A method for treating wastewater from an underground water-sealed oil depot

Abstract

This invention provides a method for treating wastewater from underground water-sealed oil depots, comprising the following steps: Wastewater from the underground water-sealed oil depot enters an oil-water separator to remove petroleum substances; then, the effluent from the oil-water separator sequentially enters the reaction zone, coagulation zone, flocculation zone, and sedimentation zone of a chemical sedimentation tank to remove heavy metals and sulfides; the effluent from the chemical sedimentation tank sequentially enters the aerobic zone, anoxic zone, and MBR zone of a biological reactor to remove COD, ammonia nitrogen, and total nitrogen, and further remove petroleum substances, sulfides, and heavy metals; the effluent from the biological reactor enters an activated carbon adsorber. The treated effluent meets the following requirements: COD ≤ 30 mg / L, petroleum substances ≤ 0.5 mg / L, sulfides ≤ 0.5 mg / L, ammonia nitrogen ≤ 1.5 mg / L, total nitrogen ≤ 1.5 mg / L, total phosphorus ≤ 0.3 mg / L, and mercury ≤ 0.001 mg / L. This invention solves the problem of poor effluent quality after wastewater treatment from underground water-sealed oil depots in existing technologies.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, in particular to a method for treating sewage of underground water-sealed oil depot. BACKGROUND

[0002] The underground water-sealed oil depot, also known as underground rock cave oil depot, refers to an oil depot excavated in a hard and integrally good rock mass below the underground water level to directly store oil products. Since there is underground water in the rock fissure and the pressure of the underground water (or water curtain) at any point of the oil storage rock cave wall is greater than the pressure of the oil product, the oil product is surrounded by the underground water in the rock cave and cannot leak out. When the water seeping into the cave reaches a certain height, it is pumped out of the cave, i.e. oil-containing fissure water. The sewage discharged by the underground water-sealed oil depot is mainly oil-containing fissure water, and a small amount of ground washing water, initial rainwater and domestic sewage. The water quality characteristics of the sewage of the underground water-sealed oil depot are as follows: (1) the concentration of petroleum is not high, generally 30-100 mg / L, mainly dispersed oil; (2) since the organic matter constituting the crude oil is mainly alkanes, cycloalkanes and aromatic hydrocarbons, etc., the solubility is very low but the structure is stable, so the COD of the fissure water is low but the biodegradability is poor, the COD is 100-300 mg / L and the B / C value is <0.2; (3) the oil contains trace amounts of heavy metals such as mercury and nickel, and part of the heavy metals are transferred to the water seeping into the cave during storage, which can cause the concentration of heavy metals in the fissure water to exceed the standard, and the concentration of mercury is generally 0.1-1 mg / L; (4) the oil contains elemental sulfur, hydrogen sulfide and other sulfides and organic sulfur compounds, and the concentration of sulfides in the fissure water can be as high as 20-100 mg / L; (5) the nitrogen content in the fissure water is not high, and the ammonia nitrogen and total nitrogen are generally less than 15 mg / L. Cr

[0003] Since the underground water-sealed oil depot needs to be constructed in a region with stable geological structure, complete rock mass and stable underground water environment, such a region is often located in a remote mountainous area, the background environmental quality is good, but there is no sewage body or the sewage capacity is very small. With the increasing emphasis on ecological environment protection in China, environmental impact assessment often requires that the sewage of the underground water-sealed oil depot be treated to reach the Class IV standard in the "Surface Water Environmental Quality Standard" GB3838-2002, i.e. COD ≤30 mg / L, petroleum ≤0.5 mg / L, sulfide ≤0.5 mg / L, ammonia nitrogen ≤1.5 mg / L, total nitrogen ≤1.5 mg / L, total phosphorus ≤0.3 mg / L, and mercury ≤0.001 mg / L.

[0004] ​The underground water-sealed oil depot in China started late, and the understanding of the sewage quality of the underground water-sealed oil depot is insufficient. At present, no patent application related to the sewage treatment of the underground water-sealed oil depot (or cave depot) can be found. The conventional oil-containing sewage treatment method is used in the engineering, and the effluent quality can only meet the requirements of the relevant sewage discharge standards, such as COD≤50 mg / L, petroleum≤1 mg / L, sulfide≤1 mg / L, ammonia nitrogen≤5 mg / L, total nitrogen≤15 mg / L, and total phosphorus≤0.5 mg / L. There is a great gap between the effluent quality and the IV standard in the Environmental Quality Standard for Surface Water (GB3838-2002). The main problems in the design of the treatment process are as follows: (1) the A / O biological reaction tank is used in the biochemical part. The advantage is that the carbon source in the influent can be used for denitrification, and no carbon source needs to be supplemented. However, the total nitrogen removal rate of A / O depends on the sludge return ratio (R) and the mixed liquid return ratio (r). In order to control the dissolved oxygen (DO) in the A section to be less than 0.5 mg / L, the sum of the sludge and mixed liquid return ratios (R+r) cannot be more than 4 times. Therefore, the denitrification rate (η=(R+r) / (1+R+r)) is generally not more than 80%, which cannot meet the requirement of total nitrogen≤1.5 mg / L in the effluent. (2) The removal of sulfide is not considered in the pretreatment. When the sulfide is greater than 20 mg / L, it will seriously inhibit the biochemical treatment system, especially the nitrification, and the denitrification capacity will be greatly reduced, accompanied by the weakening of the COD removal capacity. (3) The removal of heavy metals is not considered.

