Coal gasification wastewater treatment method and system for carbon source recovery, mitigation of hardness sludge accumulation in biochemical system, and control of scaling in aeration system

Abstract

The present invention provides a method and system for treating coal gasification wastewater for recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling the scaling of the aeration system, and belongs to the technical field of sewage treatment. The treatment method is to take coal gasification wastewater and sludge hydrolysis mixed liquid, mix and elute, then add flocculant to precipitate and separate, and the obtained supernatant is subjected to biological denitrification treatment, and the obtained residual sludge is then concentrated and alkaline hydrolyzed to obtain the sludge hydrolysis mixed liquid mixed with coal gasification wastewater; the treatment system includes a residual sludge alkaline hydrolysis device, an elution tank, a sedimentation tank, a biochemical system and an organic sludge concentration tank. The treatment method of the present invention can make a breakthrough in the scaling control of the biochemical system, and can recover the carbon source material in the residual sludge to reduce the carbon source usage of the treatment system, and can use a microporous aerator that can be lifted to improve the overall energy efficiency level of coal gasification wastewater treatment.

Description

Technical Field

[0001] The invention relates to a high-hardness wastewater treatment process, and in particular to a coal gasification wastewater treatment method and system for recovering carbon sources, alleviating hardness sludge accumulation in a biochemical system, and controlling scaling in an aeration system. Background Art

[0002] Coal gasification wastewater, especially the coal gasification wastewater produced by the entrained-bed gasifier using the quenched coal gas washing process, has the main characteristics of high ammonia nitrogen, low COD, high hardness, etc. Its sewage treatment process mostly adopts the "hardness removal + biological denitrification + post-treatment" process. The process runs relatively stably, and the system effluent COD, ammonia nitrogen, total nitrogen, etc. can be reduced to a very low level. However, there are still some problems to be solved during the operation of the system, which are specifically manifested as follows:

[0003] 1) In order to control the scaling of biochemical system process equipment, mainly the aeration system, the gasification wastewater treatment process usually sets up a hardness removal unit before the biochemical system. However, since the wastewater contains high concentrations of ammonium ions, organic acid ions and other buffer substances, it is difficult to adjust the pH of the wastewater. Usually, in order to achieve a better hardness removal effect, the pH of the wastewater needs to be adjusted to about 11. At this time, most of the ammonium ions in the wastewater are converted into NH 3 , consuming a large amount of liquid alkali; but in order to prevent the impact of the biochemical system, acid needs to be added before the effluent from the hardness removal system enters the biochemical system, and some NH 3 It is converted into ammonium ions, which in turn consumes excessive amounts of acidic agents. The presence of a large amount of buffer substances in wastewater makes the acid and alkali consumption of the pre-hardness removal unit far greater than the theoretical value calculated based on the hardness and alkalinity of the wastewater. However, for biochemical effluent hardness removal, since ammonia nitrogen, organic acids, etc. are all decomposed and removed by microorganisms, this phenomenon does not occur.

[0004] 2) Since the quality of coal gasification wastewater is easily affected by production conditions, coal quality and other factors, the hardness, alkalinity, ammonia nitrogen and other indicators in the wastewater often fluctuate. The hardness removal before biochemical treatment requires frequent adjustment of the dosage of hardness removal agents to ensure a stable hardness removal effect. However, there is generally no hardness requirement for the discharge of biochemical effluent, and it is extremely uneconomical to remove hardness only to achieve scaling control in the biochemical system. On the other hand, as far as the zero-discharge system is concerned, the effluent of the biochemical system is mostly mixed with clean wastewater for hardness removal before entering the reclaimed water membrane concentration device. This makes the operation and management personnel no longer pay much attention to the hardness removal unit before the biochemical treatment of sewage. The operation effect of the hardness removal unit is difficult to guarantee, and low hardness removal efficiency, excessively high effluent pH control and even a large number of hardness particles directly entering the biochemical system often occur; excessively high influent pH and liquid alkali and other agents added during the biochemical process will cause local OH in the biochemical system. - Excessive, it will react with the hardness ions (mainly Ca 2+ ) and HCO produced in biochemical processes 3 - , CO 2Combined with other materials to produce CaCO 3 And accumulate in the biochemical pool, the reaction process is as follows:

[0005] CO 2 +H 2 O→HCO 3 - +H + ;

[0006] OH - +H + →H 2 O;

[0007] Ca 2+ +HCO 3 - +OH - →CaCO 3 ↓+H 2 O.

