Method for gradient reinforcement of efficient release and recycling of carbon and phosphorus in sludge

Abstract

The invention relates to a method for recycling sludge, in particular to a method for enhancing efficient release and recycling of carbon and phosphorus in sludge in a gradient mode. According to the method for stepwise strengthening efficient release and recycling of carbon and phosphorus in sludge, the release efficiency of phosphorus in different occurrence forms in the sludge is improved in a targeted mode, efficient release of inorganic phosphorus and organic phosphorus is achieved through the synergistic effect of multiple steps, meanwhile, efficient release and recycling of carbon are synergistically improved, and the method has the beneficial effects of improving the utilization rate of carbon and phosphorus in sludge and improving the utilization rate of carbon and phosphorus in sludge. The method is used for improving the overall resource recycling efficiency of carbon and phosphorus in the excess sludge and comprises the following steps: 1, pretreating the sludge; 2, pre-treating the green chelating agent to intensify the release of inorganic phosphorus; 3, recovering inorganic phosphorus; 4, resuspending the sludge; 5, strengthening sludge solubilization and hydrolysis by using a peroxidant; 6, anaerobic recycling; 7, recycling carbon and phosphorus resources; the recovery process is simple and convenient, the loss rate is low, the phosphorus recovery rate can reach 80%-99.5%, the acid production efficiency is improved by 14 times or more, and the method has remarkable advantages.

Description

Technical Field

[0001] The invention relates to a method for recycling sludge. Background Art

[0002] Phosphorus resources are an indispensable element for all organisms. They are also essential substances for energy metabolism and key components of cell structures, playing a vital role in life activities. Currently, phosphorus in industrial and agricultural products mainly comes from the extraction of phosphate rock. However, as a non-renewable resource, the global proven reserves of phosphate rock are expected to be exhausted within 280 years. As the scarcity of phosphate rock resources continues to increase, the risk of resource loss and depletion is becoming increasingly prominent.

[0003] Sludge is a byproduct of the main process of sewage treatment. It has a complex composition. It contains harmful substances such as heavy metals and pathogens, and is rich in organic matter such as proteins, polysaccharides, and humus (accounting for 40% to 80% of the dry weight of sludge), as well as inorganic resources such as nitrogen and phosphorus. Among them, about 90% of the phosphorus in sewage is enriched in sludge, accounting for 2% to 5% of the dry weight of sludge. In order to meet the increasingly stringent sewage treatment discharge standards, iron and aluminum-based flocculants are often added during sewage treatment to enhance the removal of phosphorus. Therefore, the phosphorus in sludge mainly exists in the form of inorganic phosphorus (accounting for more than 50%) and organic phosphorus. Inorganic phosphorus is mainly combined with metal ions such as iron, magnesium, aluminum, and calcium, or exists in an adsorbed state on the surface of metal oxides. In summary, sludge is a potential carbon and phosphorus resource bank that needs to be explored and utilized. Therefore, sludge needs to be properly disposed of to achieve its stabilization, harmlessness and resource utilization.

[0004] Sludge anaerobic fermentation technology has been widely used due to its significant reduction effect, stable harmless treatment capacity, short operation cycle, resource utilization potential, low energy consumption and economic sustainability. However, the stable structure of colloidal extracellular polymers (EPS) and semi-rigid cell structures (cell walls and cell membranes) in sludge limits the release of soluble organic matter in sludge from the solid phase to the liquid phase, limiting the hydrolysis efficiency, which in turn leads to low bioconversion efficiency of organic matter.

[0005] In the process of anaerobic sludge resource utilization, the mainstream strategy for sludge phosphorus recovery is to rely mainly on pretreatment technology to break up and solubilize the sludge. Subsequently, in the anaerobic reaction, inorganic phosphorus (mainly iron phosphorus) or organic phosphorus in the solid phase can be released into the liquid phase through biological hydrolysis or biological reduction. Finally, phosphorus is recovered from the liquid phase after the reaction. In order to improve the release and resource efficiency of carbon and phosphorus in the anaerobic resource utilization process, the existing technology has developed a combined process for simultaneously strengthening sludge anaerobic resource utilization and phosphorus release. However, this process has many limitations: on the one hand, in the anaerobic resource process, the release efficiency of organic phosphorus in sludge is mainly limited by sludge hydrolysis, which hinders the dissolution and release of intracellular polyphosphate and extracellular organic phosphorus, making the release efficiency of organic phosphorus and soluble organic matter low and the time period long, and then the concentration of organic phosphorus hydrolyzed into phosphate in the supernatant is low. On the other hand, inorganic phosphorus such as magnesium, aluminum, calcium phosphorus in sludge is difficult to be effectively released through biological action in the anaerobic resource process; in addition, the sludge carbon resource process is inconsistent with the optimal conditions (such as pH value and release cycle) required for the efficient release of iron phosphorus and organic phosphorus, and the existing process is more biased towards carbon resource, resulting in poor timeliness of phosphorus release and recovery. At the same time, some metal ions released by hydrolysis and digestion in the supernatant will re-fix the released phosphorus into the solid phase under precipitation, further reducing the release efficiency of phosphorus, and sometimes unable to meet the minimum economic requirements for phosphorus recovery (<100mg / L), and ultimately unable to efficiently recover carbon and phosphorus resources simultaneously in the anaerobic resource process of sludge.

[0006] A Chinese invention patent (publication number: CN114195341A, publication date: March 18, 2022) discloses an enhanced pretreatment method for improving the anaerobic methanogenesis efficiency and phosphorus availability of excess sludge. This method uses citric acid or citrate and calcium hydroxide to jointly pretreat excess sludge, which can effectively promote the anaerobic digestion and methane production of sludge. Its advantage is to strengthen the lysis of sludge flocs and cells, dissolve more organic matter, thereby shortening the anaerobic digestion and methane production cycle, and significantly increase the effective phosphorus content in digested sludge that is easily absorbed by plants. However, the phosphorus resource precipitate formed by this method is mixed with the sludge, which makes the recovery of phosphorus precipitate more difficult, the recovery rate is low, and the recovery cost of phosphorus-containing minerals is high. In this patented technology, phosphorus coexists with metal ions in the same environment after release and fails to be separated in time, resulting in the failure to effectively recover phosphorus.

[0007] The Chinese invention patent (publication number: CN113087333A, publication date: July 9, 2021) proposes a resource-based process for simultaneously strengthening anaerobic acid production and phosphorus recovery in sludge. The process first pre-treats the sludge with heat-activated persulfate, adjusts the pH, and then performs anaerobic acid fermentation, followed by solid-liquid separation. Magnesium salt is added to the separated phosphorus-rich fermentation broth and the pH value is adjusted. The phosphorus in the filtrate is recovered in the form of struvite crystals, and the recovered filtrate is returned to the sewage treatment plant as a carbon source. However, this method has some limitations. First, the thermal hydrolysis activation technology consumes a lot of energy, resulting in high operating costs; on the other hand, the release of phosphorus mainly depends on iron-rich sludge dominated by Fe-P (iron phosphorus). For sludge with a high proportion of aluminum phosphorus and calcium phosphorus, the phosphorus release effect is poor, so the application range of this method is relatively narrow. Although the heat-activated persulfate combined with solid-liquid separation technology in this patented technology can achieve the separation of phosphorus and iron ions, the release effect of aluminum phosphorus and calcium phosphorus is poor, and the energy input of the thermal activation process is too high.

[0008] A Chinese invention patent (publication number: CN113772906A, publication date: December 10, 2021) proposes a method for strengthening sludge bioresource utilization by pretreatment with acidic ion exchange resin. The process adds acidic ion exchange resin to the sludge, adjusts the sludge to its isoelectric point, and then separates the pretreated sludge from the resin through a sieve. The separated resin can be recycled after acid regeneration, and the pretreated sludge is adjusted to a neutral pH and enters the subsequent anaerobic fermentation acid production or anaerobic digestion methane production process to generate anaerobic fermentation sludge. Next, the anaerobic fermentation sludge is separated into solid and liquid, the filtrate is collected, and magnesium salt is added to it, the pH is adjusted, and struvite precipitation is formed to recover phosphorus. The remaining filtrate is returned to the sewage treatment plant to achieve carbon recovery. This method has the advantages of promoting the hydrolysis of extracellular polymers (EPS) and removing metals, and can achieve efficient release of phosphorus and high value-added recovery during biological treatment. However, this method has some shortcomings: the acidic ion exchange resin used has a small particle size and is easily clogged by sludge, and the operation process is complicated and difficult to completely recover through the screen. This leads to a low recovery rate and recycling rate of the ion exchange resin, which in turn increases the economic cost and makes it lack feasibility in engineering applications. Although the acidic ion exchange resin in this patented technology can be used to capture metal ions and simultaneously achieve efficient release of comprehensive phosphorus and high value-added recovery in the biological treatment process. However, in actual applications, it has limitations such as small particle size, easy clogging, and complex operation, and lacks feasibility in engineering applications.

