Treatment method and treatment system for recycling municipal sludge press filtrate

Abstract

The invention discloses a treatment method and a treatment system for resource utilization of municipal sludge press filtrate. The treatment method comprises the following steps: adding potassium carbonate into the municipal sludge press filtrate under the condition of alkaline water for reaction and standing, adding a phosphorus-containing agent into the obtained first supernatant for reaction and standing, and filtering the obtained second supernatant to complete resource treatment. According to the method disclosed by the invention, the potassium carbonate and the phosphorus-containing medicament are used for cooperative treatment, so that the hardness of the pressure filtrate can be remarkably reduced, the removal rate is up to 90% or above, metal cations in the pressure filtrate can be effectively removed, the conductivity is remarkably reduced, and the salt content in the pressure filtrate is not increased; the problems of pH imbalance, high conductivity, high hardness, more insoluble impurities, unbalanced nutrient component proportion and the like can be solved, efficient utilization of nitrogen, phosphorus and potassium elements in the pressure filtrate can be realized by performing pretreatment and multi-stage nutrient element compounding on the pressure filtrate, and the pressure filtrate can be prepared into a liquid fertilizer product which can be directly used.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge treatment and resource utilization, and relates to a treatment method and a treatment system for resource utilization of municipal sludge filtrate. Background Art

[0002] Municipal sludge is treated by conventional sludge treatment + filter press dehydration to obtain filter press liquid, which contains a large number of various nutrient components that are beneficial to the growth of plants and microorganisms. Not only does the total content of nitrogen, phosphorus and potassium reach 3-5g / L, but the concentration of toxic and harmful heavy metals is also low, making it very suitable for resource utilization as liquid fertilizer for agriculture and forestry. However, due to the characteristics of the residual sludge and the treatment process itself, these sludge filter press liquids generally have problems such as pH imbalance, high salt content, high hardness, more insoluble impurities, and irritating odor. They cannot be used directly as liquid fertilizers, which will cause seedling burning or soil salinization. At the same time, the phosphorus content in the sludge filter press liquid is lower than the nitrogen and potassium content, and the phosphorus element is mainly present in the filter press sludge solids. The distribution ratio of nutrient components in the filtrate water phase is unbalanced, which cannot meet the nutritional needs of the plant growth cycle.

[0003] In the prior art, the sludge filtrate is mainly treated and disposed of by biological treatment or biological treatment + membrane treatment to remove nitrogen and phosphorus in the filtrate and degrade organic matter. At the same time, the heavy metal content in the filtrate is reduced by adding heavy metal chelating agents, or the heavy metals and salts in the filtrate are removed by membrane treatment. Some high calcium filtrate needs to be additionally added with decalcifiers to reduce the total hardness and calcium ions in the filtrate to ensure the stable operation of the back-end membrane biological treatment. However, these prior arts still have the following defects: (a) the nitrogen, phosphorus and potassium nutrients in the sludge filtrate are not used as a large number of elements required for plant growth for resource utilization, but are removed as pollutants; (b) the treatment of sludge filtrate by biological methods still has problems such as too high pH, ​​unbalanced carbon-nitrogen ratio, and high treatment costs; (c) the treatment of sludge filtrate by membrane treatment has defects such as high hardness, easy scaling, and the generated concentrated liquid needs further treatment. In addition, in view of the high pH and high calcium content of sludge filtrate, the prior art specifically uses alkaline sewage and acidic waste gas for acid-base neutralization to reduce the pH of the filtrate, but this method increases the concentration of other pollutants in the filtrate, and the filtrate after the pH is reduced needs to be treated by biological methods, which does not reflect the resource utilization of nitrogen, phosphorus and potassium elements. In addition, although the prior art mentions that sludge filtrate can be used as liquid fertilizer, it does not involve specific technologies and methods, and does not solve the key technical problems of preparing liquid fertilizer from sludge filtrate.

[0004] Therefore, in view of the shortcomings of sludge filtrate, such as pH imbalance, high conductivity, high hardness, large number of insoluble impurities, unbalanced nutrient group distribution ratio, and the difficulty in resource utilization of sludge filtrate in the prior art, it is necessary to provide a treatment method and treatment device for resource utilization of municipal sludge filtrate, which is of great significance for achieving the reduction, stabilization, harmless treatment and disposal of sludge and promoting the resource utilization of sludge filtrate. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a treatment method and a treatment device for resource utilization of municipal sludge filtrate, which can not only solve practical problems such as pH imbalance, high conductivity, high hardness, more insoluble impurities, and unbalanced nutrient component distribution ratio of the sludge filtrate, but also can achieve efficient utilization of nitrogen, phosphorus and potassium elements in the filtrate, and can prepare the filtrate into a liquid fertilizer product that can be directly used.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for resource utilization of municipal sludge filtrate, comprising the following steps: Step S1, adding potassium carbonate to the municipal sludge filtrate under alkaline water conditions to react, and standing to obtain a first precipitate and a first supernatant; Step S2, adding a phosphorus-containing agent to the first supernatant to react, and letting it stand to obtain a second precipitate and a second supernatant; the phosphorus-containing agent is at least one of potassium dihydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid; Step S3: filtering the second supernatant to complete the resource processing of the municipal sludge filtrate.

[0007] The above treatment method is further improved. In step S2, when the pH value of the municipal sludge filtrate is ≥11 and the total hardness is ≥2500 mg / L, it also includes the following treatment: introducing CO2 into the first supernatant for aeration treatment until the pH value of the first supernatant is <11.

[0008] The above treatment method is further improved in that the pH value of the first supernatant after aeration treatment is 6.5-7.