[0005] As described above, the sewage of the underground water-sealed oil depot contains mercury and sulfide. The common methods for removing low-concentration mercury in sewage are chemical precipitation, adsorption and ion exchange. The treatment cost of the chemical precipitation method is low. The solubility of mercury sulfide formed by the divalent sulfur ion and mercury in water is extremely low. The solubility of HgS at room temperature is 4.0×10 -53 Under the suitable conditions of pH and temperature, theoretically, all the mercury sulfide can be precipitated and separated from the sewage. However, there are some limitations in the practical application. For example, the mercury sulfide is in the form of suspended particles, which is difficult to settle. Due to the limitation of the precipitation separation technology, the residual mercury concentration can only be reduced to about 0.05 mg / L. In order to make all the mercury form mercury sulfide precipitate, it is necessary to increase the concentration of sulfide. However, the excessive sulfur ions not only increase the COD of the water body, but also form soluble complex anions [HgS2] 2- with the mercury sulfide precipitate, which reduces the removal rate of mercury. This is the reason why the concentration of sulfide in the sewage of the underground water-sealed oil depot is as high as 20-100 mg / L, which is much higher than the required concentration of the mercury sulfide precipitate, and the mercury concentration in the sewage still exceeds the standard. SUMMARY

[0006] The purpose of the present application is to provide a treatment method for the sewage of the underground water-sealed oil depot, which mainly solves the problem of poor effluent quality of the sewage of the underground water-sealed oil depot in the prior art.

[0007] In order to achieve the above object, the technical scheme adopted by the present application is: a groundwater-sealed oil depot sewage treatment method, characterized by comprising the following steps: groundwater-sealed oil depot sewage enters an oil-water separator to remove oil substances, and then the effluent of the oil-water separator enters a reaction zone, a coagulation zone, a flocculation zone and a sedimentation zone of a chemical precipitation tank in sequence to remove heavy metals and sulfides in the sewage;

[0008] The effluent of the chemical precipitation tank enters an aerobic zone, an anoxic zone and an MBR zone of a biological reaction tank in sequence to remove COD, ammonia nitrogen and total nitrogen, and further remove oil substances, sulfides and heavy metals, and the effluent of the biological reaction tank enters an activated carbon adsorber, and the treated effluent meets the requirements of COD≤30 mg / L, oil≤0.5 mg / L, sulfides≤0.5 mg / L, ammonia nitrogen≤1.5 mg / L, total nitrogen≤1.5 mg / L, total phosphorus≤0.3 mg / L and mercury≤0.001 mg / L.

[0009] Further, the oil-water separator is internally filled with composite filler, the filler at the front end of the oil-water separator is a first inclined plate, and the filler at the rear end is coalescence filter material, and the groundwater-sealed oil depot sewage enters the oil-water separator to remove oil substances, so that the concentration of the oil substances can be reduced to below 5 mg / L.

[0010] Further, alkali liquor is added to the reaction zone of the chemical precipitation tank to control the pH value to be 9-11, and the reaction time is 5-10 min, which is beneficial to the precipitation and separation of mercury sulfide.

[0011] Further, a coagulant is added to the coagulation zone of the chemical precipitation tank, and the coagulation time is 2-5 min, so that the coagulant and excess sulfides generate difficultly soluble precipitates.

[0012] Further, a flocculant is added to the flocculation zone of the chemical precipitation tank, and the flocculation time is 15-30 min, so that the precipitates form larger flocculation bodies.

[0013] Further, the precipitates are subjected to solid-liquid separation in the sedimentation zone, and the sedimentation time is 60-120 min.

[0014] A second inclined plate is arranged in the sedimentation zone; a first sludge backflow pump is arranged between the sedimentation zone and the flocculation zone, and the sludge at the bottom of the sedimentation zone is backflowed to the flocculation zone through the first sludge backflow pump, and the concentration of mercury in the effluent of the sedimentation zone can be less than 0.005 mg / L, and the concentration of sulfides can be less than 2 mg / L.

[0015] Further, a curtain-type biological filler is installed in the aerobic zone of the chemical precipitation tank, the curtain-type biological filler is a modified fiber filler with a nanometer-level wire diameter, and the specific surface area is not less than 15000 m 2 / kg; a first microporous aerator is installed at the bottom of the aerobic zone of the chemical precipitation tank, and the end dissolved oxygen (DO) is not less than 2 mg / L;

[0016] The submersible agitator is installed in the anoxic zone of the chemical precipitation tank, and the carbon source is added in the anoxic zone according to the C / N ratio of 4-5, and the dissolved oxygen DO is controlled to be less than 0.5 mg / L;

[0017] The water production pump is further arranged between the MBR zone of the chemical precipitation tank and the activated carbon adsorber, the effluent of the biological reaction tank enters the activated carbon adsorber through the water production pump, the ultrafiltration membrane assembly is installed in the MBR zone, the water outlet of the ultrafiltration membrane assembly is connected with the suction pipe of the water production pump, and the water outlet pipe of the water production pump is connected with the activated carbon adsorber;

[0018] The second micro-porous aerator is installed at the bottom of the MBR zone of the chemical precipitation tank, and the dissolved oxygen DO in the MBR zone is controlled to be not less than 2 mg / L;

[0019] The second sludge return pump is arranged between the MBR zone and the aerobic zone, the second sludge return pump returns part of sludge in the MBR zone to the aerobic zone, the return ratio is 0.25-1.0, and the other part of sludge is discharged to the sludge treatment system.

