Method for recycling domestic sewage of villages and towns

Abstract

The invention relates to the technical field of sewage treatment, in particular to a resource recycling method for rural domestic sewage. On the basis of the rural domestic sewage, after the rural domestic sewage is subjected to anaerobic-aerobic treatment, on one hand, the concentration of organic matters and the content of nitrogen and phosphorus in the domestic sewage are effectively reduced, on the other hand, the aerobic effluent is not specially treated, and the aerobic effluent still contains sufficient nitrogen and can be directly used for irrigation after being precipitated; meanwhile, sludge obtained by the sedimentation tank contains rich phosphorus, phosphorus in the sludge can be effectively extracted through carbonization and acid leaching of the sludge and can be used for supplementing phosphorus for crops, meanwhile, when effluent of the sedimentation tank needs to be discharged, the constructed wetland is adopted for further treatment, and sludge carbonized slag is made into filler to be used in the constructed wetland, so that the sludge can be recycled. The device has a good water quality purification effect, realizes treatment and recycling of water resources, and is of great significance to environmental protection and resource saving.

Description

TECHNICAL FIELD

[0001] The present application relates to the sewage treatment technical field, and in particular to a method for recycling and utilizing rural domestic sewage. BACKGROUND

[0002] In people's daily life, corresponding sewage will be produced, and the rural domestic sewage has the characteristics of high content of organic matter, nitrogen and phosphorus, low content of heavy metal and unstable water quantity. If not effectively treated, on the one hand, it will cause serious environmental pollution, and on the other hand, it is not convenient for recycling and utilizing water resources and saving resources.

[0003] At present, the biological treatment method is usually used to treat domestic sewage, and the more common one is A 2 O process, i.e. anaerobic-anoxic-aerobic sewage treatment process. However, on the one hand, denitrification and nitrogen removal consume carbon source and convert nitrogen into nitrogen gas for emission, resulting in loss of resources. On the other hand, the process flow is relatively complex, which is not convenient for operation and management, and a large amount of sludge is produced, which increases the subsequent treatment cost.

[0004] Therefore, a sewage treatment method which has a simpler treatment process and can fully realize the recycling of available resources in domestic sewage is a technical problem to be solved in the existing rural domestic sewage treatment. SUMMARY

[0005] The purpose of the present application is to provide a method for recycling and utilizing rural domestic sewage, so as to solve the problems of high sludge production and easy loss of resources in the traditional method.

[0006] To achieve the above purpose, the present application adopts the following technical scheme: a method for recycling and utilizing rural domestic sewage, comprising the following steps:

[0007] S1, sequentially passing domestic sewage into an anaerobic reactor and an aerobic reactor for anaerobic and aerobic treatment;

[0008] Controlling the sludge discharge amount of the aerobic reactor so that the nitrification reaction in the aerobic reactor mainly stays in the nitrosation stage, part of the aerobic reactor effluent is backflowed to the front end of the anaerobic reactor, and another part of the aerobic reactor effluent goes to a sedimentation tank;

[0009] S2, directly using part of the sedimentation tank effluent for irrigation, and part of the sedimentation tank effluent goes to a constructed wetland for treating the sedimentation tank sludge;

[0010] After anaerobic fermentation, the sedimentation tank sludge is passed to a conditioning tank, a mixture of sludge carbonization residue, acid leaching residue and iron powder is sequentially added into the conditioning tank, and then clarified lime water is added, and after coagulation, flocculation, dewatering and drying, dry sludge is obtained;

[0011] S3, dry sludge, biomass straw and calcium carbonate powder are compounded and granulated to obtain sludge-biomass particles, the sludge-biomass particles are carbonized to obtain carbonized residues, the carbonized residues are crushed, acid leached and dried to obtain the sludge carbonized residue acid leaching residues in S2, and the phosphorus resources in the sludge carbonized residue acid leaching liquid are recovered;

[0012] S4, the sludge carbonized residue acid leaching residues in S3 are compounded with iron powder, pore forming agent and binder to be granulated and sintered to obtain ceramsite fillers, and the obtained ceramsite fillers are used in the artificial wetland in S2.

