Method for promoting granulation and improving denitrification performance by adjusting alternating time of double-ditch oxidation ditch

Abstract

The invention discloses a method for promoting granulation and improving denitrification performance by adjusting alternating time of a double-ditch oxidation ditch. The method comprises the following steps: taking a mud-water mixed liquid sample in the double-ditch oxidation ditch, and measuring water quality and particle size; processing the data to obtain the synchronous nitrification and denitrification rate of the operation of the oxidation ditch; judging whether the double-ditch alternation time can be adjusted or not according to the particle size and the synchronous nitrification and denitrification rate; judging whether the double-ditch alternation time needs to be continuously adjusted or not according to the change of the nitrate concentration of the effluent after adjustment; the previous steps are cycled until it is judged that the double-trench alternating time does not need to be adjusted; by adjusting the double-ditch alternating time, sludge granulation in the double-ditch oxidation ditch is promoted, the simultaneous nitrification and denitrification capacity is improved, the consumption of a carbon source in the denitrification process is reduced, and the denitrification capacity of the oxidation ditch can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and in particular relates to a method for adjusting the alternation time of a double-ditch oxidation ditch to promote granulation and enhance denitrification performance. Background Art

[0002] The double-ditch alternating working oxidation ditch process has a good denitrification effect, but it still has many shortcomings. With the improvement of my country's sewage treatment plant discharge standards, some areas require the discharge of total nitrogen to be reduced from 15mg / L to 10mg / L, which has brought great pressure on sewage treatment plants to meet the total nitrogen discharge standards. In addition, the denitrification process of the ordinary double-ditch oxidation ditch has high energy consumption and requires a large amount of oxygen and energy. Therefore, it is necessary to improve the processing capacity of the original process. There is a technology to transform the oxidation ditch into an A 2 O, or add fillers to transform into MBBR, etc., but the transformation cost is relatively high; therefore, seeking technologies that can reduce operating costs and transformation costs while improving the denitrification performance of the oxidation ditch is the direction of improvement of the oxidation ditch process. Granular sludge can save floor space and increase treatment load due to its advantages such as high load, good sedimentation performance and high biomass, but it is mostly cultivated in SBR double-ditch oxidation ditches. Direct cultivation in continuous flow reactions such as oxidation ditches is more difficult; at the same time, simultaneous nitrification and denitrification (SND) is a denitrification method that is different from denitrification. It has low requirements for O2 and carbon sources, can save carbon sources, optimize carbon source utilization, and improve denitrification performance. Technologies that achieve the above two with simple regulation in the oxidation ditch, such as setting up two sedimentation tanks in the oxidation ditch, are more complex to implement and have high transformation costs.

[0003] Patent application publication number CN117486437A discloses a denitrification and phosphorus removal system and method suitable for high sludge concentrations. By improving the Carrousel oxidation ditch-MBR system and adopting a high sludge concentration operation method, the system combines MBR technology with the Carrousel oxidation ditch, adds a bottom aerator and propeller, and uses redox potential and dissolved oxygen meters to precisely control the anaerobic, anoxic, microaerobic, aerobic, and anoxic zones of the Carrousel oxidation ditch. By adjusting the reflux rate at each level in the system, the biological denitrification effect is enhanced, improving denitrification capacity. At the same time, the carbon source dosage is effectively controlled, improving treatment efficiency and effectiveness, and reducing excess sludge discharge. Compared to existing sewage treatment plants using conventional Carrousel oxidation ditch processes, the system can improve the treatment capacity and effluent water quality of existing sewage treatment plants.

[0004] Although the above existing technical solutions have improved the denitrification capacity of the sewage treatment plant, effectively controlled the amount of carbon source added, and improved the treatment capacity and effluent water quality indicators of the Carrousel oxidation ditch, the technical solution is complex to transform and adds other devices and treatment processes, which has high transformation costs and increased operating costs. Summary of the Invention

[0005] The present invention aims to solve the problems of difficulty in sludge granulation, low efficiency of simultaneous nitrification and denitrification, and high operating energy consumption in the existing double-ditch oxidation ditch process, and provides a method for adjusting the alternation time of the double-ditch oxidation ditch to promote granulation and improve denitrification performance. The method is suitable for a double-ditch oxidation ditch system with alternating operation function. By periodically monitoring the water quality of the inlet and outlet water and the mud-water mixture, calculating the simultaneous nitrification and denitrification rate, and analyzing the sludge particle size parameters, the alternation time of the double ditch is dynamically adjusted according to the simultaneous nitrification and denitrification rate and the sludge particle size parameters. Without adding additional structures or equipment, efficient cultivation of granular sludge under continuous flow conditions is achieved, while the simultaneous nitrification and denitrification capacity is improved, the carbon source utilization efficiency is optimized, and the dissolved oxygen demand is reduced, thereby effectively improving the system denitrification performance and reducing operating costs.

