Construction method of bank runoff graded purification based on water pollution control and treatment

Abstract

The application relates to a bank runoff grading purification construction method based on water pollution control and treatment, which comprises the following steps: obtaining bank runoff, sequentially introducing the bank runoff into a granular state removal stage and a pollutant directional purification stage to form to-be-judgment effluent; detecting the concentration of target pollutants in the to-be-judgment effluent and the effluent of the last purification stage, obtaining the concentration difference of the corresponding target pollutants by subtracting the concentration of the effluent of the last purification stage from the concentration of the to-be-judgment effluent; when the difference exceeds a detection error threshold, it is judged that secondary release of pollutants occurs, and the to-be-judgment effluent is backflowed to the corresponding pollutant directional purification stage; when the concentration difference of each target pollutant does not exceed the detection error threshold and reaches the effluent limit value, the to-be-judgment effluent is discharged or reused. The application can identify the pollutant reverse rising phenomenon in the purification process, avoid the secondary release of pollutants from being discharged with tail water, and improve the operation reliability of the bank runoff grading purification system.

Description

Technical Field

[0001] This invention relates to the field of water pollution control and treatment technology, specifically to a method for constructing graded purification of embankment runoff based on water pollution control and treatment. Background Technology

[0002] Existing technologies for controlling pollution in embankments, revetments, and urban runoff into rivers typically employ a combination of measures such as interception, infiltration, sedimentation, adsorption, biodegradation, and plant uptake to reduce the impact of suspended solids, organic matter, nitrogen, phosphorus, and some heavy metal pollutants in rainwater runoff or bank slope runoff on receiving water bodies. For example, Chinese patent CN113463569A discloses a water-purifying revetment for the renovation of rigid embankments. It uses structures such as gabion baskets, permeable U-shaped channels, gravel, mixed planting soil, and aquatic plants to ecologically transform rigid embankments, and utilizes the filler material and plant system to reduce runoff pollution and purify river water quality. While this type of technology can improve the ecological function of rigid embankments to some extent and enhance the bank's ability to intercept and purify pollutants, its purification process mainly relies on fixed structures and predetermined filler layers. It typically focuses on the passive removal of pollutants as they flow through the water, lacking dynamic identification of the release, transformation, and migration states of different pollutants during multi-stage purification processes.

[0003] Existing technologies also propose treatment systems for rainwater runoff diversion, purification, and reuse. For example, Chinese Patent Publication No. CN218374256U discloses a treatment system for rainwater diversion, purification, and reuse on residential roads. This system achieves rainwater diversion, purification, and reuse through a combination of rainwater inlets, storage tanks, multi-stage purification landscape pools, and water-using equipment. This type of solution is beneficial for allocating runoff destinations according to rainfall conditions and realizing rainwater resource utilization through multi-stage purification facilities. However, in the scenario of embankment runoff management, runoff is greatly affected by rainfall intensity, bank erosion, upstream water flow, sediment disturbance, and changes in hydraulic residence time. The form and concentration of pollutants fluctuate significantly. Simply relying on pre-set flow paths or fixed purification units makes it difficult to promptly determine whether re-dissolution of trapped pollutants, resuspension of deposited pollutants, or secondary release after adsorption saturation occurs at a certain purification stage.

[0004] Therefore, while existing embankment runoff purification technologies can achieve certain runoff reduction and pollutant removal through structures such as multi-layer fillers, ecological revetments, rain gardens, or landscape purification ponds, they generally suffer from problems such as a lack of concentration difference determination between purification stages, insufficient targeted purification of target pollutants, and inaccurate return of secondary releases to the corresponding purification stages. Particularly for embankment runoff containing nitrogen, phosphorus, organic, and heavy metal pollutants, judging compliance solely based on the final effluent concentration easily overlooks situations where pollutant concentrations rise during intermediate purification stages, leading to the re-entry of intercepted or fixed pollutants into the water body, affecting effluent stability and treatment reliability. Therefore, a tiered embankment runoff purification method is needed that integrates particulate removal, targeted pollutant purification, staged effluent detection, secondary release determination, and corresponding return treatment to improve the targeting and stability of embankment runoff pollution control and water pollution treatment. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing a graded purification system for embankment runoff based on water pollution control and treatment, thereby addressing some of the drawbacks and shortcomings pointed out in the background art.

[0006] The present invention adopts the following technical solution to solve the above-mentioned technical problems: Obtain the embankment runoff and sequentially introduce the embankment runoff into a particulate matter removal stage and a pollutant targeted purification stage. The pollutant targeted purification stage includes at least one of a nitrogen removal stage, a phosphorus fixation stage, an organic pollutant purification stage, and a heavy metal stabilization stage to form effluent to be determined. The concentration of the target pollutant in the effluent to be determined and the effluent from the previous purification stage is detected. The target pollutant includes at least one of nitrogen pollutants, phosphorus pollutants, organic pollutants and heavy metal pollutants. The concentration difference of the corresponding target pollutant is obtained by subtracting the concentration of the effluent from the previous purification stage from the concentration of the effluent to be determined. When the difference exceeds the detection error threshold, it is determined that a secondary release of pollutants has occurred, and the effluent to be determined is returned to the corresponding pollutant-oriented purification stage; when the concentration difference of each target pollutant does not exceed the detection error threshold and reaches the effluent limit, the effluent to be determined is discharged or reused.

[0007] Further, the total concentration and dissolved concentration of the target pollutant are detected, and the ratio of dissolved concentration to total concentration is used as the dissolved proportion. When the dissolved concentration and dissolved proportion of the effluent to be judged are higher than the corresponding values ​​of the effluent in the previous purification stage and exceed the detection error threshold, the secondary release of pollutants is judged to be a phase transfer type secondary release. The pollutant-oriented purification stage also includes a sedimentation transformation stage, an adsorption and fixation stage, or a stable binding stage, and the effluent to be judged is returned to the sedimentation transformation stage, the adsorption and fixation stage, or the stable binding stage.

[0008] Furthermore, after determining that a secondary release of pollutants has occurred, the pH value and redox potential of the effluent to be determined are detected; when the concentration difference of the target pollutant corresponding to the phosphorus pollutant exceeds the detection error threshold and the redox potential is lower than the set reduction potential threshold, the effluent to be determined is refluxed to the phosphorus fixation stage; when the concentration difference of the target pollutant corresponding to the heavy metal pollutant exceeds the detection error threshold and the pH value is lower than the set pH threshold, the effluent to be determined is refluxed to the heavy metal stabilization stage.

