treatment process, an adsorption flocculation tank, an MBR tank and an adsorption tower connected by pipelines in sequence after the sewage discharge outlet of the biochemical treatment device; the MBR tank is provided with an MBR membrane box and an aeration system, and the sludge discharge outlet of the MBR tank is connected with a sludge return pump through a sludge return pipeline; one way of the output end of the sludge return pump is connected to the biochemical treatment device, and the other way is connected to a sludge thickening tank; the sludge discharge outlet of the adsorption flocculation tank is connected to the sludge thickening tank through a pipeline; and the backwashing water outlet of the adsorption tower is connected to the biochemical treatment device through a pipeline. The invention adopts the adsorption flocculation tank, the MBR and the adsorption tank connected in sequence to remove total phosphorus, total nitrogen, ammonia nitrogen, COD, SS and other pollutants in the water body after the sewage treated by the traditional biochemical process, so as to achieve a higher discharge standard. The invention directly connects the advanced treatment unit after the existing biochemical unit, does not improve the treatment capacity of the existing biochemical unit, and causes a long subsequent process; and the integrated MBR is used for membrane biological treatment, although the aeration system is provided, but the MBR membrane still has the pollution problem.

[0005] CN211595188U discloses a parallel AAO-MBR reactor, which comprises an aerobic zone, an anaerobic zone, an anoxic zone and a sludge-water separator, the anaerobic zone and the anoxic zone are respectively provided with a sewage inlet, the aerobic zone is provided with an MBR membrane assembly, and the bottom of the aerobic zone is provided with a microporous aeration device; the outlet of the anaerobic zone and the outlet of the anoxic zone are in communication with the aerobic zone; the reactor further comprises a reflux pump for pumping the mixed liquid in the aerobic zone into the sludge-water separator, the sludge outlet of the sludge-water separator is in communication with the anaerobic zone, and the water outlet of the sludge-water separator is in communication with the anoxic zone. The patent reduces the reactor volume while ensuring the denitrification and phosphorus removal effect of the sewage system, although the microporous aeration is used, but the pollution problem of the MBR membrane still exists.

[0006] Extracellular polymeric substances (EPS) are some high molecular polymers secreted by microorganisms, mainly bacteria, outside the body under certain environmental conditions. The main components are similar to the intracellular components of microorganisms, which are some high molecular substances such as polysaccharides, proteins and nucleic acids. Due to the increase of biomass, the amount of extracellular polymeric substances increases in the traditional A2O-MBR treatment process, so the pollution of the MBR membrane is more likely to occur, which reduces the water flux, increases the operation cost of water production and aeration, and reduces the service life of the membrane. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a method and device for treating petrochemical wastewater. The method of the present application avoids membrane fouling problems, improves the removal efficiency of phosphorus, and at the same time improves the COD, ammonia nitrogen and total nitrogen treatment capacity of the primary treatment unit.

[0008] The present application provides a method for treating petrochemical wastewater, which mainly comprises the following contents:

[0009] The oil-removed petrochemical wastewater is sequentially subjected to a pretreatment unit, a biochemical unit and a phosphorus removal and precipitation unit. The pretreatment unit adopts softening-coagulation-precipitation treatment, so that the calcium hardness is 60-200 mg / L. The biochemical unit adopts A2O tank-cyclone-MBR tank treatment, the effluent of the A2O tank enters the cyclone, the underflow of the cyclone enters the MBR tank, the separated sludge returns to the A tank, and the produced water enters the phosphorus removal and precipitation unit for treatment.

[0010] In the method of the present application, the petrochemical wastewater mainly comes from the wastewater generated in the production process of petrochemical products, and usually contains main pollutants such as petroleum, COD, ammonia nitrogen and phosphorus. In the oil-removed petrochemical wastewater, the COD is generally 300-1400 mg / L, the ammonia nitrogen concentration is 50-400 mg / L, the total nitrogen concentration is 60-450 mg / L, the phosphorus concentration is 0.5-5 mg / L, the petroleum is 0-20 mg / L, and the total hardness (in terms of CaCO3, the same below) is 400-1500 mg / L, of which the calcium hardness is 250-1200 mg / L.

