An additive for sludge treatment, its preparation method and application

Abstract

This invention discloses an additive for sludge treatment, its preparation method, and its application. The additive comprises ferric hydroxide, ferric hydroxide, ferric oxide, and expanded perlite, and also includes phosphorus. The additive provided by this invention can improve the aerobic fermentation efficiency of sludge, as well as enhance the water absorption and retention properties and fertilizer efficiency of land-use products.

Description

Technical Field

[0001] This invention relates to an additive for sludge treatment, and more particularly to an additive for sludge treatment, its preparation method, and its application. Background Technology

[0002] my country has a huge amount of sludge production, and the task of treatment and disposal is urgent. Aerobic fermentation of sludge followed by land application is an effective way to achieve full utilization of sludge. Land application refers to processing the products obtained from aerobic fermentation of sludge into land-use products with good pore structure, water absorption and retention properties, and fertilization effects, and applying them to crop planting to generate economic benefits.

[0003] At present, the aerobic fermentation process of sludge has the drawback of low efficiency. At the same time, land use products have the drawbacks of low water absorption and retention capacity and short duration of fertilizer effect.

[0004] Therefore, developing an additive that can improve the efficiency of aerobic fermentation of sludge, as well as enhance the water absorption and retention properties and fertilizer effect duration of land use products has become a research direction. Summary of the Invention

[0005] This invention provides an additive for sludge treatment, which can improve the aerobic fermentation efficiency of sludge, as well as enhance the water absorption and retention properties and fertilizer efficiency of land use products.

[0006] The present invention also provides a method for preparing an additive for sludge treatment, which has the advantages of simple steps and low cost.

[0007] The present invention also provides a sludge treatment method, which has the characteristic of high treatment efficiency.

[0008] The present invention also provides a soil nutrient agent, which has the characteristics of water absorption and retention properties and fertilizer efficacy.

[0009] This invention provides an additive for sludge treatment, comprising ferric hydroxide, ferric hydroxide, ferric oxide, and expanded perlite, and also includes phosphorus.

[0010] The additive described above, wherein the iron content in the additive is 1-3 wt%.

[0011] The additive described above, wherein the phosphorus element has a mass percentage content of 0.25-2.5 wt%.

[0012] The additive described above is prepared by a method comprising the following process:

[0013] 1) Mix expanded perlite with an aqueous solution containing ferrous ions, and then sonicate the resulting mixture to obtain expanded perlite containing iron.

[0014] 2) The expanded perlite containing iron is mixed with an alkaline aqueous solution containing phosphorus, and the resulting mixture is aerated at 25-60°C to obtain the additive.

[0015] This invention also provides a method for preparing an additive for sludge treatment, comprising the following steps:

[0016] 1) Mix expanded perlite with an aqueous solution containing ferrous ions, and then sonicate the resulting mixture to obtain expanded perlite containing iron.

[0017] 2) The expanded perlite containing iron is mixed with an alkaline aqueous solution containing phosphorus, and the resulting mixture is aerated at 25-60°C to obtain the additive.

[0018] The preparation method described above includes the following steps:

[0019] 1) Mix expanded perlite with an aqueous solution containing ferrous ions, and then sonicate the resulting mixture to obtain expanded perlite containing iron.

[0020] 2) The expanded perlite containing iron is mixed with an alkaline aqueous solution containing phosphorus, and the resulting mixture is aerated at 25-60°C to obtain the additive.

[0021] In the preparation method described above, the concentration of ferrous ions in the aqueous solution containing ferrous ions is 0.1-0.5 mol / L.

[0022] The present invention also provides a sludge treatment method, wherein the method uses any of the above-mentioned additives to mix with the material to be treated and carry out aerobic fermentation.

[0023] In the sludge treatment method described above, the amount of additive used is 5-20% of the total dry weight of the aerobic fermentation material.

[0024] The present invention also provides a soil nutrient, which includes any of the above-mentioned additives.

[0025] The additive for sludge treatment provided by this invention has the characteristics of improving the water absorption and retention performance of land use products and the duration of fertilizer effect. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a photograph of expanded perlite containing iron, as shown in Example 1.

