Water treatment system combining anoxic biofilter and artificial wetland

Abstract

The present invention proposes a water treatment system that couples anoxic biofilters with artificial wetlands, belonging to the field of water treatment technology. The key technical points are: sewage is collected through a pipe network and flows into a water collection pool, and then enters a regulating / anoxic pool through a lift pump. The solid carbon source in the pool provides a carrier for microorganisms while achieving slow-release supplementation of the carbon source, thereby strengthening the denitrification reaction to remove total nitrogen. The system is then transported to a biofilter and a contact oxidation pool by a lift pump, and COD and ammonia nitrogen are removed through carbon oxidation and nitrification reactions. The effluent enters a high-efficiency clarifier, and after most of the total phosphorus and SS are removed through chemical phosphorus removal and coagulation and sedimentation, the overflow enters an artificial wetland, and is subjected to a comprehensive treatment of plant-microorganism-filler to deeply purify the pollutants and meet the discharge standards. Using the water treatment method of the present application, the effluent water quality can be improved to the Class B emission standard.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a water treatment system combining an anoxic biological filter and an artificial wetland. Background Art

[0002] The combined biofilter-constructed wetland process for treating rural domestic sewage has the characteristics of stable effect, low investment, simple management and low operating costs. It is widely used in rural domestic sewage treatment practice and is the main process for rural domestic sewage treatment facilities in Shanghai, accounting for 26.6%.

[0003] During the initial construction phase, the process design effluent standards primarily adhered to the secondary standard of the "Interim Regulations on Effluent Quality for Rural Domestic Wastewater Treatment Projects in Shanghai" (Shanghai Water Affairs

[2010] No. 323). In 2019, Shanghai issued the "Water Pollutant Discharge Standard for Rural Domestic Wastewater Treatment Facilities in Shanghai" (DB31 / T1163-2019), adjusting the water pollutant discharge control index from four to eight, and implementing either the Class A or Class B standards based on the water environment functional zoning of the discharge area. To meet the management requirements of the current standard, the biofilter-constructed wetland combined process treatment facility, which originally met the Class II design effluent standards, needed to be upgraded.

[0004] like Figure 1 As shown, the original process flow is: domestic sewage is collected through the pipe network 100 and flows into the regulating tank 200 for pretreatment. A screen 201 is installed in the regulating tank 200 to remove granular debris, and then enters the biological filter 300 for treatment through a lifting pump. The filter effluent enters the intermediate tank 400 for sedimentation, and after overflow, it enters the artificial wetland 500 for treatment. Part of it flows back to the regulating tank 200 and is discharged into the river after being treated in the artificial wetland 500.

[0005] The original process for removing pollutants mainly relied on pretreatment in regulating tanks, biofilm treatment in biofilters, and ecological treatment in artificial wetlands, and the treatment effect could not meet the current emission standards.

[0006] The main reasons are:

[0007] (1) Poor anoxic environment affects the denitrification effect. The regulating tank of the original process serves as an anoxic tank. Due to the large differences in the amount of rural domestic sewage in different time periods, the hydraulic retention time of sewage in the regulating tank is unstable. Combined with the high dissolved oxygen concentration of the return water, the regulating tank cannot form a strict anoxic environment, which reduces the denitrification effect.

[0008] (2) Structural defects in the biofilter reduce the energy efficiency of pollutant treatment. The original process biofilter uses plastic baskets to encapsulate the filler, which is laid out in layers and stacked flat. The plastic baskets deform when under pressure, which can easily cause uneven water flow through the filter layer and insufficient water drop. In the same filter layer, some areas have high water flow, while other areas have no water flow and are dry.

[0009] (3) The phosphorus removal effect is unstable. The phosphorus removal capacity of artificial wetland vegetation is limited and there will be seasonal fluctuations. The phosphorus removal effect is good in spring and summer when the vegetation is dense, and the effect is poor in autumn and winter when the vegetation withers. Summary of the Invention

[0010] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a water treatment system that couples an anoxic biological filter with an artificial wetland.

[0011] The technical solution of this application is as follows:

[0012] A water treatment system that couples anoxic biological filter and artificial wetland, comprising an inlet pipe network, a water collection tank, a regulating / anoxic tank, a biological filter, a contact oxidation tank, a high-efficiency clarifier, an artificial wetland, and an outlet pipe network that are sequentially connected according to the direction of water flow;

[0013] The water inlet pipe network is used to collect sewage and transfer the sewage to the collection tank;

[0014] The water collection tank is used to remove silt and regulate water volume;

[0015] The regulating / anoxic tank is provided with a floating body suspending a solid carbon source, which provides a carrier for microorganisms and realizes a slow-release supplement of the carbon source; the regulating / anoxic tank is used for denitrifying sewage and regulating water volume;

[0016] The biofilter is filled with composite fillers in multiple layers, which are, from top to bottom, a biological blanket layer, a porous medium sponge layer, a volcanic rock layer, a ceramsite layer, and a modified biological material layer; the biological blanket layer and the porous medium sponge layer are both used to filter particulate matter in sewage; the volcanic rock layer, the ceramsite layer, and the modified biological material layer are all used to adsorb impurities in sewage;

[0017] The high-efficiency clarifier is provided with a phosphorus removal device and a honeycomb inclined tube, and is used for removing phosphorus and clarifying water.

[0018] Furthermore, a coarse and fine grid is provided in the middle of the water collection pool to divide the water collection pool into two parts, left and right;

[0019] The water inlet pipe network is connected to the left part of the water collection tank and a gravity mud-water separation device is provided on the left part of the water collection tank;

[0020] A first lifting pump is provided on the right side of the water collection tank, and the sewage in the water collection tank is transported to the regulating / anoxic tank through the first lifting pump.

