Semi-coke wastewater double-carbon-source biochemical treatment system and process

Abstract

The invention relates to a semi-coke wastewater double-carbon-source biochemical treatment system and process, and the process comprises the following steps: pretreated semi-coke wastewater enters a front anoxic tank for denitrification reaction to remove COD and total nitrogen; effluent of the front anoxic tank enters an aerobic tank to be subjected to carbonization and nitration reaction, organic matters are removed, and ammonia nitrogen is converted into nitrite nitrogen and nitrate nitrogen; effluent of the aerobic tank enters a rear anoxic pretreatment tank for endogenous denitrification reaction; the mixed liquid in the rear anoxic pretreatment tank flows back to the front anoxic tank, and the reflux ratio is 400%-800%; and effluent of the post-anoxic pretreatment tank is subjected to mud-water separation and post-treatment to reach the standard and then is recycled. Mixed liquid backflow is carried out at the tail end of the rear anoxic pretreatment tank, the device has the advantages of being resistant to toxicity and impact, simple in technological process and low in operation cost, meanwhile, a large backflow ratio is adopted, nitrate nitrogen is removed, and meanwhile impact of biotoxicity on a biochemical system and inhibition of the biotoxicity on microorganisms are reduced.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to a dual-carbon-source biochemical treatment system and process for semi-coke wastewater. Background Technology

[0002] Semi-coke wastewater is generated during the production of semi-coke and the purification of coal gas, mainly originating from the circulating condensate of raw coal gas and the wastewater from coal gas purification. Semi-coke wastewater has a complex composition, containing large amounts of pollutants such as coal tar, phenols, ammonia nitrogen, sulfides, and cyanides. Specifically, CODcr is as high as 20,000-90,000 mg / L, ammonia nitrogen 3,000-7,000 mg / L, total phenols 10,000-15,000 mg / L, and petroleum hydrocarbons 1,000-5,000 mg / L.

[0003] The process of treating semi-coke wastewater is long and has many influencing factors. At present, there is no mature full-process semi-coke wastewater treatment technology at home and abroad. The treatment methods mainly draw on the coking wastewater treatment process with similar water quality. Semi-coke ovens usually adopt energy-saving and environmentally friendly coke quenching methods such as steam and dry methods. However, using semi-coke wastewater to quench coke after treatment will pose environmental risks. Semi-coke wastewater treatment needs to achieve zero wastewater discharge.

[0004] Currently, the commonly used zero-discharge treatment processes for semi-coke wastewater in China mainly include pretreatment, biological treatment, advanced treatment, reuse treatment, and evaporation crystallization. The commonly used pretreatment stage primarily involves "oil removal + acid and ammonia removal + evaporation and phenol removal." However, after processes such as oil removal, acid removal tower, ammonia removal tower, and evaporation concentration, the resulting evaporation condensate still contains a large amount of volatile phenols, as well as small amounts of oil and ammonia nitrogen, with CODcr reaching as high as 2000 mg / L-3500 mg / L. Directly entering the membrane system for treatment easily causes membrane fouling, requiring frequent cleaning and regeneration, affecting the membrane product's lifespan, or even causing the membrane system to malfunction. Furthermore, ammonia nitrogen can also lead to substandard quality of membrane permeate and reused water. Simultaneously, phenol-containing wastewater is biotoxic, and free ammonia has a significant biological inhibitory effect, making conventional AO biological treatment processes highly susceptible to impact. Therefore, the evaporation and phenol removal pretreatment process faces the challenge of removing pollutants from the evaporation condensate and ultimately achieving zero wastewater discharge. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a dual-carbon-source biochemical treatment system and process for semi-coke wastewater, solving the technical problems in the prior art where the evaporation phenol removal pretreatment process for semi-coke wastewater is difficult to remove pollutants from the evaporation condensate and the strong biological toxicity and biological inhibition effects lead to treatment difficulties.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a dual-carbon-source biochemical treatment process for semi-coke wastewater, comprising the following steps: S1, the pretreated semi-coke wastewater enters a pre-anoxic tank for denitrification to remove COD and total nitrogen; S2, the effluent from the pre-anoxic tank enters an aerobic tank for carbonization and nitrification to remove organic matter and convert ammonia nitrogen into nitrite and nitrate nitrogen; S3, the effluent from the aerobic tank enters a post-anoxic pretreatment tank for endogenous denitrification; the mixed liquor in the post-anoxic pretreatment tank is returned to the pre-anoxic tank at a return ratio of 400% to 800%; S4, the effluent from the post-anoxic pretreatment tank is subjected to sludge-water separation and post-treatment to meet standards for reuse.