[0008] Due to the low COD and high hardness of coal gasification wastewater, the amount of activated sludge synthesis is low, while the amount of hardness sludge accumulation is very large, which greatly reduces the organic components in the activated sludge. The sludge concentration of the biochemical system of some projects reaches 12~16g / L, but its VSS / SS is only about 0.2. The sludge activity is low, and regular sludge replenishment is required to ensure the long-term stable operation of the system. In addition, the scaling of process equipment and pipelines in the biochemical system is also very serious, which brings great troubles to the stable operation of the process. At the same time, it is difficult to use high-power-efficiency microporous aerators, and the overall energy consumption of the system is high. Summary of the invention

[0009] In view of the above problems, the present invention provides a method and system for treating coal gasification wastewater which can recover carbon sources, alleviate the accumulation of hard sludge in the biochemical system, and control scaling of the aeration system.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is:

[0011] A method for treating coal gasification wastewater for recovering carbon sources, alleviating hardness sludge accumulation in a biochemical system, and controlling scaling in an aeration system, the method comprising the following steps:

[0012] Carbon source elution and recovery: coal gasification wastewater is mixed with the sludge hydrolysis mixture obtained after alkaline hydrolysis, eluted, and then flocculants are added for precipitation and separation to obtain supernatant and sludge; the sludge is concentrated in an inorganic sludge concentration tank, filtered by a sludge filter press system, and the obtained dry sludge is directly transported out;

[0013] Biological denitrification: The supernatant is used as biochemical influent and enters the biochemical system for biological denitrification treatment to obtain biochemical effluent and residual sludge;

[0014] The biochemical effluent is directly discharged, or after biochemical post-treatment, enters the reclaimed water pretreatment system to remove hardness;

[0015] The remaining sludge enters the organic sludge thickening tank for concentration;

[0016] Alkaline hydrolysis: The concentrated residual sludge is transported to the residual sludge alkaline hydrolysis device for alkaline hydrolysis to obtain a sludge hydrolysis mixture;

[0017] Part of the sludge hydrolysis mixture is used as inoculated sludge and refluxed to the second reaction zone at the front end of the alkaline hydrolysis process to inoculate hydrolysis acidifying bacteria and accelerate the hydrolysis reaction rate;

[0018] The remaining sludge hydrolysis mixture overflows to the front end of the carbon source elution and recovery process, and is mixed and eluted with the coal gasification wastewater.

[0019] Furthermore, liquid alkali is added at the front end of the alkaline hydrolysis process.

[0020] Furthermore, after adding the alkalinity agent, the pH of the system obtained was 10-11.5; after the alkaline hydrolysis was completed, the pH of the sludge hydrolysis mixture was 6-8.

[0021] Furthermore, during the alkaline hydrolysis process, the reflux ratio of the refluxed partial sludge hydrolysis mixture is 3 to 5 times.

[0022] Furthermore, during the alkaline hydrolysis process, the total hydraulic retention time is 3 to 5 days.

[0023] Furthermore, in the carbon source elution and recovery process, the volume ratio of the coal gasification wastewater to the sludge hydrolysis mixed liquid is 40~50:1.

[0024] A coal gasification wastewater treatment system for recovering carbon sources, alleviating hardness sludge accumulation in a biochemical system, and controlling scaling in an aeration system, the coal gasification wastewater treatment system comprising a residual sludge alkaline hydrolysis device, an elution tank, a sedimentation tank, a biochemical system, and an organic sludge concentration tank;

[0025] The front end of the excess sludge alkaline hydrolysis device is connected to the rear end of the organic sludge concentration tank; the rear end of the excess sludge alkaline hydrolysis device is respectively connected to the front end of the elution tank and the second reaction zone of the front end of the excess sludge alkaline hydrolysis device;

[0026] The coal gasification wastewater and the sludge hydrolysis mixture from the alkaline hydrolysis unit first enter the elution tank arranged at the front end of the coal gasification wastewater treatment system;

[0027] The front end of the elution tank is the inlet for coal gasification wastewater;

[0028] The rear end of the elution tank is connected to the front end of the sedimentation tank;

[0029] The rear end of the sedimentation tank is connected to the front end of the biochemical system;

[0030] The biochemical system is connected to the front end of the organic sludge thickening tank.

