A method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery.

Abstract

This invention discloses a method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery, comprising: S1, pretreatment; S2, performing a blue iron oxide crystallization reaction in a crystalline phosphorus recovery reaction unit; S3, degrading organic matter in a homogeneous Fenton reaction unit; and S4, removing NH4 in an iron ammonia oxidation reaction unit. + -N; S5, wastewater carbon source reuse. The Fe used in this invention... II After the salt is used to generate lapis lazuli in the crystallization unit, the remaining portion can continue to participate in the reaction in the Fenton oxidation unit to generate ·OH to oxidize recalcitrant organic matter. The Fe produced in the homogeneous Fenton reaction unit... III The precipitate in the iron-ammonia oxidation unit can serve as Fe for the iron-ammonia oxidation reaction. III The source is used for the cascade utilization of Fe to achieve phosphorus recovery. The resulting effluent is returned to the biological system of wastewater treatment to provide a carbon source, realizing the efficient utilization of resources and near-zero discharge of sludge carbonization liquid.

Description

Technical Field

[0001] This invention patent belongs to the field of wastewater treatment technology, and in particular relates to a method for achieving near-zero discharge of urban sludge carbonization liquid and enhancing phosphorus recovery. Background Technology

[0002] Globally, the excessive use of nitrogen and phosphorus fertilizers in agricultural activities and the large-scale input of nitrogen and phosphorus through industrial wastewater and domestic sewage discharge have led to eutrophication in aquatic ecosystems, a serious environmental problem. Phosphorus is a non-renewable and depleting natural resource with a unidirectional cycle. With the increasing global population and growing demand for food production, the large-scale mining and unsustainable utilization of phosphate rock have not only depleted phosphate resources but also caused eutrophication due to the accumulation of phosphorus discharged into aquatic environments. Given these pressures on both resources and the environment, phosphorus resource recycling is an essential requirement for achieving sustainable development goals.

[0003] Currently, wastewater treatment plants commonly employ biological nitrogen and phosphorus removal. Traditional biological nitrogen removal includes processes such as nitrification and denitrification. Nitrification requires prolonged aeration in an aerobic tank to complete the ammonia oxidation process by autotrophic nitrifying bacteria, while denitrification requires organic matter as an electron donor. Biological phosphorus removal utilizes the phosphorus release and excess phosphorus uptake by polyphosphate-accumulating bacteria in alternating anaerobic and aerobic environments, achieving phosphorus removal through the discharge of phosphorus-rich sludge. Both denitrifying bacteria and polyphosphate-accumulating bacteria require carbon sources, but the carbon sources in urban wastewater often fail to meet these requirements, making it difficult to achieve efficient nitrogen and phosphorus removal. This often necessitates the addition of additional carbon sources, increasing wastewater treatment costs. Furthermore, traditional biological nitrogen and phosphorus removal generates large amounts of excess sludge, the treatment and disposal of which releases nitrogen and phosphorus again, wasting resources and posing a risk of water pollution.

[0004] Low-temperature carbonization of sludge, as a sludge reduction technology, can significantly improve the efficiency of sludge resource utilization. Approximately 90% of the phosphorus in wastewater ultimately transfers to the remaining sludge. The sludge carbonization liquid produced during the carbonization process contains high concentrations of phosphorus, ammonia nitrogen, and recalcitrant organic matter; direct discharge would cause serious environmental pollution. The treatment of sludge carbonization liquid is challenging, limiting the application of carbonization processes and representing a problem that needs to be addressed in current urban sludge carbonization technologies.

[0005] Meanwhile, in the context of achieving the "dual carbon" goal, resource recycling is an important method to reduce carbon emissions in the water treatment process. Effectively recycling phosphorus resources from sludge carbonization liquid is an important part of realizing the resource utilization of carbonization liquid, which will play an important role in promoting the development of sustainable and carbon-self-sufficient wastewater treatment plants. Summary of the Invention

[0006] This invention patent addresses the problem of high concentrations of nitrogen, phosphorus, and recalcitrant organic matter in sludge carbonization liquor, and the difficulty in its treatment. It proposes a method to achieve near-zero discharge of urban sludge carbonization liquor and enhance phosphorus recovery. The technical solution of this invention patent is implemented as follows, including the following steps:

[0007] S1: Pretreatment: Suspended solids in the carbonized sludge liquid are removed by sand filtration;

[0008] S2: Blue iron crystallization reaction is carried out in the crystalline phosphorus recovery reaction unit: the phosphorus concentration in the sludge carbonization liquid is measured and Fe is added according to the Fe:P molar ratio of 2. II Salt is used to achieve efficient crystallization of lapis lazuli by adjusting pH value and hydraulic residence time. After solid-liquid separation, phosphorus recovery product lapis lazuli is obtained, and the liquid phase enters the Fenton reaction unit.

