Stable treatment method for nitrate-nitrogen-containing wastewater

Abstract

The invention provides a stable treatment method of nitrate-nitrogen-containing wastewater, which comprises the following steps: S1, pretreating the wastewater, feeding the wastewater into a primary denitrification tank, a primary nitrification tank, a secondary denitrification tank and a secondary nitrification tank, adding phosphoric acid and methanol into the primary denitrification tank and the secondary denitrification tank, according to the nitrate nitrogen value detected in the primary denitrification tank and the inlet water nitrate nitrogen concentration of the primary denitrification tank, calculating a methanol addition value of the primary denitrification tank through an ID control algorithm; and S2, carrying out precipitation in a precipitation tank, enabling a supernatant of the precipitation tank to enter a cloth filter, and then enabling the supernatant to enter a clean water tank for up-to-standard discharge, wherein the methanol addition value of the second-stage denitrification tank is calculated according to the nitrate nitrogen value detected in the second-stage denitrification tank and the nitrate nitrogen concentration of inlet water of the second-stage denitrification tank, and then the supernatant enters a degassing tank. The device has the beneficial effects that the adding amount of methanol is not required to be continuously adjusted by personnel according to the change of the nitrate nitrogen concentration of incoming water, so that the manpower is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial production biochemical sewage treatment, and in particular relates to a stable treatment method for nitric nitrogen-containing wastewater. Background Art

[0002] Biological denitrification is an important technology in wastewater treatment, which aims to remove nitrogen compounds in wastewater to reduce water eutrophication and environmental pollution.

[0003] Its technical background is mainly based on the following aspects:

[0004] With the rapid development of industrialization and urbanization, a large amount of nitrogen-containing wastewater is discharged into water bodies. Nitrogen is one of the key factors leading to eutrophication of water bodies, which can cause a series of ecological problems such as algae proliferation, water quality deterioration, and death of aquatic organisms.

[0005] Traditional wastewater treatment methods have certain limitations in nitrogen removal. For example, physical and chemical methods are often costly and may produce secondary pollution. Biological denitrification uses the metabolism of microorganisms to convert nitrogen into harmless nitrogen gas, which has the advantages of low cost, high efficiency, and environmental friendliness. With the continuous deepening of research in microbiology and ecology, we have a clearer understanding of the types of microorganisms, metabolic pathways, and ecological relationships involved in nitrogen transformation, providing a theoretical basis for the development of biological denitrification technology. At the same time, the increasingly stringent environmental regulations on wastewater discharge standards have also prompted the continuous improvement and innovation of biological denitrification technology to meet higher environmental quality requirements.

[0006] In the process of biological denitrification, there are several difficulties in controlling the effluent concentration:

[0007] 1. Insufficient or excessive carbon source. The available organic carbon source in wastewater is limited, which is difficult to meet the carbon source demand of the denitrification process. Insufficient carbon source will lead to incomplete denitrification and affect the removal effect of total nitrogen. The external carbon source is not well controlled and added excessively, resulting in the introduction of new pollutants.

[0008] 2. Balance between nitrification and denitrification: Excessive or insufficient nitrification will affect the effect of subsequent denitrification, making it difficult to control the nitrogen concentration in the effluent.

[0009] 3. Fluctuation of influent water quality. The fluctuation of influent nitrogen concentration, organic matter content, temperature, pH and other parameters is large, which brings challenges to the stable operation of the biological denitrification system.

[0010] Limitations of monitoring and control methods: It is difficult to accurately monitor the concentration of nitrogen compounds and the activity of microorganisms in real time, which makes it difficult to adjust process parameters in time to ensure that the nitrogen concentration in the effluent meets the standard. Invention content

[0011] In view of this, the present invention aims to propose a stable treatment method for nitric nitrogen-containing wastewater to solve the problems existing in the background technology.