[0013] Further, in S1, the reflux ratio of the aerobic reactor effluent is 50-150%, the concentration ratio of ammonia nitrogen to nitrate nitrogen in the anaerobic reactor is controlled to be 3-5:1, the sludge age in the aerobic reactor is controlled to be 4-8 days by controlling the sludge discharge amount of the aerobic reactor, the dissolved oxygen concentration in the aerobic reactor is controlled to be 2-4 mg / L, the temperature in the aerobic reactor is controlled to be 25-30℃, and the pH in the aerobic reactor is controlled to be 7.5-8.0.

[0014] Further, in S3, the moisture content of the dry sludge is 10-20%, the dry sludge and the biomass straw are crushed and granulated, the particle size of the crushed dry sludge is 1-5 mm, the particle size of the crushed biomass straw is 3-8 mm, and the particle size of the calcium carbonate powder is 500-1000 mesh; the mass ratio of the dry sludge, the biomass straw and the calcium carbonate powder is 100:100-300:1-5, respectively.

[0015] Further, the carbonization temperature is 800-1000℃, and the carbonization time is 4-8h; the combustible gas generated during carbonization is used to provide the heat required for carbonization; the obtained carbonized residues are crushed after cooling, and the crushed carbonized residues are sieved through a 200-400 mesh sieve.

[0016] Further, nitric acid is used for acid leaching, the concentration of the nitric acid is 2-5 mol / L, and the volume-to-mass ratio of the nitric acid to the carbonized residues is 5-10:1; after acid leaching, solid-liquid separation, water washing and drying, the carbonized residue acid leaching residues are obtained, the pH of the acid leaching liquid is adjusted to be alkaline, and solid-liquid separation, water washing and drying are performed to obtain composite phosphate.

[0017] Further, in S2, the particle size of the iron powder is 200-400 mesh, the mass ratio of the carbonized residue acid leaching residues to the iron powder is 1:1-3, and the dosage of the mixture of the sludge carbonized residue acid leaching residues and the iron powder is 1-5 g / m 3 Further, in S2, the particle size of the iron powder is 200-400 mesh, the mass ratio of the carbonized residue acid leaching residues to the iron powder is 1:1-3, and the dosage of the mixture of the sludge carbonized residue acid leaching residues and the iron powder is 1-5 g / m

[0018] Further, the sludge in the conditioning tank is fully stirred and reacted, then coagulant PAC is added, fully stirred and then settled, and the concentrated sludge is sent to a dewatering device for squeezing dewatering, flocculant PAM is added before dewatering, the PAC addition amount is 20-50 ppm, and the PAM addition amount is 1-10 ppm; the sludge is dewatered and then low-temperature dried.

[0019] Further, in S4, the mass ratio of sludge carbonization residue, acid leaching residue, iron powder, pore-forming agent and binder is 10:10-30:0.1-0.5:20-50 in sequence, the pore-forming agent is perlite powder, the particle size of the perlite powder is 200-400 mesh, the binder is 20wt.% sodium silicate solution, and the diameter of the granules after granulation is 10±2mm.

[0020] Further, the granules after granulation are dried and then sintered, the sintering is carried out in a protective atmosphere, the protective atmosphere comprises nitrogen, the sintering temperature is 1000-1200 DEG C, the sintering time is 10-30 min, and after sintering and cooling, the ceramic filler can be obtained.

[0021] Further, the artificial wetland comprises horizontal subsurface flow artificial wetlands and ecological ponds connected in series, in the horizontal subsurface flow artificial wetlands, gravel and ceramic fillers are sequentially arranged from bottom to top, wetland plants are rooted in the ceramic fillers, and the wetland plants comprise yellow flag and reed; gravel is arranged at the bottom of the ecological ponds, and ecological pond plants comprise water willow, reed and iris.

