Method for rapidly recovering phosphorus element in activated sludge

Abstract

The invention discloses a method for rapidly recovering phosphorus element in activated sludge, which utilizes an alkaline gradient centrifugation technology to realize selective separation of high-density substances on the basis of the characteristic that the density of an adsorbent for precipitating and adsorbing phosphate of metal phosphate is greater than that of the activated sludge. After the alkaline agent is dissolved, the pH is increased, calcium and magnesium ions in the sludge and phosphate radicals are promoted to form precipitates, meanwhile, the adsorption agent is hydrolyzed to capture the phosphate radicals, and the high-density substances can be separated from the light activated sludge under the action of centrifugal force. Compared with the prior art, the treatment time of the method is only minute-hour level, and the energy consumption and the secondary pollution are obviously reduced. Only high-density precipitates instead of all sludge are treated, so that the dosage of the medicament is reduced on year-on-year basis, and the gradient centrifugation medicament can be recycled and regenerated. Process parameters are flexible and adjustable, and the device can adapt to sludge with different water contents. The recovered phosphorus can be used as a phosphorus fertilizer precursor or used in the fields of fire retardant manufacturing and the like, efficient cyclic utilization of phosphorus resources is achieved, and economic and environment-friendly values are achieved.

Description

Technical Field

[0001] This invention pertains to the technology of resource utilization of municipal activated sludge, specifically to a method for rapidly recovering phosphorus from activated sludge. Background Technology

[0002] Phosphorus is essential for the growth of organisms, being one of the basic elements of life and an indispensable fertilizer component in modern agriculture. Currently, the vast majority of usable phosphorus is obtained through mining phosphate rock in the lithosphere. However, the non-renewable nature of phosphate rock resources is causing global concern. Furthermore, the distribution of phosphate rock resources worldwide is extremely uneven, with proven reserves highly concentrated in countries such as Morocco (accounting for over 70%), China, the United States, and Russia. Therefore, the supply of phosphate rock poses a significant risk to most countries and regions. Existing phosphate rock reserves are projected to be depleted within 50-100 years. As early as 2014, the European Commission listed phosphorus, along with rare earth elements, as a key raw material for ensuring economic security and strategic industries. my country, as the largest producer and consumer of phosphate fertilizer, designated phosphate rock as a strategic mineral in 2016, implementing total mining control. Modern phosphate chemical industry produces phosphate fertilizer through the wet-process phosphoric acid production, but this process generates hundreds of millions of tons of phosphogypsum waste, fluorinated acidic gases, and fluorinated wastewater, posing a significant environmental hazard. Phosphate fertilizer production is an energy-intensive and highly polluting industry, and the treatment of the resulting phosphogypsum waste is a global challenge. Therefore, while exporting phosphate fertilizer ensures international food supply, it leaves environmental pollution within the country. In 2024, eight national ministries, including the Ministry of Industry and Information Technology, jointly issued the "Implementation Plan for Promoting the Efficient and High-Value Utilization of Phosphate Resources," proposing three measures to enhance the sustainable security of phosphate resources, requiring the broadening of phosphate resource supply channels and increased efforts in phosphate resource recovery.

[0003] Approximately 54% of phosphorus from human production and daily consumption ends up in wastewater. After treatment at wastewater treatment plants, over 90% of this phosphorus ultimately ends up in municipal sludge. Municipal sludge contains large amounts of nitrogen, phosphorus, and potassium, as well as various trace metals and organic matter essential for plant and soil ecosystems. Recovering phosphorus from municipal sludge is a future-oriented path for sludge resource utilization. European countries began exploring this approach as early as the last century and developed a series of phosphorus recovery technologies. However, efficient phosphorus recovery from sludge remains a global challenge. Research over the past 30 years, both domestically and internationally, shows that the efficiency of directly recovering phosphorus from wastewater is unlikely to exceed 50%. Only from dewatered sludge or the ash from sludge incineration can phosphorus from wastewater be efficiently (80-90%) recovered.