[0009] The above treatment method is further improved. In step S1, the amount of potassium carbonate added is 0.5g to 3.5g per liter of the municipal sludge filtrate; the municipal sludge filtrate is prepared from municipal sludge; the water quality indicators of the sludge filtrate are: pH 10 to 12, conductivity 6000μs / cm to 10000μs / cm, TN 2000 mg / L to 2500mg / L, TP 2 mg / L to 10mg / L, K 300 mg / L to 600mg / L, total hardness 5000 mg / L to 7000mg / L, Ca 2+ 800 mg / L~3000 mg / L, Mg 2+ The concentration of the first precipitation material is 10 mg / L to 100 mg / L; the first precipitation material also includes the following treatment: calcining the first precipitation material to obtain carbon dioxide and calcium oxide; the carbon dioxide is used for aeration treatment of the first supernatant; the calcium oxide is used as a raw material for front-end treatment of municipal sludge.

[0010] The above treatment method is further improved, in which in step S2, the amount of the phosphorus-containing agent added is 4g to 6g per liter of the first supernatant.

[0011] The above-mentioned treatment method is further improved. In step S3, the second supernatant is filtered by a filter so that the content of water-insoluble matter in the second supernatant is ≤10g / L, thereby obtaining a liquid fertilizer product; and the filtering accuracy of the filter is 300 mesh.

[0012] The above-mentioned treatment method is further improved, in which a treatment system is used to carry out resource treatment of municipal sludge filtrate; the treatment system includes a filtrate storage tank for storing municipal sludge filtrate, and the filtrate storage tank is connected to a first compounding device, an intermediate storage tank, a second compounding device, a filtering device and a product storage tank in sequence; the first compounding device is also connected to a first reagent tank for storing potassium carbonate; the second compounding device is also connected to a second reagent tank for storing phosphorus-containing reagents.

[0013] The above-mentioned treatment method is further improved, wherein the first compounding device includes a first stirring tank, a first sedimentation tank and a first settling tank; the water inlet of the first stirring tank is connected to the water outlet of the filtrate storage tank; the water outlet of the first stirring tank is connected to the water inlet of the first sedimentation tank; the mud outlet of the first sedimentation tank is connected to the first sedimentation tank; the first reagent tank is connected to the first stirring tank; the water outlet of the first sedimentation tank is connected to the water inlet of the intermediate storage tank; an aeration tank is also provided between the water outlet of the first sedimentation tank and the water inlet of the intermediate storage tank; the mud outlet of the aeration tank is connected to the water inlet of the first sedimentation tank; and the aeration tank is also connected to a carbon dioxide generator.

[0014] The above-mentioned treatment method is further improved, wherein the second compounding device includes a second stirring tank, a second sedimentation tank and a second settling tank; the water inlet of the second stirring tank is connected to the water outlet of the intermediate storage tank; the water outlet of the second stirring tank is connected to the water inlet of the second sedimentation tank; the mud outlet of the second sedimentation tank is connected to the second sedimentation tank; the second reagent tank is connected to the second stirring tank; and the water outlet of the second sedimentation tank is connected to the water inlet of the filtering device.

[0015] As a general technical concept, the present invention also provides a processing system for resource utilization of municipal sludge filtrate, including a filtrate storage tank for storing municipal sludge filtrate, a first compounding device, an intermediate storage tank, a second compounding device, a filtering device and a product storage tank connected in sequence to the filtrate storage tank; the first compounding device is also connected to a first reagent tank for storing potassium carbonate; the second compounding device is also connected to a second reagent tank for storing a phosphorus-containing agent.

[0016] As a further improvement of the above technical solution: the first compounding device includes a first stirring tank, a first settling tank and a first sedimentation tank; the water inlet of the first stirring tank is connected to the water outlet of the filtrate storage tank; the water outlet of the first stirring tank is connected to the water inlet of the first sedimentation tank; the mud outlet of the first sedimentation tank is connected to the first sedimentation tank; the first reagent tank is connected to the first stirring tank; the water outlet of the first sedimentation tank is connected to the water inlet of the intermediate storage tank; an aeration tank is also provided between the water outlet of the first sedimentation tank and the water inlet of the intermediate storage tank; the mud outlet of the aeration tank is connected to the water inlet of the first sedimentation tank; and the aeration tank is also connected to a carbon dioxide generator.

[0017] As a further improvement of the above technical solution: the second compounding device includes a second stirring tank, a second sedimentation tank and a second settling tank; the water inlet of the second stirring tank is connected to the water outlet of the intermediate storage tank; the water outlet of the second stirring tank is connected to the water inlet of the second sedimentation tank; the mud outlet of the second sedimentation tank is connected to the second sedimentation tank; the second reagent tank is connected to the second stirring tank; the water outlet of the second sedimentation tank is connected to the water inlet of the filtering device.