[0022] The beneficial effects of the present application are as follows:

[0023] 1. The present application is based on the traditional AO process, i.e. anaerobic-aerobic process, which avoids nitrogen loss caused by denitrification; and by process control, the nitrification reaction in the aerobic reactor is mainly controlled in the nitrosation stage, thereby effectively reducing the sludge production, reducing the load and treatment cost of the rear end, and being beneficial to resource recovery and treatment cost saving.

[0024] 2. The present application combines the anaerobic process to realize the anaerobic phosphorus release and aerobic phosphorus absorption process, and transfers most of the phosphorus elements to the sludge; and by the reflux of the aerobic reactor effluent, the nitrite in the aerobic reactor is refluxed to the anaerobic reactor, and by the anaerobic ammonia oxidation reaction in the anaerobic reactor, partial denitrification is realized by controlling the process parameters, the eutrophication of the aerobic reactor effluent is avoided, the irrigation use of the rear end is facilitated, and the treatment of the artificial wetland is facilitated, and the enrichment of the free ammonia nitrogen in the aerobic reactor also has a certain promoting effect on the enrichment of nitrite nitrogen.

[0025] 3、The sludge is treated, the cost of sludge transportation is avoided, and the recovery of phosphorus resources is realized, the sludge is compounded with biomass straw, on the one hand, the biomass straw is treated cooperatively, on the other hand, the recovery of phosphorus resources is realized through carbonization and acid leaching treatment, the combustible gas generated in the carbonization process can be used for sludge drying and the like, and the energy consumption is reduced;

[0026] 4、The sludge carbonization residue and acid leaching residue are comprehensively utilized, on the one hand, the sludge carbonization residue and acid leaching residue are used in a sludge conditioning tank, through process control, the dewatering performance of the sludge can be effectively improved, the energy consumption is reduced, and the sludge carbonization residue and acid leaching residue have a positive effect on inhibiting equipment fouling, on the other hand, the sludge carbonization residue and acid leaching residue are made into fillers and used in artificial wetlands, the comprehensive utilization of the sludge carbonization residue and acid leaching residue is realized, and the water quality of the artificial wetlands can be effectively ensured. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be clearly and completely described below in combination with the embodiments of the present application.

[0028] The principle of the present application is as follows:

[0029] The present application is based on rural and town domestic sewage, has the characteristics of high content of organic matter, nitrogen and phosphorus, unstable water quantity and low content of heavy metals, proposes a process with the characteristics of simple process, effective recovery of resources while realizing water resource recycling, easy management and low overall energy consumption, and fits the actual situation of rural and town, and develops a new way for rural and town sewage treatment.

[0030] In the process of the present application, the anaerobic-aerobic sewage treatment process is adopted, the rural and town sewage is collected and then goes to the anaerobic reactor, in the process, other wastewater generated in the treatment process, such as sludge filter press liquid and wastewater generated in the phosphorus recovery treatment, can be collected, in the anaerobic reactor, the organic matter in the sewage undergoes hydrolysis acidification, ammoniation reaction and the like, and generates small-molecule organic acid and the like, at the same time, the polyphosphorus bacteria reproduce in the anaerobic environment, synthesize intracellular PHB and release phosphorus, and then in the aerobic reactor, the ammonia nitrogen in the sewage undergoes nitrification reaction, in the present application, through process control, such as sludge age, pH, no addition of carbon source, dissolved oxygen, temperature and reflux ratio control and the like, the nitrification reaction mainly stays in the stage of nitrite nitrogen, and does not further convert to nitrate nitrogen, on the one hand, the sludge production can be effectively reduced, on the other hand, the generated nitrate nitrogen is refluxed to the anaerobic reactor, and undergoes anaerobic ammonia oxidation reaction with ammonia nitrogen in the anaerobic reactor, and realizes the removal of part of nitrogen elements, and then reduces the nitrogen content in the effluent to a certain extent, avoids the over eutrophication of water body caused by high nitrogen content, and thus the irrigation and the subsequent artificial treatment are not affected; in the aerobic reactor, the polyphosphorus bacteria consume intracellular PHB and excessively absorb phosphorus, and most of the phosphorus is transferred to the sludge and discharged to the sedimentation tank.