[0004] Known domestic and internationally validated pilot-scale and full-scale processes for phosphorus recovery from municipal sludge mainly involve two steps. The first step involves extracting or concentrating phosphorus-containing components from the sludge, a process that typically involves high-temperature, high-pressure pyrolysis, incineration, and acid or alkaline leaching. The second step involves purifying and extracting phosphate from the extracted phosphorus-rich components, again involving acid-base leaching and various precipitation reactions, ultimately recovering phosphate as low-solubility phosphates such as struvite, calcium phosphate, and sodium calcium phosphate. Technologies that directly utilize sludge include the Gifferhorn process (leaching), the Stuttgart process (leaching), the PHOXNAN process, the Aqua Reci process (supercritical water oxidation), and the MEPHREC process. Representative processes for extracting phosphorus from the ash after municipal sludge combustion include AshDec® depollution, AshDec® Rhenania, PASCH, LEACHPHOS, and EcoPhos. ICLFertilizer, an Israeli company, has one of the world’s largest and most technologically advanced plants for recovering phosphorus from sludge ash at its plant in the Netherlands. The recycled phosphate fertilizer produced annually from municipal sludge and bone meal incineration ash can replace 10% of the Netherlands’ domestic phosphorus demand, and there is potential to further expand production capacity in the future.

[0005] In addition, there are separate anaerobic sludge phosphorus extraction units designed based on the characteristic of polyphosphate-accumulating bacteria in activated sludge releasing phosphorus under anaerobic conditions. These units produce phosphorus-rich supernatant, which is then precipitated with calcium salts to obtain phosphate, such as the PhoStrip process. Some laboratory studies have used reducing organic matter such as citric acid and ascorbic acid to promote phosphorus release under anaerobic conditions, because ferric phosphate is stable under acidic conditions and ferrous phosphate is soluble in the liquid phase. However, the feasibility of this process has not yet been verified.

[0006] The phosphate precipitate obtained by the above process needs to be extracted with acid or alkali solution, and then purified by stepwise precipitation or liquid phase extraction to remove heavy metals.

[0007] Because many phosphorus recovery processes involve wastewater phosphorus removal processes developed since the mid-20th century, these are mostly technologies reported in scientific papers, resulting in relatively few related phosphorus recovery process patents. The available phosphorus recovery patents include CN202110245451.1, titled "A Method for Efficiently Recovering Phosphorus from Municipal Sludge and Simultaneously Preparing Porous Biochar." This method mainly relies on dissolved iron ions combining with phosphorus in the sludge, followed by high-temperature pyrolysis under alkaline conditions to produce biochar. Phosphate is then extracted from the biochar, and finally, magnesium and ammonium salts are added to recover phosphorus using struvite. Another patent, CN 101970360 A, titled "Method for Removing Phosphorus and Magnesium from Waste Activated Sludge and Struvite Production System," primarily utilizes the known characteristic of phosphorus-rich sludge in enhanced biological phosphorus removal units of wastewater treatment plants releasing phosphorus under anaerobic conditions. It recovers phosphorus-rich supernatant by adding magnesium and ammonium salts to precipitate phosphate using struvite to achieve phosphorus recovery. There is also a patent CN 117383983 A, entitled "A method for efficient phosphorus recovery from sludge", the main mechanism of which is "sludge conditioning". However, the process described in the patent does not conform to conventional understanding. It is extremely difficult to release phosphorus from sludge by introducing biochar and flocculants. The introduced iron or aluminum elements will obviously cause phosphate to precipitate and not enter the filtrate. Therefore, the actual efficiency of phosphorus extraction by the patent is unclear.

[0008] In summary, the existing technologies have four obvious drawbacks: (1) The methods often require the use of acidic or reducing agents to dissolve phosphate in sludge and release phosphate ions, and then introduce new agents into the leachate to achieve the precipitation reaction of phosphate ions, or add biochar or ion exchange resins that can adsorb phosphate ions to achieve the extraction of phosphate ions. The methods often involve the dissolution and reprecipitation of phosphorus-containing precipitates, and the demand for agents is large; (2) The methods involve high-temperature and high-pressure pyrolysis, supercritical water oxidation, high-temperature and high-pressure pure oxygen oxidation, and incineration of sludge. These operations result in large energy consumption, and the initial investment in incineration technology is extremely large. The carbon dioxide and flue gas containing heavy metals generated during the incineration process must be treated, which increases the cost of treatment and the risk of secondary pollution; (3) The methods are time-consuming, and the steps of drying and then incineration, leachation, and pyrolysis followed by leachation are time-consuming; (4) The phosphorus recovery rate of the process based on the anaerobic release of phosphorus by phosphorus-loving bacteria in sludge is low, and the efficiency of the actual pilot system is far lower than that of the laboratory small-scale test results. Summary of the Invention

