Domestic sewage treatment process

Abstract

The domestic sewage treatment process comprises the following steps: S1, pretreatment: filtering domestic sewage through a grid, introducing the filtered domestic sewage into an adjusting tank, and adding an agricultural waste derived carbon source carrier into the adjusting tank to obtain pretreated sewage; s2, enhanced nitrogen and phosphorus removal: the pretreated sewage is introduced into an enhanced tank, the enhanced tank comprises an anaerobic zone and an aerobic zone which are communicated in sequence, and a composite carrier is added into the enhanced tank; recovering the composite carrier from the effluent of the strengthening tank through a magnetic separation device to obtain strengthened treatment sewage; the composite carrier is prepared from magnetic biochar, nitrifying bacteria and denitrifying bacteria; and S3, deep purification: the sewage subjected to enhanced treatment is introduced into an artificial wetland, the artificial wetland is filled with a composite filler, aquatic plants are planted in the artificial wetland, the hydraulic retention time of the artificial wetland is controlled to be 4-6 h, and the effluent of the artificial wetland is up-to-standard discharge water. The problems of unreasonable carbon source supply mode, lack of microorganism immobilization mode, low process integration level and the like in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more specifically to a process for treating domestic wastewater. Background Technology

[0002] Domestic wastewater treatment is one of the core infrastructures for protecting the urban ecological environment and improving the quality of life for residents. Domestic wastewater from small and medium-sized towns has significant characteristics: large fluctuations in water volume, low carbon-to-nitrogen ratio (C / N), moderate pollutant concentrations, and complex composition, including recalcitrant organic matter such as detergents and kitchen grease. This places special demands on wastewater treatment processes.

[0003] Currently, wastewater treatment technologies are mainly divided into three categories: physicochemical treatment, biological treatment, and ecological treatment. Physicochemical treatment technologies are centered on coagulation and sedimentation, and chemical oxidation. A typical process is "bar screen ~ coagulation tank (adding PAC / PAM) ~ oxidation tank (adding sodium hypochlorite) ~ sedimentation tank". Its core advantages are fast treatment speed and strong resistance to shock loads, but it has disadvantages such as low denitrification efficiency, high cost, large sludge production, and difficult disposal. Biological treatment technologies are centered on microbial metabolism. The mainstream processes include A / O (anaerobic-aerobic), SBR (sequencing batch reactor), and MBR (membrane bioreactor). However, due to the low carbon-to-nitrogen ratio of wastewater, it has disadvantages such as insufficient carbon source leading to incomplete denitrification, easy loss of microbial agents, and high operation and maintenance threshold. Ecological treatment technologies are centered on plants and microorganisms, such as constructed wetlands and oxidation ponds. Their advantages are low cost and no secondary pollution, but they have disadvantages such as extremely poor adaptability, large scale far exceeding the carrying capacity of small and medium-sized towns, and treatment effect significantly affected by the season.

[0004] In summary, existing technologies have failed to address the core challenges in urban domestic sewage treatment, exhibiting problems such as an unreasonable carbon source supply model, a lack of microbial immobilization methods, and low process integration. Therefore, there is an urgent need for a domestic sewage treatment process that can fundamentally resolve the shortcomings of existing technologies. Summary of the Invention

[0005] The present invention aims to provide a domestic sewage treatment process that solves the problems of unreasonable carbon source supply mode, lack of microbial immobilization method and low process integration in the existing technology.

[0006] A domestic wastewater treatment process includes: S1. Pretreatment: Domestic sewage is filtered through a screen and then fed into an equalization tank. Agricultural waste-derived carbon source carriers are added to the equalization tank, and the hydraulic retention time of the equalization tank is controlled to be 1-3 hours to obtain pretreated sewage. The agricultural waste-derived carbon source carrier is at least one of straw charcoal, rice husk charcoal, or peanut shell charcoal. S2. Enhanced nitrogen and phosphorus removal: The pretreated wastewater is fed into an enhanced tank, which includes an anaerobic zone and an aerobic zone connected in sequence. A composite carrier is added to the enhanced tank. The dissolved oxygen in the anaerobic zone is controlled to be <0.2 mg / L and the hydraulic retention time is controlled to be 2-4 h. The dissolved oxygen in the aerobic zone is controlled to be 0.5-2 mg / L and the hydraulic retention time is controlled to be 3-5 h. The effluent from the enhanced tank is treated by a magnetic separation device to recover the composite carrier, thus obtaining the enhanced treated wastewater. The composite carrier consists of magnetic biochar, nitrifying bacteria, and denitrifying bacteria. S3. Deep purification: The treated wastewater is introduced into an artificial wetland, which is filled with composite filler and planted with aquatic plants. The hydraulic retention time of the artificial wetland is controlled to be 4-6 hours. The effluent from the artificial wetland is the compliant discharge water.