[0011] In the method of the present application, the pretreatment unit adopts softening-coagulation-precipitation treatment, which can be carried out in a conventional reaction tank such as a high-density clarifier. The high-density clarifier is provided with a dosing device, and the softening agent and the coagulant are added to complete the treatment. The softening agent can be one or more of calcium hydroxide, sodium hydroxide, sodium carbonate, etc., and the amount of the softening agent is to make the pH value in the range of 10-10.5. The coagulant is an iron ion flocculant, specifically at least one of ferric chloride, ferric sulfate, polymeric ferric chloride, polymeric ferric sulfate, etc., preferably polymeric ferric chloride or / and polymeric ferric sulfate, and the coagulant is added in an amount of 10-200 mg / L, preferably 20-100 mg / L.

[0012] In the method of the present application, after pretreatment, the total hardness of the wastewater is less than 400 mg / L, and the calcium hardness is controlled in the range of 60-200 mg / L, preferably 80-150 mg / L.

[0013] In the method of the present application, the pH of the pretreated wastewater is adjusted to 7-8 before entering the biochemical unit. Inorganic acid or the like can be used for adjustment, such as at least one of sulfuric acid, hydrochloric acid, etc.

[0014] In the method, the A2O tank is a conventional anaerobic-anoxic-aerobic tank combination, wherein the bottom digestion liquid of the O tank is backflowed to the anoxic tank, and the backflow ratio is 100%-400%; the effluent of the O tank is fed into a cyclone. The treatment conditions of the A tank are as follows: the dissolved oxygen is controlled below 0.5 mg / L, the temperature is 25-35 DEG C, and the pH is 7-9; the treatment conditions of the O tank are as follows: the dissolved oxygen is controlled at 1-3 mg / L, the temperature is 25-35 DEG C, and the pH is 8-9.

[0015] In the method, the cyclone preferably adopts a hydrocyclone, and the cone angle is 6-10 degrees. The discharge of the overflow port of the cyclone accounts for 2%-10% of the total feed volume into the cyclone.

[0016] In the method, the MBR tank adopts a solid-liquid separation type MBR membrane-biological reactor, the membrane adopts a microfiltration membrane, the membrane hole diameter is 2-10 μm, and preferably 5-7 μm. The membrane material can adopt any one of inorganic ceramic membranes, polypropylene, polytetrafluoroethylene, etc. A plate type membrane or a curtain type membrane assembly is selected, a water production pump, a backwashing water pump, a dosing device, a liquid level meter and a pressure gauge are arranged, and an aeration unit can also be arranged on the basis of the backwashing water pump.

[0017] In the method, a precipitant is added in the phosphorus removal and precipitation unit, and the precipitant is at least one of ferric chloride, ferrous chloride, alum, aluminum chloride, ferric sulfate, ferrous sulfate, polymeric ferric sulfate, polyaluminum chloride, etc., and preferably at least one of ferric chloride, ferric sulfate, polymeric ferric sulfate, etc. The addition amount is 2.5-70 mg / L, and preferably 5-50 mg / L.

[0018] In the method, the sludge discharged from the phosphorus removal and precipitation unit and the overflow port discharge of the cyclone are sent to a sludge treatment unit. The activated sludge which has been deflocculated or has most of the EPS removed is discharged into the sludge treatment unit, so that the amount of conditioning agents can be reduced.

