High-load aerobic tank optimization process for improving coking wastewater treatment efficiency and application

Abstract

This invention belongs to the field of coking wastewater treatment technology and discloses an optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater, including the following steps: (1) After pretreatment, the coking wastewater enters the equalization tank. A portion of the sludge mixture in the equalization tank enters the high-load aerobic tank O1 and the primary sedimentation tank in sequence, and another portion of the sludge mixture enters the low-load AO tank and the primary sedimentation tank in sequence; (2) A portion of the activated sludge in the primary sedimentation tank and the primary sedimentation tank is internally recycled and recycled back to the high-load aerobic tank O1, respectively; (3) The activated sludge in the high-load aerobic tank O1 is regulated and a continuous high-load influent operation mode is maintained. The regulation includes aeration rate regulation, nutrient regulation and sludge discharge rate regulation; (4) The effluent from the high-load aerobic tank O1 enters the low-load AO tank, and the substance content of the effluent is controlled so that the C / N ratio of the low-load AO tank is within a certain range. This invention utilizes the sludge recycling and regulation method to ensure that O1 can operate stably under high-load operation.

Description

Technical Field

[0001] This invention relates to the field of coking wastewater treatment technology, and specifically to an optimized process and application of a high-load aerobic tank for improving the treatment efficiency of coking wastewater. Background Technology

[0002] With the rapid development of modern industry, environmental pollution is becoming increasingly severe, and usable water resources are gradually decreasing, making wastewater treatment particularly urgent. Coking wastewater is a typical industrial wastewater with high toxicity. Its characteristic pollutants are mainly volatile phenols, thiocyanates, ammonia nitrogen, and polycyclic aromatic hydrocarbons, belonging to recalcitrant organic industrial wastewater, which is currently a major challenge for treatment. Recent research results indicate that it is impossible to completely remove pollutants from the source by changing the coking process. Therefore, it is crucial to find economically reasonable, technically feasible, and efficient methods for treating coking wastewater.

[0003] Currently, the main technologies for treating coking wastewater fall into three categories: physicochemical methods, biochemical methods, and physicochemical-biochemical methods. Due to its advantages such as low operating costs, simple operation, and no secondary pollution, biological methods are currently the primary process for treating coking wastewater. Biological methods can be further divided into activated sludge processes and biofilm processes. Currently, most domestic treatments combine both methods. Later, processes such as A / O, A / A / O, and O / A / O gradually evolved and have been widely applied. Most coking plants built in my country in the 1970s and 80s or earlier adopted the traditional activated sludge process for treating coking wastewater. This method involves allowing organic matter in the wastewater to fully contact with bioflocs and activated sludge. Insoluble organic matter is first converted into soluble organic matter, which is then metabolized and utilized. The soluble organic matter is absorbed and adsorbed by microorganisms and oxidized into final products (mainly water and CO2). However, using this method, it is difficult to meet the standards for pollutants such as CODcr and ammonia nitrogen in the effluent, especially ammonia nitrogen, which shows almost no degradation effect. Therefore, from the perspective of ensuring the stable operation of wastewater treatment plants, it is very urgent to establish a method for the efficient treatment of pollutants from coking wastewater.

[0004] The high levels of small particulate impurities and various toxic and harmful substances in coking wastewater hinder direct biological treatment. To reduce the content of these substances and improve its biodegradability, pretreatment is necessary before the wastewater enters the biological treatment tank. Compared to the A / O process, the O / A / O process includes an additional pre-aeration tank. The aerobic organisms in the pre-aeration tank degrade some of the organic load and toxic and harmful substances that inhibit biological denitrification, providing favorable conditions for the subsequent biological denitrification process. Through aerobic pre-aeration treatment using the O / A / O process, the CODcr entering the biological denitrification system can be appropriately controlled. Simultaneously, substances such as phenols and cyanides that inhibit or are toxic to biological denitrification in the coking wastewater are effectively removed, reducing the impact of wastewater quality on biological denitrification and ensuring the smooth progress of the nitrification reaction.

[0005] However, in existing O / A / O processes, when the O1 aerobic tank at the front end is subjected to a high concentration of organic matter, the organic matter storage capacity of the activated sludge system reaches its maximum. Initially, this can be mitigated by the adsorption of activated sludge, but as the impact time prolongs, the adsorbed organic matter cannot be completely degraded in the aerobic stage, making it difficult to recover adsorption performance. Carbon removal, nitrogen removal, phosphorus removal, and sludge settling performance all deteriorate significantly, and the greater the impact, the earlier the deterioration occurs. Research shows that the O1 system is clearly insufficient to cope with prolonged high-load water quality operation, often resulting in long recovery periods after an impact, or even complete shutdown and replacement of activated sludge in the biological treatment tank.