[0020] Further, the activated carbon adsorber is filled with granular activated carbon, the particle size of the granular activated carbon is 8-80 meshes, the iodine adsorption value is not less than 800 mg / g, the specific surface area is not less than 900 m 2 / g, the contact time of the effluent of the water production pump with the granular activated carbon is 30-90 min, and the treated effluent meets the requirements of COD≤30 mg / L, petroleum≤0.5 mg / L, sulfide≤0.5 mg / L, ammonia nitrogen≤1.5 mg / L, total nitrogen≤1.5 mg / L, total phosphorus≤0.3 mg / L and mercury≤0.001 mg / L.

[0021] Further, the adjusting tank and the water inlet lifting pump are further arranged before the oil-water separator, and the groundwater sealed oil depot sewage enters the adjusting tank, and then enters the oil-water separator through the water inlet lifting pump.

[0022] The first micro-porous aerator and the second micro-porous aerator are connected with the external air blower.

[0023] Further, the alkali liquor is sodium hydroxide, sodium carbonate or lime water, the coagulant is divalent iron salt, the flocculant is polyacrylamide, the carbon source is sodium acetate or methanol, and the pore diameter of the ultrafiltration membrane of the ultrafiltration membrane assembly is 0.005-0.1 μm.

[0024] In view of the above technical features, the present application has the following advantages:

[0025] 1、The treatment method for the groundwater sealed oil depot sewage has the advantages of short process flow, high removal efficiency and good effluent quality, and each treatment unit can remove various characteristic pollutants.

[0026] 2. Oil-water separators with internally packed composite packing can remove floating oil, dispersed oil, and emulsified oil, reducing the concentration of petroleum hydrocarbons in the effluent to below 5 mg / L. This reduces the inhibitory effect of petroleum hydrocarbons on microorganisms and improves biological treatment efficiency. Conventional oil separators or inclined plate oil-water separators can only remove floating oil and dispersed oil with larger particle sizes, resulting in low removal efficiency. This fails to meet the requirement in the "Design Code for Wastewater Treatment in Petrochemical Industry" GB 50747-2012 that the petroleum hydrocarbon concentration in the influent to the biological reactor should not exceed 30 mg / L. When using air flotation for oil removal, compressed air and chemical agents are required, increasing treatment costs and solid waste emissions.

[0027] 3. Addressing the characteristic of fissure water containing heavy metals such as mercury and sulfides, with a molar ratio of sulfides to mercury far exceeding 12, this invention employs chemical precipitation to simultaneously remove heavy metals and sulfides without the need for precipitating agents. First, the pH of the wastewater is adjusted to 9-11, causing all heavy metals in the wastewater to precipitate as heavily soluble heavy metal sulfides (the solubility of HgS at room temperature is 4.0 × 10⁻⁶). -53 To prevent excess sulfides from forming soluble complex anions [HgS2] with mercury. 2- To address the issue of poor sedimentation of mercury sulfide suspended particles, ferrous salts are added to the coagulation zone. On one hand, the ferrous salts react with excess sulfides to form insoluble FeS precipitate, eliminating the soluble complex anion [HgS2]. 2- On the other hand, Fe 2+ In alkaline water, Fe(OH)2 and Fe(OH)3 precipitates can be generated, which, together with FeS precipitate, can coagulate and co-precipitate HgS suspended particles, promoting the sedimentation of mercury sulfide particles. Finally, a polymeric flocculant is added in the flocculation zone to form a bridging effect on smaller particles, further improving the mercury removal rate. This can reduce the mercury concentration in the effluent to less than 0.005 mg / L and the sulfide concentration to less than 2 mg / L, thereby reducing the inhibitory effect on the biological treatment system and improving the denitrification rate and COD removal rate.

[0028] 4. Given the low nitrogen content in fissure water, with ammonia nitrogen and total nitrogen generally less than 15 mg / L, the biological reactor employs an O / A process with post-denitrification, eliminating the need for mixed liquor recirculation. Optimal reaction conditions such as DO and pH can be controlled in both the aerobic and anoxic zones, unaffected by mixed liquor recirculation, resulting in more thorough nitrification and denitrification with a nitrogen removal rate greater than 90%. This meets the requirement that effluent ammonia nitrogen and total nitrogen are both less than 1.5 mg / L, solving the problem of traditional A / O processes having a total nitrogen removal rate of less than 80%, failing to meet the requirement of effluent total nitrogen ≤1.5 mg / L. Due to the low influent total nitrogen concentration, the amount of carbon source added is small, and the increased reagent cost can be offset by the energy savings from mixed liquor recirculation.

[0029] 5. For fissure water with low COD but poor biodegradability, COD CrCharacterized by concentrations of 100-300 mg / L and a B / C ratio <0.2, treatment using activated sludge methods results in very low efficiency due to the low organic loading rate (F / M) and slow organic matter degradation rate. However, using a biofilm method, most microorganisms adhere to the packing material, significantly increasing the microbial concentration in the biological treatment tank and thus improving the volumetric loading rate. This invention involves installing fixed curtain-type biological packing material in the aerobic zone. This packing material is made of modified fibers with a nanometer-scale filament diameter and a specific surface area of ​​not less than 15000 m². 2 / kg, which is more than 8 times that of conventional fixed packing, provides an optimal growth environment for microorganisms, which is conducive to the reproduction of obligate bacteria and nitrifying bacteria with long generation cycles, thereby improving COD removal rate and ammonia nitrogen nitrification rate.