[0006] In order to achieve the above object: the technical solution adopted by the present invention is:

[0007] A method for adjusting the alternating time of a double-ditch oxidation ditch to promote granulation and enhance denitrification performance comprises the following steps:

[0008] Step 1: Periodically collect water samples from the two outlets and the water inlet of the double-ditch oxidation ditch to determine the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. Simultaneously, calculate the average values ​​of the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen at the two outlets. Simultaneously, collect mud-water mixtures to determine the particle size distribution of sludge in the double-ditch oxidation ditch.

[0009] Step 2, calculating 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 the inlet of the double-ditch oxidation ditch measured in step 1;

[0010] Step 3: Based on the particle size distribution of the double-channel oxidation ditch sludge obtained in step 1 and the simultaneous nitrification and denitrification rate obtained in step 2, the current operating status of the double-channel oxidation ditch is determined, and the alternation time is adjusted accordingly:

[0011] When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is between 0% and 10% and the simultaneous nitrification and denitrification rate is between 0% and 40%, the alternation time of the double-channel oxidation ditch should be extended;

[0012] When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is between 10% and 20% and the simultaneous nitrification and denitrification rate is between 40% and 50%, the alternation time of the double-channel oxidation ditch remains unchanged;

[0013] When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is greater than 20% and the simultaneous nitrification and denitrification rate is greater than 50%, the alternation time of the double-channel oxidation ditch should be shortened;

[0014] Step 4: After step 3, repeat step 1 after 1 to 30 days.

[0015] Step 5: After repeating step 1, the alternation time of the double-ditch oxidation ditch is judged and adjusted according to the average value of the nitrate nitrogen concentration of the two outlets measured in step 1:

[0016] If the average growth rate of the nitrate nitrogen concentration at the two outlets is greater than 30%, the alternation time of the double-ditch oxidation ditch shall be adjusted to the alternation time of the double-ditch oxidation ditch before the last adjustment;

[0017] If the average growth rate of nitrate nitrogen concentration at the two outlets is less than 30%, repeat step 3;

[0018] Step 6: After step 5 is completed, repeat steps 1, 2, 3, 4, and 5 for 1 to 30 days until there is no need to adjust the alternation time of the double-ditch oxidation ditch.

[0019] In step 3, the alternation time of the double-channel oxidation ditch is allowed to be adjusted for 0 to 9 hours each time; if the alternation time was shortened in the last adjustment of the double-channel oxidation ditch, the alternation time after this adjustment shall not exceed the last alternation time.

[0020] In step 3 or step 5, the alternation time of the double-channel oxidation ditch is adjusted when both ditches of the double-channel oxidation ditch are in an aeration state, and the alternation time of the double-channel oxidation ditch is 0 to 9 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention changes the anaerobic and aerobic durations by adjusting the alternation time of the double-channel oxidation ditch, thereby changing the satiety-hunger ratio of the sludge, and has the advantage of promoting the growth of the sludge particle size in the double-channel oxidation ditch, that is, promoting sludge granulation.

[0023] 2. The present invention promotes the growth of sludge particle size in the double-ditch oxidation ditch by appropriately adjusting the alternation time of the double-ditch oxidation ditch, and the particle size in the appropriate 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 has the advantages of reducing the consumption of carbon source in the denitrification process and improving the total nitrogen removal rate.

[0024] 3. Based on the original double-channel oxidation ditch, the present invention adjusts the operating parameter of the alternation time of the double-channel oxidation ditch. The operation and control are simple, and no additional equipment and processes are required. It has the advantage of being easy to operate.

[0025] In summary, the present invention 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 sewage treatment performance, and reducing operating costs by adjusting the in-situ operating conditions in the oxidation ditch. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of the double-ditch oxidation ditch treatment process according to an embodiment of the present invention.

[0027] Figure 2 This is a graph showing the particle size distribution and average size change of a double-ditch oxidation ditch at different double-ditch alternation times in an embodiment of the present invention.

