A method for enhancing the simultaneous carbon and phosphorus resource utilization of sludge based on ferric chloride pretreatment

Abstract

This invention discloses a method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment. By regulating the pH of the sludge with ferric chloride, the occurrence forms of phosphorus and organic matter in the sludge are reconstructed. This method directionally drives the release of metal-bound phosphorus such as calcium, magnesium, and aluminum, as well as extracellular polymer-bound phosphorus, and their conversion to lapis lazuli. At the same time, it induces an efficient anaerobic acid production process in the sludge. Finally, by recycling the pretreated acid solution, the clean extraction and recovery of lapis lazuli are achieved, thereby achieving an economical and efficient separation of lapis lazuli from digested sludge.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, specifically to a method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment. Background Technology

[0002] In the biological treatment of wastewater, a large amount of residual activated sludge (WAS) rich in organic matter is generated. Driven by the dual needs of sludge stabilization and resource recovery, anaerobic digestion / fermentation has become an important direction for sludge treatment under a dual-carbon environment. This process not only helps to reduce and stabilize sludge volume but also recovers valuable resources such as volatile fatty acids (VFAs) and methane, possessing significant environmental and economic implications. Among these, VFAs have attracted considerable attention due to their broad application potential. VFAs can be used not only in the production of polyhydroxyalkanoates and bioenergy but also as a supplementary carbon source for nitrogen and phosphorus removal in wastewater, thereby reducing the operating costs of wastewater treatment plants. Therefore, increasing VFA production is crucial for promoting the utilization of WAS resources.

[0003] Besides carbon resource recovery, phosphorus recovery from sludge is also a highly valuable endeavor. Related data shows that phosphorus recovered from sludge can meet nearly 20% of my country's phosphate fertilizer demand, making it a crucial pathway for effective phosphorus resource recovery. Simultaneous phosphorus recovery during anaerobic biological treatment of sludge provides the possibility for the resource-based production and application of phosphorus in sludge. Compared to struvite and Ca-P precipitates, lapis lazuli can not only serve as a raw material for phosphate fertilizer but also as a raw material for lithium battery electrodes, possessing high economic value. The anaerobic treatment environment of waste sludge provides ideal conditions for lapis lazuli formation. In anaerobic systems of waste sludge, lapis lazuli can spontaneously form using the iron and phosphate contained within, along with dissimilar metal-reducing bacteria. Therefore, the recovery of phosphorus from digested sludge in the form of lapis lazuli has attracted international attention. However, how to enhance the formation of lapis lazuli from phosphorus in sludge (mainly mineral-precipitated phosphorus and phosphorus bound to extracellular polymers) during the anaerobic process, and how to separate lapis lazuli from digested sludge, are the two major challenges in recovering lapis lazuli from digested sludge.

[0004] Studies have shown that the amount of iron added is the decisive factor in the formation ratio of lapis lazuli. Directly adding ferric chloride to the anaerobic digestion system of sludge is a common method to enhance in-situ lapis lazuli formation. Lapis lazuli formed in anaerobic digestion sludge can be separated and recovered through methods such as magnetic separation. However, this method has significant shortcomings: on the one hand, phosphorus in the sludge, bound to metals such as calcium, magnesium, and aluminum, is difficult to release during anaerobic digestion and cannot form lapis lazuli with iron; on the other hand, the addition of ferric chloride and the formation of lapis lazuli inhibit sludge hydrolysis to some extent, affecting the recovery efficiency of sludge carbon resources. Furthermore, although magnetic separation for recovering lapis lazuli from anaerobic digestion sludge has shown good efficiency in pilot-scale applications, its effectiveness varies greatly and is unstable due to factors such as the sludge matrix.