[0028] Figure 2 Photograph of additive A1 prepared in Example 1;

[0029] Figure 3 The XRD patterns of additives A1 and B6 are shown. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The first aspect of the present invention provides an additive for sludge treatment, the additive comprising ferric hydroxide, ferric hydroxide, ferric oxide and expanded perlite, and also comprising phosphorus.

[0032] The additive provided by this invention can be used in sludge treatment processes. This additive includes expanded perlite, and also includes iron hydroxyl oxide, iron hydroxide, and iron oxide, with the three iron compounds adsorbed on the surface of the expanded perlite.

[0033] The present invention does not limit the mass percentage of the above three iron compounds in the additive, and the additive may include iron hydroxyl oxide, iron hydroxide and iron oxide.

[0034] The additive provided by this invention also contains phosphorus. In this invention, phosphorus binds to the three iron compounds mentioned above through physical adsorption and / or chemical adsorption. This invention does not limit the mass percentage of phosphorus in the additive; the additive only needs to include phosphorus.

[0035] This invention does not specifically limit the particle size of expanded perlite. In one embodiment, expanded perlite with a particle size of 3-10 mm can be used. Additives made using expanded perlite with the above-mentioned particle size can give aerobic fermentation compost and land use products a suitable pore structure.

[0036] In one embodiment, the additive provided by the present invention can be used sequentially for aerobic fermentation of sludge and production of land-use products. That is, the additive is mixed with sludge and then aerobic fermentation is carried out. Subsequently, the system obtained from the fermentation is directly used for the production of land-use products, without further screening and separation of the additive.

[0037] The inventors discovered that the additive provided by this invention, when applied to the above-mentioned process, not only improves the efficiency of aerobic fermentation of sludge, but also enhances the water absorption and retention properties and fertilizer efficiency of land-use products. The inventors speculate that this is because, firstly, ferric hydroxide, ferric hydroxide, and ferric oxide themselves bind with phosphorus through physical and / or chemical adsorption, while simultaneously strengthening the phosphorus adsorption effect of expanded perlite, thus increasing the phosphorus content loaded on the expanded perlite. Since expanded perlite and the aforementioned three iron compounds all fix phosphorus, when the additive provided by this invention is used in the aerobic fermentation and land-use processes of sludge, the phosphorus fixed by the three iron compounds and expanded perlite is slowly released under the action of microorganisms. This slowly released phosphorus provides more readily available nutrients for microbial growth, thereby improving aerobic fermentation efficiency and shortening fermentation time. Secondly, expanded perlite has a high porosity, which not only helps improve the water absorption and retention properties of land-use products but also helps improve the oxygen supply of the aerobic fermentation pile, providing sufficient pore space and oxygen required for aerobic fermentation for microbial growth, thereby further improving aerobic fermentation efficiency and shortening fermentation time.

[0038] Furthermore, the three iron compounds mentioned above can adsorb ammonia and sulfur-containing compounds produced during aerobic fermentation through physical adsorption, thereby reducing odor emissions and nitrogen loss, and further improving the fertilizer efficiency of land use products.

[0039] The additive for sludge treatment provided by this invention has the characteristics of improving the aerobic fermentation efficiency of sludge, as well as enhancing the water absorption and retention performance and fertilizer efficiency of land use products.

[0040] Furthermore, in one embodiment, the additive for sludge treatment provided by the present invention contains 1-3 wt% iron. The additive with the aforementioned wt% iron content can be loaded in large quantities into the pores of expanded perlite, enhancing the adsorption of nutrients such as phosphorus by the expanded perlite, without clogging the pore structure of the expanded perlite. This makes the additive's slow-release nutrient properties and its ability to improve the pore structure of aerobic fermentation and land use products even more prominent.

[0041] Furthermore, in one embodiment, the phosphorus content in the additive for sludge treatment provided by the present invention is 0.25-2.5 wt%. The additive with the aforementioned phosphorus content can effectively increase the nutrient content in the aerobic fermentation compost and land use products without causing excessive salinity in the aerobic fermentation compost, thus effectively improving aerobic fermentation efficiency and the nutrient content of land use products.

