Method and device for treating wastewater by combining a suspended filler floating bed with a soil infiltration system

Abstract

The application provides a method and device for treating wastewater by combining a suspended filler floating bed and a soil infiltration system, and the method comprises the following steps: S1, breeding wastewater is treated by the suspended filler floating bed after passing through a hydrolysis tank, and effluent is treated in a sedimentation tank, and wastewater of the suspended filler floating bed is returned to the suspended filler floating bed for secondary treatment; S2, wastewater of the sedimentation tank is returned to the hydrolysis tank; and S3, effluent of the sedimentation tank is introduced into a soil underground infiltration system. The system provided by the application is beneficial to further strengthening the effects of denitrification, phosphorus removal and removal of suspended solids, and solves the problems of low dissolved oxygen content of influent and wastewater in the system, which is not conducive to the growth of nitrifying bacteria, and low effective volume utilization rate. In the use process, the filler does not need to be replaced, and mechanical aeration equipment does not need to be added, and the system has the advantages of low investment cost, no need to add chemical agents for treatment, obvious effect, not easy to breed mosquitoes, simple operation and management, and beautification of the environment, and has remarkable ecological and economic benefits for promoting deep purification of breeding wastewater.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater treatment equipment and methods, specifically relating to a method and apparatus for treating wastewater by combining a suspended packing floating bed with a soil infiltration system. Background Technology

[0002] Pollution from pig farming wastewater mainly comes from organic wastewater such as pig urine, pigsty cleaning, and feed, containing high concentrations of COD, ammonia nitrogen, and total phosphorus. Even if the wastewater meets the discharge standards of the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001), it may still pose a threat to the ecological environment. Soil infiltration systems, as an artificially enhanced ecological wastewater treatment technology, are currently widely used in the treatment of various polluted water bodies, especially rural domestic sewage. Soil infiltration treatment (SIT), also known as soil aquifer treatment (SAT), originated from traditional wastewater irrigation technology. Under controlled conditions, wastewater with a specific hydraulic or pollution load is fed into an aerobic / anaerobic combined process facility filled with composite soil filler. The wastewater slowly diffuses through the soil, which has excellent diffusion properties. Pollutants are removed through the action of animals, plants, and microorganisms in the soil, as well as the soil's own physical and chemical properties. This technology has advantages such as low infrastructure investment, low operating costs, and high purification efficiency. Simultaneously, the water and fertilizer resources in the wastewater can promote crop growth, achieving the harmlessness and resource utilization of wastewater. As a deep wastewater treatment process, soil infiltration systems have good resistance to shock loads and effectively remove pollutants such as dissolved organic carbon, chemical oxygen demand (COD), ammonia nitrogen, total phosphorus, suspended solids, and biochemical oxygen demand (BOD) from wastewater. The resulting reclaimed water is relatively stable, and its advantages in deep wastewater treatment are widely recognized.

[0003] Research on the pollutant purification mechanism of soil infiltration systems mainly includes removal mechanisms, influencing factors, and reaction kinetic models. Process optimization and control include the impact of process design (soil type, effective soil layer thickness, filling medium, etc.) and operating conditions (hydraulic load, water distribution method, etc.) on the operational effectiveness and stability of the soil infiltration system. Currently, soil infiltration systems have seen significant development and are widely used in practical engineering projects. For example, by 1987, the United States had over 1,000 officially operating soil infiltration systems, treating 25% of total wastewater discharge; in Tucson and Phoenix, Arizona, secondary treated effluent is used for irrigation and supplementary water after soil infiltration. Australia has transformed the 90-year-old Weribe Ranch wastewater land treatment system into a large-scale integrated wastewater treatment system; Israel's largest wastewater reuse project, the Tel Aviv soil infiltration wastewater treatment plant, has a treatment capacity of 270,000 m³. 3 / day, serving 1.3 million users. The Shenyang University of Technology soil infiltration and greywater reuse demonstration project has a wastewater treatment capacity of 50m³. 3 / day, organic loading is 11.5g BOD5 / m 2 / day, the removal rates of BOD5, SS and NH4-N were 95.9%, 87.8% and 87.9%, respectively; the soil infiltration system of the Shandong Branch of China Women's University has a treatment capacity of 800m³. 3 The system treats wastewater from washing facilities and canteens daily, ensuring effluent meets discharge standards. Simultaneously, it utilizes nitrogen and phosphorus in the wastewater to supply plant growth, achieving wastewater resource utilization. Currently, Martinez et al. have developed a pig farm wastewater purification process called "Solepur," consisting of three process units: an artificial soil infiltration system for applying excess wastewater, denitrification treatment of the soil system effluent with raw water, and use of the denitrified effluent for farmland irrigation. This process achieves a removal rate of over 90% for COD, TN, and TP. However, soil infiltration systems are not yet widely used in livestock and poultry wastewater treatment. Despite their numerous advantages, they meet the requirements for treating livestock and poultry farm wastewater and therefore have excellent application prospects.

[0004] Soil infiltration systems are effective in removing organic matter and total phosphorus during wastewater treatment, but their effectiveness in removing total nitrogen needs improvement. Nitrogen removal pathways in soil infiltration systems mainly include biological nitrification / denitrification, plant uptake, soil fixation, and ammonia volatilization, with biological nitrification / denitrification being the most significant. Carbon source is usually the main factor affecting biological denitrification in soil infiltration systems. When the influent C / N ratio is less than 3, the system's carbon source supply is insufficient, thus inhibiting the activity of denitrifying bacteria and hindering nitrogen removal.

[0005] Therefore, in response to the problems of high nitrogen concentration and imbalanced carbon-nitrogen ratio in pig farm wastewater, this study investigates the impact of using the system influent as a carbon source and combining intermediate influent diversion with a floating bed with suspended packing material on the number of denitrifying microorganisms and changes in oxidation-reduction potential (ORP) in the system. This provides a theoretical basis and data support for optimizing system operating parameters, improving wastewater treatment efficiency, and achieving efficient and low-cost treatment of pig farm wastewater using a soil infiltration system.

