Integrated process for efficient denitrification and dephosphorization of sewage

Abstract

The application discloses an efficient denitrification and dephosphorization integrated process for sewage, and relates to the technical field of sewage treatment. Multiple internal reflux liquid taking positions are arranged in multiple gradient aerobic zones to obtain two reflux fluxes. A target liquid taking position and a target internal reflux ratio are determined according to the denitrification demand of nitrate nitrogen and the upper limit of reflux oxygen load. Then, the sewage at the target position is refluxed to a front-stage anoxic zone. Finally, the unrefluxed water is made to enter a rear-stage deep anoxic zone to perform internal source denitrification. Since the target liquid taking position is simultaneously constrained by the supply of nitrate nitrogen and the introduction of dissolved oxygen, the process can meet the front-stage denitrification load while reducing the reflux oxygen input, and the residual nitrate nitrogen can be continuously treated by the rear-stage anoxic zone, so that the distribution of limited carbon source between the front-stage and rear-stage anoxic stages under the condition of low C / N is improved, and the operation stability of the denitrification and dephosphorization process is maintained.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to an integrated process for efficient nitrogen and phosphorus removal from wastewater. Background Technology

[0002] In urban wastewater with low C / N ratios, available organic carbon is relatively insufficient. Nitrification, denitrification, and biological phosphorus removal have different requirements for carbon sources and dissolved oxygen conditions. Pre-anoxic, anaerobic, aerobic, and post-anoxic processes can respectively complete denitrification, phosphorus release, nitrification phosphorus uptake, and deep nitrogen removal. Among them, internal recirculation is used to send the nitrate-containing mixed liquor formed in the aerobic stage into the pre-anoxic zone. The nitrate nitrogen load and dissolved oxygen load in the recirculation liquid will jointly affect the pre-denitrification process.

[0003] Under multi-stage gradient aerobic conditions, nitrate nitrogen concentration and dissolved oxygen levels vary along the water flow direction. If the internal recirculation sampling location and recirculation flow rate do not take into account both the nitrate nitrogen treatment needs and the tolerable oxygen load of the upstream anoxic zone, insufficient nitrate nitrogen supply may occur, or excessive dissolved oxygen may be introduced with the recirculated liquid, consuming the limited carbon source and thus increasing the load on subsequent deep denitrification. Therefore, it is necessary to coordinate the nitrate nitrogen and dissolved oxygen recirculation status at different sampling locations to improve the utilization of the limited carbon source in low C / N wastewater. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated process for efficient nitrogen and phosphorus removal from wastewater.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an integrated process for efficient nitrogen and phosphorus removal from wastewater, the process comprising: In the multi-level gradient aerobic zone, internal reflux liquid collection points are set along the water flow direction, and the nitrate nitrogen reflux flow rate and dissolved oxygen reflux flow rate corresponding to each internal reflux liquid collection point are obtained respectively. Determine at least one target liquid collection location and target internal reflux ratio from each internal reflux liquid collection location, such that the nitrate nitrogen reflux flow rate corresponding to the target liquid collection location meets the nitrate nitrogen denitrification demand, and the dissolved oxygen reflux flow rate corresponding to the target liquid collection location is not higher than the upper limit of the reflux oxygen load. Wastewater from the target intake location is returned to the pre-anoxic zone according to the target internal recirculation ratio, and the wastewater that is not returned is sent to the post-deep anoxic zone for endogenous denitrification treatment.

[0006] In a preferred embodiment, when any individual sampling location among the internal reflux sampling locations cannot simultaneously meet the nitrate nitrogen reflux flow rate to reach the nitrate nitrogen denitrification requirement and the dissolved oxygen reflux flow rate not exceed the upper limit of the reflux oxygen load within the candidate internal reflux ratio range, at least two sampling branches corresponding to the internal reflux sampling locations are simultaneously opened for combined reflux, and the flow rate ratio of each sampling branch is adjusted so that the sum of the nitrate nitrogen reflux flow rates corresponding to each sampling branch meets the nitrate nitrogen denitrification requirement, and the sum of the dissolved oxygen reflux flow rates corresponding to each sampling branch does not exceed the upper limit of the reflux oxygen load.

[0007] In a preferred embodiment, determining at least one target sampling location and a target internal reflux ratio from each internal reflux sampling location includes: For each internal reflux sampling location, the candidate internal reflux ratio is adjusted to obtain the target internal reflux ratio. The candidate sampling locations that simultaneously satisfy at least two constraints are marked as the target sampling locations.

[0008] In a preferred embodiment, when there are at least two candidate sampling locations, the dissolved oxygen reflux rate of the candidate sampling locations is compared, and the candidate sampling location with the smallest dissolved oxygen reflux rate is selected as the target sampling location.

[0009] In a preferred embodiment, the target internal reflux ratio is increased when the nitrate nitrogen reflux flow rate is lower than the nitrate nitrogen denitrification demand, and the target internal reflux ratio is stopped when the dissolved oxygen reflux flow rate reaches the upper limit of the reflux oxygen load. The target internal reflux ratio is 50% to 200%.

[0010] In a preferred embodiment, the nitrate nitrogen reflux flow rate is determined based on the nitrate nitrogen concentration and internal reflux flow rate at the corresponding internal reflux sampling location, and the dissolved oxygen reflux flow rate is determined based on the dissolved oxygen concentration and internal reflux flow rate at the corresponding internal reflux sampling location.

[0011] In a preferred embodiment, the multi-level gradient aerobic zone includes a front high-oxygen zone, a middle medium-oxygen zone, and a rear low-oxygen zone arranged along the water flow direction, with each of the front high-oxygen zone, middle medium-oxygen zone, and rear low-oxygen zone receiving independent aeration.

[0012] In a preferred embodiment, the DO in the high-oxygen zone at the front end is 1.5–2.0 mg / L, the DO in the medium-oxygen zone at the middle end is 0.8–1.2 mg / L, and the DO in the low-oxygen zone at the rear end is 0.3–0.6 mg / L.

[0013] In a preferred embodiment, the nitrate nitrogen denitrification demand is the mass of nitrate nitrogen allocated to the pre-anoxic zone to achieve the target total nitrogen removal requirement.

[0014] In a preferred embodiment, the upper limit of the reflux oxygen load is the maximum dissolved oxygen mass that can be carried into the pre-anoxic zone by the internal reflux water.

[0015] In a preferred embodiment, the DO in the post-deep anoxic zone is no higher than 0.2 mg / L, and residual nitrate nitrogen is removed by utilizing the endogenous respiration of microorganisms to consume intracellular carbon sources.

[0016] The technical effects and advantages provided by the present invention in the above technical solution are as follows: Compared to a single recirculation point treatment method, this application first sets up multiple internal recirculation sampling points in a multi-level gradient aerobic zone and obtains two recirculation rates. Then, based on the nitrate nitrogen denitrification demand and the upper limit of the recirculation oxygen load, the target sampling point and target internal recirculation ratio are determined. Next, the wastewater from the target point is recirculated to the pre-anoxic zone. Finally, the non-recirculated water enters the post-deep anoxic zone for endogenous denitrification. Since the target sampling point is constrained by both nitrate nitrogen supply and dissolved oxygen input, the recirculation oxygen input can be reduced while meeting the pre-denitrification load. The remaining nitrate nitrogen is then treated by the post-anoxic zone, thereby improving the distribution of limited carbon sources between the pre- and post-anoxic stages under low C / N conditions, which is beneficial for maintaining the operational stability of the nitrogen and phosphorus removal process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a process flow diagram under the dual-throughput constraint of the present invention.

[0019] Figure 2 This is a schematic diagram of the integrated process flow and reflux relationship of the present invention.

[0020] Figure 3 This is a schematic diagram of the multi-level gradient aerobic zone aeration structure of the present invention. Detailed Implementation

[0021] To make the technical solution, operating conditions, and relationships between parameters of the present invention clearer, further explanation is provided below in conjunction with the process flow and embodiments. The following embodiments are used to illustrate feasible implementation methods. The volume, equipment specifications, and control cycle of each functional area can be configured accordingly based on the treatment scale, influent water quality, and discharge requirements.

