A method for adjusting the alternating time of double-oxidation ditch to promote granulation and improve denitrification performance

Abstract

The application discloses a method for adjusting double-gully oxidation ditch alternation time to promote granulation and improve denitrification performance, which comprises the following steps: sampling sludge and water mixture in the double-gully oxidation ditch to measure water quality and particle size; processing data to obtain the simultaneous nitrification and denitrification rate of the oxidation ditch operation; judging whether the double-gully alternation time can be adjusted according to the particle size and the simultaneous nitrification and denitrification rate; judging whether the double-gully alternation time needs to be continuously adjusted according to the change of the effluent nitrate nitrogen concentration after adjustment; and repeating the above steps until it is judged that the double-gully alternation time does not need to be adjusted; and the method can promote sludge granulation in the double-gully oxidation ditch, improve the simultaneous nitrification and denitrification capacity, reduce the consumption of carbon sources in the denitrification process, and effectively improve the denitrification capacity of the oxidation ditch.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for adjusting the alternation time of a dual-ditch oxidation ditch to promote granulation and improve denitrification performance. Background Technology

[0002] The dual-ditch alternating oxidation ditch process has good nitrogen removal efficiency, but it still has many shortcomings. With the increasing stringency of wastewater treatment plant discharge standards in my country, some regions require a reduction in total nitrogen (TNO) from 15 mg / L to 10 mg / L. This puts significant pressure on wastewater treatment plants to meet TNO standards. Furthermore, the conventional dual-ditch oxidation ditch denitrification process is energy-intensive, requiring large amounts of oxygen and energy. Therefore, it is necessary to upgrade the treatment capacity of existing processes, and there are technologies to transform the oxidation ditch into an A... 2 Oxygen sludge can be modified into an MBBR (Multi-Melt Batch Reactor) by adding packing material, but the modification cost is high. Therefore, the direction for improving oxidation ditch processes is to find technologies that can reduce operating and modification costs while improving the denitrification performance of oxidation ditches. Granular sludge, due to its advantages of high loading capacity, good settling performance, and high biomass, can save land area and increase treatment load, but it is mostly cultivated in SBR (Sequencing Batch Reactor) dual-ditch oxidation ditches. Direct cultivation in continuous flow reactions such as oxidation ditches is difficult. At the same time, simultaneous nitrification-denitrification (SND) is a denitrification method different from denitrification, with low demand for O2 and carbon sources, which can save carbon sources, optimize carbon source utilization, and improve denitrification performance. Technologies that can achieve the above two effects through simple control within the oxidation ditch, such as setting up two sedimentation tanks within the oxidation ditch, are complex to implement and have high modification costs.

[0003] Patent application CN117486437A discloses a nitrogen and phosphorus removal system and method adapted to high sludge concentrations. By modifying the Carrousel oxidation ditch-MBR system and adopting a high sludge concentration operation method, it combines MBR technology with the Carrousel oxidation ditch, adding bottom aeration devices and propellers. It uses oxidation-reduction potential values ​​and dissolved oxygen meters to precisely control the anaerobic, anoxic, microaerobic, aerobic, and deoxygenated zones of the Carrousel oxidation ditch. By adjusting the return flow rate at each stage of the system, it enhances the biological nitrogen removal effect and improves the nitrogen removal capacity. Simultaneously, it effectively controls the carbon source dosage, improving treatment efficiency and effect while reducing excess sludge discharge. Compared to existing wastewater treatment plants using conventional Carrousel oxidation ditch processes, it can improve the treatment capacity and effluent quality indicators of existing wastewater treatment plants.

[0004] Although the above-mentioned existing technical solutions have improved the denitrification capacity of wastewater treatment plants, effectively controlled the amount of carbon source added, and improved the treatment capacity and effluent quality indicators of Carrousel oxidation ditches, the technical solutions are complex to modify and require the addition of other devices and treatment processes, resulting in high modification costs and increased operating costs. Summary of the Invention