[0009] Furthermore, when the concentration difference of the target pollutant corresponding to the organic pollutant exceeds the detection error threshold, and the nitrate nitrogen concentration in the nitrogen pollutant is higher than the designed effluent limit, the effluent to be determined is returned to the denitrification stage in the nitrogen removal stage, so that the organic pollutant is consumed as a denitrification electron donor.

[0010] Furthermore, when it is determined that the secondary release of pollutants is a phase transfer type secondary release, the difference between the proportion of dissolved state in the effluent to be determined and the proportion of dissolved state in the effluent of the previous purification stage is used as the proportion increase; when the proportion increase reaches the set increase threshold, the effluent to be determined is returned to the sedimentation and transformation stage; when the proportion increase does not reach the set increase threshold, the effluent to be determined is returned to the adsorption and fixation stage or the stable binding stage.

[0011] Further, the dissolved concentration difference is obtained by subtracting the dissolved concentration of the effluent from the previous purification stage from the dissolved concentration of the effluent to be determined, and the total concentration difference is obtained by subtracting the total concentration of the effluent from the previous purification stage from the total concentration of the effluent to be determined; when the dissolved concentration difference exceeds the detection error threshold, and the total concentration difference does not exceed the detection error threshold, it is determined that the phase transfer type secondary release originates from the dissolution of already intercepted pollutants; before reflux, the effluent to be determined is subjected to release inducing factor suppression treatment, which includes at least one of pH adjustment, redox potential adjustment, aeration control, and adsorbent addition, and enters reprocessing after the dissolved concentration drops to the reflux control limit.

[0012] Furthermore, the total concentration and dissolved concentration of the target pollutant are detected again in the effluent after recirculation and retreatment. The difference between the total concentration and the dissolved concentration is taken as the separable concentration. When the proportion of dissolved pollutants in the effluent after recirculation and retreatment is lower than that in the effluent to be determined before recirculation, and the separable concentration in the effluent after recirculation and retreatment is higher than that in the effluent to be determined before recirculation and exceeds the detection error threshold, the target pollutant is determined to have changed from dissolved to separable state. Solid-liquid separation is then performed on the effluent after recirculation and retreatment before it enters the effluent determination process.

[0013] Furthermore, before the effluent to be determined is returned to the denitrification stage, the biodegradability of the organic pollutants is tested, and the biodegradability is characterized by the ratio of BOD5 to COD. When the biodegradability is lower than a set biodegradability threshold, the organic pollutants are subjected to hydrolysis acidification pretreatment to convert them into short-chain fatty acids that can serve as electron donors for denitrification before entering the denitrification stage.

[0014] Furthermore, after the effluent to be determined is recirculated to the denitrification stage, the nitrate nitrogen concentration and the organic pollutant concentration are detected within the same detection cycle. When the nitrate nitrogen concentration decreases from before recirculation and reaches the designed effluent limit, while the organic pollutant concentration is still higher than the organic matter limit, the effluent to be determined is transferred to the organic pollutant purification stage to prevent organic pollutants from being discharged with the purified effluent.

[0015] Furthermore, the hydrolysis acidification pretreatment uses the ratio of short-chain fatty acid concentration to organic pollutant concentration as the treatment endpoint, and the adsorption-fixation stage is the adsorption-fixation unit in the organic pollutant purification stage; when the ratio reaches the set electron-donating threshold, the hydrolysis acidification pretreatment is stopped and the effluent to be determined is introduced into the denitrification stage; when the ratio does not reach the set electron-donating threshold and the organic pollutant concentration increases within two consecutive detection cycles, the effluent to be determined is transferred to the adsorption-fixation stage to reduce the entry of recalcitrant organic pollutants into the purified effluent.

[0016] This invention introduces embankment runoff sequentially into a particulate removal stage and a pollutant-oriented purification stage, thereby first intercepting particulate pollutants in the runoff. Then, according to at least one of nitrogen pollutants, phosphorus pollutants, organic pollutants, and heavy metal pollutants, a corresponding directional purification stage is set up. This allows different types of pollutants to be removed, fixed, purified, or stabilized in appropriate treatment stages, avoiding the problem that a single purification unit is not targeted enough for treating complex polluted runoff.

[0017] This invention, after forming the effluent to be judged, simultaneously detects the concentration of the target pollutant in both the effluent to be judged and the effluent from the previous purification stage. The concentration difference of the target pollutant is obtained by subtracting the concentration of the effluent from the concentration of the effluent from the concentration of the effluent to be judged. When the difference exceeds a detection error threshold, it is determined that a secondary release of pollutants has occurred, and the effluent to be judged is returned to the corresponding pollutant-oriented purification stage. Therefore, it is possible to identify the phenomenon of pollutant resurgence during the purification process through inter-stage concentration changes, preventing secondary release of pollutants from being directly discharged with the effluent and improving the stability of effluent compliance.

[0018] This invention further stipulates that the effluent to be judged is only discharged or reused when the concentration difference of each target pollutant does not exceed the detection error threshold and reaches the effluent limit, thus ensuring that the purification result simultaneously meets the requirements of process stability judgment and terminal effluent limit. This method can realize recirculation and retreatment based on actual pollutant concentration changes, reduce ineffective circulation, improve the operational reliability of the embankment runoff graded purification system, and facilitate discharge safety and reuse management in water pollution control and treatment projects. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method for constructing graded purification of embankment runoff according to the present invention.

[0020] Figure 2 This is a graph showing the difference in total phosphorus release during secondary release in Example 1 of the present invention.

[0021] Figure 3 This is a diagram showing the proportion of dissolved substances and the determination of the reflux path in Example 1 of the present invention.

[0022] Figure 4 This is a diagram showing the effect of reflux reprocessing and solid-liquid separation in Embodiment 1 of the present invention.

[0023] Figure 5 This is a graph showing the determination of organic pollutant reversion and nitrate nitrogen exceeding limits in Example 2 of the present invention.

[0024] Figure 6 This is a graph showing the determination of biodegradability and electron donation level in Example 2 of the present invention.