[0030] 6. An ultrafiltration membrane module was installed in the MBR zone. The effluent from the biological reactor is drawn from the hollow fiber membrane. Because the pore size of the ultrafiltration membrane is only 0.005–0.1 μm, it can effectively intercept activated sludge, residual petroleum hydrocarbons, mercuric sulfide particles, and recalcitrant macromolecular organic matter, resulting in high-quality effluent. The intercepted activated sludge is returned to the aerobic zone, increasing the sludge age and promoting the growth of dominant bacteria and nitrifying bacteria with long generation cycles that decompose recalcitrant pollutants. This allows for repeated utilization of microorganisms, further degrading macromolecular organic matter and improving COD and ammonia nitrogen removal rates. The MBR zone also functions to decompose excess carbon sources added to the anoxic zone. The carbon sources used are sodium acetate or methanol, which have excellent biodegradability and can be completely degraded in the MBR zone.

[0031] 7. Activated carbon has a strong adsorption capacity for pollutants such as organic matter, petroleum hydrocarbons, and heavy metals. The amount of activated carbon can be adjusted according to the pollutant removal load to ensure that the effluent meets the design requirements. The suspended solids in the MBR effluent are very low (less than 1 mg / L), which avoids the activated carbon from becoming clogged and fully utilizes its adsorption function. This reduces the amount of activated carbon consumed while ensuring that the effluent meets the standards. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the apparatus used in a method for treating wastewater from an underground water-sealed oil depot, as described in Specific Embodiment 1.

[0033] Figure 2 This is a flowchart of a method for treating wastewater from an underground water-sealed oil depot, as described in Specific Embodiment 1.

[0034] In the diagram: 1. Equalization tank; 2. Oil-water separator; 3. Chemical sedimentation tank; 4. Reaction zone; 5. Coagulation zone; 6. Flocculation zone; 7. Sedimentation zone; 8. Biological reactor; 9. Aerobic zone; 10. Anoxic zone; 11. MBR zone; 12. Activated carbon adsorber; 13. First inclined plate; 14. Cohesive filter media; 15. Granular activated carbon; 16. Second inclined plate; 17. Curtain-type biological packing; 18. First microporous aerator; 19. Submersible mixer; 20. Ultrafiltration membrane module; 21. Second microporous aerator; 22. Permeate pump; 23. Second sludge return pump; 24. First sludge return pump. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] See Figure 1 and Figure 2 Specific embodiment 1, this embodiment 1 provides a method for treating wastewater from an underground water-sealed oil depot, including the following steps: the wastewater from the underground water-sealed oil depot enters an oil-water separator 2 to remove petroleum substances, and then the effluent from the oil-water separator 2 enters the reaction zone 4, coagulation zone 5, flocculation zone 6 and sedimentation zone 7 of a chemical sedimentation tank 3 in sequence to remove heavy metals and sulfides from the wastewater;

[0037] The effluent from chemical sedimentation tank 3 sequentially enters the aerobic zone 9, anoxic zone 10, and MBR zone 11 of biological reactor 8 to remove COD, ammonia nitrogen, and total nitrogen, as well as further remove petroleum substances, sulfides, and heavy metals. The effluent from biological reactor 8 enters an activated carbon adsorber. The treated effluent meets the following requirements: COD ≤ 30 mg / L, petroleum substances ≤ 0.5 mg / L, sulfides ≤ 0.5 mg / L, ammonia nitrogen ≤ 1.5 mg / L, total nitrogen ≤ 1.5 mg / L, total phosphorus ≤ 0.3 mg / L, and mercury ≤ 0.001 mg / L. These indicators meet the relevant requirements of Class IV standards in the "Surface Water Environmental Quality Standard" GB3838-2002.

[0038] Before the oil-water separator 2, there is also an equalization tank 1 and an inlet lift pump. After the sewage from the underground water-sealed oil tank enters the equalization tank 1, the water quality and quantity are balanced to reduce the impact on the treatment facilities. Then, it enters the oil-water separator 2 through the inlet lift pump to remove petroleum.

[0039] The oil-water separator 2 is filled with composite packing. The front packing of the oil-water separator 2 is the first inclined plate 13, which separates floating oil and dispersed oil with larger particle size. The rear packing is the coalescing filter material 14, which separates dispersed oil and emulsified oil with smaller particle size. After the sewage from the underground water-sealed oil depot enters the oil-water separator 2 to remove petroleum substances, the concentration of petroleum substances can be reduced to below 5 mg / L.

[0040] The effluent from oil-water separator 2 enters the reaction zone 4, coagulation zone 5, and flocculation zone 6 of chemical sedimentation tank 3 in sequence to remove heavy metals and sulfides. Since the concentration of sulfides in the wastewater of the underground water-sealed oil depot is far higher than the concentration required to generate mercuric sulfide precipitate, no precipitant needs to be added to reaction zone 4. Only alkaline solution needs to be added, such as sodium hydroxide, sodium carbonate, or lime water, and the pH value is controlled at 9-11 (that is, the pH value of the wastewater in reaction zone 4 is controlled at 9-11). The reaction time is 5-10 minutes, which is conducive to the precipitation of mercuric sulfide.