[0009] To address the problems existing in the prior art, the purpose of this invention is to provide a method for rapidly recovering phosphorus from activated sludge, which does not involve high-temperature and high-pressure treatment, nor high-energy-consuming methods such as incineration, and can shorten the process time, improve phosphorus extraction efficiency, and reduce energy consumption.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for rapidly recovering phosphorus from activated sludge, characterized by comprising the following steps: (1) Remove water from activated sludge to a moisture content of 40%~95%, and then break it up to make it into a paste-like sludge; (2) Add phosphate adsorbent to the sludge at 1 / 1000 to 1 / 100 of the sludge mass, stir thoroughly, and obtain dewatered activated sludge after conditioning. The phosphate adsorbent is iron oxide, aluminum oxide or aluminum hydroxide. (3) Based on the density range of conventional dewatered activated sludge (1~1.2 g / cm³) 3 Gradient centrifuge solutions containing 20-70% gradient centrifuge reagent were prepared using gradient centrifuge reagents, yielding solutions with densities ranging from 1.3 to 1.9 g / cm³. 3 The gradient centrifuge liquid density is selected based on the density of the added phosphate adsorbent, ensuring that the density of the gradient centrifuge liquid is greater than the density of the activated sludge to be dewatered and less than the density of the phosphate adsorbent; the gradient centrifuge agent is sodium silicate solution or a silica nanoparticle suspension with pH adjusted to >10. (4) Add the dewatered activated sludge and the gradient centrifuged liquid to a mixer at a volume ratio of 1:(2~10), and stir the sludge and the centrifuged liquid at a low speed of no more than 500 rpm to mix them evenly. (5) After mixing, transfer the mixture into a centrifuge and set it to a centrifugal force of 3500~10000 g. Centrifuge for a certain period of time to allow the high-density phosphate and the adsorbent that adsorbed the phosphorus to precipitate together and separate from the sludge. (6) After centrifugation, the material in the centrifuge is extracted step by step. The high-density phosphorus-rich adsorbent and precipitate in the lower layer are discharged and collected through the discharge hole first. Then the gradient centrifuged liquid in the middle layer is collected. Finally, the sludge floating in the upper layer, from which phosphorus and nutrients have been removed, is collected. (7) The high-density phosphorus-rich adsorbent and precipitate are dissolved with sulfuric acid and the pH of the extract solution is made <2. The insoluble matter is collected in the sedimentation tank or clarification tank, washed with water and recycled as phosphate adsorbent. Then, alkaline agents are introduced to adjust the pH to 2-3 to precipitate ferric phosphate. Then, alkaline agents are further introduced to adjust the pH to 4-5 to precipitate ferrous alum containing jaundice. Alkaline agents are added to adjust the pH to about 8 to precipitate impurities and heavy metals. Finally, the extracted iron and aluminum phosphates are dissolved under acidic conditions, and then calcium hydroxide or calcium oxide is added. The hydrolysis precipitates of iron and aluminum are then removed under weakly alkaline conditions to obtain calcium phosphate; or magnesium hydroxide / magnesium oxide and ammonium salts are added to prepare magnesium ammonium phosphate.

[0011] Preferably, the activated sludge in step (1) is activated sludge from a municipal wastewater treatment plant, anaerobic digestion sludge, or aerobic / anaerobic activated sludge produced by an industrial organic phosphorus-containing wastewater bioreactor.

[0012] Preferably, in step (1), the activated sludge is dehydrated by centrifugation or plate and frame filtration.

[0013] Preferably, in step (2), the stirring speed of the mixer does not exceed 500 rpm and the time is from several minutes to 1 hour.

[0014] Preferably, in step (2), the iron oxide is one or more of ferric oxide, iron tetroxide and hydrated iron oxide; the aluminum oxide is aluminum oxide and / or aluminum hydroxide.

[0015] Preferably, the dewatered activated sludge after pretreatment and conditioning in step (2) is processed in step (4), or it is left to stand at room temperature or slightly below room temperature for several minutes before being processed in step (4).

[0016] Preferably, the mixing process in step (4) is carried out at or below room temperature and lasts for no more than 10 minutes.

[0017] Preferably, the centrifugation time in step (5) is 1 to 30 minutes.

[0018] Preferably, the alkaline agent in step (7) is one or more of magnesium oxide, magnesium hydroxide, and sodium hydroxide.