[0022] In this specification, C / N represents the relative ratio of biodegradable organic matter to nitrogenous pollutants in the influent; DO represents dissolved oxygen concentration; ORP represents oxidation-reduction potential; nitrate nitrogen includes at least one of nitrate nitrogen and nitrite nitrogen, and NO can be used when calculating flux. x-N concentration is indicated. The internal recirculation ratio is the ratio of the internal recirculation flow rate to the influent flow rate, and the external recirculation ratio is the ratio of the sludge recirculation flow rate to the influent flow rate.

[0023] In this embodiment, unless otherwise specified, C / N is determined according to the mass concentration ratio of influent COD to influent TN, and the same standard is used in the calculation, commissioning, and operation evaluation of the same project; nitrate nitrogen concentration C NOx,i It is the sum of nitrate nitrogen concentration and nitrite nitrogen concentration.

[0024] Nitrate nitrogen reflux flow rate is the mass of nitrate nitrogen delivered to the pre-anoxic zone by the internal reflux water at a given intake location per unit time; dissolved oxygen reflux flow rate is the mass of dissolved oxygen delivered to the pre-anoxic zone by the internal reflux water at the same intake location per unit time. Nitrate nitrogen denitrification demand is the mass of nitrate nitrogen allocated to the pre-anoxic zone to achieve the target total nitrogen removal requirement; the upper limit of reflux oxygen load is the maximum mass of dissolved oxygen allowed to be carried into the pre-anoxic zone by the internal reflux water while maintaining the anoxic state of the pre-anoxic zone.

[0025] Under continuous flow conditions, the demand for nitrate nitrogen denitrification and the upper limit of the return oxygen load are both expressed as mass load per unit time, in g / h, using the same time reference as the nitrate nitrogen return flow and dissolved oxygen return flow. When the intelligent control unit performs calculations according to the control cycle, the corresponding mass within the cycle is obtained by multiplying the mass load per unit time by the control cycle duration, avoiding direct comparison between mass and mass flux. Example 1

[0026] like Figure 2 As shown, this embodiment provides an integrated process for efficient nitrogen and phosphorus removal from wastewater. The treatment system is sequentially configured along the water flow direction, including a pre-anoxic zone, an anaerobic zone, a multi-stage gradient aerobic zone, a post-deep anoxic zone, and a sludge-water sedimentation zone. It also includes an internal recirculation system, an external recirculation system, an online water quality monitoring unit, and an intelligent control unit. After passing through each functional zone, the wastewater undergoes solid-liquid separation in the sludge-water sedimentation zone. A portion of the settled sludge is returned to the anaerobic zone via the external recirculation system, while the remaining sludge is discharged according to sludge concentration and sludge age requirements.

[0027] The pre-anoxic zone receives raw wastewater and internally returned nitrified liquid. The readily biodegradable organic matter in the raw wastewater acts as electron donors for denitrification, while the nitrate and nitrite nitrogen carried by the internally returned liquid is reduced under anoxic conditions. The pre-anoxic zone is equipped with a mixing device to ensure uniform mixing of the influent and the returned liquid from different intake points, and to prevent sludge deposition. The effluent from the pre-anoxic zone enters the anaerobic zone.

[0028] The anaerobic zone is kept oxygen-free and the introduction of nitrate nitrogen is minimized. Polyphosphate-accumulating bacteria release intracellular polyphosphates in this zone and absorb small organic molecules from the water to form intracellular storage substances, providing conditions for excessive phosphorus uptake in the subsequent aerobic stage. Externally returned sludge is introduced into the influent side of the anaerobic zone, allowing the settled sludge to re-enter the biological reaction process. The external return ratio can be adjusted within the range of 30% to 100%, taking into account the sludge level in the settling zone, the system sludge concentration, and the nitrate nitrogen load in the anaerobic zone.

[0029] like Figure 3 As shown, the multi-level gradient aerobic zone is divided into a front-end high-oxygen zone, a middle-end medium-oxygen zone, and a rear-end low-oxygen zone along the water flow direction. Each of the three zones is equipped with aeration branch pipes, airflow regulating valves, and microporous aeration components, enabling independent air distribution and oxygen control. In the front-end high-oxygen zone, the dissolved oxygen (DO) is controlled at 1.5–2.0 mg / L to complete the degradation of residual organic matter and ammonia nitrification; in the middle-end medium-oxygen zone, the DO is controlled at 0.8–1.2 mg / L to maintain nitrification and promote phosphorus uptake by polyphosphate-accumulating bacteria; and in the rear-end low-oxygen zone, the DO is controlled at 0.3–0.6 mg / L to complete the conversion of remaining ammonia nitrogen and biological phosphorus uptake, while simultaneously reducing the oxygen load entering the subsequent deep anoxic zone.

[0030] Multiple internal reflux sampling points are set along the water flow direction in the multi-level gradient aerobic zone. The first sampling point can be set on the outlet side of the high-oxygen zone at the front, the second sampling point on the outlet side of the medium-oxygen zone in the middle, and the third sampling point on the outlet side of the low-oxygen zone at the rear. Each sampling point is connected to the internal reflux main pipe through an independent sampling branch pipe, and a regulating valve and flow detection device are installed on the sampling branch pipe. After the flow from all branches merges, it is pumped to the pre-anoxic zone through the internal reflux pump. The first sampling point can be used as a backup sampling point, and during normal operation, the second and third sampling points are selected preferentially.

[0031] Each sampling location is equipped with DO and nitrate nitrogen detection points, or water samples are sent to a shared detection device via automatic sampling pipelines. The online water quality monitoring unit also collects influent COD, ammonia nitrogen, total nitrogen, and total phosphorus, as well as DO or ORP at the pre-anoxic zone, anaerobic zone, multi-stage gradient aerobic zone, post-deep anoxic zone, and effluent. All detection values ​​are transmitted to the intelligent control unit after time synchronization; the flow rate, concentration, and sampling location identifier together form the sampling status data for the current control cycle.

[0032] The flow rate, nitrate nitrogen concentration, and DO concentration at each sampling location are taken from valid values ​​within the same sampling period. When using shared detection equipment, the data timestamp is corrected based on the sampling pipeline transport time, and the concentration value is recorded after pipeline replacement. Negative values, out-of-range values, or continuously unchanged outliers are not included in the flux calculation.

[0033] For the i-th internal reflux sampling point, the nitrate nitrogen reflux flow rate can be determined based on the internal reflux flow rate and nitrate nitrogen concentration at that point, while the dissolved oxygen reflux flow rate can be determined based on the same internal reflux flow rate and dissolved oxygen concentration. The internal reflux flow rate is expressed as m. 3 When / h is used to express the concentration and mg / L is used, the product of the two values ​​corresponds to g / h. When the sampling branch is not open, both reflux rates at that location are recorded as zero.

[0034] Within each control cycle, the intelligent control unit adjusts the candidate internal reflux ratio for each liquid sampling location and calculates the corresponding nitrate nitrogen reflux rate and dissolved oxygen reflux rate. The candidate internal reflux ratio is within the range of 50% to 200% and can be adjusted continuously or in preset steps to form multiple candidate values. The liquid sampling location that meets the requirements of nitrate nitrogen reflux rate for nitrate denitrification and the dissolved oxygen reflux rate is not higher than the upper limit of the reflux oxygen load is determined as the candidate liquid sampling location.

[0035] When only one candidate sampling location satisfies both constraints, that location is designated as the target sampling location, and the corresponding candidate internal reflux ratio is designated as the target internal reflux ratio. When at least two candidate sampling locations satisfy both constraints, the dissolved oxygen reflux flow rates of each candidate sampling location are compared, and the location with the smaller dissolved oxygen reflux flow rate is selected as the target sampling location. When the dissolved oxygen reflux flow rates are the same or the difference is within the detection error range, the location with the smaller internal reflux ratio can be selected.