[0041] The effluent from reaction zone 4 enters the coagulation zone 5 of chemical sedimentation tank 3. A coagulant, such as a ferrous salt, is added to coagulation zone 5. This coagulant reacts with excess sulfides to form insoluble FeS precipitate, which on the one hand eliminates soluble complex anions [HgS2]. 2- On the other hand, FeS precipitation can act as a co-precipitation carrier for HgS, promoting its sedimentation; simultaneously, Fe... 2+ In alkaline water, Fe(OH)₂ and Fe(OH)₃ precipitates can be formed, which can coagulate and coprecipitate HgS suspended particles. The coagulation time is 2-5 minutes, allowing the coagulant to react with excess sulfides to form insoluble precipitates (such as FeS precipitate).

[0042] The effluent from coagulation zone 5 enters flocculation zone 6 of chemical sedimentation tank 3. Flocculants, such as polyacrylamide (PAM), are added to flocculation zone 6 to form larger flocs from the precipitate, thereby increasing the settling rate. The flocculation time is 15-30 minutes.

[0043] The effluent from flocculation zone 6 enters sedimentation zone 7. Sedimentation zone 7 is equipped with a second inclined plate 16. The sediment undergoes solid-liquid separation in sedimentation zone 7 to achieve the purpose of removing heavy metals and sulfides from the water at the same time. The sedimentation time is 60-120 minutes.

[0044] A first sludge return pump 24 is installed between the sedimentation zone 7 and the flocculation zone 6. The sludge at the bottom of the sedimentation zone 7 is returned to the flocculation zone 6 through the first sludge return pump 24, which enhances the collision and contact effect of HgS and FeS and improves the removal rate. Because the heavy metal concentration is low, the generated heavy metal precipitates are difficult to settle and require a long coagulation, flocculation and sedimentation time. When the reaction time is 5-10 min, the coagulation time is 2-5 min, the flocculation time is 15-30 min, and the sedimentation time is 60-120 min, the mercury concentration in the effluent of the sedimentation zone 7 can be less than 0.005 mg / L and the sulfide concentration can be less than 2 mg / L.

[0045] The effluent from chemical sedimentation tank 3 enters the aerobic zone 9, anoxic zone 10 and MBR zone 11 of biological reactor 8 in sequence to remove COD, ammonia nitrogen and total nitrogen, as well as further remove petroleum, sulfides and heavy metals.

[0046] The first microporous aerator 18 is installed at the bottom of the aerobic zone 9 of the biological reactor 8. The first microporous aerator 18 provides sufficient oxygen, with the terminal dissolved oxygen (DO) not less than 2 mg / L. Aerobic microorganisms convert organic matter (including dissolved petroleum) in the wastewater into carbon dioxide and water, ammonia nitrogen into nitrate and nitrite, and sulfides into sulfate. The first microporous aerator 18 is connected to an external blower.

[0047] A curtain-type biological packing material 17 is installed in the aerobic zone 9 of the biological reactor 8. The curtain-type biological packing material 17 is a modified fiber packing material with a filament diameter in the nanometer range and a specific surface area of ​​not less than 15,000 m². 2 / kg, which is more than 8 times that of conventional fixed packing, provides an optimal growth environment for microbial attachment, resulting in a richer variety of microorganisms and a bioload of up to 15,000-20,000 mg / L. This is conducive to the reproduction of obligate bacteria and nitrifying bacteria with long generation cycles, thereby improving COD removal rate and ammonia nitrification rate.

[0048] Submersible mixers 19 are installed in the anoxic zone 10 of the biological reactor 8. A carbon source, such as sodium acetate or methanol, is added, and the dissolved oxygen (DO) in the anoxic zone 10 is controlled to be less than 0.5 mg / L. In the anoxic zone 10 (i.e., the post-denitrification zone), nitrates and nitrites in the wastewater utilize the supplemented carbon source as electron donors for denitrification, completing the nitrogen removal process. The theoretical carbon source required for denitrification is C / N = 2.86. To improve the reaction rate and total nitrogen removal rate (i.e., denitrification rate), an excess carbon source (C / N value greater than or equal to 4) is needed. Since adding an excess carbon source not only increases reagent costs but also raises the COD value of the effluent from the anoxic zone, considering both denitrification rate and treatment cost, this invention adds the carbon source at a C / N value of 4-5. Under conditions of sufficient carbon source, DO less than 0.5 mg / L, and appropriate pH, nitrate nitrogen can be almost completely reduced to nitrogen gas by denitrifying bacteria; therefore, the total nitrogen in the effluent is close to ammonia nitrogen.

[0049] A permeate pump 22 is also installed between the MBR zone 11 of the biological reactor 8 and the activated carbon adsorber. The effluent from the biological reactor 8 enters the activated carbon adsorber after passing through the permeate pump 22. An ultrafiltration membrane module 20 is installed in the MBR zone 11. The outlet of the ultrafiltration membrane module 20 is connected to the suction pipe of the permeate pump 22, and the outlet pipe of the permeate pump 22 is connected to the activated carbon adsorber.

[0050] A second microporous aerator 21 is installed at the bottom of the MBR zone 11 in the biological reactor 8 to control the dissolved oxygen (DO) in the MBR zone 11 to be no less than 2 mg / L; the second microporous aerator 21 is connected to an external blower.

[0051] A second sludge return pump 23 is installed between MBR zone 11 and aerobic zone 9. The second sludge return pump 23 returns part of the sludge from MBR zone 11 to aerobic zone 9 with a return ratio of 0.25-1.0, and discharges the other part of the sludge to the sludge treatment system.