[0009] A Chinese invention patent (publication number: CN117327746A, publication date: January 12, 2024) proposes a method for strengthening the anaerobic fermentation of excess sludge to simultaneously produce short-chain fatty acids (VFAs) and phosphorus-containing minerals. This method strengthens the anaerobic fermentation process of sludge and simultaneously generates phosphorus-containing minerals by adding different concentrations of magnesium ferrate. This technology has significant advantages, including accelerating sludge hydrolysis, improving the biodegradability of sludge, and producing high-quality short-chain fatty acids (VFAs). However, the precipitate of phosphorus-containing minerals (such as blue iron ore and magnesium ammonium phosphate) generated by this method is mixed with the fermented sludge, resulting in a complicated subsequent recovery process of phosphorus-containing minerals and low recovery efficiency, which in turn increases the cost of phosphorus-containing mineral recovery. In this patented technology, magnesium ferrate only promotes sludge hydrolysis, but no separable phosphorus-containing minerals are obtained in the end.

[0010] A Chinese invention patent (publication number: CN118028385A, publication date: May 14, 2024) discloses a method for enhancing the anaerobic fermentation of excess sludge to produce short-chain fatty acids. This method effectively promotes the dissolution of soluble substrates and the production of short-chain fatty acids (VFAs) by adding sodium percarbonate. This technology has the advantages of a wide pH range and easy in-situ activation and sludge breaking. However, this method also has some shortcomings: on the one hand, its cost is relatively high; on the other hand, it does not involve the enhanced release and recovery of phosphorus in the sludge. In this patented technology, sodium percarbonate promotes sludge digestion through the oxidation of peroxide, but does not involve the release and recovery of phosphorus.

[0011] In the study by Wang et al. (Wang, F., Ma, S., Han, X., Liu, S. and Sun, K. 2024. Enhancing Phosphorus Release from Sewage Sludge in Anaerobic Digestion via Thermal Hydrolysis Pretreatment: Insights from Phosphorus Speciation and Molecular Biological Pathways. Environmental Science & Technology 58 (24), 10828-10838.), thermal hydrolysis pretreatment can enhance the release of phosphorus in sludge during anaerobic digestion. During the subsequent anaerobic fermentation, the phosphorus concentration in the liquid phase of the sludge treated with 170 ° C thermal hydrolysis increased significantly by 53.8% in the early stage of fermentation (within 3 days). However, during the subsequent 17-day anaerobic digestion process, due to the influence of metal precipitation, the phosphorus concentration in the supernatant gradually decreased, and finally fell below the initial concentration before anaerobic digestion. Although the thermal hydrolysis pretreatment in this technology can enhance the release of organic phosphorus and some inorganic phosphorus in the sludge during anaerobic digestion, it fails to achieve immediate and effective recovery of phosphorus. Ultimately, the phosphorus in the sludge still returns to the sludge in the form of precipitation.

[0012] A Chinese invention patent (publication number: CN115974350A, publication date: April 18, 2023) discloses a method for enhancing phosphorus release from excess sludge using ascorbic acid. Fe(III)-P in the sludge is reduced to Fe(II)-P by ascorbic acid, which dissolves under acidic conditions and releases Fe 2+ and PO 4 3- -P, Mg-P and Ca-P are partially dissolved and released due to the complexation of ascorbic acid. Then solid-liquid separation is carried out. In the separated phosphorus-rich fermentation broth, the molar ratio of ferrous iron and phosphate is adjusted to 1.5, and the pH value is further adjusted, and finally the phosphorus in the filtrate is recovered in the form of blue iron ore. This method can increase the release efficiency of phosphorus in the residual sludge to 45% to 50%. This process is simple and easy to operate, and has good environmental benefits. However, this method also has some limitations: first, a large amount of ascorbic acid needs to be added, resulting in high costs; secondly, this method is mainly suitable for sludge with high iron and phosphorus content, and its phosphorus release effect is poor for sludge with high aluminum and phosphorus content, so the scope of technical application is relatively narrow. In addition, this method only focuses on the recovery of phosphorus in sludge, and fails to fully explore the recycling value of carbon resources in the residual sludge after phosphorus release. In this patent, ascorbic acid has a good phosphorus release effect on iron-rich sludge, but is not applicable to aluminum sludge, has a narrow scope of application, and does not consider the release of organic phosphorus and the subsequent resource utilization of sludge.

[0013] A Chinese invention patent (publication number: CN116903206A, publication date: October 20, 2023) discloses a sludge treatment agent, its preparation method and application. This method can achieve a phosphorus release efficiency of more than 75% in the residual sludge by synergistically using organic acid citric acid, reducing agent ascorbic acid and metal chelating agent EDTA to complex with various metal ions in the sludge. However, if any of these three substances is missing, the phosphorus release rate will be significantly reduced. Despite this, there are some problems with this method: on the one hand, the addition of toxic EDTA may have an adverse effect on the subsequent resource utilization of the sludge; on the other hand, the simultaneous use of these three chemicals significantly increases the cost of enhancing the release of phosphorus from the residual sludge, making it economically unfeasible. This patented technology uses organic acid citric acid, reducing agent ascorbic acid and metal chelating agent EDTA in a synergistic manner. Although it has certain advantages in phosphorus release efficiency, its comprehensive economic cost is relatively high, which limits the possibility of large-scale application and does not consider the release of organic phosphorus in sludge. In addition, the biological toxicity of EDTA will have an adverse effect on the subsequent resource utilization of sludge, thus bringing potential environmental risks. Therefore, this combination does not have sufficient practicality and scalability in actual applications.

[0014] A Chinese invention patent (publication number: CN113173648A, publication date: July 27, 2021) discloses a method for preparing blue iron ore by removing phosphorus at low cost and high efficiency. An iron-reducing bacteria-iron mineral system consisting of iron-reducing bacteria, iron minerals, electron shuttles and carbon sources is added to water or phosphate-containing wastewater, the pH of the reaction system is maintained at 6-8 and in an anaerobic environment, the reaction system is allowed to settle, and the sludge containing a large amount of blue iron ore at the bottom is discharged through a sludge discharge pipe. Although this method uses biological methods to recover phosphorus and reduce production costs, the method has some limitations: the activity of iron-reducing bacteria is limited to a narrow environmental window of redox potential (-200 to -300 mV) and pH (6.5 to 7.5), and the fluctuation of microbial electron transfer efficiency and sulfide competitive inhibition (FeS precipitation) are not suitable for complex systems, resulting in poor stability of phosphorus recovery efficiency. In this patented technology, the iron-reducing bacteria-iron mineral system recovers phosphorus by breaking the Fe-P chemical bond through dissimilatory iron reduction, which has the advantage of reducing water treatment costs, but the recovery efficiency is jointly regulated by electron transfer efficiency, competitive reactions and environmental factors.

[0015] In summary: Existing technologies generally face problems such as low efficiency, high cost, limited applicability, complex operation and environmental risks in the recovery of carbon and phosphorus resources from residual sludge. Most traditional simultaneous intensification processes are incompatible with the kinetic conditions of carbon resource utilization and inorganic phosphorus and organic phosphorus release processes, and there are differences in parameters such as optimal release time and optimal pH value. Although these technologies can achieve simultaneous intensification to a certain extent, their optimal conditions are mainly aimed at enhancing carbon resource efficiency and fail to fully match the optimal parameters of phosphorus release, and cannot synergistically improve the release and recovery efficiency of carbon and phosphorus. The key restricting factor for the release efficiency of organic phosphorus and carbon in the anaerobic resource utilization process is sludge hydrolysis, and its efficiency is doubly limited by the mass transfer barrier formed by the network colloidal extracellular polymeric substances (EPS) in the sludge matrix and the semi-rigid structure of the cell wall / membrane, which significantly hinders the dissolution and release of carbon resources, intracellular polyphosphate and extracellular organic phosphorus in the sludge, resulting in low release efficiency of organic phosphorus and soluble organic matter and prolonged cycle. Moreover, the existing process mainly relies on the dissimilatory iron reduction mechanism of iron-phosphorus in inorganic phosphorus, and the activity of iron-reducing bacteria is limited by the narrow environmental window of redox potential and pH, the fluctuation of microbial electron transfer efficiency and the competitive inhibition of sulfide in complex systems, resulting in unstable phosphorus release efficiency and large fluctuations in the process of biological reduction of iron-phosphorus. In addition, a good temporal synergistic connection has not been formed between the nitrogen and phosphorus resource utilization pathways, resulting in the failure to separate phosphorus in the liquid phase in time after phosphorus release. Metal ions (Fe, Al, Ca, Mg) re-fix phosphorus components through precipitation during the anaerobic process, resulting in phosphorus heavy precipitation and difficulty in separating mud-phosphorus, resulting in low phosphorus release rate and recovery rate. In addition, the existing process lacks the enhanced release of aluminum / calcium / magnesium-bound inorganic phosphorus, resulting in a relatively low overall phosphorus release effect. In summary, the release of phosphorus and carbon in sludge is limited by intracellular / extracellular mass transfer barriers. In addition, phosphorus release is also limited by fluctuations in microbial electron transfer efficiency, metal precipitation, and lack of quality control of different forms of phosphorus, which ultimately restricts the efficient release of phosphorus in the anaerobic process of sludge and the synergistic recovery efficiency with high value-added products (such as acid and methane). At the same time, the existing technology still has many shortcomings, such as the reliance on high-dose peroxidant addition and complex solid-liquid separation process to enhance the release of organic phosphorus and carbon resource recovery, resulting in excessively high process costs, high energy consumption, low carbon and phosphorus release and recovery efficiency, and limited technical application scope. These factors together make it difficult for the existing technology to meet actual needs in terms of synergistically improving carbon and phosphorus release efficiency, cost control, applicability and environmental friendliness.