[0021] Furthermore, the regulating / anoxic tank is provided with a second lifting pump; the sewage in the regulating / anoxic tank is transported to the biological filter tank through a fifth pipeline by the second lifting pump.

[0022] Furthermore, the biological filter is provided with a third boost pump; the third boost pump is connected to the reflux system.

[0023] Furthermore, the water treatment system also includes: the reflux system, including: a guide valve, a first pipeline, a second pipeline, a third pipeline, and a fourth pipeline; the first pipeline, the second pipeline, the third pipeline, and the fourth pipeline are all connected to the guide valve; the first pipeline is connected to the regulation / anoxic tank; the second pipeline is connected to the second boost pump, the third pipeline is connected to the third boost pump, and the fourth pipeline is connected to the contact oxidation tank; through the reflux system, the flow rate of the solution coming in from the second boost pump and the third boost pump into the first pipeline or the fourth pipeline can be controlled.

[0024] Furthermore, the water distribution facility of the biological filter is composed of a balancing water tank and a tooth weir water distribution trough, wherein the balancing water tank is newly equipped with automatic backwashing and liquid level control functions to ensure uniform water distribution in the biological filter;

[0025] The balancing water tank can filter impurities with a particle size greater than 3mm in the water inlet of the anoxic pool to avoid clogging of the filter material; at the same time, the balancing water tank can also regulate the liquid level in the balancing water tank to ensure the stability of the water level in the water distribution tank;

[0026] The regulating / anoxic tank normally inflows water, which is filtered through the front-end filter and then discharged to the rear end of the balancing water tank, and flows into the tooth weir water trough through the outlet pipe. To ensure the stability of the water level in the tooth weir water trough, the second lifting pump is controlled by the liquid level sensor and the liquid level control valve in the balancing water tank to always ensure that the water level in the balancing water tank is higher than the outlet pipe. Based on the actual operating data, backwashing is carried out at regular intervals. The backwashing valve adopts a PLC or PAC control system. The backwashing clean water comes from the rear-end contact oxidation tank, and the flushing wastewater is discharged into the anoxic tank.

[0027] Furthermore, a micro-nano aeration membrane is provided at the bottom of the contact oxidation tank, and a light suspended filler is provided in the middle.

[0028] Further, the water is treated by the following steps:

[0029] S100, sewage is collected through the water inlet network and flows into the collection tank;

[0030] S200: The water from the collection tank enters the regulation / anoxic tank through the first lifting pump. The solid carbon source is suspended by the float in the tank, providing a carrier for microorganisms while achieving slow-release supplementation of the carbon source, thereby enhancing the denitrification reaction to remove total nitrogen before being transported to the biological filter and contact oxidation tank.

[0031] S300 removes COD and ammonia nitrogen through carbon oxidation and nitrification reactions. The effluent flows into the high-efficiency clarifier by gravity. After most of the total phosphorus and SS are removed through coagulation and sedimentation, the overflow enters the artificial wetland. After comprehensive treatment with plants, microorganisms and fillers, the pollutants are purified and finally transported to the effluent network.

[0032] Furthermore, a wall is provided in the regulating / anoxic tank, and a row of 10 cm × 10 cm square holes are provided on the wall, connecting the tank body; the wall is used to separate the functional areas of the regulating / anaerobic tank and improve the anaerobic environment; the agitator pump and the suspended solid carbon source are separated into different areas by the partition wall. The influent of the regulating / anoxic tank contains a certain amount of dissolved oxygen, and the stirring action of the agitator pump can reduce the dissolved oxygen in the water. The sewage overflows to the solid carbon source side through the square holes in the wall. The anoxic environment of the sewage overflowing to the solid carbon source is more stable, which is conducive to the denitrification reaction;

[0033] Lay a gravel layer on the surface of the conditioning / anoxic tank;

[0034] A variable frequency water pump is installed at the bottom of the regulating / anoxic tank, and high and low water level gauges are installed on the tank body; the variable frequency water pump adjusts the output water volume according to the measured signal of the level gauge to realize water level control of the regulating / anoxic tank and ensure that the anoxic tank maintains a stable anoxic environment.

[0035] Furthermore, the pollutant concentrations of the inlet and outlet of the regulating / anoxic tank satisfy the following relationship:

[0036] c i =c0·e -0.022t ;

[0037] The pollutant concentrations of the inlet and outlet water of the biological filter satisfy the following relationship:

[0038] c i =c0·e -0.0388t ;

[0039] Among them, c i is the effluent pollutant concentration, c0 is the influent pollutant concentration, and t is the hydraulic retention time of the pollutant.

[0040] The advantages of the technical solution of the present invention are mainly reflected in:

[0041] First, the treatment process after upgrading and increasing efficiency in this application is optimized and upgraded to the "coupled anoxic biological filter + artificial wetland" combination process based on the original "biological filter + artificial wetland" combination process. It not only continues the characteristics of the original process of simple maintenance and low energy consumption, but also upgrades and strengthens the denitrification and phosphorus removal capabilities. It is a biological + ecological comprehensive biofilm treatment process.

[0042] (1) Solid carbon source fillers are placed in the regulating / anoxic tank to provide an attachment carrier for facultative anaerobic bacteria and continuously release the carbon source required for denitrification, thereby enhancing the treatment efficiency of low-concentration wastewater and effectively removing total nitrogen in the anoxic tank. A new wall is built in the regulating / anoxic tank. A row of 10 cm × 10 cm square holes is set 20-30 cm below the liquid level to connect the tank body. The wall is used to separate the functional areas of the regulating / anaerobic tank and improve the anaerobic environment. The stirring pump and the suspended solid carbon source are separated into different areas by a partition wall. The influent of the regulating / anoxic tank contains a certain amount of dissolved oxygen. The stirring action of the stirring pump can reduce the dissolved oxygen in the water. The sewage overflows to the solid carbon source side through the square hole on the wall. The anoxic environment of the sewage overflowing to the solid carbon source is more stable, which is conducive to the denitrification reaction. In addition, a gravel layer of appropriate size (such as 5-20mm) is laid on the surface of the regulating / anoxic tank. By increasing the surface roughness of the tank body, the Reynolds number of the water flow is increased, turbulence formation is promoted, the exchange of sewage and air is accelerated, dissolved oxygen is effectively removed, and the sewage treatment effect is optimized.