[0019] The application also provides a treatment device for the above-mentioned treatment method of petrochemical wastewater, which mainly comprises a pretreatment unit, a biochemical unit and a phosphorus removal and precipitation unit. The pretreatment unit adopts softening-coagulation-precipitation treatment, is mainly carried out in a high-density tank, and is used for pretreating the petrochemical wastewater after oil removal. The biochemical unit comprises an A2O tank-cyclone-MBR tank, part of the effluent of the A2O tank is fed into the cyclone, the overflow port discharge of the cyclone is fed into the MBR tank, the separated sludge is returned to the A tank, and the produced water is fed into the phosphorus removal and precipitation unit. The phosphorus removal and precipitation unit mainly comprises a precipitation tank, a precipitant is added, and the effluent of the biochemical unit is subjected to deep treatment.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] (1) reduced the MBR membrane pollution. EPS is one of the important factors leading to membrane pollution, which is mainly composed of polysaccharides and proteins, and polysaccharides can complex with Ca ions to form larger polymers, which are easy to cause membrane pollution. The application controls the hardness removal degree before the A2O tank, controls the EPS generation amount in the A2O tank, and relies on the cyclone sorting method, which not only can maintain the properties of activated sludge particles, but also can avoid the complexation of polysaccharides and metal ions, reduce the EPS content in the sludge, and finally realize the selective separation of activated sludge particles and cell metabolites through MBR membrane separation, so that EPS is not intercepted in the MBR tank, and the MBR membrane pollution is reduced.

[0022] (2) improved the phosphorus removal capacity of the A2O-MBR process. In the traditional A2O process, the phosphorus-accumulating bacteria release phosphorus in the anaerobic zone and absorb excess phosphorus in the aerobic zone, and the MBR tank is backflowed to the anaerobic zone to enrich phosphorus to achieve phosphorus removal. However, the MBR tank also introduces dissolved oxygen and denitrifying bacteria into the anaerobic zone at the same time, which affects the release of phosphorus-accumulating bacteria in the anaerobic zone, and further affects the phosphorus removal effect. The application combines the cyclone sorting and MBR membrane separation methods to selectively separate activated sludge particles and part of EPS, which reduces the EPS in the backflow sludge, and further improves the phosphorus removal capacity of the biochemical unit.

[0023] (3) The precipitant is added in the phosphorus removal and precipitation unit, and a large amount of EPS and precipitants in the wastewater separated by the MBR membrane interact with each other, so that iron phosphate, cell metabolites and suspended solids are precipitated together, achieving the effect of simultaneous removal of COD, SS and TP. In addition, the use amount of the reagent can also be reduced by using the adsorption and flocculation properties of EPS.

[0024] (4) The process flow of the application can efficiently treat COD, ammonia nitrogen, total nitrogen, total phosphorus and SS in petrochemical wastewater, especially avoiding membrane pollution and reducing operation cost. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a process flow chart of the petrochemical wastewater treatment of the application. DETAILED DESCRIPTION

[0026] The method and effect of the application will be further described in detail by the following examples. The examples are implemented on the premise of the technical scheme of the application, and detailed implementation methods and specific operation processes are given, but the protection scope of the application is not limited to the following examples.

[0027] The experimental methods in the following examples are conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are purchased from conventional biochemical reagent stores unless otherwise specified.

[0028] The application is used in petrochemical wastewater treatmentFigure 1 The flow and device shown carry out treatment, and the wastewater is treated through a pretreatment unit, a biochemical unit and a phosphorus removal and precipitation unit. The pretreatment unit adopts a high-density pool to carry out softening-coagulation-precipitation treatment, mainly in the high-density pool, and is used for pretreating the petrochemical wastewater after oil removal; the biochemical unit adopts an A2O pool-cyclone-MBR pool treatment, the effluent of the A2O pool enters the cyclone, the underflow of the cyclone is discharged into the MBR pool, the sludge separated by the MBR pool is returned to the A pool, and the produced water enters the phosphorus removal and precipitation unit; the phosphorus removal and precipitation unit mainly includes a precipitation tank, and a precipitant is added to carry out deep treatment on the effluent of the biochemical unit. The sludge discharged from the phosphorus removal and precipitation unit and the overflow of the cyclone are sent to a sludge treatment unit.