[0005] In summary, existing technologies still face many challenges in simultaneously achieving phosphorus recovery in the form of wollastonite and efficient utilization of carbon resources during anaerobic sludge treatment. There is an urgent need for a technical solution that can address these challenges in order to promote the resource utilization of sludge. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment. By adjusting and reconstructing the occurrence forms of phosphorus and organic matter in sludge through ferric chloride, the method directionally drives the release and conversion of metal-bound phosphorus such as calcium, magnesium, and aluminum, as well as extracellular polymer-bound phosphorus, into lapis lazuli. Simultaneously, it induces an efficient anaerobic acid production process in the sludge. Finally, through the recycling of the pretreatment acid solution, the clean extraction and recovery of lapis lazuli are achieved, thereby realizing the economical and efficient separation of lapis lazuli from residual digested sludge.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0008] A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment includes the following steps:

[0009] (1) Add ferric chloride to the sludge to adjust the pH of the sludge to 2-3 to obtain acidified sludge;

[0010] (2) The acidified sludge obtained in step (1) is subjected to solid-liquid separation to obtain supernatant and residual sludge;

[0011] (3) The metal ions in the supernatant obtained in step (2) are recovered and the remaining acid solution is obtained; the residual sludge obtained in step (2) is resuspended in water to a solid content of 5-10%, the pH of the sludge is adjusted to 6.5-7.5 for high solid content anaerobic acid production, and the sludge after the high solid content anaerobic acid production is completed is subjected to solid-liquid separation to obtain a supernatant containing volatile fatty acids (VFAs) and an anaerobic residual sludge containing blue iron ore;

[0012] (4) The supernatant containing volatile fatty acids obtained in step (3) is reused in the wastewater treatment plant as a carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing ferrous ore obtained in step (3) is mixed with the residual acid solution obtained in step (3), and the pH of the mixture is adjusted to 2.5-3.5 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and residual digested sludge. The supernatant is then subjected to ferrous ore crystallization to recover phosphorus.

[0013] This invention achieves targeted regulation of carbon and phosphorus speciation in sludge through ferric chloride pretreatment, and its core mechanism is reflected in the synergistic relationship of three dimensions:

[0014] First, the acidification effect of ferric chloride (pH adjusted to 2-3) and Fe3+ The chemical bonding ability forms a synergistic effect: in an acidic environment of pH 2-3, bound phosphorus of metals such as calcium, magnesium, and aluminum dissolves, releasing phosphate ions and metal ions such as calcium, magnesium, and aluminum; simultaneously, Fe... 3+ By leveraging its high affinity for phosphate, it preferentially binds to released phosphorus to form an unstable iron-phosphorus complex. The release of calcium, magnesium, and aluminum ions in the supernatant, after centrifugation, prevents free phosphate from rebinding with these metals during anaerobic processes, thus reducing interference from metal impurities during lapis lazuli formation. This process not only achieves efficient phosphorus release but also, through Fe... 3+ Its reserve function solves the problem of "insufficient iron source leading to low blue iron ore formation rate" in traditional processes.

[0015] Secondly, the solid-liquid separation and resuspension of the pretreated sludge constitute the key nodes for carbon and phosphorus diversion: the residual sludge obtained in step (2) is resuspended and pH adjusted before entering the high-solids-content anaerobic acid production stage. The acidic conditions of pH 2-3 are close to the isoelectric point of the sludge. At this time, there is only a small amount of dissolved organic matter in the supernatant, that is, a large amount of organic matter still exists in the sludge residue. After solid-liquid separation and resuspension, the sludge residue is resuspended in the liquid. A large amount of organic matter (mainly extracellular polymers) in the solid phase will be hydrolyzed into the liquid phase due to the removal of metals in the sludge system and changes in electrostatic effects. The hydrolysis of extracellular polymers promotes the release of phosphorus bound by extracellular polymers and its conversion into lapis lazuli. The hydrolyzed organic matter is more easily decomposed by hydrolytic bacteria and acid-producing bacteria, efficiently generating VFAs mainly composed of acetic acid and propionic acid. This solves the contradiction of "iron addition inhibiting hydrolysis and mutual interference between carbon and phosphorus recovery" in the traditional process, increasing the VFA production by more than 2 times while the phosphorus recovery rate in lapis lazuli can reach more than 80%.