[0042] In one embodiment, the additive provided by the present invention is prepared by a method comprising the following process:

[0043] 1) Mix expanded perlite with an aqueous solution containing ferrous ions, and then sonicate the resulting mixture to obtain expanded perlite containing iron.

[0044] 2) Mix expanded perlite containing iron with an alkaline aqueous solution containing phosphorus, and aerate the resulting mixture at 25-60℃ to obtain an additive.

[0045] This invention does not specifically limit the composition of the aqueous solution containing ferrous ions, as long as the solution contains ferrous ions. This invention also does not specifically limit the concentration of ferrous ions in the aqueous solution containing ferrous ions.

[0046] In this invention, the alkaline aqueous solution containing phosphorus is an aqueous solution with a pH > 7 containing phosphorus. It is understood that, to facilitate the combination of expanded perlite containing iron and phosphorus, the phosphorus in this aqueous solution is dissolved in water. This invention does not limit the specific form of phosphorus; in one embodiment, phosphorus exists in the aqueous solution in the form of a phosphate. The phosphate can be orthophosphate (PO4). 3- It can also be an acid phosphate (HPO4). 2- H2PO4 - This invention does not limit the concentration of phosphorus in the aqueous solution; it can be selected according to actual needs.

[0047] Ultrasonic treatment involves subjecting a system of expanded perlite mixed with an aqueous solution containing ferrous ions to ultrasonic treatment. The resulting solid material in the system is expanded perlite containing iron. This invention does not limit the treatment frequency, time, or power of the ultrasonic treatment; these can be selected according to actual needs.

[0048] Aeration treatment involves introducing air into a mixed system comprising expanded perlite and an aqueous solution containing ferrous ions. This invention does not limit the specific process of aeration treatment; in one embodiment, the system may be stirred to introduce air. This invention does not limit the treatment time of aeration treatment and can be selected according to actual needs.

[0049] The inventors have discovered that an additive prepared using a method comprising the following steps not only enhances the efficiency of aerobic fermentation of sludge but also improves the water absorption and retention capacity and the duration of fertilizer effect of land-use products. The inventors speculate that this is because, firstly, after mixing expanded perlite with an aqueous solution containing ferrous ions, the ferrous ions are adsorbed onto the surface of the expanded perlite. During aeration, the ferrous ions on the surface of the expanded perlite are oxidized to ferric iron by oxygen in the air, and subsequently hydrolyzed into ferric hydroxide aggregates attached to the surface of the expanded perlite, forming expanded perlite containing iron. Subsequently, the expanded perlite containing iron is mixed with an alkaline aqueous solution containing phosphorus, and aeration at 25-60℃ ensures both high phosphorus adsorption efficiency of ferric hydroxide and promotes the absorption and retention of phosphorus by the ferric hydroxide. The free iron ions are converted into ferric hydroxide, ferric hydroxide, and ferric oxide, increasing the amount of phosphorus fixed. The ultrasonic treatment accelerates the reaction process and promotes the uniform distribution of phosphorus. The ferric hydroxide aggregates on the surface of expanded perlite undergo physical adsorption and / or chemical adsorption reactions with phosphorus. The phosphorus combines with ferric hydroxide to obtain the additive provided by this invention. Secondly, while ferric hydroxide, ferric hydroxide, and ferric oxide themselves combine with phosphorus through physical adsorption and / or chemical adsorption, they also enhance the phosphorus adsorption effect of expanded perlite and increase the phosphorus content loaded on expanded perlite. Since expanded perlite and the three iron compounds mentioned above all fix phosphorus, when the additive provided by this invention is used in the aerobic fermentation and land application processes of sludge, the phosphorus fixed by the three iron compounds and expanded perlite will be slowly released under the action of microorganisms. The slowly released phosphorus provides more readily available nutrients for microbial growth, thereby improving aerobic fermentation efficiency and shortening fermentation time. Secondly, expanded perlite has a high porosity, which not only helps to improve the water absorption and retention performance of land application products, but also helps to improve the oxygen supply of the aerobic fermentation pile, providing sufficient pore space and oxygen required for aerobic fermentation for microbial growth, thereby further improving aerobic fermentation efficiency and shortening fermentation time. Therefore, the above-mentioned additive not only improves the aerobic fermentation efficiency of sludge, but also improves the water absorption and retention performance and fertilizer effect duration of land application products.