[0031] Furthermore, the residual sludge alkaline hydrolysis device includes 6 to 8 reactors with stirrers connected in series; the last reactor is connected to the second reactor through a sludge return pump.

[0032] Furthermore, in the excess sludge alkaline hydrolysis device, the agitator in the first reactor is a paddle agitator, and the agitators in the remaining reactors are frame agitators;

[0033] The first reactor is equipped with a pH automatic control system; the second reactor is equipped with a temperature sensor.

[0034] Furthermore, the biochemical system is a traditional pre-denitrification biological denitrification process, including an aerobic zone, and the aerobic zone is provided with a liftable microporous aerator; the liftable microporous aerator is also equipped with an online cleaning device.

[0035] The beneficial effects of the coal gasification wastewater treatment method and system of the present invention for recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling scaling of the aeration system are as follows:

[0036] The coal gasification wastewater of the present invention has the characteristics of high ammonia nitrogen, low COD, and high hardness wastewater. The treatment method of the present invention can make a breakthrough in the scaling control of the biochemical system. At the same time, the carbon source material in the residual sludge can be recovered to reduce the carbon source usage of the treatment system, and a microporous aerator can be used to improve the overall energy efficiency level of coal gasification wastewater treatment.

[0037] The present invention eliminates the pre-hardness removal unit for coal gasification wastewater or places the hardness removal task for coal gasification wastewater in the reclaimed water pretreatment process after biological denitrification, which can prevent the adverse effects of a large amount of ammonium ions and organic acid ions contained in the coal gasification wastewater before biological denitrification on the pH adjustment process of hardness removal, thereby saving all hardness removal costs (projects where biochemical effluent can be directly discharged) or greatly reducing the amount of acid and alkali used in the pH adjustment stage of hardness removal (zero-discharge projects);

[0038] The present invention performs alkaline hydrolysis on the excess sludge, eliminates the pre-hardness removal unit, and transfers the alkalinity required to be supplemented in the aerobic zone during the biological denitrification process to the excess sludge alkaline hydrolysis device for addition, and changes the alkalinity agent directly added in the aerobic zone to the alkalinity of organic acid salts provided by the sludge hydrolysis mixed liquid to indirectly supplement the alkalinity, which can effectively control the pH of the biochemical system influent, greatly alleviating the problem of coal gasification wastewater being OH - The accumulation of hard sludge in the biochemical system caused by local excess leads to sludge degradation and scaling of process equipment;

[0039] The present invention can effectively recover the organic matter contained in the excess sludge by alkaline hydrolysis of the excess sludge, while alleviating the scaling of the biochemical system. For coal gasification wastewater with a low carbon-nitrogen ratio, the amount of external carbon source used can be effectively reduced, thereby reducing the cost of wastewater treatment.

[0040] The method of the present invention can significantly alleviate the scaling of the biochemical system, so that the liftable microporous aerator that was previously difficult to use in the treatment of high-hardness coal gasification wastewater can be used, and by setting an online cleaning device, the long-term stable operation of the liftable microporous aerator is guaranteed, thereby reducing the comprehensive energy consumption level of the treatment system;

[0041] The present invention performs alkaline hydrolysis on the excess sludge to recover the organic matter in the excess sludge, thereby reducing the sludge output of the entire system and further saving part of the sludge disposal cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a simplified structural diagram of a coal gasification wastewater treatment system for recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling scaling in the aeration system in an embodiment of the present invention;

[0043] Figure 2 Schematic diagram of the structure of an organic sludge concentration tank and a residual sludge alkaline hydrolysis device in an embodiment of the present invention;

[0044] Figure 3 It is a process flow chart of a method for treating coal gasification wastewater in an embodiment of the present invention for recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling scaling in the aeration system;