[0006] In existing technologies, Wu Xuanyun et al. used indoor soil column tests to simulate soil infiltration systems, investigating the removal effects of six matrix combinations—soil, anthracite, activated carbon, soil + anthracite, soil + activated carbon, and soil + anthracite + activated carbon—on ammonia nitrogen and total phosphorus in wastewater. The soil + anthracite + activated carbon matrix combination showed the best removal effect and could replace soil. However, the micropores of the matrix material are easily clogged, losing activity and increasing costs, and it is only suitable for treating low-concentration domestic wastewater (Wu Xuanyun et al., Research on the Treatment of Domestic Wastewater by Infiltration Systems with Different Matrix and Soil Combinations. Modern Chemical Industry, 2014). Yan Yanan et al. used a modified septic tank / underground soil infiltration system to treat rural domestic wastewater in some rural areas of Shanghai. Through improved design of the structure and reasonable selection of parameters, the average removal rates of BOD5, COD, ammonia nitrogen, TP, and SS in the wastewater were 95%, 93%, 80%, 89%, and 98%, respectively. The overall operating cost of the wastewater treatment system was approximately 0.15-0.20 yuan / m³. 3The process is stable, the effluent quality is significant, the operation is simple, the maintenance cost is low, and it has certain ecological and economic value. The effluent quality meets the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). However, the system has strict requirements on the influent concentration and the tank size should not be too large, which seriously limits the treatment effect of large amounts of wastewater (Yan Yanan et al., Improved Septic Tank / Groundwater Infiltration System for Rural Domestic Wastewater Treatment. China Water & Wastewater, 2011). Liang Chenglong used a biochar combined with aeration strategy to enhance the decontamination effect of the soil infiltration system. He found that under high hydraulic load conditions, insufficient denitrification led to a decrease in total nitrogen removal efficiency and required the supplementation of carbon source. The influent concentration should not be too high, which is not conducive to its widespread application (Liang Chenglong, Research on Biochar Combined with Aeration to Enhance Soil Infiltration System for Rural Domestic Wastewater Treatment. Northwest A&F University Dissertation, 2019). In summary, the soil infiltration treatment system is mainly used for urban and rural domestic wastewater treatment, and no engineering application cases have been found in the aquaculture industry. Currently, pig farm wastewater and manure wastewater generally employ a process of solid-liquid separation pretreatment – ​​anaerobic / aerobic treatment – ​​advanced treatment. However, the high suspended solids content in this wastewater leads to large sludge production, easily clogging and damaging equipment. High pollution loads (e.g., COD, TN, TP) increase chemical dosage and operating costs, and the effluent quality often fails to meet the requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-202), particularly with excessive TN, TP, and SS levels, making safe discharge impossible. Therefore, a soil infiltration system using a suspended packing floating bed with intermediate influent flow is beneficial for further enhancing nitrogen and phosphorus removal, removing suspended solids, innovating wastewater treatment technology, reducing wastewater treatment costs, and minimizing direct discharge of wastewater into water bodies or groundwater pollution through surface runoff and infiltration. Constructing an infiltration system primarily using soil as the packing material, and enhancing its performance and treatment capacity through substrate improvement and operational control, provides a theoretical basis and technical support for the engineering application of soil infiltration systems. Summary of the Invention

[0007] The purpose of this invention is to provide a method and apparatus for treating wastewater using a soil infiltration system with a suspended packing floating bed and intermediate influent diversion. This method offers advantages such as high efficiency, stability, shock resistance, and ease of management and operation. It further enhances nitrogen and phosphorus removal and suspended solids removal, while reducing costs. It also solves problems such as low dissolved oxygen content in the influent and wastewater within the system, which is detrimental to nitrifying bacteria growth, poor hydraulic distribution conditions, and low effective volume utilization. The apparatus of this invention does not require replacement of packing material or addition of mechanical aeration equipment during use, offering advantages such as low cost, no chemical reagent addition, and good results. Therefore, the suspended packing floating bed-intermediate influent diversion soil infiltration system process can be flexibly optimized and its operation adjusted according to changes in water quality and quantity during actual operation, minimizing operating costs.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A suspended packing floating bed device includes an SBR reactor, suspended packing balls, an aeration device, a sludge return pipe, and an overflow pipe. The SBR reactor has an upper orifice plate at its upper and lower ends, with the suspended packing balls positioned between the upper and lower orifice plates. The aeration device is located below the lower orifice plate. An inlet pipe is located at the lower external end of the SBR reactor. On the opposite side of the inlet pipe, one end of a tee pipe is connected to the lower external end of the SBR reactor, and the other end of the tee pipe is connected to a sludge discharge pipe. The middle pipe of the tee pipe is connected to the upper external end of the SBR reactor. The overflow pipe is located above the upper orifice plate.

[0010] In the suspended packing floating bed device described above, preferably, within the SBR reactor, the upper and lower perforated plates are evenly divided into four compartments by partitions. The inner wall of the SBR reactor has slots for fixing the partitions. The first compartment near the front of the tank is the anaerobic compartment, the middle two are facultative compartments, and the fourth compartment is the aerobic compartment. The suspended packing material in the anaerobic compartment is type C-Ⅰ, while the suspended packing material in the facultative and aerobic compartments is type C-Ⅱ. During operation, the dissolved oxygen concentrations in the different compartments are as follows: less than 0.5 mg / L in the anaerobic compartment, 0.5-0.8 mg / L in the facultative compartment, and 2-4 mg / L in the aerobic compartment.

[0011] In the aforementioned suspended packing floating bed device, preferably, an annular water distribution pipe is also provided at the bottom of the SBR reaction tank, and the annular water distribution pipe is connected to the inlet pipe.

[0012] A soil infiltration system comprises, from top to bottom, a plant layer, a topsoil layer, a soil-river sand mixture layer, a gravel support layer, and a sand and gravel filter layer. An inlet pipe is provided between the topsoil layer and the soil-river sand mixture layer, an intermediate diversion pipe is provided between the soil-river sand mixture layer and the gravel support layer, a water collection pipe is provided inside the sand and gravel filter layer, and a drainage pipe is provided around the sand and gravel filter layer. The inlet pipe, the intermediate diversion pipe, and the water collection pipe are all provided with multiple infiltration holes.