[0016] Therefore, the present invention aims to design a new method to specifically improve the release efficiency of phosphorus in different forms in sludge, enhance the efficient release and recovery of inorganic phosphorus and organic phosphorus in the biological treatment process, while taking into account the recovery of high value-added products (such as acid and methane), and ultimately synergistically enhance the release and recovery of carbon and phosphorus resources in residual sludge to overcome the limitations of the existing technology. Summary of the invention

[0017] In order to solve the above technical problems, the present invention provides a method for cascade-enhanced efficient release and resource utilization of carbon and phosphorus in sludge.

[0018] The present invention discloses a method for step-by-step intensification of efficient release and resource utilization of carbon and phosphorus in sludge, which specifically improves the release efficiency of phosphorus in different forms in sludge, realizes efficient release of inorganic phosphorus and organic phosphorus through the synergistic effect of multiple steps, and simultaneously synergistically improves efficient release and resource recovery of carbon (such as acid and methane), thereby improving the overall resource recovery efficiency of carbon and phosphorus in residual sludge, and comprises the following steps:

[0019] 1. Sludge pretreatment:

[0020] The sludge in the secondary sedimentation tank of the sewage treatment plant is screened to remove impurities, then refrigerated and left to stand for a period of time, and the supernatant is removed by siphoning or decanting, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0021] 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus:

[0022] Adding a green chelating agent to the concentrated excess sludge I, stirring evenly, and then placing the concentrated excess sludge in a constant temperature incubator to react for a period of time to obtain sludge pretreated with the green chelating agent;

[0023] 3. Inorganic phosphorus recovery:

[0024] ①, centrifuge or filter press the sludge pretreated with the green chelating agent to obtain liquid II and solid II;

[0025] ②, adding calcium-based metal salt to liquid II, so that the molar ratio of calcium to phosphorus in liquid II is (0.5-3):1, adjusting the pH value of liquid II to 6-13, then stirring for a period of time, then standing for a period of time, and finally centrifuging to collect the phosphorus precipitate solid and supernatant III;

[0026] 4. Sludge resuspension:

[0027] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 0.5% to 10%, and then transfer it to the anaerobic fermentation tank;

[0028] 5. Peroxidant-enhanced sludge solubilization and hydrolysis:

[0029] The pH value of the sludge in the anaerobic fermentation tank is adjusted to 6-7.5, and then a peroxidant is added to react at 25-35°C for a period of time to obtain the reacted sludge;

[0030] 6. Anaerobic resource utilization:

[0031] Adding inoculated sludge to the reacted sludge obtained in step 5, adjusting the pH value to 7, introducing nitrogen into the anaerobic fermentation tank for a period of time, and then covering the reactor with a sealing plug to keep the reactor in an anaerobic state, reacting at 30° C. to 37° C. for 2 to 40 days to obtain a reacted sludge mixture;

[0032] 7. Recycling of carbon and phosphorus resources:

[0033] ①, centrifuging or filtering the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0034] ②. Add ferrous salt to the filtrate I obtained in step seven ①, and then use alkali solution to adjust the pH value to 5-9, react under anaerobic conditions for 0.5h-2h, and then age for 0.5h-2h under nitrogen or argon conditions, and then use centrifugal treatment or filter press to separate the solid and liquid to obtain blue iron ore and filtrate II. Filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source to supplement the carbon source. The blue iron ore is vacuum dried at 35°C-60°C.

[0035] Purpose of the present invention:

[0036] The present invention aims at the key technical bottlenecks such as the existing synchronous enhanced sludge anaerobic resource utilization and phosphorus release technology, which is biased towards carbon resource utilization due to the optimal conditions, the lack of temporal synergy of the nitrogen and phosphorus resource utilization path, the poor adaptability of the polymorphic metal phosphorus form, the insufficient stability of iron-phosphorus biological reduction phosphorus release, and the low efficiency and long time of organic phosphorus release, resulting in the synergistic improvement of carbon and phosphorus release rate and recovery rate. The innovative "metal complex stripping-inorganic phosphorus recovery-organic matter release-carbon conversion and organic phosphorus recovery" cascade synergistic process system is proposed. The present invention first undergoes metal complex stripping-inorganic phosphorus recovery, then adds a peroxidant to the sludge that releases inorganic phosphorus and metal ions, and then performs anaerobic resource utilization, which can achieve efficient release of inorganic phosphorus and organic phosphorus in the sludge and improve the carbon resource utilization efficiency, thereby significantly synergistically improving the overall resource utilization efficiency of carbon and phosphorus release in the residual sludge. In addition, the method is not limited to the product form of carbon resource fixation, which can not only improve the acid production efficiency of the anaerobic fermentation process, but also improve the methane content of anaerobic digestion. If this addition sequence is changed, there is no synergistic improvement in efficiency. The present invention adopts green chelating agent to selectively dissociate metal-phosphorus composite structure, and realizes efficient release of multi-phase inorganic phosphorus forms. Secondly, the timing synergy of nitrogen and phosphorus resource utilization path is optimized to ensure timely and efficient recovery of phosphorus and metal ions in liquid phase after phosphorus release, block metal ion reprecipitation and re-fix phosphorus components, thereby reducing phosphorus heavy precipitation and mud-phosphorus difficult separation phenomenon, and improving phosphorus release and recovery rate. Then, peroxidant technology is used to crack the sludge after the disintegration of metal skeleton, more strongly break the EPS barrier and cell wall rigid structure, drive carbon-phosphorus metabolism synergy, strengthen organic matter conversion and organic phosphorus release, and realize the synergistic improvement of carbon and phosphorus release and resource utilization in sludge. This technology specifically improves the release efficiency of phosphorus in different occurrence forms in sludge, realizes the efficient release of inorganic phosphorus and organic phosphorus through the synergistic effect of multiple steps, and simultaneously strengthens the recovery of carbon resource (such as acid, methane), synergistically improves the overall resource efficiency of carbon and phosphorus in residual sludge, and realizes the dual goals of efficient phosphorus recovery and high-value conversion of carbon source. The pretreatment of peroxidant with acidic substances and citric acid in the present invention has a significant synergistic improvement effect in strengthening the anaerobic fermentation of sludge to produce volatile fatty acids. Compared with other existing methods of promoting anaerobic fermentation of sludge to produce volatile fatty acids with peroxidants, this method can significantly reduce the dosage of peroxidant, thereby greatly reducing the process cost. In addition, the method can also efficiently recover phosphorus precipitates and realize efficient resource utilization of sludge. The method of the present invention optimizes the process flow, reduces energy consumption and process costs, and makes the carbon and phosphorus synergistic recovery technology more economically feasible and meets actual needs. At the same time, this method is a phosphorus recovery technology suitable for a wide spectrum of sludge types and conditions with different metal phosphorus occurrence forms, which broadens the application scope of the technology, while reducing process costs and simplifying recovery operations, providing an efficient and low-consumption engineering solution for sludge resource utilization.

[0037] Advantages of the present invention:

[0038] 1. Efficient release of polymorphic phosphorus: The present invention uses green chelating agents to selectively dissociate metal-phosphorus composite structures to achieve efficient release of polymorphic inorganic phosphorus forms, breaking through the limitations of traditional technologies such as poor adaptability to polymorphic metal phosphorus and insufficient stability of iron phosphorus release through biological reduction, and significantly improving the release efficiency of inorganic phosphorus. In addition, the sludge after the metal skeleton is disintegrated is cracked by peroxidation technology, breaking the EPS barrier and the rigid structure of the cell wall, strengthening the conversion of organic matter and the release of organic phosphorus, and significantly improving the release efficiency of organic phosphorus. This technology can increase the phosphorus release efficiency to 40% to 80%.