[0006] Based on the above analysis, the problems and defects of the existing technology are as follows: In the existing O / A / O process, the front-end O1 aerobic tank cannot adapt to the long-term high-load operation of coking wastewater, which causes the organic load to accumulate for a long time or suddenly increase, resulting in the collapse of the coking wastewater treatment system and its inability to operate stably. Summary of the Invention

[0007] This invention provides an optimized process and application for a high-load aerobic tank to improve the treatment efficiency of coking wastewater. This addresses the technical problem in the existing O / A / O process where the front-end O1 aerobic tank cannot adapt to the long-term high-load operation of coking wastewater, resulting in the long-term accumulation or sudden increase of organic load, which leads to the collapse and unstable operation of the coking wastewater treatment system.

[0008] In a first aspect, the present invention provides an optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater, employing the following technical solution:

[0009] An optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater is characterized by the following steps:

[0010] (1) After pretreatment, the coking wastewater enters the equalization tank. Part of the sludge mixture in the equalization tank enters the high-load aerobic tank O1 and the primary sedimentation tank in sequence, and the other part of the sludge mixture enters the low-load AO tank and the primary sedimentation tank in sequence.

[0011] (2) Some of the activated sludge in the primary sedimentation tank is returned to the high-load aerobic tank O1, and some of the activated sludge in the primary sedimentation tank is returned to the high-load aerobic tank O1.

[0012] (3) The activated sludge in the high-load aerobic tank O1 is regulated and the continuous high-load water influent operation mode is maintained. The regulation includes aeration volume regulation, nutrient regulation and sludge discharge volume regulation.

[0013] (4) The effluent from the high-load aerobic tank O1 enters the low-load AO tank. The substance content of the effluent from the high-load aerobic tank O1 is controlled so that the C / N ratio of the low-load AO tank is within a certain range.

[0014] Optionally, the pretreatment in step (1) includes oil separation and flotation treatment of the coking wastewater.

[0015] Optionally, in step (2), the activated sludge return time in the settling tank is 1 to 2 hours per day, and the activated sludge return ratio is 8 to 12%.

[0016] In step (2), the internal recirculation ratio of activated sludge in the primary sedimentation tank is 300-400%.

[0017] Optionally, the low-load OA tank includes an anoxic tank A and an aerobic tank O2. The coking wastewater that has undergone denitrification in the anoxic tank A enters the aerobic tank O2, where carbonization and nitrification reactions take place.

[0018] Optionally, the retention time of coking wastewater in the high-load aerobic tank O1 is 11–26 h, the retention time of coking wastewater in the anoxic tank A is 10–16 h, and the retention time of coking wastewater in the aerobic tank O2 is 22–28 h.

[0019] The temperature in the low-load AO tank is 28–33℃ and the pH is 7–7.8.

[0020] Optionally, the aeration rate control in step (3) includes adjusting the aeration rate of the aeration equipment and controlling the dissolved oxygen concentration in the high-load aerobic tank O1.

[0021] The dissolved oxygen concentration in the middle of the high-load aerobic tank O1 is 2.0–4 mg / L, and the dissolved oxygen concentration in the effluent from the end of the high-load aerobic tank O1 is <6 mg / L.

[0022] Optionally, the nutrient regulation in step (3) includes adding potassium dihydrogen phosphate to control the content of inorganic phosphorus in the high-load aerobic tank O1 and maintain the high-load operation mode;

[0023] The dissolved inorganic phosphorus content at the O1 front end of the high-load aerobic tank is 10-15 mg / L, and the dissolved inorganic phosphorus content at the O1 end of the high-load aerobic tank is 1.63-3.02 mg / L.

[0024] Optionally, the sludge discharge regulation in step (3) includes controlling the daily sludge discharge of O1 activated sludge from the high-load aerobic tank and maintaining a continuous high-load influent mode.

[0025] Daily sludge discharge = (Daily high-load sludge production * 0.52 - Daily high-load sludge production * 0.98) + (Total amount of sludge solids returned from the primary sedimentation tank to the high-load aerobic tank O1 via the return pipe / (1 - Moisture content of sludge in the high-load aerobic tank O1, expressed as a decimal)).

[0026] Optionally, in step (4), the content of substances in the effluent from the high-load aerobic tank O1 is controlled to be COD of 500-2000 mg / L, the total amount of ammonia nitrogen and thiocyanate of 100-220 mg / L, and the C / N ratio of the influent to the low-load AO tank of 15-20.

[0027] As can be seen from the above technical solutions, the present invention has the following advantages:

[0028] The present invention provides an optimized process for high-load aerobic tanks to improve the treatment efficiency of coking wastewater. It adopts a combination of a front-end high-load aerobic tank O1 and a rear-end low-load AO tank. Through sludge recirculation from the AO sedimentation tank and sludge recirculation within the high-load aerobic tank O1, COD can be removed efficiently while maintaining a continuous high-load influent mode in the high-load aerobic tank O1, ensuring that the final effluent meets the standards.