[0029] In the present application, the COD concentration is determined by GB11914-89 "Determination of Chemical Oxygen Demand in Water - Dichromate Method", the ammonia nitrogen concentration is determined by GB7478-87 "Determination of Ammonium in Water - Distillation and Titration Method", the total nitrogen concentration is determined by GB11894-89 "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry", the total phosphorus is determined by GB11893-1989 "Ammonium Molybdate Spectrophotometry", the petroleum is determined by HJ637-2018 "Determination of Petroleum and Animal and Vegetable Oils in Water - Infrared Spectrophotometry", the total hardness is measured by GB7477-1987 "Determination of Total Calcium and Magnesium - EDTA Titration Method", and the calcium hardness is measured by GB7476-1987 "Determination of Calcium - EDTA Titration Method".

[0030] Example 1

[0031] The petrochemical wastewater generated by a petrochemical enterprise after oil removal treatment has the following water quality: COD is 750 mg / L, ammonia nitrogen is 60 mg / L, total nitrogen is 80 mg / L, total phosphorus is 3.5 mg / L, petroleum is 5.0 mg / L, total hardness is 600 mg / L, and calcium hardness is 520 mg / L.

[0032] The pretreatment unit adopts softening-coagulation-precipitation treatment: in the high-density pool, the softening agent is sodium hydroxide, the pH of the wastewater is controlled at about 10.5, and the coagulant is polymeric ferric sulfate, and the dosage is 40 mg / L. After pretreatment, the wastewater has the following water quality: COD is 700 mg / L, total hardness is 280 mg / L, calcium hardness is 150 mg / L, and the content of other substances changes little. A dosing device is arranged at the end of the high-density pool, and sulfuric acid is added to adjust the pH of the wastewater to 7-8.

[0033] The biochemical unit adopts A2O tank-hydrocyclone-MBR tank treatment: the digestion liquid at the bottom of the O tank is refluxed to the anoxic tank, and the reflux ratio is 200%; the effluent of the O tank is fed into the hydrocyclone. The treatment conditions of the A tank are as follows: the dissolved oxygen is controlled below 0.5 mg / L, the temperature is 30°C, and the pH is 7.5; the treatment conditions of the O tank are as follows: the dissolved oxygen is controlled at 2 mg / L, the temperature is 30°C, and the pH is 8. The hydrocyclone adopts a hydrocyclone with a cone angle of 8 degrees, and the discharge of the overflow port of the hydrocyclone accounts for 3% of the total feed volume into the hydrocyclone. The MBR tank adopts inorganic ceramic membrane, and the membrane hole diameter is 7 μm. After biochemical treatment, the water quality of the MBR tank is as follows: COD is 60 mg / L, ammonia nitrogen is 0.8 mg / L, total nitrogen is 25 mg / L, total phosphorus is 3.0 mg / L, petroleum is 0.51 mg / L, total hardness is 150 mg / L, and calcium hardness is 90 mg / L. The maintenance cleaning is carried out once a week, and the intensive chemical cleaning is carried out once every 9-10 months.

[0034] The phosphorus precipitation unit is carried out in the sedimentation tank: the precipitant is added, 12 mg / L of ferric chloride and 1 mg / L of polyaluminum chloride are added. The water quality after treatment is as follows: COD is 40 mg / L, ammonia nitrogen is 1.9 mg / L, total nitrogen is 24 mg / L, total phosphorus is 0.4 mg / L, petroleum is 0.45 mg / L, total hardness is 147 mg / L, and calcium hardness is 89 mg / L.

[0035] Example 2

[0036] The petrochemical wastewater is treated in the same way as in Example 1.

[0037] The pretreatment unit adopts softening-coagulation-sedimentation treatment: in the high-density tank, the softener is sodium hydroxide, the pH of the wastewater is controlled at about 10, the coagulant is polymeric ferric sulfate, and the addition amount is 40 mg / L. The water quality of the wastewater after pretreatment is as follows: COD is 710 mg / L, total hardness is 380 mg / L, calcium hardness is 180 mg / L, and the contents of other substances change little. A dosing device is arranged at the end of the high-density tank, and sulfuric acid is added to adjust the pH of the wastewater to 7-8.