[0013] In the soil infiltration system described above, preferably, the inlet pipe, intermediate branch pipe, and collection pipe are provided in multiple locations, which are evenly arranged.

[0014] In the soil infiltration system described above, preferably, the thickness of the topsoil layer is 30-40cm, the thickness of the soil-river sand mixture layer is 90-120cm, the thickness of the gravel support layer is 40-60cm, and the gravel support layer is filled with gravel material with a diameter of 20mm-30mm; the thickness of the sand and gravel filter layer is 50-60cm; the diameter of the inlet pipe, intermediate branch pipe and water collection pipe is 100-120mm, and the diameter of the drainage pipe is 140-160mm.

[0015] A method for treating aquaculture wastewater using a suspended packing floating bed combined with a soil subsurface infiltration system includes the following steps:

[0016] S1. After passing through the hydrolysis tank, the aquaculture wastewater is passed through the suspended packing floating bed device as described above. The effluent is then sent to the sedimentation tank, and the wastewater from the suspended packing floating bed is returned to the suspended packing floating bed for secondary treatment.

[0017] S2. Wastewater from the sedimentation tank is returned to the hydrolysis tank;

[0018] S3. The effluent from the sedimentation tank enters the soil infiltration system.

[0019] In the method described above, preferably, the suspended packing content in the floating bed accounts for 10-50% of the total volume between the upper and lower orifice plates, and most preferably 30%. The suspended packing in the anaerobic tank is of type CI, and the suspended packing in the facultative and aerobic tanks is of type C-II.

[0020] As described above, preferably, the soil subsurface infiltration system comprises, from top to bottom, a plant layer, a topsoil layer, a soil-river sand mixture layer, a gravel support layer, and a sand and gravel filter layer. An inlet pipe is provided between the topsoil layer and the soil-river sand mixture layer, an intermediate diversion pipe is provided between the soil-river sand mixture layer and the gravel support layer, a water collection pipe is provided inside the sand and gravel filter layer, and a drainage pipe is provided around the sand and gravel filter layer. The inlet pipe, the intermediate diversion pipe, and the water collection pipe are all provided with multiple infiltration holes.

[0021] In the method described above, preferably, the ratio of the inflow volume of the intermediate diversion pipe to the inflow pipe is 1 to 2:1, and most preferably, the ratio of the inflow volume of the intermediate diversion pipe to the inflow pipe is 1:1. When the inflow volume is equal to the outflow volume, the turnover efficiency of sewage in the bed can be accelerated and the recycling intensity of the bed can be improved.

[0022] As described above, preferably, the hydraulic load of the soil subsurface infiltration system is 0.5m. 3 / m 2 / d.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) The suspended packing floating bed provided by this invention has a large specific surface area, is easy to form biofilms, and can effectively cut air bubbles, which can significantly improve the oxygen utilization rate of the bioreactor. When the packing addition rate is 50%, under the same air-to-water ratio as ordinary aeration tank, the oxygenation capacity and oxygenation speed can be increased to more than twice that of the unpacked tank. When the suspended packing floating bed is running, the moving water body will cause the suspended packing in the floating bed to roll and ripple together, which increases the full contact between the biofilm on the packing and the sewage. At the same time, the number of microorganisms in the packing floating bed is greater, the biological activity and efficiency are higher, and the resistance to shock loads is stronger.

[0025] (2) The suspended media floating bed for treating aquaculture wastewater does not require sludge inoculation during startup and can directly support biofilm cultivation, making it convenient to operate and manage. At a dosage rate of 30%, the suspended media floating bed exhibits high removal rates for COD, SS, BOD5, TN, and TP under the same hydraulic retention time and air-to-water ratio conditions as a conventional aeration tank. Furthermore, since the media does not require support devices and does not clump, only an aeration tank at the front end of the wastewater treatment process and a screen with a particle size smaller than the media at the effluent outlet are needed to prevent media loss, making it easy to apply in aquaculture wastewater treatment processes.

[0026] (3) Soil infiltration system is a wastewater purification technology based on natural ecological principles and aimed at energy conservation. It is a composite purification process that integrates soil, filler, microorganisms, and plants to treat domestic wastewater. By rationally designing the system shape and area, it can flexibly utilize land resources and achieve better effluent quality, while having the advantage of low operating costs.

[0027] (4) In this invention, the soil infiltration system uses an upper inlet pipe and an intermediate diversion pipe regulating device to control the inflow and outflow of water, improving the applicability and feasibility of the intermediate diversion process. Simultaneously, the use of alternating wet and dry operation (where stopping water supply to the infiltration system until no water flows out of the outlet pipe constitutes dry operation, increasing the oxygen concentration in the bed's pores) not only improves the system's denitrification efficiency but also alleviates system blockage. Monitoring changes in the oxidation-reduction potential (ORP) of filter layers at different depths and supplementing with carbon sources enhances the system's denitrification capacity. The use of novel composite packing enhances system denitrification, while different packing ratios achieve optimal denitrification efficiency. When the soil infiltration system is used in conjunction with a suspended packing floating bed, appropriate addition of an external carbon source (when the BOD / COD ratio in the wastewater is less than 0.35, an external carbon source is added, as in this state, non-biodegradable organic matter dominates, requiring the addition of a carbon source with good biodegradability) effectively improves denitrification efficiency and reduces groundwater pollution caused by a lack of carbon sources in the system. This provides a new approach for the efficient and low-cost treatment of pig farm wastewater and the design of soil infiltration systems.