[0039] 2. Optimize the synergy of resource recovery paths: The present invention optimizes the timing synergy of nitrogen and phosphorus resource recovery paths to ensure that phosphorus and metal ions in the liquid phase after phosphorus release can be promptly recovered and separated from the sludge phase, effectively blocking the reprecipitation of metal ions and re-fixing phosphorus components in the sludge phase, reducing phosphorus reprecipitation and the phenomenon of mud-phosphorus separation, thereby significantly improving phosphorus release and recovery rate. The recovery process of the present invention is simple, the loss rate is low, and the phosphorus recovery rate can be as high as 80% to 99.5%, which has significant advantages.

[0040] 3. Achievement of dual goals - synergistic improvement of carbon and phosphorus resource utilization: The present invention realizes the efficient release of inorganic phosphorus and organic phosphorus through multi-step synergistic action, while taking into account the recovery of high value-added products (such as acid and methane), improving the overall resource efficiency, and achieving the dual goals of efficient phosphorus recovery and high-value carbon source conversion. In addition, sludge that has been pH-adjusted and pretreated with citric acid and peroxidizers such as sodium percarbonate show good synergistic improvement effects in enhancing anaerobic fermentation acid production. Compared with the existing single technology, the acid production efficiency has been increased by more than 1.4-3 times; and compared with sludge that has not undergone any pretreatment, the acid production efficiency has been increased by more than 14 times.

[0041] 4. Economic feasibility and broad-spectrum applicability: The present invention reduces energy consumption and process costs by optimizing the process flow, making phosphorus recovery technology more economically feasible and meeting actual needs. The technology is applicable to a wide range of sludge types and conditions with different metallic phosphorus occurrence forms, broadens the scope of application of the technology, simplifies the recovery operation, and provides an efficient and low-cost engineering solution for sludge resource utilization.

[0042] 5. Process innovation and qualitative improvement: The present invention innovatively proposes a cascade collaborative process system of "metal complex stripping-inorganic phosphorus recovery-organic matter release-carbon conversion and organic phosphorus recovery". Through the synergistic effect of multiple steps, it significantly improves the release efficiency of phosphorus in different forms in sludge, as well as the synergistic improvement of carbon and phosphorus resources in the anaerobic resource utilization process of sludge, thus realizing the process innovation from quantitative change to qualitative change.

[0043] In summary, the present invention provides an efficient, low-consumption, and broad-spectrum engineering solution for sludge resource utilization by efficiently releasing polymorphic phosphorus, optimizing the synergy of resource utilization pathways, achieving synergistic improvement of carbon and phosphorus resource utilization, improving economic feasibility and applicability, and innovating processes and improving qualitative changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a process flow chart of a method for step-by-step intensification of efficient release and resource utilization of carbon and phosphorus in sludge in the present invention;

[0045] Figure 2 The effect diagram of STP release after adding citric acid to the concentrated excess sludge I and adjusting the pH in step 2 in Examples 1 to 5 and Comparative Example 1;

[0046] Figure 3 The solid-liquid phosphorus balance effect diagram of the sludge after adding citric acid to the concentrated excess sludge I and adjusting the pH in step 2 in Examples 1 to 5 and Comparative Example 1;

[0047] Figure 4 This is a graph showing the recovery efficiency of the phosphorus precipitated solid in step 3② of Example 5;

[0048] Figure 5 XRD characterization of the phosphorus precipitated solid in step 3② of Example 5;

[0049] Figure 6 is the element content of the phosphorus precipitated solid in step 3② of Example 5;

[0050] Figure 7 The volatile acid concentration effect diagram of Examples 6 to 8 and Steps 5 and 6 of Comparative Example 2 after acid and citric acid pretreatment and sodium percarbonate co-treatment;

[0051] Figure 8 The volatile acid composition is obtained by pre-treatment with acid and citric acid and co-treatment with sodium percarbonate in steps 5 and 6 of Examples 6 to 8 and Comparative Example 2;

[0052] Fig. 9 PO 600 prepared from the steps 5 and 6 of Examples 6 to 8 and Comparative Example 2 after acid and citric acid pretreatment and sodium percarbonate co-treatment 4 3- -P effect diagram;

[0053] Fig.10 The graph showing the change of phosphorus content in the sludge mixture after the reaction obtained in steps 5 and 6 of Examples 6 to 8 and Comparative Example 2;

[0054] Fig.11 This is the XRD pattern of the blue iron ore recovered in step 7 of Example 8;

[0055] Fig.12The volatile acid concentration effect diagram of anaerobic fermentation of sludge after potassium hexaperborate acid strengthening and citric acid pretreatment in Example 9 and Control Example 3 is shown. DETAILED DESCRIPTION

[0056] Specific implementation method 1: This implementation method provides a method for step-by-step enhancement of efficient release and resource utilization of carbon and phosphorus in sludge, including the following steps:

[0057] 1. Sludge pretreatment:

[0058] The sludge in the secondary sedimentation tank of the sewage treatment plant is screened to remove impurities, then refrigerated and left to stand for a period of time, and the supernatant is removed by siphoning or decanting, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0059] 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus:

[0060] Adding a green chelating agent to the concentrated excess sludge I, stirring evenly, and then placing the concentrated excess sludge in a constant temperature incubator to react for a period of time to obtain sludge pretreated with the green chelating agent;

[0061] 3. Inorganic phosphorus recovery:

[0062] ①, centrifuge or filter press the sludge pretreated with the green chelating agent to obtain liquid II and solid II;

[0063] ②, adding calcium-based metal salt to liquid II, so that the molar ratio of calcium to phosphorus in liquid II is (0.5-3):1, adjusting the pH value of liquid II to 6-13, then stirring for a period of time, then standing for a period of time, and finally centrifuging to collect the phosphorus precipitate solid and supernatant III;

[0064] 4. Sludge resuspension:

[0065] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 0.5% to 10%, and then transfer it to the anaerobic fermentation tank;

[0066] 5. Peroxidant-enhanced sludge solubilization and hydrolysis:

[0067] The pH value of the sludge in the anaerobic fermentation tank is adjusted to 6-7.5, and then a peroxidant is added to react at 25-35°C for a period of time to obtain the reacted sludge;

[0068] 6. Anaerobic resource utilization:

[0069] Adding inoculated sludge to the reacted sludge obtained in step 5, adjusting the pH value to 5-7.5, introducing nitrogen into the anaerobic fermentation tank for a period of time, and then covering the reactor with a sealing plug to keep the reactor in an anaerobic state, reacting at 30° C.-37° C. for 2-40 days to obtain a reacted sludge mixture;

[0070] 7. Recycling of carbon and phosphorus resources:

[0071] ①, centrifuging or filtering the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0072] ②. Add ferrous salt to the filtrate I obtained in step seven ①, and then use alkali solution to adjust the pH value to 5-9, react under anaerobic conditions for 0.5h-2h, and then age for 0.5h-2h under nitrogen or argon conditions, and then use centrifugal treatment or filter press to separate the solid and liquid to obtain blue iron ore and filtrate II. Filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source to supplement the carbon source. The blue iron ore is vacuum dried at 35°C-60°C.

[0073] In step three of this embodiment, phosphorus and metal ions in inorganic phosphorus in the sludge solid phase are released and recovered, and a phosphorus recovery rate of 80% to 99.5% can be achieved. The metal ions are iron, aluminum, calcium, and magnesium ions.

[0074] In step 3 of this embodiment, calcium and phosphorus in liquid II can generate calcium phosphate aluminum calcium (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O minerals.

[0075] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that: in step 1, the secondary sedimentation tank sludge produced by the sewage treatment plant is screened with a 20-mesh to 60-mesh screen to remove impurities, and then refrigerated and left to stand at a temperature of 4°C for 4h to 48h, and then the supernatant is removed by siphoning or decanting, and the removed supernatant is collected to obtain supernatant I and concentrated excess sludge I; the secondary sedimentation tank sludge described in step 1 is a mixture of one or more of activated sludge for biological phosphorus removal, sludge for iron chemically enhanced phosphorus removal, and sludge for aluminum chemically enhanced phosphorus removal; the solid content of the concentrated excess sludge I described in step 1 is 0.5% to 10%. The other steps are the same as those in specific implementation method 1.

[0076] Specific implementation method three: This implementation method is different from specific implementation method one or two in that: the green chelating agent described in step two is a mixture of one or more of citric acid, tartaric acid, methylglycine diacetic acid, glutamic acid diacetic acid and metal acid salts; the dosage of the green chelating agent described in step two is 0.01g / gTSS~0.5g / gTSS; the temperature of the constant temperature incubator described in step two is 20℃~40℃, and the rotation speed is 100rpm~150rpm; the reaction time in the constant temperature incubator in step two is 1h~48h. The other steps are the same as specific implementation method one or two.

[0077] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that: the centrifugal speed described in step 3 ① is 5000rpm~10000rpm, and the centrifugal time is 5min~20min; the calcium-based metal salt described in step 3 ② is calcium chloride, calcium oxide or calcium hydroxide; the stirring speed described in step 3 ② is 600rpm~1000rpm, and the stirring time is 10min~60min; the standing time described in step 3 ② is 30min~120min. The other steps are the same as those of specific embodiments 1 to 3.