[0028] Figure 3 The MLSS and VSS / SS changes of the sludge in the double-ditch oxidation ditch at different double-ditch alternation times in the embodiment of the present invention.

[0029] Figure 4 This is a graph showing the change in denitrification performance of the double-ditch oxidation ditch at different double-ditch alternation times in an embodiment of the present invention; wherein, Figure 4 (a) TN and NH4 in the inlet and outlet water of the double-ditch oxidation ditch at different double-ditch alternation times + -N, Figure 4 (b) The NO3 in the inlet and outlet water of the double-channel oxidation ditch at different double-channel alternation times - -N and NO2 - -N.

[0030] Figure 5 This is a graph showing the change in sludge activity of a double-ditch oxidation ditch at different double-ditch alternation times in an embodiment of the present invention; wherein, Figure 5 (a) SOURe and RI index of sludge in double-channel oxidation ditch at different double-channel alternation times. Figure 5 (b) SOUR of sludge in double-channel oxidation ditch at different double-channel alternation times A , Figure 5 (c) SOUR of sludge in double-channel oxidation ditch at different double-channel alternation times H .

[0031] Figure 6 This is a diagram of the microbial community structure at the genus level in a double-ditch oxidation ditch at different double-ditch alternation times in an embodiment of the present invention.

[0032] 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 pusher; 6-1, first inclined baffle; 6-2, second inclined baffle; 7-1, first water outlet weir; 7-2, second water outlet weir. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] A method for adjusting the alternating time of a double-ditch oxidation ditch to promote granulation and enhance denitrification performance comprises the following steps:

[0035] Step 1: Periodically collect water samples from the two outlets and the water inlet of the double-ditch oxidation ditch to determine the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. Simultaneously calculate the average values ​​of the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen at the two outlets. Simultaneously collect mud-water mixtures and measure the particle size distribution of the double-ditch oxidation ditch sludge using a laser particle size distribution analyzer (LS230 / SVM, Beckman, USA).

[0036] Step 2, calculating 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 the inlet of the double-ditch oxidation ditch measured in step 1;

[0037] Step 3: Based on the particle size distribution of the double-channel oxidation ditch sludge obtained in step 1 and the simultaneous nitrification and denitrification rate obtained in step 2, the current operating status of the double-channel oxidation ditch is determined, and the alternation time is adjusted accordingly:

[0038] When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is between 0% and 10% and the simultaneous nitrification and denitrification rate is between 0% and 40%, the alternation time of the double-channel oxidation ditch should be extended;

[0039] When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is between 10% and 20% and the simultaneous nitrification and denitrification rate is between 40% and 50%, the alternation time of the double-channel oxidation ditch remains unchanged;

[0040] When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is greater than 20% and the simultaneous nitrification and denitrification rate is greater than 50%, the alternation time of the double-channel oxidation ditch should be shortened;

[0041] Step 4: After step 3, repeat step 1 after 1 to 30 days.

[0042] Step 5: After repeating step 1, the alternation time of the double-ditch oxidation ditch is judged and adjusted according to the average value of the nitrate nitrogen concentration of the two outlets measured in step 1:

[0043] If the average growth rate of the nitrate nitrogen concentration at the two outlets is greater than 30%, the alternation time of the double-ditch oxidation ditch shall be adjusted to the alternation time of the double-ditch oxidation ditch before the last adjustment;

[0044] If the average growth rate of nitrate nitrogen concentration at the two outlets is less than 30%, repeat step 3;

[0045] Step 6: After step 5 is completed, repeat steps 1, 2, 3, 4, and 5 for 1 to 30 days until there is no need to adjust the alternation time of the double-ditch oxidation ditch.

[0046] In step 3, the alternation time of the double-channel oxidation ditch is allowed to be adjusted for 0 to 9 hours each time; if the alternation time was shortened in the last adjustment of the double-channel oxidation ditch, the alternation time after this adjustment shall not exceed the last alternation time.

[0047] In step 3 or step 5, the alternation time of the double-channel oxidation ditch can be adjusted when both ditches of the double-channel oxidation ditch are in an aeration state. The alternation time of the double-channel oxidation ditch is 0 to 9 hours as a protection mechanism. When the alternation time of the double-channel oxidation ditch is too long, it will lead to problems such as excessively high nitrate nitrogen concentration in the effluent and poor microbial activity.

