A method for efficiently releasing and recycling carbon and phosphorus in sludge through step-by-step reinforcement

Abstract

The application discloses a method for realizing efficient release and resource utilization of carbon and phosphorus in sludge in a gradient reinforcing manner, and relates to a sludge resource utilization method.The method is characterized in that the release efficiency of different occurrence forms of phosphorus in sludge is improved in a targeted manner, and through the synergistic effect of multiple steps, efficient release of inorganic phosphorus and organic phosphorus is realized, and the efficient release and resource utilization recovery of carbon is simultaneously improved, so that the overall resource utilization recovery efficiency of carbon and phosphorus in residual sludge is improved.The method comprises the following steps: (1) sludge pretreatment; (2) green chelating agent pretreatment for reinforcing release of inorganic phosphorus; (3) inorganic phosphorus recovery; (4) sludge resuspension; (5) peroxide reinforcing sludge solubilization and hydrolysis; (6) anaerobic resource utilization; and (7) carbon and phosphorus resource recovery.The recovery process is simple, the loss rate is low, the phosphorus recovery rate can be as high as 80% to 99.5%, and the acid production efficiency is increased by more than 14 times, so that the method has remarkable advantages.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for resource utilization of sludge. BACKGROUND

[0002] Phosphorus resources are indispensable elements for all organisms, and are key components of energy metabolism and cell structure, playing a crucial 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 depleted within 280 years. With the increasing scarcity of phosphate rock resources, the risk of resource loss and depletion is also increasingly prominent.

[0003] Sludge is a by-product of the main process of wastewater treatment, which is complex in composition, containing not only harmful substances such as heavy metals and pathogens, but also organic matter (40%-80% of the dry weight of sludge) such as protein, polysaccharide, humus, and inorganic resources such as nitrogen and phosphorus. Among them, about 90% of the phosphorus in wastewater is enriched in sludge, accounting for 2%-5% of the dry weight of sludge. In order to meet the increasingly stringent discharge standards for wastewater treatment, iron and aluminum-based flocculants are often added to the wastewater treatment process to enhance phosphorus removal. Therefore, the phosphorus in sludge mainly exists in the form of inorganic phosphorus (more than 50%) and organic phosphorus, and inorganic phosphorus is mainly combined with metal ions such as iron, magnesium, aluminum, and calcium, or exists in the form of adsorption on the surface of metal oxides. In summary, sludge is a potential carbon and phosphorus resource library that needs to be tapped 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 applied due to its significant reduction effect, stable and harmless treatment capacity, short operation cycle, resource utilization potential, low energy consumption, and economic sustainability. However, the stable structure of net gelatinous extracellular polymeric substances (EPS) and semi-rigid cell structure (cell wall and cell membrane) in sludge limits the release of soluble organic matter from solid phase to liquid phase, limits the hydrolysis efficiency, and thus leads to low biological conversion efficiency of organic matter.

[0005] In the process of sludge anaerobic resourceization, the mainstream strategy of sludge phosphorus recovery mainly relies on the pretreatment technology to break and solubilize the sludge. Subsequently, in the anaerobic reaction, the 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 ends. To improve the release and resourceization efficiency of carbon and phosphorus in the process of anaerobic resourceization, the existing technology has developed a combined process of simultaneous enhanced sludge anaerobic resourceization and phosphorus release. However, this process has many limitations: on the one hand, in the process of anaerobic resourceization, the release efficiency of organic phosphorus in sludge is mainly limited by sludge hydrolysis, which hinders the dissolution and release of intracellular polyphosphorus and extracellular organic phosphorus, resulting in low release efficiency and long time period of organic phosphorus and soluble organic matter, and thus the concentration of organic phosphorus hydrolyzed to phosphate in the supernatant is low; on the other hand, the inorganic phosphorus such as magnesium, aluminum, and calcium phosphorus in sludge is difficult to be effectively released in the process of anaerobic resourceization through biological action; in addition, the optimal conditions (such as pH value and release period) required for the efficient release of sludge carbon resourceization process and iron phosphorus and organic phosphorus are not consistent, and the existing process is more biased towards carbon resourceization, resulting in poor timeliness of phosphorus release and recovery. At the same time, part of the metal ions released in the supernatant due to hydrolytic digestion will re-fix the released phosphorus to the solid phase under the action of precipitation, further reducing the release efficiency of phosphorus, sometimes failing to meet the minimum economic requirement (<100 mg / L) of phosphorus recovery, and finally failing to simultaneously and efficiently recover carbon and phosphorus resources in the process of sludge anaerobic resourceization.

[0006] A Chinese invention patent (publication number: CN114195341A, publication date: March 18, 2022) discloses a method for improving the efficiency of anaerobic methane production and the availability of phosphorus in excess sludge. This method uses citric acid or citrate and calcium hydroxide to pretreat the excess sludge, which can effectively promote the anaerobic digestion of sludge to produce methane. Its advantages lie in the fact that it can strengthen the lysis of sludge flocs and cells, dissolve more organic matter, thereby shortening the period of anaerobic digestion to produce methane, and significantly increasing the content of effective phosphorus in the digested sludge that can be easily absorbed by plants. However, the phosphorus resource precipitate formed in this method is mixed with the sludge, making it difficult to recover the phosphorus precipitate, resulting in a low recovery rate and high recovery cost of phosphorus-containing minerals. In this patent technology, phosphorus is released and coexists with metal ions in the same environment, which cannot be separated in time, resulting in the failure to achieve effective recovery of phosphorus.

[0007] A Chinese invention patent (publication number: CN113087333A, publication date: July 9, 2021) proposes a resource utilization process for simultaneous enhanced sludge anaerobic acid production and phosphorus recovery. The process first uses heat-activated persulfate to pretreat the sludge, adjusts the pH, and then performs anaerobic acid fermentation. Subsequently, solid-liquid separation is performed. Magnesium salt is added to the phosphorus-rich fermentation liquid obtained after separation, and the pH is adjusted. Phosphorus is recovered in the form of struvite crystallization from the filtrate. The recovered filtrate is then returned to the wastewater treatment plant as a carbon source. However, this method has some limitations. First, the heat hydrolysis activation technology requires a large amount of energy consumption, resulting in high operating costs. On the other hand, the release of phosphorus mainly depends on Fe-P (iron phosphorus) -rich iron sludge. The phosphorus release effect is poor for sludge with high aluminum phosphorus and calcium phosphorus content, so the application range of this method is relatively narrow. Although the heat-activated persulfate combined with solid-liquid separation technology in this patent technology can separate phosphorus and iron ions, the release effect of aluminum phosphorus and calcium phosphorus is poor, and the energy input of the heat activation process is too high.

[0008] A Chinese invention patent (publication number: CN113772906A, publication date: December 10, 2021) proposes a method for pretreating and enhancing sludge biological resource utilization using acid ion exchange resin. The process involves adding acid ion exchange resin to the sludge, adjusting the sludge to its isoelectric point, and then separating the pretreated sludge and resin through a screen. The regenerated resin can be recycled after acid regeneration, while the pretreated sludge is adjusted to neutral pH and enters the subsequent anaerobic fermentation acid production or anaerobic digestion methane production process to generate anaerobic fermentation sludge. Then, solid-liquid separation is performed on the anaerobic fermentation sludge, the filtrate is collected, and magnesium salt is added to adjust the pH to form struvite precipitation for phosphorus recovery. The remaining filtrate is returned to the wastewater treatment plant to recover carbon. This method has the advantages of promoting extracellular polymeric substance (EPS) hydrolysis and removing metals, and can achieve efficient release and high-value recovery of phosphorus during biological treatment. However, this method has some shortcomings: the acid ion exchange resin used has a small particle size, which is easily clogged by sludge, and the operation process is complex and difficult to completely recover through a screen. This results in low recovery and regeneration rates of ion exchange resin, increasing the economic cost and making it lack feasibility in engineering applications. Although the acid ion exchange resin in this patent technology can be used to capture metal ions and simultaneously achieve efficient release and high-value recovery of phosphorus during biological treatment, it has limitations such as small particle size, easy clogging, and complex operation in actual applications, lacking feasibility in engineering applications.

[0009] A Chinese invention patent (Publication No. CN117327746A, Publication Date: January 12, 2024) proposes a method for enhancing the production of short-chain fatty acids (VFAs) and phosphorus-containing minerals during anaerobic fermentation of excess sludge. This method involves adding different concentrations of magnesium ferrate to enhance the anaerobic fermentation process of sludge and simultaneously generate phosphorus-containing minerals. This technology has significant advantages, including accelerating sludge hydrolysis, improving sludge biodegradability, and producing high-quality short-chain fatty acids (VFAs). However, the phosphorus-containing minerals (such as blue vitriol and struvite) generated by this method are mixed with the fermented sludge, making the subsequent recovery process complex and inefficient, thereby increasing the cost of phosphorus-containing mineral recovery. In this patent technology, magnesium ferrate only promotes sludge hydrolysis, but ultimately does not obtain separable phosphorus-containing minerals.

[0010] A Chinese invention patent (Publication No. CN118028385A, Publication Date: May 14, 2024) discloses a method for enhancing the production of short-chain fatty acids (VFAs) during anaerobic fermentation of excess sludge. This method involves adding sodium percarbonate to effectively promote the dissolution of soluble substrates and the production of short-chain fatty acids (VFAs). This technology has the advantages of wide pH range, easy in-situ activation, and breaking down sludge. However, this method also has some shortcomings: on the one hand, it has high cost; on the other hand, it does not involve the enhanced release and recovery of phosphorus in sludge. In this patent technology, sodium percarbonate promotes sludge digestion through the oxidation of peroxide, but does not involve the release and recovery of phosphorus.

