A method and system for treating coal gasification wastewater

Abstract

The present invention discloses a method and system for treating coal gasification wastewater, including: sending coal gasification wastewater into a decyanation reaction tank, and performing decyanation treatment by adding an oxidant; the effluent of the decyanation reaction tank enters a reduction reaction tank, and performs reduction treatment by adding a reducing agent; the effluent of the reduction reaction tank enters a gas stripping internal circulation reaction tank, and ammonia nitrogen is oxidized into nitrite by microorganisms; the effluent of the gas stripping internal circulation reaction tank is subjected to separation, and the effluent after separation enters a nitrification and denitrification system, and the remaining COD, NH3-N and TN are removed under the condition of adding a carbon source to achieve standard effluent; the residual sludge generated by the reduction reaction tank, the gas stripping internal circulation reaction tank and the nitrification and denitrification system is dehydrated, and the sludge dewatering supernatant is returned to the regulating tank. The present invention adopts a combination of pretreatment+high-efficiency gas stripping internal circulation reactor+deep nitrification and denitrification system, so as to be able to efficiently remove pollutants, achieve energy saving and carbon reduction and meet emission standards.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a method and system for treating coal gasification wastewater. Background Art

[0002] Conventional coal gasification wastewater treatment systems often utilize traditional gas stripping and ammonia distillation processes, but these processes present challenges such as high energy consumption, large dosing requirements, and high operating costs, significantly impacting wastewater treatment compliance and business operations. Biochemical treatment processes, with their advantages of high microbial concentration, high efficiency, and low energy consumption, are one of the most effective technologies for removing coal gasification wastewater. Therefore, a novel biochemical reaction system is employed, utilizing physical and chemical means to remove toxic and hazardous substances such as sulfide and cyanide. Furthermore, combined with nitritation, denitrification, and nitritation, ammonia oxidation, and other technologies to remove residual high concentrations of ammonia nitrogen and COD, achieving water production compliance is highly economical. Summary of the Invention

[0003] The water quality characteristics of coal gasification wastewater from fixed-bed gasifiers, fluidized beds, entrained beds, etc. are mainly high ammonia nitrogen and low COD wastewater, and contain various substances such as cyanide, sulfide and fluoride. In order to solve the above-mentioned defects of traditional coal gasification wastewater treatment systems, the present invention provides a method and system for treating coal gasification wastewater.

[0004] The present invention discloses a method for treating coal gasification wastewater, comprising:

[0005] Step 1: Send the coal gasification wastewater into the regulating tank to balance the water quality and quantity;

[0006] Step 2: The effluent from the regulating tank is sent to a decyanation reaction tank for decyanation by adding an oxidant, i.e., the cyanide in the influent is oxidized into cyanate by the oxidant, and then further oxidized into ammonia nitrogen, nitrogen and carbon dioxide;

[0007] Step 3: The effluent from the decyanation reaction tank enters the reduction reaction tank and is reduced by adding a reducing agent, that is, by adding reducing substances such as ferrous sulfate, the excess oxidant is neutralized and the sulfide and other biotoxic and harmful substances in the wastewater are removed to form a precipitate, thereby avoiding affecting the subsequent gas stripping internal circulation reaction tank and nitrification and denitrification system;

[0008] Step 4: The effluent from the reduction reaction tank enters the air stripping internal circulation reaction tank, where it is aerated by a blower and refluxed by the air stripping device for mass transfer and mixing, and ammonia nitrogen is simultaneously oxidized to nitrite nitrogen by ammonia oxidizing bacteria. The nitrite nitrogen and ammonia nitrogen are then removed by ammonia oxidizing bacteria and nitrite reducing bacteria to remove ammonia nitrogen and COD from the wastewater.