[0016] Finally, the closed-loop advantage of acid recycling and product reuse is achieved: the residual acid (pH≤3) after metal recovery in step (3) is recycled for the leaching of lapis lazuli in step (4), which avoids the burden of acid treatment and achieves efficient leaching of lapis lazuli from anaerobic residual sludge under acidic conditions by replacing the addition of a large amount of additional acid, resulting in a high-concentration solution of phosphate and ferrous ions, which is finally crystallized into high-purity lapis lazuli (purity≥90%) under anaerobic conditions. The supernatant containing VFAs is reused as a carbon source in the wastewater treatment plant, which can directly replace traditional chemical carbon sources such as methanol and sodium acetate.

[0017] In summary, this invention, through a fully integrated design of "pretreatment-directed regulation-carbon-phosphorus diversion and conversion-product recycling," not only achieves the synergistic recovery of blue iron ore (high-value-added phosphorus product) and VFAs (low-cost carbon source), but also significantly reduces operating costs through resource recycling. It solves the technical problems of incomplete phosphorus release, carbon-phosphorus recovery conflict, and high reagent consumption in traditional processes, highlighting the technical advantages of "treating waste with waste and adding value through resource utilization."

[0018] Furthermore, in step (1), the sludge is residual activated sludge from biological phosphorus removal, which comes from a wastewater treatment plant.

[0019] Further, in step (1), the sludge has a solids content of 1.5-3% and a pH of 6.5-7.5.

[0020] Further, in step (1), the amount of ferric chloride added to the sludge is 10-30 mM; for example, it can be 10, 15, 20, 30 mM, or a range formed by any two values. The amount of ferric chloride added is affected by the solids content of the sludge.

[0021] Ferric chloride is not only a pH adjuster, but also a key medium for phosphorus transformation: its hydrolysis produces Fe... 3+ It can bind with free phosphate ions in sludge, and simultaneously promote the release of calcium, magnesium, and aluminum bound phosphorus under acidic conditions. If the dosage is too low (<10 mM), it cannot effectively adjust the pH to the target range (2-3), and Fe... 3+ Insufficient phosphorus release will lead to incomplete phosphorus release, affecting subsequent lapis lazuli formation; excessive phosphorus release (>30mM) will introduce excessive Cl. - This inhibits the activity of subsequent anaerobic microorganisms and increases the cost of the agent.

[0022] Preferably, in step (1), the amount of ferric chloride added to the sludge is 10-20 mM.

[0023] Furthermore, in step (2), the solid-liquid separation method is plate and frame filtration or centrifugal separation.

[0024] The supernatant obtained in step (2) is rich in metal ions such as calcium, magnesium, aluminum, and iron, as well as free acid (providing raw materials for subsequent metal recovery and acid recycling); the residual sludge is rich in biodegradable organic matter (providing substrate for anaerobic acid production).

[0025] Furthermore, in step (3), the metal ions mainly include one or more of calcium ions, magnesium ions, aluminum ions and iron ions.

[0026] Furthermore, in step (3), metal ions in the supernatant obtained in step (2) are recovered using ion exchange resin or adsorbent.

[0027] Furthermore, the ion exchange resin can be a 732 type cation exchange resin, and the adsorbent can be activated carbon and clay minerals, etc.

[0028] In step (3), after the metal ions are recovered, there is still free acid (pH≤3) remaining in the supernatant. This part of the acid does not need to be neutralized and can be directly used for the subsequent leaching of blue iron ore, so as to realize the recycling of acid and reduce the consumption of reagents.

[0029] In step (3), if the solid content of the resuspended sludge is too high (>10%), the sludge viscosity will increase dramatically, the mass transfer efficiency will decrease, local acid accumulation (pH<5.0) will occur in the anaerobic system, and the activity of acid-producing bacteria will be inhibited; if the solid content is too low (<5%), the acid production per unit volume will decrease and the volumetric load of the reactor will increase.

[0030] Furthermore, in step (3), a sodium hydroxide solution with a concentration of 2-4M is used to adjust the pH of the sludge to 6.5-7.5. This range is the optimal pH range for acid-producing bacteria. If pH < 6.5, the activity of acid-producing bacteria is inhibited and the production of VFAs decreases. If pH > 7.5, it will promote the activity of methanogenic bacteria, consume the generated VFAs, and reduce the carbon source recovery rate.