[0007] Working principle and beneficial effects of the present invention: Domestic sewage is first screened to remove suspended impurities (such as plastic bags and vegetable leaves) to prevent clogging of subsequent equipment; then it enters the equalization tank, where an agricultural waste-derived carbon source carrier is added. The carrier initially adsorbs COD through its rich pores and slowly releases organic carbon, thus storing carbon source for subsequent denitrifying bacteria.

[0008] The pretreated wastewater first enters the anaerobic zone and then is fed with a composite carrier. The denitrifying bacteria in the composite carrier use the organic carbon released by the carbon source carrier to convert nitrate nitrogen into nitrogen gas. Then it enters the aerobic zone, where the nitrifying bacteria in the composite carrier oxidize ammonia nitrogen into nitrate nitrogen, and the magnetic biochar simultaneously adsorbs TP in the wastewater. The effluent from the enhanced tank is then processed by a magnetic separation device to recover the composite carrier and prevent carrier loss.

[0009] Wastewater undergoes enhanced treatment before entering constructed wetlands. Composite fillers adsorb residual pollutants, while aquatic plants absorb nitrogen and phosphorus through their roots and secrete organic matter to promote microbial growth, ensuring that the effluent meets standards.

[0010] By integrating agricultural waste carbon sources and carriers into wastewater treatment, core shortcomings such as water volume fluctuations, insufficient carbon sources, and carrier waste can be addressed.

[0011] The optimized dosage of the agricultural waste-derived carbon source carrier in S1 is 5-10 g / L; the preparation method of the agricultural waste-derived carbon source carrier is as follows: cut the agricultural waste into 5-10 cm segments, carbonize it in anoxic conditions at 300-500℃ for 2-4 h, cool it, and then grind it to a particle size of 2-5 mm.

[0012] An oxygen-deficient environment prevents the complete combustion of organic matter, preserves a rich porous structure, and at the same time disrupts the crystalline structure of cellulose, thereby improving the slow release efficiency of organic carbon.

[0013] The optimized mass ratio of magnetic biochar, nitrifying bacteria and denitrifying bacteria in the composite carrier is 100:1-3:2-4.

[0014] In the composite carrier, magnetic biochar, nitrifying bacteria, and denitrifying bacteria are configured in a mass ratio of 100:1-3:2-4. Firstly, the magnetic biochar provides sufficient attachment sites to prevent the loss of the bacterial agent. The proportion of denitrifying bacteria is higher than that of nitrifying bacteria, which is suitable for wastewater with a low carbon-to-nitrogen ratio where the carbon source for denitrification is limited and the need to prioritize nitrogen removal is required. Finally, the metabolic products of nitrifying bacteria and denitrifying bacteria mutually avoid the problem of accumulation of bacterial agent metabolites that inhibit activity.

[0015] The optimized method for preparing the magnetic biochar is as follows: iron powder, ferrous sulfate and biochar are mixed at a mass ratio of 1:0.5 to 1:10, deionized water is added to form a paste, dried at 80 to 100°C, and ground to a particle size of 0.5 to 1 mm to obtain the magnetic biochar; the biochar is straw charcoal or rice husk charcoal; nitrifying bacteria solution and denitrifying bacteria solution are added to the magnetic biochar, stirred evenly, and then allowed to stand and air dry to obtain a composite carrier.

[0016] In the optimized configuration, the magnetic field strength of the magnetic separation device in S2 is 0.1 to 0.3 T. The recovered composite carrier can be repeatedly added to the enhancement tank 3 to 5 times after being rinsed with clean water.

[0017] During carrier reuse, the phosphorus (adsorbed total phosphorus) remaining on the surface is slowly released in the anaerobic zone and can be absorbed by polyphosphate-accumulating bacteria. After reuse, the TP (total phosphorus) removal rate is improved compared to single use.