[0009] Step 5: The effluent from the air stripping internal circulation reaction tank enters a high-efficiency separation system to further recover the high-efficiency bacterial strains; wherein the high-efficiency separation system further recovers the sludge through a sedimentation tank, an effluent weir, a biological filler, and a sludge screening system to increase the sludge concentration;

[0010] Step 6: The effluent from the high-efficiency separation system still contains a certain amount of nitrate and ammonia nitrogen. Therefore, the effluent from the high-efficiency separation system is fed into the nitrification and denitrification system to remove the remaining COD, NH3-N and TN under the condition of adding a carbon source to achieve effluent standards;

[0011] Step 7: The residual sludge generated by the reduction reaction tank, the gas stripping internal circulation reaction tank, and the nitrification and denitrification system is fed into the sludge dewatering system. The dewatered sludge is transported out for disposal, and the supernatant of the sludge dewatering is returned to the regulating tank.

[0012] As a further improvement of the present invention, the coal gasification wastewater includes coal gasification wastewater from fixed bed gasifiers, fluidized beds and entrained beds. The fixed bed gasifier wastewater includes one or more of the incremental water of gasifier ash water washing, conversion condensation wastewater and compressor flotation water. The main water quality characteristics are high ammonia nitrogen and low COD wastewater, and it contains a variety of substances such as cyanide, sulfide and fluoride.

[0013] As a further improvement of the present invention, the added oxidant includes at least one of sodium hypochlorite, chlorine, chlorine dioxide, hydrogen peroxide, and ozone.

[0014] The present invention provides a coal gasification wastewater treatment system for implementing the above-mentioned coal gasification wastewater treatment method, comprising: a regulating tank, a decyanation reaction tank, a reduction reaction tank, a gas stripping internal circulation reaction tank, a high-efficiency separation system, and a nitrification and denitrification system, which are sequentially arranged along the treatment direction of the coal gasification wastewater;

[0015] The decyanation reaction tank is connected to an oxidant dosing system, and the reduction reaction tank is connected to a reducing agent dosing system;

[0016] The air stripping internal circulation reaction pool includes a multi-stage reaction pool connected in series, and each reaction pool is provided with two vertical guide walls, which divide each reaction pool into a water inlet chamber, an air stripping aeration chamber and a water outlet chamber connected in sequence. An air stripping aerator is provided in the middle of the air stripping aeration chamber, and all the air stripping aerators are connected to a blower; water enters the upper end of the water inlet chamber, and water flows out from the lower end of the water inlet chamber into the lower end water inlet of the air stripping aeration chamber, and the water outlet in the middle of the air stripping aeration chamber enters the adjacent water outlet chamber. The air stripping aerator is located between the water inlet and the water outlet of the air stripping aeration chamber. The water from the upper end of the water outlet chamber enters the upper end water inlet of the water inlet chamber of the lower reaction tank, and a first inclined plate sedimentation tank is provided at the water outlet of each water outlet chamber; the water inlet chamber of the first-stage reaction tank collects the water from the reduction reaction tank, and a nutrient salt dosing system is connected to the water inlet chamber of the first-stage reaction tank. The water from the tail end reaction tank enters the reflux water tank, and part of the water from the reflux water tank flows into the high-efficiency separation system, and the remaining part flows back to the water inlet chamber of the first-stage reaction tank through the air stripping reflux pipe. The water inlet of the air stripping reflux pipe is connected to an air pipe, and the air pipe is connected to a blower;

[0017] The high-efficiency separation system includes a second inclined plate sedimentation tank, a filler separation system and a sludge screening system connected in sequence. The second inclined plate sedimentation tank returns the sludge to the water inlet chamber of the first-stage reaction tank through a sludge pump and a sludge discharge pipe;

[0018] The nitrification and denitrification system comprises a denitrification tank, a nitrification tank and a third inclined plate sedimentation tank connected in sequence. The denitrification tank is connected to a carbon source dosing system. An aerator is provided in the nitrification tank, and the aerator is connected to a blower. The nitrification tank returns the nitrified liquid to the denitrification tank through a reflux pump. The effluent from the third inclined plate sedimentation tank meets the discharge standards.

[0019] The reduction reaction tank, the gas stripping internal circulation reaction tank and the nitrification and denitrification system are connected to a sludge dewatering system, and the sludge dewatering supernatant of the sludge dewatering system is returned to the regulating tank.