[0025] Figure 7 This is a graph showing the determination of nitrogen removal after denitrification and subsequent purification of organic matter in Example 2 of the present invention. Detailed Implementation

[0026] As attached Figure 1 As shown, in one specific embodiment, the embankment runoff is first collected and then introduced into a particulate matter removal stage, where sediment, suspended solids, and pollutants attached to the particulate matter are intercepted or separated. After particulate matter removal, the effluent is further introduced into a targeted pollutant purification stage. The targeted pollutant purification stage can be configured as one or more of the following based on the characteristics of the embankment runoff water quality: nitrogen removal, phosphorus fixation, organic pollutant purification, and heavy metal stabilization. The effluent treated in the targeted pollutant purification stage is used as the effluent to be judged, determining whether the graded purification process has met the effluent requirements.

[0027] After the effluent to be evaluated is formed, water quality testing is performed on both the effluent to be evaluated and the effluent from the previous purification stage. The test targets the target pollutants, which include one or more of nitrogen, phosphorus, organic, and heavy metal pollutants. During testing, the concentration of the target pollutant in the effluent to be evaluated is subtracted from the concentration of the corresponding target pollutant in the effluent from the previous purification stage to obtain the target pollutant concentration difference. This difference in target pollutant concentration allows determination of whether the pollutant has re-entered the water body from a trapped, adsorbed, or bound state during the purification process.

[0028] When the concentration difference of any target pollutant exceeds the detection error threshold, it indicates a substantial increase in the concentration of the corresponding target pollutant in the effluent to be judged compared to the effluent from the previous purification stage, thus indicating a secondary release of pollutants. In this case, the effluent to be judged is returned to a pollutant-targeted purification stage matched with the corresponding target pollutant for retreatment, so that the released pollutants are removed, fixed, or transformed again. When the concentration differences of all target pollutants do not exceed the detection error threshold, and the effluent to be judged meets the effluent limit, the effluent to be judged is discharged as purified tailwater or reused.

[0029] The embankment runoff can be collected through intercepting ditches, collection channels, diversion pipes, and regulating wells located on the embankment slope, toe, or confluence low point, and then directed to subsequent treatment units via valves, overflow outlets, or booster pumps. The particulate matter removal stage can include one or more of the following: bar screen interception, sedimentation, settling, gravel filtration, and vegetation buffer interception, to remove floating debris, silt, and suspended particles, and to provide hydraulically stable influent for the subsequent targeted pollutant purification stage. The effluent from the previous purification stage can be taken from the effluent outlet of the adjacent treatment unit before the effluent to be judged, and the effluent to be judged can be taken from the effluent outlet at the end of the targeted pollutant purification stage. Both sampling points are sampled within the same detection cycle to reduce the impact of water quality fluctuations on the judgment results.

[0030] The nitrogen removal stage can include aerobic nitrification units, anoxic denitrification units, or facultative anaerobic biological packing units. The phosphorus fixation stage can include adsorption fixation units or precipitation fixation units formed by iron-containing, aluminum-containing, calcium-containing, or mineral-based packing materials. The organic pollutant purification stage can include biofilm degradation units, adsorption units, or oxidation treatment units. The heavy metal stabilization stage can include stabilization units formed by alkaline mineral packing materials, iron-manganese oxide packing materials, biochar packing materials, or complex stabilizing packing materials. Each stage can be connected in series according to the main pollutant types in the embankment runoff, or a bypass valve can be used to selectively introduce the corresponding purification stage, ensuring that the recirculated water enters a treatment unit matching the target pollutant during reprocessing. The detection error threshold can be predetermined based on the parallel sample deviation, blank sample results, instrument detection capability, and continuous on-site detection fluctuations of the same detection method. The effluent limits, design effluent limits, organic matter limits, recirculation control limits, and various set thresholds can be predetermined based on applicable discharge requirements, reuse requirements, or engineering design objectives, and should remain consistent within the same operating batch.

[0031] Based on the above implementation methods, to further identify the morphological changes of pollutants during the staged purification process, the total concentration and dissolved concentration of the target pollutant can be detected separately, and the ratio of dissolved concentration to total concentration can be used as the dissolved proportion. When detecting the total concentration, a thoroughly mixed water sample can be used and pretreated according to the corresponding pollutant detection specifications. When detecting the dissolved concentration, the water sample can be filtered first to separate particulate, flocculent, or precipitated substances before detection. The total concentration reflects the overall content of the target pollutant in the water body, the dissolved concentration reflects the content of the target pollutant in a migratory form, and the dissolved proportion characterizes the degree to which the target pollutant transfers from a trapped, adsorbed, or bound state to a dissolved state. When the dissolved concentration in the effluent to be determined is higher than that in the effluent of the previous purification stage, and the dissolved proportion in the effluent to be determined is higher than that in the effluent of the previous purification stage, and both changes exceed the detection error threshold, it indicates that the target pollutant has undergone a transformation from a non-dissolved form to a dissolved form during the purification process. Therefore, the secondary release of the pollutant is determined to be a phase-transfer type secondary release.

[0032] After determining that a phase-transfer type secondary release has occurred, an appropriate reflux purification path can be selected based on the degree of speciation transformation of the target pollutant. The targeted pollutant purification stage can also include a precipitation transformation stage, an adsorption fixation stage, or a stabilization binding stage. The precipitation transformation stage is used to convert dissolved pollutants into insoluble precipitates; the adsorption fixation stage is used to enrich and fix dissolved pollutants using adsorption materials; and the stabilization binding stage is used to promote the formation of stable complexed, mineralized, or other low-mobility bound states of the target pollutant. The precipitation transformation stage can be achieved by adding or contacting calcium-, iron-, aluminum-, sulfide-, or alkaline mineral materials. The adsorption fixation stage can be achieved using zeolite, activated carbon, biochar, modified minerals, or iron-manganese oxide packing materials. The stabilization binding stage can promote the formation of low-mobility bound states of pollutants using mineralized packing materials, complexing stabilizing packing materials, or microbial-induced stabilization conditions. Specifically, the difference between the dissolved content of the effluent to be determined and the dissolved content of the effluent from the previous purification stage can be used as the percentage increment. When the percentage increase reaches the set threshold, it indicates a high degree of transfer of the target pollutant to its dissolved state. The effluent to be judged is then returned to the sedimentation and transformation stage to preferentially reduce its solubility and migration. When the percentage increase does not reach the set threshold, it indicates that the degree of dissolved release of the target pollutant is within a stable range. The effluent to be judged is then returned to the adsorption and fixation stage or the stable binding stage to achieve pollutant refixation.