[0007] Secondly, this invention provides a dual-carbon-source biochemical treatment system for semi-coke wastewater, comprising a pretreatment unit, a pre-anoxic tank, an aerobic tank, a post-anoxic pretreatment tank, a secondary sedimentation tank, and a post-treatment tank. The pretreatment unit is used to pretreat and homogenize the semi-coke wastewater. The pre-anoxic tank is used to denitrify the pretreated semi-coke wastewater, removing COD and total nitrogen. The aerobic tank is used to carbonize and nitrify the effluent from the pre-anoxic tank, removing organic matter and converting ammonia nitrogen into nitrite and nitrate nitrogen. The post-anoxic pretreatment tank is used to perform endogenous denitrification on the effluent from the aerobic tank. The post-anoxic pretreatment tank is connected to the inlet area of ​​the pre-anoxic tank via a mixed liquor return pump. The secondary sedimentation tank is used to separate the sludge and water in the effluent from the post-anoxic pretreatment tank. The post-treatment tank is used to treat the effluent from the secondary sedimentation tank to meet standards for reuse.

[0008] Compared with the prior art, the beneficial effects of the present invention include: This invention utilizes the carbon source from the influent in the pre-anoxic tank for exogenous denitrification, and the post-anoxic pretreatment tank uses substances within microbial cells as both a carbon source and energy source for endogenous denitrification, achieving a synergistic effect of dual carbon sources to remove total nitrogen and reduce operating costs. Furthermore, the pre-anoxic tank (A tank) / aerobic tank (O tank) – post-anoxic pretreatment tank (PHP tank) process employed in this invention, with mixed liquor recirculation at the end of the PHP tank, effectively mitigates the impact of dissolved oxygen from the O tank recirculated mixed liquor on the A tank. This process is characterized by its resistance to toxicity and impact, simple process flow, and low operating costs. Simultaneously, the large recirculation ratio of 400%–800% reduces the impact of biological toxicity on the biochemical system and the inhibition of microorganisms while removing nitrate nitrogen. Semi-coke wastewater treated by this invention can be directly reused; the process flow is simple, the cost is low, and it facilitates the achievement of zero-discharge goals. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the dual-carbon-source biochemical treatment system for semi-coke wastewater of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] To address the shortcomings of using evaporation-based phenol removal pretreatment processes for semi-coke wastewater, such as difficulty in removing pollutants from the evaporation condensate and the challenges posed by strong biotoxicity and bioinhibition, particularly the high biotoxicity and bioinhibition properties of the effluent from evaporation-based phenol removal pretreatment, which easily leads to membrane fouling requiring frequent cleaning and regeneration, and the vulnerability of conventional AO biological treatment processes to shocks, this invention provides a dual-carbon-source biological treatment system and process for semi-coke wastewater. With its high load capacity and large reflux characteristics, this system effectively solves the above-mentioned problems. Furthermore, the wastewater treated by this invention does not require further membrane treatment and can be directly reused with zero discharge.

[0012] In a first aspect, the present invention provides a dual-carbon-source biochemical treatment process for semi-coke wastewater, comprising the following steps: S1, the pretreated semi-coke wastewater enters the pre-anoxic tank for denitrification to remove COD and total nitrogen; S2, the effluent from the pre-anoxic tank enters the aerobic tank for carbonization and nitrification to remove organic matter and convert ammonia nitrogen into nitrite and nitrate nitrogen; S3, the effluent from the aerobic tank enters the post-anoxic pretreatment tank for endogenous denitrification; the mixed liquor in the post-anoxic pretreatment tank is recycled back to the pre-anoxic tank at a recycling ratio of 400% to 800%. S4, the effluent from the post-anoxic pretreatment tank is treated by mud-water separation and post-treatment to meet the standards for reuse.

[0013] Preferably, in step S1, the pretreatment includes degreasing, deacidification and deammoniation, and evaporation and dephenolization.