[0012] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0013] A method for stabilizing treatment of nitric nitrogen-containing wastewater comprises the following steps:

[0014] S1: Pre-treat the wastewater, and then enter the primary denitrification tank, primary nitrification tank, secondary denitrification tank, and secondary nitrification tank. Phosphoric acid and methanol are added to the primary denitrification tank and the secondary denitrification tank. The methanol addition value of the primary denitrification tank is calculated by the ID control algorithm according to the nitrate nitrogen value detected in the primary denitrification tank and the nitrate nitrogen concentration of the inlet water of the primary denitrification tank; the methanol addition value of the secondary denitrification tank is calculated according to the nitrate nitrogen value detected in the secondary denitrification tank and the nitrate nitrogen concentration of the inlet water of the secondary denitrification tank, and then enter the degassing tank.

[0015] S2: The sewage treated in the degassing tank enters the sedimentation tank for sedimentation. Part of the sludge in the sedimentation tank enters the primary denitrification tank, and the other part of the sludge is discharged; the supernatant of the sedimentation tank enters the filter cloth filter tank, and then enters the clear water tank to meet the discharge standards.

[0016] Furthermore, the primary denitrification tank, the primary nitrification tank, the secondary denitrification tank, and the secondary nitrification tank are sequentially connected through pipelines; the wastewater sequentially passes through the primary denitrification tank, the primary nitrification tank, the secondary denitrification tank, and the secondary nitrification tank;

[0017] The sludge in the secondary nitrification tank enters the primary denitrification tank through a pipeline;

[0018] The sludge in the degassing tank enters the primary denitrification tank;

[0019] The sludge in the sedimentation tank enters the primary denitrification tank.

[0020] Furthermore, the water inlet pipes of the primary denitrification tank and the secondary denitrification tank are tested by the instruments in the instrument tank to obtain the average concentration within 5 minutes; the average nitric nitrogen concentration within 5 minutes is taken as the average value for 1 hour, considering that there is a submersible stirring pump in the equalization tank to stir the incoming water. Even if the concentration of the inlet water suddenly increases, its actual concentration entering the reaction tank will not rise to 130% of the current concentration or drop to 70% of the current concentration.

[0021] If the concentration increases or decreases by more than 30% within 1 hour, the compensation value will be used to make positive or negative compensation. After obtaining the average nitric nitrogen concentration of the influent for 1 hour, the total influent volume for 1 hour is used to calculate the amount of methanol added through the reaction equation.

[0022] The nitrate-nitrogen value detected in the primary denitrification tank and the calculation of the nitrate-nitrogen concentration in the influent of the primary denitrification tank are as follows:

[0023] The calculation formula is:

[0024] c=NO3-N*sum(w)*2.47+NO2-N*sum(w)*1.53+Do*sum(w)*0.87;

[0025] c is the calculated amount of methanol added, unit: mg;

[0026] NO3-N is the nitric nitrogen concentration measured per unit time, unit: mg / L;

[0027] NO2-N is the nitric nitrogen concentration measured per unit time, unit: mg / L;

[0028] sum(w) is the water intake per unit time, unit: L;

[0029] DO is the amount of dissolved oxygen per unit time, unit: mg / L;

[0030] From the practical point of view, the nitrite nitrogen in the water is very small and can be ignored, so the coefficient of 1.53 nitrite nitrogen can be ignored, and the dissolved oxygen value is not much, so the final formula is

[0031] c=∑(NO3-N+NO)*2.75*methanol(100%);

[0032] c: Calculated amount of methanol added, unit: mg;

[0033] ∑(NO3-N+DO): Total amount of nitrate nitrogen and dissolved oxygen (unit: mg);

[0034] 2.75 coefficient: 2.47 coefficient for nitrate-nitrogen and 0.28 coefficient for dissolved oxygen optimization.

[0035] Methanol (100%): 100% methanol concentration: unit: mg;

[0036] The nitric nitrogen value detected in the primary denitrification tank and the calculation of the nitric nitrogen concentration in the influent of the primary denitrification tank: the calculation formula is: calculated methanol consumption = ∑(NO3+NO2+O2)*2.75*methanoL(100%).

[0037] Furthermore, the nitric nitrogen detection instrument is placed in the liquid to be detected for 6 minutes in one hour to obtain the instrument measurement value, wherein it takes 48 seconds from the time of placing it in the liquid to the time when the detection value is stable and reliable.