[0011] 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.) studied that thermal hydrolysis pretreatment can enhance phosphorus release from sewage sludge in anaerobic digestion. The phosphorus concentration in the liquid phase of the sludge pretreated by thermal hydrolysis at 170°C increased significantly by 53.8% in the initial stage of the subsequent anaerobic fermentation process (within 3 days). However, during the subsequent 17-day anaerobic digestion process, the phosphorus concentration in the supernatant gradually decreased due to the influence of metal precipitation, eventually being lower than the initial concentration before anaerobic digestion. Although thermal hydrolysis pretreatment in this technology can enhance the release of organic phosphorus and part of inorganic phosphorus in the sludge during anaerobic digestion, it fails to achieve immediate and effective recovery of phosphorus, and the phosphorus in the final sludge still returns to the sludge in the form of precipitation.

[0012] A Chinese invention patent (Publication No. 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, dissolved under acidic conditions, and Fe 2+ and PO4 3- -P, Mg-P and Ca-P are dissolved and released in small amounts due to the complexation of ascorbic acid. Then solid-liquid separation is carried out, and in the phosphorus-rich fermentation liquid obtained by separation, the molar ratio of ferrous ion to 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 vivianite. This method can increase the phosphorus release efficiency of excess 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 cost; second, 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 application range of the technology is relatively narrow. In addition, this method only focuses on the recovery of phosphorus in the sludge, and fails to fully exploit the value of carbon resource recovery and utilization in the remaining sludge after phosphorus release. In this patent, ascorbic acid has good phosphorus release effect on iron-rich sludge, but it is not suitable for aluminum sludge, the application range is narrow, and the release of organic phosphorus and the subsequent resource utilization of sludge are not considered.

[0013] A Chinese invention patent (publication number: CN116903206A, publication date: October 20, 2023) discloses a sludge treatment agent and its preparation method and application. The method can complex various metal ions in the sludge by using organic acid citric acid, reducing agent ascorbic acid and metal complexing agent EDTA, and can make the release efficiency of phosphorus in the residual sludge reach more than 75%. However, if any of the three substances is missing, the release rate of phosphorus will be significantly reduced. Despite this, the method also has some problems: on the one hand, the addition of toxic EDTA may have an adverse effect on the subsequent resource utilization of sludge; on the other hand, the simultaneous use of the three chemicals significantly increases the cost of strengthening the release of phosphorus in residual sludge, making it economically unfeasible. This patent technology uses organic acid citric acid, reducing agent ascorbic acid and metal complexing agent EDTA in combination, which has certain advantages in phosphorus release efficiency, but the overall economic cost is high, limiting the possibility of large-scale application, and it 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 process of sludge, thereby bringing potential environmental risks. Therefore, this combination does not have enough practicality and generalizability in actual application.

[0014] A Chinese invention patent (publication number: CN113173648A, publication date: July 27, 2021) discloses a method for preparing vivianite with low cost and high efficiency of phosphorus removal. An iron-reducing bacteria-iron mineral system composed of iron-reducing bacteria, iron minerals, electron shuttles and carbon sources is added to water or phosphorus-containing wastewater, the pH of the reaction system is maintained at 6-8 and it is placed in an anaerobic environment, the reaction system is allowed to settle and precipitate, and the sludge containing a large amount of vivianite at the bottom is discharged through a sludge discharge pipe. Although this method uses biological methods to recover phosphorus and reduces production costs, there are 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), the fluctuation of microbial electron transfer efficiency and the competitive inhibition of sulfide (FeS precipitation) are not suitable for complex systems, resulting in poor stability of phosphorus recovery efficiency. In this patent technology, the iron-reducing bacteria-iron mineral system recovers phosphorus by dissimilatory iron reduction to break the Fe-P chemical bond, which has the advantage of reducing water treatment costs, but the recovery efficiency is regulated by electron transfer efficiency, competitive reactions and environmental factors.

[0015] In summary: the existing technology generally faces the problems of low efficiency, high cost, limited applicability, complex operation and environmental risk in the recovery of carbon and phosphorus resources in excess sludge. Most traditional simultaneous enhanced processes are incompatible in the kinetics conditions of carbon resourceization and inorganic and organic phosphorus release process, with differences in optimal release time, optimal pH value and other parameter conditions. Although these technologies can achieve simultaneous enhancement to some extent, due to the optimal conditions mainly focusing on the enhancement of carbon resourceization efficiency, they cannot fully match the optimal parameters of phosphorus release, and cannot synergistically improve the release and recovery efficiency of carbon and phosphorus. The key limiting factor of the release efficiency of organic phosphorus and carbon in the anaerobic resourceization process is the sludge hydrolysis, and its efficiency is limited by the mass transfer barrier formed by the network colloidal extracellular polymeric substance (EPS) in the sludge substrate and the double restriction of the semi-rigid structure of cell wall / membrane, which significantly hinders the dissolution and release of carbon resources, intracellular polyphosphorus and extracellular organic phosphorus in the sludge, resulting in low release efficiency of organic phosphorus and soluble organic matter and prolonged period. 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 oxidation-reduction potential and pH, the fluctuation of microbial electron transfer efficiency and the competitive inhibition of sulfide in the complex system, resulting in unstable phosphorus release efficiency in the biological reduction of iron-phosphorus process, with large fluctuation range. In addition, there is no good time sequence coordination between the nitrogen and phosphorus resourceization paths, so that the phosphorus in the post-phosphorus release liquid phase cannot be separated in time, and the metal ions (Fe, Al, Ca, Mg) re-fix the phosphorus components through precipitation in the anaerobic process, resulting in the phenomena of phosphorus re-precipitation and sludge-phosphorus separation difficulty, leading to low phosphorus release rate and recovery rate. In addition, the existing process lacks the enhanced release of aluminum / calcium / magnesium combined inorganic phosphorus, resulting in relatively low overall phosphorus release effect. In summary, the release of phosphorus and carbon in sludge is limited by intracellular / extracellular mass transfer barrier, in addition, the release of phosphorus is also limited by the fluctuation of microbial electron transfer efficiency, metal precipitation, lack of separate quality regulation of different forms of phosphorus, ultimately restricting the efficient release of phosphorus in sludge anaerobic process and the synergistic recovery efficiency of high value-added products (such as acid, methane). At the same time, the existing technology also has many deficiencies, such as the dependence on high-dose addition of peroxide agent, complex solid-liquid separation process in the process of enhancing the release of organic phosphorus and carbon resourceization recovery, resulting in high process cost, large energy consumption, low carbon and phosphorus release and recovery efficiency, and limited application range, which together lead to the difficulty of the existing technology in meeting the actual demand in the aspects of synergistically improving the release efficiency of carbon and phosphorus, cost control, applicability and environmental friendliness.

[0016] Therefore, the present application aims to design a new method to specifically improve the release efficiency of different forms of phosphorus in sludge, to enhance the efficient release and recovery of inorganic and organic phosphorus in the biological treatment process, and to consider the recovery of high value-added products (such as acid, methane) at the same time, and finally to synergistically improve the release and recovery of carbon and phosphorus resources in excess sludge, in order to overcome the limitations of the existing technology. SUMMARY

[0017] To solve the above technical problems, the present application provides a method for step-by-step enhanced efficient release and resource utilization of carbon and phosphorus in sludge.

[0018] The method for step-by-step enhanced efficient release and resource utilization of carbon and phosphorus in sludge disclosed in the present application realizes efficient release of inorganic phosphorus and organic phosphorus through the synergistic effect of multiple steps by improving the release efficiency of different occurrence forms of phosphorus in sludge, and simultaneously improves the efficient release and resource utilization of carbon (such as acid and methane), improves the overall resource utilization efficiency of carbon and phosphorus in residual sludge, and comprises the following steps:

[0019] I. Sludge pretreatment:

[0020] The sludge in the secondary sedimentation tank of the sewage treatment plant is screened to remove impurities, then is refrigerated and left for a period of time, then the supernatant is removed by siphon method or water decanter, the removed supernatant is collected, and supernatant I and concentrated residual sludge I are obtained;

[0021] II. Green chelating agent pretreatment for enhanced release of inorganic phosphorus:

[0022] The green chelating agent is added to the concentrated residual sludge I, stirred uniformly, and then placed in a constant temperature incubator for a period of time to obtain sludge pretreated by green chelating agent;

[0023] III. Inorganic phosphorus recovery:

[0024] ①. The sludge pretreated by green chelating agent is centrifuged or pressure-filtered to obtain liquid II and solid II;

[0025] ②. Calcium-based metal salt is added to the liquid II to make the molar ratio of calcium to phosphorus in the liquid II be (0.5-3):1, the pH value of the liquid II is adjusted to 6-13, then the mixture is stirred for a period of time, left for a period of time, and finally centrifuged to collect phosphorus precipitate solid and supernatant III;

[0026] IV. Reslurry of sludge:

[0027] ①. The supernatant III and the supernatant I are mixed, and then the mixed solution is used to dissolve the solid II to make the solid content of the solid II be 0.5%-10%, and then the mixture is transferred to an anaerobic fermentation tank;

[0028] V. Peroxidizing agent for 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 peroxidizing agent is added, and the mixture is reacted at 25-35℃ for a period of time to obtain reacted sludge;

[0030] VI. Anaerobic resource utilization:

[0031] The inoculated sludge is added into the reacted sludge obtained in step five, and the pH value is adjusted to 7; nitrogen is introduced into the anaerobic fermentation tank for a period of time, and then a sealing plug is covered to keep the reactor in an oxygen-free state; and the reaction is carried out at 30-37 DEG C for 2-40 days to obtain a reacted sludge mixture;

[0032] Seven, carbon and phosphorus resources are recovered:

[0033] ① The reacted sludge mixture obtained in step six is subjected to centrifugal treatment or pressure filtration to obtain residual solid and filtrate I;

[0034] ② The ferrous-based salt is added into the filtrate I obtained in step seven ①, and the pH value is adjusted to 5-9 by using alkali liquor; the reaction is carried out under anaerobic condition for 0.5-2 hours, and then aging is carried out under nitrogen or argon condition for 0.5-2 hours; then the solid-liquid separation is carried out by using centrifugal treatment or pressure filtration to obtain blue vitriol and filtrate II; the filtrate II is returned to the main sewage treatment plant as carbon source to supplement the carbon source; and the blue vitriol is vacuum dried at 35-60 DEG C.