[0052] MBR zone 11 serves a dual purpose: removing excess carbon source added to anoxic zone 10 and separating sludge from water. On one hand, the effective volume and aeration volume of MBR zone 11 must simultaneously meet the requirements for installing and cleaning the ultrafiltration membrane module 20 (i.e., the hollow fiber membrane fibers of the ultrafiltration membrane module 20) and for degrading and oxidizing excess carbon source, controlling dissolved oxygen (DO) to be no less than 2 mg / L to eliminate COD increases caused by excess carbon source. On the other hand, negative pressure suction is used to extract effluent from the hollow fiber membrane. Because the pore size of the ultrafiltration membrane is only 0.005–0.1 μm, it can intercept suspended solids, colloids, petroleum hydrocarbons, mercuric sulfide particles, microorganisms, and large molecular organic pollutants, resulting in high-quality effluent. Simultaneously, the ultrafiltration membrane effectively retains activated sludge, which is returned to aerobic zone 9 via the second sludge return pump 23. This promotes the growth of dominant bacteria and nitrifying bacteria with long generation cycles that decompose recalcitrant pollutants, thereby improving COD and ammonia nitrogen removal rates.

[0053] The effluent from MBR zone 11 enters activated carbon adsorber 12 via product water pump 22. Activated carbon adsorber 12 is filled with granular activated carbon 15, which has a particle size of 8-80 mesh, an iodine adsorption value of not less than 800 mg / g, and a specific surface area of ​​not less than 900 m². 2 / g, activated carbon has a strong adsorption effect on pollutants such as organic matter, petroleum and heavy metals, further removing residual COD, petroleum and heavy metals from the effluent of biological reactor 8; the contact time between the effluent of product water pump 22 and granular activated carbon 15 is 30-90min, and the treated effluent meets the following requirements: COD≤30mg / L, petroleum≤0.5mg / L, sulfide≤0.5mg / L, ammonia nitrogen≤1.5mg / L, total nitrogen≤1.5mg / L, total phosphorus≤0.3mg / L, mercury≤0.001mg / L, and the corresponding indicators meet the relevant requirements of Class IV standard in "Surface Water Environmental Quality Standard" GB3838-2002.

[0054] For example, in scenario one, the wastewater from a certain underground water-sealed oil depot has the following characteristics: petroleum hydrocarbons 100 mg / L, COD 300 mg / L, sulfides 80 mg / L, mercury 1.1 mg / L, ammonia nitrogen less than 10 mg / L, and total nitrogen less than 15 mg / L.

[0055] The above-mentioned treatment method for wastewater from underground water-sealed oil depots was adopted, with the following parameters selected:

[0056] Sodium hydroxide solution is added to reaction zone 4 of chemical sedimentation tank 3 to control the pH value to about 10.5, and the reaction time is 10 min; polyferrous sulfate solution is added to coagulation zone 5, and the coagulation time is 5 min; PAM (i.e. polyacrylamide) is added to flocculation zone 6, and the flocculation time is 25 min; a second inclined plate 16 is installed in sedimentation zone 7, and the residence time is 120 min; the sludge in sedimentation zone 7 is returned to flocculation zone 6 via the first sludge return pump 24.

[0057] The aerobic zone 9 of the biological reactor 8 is filled with curtain-type biological packing material 17. The packing material is a modified fiber packing material with a filament diameter in the nanometer range and a specific surface area of ​​15,000 m². 2 / kg, a first microporous aerator 18 is installed at the bottom to control the dissolved oxygen (DO) at the end to about 3mg / L; a submersible mixer 19 is installed in the anoxic zone 10, and sodium acetate solution is added according to C / N≈5, while controlling the dissolved oxygen (DO) to be less than 0.5mg / L; an ultrafiltration membrane module 20 and a second microporous aerator 21 are installed in the MBR zone 11, along with a corresponding permeate pump 22 and a second sludge return pump 23, etc. The suction pipe of the permeate pump 22 is connected to the outlet of the ultrafiltration membrane module 20 to pump the effluent from the MBR zone 11 to the activated carbon adsorber 12; the second microporous aerator 21 is connected to an external blower to control the dissolved oxygen (DO) in the MBR zone 11 to be not less than 2mg / L; the second sludge return pump 23 returns part of the sludge from the MBR zone 11 to the aerobic zone 9 at a return ratio of 0.5, and discharges the other part of the sludge to the sludge treatment system (e.g., through a sludge discharge pipe).

[0058] Granular activated carbon 15 has a particle size of 8-40 mesh, an iodine adsorption value of approximately 850 mg / g, and a specific surface area of ​​approximately 1100 m².2 / g; The contact time between wastewater and activated carbon bed is 60min, which is the contact time between the effluent from water pump 22 and granular activated carbon 15.

[0059] After treatment using the above methods, the effluent had a COD of 18 mg / L, petroleum hydrocarbons of 0.05 mg / L, sulfides of 0.15 mg / L, ammonia nitrogen of 0.58 mg / L, total nitrogen of 0.95 mg / L, total phosphorus of 0.13 mg / L, and mercury levels of less than 0.001 mg / L.

[0060] For example, in scenario two, the wastewater from a certain underground water-sealed oil depot has the following characteristics: petroleum hydrocarbons 50 mg / L, COD 250 mg / L, sulfides 45 mg / L, mercury 0.5 mg / L, ammonia nitrogen 8 mg / L, and total nitrogen 12 mg / L.