[0029] The technical solution of this invention can be used for emergency response to water quality safety under impact in wastewater treatment plants in the coking industry. By regulating the reflux of the high-load aerobic tank O1, including regulating the aeration rate, nutrients, and sludge discharge, the COD content, ammonia nitrogen and thiocyanate content, and C / N ratio in the effluent of the high-load aerobic tank O1 are controlled, thereby reducing the organic load of the high-load aerobic tank O1. This effectively reduces the risk of effluent exceeding standards caused by water quality impact on wastewater treatment plants, protects microorganisms from the impact, maintains high and stable treatment efficiency, and avoids the long-term accumulation or sudden increase of organic load under high-load operation, which could lead to the collapse or unstable operation of the coking wastewater treatment system.

[0030] The technical solution of this invention is simple to operate, low in cost and requires little capital investment, which reduces the burden on sewage treatment plants and reduces the risk of adverse events such as system failure and activated sludge replacement under the impact of sewage treatment plant shocks, and has great commercial value.

[0031] This invention proposes for the first time a complete operational scheme utilizing a combination of high-load O1 sludge internal recirculation and low-load AO sludge intermittent recirculation, achieving both comprehensive effectiveness and economy. It is suitable for regulating coking wastewater under high-load operation and offers significant advantages compared to existing technologies. This proposed solution fills the gap in coking wastewater treatment plants regarding the lack of effective measures and technologies to address O1 under water quality shocks in the O / A / O system.

[0032] Secondly, the present invention also provides an application of a high-load aerobic tank optimization process for improving the treatment efficiency of coking wastewater in the treatment of coking wastewater. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the optimized process and application of a high-load aerobic tank for improving the treatment efficiency of coking wastewater provided in an embodiment of the present invention.

[0034] Figure 2 This is a comparison chart of CODcr removal rates in O1 of a high-load aerobic tank during the regulation and unregulated periods provided in this embodiment of the invention.

[0035] Figure 3 This is a comparison chart of sludge concentration in the high-load aerobic tank O1 during the regulation period and the unregulated period provided in this embodiment of the invention;

[0036] Figure 4 This is a comparison chart of the sludge index in the high-load aerobic tank O1 during the regulation period and the unregulated period provided in this embodiment of the invention. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Please see Figure 1 The present invention discloses an optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater, comprising treating the effluent from the equalization tank in a front-end high-load aerobic tank O1 and a post-load AO tank, respectively. During the high-load aerobic tank O1 treatment, the activated sludge is regulated and a continuous high-load influent operation mode is maintained. The post-load AO tank includes an anoxic tank A and an aerobic tank O2. The outlet of the anoxic tank A is connected to the inlet of the aerobic tank O2 through an overflow weir. The outlet of the aerobic tank O2 is connected to a sedimentation tank. The sedimentation tank is connected to a sludge return pump through a pipeline. The sedimentation tank is connected to the high-load aerobic tank O1, the anoxic tank A, and the aerobic tank O2 through pipelines respectively.

[0039] Part of the wastewater from the equalization tank enters the high-load aerobic tank O1. The outlet of the high-load aerobic tank O1 is connected to a primary sedimentation tank. The primary sedimentation tank is connected to the front end of the high-load aerobic tank O1 through an internal return pipe. Sludge-water separation is carried out in the primary sedimentation tank. Part of the settled sludge becomes excess sludge and is discharged to the sludge thickening tank for treatment. The other part of the sludge is returned to the inlet of the high-load aerobic tank O1 through the internal return pipe via a sludge return pump.

[0040] The high-load aerobic tank O1 is connected to the anoxic tank A via an overflow weir. After passing through the primary sedimentation tank of the high-load aerobic tank O1, the effluent flows by gravity into the anoxic tank A, controlling the substance content in the effluent so that the C / N ratio in the post-AO tank reaches a certain range. With the organic matter brought in from the raw water in the equalization tank, denitrification occurs in the anoxic tank A, and then the effluent flows by gravity into the aerobic tank O2, where carbonization and nitrification occur before entering the primary sedimentation tank.

[0041] Part of the wastewater from the equalization tank passes through the anoxic tank A and the aerobic tank O2 in sequence and then enters the primary sedimentation tank. In the primary sedimentation tank, sludge and water are separated. Part of the settled sludge becomes excess sludge and is discharged for treatment, while the other part of the sludge is returned to the inlet of the high-load aerobic tank O1 through the return pipe via the sludge return pump.

[0042] It should be noted that the term "high load" in this invention refers to the field of wastewater treatment, indicating a larger organic load processed per unit volume or unit surface area. This may involve higher biological activity, shorter retention time, etc. Therefore, the use of the term "high load" in the O1 tank conveys the special properties of the O1 tank in treating higher loads of organic matter.