[0005] This invention aims to solve the problems of sludge granulation difficulties, low simultaneous nitrification and denitrification efficiency, and high operating energy consumption in existing dual-ditch oxidation ditch processes. It provides a method for adjusting the alternation time of the dual-ditch oxidation ditch to promote granulation and improve denitrification performance. This method is applicable to dual-ditch oxidation ditch systems with alternating operation capabilities. By periodically monitoring the influent and effluent water quality and the sludge-water mixture, calculating the simultaneous nitrification and denitrification rate, and analyzing sludge particle size parameters, the alternation time of the two ditches is dynamically adjusted based on these parameters. This achieves efficient cultivation of granular sludge under continuous flow conditions without adding additional structures or equipment, while simultaneously improving simultaneous nitrification and denitrification capabilities, optimizing carbon source utilization efficiency, and reducing dissolved oxygen demand. This effectively improves the system's denitrification performance and reduces operating costs.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: A method for adjusting the alternation time of a dual-ditch oxidation ditch to promote granulation and improve denitrification performance includes the following steps: Step 1: Periodically collect water samples from the two outlets and the inlet of the dual-ditch oxidation ditch, and determine the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. At the same time, calculate the average concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen from the two outlets, and simultaneously collect the mud-water mixture to determine the particle size distribution of sludge in the dual-ditch oxidation ditch. Step 2: Calculate the simultaneous nitrification and denitrification rate based on the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen in the water samples from the two outlets and inlet of the dual-ditch oxidation ditch measured in Step 1. Step 3: Based on the sludge particle size distribution of the dual-ditch oxidation ditch obtained in Step 1 and the simultaneous nitrification / denitrification rate obtained in Step 2, determine the current operating status of the dual-ditch oxidation ditch and adjust the alternation time accordingly. When the proportion of sludge particles larger than 200 μm in the dual-ditch oxidation ditch is 0% to 10% and the simultaneous nitrification and denitrification rate is 0% to 40%, the alternation time of the dual-ditch oxidation ditch should be extended. When the proportion of sludge particles with a diameter of 200 μm or larger in the dual-ditch oxidation ditch is 10% to 20% and the simultaneous nitrification and denitrification rate is 40% to 50%, the alternation time of the dual-ditch oxidation ditch remains unchanged. When the proportion of sludge particles with a diameter of 200 μm or larger in the dual-ditch oxidation ditch is greater than 20% and the simultaneous nitrification and denitrification rate is greater than 50%, the alternation time of the dual-ditch oxidation ditch should be shortened. Step 4: After completing Step 3, repeat Step 1 after an interval of 1 to 30 days. Step 5: After repeating Step 1, based on the average nitrate nitrogen concentration at the two outlets measured in Step 1, determine and adjust the alternation time of the dual-ditch oxidation ditch: If the average growth rate of nitrate nitrogen concentration at the two outlets is greater than 30%, the alternation time of the dual-ditch oxidation ditch will be adjusted to the alternation time of the dual-ditch oxidation ditch before the last adjustment. If the average growth rate of nitrate nitrogen concentration at the two outlets is less than 30%, repeat step 3; After completing steps 6 and 5, repeat steps 1, 2, 3, 4, and 5 every 1 to 30 days until the alternation time of the dual-ditch oxidation ditch no longer needs to be adjusted.

[0007] In step 3, the alternation time of the dual-ditch oxidation ditch can be adjusted for a duration of 0 to 9 hours each time; if the previous adjustment of the dual-ditch oxidation ditch shortened the alternation time, the alternation time after this adjustment shall not exceed the previous alternation time.

[0008] In step 3 or step 5, the alternation time of the dual-ditch oxidation ditch is adjusted when both ditches of the dual-ditch oxidation ditch are in the aeration state, and the alternation time of the dual-ditch oxidation ditch is 0 to 9 hours.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention, by adjusting the alternation time of the dual-ditch oxidation ditch, changes the duration of anaerobic and aerobic cycles, thereby altering the saturation-starvation ratio of the sludge. This has the advantage of promoting the particle size growth of the sludge in the dual-ditch oxidation ditch, which is to say, promoting sludge granulation.

[0010] 2. This invention promotes the growth of sludge particle size in the dual-ditch oxidation ditch by appropriately adjusting the alternation time of the dual-ditch oxidation ditch. The appropriate particle size range can systematically improve the simultaneous nitrification and denitrification capacity. At the same time, the adjusted dissolved oxygen distribution also promotes the simultaneous nitrification and denitrification rate. It has the advantages of reducing the consumption of carbon source during the denitrification process and improving the total nitrogen removal rate.

[0011] 3. Based on the original dual-ditch oxidation ditch, this invention adjusts the alternation time of the dual-ditch oxidation ditch as an operating parameter. The operation and control are simple, and no additional equipment or processes are required. It has the advantages of being easy to operate.

[0012] In summary, this invention, by adjusting the in-situ operating conditions in the oxidation ditch, has the advantages of simple and easy operation, promoting particle growth, improving dissolved oxygen distribution, increasing the simultaneous nitrification and denitrification rate of the system, improving the total nitrogen removal efficiency of the system, reducing carbon source consumption, improving wastewater treatment performance, and reducing operating costs. Attached Figure Description

[0013] Figure 1 This is a flow chart of the dual-ditch oxidation ditch treatment process according to an embodiment of the present invention.

[0014] Figure 2This is a graph showing the particle size distribution and average size variation of the dual-ditch oxidation ditch in an embodiment of the present invention at different dual-ditch alternation times.

[0015] Figure 3 The figures show the changes in MLSS and VSS / SS of sludge in the dual-ditch oxidation ditch at different dual-ditch alternation times in this embodiment of the invention.

