Sludge resource utilization method based on hydrothermal solid-liquid product reverse circulation technology

Abstract

The application provides a sludge resource utilization method based on a hydrothermal solid-liquid product reverse circulation technology. The hydrothermal solid-liquid product reverse circulation technology is a hydrothermal liquid phase forward circulation and hydrothermal solid phase reverse circulation coupling technology; and comprises the following steps: the hydrothermal solid-liquid product reverse circulation technology comprises the following steps: carrying out N-stage hydrothermal treatment on a hydrothermal medium and sludge to obtain N-stage hydrothermal solid phase and N-stage hydrothermal liquid phase, and carrying out 1-stage hydrothermal treatment on the N-stage hydrothermal solid phase in a reverse direction to obtain 1-stage hydrothermal solid phase product and 1-stage hydrothermal liquid phase product; the hydrothermal solid-liquid product reverse circulation technology improves the nitrogen and phosphorus contents of the final hydrothermal liquid phase and the carbonization rate of the sludge, and realizes the synergistic management of nitrogen and phosphorus accumulation, organic pollution removal and energy recovery of the hydrothermal liquid phase.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, specifically relating to a method for the resource utilization of sludge based on hydrothermal solid-liquid product reverse recycling technology. Background Technology

[0002] Municipal wastewater thermal treatment plays a vital role in maintaining the sustainable and healthy development of urban aquatic ecosystems, ensuring the high-quality construction of "happy rivers and lakes," and enhancing urban residents' sense of well-being regarding a beautiful and livable environment. Currently, over 80% of urban wastewater thermal treatment plants in my country utilize activated sludge treatment technology, which inevitably leads to the generation, treatment, and disposal of sludge during the wastewater treatment process.

[0003] The remaining activated sludge contains high levels of organic matter, nitrogen, and phosphorus, exceeding 60%, 10%, and 5% respectively, representing abundant resources. Traditional sludge disposal methods, including thickening, conditioning, drying, incineration, and landfilling, only achieve sludge dewatering and volume reduction, and the physical isolation or transfer of pollutants to render them harmless. These methods fail to meet the requirements for pollutant reduction and green resource utilization. Therefore, the development of sludge resource utilization technologies is highly sought after. However, existing technologies such as anaerobic fermentation and high-temperature pyrolysis primarily focus on energy recovery from the organic matter in the sludge, while neglecting the recovery of abundant nitrogen and phosphorus nutrients.

[0004] To address the issue of insufficient nitrogen and phosphorus recovery in the resource utilization of activated sludge, Chinese patent (CN102633416A) proposes a method based on anaerobic fermentation to release nitrogen and phosphorus elements from sludge. This involves further adding magnesium salts and orthophosphates to the fermentation broth to adjust the ammonia nitrogen, phosphorus, and magnesium ratio to 1:1:1, promoting struvite formation and achieving nitrogen and phosphorus recovery. Another Chinese patent (CN112125483A) proposes an acidification and hydrolysis method to promote the release of nitrogen and phosphorus elements from anaerobic sludge. This involves adding cation exchange resin to the acid-dissolved product filtrate to remove metal impurities, then adding magnesium salts and adjusting the pH to form struvite precipitate, thus achieving nitrogen and phosphorus recovery. Currently, struvite is commonly used in agriculture, limiting the industrial application of nitrogen and phosphorus. Furthermore, due to the imbalance of high nitrogen and low phosphorus ratios, large amounts of magnesium salts, phosphates, acids, and alkalis need to be added, especially magnesium salts and phosphates, increasing operating costs and process complexity, resulting in limited economic benefits. To improve the industrial application feasibility of recovering nitrogen and phosphorus from sludge, Chinese patent (CN108423953B) discloses a nitrogen and phosphorus recovery system and method for urban sludge based on supercritical technology. This technology utilizes the special properties of water in a supercritical state (Tc=374℃, Pc=22.1MPa) to promote the release of phosphorus and nitrogen. Furthermore, ammonia and phosphorus recovery systems are used to recover the nitrogen and phosphorus released into the liquid phase, obtaining ammonia water and struvite products to expand the application scenarios of nitrogen and phosphorus. However, this technology requires high temperature and high pressure to maintain the supercritical state, resulting in high process technology costs and energy consumption, and low compatibility with the "dual carbon" target.