[0018] Compared with the prior art, the advantages of the present invention are: (1) In view of the shortcomings of sludge filtrate, such as pH imbalance, high conductivity, high hardness, more insoluble impurities, unbalanced nutrient component distribution ratio, etc., as well as the defects of the prior art that it is difficult to realize resource utilization of sludge filtrate, the present invention creatively provides a treatment method for resource utilization of municipal sludge filtrate, wherein potassium carbonate is reacted with municipal sludge filtrate under alkaline water conditions, and potassium carbonate can be used to convert calcium and magnesium ions in the filtrate into carbonate precipitates, thereby effectively reducing the hardness of the filtrate through filtration. In particular, compounding under alkaline conditions can ensure the maximum hardness removal effect, and the added potassium carbonate can supplement potassium nutrient elements without causing an increase in the salinity of the filtrate. On this basis, a phosphorus-containing agent is continuously added to the filtrate treated with potassium carbonate for reaction. On the one hand, the phosphorus-containing agent can be used to react with the residual calcium ions in the filtrate to form The phosphorus-containing precipitate mainly composed of hydroxyapatite (Ca5(PO4)3(OH)) and dihydrate of calcium hydrogen phosphate (Ca(HPO4)(H2O)2) can further reduce the hardness of the filtrate and supplement the phosphorus nutrient element in the filtrate by filtering. In particular, when the phosphorus-containing agent is potassium dihydrogen phosphate and ammonium dihydrogen phosphate, nitrogen, phosphorus and potassium nutrient elements can be supplemented at the same time, making the nutrient composition of the filtrate more balanced. At the same time, the hydroxyapatite formed has a strong ability to absorb chemical substances, which can be used to absorb metal cations in the filtrate, and can further reduce the conductivity of the filtrate. On the other hand, since the phosphorus-containing agent is a weakly acidic agent, it can effectively reduce the pH value of the filtrate, so that the pH value of the filtrate can meet the use requirements of liquid fertilizers. Finally, the water-insoluble matter in the filtrate is removed by filtration to obtain a liquid fertilizer product, thereby completing the resource processing of municipal sludge filtrate. The treatment method for resource utilization of municipal sludge filtrate of the present invention can significantly reduce the hardness of the filtrate by synergistically treating the sludge filtrate with potassium carbonate and a phosphorus-containing agent, with a removal rate of more than 90%, and can effectively remove metal cations in the filtrate, thereby significantly reducing the conductivity of the filtrate, so that the conductivity of the liquid fertilizer product prepared by the present invention is significantly lower than that of a general liquid fertilizer with the same nutrient element concentration, and at the same time, the salt content in the filtrate is not increased, and the practical problems of pH imbalance, high conductivity, high hardness, more insoluble impurities, unbalanced nutrient component distribution ratio, etc. of the sludge filtrate can be solved. Moreover, by pretreating the filtrate and compounding the multi-stage nutrient elements, efficient utilization of nitrogen, phosphorus and potassium elements in the filtrate can be achieved, and the filtrate can be prepared into a liquid fertilizer product that can be directly used. In addition, the method of the present invention can broaden the ways of treating and disposing of sludge filtrate, and can turn waste into treasure by making sludge filtrate into liquid fertilizer, thereby promoting the resource utilization and economic income of sludge. It is of great significance to solving the technical problems currently faced by municipal sludge filtrate, and is worthy of further research and promotion.

[0019] (2) In the treatment method of the present invention, when the pH value of the municipal sludge filtrate is ≥11 and the total hardness is ≥2500 mg / L, the following treatment is also included: CO2 is introduced into the first supernatant for aeration treatment until the pH value of the first supernatant is less than 11. In particular, the pH value of the first supernatant is adjusted to 6.5-7 by aeration treatment. On the one hand, CO2 can react with calcium ions in the filtrate to form calcium carbonate precipitation, further reducing the hardness of the filtrate. On the other hand, CO2 can also be used to consume hydroxide ions in the filtrate, thereby reducing the pH value of the filtrate. In particular, the use of CO2 aeration to adjust the pH of the filtrate can play a carbon fixation role. In addition, in the present invention, after CO2 aeration treatment, the removal effect of phosphorus-containing agents on calcium ions in the filtrate can be significantly improved, and it is also more conducive to using phosphorus-containing agents to reduce the pH value of the filtrate, so that the pH value of the filtrate can more easily meet the use requirements of liquid fertilizers.

[0020] (3) In the treatment method of the present invention, carbonate is added first and then the phosphorus-containing agent is added, which is more conducive to achieving effective removal of hardness. While facilitating the adjustment of the pH value of the filtrate, it also effectively reduces the amount of agent used, thereby helping to reduce the treatment cost. This is because: there is a close relationship between the solubility of the generated precipitated calcium carbonate and the pH value. Under acidic conditions, the solubility of calcium carbonate is relatively high. Under neutral conditions, dissolution and precipitation reach a balance. Under alkaline conditions, the solubility of calcium carbonate is relatively low. Therefore, the reaction of potassium carbonate is carried out under alkaline conditions to ensure that the hardness removal effect is maximized. At the same time, the solubility of hydroxyapatite and calcium hydrogen phosphate is also related to pH. Under acidic conditions, the solubility increases significantly. Under neutral conditions, the dissolution rate is relatively slow, but there is still a certain solubility. Under alkaline conditions, the solubility decreases significantly. Therefore, adding potassium carbonate to the filtrate for reaction first, or aerating the filtrate with carbon dioxide and then introducing the phosphorus-containing agent, can increase the more suitable reaction pH value, thereby ensuring that calcium ions are efficiently converted into phosphorus-containing precipitates after adding the phosphorus-containing agent. At the same time, the pH value of the filtrate is significantly reduced after potassium carbonate or carbon dioxide aeration, which is more conducive to the effective regulation of the pH value of the filtrate by the phosphorus-containing agent, while reducing the amount of the agent used and effectively reducing the pH value of the filtrate.

[0021] (4) In the treatment method of the present invention, the calcium carbonate obtained after the potassium carbonate reaction can be further utilized as a resource. For example, the calcium carbonate can be converted into CO2 and calcium oxide by high-temperature decomposition, wherein the CO2 produced can be used as a gas source for aeration at the rear end, and the calcium oxide solid produced by high-temperature decomposition can be used as an additional raw material for alkaline thermal hydrolysis at the front end. In addition, the phosphorus-containing precipitate obtained after the phosphorus-containing agent reaction can also achieve the recycling of products and raw materials.