[0036] When none of the individual sampling locations can simultaneously meet the above two constraints within the candidate internal reflux ratio range of 50% to 200%, the intelligent control unit does not directly determine that there is no feasible sampling scheme in the current control cycle. Instead, it switches to a multi-point combined sampling mode, simultaneously opening the sampling branches corresponding to at least two available sampling locations, and using the internal reflux flow ratio of each sampling branch as the combined adjustment variable. For any branch combination, the branch reflux flow rate is calculated using the actual or candidate flow rate of each branch and the corresponding nitrate nitrogen concentration and DO concentration within the same control cycle. Then, the nitrate nitrogen reflux flow rate and dissolved oxygen reflux flow rate of each branch are summed. When the total nitrate nitrogen reflux flow rate after combination reaches the nitrate nitrogen denitrification demand and the total dissolved oxygen reflux flow rate is not higher than the upper limit of the reflux oxygen load, the branch combination is determined as a feasible combination, and the at least two sampling locations constituting the combination are jointly determined as the target sampling locations.

[0037] For feasible multi-point combined intake schemes, the intelligent control unit continues to adjust the flow ratio of each intake branch to limit dissolved oxygen entrainment while meeting the nitrate nitrogen supply requirements. While ensuring the total nitrate nitrogen return flow meets the nitrate nitrogen denitrification demand, the flow ratio of intake locations with higher dissolved oxygen (DO) can be reduced, while the flow ratio of intake locations with lower DO but still available nitrate nitrogen load can be increased. The ratio of the sum of the flow rates of each branch to the influent flow rate serves as the target internal recirculation ratio under the combined state. When multiple feasible combinations exist, the combination with the smaller total dissolved oxygen return flow rate is prioritized; when the total dissolved oxygen return flow rates are similar, the combination with the smaller total internal recirculation ratio is then selected, thus ensuring that the combined intake remains consistent with the original single-point screening logic under dual-flux constraints.

[0038] After determining the target sampling location and target internal recirculation ratio, in single-point sampling mode, non-target sampling branches are closed or kept in standby mode, while the target sampling branch is opened. In combined sampling mode, sampling branches not entering the target combination are closed or kept in standby mode, while at least two sampling branches constituting the target sampling location are opened and recirculated together according to the determined flow ratio of each branch. Subsequently, the wastewater from the target sampling location is recirculated to the pre-anoxic zone according to the target internal recirculation ratio. The unextracted wastewater continues to flow along the multi-level gradient aerobic zone and enters the post-deep anoxic zone. The DO in the post-deep anoxic zone is controlled to be no higher than 0.2 mg / L, and microorganisms utilize intracellular carbon sources and available substances produced during endogenous respiration to perform deep denitrification of the remaining nitrate nitrogen.

[0039] The effluent from the post-deep anoxic zone enters the sludge-water sedimentation zone. The sludge-water sedimentation zone can employ an inclined tube sedimentation structure to shorten the particle settling path and complete the separation of sludge and water in the mixed liquor. The supernatant is used as treated effluent, while the bottom sludge is returned to the anaerobic zone at an external return ratio of 30%–100%. Any sludge exceeding the system's sludge concentration control requirements is discharged as excess sludge.

[0040] This embodiment utilizes the differences in nitrate nitrogen concentration and dissolved oxygen (DO) formed along the multi-level gradient aerobic zone for selecting the internal reflux liquid intake. The target location is not determined solely by nitrate nitrogen concentration or DO, but is constrained by both the nitrate nitrogen supply and oxygen entrainment. Therefore, it can provide denitrification load to the preceding anoxic zone while limiting the dissolved oxygen entering with the internal reflux, and the remaining nitrate nitrogen not allocated to the preceding anoxic zone is treated by the subsequent deep anoxic zone. Example 2

[0041] Based on the process structure of Example 1, this embodiment further explains the determination process of the required amount of nitrate nitrogen for denitrification, the upper limit of the reflux oxygen load, and the liquid sampling location.

[0042] The nitrate nitrogen denitrification demand is updated according to the control cycle. The intelligent control unit reads the influent flow rate, influent total nitrogen, effluent total nitrogen control target, and the actual effluent total nitrogen of the previous control cycle, and determines the current total nitrogen removal load. Based on the available primary carbon source status in the pre-anoxic zone, a portion of the total nitrogen removal load is allocated to the pre-anoxic zone, and the remainder is handled by the post-deep anoxic zone. The allocation ratio can be adjusted based on influent COD, C / N ratio, pre-anoxic zone ORP, and historical denitrification rate.

[0043] In one calculation method, the influent flow rate is Q. in The total nitrogen concentration in the influent is C TN,in The target total nitrogen concentration in the effluent is C. TN,target If the load allocated to the pre-anoxic zone is α, then the nitrate nitrogen denitrification demand M DN It is determined by the influent flow rate, the total nitrogen concentration difference between the influent and the target effluent, and the load ratio. in Using m 3 / h, when the concentration is in mg / L, M DN The unit is g / h. α takes a value greater than zero and not greater than one, and its value varies with the state of the influent carbon source, rather than fixing the entire total nitrogen removal load to the pre-anoxic zone.

[0044] M DN =Q in ×(C TN,in -C TN,target )×α; In the formula, M DN This represents the demand for nitrate nitrogen denitrification, expressed in g / h; Q in This refers to the influent flow rate, expressed in meters (m³). 3 / h;C TN,in The total nitrogen concentration in the influent is expressed in mg / L; C TN,target The target total nitrogen concentration in the effluent is expressed in mg / L; α represents the proportion of total nitrogen removal load allocated to the pre-anoxic zone.

[0045] The above formula yields the initial load distribution for the pre-anoxic zone. When C TN,in Not higher than C TN,target At that time, the initial load allocation was treated as zero; the final M was adopted. DN It is still not higher than the nitrate nitrogen mass load that the current multi-stage gradient aerobic zone can provide and the denitrification capacity obtained by the pre-anoxic zone after commissioning, and can be checked by the following formula: M DN =min[max(0,M DN,0 ),M NOx,avail M DN,cap ]; In the formula, M DN,0The initial distribution load is calculated based on the difference between the influent TN and the target TN; M NOx,avail M represents the upper limit of nitrate nitrogen mass load that each available sampling location can provide within the current control cycle. DN,cap This refers to the denitrification capacity of the pre-anoxic zone under the current water temperature, sludge concentration, and available carbon source conditions. If the initial load exceeds any upper limit, the excess portion will be transferred to the post-deep anoxic zone.

[0046] When assessing the availability of carbon sources in the pre-anoxic zone, influent COD, the COD difference between the influent and effluent of the pre-anoxic zone, and the ORP trend can be used. If the influent COD increases while the pre-anoxic zone ORP remains within the operating range corresponding to anoxic denitrification, α can be appropriately increased. Conversely, if the influent COD decreases, the ORP continues to rise, or the nitrate nitrogen in the pre-anoxic zone effluent increases, α should be decreased to retain more excess nitrate nitrogen for subsequent deep anoxic zone treatment. This approach ensures that demand is matched with currently available carbon sources.

[0047] The upper limit of the reflux oxygen load is determined based on the oxygen consumption capacity of the pre-anoxic zone. The oxygen consumption rate of the pre-anoxic mixture can be measured periodically during system commissioning or operation. During measurement, a representative sample of the mixture is taken, and the decrease in dissolved oxygen (DO) over time is recorded while external oxygen supply is stopped and stirring is maintained. This yields the oxygen consumption rate per unit volume of the mixture. The product of the oxygen consumption rate and the effective volume of the pre-anoxic zone represents the mass of oxygen that this zone can consume per unit time.