[0050] A second aspect of this invention provides a method for preparing an additive, which can be used to obtain any of the above-mentioned additives for sludge treatment. The method includes the following steps:

[0051] 1) Mix expanded perlite with an aqueous solution containing ferrous ions, and then sonicate the resulting mixture to obtain expanded perlite containing iron.

[0052] 2) Mix expanded perlite containing iron with an alkaline aqueous solution containing phosphorus, and aerate the resulting mixture at 25-60℃ to obtain an additive.

[0053] The meanings of aeration treatment, heating treatment and ultrasonic treatment are the same as those mentioned above, and will not be repeated here.

[0054] The method for preparing the additive for sludge treatment provided by this invention uses readily available raw materials and can produce an additive with the characteristics of improving the aerobic fermentation efficiency of sludge, enhancing the water absorption and retention performance of land use products, and extending the duration of fertilizer effect through simple steps. It is characterized by simple steps and low cost.

[0055] In one embodiment, the ultrasonic treatment frequency is 28-40 kHz, and the treatment power is 5-10 W per kilogram of the material to be treated. The material to be treated refers to the mass of a mixture of aqueous solution and solid matter. When the ultrasonic treatment has the above-mentioned frequency and power, this frequency and power range can accelerate the binding rate and uniformity of ferrous ions with expanded perlite without damaging the porous structure of the expanded perlite. The resulting additive possesses both sufficient porosity and iron content.

[0056] Furthermore, in one embodiment, the aqueous solution containing ferrous ions has a ferrous ion concentration of 0.1-0.5 mol / L. An aqueous solution with this concentration of ferrous ions is less likely to form precipitates containing iron, while ensuring that the expanded perlite is loaded with a sufficient amount of iron.

[0057] To facilitate the use of the additive, in one embodiment, after mixing expanded perlite containing iron with an aqueous solution of phosphorus, the mixture is further filtered, and the filtered solid material is air-dried at room temperature to obtain an additive for sludge treatment.

[0058] A third aspect of this invention provides a sludge treatment method, comprising mixing any of the above-mentioned additives for sludge treatment with a material to be treated, and then performing aerobic fermentation. This invention does not specifically limit the type of material to be treated; common biochemically treatable wastes within the art can be used as the material to be treated. In one embodiment, the material to be treated is sludge; in another embodiment, the material to be treated includes sludge, backmixture, and organic additives, wherein the organic additives include at least one of leaves, straw, rice husks, mushroom residue, etc., and further, the moisture content of the material to be treated is 55-65%. This moisture content helps to further improve the efficiency of aerobic fermentation treatment.

[0059] This invention does not specifically limit the amount of additives added; they can be mixed with the material to be treated as needed.

[0060] This invention does not limit the conditions for aerobic fermentation, and commonly used aerobic fermentation conditions in the art can be used. In one embodiment, the aerobic fermentation conditions are: an initial moisture content of 60% in the fermentation pile, ventilation once per hour, and turning the pile once during the high-temperature period.

[0061] Since the additive provided in the first aspect of this invention has the characteristic of improving the aerobic fermentation efficiency of sludge, the sludge treatment method provided by this invention has the characteristic of high treatment efficiency.

[0062] Furthermore, the sludge treatment method provided by the present invention also includes adding different inorganic salts or light aggregates to the system obtained by aerobic fermentation treatment as needed, and carrying out deep processing such as granulation or rod making to obtain land use products.

[0063] Specifically, when the demand is for phosphorus-rich products, the phosphorus content of the fermentation products is calculated based on the phosphorus content of the products and the required phosphorus content of the products. A certain amount of inorganic phosphate fertilizer is then added to ensure that the phosphorus content of the products meets the demand before further processing.