[0038] The biochemical unit adopts A2O tank-hydrocyclone-MBR tank treatment: the bottom digestion liquid of O tank is refluxed to the anoxic tank, and the reflux ratio is 300%; the O tank effluent enters the hydrocyclone. The treatment conditions of A tank are as follows: the dissolved oxygen is controlled below 0.5 mg / L, the temperature is 25°C, and the pH is 7; the treatment conditions of O tank are as follows: the dissolved oxygen is controlled at 1 mg / L, the temperature is 25°C, and the pH is 8. The hydrocyclone adopts a hydrocyclone, the cone angle is 8 degrees, and the discharge of the overflow port of the hydrocyclone accounts for 5% of the total feed volume entering the hydrocyclone. The MBR tank adopts inorganic ceramic membrane, and the membrane hole diameter is 5 μm. After biochemical treatment, the MBR tank produces water with the following quality: COD is 55 mg / L, ammonia nitrogen is 3.5 mg / L, total nitrogen is 30 mg / L, total phosphorus is 2.6 mg / L, petroleum is 0.48 mg / L, total hardness is 180 mg / L, and calcium hardness is 100 mg / L. Maintenance cleaning is carried out once a week, and intensive chemical cleaning is carried out once every 9-10 months.

[0039] The phosphorus precipitation unit is carried out in the sedimentation tank: 13.5 mg / L of ferric chloride and 1 mg / L of polyaluminum chloride are added as precipitants. The water quality after treatment is as follows: COD is 45 mg / L, ammonia nitrogen is 3.3 mg / L, total nitrogen is 29 mg / L, total phosphorus is 0.5 mg / L, petroleum is 0.44 mg / L, total hardness is 175 mg / L, and calcium hardness is 98 mg / L.

[0040] Example 3

[0041] The petrochemical wastewater is treated in the same way as in Example 1.

[0042] The pretreatment unit adopts softening-coagulation-sedimentation treatment: in the high-density tank, the softener is sodium hydroxide, the pH of the wastewater is controlled at about 10.5, and the coagulant is polyaluminum chloride, and the dosage is 40 mg / L. The wastewater quality after pretreatment is as follows: COD is 705 mg / L, total hardness is 285 mg / L, calcium hardness is 155 mg / L, and the contents of other substances change little. A dosing device is provided at the end of the high-density tank to adjust the pH of the wastewater to 7-8 by adding sulfuric acid.

[0043] Biochemical unit adopts A2O tank-cyclone-MBR tank treatment: O tank bottom digestion liquid refluxes to anoxic tank, reflux ratio is 400%; O tank effluent enters cyclone. A tank treatment condition is: dissolved oxygen is controlled below 0.5 mg / L, temperature is 35°C, pH is 8; O tank treatment condition is: dissolved oxygen is controlled at 3 mg / L, temperature is 35°C, pH is 8.5. Cyclone adopts hydraulic cyclone, cone angle is 8 degrees, control cyclone overflow port discharge accounts for 2% of total feed volume entering cyclone. MBR tank adopts inorganic ceramic membrane, membrane hole diameter is 10 μm. After biochemical treatment, MBR tank water quality is: COD is 70 mg / L, ammonia nitrogen is 1.3 mg / L, total nitrogen is 36 mg / L, total phosphorus is 3.3 mg / L, petroleum is 0.58 mg / L, total hardness is 153 mg / L, calcium hardness is 92 mg / L. Maintenance cleaning is carried out once a week, intensive chemical cleaning is carried out once every 10-12 months.

[0044] Phosphorus precipitation unit is carried out in a sedimentation tank: 16 mg / L polymeric ferric sulfate is added as a precipitant. After treatment, the water quality is: COD is 53 mg / L, ammonia nitrogen is 4.8 mg / L, total nitrogen is 35 mg / L, total phosphorus is 0.4 mg / L, petroleum is 0.49 mg / L, total hardness is 146 mg / L, calcium hardness is 88 mg / L.