[0019] Preferably, the gradient centrifuge liquid collected in step (6) is used in the next centrifugation cycle until it becomes turbid or its density decreases to be equal to or lower than that of the sludge due to contact with the sludge. Gradient centrifuge liquid with excessively low density is collected, evaporated and dehydrated until its density is restored, and then recycled. Turbid gradient centrifuge liquid is collected, evaporated and dehydrated, and the distilled water is recycled. The dehydrated reagent is heated to 550°C to remove the mixed organic matter from the activated sludge and the gradient centrifuge reagent is recovered. The upper sludge collected in step (6) is adjusted to neutral pH using acid or alkali solution, and then subjected to aerobic or anaerobic composting or other sludge stabilization and reduction treatments before being disposed of in accordance with relevant regulations.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a novel, simple, and effective method for phosphorus resource recovery. Based on the fact that the density of metal phosphate precipitates and the density of the adsorbent that adsorbs phosphate are both greater than the density of activated sludge biomass, the high-density material is removed from the sludge bulk using gradient centrifugation. Based on the density differences and compositional characteristics of the components in the activated sludge, high-density phosphate precipitates are selectively and efficiently extracted with the assistance of an alkaline gradient centrifugation reagent. During the process, the alkaline gradient centrifugation reagent itself dissolves, causing a pH increase, or sodium hydroxide is added to adjust the pH, promoting the formation of high-density precipitates of calcium and magnesium ions and phosphate ions in the sludge. Furthermore, the added adsorbent undergoes hydrolysis and adsorbs some of the phosphate ions.

[0021] Compared to existing technologies, this invention significantly improves the efficiency of phosphorus recovery from sludge, with core operation times measured in minutes or hours, and greatly reduces energy consumption and secondary pollution. The method involves the addition of reagents, but because the volume of precipitate involved in the extraction is significantly reduced compared to the original sludge, the reagent dosage is proportionally reduced. Furthermore, the gradient centrifugation reagents involved in the process are recycled and regenerated after a certain number of uses, allowing for reuse. This gradient centrifugation method can tailor centrifuge solutions for sludge with different organic matter contents, and the process parameters are flexibly adjustable. Only simple pre-experiments are needed to modify the equipment parameters to adapt to new sludge raw materials. Compared to known methods, this invention greatly reduces the phosphorus extraction cycle. The recovered phosphorus can be used as a precursor for phosphate fertilizers or in other fields (such as the manufacture of flame retardants), and the process facilitates the recycling and utilization of phosphorus resources.

[0022] 1) The time required for the core sludge phosphorus recovery step can be reduced to about 30 minutes, which is much faster than the traditional process that takes several days. This greatly improves the efficiency of sludge phosphorus recovery and significantly shortens the operating cycle of sludge resource utilization.

[0023] 2) The phosphorus recovery process from sludge does not involve extreme acidification or alkalization of the original sludge, nor does it involve conventional operations such as anaerobic fermentation and the addition of small-molecule organic matter to release phosphate ions from the sludge. It only requires maintaining the system under actual operating conditions, such as sodium silicate gradient centrifugation or appropriate adjustment to ensure the pH of the silica nanoparticle gradient centrifugation system is >10, or adding a small amount of reagent after phosphorus recovery to adjust the upper floating sludge to neutral. The wastewater generated from removing heavy metals from phosphorus-containing substances requires further treatment. Since the amount of heavy metals to be treated is relatively small, the amount of rinsing solution required is also small.

[0024] 3) The new process of this invention relies on gradient centrifugation reagents and adsorbents to be regenerated after the use cycle through simple steps such as dehydration, baking, and washing. Even if some adsorbents, such as aluminum-containing substances, are lost during the process cycle, the overall process has the characteristics of low initial investment and low subsequent maintenance costs. Attached Figure Description

[0025] Figure 1 A simplified process flow diagram of the method of this invention; Figure 2 The effect of the method of the present invention on phosphorus recovery from municipal sludge after different dewatering treatments at two reclaimed water plants is shown in the figure. Figure 3 The diagram shows the effect of the method of the present invention on potassium recovery from municipal sludge after different dewatering treatments at two reclaimed water plants. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments, but this is not intended to limit the present invention.

[0027] like Figure 1 As shown, the method for rapidly recovering phosphorus from activated sludge according to the present invention includes the following steps: (1) Using activated sludge from municipal wastewater treatment plants and anaerobic activated sludge from industrial organic wastewater anaerobic biological reaction units as initial raw materials, the sludge is dewatered through mature solid-liquid separation processes such as centrifugal dewatering and plate and frame filter press. The sludge moisture content is generally between 40% and 95%. For sludge materials that form lumps after plate and frame filter press, economical and feasible treatment methods are required to obtain uniform paste-like sludge raw materials to meet the requirements of subsequent processes.