[0028] This invention provides a device for treating wastewater using a suspended packing floating bed combined with a soil infiltration system. This device effectively enhances nitrogen and phosphorus removal and suspended solids removal, solving problems such as low dissolved oxygen content in the influent and wastewater within the system, which hinders the growth of nitrifying bacteria, poor hydraulic conditions, numerous dead zones where wastewater cannot flow, and low effective volume utilization. During operation, it eliminates the need to replace packing materials or add mechanical aeration equipment. It offers advantages such as low investment cost, no need for chemical treatment, significant therapeutic effect, low mosquito breeding, simple operation and management, and environmental beautification. It has significant ecological and economic benefits in promoting the deep purification of aquaculture wastewater. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a wastewater treatment process based on a suspended packing floating bed-soil underground infiltration system.

[0030] Figure 2 This is a schematic diagram of the engineering structure of an SBR reactor and a floating bed aquaculture wastewater treatment device.

[0031] Figure 3 A schematic diagram of the engineering structure of a soil underground infiltration system for deep treatment of aquaculture wastewater. Detailed Implementation

[0032] This invention requires that the influent wastewater to be treated have the following characteristics: COD < 1500 mg / L, BOD5 < 500 mg / L, SS < 600 mg / L, NH3-N < 800 mg / L, TN < 1000 mg / L, TP < 100 mg / L, and pH 6.5-8.5; the effluent should have the following characteristics: COD < 50 mg / L, BOD5 < 20 mg / L, SS < 30 mg / L, NH3-N < 40 mg / L, and TN < 1000 mg / L, with a pH of 6.5-8.5; N < 50 mg / L, TP < 5 mg / L and pH value 6.5-8.5; COD, BOD5, SS, NH3-N, TN and TP removal rates are higher than 97%, 96%, 95%, 95%, 95% and 95%, respectively, that is, the treated wastewater has COD < 45 mg / L, BOD5 < 20 mg / L, SS < 30 mg / L, NH3-N < 40 mg / L, TN < 50 mg / L and TP < 5 mg / L.

[0033] This invention provides a soil infiltration system with a suspended packing floating bed and intermediate water inlet flow mode. Figure 1As shown in the figure, this method is beneficial for further enhancing the effects of nitrogen and phosphorus removal and suspended solids removal. It solves problems such as low dissolved oxygen content in the influent and sewage within the system, which is not conducive to the growth of nitrifying bacteria, poor hydraulic conditions of the system, a large number of dead zones where sewage cannot flow through, and low effective volume utilization rate of the system. It explores a method that is simple in principle, fast in construction, low in cost, and has good harmless effect. Sewage is purified through capillary infiltration and soil filtration, utilizing the natural purification system of soil-plant-microorganisms. Through physical sedimentation, interception, chemical adsorption, and microbial degradation, the sewage is purified. It has the advantages of low cost, obvious treatment effect, less mosquito breeding, simple operation and management, and environmental beautification. It has significant ecological and economic benefits for promoting the deep purification of aquaculture sewage.

[0034] (1) The purpose of this invention is achieved through the following technical solution: A suspended packing floating bed is a highly efficient wastewater treatment method that combines the advantages of traditional fluidized bed and biological contact oxidation processes. First, a suspended packing material with a density similar to water is directly added to the aeration tank as an active carrier for microorganisms. It is fluidized by the aeration and water flow in the aeration tank, allowing the wastewater to fully contact the biofilm on the packing material. Because the suspended packing material has a large specific surface area, the number and types of microorganisms attached to the surface and inside the packing material are large, forming a food chain from bacteria to protozoa to metazoa within the packing unit, which accelerates the degradation and purification of pollutants in the wastewater. At the same time, through the mutual collision between the suspended packing materials in the fluidized state, the aging biofilm gradually falls off on its own. Because the biological sludge that falls off the biofilm has a large density and good sludge settling performance, it is easy to separate solids and liquids, so the effluent quality is good. Specifically, the volume of the suspended packing floating bed occupies 60%-80% of the SBR reactor volume. After successful biofilm formation on the suspended packing floating bed, a large number of aerobic and anaerobic microorganisms attach to and multiply on the suspended packing balls, forming a fixed microbial filter membrane layer. The porous structure of the suspended packing balls in the suspended packing floating bed serves as a channel for microorganisms to take in food, oxygen, and excrete metabolites, allowing the microbial filter membrane layer attached to the suspended packing balls to simultaneously possess aerobic, facultative anaerobic, and anaerobic microenvironments. This enables aerobic decomposition of organic matter and nitrification of ammonia nitrogen, as well as anaerobic hydrolysis and denitrification processes. Due to the internal mass transfer, nitrification / denitrification and hydrolysis / aerobic oxidation processes can occur sequentially within the same suspended packing ball, thus improving the nitrogen removal efficiency of the biological sludge. The suspended packing floating bed achieves solid-liquid separation through sedimentation of the sloughed biofilm and suspended solids in the water. The supernatant is discharged from the top outlet, and part of the concentrated sludge liquid is returned through the sludge return pipe, while part of the sludge liquid is discharged. This achieves the purpose of retaining microorganisms to control the sludge age and ensuring the phosphorus removal effect of the process.

[0035] The dimensions of the suspended packing floating bed are set at 8m × 10m × 3.5m, and the interior is divided into 4 equal compartments. The first compartment at the front of the tank is an anaerobic compartment, the two middle compartments are facultative anaerobic compartments with intermittent micro-aeration, and the fourth compartment is an aerobic compartment with aeration. Wastewater flows through the hydrolysis tank and enters the suspended packing floating bed, operating in an anaerobic / anoxic / aerobic mode. A suspended packing floating bed device includes an SBR reactor, suspended packing balls, an aeration device, a sludge return pipe, and an overflow pipe. The SBR reactor has an upper perforated plate and a lower perforated plate at its upper and lower ends. The suspended packing balls are located between the upper and lower perforated plates, and the aeration device is located above and below the lower perforated plate. An inlet pipe is located at the lower external end of the SBR reactor. On the opposite side of the inlet pipe, one end of a tee pipe is connected to the lower external end of the SBR reactor, and the other end of the tee pipe is connected to a sludge discharge pipe. The middle pipe of the tee pipe is connected to the upper external end of the SBR reactor. An overflow pipe is connected to the upper external end of the SBR reactor, and the overflow pipe is located above the upper perforated plate. The upper and lower perforated plates are divided into four equal sections, each separated by a partition and connected in series by water pipes. The tank body has slots for securing the partitions. The first section at the front is the anaerobic tank, the two middle sections with intermittent micro-aeration are facultative anaerobic tanks, and the fourth section with aeration is the aerobic tank. C-I type suspended packing material with a specific surface area of ​​180 m² is added to the anaerobic tank. 2 / m 3 C-II type suspended packing material with a specific surface area of ​​400 m² was added to both the anaerobic and aerobic tanks. 2 / m 3 Type C-I and C-II suspension packings, due to their large specific surface area, can maintain a large biofilm quantity and biological activity under fluidized conditions, with a volumetric loading rate typically reaching 3-10 kg BOD5 / (m³). 3 / d), which has good organic matter degradation ability and shock resistance, stable effluent quality and small footprint. Among them, the suspended packing floating bed is connected to a horizontal flow sedimentation tank with a size of 12m×20m×6m, which is mainly used to achieve solid-liquid separation by natural sedimentation of suspended solids and reduce the concentration of suspended solids in the effluent.