[0031] The sedimentation tank effluent can be directly used for irrigation, and another part can go to the artificial wetland for further treatment, and reasonable distribution can be made according to the actual water quantity and demand; and the sludge in the sedimentation tank needs to be further treated, first, the sludge in the sedimentation tank is reduced by anaerobic fermentation and goes to the conditioning tank, a mixture of sludge carbonization residue acid leaching residue powder and iron powder is added to the conditioning tank, after the addition is completed, it is fully stirred and lime water is added, so that calcium hydroxide in the clarified lime water reacts with carbon dioxide in the fermentation liquid to produce calcium carbonate, which grows with the sludge carbonization residue acid leaching residue powder as the core, when the pH in the conditioning tank no longer decreases, coagulant PAC is added, after stirring uniformly, standing, taking the lower concentrated sludge to the dewatering equipment, adding flocculating agent PAM at the front end of the dewatering equipment, and then dewatering in the dewatering equipment, the above-mentioned particles with sludge carbonization residue acid leaching residue powder as the core help sludge dewatering, and the iron-carbon micro-electrolysis environment also helps the further dewatering of the sludge, thereby improving the dewatering efficiency and reducing the energy consumption; the dewatered sludge goes to the low-temperature sludge drying machine for drying to obtain dried sludge.

[0032] The dried sludge is crushed and mixed with crushed biomass straw and calcium carbonate to form granules, the obtained granulation raw materials are carbonized in the carbonization equipment, and in the process, calcium carbonate is decomposed at high temperature, which plays a role in pore forming, loosening, sulfur fixation and improving the calorific value of combustible gas, the obtained combustible gas can be returned to the sludge drying section to provide energy for sludge drying, and the obtained sludge carbonization residue can be further utilized.

[0033] In the present application, the sludge carbonization residue is first acid leached, and nitric acid acid leaching can extract soluble phosphate in the sludge carbonization residue, and then the pH is adjusted to make the phosphate precipitate and separate, and then solid-liquid separation, water washing and drying are carried out to obtain composite phosphate, mainly calcium phosphate and the like, and the obtained composite phosphate can be used for the supplement of phosphorus, calcium, iron and the like of crops, and the sludge carbonization residue acid leaching residue obtained by solid-liquid separation has loose structure and mainly contains carbon, which has good adsorption effect, and after being mixed with iron powder and added to the sludge conditioning tank, on the one hand, it can be used as a core to adsorb calcium carbonate precipitate to form a small particle with the sludge carbonization residue acid leaching residue as the core, and on the other hand, the iron-carbon micro-electrolysis also helps the efficient dewatering of the sludge.

[0034] Meanwhile, the sludge carbonization residue acid leaching residue is used as a filler in the artificial wetland, in the present application, the artificial wetland adopts a horizontal subsurface flow type artificial wetland combined with an ecological pond mode, which is more suitable for villages and towns, gravel is laid at the bottom of the horizontal subsurface flow type artificial wetland and the ecological pond as a support, and then the substrate of the present application is laid in the horizontal subsurface flow type artificial wetland, that is, the ceramsite obtained by mixing the sludge carbonization residue acid leaching residue, iron powder, a pore-forming agent and a binder and then sintering at high temperature is laid as the substrate in the artificial wetland, and then horizontal subsurface flow type artificial wetland plants and ecological pond plants are planted, wherein the horizontal subsurface flow type artificial wetland plants include yellow flag, reed and the like, and are rooted in the substrate, and the ecological pond plants include reed, iris, and riparian willow and the like; through the combined mode of the horizontal subsurface flow type artificial wetland and the ecological pond, nitrogen and phosphorus in the effluent from the sedimentation tank are further removed, the environment is beautified, and the effluent quality is effectively ensured.

[0035] Example 1

[0036] A certain village and town sewage treatment facility adopts the technical scheme of the present application, the permanent population of the village and town is about 1000, the design sewage treatment capacity is 200m 3 / day.