[0045] Among them, 1. Organic sludge thickening tank; 2. Sludge pump; 3. Residual sludge alkaline hydrolysis device; 31. Paddle mixer; 32. Frame mixer; 33. Reflux pump; 34. pH automatic control system; 341. pH detector; 342. Liquid alkali dosing pump; 343. Liquid alkali storage tank; 344. PLC control system; 35. Temperature sensor. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present invention are described clearly and completely below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0047] Embodiment A method and system for treating coal gasification wastewater for recovering carbon source, alleviating hardness sludge accumulation in biochemical system, and controlling scaling of aeration system

[0048] 1. A coal gasification wastewater treatment system that recovers carbon sources, alleviates the accumulation of hard sludge in the biochemical system, and controls scaling in the aeration system

[0049] like Figure 1 As shown, this embodiment is a coal gasification wastewater treatment system for recovering carbon sources, alleviating hardness sludge accumulation in the biochemical system, and controlling scaling of the aeration system, comprising a residual sludge alkaline hydrolysis device 3, an elution tank, a sedimentation tank, a biochemical system, an organic sludge concentration tank 1, an inorganic sludge concentration tank and a sludge filter press system; the front end of the residual sludge alkaline hydrolysis device 3 is connected to the rear end of the organic sludge concentration tank 1; the rear end of the residual sludge alkaline hydrolysis device 3 is respectively connected to the front end of the elution tank and the front end of the residual sludge alkaline hydrolysis device; the coal gasification wastewater and the sludge hydrolysis mixed liquid from the alkaline hydrolysis unit first enter the elution tank arranged at the front end of the entire coal gasification wastewater treatment system; the front end of the elution tank is the inlet of the coal gasification wastewater; the rear end of the elution tank is connected to the front end of the sedimentation tank; the rear end of the sedimentation tank is connected to the front end of the biochemical system; the bottom of the sedimentation tank is connected to the inorganic sludge concentration tank; the inorganic sludge concentration tank is connected to the sludge filter press system; the biochemical system is connected to the front end of the organic sludge concentration tank 1.

[0050] like Figure 2 As shown, the excess sludge alkaline hydrolysis device 3 includes 6 to 8 reactors with stirrers connected in series (in this embodiment, the excess sludge alkaline hydrolysis device 3 includes 6 reactors connected in series).

[0051] In the excess sludge alkaline hydrolysis device 3 , the agitator in the first reactor is a paddle agitator 31 , and the agitators in the remaining reactors are frame agitators 32 .

[0052] A pH automatic control system 34 is provided in the first reactor; the pH automatic control system 34 consists of a pH detector 341, a liquid alkali dosing pump 342, a liquid alkali storage tank 343 and a PLC control system 344, the PLC control system 344 is electrically connected to the pH detector 341 and the liquid alkali dosing pump 342 respectively, and the pH in the first reactor is controlled between 10 and 11.5 through the PLC control system 344; the liquid alkali storage tank 343 is connected to the first reactor through the liquid alkali dosing pump 342.

[0053] A temperature sensor 35 is provided in the second reactor. Since the water temperature in the entire treatment system can generally meet the hydrolysis requirement of 30-40°C, the temperature sensor 35 is only provided in the second reactor. By detecting the temperature in the second reactor, the water temperature in the entire treatment system is detected.

[0054] The last reactor is connected to the second reactor via a sludge return pump 33 .

[0055] The first reactor at the front end of the excess sludge alkaline hydrolysis device 3 is connected to the rear end of the organic sludge concentration tank 1 through the sludge pump 2; the last reactor at the rear end of the excess sludge alkaline hydrolysis device 3 is connected to the front end of the elution tank.

[0056] Furthermore, the biochemical system is a traditional pre-denitrification biological denitrification process, including an aerobic zone, wherein the aerobic zone is provided with a liftable microporous aerator, and the liftable microporous aerator is also equipped with an online cleaning device. Among them, the liftable microporous aerator and its matching online cleaning device are conventional liftable microporous aerators and online cleaning devices (not shown in the figure).