[0036] (2) The objective of this invention is achieved through the following technical solution: a soil infiltration system structure as follows Figure 3 As shown, the area of ​​the single-unit percolation system is 30m². 2 (Length × Width × Depth, 6m × 5m × 2.1m), the total thickness of the system filler is 210cm, of which 9 represents ryegrass planted within the system at a planting density of 50 plants / m². 2The structure consists of: 10 a 30cm thick topsoil layer; 11 a 100mm diameter PVC inlet pipe; 12 a 90cm thick soil-river sand mixture layer; 13 a middle branch pipe; 14 a 40cm thick gravel support layer filled with 20-30mm diameter gravel; 15 a 100mm diameter PVC collection pipe; 16 a 50cm thick sand and gravel filter layer; and 17 a 160mm diameter PVC drainage pipe that allows effluent to enter the soil diffusion system. To ensure uniform water distribution, there are 20 inlet pipes and 20 branch pipes, laid to depths of 20cm and 80cm respectively. The hydraulic load (HLR) of the infiltration system is set to 0.5m. 3 / m 2 / d, meaning the influent flow rate of a single infiltration system is 15m³. 3 / d. Inlet flow rate of the intermediate branch pipe in the infiltration system (m³) 3 / d) and the water inflow rate of the upper inlet pipe (m 3 The ratio of / d) is the diversion ratio of the soil infiltration system. Based on the different diversion ratios, the soil infiltration system is divided into 4 types. The setting of the diversion ratio and the diversion water volume are shown in Table 1. The specific influent water quality is as described above.

[0037] Table 1. Water inflow of soil subsurface infiltration system under four different flow ratios.

[0038]

[0039] (3) The objective of this invention is achieved through the following technical solution: To periodically monitor changes in the water quality of the system's influent and effluent, the analytical methods for COD, SS, TN, BOD5, and TP in the water samples are based on the standard methods in "Water and Wastewater Monitoring and Analysis Methods". Specifically, COD is determined using the potassium dichromate method, SS using the gravimetric method, TN using the potassium persulfate oxidation-ultraviolet spectrophotometric method, BOD5 using the dilution inoculation method, and TP using the ammonium molybdate spectrophotometric method. Electrodes are pre-embedded at depths of 50, 140, and 180 cm in the system's packing layer to monitor changes in the oxidation-reduction potential (ORP) within the packing layer. Samples are collected from the packing layer at different depths (50, 140, and 180 cm), and the quantities of ammonifying bacteria, nitrifying bacteria, nitrifying bacteria, and denitrifying bacteria in the packing samples are determined according to the standard methods in "Modern Microbiology Experimental Techniques".

[0040] The following embodiments are used to further illustrate the present invention, but should not be construed as limiting the present invention. Any modifications or substitutions made to the present invention without departing from its spirit and essence are within the scope of the present invention.

[0041] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, all reagents used in this method are of analytical grade or higher.

[0042] Example 1: Application Case of a Suspended Packing Floating Bed Combined with Soil Subsurface Infiltration System

[0043] In 2022, a demonstration project of a suspended packing floating bed combined with soil subsurface infiltration system was carried out in the pig farm wastewater deep treatment park in Guyuan Village, Tongmu Town, Jinxiu Yao Autonomous County, Laibin City, Guangxi Zhuang Autonomous Region. The specific operation process is as follows:

[0044] A suspended media floating bed combined with a soil subsurface infiltration system provides a new approach for the efficient and low-cost treatment of pig farm wastewater. This system enhances the system's resistance to shock loads, regulates the influent and effluent flow rates of the soil subsurface infiltration system using an upper inlet pipe and a middle diversion pipe, and improves the system's denitrification efficiency through dry-wet operation. The system and apparatus mainly include the design of the suspended media floating bed and soil subsurface infiltration system, as well as the analysis of the system's effluent quality.