[0031] Further, in step (3), the specific operation of the high solids anaerobic acid production is as follows: the resuspended sludge and the inoculated sludge are mixed at a volatile solids (VS) mass ratio of 1:(0.5-1), and the high solids anaerobic acid production is carried out at 33-37℃ for 7-12 days.

[0032] Furthermore, the inoculated sludge is selected from acclimatized sludge rich in acid-producing microorganisms (such as acid-producing bacteria and hydrolytic bacteria). A VFA mass ratio of 1:(0.5-1) can ensure that there are sufficient microorganisms in the system. If the ratio is too low (<1:0.5), there will be insufficient microorganisms and low hydrolysis acid production efficiency. If the ratio is too high (>1:1), the microorganisms will consume too much organic matter due to their own metabolism, resulting in a decrease in VFA production.

[0033] In step (4), the solid content of the mixture obtained by mixing the anaerobic residual sludge containing blue iron ore obtained in step (3) with the residual acid solution obtained in step (3) is 3-5%. When the pH of the mixture is insufficient to meet the pH requirement of 2.5-3.5, a 2-4M hydrochloric acid solution is used to supplement and adjust it.

[0034] In step (4), the pH of the mixture is 2.5-3.5. If the pH is less than 2.5, it will lead to excessive dissolution of blue iron ore and an imbalance in the iron-phosphorus ratio. If the pH is greater than 3.5, the phosphate and ferrous iron will not dissolve completely, reducing the recovery rate.

[0035] Further, in step (4), the specific operation of the phosphorus recovery by the blue iron ore crystallization method is as follows: the pH of the supernatant containing phosphate and ferrous ions is adjusted to 6-8 under anaerobic conditions to recover phosphorus by the blue iron ore crystallization method.

[0036] Furthermore, the anaerobic conditions are as follows: nitrogen or argon is introduced to maintain dissolved oxygen (DO) <0.5 mg / L; the anaerobic environment can prevent ferrous iron from being oxidized to ferric iron (ferric iron easily forms ferric hydroxide precipitate, which interferes with the purity of lapis lazuli).

[0037] The beneficial effects of this invention are:

[0038] 1. This invention significantly improves the formation efficiency and quality of lapis lazuli in sludge anaerobic digestion systems through directional reconstruction of ferric chloride and acid circulation regulation. On the one hand, the conversion ratio of phosphorus to lapis lazuli in sludge is more than twice that of traditional processes, solving the bottleneck of calcium-magnesium-aluminum bound phosphorus being difficult to release and convert. On the other hand, through selective acid dissolution and solid-liquid separation of calcium, magnesium, aluminum and other metal ions, the content of coexisting interfering metal ions in lapis lazuli is reduced by more than 90%, and the product purity can reach more than 90%, laying the foundation for its high-value application as a phosphate fertilizer or lithium battery electrode raw material.

[0039] 2. In terms of carbon resource recovery, this invention eliminates the inhibitory effect of traditional iron salt addition on sludge hydrolysis by targeted destruction of EPS during the pretreatment stage, which greatly improves the utilization efficiency of organic matter by microorganisms during anaerobic acid production. The yield of maximum volatile fatty acids (VFAs) is more than twice that of existing technologies, thus enhancing the practical value of carbon sources.