[0048] Since the initial DO of the pre-anoxic mixture is usually low, the measurement of r O First, a representative sample is slowly oxygenated to a measurable initial DO level, such as 1.0–2.0 mg / L. Then, oxygenation is stopped, and the stirring intensity and temperature are maintained at a similar level as in the tank. The rate of change of DO within the linear decreasing range is recorded. At least two parallel measurements are performed, and instrument drift is subtracted. The resulting oxygen consumption rate per unit volume is used to calculate the upper limit of the reflux oxygen load.

[0049] When determining the upper limit of the return oxygen load, the dissolved oxygen mass carried by the raw wastewater is deducted from the above-mentioned consuming oxygen mass, and a safety margin is reserved to maintain the anoxic state. When the ORP in the pre-anoxic zone rises or the DO approaches the set upper limit, the intelligent control unit reduces the upper limit of the return oxygen load; when the ORP and DO in the pre-anoxic zone remain stable for several consecutive control cycles, and the effluent nitrate nitrogen does not increase, the upper limit of the return oxygen load can be gradually restored under the condition that it does not exceed the range confirmed during commissioning.

[0050] M O,lim =max[0,V A ×r O -Q in ×C DO,in -M s ]; In the formula, M O,lim This represents the upper limit of the reflux oxygen load, expressed in g / h; V A The effective volume of the pre-anoxic zone is expressed in m³. 3 ;r O The oxygen consumption rate per unit volume of the mixture, expressed in g / (m³). 3 ·h); Q in This refers to the influent flow rate, expressed in meters (m³). 3 / h;C DO,in M represents the dissolved oxygen concentration in the raw wastewater, in mg / L. s The oxygen load safety margin for maintaining a pre-hypoxic state is expressed in g / h.

[0051] All terms in the formula are converted to g / h and use the same control time period. M s A positive value is used to reserve the oxygen consumption margin for maintaining the pre-anoxic state; its value is determined by the response of DO, ORP, and effluent nitrate nitrogen in the pre-anoxic zone during commissioning. When V A ×r O -Q in ×C DO,in Not greater than M s At that time, M O,lim Set the value to zero. At this point, the internal reflux ratio will not be increased further, and the available sampling position with the lowest DO will be selected first.

[0052] For the i-th liquid collection position, let its candidate internal reflux flow rate be Q. r,i The concentration of nitrate nitrogen is C NOx,i DO concentration is C DO,i The candidate internal reflux ratio is R i Then the reflux flux of nitrate nitrogen J N,i By Q r,i With C NOx,i Determine the dissolved oxygen reflux flow rate J. O,i By Q r,i With C DO,i Confirmed. The candidate internal reflux flow rate is determined by the candidate internal reflux ratio and the influent flow rate. Therefore, when the candidate internal reflux ratio at the same sampling location increases, both reflux flow rates increase accordingly.

[0053] J N,i =Q r,i ×C NOx,i ; J O,i =Q r,i ×C DO,i ; Q r,i =R i ×Q in ; When two or more liquid intake points share a common reflux, the total flux is calculated using the flow rate and concentration of each branch under the same control cycle. The total internal reflux ratio is determined by the sum of the flow rates of each branch and the influent flow rate. J N,Σ =Σ i Q r,i ×C NOx,i ; J O,Σ =Σ i Q r,i ×C DO,i ; R Σ =(Σ i Q r,i / Q in )×100%; In the formula, J N,Σ and J O,Σ These represent the total nitrate nitrogen reflux rate and the total dissolved oxygen reflux rate, respectively; R Σ This is the total internal reflux ratio. Only in J... N,Σ Reaching M DN And J O,Σ Not higher than M O,lim When that happens, the corresponding branch combination is determined as a feasible solution.

[0054] like Figure 1 As shown, during the specific screening process, a candidate internal reflux ratio of 50% can be started, and increased incrementally in increments of 5% to 25%. For each sampling location and each candidate internal reflux ratio, first determine whether the nitrate nitrogen reflux flow rate meets the nitrate nitrogen denitrification requirement; if not, continue to increase the candidate internal reflux ratio at that location. After meeting the requirement, then determine whether the dissolved oxygen reflux flow rate exceeds the upper limit of the reflux oxygen load; if not, that location and the candidate internal reflux ratio constitute a feasible combination; if they exceed, stop further increasing the candidate internal reflux ratio at that location.

[0055] For example, the nitrate nitrogen concentration at the effluent side of the mid-stage medium-oxygen zone is relatively high, but the dissolved oxygen (DO) may also be higher than that of the downstream low-oxygen zone; the DO at the effluent side of the downstream low-oxygen zone is relatively low, but the nitrate nitrogen concentration differs from that at the mid-stage under certain operating conditions. By simultaneously calculating both mass fluxes, it is possible to distinguish between different operating states such as "lower concentration but larger return flow" and "higher concentration but smaller return flow," avoiding selection bias caused by comparing only a single point concentration.

[0056] When both the intermediate and rear liquid sampling positions form feasible combinations, the combination with the smaller dissolved oxygen reflux flow rate should be prioritized. If the difference in dissolved oxygen reflux flow rate between the two combinations is less than the uncertainty range formed by the combined accuracy of DO detection and flow rate detection, then the target internal reflux ratio should be compared, and the combination with the smaller internal reflux ratio should be prioritized. If a distinction still cannot be made, the current liquid sampling position can be maintained to reduce frequent switching of valves and pumps.

[0057] To avoid repeated switching of sampling locations due to fluctuations in detection values ​​near constraint boundaries, the intelligent control unit can be set with a holding time. A new candidate location must meet both constraints for two to five consecutive control cycles before replacing the current target location. If the dissolved oxygen reflux rate at the current target location significantly exceeds the upper limit of the reflux oxygen load, or the nitrate nitrogen reflux rate is continuously lower than the required rate, the location can be directly re-screened without a holding time.

[0058] The internal reflux ratio is adjusted in the order of first meeting the nitrate nitrogen demand, and then verifying the oxygen load. When the nitrate nitrogen reflux rate is lower than the demand, the internal reflux ratio is increased; when the dissolved oxygen reflux rate reaches its upper limit, the increase is stopped. If the nitrate nitrogen denitrification demand cannot be met even at a 200% internal reflux ratio, the load distribution ratio between the pre-anoxic and post-anoxic zones is redefined, reducing the demand allocated to the pre-anoxic zone, and allowing the nitrate nitrogen not handled by the pre-anoxic zone to be treated in the post-deep anoxic zone.

[0059] If no feasible solutions exist for single-point intake and combined intake within the internal recirculation ratio range of 50%–200%, the intelligent control unit will no longer increase the recirculation flow. Instead, it will sequentially reduce the load proportion allocated to the pre-anoxic zone, check the nitrification status of the multi-stage gradient aerobic zone, and assess the remaining treatment capacity of the post-deep anoxic zone. Evaluation will be conducted again after at least one hydraulic response time following the redistribution to prevent distorted judgments caused by multiple adjustments within the same control cycle.

[0060] This embodiment clarifies the physical meaning and acquisition methods of demand, oxygen load limit, and two types of reflux rates, providing an executable data basis for determining the liquid intake location and internal reflux ratio. Using mass flux as a constraint simultaneously reflects changes in concentration and flow rate, making it suitable for continuous treatment processes where influent flow rate, water quality concentration, and aerobic zone operating status change over time. Example 3

[0061] This embodiment illustrates the operation mode under conditions of combined sampling at at least two sampling locations and water quality fluctuations. The system is equipped with a mid-section sampling branch pipe and a rear-section sampling branch pipe. Each branch pipe has a regulating valve, a flow meter, a check valve assembly, and a sampling interface. After converging into the internal return main pipe, the water is transported to the pre-anoxic zone by the same internal return pump. The intelligent control unit can provide target flow rates for each of the two branch pipes, ensuring that the two locations together constitute the target sampling location.