[0045] (1) Design of suspended packing floating bed and soil infiltration system

[0046] The size of the suspended packing floating bed can be set to 8m×10m×3.5m, and it is divided into 4 compartments according to the partition of the tank body. The side wall of the tank body is equipped with slots for fixing the partitions. The middle 2 compartments are intermittently micro-aerated and are in an anaerobic state (in order to balance the rate of nutrient consumption and oxygen supply intensity in the wastewater, a cycle mode of micro-aeration for 1 hour and aeration stop for 1 hour is adopted); continuous aeration is carried out and is in an aerobic state (the packing layer can also be divided into two layers to improve the micro-aeration efficiency). Anaerobic tanks do not use an aeration system; dissolved oxygen levels are controlled below 0.2 mg / L, and pollutant concentrations are relatively high. Only suspended packing material is used, suitable for anaerobic microbial activity. Anoxic tanks have insufficient or no aeration; dissolved oxygen levels are controlled below 0.5 mg / L. Suspended packing material is used, and submersible mixers can be employed for micro-aeration. Organic matter requiring treatment is degraded and utilized by facultative microorganisms and biofilms. Aerobic tanks have dissolved oxygen levels of 2-4 mg / L, using suspended packing material and continuous aeration with submersible mixers. Wastewater flows through a hydrolysis tank into a suspended packing floating bed, operating sequentially in anaerobic / anoxic / aerobic modes. Specifically, for example... Figure 2As shown, the suspended packing floating bed device includes an SBR reactor 1. The SBR reactor 1 has an upper perforated plate 21 and a lower perforated plate 23 at its upper and lower ends, respectively. The upper perforated plate 21 and the lower perforated plate 23 are divided into four compartments by a partition. The first compartment near the front of the reactor is an anaerobic compartment, the middle two are facultative anaerobic compartments, and the fourth compartment is an aerobic compartment. The side wall of the reactor has slots for fixing the partitions. The partitions have multiple through holes in the middle, with a through hole between the upper perforated plate 21 and the lower perforated plate 23. The SBR reactor contains suspended packing balls 22, with a floating bed 2 in the middle. An intermittent aeration device 3 is located at the lower end of the SBR reactor, below the lower orifice plate 23. An inlet pipe 4 is located at one end of the lower exterior of the reactor 1, and a ring-shaped water distribution pipe 5 is located at the lower interior of the reactor 1. A three-way pipe is located at the other end of the lower exterior of the reactor 1, with one end connected to a sludge return pipe 6 and the other end connected to a sludge discharge pipe 7. An overflow pipe 8 is located at the upper end of the SBR reactor 1, above the upper orifice plate 21. C-Ⅰ type suspended packing (honeycomb packing, HDPE material, available from Nanjing Green Island Environmental Engineering Co., Ltd.) with a specific surface area of ​​180 m² is added to the anaerobic tank. 2 / m 3 Add C-II type suspended packing material (melon-shaped packing material, polyurethane material, available from Nanjing Green Island Environmental Engineering Co., Ltd.) with a specific surface area of ​​400 m² to the anaerobic and aerobic tanks. 2 / m 3 Type C-I and C-II suspension packings, due to their large specific surface area, can maintain a large biofilm quantity and biological activity under fluidized conditions, with a volumetric loading rate typically reaching 3-10 kg BOD5 / (m³). 3 It has good organic matter degradation ability and shock resistance, stable effluent quality and small footprint. During operation, the dissolved oxygen concentration in different tanks is as follows: the dissolved oxygen concentration in the anaerobic tank is less than 0.5 mg / L, the dissolved oxygen concentration in the facultative tank is 0.5-0.8 mg / L, and the dissolved oxygen concentration in the aerobic tank is 2-4 mg / L.

[0047] A soil infiltration system, with the following structure Figure 3 As shown, the area of ​​the single-unit percolation system is 30m². 2 (Length × Width × Depth, 6m × 5m × 2.1m), the total thickness of the system filler is 210cm, consisting of a plant layer, a topsoil layer, a soil-river sand mixture layer, a gravel support layer, and a sand and gravel filter layer from top to bottom. The plant layer consists of ryegrass 9 planted within the system, with a planting density of 50 plants / m². 2The topsoil layer 10 is 30cm thick. A 100mm diameter PVC inlet pipe 11 is installed between the topsoil layer and the soil-river sand mixture layer. The soil-river sand mixture layer 12 is 90cm thick. An intermediate diversion pipe 13 is installed between the soil-river sand mixture layer 12 and the gravel support layer 14. The gravel support layer 14 is 40cm thick and filled with gravel material with a diameter of 20mm-30mm. The sand and gravel filter layer 16 is 50cm thick. A 100mm diameter PVC collection pipe 15 is installed inside the sand and gravel filter layer. A 160mm diameter PVC drainage pipe 17 is installed on the outside of the sand and gravel filter layer, perpendicular to the collection pipe 15, so that the effluent enters the soil diffusion system. To ensure uniform water distribution, there are 20 inlet pipes and 20 intermediate diversion pipes, laid to depths of 20cm and 80cm respectively. The hydraulic load (HLR) of the infiltration system is set to 0.5m. 3 / m 2 / d, meaning the inflow rate of a single independent soil infiltration system is 15m³. 3 / d. Among them, the water inlet pipe 11 is the effluent from the suspended packing bed; the function of the intermediate diversion pipe 13 is to redistribute the sewage that has passed through the surface soil of the soil infiltration system evenly; the function of the collection pipe 15 is to collect the sewage that has passed through the gravel layer; all pipes are equipped with infiltration holes, and the sewage flows out naturally inside the filter layer by gravity.

[0048] A method for treating aquaculture wastewater using a suspended packing floating bed combined with a soil subsurface infiltration system includes the following steps:

[0049] S1. After passing through the hydrolysis tank, the aquaculture wastewater is fed into the sedimentation tank via the suspended packing floating bed device. The wastewater from the suspended packing floating bed is then returned to the suspended packing floating bed for secondary treatment.

[0050] S2. Wastewater from the sedimentation tank is returned to the hydrolysis tank;

[0051] S3. The effluent from the sedimentation tank enters the soil infiltration system. The hydrolysis tank's function is to decompose solids, large molecules, and non-degradable organic matter in the wastewater into smaller molecules and biodegradable substances, improving the wastewater's biodegradability. A high-resistance water distribution system is installed at the bottom of the hydrolysis tank, ensuring uniform water intake and thorough mixing. It does not require a high-powered agitator, and a sludge conveying device prevents settling. No sludge scraper or sludge pump is needed within the sedimentation tank. The entire hydrolysis tank has a simple structure, requires minimal power, and can be designed in a square shape, saving land. The returned sludge from the sedimentation tank agitates the sludge at the bottom of the hydrolysis acidification tank, keeping it in suspension and thoroughly mixing it with the incoming wastewater, thereby improving the treatment efficiency of the hydrolysis tank and reducing the load on subsequent aerobic treatment. Returning sludge from the sedimentation tank to the hydrolysis tank increases the sludge concentration, improving treatment efficiency. Simultaneously, the sludge is digested, reducing the amount of excess sludge discharged and lowering sludge treatment costs. The bottom of the sedimentation tank is sloping, and there is a sludge valve at the lowest point of the bottom. The sedimentation tank is also equipped with multiple directional flow inclined plates. The sedimentation tank also includes an effluent trough and multiple overflow pipes. The overflow pipe outlets are collected in the effluent trough and enter the soil underground infiltration system.