[0033] In another embodiment, the source of phase-transfer secondary release can also be determined by the concentration difference. Specifically, the dissolved concentration difference is obtained by subtracting the dissolved concentration of the effluent from the previous purification stage from the dissolved concentration of the effluent to be determined; the total concentration difference is obtained by subtracting the total concentration of the effluent from the previous purification stage from the total concentration of the effluent to be determined. When the dissolved concentration difference exceeds the detection error threshold, while the total concentration difference does not exceed the detection error threshold, it indicates that the total content of the target pollutant in the water body has not substantially increased, but the dissolved portion has increased significantly. Therefore, it can be determined that the phase-transfer secondary release originates from the dissolution of the already retained pollutants. In this case, before recirculation and retreatment, the effluent to be determined can be treated to inhibit the release inducing factors. The release inducing factor inhibition treatment includes one or more of the following: pH adjustment, redox potential adjustment, aeration control, and adsorbent addition. These methods are used to weaken the conditions for the continued dissolution of the already retained pollutants and reduce the dissolved concentration to the recirculation control limit before the effluent to be determined is introduced into the corresponding purification stage for retreatment. pH adjustment can be achieved through acidic regulators, alkaline regulators, or buffer packing materials. Redox potential adjustment can be achieved through aeration, hypoxia control, reducing packing materials, or oxidizing packing materials. Adsorbent addition can be done using mineral adsorbents, carbon-based adsorbents, or metal oxide adsorbents that match the target pollutants.

[0034] After the recirculation treatment is completed, the total concentration and dissolved concentration of the target pollutant in the recirculated effluent can be measured again, and the difference between the total concentration and the dissolved concentration is taken as the separable concentration. The separable concentration characterizes the portion of the target pollutant that exists in the form of sediment, particulates, flocs, or adsorbed material and can be removed by solid-liquid separation. When the dissolved proportion of the recirculated effluent is lower than that of the effluent before recirculation, and the separable concentration of the recirculated effluent is higher than that of the effluent before recirculation, and the change in the separable concentration exceeds the detection error threshold, it indicates that the target pollutant has been converted from a dissolved state to a separable state. At this point, the recirculated effluent is subjected to sedimentation, filtration, membrane separation, or other solid-liquid separation treatments to remove the converted separable pollutant from the water body before proceeding to the effluent assessment step. Sedimentation can be completed in sedimentation tanks, sedimentation wells or sedimentation troughs. Filtration can be carried out by sand filtration, gravel filtration, fiber filter media filtration or porous media filtration. Membrane separation can be carried out by membrane modules that can retain particulate, flocculent or colloidal pollutants.

[0035] Based on the above implementation methods, after determining that secondary release of pollutants has occurred, the pH value and redox potential of the effluent to be tested can be further detected to identify the environmental causes of the secondary release. pH value reflects the acidity or alkalinity of the water body, and redox potential reflects the redox state of the water body; both affect the form and stability of phosphorus and heavy metal pollutants in the water body. By comparing the pH value and redox potential with corresponding thresholds, the appropriate recirculation purification path for the effluent to be tested can be determined. pH value and redox potential can be detected immediately at the sampling site, or they can be sent for testing while maintaining a sealed and minimally disturbed environment to reduce the impact of air contact, sedimentation stratification, or temperature changes on the test results.

[0036] When the concentration difference between the target pollutant and the phosphorus pollutant exceeds the detection error threshold, and the oxidation-reduction potential is lower than the set reduction potential threshold, it indicates that under conditions of enhanced reducing power, the phosphorus pollutants that have been fixed or adsorbed may be released back into the water body. In this case, the effluent to be assessed is recirculated to the phosphorus fixation stage. During this stage, by improving phosphorus binding stability, promoting phosphorus precipitation, or enhancing phosphorus adsorption and fixation, the released phosphorus pollutants are transformed back into a low-mobility form, thereby reducing the risk of phosphorus pollutants being discharged with the effluent. The phosphorus fixation stage can utilize iron salts, aluminum salts, calcium-based materials, iron-modified fillers, aluminum-modified fillers, or mineral adsorption fillers to fix phosphorus pollutants through adsorption, precipitation, or mineral binding.

[0037] When the concentration difference between the target pollutant and the heavy metal pollutant exceeds the detection error threshold, and the pH value is lower than the set pH threshold, it indicates that the water body is becoming more acidic, leading to an increased risk of heavy metal pollutant leaching. In this case, the effluent to be assessed is recirculated to the heavy metal stabilization stage. During this stage, pH adjustment, precipitation, adsorption, or complexation stabilization are used to transform the heavy metal pollutants from their easily migratable forms to stable forms. The effluent after the heavy metal stabilization stage can then proceed to the subsequent effluent assessment process to confirm whether the heavy metal pollutant concentration meets the effluent control requirements. The heavy metal stabilization stage can utilize limestone, zeolite, biochar, iron and manganese oxides, sulfide materials, or stabilizing fillers containing functional groups to precipitate, adsorb, complex, or mineralize and fix the heavy metal pollutants.

[0038] Based on the above implementation method, when the concentration difference between the target pollutants and organic pollutants exceeds the detection error threshold, and the nitrate nitrogen concentration in the nitrogen pollutants is higher than the designed effluent limit, it indicates that nitrate nitrogen still exists in the effluent to be determined and needs to be removed. Simultaneously, organic pollutants can serve as electron donors for the denitrification process. In this case, the effluent to be determined is recirculated to the denitrification stage of the nitrogen removal process, allowing denitrifying microorganisms to utilize the organic pollutants for metabolism and reduce nitrate nitrogen to nitrogen gas or other low-hazard nitrogen-containing products. This reduces the nitrate nitrogen concentration while consuming some organic pollutants. The denitrification stage can be equipped with anoxic packed beds, denitrifying biological filters, subsurface flow wetland anoxic zones, or biofilm reaction units, maintaining an anoxic environment so that denitrifying microorganisms can utilize organic pollutants to complete nitrate nitrogen removal.