[0009] S3: Degradation of organic matter in a homogeneous Fenton reaction unit: This involves decomposing some of the recalcitrant organic matter in the liquid phase of step S2 within the homogeneous Fenton reaction unit, based on the remaining Fe in S2. II The content of Fe was increased by adding it in proportion. II Salt was added and H2O2 was added. The pH value of the reaction process was controlled and aeration was carried out. After the Fenton reaction, the product contained Fe. III The effluent mixture enters the iron ammonia oxidation reaction unit;

[0010] S4: Removal of NH4 in the iron ammonia oxidation reaction unit + -N: Adjusts the pH of the mixture in step S3. Under anaerobic conditions and a certain hydraulic retention time, the Fe in the mixture... III and NH4 + -N is converted into N2 by iron-ammonia oxidizing bacteria, thus achieving NH4+. + Removal of -N;

[0011] S5: Reuse of carbon source in effluent: The effluent from step S4 is returned to the anoxic section of the biological system of the wastewater treatment plant as a supplementary carbon source for denitrification.

[0012] Preferably, the pH value mentioned in S2 should be adjusted according to the concentration of PO4-P in the sludge carbonization liquid within the range of 6.0–7.0, and the optimal pH value increases with the increase of the concentration of dissolved organic matter.

[0013] Preferably, the hydraulic residence time of the sapphire crystallization reaction process in S2 is controlled to be 0.5–1 h;

[0014] Preferably, the pH value of the reaction process described in S3 should be controlled between 3.0 and 4.0;

[0015] Preferably, the mass ratio of H2O2 to COD added in S3 is 1:1–2:1, Fe IIThe amount of salt to be added is based on its proportion to the remaining Fe in S2. II The sum of the contents and the molar ratio of H2O2 are determined to be 1:2–1:3;

[0016] Preferably, the pH value described in S4 is 7.0–7.5;

[0017] Preferably, the hydraulic residence time of the iron-ammonia oxidation reaction process in S4 is controlled to be 12–24 h;

[0018] The present invention has the following advantages:

[0019] ① Phosphorus is recovered while removing and utilizing recalcitrant organic matter and total nitrogen from the carbonization liquid, achieving sustainable recycling of phosphorus resources; ② Fe II After the salt is used for the formation of lapis lazuli in the crystallization unit, the remaining portion can continue to act as a reactant in the Fenton oxidation unit to generate ·OH to oxidize recalcitrant organic matter. The Fe produced in the homogeneous Fenton reaction unit... III The precipitate in the iron-ammonia oxidation unit can serve as Fe for the iron-ammonia oxidation reaction. III ③ The effluent from the iron ammonia oxidation reaction unit is returned to the biochemical system of the sewage treatment plant. The remaining organic matter serves as an internal carbon source, which can reduce the sewage treatment plant's need for external carbon sources and achieve near-zero discharge of sludge carbonization liquid. Attached Figure Description

[0020] Figure 1 Flowchart of a method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery

[0021] Figure 2 A schematic diagram of a process route for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery. Detailed Implementation

[0022] The following examples further illustrate this patent in detail. However, these examples are merely exemplary and do not constitute any limitation on the scope of the invention. Modifications and substitutions to the details and form of the technical solution of the invention can be made without departing from the scope of the invention, but all such modifications and substitutions fall within the protection scope of the invention. A method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery includes the following steps:

[0023] S1: Pretreatment: Suspended solids in the carbonized sludge liquid are removed by sand filtration;

[0024] S2: Blue iron crystallization reaction is carried out in the crystalline phosphorus recovery reaction unit: the phosphorus concentration in the sludge carbonization liquid is measured and Fe is added according to the Fe:P molar ratio of 2:1. IISalt was used to achieve efficient crystallization of lapis lazuli by adjusting the pH value to 6.0–7.0 and the hydraulic retention time to 0.5–1 h. The selected optimal pH value increased with the increase of the concentration of dissolved organic matter. After solid-liquid separation, lapis lazuli was obtained as a phosphorus recovery product, and the liquid phase entered the homogeneous Fenton reaction unit.

[0025] S3: Degradation of organic matter in a homogeneous Fenton reactor: Part of the recalcitrant organic matter in the liquid phase of step S2 is decomposed in a homogeneous Fenton reactor. H2O2 is added at a mass ratio of 1:1–2:1 to COD. II The amount of salt to be added is based on its proportion to the remaining Fe in S2. II The sum of the contents and the molar ratio of H2O2 were determined to be 1:2–1:3. The pH value of the reaction process was controlled at 3.0–4.0, and aeration was carried out. After the Fenton reaction, the content of Fe was determined. III The effluent mixture enters the iron ammonia oxidation reaction unit;

[0026] S4: Removal of NH4 in the iron ammonia oxidation reaction unit + -N: Adjust the pH of the mixture in step S3 to 7.0–7.5. Under anaerobic conditions and a hydraulic retention time of 12–24 h, the Fe in the mixture... III and NH4 + -N utilizes the action of iron-ammonia oxidizing bacteria to generate N2, thus achieving NH4+. + Removal of -N;

[0027] S5: Reuse of carbon source in effluent: The effluent from step S4 is returned to the anoxic section of the biological system of the wastewater treatment plant as a supplementary carbon source for denitrification. Specific Implementation Example 1