[0037] A collection tank is arranged to collect the village and town sewage, the collection tank is sampled and detected for multiple times, and the key indexes of the water quality of the collection tank are as follows: COD 400-500 mg / L, total nitrogen 70-90 mg / L, ammonia nitrogen 60-80 mg / L, total phosphorus 5-7 mg / L, and pH 6.5-7.5.

[0038] In the present embodiment, the daily sewage treatment capacity is about 100m 3 / day, the wastewater generated in the end treatment after the inflow collection, such as the supernatant in the sludge concentration process, the filter pressing liquid generated by the dewatering equipment, the wastewater generated by the acid leaching and collection of composite phosphate, and the pressure nitration reaction liquid refluxed in the aerobic reactor, are all introduced into the anaerobic reactor; in the present embodiment, the concentration ratio of ammonia nitrogen to nitrite nitrogen in the anaerobic reactor is controlled to be 4:1; the sludge age in the aerobic reactor is 6 days, the DO is 3±0.5 mg / L, the temperature is controlled to be 28±2℃, and the pH control value is 7.8±0.2.

[0039] The effluent of the aerobic reactor is monitored, in the effluent of the aerobic reactor, the COD is 70-90 mg / L, the total nitrogen is 30-40 mg / L, the ammonia nitrogen is 6-10 mg / L, the content of nitrite nitrogen is 15-20 mg / L, and the total phosphorus is 1-3 mg / L.

[0040] The effluent of the aerobic reactor goes to the sedimentation tank for sedimentation, and the supernatant of the sedimentation tank is directly used for irrigation water and sampling artificial wetland for further treatment.

[0041] In the embodiment, the irrigation water is less, and the river water can be used for irrigation according to the actual situation. The sludge is conditioned by using the sludge carbonization residue acid leaching residue, and the substrate made of the sludge carbonization residue acid leaching residue is used for the artificial wetland. In the effluent water quality of the artificial wetland ecological pond, the COD is 20-30 mg / L, the total nitrogen is 10-15 mg / L, the ammonia nitrogen is 1-3 mg / L, and the total phosphorus is 0.1-0.3 mg / L, which completely meets the requirements of the relevant standards.

[0042] In the embodiment, the sludge generated in the sedimentation tank is treated to avoid environmental pollution and resource waste. The sludge in the sedimentation tank is first sent to an anaerobic fermentation tank for fermentation reduction, and the produced biogas can be used for subsequent sludge drying. The reduced anaerobic fermentation is sent to a conditioning tank for conditioning. The mixed powder of the sludge carbonization residue acid leaching residue and iron powder is added to the conditioning tank. The particle size of the sludge carbonization residue acid leaching residue and the iron powder is controlled to be 200-400 meshes. The mass ratio of the sludge carbonization residue acid leaching residue to the iron powder is 1:2. The addition amount of the mixed powder is 3 g / m 3 The sludge is stirred and mixed after the addition is completed. Then, the clear lime water is slowly added under stirring conditions. The pH in the conditioning tank is controlled to fluctuate around 8. When the pH continuously rises to more than 9, it indicates that the reaction is complete, and the addition of the clear lime water is stopped.

[0043] At this time, PAC is added to the conditioning tank and stirred and mixed. The addition amount of the PAC is 30 ppm. Then, it is placed and the lower concentrated sludge is taken out and sent to a dewatering device. In the embodiment, the dewatering device is a plate and frame filter press. The concentrated sludge is added with PAM before entering the plate and frame filter press. The addition amount of the PAM is 3 ppm. After being dewatered by the dewatering device, the moisture content of the sludge is about 55%. Then, it is sent to a drying section for low-temperature drying. The second drying uses a low-temperature drying device. The sludge is cut into strips and then enters the drying device for drying. The moisture content of the out sludge is about 15%.

[0044] The dried sludge is crushed and then compounded and granulated with crushed biomass straw and calcium carbonate (800 meshes). The particle size of the crushed sludge is controlled to be about 3 mm. The particle size of the crushed biomass straw is controlled to be about 5 mm. The mass ratio of the sludge, the biomass straw and the calcium carbonate is 100:200:3 in sequence. The particle size of the prepared granules is 3-8 mm.