[0039] Before recirculating the effluent to the denitrification stage, the biodegradability of organic pollutants can be tested. Biodegradability is characterized by the BOD5 to COD ratio, used to determine whether organic pollutants can be effectively utilized by denitrifying microorganisms. When the biodegradability is below a set threshold, it indicates a high proportion of recalcitrant components in the organic pollutants, making them unsuitable as effective electron donors for direct entry into the denitrification stage. In this case, hydrolysis and acidification pretreatment is performed on the organic pollutants to convert large molecules or recalcitrant organic matter into short-chain fatty acids, which can serve as electron donors for denitrification. After hydrolysis and acidification pretreatment, the effluent is then introduced into the denitrification stage to improve the nitrogen removal efficiency of the denitrification process. Hydrolysis and acidification pretreatment can be carried out in anaerobic or facultative anaerobic packing units, and the conversion of organic pollutants can be promoted through hydraulic retention adjustment, sludge or biofilm inoculation, stirring, or recirculation mixing.

[0040] After the effluent to be judged is recirculated to the denitrification stage, nitrate nitrogen concentration and organic pollutant concentration can be measured within the same monitoring cycle to determine whether the denitrification process matches the organic pollutant consumption process. When the nitrate nitrogen concentration decreases from before recirculation and reaches the design effluent limit, while the organic pollutant concentration remains above the organic matter limit, it indicates that the denitrification stage has completed nitrate nitrogen removal, but residual organic pollutants still exist. At this point, the effluent to be judged is transferred to the organic pollutant purification stage, where the organic pollutant concentration is further reduced through adsorption, oxidation, biodegradation, or other organic pollutant removal methods to prevent organic pollutants from being discharged with the purified effluent. The organic pollutant purification stage can employ one or more of the following: activated carbon adsorption, biofilm degradation, aeration oxidation, catalytic oxidation, wetland plant root zone degradation, or porous packing material retention degradation.

[0041] In the hydrolysis-acidification pretreatment process, the ratio of short-chain fatty acid concentration to organic pollutant concentration can be used as the basis for determining the treatment endpoint. This ratio characterizes the degree to which organic pollutants are converted into electron-donating components. When the ratio reaches the set electron-donating threshold, it indicates that the hydrolysis-acidification pretreatment has produced short-chain fatty acids sufficient for denitrification. At this point, the hydrolysis-acidification pretreatment is stopped, and the effluent to be evaluated is introduced into the denitrification stage. When the ratio does not reach the set electron-donating threshold, and the organic pollutant concentration increases within two consecutive monitoring cycles, it indicates that the organic pollutants are unlikely to form effective electron donors through hydrolysis-acidification, and there is a risk of them continuing to enter the purification effluent. In this case, the effluent to be evaluated is transferred to the adsorption-fixation stage. The adsorption-fixation stage serves as the adsorption-fixation unit in the organic pollutant purification stage, used to retain and fix recalcitrant organic pollutants, thereby reducing the amount of recalcitrant organic pollutants entering the purification effluent. The adsorption-fixation stage can be equipped with activated carbon, biochar, resin, porous minerals, modified clay, or composite adsorption packing materials. After the adsorption capacity decreases, the retention and fixation effect on recalcitrant organic pollutants can be maintained by replacement, regeneration, or combination with a solid-liquid separation unit.

[0042] Example 1: Company A adopted the graded purification method for riverbank runoff in this embodiment during a post-rainfall runoff management project. After rainfall, the riverbank runoff first flows into a regulating well via a slope interception ditch, and then is pumped into the particulate removal stage. The particulate removal stage uses a screen, sedimentation zone, and gravel filter layer to sequentially intercept floating debris, silt, and suspended particles, thus retaining pollutants attached to the particles. The effluent then enters the targeted pollutant purification stage.

[0043] In this embodiment, the targeted pollutant purification stage includes a phosphorus fixation stage, a precipitation transformation stage, and an adsorption fixation stage. The phosphorus fixation stage incorporates iron-modified mineral packing and calcium-based packing. The precipitation transformation stage promotes the formation of insoluble precipitates from dissolved phosphorus, and the adsorption fixation stage enriches and fixes the remaining dissolved phosphorus. The effluent treated by the targeted pollutant purification stage is then used as the effluent to be evaluated.

[0044] Within the same testing cycle, effluent from the previous purification stage and effluent to be evaluated are collected separately, and the total phosphorus concentration in both is measured. The difference in target pollutant concentration is determined according to the following formula:

[0045] in, Indicates the first Concentration difference of target pollutants, Indicates the first item to be determined in the water Concentration of target pollutants, This indicates the first stage of purification in the effluent. The above formula is used to compare the concentration of the target pollutant in the effluent to be determined with the concentration of the effluent in the previous purification stage, thereby determining whether the target pollutant will increase in subsequent purification processes.

[0046] In this embodiment, the total phosphorus concentration in the effluent from the previous purification stage was 0.36 mg / L, the total phosphorus concentration in the effluent to be determined was 0.48 mg / L, and the detection error threshold was 0.05 mg / L. The upper limit of the error threshold was obtained by superimposing the total phosphorus concentration from the previous purification stage onto the detection error threshold, resulting in an error threshold of 0.41 mg / L. The total phosphorus concentration in the effluent to be determined, at 0.48 mg / L, had entered the secondary release determination zone. Figure 2 The judgment process is represented by bar charts, dashed threshold lines, and shaded judgment areas, allowing the relationship between the effluent from the previous stage, the effluent to be judged, and the difference between them to be directly correlated with the secondary release judgment conditions. Substituting into the above formula, we get:

[0047] in, This indicates the difference in total phosphorus concentration. Since 0.12 mg / L is greater than the detection error threshold of 0.05 mg / L, it indicates that the total phosphorus concentration in the effluent to be judged has substantially increased compared to the effluent from the previous purification stage, and it is determined that a secondary release of phosphorus pollutants has occurred.