[0048] Example

[0049] Firstly, sludge from a sewage treatment plant in Xi'an was inoculated into a double-ditch oxidation ditch built in the laboratory.

[0050] like Figure 1 As shown, the double-ditch oxidation ditch system is made of organic glass and consists of a double-ditch oxidation ditch, a central radial flow sedimentation tank, and a reflux system. The double-ditch oxidation ditch is composed of two identical oxidation ditches, A and B, with holes in the middle partition opening to connect them. The two ditches operate in series. When the oxidation ditch is running, the water inlet of ditch A switches to the water inlet of ditch B, which is the oxidation ditch alternation. The time interval between the two alternations of the oxidation ditch is the alternation time. The specific structure of the double-ditch oxidation ditch is:

[0051] In stage I, the influent is sent into the double-channel oxidation ditch by the first peristaltic pump 2-1. At this time, the first electric valve 3-1 is opened, and the influent enters the A channel from the first electric valve 3-1 and is pushed by the flow pusher 5 to run in the double-channel 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 of the A channel is closed, and the second microporous aeration head 4-2 of the B channel is turned on. At this time, the fourth electric valve 3-4 is opened, and the effluent passes through the second inclined baffle 6-2 and out of the second outlet weir 7-2. The fourth electric valve 3-4 enters the secondary sedimentation tank; in stage II, the influent is sent in by the first peristaltic pump 2-1, passes through the first electric valve 3-1, and is pushed by the flow pusher 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 of ditch A is turned on, and the second microporous aeration head 4-2 of ditch B is turned on. At this time, the fourth electric valve 3-4 is opened, and the effluent passes through the second inclined baffle 6-2, out of the second outlet weir 7-2, and enters the second sedimentation tank through the fourth electric valve 3-4. Sedimentation tank; In stage III, the influent is sent into the double-channel oxidation ditch by the first peristaltic pump 2-1. At this time, the influent enters the B channel through the second electric valve 3-2 and is pushed by the flow pusher 5 to run in the double-channel oxidation ditch. The first aeration pump 1-1 is turned on, and the second aeration pump 1-2 is turned on. At this time, the first microporous aeration head 4-1 of the A channel is opened, and the second microporous aeration head 4-2 of the B channel is closed. The effluent passes through the first inclined baffle 6-1, exits from the first outlet weir 7-1, and enters the secondary sedimentation tank through the third electric valve 3-3; In stage IV The influent is delivered to the double-channel oxidation ditch by the first peristaltic pump 2-1. At this point, the influent enters ditch B through the second electric valve 3-2 and is propelled by the flow pusher 5 within the double-channel oxidation ditch. The first aeration pump 1-1 and the second aeration pump 1-2 are turned on. The first microporous aeration head 4-1 of ditch A opens, and the second microporous aeration head 4-2 of ditch B opens. At this point, the third electric valve 3-3 opens, and the effluent passes through the first inclined baffle 6-1, out of the first outlet weir 7-1, and through the third electric valve 3-3 into the secondary sedimentation tank. Throughout the operation of the double-channel oxidation ditch, the second peristaltic pump 2-2 remains open, transporting some of the sludge from the secondary sedimentation tank to the inlet, where it enters the double-channel oxidation ditch along with the influent, maintaining a stable sludge concentration within the double-channel oxidation ditch. The switches 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 of the double-channel oxidation ditch and the switches of the first microporous aeration head 4-1 and the second microporous aeration head 4-2 are all controlled by PLC.

[0052] The operation stages of the double-ditch oxidation ditch are described as follows:

[0053] The operation process of the double-ditch oxidation ditch is divided into four stages. In stage I, water flows into ditch A and flows out of ditch B. At this time, ditch A is not aerated, but ditch B is aerated; in stage II, water flows into ditch A and flows out of ditch B. At this time, ditch A and ditch B are aerated; in stage III, water flows into ditch B and flows out of ditch A. At this time, ditch B is not aerated, but ditch A is aerated; in stage IV, water flows into ditch B and flows out of ditch A. At this time, ditch B and ditch A are aerated.

[0054] In step 1, the water samples taken from the two water outlets (the first water outlet 7-1 and the second water outlet 7-2) at the end of stages I and II, or the water samples from the two water outlets (the first water outlet 7-1 and the second water outlet 7-2) at the end of stages III and IV, and the measured water quality parameters include ammonia nitrogen concentration, nitrate nitrogen concentration, and nitrite nitrogen concentration.