[0043] In existing OAO wastewater treatment processes, a higher volumetric loading rate in the upstream O1 tank is generally considered a "high load." This is because a high load implies higher organic sludge loading, activated sludge growth rate, organic matter removal rate, and oxygen utilization rate. However, a high sludge load can easily lead to substandard effluent. Furthermore, due to strong microbial activity, sludge is less likely to aggregate and settle, resulting in poor separation from water and potentially causing low treatment efficiency or even system collapse. Conversely, a low load has the opposite effect. Therefore, existing OAO wastewater treatment processes aim to balance sludge loading, bacterial activity, microbial nutrition, and wastewater treatment efficiency by controlling the sludge loading at an appropriate level, rather than allowing the wastewater treatment system to remain continuously under high or low load conditions.

[0044] This invention differs from existing technologies by employing a high-load aerobic tank O1 at the front end. The high-load aerobic tank O1 continuously maintains a high-load operation state and is continuously regulated. Even under conditions of high organic load, it can still ensure efficient degradation of adsorbed organic matter and produce qualified effluent. This avoids the long-term accumulation of substrates in the high-load aerobic tank O1, which could lead to low system treatment efficiency or even system collapse.

[0045] Specifically, it includes the following steps:

[0046] (1) After oil separation and flotation treatment, the coking wastewater enters the equalization tank. Another part of the sludge mixture in the equalization tank enters the high-load aerobic tank O1. The high-load aerobic tank O1 degrades pollutants such as phenol and cyanide in the tank, reducing the inhibitory effect of pollutant toxicity on microorganisms in subsequent biochemical processes.

[0047] Another portion of the sludge mixture in the equalization tank sequentially enters the anoxic tank A, the aerobic O2 tank, and the primary sedimentation tank. In the anoxic tank A, denitrification occurs, reducing nitrate nitrogen to nitrogen gas, which then escapes, thus degrading the COD in the wastewater. After the reaction in the anoxic tank A, the coking wastewater flows by gravity into the aerobic O2 tank for carbonization and nitrification, oxidizing ammonia nitrogen to nitrite nitrogen, which is then oxidized from nitrite to nitrate nitrogen, while simultaneously degrading organic matter.

[0048] The retention time of coking wastewater in the high-load aerobic tank O1 is 11–26 h, the retention time of coking wastewater in the anoxic tank A is 10–16 h, and the retention time of coking wastewater in the aerobic tank O2 is 22–28 h.

[0049] The internal temperature of the anoxic tank A and the aerobic tank O2 was 28–33℃, and the pH was 7–7.8.

[0050] (2) Turn on the sludge return pump to return part of the activated sludge in the primary sedimentation tank to the high-load aerobic tank O1 through the primary sedimentation tank return pipe. The internal return ratio is 300-400%.

[0051] The sludge return pump is turned on to return a portion of the low-load, high-sludge-age activated sludge in the primary sedimentation tank through the primary sedimentation tank return pipe. It enters the high-load aerobic tank O1 together with the internal return sludge of the high-load aerobic tank O1. The high-load aerobic tank O1 quickly adsorbs organic matter in the influent and increases the sludge concentration in the high-load aerobic tank O1. The activated sludge return time in the primary sedimentation tank is 1 to 2 hours per day, and the activated sludge return ratio is 8 to 12%.

[0052] (3) The activated sludge in the high-load aerobic tank O1 is regulated and the continuous high-load water influent operation mode is maintained.

[0053] It should be noted that during the operation of the wastewater treatment system, in order to adapt to changes in external load, changes in wastewater quality characteristics, and the long-term stability of the system, the O1 of the high-load aerobic tank needs to be adjusted multiple times.

[0054] 1) Changes in external load: Sometimes, wastewater treatment systems may face changes in external load, such as changes in industrial production processes or the introduction of new wastewater sources. These changes may lead to adjustments in system performance, such as adjusting the influent ratio at both ends, namely the high-load aerobic tank O1 and the anoxic tank A, so that the C / N ratio reaches the set range.

[0055] 2) Changes in wastewater characteristics: Different times, seasons, or production cycles may cause changes in wastewater quality characteristics. Parameters such as organic load, nitrogen load, and phosphorus load of wastewater may change over time, so it is necessary to adjust them according to these changes.

[0056] 3) System stability requirements: In order to maintain the long-term stability of the system, it is necessary to monitor and adjust the operating parameters regularly. This helps to prevent the system from having problems when faced with changes and ensures that wastewater is treated stably and efficiently.

[0057] The method for determining the control is based on the treatment capacity of high-load aerobic microorganisms, which is reflected by the COD reduction rate of activated sludge. The treatment capacity of the high-load aerobic tank changes with temperature. Due to the characteristics of coking wastewater, some recalcitrant substances cannot be completely reduced with the effective retention time. Therefore, the control is ultimately determined by comparing the final effluent of O1 from the high-load aerobic tank with the effluent of O2 from the sedimentation tank.