[0048] To further determine whether this secondary release is a phase-transfer type, the dissolved phosphorus concentration and total phosphorus concentration in the effluent from the previous purification stage and the effluent to be determined were monitored, and the proportion of dissolved phosphorus and its increase were calculated. The proportion of dissolved phosphorus and its increase were determined according to the following formula:

[0049] in, Indicates the first The proportion of dissolved pollutants of the target class Indicates the first The dissolved concentration of the target pollutant Indicates the first Total concentration of target pollutants, This indicates the increase in the proportion of dissolved substances in the effluent to be judged relative to the effluent from the previous purification stage. Indicates the first item to be determined in the water The proportion of dissolved pollutants of the target class This indicates the first stage of purification in the effluent. The proportion of dissolved pollutants in the target form. This calculation formula first divides the dissolved concentration by the total concentration to obtain the proportion of the target pollutant in the water body that can migrate, and then the difference in the proportion of dissolved pollutants between the two purification stages characterizes the degree of phase transfer.

[0050] In this embodiment, the dissolved phosphorus concentration in the effluent from the previous purification stage was 0.08 mg / L, and the total phosphorus concentration was 0.36 mg / L. The dissolved phosphorus concentration in the effluent to be determined was 0.19 mg / L, and the total phosphorus concentration was 0.48 mg / L. Therefore, the proportion of dissolved phosphorus in the effluent from the previous purification stage was approximately 0.22%, and the proportion of dissolved phosphorus in the effluent to be determined was approximately 0.40%. The increase in the proportion of dissolved phosphorus calculated based on the original detection data was approximately 0.17. Setting the increase threshold to 0.12, since 0.17 reaches the set increase threshold of 0.12, it indicates a high degree of transfer of phosphorus pollutants from the trapped, adsorbed, or bound state to the dissolved state. Therefore, this secondary release is determined to be a phase transfer type secondary release.

[0051] After determining it to be a phase-transfer type secondary release, the redox potential of the effluent to be tested was further monitored. The test results showed that the redox potential of the effluent to be tested was 75mV, and the reduction potential threshold was set at 120mV. Figure 3 The increase in the proportion of dissolved phosphorus and the redox potential threshold were placed in the same judgment diagram. The proportion of dissolved phosphorus increased from 0.22 to 0.40, which met the reflux judgment condition. At the same time, the redox potential of the effluent to be judged was lower than the reduction potential threshold, indicating that the effluent to be judged was in a state of enhanced reductiveness. There was a risk of re-release of fixed or adsorbed phosphorus pollutants. Therefore, the effluent to be judged was refluxed to the precipitation conversion unit in the phosphorus fixation stage, and calcium-based fillers and iron-modified mineral fillers were used to promote the formation of low-migration precipitates or adsorbed states of dissolved phosphorus.

[0052] During the reflux reprocessing, the effluent to be determined first enters the sedimentation and transformation stage, where dissolved phosphorus comes into contact with calcium-based and iron-based active components and is transformed into a poorly soluble form. Subsequently, it enters the adsorption and fixation stage, where incompletely precipitated dissolved phosphorus is further adsorbed and fixed by iron-modified mineral packing. This reflux path can preferentially reduce the solubility and mobility of phosphorus pollutants and cause the released phosphorus pollutants to revert to a low-mobility form.

[0053] Before solid-liquid separation after refluxing and retreatment, the total phosphorus concentration and dissolved phosphorus concentration in the effluent were measured again. The results showed that the total phosphorus concentration in the effluent after refluxing and retreatment was 0.55 mg / L, and the dissolved phosphorus concentration decreased to 0.06 mg / L. The separable phosphorus concentration in the effluent before refluxing was 0.29 mg / L, while the separable phosphorus concentration in the effluent after refluxing and retreatment was 0.49 mg / L. Furthermore, the proportion of dissolved phosphorus in the effluent after refluxing and retreatment was approximately 0.11%, lower than the 0.40% proportion in the effluent before refluxing and retreatment, indicating that phosphorus pollutants had transformed from dissolved to precipitated, particulate, or adsorbed states. Figure 4 The compositional changes of dissolved phosphorus and separable phosphorus are represented by stacked bars, and the concentration changes of total phosphorus during the reflux conversion stage and the solid-liquid separation stage are shown by a line graph. After reflux and reprocessing, the separable phosphorus increased to 0.49 mg / L, which can reflect that the reflux conversion transforms the pollutant from a migratory form to a separable form.

[0054] Subsequently, the effluent after recirculation and retreatment is introduced into the solid-liquid separation unit. This unit employs a combination of a settling zone and a filter layer to separate precipitated, particulate, and adsorbed phosphorus pollutants from the water. After solid-liquid separation, the total phosphorus concentration in the effluent drops to 0.29 mg / L, and the dissolved phosphorus concentration is 0.06 mg / L, at which point it re-enters the effluent evaluation step. When the concentration differences of all target pollutants do not exceed the detection error threshold and the total phosphorus concentration reaches the effluent limit, the effluent is either discharged as purified tailwater or reused.

[0055] Example 2: Company A adopted the graded purification method for embankment runoff in this embodiment during a post-rainfall runoff management project. After confluence with the slope, the embankment runoff enters the interception ditch, where the flow is equalized by regulating wells. Subsequently, it is sequentially introduced into a particulate matter removal stage and a targeted pollutant purification stage. The particulate matter removal stage uses screens, sedimentation zones, and gravel filters to remove floating debris, silt, and suspended particles. The targeted pollutant purification stage includes an organic pollutant purification stage and a nitrogen removal stage.

[0056] The effluent after primary organic pollutant purification is considered the effluent from the previous purification stage, while the effluent after subsequent treatment is considered the effluent to be evaluated. Within the same monitoring cycle, the concentrations of organic pollutants in the effluent from the previous purification stage and the effluent to be evaluated are measured separately, with COD used as the indicator of organic pollutant concentration. The difference in organic pollutant concentration is determined according to the following formula:

[0057] in, This represents the difference in concentration of organic pollutants. This indicates the concentration of organic pollutants in the effluent to be determined. This indicates the concentration of organic pollutants in the effluent from the previous purification stage. This formula is used to compare the effluent to be evaluated with the effluent from the previous purification stage using the same indicators to determine whether the concentration of organic pollutants has increased during the purification process.