[0005] In summary, there is an urgent need to develop a new technological solution to address the problems of harsh reaction conditions, complex processes, high energy consumption, high material consumption, and high costs associated with existing technologies. This is crucial to meeting the needs of municipal sludge reduction and resource utilization, while simultaneously promoting the achievement of zero-emission sludge treatment goals. Hydrothermal technology, under certain temperature and autogenous pressure conditions, promotes the hydrolysis of organic matter in sludge through heat conduction and water vaporization pressure, converting the sludge into a three-phase product (solid, liquid, and gas). Compared to high-temperature pyrolysis, hydrothermal technology is a simple, efficient, and cost-effective sludge reduction and resource utilization technology, characterized by its simple and rapid reaction process and mild reaction conditions. Therefore, it is necessary to develop sludge reduction and elemental resource extraction technologies based on hydrothermal technology with mild reaction conditions. Achieving low solid-phase yield, high hydrothermal calorific value, and high nitrogen and phosphorus release rates in sludge hydrothermal treatment is key to volume reduction and resource utilization, with hydrothermal temperature being a crucial controlling factor. High temperatures promote the hydrolysis and carbonization of organic matter in sludge, releasing nitrogen and phosphorus elements, increasing the liquid phase pH, and inducing the conversion of organic phosphorus and polyphosphates to orthophosphates. However, phosphate ions formed under high-temperature hydrothermal conditions easily combine with calcium and magnesium ions to form stable phosphate precipitates or adsorb onto the surface of aluminum and iron minerals, thereby reducing the phosphorus concentration in the hydrothermal liquid phase. Therefore, hydrothermal treatment technology based on the one-pot process suffers from the problem of low phosphorus concentration in the hydrothermal liquid phase.

[0006] Based on this, the present invention provides a method and technology for the resource utilization of sludge based on hydrothermal solid-liquid product reverse circulation technology, in order to solve the shortcomings of the above-mentioned technical solutions and achieve the goal of "dual improvement" of nitrogen and phosphorus concentration in hydrothermal liquid phase. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a sludge resource utilization method based on hydrothermal solid-liquid product reverse circulation technology, which solves the problems of harsh reaction conditions, high energy consumption, high material consumption, high cost, and low nitrogen and phosphorus concentrations in the liquid phase in existing technologies.

[0008] The present invention aims to provide a method for the resource utilization of sludge based on hydrothermal solid-liquid product reverse recycling technology, which is achieved through the following technical solution.

[0009] A method for sludge resource utilization based on hydrothermal solid-liquid product reverse circulation technology, wherein the hydrothermal solid-liquid product reverse circulation technology is a coupling technology of hydrothermal liquid phase forward circulation and hydrothermal solid phase reverse circulation.

[0010] The hydrothermal solid-liquid product reverse circulation technology includes the following steps:

[0011] The n-1 stage hydrothermal liquid phase and sludge are subjected to n-stage hydrothermal treatment. After N cycles, the hydrothermal liquid phase is obtained as the N-stage hydrothermal liquid phase, which generates 2-N stage hydrothermal solid phases. Each 2-N stage hydrothermal solid phase product is subjected to 1 stage hydrothermal treatment to generate the 1-stage hydrothermal solid phase product. N = 2, 3, ..., n, ..., N.

[0012] The N-stage hydrothermal liquid phase product is subjected to hydrothermal treatment to enhance the hydrolysis of organic matter in the liquid phase and the formation of orthophosphate, resulting in the N+1-stage hydrothermal liquid phase product (without hydrothermal solid phase formation).