[0043] (2) The composite filler of the biological filter is a combination of multi-layer inorganic filler and organic polymer filler. The filler surface has abundant micropores, huge specific surface area, good hydrophilicity, and modular structural units designed in combination with the characteristics of different groups of microorganisms. The removal rate of COD by heterotrophic bacteria in the biofilm can be stably maintained between 70% and 80%, and the removal rate of ammonia nitrogen by nitrifying bacteria can be stably maintained at more than 85%.

[0044] (3) As a supplement and strengthening link of the aerobic process section, the contact oxidation tank further consolidates and improves the system's ability to resist shock loads, and at the same time greatly enhances the treatment effect in winter and low temperature conditions.

[0045] (4) The addition of a high-efficiency clarification tank and a phosphorus removal dosing system can achieve high-efficiency phosphorus removal and SS removal capabilities with a small amount of reagent addition.

[0046] (5) Air lift sludge discharge devices are added to the water collection tank, micro-nano aerated biological filter, and high-efficiency clarification tank to discharge the muddy sewage into the gravity mud-water separation device installed in the water collection tank. The sludge can be easily disposed of through daily maintenance, avoiding the problems of sludge accumulation and pollutant re-release in the treatment tank.

[0047] Second, the method of the present application: sewage is collected through the pipe network and flows into the collection pool, and then enters the regulation / anoxic pool through the lifting pump. The solid carbon source in the pool provides a carrier for microorganisms while realizing the slow-release supplement of carbon source, thereby strengthening the denitrification reaction to remove total nitrogen, and then is transported to the biological filter and contact oxidation pool by the lifting pump. COD and ammonia nitrogen are removed through carbon oxidation reaction and nitrification reaction, and the effluent flows into the high-efficiency clarification pool by gravity. After most of the total phosphorus and SS are removed through coagulation and sedimentation, the overflow enters the artificial wetland, and is deeply treated by the comprehensive treatment of plants, microorganisms and fillers to meet the discharge standards.

[0048] Third, this application proposes relationships between pollutant concentrations in the inlet and effluent of conditioning / anoxic tanks, as well as in the inlet and effluent of biofilters. The following formulas reflect the impact of factors such as pollutant concentration and hydraulic retention time on the anoxic biochemical reaction / biofilm reaction process, further guiding the effectiveness of treatment facilities in wastewater treatment.

[0049] Relationship between the inlet and outlet pollutant concentrations of the regulating / anoxic tank: c i =c0·e -0.022t ;

[0050] Relationship between the inlet and outlet pollutant concentrations of the biological filter: c i =c0·e -0.0388t ;

[0051] Among them, c i is the effluent pollutant concentration, c0 is the influent pollutant concentration, and t is the hydraulic retention time of the pollutant. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention will be further described in detail below with reference to the embodiments in the accompanying drawings, but this does not constitute any limitation to the present invention.

[0053] Figure 1 It is a structural diagram of a water treatment system in the prior art.

[0054] Figure 2 It is a structural diagram of the water treatment system of this application.

[0055] Figure 3 It is the removal effect of COD, NH3-N, TN, TP, and SS.

[0056] Figure 4 This is the pH result diagram of each treatment structure.

[0057] Figure 5 This is the COD removal effect monitoring result diagram.

[0058] Figure 6 This is the monitoring result diagram of NH3-N removal effect.

[0059] Figure 7 This is a graph showing the monitoring results of TN removal effect.

[0060] Figure 8 This is the TP removal effect monitoring result diagram.

[0061] Figure 9 This is a graph showing the monitoring results of the suspended solids (SS) removal effect.

[0062] Figure 10 This is a diagram of the structure of the regulation / anoxic tank.

[0063] Figure 11 This is a cross-sectional view of the biofilter.

[0064] Figure 12 This is an overhead view of the biofilter.

[0065] Figure 13 It is a three-dimensional design diagram of the balancing water tank.

[0066] The following are the descriptions of the reference numerals:

[0067] Existing domestic sewage pipe network 100, existing regulating tank 200, existing grille 201, existing biological filter 300, existing intermediate tank 400, existing artificial wetland 500;

[0068] Water treatment system 2000, water inlet network 2010, water collection tank 2020, regulation / anoxic tank 2030, biological filter 2040, contact oxidation tank 2050, high-efficiency clarifier 2060, artificial wetland 2070, water outlet network 2080, return system 2090;

[0069] Grille 2023, gravity mud-water separator 2022, first lift pump 2021;

[0070] A second lift pump 2031 and a floating body suspending a solid carbon source 2032;

[0071] Ecological blanket layer 2041, porous medium cotton layer 2042, volcanic rock layer 2043, ceramsite layer 2044, modified biological material layer 2045;

[0072] third lift pump 2046;

[0073] Balancing water tank 2141, tooth weir water tank 2142, liquid level sensor 21411, liquid level control valve 21412, front-end filter 21413, backwash pipe 2143, backwash pump 2144. DETAILED DESCRIPTION

[0074] The objects, advantages and features of the present invention are explained through the following non-limiting description of preferred embodiments. These embodiments are merely typical examples of the application of the technical solutions of the present invention. Any technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

[0075] Example 1: Upgrading and renovation project of a rural domestic sewage treatment station in a town in Jiading District, Shanghai

[0076] 1. Project Overview

[0077] This project upgrades a rural domestic sewage treatment station in a town in Jiading District, Shanghai. Built in 2017, the station serves a non-rural tourism area, serving 39 rural households and a permanent population of 380. The sewage collection system is 3.2 kilometers long, with a designed capacity of 40 tons per day. The effluent is designed to meet Class II standards, utilizing a fully buried biofilter and constructed wetland process. The station will be upgraded to Class IB standards in 2023.