[0057] 2. A method for treating coal gasification wastewater by recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling scaling in the aeration system

[0058] like Figure 3 As shown, this embodiment is a method for treating coal gasification wastewater for recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling scaling of the aeration system. The above-mentioned treatment system is used to treat the coal gasification wastewater, and specifically includes the following steps:

[0059] S1. Carbon source elution and recovery

[0060] According to the volume ratio of coal gasification wastewater to sludge hydrolysis mixed liquid of 40-50:1, the coal gasification wastewater and the sludge hydrolysis mixed liquid obtained after alkaline hydrolysis are simultaneously put into the elution tank for mixing and elution, and a large amount of coal gasification wastewater is used to elute the soluble carbon source contained in the sludge hydrolysis mixed liquid, so that the soluble carbon source subsequently enters the biochemical system together with the supernatant;

[0061] After the coal gasification wastewater and the sludge hydrolysis mixture are mixed and eluted, flocculants such as PAC and / or PAM are added to flocculate the remaining inorganic sludge and suspended impurities such as coal ash in the coal gasification wastewater into larger flocs, which are then separated into supernatant and precipitated sludge in the sedimentation tank; the residence time in the elution tank is 20~40min.

[0062] The supernatant is then used as biochemical influent and enters the biochemical system for biological denitrification treatment.

[0063] The precipitated sludge is concentrated in the inorganic sludge thickening tank and filtered by the sludge filter press system, and the resulting dry sludge is directly transported out.

[0064] The sludge hydrolysis mixture obtained after alkaline hydrolysis can convert a large amount of organic matter in the activated sludge into soluble carbon sources such as small molecular organic acid salts. These soluble carbon sources are all soluble in water. By mixing the sludge hydrolysis mixture with coal gasification wastewater, these soluble carbon sources can be dissolved in the supernatant and enter the biochemical system together with the supernatant for denitrification treatment.

[0065] S2. Biological denitrification

[0066] The biochemical influent enters the biochemical system and undergoes biological denitrification processes such as organic matter oxidation and decomposition, nitrification and denitrification. Since the fluidized bed coal gasification wastewater contains a large amount of formate, the organic acid salt can produce a large amount of alkalinity (i.e. HCO) through the biological decomposition process. 3 - ) Assisted by the organic acid salts produced in the alkaline hydrolysis process, it is basically possible to ensure that there is no need to add alkalinity agents in the biochemical aerobic pool. And because the alkalinity added by the degradation of organic acid salts will not cause local OH in the biochemical system - The alkalinity substances produced during the decomposition process are also gradually produced and are immediately consumed by nitrification reaction after production. Therefore, local OH will not occur during the biological denitrification process. - and HCO 3 - The problem of excessive alkalinity is avoided, thereby avoiding the problem of hardness ion deposition.

[0067] After biological denitrification is completed, biochemical effluent and residual sludge are obtained.

[0068] The biochemical effluent is directly discharged, or after biochemical post-treatment (such as flocculation with flocculants such as PAC and / or PAM), it enters the reclaimed water pretreatment system for hardness removal. The coal gasification wastewater treatment system for carbon source recovery, mitigation of hardness sludge accumulation in the biochemical system, and control of scaling in the aeration system no longer has a hardness removal unit. During the biochemical post-treatment process, the sludge obtained by flocculation (not the residual sludge produced by biochemical denitrification) is concentrated in the inorganic sludge thickening tank and filtered by the sludge filter press system before being transported out as dry sludge.

[0069] The biochemical system is generally a biological denitrification system, which adopts traditional biological denitrification processes (such as AOAO or SBR, etc.), including an aerobic zone. The aeration system in the aerobic zone (generally an aerobic tank) adopts a liftable microporous aerator equipped with an online cleaning device. The online cleaning device consists of a formic acid dosing pump, an atomizing nozzle installed on the main pipe of the online cleaning device, a pressure sensor and an automatic control system. The pressure sensor detects the resistance change of the online cleaning device. When the resistance of the online cleaning device exceeds the initial value of 3~5kPa, the formic acid dosing pump is started, and the formic acid is atomized through the atomizing nozzle and then sprayed into the main air duct of the liftable microporous aerator; the rapidly evaporated formic acid is transported to the micropores of the online cleaning device by compressed air to dissolve the CaCO accumulated on the pore wall. 3 Each cleaning time is 30~60min.