[0013] The N+1 stage hydrothermal liquid phase products are subjected to deammoniation and dephosphorization treatment to generate deammoniation and dephosphorization tailwater.

[0014] The n-1 stage hydrothermal liquid phase is a hydrothermal medium;

[0015] The hydrothermal medium for the first-stage hydrothermal treatment is the ammonia and phosphorus removal tailwater.

[0016] The N≥2, preferably, the N is 2-4.

[0017] Furthermore, the first-stage hydrothermal solid product is hydrothermal carbon.

[0018] The above technical solution is based on the principle of hydrothermal technology. It utilizes the coupling technology of hydrothermal liquid phase forward circulation and hydrothermal solid phase reverse circulation to maximize the utilization of resources such as nitrogen, phosphorus and organic matter in the remaining sludge. The prepared high nitrogen and phosphorus hydrothermal liquid phase is sequentially fed into the ammonia / phosphorus recovery system. Ammonia water / struvite products are used to recover nitrogen and phosphorus from the sludge, and organic matter in the sludge is utilized as a resource in the form of hydrothermal carbon materials.

[0019] Furthermore, the sludge hydrothermal liquid-phase circulation involves repeatedly recycling the hydrothermal liquid-phase products as a hydrothermal medium to promote the accumulation of nitrogen and phosphorus concentrations in the liquid phase. The liquid-phase products are categorized as level 1, level 2, ..., level n, ..., level N (N = 1, 2, ..., n, ..., N, preferably level 2-4) based on the number of hydrothermal liquid-phase circulation cycles. The higher the level of the liquid-phase product (i.e., the more times it is recycled), the greater the cumulative concentration of nitrogen and phosphorus in the hydrothermal liquid phase.

[0020] The recycling mode involves using the n-1 stage hydrothermal liquid phase product as a fresh sludge hydrothermal medium for n stages of hydrothermal treatment. The first stage hydrothermal liquid phase is recycled sequentially. After N stages of hydrothermal treatment, the N stage liquid phase product is obtained. The N stage liquid phase product is then directly subjected to N+1 stage hydrothermal treatment to enhance the hydrolysis of organic matter in the liquid phase and the formation of orthophosphate, resulting in the N+1 stage liquid phase product. The N+1 stage liquid phase product then sequentially enters the ammonia recovery system and the phosphorus recovery system for nitrogen and phosphorus recovery. After nitrogen and phosphorus recovery, the liquid phase is recycled as a first stage hydrothermal medium. Each of the 2-N stage solid phase products undergoes first stage hydrothermal treatment to generate a first stage hydrothermal liquid phase product. This cycle is repeated sequentially and is called the liquid phase "forward circulation".

[0021] Furthermore, the sludge hydrothermal solid-phase circulation involves circulating the hydrothermal solid-phase products from stages 2-N through hydrothermal treatment to promote the release of solid nitrogen and phosphorus and the carbonization of organic matter. The hydrothermal solid-phase products from stages 2-N undergo a first-stage hydrothermal treatment to generate hydrothermal carbon. Because the direction of the hydrothermal solid-phase circulation is opposite to that of the liquid-phase circulation, the solid-phase circulation is referred to as "reverse circulation."

[0022] Furthermore, the hydrothermal liquid phase forward circulation and hydrothermal solid phase reverse circulation coupling technology can greatly improve the resource conversion rate and utilization rate of nitrogen, phosphorus and organic matter in sludge. The hydrothermal liquid phase forward circulation technology promotes the accumulation of nitrogen and phosphorus in the liquid phase and the carbonization of organic matter in the liquid phase, while the hydrothermal solid phase reverse circulation technology promotes the release of nitrogen and phosphorus in the solid phase and the carbonization of organic matter in the solid phase.

[0023] Furthermore, adjusting the solid-liquid ratio and pH of the remaining sludge allows the hydrothermal treatment system to operate within its optimal range, thereby maximizing the release of nitrogen and phosphorus from the sludge and promoting the carbonization of organic matter.