[0018] In the optimized S3, the composite filler is composed of zeolite, crushed red bricks, and agricultural waste-derived carbon source carrier in a mass ratio of 5:3 to 4:2 to 3; the zeolite has a particle size of 5 to 10 mm, the crushed red bricks has a particle size of 10 to 20 mm, and the agricultural waste-derived carbon source carrier has a particle size of 2 to 5 mm. Detailed Implementation

[0019] The following detailed description illustrates the specific implementation method: A domestic wastewater treatment process includes: S1. Pretreatment: Domestic sewage is filtered through a screen and then fed into an equalization tank. Agricultural waste-derived carbon source carriers are added to the equalization tank, and the hydraulic retention time of the equalization tank is controlled at 2 hours to obtain pretreated sewage. The agricultural waste-derived carbon source carrier is at least one of straw charcoal, rice husk charcoal, or peanut shell charcoal. The dosage of the agricultural waste-derived carbon source carrier in S1 is 5-10 g / L; the preparation method of the agricultural waste-derived carbon source carrier is as follows: cut the agricultural waste into 10 cm pieces, carbonize it in an anaerobic environment at 400°C for 3 h, cool it and grind it to a particle size of 4 mm. S2. Enhanced Nitrogen and Phosphorus Removal: Pretreated wastewater is fed into an enhanced tank, which consists of sequentially connected anaerobic and aerobic zones. A composite carrier is added to the enhanced tank. The dissolved oxygen in the anaerobic zone is controlled to be <0.2 mg / L and the hydraulic retention time to be 3 h. The dissolved oxygen in the aerobic zone is controlled to be 2 mg / L and the hydraulic retention time to be 5 h. The effluent from the enhanced tank is treated by a magnetic separation device to recover the composite carrier, resulting in enhanced treated wastewater. The magnetic field strength of the magnetic separation device is 0.3 T. The composite carrier consists of magnetic biochar, nitrifying bacteria, and denitrifying bacteria. The mass ratio of magnetic biochar, nitrifying bacteria (Nitrobacterium nitrification) and denitrifying bacteria (Pseudomonas fluorescens) in the composite carrier is 100:1~3:2~4.

[0020] The preparation method of magnetic biochar is as follows: iron powder, ferrous sulfate and biochar are mixed at a mass ratio of 1:0.5:10, deionized water is added to form a paste, dried at 100℃, and ground to a particle size of 1mm to obtain magnetic biochar; the biochar is straw charcoal or rice husk charcoal; nitrifying bacteria solution and denitrifying bacteria solution are added to magnetic biochar, stirred evenly and then allowed to stand and air dry to obtain composite carrier.

[0021] S3. Deep purification: The treated wastewater is introduced into an artificial wetland, which is filled with composite filler and planted with aquatic plants. The hydraulic retention time of the artificial wetland is controlled at 6 hours, and the effluent from the artificial wetland is the compliant discharge water.

[0022] The composite filler in S3 is composed of zeolite, crushed red bricks, and agricultural waste-derived carbon source carrier in a mass ratio of 5:3:2; the zeolite has a particle size of 10 mm, the crushed red bricks has a particle size of 20 mm, and the agricultural waste-derived carbon source carrier has a particle size of 5 mm.

[0023] Based on the above processing technology, the following control group was designed, with the following differences: Example 1: The dosage of the carbon source carrier derived from agricultural waste was 5 g / L, and the mass ratio of magnetic biochar, nitrifying bacteria and denitrifying bacteria in the composite carrier was 100:1:2. The carbon source carrier derived from agricultural waste was straw char.

[0024] Example 2: The dosage of the agricultural waste-derived carbon source carrier was 8 g / L, and the mass ratio of magnetic biochar, nitrifying bacteria, and denitrifying bacteria in the composite carrier was 100:2:3. The agricultural waste-derived carbon source carrier was straw char.

[0025] Example 3: The dosage of the carbon source carrier derived from agricultural waste was 10 g / L, and the mass ratio of magnetic biochar, nitrifying bacteria and denitrifying bacteria in the composite carrier was 100:3:4. The carbon source carrier derived from agricultural waste was straw char.

[0026] Example 4: The difference from Example 2 is that the carbon source carrier derived from agricultural waste is rice husk char.

[0027] Example 5: The difference from Example 2 is that the carbon source carrier derived from agricultural waste is peanut shell char.