[0078] In this service area, many farmers rent out their land, the floating population fluctuates greatly, the water quality and quantity of rural domestic sewage fluctuate greatly, and there is a certain amount of external water intrusion into the pipeline network.

[0079] 2. Design inlet and outlet water quality

[0080] Table 1 shows the design inlet and outlet water qualities.

[0081] Table 1 Designed inlet and outlet water quality

[0082]

[0083] 3. Ideas for process transformation

[0084] The original facilities and structures were renovated, the process was optimized into a multi-stage coupled biological module, the pre-process was improved, and subsequent processes were added to enhance the nitrogen and phosphorus removal effects of the process and ensure that the effluent quality was stable and met the standards.

[0085] 1) In order to solve the problem of poor anoxic environment in pretreatment, a partition wall was installed in the original regulating tank to transform it into a water collection tank and a regulating / anoxic tank. A new grid was installed in the water collection tank to remove large particle pollutants, and a suspended solid carbon source was installed in the regulating / anoxic tank.

[0086] like Figure 10The following figure shows a detailed design of the conditioning / anoxic tank. A new wall is constructed within the conditioning / anoxic tank. A row of 10cm x 10cm square holes is located 20-30cm below the liquid level, connecting the tank body. The wall serves to separate the functional areas of the conditioning / anaerobic tank and enhance the anaerobic environment. The partition wall separates the agitator pump and the suspended solid carbon source into separate zones. The influent to the conditioning / anoxic tank contains a certain amount of dissolved oxygen, and the agitation of the agitator pump reduces this dissolved oxygen. The wastewater overflows through the square holes in the wall to the solid carbon source, creating a more stable anoxic environment and promoting denitrification. Furthermore, a layer of gravel of appropriate size (e.g., 5-20mm) is laid on the surface of the conditioning / anoxic tank. This increases the surface roughness of the tank, increases the Reynolds number of the water flow, promotes turbulence, accelerates the exchange of wastewater with air, effectively removes dissolved oxygen, and optimizes wastewater treatment.

[0087] A variable frequency pump is installed at the bottom of the regulating / anoxic tank, along with high and low water level gauges installed in the tank. The variable frequency pump adjusts the water output based on the measured signal from the level gauge, controlling the water level in the regulating / anoxic tank and ensuring a stable anoxic environment.

[0088] formula:

[0089] The degradation of pollutants in the sewage in the conditioning / anoxic tank is related to the hydraulic retention time of the sewage and the concentration of microorganisms in the pollutants. The pollutant degradation formula is constructed: i =c0·e -μt

[0090] The actual calculation shows that the hydraulic retention time is 12.86h. The influent COD concentration c0=80.4mg / L, c i = 60.6 mg / L into the calculation, we get μ = 0.022h -1 , from which we can conclude that c i =c0·e -0.022t .

[0091] 2) To address the low treatment efficiency of the biofilter, the original stacked packing structure was transformed into a composite, multi-layered, standardized box assembly. The packing boxes are stacked on horizontally sliding stainless steel supports, with each group consisting of five layers of uniform height. From top to bottom, they comprise: an ecological blanket layer 2041, a porous media sponge layer 2042, a volcanic rock layer 2043, a ceramsite layer 2044, and a modified biomaterial layer 2045. This modification reduces the cross-sectional area of ​​the biofilter and allows for a more uniform flow from top to bottom. This eliminates the risk of excessive overflow in some filter media due to deformation of the filter basket, while ensuring uniform flow across all filter components. The bioblanket and porous media sponge possess good water permeability, enabling them to filter particulate matter from wastewater and facilitate regular cleaning. The volcanic rock, ceramsite, and modified biomaterial all possess high porosity and large specific surface area, resulting in excellent adsorption properties. Microorganisms in the biofilter exhibit a certain distribution pattern and stratified aggregation in the vertical direction due to changes in dissolved oxygen and pollutant concentrations, forming a rich microbial community and enhancing treatment efficiency. Diversion devices are installed at all levels of the filler frame to avoid the formation of concentrated water points and improve filter media treatment efficiency.

[0092] 3)Formula:

[0093] The degradation of pollutants in the biological filter is related to the hydraulic retention time of the sewage and the concentration of microorganisms in the pollutants. The pollutant degradation formula is constructed: c i =c0·e -μt .

[0094] The actual calculation shows that the hydraulic retention time is 14h. The influent COD concentration c0=60.6mg / L, c i =35.2mg / L into the calculation, we get μ=0.0388h -1 , from this we can conclude that: c i =c0·e -0.0388t .

[0095] 3) To address the poor phosphorus removal performance of the process, a partition wall was installed in the original intermediate tank, which was converted into a contact oxidation tank and a high-efficiency clarification tank, and an artificial wetland was constructed. A nano-aeration membrane device was installed at the bottom of the contact oxidation tank, and a lightweight suspended filler was installed in the middle to enhance the aerobic treatment effect. A reaction hood was installed in the high-efficiency clarification tank, and a phosphorus removal agent was dripped into the reaction hood through a dosing system. Honeycomb inclined tubes were installed outside the reaction hood to intercept suspended matter in the water, achieving phosphorus removal and water clarification. The channels and pipes of the artificial wetland were rebuilt, and new slow-release phosphorus removal fillers were laid. Plants with well-developed root systems were replaced to enhance the wetland's ability to absorb nitrogen and phosphorus.