[0016] Figure 4 This is a graph showing the variation of denitrification performance of the dual-ditch oxidation ditch in an embodiment of the present invention at different dual-ditch alternation times; wherein, Figure 4 (a) TN and NH4 in the influent and effluent of a dual-ditch oxidation ditch at different dual-ditch alternation times. + -N, Figure 4 (b) NO3 in the influent and effluent of a dual-ditch oxidation ditch at different dual-ditch alternation times - -N and NO2 - -N.

[0017] Figure 5 This is a graph showing the change in sludge activity in a dual-ditch oxidation ditch at different dual-ditch alternation times in an embodiment of the present invention; wherein, Figure 5 (a) represents the sludge SOURe and RI indices of a dual-ditch oxidation ditch at different dual-ditch alternation times. Figure 5 (b) SOUR of sludge in a dual-ditch oxidation ditch at different dual-ditch alternation times A , Figure 5 (c) SOUR of sludge in a dual-ditch oxidation ditch at different dual-ditch alternation times H .

[0018] Figure 6 This is a diagram showing the genus-level microbial community structure of the double-ditch oxidation ditch in an embodiment of the present invention at different double-ditch alternation times.

[0019] Among them, 1-1, first aeration pump; 1-2, second aeration pump; 2-1, first peristaltic pump; 2-2, second peristaltic pump; 3-1, first electric valve; 3-2, second electric valve; 3-3, third electric valve; 3-4, fourth electric valve; 4-1, first microporous aeration head; 4-2, second microporous aeration head; 5, flow propeller; 6-1, first inclined baffle; 6-2, second inclined baffle; 7-1, first effluent weir; 7-2, second effluent weir. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] A method for adjusting the alternation time of a dual-ditch oxidation ditch to promote granulation and improve denitrification performance includes the following steps: Step 1: Periodically collect water samples from the two outlets and the inlet of the dual-ditch oxidation ditch, and determine the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. At the same time, calculate the average concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen from the two outlets, and simultaneously collect the sludge-water mixture. The particle size distribution of the sludge in the dual-ditch oxidation ditch is determined using a laser particle size analyzer (LS230 / SVM, Beckman Coulter, USA). Step 2: Calculate the simultaneous nitrification and denitrification rate based on the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen in the water samples from the two outlets and inlet of the dual-ditch oxidation ditch measured in Step 1. Step 3: Based on the sludge particle size distribution of the dual-ditch oxidation ditch obtained in Step 1 and the simultaneous nitrification / denitrification rate obtained in Step 2, determine the current operating status of the dual-ditch oxidation ditch and adjust the alternation time accordingly. When the proportion of sludge particles larger than 200 μm in the dual-ditch oxidation ditch is 0% to 10% and the simultaneous nitrification and denitrification rate is 0% to 40%, the alternation time of the dual-ditch oxidation ditch should be extended. When the proportion of sludge particles with a diameter of 200 μm or larger in the dual-ditch oxidation ditch is 10% to 20% and the simultaneous nitrification and denitrification rate is 40% to 50%, the alternation time of the dual-ditch oxidation ditch remains unchanged. When the proportion of sludge particles with a diameter of 200 μm or larger in the dual-ditch oxidation ditch is greater than 20% and the simultaneous nitrification and denitrification rate is greater than 50%, the alternation time of the dual-ditch oxidation ditch should be shortened. Step 4: After completing Step 3, repeat Step 1 after an interval of 1 to 30 days. Step 5: After repeating Step 1, based on the average nitrate nitrogen concentration at the two outlets measured in Step 1, determine and adjust the alternation time of the dual-ditch oxidation ditch: If the average growth rate of nitrate nitrogen concentration at the two outlets is greater than 30%, the alternation time of the dual-ditch oxidation ditch will be adjusted to the alternation time of the dual-ditch oxidation ditch before the last adjustment. If the average growth rate of nitrate nitrogen concentration at the two outlets is less than 30%, repeat step 3; After completing steps 6 and 5, repeat steps 1, 2, 3, 4, and 5 every 1 to 30 days until the alternation time of the dual-ditch oxidation ditch no longer needs to be adjusted.

[0022] In step 3, the alternation time of the dual-ditch oxidation ditch can be adjusted for a duration of 0 to 9 hours each time; if the previous adjustment of the dual-ditch oxidation ditch shortened the alternation time, the alternation time after this adjustment shall not exceed the previous alternation time.

[0023] In step 3 or step 5, the adjustment of the alternation time of the dual-ditch oxidation ditch can be made when both ditches of the dual-ditch oxidation ditch are in the aeration state. The alternation time of the dual-ditch oxidation ditch is 0 to 9 hours as a protection mechanism. When the alternation time of the dual-ditch oxidation ditch is too long, it will lead to problems such as excessively high nitrate nitrogen concentration in the effluent and poor microbial activity.