[0020] As a further improvement of the present invention, the air stripping reflux pipe is aerated through a perforated pipe to perform air stripping reflux, and the reflux ratio is 5-30 times.

[0021] As a further improvement of the present invention, the filler of the filler separation system adopts high-density polyurethane filler with a pore size of 2-4 mm, and the sludge screening system adopts a hydraulic screen or a rotary screen interception system with a screen pore size of 0.5-1 mm.

[0022] As a further improvement of the present invention, the sludge produced by the reduction reaction tank is mainly iron sulfide, which can be used to remove the sulfur source of the deep sulfur autotrophic denitrification filter for sewage treatment, and remove pollutants through the flocculation effect of iron salts to improve the effluent water quality.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention adopts a combination of pretreatment + high-efficiency gas stripping internal circulation reactor + deep nitrification and denitrification system, which can effectively remove pollutants, achieve energy conservation and carbon reduction and meet emission standards, reduce chemical addition and operating costs, and has extremely broad economic value, environmental significance and market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the method and system for treating coal gasification wastewater disclosed in the present invention;

[0026] Figure 2 It is a structural schematic diagram of the gas lift internal circulation reaction tank, high-efficiency separation system and digestion and denitrification system disclosed in the present invention.

[0027] In the picture:

[0028] 10. Equalization tank; 20. Decyanide reaction tank; 21. Oxidant dosing system; 30. Reduction reaction tank; 31. Reductant dosing system; 40. Air lift internal circulation reaction tank; 41. Reaction tank; 42. Diversion wall; 43. Water inlet chamber; 44. Air lift aeration chamber; 45. Water outlet chamber; 46. Air lift aerator; 47. First inclined plate sedimentation tank; 48. Nutrient dosing system; 49. Return water tank; 410. Air lift return pipe; 50. High-efficiency separation system; 51. Second inclined plate sedimentation tank; 52. Filler separation system; 53. Sludge screening system; 54. Sludge discharge pipe; 60. Nitrification and denitrification system; 61. Denitrification tank; 62. Nitrification tank; 63. Third inclined plate sedimentation tank; 64. Carbon source dosing system; 70. Sludge dewatering system; 80. Blower. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] The present invention is described in further detail below with reference to the accompanying drawings:

[0031] like Figure 1 As shown, the present invention provides a method for treating coal gasification wastewater, comprising:

[0032] Step 1: Send the coal gasification wastewater into the regulating tank for balanced water quality and water quantity regulation; wherein, the coal gasification wastewater includes coal gasification wastewater from fixed bed gasifier, fluidized bed and entrained bed, and the fixed bed gasifier wastewater includes one or more of the incremental water of gasifier ash water washing, shift condensation wastewater and compressor flotation water. The main water quality characteristics are high ammonia nitrogen and low COD wastewater, and contain various substances such as cyanide, sulfide and fluoride.

[0033] Step 2: sending the effluent from the regulating tank to a decyanation reaction tank for decyanation treatment by adding an oxidant, that is, oxidizing the cyanide in the influent into cyanate by the oxidant, and further oxidizing it into ammonia nitrogen, nitrogen and carbon dioxide; wherein the added oxidant includes at least one of sodium hypochlorite, chlorine, chlorine dioxide, hydrogen peroxide and ozone.

[0034] Step 3: The effluent from the decyanation reaction tank enters the reduction reaction tank and is reduced by adding a reducing agent, that is, by adding reducing substances such as ferrous sulfate and sodium bisulfite, the excess oxidant is neutralized and the sulfide and other biotoxic and harmful substances in the wastewater are removed to form a precipitate, thereby avoiding affecting the subsequent gas lift internal circulation reaction tank and nitrification and denitrification system.

[0035] Step 4: The effluent from the reduction reaction tank enters the air stripping internal circulation reaction tank, where it is aerated by a blower and refluxed by air stripping for mass transfer and mixing, and ammonia nitrogen is simultaneously oxidized into nitrite nitrogen by ammonia oxidizing bacteria. The nitrite nitrogen and ammonia nitrogen are removed by ammonia oxidizing bacteria and nitrite reducing bacteria to remove ammonia nitrogen and COD in the wastewater.