[0096] 4. Process flow after transformation

[0097] like Figure 2As shown, a water treatment system 2000 coupled with an anoxic biological filter and an artificial wetland includes, in order of water flow direction: an inlet pipe network 2010, a collection tank 2020, a regulating / anoxic tank 2030, a biological filter 2040, a contact oxidation tank 2050, a high-efficiency clarifier 2060, an artificial wetland 2070, an outlet pipe network 2080, and a return system 2090.

[0098] The water inlet pipe network 2010 is used to collect sewage and transfer the sewage to the collection tank 2020.

[0099] A coarse and fine grid 2023 is provided in the middle of the water collection tank 2020, dividing the water collection tank 2020 into two parts, left and right. The water inlet pipe network 2010 is connected to the left part of the water collection tank 2020 and a gravity mud-water separation device 2022 is provided on the left part of the water collection tank 2020 (the gravity mud-water separation device 2022 is used to regularly remove the separated sludge during operation and maintenance work, thereby avoiding sludge accumulation and affecting normal functions); a first lifting pump 2021 is provided on the right part of the water collection tank 2020; the sewage in the water collection tank 2020 is transported to the regulation / anoxic tank 2030 through the first lifting pump 2021; the first lifting pump 2021 is used to ensure that the water collection tank operates at a low water level while realizing the water volume regulation function.

[0100] The regulating / anoxic tank 2030 is provided with a second lifting pump 2031; the sewage of the regulating / anoxic tank 2030 is transported to the biological filter water distribution facility 2040 through the fifth pipeline by the second lifting pump 2031; a floating suspended solid carbon source 2032 ("solid carbon source deep denitrification and water purification technology", solid carbon source is arranged in the regulating / anoxic tank by floating suspension) is provided in the regulating / anoxic tank 2030, which provides a carrier for microorganisms while realizing slow-release supplement of carbon source, avoiding the problem of excessive or insufficient addition of carbon source.

[0101] At the same time, high and low water level gauges are installed in the regulating / anoxic tank 2030 to adjust the output water volume and achieve automatic adjustment of the operating liquid level: above the high liquid level, it enters forced discharge mode, with high flow and low return ratio; between the high and low liquid levels, it enters storage mode, with normal flow and moderate return ratio; below the low liquid level, it enters circulation mode, with full return. The regulating / anoxic tank is set with an appropriate minimum water level to ensure hydraulic retention time.

[0102] The biological filter 2040 is filled with composite fillers in multiple levels to further build a rich biological community, and the filling levels are arranged according to the characteristics of different biological phases to enhance the treatment efficiency. That is, the biological filter 2040 adopts a composite multi-level standardized box assembly structure. The filler boxes are stacked on a horizontally sliding stainless steel bracket. Each group has 5 layers with the same layer height. From top to bottom, they are an ecological blanket layer, a porous medium cotton layer, a volcanic rock layer, a ceramsite layer, and a modified biological material layer. The biological blanket layer and the porous medium cotton layer have good water permeability and can filter particulate matter in sewage, which is convenient for regular cleaning; the volcanic rock layer, the ceramsite layer, and the modified biological material layer all have the characteristics of large porosity and large specific surface area, and have good adsorption properties. The microorganisms in the vertical direction of the biological filter show a certain distribution pattern and stratified aggregation phenomenon due to changes in dissolved oxygen and pollutant concentrations, forming a rich microbial community and enhancing the treatment efficiency. Each level of the filler frame is equipped with a diversion device to avoid the formation of concentrated water points and improve the filter material treatment efficiency.

[0103] like Figure 12 It can be seen that the water distribution facilities of the biological filter are composed of a balancing water tank 2141 and a tooth weir water distribution trough 2142, wherein the balancing water tank has automatic backwashing and liquid level control functions to ensure uniform water distribution in the biological filter.

[0104] The balancing water tank 2141 has two main functions: (1) filtering impurities with a particle size greater than 3 mm in the water entering the anoxic tank to prevent filter media from clogging; (2) regulating the liquid level in the balancing water tank to ensure a stable water level in the water distribution tank.

[0105] The operating principle of the balancing water tank: the regulating / anoxic tank normally takes in water, and the water is discharged to the rear end of the balancing water tank 2141 after being filtered by the front-end filter 21413, and flows into the tooth weir water trough 2142 through the outlet pipe; in order to ensure the stability of the water level in the tooth weir water trough, the regulating / anoxic tank inlet pump (i.e., the second lifting pump 2031) is controlled by the liquid level sensor 21411 and the liquid level control valve 21412 in the balancing water tank to always ensure that the water level in the balancing water tank is higher than the outlet pipe; according to the actual operating data, backwashing is performed at regular intervals, and the backwashing valve adopts a PLC or PAC control system. The backwashing clean water comes from the rear end and contacts the regulating / anoxic tank, and the flushing sewage is discharged into the anoxic tank.

[0106] The biological filter 2040 is provided with a third lift pump 2046 ; the third lift pump 2046 is connected to the reflux system 2090 .

[0107] The contact oxidation tank 2050 supplements and regulates the aerobic treatment capacity of the biofilter, with an internal circulation system installed between the two. A micro-nano aeration membrane 2051 is installed at the bottom of the contact oxidation tank, and lightweight suspended filler 2052 is installed in the middle. Through bottom micro-aeration, high pollutant removal capacity is achieved with low energy consumption.

[0108] The high-efficiency clarifier 2060 has excellent sedimentation performance. The addition of a phosphorus removal device 2061 and the addition of a phosphorus removal agent simultaneously removes phosphorus and clarifies the water, significantly improving the SS content of the effluent. The high-efficiency clarifier 2060 is equipped with honeycomb inclined tubes 2061, which achieve rapid sedimentation and separation of suspended solids through settling.