[0040] 3. This invention achieves a recovery efficiency of over 90% for multivalent metals (calcium, magnesium, aluminum, and iron) using ion exchange resins or adsorbents. The recovered iron source can be recycled for the pretreatment stage, reducing reagent consumption. Simultaneously, heavy metals (such as lead and cadmium) in the residual digested sludge are removed from the sludge through solid-liquid separation after being dissolved by acid, with the content reduced by more than 50% compared to before treatment. This not only improves the environmental safety of the sludge but also realizes the cascade utilization of metal resources, significantly reducing the operating cost of the process. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the process for the co-resource utilization method of sludge carbon and phosphorus based on ferric chloride pretreatment according to the present invention. Detailed Implementation

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0045] This invention provides a method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment, comprising the following steps:

[0046] (1) Add ferric chloride to the sludge to adjust the pH of the sludge to 2-3 to obtain acidified sludge;

[0047] (2) The acidified sludge obtained in step (1) is subjected to solid-liquid separation to obtain supernatant and residual sludge;

[0048] (3) The metal ions in the supernatant obtained in step (2) are recovered and the remaining acid solution is obtained; the residual sludge obtained in step (2) is resuspended in water to a solid content of 5-10%, the pH of the sludge is adjusted to 6.5-7.5 for high solid content anaerobic acid production, and the sludge after the high solid content anaerobic acid production is completed is subjected to solid-liquid separation to obtain a supernatant containing volatile fatty acids (VFAs) and an anaerobic residual sludge containing blue iron ore;

[0049] (4) The supernatant containing volatile fatty acids obtained in step (3) is reused in the wastewater treatment plant as a carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing ferrous ore obtained in step (3) is mixed with the residual acid solution obtained in step (3), and the pH of the mixture is adjusted to 2.5-3.5 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and residual digested sludge. The supernatant is then subjected to ferrous ore crystallization to recover phosphorus.

[0050] In a specific implementation, a flowchart illustrating the sludge carbon-phosphorus co-resource utilization method based on ferric chloride pretreatment is shown below. Figure 1 As shown, it includes the following steps:

[0051] (1) Add ferric chloride to the sludge from the sewage treatment plant to adjust the pH of the sludge to 2-3 to obtain acidified sludge;

[0052] (2) The acidified sludge obtained in step (1) is subjected to solid-liquid separation to obtain a metal-rich supernatant and residual solids (i.e. residual sludge);

[0053] (3) Use ion exchange resin or adsorbent to recover the metal in the metal-rich supernatant obtained in step (2), and reuse the water (i.e. the residual acid liquid) after metal recovery for subsequent processes; add water to the residual solid obtained in step (2) and resuspend it to a solid content of 5-10%, adjust the pH of the sludge to 6.5-7.5 for high solid content anaerobic acid production, and perform solid-liquid separation on the sludge after the high solid content anaerobic acid production to obtain a supernatant rich in VFAs and a residual sludge rich in blue iron ore;

[0054] (4) The supernatant rich in VFAs obtained in step (3) is reused in the wastewater treatment plant for carbon recovery; the residual sludge rich in patina obtained in step (3) is mixed with the residual acid solution obtained in step (3), the pH of the mixture is adjusted to 2.5-3.5 and solid-liquid separation is performed to obtain a supernatant rich in phosphate and ferrous iron and residual digested sludge (i.e. residual sludge), and the supernatant is subjected to patina crystallization recovery.

[0055] The sludge in the following examples came from a wastewater treatment plant in Shanghai. It had a solids content of 2%, a pH of 7, a phosphorus content of 23.5 mg / gTS, and calcium, magnesium, aluminum, and iron contents of 25.4, 5.6, 25.9, and 15.6 mg / gTS, respectively. The contents of heavy metals arsenic, chromium, copper, nickel, lead, and zinc were 0.0007, 0.0626, 0.140, 0.0208, 0.0446, and 0.798 mg / gTS, respectively.

[0056] Example 1

[0057] A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment includes the following steps:

[0058] (1) Add ferric chloride (10 mM) to the remaining activated sludge, stir and mix for 30 min, and then adjust the pH of the sludge to 3 to obtain acidified sludge.

[0059] (2) The acidified sludge above is subjected to solid-liquid separation to obtain supernatant and residual sludge.