[0078] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the centrifugal treatment speed in step 3 ② is 8000 rpm to 12000 rpm, and the centrifugal treatment time is 5 min to 20 min; in step 3 ②, a sodium hydroxide solution or potassium hydroxide solution with a concentration of 1 mol / L to 6 mol / L is used to adjust the pH value of the liquid to 6 to 13; the composition of the phosphorus precipitate solid in step 3 ② is (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O. The other steps are the same as those in Specific Embodiments 1 to 4.

[0079] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: the volume ratio of supernatant III and supernatant I described in step 4① is (0-5): (0-5); the peroxidant described in step 5 is sodium percarbonate, potassium percarbonate, sodium perborate, potassium perborate, calcium peroxide, magnesium peroxide, sodium ferrate, potassium ferrate, sodium periodate, potassium periodate, hydrogen peroxide, peracetic acid, sodium hypochlorite or potassium hypochlorite. The other steps are the same as those of specific embodiments 1 to 5.

[0080] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that: the reaction time at 25°C to 35°C in step 5 is 4h to 24h; the dosage of the peroxidant in step 5 is 0.01g / gTSS to 0.5g / gTSS. The other steps are the same as those in specific embodiments 1 to 6.

[0081] Specific embodiment eight: The difference between this embodiment and specific embodiments one to seven is that the preparation method of the inoculated sludge described in step six is ​​as follows: the concentrated excess sludge I obtained in step one is first boiled at 90°C to 100°C for 1h to 4h, transferred to a reactor, and after cooling, the following substances are added thereto: 14.4 g / L of glucose, 3.2 g / L of yeast extract, 0.56 g / L of potassium dihydrogen phosphate, 0.96 g / L of magnesium sulfate heptahydrate, 2.4 g / L of ammonium chloride, 0.72g / L of anhydrous calcium chloride, 0.96g / L of sodium bicarbonate, 0.11g / L of manganese chloride, and 0.12g / L of ferrous sulfate heptahydrate are added to obtain a sludge mixture; then nitrogen is introduced for 10min to 40min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and long-term acclimation is performed at 33°C to 37°C, 0.5L of sludge is discharged from the reactor every 7 days, and 0.5L of the prepared sludge mixture is added, and long-term operation is performed every 7 days to obtain inoculated sludge. The other steps are the same as those in the first to seventh embodiments.

[0082] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: the mass ratio of the inoculated sludge described in step 6 to the sludge after the reaction obtained in step 5 is (0-1): (1-5), and the pH value is adjusted to 5-7.5; the time for passing nitrogen into the anaerobic fermentation tank in step 6 is 10min-30min; the speed of the centrifugal treatment described in step 7① is 5000rpm-10000rpm, and the time of the centrifugal treatment is 5min-15min. The other steps are the same as specific embodiments 1 to 8.

[0083] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: the ferrous salt described in step 7 ② is ferrous chloride or ferrous sulfate; the molar ratio of the ferrous salt described in step 7 ② to phosphorus in filtrate I is (1 to 2): 1; the alkali solution described in step 7 ② is sodium hydroxide solution or potassium hydroxide solution, and the concentration is 1 mol / L to 6 mol / L. The other steps are the same as those of specific embodiments 1 to 9.

[0084] The following examples are used to verify the beneficial effects of the present invention:

[0085] Example 1: A method for cascade-enhanced efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0086] 1. Sludge pretreatment:

[0087] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0088] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0089] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0090] 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus:

[0091] Add a green chelating agent to 500 mL of concentrated excess sludge I, the dosage of the green chelating agent is 0.08 g / g TSS (i.e., add 1.87 g of citric acid to 500 mL of concentrated excess sludge I), stir evenly, and then place in a constant temperature incubator to react for a period of time to obtain a green chelating agent pretreated sludge with a pH value of 4.33;

[0092] The green chelating agent described in step 2 is citric acid;

[0093] The temperature of the constant temperature incubator described in step 2 is 35°C and the rotation speed is 140 rpm;

[0094] The reaction time in the constant temperature incubator in step 2 is 18 hours;

[0095] 3. Inorganic phosphorus recovery:

[0096] ①, centrifuge the sludge pretreated with the green chelating agent to obtain liquid II and solid II;

[0097] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0098] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0099] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0100] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O;

[0101] 4. Sludge resuspension:

[0102] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0103] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1;

[0104] 5. Peroxidant-enhanced sludge solubilization and hydrolysis:

[0105] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 7.2, and then a peroxidant was added, and the reaction was carried out at 25° C. for 12 hours to obtain a reacted sludge;

[0106] The peroxidant described in step 5 is sodium percarbonate;

[0107] The dosage of the peroxidant in step 5 is 0.1 g / g TSS;

[0108] 6. Anaerobic resource utilization:

[0109] Add the inoculated sludge to the reacted sludge obtained in step 5, adjust the pH value to 5, introduce nitrogen into the anaerobic fermentation tank for 15 minutes, cover the reactor with a sealing plug to keep the reactor in an anaerobic state, and react at 35° C. for 12 days to obtain a reacted sludge mixture;

[0110] The preparation method of the inoculum sludge described in step 6 is as follows: the concentrated excess sludge I obtained in step 1 is first boiled at 100°C for 2h, transferred to a reactor, and after cooling, the following substances are added thereto: 14.4g / L glucose, 3.2g / L yeast extract, 0.56g / L potassium dihydrogen phosphate, 0.96g / L magnesium sulfate heptahydrate, 2.4g / L ammonium chloride, 0.72g / L anhydrous calcium chloride, 0.96g / L sodium bicarbonate, 0.11g / L manganese chloride, 0.12g / L ferrous sulfate heptahydrate, to obtain a sludge mixture; then nitrogen is introduced for 10min to 40min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and long-term acclimation is carried out at 33°C to 37°C, 0.5L sludge is discharged from the reactor every 7 days, and 0.5L of the prepared sludge mixture is added, and long-term operation is carried out with a cycle of every 7 days to obtain inoculum sludge;

[0111] The mass ratio of the inoculated sludge in step 6 to the reacted sludge obtained in step 5 is 1:2;

[0112] 7. Recycling of carbon and phosphorus resources:

[0113] ①, centrifuging or filtering the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0114] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0115] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0116] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0117] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0118] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0119] Example 2: The difference between this example and Example 1 is that in step 2, a green chelating agent is added to 500 mL of concentrated excess sludge I, and the amount of green chelating agent added is 0.16 g / g TSS (i.e., 3.74 g of citric acid is added to 500 mL of concentrated excess sludge I), stirred evenly, and then placed in a constant temperature incubator to react for a period of time to obtain a green chelating agent pretreated sludge with a pH value of 3.8. The other steps and parameters are the same as steps 1 to 7 of Example 1.

[0120] Example 3: The difference between this example and Example 1 is that in step 2, a green chelating agent is added to 500 mL of concentrated excess sludge I, and the amount of green chelating agent added is 0.32 g / g TSS (i.e., 7.48 g of citric acid is added to 500 mL of concentrated excess sludge I), stirred evenly, and then placed in a constant temperature incubator for reaction for a period of time to obtain a green chelating agent pretreated sludge with a pH value of 3.43. The other steps and parameters are the same as steps 1 to 7 of Example 1.

[0121] Example 4: The difference between this example and Example 1 is that in step 2, 500 mL of concentrated excess sludge I is adjusted to pH 3.0 using hydrochloric acid with a concentration of 3.5 mol / L, and then placed in a constant temperature incubator for a period of time to obtain pretreated sludge. The other steps and parameters are the same as steps 1 to 7 of Example 1.

[0122] Example 5: The difference between this example and Example 1 is that a green chelating agent is added to 500 mL of concentrated excess sludge I, and the amount of green chelating agent added is 0.08 g / g TSS (i.e., 1.87 g of citric acid is added to 500 mL of concentrated excess sludge I), and then the pH value of the system is adjusted to 3.0 using 4 mol / L hydrochloric acid, stirred evenly, and then placed in a constant temperature incubator for a period of reaction to obtain a green chelating agent pretreated sludge with a pH value of 3.0. The other steps and parameters are the same as steps 1 to 7 of Example 1.

[0123] Comparative Example 1: The difference between this example and Example 1 is that in step 2, 500 mL of concentrated excess sludge I is placed in a constant temperature incubator at 35°C and a rotation speed of 140 rpm for 18 hours to obtain pretreated sludge. The other steps and parameters are the same as steps 1 to 7 of Example 1.