[0022] (5) The present invention also provides a treatment system for realizing resource recovery treatment of municipal sludge filtrate, comprising a filtrate storage tank for storing municipal sludge filtrate, a first compounding device, an intermediate storage tank, a second compounding device, a filtering device and a product storage tank which are sequentially connected to the filtrate storage tank, wherein the first compounding device is also connected to a first reagent tank for storing potassium carbonate, and the second compounding device is also connected to a second reagent tank for storing a phosphorus-containing reagent. In the present invention, the municipal sludge filtrate is first stored in a filtrate storage tank, and then sequentially passes through a first compounding device, a second compounding device, and a filtering device for two precipitation reactions and filtrations, so that the sludge filtrate can be synergistically treated with potassium carbonate and a phosphorus-containing agent, and the hardness of the filtrate can be significantly reduced, with a removal rate of more than 90%, and the metal cations in the filtrate can be effectively removed, thereby significantly reducing the conductivity of the filtrate, while not increasing the salt content in the filtrate, and can solve practical problems such as pH imbalance, high conductivity, high hardness, more insoluble impurities, and unbalanced nutrient component distribution ratio of the sludge filtrate. Moreover, the filtrate is pretreated and multi-stage nutrient element compounded by the first compounding device, the second compounding device, and the filtering device, so that the nitrogen, phosphorus, and potassium elements in the filtrate can be efficiently utilized, and the filtrate can be prepared into a liquid fertilizer product that can be directly used. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0024] Figure 1 This is a schematic diagram of the structure of a treatment system for resource utilization of municipal sludge filtrate in Example 2 of the present invention.

[0025] Legend: 1. Filtrate storage tank; 2. First compounding device; 21. First stirring tank; 22. First sedimentation tank; 23. First sedimentation tank; 3. Aeration tank; 4. Intermediate storage tank; 5. Second compounding device; 51. Second stirring tank; 52. Second sedimentation tank; 53. Second sedimentation tank; 6. Filtration device; 7. Product storage tank. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0027] In the following examples of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0028] In view of the shortcomings of sludge filtrate, such as pH imbalance, high conductivity, high hardness, more insoluble impurities, unbalanced nutrient component distribution ratio, etc., as well as the defects of the prior art that it is difficult to realize resource utilization of sludge filtrate, the present invention creatively provides a treatment method for resource utilization of municipal sludge filtrate, wherein potassium carbonate is first reacted with municipal sludge filtrate under alkaline water conditions, and potassium carbonate can be used to convert calcium and magnesium ions in the filtrate into carbonate precipitates, thereby effectively reducing the hardness of the filtrate through filtration. In particular, compounding under alkaline conditions can ensure the maximization of the hardness removal effect, and the added potassium carbonate can supplement potassium nutrient elements without causing an increase in the salinity of the filtrate; on this basis, a phosphorus-containing agent is continuously added to the filtrate treated with potassium carbonate for reaction. On the one hand, the phosphorus-containing agent can be used to react with the residual calcium ions in the filtrate to form a hydroxylated precipitate. The phosphorus-containing precipitate mainly composed of calcium apatite (Ca5(PO4)3(OH)) and dihydrate of calcium hydrogen phosphate (Ca(HPO4)(H2O)2) can be filtered to further reduce the hardness of the filtrate and supplement the phosphorus nutrient element in the filtrate. In particular, when the phosphorus-containing agent is potassium dihydrogen phosphate and ammonium dihydrogen phosphate, nitrogen, phosphorus and potassium nutrient elements can be supplemented at the same time, making the nutrient composition of the filtrate more balanced. At the same time, the hydroxyapatite formed has a strong ability to absorb chemical substances, which can be used to absorb metal cations in the filtrate, and can further reduce the conductivity of the filtrate. On the other hand, since the phosphorus-containing agent is a weakly acidic agent, it can effectively reduce the pH value of the filtrate, so that the pH value of the filtrate can meet the use requirements of liquid fertilizers. Finally, the water-insoluble matter in the filtrate is removed by filtration to obtain a liquid fertilizer product, thereby completing the resource processing of municipal sludge filtrate. The treatment method for resource utilization of municipal sludge filtrate of the present invention can significantly reduce the hardness of the filtrate by synergistically treating the sludge filtrate with potassium carbonate and a phosphorus-containing agent, with a removal rate of more than 90%, and can effectively remove metal cations in the filtrate, thereby significantly reducing the conductivity of the filtrate, so that the conductivity of the liquid fertilizer product prepared by the present invention is significantly lower than that of a general liquid fertilizer with the same nutrient element concentration, and at the same time, the salt content in the filtrate is not increased, and the practical problems of pH imbalance, high conductivity, high hardness, more insoluble impurities, unbalanced nutrient component distribution ratio, etc. of the sludge filtrate can be solved. Moreover, by pretreating the filtrate and compounding the multi-stage nutrient elements, efficient utilization of nitrogen, phosphorus and potassium elements in the filtrate can be achieved, and the filtrate can be prepared into a liquid fertilizer product that can be directly used. In addition, the method of the present invention can broaden the ways of treating and disposing of sludge filtrate, and can turn waste into treasure by making sludge filtrate into liquid fertilizer, thereby promoting the resource utilization and economic income of sludge. It is of great significance to solving the technical problems currently faced by municipal sludge filtrate, and is worthy of further research and promotion.

[0029] In order to better understand the innovation of the technical solution of the present invention, the following embodiments and comparative examples are provided.