[0014] It is understood that this invention is applicable to the biochemical treatment of wastewater containing biotoxic organic matter and ammonia nitrogen, and is particularly suitable for the biochemical treatment of semi-coke wastewater pretreated with evaporation dephenolization. The pretreatment in this invention involves a simple pretreatment of the semi-coke wastewater to remove suspended solids, oils, and other pollutants that affect microbial growth. This is a conventional technique. Specifically, the pretreatment can employ gravity oil removal, cyclone oil removal, coalescence oil removal, or a combination thereof; deacidification and deammoniation can be performed using a double-tower or single-tower process; evaporation dephenolization can employ multi-effect evaporation or mechanical steam recompression evaporation; the produced water meets the characteristics of the influent water quality of this invention and does not affect the overall treatment objective of this invention. It can also be understood that the actual treated water of this invention is the pretreated evaporation condensate, which has a low salt content but carries pollutants such as oil, CODcr, and ammonia nitrogen. The CODcr component is mainly volatile phenols, which have certain biotoxicity; and ammonia nitrogen also has a bioinhibitory effect.

[0015] It should be noted that the reflux ratio of the mixed liquor mentioned in this invention refers to the ratio of the refluxed mixed liquor to the influent volume of the pretreated wastewater entering the pre-anoxic tank.

[0016] Preferably, in step S1, the dissolved oxygen in the pre-anoxic tank is 0.1-0.5 mg / L, the sludge concentration is 4-8 mg / L, and the hydraulic retention time is 8-25 h.

[0017] In a further optimized approach, packing material is installed in the pre-anaerobic tank to couple the biofilm process with the activated sludge process, maintaining a high sludge concentration to cope with the high phenol and ammonia shock from the influent. When the total nitrogen content of the influent is high, a longer retention time is selected; when the total nitrogen content of the influent is low, a shorter retention time is selected; to ensure that the denitrification reaction is fully completed.

[0018] Preferably, in step S2, the dissolved oxygen in the aerobic tank is 2-5 mg / L, the sludge concentration is 3-5 mg / L, and the hydraulic retention time is 40-65 h.

[0019] In this invention, when the COD and ammonia nitrogen content of the incoming water in the aerobic tank is high, a longer retention time is selected; when the COD and ammonia nitrogen content of the incoming water is low, a shorter retention time is selected, so as to fully complete the carbonization and nitrification reactions.

[0020] Preferably, in step S3, the dissolved oxygen in the post-hypoxic preconditioning (PHP) tank is 0.1–0.5 mg / L, the sludge concentration is 3–5 mg / L, and the hydraulic retention time is 6–12 h.

[0021] In this invention, when the total nitrogen content of the influent to the post-anoxic pretreatment tank is high, a longer retention time is selected; when the total nitrogen content of the influent is low, a shorter retention time is selected, so as to fully complete the denitrification reaction.

[0022] This invention employs the A / O-PHP process, which differs from the traditional A / O-A process in the following ways: ① The nitrification liquor recirculation location is different: In the traditional A / OA process, the recirculation generally occurs before the second A tank, i.e., the nitrification liquor from the aerobic tank is recirculated to the anoxic tank; while in this invention, the mixed liquor recirculation in the PHP tank is at the end of the PHP tank; ② The recirculation ratio is different: The main purpose of nitrification liquor recirculation in the A / OA process is to remove nitrate nitrogen, and the recirculation ratio is generally relatively low; The main purpose of mixed liquor recirculation in the A / O-PHP process of this invention is to remove nitrate nitrogen while reducing the impact of biological toxicity on the biochemical system, resulting in a high recirculation ratio; ③ The functions are different: In the traditional second A tank, an external carbon source is often required for post-denitrification to remove total nitrogen, which may lead to excessive organic matter due to excessive external carbon source; However, due to the different nitrification liquor recirculation location and recirculation ratio in this invention, the PHP tank utilizes the carbon source within the microorganisms for denitrification to remove total nitrogen (nitrate nitrogen) and organic matter, while simultaneously creating a pre-anoxic environment, providing a basis for the design of other functions in this invention.

[0023] Preferably, in step S3, the mixed liquid in the post-anoxic pretreatment tank is stirred and then refluxed.

[0024] Preferably, in step S4, the sludge obtained from the sludge-water separation is returned to the pre-anoxic tank; the sludge return ratio is 100%.