[0055] The inoculum sludge was taken from the water distribution well of the double-channel oxidation ditch of a municipal sewage 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 and inoculated into the laboratory double-channel oxidation ditch for cultivation after 24 hours of aeration. The detailed operating conditions of the double-channel oxidation ditch system are shown in Table 2.

[0056] Table 2 Double-ditch oxidation ditch system and its operating conditions

[0057]

[0058]

[0059] The double-ditch oxidation ditch system was operated continuously in a periodic operation mode. Each cycle consisted of four stages. The double-ditch oxidation ditch was operated for 122 days. During this period, the double-ditch alternation time was adjusted three times. The operating conditions are shown in Table 3.

[0060] Table 3 Double-ditch oxidation ditch operating conditions

[0061]

[0062]

[0063] The various indicators of activated sludge in the double-ditch oxidation ditch system were measured at different double-ditch alternation times to test the performance of the double-ditch oxidation ditch.

[0064] The following methods are used to measure various indicators of activated sludge:

[0065] The respiration rate was measured by respirometry through long-term artificial sampling and monitoring of the activated sludge to evaluate the changes in microbial activity in the double-channel oxidation ditch.

[0066] The polysaccharide (PS) content in EPS was determined by the sulfuric acid-anthrone method, and the protein (PN) content was determined by the modified Lowry method.

[0067] The Zeta potential of the test sludge was measured using a Zetasizer Nano ZS 90, Malvern Instruments Ltd., and the pH of the sample was controlled at 7.0-7.2.

[0068] The size of the sludge samples was measured using a laser particle size distribution analyzer (LS230 / SVM, Beckman, USA) with a detection range of 0.04–2000 μm.

[0069] Ammonia nitrogen was analyzed using the Nessler's reagent spectrophotometric method (HJ535-2009). Nitrate nitrogen was analyzed using the ultraviolet spectrophotometric method (HJ / T346-2007). Nitrite nitrogen was analyzed using the spectrophotometric method (GB7493-87).

[0070] The MLSS concentration of mixed liquor suspended solids of sludge and conventional water quality indicators are determined according to national standard methods.

[0071] The calculation formulas for total nitrogen (TN) removal rate and simultaneous nitrification and denitrification (SND) rate are:

[0072]

[0073] Among them, TN 进水 Refers to the total nitrogen concentration in the water before entering the double-channel oxidation ditch, TN 出水 Refers to the total nitrogen concentration in the supernatant of the sedimentation tank after double-ditch oxidation ditch treatment.

[0074]

[0075] Where: ΔNH4 + -N is the NH4 at the beginning of the aeration phase + -N concentration (including NH4 at the end of the non-aerated stage + -N concentration and NH4 in the influent during aeration + -N concentration) and NH4 at the end of the aeration stage + -Difference in N concentration, unit: mg / L; ΔNO3 - Indicates the NO3 produced from the beginning to the end of the aeration phase - -N concentration change, calculated as NO3 at the end of the aeration stage - -N concentration plus NO3 in the effluent of this stage - -N, minus the NO3 in the reflux - -N concentration and NO3 at the end of the non-aeration stage - Concentration, unit is mg / L; similarly ΔNO2 - -N is NO2 at the end of the aeration phase- -N concentration plus NO2 in the effluent of this stage - -N concentration minus the NO2 in the return flow - -N concentration and NO2 at the end of the non-aerated period - -The difference in N concentration, in mg / L.

[0076] Further, the experimental results were analyzed

[0077] 1) Effect of adjusting the double-ditch alternation time on oxidation ditch sludge granulation

[0078] like Figure 2 As shown, during the operation with a double-ditch alternation time of 3h to 4h, the average particle size of the sludge fluctuated in a small range of 51.51-55.31μm, and basically did not grow. At this time, the sludge in the double-ditch oxidation ditch did not form particles larger than 200μm, and the sludge was in a flocculent state. When the double-ditch alternation time was further extended to 6h, the sludge particle size grew rapidly, and the growth rate gradually accelerated. Sludge with a particle size larger than 200μm gradually appeared in the double-ditch oxidation ditch, accounting for 8.04%, and there was a trend of continued granulation. When the double-ditch alternation time was further extended to 9h, the proportion of sludge with a particle size larger than 200μm in the double-ditch oxidation ditch increased to 39.8%, and the average particle size reached 230.8μm. However, continued operation found that, as Figure 3 As shown in the figure, MLSS decreases rapidly, and sludge volume decreases. This is because sludge bulking in the double-ditch oxidation ditch leads to biomass loss, and the proportion of sludge particles larger than 200 μm decreases. This result indicates that the sludge granulation level is enhanced with an appropriate double-ditch alternation time. However, continuously extending the double-ditch alternation time will cause system instability and further collapse.