[0062] When any single liquid intake point cannot simultaneously meet both constraints within an internal reflux ratio range of 50%–200%, the intelligent control unit generates a combined intake scheme. The combined scheme uses the mid-end and rear-end liquid intake flow rates as variables, calculating the sum of the nitrate nitrogen reflux flow rates and the sum of the dissolved oxygen reflux flow rates at both locations. If the total nitrate nitrogen reflux flow rate after the combination reaches the nitrate nitrogen denitrification requirement and the total dissolved oxygen reflux flow rate does not exceed the upper limit of the reflux oxygen load, the combination is considered a feasible scheme.

[0063] If multiple combination schemes are feasible, first compare the total dissolved oxygen reflux flow rate and select the scheme with the smaller total dissolved oxygen reflux flow rate; if the total dissolved oxygen reflux flow rates are close, then compare the total internal reflux ratio and select the scheme with the smaller total internal reflux ratio. The middle intake branch mainly replenishes the nitrate nitrogen mass, while the rear intake branch is mainly used to reduce the average DO of the combined reflux liquid. The flow rate ratio of the two is determined by the current concentration data.

[0064] Combined intake does not mean keeping both branches at the same opening degree indefinitely. The intelligent control unit can first open the rear intake branch and gradually increase its flow rate; when the rear intake still cannot meet the nitrate nitrogen requirement at the maximum allowable reflux ratio, the middle intake branch is then opened to make up the nitrate nitrogen difference. After the flow rate of the middle branch is increased, the total dissolved oxygen reflux flow rate is recalculated, and the increase stops once it approaches the upper limit of the reflux oxygen load. The remaining total nitrogen removal is completed by adjusting the load distribution between the anoxic zones before and after the intake.

[0065] When the influent organic matter concentration decreases briefly, the available carbon source in the pre-anoxic zone decreases, and the upper limit of the recirculation oxygen load is correspondingly lowered. In this case, the intake ratio of the downstream low-oxygen zone is prioritized, while the intake ratio of the intermediate medium-oxygen zone is reduced. If the recirculation oxygen load limit still cannot be met, the total internal recirculation ratio is reduced, and a larger portion of the unrecirculated mixed liquor is sent to the downstream deep anoxic zone. The downstream deep anoxic zone continues to rely on intracellular carbon sources and endogenous respiration to remove the remaining nitrate nitrogen.

[0066] When the influent ammonia nitrogen concentration increases while the COD change is relatively small, the nitrification load in the upstream hyperacid zone and the midstream mesoacid zone increases. The intelligent control unit first increases the aeration rate in the upstream hyperacid zone based on the ammonia nitrogen detection value to maintain DO at 1.5–2.0 mg / L, and then recalculates the flux based on the nitrate nitrogen concentration at the midstream and downstream intake points. If a high nitrate nitrogen concentration has already been achieved at the midstream position and the oxygen load is acceptable, a combination of intake at the midstream or downstream positions can be selected.

[0067] When the total phosphorus in the influent increases, the intelligent control unit maintains the phosphorus release conditions in the anaerobic zone and adjusts the aeration rate in the intermediate-aerobic zone and the hypoxic zone at the end according to the TP changes in the aerobic zone, so that polyphosphate-accumulating bacteria can complete phosphorus uptake during the aerobic stage. The selection of internal reflux liquid intake is still constrained by nitrate nitrogen flux and dissolved oxygen flux, and the dual constraints are not canceled due to changes in total phosphorus alone, thereby avoiding the introduction of more dissolved oxygen into the pre-anoxic zone after increasing aeration to enhance phosphorus uptake.

[0068] The online water quality monitoring unit can collect data in cycles of 1 to 10 minutes. For DO, ORP, and nitrate nitrogen values, which are susceptible to the effects of air bubbles, sludge adhesion, or instantaneous hydraulic disturbances, the median or moving average of multiple consecutive measurements can be used as the effective value for the current control cycle. The detection equipment is calibrated for zero point and range according to the system commissioning plan, and the correspondence between the flow meter and the regulating valve is confirmed through clean water tests or actual wastewater operation tests.

[0069] When the nitrate nitrogen sensor or DO sensor at a certain sampling location exceeds its range, remains unchanged for an extended period, or exhibits a significantly inconsistent change with adjacent locations, that location is marked as abnormal. Abnormal locations are not included in the target screening for this control cycle, and the system can use other normal locations to complete the sampling. If only the sampling location in the downstream low-oxygen zone remains normal, the system temporarily switches to downstream sampling and uses the most recent effective internal reflux ratio or a preset safe internal reflux ratio.

[0070] When critical detection data from all sampling locations are abnormal, the intelligent control unit stops the automatic sampling function, maintains fixed sampling in the hypoxic zone at the back end, and limits the internal reflux ratio to a safe range confirmed through debugging, while issuing a calibration prompt. At this time, the reflux pump can still be protectively adjusted based on the DO and ORP of the pre-hypoxic zone; after the sensor recovers and is confirmed through several consecutive effective cycles, dual-throughput sampling is resumed.

[0071] When switching the liquid intake location, first reduce the current branch flow rate, then gradually open the new branch to keep the change in the total internal return flow rate within the allowable range of the pump and reaction zone. When combining two branch intakes, first stabilize the total return flow rate, then distribute the branch flow rate to avoid sludge agitation or short-circuiting in the pre-anoxic zone due to instantaneous hydraulic impact. After adjusting the valve opening, wait for the pipeline delivery lag time before using the new detection values ​​to evaluate the switching effect.

[0072] This embodiment expands the feasibility of single-point screening by utilizing multi-location combined flow intake, and maintains operational continuity through hold time, anomaly rejection, and safe liquid intake methods. The combined flow intake is still based on the total nitrate nitrogen reflux rate and the total dissolved oxygen reflux rate, thus not changing the technical relationship of the dual constraints. Example 4

[0073] This embodiment illustrates the complete process of the integrated process from startup to stable operation. The system treats low C / N urban wastewater, with the influent C / N not exceeding 3. In the basic operating mode, no external carbon sources such as sodium acetate or glucose are added. Instead, it utilizes the influent's native carbon source, substances stored within polyphosphate-accumulating bacteria cells, and usable substances produced by microbial endogenous respiration to complete both the initial and final stages of denitrification.

[0074] Before startup, check the sealing, connectivity, and agitation status of the pre-anaerobic zone, anaerobic zone, multi-stage gradient aerobic zone, post-deep anoxic zone, and sludge sedimentation zone. Also check the operating status of the internal and external return pumps, aeration blowers, aeration branch pipes, liquid intake branch pipes, and regulating valves. Calibrate the COD, ammonia nitrogen, total nitrogen, total phosphorus, DO, ORP, nitrate nitrogen, and flow rate monitoring devices, and set the initial hydraulic retention time, aeration rate, internal return ratio, and external return ratio according to the design treatment capacity.

[0075] After the system receives water, the wastewater first enters the pre-anoxic zone. The internal return main is connected on the inlet side or at a location with strong agitation to ensure rapid mixing of the nitrate-containing return liquid with the raw wastewater. Denitrifying microorganisms preferentially utilize readily degradable organic matter in the raw wastewater to reduce nitrate nitrogen. The intelligent control unit records the nitrate nitrogen, COD, DO, and ORP of the influent and effluent from the pre-anoxic zone, which is used to update the denitrification demand and the upper limit of the return oxygen load.

[0076] The effluent from the pre-anoxic zone enters the anaerobic zone. The anaerobic zone is continuously agitated without aeration, and externally returned sludge is recycled from the sludge-water sedimentation zone to the inlet of the anaerobic zone. Polyphosphate-accumulating organisms (PAOs) release phosphorus and absorb small-molecule organic matter in the anaerobic environment. By controlling the external return ratio and the degree of pre-anoxic treatment, nitrate nitrogen and dissolved oxygen entering the anaerobic zone are reduced, providing conditions for PAOs to release phosphorus and store carbon.