[0060] (3) The supernatant was treated with a 732 type strong acid cation exchange resin to recover metal ions, including calcium ions, magnesium ions, aluminum ions and iron ions (the total recovery rate of calcium ions, magnesium ions, aluminum ions and iron ions was 80%), and the remaining acid solution was obtained. The remaining sludge was resuspended in water and adjusted to a solid content of 7%. The pH of the sludge was adjusted to 7.0 with a 3M sodium hydroxide solution. The resuspended sludge was mixed with the inoculated sludge at a VFA mass ratio of 1:0.8 and placed in a 35℃ constant temperature water bath reactor for high solid content anaerobic acid production for 10 days. The sludge after the high solid content anaerobic acid production was completed was subjected to solid-liquid separation to obtain a supernatant containing VFAs and an anaerobic residual sludge containing lapis lazuli. The conversion ratio of phosphorus to lapis lazuli in the sludge reached 80%.

[0061] (4) The supernatant containing VFAs (the VFAs yield was tested to be 220.6 mg COD / gVS, of which acetic acid was the main component, accounting for 60%) was transported to the wastewater treatment plant as a supplementary carbon source for nitrogen and phosphorus removal; the anaerobic residual sludge containing patina was mixed with the residual acid solution obtained in step (3), and the pH of the mixture was adjusted to 3 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and residual digested sludge (the heavy metal content was reduced by 50% compared with that before treatment). The supernatant was placed in an anaerobic reactor (nitrogen was introduced to maintain dissolved oxygen DO < 0.5 mg / L), and the pH was adjusted to 7.0 with 3M sodium hydroxide solution. After standing for crystallization for 24 hours, patina crystallization was carried out to recover phosphorus, and finally patina product (the purity was tested to be 90%) was obtained.

[0062] Example 2

[0063] A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment includes the following steps:

[0064] (1) Add ferric chloride (15 mM) to the remaining activated sludge, stir and mix for 20 min, and then adjust the pH of the sludge to 2.5 to obtain acidified sludge.

[0065] (2) The acidified sludge above is subjected to solid-liquid separation to obtain supernatant and residual sludge.

[0066] (3) The supernatant was treated with a 732 type strong acid cation exchange resin to recover metal ions, and calcium ions, magnesium ions, aluminum ions and iron ions were recovered (total recovery rate of 85%), and the remaining acid solution was obtained. The remaining sludge was added to water for resuspension and adjusted to a solid content of 6%. The pH of the sludge was adjusted to 6.8 with a 3M sodium hydroxide solution. The resuspended sludge was mixed with the inoculated sludge at a VFA mass ratio of 1:0.6 and placed in a 34℃ constant temperature water bath reactor for high solid content anaerobic acid production for 9 days. The sludge after the high solid content anaerobic acid production was completed was subjected to solid-liquid separation to obtain a supernatant containing VFAs and an anaerobic residual sludge containing lapis lazuli. The conversion ratio of phosphorus to lapis lazuli in the sludge reached 85%.

[0067] (4) The supernatant containing VFAs (the VFAs yield was 225 mg COD / g VS, of which acetic acid was the main component, accounting for 60%) was transported to the wastewater treatment plant as a supplementary carbon source for nitrogen and phosphorus removal. The anaerobic residual sludge containing patina was mixed with the residual acid solution obtained in step (3), and the pH of the mixture was adjusted to 3 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and residual digested sludge (the heavy metal content was reduced by 60% compared with that before treatment). The supernatant was placed in an anaerobic reactor (nitrogen was introduced to maintain dissolved oxygen DO < 0.5 mg / L), and the pH was adjusted to 7.0 with 3M sodium hydroxide solution. The mixture was allowed to stand for crystallization for 24 hours to recover phosphorus by patina crystallization, and finally a patina product (the purity was 93%) was obtained.

[0068] Example 3

[0069] A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment includes the following steps:

[0070] (1) Add ferric chloride (20 mM) to the remaining activated sludge, stir and mix for 40 min, and then adjust the pH of the sludge to 2.0 to obtain acidified sludge.

[0071] (2) The acidified sludge above is subjected to solid-liquid separation to obtain supernatant and residual sludge.