[0035] The purpose of the present application is:

[0036] The present application is directed to the key technical bottlenecks of the existing synchronous enhanced sludge anaerobic resourceization and phosphorus release technology, such as the lack of time sequence synergy of optimal condition biased carbon resourceization, nitrogen and phosphorus resourceization path, poor adaptability of multi-form metal phosphorus form, insufficient stability of iron and phosphorus biological reduction and phosphorus release, low organic phosphorus release efficiency and long time, etc., which limits the simultaneous improvement of carbon and phosphorus release rate and recovery rate. The present application innovatively proposes a gradient synergistic process system of "metal complex stripping-inorganic phosphorus recovery-organic matter release-carbon conversion and organic phosphorus recovery". The present application first performs metal complex stripping-inorganic phosphorus recovery, then adds a peroxide agent in the sludge from which inorganic phosphorus and metal ions are released, and then performs anaerobic resourceization, which can realize efficient release of inorganic phosphorus and organic phosphorus in sludge and improve carbon resourceization efficiency, thereby significantly improving the overall resourceization efficiency of carbon and phosphorus release in residual sludge. In addition, this method is not limited to forming a product form of carbon resourceization fixation, which can not only improve the acid production efficiency of anaerobic fermentation process, but also improve the methane content of anaerobic digestion. If the order of addition is changed, there is no synergistic improvement effect. The present application uses a green chelating agent to selectively dissociate the metal-phosphorus complex structure, realizing efficient release of multi-phase inorganic phosphorus form. Secondly, the time sequence synergy of the nitrogen and phosphorus resourceization path is optimized to ensure the timely and efficient recovery of phosphorus and metal ions in the liquid phase after phosphorus release, block the reprecipitation of metal ions to fix the phosphorus components again, thereby reducing the phenomenon of phosphorus reprecipitation and sludge-phosphorus separation, and improving the release and recovery rate of phosphorus. Then, the peroxide agent technology is used to crack the sludge after the collapse of the metal skeleton, which can more strongly break the EPS barrier and the rigid structure of the cell wall, drive the synergistic effect of carbon and phosphorus metabolism, strengthen the conversion of organic matter and the release of organic phosphorus, and realize the synergistic improvement of carbon and phosphorus release and resourceization in sludge. This technology can improve the release efficiency of different forms of phosphorus in sludge, realize the efficient release of inorganic phosphorus and organic phosphorus through multi-step synergistic effect, and improve the recovery of carbon resourceization (such as acid and methane), thereby improving the overall resourceization efficiency of carbon and phosphorus in residual sludge, achieving the dual goals of efficient phosphorus recovery and high-value carbon source conversion. The pretreatment of peroxide agent, acid and citric acid in the present application has a significant synergistic effect in strengthening the production of volatile fatty acids in sludge anaerobic fermentation. Compared with other methods of using peroxide agent to promote the production of volatile fatty acids in sludge anaerobic fermentation, the present method can significantly reduce the dosage of peroxide agent, thereby greatly reducing the process cost. In addition, this method can also efficiently recover phosphorus precipitate, realizing efficient resourceization of sludge. The present application optimizes the process flow, reduces energy consumption and process cost, makes the carbon and phosphorus recovery technology more economically feasible, and meets the actual demand. At the same time, this method is a phosphorus recovery technology suitable for different metal phosphorus forms, which can be applied to a wide range of sludge types and conditions, broaden the application range of the technology, reduce the process cost, and simplify the recovery operation, thereby providing an efficient and low-cost engineering solution for sludge resourceization.

[0037] Advantages of the present application:

[0038] One, efficient release of multi-form phosphorus: The present application uses a green chelating agent to selectively dissociate metal-phosphorus complex structures, achieving efficient release of multi-phase inorganic phosphorus forms. This breaks through the limitations of traditional technologies in terms of poor adaptability to multi-form metal phosphorus and insufficient stability of iron-phosphorus in biological reduction phosphorus release, significantly improving the release efficiency of inorganic phosphorus. In addition, through the use of peroxide technology to break down the sludge after the collapse of the metal skeleton, the EPS barrier and the rigid structure of the cell wall are broken, and the conversion of organic matter and the release of organic phosphorus are strengthened, significantly improving the release efficiency of organic phosphorus. This technology can increase the phosphorus release efficiency to 40% to 80%.

[0039] Two, optimization of resourceization path synergy: The present application optimizes the timing synergy of the nitrogen and phosphorus resourceization path to ensure that phosphorus and metal ions in the liquid phase after phosphorus release can be recovered and separated from the sludge phase in a timely manner, effectively blocking the re-precipitation of metal ions and re-fixing phosphorus components in the sludge phase, reducing the phenomenon of phosphorus re-precipitation and sludge-phosphorus separation, thereby significantly improving the release and recovery rate of phosphorus. The recovery process of the present application is simple, with low loss rate, and the phosphorus recovery rate can be as high as 80% to 99.5%, with significant advantages.

[0040] Three, dual target realization - synergistic improvement of carbon and phosphorus resourceization: Through multi-step synergy, the present application achieves efficient release of inorganic and organic phosphorus, while also considering the recovery of high-value products such as acid and methane, improving the overall resourceization efficiency and achieving the dual goals of efficient phosphorus recovery and high-value conversion of carbon sources. In addition, sludge pretreated by pH adjustment and citric acid and peroxide agents such as sodium percarbonate show good synergistic improvement effect in strengthening anaerobic fermentation to produce acid. Compared with existing single technologies, the acid production efficiency is increased by more than 1.4 to 3 times; compared with sludge without any pretreatment, the acid production efficiency is increased by more than 14 times.

[0041] Four, economic feasibility and broad applicability: By optimizing the process flow, the present application reduces energy consumption and process cost, making the phosphorus recovery technology more economically feasible and meeting actual needs. This technology is suitable for a wide range of sludge types and conditions with different metal phosphorus occurrence forms, broadening the application range of the technology and simplifying the recovery operation, providing an efficient and low-cost engineering solution for sludge resourceization.

[0042] Five, process innovation and qualitative improvement: The present application innovatively proposes a "metal complex stripping-inorganic phosphorus recovery-organic matter release-carbon conversion and organic phosphorus recovery" hierarchical synergistic process system, which significantly improves the release efficiency of different occurrence forms of phosphorus in sludge and the synergistic improvement of carbon and phosphorus resources in the anaerobic resourceization process of sludge, achieving process innovation from quantitative change to qualitative change.

[0043] In summary, the present application provides an efficient, low-consumption, broad-spectrum engineering solution for sludge resource utilization by efficiently releasing polymorphic phosphorus, optimizing resource utilization path synergy, achieving carbon and phosphorus resource utilization synergy, improving economic feasibility and applicability, and process innovation and quality change. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Process flow chart for the method of step-by-step reinforced sludge carbon and phosphorus efficient release and resource utilization in the present application;

[0045] Figure 2 Effect diagram of STP release after adding citric acid and adjusting pH of the concentrated residual sludge I in step two of Examples 1-5 and Comparative Example 1;

[0046] Figure 3 Effect diagram of sludge solid-liquid phosphorus balance after adding citric acid and adjusting pH of the concentrated residual sludge I in step two of Examples 1-5 and Comparative Example 1;

[0047] Figure 4 Recovery efficiency diagram of phosphorus precipitation solids in step three ② of Example 5;

[0048] Figure 5 XRD characterization of phosphorus precipitation solids in step three ② of Example 5;

[0049] Figure 6 Elemental content of phosphorus precipitation solids in step three ② of Example 5;

[0050] Figure 7 Effect diagram of volatile acid concentration after acid and citric acid pretreatment and sodium percarbonate synergistic disposal in steps five and six of Examples 6-8 and Comparative Example 2;

[0051] Figure 8 Volatile acid composition after acid and citric acid pretreatment and sodium percarbonate synergistic disposal in steps five and six of Examples 6-8 and Comparative Example 2;

[0052] Figure 9 PO4-P effect diagram after acid and citric acid pretreatment and sodium percarbonate synergistic disposal in steps five and six of Examples 6-8 and Comparative Example 2; 3-

[0053] Figure 10 Change diagram of phosphorus content in the reacted sludge mixture obtained in steps five and six of Examples 6-8 and Comparative Example 2;

[0054] Figure 11 XRD diagram of the recovered vivianite in step seven of Example 8;

[0055] Figure 12 ​Figure of effect of volatile acid concentration of anaerobic fermentation of sludge pretreated by potassium peroxoborate and citric acid in example 9 and control example 3 through steps one to six. DETAILED DESCRIPTION

[0056] Specific embodiment one: the method of this embodiment is a step-by-step method for enhancing the efficient release and resource utilization of carbon and phosphorus in sludge, which includes the following steps:

[0057] I. Sludge pretreatment:

[0058] Screen the sludge in the secondary sedimentation tank in a sewage treatment plant to remove impurities, then refrigerate and stand for a period of time, then remove the supernatant using a siphon method or a decanter, collect the removed supernatant, and obtain supernatant I and concentrated residual sludge I;

[0059] II. Green chelating agent pretreatment for enhanced release of inorganic phosphorus:

[0060] Add a green chelating agent to the concentrated residual sludge I, stir until uniform, then place in a constant-temperature incubator and react for a period of time to obtain sludge pretreated by a green chelating agent;

[0061] III. Inorganic phosphorus recovery:

[0062] ①. Centrifuge or filter press the sludge pretreated by a green chelating agent to obtain liquid II and solid II;

[0063] ②. Add a calcium-based metal salt to liquid II so that the molar ratio of calcium to phosphorus in liquid II is (0.5-3):1, adjust the pH of liquid II to 6-13, then stir for a period of time, stand for a period of time, and finally centrifuge to collect the phosphorus precipitate solid and supernatant III;

[0064] IV. Reslurry of sludge:

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

[0066] V. Peroxidizing agent for enhanced solubilization and hydrolysis of sludge:

[0067] Adjust the pH of the sludge in the anaerobic fermentation tank to 6-7.5, then add a peroxidizing agent, react at 25-35°C for a period of time, and obtain the reacted sludge;

[0068] VI. Anaerobic resource utilization:

[0069] adding inoculated sludge to the reacted sludge obtained in step five, adjusting pH value to 5-7.5, passing nitrogen into the anaerobic fermentation tank for a period of time, covering the tank with a sealing plug to keep the reactor in an oxygen-free state, and reacting at 30-37℃ for 2-40 days to obtain a reacted sludge mixture;

[0070] VII. Recycling carbon and phosphorus resources:

[0071] ①. Centrifuging or pressure-filtering the reacted sludge mixture obtained in step VI to obtain residual solids and filtrate I;

[0072] ②. Adding ferrous salt to the filtrate I obtained in step VII ①, adjusting pH value to 5-9 using alkali, reacting under anaerobic conditions for 0.5-2 hours, then aging under nitrogen or argon for 0.5-2 hours, and then performing solid-liquid separation by centrifugation or pressure filtration to obtain vivianite and filtrate II, which is returned to the main sewage treatment plant as a carbon source, and the vivianite is vacuum dried at 35-60℃.