[0109] The bottom of the artificial wetland 2070 is paved with a new slow-release phosphorus removal filler and planted with plants such as evergreen iris, canna, and pennywort. The absorption effect of the plant roots in the artificial wetland and the adsorption effect of the new slow-release phosphorus removal filler can both improve the phosphorus removal effect.

[0110] The reflux system 2090 includes: a guide valve, a first pipeline, a second pipeline, a third pipeline, and a fourth pipeline; the first pipeline, the second pipeline, the third pipeline, and the fourth pipeline are all connected to the guide valve; the first pipeline is connected to the regulating / anoxic tank 2030; the second pipeline is connected to the second lift pump 2031, the third pipeline is connected to the third lift pump 2046, and the fourth pipeline is connected to the contact oxidation tank 2050; through the reflux system 2090, the flow can be adjusted back to obtain the flow of the regulating / anoxic tank 2030.

[0111] 5. Monitoring results

[0112] After the project was completed, the average effluent concentrations of pH, COD, NH3-N, TN, TP and SS were 7.8, 21, 3.3, 10.70, 0.55 and 7.8 mg / L respectively. Monitoring data showed that the average effluent quality of the site after the renovation was significantly improved compared with that before the renovation. The improvement rates of COD, NH3-N, TN, TP and SS were 64%, 79%, 62%, 74% and 48% respectively. Among them, the removal effects of ammonia nitrogen, total nitrogen and total phosphorus were significant, verifying the denitrification and phosphorus removal effectiveness of the modified process. Figure 3 .

[0113] 6. Operation effect analysis

[0114] In order to analyze the operating effect of each treatment structure, the pH, COD, NH3-N, TN, TP, and SS values ​​of the effluent water quality at six points, including the water collection tank, regulation / anoxic tank, biological filter / aeration tank, contact oxidation tank, high-efficiency clarifier, and outlet of the treatment station were tested for five consecutive days.

[0115] 6.1 pH value

[0116] The pH values ​​of each treatment structure are as follows: Figure 4 As shown, the pH value is in the range of 7.1 to 7.6, meeting the Class B discharge standard.

[0117] The pH value increased slightly in the regulating / anoxic pond and artificial wetland. Since the regulating / anoxic pond and artificial wetland are in an anoxic environment, denitrifying bacteria undergo denitrification reaction, reducing nitrate nitrogen (such as nitrate and nitrite) to nitrogen gas and producing hydroxide ions (OH - ), resulting in an increase in the pH value of the water.

[0118] The pH value decreased slightly in the biofilter and contact oxidation tank, likely due to the production of acidic substances by microorganisms decomposing organic matter in an aerobic environment. The pH change in the high-efficiency clarifier is likely related to the addition of phosphorus removal agents. The fillers in the constructed wetland are primarily synthetic and slightly alkaline, resulting in a stable effluent pH.

[0119] 6.2COD Removal

[0120] The COD removal effect of each treatment structure is as follows Figure 5 As shown. The COD inlet concentration range is 71-89 mg / L (average is about 80.4 mg / L), the effluent COD concentration range is 20-26 mg / L (average is 23.6 mg / L), the removal rate is 64.8%-77.0%, average is 70.6%, meeting the Class B discharge standard (≤60 mg / L). The COD inlet concentration is lower than the design value of 300 mg / L because:

[0121] (1) After farmers’ sewage is treated in septic tanks, the concentration of septic tank overflow sewage is low (less than 100 mg / L);

[0122] (2) The construction of the rainwater pipe network in the service area is not perfect, and there is a problem of mixed connection between rainwater and sewage;

[0123] (3) The groundwater level in Shanghai is high, and there is a problem of groundwater infiltration into the sewage pipe network. Monthly effluent water quality monitoring data for one consecutive year has met the design effluent standards, fully demonstrating that the modified process has a strong adaptability to low influent COD concentrations.

[0124] The COD concentration changes in the three treatment units, namely the collection tank, the regulating / anoxic tank, and the biological filter, are the most significant. After the sewage enters the regulating / anoxic tank, the backflow has a certain dilution effect on the COD. At the same time, the denitrifying bacteria use the nitrate and nitrite in the reflux liquid as electron acceptors and use COD as a carbon source and electron donor to carry out denitrification reactions, thereby achieving COD treatment.

[0125] Figure 5It shows that the average COD removal rate of the biological filter is the highest, reaching 42%, which is mainly based on the good ventilation and water distribution effect between the filter media layers. The biological filter is fully reoxygenated during the uniform water distribution and water drop process, so that a large number of microorganisms grow on the surface and inside the filler. At the same time, the filter media intercepts solid suspended particles, proteins, enzymes and other large molecular organic matter in the sewage, which increases the contact time between microorganisms and organic matter, and improves the utilization rate of organic matter by the biofilm attached to the filler.

[0126] 6.3 Removal of NH3-N

[0127] The removal effect of each treatment structure on NH3-N is as follows Figure 6 As shown in the figure, the influent NH3-N concentration ranged from 16.7 to 21.1 mg / L (average approximately 18.8 mg / L), and the effluent NH3-N concentration ranged from 1.8 to 3.1 mg / L (average 2.5 mg / L). The removal rate was 82.8% to 89.7%, with an average of 86.7%, meeting the Class I B discharge standard (≤15 mg / L). In the conditioning / anoxic tank, ammonia-forming bacteria ammonify other forms of nitrogen in the water, converting them into ammoniacal nitrogen. This maintained a high ammoniacal nitrogen concentration in the conditioning / anoxic tank, averaging 16.6 mg / L. Figure 6 As shown in the figure, the treatment structures with the highest NH3-N removal rates are the conditioning / anoxic tank and the contact oxidation tank. Due to the presence of a complete nitrification-denitrification microbial system in the lower and middle sections of the biofilter, the biofilm structure is robust, effectively degrading organic matter while removing ammonia nitrogen from the water. The average ammonia nitrogen removal rate in the biofilter is 51.9%. The contact oxidation tank is the treatment unit with the highest ammonia nitrogen removal efficiency, with an average removal rate of 54.9%. The contact oxidation tank uses micro-nano aeration to increase the dissolved oxygen content in the water. This higher dissolved oxygen concentration facilitates the removal of ammonia nitrogen by nitrifying bacteria.