[0038] Furthermore, after the detection probe is separated from the sewage, the probe surface needs to be cleaned with water so that the sewage on the surface of the electrode diaphragm is fully replaced by new water. The diameter of the flushing water pipes on its left and right sides needs to be greater than or equal to 800 mm, the water pressure of the flushing water pipes is 0.001-0.003MPa, and the upward angle of the flushing water pipes is between 30° and 38°.

[0039] Furthermore, if the nitric nitrogen is higher or lower than the target value, a compensation mechanism is introduced to ensure that the reaction value can reach the target value. The maximum compensation value of the compensation mechanism should be 50% of the maximum amount of methanol added; the minimum value should reach minus 20% of the maximum amount of methanol added. That is, if the amount of methanol added is 500 liters / hour, the maximum compensation value is 250 liters / hour and the minimum value is -100 liters / hour; that is, if the amount of methanol added is 500 liters / hour, the maximum compensation value is 250 liters / hour and the minimum value is -100 liters / hour.

[0040] Furthermore, the maximum compensation value is 250 liters / hour, the minimum value is -100 liters / hour, and the calculation formula of the compensated methanol value calculated by the controller is:

[0041] Compensated methanol value = (maximum compensation value - minimum compensation value) * controller output value.

[0042] As the instrument is used for a longer time, the calcium contained in the incoming water will damage the instrument's detection system and contaminate the electrolyte of the detection probe. Once damaged, there is no other way to eliminate the impact except replacing spare parts. However, if the compensation system is running, although its value will be affected, the compensation controller will calculate the residual difference between the measured value and the set value through a closed-loop algorithm, and ultimately eliminate the impact caused by the measurement error.

[0043] Furthermore, the wastewater is pretreated including conveying the wastewater to a regulating tank, entering a neutralization tank, and adjusting the pH of the wastewater to 6-8 after two neutralization adjustments in the neutralization tank, and then entering a temperature control tank.

[0044] Furthermore, the return flow rate of the primary denitrification tank or the secondary denitrification tank must be more than three times the inlet flow rate; the return flow rate of the final sedimentation tank needs to be more than one times the inlet flow rate.

[0045] Compared with the prior art, the stable treatment method for nitric nitrogen-containing wastewater created by the present invention has the following advantages:

[0046] Through this method, closed-loop control of nitrate nitrogen concentration is achieved. It is no longer necessary for personnel to constantly adjust the amount of methanol added according to the change of nitrate nitrogen concentration in the incoming water, which saves manpower. Its core control method adopts PID control algorithm. This method is simple and easy to implement, and does not require complex mathematical models. The PID controller has three adjustable parameters, namely the proportional coefficient (P), the integral time constant (I) and the differential time constant (D). By adjusting these three parameters, the control effect of the controller can be flexibly changed to meet the control requirements of different systems, so that the system can achieve fast, stable and accurate control performance. Good robustness: There is a certain tolerance for external disturbances and changes in system parameters, and the stability and control performance of the system can be maintained to a certain extent. Even if there is a certain uncertainty in the system or it is disturbed by the outside world, the PID controller can still work well and keep the controlled variable near the set value. High control accuracy: When the parameters of the PID controller are adjusted appropriately, the steady-state error of the system can be close to zero, thereby achieving higher control accuracy and meeting the control requirements of the nitrate nitrogen concentration in the effluent during field operation. This application ensures that the nitrate nitrogen value of the effluent is less than 8mg / l and the cod value is less than 25mg / l. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0048] Figure 1 A schematic flow chart of a method for stabilizing the treatment of nitric nitrogen-containing wastewater according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0050] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0051] like Figure 1 As shown, the production wastewater is transported from the plant network to the regulating tank. After being homogenized and equalized in the regulating tank, it is pressurized by the pump and enters the neutralization tank. After two neutralization adjustments, the pH of the wastewater is adjusted to 6-8, and then enters the temperature control tank. The wastewater cooled by the cooling tower enters the secondary AO system, and phosphoric acid and methanol are added to the secondary AO system to maintain the carbon and phosphorus required for normal biochemical denitrification. The wastewater denitrified by the secondary AO system enters the degassing tank, and after stirring, the dissolved oxygen in the digestate is removed, and the excess COD is further removed, and then it flows into the sedimentation tank for mud and water separation. The supernatant is deeply treated through the filter cloth filter tank, and finally discharged through the clear water tank to meet the standards. The residual sludge in the sedimentation tank is discharged from the system using the residual sludge pump.