[0073] In step III of the present embodiment, the phosphorus and metal ions in the inorganic phosphorus in the sludge solid phase are released and recovered, and the phosphorus recovery rate can reach 80-99.5%, and the metal ions are iron, aluminum, calcium and magnesium ions.

[0074] In step III of the present embodiment, calcium and phosphorus in liquid II can form struvite (CaFeMg2Al2(PO4)4(OH)2·8H2O mineral.

[0075] Specific embodiment two: The difference between the present embodiment and specific embodiment one is that: in step one, the secondary sedimentation tank sludge produced by the sewage treatment plant is screened through a 20-60 mesh sieve to remove impurities, then the sludge is refrigerated at 4℃ for 4-48 hours, and then the supernatant is removed by siphoning or a decanter, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I; the secondary sedimentation tank sludge in step one is one or more of activated sludge for biological phosphorus removal, sludge for iron chemical enhanced phosphorus removal, and sludge for aluminum chemical enhanced phosphorus removal; and the solid content of the concentrated residual sludge I in step one is 0.5-10%. The other steps are the same as those in specific embodiment one.

[0076] Specific embodiment three: the difference between this embodiment and one or two of the specific embodiments is that the green chelating agent in step two is one or a mixture of several of citric acid, tartaric acid, methyl glycine diacetic acid, glutamic acid diacetic acid and metal acid salt; the dosage of the green chelating agent in step two is 0.01 g / gTSS-0.5 g / gTSS; the temperature of the constant temperature incubator in step two is 20-40℃, and the rotation speed is 100-150 rpm; the reaction time in the constant temperature incubator in step two is 1-48 h. The other steps are the same as those in one or two of the specific embodiments.

[0077] Specific embodiment four: the difference between this embodiment and one to three of the specific embodiments is that the speed of centrifugation in step three ① is 5000-10000 rpm, and the centrifugation time is 5-20 min; the calcium-based metal salt in step three ② is calcium chloride, calcium oxide or calcium hydroxide; the stirring speed in step three ② is 600-1000 rpm, and the stirring time is 10-60 min; the standing time in step three ② is 30-120 min. The other steps are the same as those in one to three of the specific embodiments.

[0078] Specific embodiment five: the difference between this embodiment and one to four of the specific embodiments is that the speed of centrifugation in step three ② is 8000-12000 rpm, and the centrifugation time is 5-20 min; the concentration of the sodium hydroxide solution or potassium hydroxide solution used to adjust the pH value of the liquid in step three ② is 1-6 mol / L, and the pH value is adjusted to 6-13; the composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O. The other steps are the same as those in one to four of the specific embodiments.

[0079] Specific embodiment six: the difference between this embodiment and one to five of the specific embodiments is that the volume ratio of the supernatant III to the supernatant I in step four ① is (0-5):(0-5); the peroxidation agent in step five is sodium percarbonate, potassium percarbonate, sodium perborate, potassium perborate, calcium peroxide, magnesium peroxide, sodium ferrate, potassium ferrate, sodium periodate, potassium periodate, hydrogen peroxide, peroxyacetic acid, sodium hypochlorite or potassium hypochlorite. The other steps are the same as those in one to five of the specific embodiments.

[0080] Specific embodiment seven: the difference between this embodiment and one to six of the specific embodiments is that the reaction time in step five at 25-35℃ is 4-24 h; the dosage of the peroxidation agent in step five is 0.01 g / gTSS-0.5 g / gTSS. The other steps are the same as those in one to six of the specific embodiments.

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

[0082] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the mass ratio of the inoculated sludge in step six to the reacted sludge in step five is (0-1):(1-5), and the pH value is adjusted to 5-7.5; the nitrogen blowing time in the anaerobic fermentation tank in step six is 10-30min; the speed of the centrifugal treatment in step seven ① is 5000-10000rpm, and the centrifugal treatment time is 5-15min. The other steps are the same as those in the specific embodiments one to eight.

[0083] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the ferrous-based salt in step seven ② is ferrous chloride or ferrous sulfate; the molar ratio of the ferrous-based salt in step seven ② to phosphorus in the filtrate I is (1-2):1; the alkali solution in step seven ② is sodium hydroxide solution or potassium hydroxide solution, and the concentration is 1-6mol / L. The other steps are the same as those in the specific embodiments one to nine.

[0084] The beneficial effects of the present application are verified by the following examples:

[0085] Example 1: a method for step-by-step strengthening of carbon and phosphorus efficient release and resource utilization in sludge, comprising the following steps:

[0086] I. sludge pretreatment:

[0087] The secondary sedimentation tank sludge generated by the sewage treatment plant is passed through a 40-mesh screen to remove impurities (stones, plastics, branches, etc. large-particle impurities), then stored and placed at 4℃ for 24h, and then the supernatant is removed by siphoning, and the removed supernatant is collected to obtain the supernatant I and the concentrated residual sludge I;

[0088] The total solid content of the concentrated residual sludge I in step one is 46.76 g / L, the volatile total solid content is 22.77 g / L, the total COD is 29600 mg / L, the water content is 95.15%, the iron element in the residual sludge is 35.3 mg / g TSS, the phosphorus element content is 26.33 mg / g TSS, and the aluminum element content is 16.8 mg / g TSS;

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

[0090] II. Green chelating agent pretreatment for strengthening release of inorganic phosphorus:

[0091] Green chelating agent is added to 500 mL of the concentrated residual sludge I, and the dosage of the green chelating agent is 0.08 g / g TSS (i.e. 1.87 g of citric acid is added to 500 mL of the concentrated residual sludge I), and the mixture is stirred uniformly, and then is placed in a constant temperature incubator for a period of time to obtain sludge pretreated by the green chelating agent with a pH value of 4.33;

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

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

[0094] The reaction time of the sludge in the constant temperature incubator in step two is 18 h;

[0095] III. Inorganic phosphorus recovery:

[0096] ① The sludge pretreated by the green chelating agent is centrifuged to obtain liquid II and solid II;

[0097] The centrifugation speed in step three ① is 8000 rpm, and the centrifugation time is 5 min;

[0098] ② Calcium chloride is added to the liquid II to make the molar ratio of calcium to phosphorus in the liquid II be 1.5:1, the pH value of the liquid II is adjusted to 8.7, then the liquid II is stirred at 600 rpm for 30 min, and is left to stand for 30 min to make the metal ions fully react with the phosphorus, and finally the liquid II is centrifuged at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0099] The pH value of the liquid is adjusted to 8.7 by using a sodium hydroxide solution with a concentration of 4 mol / L in step three ②;

[0100] The composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0101] Four, sludge resuspension:

[0102] ①, the supernatant III and the supernatant I are mixed, and then the mixed solution is used to dissolve solid II, so that the solid content of solid II is 4.6%, and then the solid II is transferred to an anaerobic fermentation tank;

[0103] The volume ratio of the supernatant III to the supernatant I in step four ① is 0:1;

[0104] Five, peroxide enhanced sludge solubilization and hydrolysis:

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

[0106] The peroxide in step five is sodium percarbonate;

[0107] The addition amount of the peroxide in step five is 0.1g / gTSS;

[0108] Six, anaerobic resource utilization:

[0109] Inoculated sludge is added to the reacted sludge obtained in step five, and then the pH value is adjusted to 5, nitrogen is introduced into the anaerobic fermentation tank for 15min, and then a sealing plug is covered, so that the reactor is kept in an anaerobic state, and the reaction is carried out at 35°C for 12 days to obtain a reacted sludge mixture;

[0110] The preparation method of the inoculated sludge in step six is as follows: the concentrated residual sludge I obtained in step one is first boiled at 100°C for 2h, and then transferred to a reactor, and after cooling, the following substances are added thereto: glucose 14.4g / L, yeast paste 3.2g / L, potassium dihydrogen phosphate 0.56g / L, magnesium sulfate heptahydrate 0.96g / L, ammonium chloride 2.4g / L, anhydrous calcium chloride 0.72g / L, sodium bicarbonate 0.96g / L, manganese chloride 0.11g / L, ferrous sulfate heptahydrate 0.12g / L, to obtain a sludge mixture; then nitrogen is introduced for 10min to 40min, and then a sealing plug is covered, so that the reactor is kept 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 prepared sludge mixture is supplemented, so that the long-term operation is carried out every 7 days as a period, to obtain the inoculated sludge;

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

[0112] Seven, recovery of carbon and phosphorus resources:

[0113] ①, the reacted sludge mixture obtained in step six is subjected to centrifugal treatment or pressure filtration to obtain residual solid and filtrate I;

[0114] The centrifugal treatment speed in step seven 1 is 8000 rpm, and the centrifugal treatment time is 15 min;

[0115] In step seven 2, the ferrous salt is ferrous sulfate heptahydrate.