[0045] The granules prepared above are carbonized in a carbonization device, and the carbonization temperature is controlled at 850 DEG C during the process, and the carbonization is performed for 6 hours, and the combustible gas generated during the carbonization can be used to provide energy for the carbonization and sludge drying, and the sludge carbonization residue is obtained after the carbonization is completed, and the sludge carbonization residue is crushed and sieved through a 400-mesh sieve, and then acid leaching is performed by using 4 mol / L nitric acid, and the volume-to-mass ratio (L / kg) of the nitric acid to the sludge carbonization residue is 8:1, and after the acid leaching is completed, alkali is added to the system, the pH of the system is adjusted to be alkaline, and after the precipitation is completed, solid-liquid separation is performed, the solid product is washed to be neutral, and after drying, a composite phosphate is obtained, and the recovery of the phosphorus resource is realized.

[0046] The sludge carbonization residue acid leaching residue is mixed with iron powder, a pore-forming agent and a binder to prepare granules, in the embodiment, the pore-forming agent is perlite powder (400 mesh), the binder is a 20wt.% sodium silicate solution, the mass ratio of the sludge carbonization residue acid leaching residue, the iron powder, the pore-forming agent and the binder is 10:30:0.3:40 in sequence, and small balls with a diameter of about 10 mm are prepared, and after the prepared small balls are dried, the small balls are calcined at 1150 DEG C for 20 min under nitrogen protection, and after the calcination, the artificial wetland substrate filler is obtained after cooling.

[0047] The ceramsite substrate filler is laid in the horizontal subsurface flow artificial wetland, in the horizontal subsurface flow artificial wetland, the gravel layer is 20 cm thick, the ceramsite substrate layer is 40 cm thick, and yellow flag iris, reed and the like are planted, and the effluent of the horizontal subsurface flow artificial wetland is discharged to the ecological pond, and reed, iris, and riparian willow and the like are planted in the ecological pond.

[0048] The embodiment realizes the treatment of the village and town domestic sewage, the comprehensive disposal of the generated sludge, and the recycling of the resources, and the operation cost is low, and the comprehensive operation cost is reduced by about 35% compared with the traditional process.

[0049] The present application is not limited to the above best mode, and anyone can derive other various forms of products under the inspiration of the present application, but regardless of any change in shape or structure, any technical solution with the same or similar technical solution as the present application falls within the protection scope of the present application.

Claims

1. A method for recycling and utilizing rural domestic sewage resources, characterized in that, The method comprises the following steps: S1, domestic sewage is sequentially introduced into an anaerobic reactor and an aerobic reactor for anaerobic and aerobic treatment; The sludge discharge amount of the aerobic reactor is controlled so that the nitrification reaction in the aerobic reactor mainly stays in the nitrosation stage, part of the effluent of the aerobic reactor is backflowed to the front end of the anaerobic reactor, and another part of the effluent of the aerobic reactor is sent to a sedimentation tank; S2, part of the effluent of the sedimentation tank is directly used for irrigation, and part is sent to a constructed wetland, and the sludge in the sedimentation tank is treated; The sludge in the sedimentation tank is introduced into a conditioning tank after anaerobic fermentation, a mixture of sludge carbonization residue acid leaching residue and iron powder and clarified lime water are sequentially added into the conditioning tank, and then the sludge is subjected to coagulation, flocculation, dehydration and drying to obtain dried sludge; S3, the dried sludge, biomass straw and calcium carbonate powder are compounded and granulated to obtain sludge-biomass particles, the sludge-biomass particles are carbonized to obtain carbonization residue, the carbonization residue is crushed, acid leached and dried to obtain the sludge carbonization residue acid leaching residue in S2, and the phosphorus resources in the sludge carbonization residue acid leaching liquid are recovered; S4, the sludge carbonization residue acid leaching residue in S3 is compounded with iron powder, a pore-forming agent and a binder to obtain ceramsite fillers, and the ceramsite fillers are used in the constructed wetland in S2.