[0052] Regulating tank: The regulating tank is located in the underground layer of the entire water treatment system, with an effective volume of 1316m3 and a hydraulic retention time of about 14 hours. It can have a good homogenization and equalization effect on the incoming water and has a certain impact resistance to the incoming water. In order to achieve the homogenization effect and effectively utilize its volume, it is necessary to stir the sewage in the regulating tank, using a submersible mixer.

[0053] Neutralization tank: Since the influent is alkaline, which hinders the growth of microorganisms, a two-stage neutralization tank is used to accurately adjust the pH value of the sewage to make it neutral. Hydrochloric acid is used for adjustment because there is a large amount of calcium hardness in the water. Using sulfuric acid for pH adjustment will produce a large amount of SS, which will further deteriorate the water quality and is not conducive to the growth of microorganisms. Sulfate ions will also have a certain inhibitory effect on microorganisms in the water. The sewage needs to be stirred during the neutralization process in the neutralization tank to enhance the effect of pH adjustment.

[0054] Temperature control pool: The inlet water temperature in summer is around 40°C. Such high temperature will inhibit the activity of microorganisms, reduce the capacity of the entire nitrification and denitrification system, and fail to reach the designed treatment capacity. Therefore, a temperature control pool is added and a cooling tower is used to lower the sewage temperature to meet the optimal temperature for the survival of microorganisms.

[0055] In winter, the average temperature of January, the coldest month, is -2°C. At this time, the growth of microorganisms is extremely slow, and steam needs to be introduced into the temperature control pool to ensure the sewage temperature and maintain the stability of the biochemical treatment system.

[0056] Biochemical system A / O / AO pool

[0057] The main pollutant in this sewage system is nitrate nitrogen, which is about 200-425 mg / L. The denitrification treatment method is to use the nitrification and denitrification of microorganisms to denitrify nitrate nitrogen into N2 for removal. Microorganisms need to consume energy during the nitrification and denitrification process, and the BOD5 in this sewage is about 27, which is far from meeting the denitrification needs of microorganisms. According to experience, microorganisms need 3 mg / L of BOD5 to remove 1 mg / L of nitrate nitrogen. Therefore, a large amount of methanol must be added to this sewage system as a carbon source. The primary denitrification tank and the secondary denitrification tank are equipped with an instrument tank for inlet concentration detection at the inlet pipe.

[0058] The total amount of sewage to be treated is first detected by the instrument in the instrument tank to obtain the average concentration within five minutes. Due to the stratification of water, the measured concentration within five minutes can represent the average concentration of the influent water for one hour; if the concentration increases or decreases by more than 30% within one hour, the compensation value will be used to make positive or negative compensation. After obtaining the average concentration of nitrate nitrogen in the influent water for one hour, the total amount of influent water for one hour can be used to calculate the amount of methanol added through the reaction equation.

[0059] The denitrification reaction proceeds according to the following reaction:

[0060]

[0061] ΔG = -333 kJ / moL;

[0062] These include the following four reduction reactions:

[0063] Nitrates Reduction to nitrite

[0064]

[0065] Nitrite Reduction to nitric oxide (NO):

[0066]

[0067] Nitric oxide (NO) is reduced to nitrous oxide (N2O):

[0068] 2NO+2H + +2e - →N2O+H2O;

[0069] Nitrous oxide (N2O) is reduced to nitrogen (N2):

[0070] N2O+2H + +2e - →N2+H2O;

[0071] When methanol is used as a carbon source organic matter, the total denitrification process with nitrate nitrogen can be expressed by the following equation:

[0072] When methanol is used as a carbon source organic matter, the overall denitrification process with nitrite nitrogen can be expressed by the following equation:

[0073]

[0074] Since dissolved oxygen must exist in water, the total denitrification process of methanol as a carbon source organic matter and nitrite nitrogen can be expressed by the following equation:

[0075]

[0076] According to the formula, the treated wastewater contains nitrate, nitrite and dissolved oxygen, and the coefficient of added methanol is 2.68, so the consumption of methanol added per hour is obtained.