[0028] (2) After obtaining suitable sludge, add phosphate adsorbent to the sludge. The mass percentage of the adsorbent is 1 / 1000 to 1 / 100. Stir thoroughly, generally for several minutes to 1 hour. The stirring speed should not exceed 500 rpm. The conditioned dewatered activated sludge can then be obtained. The phosphate adsorbent is iron oxide or aluminum oxide. The iron oxide is one or more of ferric oxide, magnetite, and hydrated iron oxide, or a high-density material loaded with these substances, metal-doped / loaded iron oxide and hydrate, and a mixture of these substances. The aluminum oxide particles are aluminum oxide, aluminum hydroxide, high-density material loaded with these substances, metal-doped / loaded aluminum oxide and hydrate, and a mixture of these substances. Or the iron oxide particles are natural iron mineral powder of magnetite or ferroalloy.

[0029] (3) After the pretreatment in step (2), proceed to step (4) for further treatment, or let it stand at room temperature or slightly below room temperature for a few minutes before proceeding to step (4) for further treatment.

[0030] (4) Based on the density range of conventional dewatered activated sludge (1~1.2 g / cm³) 3 Centrifuge solutions containing 20-70% gradient centrifugation reagent were prepared using gradient centrifugation reagents, yielding solutions with densities ranging from 1.3 to 1.9 g / cm³. 3The gradient centrifugation solution should be denser than the activated sludge to be dewatered. The density of the centrifugation solution should be selected based on the density of the added phosphate adsorbent, with the basic principle being that the density of the adsorbent and the density of the centrifugation solution should increase or decrease together. The gradient centrifugation reagent of this invention refers to a sodium silicate solution or a suspension of silica nanoparticles with pH adjusted to >10.

[0031] (5) Add appropriate amounts of the sludge and centrifuge liquid obtained in step (3) to the mixer at a volume ratio of 1:(2~10) of dewatered activated sludge to gradient centrifuge liquid. Agitate and mix the sludge and centrifuge liquid at no more than 500 rpm. The temperature should be controlled at room temperature or below during mixing, and the mixing time should be measured in minutes until well mixed.

[0032] (6) After stirring thoroughly, transfer the mixture to a centrifuge and set the centrifugal force to 3500~10000 g to separate the high-density phosphate precipitate and the metal oxides that have adsorbed phosphorus. Centrifugation is generally carried out for 1~30 minutes.

[0033] (7) After centrifugation, the materials in the centrifuge are extracted step by step. The high-density phosphorus-rich adsorbent and precipitate in the lower layer are discharged and collected through the discharge port. Then the gradient centrifuged liquid in the middle layer is collected, and finally the sludge floating in the upper layer, from which phosphorus and nutrients have been removed, is collected.

[0034] (8) High-density phosphorus-rich adsorbents and precipitates are calcined at 550°C to remove mixed organic matter, or phosphates and possible heavy metal precipitates are separated by dissolving in sulfuric acid and step-by-step precipitation.

[0035] If sulfuric acid is used to dissolve the extract to make the pH of the solution <2, the insoluble substances, such as ferric oxide or aluminum oxide particles, are collected in a sedimentation tank or clarification tank, washed with water, and reused as an adsorbent. Then, an alkaline agent (such as magnesium oxide) is introduced to adjust the pH to 2-3 to precipitate ferric phosphate. Then, an alkaline agent is further introduced to adjust the pH to 4-5 to precipitate ferric alum containing jaundice. Alkaline agents are added again to adjust the pH to about 8 to precipitate impurities and heavy metals. Finally, the extracted iron and aluminum phosphates are dissolved under acidic conditions, and calcium hydroxide or calcium oxide is added. Under weakly alkaline conditions, the hydrolysis precipitates of iron and aluminum are precipitated to obtain calcium phosphate. Alternatively, magnesium hydroxide / magnesium oxide and ammonium salts are added to produce magnesium ammonium phosphate (struvite).

[0036] Since these steps target only the high-density material with a small bottom volume produced by centrifugation, rather than the original activated sludge, the required dosage of chemicals is less.