[0052] (2) Screening study on the optimal addition rate of suspended packing in floating bed

[0053] The suspended packing in the floating bed was set with four suspension packing addition rates (the volume of the suspended packing between the upper and lower orifice plates of the SBR reactor), namely 0%, 10%, 30%, and 50%. Among them, the suspended packing in the anaerobic tank was of type CI, and the suspended packing in the facultative and aerobic tanks was of type C-II. The suspended packing was added to each tank on an average basis. The operation results of the demonstration project are shown in Table 2. The results showed that without the addition of suspended packing, the removal rates of COD, BOD5, SS, TN, and TP were 7.88%, 6.02%, 7.69%, 7.45%, and 11.96%, respectively; with a suspended packing addition rate of 10%, the removal rates were 42.9%, 76.6%, 75.6%, 77.7%, and 48.9%, respectively; with a suspended packing addition rate of 30%, the removal rates were 90.8%, 82.2%, 85.7%, 88.9%, and 82.6%, respectively; and with a suspended packing addition rate of 50%, the removal rates were 80.5%, 80.5%, 84.2%, 87.5%, and 76.1%, respectively. Therefore, a 30% packing material addition rate is preferred, which has a high removal rate for major pollutants and ensures that the biofilm does not detach due to violent movement of the packing material during aeration, thus achieving stable system operation.

[0054] Table 2 Treatment effect of suspended packing floating bed under different suspended packing addition rates

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[0056] (3) Study on the effect of different diversion ratios on pollutant removal in soil subsurface infiltration systems

[0057] Preferably, the effluent with a suspended packing material dosage of 30% was used as the influent under different split ratios, i.e., COD 135 mg / L, BOD5 83 mg / L, SS 76 mg / L, TN 107 mg / L, and TP 16 mg / L. Table 3 shows the removal efficiency of the soil infiltration system for pollutants in pig farm wastewater under different split ratios (i.e., the ratio of influent flow from the influent pipe to the intermediate split pipe). As shown in Table 3, under all four split ratios, the system achieved high COD removal rates, with an average removal rate exceeding 90%. Increasing the split ratio did not affect SS removal. The soil infiltration system primarily removes SS through the adsorption and retention by the packing material layer and plant roots, as well as the sedimentation of SS itself. No waterlogging occurred under any of the four split ratios. Meanwhile, when the split ratios were 0:1, 1:3, 1:2, and 1:1, the soil infiltration system exhibited high removal efficiencies for BOD5 and TP. However, with further increases in the split ratio, the removal rates of BOD5 and TP decreased slightly. When the split ratio increased to 1:1, the removal rates of BOD5 and TP decreased to 81.4% and 84.4%, respectively. The removal of COD and BOD5 by the soil infiltration system mainly relied on plant uptake and the action of microorganisms in the packing layer, while phosphorus removal mainly relied on the adsorption and precipitation of the packing layer and plant uptake. The removal of TN by the soil infiltration system increased significantly with increasing split ratio, reaching a peak at 1:2, and then decreased at 1:1. As the system separation ratio increased, the residence time of wastewater in the system became very short, which was not conducive to the removal of COD and phosphorus, leading to a decrease in the removal efficiency of COD and phosphorus by the soil infiltration system. Nitrogen is the most difficult pollutant to remove during the operation of soil infiltration systems. A split-flow influent method can effectively improve the nitrogen removal capacity of soil infiltration systems. When the split ratio is 0:1, the system lacks the carbon source required for denitrification, resulting in poor nitrogen removal. When the split ratio is 1:3 and 1:2, the split influent provides the carbon source needed for denitrification, thus improving the system's nitrogen removal capacity to some extent. When the split ratio increases to 1:1, due to the large influent volume and poor aeration of the packing layer at the intermediate split pipe, dissolved oxygen is insufficient, which is not conducive to nitrification. This causes some ammonia nitrogen in the wastewater to flow out of the system before completing the nitrification process, leading to a decrease in the system's nitrogen removal rate. Therefore, when the split ratio is 1:2, the soil infiltration system has a better pollutant removal effect.

[0058] Table 3 Treatment effects of soil infiltration system under four split ratios

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[0060]

[0061] (4) Comparative study on the number of denitrifying microorganisms in the system under different split ratios