[0077] The effluent from the anaerobic zone sequentially enters the upstream high-oxygen zone, the midstream medium-oxygen zone, and the downstream low-oxygen zone. In the upstream high-oxygen zone, the aeration fan frequency and branch pipe valves are adjusted according to the ammonia nitrogen load to maintain dissolved oxygen (DO) at 1.5–2.0 mg / L; in the midstream medium-oxygen zone, DO is maintained at 0.8–1.2 mg / L; and in the downstream low-oxygen zone, DO is maintained at 0.3–0.6 mg / L. These three zones respectively handle organic matter degradation, nitrification, and phosphorus uptake, forming an oxygen supply gradient along the water flow direction that adapts to changes in pollutants.

[0078] In the initial stage of operation, the effluent side of the low-oxygen zone at the rear end can be used as the internal reflux sampling point, and the internal reflux ratio can be set in the range of 50% to 100%. After the detection data stabilizes, multi-location scanning is started: the nitrate nitrogen concentration, DO concentration and available flow rate at the front, middle and rear sampling points are acquired sequentially to form two reflux flow rates, and the target internal reflux ratio is determined in the range of 50% to 200%.

[0079] After the internal return water enters the pre-anoxic zone, the mixed liquor not extracted by the return flow enters the post-deep anoxic zone. The post-deep anoxic zone does not have conventional aeration; if necessary, sludge suspension is maintained solely through agitation, with dissolved oxygen (DO) controlled below 0.2 mg / L. This zone primarily utilizes intracellular carbon sources stored in microorganisms and endogenous respiration for deep denitrification, further reducing the residual nitrate nitrogen not handled by the pre-anoxic zone.

[0080] The endogenous electron donors utilized in the post-deep anoxic zone include intracellular storage of polyphosphate-accumulating bacteria and other microorganisms, as well as biodegradable organic matter released during the endogenous metabolism and decay of sludge. Denitrification is not completed under conditions without electron donors. Before operation, the endogenous denitrification rate per unit volume of mixed liquor was determined through batch tests, and the treatment capacity of this zone was verified using the following formula: V PD ×r DN,end ≥M NOx,rem ; In the formula, V PD This refers to the effective volume of the post-deep anoxic zone, in cubic meters (m³). 3 ;r DN,end The intrinsic denitrification rate per unit volume under current water temperature and sludge conditions is expressed in g / (m³). 3 ·h); M NOx,rem The remaining nitrate nitrogen mass load before entering the post-deep anoxic zone is expressed in g / h. When the check relationship is not met, corrections are made by extending the hydraulic retention time, reducing the load distribution ratio of the pre-anoxic zone, or adjusting the sludge concentration.

[0081] The effluent from the post-deep anoxic zone enters the sludge sedimentation zone. Inclined tube assemblies provide a short settling distance for the sludge flocs, and the supernatant is discharged from the effluent weir. A portion of the bottom sludge is pumped to the anaerobic zone via an external recirculation pump, with the external recirculation ratio adjusted within the range of 30%–100%; the remaining portion is discharged as excess sludge to maintain the set sludge concentration and sludge age. When the sludge level in the sedimentation zone rises, the external recirculation or sludge discharge rate can be appropriately increased, but excessive nitrate nitrogen and dissolved oxygen should be avoided from being introduced into the anaerobic zone.

[0082] The online water quality monitoring unit transmits data from each functional zone and the effluent outlet to the intelligent control unit. The intelligent control unit assesses changes in influent COD, ammonia nitrogen, TN, and TP, and accordingly adjusts the aeration fan frequency, aeration rate in each zone, target liquid sampling location, internal recirculation ratio, external recirculation ratio, and hydraulic retention time. The adjustment sequence can be set to first stabilize the nitrification state in the aerobic zone, then perform dual-flux liquid sampling and screening, and finally adjust the anoxic load distribution before and after based on TN changes in the subsequent deep anoxic zone and the effluent outlet.

[0083] For operating conditions with increased influent flow, the intelligent control unit first synchronously calculates the candidate internal recirculation flow based on the influent flow and recalculates the two recirculation flows; at the same time, it checks the hydraulic residence time based on the effective volume of each functional zone. For operating conditions with decreased influent flow, the flow rates of the internal and external recirculation pumps are reduced accordingly to avoid short-circuiting caused by excessively high recirculation ratios or to prevent excessive dissolved oxygen from being carried into the pre-anoxic zone.

[0084] For sustained low-load conditions, the aeration airflow in the upstream hyperoxic zone can be reduced, while maintaining dissolved oxygen (DO) within the specified range, and prioritizing air intake from the downstream hypoxic zone. For short-term high-load conditions, the aeration airflow and internal recirculation ratio in the upstream hyperoxic zone can be increased, but the increase in the internal recirculation ratio is limited to ensuring that the dissolved oxygen recirculation flow does not exceed the upper limit. Thus, aeration regulation and internal recirculation regulation are constrained by the aerobic nitrification state and the upstream anoxic oxygen load, respectively.

[0085] This embodiment sequentially connects pre-generated primary carbon source denitrification, anaerobic phosphorus release, gradient aerobic nitrification phosphorus uptake, and post-generated endogenous denitrification, while embedding multi-site internal reflux control into the overall process. Each functional zone maintains its original biological reaction activity, while coordinating the nitrate nitrogen load in the anoxic zones before and after by using target liquid intake locations and target internal reflux ratios. Example 5

[0086] This embodiment provides a set of exemplary operating parameters to illustrate the site selection and reflux ratio determination process. These parameters are used to illustrate the calculation relationships and operational sequence, and do not represent a sole limitation on the treatment scale, influent concentration, or effluent parameters. The average influent flow rate of the treatment system is set to 100 m³ / h. 3 / h, the influent COD is 90mg / L, ammonia nitrogen is 28mg / L, TN is 32mg / L, TP is 3.5mg / L, and C / N is not higher than 3.

[0087] The system controls the dissolved oxygen (DO) in the high-oxygen zone at approximately 1.8 mg / L, in the medium-oxygen zone at approximately 1.0 mg / L, and in the low-oxygen zone at approximately 0.5 mg / L; the DO in the deep anoxic zone is controlled below 0.2 mg / L. The external reflux ratio is initially set at 60%, and adjusted within the range of 30% to 100% based on the sludge level in the sedimentation zone and the operating status of the anaerobic zone.

[0088] Assuming the current total nitrogen (TN) control target is 10 mg / L, based on the influent carbon source status and the historical denitrification capacity of the pre-anoxic zone, 40% of the current TN removal load is allocated to the pre-anoxic zone. The current nitrate nitrogen denitrification demand is determined to be 880 g / h based on the influent flow rate, the concentration difference between the influent TN and the target TN, and the allocation ratio. In practical applications, adjustments can be made based on the influent ammonia nitrogen nitrification degree, the effluent TN from the previous cycle, and the nitrate nitrogen removal status of the subsequent deep anoxic zone.

[0089] In this example, 880 g / h is the initial load allocation obtained based on the total nitrogen difference and the load ratio. In actual control, it is also checked according to the available nitrate nitrogen mass load and the denitrification capacity of the pre-anoxic zone. If any upper limit is lower than 880 g / h, the smaller value is used as the current nitrate nitrogen denitrification demand.

[0090] After measuring the oxygen consumption rate and deducting the oxygen load brought in by the original wastewater, the upper limit of the return oxygen load for the current control cycle is set at 100 g / h. This value is adjusted downwards when the ORP or DO increases in the pre-anaerobic zone, and gradually restored when the ORP, DO, and effluent nitrate nitrogen remain continuously stable.

[0091] The concentrations of nitrate nitrogen and dissolved oxygen (DO) measured at the mid-stage sampling point were 12 mg / L and 1.0 mg / L, respectively; the concentrations at the rear-stage sampling point were 9 mg / L and 0.4 mg / L, respectively. If an 80% internal reflux ratio is used at the mid-stage sampling point, the internal reflux flow rate is 80 m³ / L. 3 The nitrate nitrogen reflux rate is 960 g / h, the dissolved oxygen reflux rate is 80 g / h, and it simultaneously meets the nitrate nitrogen denitrification demand of 880 g / h and the upper limit of reflux oxygen load of 100 g / h.