[0124] Figure 2 and Figure 3The change of total phosphorus concentration over time in the supernatant in the reactor (the supernatant is obtained by centrifuging the pretreated sludge obtained in step 2 and passing the liquid through the membrane) is shown. Within the first 48 hours, the total phosphorus concentration of the supernatant in each example showed a trend of first increasing and then decreasing. Among them, Example 3 reached the highest total phosphorus concentration (STP) of 703 mg / L at 36 hours, and the phosphorus release rate was as high as 68%, which was 52% higher than that of Control Example 1. Within 24 hours, the STP concentration of the supernatant of Example 1 was 587 mg / L, while the STP concentration of Example 5 was 645 mg / L, which were 42% and 47% higher than those of Control Example 1, respectively. Within the first 24 hours, the STP concentration of the supernatant in each example reached more than 450 mg / L, showing a high phosphorus recovery value.

[0125] The phosphorus recovery rate in step 3 ② of Example 5 is as follows Figure 4 As shown, phosphorus precipitation is characterized as Figure 5 As shown, the element content of phosphorus precipitation is as follows Figure 6 As shown;

[0126] Figure 4 This is a graph showing the recovery efficiency of the phosphorus precipitated solid in step 3② of Example 5;

[0127] Figure 5 XRD characterization of the phosphorus precipitated solid in step 3② of Example 5;

[0128] Figure 6 is the element content of the phosphorus precipitated solid in step 3② of Example 5;

[0129] After adding calcium chloride and adjusting the pH value in the liquid II of Example 5, the phosphate concentration therein dropped to 5.6 mg / L, and the recovery rate of phosphorus precipitation reached 99.1% (e.g. Figure 4 As shown in Figure 2, the quantitative analysis of XRD and metal ions showed that the phosphorus precipitation recovery was whiteite (CaFeMg)-(CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 Phosphorus-containing minerals mainly in O form (such as Figure 5-6 As shown), and P in the mineral 2 O 5 The content is 23.7%. In addition, the citric acid used in the present invention is cheap, about 600 US dollars per ton. In contrast, the ascorbic acid used in the Chinese patent document CN115974350A is more expensive (about 3000 US dollars per ton) and the dosage is larger. Therefore, the present invention has a significant advantage in terms of economy, and the recovery cost of phosphorus is estimated to be only 23.24 yuan / kg-P.

[0130] Example 6: A method for cascade-enhanced efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0131] 1. Sludge pretreatment:

[0132] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0133] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0134] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0135] 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus:

[0136] A green chelating agent was added to 500 mL of concentrated residual sludge I, and the dosage of the green chelating agent was 0.08 g / g TSS (i.e., 1.87 g of citric acid was added to 500 mL of concentrated residual sludge I). The pH value of the system was adjusted to 3.0 using 4 mol / L hydrochloric acid, and the mixture was stirred evenly. The mixture was placed in a constant temperature incubator and reacted for a period of time to obtain sludge pretreated with a green chelating agent having a pH value of 3.0.

[0137] 3. Inorganic phosphorus recovery:

[0138] ①, centrifuge the sludge pretreated with the green chelating agent to obtain liquid II and solid II;

[0139] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0140] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0141] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0142] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O;

[0143] 4. Sludge resuspension:

[0144] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0145] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1; five,

[0147] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 6.88, and the sludge was shaken and reacted at 25° C. and 140 rpm for 12 h to obtain the reacted sludge;

[0148] 6. Anaerobic resource utilization:

[0149] The anaerobic fermentation tank was filled with nitrogen for 15 minutes, and then the sealing plug was put on to keep the reactor in an anaerobic state, and the reaction was carried out at 35°C for 12 days to obtain a sludge mixture after the reaction;

[0150] 7. Recycling of carbon and phosphorus resources:

[0151] ①, centrifuging the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0152] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0153] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0154] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0155] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0156] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0157] Example 7: A method for cascade-enhanced efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0158] 1. Sludge pretreatment:

[0159] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0160] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0161] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0162] 2. Place 500 mL of concentrated excess sludge I in a constant temperature incubator at 35°C and 140 rpm for 18 hours to obtain pretreated sludge;

[0163] 3. Inorganic phosphorus recovery:

[0164] ①, centrifuge or filter press the pretreated sludge to obtain liquid II and solid II;

[0165] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0166] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0167] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0168] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al 2(PO 4 ) 4 (OH) 2 8H 2 O;

[0169] 4. Sludge resuspension:

[0170] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0171] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1;

[0172] 5. Peroxidant-enhanced sludge solubilization and hydrolysis:

[0173] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 6.88, and then a peroxidant was added, and the reaction was carried out at 25° C. for 12 hours to obtain the reacted sludge;

[0174] The peroxidant described in step 5 is sodium percarbonate;

[0175] The dosage of the peroxidant in step 5 is 0.1 g / g TSS;

[0176] 6. Anaerobic resource utilization:

[0177] The anaerobic fermentation tank was filled with nitrogen for 15 minutes, and then the sealing plug was put on to keep the reactor in an anaerobic state, and the reaction was carried out at 35°C for 12 days to obtain a sludge mixture after the reaction;

[0178] 7. Recycling of carbon and phosphorus resources:

[0179] ①, centrifuging the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0180] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0181] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0182] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0183] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0184] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0185] Example 8: A method for cascade-enhanced efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0186] 1. Sludge pretreatment:

[0187] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0188] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0189] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0190] 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus:

[0191] Add a green chelating agent to 500 mL of concentrated excess sludge I, the dosage of the green chelating agent is 0.08 g / g TSS (i.e., add 1.87 g of citric acid to 500 mL of concentrated excess sludge I), then use 4 mol / L hydrochloric acid to adjust the pH value of the system to 3.0, stir evenly, and then place it in a constant temperature incubator to react for a period of time to obtain sludge pretreated with a green chelating agent with a pH value of 3.0;

[0192] 3. Inorganic phosphorus recovery:

[0193] ①, centrifuge or filter press the sludge pretreated with the green chelating agent to obtain liquid II and solid II;

[0194] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0195] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0196] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0197] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O;

[0198] 4. Sludge resuspension:

[0199] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0200] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1;

[0201] 5. Peroxidant-enhanced sludge solubilization and hydrolysis:

[0202] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 6.88, and then a peroxidant was added, and the reaction was carried out at 25° C. for 12 hours to obtain the reacted sludge;

[0203] The peroxidant described in step 5 is sodium percarbonate;

[0204] The dosage of the peroxidant in step 5 is 0.1 g / g TSS;

[0205] 6. Anaerobic resource utilization:

[0206] The anaerobic fermentation tank was filled with nitrogen for 15 minutes, and then the sealing plug was put on to keep the reactor in an anaerobic state, and the reaction was carried out at 35°C for 12 days to obtain a sludge mixture after the reaction;

[0207] 7. Recycling of carbon and phosphorus resources:

[0208] ①, centrifuging the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0209] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0210] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0211] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0212] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0213] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0214] Comparative Example 2: A method for stepwise enhanced efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0215] 1. Sludge pretreatment:

[0216] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0217] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0218] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0219] 2. Place 500 mL of concentrated excess sludge I in a constant temperature incubator at 35°C and 140 rpm for 18 h to obtain pretreated sludge;

[0220] 3. Inorganic phosphorus recovery:

[0221] ①, centrifuge the pretreated sludge to obtain liquid II and solid II;

[0222] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0223] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0224] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0225] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O;

[0226] 4. Sludge resuspension:

[0227] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0228] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1; five,

[0230] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 6.88, and the sludge was shaken and reacted at 25° C. and 140 rpm for 12 h to obtain the reacted sludge;

[0231] 6. Anaerobic resource utilization:

[0232] The anaerobic fermentation tank was filled with nitrogen for 15 minutes, and then the sealing plug was put on to keep the reactor in an anaerobic state, and the reaction was carried out at 35°C for 12 days to obtain a sludge mixture after the reaction;

[0233] 7. Recycling of carbon and phosphorus resources:

[0234] ①, centrifuging the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0235] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0236] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0237] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0238] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0239] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0240] At pH 7, 0.2 M K 2 HPO 4 ·3H 2 O and 0.3 M FeSO 4 7H 2 O solution to synthesize the standard (reference) sample and obtain pure crystals.