[0030] Example 1 A method for resource utilization of municipal sludge filtrate, comprising the following steps: Step S1: adding 0.8 g of potassium carbonate per liter of municipal sludge filtrate, adding potassium carbonate (the mass fraction of potassium carbonate (K2CO3) ≥ 99%) to the municipal sludge filtrate under alkaline water conditions to react, and the reaction that occurs is: On the one hand, it can reduce the hardness, and on the other hand, it can also supplement potassium. The precipitate after the reaction is allowed to stand to obtain a first precipitate and a first supernatant, wherein the main component of the first precipitate is calcium carbonate precipitate. Its subsequent resource processing includes: calcining the first precipitate to obtain CO2 and calcium oxide, and using the collected CO2 for aeration treatment of the first supernatant; using the collected calcium oxide as an added raw material for front-end alkaline thermal hydrolysis to treat municipal sludge.

[0031] In step S1, the municipal sludge filter press liquid used is the sludge filter press liquid obtained by alkaline thermal hydrolysis and filter press dehydration treatment of the sludge of a municipal sludge treatment plant, and the water quality of the sludge filter press liquid is shown in Figure 1. It can be seen from the indicators in Figure 1 that the sludge filter press liquid of the plant has a high pH, ​​high hardness, and unbalanced nitrogen, phosphorus and potassium nutrient element indicators, mainly nitrogen, low potassium, and lack of phosphorus.

[0032] In step S1, when the pH value of the municipal sludge filtrate is ≥11 and the total hardness is ≥2500 mg / L, the following treatment is also included: CO2 is introduced into the first supernatant for aeration treatment for 30 minutes, and the pH value is monitored in real time by a pH online monitoring instrument until the pH value of the first supernatant is 6.5-7.0. In this step, the CO2 used for aeration treatment of the first supernatant can be the CO2 generated during the calcination of calcium carbonate, or it can be waste gas containing a large amount of CO2 gas (such as biogas combustion gas that has been desulfurized and purified).

[0033] In the present invention, other potassium salts cannot be used to replace potassium carbonate. For example, potassium sulfate cannot be used to replace potassium carbonate for two reasons: first, after adding potassium sulfate, the calcium sulfate formed is slightly soluble, and its solubility is significantly higher than that of calcium carbonate, which is not conducive to effectively reducing the hardness; second, the calcium sulfate formed is difficult to recycle and utilize as a resource.

[0034] Step S2: Add the phosphorus-containing agent (potassium dihydrogen phosphate) to the first supernatant in an amount of 5.4 g per liter of the first supernatant to react. During the reaction, the calcium ions remaining in the filtrate react with the hydrogen phosphate ions and phosphate ions to generate phosphorus-containing precipitates mainly composed of hydroxyapatite (Ca5(PO4)3(OH)) and dihydrate of calcium hydrogen phosphate (Ca(HPO4)(H2O)2). On the one hand, the hardness of the filtrate can be reduced and the proportion of nitrogen, phosphorus and potassium in the filtrate can be adjusted through the reaction, so that the nitrogen, phosphorus and potassium nutrient elements in the filtrate are balanced. On the other hand, the pH value of the filtrate can also be reduced through the reaction, so that the pH value of the filtrate can meet the use requirements of the liquid fertilizer product. More importantly, the formed hydroxyapatite has a strong ability to absorb chemical substances and can be used to absorb metal cations in the filtrate to further reduce the conductivity in the filtrate. The precipitated product after the reaction is then allowed to stand to obtain a second precipitate and a second supernatant.

[0035] Step S3: Filter the second supernatant with a bag filter of 300 mesh to remove water-insoluble matter in the filtrate, so that the content of water-insoluble matter in the second supernatant is ≤10 g / L, obtain a liquid fertilizer product, and complete the resource processing of the municipal sludge filtrate.

[0036] In this embodiment, when implementing the above-mentioned treatment method, a treatment system can be used to carry out resource treatment of municipal sludge filtrate. The treatment system used includes a filtrate storage tank 1 for storing municipal sludge filtrate, and the filtrate storage tank 1 is connected to a first compounding device 2, an intermediate storage tank 4, a second compounding device 5, a filtering device 6 and a product storage tank 7 in sequence; the first compounding device 2 is also connected to a first reagent tank for storing potassium carbonate; the second compounding device 5 is also connected to a second reagent tank for storing a phosphorus-containing agent.

[0037] In this embodiment, the first compounding device 2 includes a first stirring tank 21, a first settling tank 22 and a first sedimentation tank 23; the water inlet of the first stirring tank 21 is connected to the water outlet of the filtrate storage tank 1; the water outlet of the first stirring tank 21 is connected to the water inlet of the first settling tank 22; the mud outlet of the first settling tank 22 is connected to the first sedimentation tank 23; the first reagent tank is connected to the first stirring tank 21; the water outlet of the first settling tank 22 is connected to the water inlet of the intermediate storage tank 4; an aeration tank 3 is also provided between the water outlet of the first settling tank 22 and the water inlet of the intermediate storage tank 4; the mud outlet of the aeration tank 3 is connected to the water inlet of the first settling tank 22; and a carbon dioxide generator is also connected to the aeration tank 3.

[0038] In this embodiment, the second compounding device 5 includes a second stirring tank 51, a second sedimentation tank 52 and a second sedimentation tank 53; the water inlet of the second stirring tank 51 is connected to the water outlet of the intermediate storage tank 4; the water outlet of the second stirring tank 51 is connected to the water inlet of the second sedimentation tank 52; the mud outlet of the second sedimentation tank 52 is connected to the second sedimentation tank 53; the second reagent tank is connected to the second stirring tank 51; the water outlet of the second sedimentation tank 52 is connected to the water inlet of the filtering device 6.