[0077] Calculated consumption of methanol = ∑(NO3+NO2+O2)*factor*methanoL(100%);

[0078] The theoretical calculation value factor of methanol consumption in the formula is 2.68; because nitrate nitrogen is mainly eliminated, the amount of nitrate nitrogen converted into nitrite nitrogen is 1:1, and the factor value is appropriately increased in actual production for oxygen consumption of dissolved oxygen. The nitrate nitrogen value detected in the primary denitrification tank and the calculation of the nitrate nitrogen concentration in the influent of the primary denitrification tank are:

[0079] The calculation formula is:

[0080] c=NO3-N*sum(w)*2.47+NO2-N*sum(w)*1.53+DO*sum(w)*0.87; c is the calculated amount of methanol added, unit: mg;

[0081] NO3-N is the nitric nitrogen concentration measured per unit time, unit: mg / L;

[0082] NO2-N is the nitric nitrogen concentration measured per unit time, unit: mg / L;

[0083] sum(w) is the water intake per unit time, unit: L;

[0084] DO is the amount of dissolved oxygen per unit time, unit: mg / L;

[0085] As the instrument is used for a longer time, the calcium contained in the incoming water will damage the instrument's detection system and contaminate the electrolyte of the detection probe. Once damaged, there is no other way to eliminate the impact except replacing spare parts. However, if the compensation system is running, although its value will be affected, the compensation controller will calculate the residual difference between the measured value and the set value through a closed-loop algorithm, and ultimately eliminate the impact caused by the measurement error.

[0086] From the practical point of view, the nitrite nitrogen in the water is very small and can be ignored, so the coefficient of 1.53 nitrite nitrogen can be ignored, and the dissolved oxygen value is not much, so the final formula is

[0087] c=∑(NO3-N+DO)*2.75*methanol(100%);

[0088] c: Calculated amount of methanol added, unit: mg;

[0089] ∑(NO3-N+DO): Total amount of nitrate nitrogen and dissolved oxygen (unit: mg);

[0090] 2.75 coefficient: 2.47 coefficient for nitrate-nitrogen and 0.28 coefficient for dissolved oxygen optimization.

[0091] Methanol (100%): 100% methanol concentration: unit: mg;

[0092] The nitrate-nitrogen value detected in the primary denitrification tank and the calculation of the nitrate-nitrogen concentration in the influent of the primary denitrification tank;

[0093] The calculation formula is: calculated methanol consumption = ∑(NO3+NO2+O2)*2.75*methanoL(100%).

[0094] To obtain the concentration of nitrate nitrogen, the nitrate nitrogen detection instrument is placed in the liquid to be tested for 6 minutes in one hour to obtain the instrument measurement value. The purpose is to obtain the nitrate nitrogen concentration while increasing the service life of the instrument. If the instrument is always placed in the system, the sulfate ions in the sewage will penetrate the membrane and affect the instrument detection results. The calcium ions in the sewage will also adhere to the surface of the probe, affecting the ion exchange between the electrode and the measured substance, reducing the service life of the instrument. It is placed in the test liquid for 6 minutes, and it takes 48 seconds from the time it is placed in the liquid to the time the detection value is stable and reliable. Therefore, the detection values ​​in the first minute of being placed in the liquid are all ignored, and only the concentration detection values ​​in the last 5 minutes are taken as valid values.

[0095] In order to increase the service life of the instrument, after lifting the detection probe away from the sewage, the probe surface needs to be cleaned with water so that the sewage on the surface of the electrode membrane is fully replaced by new water, so that it remains moist and the elements harmful to the electrode are washed away. The diameter of the flushing water pipes on both sides needs to be greater than or equal to 800 mm, the pressure is 0.001-0.003MPa, and the upward angle is between 30°--38°.

[0096] In addition to nitrate nitrogen, methanol addition also includes nitrite nitrogen and dissolved oxygen, which will consume methanol. According to the characteristics of the unit, the actual nitrite nitrogen and dissolved oxygen values ​​of the unit are at a relatively low level. Therefore, the theoretical calculation value factor is increased from 2.68 to 2.75 to compensate for the trace dissolved oxygen and nitrite nitrogen contained.