[0058] If the COD(C1) of the effluent from the high-load aerobic tank O1 minus 1.57 times the COD(C2) of the AO sedimentation tank is greater than zero (i.e., C1 - 1.57 * C2 > 0), it indicates that the rapidly biodegrading dissolved organic matter inside the high-load aerobic tank O1 has been completely degraded, while the slowly biodegrading dissolved organic matter has not been degraded or has not been completely degraded. In this case, there are several possibilities, and internal reflux control is required:

[0059] i) The dissolved oxygen in the high-load aerobic tank is always <3mg / L from the front end to the end of the effluent, so the growth and hydrolysis of abnormal bacteria are limited by dissolved oxygen.

[0060] ii) The dissolved oxygen in the effluent from the high-load aerobic tank O1 is >3 mg / L, thus there is a potential inhibition of the degradation of abnormal bacteria in the high-load aerobic tank O1, such as the accumulation of phenol.

[0061] It should be noted that phenol is a major pollutant in wastewater from industrial processes such as the production of certain polymer resins, papermaking, petroleum refining, and pharmaceuticals (such as aspirin). When it enters a wastewater biological treatment system, it will affect the activated sludge microorganisms, thereby affecting the wastewater treatment effect.

[0062] Specifically, the regulation includes aeration volume regulation, nutrient regulation and sludge discharge volume regulation; among which, aeration volume regulation includes adjusting the aeration volume of the aeration equipment, controlling the dissolved oxygen concentration in the middle of the high-load aerobic tank O1 to be 2.0-4 mg / L, and the dissolved oxygen concentration in the effluent at the end of the high-load aerobic tank O1 to be <6 mg / L.

[0063] It should be noted that different types of aeration equipment (e.g., drag-type aerators, brush aerators, air lift pumps, etc.) have different specific adjustment parameters and may have different gas transfer efficiencies under the same conditions, which will affect the setting of aeration volume. Therefore, the range of aeration volume adjustment parameters in this solution is mainly based on dissolved oxygen demand, and the aeration volume is set by using the target dissolved oxygen demand as the adjustment parameter. The specific adjustment parameters of aeration volume are not limited here.

[0064] When the high-load aerobic tank O1 is running, it is necessary to measure the dissolved oxygen concentration at the front, middle and end of the high-load aerobic tank O1. The control of dissolved oxygen in the high-load aerobic tank O1 is determined by the following (correlation between the positions of the front, middle and end of O1, the unique characteristics of each position, and dynamic changes). The front of O1 is the initial area where sewage enters the high-load aerobic tank O1. In this area, the sewage in the aerobic tank is constantly flowing and mixing with a short residence time, and microorganisms begin to absorb a large amount of oxygen to decompose organic matter. This means that the dissolved oxygen measurement results at the front may not fully reflect the condition at the front. Therefore, it is quite difficult to control the dissolved oxygen at the front of O1 to maintain it within a certain range. During continuous water inflow, the change of dissolved oxygen in the middle of O1 can generally predict whether the oxygen supply at the front of O1 is sufficient. Therefore, in this invention, controlling the dissolved oxygen concentration in the middle and end of the tank can more accurately reflect the state of the activated sludge.

[0065] If the dissolved oxygen in the effluent from the high-load aerobic tank O1 is greater than 3 mg / L, the degradation rate of heterotrophic bacteria will decrease. This will lead to the accumulation of phenol, which will inhibit the degradation of thiocyanate at the end. Excessive dissolved oxygen overflowing into the anoxic tank A at the end will delay the start-up time of the denitrification reaction. Secondly, the end of the high-load aerobic tank O1 is the main habitat of ammonia-oxidizing bacteria. Excessive dissolved oxygen will reduce the uptake of carbon dioxide by the AOB ammonia-oxidizing bacteria, thus affecting their life activities (similar to the CBB cycle).

[0066] Nutrient regulation includes adding potassium dihydrogen phosphate to control the content of dissolved inorganic phosphorus at the front end of O1 in the high-load aerobic tank to 10-15 mg / L, and the content of dissolved inorganic phosphorus at the end of O1 in the high-load aerobic tank to 1.63-3.02 mg / L, while maintaining the high-load operation mode;

[0067] Sludge discharge regulation includes controlling the daily sludge discharge from the high-load aerobic tank O1 activated sludge to maintain a continuous high-load influent mode;

[0068] Daily sludge discharge = (Daily high-load sludge production * 0.52 - Daily high-load sludge production * 0.98) + (Total amount of sludge solids returned from the primary sedimentation tank to the high-load aerobic tank O1 via the return pipe / (1 - Moisture content of sludge in the high-load aerobic tank O1, expressed as a decimal));

[0069] (4) The effluent from the high-load aerobic tank O1 enters the low-load AO tank. The COD of the effluent from the high-load aerobic tank O1 is controlled to be 500-2000 mg / L, and the total amount of ammonia nitrogen and thiocyanate is 100-220 mg / L, so that the C / N ratio of the influent to the low-load AO tank is 15-20.

[0070] It should be noted that the COD removal efficiency and the total amount of ammonia nitrogen and thiocyanate in the high-load aerobic tank O1 section directly affect the denitrification effect of the subsequent low-load A / O tank denitrification biological denitrification section, and even the overall system's ability to remove pollutants. Therefore, it is necessary to control the COD content, ammonia nitrogen, and thiocyanate in the effluent of the high-load aerobic tank O1.