[0025] It should be noted that the sludge return ratio mentioned in this invention refers to the ratio of the returned sludge to the amount of pretreated wastewater entering the pre-anoxic tank.

[0026] Secondly, see Figure 1 This invention provides a dual-carbon-source biochemical treatment system for semi-coke wastewater, comprising a pretreatment unit, a pre-anoxic tank, an aerobic tank, a post-anoxic pretreatment tank, a secondary sedimentation tank, and a post-treatment tank, wherein... The pretreatment unit is used to pretreat and mix the semi-coke wastewater. The pre-anaerobic tank is used to denitrify the pretreated semi-coke wastewater to remove COD and total nitrogen; The aerobic tank is used to carbonize and nitrify the effluent from the pre-anoxic tank, remove organic matter, and convert ammonia nitrogen into nitrite and nitrate nitrogen. The post-anoxic pretreatment tank is used to perform endogenous denitrification treatment on the effluent from the aerobic tank; and the post-anoxic pretreatment tank is connected to the inlet area of ​​the pre-anoxic tank through a mixed liquor return pump. The secondary sedimentation tank is used to separate mud and water in the effluent from the post-anoxic pretreatment tank. The post-treatment tank is used to treat the effluent from the secondary sedimentation tank to meet standards for reuse.

[0027] Preferably, submersible mixing devices are installed in both the pre-anoxic tank and the post-anoxic pretreatment tank; and an aeration system is installed in the aerobic tank.

[0028] Preferably, the surface loading rate of the secondary sedimentation tank is 0.5–1.0 m³ / m² / h.

[0029] Preferably, the secondary sedimentation tank is connected to the inlet area of ​​the pre-anoxic tank via a sludge return pump.

[0030] Preferably, the post-processing pool includes the PACT pool.

[0031] It is understood that the A tank of this invention may or may not have an independent influent mixing zone, without affecting the overall function of the A tank; the biological sludge from the secondary sedimentation tank and the physicochemical sludge from the sludge storage tank may be collected and treated separately, or they may be disposed of together; the post-treatment may employ ozone oxidation, catalytic oxidation, or activated carbon adsorption, filtration and other post-treatment processes, all of which can effectively remove residual organic matter and introduce little or no TDS, and the post-treated water can be directly reused.

[0032] The main mechanism of action and advantages of this invention are as follows: (1) The pretreated effluent is fed into Tank A, where microorganisms remove CODcr and total nitrogen in an anaerobic environment. Tank A is equipped with elastic packing material and adopts a biofilm coupled activated sludge treatment process to increase sludge concentration, improve volumetric loading, and enhance shock resistance. At the same time, a submersible mixer is installed to ensure mass transfer while preventing sludge settling.

[0033] (2) The effluent from pool A enters pool O, where microorganisms remove organic matter in an aerobic environment and convert ammonia nitrogen into nitrite and nitrate nitrogen. Pool O is equipped with an aeration device to maintain the aerobic environment required by the aerobic bacteria in the pool and to achieve a mixing effect.

[0034] (3) The effluent from the O tank then enters the PHP tank to form a pre-anoxic environment, and intracellular substances are used for endogenous denitrification to remove total nitrogen. A submersible agitator is installed in the PHP tank to ensure the mixing of mud and water. At the same time, a mixed liquor return pump is installed to return the mixed liquor, with a return ratio of 400% to 800% (adjustable). This invention uses a high-ratio return to dilute toxic and harmful substances in the incoming water. If the return ratio is too low, it is difficult to effectively solve the inhibition of microorganisms by toxic and harmful substances in the incoming water; if the return ratio is too high, the short residence time makes it difficult to effectively remove pollutants.

[0035] (4) The effluent from the PHP tank enters the secondary sedimentation tank for sludge-water separation. Part of the sludge from the secondary sedimentation tank is returned to the front end of the A tank, with 50% to 100% of the sludge being returned. Part of the sludge is discharged to the sludge thickening tank for concentration and dewatering.

[0036] (5) The effluent from the secondary sedimentation tank enters the post-treatment system to further remove organic matter. After treatment, the effluent can meet the water quality standards for reclaimed water used for cooling circulating water and can be directly reused.