[0036] Step 5: The effluent from the air stripping internal circulation reaction tank enters a high-efficiency separation system to further recover the high-efficiency bacteria (activated sludge). The high-efficiency separation system further recovers the sludge through a sedimentation tank, an effluent weir, biological fillers, and a sludge screening system to increase the sludge concentration.

[0037] Step 6: The effluent from the high-efficiency separation system still contains a certain amount of nitrate and ammonia nitrogen. Therefore, the effluent from the high-efficiency separation system enters the nitrification and denitrification system to remove the remaining COD, NH3-N and TN under the condition of adding carbon source to achieve effluent that meets the standards.

[0038] Step 7: The residual sludge generated by the reduction reaction tank, the gas stripping internal circulation reaction tank, and the nitrification and denitrification system is fed into the sludge dewatering system. The dewatered sludge is transported out for disposal, and the supernatant of the sludge dewatering is returned to the regulating tank.

[0039] like Figure 1 、 2As shown, the present invention provides a coal gasification wastewater treatment system for implementing the above-mentioned coal gasification wastewater treatment method, comprising: a regulating tank 10, a decyanation reaction tank 20, a reduction reaction tank 30, a gas stripping internal circulation reaction tank 40, a high-efficiency separation system 50, a nitrification and denitrification system 60, and a sludge dewatering system 70, which are sequentially arranged along the treatment direction of the coal gasification wastewater; wherein,

[0040] The regulating tank 10 is used to receive coal gasification wastewater and regulate the coal gasification wastewater to balance water quality and quantity.

[0041] The decyanation reaction tank 20 is connected to an oxidant dosing system 21, which feeds oxidant into the decyanation reaction tank 20 to oxidize cyanide in the influent into cyanate, which is then further oxidized into ammonia nitrogen, nitrogen, and carbon dioxide. Furthermore, both the decyanation reaction tank 20 and the reduction reaction tank 30 require online monitoring devices such as ORP.

[0042] Reducing agent dosing system 31 is connected to the reduction reaction tank 30. This system adds reducing substances such as ferrous sulfate to the reduction reaction tank 30, neutralizing excess oxidants and removing biotoxic and harmful substances such as sulfide from the wastewater. This precipitates the sludge, preventing it from impacting the subsequent gas lift internal circulation reaction tank and nitrification and denitrification systems. Furthermore, the sludge produced by the reduction reaction tank is primarily composed of iron sulfide, which can be used to remove sulfur from the deep sulfur autotrophic denitrification filter in wastewater treatment. The flocculation of iron salts removes pollutants and improves effluent quality.

[0043] The air stripping internal circulation reaction tank 40 includes a multi-stage reaction tank 41 connected in series, and the reaction tank 41 has a conical bottom structure; each reaction tank 41 is provided with two vertical guide walls 42, and the two guide walls 42 divide each reaction tank 41 into a water inlet chamber 43, an air stripping aeration chamber 44 and a water outlet chamber 45 connected in sequence. An air stripping aerator 46 is provided in the middle of the air stripping aeration chamber 45, and all air stripping aerators 46 are connected to the blower 80; in each reaction tank 41, water enters the upper end of the water inlet chamber 43, and water flows out from the lower end of the water inlet chamber 43 into the lower water inlet of the air stripping aeration chamber 44, and the water outlet in the middle of the air stripping aeration chamber 44 enters the adjacent water outlet chamber 45, and the air stripping aerator 46 is located at Between the water inlet and the water outlet of the air lift aeration chamber 44, the water outlet from the upper end of the water outlet chamber 45 enters the upper end water inlet of the water inlet chamber of the lower reaction tank 41, and a first inclined plate sedimentation tank 47 is provided at the water outlet of each water outlet chamber; the water inlet chamber of the first-stage reaction tank collects the water outlet of the reduction reaction tank 30, and a nutrient salt dosing system 48 is connected to the water inlet chamber of the first-stage reaction tank. The water outlet of the tailmost reaction tank enters the reflux water tank 49, and part of the water outlet of the reflux water tank 49 flows into the high-efficiency separation system 50, and the remaining part flows back to the water inlet chamber of the first-stage reaction tank through the air lift reflux pipe 410. The water inlet of the air lift reflux pipe is connected to an air pipe, and the air pipe is connected to the blower 80.