[0061] The above-mentioned treatment method for wastewater from underground water-sealed oil depots was adopted, with the following parameters selected:

[0062] Sodium hydroxide solution is added to reaction zone 4 of chemical sedimentation tank 3 to control the pH value to about 10, and the reaction time is 8 minutes; polyferrous sulfate solution is added to coagulation zone 5, and the coagulation time is 3 minutes; PAM is added to flocculation zone 6, and the flocculation time is 20 minutes; a second inclined plate 16 is provided in sedimentation zone 7, and the residence time is 90 minutes; the sludge in sedimentation zone 7 is returned to flocculation zone 6 via the first sludge return pump 24.

[0063] The aerobic zone 9 of the biological reactor 8 is filled with curtain-type biological packing material 17. The packing material is a modified fiber packing material with a filament diameter in the nanometer range and a specific surface area of ​​18,000 m². 2 / kg, a first microporous aerator 18 is installed at the bottom to control the dissolved oxygen (DO) at the end to about 2.5 mg / L; a submersible mixer 19 is installed in the anoxic zone 10, and sodium acetate solution is added according to C / N≈4.5, while controlling the dissolved oxygen (DO) to be less than 0.5 mg / L; an ultrafiltration membrane module 20 and a second microporous aerator 21 are installed in the MBR zone 11, along with a permeate pump 22 and a second sludge return pump 23, etc. The suction pipe of the permeate pump 22 is connected to the outlet of the ultrafiltration membrane module 20 to pump the effluent from the MBR zone 11 to the activated carbon adsorber 12; the second microporous aerator 21 is connected to an external blower to control the dissolved oxygen (DO) in the MBR zone 11 to be not less than 2 mg / L; the sludge pump returns part of the sludge from the MBR zone 11 to the aerobic zone 9 at a return ratio of 1.0, and discharges the other part of the sludge to the sludge treatment system.

[0064] Granular activated carbon 15 has a particle size of 20-80 mesh, an iodine adsorption value of approximately 900 mg / g, and a specific surface area of ​​approximately 1200 m². 2 / g; The contact time between wastewater and the activated carbon bed is 45 min.

[0065] After treatment using the above methods, the effluent had a COD of 23 mg / L, petroleum hydrocarbons of 0.15 mg / L, sulfides of 0.22 mg / L, ammonia nitrogen of 0.91 mg / L, total nitrogen of 1.1 mg / L, total phosphorus of 0.2 mg / L, and mercury of less than 0.001 mg / L.

[0066] For example, in scenario three, the wastewater from an underground water-sealed oil depot has the following characteristics: petroleum hydrocarbons 30 mg / L, COD 150 mg / L, sulfides 25 mg / L, mercury 0.1 mg / L, ammonia nitrogen 5 mg / L, and total nitrogen 10 mg / L.

[0067] The above-mentioned treatment method for wastewater from underground water-sealed oil depots was adopted, with the following parameters selected:

[0068] Sodium hydroxide solution is added to reaction zone 4 of chemical sedimentation tank 3 to control the pH value to about 9.5, and the reaction time is 5 minutes; polyferrous sulfate solution is added to coagulation zone 5, and the coagulation time is 2 minutes; PAM is added to flocculation zone 6, and the flocculation time is 15 minutes; a second inclined plate 16 is provided in sedimentation zone 7, and the residence time is 60 minutes; the sludge in sedimentation zone 7 is returned to flocculation zone 6 via the first sludge return pump 24.

[0069] The aerobic zone 9 of the biological reactor 8 is filled with curtain-type biological packing material 17. The packing material is a modified fiber packing material with a filament diameter in the nanometer range and a specific surface area of ​​16,000 m². 2 / kg, a first microporous aerator 18 is installed at the bottom to control the dissolved oxygen (DO) at the end to about 2mg / L; a submersible mixer 19 is installed in the anoxic zone 10, methanol is added according to C / N≈4, and the dissolved oxygen (DO) is controlled to be less than 0.5mg / L; an ultrafiltration membrane module 20 and a second microporous aerator 21 are installed in the MBR zone 11, corresponding to a permeate pump 22 and a second sludge return pump 23, etc. The suction pipe of the permeate pump 22 is connected to the outlet of the ultrafiltration membrane module 20 to pump the effluent from the MBR zone 11 to the activated carbon adsorber 12; the second microporous aerator 21 is connected to an external fan to control the dissolved oxygen (DO) in the MBR zone 11 to be not less than 2mg / L; the sludge pump returns part of the sludge from the MBR zone 11 to the aerobic zone 9 with a return ratio of 0.25, and discharges the other part of the sludge to the sludge treatment system.

[0070] Granular activated carbon 15 has a particle size of 10-60 mesh, an iodine adsorption value of approximately 835 mg / g, and a specific surface area of ​​approximately 950 m². 2 / g; The contact time between wastewater and the activated carbon bed is 30 minutes.

[0071] After treatment using the above methods, the effluent had a COD of 26.5 mg / L, petroleum hydrocarbons of 0.35 mg / L, sulfides of 0.28 mg / L, ammonia nitrogen of 0.75 mg / L, total nitrogen of 1.29 mg / L, total phosphorus of 0.15 mg / L, and mercury levels less than 0.001 mg / L.