[0024] Furthermore, the sludge organic matter recycling hydrothermal process converts the organic matter in the sludge into hydrothermal carbon, forming hydrothermal carbon materials. Organic matter released into the lower-level liquid phase during sludge hydrothermal treatment enters the next hydrothermal stage via the forward circulation of the hydrothermal liquid phase. This inhibits the release of organic matter from the sludge and indirectly promotes the carbon conversion of solid-phase organic matter. Simultaneously, the organic matter in the hydrothermal liquid phase also carbonizes and deposits on the solid-phase surface. In addition, insufficiently carbonized organic matter in the 2-N stage hydrothermal solid-phase products will be further carbonized via the reverse circulation of the solid-phase products. Through the coupling of the forward circulation of the hydrothermal liquid phase and the reverse circulation of the hydrothermal solid phase, the carbonization rate of organic matter in the sludge is improved.

[0025] Furthermore, the solid-liquid ratio is 1:10-2:5, the hydrothermal temperature is 200-260℃, and the reaction time is 30-60min.

[0026] Furthermore, the ammonia removal process involves adjusting the temperature of the N+1 stage hydrothermal fluid to 80-90℃, further adjusting the pH to 10-11 using NaOH, and performing ammonia removal and enrichment. The enriched ammonia is then subjected to ammonia vapor condensation, ammonia purification, and ammonia distillation to obtain ammonia water and ammonia-removed wastewater, wherein the concentration of the ammonia water is 10-20%.

[0027] Furthermore, the phosphorus removal treatment utilizes the magnesium ammonium phosphate method to recover phosphorus from the liquid phase in the form of struvite. Magnesium salt is added to the hydrothermal liquid after ammonia removal treatment to adjust the molar ratio of ammonia, phosphorus, and magnesium in the wastewater to 1:1-1.5:1.5-2.0. Phosphorus is recovered by struvite precipitation. The struvite and tailwater mixture is separated in a sedimentation tank, and the supernatant is fed into the pretreatment system via a circulation system as the reaction medium for the first-stage hydrothermal treatment, thereby realizing the system's water recycling.

[0028] Preferably, the magnesium salt is one or more of magnesium sulfate or magnesium chloride.

[0029] Furthermore, the hydrothermal liquid phase with low nitrogen and phosphorus concentrations is used as the reaction medium for the hydrothermal solid phase with high nitrogen and phosphorus content. The forward circulation of the hydrothermal liquid phase promotes the accumulation of nitrogen and phosphorus in the hydrothermal liquid phase, while the reverse circulation of the hydrothermal solid phase products enhances the carbonization of organic matter in the solid phase.

[0030] The sludge resource utilization method based on hydrothermal solid-liquid product reverse circulation technology provided by this invention has the following beneficial effects:

[0031] 1. The hydrothermal liquid phase forward circulation and hydrothermal solid phase reverse circulation coupling technology of the present invention can directly solve the problem that the content of target substances such as nitrogen and phosphorus in hydrothermal liquid phase is low, resulting in low value of deep resource utilization of hydrothermal liquid phase. At the same time, it can greatly improve the carbonization rate of organic matter in sludge resources and realize the coordinated management of organic pollution removal and energy recovery.

[0032] 2. This invention uses urban waste sludge as raw material. While meeting the city's needs for the reduction and harmless disposal of activated sludge and alleviating the urban sludge siege, it also synergistically utilizes nitrogen, phosphorus, organic matter and other resources in waste sludge to generate high-value-added products such as ammonia water, struvite and hydrothermal carbon materials. This reduces the use of products such as magnesium salts and expands the application prospects of sludge nitrogen resources.