[0044] Furthermore, the gas stripping internal circulation reaction tank 40 can adopt a combination of one or more gas stripping reaction tanks to cope with processing requirements of different loads.

[0045] Furthermore, the air lift aerator 46 of the air lift internal circulation reaction tank 40 adopts microporous aeration, and a guide wall is set in the reaction tank to realize air lift reflux, promote the mixing of the influent and reflux systems, and improve the reaction and mass transfer efficiency.

[0046] Furthermore, the air stripping reflux pipe 410 uses perforated pipe aeration to provide air stripping reflux, improving air stripping capacity and increasing the reflux dilution ratio. The reflux ratio of the air stripping reflux pipe 410 is 5-30 times. This high-fold reflux creates a concentration gradient configuration with high inlet load and low outlet load. This not only avoids the inhibitory effects of high-concentration ammonia nitrogen and other pollutants, but also improves treatment capacity and increases buffering.

[0047] The high-efficiency separation system 50 of the present invention comprises a second inclined plate sedimentation tank 51, a filler separation system 52, and a sludge screening system 53, which are connected in sequence. The second inclined plate sedimentation tank 51 returns sludge to the water inlet chamber of the first-stage reaction tank 41 via a sludge pump and a sludge discharge pipe 54. During operation, the high-efficiency separation system 50 first intercepts and separates large sludge particles in the second inclined plate sedimentation tank 51. The filler separation system 52 further intercepts high-efficiency bacterial strains in the produced water flocculent sludge. Finally, the sludge screening system 53 further intercepts high-efficiency bacterial strains that overflow from the produced water. This prevents water load shocks that could lead to the loss of system microbial inhibitors and further reduce treatment efficiency.

[0048] Furthermore, the filler of the filler separation system 52 is a high-density polyurethane filler with a pore size of 2-4 mm.

[0049] Furthermore, the sludge screening system 53 is preferably a retention system such as a hydraulic screen or a rotary screen, with a screen aperture of 0.5-1 mm.

[0050] Furthermore, the second inclined plate sedimentation tank 51 and the filler separation system 52 can be set up separately or combined in different tanks.

[0051] The nitrification and denitrification system 60 includes a denitrification tank 61, a nitrification tank 62, and a third inclined plate sedimentation tank 63, which are connected in sequence. The denitrification tank 61 is connected to a carbon source dosing system 64. The nitrification tank 62 is equipped with an aerator connected to a blower 80. A reflux pump returns nitrified liquid from the nitrification tank 62 to the denitrification tank 61. The effluent from the third inclined plate sedimentation tank 63 meets discharge standards. Furthermore, to meet different drainage requirements, the effluent from the airlift internal circulation reaction tank can be treated in a single-stage or multi-stage nitrification and denitrification system for further treatment to meet discharge standards.

[0052] The reduction reaction tank 30 , the gas stripping internal circulation reaction tank 40 and the nitrification and denitrification system 60 are connected to the sludge dewatering system 70 , and the sludge dewatering supernatant of the sludge dewatering system is returned to the regulating tank 10 .

[0053] Example:

[0054] The present invention provides a method for treating coal gasification wastewater, comprising:

[0055] S1. Fixed-bed coal gasification wastewater enters the regulating tank 10 and is pumped into the decyanation reaction tank 20. Cyanide in the influent is removed by adding oxidizing substances such as sodium hypochlorite, ozone, hydrogen peroxide, chlorine, and chlorine dioxide. The residence time in the decyanation reaction tank is not less than 30 minutes.

[0056] S2, the effluent from the decyanation reaction tank 20 is reduced to the reaction tank 30, and sulfides and excess oxidants in the reduction reaction tank are removed by adding ferrous sulfate or sodium bisulfite to form iron sulfide or sulfide precipitation. An ORP online monitor is installed for the effluent, and the effluent ORP does not exceed 50mv.