[0079] 2) Effect of adjusting the double-ditch alternation time on the denitrification performance of the oxidation ditch

[0080] As shown in Table 4, the SND rates when the double-ditch alternation time was 3h, 4h, and 6h were 26.30%, 40.02%, and 42.76%, respectively. This indicates that extending the double-ditch alternation time will increase the SND rate, with the best performance when the double-ditch alternation time was 6h. This indicates that extending the double-ditch alternation time can improve the simultaneous nitrification and denitrification effect of the double-ditch oxidation ditch. In this experiment, as the double-ditch alternation time was extended, the concentration of nitrate gradually increased during the aerobic period, but NO3 - The accumulation of -N concentration did not inhibit simultaneous nitrification and denitrification, and the inhibition of SND as reported in the literature did not occur. Because the double-ditch oxidation ditch will alternately infuse water, the NO3 accumulated during the aerobic period --N can be removed by denitrification in the anoxic section using the influent carbon source. Studies have shown that low DO conditions are more conducive to SND. The DO concentration in the aerobic section of the oxidation ditch decreases slightly as the alternating time between the two ditches increases, which may be one of the reasons for the improved SND efficiency.

[0081] Table 4 Water quality changes and SND rates at the end of each stage along the course at different double-ditch alternation times

[0082]

[0083] During the system operation, TN changes as follows: Figure 4 As shown in (a), the average TN removal rates of the double-ditch alternation time of 3h, 4h, 6h and 9h are 81.61%, 82.34%, 84.8% and 76.29% respectively. This shows that with the extension of the double-ditch alternation time, the TN removal rate shows an upward trend, and the SND data trend is consistent. However, when the double-ditch alternation time is extended to 9h, the TN removal efficiency decreases, which may be due to the decrease in sludge concentration affecting the TN removal rate. During the entire operation of the double-ditch oxidation ditch, NH4 + -N is basically completely removed, and the nitrogen compounds in the effluent are mainly NO3 - -N, such as Figure 4 As shown in (b), the average concentrations of NO2 in the ditch at 3h, 4h, 6h, and 9h were 8.52mg / L, 8.51mg / L, 7.57mg / L, and 11.04mg / L, respectively, while almost no NO2 was detected in the effluent water. - Compared with the double-ditch alternation time of 3h and 4h, the enhanced TN removal effect of 6h may be related to the high degree of sludge granulation, which also provides the conditions for simultaneous nitrification and denitrification. When the double-ditch alternation time is 9h, because the effluent NO3 - -N increased significantly, resulting in a decrease in TN removal rate.

[0084] 3) Effect of adjusting the double-ditch alternation time on the biological activity of the oxidation ditch

[0085] SOUR e It is an effective indicator to measure the activity of sludge microorganisms. e When the value of SOUR increases, it usually indicates that the sewage treatment system may be subject to external shocks, which has an early warning effect; on the contrary, when SOUR e When the value decreases, it indicates that the microbial activity of the sludge is low. Figure 5 As shown in (a), when the double-channel oxidation ditch has a double-channel alternation time of 3h, the substrate is diluted after entering the double-channel oxidation ditch because the double-channel oxidation ditch has the characteristics of both plug flow and complete mixing. The microorganisms in the sludge will perform endogenous respiration and consume their own substances to maintain survival in this environment for a long time, thus SOUR eThe value shows an upward trend. As the operation time increases, the microorganisms gradually adapt to this environment and the value stops rising. When the double-channel alternation time is extended to 6 hours, the change in operating conditions brings a shock to the system, stimulating the respiration rate of the microorganisms, making SOUR e The value rises briefly. As the double-ditch oxidation ditch runs stably, SOUR e The value shows a downward trend again. This may be related to the enhanced adsorption performance of microbial aggregates after the sludge particle size increases. Some studies have pointed out that this phenomenon occurs when the density of sludge structure increases or when granular sludge is generated. Endogenous respiration rate ratio = OUR e / OUR T , which was named RI in previous studies, and the RI in the efficient metabolic zone of 8% to 16% was defined as the sludge active healthy zone. Figure 5 As shown in Figure (a), during the operation of the double-ditch oxidation ditch, the RI value fluctuated within the normal range. However, when the double-ditch alternation time was extended to 9 hours, the sludge RI value remained below 8%. This indicates that if the double-ditch alternation time is continuously extended, the sludge will enter an unhealthy state, which is detrimental to the activated sludge system.