[0072] (3) The supernatant was treated with a 732 type strong acid cation exchange resin to recover metal ions, and calcium ions, magnesium ions, aluminum ions and iron ions were recovered (total recovery rate of 90%), and residual acid was obtained. The residual sludge was added to water for resuspension and adjusted to a solid content of 8%. The pH of the sludge was adjusted to 7.2 with a 3M sodium hydroxide solution. The resuspended sludge was mixed with the inoculated sludge at a VFA mass ratio of 1:0.9 and placed in a 36℃ constant temperature water bath reactor for high solid content anaerobic acid production for 11 days. The sludge after the high solid content anaerobic acid production was completed was subjected to solid-liquid separation to obtain a supernatant containing VFAs and an anaerobic residual sludge containing lapis lazuli. The conversion ratio of phosphorus to lapis lazuli in the sludge reached 85%.

[0073] (4) The supernatant containing VFAs (the VFAs yield was tested to be 225 mg COD / g VS, of which acetic acid was the main component, accounting for 60%) was transported to the wastewater treatment plant as a supplementary carbon source for nitrogen and phosphorus removal; the anaerobic residual sludge containing patina was mixed with the residual acid solution obtained in step (3), and the pH of the mixture was adjusted to 3 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and residual digested sludge (the heavy metal content was reduced by 95% compared with that before treatment). The supernatant was placed in an anaerobic reactor (nitrogen was introduced to maintain dissolved oxygen DO < 0.5 mg / L), and the pH was adjusted to 7.0 with 3M sodium hydroxide solution. After standing for crystallization for 24 hours, patina crystallization was carried out to recover phosphorus, and finally patina product (the purity was tested to be 95%) was obtained.

[0074] Comparative Example 1

[0075] A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment includes the following steps:

[0076] (1) Add ferric chloride (6 mM) to the remaining activated sludge and stir for 30 min. At this time, the pH of the sludge is 4, and acidified sludge is obtained.

[0077] (2) The acidified sludge above is subjected to solid-liquid separation to obtain supernatant and residual sludge.

[0078] (3) The supernatant was treated with a 732 type strong acid cation exchange resin to recover metal ions, and calcium ions, magnesium ions, aluminum ions and iron ions were recovered (total recovery rate of 25%), and the remaining acid solution was obtained. The remaining sludge was added to water for resuspension and adjusted to a solid content of 7%. The pH of the sludge was adjusted to 7.0 with a 3M sodium hydroxide solution. The resuspended sludge was mixed with the inoculated sludge at a VFA mass ratio of 1:0.8 and placed in a 35℃ constant temperature water bath reactor for high solid content anaerobic acid production for 10 days. The sludge after the high solid content anaerobic acid production was completed was subjected to solid-liquid separation to obtain a supernatant containing VFAs and an anaerobic residual sludge containing lapis lazuli. The conversion ratio of phosphorus to lapis lazuli in the sludge was only 40%.

[0079] (4) The supernatant containing VFAs (the VFAs yield was tested to be 145 mg COD / g VS, of which acetic acid was the main component, accounting for 50%) was transported to the wastewater treatment plant as a supplementary carbon source for nitrogen and phosphorus removal; the anaerobic residual sludge containing patina was mixed with the residual acid solution obtained in step (3), and the pH of the mixture was adjusted to 3 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and anaerobic digested sludge (the heavy metal content was reduced by 20% compared with that before treatment). The supernatant was placed in an anaerobic reactor (nitrogen was introduced to maintain dissolved oxygen DO < 0.5 mg / L), and the pH was adjusted to 7.0 with 3M sodium hydroxide solution. After standing for crystallization for 24 hours, patina crystallization was carried out to recover phosphorus, and finally patina product (the purity was tested to be 60%) was obtained.

[0080] Comparative Example 2

[0081] A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment includes the following steps:

[0082] (1) Add ferric chloride (10 mM) to the remaining activated sludge, stir and mix for 30 min, and then adjust the pH of the sludge to 3 to obtain acidified sludge.

[0083] (2) The acidified sludge was placed in a 35°C constant temperature water bath reactor for 10 days of high solid content anaerobic acid production. After the acid production was completed, the sludge was subjected to solid-liquid separation to obtain a supernatant containing VFAs and an anaerobic residual sludge containing blue iron ore. The conversion ratio of phosphorus to blue iron ore in the sludge reached 60%.