[0057] S3. The effluent from the reduction reaction tank 30 enters the gas lift internal circulation reaction tank 40. A nutrient salt addition system is provided at the inlet. After the nutrient salt is added, the effluent enters the gas lift internal circulation reaction tank. The reaction tanks can be provided with one or more groups according to the processing load. A microporous aerator is provided in each group, which is used for both aerobic removal of pollutants and aeration lifting. A guide wall is provided simultaneously to form an internal circulation to achieve the circulation flow and efficient mass transfer of sludge. DO, PH and temperature online monitors are provided in each group of tanks, which are adjusted in real time according to the influent load. DO is less than 0.5 mg / l, PH is 7.5-8.5, and the temperature is 28-38°C.

[0058] S4. The effluent from the gas lift internal circulation reaction tank 40 passes through the last gas lift pipe and is refluxed into the water inlet for circulation treatment. The gas pipe adopts a perforated pipe and the reflux ratio is 5-30 times.

[0059] S5, the effluent from the air stripping internal circulation reaction tank 40 enters the high-efficiency separation system 50 to further intercept the high-efficiency bacteria, and the sludge from the sedimentation tank is returned to the front section through the sludge pump; wherein, the inlet and outlet water loads of the air stripping internal circulation reaction tank 40 are configured in a gradient, and the TN load removed at the inlet end can reach 1.5kgTN / m 3 The last grid of water outlet TN volume load can reach 0.3-0.5kgTN / m 3 .

[0060] S6. The effluent from the gas lift internal circulation reaction tank 40 enters the back-end nitrification and denitrification system 60. Carbon source is added to further remove the remaining pollutants to achieve water production standards. The operating conditions can be selected to be controlled as nitrite denitrification or nitrification denitrification.

[0061] S7, the remaining sludge from the reduction reaction tank 30, the gas stripping internal circulation reaction tank 40, and the nitrification and denitrification system 60 is processed by the sludge dewatering system 70 and then transported to a waste disposal site.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for treating coal gasification wastewater, characterized in that: include: Step 1: Send the coal gasification wastewater into the regulating tank for homogenization and equalization; Step 2: sending the effluent from the regulating tank to the decyanation reaction tank for decyanation treatment by adding an oxidant; Step 3: The effluent from the decyanation reaction tank enters a reduction reaction tank and is reduced by adding a reducing agent; Step 4: The effluent from the reduction reaction tank enters the air stripping internal circulation reaction tank, where it is aerated by a blower and refluxed by the air stripping device for mass transfer and mixing, and ammonia nitrogen is simultaneously oxidized to nitrite nitrogen by ammonia oxidizing bacteria. The nitrite nitrogen and ammonia nitrogen are then removed by ammonia oxidizing bacteria and nitrite reducing bacteria to remove ammonia nitrogen and COD from the wastewater. Step 5: The effluent from the air stripping internal circulation reaction tank enters a high-efficiency separation system; wherein the high-efficiency separation system includes a second inclined plate sedimentation tank, a filler separation system, and a sludge screening system connected in sequence; the second inclined plate sedimentation tank returns the sludge to the water inlet chamber of the first-stage reaction tank through a sludge pump and a sludge discharge pipe; Step 6: The effluent separated by the high-efficiency separation system enters the nitrification and denitrification system to remove the remaining COD, NH3-N and TN under the condition of adding a carbon source to achieve effluent that meets the standards; Step 7: The residual sludge generated by the reduction reaction tank, the gas stripping internal circulation reaction tank, and the nitrification and denitrification system is fed into the sludge dewatering system. The dewatered sludge is transported out for disposal, and the supernatant of the sludge dewatering is returned to the regulating tank.

2. The method for treating coal gasification wastewater according to claim 1, wherein: The coal gasification wastewater includes coal gasification wastewater from fixed bed gasifiers, fluidized bed and entrained bed gasifiers. The wastewater from fixed bed gasifiers includes incremental water from washing ash water from gasifiers, shift condensation wastewater and compressor flotation water.