[0092] If the back-end location uses a 100% internal recirculation ratio, the internal recirculation flow rate is 100m³ / h. 3 The nitrate nitrogen reflux rate is 900 g / h, and the dissolved oxygen reflux rate is 40 g / h, which simultaneously satisfies both constraints. Since the dissolved oxygen reflux rate at the rear end is less than that at the middle end, the intelligent control unit determines the rear end as the target liquid extraction position and sets 100% as the target internal reflux ratio.

[0093] Once the target location is determined, the downstream intake branch is gradually opened to the corresponding flow rate, while the midstream intake branch is closed or kept on standby. The internal reflux liquid is sent to the pre-anoxic zone, and the non-reflux mixed liquid enters the post-deep anoxic zone. The post-deep anoxic zone continues to remove residual nitrate nitrogen using intracellular carbon sources, and the effluent is discharged after separation in the sludge-water sedimentation zone.

[0094] In the next control cycle, if the nitrate nitrogen concentration at the downstream end drops to 7 mg / L, the nitrate nitrogen reflux flow rate at a 100% internal reflux ratio will be 700 g / h, lower than the current demand. The intelligent control unit increases the candidate internal reflux ratio at the downstream end. When the internal reflux ratio increases to 130%, the nitrate nitrogen reflux flow rate is 910 g / h, and the dissolved oxygen reflux flow rate is 52 g / h, still not exceeding the upper limit of the reflux oxygen load. Therefore, the target internal reflux ratio can be adjusted to 130%.

[0095] If the dissolved oxygen (DO) at the downstream position simultaneously rises to 0.9 mg / L, the dissolved oxygen reflux rate at a 130% internal reflux ratio is 117 g / h, exceeding the upper limit of 100 g / h, rendering this candidate combination infeasible. In this case, the intelligent control unit will re-evaluate the mid-position and mid-to-reverse combined intake schemes, or reduce the load allocation ratio of the upstream anoxic zone, allowing some nitrate nitrogen to be transferred to the downstream deep anoxic zone.

[0096] For example, using a rear position of 80m 3 / h and mid-range position 20m 3When using a combined feed rate of 820 g / h, if the nitrate nitrogen concentration at the downstream end is 7 mg / L and the dissolved oxygen (DO) is 0.5 mg / L, and the nitrate nitrogen concentration at the midstream end is 13 mg / L and the DO is 1.2 mg / L, then the total nitrate nitrogen return flow rate is 820 g / h, and the total dissolved oxygen return flow rate is 64 g / h. This combination meets the oxygen loading limit, but the nitrate nitrogen flux is still below 880 g / h, therefore it is not considered the current target scheme.

[0097] Increase the mid-range liquid collection flow rate to 30m 3 / h, maintain back-end liquid extraction flow rate at 80m 3 At a flow rate of 950 g / h, the total nitrate nitrogen reflux rate is 950 g / h, and the total dissolved oxygen reflux rate is 76 g / h, both constraints are met. This combination can be used as the target flow intake scheme, with a total internal reflux ratio of 110%. The regulating valve operates in a manner that first stabilizes the total flow rate and then distributes the branch flow rates.

[0098] In the above example, if the ORP in the pre-anoxic zone continuously increases and DO accumulates, the upper limit of the return oxygen load should be reduced, and the mid-end liquid intake flow rate should be decreased first. If the nitrate nitrogen in the effluent from the pre-anoxic zone increases while the DO remains low, the downstream liquid intake flow rate should be increased first, or the mid-end liquid intake flow rate should be increased appropriately. After each adjustment, the pipeline delivery time and a reaction evaluation cycle should be considered before deciding whether to continue adjusting.

[0099] When the system is running stably, the effluent control targets can be set as follows: COD no higher than 30 mg / L, ammonia nitrogen no higher than 1.5 mg / L, TN no higher than 10 mg / L, and TP no higher than 0.3 mg / L. These targets are used by the intelligent control unit to calculate the processing load and judge the operating trend. The actual control values ​​can be determined in combination with applicable discharge requirements, temperature, and influent water quality.

[0100] The calculation results of this embodiment show that, when the nitrate nitrogen return flow rate can meet the requirements of pre-denitrification, different liquid intake locations may correspond to different dissolved oxygen return flow rates. By comparing mass fluxes and selecting feasible schemes with lower oxygen loads, the spatial state differences in the gradient aerobic zone can be used to complete the selection of the return source, rather than simply adjusting the return pump flow rate at a fixed effluent end.

[0101] To further illustrate the operational differences between the aforementioned dual-flux constrained intake method and the conventional fixed aerobic terminal single-point internal recirculation method, this embodiment sets up a control operation based on the aforementioned exemplary operating parameters. The control group and the present invention group used the same influent source, effective volume, hydraulic retention time, sludge age, external recirculation ratio, and DO control range in the gradient aerobic zone, and neither added an external carbon source. The control group consistently drew liquid from the effluent side of the low-oxygen zone at the rear, maintaining an internal recirculation ratio of approximately 110%. The present invention group used single-point or multi-point combined intake based on nitrate nitrogen recirculation flow and dissolved oxygen recirculation flow, dynamically adjusting the total internal recirculation ratio within the range of 80% to 130%. During the statistical period, the average total internal recirculation ratio was approximately 108%, thus keeping the total recirculation levels of the two groups similar.

[0102] After both sets of devices stabilized, they were continuously observed for 10 operating days, and the average value was calculated based on the test results of the mixed water samples taken daily for 24 hours. To avoid judgment bias caused by differences in influent, the daily average difference in total nitrogen and total phosphorus concentrations between the two sets of devices was controlled within the allowable fluctuation range for testing. Simultaneously, the dissolved oxygen (DO) in the pre-anoxic zone, the dissolved oxygen mass load carried by the internal recirculation, and the aeration power consumption per unit volume of treated water were recorded. The data in the table below are a set of exemplary control operation results matching the parameters of this embodiment, used to illustrate the control verification method and reasonable variation range. Actual engineering results are subject to on-site measurements.

[0103] Table 1. Exemplary comparison results between conventional fixed-end current collection and the dual-flux-constrained current collection of the present invention. Evaluation Project Conventional control group This invention group Average influent COD (mg / L) 90.2 90.0 Average influent total nitrogen (TN) (mg / L) 31.9 31.8 Average influent TP (mg / L) 3.50 3.49 Average effluent COD (mg / L) 28.7 27.9 Average effluent TN (mg / L) 11.4 10.0 Total nitrogen removal rate (%) 64.3 68.6 Average effluent TP (mg / L) 0.36 0.31 Total phosphorus removal rate (%) 89.7 91.1 Average reflux oxygen load (g / h) 88 64 Average DO (mg / L) in the pre-hypoxic zone 0.25 0.17 <![CDATA[Aeration power consumption per unit of treated water (kWh / m 3 )]]> 0.236 0.221 As shown in Table 1, under similar influent water quality and total internal recirculation levels, the average effluent TN of the group of this invention decreased from 11.4 mg / L to 10.0 mg / L, and the total nitrogen removal rate increased from 64.3% to 68.6%, an increase of approximately 4.3 percentage points; the average effluent TP decreased from 0.36 mg / L to 0.31 mg / L, and the total phosphorus removal rate increased from 89.7% to 91.1%, an increase of approximately 1.4 percentage points. Simultaneously, the average recirculation oxygen load decreased from 88 g / h to 64 g / h, a decrease of approximately 27.3%, and the average DO in the pre-anoxic zone decreased from 0.25 mg / L to 0.17 mg / L, with a decrease in aeration power consumption per unit treated water volume of approximately 6.4%. These results indicate that the main improvement of this invention is primarily reflected in reducing internal recirculation oxygenation and maintaining pre-anoxic conditions, thereby achieving a relatively mild improvement in total nitrogen and total phosphorus removal efficiency, without exaggerating short-term operational differences as a fixed increase ratio under all operating conditions.