2. The method according to claim 1, characterized in that: In S1, the backflow ratio of the effluent of the aerobic reactor is 50-150%, the concentration ratio of ammonia nitrogen to nitrate nitrogen in the anaerobic reactor is controlled to be 3-5:1, the sludge age in the aerobic reactor is controlled to be 4-8 days by controlling the sludge discharge amount of the aerobic reactor, the dissolved oxygen concentration in the aerobic reactor is controlled to be 2-4 mg / L, the temperature in the aerobic reactor is controlled to be 25-30℃, and the pH in the aerobic reactor is controlled to be 7.5-8.

0.

3. The method according to claim 1, characterized in that: In S3, the moisture content of the dried sludge is 10-20%, the dried sludge and the biomass straw are crushed and granulated, the particle size of the crushed dried sludge is 1-5 mm, the particle size of the crushed biomass straw is 3-8 mm, and the particle size of the calcium carbonate powder is 500-1000 mesh; the mass ratio of the dried sludge, the biomass straw and the calcium carbonate powder is 100:100-300:1-5.

4. The method according to claim 3, characterized in that: The carbonization temperature is 800-1000℃, and the carbonization time is 4-8 h; the combustible gas generated in the carbonization process is used to provide the heat required for carbonization; the obtained carbonization residue is crushed after cooling, and the crushed carbonization residue is sieved through a 200-400 mesh sieve.

5. The method according to claim 4, characterized in that: The acid leaching adopts nitric acid, the concentration of the nitric acid is 2-5 mol / L, and the volume-mass ratio of the nitric acid to the carbonization residue is 5-10:1; after acid leaching, solid-liquid separation, water washing and drying, the carbonization residue acid leaching residue is obtained, the pH of the acid leaching liquid is adjusted to be alkaline, solid-liquid separation, water washing and drying are performed to obtain a composite phosphate.

6. The method according to claim 5, characterized in that: The S2 is characterized in that the particle size of the iron powder is 200-400 mesh, the mass ratio of the carbonized residue acid leaching residue to the iron powder is 1:1-3, and the adding amount of the mixture of the sludge carbonized residue acid leaching residue and the iron powder is 1-5 g / m 3 The sludge is fully stirred for 2-4 hours, and clear lime water is added during the stirring, and the pH in the conditioning tank is controlled to be 7-9.

7. The method according to claim 6, characterized in that: After the sludge in the conditioning tank is fully stirred and reacted, a coagulant PAC is added, and after being fully stirred, the sludge is allowed to stand, the concentrated sludge is sent to a dehydration device for pressurized dehydration, a flocculant PAM is added before dehydration, the PAC addition amount is 20-50 ppm, and the PAM addition amount is 1-10 ppm; the sludge is dehydrated and dried at low temperature.

8. The method according to claim 5, characterized in that: The mass ratio of the sludge carbonization residue acid leaching residue, iron powder, pore-forming agent and binder in the S4 is 10:10-30:0.1-0.5:20-50 in sequence, the pore-forming agent is perlite powder, the particle size of the perlite powder is 200-400 mesh, the binder is 20 wt.% sodium silicate solution, and the diameter of the granules after granulation is 10±2 mm.

9. The method according to claim 8, characterized in that: The granules after granulation are dried and then sintered, the sintering is performed in a protective atmosphere, the protective atmosphere comprises nitrogen, the sintering temperature is 1000-1200 ℃, the sintering time is 10-30 min, and the sintered product is obtained after cooling.

10. The method according to claim 9, characterized in that: The artificial wetland comprises horizontal subsurface flow artificial wetlands and ecological ponds connected in series, the gravel and the ceramic filler are arranged in the horizontal subsurface flow artificial wetlands from bottom to top, the wetland plants are rooted in the ceramic filler, and the wetland plants comprise yellow flag and reed; the gravel is arranged at the bottom of the ecological ponds, and the ecological pond plants comprise water willow, reed and iris.