3. The method for treating coal gasification wastewater according to claim 1, wherein: The added oxidant includes at least one of sodium hypochlorite, chlorine, chlorine dioxide, hydrogen peroxide and ozone.

4. The method for treating coal gasification wastewater according to claim 1, wherein: The added reducing agents include ferrous sulfate and sodium bisulfite.

5. A system for treating coal gasification wastewater, for implementing the method for treating coal gasification wastewater according to any one of claims 1 to 4, characterized in that: include: The regulating tank, decyanation reaction tank, reduction reaction tank, gas stripping internal circulation reaction tank, high-efficiency separation system and nitrification and denitrification system are arranged in sequence along the treatment direction of coal gasification wastewater; The decyanation reaction tank is connected to an oxidant dosing system, and the reduction reaction tank is connected to a reducing agent dosing system; The air stripping internal circulation reaction pool includes a multi-stage reaction pool connected in series, and each reaction pool is provided with two vertical guide walls, which divide each reaction pool into a water inlet chamber, an air stripping aeration chamber and a water outlet chamber connected in sequence. An air stripping aerator is provided in the middle of the air stripping aeration chamber, and all the air stripping aerators are connected to a blower; water enters the upper end of the water inlet chamber, and water flows out from the lower end of the water inlet chamber into the lower end water inlet of the air stripping aeration chamber, and the water outlet in the middle of the air stripping aeration chamber enters the adjacent water outlet chamber. The air stripping aerator is located between the water inlet and the water outlet of the air stripping aeration chamber. The water from the upper end of the water outlet chamber enters the upper end water inlet of the water inlet chamber of the lower reaction tank, and a first inclined plate sedimentation tank is provided at the water outlet of each water outlet chamber; the water inlet chamber of the first-stage reaction tank collects the water from the reduction reaction tank, and a nutrient salt dosing system is connected to the water inlet chamber of the first-stage reaction tank. The water from the tail end reaction tank enters the reflux water tank, and part of the water from the reflux water tank flows into the high-efficiency separation system, and the remaining part flows back to the water inlet chamber of the first-stage reaction tank through the air stripping reflux pipe. The water inlet of the air stripping reflux pipe is connected to an air pipe, and the air pipe is connected to a blower; The high-efficiency separation system includes a second inclined plate sedimentation tank, a filler separation system and a sludge screening system connected in sequence. The second inclined plate sedimentation tank returns the sludge to the water inlet chamber of the first-stage reaction tank through a sludge pump and a sludge discharge pipe; The nitrification and denitrification system comprises a denitrification tank, a nitrification tank and a third inclined plate sedimentation tank connected in sequence. The denitrification tank is connected to a carbon source dosing system. An aerator is provided in the nitrification tank, and the aerator is connected to a blower. The nitrification tank returns the nitrified liquid to the denitrification tank through a reflux pump. The effluent from the third inclined plate sedimentation tank meets the discharge standards. The reduction reaction tank, the gas stripping internal circulation reaction tank and the nitrification and denitrification system are connected to a sludge dewatering system, and the sludge dewatering supernatant of the sludge dewatering system is returned to the regulating tank.

6. The coal gasification wastewater treatment system according to claim 5, characterized in that: The air stripping reflux pipe is aerated through a perforated pipe for air stripping reflux, and the reflux ratio is 5-30 times.

7. The coal gasification wastewater treatment system according to claim 5, characterized in that: The filler of the filler separation system adopts high-density polyurethane filler with a pore size of 2-4mm, and the sludge screening system adopts a hydraulic screen or rotary screen interception system with a screen pore size of 0.5-1mm.

8. The coal gasification wastewater treatment system according to claim 4, characterized in that: The sludge produced by the reduction reaction tank is mainly iron sulfide or elemental sulfur, which is used to remove the sulfur source of the sulfur autotrophic denitrification filter for sewage deep treatment, and remove pollutants through the flocculation of iron salts to improve the effluent water quality.

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