[0028] Example 6: The difference from Example 2 is that the mass ratio of magnetic biochar, nitrifying bacteria and denitrifying bacteria in the composite carrier is 100:3:2.

[0029] Example 7: The difference from Example 2 is that: S2, enhanced nitrogen and phosphorus removal: the pretreated wastewater is introduced into the enhanced tank, which includes an anaerobic zone and an aerobic zone connected in sequence, and a composite carrier that has been recycled once is added to the enhanced tank.

[0030] Example 8: The difference from Example 2 is that: S2, enhanced nitrogen and phosphorus removal: the pretreated wastewater is introduced into the enhanced tank, which includes an anaerobic zone and an aerobic zone connected in sequence, and a composite carrier that has been recycled twice is added into the enhanced tank.

[0031] Control group 1: The difference from Example 2 is that it does not have agricultural waste-derived carbon source carriers or composite carriers.

[0032] Control group 2: The difference from Example 2 is that there is no carbon source carrier derived from agricultural waste.

[0033] Wastewater from a typical village (from the same source as the wastewater in Examples 1-8) was used. The sampling period was during the non-rainy season of 2025, when the water quality was stable. The initial water quality parameters are as follows: COD (Chemical Oxygen Demand): 420±15 mg / L (reflects organic matter content) TN (Total Nitrogen): 52±3 mg / L (Reflects the degree of nitrogen pollution, including ammonia nitrogen, nitrate nitrogen, etc.) TP (Total Phosphorus): 6.5 ± 0.4 mg / L (Reflects the degree of phosphorus pollution, including phosphates, organophosphates, etc.) The wastewater was treated using the various grouping methods described above, and the treated wastewater was tested. The data is shown in Table 1 below: Table 1 - Test data after wastewater treatment

[0034] Conclusion Analysis: (1) The treatment effect of Comparative Example 1, which only has basic filtration and equalization tank retention, is extremely poor. The removal rates of COD / TN / TP are only 20.0% / 10.0% / 15.4%, and the COD (336mg / L), TN (46.8mg / L), and TP (5.5mg / L) of the effluent are far below the relevant requirements.

[0035] (2) Comparative Example 2 did not provide a carbon source carrier derived from agricultural waste, i.e., no carbon source was provided. Compared with Example 2, the COD / TN / TP removal rates of Example 2 (92.1% / 88.1% / 93.1%) were 17.1% / 23.1% / 23.1% higher than those of Comparative Example 2 (75.0% / 65.0% / 70.0%), respectively, and the effluent TP (0.45 mg / L) met the standard, while the TP (1.95 mg / L) of Comparative Example 2 did not meet the standard. This indicates that insufficient carbon source will directly lead to the lack of energy for microorganisms to degrade pollutants.

[0036] (3) Comparing Examples 1 to 3, the amount of carbon source carrier added ranged from 5 to 10, and the mass ratio of magnetic biochar, nitrifying bacteria and denitrifying bacteria in the composite carrier ranged from 100:1:2 to 100:3:4.

[0037] TN removal rate increased from 85.0% to 88.8%, primarily due to the synergistic effect of carbon source supplementation and an increased proportion of denitrifying bacteria. The increased carbon source dosage provides more energy for denitrifying bacteria, and the increased proportion of denitrifying bacteria (from 2 to 4) enhances their metabolic capacity. Both factors jointly drive the conversion efficiency of nitrate nitrogen and nitrogen gas. TP removal rate increased from 90.0% to 93.5%, as the increased carbon source promotes the synthesis of PHB by polyphosphate-accumulating bacteria, enhancing the excess phosphorus uptake capacity in the aerobic zone. Simultaneously, the increased proportion of nitrifying bacteria (from 1 to 3) improves ammonia nitrogen oxidation efficiency, indirectly providing a better environment for polyphosphate-accumulating bacteria. The COD removal rate showed a smaller increase, indicating that the impact of the carbon source and bacterial agent ratio on COD has reached saturation.

[0038] (4) The difference between Examples 2, 4, and 5 is that the carbon source carriers derived from agricultural waste are straw charcoal, rice husk charcoal, and peanut shell charcoal, respectively. Straw charcoal has the best effect.

[0039] (5) The difference between Example 6 and Example 2 is that the mass ratio of nitrifying bacteria is higher than that of denitrifying bacteria.