[0037] Therefore, this invention innovatively adopts the A / O-PHP process. Compared with the conventional AO and AAO processes where the mixed liquor is refluxed in the O tank, the mixed liquor is refluxed in the PHP tank, which can effectively solve the impact of dissolved oxygen in the mixed liquor refluxed in the O tank on the A tank. It has the characteristics of toxicity resistance, impact resistance, simple process flow and low operating cost. At the same time, the use of a large reflux ratio can effectively solve the impact (biotoxicity) and inhibition problems of toxic organic matter in semi-coke wastewater.

[0038] Since the incoming water contains a carbon source, i.e., an external carbon source, microorganisms preferentially consume the external carbon source to maintain their life activities when it is available. In this invention, the incoming water (pretreated semi-coke wastewater) first enters tank A, where the external carbon source is sufficient. Denitrification occurs in tank A, consuming the external carbon source while removing total nitrogen. The effluent from tank A enters tank O, further consuming the remaining external carbon source. Then it enters tank PHP, where the external carbon source is basically consumed. Therefore, it consumes the internal carbon source in tank PHP to carry out denitrification. Thus, in this invention, tank PHP uses substances within microbial cells as a carbon source and energy source for internal denitrification, while tank A uses the carbon source from the influent for external denitrification. The A / O-PHP process is adopted to achieve the synergistic effect of dual carbon sources to remove total nitrogen and reduce operating costs.

[0039] The semi-coke wastewater can be directly reused after being treated by the process of this invention. The process is simple and does not require a membrane system or an evaporation and crystallization system.

[0040] The present invention will be further described in detail below through specific embodiments.

[0041] Example 1 The incoming water is semi-coke wastewater that has undergone gravity sedimentation + coconut shell filtration for oil removal, double-tower deacidification and deammoniation removal in a deacidification tower + deammoniation tower, and triple-effect evaporation for phenol removal. Its oil content is 218 mg / L, NH3-N content is 87.52 mg / L, CODcr content is 2882.46 mg / L, and TDS (total dissolved substances in water) content is 50 mg / L.

[0042] A dual-carbon-source biochemical treatment process for semi-coke wastewater includes the following steps: S1: Wastewater first enters the equalization tank, where it stays for 24 hours. A mixing and stirring device is installed in the equalization tank to homogenize and equalize the flow. The wastewater from the equalization tank is pumped into the inlet area of ​​Tank A. Tank A is equipped with a submersible mixing and propulsion device with a mixing power of 8w / m³. Under the action of denitrifying bacteria, organic matter and total nitrogen in the wastewater are removed. The retention time in Tank A is 10.4 hours, the dissolved oxygen is 0.1mg / L, and the sludge concentration is 5 mg / L.

[0043] The effluent from S2 and A tanks enters tank O, where an aeration system is installed. Aerobic bacteria remove organic matter, while nitrifying bacteria convert ammonia nitrogen into nitrite and nitrate nitrogen. The retention time in tank O is 52 hours, with dissolved oxygen at 3 mg / L and sludge concentration at 4 mg / L.

[0044] The effluent from the S3 and O tanks then enters the PHP tank, which is equipped with a submersible mixer to ensure proper mixing of the sludge and water. Simultaneously, the dissolved oxygen content in the mixed liquor from the O tank is reduced to create a pre-anoxic state. Under anoxic conditions, microorganisms utilize intracellular substances as a carbon and energy source for endogenous denitrification, removing some total nitrogen. The PHP tank has a retention time of 7.2 hours, a dissolved oxygen concentration of 0.4 mg / L, and a sludge concentration of 4 mg / L.

[0045] The PHP pool is equipped with a mixed liquor return pump to return the mixed liquor to the inlet area of ​​pool A (which mixes with the wastewater in the equalization tank before entering pool A), with a mixed liquor return ratio of 500%.

[0046] The effluent from the S4 and PHP tanks enters the secondary sedimentation tank for sludge-water separation. The secondary sedimentation tank is equipped with a sludge return pump, and part of the sludge is returned to the inlet area at the front end of the A treatment tank, with a sludge return ratio of 100%. Part of the sludge is discharged to the sludge thickening tank for concentration and dewatering.

[0047] The effluent from the secondary sedimentation tank enters the PACT tank, where 600 ppm activated carbon, 600 ppm PAC, and 0.8 ppm PAM are added to further remove organic pollutants from the wastewater. Part of the sludge at the bottom of the PACT tank is returned to the inlet area of ​​the A tank. Activated carbon powder is used as a microbial growth carrier, which can effectively increase the sludge concentration and enhance the shock resistance of the flocs.