[0039] In this embodiment, the water quality data of the sludge filtrate before and after being treated by the above technical solution and the indicators of conventional liquid fertilizers on the market are compared, as shown in Tables 1 and 2. The qualitative and quantitative analysis results of the second precipitated material are shown in Table 3.

[0040] As can be seen from Table 1, after the sludge filter press is pretreated and compounded with two-stage nutrient elements, the pH value of the filter press is greatly reduced, from strong alkalinity to weak acidity, and the total hardness is reduced by more than 90%, which can effectively solve the soil caking problem that occurs during the use of high calcium filtrate for fertilizer. At the same time, after pretreatment and compounding of two-stage nutrient elements, the phosphorus and potassium nutrient elements lacking in the sludge filter press are effectively supplemented, and the salt increase of the sludge filter press is controllable, and the conductivity is lower than that of the general liquid fertilizer (conventional liquid fertilizer) with the same nutrient element concentration. As can be seen from Tables 2 and 3, after pretreatment and compounding of two-stage nutrient elements, the concentrations of arsenic, lead and chromium heavy metals in the sludge filter press are reduced to a certain extent. It can be seen that the present invention effectively solves the practical problems of high pH, ​​high salinity, high hardness, and imbalance of nutrient elements in the filtrate after pretreatment and compounding of two-stage nutrient elements, and can achieve efficient utilization of nitrogen and potassium elements in the sludge filter press, and can be prepared into a liquid fertilizer product that can be directly used. In particular, the liquid fertilizer prepared from the sludge filtrate in this embodiment can be directly used for plant fertilization after being diluted 10 times.

[0041] Table 1 Comparison results of indicators of the liquid fertilizer prepared in Example 1 of the present invention and conventional liquid fertilizer

[0042] Table 2 Comparison results of indicators of the liquid fertilizer prepared in Example 1 of the present invention and conventional liquid fertilizer

[0043] In Table 2, L indicates that the value in the corresponding test result is lower than the minimum detection limit of the adopted test method or test equipment.

[0044] Table 3 Qualitative and quantitative analysis results of the second precipitate prepared in Example 1 of the present invention

[0045] From the above results, it can be seen that the treatment method for resource utilization of municipal sludge filter press liquid of the present invention can significantly reduce the hardness of the filtrate by using potassium carbonate and phosphorus-containing agents to synergistically treat the sludge filter press liquid, with a removal rate of more than 90%, and can effectively remove metal cations in the filtrate, thereby significantly reducing the conductivity of the filtrate, while not increasing the salt content in the filtrate, and can solve the practical problems of pH imbalance, high conductivity, high hardness, more insoluble impurities, and unbalanced nutrient component distribution ratio of the sludge filter press liquid, and by pre-treating the filtrate and compounding multi-level nutrient elements, it is possible to achieve efficient utilization of nitrogen, phosphorus, and potassium elements in the filter press liquid, and the filter press liquid can be prepared into a liquid fertilizer product that can be directly used. In addition, the method of the present invention can broaden the way of treating and disposing the sludge filter press liquid, and by making the sludge filter press liquid into liquid fertilizer, it can realize turning waste into treasure, thereby promoting the resource utilization of sludge and economic income generation, which is of great significance to solving the technical problems currently faced by municipal sludge filter press liquid, and is worthy of further research and promotion.

[0046] Example 2 like Figure 1 As shown, the treatment system for resource utilization of municipal sludge filtrate in this embodiment includes a filtrate storage tank 1 for storing municipal sludge filtrate, a first compounding device 2, an intermediate storage tank 4, a second compounding device 5, a filtering device 6 and a product storage tank 7 which are sequentially connected to the filtrate storage tank 1; the first compounding device 2 is also connected to a first reagent tank for storing potassium carbonate (not shown in the figure); the second compounding device 5 is also connected to a second reagent tank for storing a phosphorus-containing agent (not shown in the figure).

[0047] In this embodiment, the first compounding device 2 includes a first stirring tank 21, a first settling tank 22 and a first sedimentation tank 23; the water inlet of the first stirring tank 21 is connected to the water outlet of the filtrate storage tank 1; the water outlet of the first stirring tank 21 is connected to the water inlet of the first settling tank 22; the mud outlet of the first settling tank 22 is connected to the first sedimentation tank 23; the first reagent tank is connected to the first stirring tank 21; the water outlet of the first settling tank 22 is connected to the water inlet of the intermediate storage tank 4; an aeration tank 3 is also provided between the water outlet of the first settling tank 22 and the water inlet of the intermediate storage tank 4; the mud outlet of the aeration tank 3 is connected to the water inlet of the first settling tank 22; and a carbon dioxide generator is also connected to the aeration tank 3.

[0048] In this embodiment, the second compounding device 5 includes a second stirring tank 51, a second sedimentation tank 52 and a second sedimentation tank 53; the water inlet of the second stirring tank 51 is connected to the water outlet of the intermediate storage tank 4; the water outlet of the second stirring tank 51 is connected to the water inlet of the second sedimentation tank 52; the mud outlet of the second sedimentation tank 52 is connected to the second sedimentation tank 53; the second reagent tank is connected to the second stirring tank 51; the water outlet of the second sedimentation tank 52 is connected to the water inlet of the filtering device 6.