[0241] Figure 7 The volatile acid concentration effect diagram of Examples 6 to 8 and Steps 5 and 6 of Comparative Example 2 after acid and citric acid pretreatment and sodium percarbonate co-treatment;

[0242] Figure 8 The volatile acid composition is obtained by pre-treatment with acid and citric acid and co-treatment with sodium percarbonate in steps 5 and 6 of Examples 6 to 8 and Comparative Example 2;

[0243] After 10 days of anaerobic fermentation, on the 9th day, the total amount of short-chain volatile fatty acids (VFAs) in the sludge of Example 8 reached the highest value, which was 316.5 mg / g VSS, which was 14 times higher than the highest concentration (the fourth day) of Comparative Example 2 (as shown in Figure 2). Figure 7 At the same time, the total amount of VFAs in the sludge of Example 7 and Example 6 reached 89.5 mg / g VSS and 205.48 mg / g VSS, respectively, which was 3.5 times and 1.5 times higher than that of Comparative Example 2 (as shown in FIG. Figure 7 As shown). The proportion of acetic acid in Example 6 and Example 8 was increased by 15% compared with that in Comparative Example 2 and Example 7, indicating that the sludge from which metal ions and phosphorus were removed can directionally regulate the acid production pathway during the anaerobic fermentation process, synergistically increase the production of volatile fatty acids (VFAs) and the proportion of acetic acid, and enhance the application and economic value of the fermentation broth as a supplementary carbon source for sewage treatment plants (such as Figure 8These results indicate that the free radicals of sodium percarbonate are fully utilized by the pretreatment of sludge with acid and citric acid and the synergistic co-pretreatment with sodium percarbonate, which can more thoroughly break up the sludge and significantly increase the yield of short-chain volatile fatty acids, while reducing the dosage of sodium percarbonate and thus reducing the cost of use.

[0244] Fig. 9 PO 600 prepared from the steps 5 and 6 of Examples 6 to 8 and Comparative Example 2 after acid and citric acid pretreatment and sodium percarbonate co-treatment 4 3- -P effect diagram;

[0245] Fig.10 The graph showing the change of phosphorus content in the sludge mixture after the reaction obtained in steps 5 and 6 of Examples 6 to 8 and Comparative Example 2;

[0246] After 12 days of anaerobic fermentation, the PO content in the supernatant of each group 4 3- -P concentration gradually increased with the fermentation process. 4 3- The highest concentration of -P was 172 mg / L, which was 16.2% and 10.9% higher than that of Example 6 and Example 7, respectively, indicating that sodium percarbonate enhancement and metal ion removal can synergistically increase the PO in the supernatant. 4 3- -P concentration (such as Fig. 9 ). Fig.10 The change in phosphorus content in the solid phase shows that it is mainly due to the release of organic phosphorus in the sludge during anaerobic biological treatment, which leads to an increase in the concentration of organic phosphorus in the supernatant. The reason may be that, for phosphorus release, on the one hand, citric acid pretreatment and pre-solid-liquid separation can enhance the hydrolysis of organic matter while promoting the hydrolysis and release of organic phosphorus and removing inorganic phosphorus and metal ions, hindering the combination of metal and phosphorus. On the other hand, sodium percarbonate enhances the solubilization, rupture and hydrolysis efficiency of sludge through its oxidation, and enhances the further release of organic phosphorus in the sludge.

[0247] The recovery rates of phosphorus and ferrous iron in Example 8 are shown in Table 1 below. The recovery rates of phosphorus and ferrous iron are 83.1% and 93%, respectively, indicating the feasibility of recovering the two elements. XRD characterization shows that the blue iron ore is successfully recovered (e.g. Fig.11 shown).

[0248] Table 1 Phosphate and ferrous iron concentrations in the supernatant before and after phosphorus recovery

[0249]

[0250] Example 9: A method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge, comprising the following steps:

[0251] 1. Sludge pretreatment:

[0252] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0253] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0254] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0255] 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus:

[0256] Add a green chelating agent to 500 mL of concentrated excess sludge I, the dosage of the green chelating agent is 0.08 g / g TSS (i.e., add 1.87 g of citric acid to 500 mL of concentrated excess sludge I), then use 4 mol / L hydrochloric acid to adjust the pH value of the system to 3.0, stir evenly, and then place it in a constant temperature incubator to react for a period of time to obtain sludge pretreated with a green chelating agent with a pH value of 3.0;

[0257] 3. Inorganic phosphorus recovery:

[0258] ①, centrifuge or filter press the sludge pretreated with the green chelating agent to obtain liquid II and solid II;

[0259] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0260] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0261] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0262] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al2 (PO 4 ) 4 (OH) 2 8H 2 O;

[0263] 4. Sludge resuspension:

[0264] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0265] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1;

[0266] 5. Peroxidant-enhanced sludge solubilization and hydrolysis:

[0267] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 6.88, and then a peroxidant was added, and the reaction was carried out at 25° C. for 12 hours to obtain the reacted sludge;

[0268] The peroxidant described in step 5 is potassium perborate;

[0269] The dosage of the peroxidant in step 5 is 0.1 g / g TSS;

[0270] 6. Anaerobic resource utilization:

[0271] Add the inoculated sludge to the reacted sludge obtained in step 5, adjust the pH value to 7, introduce nitrogen into the anaerobic fermentation tank for 15 minutes, cover the reactor with a sealing plug to keep the reactor in an anaerobic state, and react at 35° C. for 12 days to obtain a reacted sludge mixture;

[0272] The preparation method of the inoculum sludge described in step 6 is as follows: the concentrated excess sludge I obtained in step 1 is first boiled at 100°C for 2h, transferred to a reactor, and after cooling, the following substances are added thereto: 14.4g / L of glucose, 3.2g / L of yeast extract, 0.56g / L of potassium dihydrogen phosphate, 0.96g / L of magnesium sulfate heptahydrate, 2.4g / L of ammonium chloride, 0.72g / L of anhydrous calcium chloride, 0.96g / L of sodium bicarbonate, 0.11g / L of manganese chloride, and 0.12g / L of ferrous sulfate heptahydrate to obtain a sludge mixture; then nitrogen is introduced for 10min to 40min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and long-term acclimation is carried out at 33°C to 37°C, 0.5L of sludge is discharged from the reactor every 7 days, and 0.5L of the above-prepared sludge mixture is added, and long-term operation is carried out with a cycle of every 7 days to obtain inoculum sludge;

[0273] The mass ratio of the inoculated sludge in step 6 to the reacted sludge obtained in step 5 is 1:2;

[0274] 7. Recycling of carbon and phosphorus resources:

[0275] ①, centrifuging the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0276] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0277] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0278] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0279] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0280] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0281] Comparative Example 3: A method for stepwise enhanced efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0282] 1. Sludge pretreatment:

[0283] The secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 40-mesh sieve to remove impurities (stones, plastics, branches and other large particles), and then refrigerated and left to stand at 4°C for 24 hours, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0284] The concentrated excess sludge I described in step 1 has a total solid content of 46.76 g / L, a volatile total solid content of 22.77 g / L, a total COD of 29600 mg / L, a moisture content of 95.15%, an iron content of 35.3 mg / g TSS, a phosphorus content of 26.33 mg / g TSS, and an aluminum content of 16.8 mg / g TSS;

[0285] The secondary sedimentation tank sludge described in step 1 is activated sludge for biological phosphorus removal, which is A 2 / Excess sludge produced by O process;

[0286] 2. Place 500 mL of concentrated excess sludge I in a constant temperature incubator at 35°C and 140 rpm for 18 hours to obtain pretreated sludge;

[0287] 3. Inorganic phosphorus recovery:

[0288] ①, centrifuge the pretreated sludge to obtain liquid II and solid II;

[0289] The centrifugal speed in step 3① is 8000 rpm and the centrifugal time is 5 min;

[0290] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II be 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and then standing for 30 min to allow the metal ions and phosphorus to fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0291] In step 3②, a 4 mol / L sodium hydroxide solution is used to adjust the pH value of the liquid to 8.7;

[0292] The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg 2 Al 2 (PO 4 ) 4 (OH) 2 8H 2 O;

[0293] 4. Sludge resuspension:

[0294] ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 4.6%, and then transfer it to the anaerobic fermentation tank;

[0295] The volume ratio of supernatant III and supernatant I described in step 4① is 0:1; five,

[0297] The pH value of the sludge in the anaerobic fermentation tank was adjusted to 6.88, and the sludge was shaken and reacted at 25° C. and 140 rpm for 12 h to obtain the reacted sludge;

[0298] 6. Anaerobic resource utilization:

[0299] Add the inoculated sludge to the reacted sludge obtained in step 5, adjust the pH value to 7, introduce nitrogen into the anaerobic fermentation tank for 15 minutes, cover the reactor with a sealing plug to keep the reactor in an anaerobic state, and react at 35° C. for 12 days to obtain a reacted sludge mixture;

[0300] The preparation method of the inoculum sludge described in step 6 is as follows: the concentrated excess sludge I obtained in step 1 is first boiled at 100°C for 2h, transferred to a reactor, and after cooling, the following substances are added thereto: 14.4g / L of glucose, 3.2g / L of yeast extract, 0.56g / L of potassium dihydrogen phosphate, 0.96g / L of magnesium sulfate heptahydrate, 2.4g / L of ammonium chloride, 0.72g / L of anhydrous calcium chloride, 0.96g / L of sodium bicarbonate, 0.11g / L of manganese chloride, and 0.12g / L of ferrous sulfate heptahydrate to obtain a sludge mixture; then nitrogen is introduced for 10min to 40min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and long-term acclimation is carried out at 33°C to 37°C, 0.5L of sludge is discharged from the reactor every 7 days, and 0.5L of the above-prepared sludge mixture is added, and long-term operation is carried out with a cycle of every 7 days to obtain inoculum sludge;