[0058] In this embodiment, the COD of the effluent from the previous purification stage is 42 mg / L, the COD of the effluent to be determined is 58 mg / L, and the detection error threshold is 8 mg / L. Substituting into the above formula, we get:

[0059] in, This represents the COD difference. Since 16 mg / L is greater than the detection error threshold of 8 mg / L, it indicates that the concentration of organic pollutants in the effluent to be determined has substantially increased compared to the effluent from the previous purification stage, indicating that secondary release of organic pollutants has occurred or that the concentration has increased after purification. Figure 5 The determination process is illustrated by comparing COD bar charts, upper limit of error threshold, nitrate nitrogen limit, and nitrate nitrogen detection point to be determined. The COD to be determined has exceeded the upper limit of error threshold, and the nitrate nitrogen concentration to be determined is simultaneously higher than the limit. This indicates that the effluent simultaneously meets the two backflow trigger conditions of organic pollutant backflow and nitrate nitrogen exceeding the limit.

[0060] After determining that the concentration of organic pollutants had increased, the nitrate nitrogen concentration in the effluent to be tested was further monitored. The test results showed that the nitrate nitrogen concentration in the effluent to be tested was 14.6 mg / L, while the design limit for effluent was 10 mg / L. Since the nitrate nitrogen concentration in the effluent to be tested exceeded the design limit, and the difference in organic pollutant concentrations exceeded the detection error threshold, the effluent to be tested was deemed suitable for recirculation to the denitrification stage, allowing the organic pollutants to be consumed as electron donors in denitrification.

[0061] Before refluxing to the denitrification stage, the biodegradability of organic pollutants in the effluent to be determined is tested. In this embodiment, the ratio of BOD5 to COD is used to characterize biodegradability, and the calculation formula is as follows:

[0062] in, Indicates the biodegradability of organic pollutants. Indicates BOD5 concentration. This represents the COD concentration. This formula is used to determine whether organic pollutants in the effluent can be effectively utilized by denitrifying microorganisms. In this embodiment, the BOD5 of the effluent to be tested is 12 mg / L, the COD is 58 mg / L, and the degradation threshold is set to 0.30. Substituting into the above formula, we get:

[0063] Since 0.21 is less than the set degradable threshold of 0.30, it indicates that the proportion of recalcitrant organic pollutants in the effluent to be assessed is relatively high, making it difficult for them to serve as effective electron donors when directly entering the denitrification stage. Therefore, before entering the denitrification stage, the effluent to be assessed is first introduced into a hydrolysis acidification pretreatment unit to convert large molecules or recalcitrant organic matter into short-chain fatty acids.

[0064] The hydrolysis-acidification pretreatment unit is configured as an anaerobic packed bed, and the contact between organic pollutants and the biofilm is improved through reflux mixing. After hydrolysis-acidification pretreatment, the concentration of short-chain fatty acids is 21 mg / L, and the concentration of organic pollutants (calculated as COD) is 62 mg / L. The electron-donating degree of short-chain fatty acids is determined according to the following formula:

[0065] in, Indicates the degree of electron donation by short-chain fatty acids. Indicates the concentration of short-chain fatty acids. This represents the concentration of organic pollutants, expressed as COD. Substituting the detection data yields:

[0066] Since the value of 0.34 reaches the set electron-donating threshold of 0.30, it indicates that the hydrolysis acidification pretreatment has produced electron-donating components that meet the requirements of denitrification. At this point, the hydrolysis acidification pretreatment is stopped, and the effluent to be determined is introduced into the denitrification stage of the nitrogen removal stage. Figure 6 The ratio of biodegradability and the ratio of electron donation are placed in the same threshold judgment chart. When the former is lower than the set threshold, it corresponds to hydrolysis acidification pretreatment, and when the latter is higher than the set threshold, it corresponds to the introduction of the denitrification stage, thereby reflecting the change in the utilization properties of organic matter before and after hydrolysis acidification.

[0067] The denitrification stage employs an anoxic biological filter, with denitrifying biological packing material installed within the filter, maintaining anoxic operating conditions. Once the effluent is determined to have entered the denitrification stage, the denitrifying microorganisms utilize the short-chain fatty acids and other degradable organic matter formed by hydrolysis and acidification for metabolism, reducing nitrate nitrogen to nitrogen gas or other low-hazard nitrogen-containing products, while simultaneously consuming some organic pollutants.

[0068] After the effluent was recirculated to the denitrification stage, nitrate nitrogen and organic pollutant concentrations were measured within the same monitoring cycle. The test results showed that the nitrate nitrogen concentration decreased from 14.6 mg / L before recirculation to 8.2 mg / L, which has reached the design effluent limit of 10 mg / L; COD decreased to 45 mg / L, but was still higher than the organic matter limit of 40 mg / L. Figure 7 The synchronous changes of nitrate nitrogen and COD before and after denitrification are represented by a biaxial broken line. The nitrate nitrogen curve decreases and exceeds the nitrate nitrogen limit, while the COD curve decreases synchronously but remains above the organic matter limit. This indicates that the denitrification stage has completed the removal of nitrate nitrogen, but there are still residual organic pollutants.

[0069] When the nitrate nitrogen concentration reaches the design effluent limit but the COD is still higher than the organic matter limit, the effluent from the denitrification stage will be transferred to the organic pollutant purification stage. The organic pollutant purification stage uses a combination of biofilm degradation and adsorption units to further reduce the concentration of organic pollutants through biodegradation, adsorption fixation, and oxidation, thereby further reducing the COD to below the organic matter limit.

[0070] In another operating cycle, if the ratio of the concentration of short-chain fatty acids after hydrolysis and acidification pretreatment to the concentration of organic pollutants (based on COD) does not reach the set electron-donating threshold, and the COD increases within two consecutive detection cycles, it is determined that this portion of organic pollutants is unlikely to form effective electron donors through hydrolysis and acidification. In this case, the effluent to be evaluated is transferred to the adsorption and fixation unit in the organic pollutant purification stage. The adsorption and fixation unit uses activated carbon, biochar, or porous mineral packing to trap and fix recalcitrant organic pollutants, thereby reducing the risk of recalcitrant organic pollutants entering the purified effluent.