[0037] (9) The gradient centrifuge liquid in the middle layer is used in the next centrifugation cycle until it becomes more turbid or its density decreases to equal or lower than that of the sludge due to contact with the sludge. Gradient centrifuge liquid with excessively low density is collected, evaporated and dehydrated until the density is restored, and then recycled. Turbid gradient centrifuge liquid is collected, evaporated and dehydrated, and the distilled water is recycled. The dehydrated reagent is heated to 550°C to remove the mixed organic matter from the activated sludge and the gradient centrifuge reagent is recovered. (10) The upper sludge is adjusted to neutral pH using acid or alkali solution and then enters aerobic or anaerobic composting or other common sludge stabilization and reduction treatment processes.

[0038] The centrifugal phosphorus recovery process described in this invention is simple to operate, takes only hours, and is highly effective. Compared with the traditional and most common acid leaching and anaerobic fermentation-coupled phosphorus precipitation methods, it significantly reduces the time required and the dosage of reagents used.

[0039] Application examples: Example 1: Residual activated sludge from the secondary sedimentation tank of a wastewater treatment plant was taken, flocculated and conditioned with PAM, and then centrifuged to obtain dewatered sludge with a moisture content ≥80%. Iron oxide phosphate adsorbent (1 / 100 of the sludge mass) was added to the sludge and stirred thoroughly to obtain conditioned dewatered activated sludge. A gradient centrifuge solution containing 20-70% of the gradient centrifuge reagent (sodium silicate solution) was prepared, with a density of 1.45 g / cm³. 3 The centrifuged liquid and dewatered activated sludge were added to a mixer at a volume ratio of 5:1. The mixture was agitated at a low speed (not exceeding 500 rpm) to ensure homogeneity. After mixing, the mixture was centrifuged for a certain period to allow the high-density phosphate and the phosphorus-adsorbent to co-precipitate and separate from the sludge. The lower layer of high-density, phosphorus-rich adsorbent and precipitate was extracted and collected through a discharge port. The high-density, phosphorus-rich adsorbent and precipitate were dissolved in sulfuric acid to achieve a pH < 2. The insoluble residue was collected in a sedimentation tank or clarification tank, washed with water, and reused as phosphate adsorbent. Then, an alkali was introduced... The pH is adjusted to 2-3 with an alkaline reagent to precipitate ferric phosphate. Then, an alkaline reagent is introduced to adjust the pH to 4-5 to precipitate ferrous alum containing jaundice. The alkaline reagent is then added to adjust the pH to around 8 to precipitate impurities and heavy metals. Finally, the extracted iron and aluminum phosphates are dissolved under acidic conditions, and then calcium hydroxide or calcium oxide is added. Under weakly alkaline conditions, the hydrolysis precipitates of iron and aluminum are precipitated to remove the precipitates, thus obtaining calcium phosphate. Alternatively, magnesium hydroxide / magnesium oxide and ammonium salts are added to prepare magnesium ammonium phosphate, thus obtaining phosphate. The phosphorus recovery rate is 81.1%.

[0040] Example 2: Take the residual activated sludge after conventional plate and frame filtration, add polyaluminum chloride (PAC) dewatering agent for conditioning, and then perform deep dewatering via steam-assisted plate and frame filtration to obtain dewatered sludge with a moisture content ≥40%. After crushing and homogenization, a uniform paste-like sludge is finally prepared. Add 5 / 1000 of the sludge mass of iron oxide phosphate adsorbent to the sludge and stir thoroughly to obtain conditioned dewatered activated sludge. Prepare a gradient centrifuge solution containing 20-70% of the gradient centrifuge agent (sodium silicate solution) with a density of 1.35 g / cm³. 3 The centrifuged liquid and dewatered activated sludge were added to a mixer at a volume ratio of 10:1. The mixture was agitated at a low speed not exceeding 500 rpm to ensure homogeneity. After mixing, the mixture was centrifuged for a certain period to allow the high-density phosphate and the phosphorus-adsorbent to co-precipitate and separate from the sludge. The lower layer of high-density, phosphorus-rich adsorbent and precipitate was extracted from the centrifuge and discharged through the discharge port. The high-density, phosphorus-rich adsorbent and precipitate were dissolved in sulfuric acid to achieve a pH < 2. The insoluble residue was collected in a sedimentation tank or clarification tank, washed with water, and reused as phosphate adsorbent. Then, alkali was introduced... The pH is adjusted to 2-3 with an alkaline reagent to precipitate ferric phosphate. Then, an alkaline reagent is introduced to adjust the pH to 4-5 to precipitate ferric alum containing jaundice. The alkaline reagent is then added to adjust the pH to around 8 to precipitate impurities and heavy metals. Finally, the extracted iron and aluminum phosphates are dissolved under acidic conditions, and then calcium hydroxide or calcium oxide is added. Under weakly alkaline conditions, the hydrolysis precipitates of iron and aluminum are precipitated to remove the precipitates, thus obtaining calcium phosphate. Alternatively, magnesium hydroxide / magnesium oxide and ammonium salts are added to prepare magnesium ammonium phosphate, thus obtaining phosphate. The phosphorus recovery rate is 88.3%.