[0049] The process of recycling municipal sludge filtrate by using the treatment system in the present embodiment includes the following steps: (1) The sludge press liquid obtained after the sludge from a municipal sludge treatment plant was treated with alkaline thermal hydrolysis and filter press dehydration was stored in a filtrate storage tank. The water quality of the sludge press liquid was as follows: pH 10.82, conductivity 6595 μs / cm, TN 2359 mg / L, TP 2.78 mg / L, K 393 mg / L, total hardness (calculated as CaCO3) 2313 mg / L, Ca 2+ 893mg / L, Mg 2+ The pH of the above-mentioned sludge filtrate is less than 11, and the total hardness (calculated as calcium carbonate) is less than 2500 mg / L. Therefore, the filtrate does not undergo aeration treatment by the aeration device, and the supernatant in the first sedimentation tank directly enters the rear-end intermediate storage tank through the bypass pipeline.

[0050] (2) According to the addition amount of potassium carbonate of 0.5 g per liter of municipal sludge filtrate, the municipal sludge filtrate in the filtrate storage tank is transported to the first stirring tank, and potassium carbonate (the mass fraction of potassium carbonate (K2CO3) ≥ 99%) in the first reagent tank (not shown in the figure) is added to react under alkaline water conditions. The reaction that occurs is: On the one hand, it can reduce the hardness, and on the other hand, it can also supplement potassium. The precipitate after the reaction is allowed to stand to obtain the first precipitate and the first supernatant. The first precipitate is transferred to the first sedimentation tank for standing. The main component of the precipitate is calcium carbonate precipitation. Its subsequent resource processing includes: calcining the first precipitate to obtain CO2 and calcium oxide, and using the collected CO2 for aeration treatment of the first supernatant; using the collected calcium oxide as an additional raw material for front-end alkaline thermal hydrolysis to treat municipal sludge. In this step, the obtained first supernatant is directly transported to the intermediate storage tank through a bypass pipeline for standby.

[0051] (3) According to the addition amount of phosphorus-containing reagent, 5.5 g of potassium dihydrogen phosphate and 0.8 mL of phosphoric acid are added to each liter of the first supernatant, the first supernatant in the intermediate storage tank is transported to the second stirring tank, and the phosphorus-containing reagent (potassium dihydrogen phosphate and phosphoric acid) in the second reagent tank (not shown in the figure) is added to react. The mass fraction of potassium dihydrogen phosphate (KH2PO4) used is ≥98%, and the mass fraction of phosphoric acid is ≥98%. During the reaction, the residual calcium ions in the filtrate react with the hydrogen phosphate ions and phosphate ions to generate hydroxyapatite (Ca5(PO4)3(OH)) and dihydrate of calcium hydrogen phosphate ( The phosphorus-containing precipitate mainly composed of Ca(HPO4)(H2O)2) can, on the one hand, reduce the hardness of the filtrate and adjust the proportion of nitrogen, phosphorus and potassium in the filtrate through reaction, so that the nitrogen, phosphorus and potassium nutrient elements in the filtrate can reach a balance. On the other hand, it can also reduce the pH value of the filtrate through reaction, so that the acidity and alkalinity of the filtrate can meet the use requirements of liquid fertilizer products. More importantly, the hydroxyapatite formed has a strong ability to absorb chemical substances, which can be used to absorb metal cations in the filtrate, further reducing the conductivity of the filtrate, and then the precipitated product after the reaction is allowed to stand to obtain a second precipitate and a second supernatant. In this step, the obtained second precipitate is transported to the second sedimentation tank for further standing treatment and solid-liquid separation. The obtained second supernatant is transported from the outlet of the second sedimentation tank to the filtration device.

[0052] (4) In the filtering device, a bag filter with a filtering accuracy of 300 mesh is used to filter the second supernatant to remove water-insoluble matter in the filtrate, so that the content of water-insoluble matter in the second supernatant is ≤10g / L, and a liquid fertilizer product is obtained, thereby completing the resource recovery treatment of the municipal sludge filtrate. In this step, the obtained liquid fertilizer product is stored in a product storage tank.

[0053] In this embodiment, the comparison results of the water quality data of the sludge filtrate before and after being treated by the above technical solution and the indicators of conventional liquid fertilizers on the market are shown in Table 4 below.

[0054] As can be seen from Table 4, after two-stage nutrient element compounding and filtration and impurity removal, the sludge filtrate can effectively reduce the pH of the filtrate by adjusting the type and dosage of compound agents without CO2 aeration treatment, and the total hardness and calcium ions are significantly reduced. The removal efficiency of the total hardness is about 70%, but additional phosphoric acid needs to be added to supplement the phosphorus element. The liquid fertilizer prepared from the sludge filtrate in this embodiment can be directly used for plant fertilization after being diluted 10 times.

[0055] Table 4 Comparison results of indicators of liquid fertilizer prepared in Example 2 of the present invention and conventional liquid fertilizer

[0056] It can be seen from the above results that in the present invention, the municipal sludge filtrate is first stored in a filtrate storage tank, and then passes through the first compounding device, the second compounding device, and the filtering device in sequence for two precipitation reactions and filtration, so that the sludge filtrate can be synergistically treated with potassium carbonate and phosphorus-containing agents, which can significantly reduce the hardness of the filtrate, and the removal rate is as high as more than 90%, and the metal cations in the filtrate can be effectively removed, thereby significantly reducing the conductivity of the filtrate, and at the same time will not increase the salt content in the filtrate, and can solve the practical problems of pH imbalance, high conductivity, high hardness, more insoluble impurities, and unbalanced nutrient component distribution ratio of the sludge filtrate. Moreover, by pre-treating the filtrate and compounding the nutrient elements at multiple levels through the first compounding device, the second compounding device, and the filtering device, it is also possible to achieve efficient utilization of nitrogen, phosphorus, and potassium elements in the filtrate, and the filtrate can be prepared into a liquid fertilizer product that can be directly used.