[0116] In step seven 2, the ferrous salt is ferrous sulfate heptahydrate.

[0117] In step seven 2, the molar ratio of the ferrous salt to phosphorus in the filtrate I is 1.5:1.

[0118] In step seven 2, the alkali solution is 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 two, 500 mL of concentrated residual sludge I is added with green chelating agent, and the addition amount of green chelating agent is 0.16 g / g TSS (i.e. 3.74 g of citric acid is added to 500 mL of concentrated residual sludge I), and then stirred uniformly, and then placed in a constant temperature incubator for a period of time to obtain sludge pretreated by green chelating agent with a pH value of 3.8. The other steps and parameters are the same as steps one to seven of example 1.

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

[0121] Example 4: The difference between this example and example 1 is that in step two, 500 mL of concentrated residual sludge I is adjusted to a pH value of 3.0 by 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 one to seven of example 1.

[0122] Example 5: The difference between this example and Example 1 is that green chelating agent is added to 500 mL of concentrated residual sludge I, 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 residual sludge I), then hydrochloric acid with a concentration of 4 mol / L is used to adjust the pH value of the system to 3.0, and then the system is stirred uniformly and placed in a constant temperature incubator for a period of time to obtain sludge pretreated by green chelating agent with a pH value of 3.0. The other steps and parameters are the same as steps one to seven of Example 1.

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

[0124] Figure 2 and Figure 3 The total phosphorus concentration of the supernatant (the supernatant is obtained by centrifuging the pretreated sludge obtained in step two and filtering the liquid) in the reactor is shown to change with time. In the first 48 hours, the total phosphorus concentration of the supernatant of each example shows a trend of first increasing and then decreasing. Among them, the highest total phosphorus concentration (STP) of 703 mg / L is reached at 36 hours in Example 3, and the phosphorus release rate is as high as 68%, which is 52% higher than that of Comparative Example 1. At 24 hours, the STP concentration of the supernatant of Example 1 is 587 mg / L, and the STP concentration of the supernatant of Example 5 is 645 mg / L, which is 42% and 47% higher than that of Comparative Example 1, respectively. In the first 24 hours, the STP concentration of the supernatant of each example is above 450 mg / L, showing a high value of phosphorus recovery.

[0125] The phosphorus recovery rate in step three ② of Example 5 is shown in Figure 4 , the phosphorus precipitation characterization is shown in Figure 5 , and the elemental content of the phosphorus precipitation is shown in Figure 6 ;

[0126] Figure 4 The recovery efficiency diagram of the phosphorus precipitation solid in step three ② of Example 5 is shown in

[0127] Figure 5 The XRD characterization of the phosphorus precipitation solid in step three ② of Example 5 is shown in

[0128] Figure 6 The elemental content of the phosphorus precipitation solid in step three ② of Example 5 is shown in

[0129] After adding calcium chloride and adjusting the pH value, the phosphate concentration in liquid II of Example 5 is reduced to 5.6 mg / L, and the recovery rate of the phosphorus precipitation reaches 99.1% (as shown in Figure 4XRD and quantitative analysis of metal ions, it is preliminarily considered that the phosphorus precipitation recovery is mainly in the form of whiteite (CaFeMg)-(CaFeMg2Al2(PO4)4(OH)2·8H2O) containing phosphorus minerals (such as Figures 5-6 As shown in the figure), and the P2O5 content in the mineral is 23.7%. In addition, the citric acid used in the present application is low in price, about 600 US dollars per ton, while the ascorbic acid used in the Chinese patent document CN115974350A is relatively high in price (about 3000 US dollars per ton) and has a large dosage. Therefore, the present application has a significant advantage in economy, and the estimated cost of phosphorus recovery is only 23.24 yuan / kg-P.

[0130] Example 6: A method for efficiently releasing and recycling carbon and phosphorus in sludge by gradient strengthening, comprising the following steps:

[0131] I. Sludge pretreatment:

[0132] The secondary sedimentation tank sludge generated by the sewage treatment plant is passed through a 40-mesh screen to remove impurities (stones, plastics, branches, and other large-particle impurities), then is stored at a temperature of 4°C for 24 h, and then the supernatant is removed by siphoning. The removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0133] The total solid content of the concentrated residual sludge I described in step one is 46.76 g / L, the volatile total solid content is 22.77 g / L, the total COD is 29600 mg / L, the water content is 95.15%, the iron element in the residual sludge is 35.3 mg / g TSS, the phosphorus element content is 26.33 mg / g TSS, and the aluminum element content is 16.8 mg / g TSS;

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

[0135] II. Green chelating agent pretreatment for enhanced release of inorganic phosphorus:

[0136] Green chelating agent is added to 500 mL of concentrated residual sludge I, and the dosage of green chelating agent is 0.08 g / g TSS (i.e. 1.87 g of citric acid is added to 500 mL of concentrated residual sludge I), then hydrochloric acid with a concentration of 4 mol / L is used to adjust the pH value of the system to 3.0, and the system is stirred uniformly, then is placed in a constant temperature incubator for a period of time to obtain sludge pretreated by green chelating agent with a pH value of 3.0.

[0137] III. Inorganic phosphorus recovery:

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

[0139] The centrifuging speed in step three ① is 8000 rpm, and the centrifuging time is 5 min;

[0140] ②, adding calcium chloride into 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 be 8.7, then stirring at 600 rpm for 30 min, and standing for 30 min to make the metal ions fully react with phosphorus, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0141] The pH value of liquid is adjusted to be 8.7 by using sodium hydroxide solution with a concentration of 4 mol / L in step three ②;

[0142] The composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0143] Four, sludge resuspension:

[0144] ①, mixing supernatant III and supernatant I, and then using the mixed solution to dissolve solid II to make the solid content of solid II be 4.6%, and then transferring to the anaerobic fermentation tank;

[0145] The volume ratio of supernatant III to supernatant I in step four ① is 0:1;

[0146] Five, adjusting the pH value of the sludge in the anaerobic fermentation tank to be 6.88, and oscillating at 25℃ and 140 rpm for 12 h to obtain the reacted sludge;

[0147] Six, anaerobic resource utilization:

[0148] Passing nitrogen into the anaerobic fermentation tank for 15 min, and then covering the sealing plug to make the reactor keep anaerobic state, and reacting at 35℃ for 12 days to obtain the reacted sludge mixture;

[0149] Seven, recovery of carbon and phosphorus resources:

[0150] ①, centrifuging the reacted sludge mixture obtained in step six to obtain residual solid and filtrate I;

[0151] The centrifuging speed in step seven ① is 8000 rpm, and the centrifuging time is 15 min;

[0152] ②, to the filtrate I obtained in step seven ①, add ferrous salt, and then use lye to adjust the pH value to 7.0, react under anaerobic conditions for 1h, then age under nitrogen conditions for 2h, and then perform solid-liquid separation by centrifugation at 10000rpm for 10min to obtain blue vitriol and filtrate II, the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue vitriol is vacuum dried at 50℃;

[0153] The ferrous salt in step seven ② is ferrous sulfate heptahydrate;

[0154] The molar ratio of the ferrous salt to phosphorus in the filtrate I in step seven ② is 1.5:1;

[0155] The lye in step seven ② is sodium hydroxide solution with a concentration of 3mol / L.

[0156] Example 7: A method for step-by-step strengthening of efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0157] I. Sludge pretreatment:

[0158] Screen the sludge from the secondary sedimentation tank of a sewage treatment plant through a 40-mesh screen to remove impurities (stones, plastics, branches, and other large-particle impurities), then store the sludge at a temperature of 4℃ for 24h, and then remove the supernatant using the siphon method, collect the removed supernatant, and obtain supernatant I and concentrated residual sludge I;

[0159] The total solid content of the concentrated residual sludge I in step one is 46.76g / L, the volatile total solid content is 22.77g / L, the total COD is 29600mg / L, the water content is 95.15%, the iron element in the residual sludge is 35.3mg / g TSS, the phosphorus element content is 26.33mg / g TSS, and the aluminum element content is 16.8mg / g TSS;

[0160] The sludge from the secondary sedimentation tank in step one is activated sludge for biological phosphorus removal, which is the residual sludge produced by the A 2 / O process;

[0161] II. Put 500mL of the concentrated residual sludge I into a constant-temperature incubator at 35℃ and at a rotation speed of 140rpm to react for 18h, and obtain pretreated sludge;

[0162] III. Inorganic phosphorus recovery:

[0163] ①, centrifuge or filter press the pretreated sludge to obtain liquid II and solid II;

[0164] The speed of centrifugation in step three ① is 8000rpm, and the centrifugation time is 5min;

[0165] ②, adding calcium chloride into liquid II, so that the molar ratio of calcium to phosphorus in liquid II is 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, and standing for 30 min, so that the metal ions and phosphorus fully react, and finally centrifuging at 8000 rpm for 10 min, collecting the phosphorus precipitate solid and supernatant III;

[0166] In step three ②, the pH value of the liquid is adjusted to 8.7 using a sodium hydroxide solution with a concentration of 4 mol / L;

[0167] The composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0168] Four, sludge resuspension:

[0169] ①, mixing supernatant III and supernatant I, and then dissolving solid II using the mixed solution, so that the solid content of solid II is 4.6%, and then transferring to an anaerobic fermentation tank;

[0170] In step four ①, the volume ratio of supernatant III to supernatant I is 0:1;

[0171] Five, peroxide enhanced sludge solubilization and hydrolysis:

[0172] Adjusting the pH value of the sludge in the anaerobic fermentation tank to 6.88, and then adding a peroxide agent, and reacting at 25°C for 12 h to obtain the reacted sludge;

[0173] The peroxide agent in step five is sodium percarbonate;

[0174] The addition amount of the peroxide agent in step five is 0.1 g / g TSS;

[0175] Six, anaerobic resource utilization:

[0176] Passing nitrogen into the anaerobic fermentation tank for 15 min, and then covering a sealing plug to keep the reactor in an oxygen-free state, and reacting at 35°C for 12 days to obtain the reacted sludge mixture;

[0177] Seven, recovery of carbon and phosphorus resources:

[0178] ①, centrifuging the reacted sludge mixture obtained in step six to obtain residual solid and filtrate I;

[0179] In step seven ①, the centrifuging speed is 8000 rpm, and the centrifuging time is 15 min;

[0180] ②, to the filtrate I obtained in step seven ①, add ferrous salt, and then use lye to adjust the pH value to 7.0, react under anaerobic conditions for 1 h, then age under nitrogen conditions for 2 h, and then perform solid-liquid separation by centrifugation at 10000 rpm for 10 min, to obtain blue vitriol and filtrate II, the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue vitriol is vacuum dried at 50℃;

[0181] The ferrous salt in step seven ② is ferrous sulfate heptahydrate;

[0182] The molar ratio of the ferrous salt to phosphorus in the filtrate I in step seven ② is 1.5:1;

[0183] The lye in step seven ② is sodium hydroxide solution with a concentration of 3 mol / L.