[0128] 6.4TN removal

[0129] The removal effect of each treatment structure on TN is as follows Figure 7 As shown in the figure, the influent TN concentration ranged from 28.9 to 34.5 mg / L (average approximately 32.1 mg / L), and the effluent TN concentration ranged from 9.6 to 10.9 mg / L (average 10.35 mg / L). The removal efficiency ranged from 66.6% to 55.5%, with an average of 68.7%, meeting the Class I B discharge standard (≤25 mg / L). The treatment process primarily relies on denitrification to remove TN. Figure 7As shown, the highest TN removal efficiency was achieved in the conditioning / anoxic tank, with an average removal rate of 44.5%. This was followed by the biofilter and constructed wetland, with average removal rates of 24.7% and 19.6%, respectively. The influent COD / TN ratio was approximately 2.5, indicating a low carbon-to-nitrogen ratio. Insufficient carbon sources in the wastewater resulted in low nitrogen removal efficiency. The addition of a solid carbon source in the conditioning / anoxic tank not only addressed the low carbon content of the wastewater by slowly releasing and replenishing the carbon source, but also provided a substrate for microbial biofilm formation, improving carbon source utilization efficiency and further enhancing denitrification. Due to the gradient of substrate and dissolved oxygen concentrations within the biofilm on the biofilter filler, the dissolved oxygen concentrations create aerobic, anoxic, and anaerobic microenvironments within the biofilm, providing a niche for microbial denitrification and achieving TN removal. Constructed wetlands remove nitrogen through plant root absorption of nitrogen from the wastewater and denitrification in the anaerobic zone near the filler layer.

[0130] 6.5TP removal

[0131] The removal effect of each treatment structure on TP is as follows Figure 8 As shown. The TP inlet concentration ranged from 1.9-2.4 mg / L (average approximately 2.2 mg / L), and the effluent TP concentration ranged from 0.4-0.6 mg / L (average 0.46 mg / L). The removal rate was between 71.4% and 81.8%, with an average of 78.9%, meeting the Class I B discharge standard (≤2 mg / L). After the wastewater was treated in the conditioning / anoxic tank, biological filter, and contact oxidation tank, the total phosphorus concentration remained almost unchanged. Due to the lack of alternating aerobic and anaerobic environments in the biological filter, the activated sludge content was low, and the biological phosphorus removal effect was poor. Other combined processes are needed to meet phosphorus removal requirements in the treatment of domestic sewage. Therefore, adding a phosphorus removal agent to the high-efficiency clarifier to form an insoluble precipitate with the phosphates in the sewage can compensate for the shortcomings of biological phosphorus removal and achieve stable phosphorus removal. The absorption effect of plant roots in the constructed wetland and the adsorption effect of the new slow-release phosphorus removal filler can both improve phosphorus removal efficiency.

[0132] 6.6SS removal

[0133] The SS removal effect of each treatment unit is as follows Figure 9As shown. The SS inlet concentration range is 45-75 mg / L (average is about 62.4 mg / L), the effluent SS concentration range is 5-8 mg / L (average is 7 mg / L), the removal rate is 87.5%-90.0%, and the average is 88.8%, meeting the Class I B emission standard (≤20 mg / L). The efficient removal of SS mainly relies on the filler filtration in the biological filter and the sedimentation effect of the high-efficiency clarifier. The filler in the biological filter has a large specific surface area and porosity, which can effectively intercept and adsorb suspended particles in the sewage; at the same time, the microbial film on the surface of the filler can secrete substances such as mucus to further enhance the adsorption effect. In the high-efficiency clarifier, the rapid sedimentation and separation of suspended matter is achieved through honeycomb inclined tube sedimentation. Figure 9 As shown in Figure 2, aeration in the contact oxidation pond caused a significant increase in SS concentration. When wastewater overflowed from the high-efficiency clarifier to the constructed wetland, the scouring effect of the water flow may have caused a small increase in SS concentration in the effluent of the constructed wetland.

[0134] The above embodiments are preferred implementation modes of the present invention and are only used to facilitate the explanation of the present invention. They are not intended to limit the present invention in any form. Any person with ordinary knowledge in the technical field can, without departing from the scope of the technical features of the present invention, make partial changes or modifications to the technical contents disclosed in the present invention and make equivalent embodiments without departing from the technical features of the present invention. Such modifications still fall within the scope of the technical features of the present invention.