[0104] In new construction projects, functional areas can be arranged in series of independent tanks, or they can be divided within the same structure by partition walls. In the renovation of existing wastewater treatment plants, existing anoxic, anaerobic, and aerobic tanks can be used for functional zoning, and independent aeration branch pipes, liquid intake branch pipes, and online monitoring points can be added to the multi-level gradient aerobic zone. As long as the water flow sequence, return flow connection relationship, and dual-flux point selection logic remain consistent, the planar shape and specific dimensions of the tanks are not restricted.

[0105] The intelligent control unit can employ a programmable logic controller (PLC), an industrial computer, or control equipment with data acquisition and processing capabilities. Its inputs are connected to COD, ammonia nitrogen, TN, TP, DO, ORP, nitrate nitrogen, and flow rate detection devices. Its outputs are connected to aeration blowers, zone aeration valves, internal reflux pumps, regulating valves for each liquid intake branch pipe, external reflux pumps, and actuators for adjusting the hydraulic retention time. The control equipment saves the detection values, target liquid intake location, target internal reflux ratio, and abnormal states for each control cycle, facilitating operational verification.

[0106] Operational evaluation may include total nitrogen removal rate, total phosphorus removal rate, effluent concentration fluctuation, return oxygen load, and aeration energy consumption per unit volume of treated water. With on-site comparative data available, a fixed aerobic end-of-pipe intake method can be used as a control, comparing dissolved oxygen return flow rate, DO in the pre-anoxic zone, effluent TN, effluent TP, and aeration power consumption under the same influent C / N ratio and similar total internal return levels. Taking the aforementioned exemplary control results as an example, the total nitrogen removal rate increased by approximately 4.3 percentage points, the total phosphorus removal rate increased by approximately 1.4 percentage points, while the return oxygen load decreased by approximately 27.3%. Since influent water quality, temperature, sludge condition, and structural conditions vary between different projects, project validation does not presuppose a fixed improvement ratio; the actual effect is subject to on-site measurement.

[0107] Multi-stage gradient aeration can distribute oxygen supply according to the pollutant load along the process. The front-end zone bears a higher load of organic matter degradation and nitrification, while the middle and rear zones gradually reduce the oxygen supply, reducing ineffective aeration while maintaining nitrification and phosphorus uptake. Through online monitoring and zoned adjustment, long-term insufficient or excessive oxygen supply in a single area can be avoided, and a recognizable combination of nitrate nitrogen and dissolved oxygen (DO) can be established for different liquid intake locations.

[0108] Under basic operating mode, this process does not include an external carbon source step. Limited carbon sources are used sequentially for pre-denitrification, anaerobic carbon storage, and post-internal denitrification. In case of abnormal situations where the influent water quality exceeds the design range, operation should be restored first by adjusting the hydraulic retention time, sludge return, gradient aeration, and the distribution of anoxic loads before and after the process. Whether to take other emergency measures can be determined separately by the specific project's safety operation plan.

[0109] The structures and operating methods described in the above embodiments can be combined without technical conflicts. The number of liquid sampling locations can be determined based on the number of zones in the multi-level gradient aerobic zone and the tank structure; the detection method can use independent sensors at each location or a shared detection device after automatic sampling; the target liquid sampling location can be one or two or more sampling locations combined in proportion.

[0110] In engineering applications, all parameters should be adjusted within the allowable range of the equipment and the stable range of biological treatment. For different water temperatures, sludge concentrations, and influent pollutant compositions, the denitrification capacity of the pre-anoxic zone, oxygen consumption rate, and typical concentration distribution at each liquid intake location can be obtained through startup and commissioning. Based on this, the control cycle, candidate internal reflux ratio step size, holding time, and safe operating range can be set.

[0111] The above description represents an exemplary embodiment of the present invention. Any equivalent adjustments made to the number of liquid sampling branches, the arrangement of the detection device, the method for generating the candidate internal reflux ratio, or the control cycle under the technical concept of the present invention can be used to achieve liquid sampling and reflux control under the joint constraints of nitrate nitrogen reflux flow rate and dissolved oxygen reflux flow rate.

Claims

1. A high-efficiency integrated process for nitrogen and phosphorus removal from wastewater, characterized in that, The process includes: In the multi-level gradient aerobic zone, internal reflux liquid collection positions are set along the water flow direction, and the corresponding nitrate nitrogen reflux flow rate and dissolved oxygen reflux flow rate of each internal reflux liquid collection position are obtained respectively. Determine at least one target liquid collection location and target internal reflux ratio from the internal reflux liquid collection locations, such that the nitrate nitrogen reflux flow rate corresponding to the target liquid collection location meets the nitrate nitrogen denitrification demand, and the dissolved oxygen reflux flow rate corresponding to the target liquid collection location is not higher than the upper limit of the reflux oxygen load. Wastewater from the target sampling location is returned to the pre-anoxic zone according to the target internal return ratio, and the wastewater that is not returned is sent to the post-deep anoxic zone for endogenous denitrification treatment.

2. The process according to claim 1, characterized in that, When any single sampling point among the internal reflux sampling points cannot simultaneously meet the nitrate nitrogen reflux flow rate to reach the nitrate nitrogen denitrification requirement and the dissolved oxygen reflux flow rate not exceed the upper limit of the reflux oxygen load within the candidate internal reflux ratio range, at least two sampling branches corresponding to the internal reflux sampling points shall be opened simultaneously for combined reflux, and the flow rate ratio of each sampling branch shall be adjusted so that the sum of the nitrate nitrogen reflux flow rates corresponding to each sampling branch meets the nitrate nitrogen denitrification requirement, and the sum of the dissolved oxygen reflux flow rates corresponding to each sampling branch does not exceed the upper limit of the reflux oxygen load.

3. The process according to claim 1, characterized in that, Determining at least one target sampling location and target internal reflux ratio from the various internal reflux sampling locations includes: For each internal reflux sampling location, the candidate internal reflux ratio is adjusted to obtain the target internal reflux ratio, and the candidate sampling location that simultaneously satisfies at least two constraints is marked as the target sampling location.

4. The process according to claim 3, characterized in that, When there are at least two candidate sampling locations, the dissolved oxygen reflux flow rate of the candidate sampling locations is compared, and the candidate sampling location with the smallest dissolved oxygen reflux flow rate is selected as the target sampling location.

5. The process according to claim 4, characterized in that, When the nitrate nitrogen reflux flow rate is lower than the nitrate nitrogen denitrification demand, the target internal reflux ratio is increased. When the dissolved oxygen reflux flow rate reaches the upper limit of the reflux oxygen load, the increase of the target internal reflux ratio is stopped. The target internal reflux ratio is 50% to 200%.

6. The process according to claim 5, characterized in that, The nitrate nitrogen reflux flow rate is determined based on the nitrate nitrogen concentration and internal reflux flow rate at the corresponding internal reflux sampling location, and the dissolved oxygen reflux flow rate is determined based on the dissolved oxygen concentration and internal reflux flow rate at the corresponding internal reflux sampling location.

7. The process according to any one of claims 1-6, characterized in that, The multi-level gradient aerobic zone includes a front high-oxygen zone, a middle medium-oxygen zone, and a rear low-oxygen zone set along the water flow direction. Each of the front high-oxygen zone, the middle medium-oxygen zone, and the rear low-oxygen zone is independently aerated.

8. The process according to claim 7, characterized in that, The DO concentration in the high-oxygen zone at the front end is 1.5–2.0 mg / L, the DO concentration in the medium-oxygen zone at the middle end is 0.8–1.2 mg / L, and the DO concentration in the low-oxygen zone at the rear end is 0.3–0.6 mg / L.

9. The process according to claim 8, characterized in that, The required amount of nitrate nitrogen for denitrification is the mass of nitrate nitrogen allocated to the pre-anoxic zone to achieve the target total nitrogen removal requirement.

10. The process according to claim 9, characterized in that, The upper limit of the reflux oxygen load is the maximum dissolved oxygen mass that can be carried into the pre-anoxic zone by the internal reflux water.

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