[0071] In this embodiment, when both organic pollutant concentrations rise and nitrate nitrogen exceed limits, the effluent to be determined is introduced into the hydrolysis acidification pretreatment and denitrification stage, so that organic pollutants are converted into electron-available components and participate in the denitrification process. When denitrification is completed but organic pollutants still exceed limits, the process is then switched to the organic pollutant purification stage, thereby achieving synergistic treatment of nitrate nitrogen removal and organic pollutant control in embankment runoff.

Claims

1. A method for constructing a graded purification system for embankment runoff based on water pollution control and treatment, characterized in that, include: Obtain the embankment runoff and sequentially introduce the embankment runoff into a particulate matter removal stage and a pollutant targeted purification stage. The pollutant targeted purification stage includes at least one of a nitrogen removal stage, a phosphorus fixation stage, an organic pollutant purification stage, and a heavy metal stabilization stage to form effluent to be determined. The concentration of the target pollutant in the effluent to be determined and the effluent from the previous purification stage is detected. The target pollutant includes at least one of nitrogen pollutants, phosphorus pollutants, organic pollutants and heavy metal pollutants. The concentration difference of the corresponding target pollutant is obtained by subtracting the concentration of the effluent from the previous purification stage from the concentration of the effluent to be determined. When the difference exceeds the detection error threshold, it is determined that a secondary release of pollutants has occurred, and the effluent to be determined is returned to the corresponding pollutant-oriented purification stage; when the concentration difference of each target pollutant does not exceed the detection error threshold and reaches the effluent limit, the effluent to be determined is discharged or reused.

2. The method according to claim 1, characterized in that, The total concentration and dissolved concentration of the target pollutant are detected, and the ratio of dissolved concentration to total concentration is used as the proportion of dissolved state. When the dissolved concentration and dissolved state proportion of the effluent to be judged are higher than the corresponding values ​​of the effluent in the previous purification stage and exceed the detection error threshold, the secondary release of pollutants is judged to be a phase transfer type secondary release. The targeted purification stage for pollutants also includes a sedimentation and transformation stage, an adsorption and fixation stage, or a stable binding stage, and the effluent to be determined is returned to the sedimentation and transformation stage, the adsorption and fixation stage, or the stable binding stage.

3. The method according to claim 1, characterized in that, The pH value and oxidation-reduction potential of the effluent to be judged are detected; when the concentration difference of the target pollutant corresponding to the phosphorus pollutant exceeds the detection error threshold and the oxidation-reduction potential is lower than the set reduction potential threshold, the effluent to be judged is returned to the phosphorus fixation stage; When the concentration difference of the target pollutant corresponding to the heavy metal pollutant exceeds the detection error threshold and the pH value is lower than the set pH threshold, the effluent to be judged is returned to the heavy metal stabilization stage.

4. The method according to claim 1, characterized in that, When the concentration difference of the target pollutant corresponding to the organic pollutant exceeds the detection error threshold, and the nitrate nitrogen concentration in the nitrogen pollutant is higher than the designed effluent limit, the effluent to be judged is returned to the denitrification stage in the nitrogen removal stage, so that the organic pollutant is consumed as a denitrification electron donor.

5. The method according to claim 2, characterized in that, The difference between the dissolved state ratio of the effluent to be determined and the dissolved state ratio of the effluent from the previous purification stage is used as the percentage increase; when the percentage increase reaches a set increase threshold, the effluent to be determined is returned to the sedimentation and transformation stage; when the percentage increase does not reach the set increase threshold, the effluent to be determined is returned to the adsorption and fixation stage or the stable binding stage.

6. The method according to claim 2, characterized in that, The dissolved concentration difference is obtained by subtracting the dissolved concentration of the effluent from the previous purification stage from the dissolved concentration of the effluent to be determined, and the total concentration difference is obtained by subtracting the total concentration of the effluent from the previous purification stage from the total concentration of the effluent to be determined. When the concentration difference of the dissolved state exceeds the detection error threshold, and the total concentration difference does not exceed the detection error threshold, it is determined that the phase transfer type secondary release originates from the dissolution of the retained pollutants. Before reflux, the effluent to be judged is subjected to release inducing factor suppression treatment, which includes at least one of pH adjustment, redox potential adjustment, aeration control and adsorbent addition, and enters reprocessing after the dissolved concentration drops to the reflux control limit.

7. The method according to claim 2, characterized in that, The total concentration and dissolved concentration of the target pollutant are detected again in the effluent after recirculation and retreatment. The difference between the total concentration and the dissolved concentration is taken as the separable concentration. When the proportion of dissolved pollutants in the effluent after recirculation and retreatment is lower than that in the effluent before recirculation and the separable concentration in the effluent after recirculation and retreatment is higher than that in the effluent before recirculation and exceeds the detection error threshold, the target pollutant is determined to have changed from dissolved to separable state. Solid-liquid separation is then performed on the effluent after recirculation and retreatment before it enters the effluent determination process.

8. The method according to claim 4, characterized in that, Before the effluent to be determined is returned to the denitrification stage, the biodegradability of the organic pollutants is tested. The biodegradability is characterized by the ratio of BOD5 to COD. When the biodegradability is lower than the set biodegradability threshold, the organic pollutants are subjected to hydrolysis acidification pretreatment to convert them into short-chain fatty acids that can serve as electron donors for denitrification before entering the denitrification stage.

9. The method according to claim 4, characterized in that, After the effluent to be judged is recirculated to the denitrification stage, the nitrate nitrogen concentration and the organic pollutant concentration are detected within the same detection cycle. When the nitrate nitrogen concentration decreases from before recirculation and reaches the design effluent limit, while the organic pollutant concentration is still higher than the organic matter limit, the effluent to be judged is transferred to the organic pollutant purification stage to prevent organic pollutants from being discharged with the purified effluent.

10. The method according to claim 8, characterized in that, The hydrolysis acidification pretreatment uses the ratio of short-chain fatty acid concentration to organic pollutant concentration as the treatment endpoint, and the adsorption and fixation stage is the adsorption and fixation unit in the organic pollutant purification stage; when the ratio reaches the set electron donation threshold, the hydrolysis acidification pretreatment is stopped and the effluent to be determined is introduced into the denitrification stage. When the ratio does not reach the set electron-donating threshold and the concentration of organic pollutants increases within two consecutive detection cycles, the effluent to be judged is transferred to the adsorption and fixation stage to reduce the entry of recalcitrant organic pollutants into the purified effluent.

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