[0041] Example 3: Take activated sludge from a secondary sedimentation tank without added dewatering agents, and centrifuge it at 6900 g to obtain dewatered sludge with a moisture content ≥90%. Add 5 / 1000 of the sludge mass of hydrated iron oxide phosphate adsorbent to the sludge, and stir thoroughly to obtain conditioned dewatered activated sludge. Prepare a gradient centrifuge solution containing 20-70% of the gradient centrifuge agent (sodium silicate solution), with a density of 1.38 g / cm³. 3The centrifuged liquid and dewatered activated sludge were added to a mixer at a volume ratio of 3:1. The mixture was agitated at a low speed not exceeding 500 rpm to ensure thorough mixing. After mixing, the mixture was placed in a centrifuge at a pressure of 7000... Centrifugation for 5 minutes under g centrifugal force causes high-density phosphate and phosphorus-adsorbent to co-precipitate and separate from the sludge. After centrifugation, the lower layer of high-density phosphorus-rich adsorbent and precipitate in the centrifuge is first discharged and collected through the discharge port. The high-density phosphorus-rich adsorbent and precipitate are dissolved with sulfuric acid to make the pH of the extract solution <2. The insoluble matter is collected in the sedimentation tank or clarification tank, washed with water, and recovered as phosphate adsorbent. Then, alkaline agents are introduced to adjust the pH to 2-3 to precipitate iron phosphate. Then, alkaline agents are further introduced to adjust the pH to 4-5 to precipitate ferrous sulfate containing potassium sulfide. Alkaline agents are added again to adjust the pH to about 8 to precipitate impurities and heavy metals. Finally, the extracted iron and aluminum phosphates are dissolved under acidic conditions, and then calcium hydroxide or calcium oxide is added. Under weakly alkaline conditions, the hydrolysis precipitates of iron and aluminum are removed to obtain calcium phosphate. Alternatively, magnesium hydroxide / magnesium oxide and ammonium salts are added to produce magnesium ammonium phosphate to obtain phosphate. The phosphorus recovery rate is over 92.6%.

[0042] like Figure 2 and Figure 3 As shown, multiple application examples of the present invention demonstrate the effectiveness of the method for recovering phosphorus and potassium from sludge. The method achieves a phosphorus recovery rate of 63-88% from raw sludge with a moisture content of 45-95%, and a potassium recovery rate of 44-79% from the sludge. The method can be further optimized to improve the recovery rate of these elements.

[0043] This invention employs an innovative ambient temperature and pressure process route, completely avoiding the high-energy-consuming stages of traditional high-temperature and high-pressure treatment and incineration, achieving a breakthrough in phosphorus resource recovery technology. The core process demonstrates significant economic and technological advantages in actual operation: the estimated overall treatment cost is reduced by approximately 70% and 31% compared to sludge incineration alone and co-incineration in thermal power plants, respectively; and the energy consumption per unit mass of sludge treated is reduced by 18-40%. This green and low-carbon technology solution not only fundamentally solves the industry pain points of high energy consumption, high cost, and low efficiency of traditional processes, but also significantly reduces the equipment investment threshold and operation and maintenance difficulties, providing an innovative solution for the sustainable and efficient recovery of phosphorus resources that is both economically feasible and environmentally friendly, with broad prospects for industrial application.