[0024] Example First, sludge from a wastewater treatment plant in Xi'an was inoculated into a double-ditch oxidation ditch built in the laboratory.

[0025] like Figure 1 As shown, the dual-ditch oxidation ditch system is made of plexiglass and consists of a dual-ditch oxidation ditch, a central radial flow sedimentation tank, and a reflux system. The dual-ditch oxidation ditch comprises two identical oxidation ditches, A and B, connected by a perforated partition. The two ditches operate in series. During operation, the flow of water from ditch A to ditch B constitutes the alternation of oxidation ditches. The time interval between two alternations is called the alternation time. The specific structure of the dual-ditch oxidation ditch is as follows: In stage I, the influent is pumped into the dual-ditch oxidation ditch by the first peristaltic pump 2-1. At this time, the first electric valve 3-1 opens, and the influent enters ditch A through the first electric valve 3-1. It is then propelled by the flow actuator 5 to run within the dual-ditch oxidation ditch. The first aeration pump 1-1 and the second aeration pump 1-2 are activated. The first microporous aeration head 4-1 in ditch A closes, and the second microporous aeration head 4-2 in ditch B opens. At this time, the fourth electric valve 3-4 opens, and the effluent passes through the second inclined baffle 6-2 and exits from the second effluent weir 7-2. The fourth electric valve 3-4 enters the secondary sedimentation tank; during stage II, the influent is fed in by the first peristaltic pump 2-1, passes through the first electric valve 3-1, and is pushed by the thruster 5 to run in the double-ditch oxidation ditch. The first aeration pump 1-1 is turned on, the second aeration pump 1-2 is turned on, the first microporous aeration head 4-1 in ditch A is opened, and the second microporous aeration head 4-2 in ditch B is opened. At this time, the fourth electric valve 3-4 is opened, and the effluent passes through the second inclined baffle 6-2, exits from the second effluent weir 7-2, and enters the secondary sedimentation tank through the fourth electric valve 3-4. Settling tank; In stage III, influent is fed into the double-ditch oxidation ditch by the first peristaltic pump 2-1. At this time, the influent enters ditch B through the second electric valve 3-2 and is propelled by the thruster 5 to run in the double-ditch oxidation ditch. The first aeration pump 1-1 and the second aeration pump 1-2 are turned on. At this time, the first microporous aeration head 4-1 in ditch A is opened, and the second microporous aeration head 4-2 in ditch B is closed. The effluent passes through the first inclined baffle 6-1, exits from the first effluent weir 7-1, and enters the secondary settling tank through the third electric valve 3-3; In stage IV... The influent is pumped into the dual-ditch oxidation ditch by the first peristaltic pump 2-1. At this time, the influent passes through the second electric valve 3-2 into ditch B, and is propelled within the dual-ditch oxidation ditch by the propeller 5. The first aeration pump 1-1 and the second aeration pump 1-2 are activated. Simultaneously, the first microporous aeration head 4-1 in ditch A and the second microporous aeration head 4-2 in ditch B are opened. The third electric valve 3-3 is also opened. The effluent passes through the first inclined baffle 6-1, exits from the first effluent weir 7-1, and enters the secondary sedimentation tank through the third electric valve 3-3. Throughout the entire operation of the dual-ditch oxidation ditch, the second peristaltic pump 2-2 remains open, transporting some of the sludge from the secondary sedimentation tank to the influent point, where it enters the dual-ditch oxidation ditch along with the influent, maintaining a stable sludge concentration in the dual-ditch oxidation ditch. The switching of the first electric valve 3-1, the second electric valve 3-2, the third electric valve 3-3, and the fourth electric valve 3-4 in the dual-groove oxidation ditch, as well as the switching of the first microporous aeration head 4-1 and the second microporous aeration head 4-2, are all controlled by a PLC.

[0026] The operational stages of a dual-ditch oxidation ditch are described below: The operation of the dual-ditch oxidation ditch is divided into four stages: Stage I: water enters from ditch A and exits from ditch B. At this time, ditch A is not aerated, while ditch B is aerated; Stage II: water enters from ditch A and exits from ditch B. At this time, both ditch A and ditch B are aerated; Stage III: water enters from ditch B and exits from ditch A. At this time, ditch B is not aerated, while ditch A is aerated; Stage IV: water enters from ditch B and exits from ditch A. At this time, both ditch B and ditch A are aerated.

[0027] In step 1, the water samples taken from the outlets are either the first outlet weir 7-1 and the second outlet weir 7-2 at the end of stages I and II, or the two outlets (first outlet weir 7-1 and second outlet weir 7-2) at the end of stages III and IV. The water quality parameters measured include ammonia nitrogen concentration, nitrate nitrogen concentration, and nitrite nitrogen concentration.