[0097] After adding methanol, if the nitric nitrogen is higher or lower than the target value, a compensation mechanism is introduced to ensure that the reaction value can reach the target value. The maximum compensation value of the compensation mechanism should be 50% of the maximum amount of methanol added. The minimum value should reach minus 20% of the maximum amount of methanol added. That is, if the amount of methanol added is 500 liters / hour, the maximum compensation value is 250 liters / hour and the minimum value is -100 liters / hour.

[0098] The compensation controller adopts proportional control and integral time control mode. There is a nitric nitrogen detection instrument in the first-level anaerobic zone, which feeds back the current nitric nitrogen value in real time. The measured value of nitric nitrogen is compared and calculated with the set expected value. The compensated methanol value is added to the calculated methanol consumption value to get the actual methanol addition value.

[0099] The maximum compensation value is 250 liters / hour, the minimum value is -100 liters / hour, and the calculation formula of the methanol value calculated by the controller is:

[0100] Compensated methanol value = (maximum compensation value - minimum compensation value) * controller output value.

[0101] The main comparison is about the role of glucose and methanol in the nitrification and denitrification process. When both carbon sources are sufficient, nitrate can be completely removed, but the optimal carbon-nitrogen ratio of glucose as the carbon source is 6:1-7:1 (glucose: nitrate nitrogen), while the optimal carbon-nitrogen ratio of methanol is 3:1 (methanol: nitrate nitrogen), and the operating cost is higher than that of methanol. When the carbon source is insufficient, nitrite accumulates in the denitrification process, and the accumulation is more serious when glucose is used as the carbon source, resulting in incomplete treatment and deterioration of the effluent, which increases the difficulty of system operation and debugging. In addition, the denitrification rate using methanol as the carbon source is much faster than that using glucose as the carbon source, 3 times faster under the same conditions, which is equivalent to the nitrification and denitrification system with glucose as the carbon source. The pool is 3 times larger than the pool with methanol as the carbon source, and the cost is much higher than the nitrification and denitrification system with methanol as the carbon source. The effluent quality requirements of this water treatment are COD cr Below 50mg / L, total nitrogen below 15mg / L, total nitrogen and COD cr Therefore, methanol is selected as the carbon source due to its low dosage, fast reaction speed and easy control, so that the effluent can stably meet the standards.

[0102] During the growth of microorganisms, carbon source, nitrogen source and phosphorus source are required at the same time. Therefore, during the operation of this biochemical system, a certain amount of phosphoric acid needs to be added into the system as a phosphorus source to meet the nutritional needs of microorganisms and enable the system to operate stably.

[0103] In the two-stage nitrification pool, the pool needs to be aerated. Considering the scaling and clogging problems caused by the high calcium hardness in the sewage, perforated tube aeration and microporous aeration cannot be used in this system. The jet aeration system aerates the two-stage nitrification pool. Jet aeration uses three-dimensional aeration to ensure that there are no dead corners in the pool, no sedimentation at the bottom of the pool, high oxygen utilization rate of more than 25%, wide flow channel, high flow rate, not easy to scale and block, suitable for the aeration of high-calcium wastewater, and long service life.

[0104] 5) Degassing tank

[0105] After the sewage is treated by A / O / A / O nitrification and denitrification, the nitrified liquid needs to be returned to the primary denitrification tank. This liquid contains a large amount of dissolved oxygen, and part of the dissolved oxygen needs to be removed in the degassing tank before it can be returned to the primary denitrification tank. Otherwise, the large amount of dissolved oxygen brought by the nitrified liquid return will greatly increase the consumption of methanol. In order to remove the dissolved oxygen in the sewage, the sewage in the degassing tank needs to be stirred by plug flow. We use a submersible plug flow device, which is easy to operate and easy to manage.