[0070] At the same time, there is no need to add liquid alkali to the aerobic zone, as the alkalinity required for nitrification is supplemented by the decomposition of soluble carbon sources (including small molecular organic acid salts, etc.) dissolved in the supernatant.

[0071] Conventional biochemical system scaling or CaCO 3The accumulation is mainly due to the pre-hardness removal unit set at the front end of the biochemical system. The pre-hardness removal unit is improperly controlled or unstable, and hardness particles enter the biochemical system; or the pH of the effluent from the pre-hardness removal unit is too high, causing the OH at the front end of the biochemical system to accumulate. - Excessive, thus inducing CaCO 3 At the same time, due to the high ammonia nitrogen content in the coal gasification wastewater and insufficient influent alkalinity, it is necessary to supplement liquid alkali in the aerobic zone, and the supplementation of liquid alkali will cause OH in the local area of ​​the aerobic zone. - Excessive, thus inducing CaCO 3 The present invention does not need to set up a pre-hardness removal unit before the biochemical system, and the aerobic zone does not need to add liquid alkali, which can maintain the biochemical system without local OH - Excess area, so that the Ca in the supernatant (i.e. the supernatant after the mixture of coal gasification wastewater and sludge hydrolysis mixture) 2+ Basically, there will be no scaling and precipitation in the biochemical system, so that a microporous aerator with higher energy efficiency can be used in the biochemical system. At the same time, in order to further control the scaling and clogging of the microporous aerator, the microporous aerator is also equipped with an online cleaning device. When the resistance of the microporous aerator is higher than the initial value of 3~5kPa, the online cleaning can be started. The atomized formic acid is sprayed into the pipeline of the microporous aerator through the online cleaning device to dissolve the CaCO accumulated in the micropores of the microporous aerator. 3 And other substances can reduce the resistance of the microporous aerator.

[0072] S3, excess sludge concentration

[0073] The residual sludge generated by the biochemical system enters the organic sludge thickening tank 1 and is concentrated to 15-30 g / L to obtain concentrated residual sludge.

[0074] S4, alkaline hydrolysis

[0075] The concentrated residual sludge is transported to the residual sludge alkaline hydrolysis device 3, and an alkalinity agent (such as liquid caustic soda) is added to perform alkaline hydrolysis (i.e., perform hydrolysis and acidification reaction) to obtain a sludge hydrolysis mixture with a pH of 6-8.

[0076] The tail gas generated in the residual sludge alkaline hydrolysis device 3 is directly transported to the VOC system for treatment.

[0077] The total hydraulic retention time in the residual sludge alkaline hydrolysis device 3 is 3 to 5 days, the pH of the reaction system gradually decreases to between 6 and 8, and the macromolecular organic matter in the residual sludge is gradually decomposed into small molecular substances, such as organic acid salts, ammonia nitrogen, phosphates, etc.

[0078] The residual sludge alkaline hydrolysis device 3 includes 6 to 8 reactors with stirrers connected in series, and the reaction temperature is 30 to 40°C. The concentrated residual sludge is transported to the first reactor (i.e., the front end of the residual sludge alkaline hydrolysis device 3), and liquid alkali is added to the first reactor to adjust the pH to 10 to 11.5 (generally, the pH is adjusted to about 10.5) to destroy the sludge floc structure and part of the microbial cell wall, which is beneficial to improve the hydrolysis and acidification efficiency and facilitate the release of microbial cell substances; then, in the remaining reactors of the residual sludge alkaline hydrolysis device 3, the organic matter in the residual sludge is hydrolyzed and acidified by culturing hydrolysis and acidification bacteria.

[0079] At the end of the excess sludge alkaline hydrolysis device 3 (i.e. the last reactor), a part of the sludge hydrolysis mixture is refluxed as inoculated sludge to the front end of the excess sludge alkaline hydrolysis device 3 (i.e. the second reactor) through the sludge reflux pump 33, and the reflux ratio is 3 to 5 times to maintain the stability of the pH in the reactors except the first reactor, which is conducive to the rapid progress of the hydrolysis acidification reaction.