[0084] (3) The supernatant containing VFAs (with a VFA yield of 75 mg COD / g VS) was transported to the wastewater treatment plant as a supplementary carbon source for nitrogen and phosphorus removal. The anaerobic residual sludge containing patina was mixed with acid, and the pH of the mixture was adjusted to 3 for solid-liquid separation to obtain a supernatant containing phosphate and ferrous ions and residual digested sludge. The supernatant was placed in an anaerobic reactor (nitrogen was introduced to maintain dissolved oxygen DO < 0.5 mg / L), and the pH was adjusted to 7.0 with 3M sodium hydroxide solution. The mixture was allowed to stand for crystallization for 24 hours to recover phosphorus by patina crystallization, and finally a patina product (with a purity of 40%) was obtained.

[0085] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for enhancing the simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment, characterized in that, Includes the following steps: (1) Add ferric chloride to the sludge and adjust the pH of the sludge to 2-3 to obtain acidified sludge; (2) The acidified sludge obtained in step (1) is subjected to solid-liquid separation to obtain supernatant and residual sludge; (3) The metal ions in the supernatant obtained in step (2) are recovered and the remaining acid solution is obtained; the residual sludge obtained in step (2) is resuspended in water to a solid content of 5-10%, the pH of the sludge is adjusted to 6.5-7.5 for high solid content anaerobic acid production, and the sludge after the high solid content anaerobic acid production is completed is subjected to solid-liquid separation to obtain a supernatant containing volatile fatty acids and an anaerobic residual sludge containing blue iron ore; (4) The supernatant containing volatile fatty acids obtained in step (3) is reused in the sewage treatment plant as a carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing ferrous ore obtained in step (3) is mixed with the residual acid liquid obtained in step (3), and the pH of the mixture is adjusted to 2.5-3.5 for solid-liquid separation to obtain supernatant containing phosphate and ferrous ions and residual digested sludge. The supernatant is subjected to ferrous ore crystallization to recover phosphorus.

2. The method according to claim 1, characterized in that, In step (1), the sludge is the residual activated sludge from biological phosphorus removal, and the sludge has a solids content of 1.5-3% and a pH of 6.5-7.

5.

3. The method according to claim 1, characterized in that, In step (1), the amount of ferric chloride added to the sludge is 10-30 mM.

4. The method according to claim 1, characterized in that, In step (2), the solid-liquid separation method is plate and frame filtration or centrifugal separation.

5. The method according to claim 1, characterized in that, In step (3), the metal ions include one or more of calcium ions, magnesium ions, aluminum ions and iron ions.

6. The method according to claim 1 or 5, characterized in that, In step (3), metal ions in the supernatant obtained in step (2) are recovered using ion exchange resin or adsorbent.

7. The method according to claim 1, characterized in that, In step (3), the pH of the sludge is adjusted to 6.5-7.5 using a sodium hydroxide solution with a concentration of 2-4 M.

8. The method according to claim 1, characterized in that, In step (3), the specific operation of the high solids anaerobic acid production is as follows: the resuspended sludge and the inoculated sludge are mixed at a volatile solids mass ratio of 1:(0.5-1), and the high solids anaerobic acid production is carried out at 33-37℃ for 7-12 days.

9. The method according to claim 1, characterized in that, In step (4), the solid content of the mixture obtained by mixing the anaerobic residual sludge containing blue iron ore obtained in step (3) with the residual acid solution obtained in step (3) is 3-5%. When the pH of the mixture is insufficient to meet the pH requirement of 2.5-3.5, a hydrochloric acid solution with a concentration of 2-4 M is used to supplement and adjust it.

10. The method according to claim 1, characterized in that, In step (4), the specific operation of recovering phosphorus by the blue iron ore crystallization method is as follows: the pH of the supernatant containing phosphate and ferrous ions is adjusted to 6-8 under anaerobic conditions to recover phosphorus by the blue iron ore crystallization method.

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