[0033] 3. This invention addresses the need for the transformation of waste from harmless treatment to resource utilization, and proposes sludge resource recovery and mining technology, providing technical support for the sustainable development and utilization of resources such as nitrogen and phosphorus, and avoiding environmental and ecological risks of sludge. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the 5-stage hydrothermal treatment technology of the present invention;

[0035] Figure 2 Van Krevelen diagram of sludge and hydrothermal solid products, good solid carbonaceous fuel coal;

[0036] Figure 3 This is a graph showing the relationship between hydrothermal solid phase yield and hydrothermal temperature. Detailed Implementation

[0037] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0038] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0039] The sludge in this embodiment of the invention is taken from the dewatered residual sludge of a sewage treatment plant in Guangzhou.

[0040] Example 1

[0041] A method for sludge resource utilization based on hydrothermal solid-liquid product reverse recycling technology includes the following steps:

[0042] S1. The tailwater from the ammonia and phosphorus removal process and the second-stage hydrothermal solid phase are subjected to a first-stage hydrothermal treatment. After the hydrothermal treatment, the mixed slurry is separated into a first-stage hydrothermal liquid phase and hydrothermal carbon material.

[0043] S2. The first-stage hydrothermal liquid phase and fresh sludge are subjected to second-stage hydrothermal treatment. After the second-stage hydrothermal treatment, the mixed sludge is separated into a second-stage hydrothermal liquid phase and a second-stage hydrothermal solid phase.

[0044] S3. The second-stage hydrothermal liquid phase is subjected to a third-stage hydrothermal treatment to promote the hydrolysis of organic matter in the liquid phase and the formation of orthophosphate. After the third-stage hydrothermal treatment, a third-stage hydrothermal liquid phase is obtained.

[0045] S4. After sequentially recovering ammonia and phosphorus from the three-stage hydrothermal liquid phase, ammonia- and phosphorus-removed tailwater is obtained;

[0046] Furthermore, the solid-liquid ratio of the sludge is 1:10.

[0047] Furthermore, the specific preparation steps of the deamination treatment include:

[0048] The temperature of the three-stage hydrothermal liquid phase was adjusted to 90℃, and the pH was adjusted to 10.5 using NaOH to carry out ammonia removal and ammonia enrichment. The enriched ammonia was then subjected to ammonia vapor condensation, ammonia gas purification, and ammonia distillation to obtain ammonia water and ammonia-removed wastewater.

[0049] Furthermore, the specific preparation steps for the phosphorus removal treatment include:

[0050] Magnesium chloride is added to the hydrothermal solution after ammonia removal, and phosphorus is recovered by struvite precipitation. The struvite and effluent mixture is separated in a sedimentation tank to obtain supernatant and struvite. The molar ratio of ammonia, phosphorus, and magnesium in the phosphorus removal wastewater is 1:1:1.5.

[0051] Furthermore, the hydrothermal temperature of the first-stage hydrothermal treatment is 250°C, the hydrothermal temperature of the second-stage hydrothermal treatment is 200°C, the hydrothermal temperature of the third-stage hydrothermal treatment is 250°C, and the reaction time is 30 minutes.

[0052] Example 2

[0053] A method for sludge resource utilization based on hydrothermal solid-liquid product reverse recycling technology includes the following steps:

[0054] S1. The tailwater from the ammonia and phosphorus removal process, along with the second-stage and third-stage hydrothermal solid phases, are subjected to a first-stage hydrothermal treatment. After the hydrothermal treatment, the mixed slurry is separated into a first-stage hydrothermal liquid phase and hydrothermal carbon material.

[0055] S2. The first-stage hydrothermal liquid phase and fresh sludge are subjected to second-stage hydrothermal treatment. After the second-stage hydrothermal treatment, the mixed sludge is separated into a second-stage hydrothermal liquid phase and a second-stage hydrothermal solid phase.

[0056] S3. The second-stage hydrothermal liquid phase and fresh sludge are subjected to a third-stage hydrothermal treatment. After the third-stage hydrothermal treatment, the mixed sludge is separated into a third-stage hydrothermal liquid phase and a third-stage hydrothermal solid phase.