Claims

1. A water treatment system that couples anoxic biological filter and artificial wetland, characterized in that: The water treatment system includes an inlet pipe network, a water collection tank, a regulation / anoxic tank, a biological filter, a contact oxidation tank, a high-efficiency clarifier, an artificial wetland, and an outlet pipe network that are connected in sequence according to the direction of water flow; The water inlet network is used to collect sewage and transfer it to a water collection tank; the water collection tank is used to remove silt and regulate water volume; a coarse and fine grid is provided in the middle of the water collection tank to divide the water collection tank into left and right parts; the water inlet network is connected to the left part of the water collection tank, and a gravity mud and water separation device is provided on the left part of the water collection tank; a first lift pump is provided on the right part of the water collection tank, and the sewage in the water collection tank is transferred to the regulating / anoxic tank by the first lift pump; The water collection tank, biological filter and high-efficiency clarifier are equipped with air lift mud discharge devices, which are used to discharge mud-containing sewage into the gravity mud-water separation device installed in the water collection tank; the regulating / anoxic tank is equipped with a floating body to suspend a solid carbon source, which provides a carrier for microorganisms and realizes slow-release supplementation of the carbon source; the regulating / anoxic tank is used for sewage denitrification and water volume regulation; The structure of the biological filter tank adopts a composite multi-level standardized box assembly structure, and the filling boxes are stacked on a horizontally sliding stainless steel bracket, with 5 layers in each group and the layer height being the same; the filler of the biological filter tank adopts a composite filler multi-level filling, which are from top to bottom: biological blanket layer, porous medium sponge layer, volcanic rock layer, ceramsite layer, modified biological material layer; the biological blanket layer and the porous medium sponge layer are both used to filter particulate matter in sewage; the volcanic rock layer, the ceramsite layer, and the modified biological material layer are all used to adsorb impurities in sewage; the water distribution facilities of the biological filter tank are composed of a balancing water tank and a tooth weir water distribution trough, wherein the balancing water tank has newly added automatic backwashing and liquid level control functions to ensure uniform water distribution in the biological filter tank; the balancing water tank can filter impurities with a particle size greater than 3mm in the influent of the anoxic tank to avoid clogging of the filter material; at the same time, the balancing water tank can also regulate the liquid level in the balancing water tank to ensure the stability of the water level in the water distribution trough; The high-efficiency clarifier is provided with a phosphorus removal device and a honeycomb inclined tube, and is used for removing phosphorus and clarifying water; A wall is provided in the regulating / anoxic tank, and a row of 10cm×10cm square holes are provided on the wall to connect the tank body. The partition wall separates the stirring pump and the suspended solid carbon source into different areas. The influent of the regulating / anoxic tank contains a certain amount of dissolved oxygen. The stirring action of the stirring pump can reduce the dissolved oxygen in the water. The sewage overflows to the solid carbon source side through the square holes in the wall. The anoxic environment of the sewage overflowing to the solid carbon source is more stable, which is conducive to the denitrification reaction. Lay a gravel layer on the surface of the conditioning / anoxic tank; A variable frequency water pump is installed at the bottom of the regulating / anoxic tank, and high and low water level gauges are installed on the tank body. The variable frequency water pump adjusts the output water volume based on the measured signal of the level gauge to control the water level of the regulating / anoxic tank and ensure that the anoxic tank maintains a stable anoxic environment. The bottom of the artificial wetland is paved with a slow-release phosphorus removal filler; The bottom of the contact oxidation tank is provided with a micro-nano aeration membrane, and the middle is provided with a light suspended filler; The following steps are used to treat the water: S100, sewage is collected through the water inlet network and flows into the collection tank; S200: The sewage from the collection tank enters the regulation / anoxic tank through the first lifting pump. The solid carbon source is suspended by the floating body in the tank, providing a carrier for microorganisms while achieving slow-release replenishment of the carbon source, thereby enhancing the denitrification reaction to remove total nitrogen before being transported to the biological filter and contact oxidation tank. S300 removes COD and ammonia nitrogen through carbon oxidation and nitrification reactions. The effluent flows into the high-efficiency clarifier by gravity. After removing most of the total phosphorus and SS through coagulation and sedimentation, the overflow enters the constructed wetland. After a comprehensive treatment process of plants, microorganisms and fillers, the pollutants are purified and finally transported to the effluent network. The COD pollutant concentrations of the inlet and outlet water of the regulating / anoxic tank meet the following relationship: c i = c0·e -0.022t ; The COD pollutant concentrations of the inlet and outlet water of the biological filter satisfy the following relationship: c i = c0·e -0.0388t ; Among them, c i is the effluent pollutant concentration, c0 is the influent pollutant concentration, and t is the hydraulic retention time of the pollutant.

2. The water treatment system according to claim 1, characterized in that: The regulating / anoxic tank is provided with a second lifting pump; the sewage in the regulating / anoxic tank is transported to the biological filter tank through a fifth pipeline by the second lifting pump.

3. The water treatment system coupled with anoxic biofilter and artificial wetland according to claim 2, characterized in that: The biological filter is provided with a third lifting pump; the third lifting pump is connected to the reflux system.

4. The water treatment system coupled with anoxic biofilter and artificial wetland according to claim 3, characterized in that: The water treatment system also includes: the reflux system, including: a guide valve, a first pipeline, a second pipeline, a third pipeline, and a fourth pipeline; the first pipeline, the second pipeline, the third pipeline, and the fourth pipeline are all connected to the guide valve; the first pipeline is connected to the regulation / anoxic tank; the second pipeline is connected to the second lift pump, the third pipeline is connected to the third lift pump, and the fourth pipeline is connected to the contact oxidation tank; through the reflux system, the flow rate of the solution transported by the second lift pump and the third lift pump into the first pipeline or the fourth pipeline can be controlled.

5. A water treatment system coupled with anoxic biofilter and artificial wetland according to claim 3 or 4, characterized in that: When the regulating / anoxic tank is normally inflowing water, the inflowing water is filtered by the front-end filter and then discharged to the rear end of the balancing water tank, and flows into the tooth weir water trough through the outlet pipe; in order to ensure the stability of the water level in the tooth weir water trough, the second lifting pump is controlled by the liquid level sensor and the liquid level control valve in the balancing water tank to always ensure that the water level in the balancing water tank is higher than the outlet pipe; according to the actual operation data, backwashing is carried out at regular intervals, and the backwashing valve adopts a PLC control system. The backwashing clean water comes from the rear-end contact oxidation tank, and the flushing wastewater is discharged into the anoxic tank.

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