[0071] Example 1

[0072] (1) After oil separation and flotation treatment, the coking wastewater enters the equalization tank, and another part of the sludge mixture in the equalization tank enters the high-load aerobic tank O1.

[0073] Another portion of the sludge mixture in the equalization tank sequentially enters the anoxic tank A, the aerobic O2 tank, and the primary sedimentation tank. In the anoxic tank A, denitrification occurs, reducing nitrate nitrogen to nitrogen gas, which then escapes, thus degrading the COD in the wastewater. After the reaction in the anoxic tank A, the coking wastewater flows by gravity into the aerobic O2 tank for carbonization and nitrification, oxidizing ammonia nitrogen to nitrite nitrogen, which is then oxidized from nitrite to nitrate nitrogen, while simultaneously degrading organic matter.

[0074] The retention time of coking wastewater in the high-load aerobic tank O1 is 18h, the retention time in the anoxic tank A is 13h, and the retention time of coking wastewater in the aerobic tank O2 is 25h.

[0075] The temperature inside both the anoxic tank A and the aerobic tank O2 was 30℃, and the pH was 7.4.

[0076] (2) Turn on the sludge return pump to return part of the activated sludge in the primary sedimentation tank to the high-load aerobic tank O1 through the primary sedimentation tank return pipe. The internal return ratio is 350%.

[0077] The sludge return pump is turned on to return a portion of the low-load, high-sludge-age activated sludge from the primary sedimentation tank through the primary sedimentation tank return pipe. The sludge is then returned to the high-load aerobic tank O1 along with the internal return sludge from the high-load aerobic tank O1. The high-load aerobic tank O1 rapidly adsorbs organic matter from the influent, increasing the sludge concentration in the high-load aerobic tank O1. The activated sludge return time from the primary sedimentation tank is 1.5 hours per day, and the activated sludge return ratio is 10%.

[0078] (3) The activated sludge in the high-load aerobic tank O1 is regulated and the continuous high-load water influent operation mode is maintained. The regulation includes aeration volume regulation, nutrient regulation and sludge discharge volume regulation.

[0079] Among them, the aeration volume control includes adjusting the aeration volume of the aeration equipment, controlling the dissolved oxygen concentration in the middle of the high-load aerobic tank O1 to 3 mg / L, and the dissolved oxygen concentration in the effluent at the end of the high-load aerobic tank O1 to <6 mg / L.

[0080] Nutrient regulation includes adding potassium dihydrogen phosphate to control the dissolved inorganic phosphorus content at the front end of the high-load aerobic tank O1 to 12.5 mg / L and the dissolved inorganic phosphorus content at the end of the high-load aerobic tank O1 to 2.32 mg / L, while maintaining the high-load operation mode;

[0081] Sludge discharge regulation includes controlling the daily sludge discharge from the high-load aerobic tank O1 activated sludge to maintain a continuous high-load influent mode;

[0082] Daily sludge discharge = (Daily high-load sludge production * 0.52 - Daily high-load sludge production * 0.98) + (Total amount of sludge solids returned from the primary sedimentation tank to the high-load aerobic tank O1 via the return pipe / (1 - Moisture content of sludge in the high-load aerobic tank O1, expressed as a decimal));

[0083] (4) The effluent from the high-load aerobic tank O1 enters the low-load AO tank. The COD of the effluent from the high-load aerobic tank O1 is controlled at 1250 mg / L, and the total amount of ammonia nitrogen and thiocyanate is 160 mg / L, so that the C / N ratio of the influent to the low-load AO tank is 17.5.

[0084] Example 2

[0085] The difference from Example 1 is as follows:

[0086] In step (1), the retention time of coking wastewater in the high-load aerobic tank O1 is 11h, the retention time in the anoxic tank A is 10h, and the retention time of coking wastewater in the aerobic tank O2 is 22h.

[0087] The temperature inside the anoxic tank A and the aerobic tank O2 is 28℃ and the pH is 7;

[0088] In step (2), the internal reflux ratio is 300%; the activated sludge reflux time in the primary sedimentation tank is 1 hour per day, and the activated sludge reflux ratio is 12%.

[0089] In step (3), the aeration rate is adjusted to control the dissolved oxygen concentration in the middle of the high-load aerobic tank O1 to 2 mg / L and the dissolved oxygen concentration at the end of the high-load aerobic tank O1 to <6 mg / L.

[0090] Nutrient regulation was implemented, controlling the content of dissolved inorganic phosphorus at the O1 front end of the high-load aerobic tank to 10 mg / L and the content of dissolved inorganic phosphorus at the O1 end of the high-load aerobic tank to 1.63 mg / L.