[0048] The effluent from the PACT pool was tested, and its indicators are shown in Table 1 below.

[0049] Table 1 Water quality indicators of PACT tank effluent

[0050] As shown in Table 1, the effluent water treated by the process of this invention meets the water quality indicators of the make-up water for the indirect cooling open circulating cooling water system in the "Design Code for Industrial Circulating Cooling Water Treatment" (GB50050-2017), and can be used as make-up water for circulating water.

[0051] Example 2 Compared with Example 1, the only difference is that the recirculation ratio of the mixed liquor from the PHP pool to the influent zone of pool A is adjusted; all other steps and conditions are the same as in Example 1. To verify the effect of the biochemical system on the effluent in this invention, the COD, ammonia nitrogen, and total nitrogen of the secondary sedimentation tank effluent were measured, as shown in Table 2 below.

[0052] Table 2. Effluent water quality indicators for different mixed liquor reflux ratios

[0053] As shown in Table 2, when the mixed liquor reflux ratio is less than 300%, the CODcr, ammonia nitrogen, and total nitrogen in the effluent from the secondary sedimentation tank are all high, and the removal of ammonia nitrogen and total nitrogen is significantly affected; after treatment in the PACT tank, the effluent quality still exceeds the standard.

[0054] When the mixed liquor reflux ratio is between 400% and 800%, the CODcr, ammonia nitrogen, and total nitrogen in the effluent from the secondary sedimentation tank can all meet the control targets; after treatment in the PACT tank, the effluent quality can meet the makeup water standards for the indirect cooling open circulating cooling water system.

[0055] When the mixed liquor reflux ratio reaches 900%, the CODcr, ammonia nitrogen, and total nitrogen in the secondary sedimentation tank effluent show a significant increasing trend.

[0056] According to the results of Example 2, when the PHP pool recirculation ratio is below 300%, microbial activity is significantly inhibited, and CODcr cannot be effectively removed through the denitrification reaction in pool A, thereby inhibiting the nitrification reaction in pool O, resulting in excessive levels of CODcr, ammonia nitrogen, and total nitrogen. When the PHP pool recirculation ratio reaches 900%, the wastewater does not have sufficient retention time in pool A, and CODcr, ammonia nitrogen, and total nitrogen cannot be effectively removed, resulting in a significant increase in CODcr, ammonia nitrogen, and total nitrogen in the secondary sedimentation tank effluent. When the PHP pool recirculation ratio is between 400% and 800%, the effluent quality can meet the reuse standards. Among these, when the recirculation ratio is 500%, the CODcr in the secondary sedimentation tank effluent is at the optimal level, saving on reagents and operating costs.

[0057] Comparative Example 1 Compared with Example 1, the only difference is that the PHP pool is removed and the effluent from the O pool is used as a mixed liquid for reflux. The other steps and conditions are the same as in Example 1.

[0058] The results showed that using the effluent from the O tank as mixed liquor recirculation, at a recirculation ratio of 500%, significantly inhibited the denitrification reaction in the A tank, resulting in insufficient denitrification in the A tank and excessive carbon source entering the O tank, which inhibited the nitrification reaction in the O tank. At the same time, the lack of a PHP tank for further removal of total nitrogen led to significant exceedances of CODcr (262.5 mg / L), ammonia nitrogen (12.66 mg / L), and total nitrogen (32.15 mg / L) in the secondary sedimentation tank effluent.

[0059] Comparative Example 2 Compared with Example 1, the only difference is that the PHP pool is not mechanically stirred, but aerated through membrane disc micropores. The other steps and conditions are the same as in Example 1.

[0060] The results showed that when the aeration rate was low, significant sludge deposition occurred in the PHP tank; when the aeration rate was increased, sludge deposition did not occur in the PHP tank, but the dissolved oxygen reached 1.0–2.0 mg / L, which was difficult to control to below 0.5 mg / L, making the system difficult to control and unable to operate stably.