[0028] The inoculated sludge was taken from the distribution well of a double-ditch oxidation ditch in a wastewater treatment plant in Xi'an. The MLSS was about 9273 mg / L and the SVI was about 79 mL / g. It was diluted to 4050 mg / L, aerated for 24 h, and then inoculated into a laboratory double-ditch oxidation ditch for cultivation. The detailed operating conditions of the double-ditch oxidation ditch system are shown in Table 2.

[0029] Table 2. Dual-ditch oxidation ditch system and its operating conditions Sedimentation tank size The sedimentation tank has a diameter of 0.35m and an effective volume of 58L. Inlet water flow rate (mL / min) 250 C:N:P 100:10:1 Trace elements <![CDATA[9mg / L CaCl2,60mg / L MgSO4·7H2O,0.06mg / L H3BO3,0.012 mg / L CuSO4·5H2O,0.072mg / L KI,0.048 mg / L MnCl2·4H2O,0.616 mg / L FeSO4·7H2O,0.024 mg / L Na2MoO4·2H2O,0.048 mg / L ZnSO4·7H2O,0.06 mg / L CoCl2·6H2O, 5.096 mg / L EDTA]]> Hydraulic residence time (h) 10 Sludge age (d) 20 sludge return ratio (%) 90 The dual-ditch oxidation ditch system operates continuously in a periodic mode, with each cycle consisting of four stages. The dual-ditch oxidation ditch operates for 122 days, during which the alternation time between the two ditches is adjusted three times. The operating conditions are shown in Table 3.

[0030] Table 3 Operating Conditions of Dual-Ditch Oxidation Ditch

[0031] Various indicators of activated sludge in a dual-ditch oxidation ditch system were measured under different dual-ditch alternation times to test the performance of the dual-ditch oxidation ditch.

[0032] The following methods were used to measure various indicators of activated sludge: The respiration rate was measured using the respiration metering method, which involved long-term manual sampling and monitoring of the respiration rate of activated sludge to evaluate changes in microbial activity within the dual-ditch oxidation ditch.

[0033] The polysaccharide (PS) content in EPS was determined using the sulfuric acid-anthrone method. The protein (PN) content was determined using the modified Lowry method.

[0034] The zeta potential of the test sludge was measured using a Zeta potential meter (Zetasizer Nano ZS 90, Malvern Instruments Ltd.), and the sample pH was controlled at 7.0~7.2.

[0035] The laser particle size distribution analyzer (LS230 / SVM, Beckman Coulter, USA) measures the size of sludge samples, with a detection range of 0.04-2000 μm.

[0036] Ammonia nitrogen was analyzed using the method specified in "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method HJ535—2009". Nitrate nitrogen was analyzed using the method specified in "Determination of Nitrate Nitrogen in Water - Ultraviolet Spectrophotometric Method HJ / T346—2007". Nitrite nitrogen was analyzed using the method specified in "Determination of Nitrite Nitrogen in Water - Spectrophotometric Method GB7493—87".

[0037] The mixed liquor suspended solids concentration (MLSS) and conventional water quality indicators of the sludge were determined according to national standard methods.

[0038] The formulas for calculating the total nitrogen (TN) removal rate and the simultaneous nitrification-denitrification (SND) rate are as follows:

[0039] Among them, TN 进水 This refers to the concentration of total nitrogen (TN) in the water flowing into the dual-ditch oxidation ditch. 出水 The total nitrogen concentration refers to the concentration of the supernatant in the sedimentation tank after treatment by a double-ditch oxidation ditch.

[0040]

[0041] Where: ΔNH4 + -N is the NH4+ that begins the aeration phase. + -N concentration (including NH4+ at the end of the non-aeration phase) + -N concentration and NH4+ in the influent during the aeration stage + The sum of -N concentrations and the NH4+ at the end of the aeration phase + The difference in NO3- concentration, expressed in mg / L; ΔNO3 - This indicates the NO3 produced from the start to the end of the aeration phase. - The change in NO3- concentration is calculated as the NO3- concentration change at the end of the aeration stage. - -N concentration plus NO3 in the effluent during this stage - -N, minus the NO3 in the reflux. - -N concentration and NO3 at the end of the non-aeration phase - Concentration, unit mg / L; similarly, ΔNO2 - -N represents NO2 at the end of the aeration phase. - -N concentration plus NO2 in the effluent during this stage - -N concentration minus the refluxing NO2 - -N concentration and NO2 at the end of the non-aeration phase - The difference in -N concentration, expressed in mg / L.