[0029] The PO4-P concentration in the carbonized liquid produced by the low-temperature carbonization process of a wastewater treatment plant in Jinzhong City, Shanxi Province, was 327 mg / L, and the NH4+ concentration was also high. + The sludge carbonized liquor had a PO4-P concentration of 1198 mg / L, COD of 13375 mg / L, and BOD5 of 3605 mg / L. After sand filtration to remove suspended solids, the carbonized liquor underwent a lapis lazuli crystallization reaction in the crystalline phosphorus recovery reaction unit. The carbonized liquor, with a PO4-P content of 327 mg / L, and Fe... II A ferrous salt solution with a concentration of 118.14 g / L was pumped into the lapis lazuli crystallization unit at flow rates of 400 L / h and 4 L / h, respectively, to induce Fe... II The molar ratio of phosphorus to phosphorus (P) was 2:1. NaOH solution was continuously injected into the crystallization reaction unit via multi-point dosing to maintain the pH at 7.0. Blue iron crystals were collected at the bottom outlet of the crystallization reaction unit, with the liquid phase entering the homogeneous Fenton reaction unit. Sulfuric acid was added to adjust the pH of the wastewater to 3.5, and the Fe content in the liquid phase was tested. IIThe concentration was adjusted by adding 30% H2O2 solution and Fe at a molar ratio of 2:1. II Solution, add Fe II Fe in the liquid phase after salting II The content was 28.5 g / L; H2O2 solution and Fe were added at flow rates of 31.23 L / h and 1 L / h, respectively. II The solution was injected into the homogeneous Fenton reaction zone, and sulfuric acid was automatically added in real time to adjust the pH of the reaction process to 3.5 through an online pH control system. The reaction time was 30 minutes. After the homogeneous Fenton reaction was completed, the pH of the mixture was adjusted to 7.0 and then pumped into the iron ammonia oxidation unit for iron ammonia oxidation reaction at a hydraulic retention time of 12 hours. The effluent from the iron ammonia oxidation unit was returned to the anoxic section of the plant's biological system as a supplementary carbon source for denitrification.

[0030] After treatment of municipal sludge carbonized liquor using this method, the effluent PO4-P was consistently below 20.6 mg / L, and COD and NH4 were also significantly reduced. + The removal rates of phosphorus and nitrogen (N) reached 85% and 90%, respectively. The nitrogen can be returned to the anoxic section of the biological system to supplement the carbon source for denitrification, thus realizing the efficient recovery of phosphorus from sludge carbonization liquid and the resource utilization of sludge carbonization liquid.

Claims

1. A method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery, comprising the following steps: S1: Pretreatment: Suspended solids in the carbonized sludge liquid are removed by sand filtration; S2: Blue iron crystallization reaction is carried out in the crystalline phosphorus recovery reaction unit: the phosphorus concentration in the sludge carbonization liquid is measured and Fe is added according to the Fe:P molar ratio of 2:

1. II Salt is used to crystallize lapis lazuli by adjusting the pH value and hydraulic residence time. After solid-liquid separation, phosphorus recovery product lapis lazuli is obtained, and the liquid phase enters the homogeneous Fenton reaction unit. S3: Degradation of organic matter in a homogeneous Fenton reaction unit: This involves decomposing some of the recalcitrant organic matter in the liquid phase of step S2 within the homogeneous Fenton reaction unit, based on the remaining Fe in S2. II The content of Fe was increased by adding it in proportion. II Salt was added and H2O2 was added. The pH value of the reaction process was controlled and aeration was carried out. After the Fenton reaction, the product contained Fe. III The effluent mixture enters the iron ammonia oxidation reaction unit; S4: Removal of NH4 in the iron ammonia oxidation reaction unit + -N: Adjusts the pH of the mixture in step S3. Under anaerobic conditions and a certain hydraulic retention time, the Fe in the mixture... III and NH4 + -N is converted into N2 by iron-ammonia oxidizing bacteria, thus achieving NH4+. + Removal of -N; S5: Reuse of carbon source in effluent: The effluent from step S4 is returned to the anoxic section of the biological system of the wastewater treatment plant as a supplementary carbon source for denitrification.

2. The method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery according to claim 1, characterized in that, The pH value mentioned in S2 should be adjusted within the range of 6.0–7.0 based on the concentration of PO4-P in the sludge carbonization liquid. The optimal pH value increases with the increase of the concentration of dissolved organic matter.

3. The method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery according to claim 1, characterized in that, The hydraulic residence time described in S2 is controlled at 0.5–1 h.

4. The method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery according to claim 1, characterized in that, The pH value of the reaction process described in S3 should be controlled between 3.0 and 4.

0.

5. The method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery according to claim 1, characterized in that, The mass ratio of H2O2 to COD added in S3 is 1:1–2:1, Fe II The amount of salt to be added is based on its proportion to the remaining Fe in S2. II The sum of the contents and the molar ratio of H2O2 are determined to be 1:2–1:

3.

6. The method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery according to claim 1, characterized in that, The pH value described in S4 is 7.0–7.

5.

7. The method for achieving near-zero discharge of urban sludge carbonization liquid and enhanced phosphorus recovery according to claim 1, characterized in that, The hydraulic residence time of the iron-ammonia oxidation reaction process described in S4 is controlled at 12–24 h.

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