[0106] 6) Sedimentation tank

[0107] After the sewage is treated by the biochemical stage, the total nitrogen and COD cr The SS in the sewage is basically removed in the sedimentation tank in the form of sludge. The sludge in the sedimentation tank needs to be returned to the front-end primary denitrification tank at a return ratio of 100% to replenish the sludge concentration in the system. The sedimentation tank is designed according to the specifications of the secondary sedimentation tank, and the surface load rate is about 0.59m 3 / (m 2 .h), adopting the method of central water inlet and peripheral overflow weir water outlet, can have a better removal ability for SS.

[0108] 7) Filter cloth filter

[0109] The sewage treated in the sedimentation tank needs to be deeply treated. We use vertical fiber filter cloth to deeply filter the effluent from the sedimentation tank, which can further reduce the SS of the sewage. It has its own PLC control system, which is simple to operate, has stable effluent, and is not easy to clog. The water treated in the filter cloth filter tank is discharged through the clean water tank. Compared with the traditional deep filtration system, it has the following advantages:

[0110] (1) The effluent quality is good and stable. The backwashing intensity is 333L / ms, and the backwashing frequency is high, once every two hours, to prevent the growth of green algae and prevent the filter cloth from being blocked or hardened.

[0111] (2) The operating cost of the vertical fiber cloth filter is very low. The operating cost of treating one ton of water is only 0.004 yuan (4 cents), while the operating cost of traditional processes (V-type filter, D-type filter, fiber bundle / ball filter) is 0.2-0.3 yuan.

[0112] (3) Compared with the traditional process, the vertical fiber filter cloth filter tank eliminates the need for construction such as the blower room, lift pump room, chlorination room, clear water tank, and sedimentation tank, and saves land.

[0113] (4) The vertical fiber cloth filter tank eliminates many structures, valves, pipelines, etc., making the maintenance and repair of the equipment simple and convenient, and the operation is highly automated. Therefore, there is no need for special personnel to supervise, and the labor intensity of workers is greatly reduced.

[0114] (5) Compared with traditional filter tanks, the vertical fiber cloth filter tank eliminates the need for pre-chlorination, which not only reduces operating costs but also avoids unsafe operating hazards for workers (high CLO2 concentration may cause flash explosions, endangering the lives of workers).

[0115] Its core control method adopts PID control algorithm. This method is simple and easy, and does not require complex mathematical models. The PID controller has three adjustable parameters, namely the proportional coefficient (P), the integral time constant (I) and the differential time constant (D). By adjusting these three parameters, the control effect of the controller can be flexibly changed to meet the control requirements of different systems, so that the system can achieve fast, stable and accurate control performance. Good robustness: There is a certain tolerance for external disturbances and changes in system parameters, and the stability and control performance of the system can be maintained to a certain extent. Even if there is a certain uncertainty in the system or it is disturbed by the outside world, the PID controller can still work well to keep the controlled variable near the set value. High control accuracy: When the parameters of the PID controller are adjusted appropriately, the steady-state error of the system can be close to zero, thereby achieving higher control accuracy and meeting the control requirements of the nitrate nitrogen concentration in the effluent during field operation.

[0116] Compared with no precise control

[0117] When precise control is not adopted, personnel need to measure the concentration on site, then input the measured value into the formula, and then manually input the calculated amount of methanol to control the nitrate nitrogen on site through this amount of methanol. The limitation of this method is that there are intervals between the time points of measurement. During the interval time period, the nitrate nitrogen concentration may change greatly, so the calculated methanol value cannot meet the function of suppressing the nitrate nitrogen value. At the same time, the fluctuation value of personnel detection is large. If the measurement is inaccurate, resulting in excessive addition of methanol, the COD in the effluent index will exceed the standard due to the excessive addition of methanol, affecting the effluent effect.