[0072] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for treating wastewater from an underground water-sealed oil reservoir, characterized by: The method comprises the following steps: groundwater sealed oil depot sewage enters an oil-water separator (2) to remove oil substances, and the effluent of the oil-water separator (2) enters a reaction zone (4), a coagulation zone (5), a flocculation zone (6) and a sedimentation zone (7) of a chemical precipitation tank (3) in sequence to remove heavy metals and sulfides in the sewage; The effluent of the chemical precipitation tank (3) enters an aerobic zone (9), an anoxic zone (10) and an MBR zone (11) of a biological reaction tank (8) in sequence to remove COD, ammonia nitrogen and total nitrogen, and further remove oil substances, sulfides and heavy metals; the effluent of the biological reaction tank (8) enters an activated carbon adsorber, and the treated effluent meets the requirements of COD≤30 mg / L, oil substances≤0.5 mg / L, sulfides≤0.5 mg / L, ammonia nitrogen≤1.5 mg / L, total nitrogen≤1.5 mg / L, total phosphorus≤0.3 mg / L and mercury≤0.001 mg / L; The oil-water separator (2) is internally filled with composite filler, the filler at the front end of the oil-water separator (2) is a first inclined plate (13), and the filler at the rear end is a coalescence filter material (14); the groundwater sealed oil depot sewage enters the oil-water separator (2) to remove oil substances, so that the concentration of the oil substances is reduced to below 5 mg / L; Alkaline solution is added to the reaction zone (4) of the chemical precipitation tank (3) to control the pH value to be 9-11, and the reaction time is 5-10 min, which is beneficial to the precipitation of mercury sulfide; The coagulation zone (5) of the chemical precipitation tank (3) is added with a coagulant, and the coagulation time is 2-5 min, so that the coagulant and excess sulfides generate difficult-to-dissolve precipitates; The aerobic zone (9) of the biological reaction tank (8) is internally provided with a curtain type biological filler (17); The MBR zone (11) of the biological reaction tank (8) is internally provided with a second micro-porous aerator (21) at the bottom, and the dissolved oxygen DO in the MBR zone (11) is controlled to be not less than 2 mg / L; A second sludge backflow pump (23) is arranged between the MBR zone (11) and the aerobic zone (9), the second sludge backflow pump (23) backflows part of sludge in the MBR zone (11) to the aerobic zone (9), the backflow ratio is 0.25-1.0, and the other part of sludge is discharged to a sludge treatment system; The coagulant is a divalent iron salt.

2. A method of treating wastewater from an underground water sealed oil reservoir according to claim 1, characterized in that: The flocculation zone (6) of the chemical precipitation tank (3) is added with a flocculant, and the flocculation time is 15-30 min, so that the precipitates form larger flocculation bodies.

3. A method of treating wastewater from an underground water sealed oil reservoir according to claim 2, characterized in that: The precipitates are subjected to solid-liquid separation in the sedimentation zone (7), and the sedimentation time is 60-120 min; The sedimentation zone (7) is internally provided with a second inclined plate (16), and a first sludge backflow pump (24) is arranged between the sedimentation zone (7) and the flocculation zone (6), the sludge at the bottom of the sedimentation zone (7) is backflowed to the flocculation zone (6) through the first sludge backflow pump (24), the mercury concentration in the effluent of the sedimentation zone (7) is less than 0.005 mg / L, and the sulfide concentration is less than 2 mg / L.

4. The method of claim 3, wherein: The curtain type biological filler (17) is a modified fiber filler with nanometer level wire diameter, and the specific surface area is not less than 15000 m 2 / kg; a first microporous aerator (18) is installed at the bottom of the aerobic zone (9) of the biological reaction tank (8), and the end dissolved oxygen DO is not less than 2 mg / L; The anoxic zone (10) of the biological reaction tank (8) is internally provided with a submersible agitator (19), and the anoxic zone (10) is added with a carbon source according to a C / N ratio of 4-5, and the dissolved oxygen DO is controlled to be less than 0.5 mg / L; The MBR area (11) of the biological reaction tank (8) and the activated carbon adsorber are further provided with a water production pump (22), the effluent of the biological reaction tank (8) enters the activated carbon adsorber (12) after passing through the water production pump (22), the ultrafiltration membrane assembly (20) is installed in the MBR area (11), the water outlet of the ultrafiltration membrane assembly (20) is connected with the suction pipe of the water production pump (22), and the water outlet pipe of the water production pump (22) is connected with the activated carbon adsorber (12).

5. A method of treating wastewater from an underground water sealed oil reservoir according to claim 4, characterized in that: The activated carbon adsorber (12) is filled with granular activated carbon (15) having a particle size of 8-80 mesh, an iodine adsorption value of not less than 800 mg / g, and a specific surface area of not less than 900 m 2 / g. The contact time of the water outlet of the water production pump (22) with the granular activated carbon (15) is 30-90 min.

6. A method of treating wastewater from an underground water sealed oil reservoir according to claim 5, characterized in that: The adjusting tank (1) and the water inlet lifting pump are further arranged before the oil-water separator (2), the underground water-sealed oil depot sewage enters the adjusting tank (1), and then enters the oil-water separator (2) through the water inlet lifting pump; The first microporous aerator (18) and the second microporous aerator (21) are connected with external air fans.

7. A method of treating wastewater from an underground water sealed oil reservoir according to claim 6, characterized in that: The lye is sodium hydroxide, sodium carbonate or lime water; the flocculant is polyacrylamide; the carbon source is sodium acetate or methanol; and the pore diameter of the ultrafiltration membrane assembly (20) is 0.005-0.1 μm.

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