[0301] The mass ratio of the inoculated sludge in step 6 to the reacted sludge obtained in step 5 is 1:2;

[0302] 7. Recycling of carbon and phosphorus resources:

[0303] ①, centrifuging the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I;

[0304] The centrifugal treatment speed in step 7① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0305] ②, add ferrous salt to the filtrate I obtained in step 7①, then use alkali solution to adjust the pH value to 7.0, react under anaerobic conditions for 1 hour, then age for 2 hours under nitrogen conditions, and then centrifuge at 10000rpm for 10 minutes for solid-liquid separation to obtain blue iron ore and filtrate II, filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source for supplementing the carbon source, and the blue iron ore is vacuum dried at 50°C;

[0306] The ferrous salt described in step 7② is ferrous sulfate heptahydrate;

[0307] The molar ratio of the ferrous salt described in step 7② to the phosphorus in the filtrate I is 1.5:1;

[0308] The alkali solution described in step 7② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0309] Fig.12 The volatile acid concentration effect diagram of anaerobic fermentation of sludge after potassium hexaperborate fortification and citric acid pretreatment in Example 9 and Comparative Example 3;

[0310] After 8 days of anaerobic fermentation, the total amount of short-chain volatile fatty acids (VFAs) in the sludge of Example 9 reached the highest concentration on the 6th day, which was 208 mg / g VSS, which was 1.6 times that of the control example 3 ( Fig.12 This result shows that acid and citric acid pretreatment and potassium perborate co-pretreatment have a significant synergistic effect in promoting anaerobic fermentation of sludge to produce volatile acids. Through this synergistic pretreatment method, while achieving the same or even higher short-chain volatile fatty acid production, the dosage of potassium perborate can be effectively reduced, thereby reducing process costs.

Claims

1. A method for stepwise intensified efficient release and resource utilization of carbon and phosphorus in sludge, characterized in that The method comprises the following steps:

1. Sludge pretreatment: The sludge in the secondary sedimentation tank of the sewage treatment plant is screened to remove impurities, then refrigerated and left to stand for a period of time, and the supernatant is removed by siphoning or decanting, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I; 2. Green chelating agent pretreatment to enhance the release of inorganic phosphorus: Adding a green chelating agent to the concentrated excess sludge I, stirring evenly, and then placing the concentrated excess sludge in a constant temperature incubator to react for a period of time to obtain sludge pretreated with the green chelating agent; 3. Inorganic phosphorus recovery: ①, centrifuge or filter press the sludge pretreated with the green chelating agent to obtain liquid II and solid II; ②, adding calcium-based metal salt to liquid II, so that the molar ratio of calcium to phosphorus in liquid II is (0.5-3):1, adjusting the pH value of liquid II to 6-13, then stirring for a period of time, then standing for a period of time, and finally centrifuging to collect the phosphorus precipitate solid and supernatant III; 4. Sludge resuspension: ①. Mix the supernatant III and the supernatant I, and then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 0.5% to 10%, and then transfer it to the anaerobic fermentation tank; 5. Peroxidant-enhanced sludge solubilization and hydrolysis: The pH value of the sludge in the anaerobic fermentation tank is adjusted to 6-7.5, and then a peroxidant is added to react at 25-35°C for a period of time to obtain the reacted sludge; 6. Anaerobic resource utilization: Adding inoculated sludge to the reacted sludge obtained in step 5, adjusting the pH value to 5-7.5, introducing nitrogen into the anaerobic fermentation tank for a period of time, and then covering the reactor with a sealing plug to keep the reactor in an anaerobic state, reacting at 30° C.-37° C. for 2-40 days to obtain a reacted sludge mixture; 7. Recycling of carbon and phosphorus resources: ①, centrifuging or filtering the sludge mixture after the reaction obtained in step 6 to obtain residual solids and filtrate I; ②. Add ferrous salt to the filtrate I obtained in step seven ①, and then use alkali solution to adjust the pH value to 5-9, react under anaerobic conditions for 0.5h-2h, and then age for 0.5h-2h under nitrogen or argon conditions, and then use centrifugal treatment or filter press to separate the solid and liquid to obtain blue iron ore and filtrate II. Filtrate II is refluxed to the mainstream sewage treatment plant as a carbon source to supplement the carbon source. The blue iron ore is vacuum dried at 35°C-60°C.

2. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1 is characterized in that In step 1, the secondary sedimentation tank sludge produced by the sewage treatment plant is passed through a 20-mesh to 60-mesh sieve to remove impurities, and then refrigerated and allowed to stand at a temperature of 4°C for 4h to 48h, and then the supernatant is removed by a siphon method or a decanter, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I; the secondary sedimentation tank sludge described in step 1 is a mixture of one or more of activated sludge for biological phosphorus removal, sludge for iron chemically enhanced phosphorus removal, and sludge for aluminum chemically enhanced phosphorus removal; the solid content of the concentrated residual sludge I described in step 1 is 0.5% to 10%.

3. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1 is characterized in that The green chelating agent described in step 2 is a mixture of one or more of citric acid, tartaric acid, methylglycine diacetic acid, glutamic acid diacetic acid and metal acid salts; the dosage of the green chelating agent described in step 2 is 0.01g / gTSS~0.5g / gTSS; the temperature of the constant temperature incubator described in step 2 is 20℃~40℃, and the rotation speed is 100rpm~150rpm; the reaction time in the constant temperature incubator in step 2 is 1h~48h.

4. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1, characterized in that The centrifugal speed described in step 3① is 5000rpm~10000rpm, and the centrifugal time is 5min~20min; the calcium-based metal salt described in step 3② is calcium chloride, calcium oxide or calcium hydroxide; the stirring speed described in step 3② is 600rpm~1000rpm, and the stirring time is 10min~60min; the standing time described in step 3② is 30min~120min.

5. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1, characterized in that The speed of the centrifugal treatment described in step 3② is 8000rpm~12000rpm, and the time of the centrifugal treatment is 5min~20min; In step 3②, a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 1mol / L~6mol / L is used to adjust the pH value of the liquid to 6~13; The composition of the phosphorus precipitated solid described in step 3② is (CaFeMg2Al2(PO4)4(OH)2·8H2O.

6. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1, characterized in that The volume ratio of supernatant III and supernatant I described in step 4① is (0-5):(0-5); the peroxidant described in step 5 is sodium percarbonate, potassium percarbonate, sodium perborate, potassium perborate, calcium peroxide, magnesium peroxide, sodium ferrate, potassium ferrate, sodium periodate, potassium periodate, hydrogen peroxide, peracetic acid, sodium hypochlorite or potassium hypochlorite.

7. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1, characterized in that The reaction time in step 5 at 25° C. to 35° C. is 4 h to 24 h; the dosage of the peroxidant in step 5 is 0.01 g / gTSS to 0.5 g / gTSS.

8. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1, characterized in that The preparation method of the inoculum sludge described in step six is ​​as follows: the concentrated excess sludge I obtained in step one is first boiled at 90°C to 100°C for 1h to 4h, transferred to a reactor, and after cooling, the following substances are added thereto: 14.4g / L of glucose, 3.2g / L of yeast extract, 0.56g / L of potassium dihydrogen phosphate, 0.96g / L of magnesium sulfate heptahydrate, 2.4g / L of ammonium chloride, 0.72g / L of anhydrous calcium chloride, 0.96g / L of sodium bicarbonate, 0.11g / L of manganese chloride, and 0.12g / L of ferrous sulfate heptahydrate to obtain a sludge mixture; then nitrogen is introduced for 10min to 40min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and long-term acclimation is carried out at 33°C to 37°C, 0.5L of sludge is discharged from the reactor every 7 days, and 0.5L of the above-prepared sludge mixture is supplemented, and long-term operation is carried out with a cycle of every 7 days to obtain inoculum sludge.

9. The method for efficiently releasing and recycling carbon and phosphorus in cascade-enhanced sludge according to claim 1, characterized in that The mass ratio of the inoculated sludge described in step 6 to the reacted sludge obtained in step 5 is (0-1):(1-5), and the pH value is adjusted to 5-7.5; the time for introducing nitrogen into the anaerobic fermentation tank in step 6 is 10min-30min; the speed of the centrifugal treatment described in step 7① is 5000rpm-10000rpm, and the time of the centrifugal treatment is 5min-15min.

10. The method for efficiently releasing and recycling carbon and phosphorus in cascade enhanced sludge according to claim 1, characterized in that The ferrous salt described in step 7② is ferrous chloride or ferrous sulfate; the molar ratio of the ferrous salt described in step 7② to phosphorus in filtrate I is (1-2):1; the alkali solution described in step 7② is sodium hydroxide solution or potassium hydroxide solution, and the concentration is 1 mol / L-6 mol / L.

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