[0184] Example 8: A method for step-by-step strengthening of efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0185] I. Sludge pretreatment:

[0186] Screen the sludge from the secondary sedimentation tank of a sewage treatment plant through a 40-mesh sieve to remove impurities (stones, plastics, branches, and other large-particle impurities), then store the sludge at a temperature of 4℃ for 24 h, remove the supernatant by siphoning, collect the removed supernatant, and obtain supernatant I and concentrated residual sludge I;

[0187] The total solid content of the concentrated residual sludge I in step one is 46.76 g / L, the volatile total solid content is 22.77 g / L, the total COD is 29600 mg / L, the water content is 95.15%, the iron element content in the residual sludge is 35.3 mg / g TSS, the phosphorus element content is 26.33 mg / g TSS, and the aluminum element content is 16.8 mg / g TSS;

[0188] The sludge from the secondary sedimentation tank in step one is activated sludge for biological phosphorus removal, which is residual sludge produced by the A 2 / O process;

[0189] II. Green chelating agent pretreatment for strengthening release of inorganic phosphorus:

[0190] Add green chelating agent to 500 mL of concentrated residual sludge I, the addition amount of green chelating agent is 0.08 g / g TSS (i.e. 1.87 g of citric acid is added to 500 mL of concentrated residual sludge I), then use hydrochloric acid with a concentration of 4 mol / L to adjust the pH value of the system to 3.0, stir uniformly, and then place in a constant-temperature incubator for a period of time to obtain sludge pretreated by green chelating agent with a pH value of 3.0;

[0191] III. Inorganic phosphorus recovery:

[0192] ①, centrifuging or filter pressing the sludge pretreated by green chelating agent to obtain liquid II and solid II;

[0193] The centrifugation speed in step three ① is 8000 rpm, and the centrifugation time is 5 min;

[0194] 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 make the metal ions fully react with phosphorus, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0195] In step three ②, the pH value of the liquid is adjusted to 8.7 using a sodium hydroxide solution with a concentration of 4 mol / L;

[0196] The composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0197] Four, sludge resuspension:

[0198] ①, mixing supernatant III and supernatant I, and then using the mixed solution to dissolve solid II to make the solid content of solid II be 4.6%, and then transferring to an anaerobic fermentation tank;

[0199] In step four ①, the volume ratio of supernatant III to supernatant I is 0:1;

[0200] Five, peroxide enhanced sludge solubilization and hydrolysis:

[0201] Adjusting the pH value of the sludge in the anaerobic fermentation tank to 6.88, and then adding a peroxide agent, and reacting at 25°C for 12 h to obtain the reacted sludge;

[0202] The peroxide agent in step five is sodium percarbonate;

[0203] The addition amount of the peroxide agent in step five is 0.1 g / g TSS;

[0204] Six, anaerobic resource utilization:

[0205] Passing nitrogen into the anaerobic fermentation tank for 15 min, and then covering a sealing plug to keep the reactor in an oxygen-free state, and reacting at 35°C for 12 days to obtain the reacted sludge mixture;

[0206] Seven, recovery of carbon and phosphorus resources:

[0207] ①, centrifuging the reacted sludge mixture obtained in step six to obtain residual solid and filtrate I;

[0208] The centrifugal treatment speed in step seven 1 is 8000 rpm, and the centrifugal treatment time is 15 min;

[0209] ②, ferrous-based salt is added to the filtrate I obtained in step seven 1, and the pH value is adjusted to 7.0 using lye, and then reacted under anaerobic conditions for 1 h, and then aged under nitrogen conditions for 2 h, and then separated by centrifugation at 10000 rpm for 10 min to obtain blue vitriol and filtrate II, and the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue vitriol is vacuum dried at 50℃;

[0210] The ferrous-based salt in step seven 2 is ferrous sulfate heptahydrate;

[0211] The molar ratio of the ferrous-based salt to phosphorus in the filtrate I in step seven 2 is 1.5:1;

[0212] The lye in step seven 2 is a sodium hydroxide solution with a concentration of 3 mol / L.

[0213] Comparative example 2: A method for step-by-step strengthening of sludge carbon and phosphorus efficient release and resource utilization, comprising the following steps:

[0214] I. Sludge pretreatment:

[0215] The sludge produced by the sewage treatment plant is passed through a 40-mesh screen to remove impurities (stones, plastics, branches, etc. Large particle impurities), and then stored at 4℃ for 24 h, and then the supernatant is removed by siphon method, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I;

[0216] The total solid content of the concentrated residual sludge I in step one is 46.76 g / L, the volatile total solid content is 22.77 g / L, the total COD is 29600 mg / L, the water content is 95.15%, the iron element in the residual sludge is 35.3 mg / g TSS, the phosphorus element content is 26.33 mg / g TSS, and the aluminum element content is 16.8 mg / g TSS;

[0217] The secondary sludge in step one is an activated sludge for biological phosphorus removal, which is the residual sludge produced by the A 2 / O process;

[0218] II. 500 mL of concentrated residual sludge I is placed in a constant temperature incubator at 35℃ with a rotation speed of 140 rpm for 18 h to obtain pretreated sludge;

[0219] III. Inorganic phosphorus recovery:

[0220] ①, the pretreated sludge is centrifuged to obtain liquid II and solid II;

[0221] The speed of centrifugation in step three 1 is 8000 rpm, and the centrifugation time is 5 min;

[0222] ②, calcium chloride is added to liquid II, the molar ratio of calcium to phosphorus in liquid II is 1.5:1, the pH value of liquid II is adjusted to 8.7, then stirred at 600 rpm for 30 min, and then stand for 30 min, so that the metal ions and phosphorus fully react, and finally centrifugal treatment at 8000 rpm for 10 min, collect the phosphorus precipitate solid and supernatant III;

[0223] The concentration of sodium hydroxide solution used in step three 2 is 4 mol / L, and the pH value of the liquid is adjusted to 8.7;

[0224] The composition of the phosphorus precipitate solid in step three 2 is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0225] Four, sludge resuspension:

[0226] ①, the supernatant III and the supernatant I are mixed, and then the mixed solution is used to dissolve solid II, so that the solid content of solid II is 4.6%, and then transferred to the anaerobic fermentation tank;

[0227] The volume ratio of supernatant III to supernatant I in step four 1 is 0:1;

[0228] Five, adjust the pH value of the sludge in the anaerobic fermentation tank to 6.88, and oscillate at 25℃ and 140 rpm for 12h to obtain the reacted sludge;

[0229] Six, anaerobic resource:

[0230] Nitrogen is introduced into the anaerobic fermentation tank for 15 min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and the reaction is carried out at 35℃ for 12 days to obtain the reacted sludge mixture;

[0231] Seven, recovery of carbon and phosphorus resources:

[0232] ①, the reacted sludge mixture obtained in step six is centrifuged to obtain residual solid and filtrate I;

[0233] The speed of centrifugation in step seven 1 is 8000 rpm, and the centrifugation time is 15 min;

[0234] ②, to the filtrate I obtained in step seven ①, add ferrous salt, and then use lye to adjust the pH value to 7.0, react under anaerobic conditions for 1 h, then age under nitrogen conditions for 2 h, and then perform solid-liquid separation by centrifugation at 10000 rpm for 10 min, to obtain blue vitriol and filtrate II, the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue vitriol is dried under vacuum at 50℃;

[0235] The ferrous salt in step seven ② is ferrous sulfate heptahydrate;

[0236] The molar ratio of the ferrous salt to phosphorus in the filtrate I in step seven ② is 1.5:1;

[0237] The lye in step seven ② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0238] Under the condition of pH 7, a standard (reference) sample is synthesized by using 0.2M K2HPO4·3H2O and 0.3M FeSO4·7H2O solutions to obtain pure crystals.

[0239] Figure 7 The volatile acid concentration effect diagram of the sludge pretreated by acid and citric acid and disposed by sodium percarbonate in steps five and six of Examples 6-8 and Comparative Example 2;

[0240] Figure 8 The volatile acid composition of the sludge pretreated by acid and citric acid and disposed by sodium percarbonate in steps five and six of Examples 6-8 and Comparative Example 2;

[0241] After 10 days of anaerobic fermentation, the total amount of short-chain volatile fatty acids (VFAs) in the sludge of Example 8 reached the highest value of 316.5 mg / gVSS on the 9th day, which was 14 times higher than the highest concentration of Comparative Example 2 (the fourth day) (as shown in Figure 7 Meanwhile, the total amount of VFAs in the sludge of Example 7 and Example 6 reached the highest values of 89.5 mg / gVSS and 205.48 mg / gVSS, respectively, which were 3.5 times and 1.5 times higher than those of Comparative Example 2 (as shown in Figure 7 Example 6 and Example 8, respectively (as shown in Figure 8 These results show that the sludge pretreated by acid and citric acid and disposed by sodium percarbonate can be more thoroughly broken down, thereby significantly increasing the production of short-chain volatile fatty acids, while reducing the dosage of sodium percarbonate, thereby reducing the cost of use.