[0064] When the requirement is for lightweight and porous materials, calculations are made based on the density of the fermentation products and the required density of the product. A certain amount of lightweight aggregate is added to ensure that the product density meets the requirements before further processing.

[0065] In one embodiment, the sludge treatment method provided by the present invention uses an additive at a rate of 5-20% of the total dry weight of the aerobic fermentation material, preferably 7-14% of the total dry weight of the aerobic fermentation material. The total dry weight of the aerobic fermentation material is the sum of the additive's mass and the dry weight of the material to be treated. This dosage helps to further increase the efficiency of aerobic fermentation.

[0066] A third aspect of this invention provides a land nutrient agent comprising any of the aforementioned additives. This invention does not limit the mass fraction of the aforementioned additives in the land nutrient agent, and the additives can be selected according to actual needs. This invention also does not limit the preparation method of the land nutrient agent. In one embodiment, the additives provided by this invention are mixed with a material to be treated, including sludge, and then subjected to aerobic fermentation treatment to obtain the land nutrient agent provided by this invention.

[0067] The following examples further illustrate the additives for sludge treatment provided by the present invention.

[0068] Example 1

[0069] This embodiment uses the following method to prepare an additive for sludge treatment:

[0070] 1) Prepare 4 L of 0.15 mol / L ferrous sulfate aqueous solution;

[0071] 2) Mix 1000g of expanded perlite with the above-mentioned ferrous sulfate aqueous solution. After sequentially subjecting the resulting mixture to ultrasonic treatment, perform solid-liquid separation on the treated system. The resulting solid phase is... Figure 1 The image shows expanded perlite containing iron. The ultrasonic treatment conditions were: frequency 40 kHz, power 30 W, and duration 20 min.

[0072] 3) Dissolve 380g Na3PO4·12H2O in 4L of deionized water to obtain a sodium phosphate aqueous solution. Adjust the pH of the aqueous solution to 8 using phosphoric acid / sodium hydroxide.

[0073] 4) Mix the solid phase of the system obtained in step 2) with the sodium phosphate aqueous solution obtained in step 3). Aerate the resulting mixture at 50°C with stirring. After 8 hours, filter the mixture and air-dry the solid phase at room temperature to obtain the final product. Figure 2 Additive A1 is shown.

[0074] Example 2

[0075] This embodiment is basically the same as Example 1, except that in step 1), the ferrous ion concentration is 0.4 mol / L. Additive A2 is thus prepared.

[0076] Example 3

[0077] This embodiment is basically the same as Example 1, except that in step 3), the mass of Na3PO4·12H2O is 38g. Additive A3 is obtained.

[0078] Example 4

[0079] This embodiment is basically the same as Example 1, except that in step 1), the concentration of the ferrous sulfate aqueous solution is 0.04 mol / L. Additive A4 is thus prepared.

[0080] Example 5

[0081] This embodiment is basically the same as Example 1, except that in step 1), the concentration of the ferrous sulfate aqueous solution is 0.7 mol / L. Additive A5 is thus prepared.

[0082] Example 6

[0083] This embodiment is basically the same as Embodiment 1, except that in step 2), the frequency of ultrasonic treatment is 50 kHz. Additive A6 is obtained.

[0084] Example 7

[0085] This embodiment is basically the same as Example 1, except that in step 3), the mass of Na3PO4·12H2O is 28g. Additive A7 is obtained.

[0086] Example 8

[0087] This embodiment is basically the same as Embodiment 1, except that in step 3), the mass of Na3PO4·12H2O is 475g. Additive A8 is obtained.

[0088] Comparative Example 1

[0089] This comparative example is basically the same as Example 1, except that in step 4), the obtained mixture is aerated by stirring at 10°C to obtain additive B1.

[0090] Comparative Example 2

[0091] This comparative example is basically the same as Example 1, except that in step 4), the obtained mixture is aerated by stirring at 70°C. Additive B2 is thus obtained.