[0062] Under the condition of a 30% suspended filter media addition rate, the nitrogen removal effect of the soil infiltration system at different split ratios and under different filter layers is correlated with the number of ammonifying bacteria, nitrifying bacteria, nitrifying bacteria, and denitrifying bacteria in the system. The MPN multiple tube fermentation method was used to detect the number of these nitrogen-depleting microorganisms in the filter media layer at different depths of the soil infiltration system when the split ratios were 0:1, 1:3, 1:2, and 1:1. The results are shown in Table 4. Table 4 shows that when the split ratio is 0:1, the number of ammonifying bacteria, nitrifying bacteria, and nitrifying bacteria is highest at 50 cm of the filter media layer; followed by 140 cm; and lowest at 180 cm. When the split ratio increases to 1:1, the number of ammonifying bacteria, nitrifying bacteria, and nitrifying bacteria at 50 cm of the filter media layer does not change significantly, while the number of ammonifying bacteria increases at 140 cm and 180 cm, while the number of nitrifying bacteria and nitrifying bacteria decreases significantly. Meanwhile, when the split ratio is 0:1, the number of denitrifying bacteria in the system increases with the depth of the packing layer. When the split ratio increases to 1:1, the number of denitrifying bacteria at 140cm and 180cm in the packing layer increases to 2.9 × 10⁻⁶. 11 MPN / g and 3.4×10 10The MPN / g of the denitrifying bacteria remained relatively constant at a depth of 20 cm, while the number of denitrifying bacteria at this depth did not change significantly. Therefore, the split ratio had a substantial impact on the number of denitrifying microorganisms in the soil infiltration system, with an increase in the split ratio effectively stimulating the growth of denitrifying bacteria. Simultaneously, with increasing split ratio, the decrease in DO (dissolved oxygen) and the increase in carbon source inhibited the growth of nitrite-oxidizing and nitrifying bacteria in the 140-180 cm packing layer, causing a sharp decline in their numbers. Conversely, the increase in organic nitrogen concentration promoted the increase in ammonifying bacteria. Furthermore, the number of nitrifying bacteria in the 50-140 cm packing layer did not decrease with increasing split ratio. In conclusion, increasing the split ratio to 1:2 can enhance the denitrification effect of the soil infiltration system. Oxidation-reduction potential (ORP) comprehensively reflects the redox properties of the biochemical reactions within the infiltration system. The split ratio significantly affected the ORP changes in the packing layer at different depths (50, 140, and 180 cm) of the soil infiltration system, and the changes in ORP in the packing layer were closely related to the number of denitrifying microorganisms in the system. When the split ratio is 0:1, the ORP at 50, 140, and 180 cm in the system are 117, -85, and -162 mV, respectively. In the 50-140 cm region of the packing layer, due to the good reoxygenation effect of the system, the oxygen consumed by the degradation of pollutants in the influent is replenished in time, resulting in a higher ORP in this region. The number of nitrifying and denitrifying bacteria is large, while the number of nitrifying bacteria is small, and the oxidizing environment dominates. As the ORP value decreases, the number of nitrifying and denitrifying bacteria also decreases, and the reducing environment dominates. With increasing split ratio, the ORP at 50 cm in the packing layer does not change significantly, while the ORP at 140 cm and 180 cm decreases. When the split ratio is 1:1, the ORP at 140 cm and 180 cm in the packing layer drops to -152 and -263 mV, respectively. Therefore, as the split ratio increases, the influent flow rate at the intermediate split pipe increases, leading to a corresponding increase in oxygen consumption in the 140-180cm section of the packing layer. This results in a low ORP value in this area, with a dominant reducing environment. The number of nitrifying and denitrifying bacteria decreases sharply, while the increased carbon source and anoxic environment stimulate the growth of denitrifying bacteria, leading to an increase in the number of nitrifying bacteria in this area. The system achieves the best pollutant removal efficiency when the split ratio is 1:2. Therefore, the intermediate split measure and appropriate split ratio significantly improve the removal of total nitrogen from wastewater by the soil infiltration system, effectively solving the problem of insufficient carbon source during denitrification when treating pig farm wastewater using a soil infiltration system. This approach features simple process construction and good operational performance.Specifically, under the conditions of a flow ratio of 1:2 and a 30% packing material addition rate, the combined treatment of wastewater using a suspended packing floating bed and a soil infiltration system achieves high removal rates of COD, SS, BOD5, TN, and TP in aquaculture wastewater. The effluent quality indicators after sedimentation are: COD < 200 mg / L, BOD5 < 100 mg / L, SS < 80 mg / L, NH3-N < 100 mg / L, TN < 100 mg / L, TP < 15 mg / L, and pH 6.5-8.5. The effluent quality indicators at the outlet pipe 17 of the soil infiltration system are: COD < 15 mg / L, BOD5 < 10 mg / L, SS < 10 mg / L, NH3-N < 15 mg / L, TN < 10 mg / L, TP < 5 mg / L, and pH 6.5-8.5. This engineering scheme reduces wastewater treatment costs by 3 yuan / ton, resulting in an annual reduction of 150,000 yuan in wastewater treatment expenses.

[0063] Comparative Example

[0064] To verify the wastewater treatment effects of suspended media floating bed and soil infiltration systems, a soil infiltration purification system was set up for comparison. Specifically, the effluent from the suspended media floating bed was directly filtered and purified through a 40-100cm soil layer via a submerged pipe. This comparative example is based on effluent with a 30% suspended media ratio. The results are shown in Table 4. Specifically, after filtration and purification using a 40-100cm soil layer, the removal rates of COD, BOD5, SS, TN, and TP were 6.8%, 9.3%, 3.5%, 8.2%, and 12.4%, respectively; while the removal rates of the soil infiltration system were 81.1%, 80.5%, 83.3%, 88.0%, and 78.7%, respectively.

[0065] Table 4 Treatment effect of soil infiltration system

[0066]

[0067] In summary, the combined treatment of livestock and poultry wastewater using a suspended packing floating bed and a soil infiltration system can significantly reduce the main pollutant indicators in the wastewater, and the effluent meets the "Emission Standard of Pollutants for Livestock and Poultry Farming" (GB18596-2001). Furthermore, the system operates stably under shock load conditions and can well meet the needs of livestock and poultry wastewater treatment, thus having high application and promotion value.

Claims

1. A soil subsurface infiltration system, characterized in that, The structure consists of, from top to bottom, a plant layer, a topsoil layer, a soil-river sand mixture layer, a gravel support layer, and a sand and gravel filter layer. An inlet pipe connects the topsoil layer and the soil-river sand mixture layer; an intermediate branch pipe connects the soil-river sand mixture layer and the gravel support layer; a collection pipe is located within the sand and gravel filter layer; and a drainage pipe surrounds the sand and gravel filter layer. Each of the inlet pipe, intermediate branch pipe, and collection pipe has multiple infiltration holes. The topsoil layer is 30–40 cm thick; the soil-river sand mixture layer is 90–120 cm thick; the gravel support layer is 40–60 cm thick and filled with gravel material with a diameter of 20–30 mm; the sand and gravel filter layer is 50–60 cm thick; the inlet pipe, intermediate branch pipe, and collection pipe have diameters of 100–120 mm; and the drainage pipe has a diameter of 140–160 mm.

2. The soil subsurface infiltration system according to claim 1, characterized in that, The inlet pipe, intermediate branch pipe, and water collection pipe are provided in multiple locations, which are evenly arranged.

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