[0086] Changes in the external environment will have a certain impact on the population structure of sludge microorganisms. Autotrophic bacteria participate in biological reactions with a smaller respiration ratio and show a higher sensitivity to environmental changes; in contrast, heterotrophic bacteria have a larger respiration ratio and have stronger adaptability. Figure 5 As shown in (b), when the double-channel alternation time is 3h and 4h, the SOUR in the system A The value fluctuated around 3mgO2 / gSS / h; when the double-channel alternation time was adjusted from 4h to 6h, SOUR A The value increased from 2.741mgO2 / gSS / h to 7.845mgO2 / gSS / h. When the double-groove alternation time was extended to 9h, the autotrophic bacteria were impacted, and SOUR A The value shows a downward trend. As the double groove alternation time increases, SOUR A The values ​​showed an overall upward trend, which means that extending the double-ditch alternation time enhanced the biological activity of sludge autotrophic bacteria. Figure 5 As shown in (c), during the operation with a double-channel alternation time of 3 h, the heterotrophic bacteria gradually adapted to the environment, SOUR H The value showed an upward trend. As the double-channel alternation time prolonged, the starvation time increased, which made the heterotrophic bacteria obtain less substrate. H Fluctuates between 17.47-35.79mgO2 / gSS / h. When the double groove alternation time is 9h, SOUR H The sudden increase in the value may be related to the sharp increase in F / M after the sludge concentration decreased.

[0087] 4) Effect of adjusting the double groove alternation time on microbial populations

[0088] The structure at the microbial genus level is as follows Figure 6 As shown, the main bacterial genera in the three sludge samples included Thiothrix, norank_f_Saprospiraceae, Pseudomonas, and Chryseobacterium. The relative abundance of Thiothrix in the original sludge, sludge samples with 3h and 6h double-channel alternation times was 0.01%, 18.38%, and 54.07%, respectively. Thiothrix is ​​a filamentous bacterial genus, and its increase in relative abundance is associated with excessive growth of filamentous bacteria and deteriorating sedimentation performance. The abundance of this genus increased significantly at 3h and 6h double-channel alternation times, consistent with the sedimentation data. In addition, the high abundance of this genus in the plug-flow double-channel oxidation ditch can provide a framework for the formation of AGS and play a positive role in its formation. The norank_f_Saprospiraceae genus often attaches to bacterial surfaces, 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 double-ditch alternation time was adjusted to 6 hours, the new genera Pseudomonas and Chryseobacterium were added, with relative abundances of 5.93% and 6.69%, respectively. These two genera can stimulate the production of EPS, thereby promoting the self-aggregation of microorganisms and facilitating the formation and stabilization of sludge particles. In addition, many species in Pseudomonas have been identified as having the ability to simultaneously nitrify and denitrify. It can be seen that adjusting the double-ditch alternation time promoted the growth of synchronous nitrifying and nitrifying bacteria in the oxidation ditch, which is also a reason for improving the simultaneous nitrification and denitrification capacity of the oxidation ditch.

[0089] Example Analysis

[0090] In this example, after adjusting the double-ditch alternation time to 3h, 4h, 6h, and 9h in a double-ditch oxidation ditch, the particle size, denitrification performance, sludge activity, bacterial species, etc. at different double-ditch alternation times were analyzed. From the experimental results, it can be seen that with the extension of the double-ditch alternation time, the respiratory activity of the autotrophic bacteria of the sludge microorganisms is significantly enhanced. AIt shows an upward trend. When the double-ditch alternation time is 6h, the sludge particle size grows rapidly, and the growth rate gradually accelerates. When the double-ditch alternation time is 9h, the proportion of particles larger than 200μm increases to 39.8%, and the average particle size reaches 230.8μm. In addition, when the double-ditch alternation time increases from 3 hours to 6 hours, SND increases from 26.30% to 42.76%. The system's simultaneous nitrification and denitrification capabilities and TN removal efficiency increase with the extension of the double-ditch alternation time. It can be seen that the increase in the double-ditch alternation time from 3h to 6h promotes the growth of particle size and the system's TN removal efficiency. The double-ditch alternation time of 6h provides relatively optimal conditions, while continuing to extend the double-ditch alternation time to 9h, the microbial respiratory activity decreases, the sedimentation performance deteriorates, and the system tends to collapse.