[0042] Furthermore, the experimental results were analyzed. 1) The effect of adjusting the alternation time of the two ditches on the granulation of sludge in the oxidation ditch like Figure 2 As shown, during the operation with a dual-ditch alternation time of 3-4 hours, the average particle size of the sludge fluctuated within a small range of 51.51-55.31 μm, with virtually no increase. At this time, the sludge in the dual-ditch oxidation ditch did not form particles larger than 200 μm, and the sludge exhibited a flocculent state. When the dual-ditch alternation time was further extended to 6 hours, the sludge particle size increased rapidly, and the rate of increase gradually accelerated. Sludge with a particle size larger than 200 μm gradually appeared in the dual-ditch oxidation ditch, accounting for 8.04%, and there was a trend of further granulation. When the dual-ditch alternation time was further extended to 9 hours, the proportion of sludge with a particle size larger than 200 μm in the dual-ditch oxidation ditch increased to 39.8%, and the average particle size reached 230.8 μm. However, continued operation revealed that, as... Figure 3 As shown, the MLSS decreased rapidly, and the sludge volume decreased. This is because sludge bulking in the dual-ditch oxidation ditch led to biomass loss, at which point the proportion of sludge particles larger than 200 μm decreased. This result indicates that under appropriate dual-ditch alternation time, the granularity of the sludge is enhanced. However, continuously extending the dual-ditch alternation time will cause system instability and further disintegration.

[0043] 2) The effect of adjusting the alternation time of the two ditches on the denitrification performance of the oxidation ditch As shown in Table 4, the SND rates for alternating double-ditch times of 3 h, 4 h, and 6 h were 26.30%, 40.02%, and 42.76%, respectively. This indicates that extending the alternating time of the double ditches increases the SND rate, with the best performance observed at 6 h. This suggests that extending the alternating time of the double ditches can improve the simultaneous nitrification and denitrification effect of the double-ditch oxidation ditch. In this experiment, nitrate concentration gradually increased during the aerobic period with the extension of the alternating time of the double ditches, but NO3... - The accumulation of NO3- did not inhibit simultaneous nitrification and denitrification, nor did it inhibit SND as reported in the literature. This is because the dual-ditch oxidation ditch involves alternating influent, and the NO3- accumulated during the aerobic phase... - -N can be removed in the anoxic section by denitrification using influent carbon sources. Studies have shown that low DO conditions are more conducive to SND (Self-Nutrition Discharge), and the DO concentration in the aerobic section of the oxidation ditch slightly decreases with the extension of the alternation time between the two ditches, which may be one of the reasons for the improved SND efficiency.

[0044] Table 4. Water quality changes and SND rates at the end of each stage along the course of the river at different double-ditch alternation times.

[0045] TN changes during system operation, such as Figure 4 As shown in (a), the average TN removal rates for alternating ditch times of 3h, 4h, 6h, and 9h were 81.61%, 82.34%, 84.8%, and 76.29%, respectively. This indicates that the TN removal rate increases with the extension of the alternating ditch time, consistent with the trend in the SND data. However, extending the alternating ditch time to 9h resulted in a decrease in TN removal efficiency, possibly due to the decrease in sludge concentration affecting the TN removal rate. Throughout the entire operation of the dual-ditch oxidation ditch, NH4+... + -N was almost completely removed, and the main nitrogen compounds in the effluent were NO3. - -N, such as Figure 4 As shown in (b), the average concentrations of NO2 in the effluent at 3 h, 4 h, 6 h, and 9 h were 8.52 mg / L, 8.51 mg / L, 7.57 mg / L, and 11.04 mg / L, respectively, while almost no NO2 was detected in the effluent. - The accumulation of nitrogen (TN) is observed. Compared to the TN removal efficiency of 3 h and 4 h with alternating ditch times, the enhanced TN removal efficiency at 6 h may be related to the higher degree of sludge granulation, which also provides conditions for simultaneous nitrification and denitrification. However, at a TN removal efficiency of 9 h with alternating ditch times, the effluent NO3... - The significant increase in -N leads to a decrease in TN removal rate.