[0092] Comparative Example 3

[0093] This comparative example is basically the same as Example 1, except that the sodium phosphate aqueous solution obtained in step 3) is replaced with an equal volume of deionized water and applied in step 4) to obtain additive B3.

[0094] Comparative Example 4

[0095] This comparative example is basically the same as Example 1, except that in step 1), the ferrous sulfate aqueous solution is replaced with a ferric chloride aqueous solution, wherein the iron ion concentration in the ferric chloride aqueous solution is the same as the ferrous ion concentration in the ferrous sulfate aqueous solution. Additive B4 is thus prepared.

[0096] Comparative Example 5

[0097] This comparative example is basically the same as Example 1, except that ultrasonic treatment is not performed in step 2). Additive B5 is obtained.

[0098] Comparative Example 6

[0099] This comparative example uses expanded perlite, which was used in Example 1, as additive B6.

[0100] Experimental Example 1

[0101] XRD analysis was performed on additives A1 and B6 respectively. The results are shown in the figure. Figure 3 .

[0102] Depend on Figure 3As can be seen, compared with the XRD pattern of expanded perlite, additive A1 has obvious characteristic peaks of ferric hydroxide, ferric oxide, and ferric hydroxide. Since additive A1 is prepared from the intermediate "expanded perlite containing iron", which is obtained by solid-liquid separation after contacting expanded perlite with a solution containing ferrous ions, the iron in additive A1 comes from the solution containing ferrous ions. This indicates that in additive A1, ferric hydroxide, ferric oxide, and ferric hydroxide are bonded to the surface of expanded perlite.

[0103] Experimental Example 2

[0104] The iron and phosphorus content of the additives prepared in each comparative example and embodiment was determined by the test method described in HJ 780-2015. The test results are shown in Table 1.

[0105] Table 1 Element Content Test Table

[0106]

[0107]

[0108] As shown in Table 1, additives A1-A8 all contain iron and phosphorus. Among them, the mass percentage of iron in additives A1-A3 is 1-3 wt%, and the mass percentage of phosphorus is 0.25-2.5 wt%. Additives B1, B2, B4, and B5 also contain phosphorus and iron. Additive B3 does not contain phosphorus because no phosphorus source was used in its preparation process. Additive B6 is expanded perlite, and therefore does not contain phosphorus or iron.

[0109] Experimental Example 3

[0110] The additives obtained from the various embodiments and comparative examples were used for aerobic fermentation, and the aerobic fermentation efficiency of the sludge was measured.

[0111] The specific contents of the aerobic fermentation experiment include: mixing sludge with a moisture content of 80%, backmixed material with a moisture content of 40%, and dried additives at a mass ratio of 12:8:1 (wet weight) to obtain a mixed pile with a moisture content of 61.0%; placing the mixed pile into a 50L cylindrical reactor for aerobic fermentation, ventilating once per hour for 2 minutes each time, and turning the pile once on the 10th day of fermentation; measuring the temperature of the aerobic fermentation pile twice a day, subtracting 15℃ (biological zero degree) from the pile temperature to obtain the biologically effective temperature, plotting the curve of biologically effective temperature versus time, and using an integration tool to obtain the effective accumulated temperature.

[0112] The test results are shown in Table 2.

[0113] Table 2 Aerobic fermentation efficiency of sludge

[0114]

[0115]

[0116] As shown in Table 2, compared with additives B1-B6 prepared in the comparative examples, additives A1-A8 prepared in each example have a higher effective accumulated temperature, indicating that the additives prepared in each example have a more prominent effect on improving the aerobic fermentation efficiency of sludge. Furthermore, compared with additives A4-A8, additives A1-A3 have a more prominent effect on improving the aerobic fermentation efficiency of sludge, possibly because additives A1-A3 have more suitable iron and phosphorus mass fractions.

[0117] Test Example 4

[0118] Based on the phosphorus and iron content measured in Table 1, a certain amount of sodium phosphate and ferrous sulfate powder were mixed into unmodified expanded perlite. After thorough mixing, comparative additives A1'-A8' with the same mass fraction of phosphorus and iron as A1-A8 were obtained.