[0091] As can be seen from the embodiments, compared with the prior art, the present invention has the following advantages:

[0092] 1. Promote sludge granulation: In the existing sewage treatment process, oxidation ditch and A 2 It is difficult to achieve sludge granulation in a continuous flow double-channel oxidation ditch such as O. However, the activated sludge of the present invention can promote the particle size growth of sludge in the double-channel oxidation ditch by adjusting the double-channel alternation time and changing the anaerobic and aerobic time.

[0093] 2. Improve denitrification effect: The present invention promotes the growth of particle size by adjusting the double-ditch alternation time, and the particle size in the appropriate 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 in the denitrification process and improve the total nitrogen removal rate.

[0094] 3. Simple and easy operation: Based on the original oxidation ditch, the present invention combines the denitrification performance and particle size of the oxidation ditch itself, and adopts the method of adjusting the alternating time of the double ditches to improve the treatment effect of the oxidation ditch. The operation and control are simple and no additional equipment and processes are required.

[0095] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features therein according to the disclosed technical content without creative labor, and these substitutions and modifications are all within the protection scope of the present invention.

Claims

1. A method for adjusting the alternating time of a double-ditch oxidation ditch to promote granulation and enhance denitrification performance, characterized in that: The following steps are involved: Step 1: Periodically collect water samples from the two outlets and the water inlet of the double-ditch oxidation ditch to determine the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. Simultaneously, calculate the average values ​​of the concentrations of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen at the two outlets. Simultaneously, collect mud-water mixtures to determine the particle size distribution of sludge in the double-ditch oxidation ditch. Step 2, calculating 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 the inlet of the double-ditch oxidation ditch measured in step 1; Step 3: Based on the particle size distribution of the double-channel oxidation ditch sludge obtained in step 1 and the simultaneous nitrification and denitrification rate obtained in step 2, the current operating status of the double-channel oxidation ditch is determined, and the alternation time is adjusted accordingly: When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is between 0% and 10% and the simultaneous nitrification and denitrification rate is between 0% and 40%, the alternation time of the double-channel oxidation ditch should be extended; When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is between 10% and 20% and the simultaneous nitrification and denitrification rate is between 40% and 50%, the alternation time of the double-channel oxidation ditch remains unchanged; When the proportion of sludge particles with a diameter of more than 200 μm in the double-channel oxidation ditch is greater than 20% and the simultaneous nitrification and denitrification rate is greater than 50%, the alternation time of the double-channel oxidation ditch should be shortened; Step 4: After step 3, repeat step 1 after 1 to 30 days. Step 5: After repeating step 1, the alternation time of the double-ditch oxidation ditch is judged and adjusted according to the average value of the nitrate nitrogen concentration of the two outlets measured in step 1: If the average growth rate of the nitrate nitrogen concentration at the two outlets is greater than 30%, the alternation time of the double-ditch oxidation ditch shall be adjusted to the alternation time of the double-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; Step 6: After step 5 is completed, repeat steps 1, 2, 3, 4, and 5 for 1 to 30 days until there is no need to adjust the alternation time of the double-ditch oxidation ditch.

2. The method of adjusting the alternating time of a double-ditch oxidation ditch to promote granulation and enhance denitrification performance according to claim 1, characterized in that: In step 3, the alternation time of the double-channel oxidation ditch is allowed to be adjusted for 0 to 9 hours each time; if the alternation time was shortened in the last adjustment of the double-channel oxidation ditch, the alternation time after this adjustment shall not exceed the last alternation time.

3. The method of adjusting the alternating time of a double-ditch oxidation ditch to promote granulation and enhance denitrification performance according to claim 1, characterized in that: In step 3 or step 5, the alternation time of the double-channel oxidation ditch is adjusted when both ditches of the double-channel oxidation ditch are in an aeration state, and the alternation time of the double-channel oxidation ditch is 0 to 9 hours.

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