[0057] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for resource utilization of municipal sludge filtrate, characterized in that: The following steps are involved: Step S1, adding potassium carbonate to the municipal sludge filtrate under alkaline water conditions to react, and standing to obtain a first precipitate and a first supernatant; Step S2, adding a phosphorus-containing agent to the first supernatant to react, and letting it stand to obtain a second precipitate and a second supernatant; the phosphorus-containing agent is at least one of potassium dihydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid; Step S3: filtering the second supernatant to complete the resource processing of the municipal sludge filtrate.

2. The processing method according to claim 1, characterized in that: In step S2, when the pH value of the municipal sludge filtrate is ≥11 and the total hardness is ≥2500 mg / L, the following treatment is also included: CO2 is introduced into the first supernatant for aeration treatment until the pH value of the first supernatant is <11.

3. The processing method according to claim 2, characterized in that: The pH value of the first supernatant after aeration treatment is 6.5-7.

4. The processing method according to any one of claims 1 to 3, characterized in that: In step S1, the amount of potassium carbonate added is 0.5g to 3.5g per liter of the municipal sludge filtrate; the municipal sludge filtrate is prepared from municipal sludge; the water quality indicators of the sludge filtrate are: pH 10 to 12, conductivity 6000μs / cm to 10000μs / cm, TN 2000 mg / L to 2500mg / L, TP 2 mg / L to 10mg / L, K 300 mg / L to 600mg / L, total hardness 5000 mg / L to 7000mg / L, Ca 2+ 800 mg / L~3000 mg / L, Mg 2+ The concentration of the first precipitation material is 10 mg / L to 100 mg / L; the first precipitation material also includes the following treatment: calcining the first precipitation material to obtain carbon dioxide and calcium oxide; the carbon dioxide is used for aeration treatment of the first supernatant; the calcium oxide is used as a raw material for front-end treatment of municipal sludge.

5. The processing method according to any one of claims 1 to 3, characterized in that: In step S2, the amount of the phosphorus-containing agent added is 4 g to 6 g per liter of the first supernatant.

6. The processing method according to any one of claims 1 to 3, characterized in that: In step S3, the second supernatant is filtered by a filter so that the content of water-insoluble matter in the second supernatant is ≤10 g / L, thereby obtaining a liquid fertilizer product; the filtering accuracy of the filter is 300 meshes.

7. The processing method according to claim 1, characterized in that: In the treatment method, a treatment system is used to carry out resource treatment on municipal sludge filtrate; the treatment system includes a filtrate storage tank for storing municipal sludge filtrate, a first compounding device, an intermediate storage tank, a second compounding device, a filtering device and a product storage tank which are sequentially connected to the filtrate storage tank; the first compounding device is also connected to a first reagent tank for storing potassium carbonate; the second compounding device is also connected to a second reagent tank for storing a phosphorus-containing reagent.

8. The processing method according to claim 7, characterized in that: The first compounding device comprises a first stirring tank, a first settling tank and a first sedimentation tank; the water inlet of the first stirring tank is connected to the water outlet of the filtrate storage tank; the water outlet of the first stirring tank is connected to the water inlet of the first sedimentation tank; the mud outlet of the first sedimentation tank is connected to the first sedimentation tank; the first reagent tank is connected to the first stirring tank; the water outlet of the first sedimentation tank is connected to the water inlet of the intermediate storage tank; an aeration tank is also provided between the water outlet of the first sedimentation tank and the water inlet of the intermediate storage tank; the mud outlet of the aeration tank is connected to the water inlet of the first sedimentation tank; the aeration tank is also connected to a carbon dioxide generator; The second compounding device includes a second stirring tank, a second sedimentation tank and a second settling tank; the water inlet of the second stirring tank is connected to the water outlet of the intermediate storage tank; the water outlet of the second stirring tank is connected to the water inlet of the second sedimentation tank; the mud outlet of the second sedimentation tank is connected to the second sedimentation tank; the second reagent tank is connected to the second stirring tank; the water outlet of the second sedimentation tank is connected to the water inlet of the filtering device.

9. A treatment system for resource utilization of municipal sludge filtrate, characterized in that: It comprises a filtrate storage tank for storing municipal sludge filtrate, a first compounding device, an intermediate storage tank, a second compounding device, a filtering device and a product storage tank which are sequentially connected to the filtrate storage tank; the first compounding device is also connected to a first reagent tank for storing potassium carbonate; the second compounding device is also connected to a second reagent tank for storing a phosphorus-containing reagent.

10. The processing system according to claim 9, characterized in that The first compounding device comprises a first stirring tank, a first settling tank and a first sedimentation tank; the water inlet of the first stirring tank is connected to the water outlet of the filtrate storage tank; the water outlet of the first stirring tank is connected to the water inlet of the first sedimentation tank; the mud outlet of the first sedimentation tank is connected to the first sedimentation tank; the first reagent tank is connected to the first stirring tank; the water outlet of the first sedimentation tank is connected to the water inlet of the intermediate storage tank; an aeration tank is also provided between the water outlet of the first sedimentation tank and the water inlet of the intermediate storage tank; the mud outlet of the aeration tank is connected to the water inlet of the first sedimentation tank; the aeration tank is also connected to a carbon dioxide generator; The second compounding device includes a second stirring tank, a second sedimentation tank and a second settling tank; the water inlet of the second stirring tank is connected to the water outlet of the intermediate storage tank; the water outlet of the second stirring tank is connected to the water inlet of the second sedimentation tank; the mud outlet of the second sedimentation tank is connected to the second sedimentation tank; the second reagent tank is connected to the second stirring tank; the water outlet of the second sedimentation tank is connected to the water inlet of the filtering device.

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