Claims

1. A method for rapidly recovering phosphorus from activated sludge, characterized in that... Includes the following steps: (1) Remove water from activated sludge to a moisture content of 40%~95%, and then break it up to make it into a paste-like sludge; (2) Add phosphate adsorbent to the sludge at 1 / 1000 to 1 / 100 of the sludge mass, stir thoroughly, and obtain dewatered activated sludge after conditioning. The phosphate adsorbent is iron oxide, aluminum oxide or aluminum hydroxide. (3) Based on the density range of conventional dewatered activated sludge (1~1.2 g / cm³) 3 Gradient centrifuge solutions containing 20-70% gradient centrifuge reagent were prepared using gradient centrifuge reagents, yielding solutions with densities ranging from 1.3 to 1.9 g / cm³. 3 The gradient centrifuge liquid density is selected based on the density of the added phosphate adsorbent, ensuring that the density of the gradient centrifuge liquid is greater than the density of the activated sludge to be dewatered and less than the density of the phosphate adsorbent; the gradient centrifuge agent is sodium silicate solution or silica nanoparticle suspension with pH adjusted to >10. (4) Add the dewatered activated sludge and the gradient centrifuged liquid to a mixer at a volume ratio of 1:(2~10), and stir the sludge and the centrifuged liquid at a low speed of no more than 500 rpm to mix them evenly. (5) After mixing, transfer the mixture into a centrifuge and set it to a centrifugal force of 3500~10000 g. Centrifuge for a certain period of time to allow the high-density phosphate and the adsorbent that adsorbed the phosphorus to precipitate together and separate from the sludge. (6) After centrifugation, the material in the centrifuge is extracted step by step. The high-density phosphorus-rich adsorbent and precipitate in the lower layer are discharged and collected through the discharge hole first. Then the gradient centrifuged liquid in the middle layer is collected. Finally, the sludge floating in the upper layer, from which phosphorus and nutrients have been removed, is collected. (7) The high-density phosphorus-rich adsorbent and precipitate are dissolved with sulfuric acid and the pH of the extract solution is made <2. The insoluble matter is collected in the sedimentation tank or clarification tank, washed with water and recycled as phosphate adsorbent. Then, alkaline agents are introduced to adjust the pH to 2-3 to precipitate ferric phosphate. Then, alkaline agents are further introduced to adjust the pH to 4-5 to precipitate ferrous alum containing jaundice. Alkaline agents are added to adjust the pH to about 8 to precipitate impurities and heavy metals. Finally, the extracted iron and aluminum phosphates are dissolved under acidic conditions, and then calcium hydroxide or calcium oxide is added. The hydrolysis precipitates of iron and aluminum are removed under weakly alkaline conditions to obtain calcium phosphate. Alternatively, magnesium hydroxide / magnesium oxide and ammonium salts are added to prepare magnesium ammonium phosphate.

2. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: The activated sludge in step (1) is activated sludge from municipal wastewater treatment plants, anaerobic digestion sludge, or aerobic or anaerobic activated sludge produced by industrial organic phosphorus-containing wastewater bioreactors.

3. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: In step (1), the activated sludge is dehydrated by centrifugation or plate and frame filtration.

4. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: In step (2), the stirring speed of the mixer does not exceed 500 rpm, and the time is from several minutes to 1 hour.

5. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: In step (2), the iron oxide is one or more of ferric oxide, iron tetroxide and hydrated iron oxide; the aluminum oxide is aluminum oxide and / or aluminum hydroxide.

6. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: The dewatered activated sludge after pretreatment and conditioning in step (2) is then processed in step (4), or it is left to stand at room temperature or slightly below room temperature for a few minutes before being processed in step (4).

7. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: The mixing process in step (4) is carried out at or below room temperature and lasts for no more than 10 minutes.

8. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: The centrifugation time in step (5) is 1 to 30 minutes.

9. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: In step (7), the alkaline agent is one or more of magnesium oxide, magnesium hydroxide, and sodium hydroxide.

10. The method for rapidly recovering phosphorus from activated sludge as described in claim 1, characterized in that: The gradient centrifuge liquid collected in step (6) will continue to be used in the next centrifugation cycle until it becomes more turbid or its density decreases to be equal to or lower than that of the sludge due to contact with the sludge. Gradient centrifuge liquid with too low density will be collected, evaporated and dehydrated until the density is restored, and then recycled. Turbid gradient centrifuge liquid will be collected, evaporated and dehydrated, and the distilled water will be recycled. The dehydrated reagent will be heated to 550°C to remove the mixed organic matter from the activated sludge and the gradient centrifuge reagent will be recovered. The upper sludge collected in step (6) is adjusted to neutral pH using acid or alkali solution, and then subjected to aerobic or anaerobic composting or other sludge stabilization and reduction treatments before being disposed of in accordance with relevant regulations.

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