[0045] Example 4

[0046] The wastewater is treated and the treatment process is the same as in Example 1, except that: the softener is calcium hydroxide and sodium carbonate with a mass ratio of 1:2, and the pH of the wastewater is controlled at about 10.5; the coagulant is ferric chloride, and the dosage is 60 mg / L. After pretreatment, the wastewater quality is: COD is 713 mg / L, total hardness is 310 mg / L, calcium hardness is 198 mg / L, and other substance contents change little.

[0047] After biochemical treatment, the MBR tank water quality is: COD is 57 mg / L, ammonia nitrogen is 0.5 mg / L, total nitrogen is 26 mg / L, total phosphorus is 2.8 mg / L, petroleum is 0.46 mg / L, total hardness is 182 mg / L, calcium hardness is 105 mg / L. Maintenance cleaning is carried out once a week, intensive chemical cleaning is carried out once every 8-9 months.

[0048] After adding the precipitant, the water quality is: COD is 48 mg / L, ammonia nitrogen is 0.5 mg / L, total nitrogen is 23 mg / L, total phosphorus is 0.4 mg / L, petroleum is 0.35 mg / L, total hardness is 170 mg / L, calcium hardness is 95 mg / L.

[0049] Example 5

[0050] The wastewater treatment and process are the same as in Example 1, except that the cone angle of the hydrocyclone is 6 degrees and the discharge from the overflow port of the hydrocyclone is controlled to account for 10% of the total feed volume into the hydrocyclone.

[0051] After biological treatment, the permeate water quality of the MBR tank is as follows: COD 68 mg / L, ammonia nitrogen 5.0 mg / L, total nitrogen 30 mg / L, total phosphorus 3.2 mg / L, petroleum hydrocarbons 0.38 mg / L, total hardness 160 mg / L, and calcium hardness 95 mg / L. A maintenance cleaning is performed weekly, and an intensive chemical cleaning is performed every 8-9 months of operation.

[0052] After phosphorus removal and precipitation treatment, the water quality was as follows: COD 42 mg / L, ammonia nitrogen 4.7 mg / L, total nitrogen 28 mg / L, total phosphorus 0.4 mg / L, petroleum hydrocarbons 0.42 mg / L, total hardness 150 mg / L, and calcium hardness 93 mg / L.

[0053] Example 6

[0054] The wastewater treatment and process are the same as in Example 1, except that the MBR tank uses a polypropylene membrane with a pore diameter of 5 μm.

[0055] After biological treatment, the permeate water quality of the MBR tank is as follows: COD 58 mg / L, ammonia nitrogen 0.5 mg / L, total nitrogen 24 mg / L, total phosphorus 2.7 mg / L, petroleum hydrocarbons 0.44 mg / L, total hardness 153 mg / L, and calcium hardness 88 mg / L. A maintenance cleaning is performed weekly, and an intensive chemical cleaning is performed every 8-9 months of operation.

[0056] After phosphorus removal and precipitation treatment, the water quality is as follows: COD 42 mg / L, ammonia nitrogen 0.5 mg / L, total nitrogen 25 mg / L, total phosphorus 0.3 mg / L, petroleum hydrocarbons 0.43 mg / L, total hardness 152 mg / L, and calcium hardness 82 mg / L.

[0057] Example 7

[0058] The wastewater treatment process is the same as in Example 1, except that ferrous sulfate is used as the precipitant. After phosphorus removal and precipitation treatment, the water quality is as follows: COD 46 mg / L, ammonia nitrogen 0.9 mg / L, total nitrogen 24 mg / L, total phosphorus 0.5 mg / L, petroleum hydrocarbons 0.39 mg / L, total hardness 148 mg / L, and calcium hardness 88 mg / L.

[0059] Comparative Example 1

[0060] Similar to Example 1, except that no hardness control was performed, and the pH was adjusted to 11.5. The pretreated wastewater quality was as follows: COD approximately 720 mg / L, total hardness approximately 100 mg / L, calcium hardness approximately 55 mg / L, and the content of other substances remained largely unchanged.