[0046] 3) The effect of adjusting the alternation time of the two ditches on the biological activity of the oxidation ditch SOUR e It is an effective indicator for measuring the activity of sludge microorganisms. When SOUR e An increase in SOUR usually indicates that the wastewater treatment system may be under external shock, serving as an early warning system; conversely, when SOUR... e A decrease in the value indicates lower microbial activity in the sludge. For example... Figure 5 As shown in (a), when the alternation time of the two ditches in a dual-ditch oxidation ditch is 3 h, because the dual-ditch oxidation ditch combines the characteristics of plug flow and completely mixed dual-ditch oxidation ditch, the substrate is diluted after entering the dual-ditch oxidation ditch. Microorganisms in the sludge, living in this environment for a long time, will undergo endogenous respiration and consume their own substances to maintain survival, thus reducing SOUR. e The value showed an upward trend. As the operating time increased, the microorganisms gradually adapted to this environment, and the value stopped increasing. When the alternation time between the two channels was extended to 6 hours, the change in operating conditions impacted the system, stimulating the respiration rate of the microorganisms and causing the SOUR... e The value briefly increased. As the dual-ditch oxidation ditch stabilized, SOUR... e The value then showed a downward trend. This may be related to the enhanced adsorption capacity of microbial aggregates after the sludge particle size increases. Some studies have indicated that this phenomenon occurs when the density of the sludge structure increases or when granular sludge is formed. Endogenous respiration rate ratio = OURe / OUR T Previous studies have named this RI, and the high-efficiency metabolic zone with an RI of 8%–16% is defined as the sludge active health zone. Figure 5 As shown in (a), the RI values ​​of the dual-ditch oxidation ditch fluctuated within the normal range during operation. However, when the dual-ditch alternation time was extended to 9 hours, the sludge RI value was less than 8%. This indicates that continuously extending the dual-ditch alternation time will result in the sludge being in an unhealthy state, which is detrimental to the activated sludge system.

[0047] Changes in the external environment can affect the community structure of sludge microorganisms. Autotrophic bacteria participate in biological reactions with a relatively small proportion of respiration and show high sensitivity to environmental changes; in contrast, heterotrophic bacteria account for a larger proportion of respiration and have stronger adaptability. Figure 5 As shown in (b), when the alternation time of the two channels is 3 h and 4 h, the SOUR in the system is... A The value fluctuated around 3 mgO2 / gSS / h; while when the alternation time of the two channels was adjusted from 4 h to 6 h, SOUR A The value increased from 2.741 mgO2 / gSS / h to 7.845 mgO2 / gSS / h; when the alternation time of the two grooves was extended to 9 h, the autotrophic bacteria were impacted, and SOUR... A The value shows a downward trend. As the alternation time of the two channels increases, SOUR... A The overall value showed an upward trend, indicating that extending the alternation time between the two ditches enhanced the biological activity of sludge autotrophic bacteria. For example... Figure 5 As shown in (c), during the operation with a double-sulcus alternation time of 3 h, heterotrophic bacteria gradually adapted to the environment, and SOUR H The value shows an upward trend. With the extension of the bi-sulcus alternation time, the increased starvation time results in less substrate available to heterotrophic bacteria, thus reducing SOUR. H It fluctuated between 17.47 and 35.79 mgO2 / gSS / h. When the dual-sulcus alternation time was 9 h, SOUR... H The sudden increase in the value may be related to the significant increase in F / M after the sludge concentration decreased.

[0048] 4) The impact of adjusting the alternation time of the two ditches on the microbial population Structures at the genus level of microorganisms, such as Figure 6 As shown, the main bacterial genera in the three sludge samples include Thiothrix , norank_f_Saprospiraceae , Pseudomonas as well as Chryseobacterium . Thiothrix The relative abundances in the three sludge samples—original sludge, sludge with alternating ditch times of 3 h, and sludge with alternating ditch times of 6 h—were 0.01%, 18.38%, and 54.07%, respectively. ThiothrixThis is a filamentous bacteria genus, and its increased relative abundance is accompanied by excessive growth of filamentous bacteria and continuously deteriorating settling performance. The abundance of this genus increased significantly at alternating ditch times of 3 h and 6 h, consistent with the settling data. Furthermore, the high abundance of this genus in plug-flow dual-ditch oxidation ditches can provide a framework for AGS formation and play a positive role in its formation. norank_f_ Saprospiraceae The bacteria genus typically attaches to the surface of bacteria, providing a carbon source for denitrifying bacteria to carry out denitrification, thereby promoting nitrogen removal. The relative abundance of this genus in the three sludge samples was 4.78%, 0.67%, and 6.32%, respectively, showing consistency with the total nitrogen removal efficiency. When the alternation time between the two ditches was adjusted to 6 h, the newly added bacteria genus... Pseudomonas and Chryseobacterium The relative abundances were 5.93% and 6.69%, respectively. These two genera can stimulate EPS production, thereby promoting microbial self-aggregation and facilitating sludge particle formation and stability. Furthermore, Pseudomonas Many species in the oxidation ditch have been identified as having the ability to simultaneously nitrify and denitrify. It is evident that adjusting the alternation time of the two ditches promotes the growth of synchronous nitrifying bacteria in the oxidation ditch, which is also a reason for improving the synchronous nitrification and denitrification capacity of the oxidation ditch.