[0061] In summary, this invention utilizes the substances within microbial cells as both a carbon and energy source for endogenous denitrification in the PHP tank, while the A tank employs the carbon source from the influent for exogenous denitrification. The A / O-PHP process achieves synergistic removal of total nitrogen through dual carbon sources, reducing operating costs. Furthermore, the mixed liquor recirculation in the PHP tank effectively mitigates the impact of dissolved oxygen from the recirculated mixed liquor in the O tank on the A tank, exhibiting characteristics of toxicity resistance, impact resistance, simple process flow, and low operating costs. Simultaneously, the high recirculation ratio effectively addresses the impact (biotoxicity) and inhibition issues associated with toxic organic matter in semi-coke wastewater.

[0062] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A dual-carbon-source biochemical treatment process for semi-coke wastewater, characterized in that, Includes the following steps: S1, the pretreated semi-coke wastewater enters the pre-anoxic tank for denitrification to remove COD and total nitrogen; S2, the effluent from the pre-anoxic tank enters the aerobic tank for carbonization and nitrification to remove organic matter and convert ammonia nitrogen into nitrite nitrogen and nitrate nitrogen; S3, the effluent from the aerobic tank enters the post-anoxic pretreatment tank for endogenous denitrification; the mixed liquor in the post-anoxic pretreatment tank is recycled to the pre-anoxic tank at a recycling ratio of 400% to 800%. S4, the effluent from the post-anoxic pretreatment tank is subjected to mud-water separation and post-treatment to meet the standards for reuse.

2. The dual-carbon-source biochemical treatment process for semi-coke wastewater according to claim 1, characterized in that, In step S1, the pretreatment includes degreasing, deacidification and deammoniation, and evaporation and dephenolization.

3. The dual-carbon-source biochemical treatment process for semi-coke wastewater according to claim 1, characterized in that, In step S1, the dissolved oxygen in the pre-anaerobic tank is 0.1-0.5 mg / L, the sludge concentration is 4-8 mg / L, and the hydraulic retention time is 8-25 h.

4. The dual-carbon-source biochemical treatment process for semi-coke wastewater according to claim 1, characterized in that, In step S2, the dissolved oxygen in the aerobic tank is 2-5 mg / L, the sludge concentration is 3-5 mg / L, and the hydraulic retention time is 40-65 h.

5. The dual-carbon-source biochemical treatment process for semi-coke wastewater according to claim 1, characterized in that, In step S3, the dissolved oxygen in the post-anoxic pretreatment tank is 0.1-0.5 mg / L, the sludge concentration is 3-5 mg / L, and the hydraulic retention time is 6-12 h.

6. The dual-carbon-source biochemical treatment process for semi-coke wastewater according to claim 1, characterized in that, In step S3, the mixed liquid in the post-anoxic pretreatment tank is stirred and then refluxed.

7. The dual-carbon-source biochemical treatment process for semi-coke wastewater according to claim 1, characterized in that, In step S4, the sludge obtained from the sludge-water separation is returned to the pre-anoxic tank.

8. A dual-carbon-source biochemical treatment system for semi-coke wastewater in the process described in any one of claims 1-7, characterized in that, It includes a pretreatment unit, a pre-anoxic tank, an aerobic tank, a post-anoxic pretreatment tank, a secondary sedimentation tank, and a post-treatment tank. The pretreatment unit is used to pretreat and mix the semi-coke wastewater. The pre-anaerobic tank is used to denitrify the pretreated semi-coke wastewater to remove COD and total nitrogen. The aerobic tank is used to carbonize and nitrify the effluent from the pre-anoxic tank, remove organic matter, and convert ammonia nitrogen into nitrite nitrogen and nitrate nitrogen. The post-anoxic pretreatment tank is used to perform endogenous denitrification treatment on the effluent from the aerobic tank; and the post-anoxic pretreatment tank is connected to the inlet area of ​​the pre-anoxic tank through a mixed liquor return pump. The secondary sedimentation tank is used to separate mud and water in the effluent from the post-anoxic pretreatment tank. The post-treatment tank is used to treat the effluent from the secondary sedimentation tank to meet standards for reuse.

9. The dual-carbon-source biochemical treatment system for semi-coke wastewater according to claim 8, characterized in that, Submersible mixing devices are installed in both the pre-anoxic tank and the post-anoxic pretreatment tank; an aeration system is installed in the aerobic tank.

10. The dual-carbon-source biochemical treatment system for semi-coke wastewater according to claim 8, characterized in that, The secondary sedimentation tank is connected to the inlet area of ​​the pre-anoxic tank via a sludge return pump.

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