[0091] In step (4), the COD of the effluent from the high-load aerobic tank O1 is controlled to be 500 mg / L, and the total amount of ammonia nitrogen and thiocyanate is 100 mg / L, so that the C / N ratio of the influent to the low-load AO tank is 15.

[0092] The remaining process is the same as in Example 1.

[0093] Example 3

[0094] The difference from Example 1 is as follows:

[0095] In step (1), the retention time of coking wastewater in the high-load aerobic tank O1 is 26h, the retention time in the anoxic tank A is 16h, and the retention time of coking wastewater in the aerobic tank O2 is 28h.

[0096] The internal temperature of the anoxic tank A and the aerobic tank O2 was 33℃ and the pH was 7.8.

[0097] In step (2), the internal reflux ratio is 400%; the activated sludge reflux time in the primary sedimentation tank is 2 hours per day, and the activated sludge reflux ratio is 12%.

[0098] In step (3), the aeration rate is adjusted to control the dissolved oxygen concentration in the middle of the high-load aerobic tank O1 to 4 mg / L and the dissolved oxygen concentration in the effluent at the end of the high-load aerobic tank O1 to <6 mg / L.

[0099] Nutrient regulation was implemented to control the dissolved inorganic phosphorus content at the O1 front end of the high-load aerobic tank to 15 mg / L and the dissolved inorganic phosphorus content at the O1 end of the high-load aerobic tank to 3.02 mg / L.

[0100] In step (4), the COD of the effluent from the high-load aerobic tank O1 is controlled to be 2000 mg / L, and the total amount of ammonia nitrogen and thiocyanate is 220 mg / L, so that the C / N ratio of the influent to the low-load AO tank is 20.

[0101] The remaining process is the same as in Example 1.

[0102] Comparative Example 1

[0103] The comparative example also uses the OAO wastewater treatment process, but no control is performed in the high-load aerobic tank O1 at the front end. That is, the sludge in the primary sedimentation tank is also internally returned to the high-load aerobic tank O1, but the dissolved oxygen control, the calculation of the discharge of mixed residual sludge under high and low loads, the control of low-load sludge return, and the C / N ratio of the effluent from the high-load aerobic tank O1 to the influent from the anoxic tank A are not performed as in Example 1.

[0104] Please see Figures 2 to 4 Under the same influent volumetric load, the influent and effluent COD of the high-load aerobic tank O1 during the uncontrolled period (Comparative Example 1) and the controlled period (Example 1) were compared. Figure 2 It can be seen that the influent COD of the high-load aerobic tank O1 during the uncontrolled period was about 5269 mg / L, and the effluent COD was about 1534 mg / L, with a COD removal rate of 70% during the uncontrolled period; while the influent COD of the high-load aerobic tank O1 during the controlled period was about 5699 mg / L, and the effluent COD was about 610 mg / L, with a COD removal rate of 89% during the controlled period. Compared with the uncontrolled period, the COD removal rate is higher in this invention through control.

[0105] Depend on Figure 3 It can be seen that, under the same influent volume load, the high-load sludge concentration in the high-load aerobic tank O1 during the uncontrolled period is always much higher than that during the controlled period. This indicates that the high-load aerobic tank O1 in Example 1 is in a high-load state for a long time, reflecting the degradation of organic matter in the high-load aerobic tank O1. Moreover, as time goes by, the sludge concentration in the high-load aerobic tank O1 during the controlled period gradually increases and then slowly decreases, indicating that the wastewater treatment system is in a stable state. However, as time goes by, the sludge concentration in the uncontrolled period shows a slow increase and then a sudden decrease, indicating that the wastewater treatment system cannot adapt well to the continuous high-load influent state.

[0106] Depend on Figure 4 It can be seen that the sludge index in the high-load aerobic tank O1 during the uncontrolled period is unstable, while the sludge index in the high-load aerobic tank O1 during the controlled period is relatively stable, which can effectively treat the organic matter in the wastewater.

[0107] This invention utilizes intermittent recirculation of low-load, high-sludge-age activated sludge to rapidly adsorb organic matter in the influent of the equalization tank, thereby increasing the sludge concentration and biological population in the high-load aerobic tank O1. Simultaneously, the high-load, high-sludge-age activated sludge contains a greater variety and quantity of microorganisms and enzymes, enabling the hydrolysis of organic matter that native microorganisms in the raw water or microorganisms in the high-load aerobic tank O1 cannot hydrolyze. This accelerates the degradation of substrates such as phenol, reduces phenol accumulation among microorganisms, prevents system collapse, and lowers the risk of sludge poisoning. Furthermore, sludge with a high sludge-age, when recirculated through the pipe to the high-load aerobic tank O1, will decompose if it is not adapted, providing adenosine and inorganic phosphorus to O1, thus better degrading organic matter in O1.