[0080] The remaining sludge hydrolysis mixed liquid overflowing from the end of the remaining sludge alkaline hydrolysis device 3 (i.e., the last reactor) enters the elution tank and is mixed and eluted with the coal gasification wastewater (see step S1 for details).

[0081] The present invention recovers the carbon source in the excess sludge by alkaline hydrolysis of the excess sludge, so that the C / N / P ratio of the sludge hydrolysis mixture is about 45-50:5-6:1, wherein the carbon-nitrogen ratio is about 9-10:1, which is much larger than the carbon-nitrogen ratio of 4:1 required for denitrification, and can save part of the external carbon source of the biochemical system;

[0082] Among them, the excess sludge alkaline hydrolysis device 3 can decompose part of the carbon source in the excess sludge into soluble organic acid salts (such as formate, acetate, etc.). As part of the soluble carbon source, the organic acid salt is subsequently decomposed in the biochemical system to produce alkalinity substances to provide alkalinity for the nitrification reaction;

[0083] After entering the biochemical system, organic acid salts are decomposed to produce bicarbonate (i.e. HCO 3 - ), providing alkalinity to the biochemical system. Some of the reactions in the biochemical system include:

[0084] Formate decomposition: 1 / 2 HCOO - +1 / 4O 2 =1 / 2HCO 3 - ;

[0085] Acetate decomposition: 1 / 8CH 3 COO - +1 / 4O 2 =1 / 8CO2 +1 / 8HCO 3 - +1 / 8H 2 O;

[0086] Carbohydrate decomposition: 1 / 4CH 2 O+1 / 4O 2 =1 / 4CO 2 +1 / 4H 2 O;

[0087] Ethanol decomposition: 1 / 12CH 3 CH 2 OH+1 / 4O 2 =1 / 6CO 2 +1 / 4H 2 O;

[0088] Oil decomposition: 1 / 46C 8 H 16 O+1 / 4O 2 =1 / 6CO 2 +4 / 23H 2 O.

[0089] It can be seen that organic acid salts can produce a large amount of alkalinity (i.e. HCO 3 - ), while organic substances such as carbohydrates, alcohols and lipids cannot produce alkalinity. Coal gasification wastewater contains a large amount of formate, and its alkalinity requirement in the biological denitrification process is much lower than the alkalinity requirement in the biological denitrification process of conventional wastewater. The soluble carbon source provided by the residual sludge alkaline hydrolysis device 3 after treatment in the present invention can basically meet the alkalinity requirement in the biological denitrification process, thereby further avoiding the local OH caused by adding alkalinity agents (such as liquid caustic soda) in the biochemical system. - Excessive CaCO 3 Precipitation accumulation occurs.

[0090] At the same time, the present invention changes the alkalinity agent added in the biochemical system in the prior art to be added in the excess sludge alkaline hydrolysis device 3, thereby improving the hydrolysis and acidification efficiency by destroying the floc structure of the excess sludge. At the same time, as the hydrolysis and acidification proceed, a large amount of microbial organic matter is hydrolyzed into small molecular organic acids, neutralizing OH in the wastewater. -, The organic acid salts are generated, so that the pH of the sludge hydrolysis mixed solution gradually drops to between 6 and 8. The organic acid salts can be subsequently decomposed into alkalinity substances in the biochemical system. Therefore, the alkalinity of the biochemical influent can basically meet the nitrification requirements without increasing the pH of the biochemical influent. The present invention indirectly supplements the alkalinity required by the biochemical system by setting up a residual sludge alkaline hydrolysis device to prevent the biochemical system from being damaged by OH. -Local excess leads to problems such as sludge degradation and scaling of process equipment.

[0091] Furthermore, although the present invention does not perform pre-hardness removal, the degree of inorganic particle accumulation in the biochemical system is much lower than that of the existing biochemical system with pre-hardness removal (sludge VSS / SS is about 0.45);

[0092] The alkalinity of the biochemical influent (mainly the alkalinity produced by biosynthesis of organic acid salts in the biochemical system) can meet the needs of nitrification reaction. The properties of the activated sludge are no different from those of conventional activated sludge, and there is basically no hardness sludge accumulated in the biochemical system (sludge VSS / SS is between 0.6 and 0.7, and the sludge concentration is basically at the normal level, generally about 4 to 5 g / L).