[0049] Example Analysis This example involved adjusting the alternation time of the two ditches in a dual-ditch oxidation ditch to 3h, 4h, 6h, and 9h, and analyzing the particle size, denitrification performance, sludge activity, and bacterial species under different alternation times. The experimental results show that with the extension of the alternation time, the respiration activity of autotrophic bacteria in the sludge significantly increased. A The trend shows an upward trend. When the alternation time between the two channels is 6 hours, the sludge particle size increases rapidly, and the rate of increase gradually accelerates. When the alternation time is 9 hours, the proportion of particles larger than 200 μm increases to 39.8%, and the average particle size reaches 230.8 μm. Furthermore, as the alternation time increases from 3 hours to 6 hours, the SND (Synthetic Nitrification and Denitrification) increases from 26.30% to 42.76%. The system's simultaneous nitrification and denitrification capabilities and TN (Total Nitrogen Removal) removal efficiency increase with the extension of the alternation time. It is evident that the increase in alternation time from 3 hours to 6 hours promotes particle size growth and improves the system's TN removal efficiency. A 6-hour alternation time provides relatively optimal conditions, while further extending the alternation time to 9 hours leads to a decrease in microbial respiration activity, deterioration of settling performance, and a tendency for system collapse.

[0050] As can be seen from the embodiments, compared with the prior art, the present invention has the following advantages: 1. Promote sludge granulation: In existing wastewater treatment processes, oxidation ditches and A 2It is difficult to achieve sludge granulation in continuous flow dual-ditch oxidation ditches, but the activated sludge of this invention can promote the particle size growth of sludge in dual-ditch oxidation ditches by adjusting the alternation time of the two ditches and changing the duration of anaerobic and aerobic processes.

[0051] 2. Improved nitrogen removal efficiency: This invention promotes particle size growth by adjusting the alternation time of the two channels. The appropriate particle size range can systematically improve the simultaneous nitrification and denitrification capacity. At the same time, the adjusted dissolved oxygen distribution also promotes the simultaneous nitrification and denitrification rate, which can reduce the consumption of carbon source during the nitrogen removal process and improve the total nitrogen removal rate.

[0052] 3. Simple and easy to operate: Based on the original oxidation ditch, this invention combines the denitrification performance and particle size of the oxidation ditch itself, and improves the treatment effect of the oxidation ditch by adjusting the alternation time of the two ditches. The operation and control are simple and do not require additional equipment and processes.

[0053] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for adjusting the alternation time of a dual-ditch oxidation ditch to promote granulation and improve denitrification performance, characterized in that, Includes the following steps: Step 1: Periodically collect water samples from the two outlets and the inlet of the dual-ditch oxidation ditch, and determine the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. At the same time, calculate the average concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen from the two outlets, and simultaneously collect the mud-water mixture to determine the particle size distribution of sludge in the dual-ditch oxidation ditch. Step 2: Calculate the simultaneous nitrification and denitrification rate based on the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen in the water samples from the two outlets and inlet of the dual-ditch oxidation ditch measured in Step 1. Step 3: Based on the sludge particle size distribution of the dual-ditch oxidation ditch obtained in Step 1 and the simultaneous nitrification / denitrification rate obtained in Step 2, determine the current operating status of the dual-ditch oxidation ditch and adjust the alternation time accordingly. When the proportion of sludge particles larger than 200μm in the dual-ditch oxidation ditch is 0% to 10% and the simultaneous nitrification and denitrification rate is 0% to 40%, the alternation time of the dual-ditch oxidation ditch should be extended. When the proportion of sludge particles with a diameter of 200μm or larger in the dual-ditch oxidation ditch is 10% to 20% and the simultaneous nitrification and denitrification rate is 40% to 50%, the alternation time of the dual-ditch oxidation ditch remains unchanged. When the proportion of sludge with a particle size of 200μm or larger in the dual-ditch oxidation ditch is greater than 20% and the simultaneous nitrification and denitrification rate is greater than 50%, the alternation time of the dual-ditch oxidation ditch should be shortened. Step 4: After completing Step 3, repeat Step 1 after an interval of 1 to 30 days. Step 5: After repeating Step 1, based on the average nitrate nitrogen concentration at the two outlets measured in Step 1, determine and adjust the alternation time of the dual-ditch oxidation ditch: If the average growth rate of nitrate nitrogen concentration at the two outlets is greater than 30%, the alternation time of the dual-ditch oxidation ditch will be adjusted to the alternation time of the dual-ditch oxidation ditch before the last adjustment. If the average growth rate of nitrate nitrogen concentration at the two outlets is less than 30%, repeat step 3; After completing steps 6 and 5, repeat steps 1, 2, 3, 4, and 5 every 1 to 30 days until the alternation time of the dual-ditch oxidation ditch no longer needs to be adjusted. The alternation time for the dual-ditch oxidation ditch is 3-6 hours.

2. The method for adjusting the alternation time of a dual-ditch oxidation ditch to promote granulation and improve denitrification performance according to claim 1, characterized in that, In step 3 or step 5, the alternation time of the dual-ditch oxidation ditch is adjusted when both ditches of the dual-ditch oxidation ditch are in the aeration state.

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