[0057] S4. The third-stage hydrothermal liquid phase is subjected to a fourth-stage hydrothermal treatment to promote the hydrolysis of organic matter in the liquid phase and the formation of orthophosphate. After the fourth-stage hydrothermal treatment, a fourth-stage hydrothermal liquid phase is obtained.

[0058] S5. After sequentially recovering ammonia and phosphorus from the 4-stage hydrothermal fluid, ammonia- and phosphorus-removed tailwater is obtained.

[0059] Furthermore, the solid-liquid ratio of the second-stage hydrothermal treatment and the third-stage hydrothermal treatment is 1:10, and the solid-liquid ratio of the first-stage hydrothermal treatment is 2:5.

[0060] Furthermore, the specific preparation steps of the ammonia removal treatment include: adjusting the temperature of the four-stage hydrothermal liquid phase to 90°C, adjusting the pH to 10.5 using NaOH, performing ammonia removal and ammonia enrichment, and subjecting the enriched ammonia to ammonia vapor condensation, ammonia purification, and ammonia distillation to obtain ammonia water and ammonia-removed wastewater.

[0061] Furthermore, the specific preparation steps of the phosphorus removal treatment include: adding magnesium chloride to the hydrothermal liquid after ammonia removal, recovering phosphorus by precipitating with struvite, and separating the struvite and tailwater mixture in a sedimentation tank to obtain supernatant and struvite. The molar ratio of ammonia, phosphorus, and magnesium in the phosphorus removal wastewater is 1:1:1.5.

[0062] Furthermore, the hydrothermal temperature of the first-stage hydrothermal treatment is 250°C, the hydrothermal temperatures of the second-stage and third-stage hydrothermal treatments are 200°C, the hydrothermal temperature of the fourth-stage hydrothermal treatment is 250°C, and the reaction time is 30 minutes.

[0063] Example 3

[0064] A method for sludge resource utilization based on hydrothermal solid-liquid product reverse recycling technology includes the following steps:

[0065] S1. The tailwater from the ammonia and phosphorus removal process and the second-stage, third-stage, and fourth-stage hydrothermal solid phases are subjected to first-stage hydrothermal treatment. After the hydrothermal treatment, the mixed slurry is separated into first-stage hydrothermal liquid phase and hydrothermal carbon material.

[0066] S2. The first-stage hydrothermal liquid phase and fresh sludge are subjected to second-stage hydrothermal treatment. After the second-stage hydrothermal treatment, the mixed sludge is separated into a second-stage hydrothermal liquid phase and a second-stage hydrothermal solid phase.

[0067] S3. The second-stage hydrothermal liquid phase and fresh sludge are subjected to a third-stage hydrothermal treatment. After the third-stage hydrothermal treatment, the mixed sludge is separated into a third-stage hydrothermal liquid phase and a third-stage hydrothermal solid phase.

[0068] S4. The third-stage hydrothermal liquid phase and fresh sludge are subjected to fourth-stage hydrothermal treatment. After the fourth-stage hydrothermal treatment, the mixed sludge is separated into a fourth-stage hydrothermal liquid phase and a fourth-stage hydrothermal solid phase.

[0069] S5. The 4-stage hydrothermal liquid phase is subjected to a 5-stage hydrothermal treatment to promote the hydrolysis of organic matter in the liquid phase and the formation of orthophosphate. After the 5-stage hydrothermal treatment, a 5-stage hydrothermal liquid phase is obtained.

[0070] S6. After sequentially recovering ammonia and phosphorus from the 5-stage hydrothermal fluid, ammonia- and phosphorus-removed tailwater is obtained.

[0071] Furthermore, the solid-liquid ratio of the second-stage hydrothermal solid phase, the third-stage hydrothermal solid phase, and the fourth-stage hydrothermal solid phase is 1:10, and the solid-liquid ratio of the first-stage hydrothermal phase is 2:5.