[0040] Example 2: Nitrifying bacteria have a low demand for carbon sources and preferentially supply carbon sources to polyphosphate-accumulating bacteria and denitrifying bacteria. Polyphosphate-accumulating bacteria have high efficiency in excessive phosphorus uptake in the aerobic zone, with a TP removal rate of 93.1%.

[0041] Example 6: Although excessive nitrifying bacteria use ammonia nitrogen as the main substrate, they still consume some easily degradable carbon sources (such as glucose and organic acids), resulting in a 30% reduction in carbon sources obtained by polyphosphate-accumulating bacteria in the anaerobic zone, a decrease in PHB synthesis, and a weakening of the excessive phosphorus uptake capacity in the aerobic zone. At the same time, insufficient denitrifying bacteria lead to the incomplete utilization of carbon sources, and the residual carbon sources inhibit the adsorption of phosphorus by magnetic biochar, causing the TP removal rate to drop to 89.2%, with effluent TP of 0.72 mg / L.

[0042] (6) In Examples 2, 7 and 8, the treatment effect gradually decreased with the increase of the number of recycling cycles, but the decrease was controllable.

[0043] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A domestic sewage treatment process, characterized in that, include: S1. Pretreatment: Domestic sewage is filtered through a screen and then fed into an equalization tank. Agricultural waste-derived carbon source carriers are added to the equalization tank, and the hydraulic retention time of the equalization tank is controlled to be 1-3 hours to obtain pretreated sewage. The agricultural waste-derived carbon source carrier is at least one of straw charcoal, rice husk charcoal, or peanut shell charcoal. S2. Enhanced nitrogen and phosphorus removal: The pretreated wastewater is fed into an enhanced tank, which includes an anaerobic zone and an aerobic zone connected in sequence. A composite carrier is added to the enhanced tank. The dissolved oxygen in the anaerobic zone is controlled to be <0.2 mg / L and the hydraulic retention time is controlled to be 2-4 h. The dissolved oxygen in the aerobic zone is controlled to be 0.5-2 mg / L and the hydraulic retention time is controlled to be 3-5 h. The effluent from the enhanced tank is treated by a magnetic separation device to recover the composite carrier, thus obtaining the enhanced treated wastewater. The composite carrier consists of magnetic biochar, nitrifying bacteria, and denitrifying bacteria. S3. Deep purification: The treated wastewater is introduced into an artificial wetland, which is filled with composite filler and planted with aquatic plants. The hydraulic retention time of the artificial wetland is controlled to be 4-6 hours. The effluent from the artificial wetland is the compliant discharge water.

2. The domestic sewage treatment process according to claim 1, characterized in that, The dosage of the agricultural waste-derived carbon source carrier in S1 is 5-10 g / L; the preparation method of the agricultural waste-derived carbon source carrier is as follows: cut the agricultural waste into 5-10 cm segments, carbonize it in anoxic conditions at 300-500℃ for 2-4 h, cool it, and then grind it to a particle size of 2-5 mm.

3. The domestic sewage treatment process according to claim 2, characterized in that, The mass ratio of magnetic biochar, nitrifying bacteria and denitrifying bacteria in the composite carrier is 100:1-3:2-4.

4. The domestic sewage treatment process according to claim 3, characterized in that, The magnetic biochar is prepared by mixing iron powder, ferrous sulfate and biochar at a mass ratio of 1:0.5 to 1:10, adding deionized water to form a paste, drying at 80 to 100°C, and grinding to a particle size of 0.5 to 1 mm to obtain the magnetic biochar; the biochar is straw charcoal or rice husk charcoal; adding nitrifying bacteria solution and denitrifying bacteria solution to the magnetic biochar, stirring evenly, and then letting it stand and air dry to obtain a composite carrier.

5. The domestic sewage treatment process according to claim 4, characterized in that, The magnetic field strength of the magnetic separation device in S2 is 0.1 to 0.3 T. The recovered composite carrier can be repeatedly put into the enhancement tank 3 to 5 times after being rinsed with clean water.

6. The domestic sewage treatment process according to claim 5, characterized in that, The composite filler in S3 is composed of zeolite, crushed red bricks, and agricultural waste-derived carbon source carrier in a mass ratio of 5:3 to 4:2 to 3; the zeolite has a particle size of 5 to 10 mm, the crushed red bricks has a particle size of 10 to 20 mm, and the agricultural waste-derived carbon source carrier has a particle size of 2 to 5 mm.

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