[0108] This invention utilizes intermittent recirculation of activated sludge from a low-load, high-sludge-age sedimentation tank in the AO (Aerobic Settling Tank) to alter the extracellular polymers (EPS) of native microorganisms in the high-load aerobic tank O1. The EPS content of the original sludge initially increases, then decreases, and finally stabilizes, ensuring the efficiency of wastewater treatment in the high-load aerobic tank O1. The activated sludge in the high-load aerobic tank O1 tends towards semi-granularity, which can retain a large number of microorganisms, has a longer sludge age, higher microbial diversity, and a denser structure, making it resistant to the toxicity of some substances in the wastewater. When the influent phenol concentration is higher than 20 mg / L, as the phenol load increases, polysaccharides and different functional groups fold, and the aerobic sludge particles maintain structural stability by increasing the production of EPS, enabling them to better cope with high-load operation and effectively degrade phenol in the wastewater as well as remove organic matter and ammonia nitrogen. After regulation, the sludge in the high-load aerobic tank O1 has the advantages of retaining a large amount of MLSS and easy and rapid settling, providing favorable conditions for the treatment of high-concentration organic wastewater.

[0109] Example 4

[0110] An optimized high-load aerobic tank process for improving the treatment efficiency of coking wastewater is applied to coking wastewater treatment. Applying the coking wastewater treatment process of this invention to coking wastewater treatment can reduce the burden on wastewater treatment plants and reduce the risk of adverse events such as system failure and activated sludge replacement under the impact of wastewater treatment plant shocks, thus having greater application prospects.

[0111] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater, characterized in that, Includes the following steps: (1) After pretreatment, the coking wastewater enters the equalization tank. A portion of the sludge mixture in the equalization tank enters the high-load aerobic tank O1 and the primary sedimentation tank in sequence, and another portion of the sludge mixture enters the low-load AO tank and the primary sedimentation tank in sequence. The pretreatment in step (1) includes oil separation and flotation treatment of the coking wastewater. The low-load AO tank includes an anoxic tank A and an aerobic tank O2. The coking wastewater undergoing denitrification in the anoxic tank A enters the aerobic tank O2, where carbonization and nitrification reactions take place. (2) A portion of the activated sludge in the primary sedimentation tank is returned to the high-load aerobic tank O1, and a portion of the activated sludge in the primary sedimentation tank is returned to the high-load aerobic tank O1; the return ratio of activated sludge in the primary sedimentation tank in step (2) is 300~400%; the return time of activated sludge in the primary sedimentation tank in step (2) is 1~2 hours per day, and the return ratio of activated sludge is 8~12%; (3) The activated sludge in the high-load aerobic tank O1 is regulated and the continuous high-load influent operation mode is maintained. The regulation includes aeration volume regulation, nutrient regulation and sludge discharge volume regulation. The aeration volume regulation in step (3) includes adjusting the aeration volume of the aeration equipment and controlling the dissolved oxygen concentration in the high-load aerobic tank O1. The dissolved oxygen concentration in the middle of the high-load aerobic tank O1 is 2.0~4mg / L, and the dissolved oxygen concentration in the effluent at the end of the high-load aerobic tank O1 is <6mg / L. The sludge discharge volume regulation in step (3) includes controlling the daily sludge discharge volume of the activated sludge in the high-load aerobic tank O1 and maintaining the continuous high-load influent mode. The daily sludge discharge volume = (daily high-load sludge production) 0.52 times - Daily high-load sludge production 0.98 times) + (Total solids of O1 sludge returned to the high-load aerobic tank via the return pipe daily / (1 - Moisture content of O1 sludge in the high-load aerobic tank, expressed as a decimal)); (4) The effluent from the high-load aerobic tank O1 enters the low-load AO tank. The content of substances in the effluent from the high-load aerobic tank O1 is controlled so that the C / N ratio of the low-load AO tank is within a certain range. The content of substances in the high-load aerobic tank O1 effluent controlled in step (4) includes controlling COD to 500~2000 mg / L, the total amount of ammonia nitrogen and thiocyanate to 100~220 mg / L, and the C / N ratio of the influent to the low-load AO tank to 15~20.

2. The optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater according to claim 1, characterized in that, The retention time of coking wastewater in the high-load aerobic tank O1 is 11~26h, the retention time of coking wastewater in the anoxic tank A is 10~16h, and the retention time of coking wastewater in the aerobic tank O2 is 22~28h. The temperature in the low-load AO tank is 28~33℃ and the pH is 7~7.

8.

3. The optimized process for a high-load aerobic tank to improve the treatment efficiency of coking wastewater according to claim 1, characterized in that, The nutrient regulation in step (3) includes adding potassium dihydrogen phosphate to control the content of inorganic phosphorus in the high-load aerobic tank O1 and maintain the high-load operation mode. The content of dissolved inorganic phosphorus at the front end of the high-load aerobic tank O1 is 10~15 mg / L, and the content of dissolved inorganic phosphorus at the end of the high-load aerobic tank O1 is 1.63~3.02 mg / L.

4. The application of the high-load aerobic tank optimization process for improving coking wastewater treatment efficiency as described in any one of claims 1-3 in coking wastewater treatment.

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