[0072] Furthermore, the specific preparation steps of the ammonia removal treatment include: adjusting the temperature of the 5-stage hydrothermal liquid to 90℃, adjusting the pH to 10.5 using NaOH, performing ammonia removal and ammonia enrichment, and subjecting the enriched ammonia to ammonia vapor condensation, ammonia purification, and ammonia distillation to obtain ammonia water and ammonia-removed wastewater.

[0073] Furthermore, the specific preparation steps of the phosphorus removal treatment include: adding magnesium chloride to the hydrothermal liquid after ammonia removal, recovering phosphorus by precipitating with struvite, and separating the struvite and tailwater mixture in a sedimentation tank to obtain supernatant and struvite. The molar ratio of ammonia, phosphorus, and magnesium in the phosphorus removal wastewater is 1:1:1.5.

[0074] Furthermore, the hydrothermal temperature of the first-stage hydrothermal treatment is 250°C, the hydrothermal temperatures of the second-stage, third-stage, and fourth-stage hydrothermal treatments are 200°C, the hydrothermal temperature of the fifth-stage hydrothermal treatment is 250°C, and the reaction time is 30 minutes.

[0075] Comparative Example 1

[0076] The materials and operating methods used in Comparative Example 1 and Example 2 are the same, the only difference being that only the liquid phase positive circulation hydrothermal treatment is performed, and the solid phase is not subjected to reverse circulation hydrothermal treatment.

[0077] Comparative Example 2

[0078] The materials and operating methods used in Comparative Example 2 and Example 2 are the same, the only difference being that solid-liquid phase circulation is not performed.

[0079] Comparative Example 3

[0080] The materials and operating methods used in Comparative Example 3 and Example 2 are the same, the only difference being that the hydrothermal temperature in S1-S4 is 200°C.

[0081] Comparative Example 4

[0082] The materials and operating methods used in Comparative Example 4 and Example 2 are the same, the only difference being that the hydrothermal temperature in S1-S4 is 250°C.

[0083] Test case

[0084] Examples 1-3 and Comparative Examples 1-4 were tested, and the specific test methods and results are as follows:

[0085] Test Methods: According to the standard test method in "Methods for Detection and Analysis of Water and Wastewater (Fourth Edition)," the hydrothermal liquid phase was diluted 100-1000 times, and sodium hypobromite oxidant was added to oxidize ammonia and ammonium salts to nitrite. The ammonia nitrogen content in the water sample was determined using gas-phase molecular absorption spectroscopy of nitrite nitrogen. The hydrothermal carbon yield was reflected by the sludge solid phase change rate during hydrothermal treatment, and the hydrothermal carbon yield (HTC) was further calculated using the following formula: Hydrothermal Carbon Yield (HTC) = Residual Solid Phase Mass / Initial Sludge Mass × 100%. The calorific values ​​of hydrothermal carbon and sludge were measured using an oxygen bomb calorimeter, and the hydrothermal carbon energy recovery ratio (ER) was further calculated using the following formula: Hydrothermal Carbon Energy Recovery Ratio (ER) = Calorific Value of Hydrothermal Carbon (HTC) / Calorific Value of Sludge (SS). The content of metal ions affecting phosphorus release in the sludge is shown in Table 1, and the test results are shown in Table 2, where the calorific value of the sludge is 10.42 MJ / kg.

[0086] Table 1. Metal ion content in sludge

[0087] type Fe Al Ca Mg Content (mg / g) 23.92 46.60 3.83 2.58

[0088] Table 2. Test results of the examples and comparative examples.

[0089]

[0090]