[0242] Figure 9 PO4 in the reaction mixture obtained in steps five and six for examples 6-8 and comparative example 2 with acid and citric acid pretreatment and sodium percarbonate treatment 3- - P effect diagram;

[0243] Figure 10 PO4 in the reaction mixture obtained in steps five and six for examples 6-8 and comparative example 2 with acid and citric acid pretreatment and sodium percarbonate treatment

[0244] 12 days of anaerobic fermentation, PO4 in the supernatant of each group 3- -P concentration gradually increased with fermentation, PO4 in the supernatant of example 8 3- -P concentration was as high as 172 mg / L, which was 16.2% and 10.9% higher than examples 6 and 7 respectively, indicating that sodium percarbonate strengthening and metal ion removal can synergistically improve PO4 in the supernatant 3- -P concentration (as shown in Figure 9 According to the change of phosphorus content in the solid phase in Figure 10 , it is mainly the release of organic phosphorus in the sludge in anaerobic biological treatment, and then the increase of organic phosphorus concentration in the supernatant. The reason may be that for phosphorus release, on the one hand, citric acid pretreatment and pre-solid-liquid separation can strengthen the hydrolysis of organic matter, promote the hydrolysis and release of organic phosphorus, and remove inorganic phosphorus and metal ions, which hinder the combination of metal and phosphorus. On the other hand, sodium percarbonate can strengthen the solubilization and hydrolysis efficiency of sludge by its oxidation effect, and further release the organic phosphorus in the sludge.

[0245] The phosphorus and ferrous iron recovery rates in example 8 are shown in table 1, the phosphorus recovery rates are 83.1%, and the ferrous ion recovery rates are 93%, indicating the feasibility of recovering the two elements. XRD characterization shows that the vivianite is successfully recovered (as shown in Figure 11 ).

[0246] Table 1 phosphate and ferrous ion concentration in the supernatant before and after phosphorus recovery

[0247]

[0248] Example 9: A method for step-by-step strengthening of efficient release and resource utilization of carbon and phosphorus in sludge, comprising the following steps:

[0249] I. Sludge pretreatment:

[0250] The secondary sedimentation tank sludge generated by the sewage treatment plant was screened through a 40-mesh screen to remove impurities (stones, plastics, branches and other large-particle impurities), then stored at 4℃ for 24h, and then the supernatant was removed by siphon method. The removed supernatant was collected to obtain supernatant I and concentrated sludge I;

[0251] The total solid content of the concentrated residual sludge I in step one is 46.76 g / L, the volatile total solid content is 22.77 g / L, the total COD is 29600 mg / L, the water content is 95.15%, the iron element in the residual sludge is 35.3 mg / g TSS, the phosphorus element content is 26.33 mg / g TSS, and the aluminum element content is 16.8 mg / g TSS;

[0252] The sludge in the secondary sedimentation tank in step one is the activated sludge for biological phosphorus removal, which is the residual sludge produced by the A 2 / O process;

[0253] II. Green chelating agent pretreatment for enhanced release of inorganic phosphorus:

[0254] Green chelating agent is added to 500 mL of the concentrated residual sludge I, and the dosage of the green chelating agent is 0.08 g / g TSS (i.e. 1.87 g of citric acid is added to 500 mL of the concentrated residual sludge I), then hydrochloric acid with a concentration of 4 mol / L is used to adjust the pH value of the system to 3.0, and the mixture is stirred uniformly, and then is placed in a constant temperature incubator for a period of time to obtain the sludge pretreated by the green chelating agent with a pH value of 3.0;

[0255] III. Inorganic phosphorus recovery:

[0256] ① The sludge pretreated by the green chelating agent is centrifuged or pressure-filtered to obtain liquid II and solid II;

[0257] The speed of the centrifugation in step three ① is 8000 rpm, and the centrifugation time is 5 min;

[0258] ② Calcium chloride is added to the liquid II to make the molar ratio of calcium to phosphorus in the liquid II be 1.5:1, the pH value of the liquid II is adjusted to 8.7, then the mixture is stirred at 600 rpm for 30 min, and is left to stand for 30 min to make the metal ions fully react with the phosphorus, finally the mixture is centrifuged at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0259] The pH value of the liquid is adjusted to 8.7 by using sodium hydroxide solution with a concentration of 4 mol / L in step three ②;

[0260] The composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0261] IV. Reslurry of sludge:

[0262] ① The supernatant III and the supernatant I are mixed, and then the mixed solution is used to dissolve the solid II to make the solid content of the solid II be 4.6%, and then the mixture is transferred to an anaerobic fermentation tank;

[0263] The volume ratio of supernatant III to supernatant I in step four 1 is 0:1;

[0264] V. Peroxidant-enhanced sludge solubilization and hydrolysis

[0265] The pH value of the sludge in the anaerobic fermentation tank is adjusted to 6.88, and a peroxidant is added, and the reaction is carried out at 25°C for 12h to obtain the reacted sludge;

[0266] The peroxidant in step V is potassium peroxoborate;

[0267] The addition amount of the peroxidant in step V is 0.1g / g TSS;

[0268] VI. Anaerobic resource utilization

[0269] The inoculated sludge is added to the reacted sludge obtained in step V, and the pH value is adjusted to 7, nitrogen gas is introduced into the anaerobic fermentation tank for 15min, and then a sealing plug is covered to keep the reactor in an anaerobic state, and the reaction is carried out at 35°C for 12 days to obtain a reacted sludge mixture;

[0270] The preparation method of the inoculated sludge in step VI is as follows: the concentrated residual sludge I obtained in step I is first boiled at 100°C for 2h, transferred to a reactor, and after cooling, the following substances are added thereto: glucose 14.4g / L, yeast paste 3.2g / L, potassium dihydrogen phosphate 0.56g / L, magnesium sulfate heptahydrate 0.96g / L, ammonium chloride 2.4g / L, anhydrous calcium chloride 0.72g / L, sodium bicarbonate 0.96g / L, manganese chloride 0.11g / L, ferrous sulfate heptahydrate 0.12g / L, to obtain a sludge mixture; then nitrogen gas is introduced for 10min to 40min, 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 prepared sludge mixture is supplemented, with a period of every 7 days, to obtain the inoculated sludge;

[0271] The mass ratio of the inoculated sludge in step VI to the reacted sludge obtained in step V is 1:2;

[0272] VII. Recovery of carbon and phosphorus resources

[0273] ①, the reacted sludge mixture obtained in step VI is subjected to centrifugal treatment to obtain residual solids and filtrate I;

[0274] The speed of the centrifugal treatment in step VII 1 is 8000rpm, and the centrifugal treatment time is 15min;

[0275] ②, to the filtrate I obtained in step seven ①, add ferrous salt, and then use lye to adjust the pH value to 7.0, react under anaerobic conditions for 1 h, then age under nitrogen conditions for 2 h, and then perform solid-liquid separation by centrifugation at 10000 rpm for 10 min to obtain blue iron ore and filtrate II, the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue iron ore is dried at 50°C under vacuum;

[0276] The ferrous salt in step seven ② is ferrous sulfate heptahydrate;

[0277] The molar ratio of the ferrous salt to phosphorus in the filtrate I in step seven ② is 1.5:1;

[0278] The lye in step seven ② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0279] Comparative Example 3: A method for step-by-step strengthening of carbon and phosphorus efficient release and resource utilization in sludge, comprising the following steps:

[0280] I. Sludge pretreatment:

[0281] Screen the sludge from the secondary sedimentation tank of a sewage treatment plant through a 40-mesh screen to remove impurities (stones, plastics, branches, and other large-particle impurities), then store it at 4°C for 24 h, and then remove the supernatant using the siphon method, collect the removed supernatant, and obtain supernatant I and concentrated residual sludge I;

[0282] The total solid content of the concentrated residual sludge I in step one is 46.76 g / L, the volatile total solid content is 22.77 g / L, the total COD is 29600 mg / L, the water content is 95.15%, the iron element in the residual sludge is 35.3 mg / g TSS, the phosphorus element content is 26.33 mg / g TSS, and the aluminum element content is 16.8 mg / g TSS;

[0283] The sludge from the secondary sedimentation tank in step one is activated sludge for biological phosphorus removal, which is residual sludge produced by the A 2 / O process;

[0284] II. Put 500 mL of concentrated residual sludge I into a constant-temperature incubator at 35°C with a rotation speed of 140 rpm and react for 18 h to obtain pretreated sludge;

[0285] III. Inorganic phosphorus recovery:

[0286] ①, centrifuge the pretreated sludge to obtain liquid II and solid II;

[0287] The speed of centrifugation in step three ① is 8000 rpm, and the centrifugation time is 5 min;

[0288] ②, adding calcium chloride to liquid II to make the molar ratio of calcium to phosphorus in liquid II 1.5:1, adjusting the pH value of liquid II to 8.7, then stirring at 600 rpm for 30 min, standing for 30 min to make the metal ions and phosphorus fully react, and finally centrifuging at 8000 rpm for 10 min to collect the phosphorus precipitate solid and supernatant III;

[0289] In step three ②, the pH value of the liquid is adjusted to 8.7 using a sodium hydroxide solution with a concentration of 4 mol / L;

[0290] The composition of the phosphorus precipitate solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O;

[0291] Four, resuspension of sludge:

[0292] ①, mixing supernatant III and supernatant I, then dissolving solid II using the mixed solution to make the solid content of solid II 4.6%, and then transferring to an anaerobic fermentation tank;

[0293] In step four ①, the volume ratio of supernatant III to supernatant I is 0:1;

[0294] Five, adjusting the pH value of the sludge in the anaerobic fermentation tank to 6.88, oscillating at 25℃ and 140 rpm for 12 h to obtain the reacted sludge;

[0295] Six, anaerobic resource utilization:

[0296] Adding inoculated sludge to the reacted sludge obtained in step five, adjusting the pH value to 7, introducing nitrogen into the anaerobic fermentation tank for 15 min, then covering the sealing plug to keep the reactor in an anaerobic state, and reacting at 35℃ for 12 days to obtain a reacted sludge mixture;

[0297] The preparation method of the inoculated sludge in step six is as follows: the concentrated residual sludge I obtained in step one is first boiled at 100℃ for 2 h, transferred to a reactor, and after cooling, the following substances are added thereto: glucose 14.4 g / L, yeast paste 3.2 g / L, potassium dihydrogen phosphate 0.56 g / L, magnesium sulfate heptahydrate 0.96 g / L, ammonium chloride 2.4 g / L, anhydrous calcium chloride 0.72 g / L, sodium bicarbonate 0.96 g / L, manganese chloride 0.11 g / L, ferrous sulfate heptahydrate 0.12 g / L, to obtain a sludge mixture; then nitrogen is introduced for 10-40 min, the sealing plug is covered to keep the reactor in an anaerobic state, and long-term acclimation is carried out at 33-37℃, 0.5 L of sludge is discharged from the reactor every 7 days, and 0.5 L of the prepared sludge mixture is supplemented, with a period of every 7 days, to obtain the inoculated sludge;

[0298] The mass ratio of the inoculated sludge to the reacted sludge obtained in step five is 1:2 in step six;

[0299] Seven, recycling carbon and phosphorus resources:

[0300] ① The reacted sludge mixture obtained in step six is subjected to centrifugal treatment to obtain residual solids and filtrate I;

[0301] The centrifugal treatment speed in step seven ① is 8000 rpm, and the centrifugal treatment time is 15 min;

[0302] ② Ferrous-based salt is added to the filtrate I obtained in step seven ①, and an alkali solution is used to adjust the pH value to 7.0, and then reacted under anaerobic conditions for 1 h, and then aged under nitrogen conditions for 2 h, and then subjected to solid-liquid separation by centrifugal treatment at 10000 rpm for 10 min to obtain blue vitriol and filtrate II, the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue vitriol is vacuum dried at 50°C;

[0303] The ferrous-based salt in step seven ② is ferrous sulfate heptahydrate;

[0304] The molar ratio of the ferrous-based salt to phosphorus in the filtrate I in step seven ② is 1.5:1;

[0305] The alkali solution in step seven ② is a sodium hydroxide solution with a concentration of 3 mol / L.

[0306] Figure 12 The volatile acid concentration effect diagram of the sludge pretreated by potassium peroxoborate, acid and citric acid in example 9 and control example 3 through steps one to six anaerobic fermentation;

[0307] After 8 days of anaerobic fermentation, the total amount of short-chain volatile fatty acids (VFAs) of the sludge in example 9 reached the highest concentration of 208 mg / g VSS on the 6th day, which was 1.6 times that of control example 3 (as shown in Figure 12 This result shows that the pretreatment of acid and citric acid and the synergistic pretreatment of potassium peroxoborate have a significant synergistic effect in promoting the production of volatile acids in sludge anaerobic fermentation. Through this synergistic pretreatment method, the same or even higher short-chain volatile fatty acid yield can be achieved while effectively reducing the dosage of potassium peroxoborate, thereby reducing the process cost.

Claims

1. A method for efficient release and resource utilization of carbon and phosphorus in sludge by stepwise reinforcement, characterized in that The method comprises the following steps: I. Sludge pretreatment: Screen the sludge in the secondary sedimentation tank in a sewage treatment plant, remove impurities, then refrigerate and stand for a period of time, then remove supernatant by siphon method or water decanter, collect the removed supernatant, obtain supernatant I and concentrated residual sludge I; II. Green chelating agent pretreatment for enhanced release of inorganic phosphorus: Add green chelating agent to the concentrated residual sludge I, stir uniformly, then put into a constant-temperature incubator for a period of time, obtain sludge pretreated by green chelating agent; The green chelating agent in step II is one or a mixture of several of citric acid, tartaric acid, methyl glycine diacetic acid and glutamic acid diacetic acid; The dosage of the green chelating agent in step II is 0.01 g / g TSS~0.5 g / g TSS; The temperature of the constant-temperature incubator in step II is 20℃~40℃, and the rotation speed is 100 rpm~150 rpm; The time for reaction in the constant-temperature incubator in step II is 1 h~48 h; III. Inorganic phosphorus recovery: ①Centrifuge or filter press the sludge pretreated by green chelating agent, obtain liquid II and solid II; ②Add calcium-based metal salt to the liquid II, so that the molar ratio of calcium to phosphorus in the liquid II is (0.5~3):1, adjust the pH value of the liquid II to 6~13, then stir for a period of time, stand for a period of time, and finally centrifuge, collect phosphorus precipitate solid and supernatant III; IV. Sludge resuspension: ①Mix the supernatant III and the supernatant I, then use the mixed solution to dissolve the solid II, so that the solid content of the solid II is 0.5%~10%, then transfer to an anaerobic fermentation tank; V. Peroxidizing agent for enhanced sludge solubilization and hydrolysis: Adjust the pH value of the sludge in the anaerobic fermentation tank to 6~7.5, then add a peroxidizing agent, react for a period of time at 25℃~35℃, obtain the reacted sludge; VI. Anaerobic resource utilization: Add inoculated sludge to the reacted sludge obtained in step V, adjust the pH value to 5~7.5, introduce nitrogen into the anaerobic fermentation tank for a period of time, then cover with a sealing plug, so that the reactor maintains an anaerobic state, react at 30℃~37℃ for 2 days~40 days, obtain a reacted sludge mixture; The preparation method of the inoculated sludge in step VI is as follows: first, cook the concentrated residual sludge I obtained in step I at 90℃~100℃ for 1 h~4 h, transfer to a reactor, cool, then add the following substances: glucose 14.4 g / L, yeast paste 3.2 g / L, potassium dihydrogen phosphate 0.56 g / L, magnesium sulfate heptahydrate 0.96 g / L, ammonium chloride 2.4 g / L, anhydrous calcium chloride 0.72 g / L, sodium bicarbonate 0.96 g / L, manganese chloride 0.11 g / L, ferrous sulfate heptahydrate 0.12 g / L, to obtain a sludge mixture; then introduce nitrogen for 10 min~40 min, cover with a sealing plug, so that the reactor maintains an anaerobic state, carry out long-term acclimation at 33℃~37℃, discharge 0.5 L of sludge from the reactor every 7 days, and supplement 0.5 L of the prepared sludge mixture, to carry out long-term operation with a period of 7 days, to obtain the inoculated sludge; VII. Recovery of carbon and phosphorus resources: ①, the reacted sludge mixture obtained in step six is subjected to centrifugal treatment or pressure filtration to obtain residual solids and filtrate I; ②, ferrous-based salt is added to the filtrate I obtained in step seven ①, and then lye is used to adjust the pH value to 5-9, and the reaction is carried out under anaerobic conditions for 0.5 h-2 h, and then aging is carried out under nitrogen or argon conditions for 0.5 h-2 h, and then solid-liquid separation is carried out by using centrifugal treatment or pressure filtration to obtain blue vitriol and filtrate II, the filtrate II is returned to the main sewage treatment plant as a carbon source to supplement the carbon source, and the blue vitriol is vacuum dried at 35℃-60℃.

2. The method according to claim 1, wherein The sludge generated by the secondary sedimentation tank of the sewage treatment plant is screened through a 20-60 mesh screen to remove impurities, and then it is stored at a temperature of 4℃ for 4 h-48 h, and then the supernatant is removed by using a siphon method or a decanter, and the removed supernatant is collected to obtain supernatant I and concentrated residual sludge I; the sludge of the secondary sedimentation tank in step one is one or more of activated sludge for biological phosphorus removal, sludge for iron chemical enhanced phosphorus removal, and sludge for aluminum chemical enhanced phosphorus removal; the solid content of the concentrated residual sludge I in step one is 0.5%-10%.

3. The method according to claim 1, wherein The speed of the centrifugation in step three ① is 5000 rpm-10000 rpm, and the centrifugation time is 5 min-20 min; the calcium-based metal salt in step three ② is calcium chloride, calcium oxide or calcium hydroxide; the stirring speed in step three ② is 600 rpm-1000 rpm, and the stirring time is 10 min-60 min; the standing time in step three ② is 30 min-120 min.

4. The method according to claim 1, wherein The speed of the centrifugal treatment in step three ② is 8000 rpm-12000 rpm, and the centrifugal treatment time is 5 min-20 min; the pH value of the liquid is adjusted to 6-13 by using a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 1 mol / L-6 mol / L in step three ②; the composition of the phosphorus precipitation solid in step three ② is (CaFeMg2Al2(PO4)4(OH)2·8H2O.

5. The method according to claim 1, wherein The volume ratio of the supernatant III to the supernatant I in step four ① is (0-5):(0-5); the peroxidation agent in step five is sodium percarbonate, potassium percarbonate, sodium perborate, potassium perborate, calcium peroxide, magnesium peroxide, hydrogen peroxide, and peracetic acid.

6. The method according to claim 1, wherein The reaction time at 25℃-35℃ in step five is 4 h-24 h; the addition amount of the peroxidation agent in step five is 0.01 g / gTSS-0.5 g / gTSS.

7. The method according to claim 1, wherein the method is characterized by The mass ratio of the inoculated sludge to the reacted sludge obtained in step five in step six is (0-1):(1-5), and then the pH value is adjusted to 5-7.5; the nitrogen gas is introduced into the anaerobic fermentation tank for 10 min-30 min in step seven ①; the speed of the centrifugal treatment in step seven ① is 5000 rpm-10000 rpm, and the centrifugal treatment time is 5 min-15 min.

8. The method according to claim 1, wherein The ferrous salt in step seven ② is ferrous chloride or ferrous sulfate; the molar ratio of the ferrous salt to phosphorus in the filtrate I in step seven ② is (1-2):1; and the alkali solution in step seven ② is a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 1 mol / L-6 mol / L.

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