[0119] Aerobic fermentation experiments were conducted for 21 days using additives A1-A8 and control additives A1'-A8' (parameters same as in Experiment 2). The total nutrient content (N+P2O5+K2O) of the aerobic fermentation products on day 21 was determined using the NYT 525-2021 method.

[0120] The results are recorded in Table 3.

[0121] Table 3

[0122]

[0123]

[0124] Table 3 shows that, compared to the control additives A1'-A8', the aerobic fermentation of sludge using additives A1'-A8 resulted in a higher total nutrient content of the aerobic fermentation products on day 21. This indicates that the expanded perlite and the iron oxide, iron hydroxide, and iron hydroxyl oxide adsorbed on its surface in additives A1'-A8 possess better pore structure and adsorption capacity, reducing ammonia release and thus reducing nitrogen loss. When phosphorus and iron are simply mixed with expanded perlite rather than adsorbed on its surface, the above effects are greatly weakened. Therefore, the total nutrient content of the aerobic fermentation products on day 21 is lower when using additives A1'-A8' for aerobic fermentation of sludge.

[0125] Test Example 5

[0126] Based on the phosphorus and iron content of each additive measured in Table 1, a certain amount of sodium phosphate and iron oxide, iron hydroxide and iron hydroxide powder (molar ratio of the three is 1:2:4) were mixed into unmodified expanded perlite. After thorough mixing, comparative additives A1”-A8 with the same mass fraction of phosphorus and iron as A1-A8 were obtained.

[0127] An aerobic fermentation experiment was conducted for 21 days using additives A1-A8 and comparative additives A1”-A8 (parameters same as in Experiment 2). The total nutrient content (N+P2O5+K2O) of the aerobic fermentation product on day 21 was determined using the NYT 525-2021 method.

[0128] The results are recorded in Table 4.

[0129] Table 4

[0130]

[0131]

[0132] Table 4 shows that, compared to the comparative additives A1”-A8, the aerobic fermentation of sludge using additives A1”-A8 resulted in a higher total nutrient content of the aerobic fermentation products on day 21. This indicates that, with additives A1”-A8, the ammonia reduction effect of expanded perlite is enhanced only when iron oxide, iron hydroxide, and iron hydroxyl oxide are adsorbed onto the surface of expanded perlite. When iron oxide, iron hydroxide, and iron hydroxyl oxide are simply mixed with expanded perlite instead of being adsorbed onto the surface of expanded perlite, the above effect is greatly weakened. Therefore, when using additives A1”-A8” for aerobic fermentation of sludge, the total nutrient content of the aerobic fermentation products on day 21 in the reaction system is lower.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. An additive for sludge treatment, characterized in that, It includes iron hydroxide, iron oxide, iron oxide, and expanded perlite, as well as phosphorus. The additive is prepared by a method comprising the following process: 1) Mix expanded perlite with an aqueous solution containing ferrous ions, and then sonicate the resulting mixture to obtain expanded perlite containing iron. 2) The expanded perlite containing iron is mixed with an alkaline aqueous solution containing phosphorus, and the resulting mixture is aerated at 25-60°C to obtain the additive.

2. The additive according to claim 1, characterized in that, The additive contains 1-3 wt% iron.

3. The additive according to claim 1 or 2, characterized in that, The phosphorus content is 0.25-2.5 wt%.

4. The additive according to claim 1, characterized in that, The ultrasonic treatment has a processing frequency of 28-40 kHz and a processing power of 5-10 W per kilogram of material to be treated.

5. The additive according to claim 1, characterized in that, The aqueous solution containing ferrous ions has a ferrous ion concentration of 0.1-0.5 mol / L.

6. A sludge treatment method, characterized in that, The additives according to any one of claims 1-5 are mixed with the material to be treated for aerobic fermentation.

7. The method according to claim 6, characterized in that, The amount of the additive used is 5-20% of the total dry weight of the aerobic fermentation material.

8. A soil nutrient agent, characterized in that, The additive includes any one of claims 1-5, wherein the land nutrient is prepared by mixing the additive with a material to be treated, including sludge, and then subjecting it to aerobic fermentation.

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