[0091] Table 2 shows that the cumulative concentration of ammonia nitrogen in the five-stage hydrothermal liquid phase of this invention is as high as 11000 mg / L, and the cumulative concentration of phosphorus is as high as 400 mg / L. After the first stage of hydrothermal treatment in the reverse circulation of each of the 2-N stages of hydrothermal solid phase, the yield of hydrothermal carbon material is 75%, and the energy recovery ratio of hydrothermal carbon (the ratio of hydrothermal carbon energy to sludge energy) is 77%. The hydrothermal carbon yield and energy recovery of the examples and comparative examples are not significantly different. However, the cumulative concentration of ammonia nitrogen and phosphorus in the liquid phase of Example 3 is significantly better than that of other examples and comparative examples. At the same time, the cumulative concentration of ammonia nitrogen and phosphorus in the liquid phase of Example 2 is also better than that of comparative examples 1-2. This indicates that the forward circulation of hydrothermal liquid phase and the reverse circulation coupling technology of hydrothermal solid phase can improve the cumulative concentration of ammonia nitrogen and phosphorus in hydrothermal liquid phase, providing a basic guarantee for the recovery of nitrogen and phosphorus from sludge.

[0092] Please see Figure 2-3The O / C and H / C scattering points of sludge hydrothermal products differ from those of anthracite, bituminous coal, and lignite. Furthermore, sludge hydrothermal carbon contains high levels of oxygen and inorganic components, thus it cannot yet be considered a suitable solid carbonaceous fuel. Regarding the relationship between sludge hydrothermal temperature and solid phase yield, the solid phase yield decreases with increasing temperature, primarily because high temperatures promote the hydrolysis and release of organic matter in the sludge.

[0093] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0094] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for sludge resource utilization based on hydrothermal solid-liquid product reverse recycling technology, characterized in that, The hydrothermal solid-liquid product reverse circulation technology is a coupling technology of hydrothermal liquid phase forward circulation and hydrothermal solid phase reverse circulation; The hydrothermal solid-liquid product reverse circulation technology includes, in sequence: pre-hydrothermal treatment, N-stage hydrothermal treatment and post-hydrothermal treatment; The hydrothermal solid-liquid product reverse circulation technology includes the following steps: The hydrothermal medium and sludge are subjected to N-stage hydrothermal treatment to obtain N-stage hydrothermal solid phase and N-stage hydrothermal liquid phase. The N-stage hydrothermal solid phase is reverse-circulated for pre-hydrothermal treatment to obtain pre-hydrothermal solid phase product and pre-hydrothermal liquid phase product. In the N-stage hydrothermal treatment, the hydrothermal medium of the 1-stage hydrothermal treatment is the pre-hydrothermal liquid phase product. The hydrothermal medium for N-stage hydrothermal treatment, excluding the first-stage hydrothermal treatment, is the N-1 stage hydrothermal liquid phase; The post-hydrothermal liquid phase in the post-hydrothermal treatment is subjected to deammoniation and dephosphorization treatment to generate deammoniation and dephosphorization tailwater. The pre-hydrothermal solid product is hydrothermal carbon; The hydrothermal medium for the pre-treatment hydrothermal treatment is the deammoniation and phosphorus removal tailwater; The N≥2; The value of N is 2-4; The solid-liquid ratio of the hydrothermal treatment is 1:10-2:5; The hydrothermal treatment temperature is 200-260℃, and the reaction time is 30-60 min; The temperature for the deammoniation treatment is 80-90℃.

2. The sludge resource utilization method based on hydrothermal solid-liquid product reverse recycling technology as described in claim 1, characterized in that, The specific preparation steps of the deammoniation treatment include: deammonising and enriching the post-hydrothermal liquid, condensing the ammonia vapor, purifying and distilling it to obtain ammonia water.

3. The sludge resource utilization method based on hydrothermal solid-liquid product reverse recycling technology as described in claim 1, characterized in that, The pH of the deammoniation treatment is 10-11.

4. The sludge resource utilization method based on hydrothermal solid-liquid product reverse recycling technology as described in claim 1, characterized in that, The specific preparation steps of the phosphorus removal treatment include: adding magnesium salt to the hydrothermal liquid after ammonia removal treatment, and obtaining struvite after precipitation.

5. The sludge resource utilization method based on hydrothermal solid-liquid product reverse circulation technology as described in claim 4, characterized in that, The molar ratio of ammonia, phosphorus, and magnesium in the hydrothermal fluid is 1:1-1.5:1.5-2.0.

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