[0093] Since the treatment method of the present invention is a continuous dynamic process, the water quality of coal gasification wastewater and various process parameters are dynamically changing parameters. Therefore, during the treatment process, it is only necessary to control the various process parameters within the parameter range specified in the above embodiment, and there is no need to list the parameter point values ​​at a specific moment.

[0094] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for treating coal gasification wastewater by recovering carbon sources, alleviating the accumulation of hard sludge in the biochemical system, and controlling scaling in the aeration system, characterized in that: The processing method comprises the following steps: Carbon source elution and recovery: coal gasification wastewater is mixed with the sludge hydrolysis mixture obtained after alkaline hydrolysis, washed, and then a flocculant is added for precipitation and separation to obtain a supernatant and sludge; In the carbon source elution and recovery process, the volume ratio of coal gasification wastewater to sludge hydrolysis mixed liquid is 40~50:1; Biological denitrification: The supernatant is subjected to biological denitrification treatment to obtain biochemical effluent and residual sludge; Excess sludge thickening; Alkaline hydrolysis: The concentrated residual sludge is subjected to alkaline hydrolysis to obtain a sludge hydrolysis mixture; Part of the sludge hydrolysis mixture flows back to the second reaction zone at the front end of the alkaline hydrolysis process to inoculate hydrolysis acidifying bacteria to accelerate the hydrolysis reaction rate; At the front end of the alkaline hydrolysis process, liquid alkali is added; the pH of the system obtained after adding liquid alkali is 10~11.5; after the alkaline hydrolysis is completed, the pH of the sludge hydrolysis mixture is 6~8; During the alkaline hydrolysis process, microbial organic matter is hydrolyzed to form organic acid salts, which provide alkalinity substances for the biological denitrification process; The remaining sludge hydrolysis mixture overflows to the front end of the carbon source elution and recovery process, and is mixed and eluted with the coal gasification wastewater.

2. The processing method according to claim 1, characterized in that: During the alkaline hydrolysis process, the reflux ratio of the refluxed partial sludge hydrolysis mixture is 3 to 5 times.

3. The processing method according to claim 1, characterized in that: During the alkaline hydrolysis process, the total hydraulic retention time is 3~5d.

4. A coal gasification wastewater treatment system for recovering carbon sources, alleviating hardness sludge accumulation in the biochemical system, and controlling scaling in the aeration system, using the treatment method described in any one of claims 1 to 3, characterized in that: The coal gasification wastewater treatment system includes a residual sludge alkaline hydrolysis device, an elution tank, a sedimentation tank, a biochemical system and an organic sludge concentration tank; The front end of the excess sludge alkaline hydrolysis device is connected to the rear end of the organic sludge concentration tank; the rear end of the excess sludge alkaline hydrolysis device is respectively connected to the front end of the elution tank and the second reaction zone of the front end of the excess sludge alkaline hydrolysis device; The coal gasification wastewater and the sludge hydrolysis mixture from the alkaline hydrolysis unit first enter the elution tank set at the front end of the coal gasification wastewater treatment system; The rear end of the elution tank is connected to the front end of the sedimentation tank; The rear end of the sedimentation tank is connected to the front end of the biochemical system; The biochemical system is connected to the front end of the organic sludge thickening tank.

5. The processing system according to claim 4, characterized in that The residual sludge alkaline hydrolysis device includes 6 to 8 reactors with agitators connected in series; the last reactor is connected to the second reactor through a sludge return pump; The second reactor is the second reaction zone.

6. The processing system according to claim 4 or 5, characterized in that In the residual sludge alkaline hydrolysis device, the agitator in the first reactor is a paddle agitator, and the agitators in the remaining reactors are frame agitators; The first reactor is equipped with a pH automatic control system; the second reactor is equipped with a temperature sensor.

7. The processing system according to claim 4 or 5, characterized in that: The biochemical system is a traditional pre-denitrification biological denitrification process, including an aerobic zone, in which a liftable microporous aerator is provided.

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