[0061] After biochemical treatment, the water quality produced by the MBR tank is: COD 80 mg / L, ammonia nitrogen 8.0 mg / L, total nitrogen 40 mg / L, total phosphorus 3.1 mg / L, petroleum 1.5 mg / L, total hardness 90 mg / L, calcium hardness 48 mg / L. The suspended solids of the produced water are high, and maintenance cleaning is performed once a week, and intensive chemical cleaning is required once every 2-3 months.

[0062] After phosphorus precipitation treatment, the water quality is: COD 60 mg / L, ammonia nitrogen 7.5 mg / L, total nitrogen 38 mg / L, total phosphorus 2.3 mg / L, petroleum 1.4 mg / L, total hardness 88 mg / L, calcium hardness 46 mg / L.

[0063] Comparative Example 2

[0064] The same as Example 1, except that the cyclone is not set, and the effluent of the A2O tank directly enters the MBR tank in a conventional manner.

[0065] After biochemical treatment, the water quality produced by the MBR tank is: COD 72 mg / L, ammonia nitrogen 7.5 mg / L, total nitrogen 35 mg / L, total phosphorus 3.2 mg / L, petroleum 0.32 mg / L, total hardness 160 mg / L, calcium hardness 98 mg / L. Maintenance cleaning is performed once a week, and intensive chemical cleaning is required once every 3-6 months.

[0066] After phosphorus precipitation treatment, the water quality is: COD 62 mg / L, ammonia nitrogen 7.4 mg / L, total nitrogen 31 mg / L, total phosphorus 1.1 mg / L, petroleum 0.55 mg / L, total hardness 157 mg / L, calcium hardness 95 mg / L.

[0067] Comparative Example 3

[0068] The same as Example 1, except that the discharge of the overflow port of the cyclone accounts for 20% of the total material entering the cyclone.

[0069] After biochemical treatment, the water quality produced by the MBR tank is: COD 60 mg / L, ammonia nitrogen 11 mg / L, total nitrogen 40 mg / L, total phosphorus 3.3 mg / L, petroleum 0.61 mg / L, total hardness 128 mg / L, calcium hardness 64 mg / L. Maintenance cleaning is performed once a week, and intensive chemical cleaning is required once every 3-6 months.

[0070] After phosphorus precipitation treatment, the water quality is: COD 55 mg / L, ammonia nitrogen 10.2 mg / L, total nitrogen 37 mg / L, total phosphorus 0.5 mg / L, petroleum 0.52 mg / L, total hardness 125 mg / L, calcium hardness 60 mg / L.

[0071] Comparative Example 4

[0072] The same as example 1, except that the membrane pore diameter of the MBR is 20 μm. After biochemical treatment, the water quality of the MBR tank is: COD is 106 mg / L, ammonia nitrogen is 10.8 mg / L, total nitrogen is 58 mg / L, total phosphorus is 2.6 mg / L, petroleum is 0.59 mg / L, total hardness is 162 mg / L, calcium hardness is 99 mg / L. The produced water contains a large amount of suspended solids, and is cleaned once a week. The system is chemically cleaned once every 2-3 months. After a long time of running, the sludge concentration of the system is reduced, resulting in unstable operation of the system.

[0073] After phosphorus precipitation treatment, the water quality is: COD is 78 mg / L, ammonia nitrogen is 10.4 mg / L, total nitrogen is 56 mg / L, total phosphorus is 0.4 mg / L, petroleum is 0.51 mg / L, total hardness is 157 mg / L, calcium hardness is 98 mg / L.