[0118] After adding precise control, the nitric nitrogen value on site is measured every 5 seconds, and then the controller calculates and adjusts the amount of methanol added in real time to ensure that the difference between the nitric nitrogen concentration in the outlet water and the set value is less than 2 mg / L. The staff compares the on-site measuring instrument with the manual test results once a day and checks the measured values, which can make the outlet water value and the set value very stable. At the same time, it also saves manpower.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for stabilizing treatment of nitric nitrogen-containing wastewater, characterized in that: The steps include: S1: pre-treat the wastewater, and then enter the primary denitrification tank, the primary nitrification tank, the secondary denitrification tank, and the secondary nitrification tank, add phosphoric acid and methanol to the primary denitrification tank and the secondary denitrification tank, and calculate the methanol addition value of the primary denitrification tank through the ID control algorithm according to the nitrate nitrogen value detected in the primary denitrification tank and the nitrate nitrogen concentration of the influent of the primary denitrification tank; The methanol addition value of the secondary denitrification pool is calculated based on the nitrate-nitrogen value detected in the secondary denitrification pool and the nitrate-nitrogen concentration of the influent of the secondary denitrification pool, and then enters the degassing pool; S2: The sewage treated in the degassing tank enters the sedimentation tank for sedimentation. Part of the sludge in the sedimentation tank enters the primary denitrification tank, and the other part of the sludge is discharged; the supernatant of the sedimentation tank enters the filter cloth filter tank, and then enters the clear water tank to meet the discharge standards.

2. The method for stabilizing nitric nitrogen-containing wastewater according to claim 1, characterized in that: The primary denitrification pool, the primary nitrification pool, the secondary denitrification pool, and the secondary nitrification pool are connected in sequence through pipelines; the wastewater passes through the primary denitrification pool, the primary nitrification pool, the secondary denitrification pool, and the secondary nitrification pool in sequence; The sludge in the secondary nitrification tank enters the primary denitrification tank through a pipeline; The sludge in the degassing tank enters the primary denitrification tank; The sludge in the sedimentation tank enters the primary denitrification tank.

3. The method for stabilizing nitric nitrogen-containing wastewater according to claim 1, characterized in that: The water inlet pipes of the primary denitrification tank and the secondary denitrification tank are tested by the instrument in the instrument tank to obtain the average concentration within 5 minutes; If the concentration increases or decreases by more than 30% within 1 hour, the compensation value will be used to compensate for it by adding more methanol or reducing the amount of methanol. After obtaining the average nitric nitrogen concentration of the influent for 1 hour, the total influent volume for 1 hour is used, and the amount of methanol added is calculated through the reaction equation.

4. The method for stabilizing nitric nitrogen-containing wastewater according to claim 3, characterized in that: It takes one hour to put the nitrate nitrogen detection instrument into the liquid to be tested for 6 minutes to obtain the instrument measurement value, of which 48 seconds are required from the time the instrument is put into the liquid to the time the detection value becomes stable and reliable.

5. The method for stabilizing nitric nitrogen-containing wastewater according to claim 3, characterized in that: After the detection probe is separated from the sewage, the probe surface needs to be cleaned with water so that the sewage on the surface of the electrode diaphragm is fully replaced by new water. The diameter of the flushing water pipes on both sides needs to be greater than or equal to 800 mm, the water pressure of the flushing water pipes is 0.001-0.003MPa, and the upward angle of the flushing water pipes is between 30° and 38°.

6. The method for stabilizing nitric nitrogen-containing wastewater according to claim 3, characterized in that: If the nitric nitrogen content is higher or lower than the target value, a compensation mechanism is introduced to ensure that the reaction value can reach the target value. The maximum compensation value of the compensation mechanism should be 50% of the maximum amount of methanol added; the minimum value should reach minus 20% of the maximum amount of methanol added.

7. The method for stabilizing the treatment of nitric nitrogen-containing wastewater according to claim 3, characterized in that: The maximum compensation value is 250 liters / hour, the minimum value is -100 liters / hour, and the calculation formula for the methanol value calculated by the controller is: Compensated methanol value = (maximum compensation value - minimum compensation value) * controller output value.

8. The method for stabilizing nitric nitrogen-containing wastewater according to claim 1, characterized in that: The pretreatment of wastewater includes conveying the production wastewater to the equalization tank, entering the neutralization tank, and adjusting the pH of the wastewater to 6-8 after two neutralization adjustments in the neutralization tank, and then entering the temperature control tank.

9. The method for stabilizing nitric nitrogen-containing wastewater according to claim 1, characterized in that: The return flow of the primary denitrification tank or the secondary denitrification tank must be more than three times the inlet flow; the return flow of the final sedimentation tank needs to be more than one times the inlet flow.

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