Claims

1. A method of treating petrochemical wastewater, characterized by The method comprises the following steps: the oil-removed petrochemical wastewater is sequentially subjected to a pretreatment unit, a biochemical unit and a phosphorus removal and precipitation unit, wherein the pretreatment unit adopts softening-coagulation-precipitation treatment, the pH value is controlled to be 10-10.5 in the softening step, and the calcium hardness is 60-200 mg / L; the biochemical unit adopts A2O tank-cyclone-MBR tank treatment, the effluent of the A2O tank is fed into the cyclone, the underflow of the cyclone is discharged into the MBR tank, the separated sludge is returned to the A tank, and the water production is fed into the phosphorus removal and precipitation unit for treatment; the discharge of the overflow of the cyclone accounts for 2%-10% of the total feed volume of the cyclone; the MBR tank adopts a solid-liquid separation type MBR membrane-bioreactor, the membrane adopts a microfiltration membrane, and the membrane hole diameter is 2-10 μm. In the oil-removed petrochemical wastewater, the COD is 300-1400 mg / L, the ammonia nitrogen concentration is 50-400 mg / L, the total nitrogen concentration is 60-450 mg / L, the phosphorus concentration is 0.5-5 mg / L, the petroleum is 0-20 mg / L, and the total hardness is 400-1500 mg / L in terms of CaCO3, wherein the calcium hardness is 250-1200 mg / L.

2. The method of claim 1, wherein: The pretreatment unit adopts softening-coagulation-precipitation treatment, and the softening and coagulation are completed by adding a softening agent and a coagulant, wherein the softening agent adopts one or more of calcium hydroxide, sodium hydroxide and sodium carbonate; and the coagulant adopts an iron ion flocculant.

3. The method of claim 2, wherein: The coagulant adopts at least one of ferric chloride, ferrous sulfate, polymeric ferric chloride and polymeric ferrous sulfate.

4. The method according to claim 2 or 3, characterized in that: The coagulant addition amount is 10-200 mg / L.

5. The method of claim 1 or 2, wherein: After the pretreatment, the total hardness of the wastewater is less than 400 mg / L, and the calcium hardness is 80-150 mg / L.

6. The method of claim 1, wherein: The pH of the pretreated wastewater is adjusted to 7-8 before entering the biochemical unit, and inorganic acid is used for the adjustment.

7. The method of claim 1, wherein: The A2O tank is an anaerobic-anoxic-aerobic tank combination, wherein the digestion liquid at the bottom of the O tank is returned to the anoxic tank, and the return ratio is 100%-400%, and the effluent of the O tank is fed into the cyclone.

8. The method of claim 1 or 7, wherein: The treatment conditions of the A tank are as follows: the dissolved oxygen is controlled to be below 0.5 mg / L, the temperature is 25-35 DEG C, and the pH is 7-9; the treatment conditions of the O tank are as follows: the dissolved oxygen is controlled to be 1-3 mg / L, the temperature is 25-35 DEG C, and the pH is 8-9.

9. The method of claim 1, wherein: The cyclone adopts a hydrocyclone, and the cone angle is 6-10 degrees.

10. The method of claim 1, wherein: The membrane hole diameter of the MBR membrane is 5-7 μm.

11. The method of claim 1, wherein: A precipitant is added in the phosphorus removal and precipitation unit, and the precipitant is at least one of ferric chloride, ferrous chloride, alum, aluminum chloride, ferrous sulfate, ferrous sulfate, polymeric ferrous sulfate, polymeric aluminum chloride and other composite iron and aluminum salt precipitants.

12. The method of claim 1 or 11, wherein: The precipitant is added in the phosphorus removal and precipitation unit, and the addition amount is 2.5-70 mg / L.

13. A treatment device for use in the method of any one of claims 1 to 12, characterized in that It mainly comprises a pretreatment unit, a biochemical unit and a phosphorus removal and precipitation unit, wherein the pretreatment unit adopts softening-coagulation-precipitation treatment, mainly carried out in a high-density tank, for pretreating the petrochemical wastewater after oil removal; the biochemical unit comprises an A2O tank, a cyclone and an MBR tank, the effluent of the A2O tank is partially fed into the cyclone, the underflow of the cyclone is discharged into the MBR tank, the separated sludge is returned to the A tank, and the produced water is fed into the phosphorus removal and precipitation unit; the phosphorus removal and precipitation unit mainly comprises a precipitation tank, a precipitant is added, and the effluent of the biochemical unit is subjected to deep treatment.

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