Method for strengthening synchronous recycling of sludge carbon and phosphorus based on ferric chloride pretreatment

Abstract

The invention discloses a method for strengthening synchronous recycling of sludge carbon and phosphorus based on ferric chloride pretreatment, which comprises the following steps: regulating the pH value of sludge through ferric chloride to reconstruct the occurrence form of phosphorus and organic matters in the sludge, and directionally driving release of metal combined phosphorus such as calcium, magnesium and aluminum and extracellular polymer combined phosphorus in the sludge and conversion to blue iron ore; meanwhile, the efficient anaerobic acid production process of the sludge is induced, and finally clean extraction and recovery of the blue iron ore are achieved by means of cyclic utilization of a pretreatment acid solution, so that economical and efficient separation of the blue iron ore in the digested sludge is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge treatment, and particularly relates to a method for strengthening sludge carbon-phosphorus synchronous resourceization based on ferric chloride pretreatment. BACKGROUND

[0002] In the process of wastewater biological treatment, a large amount of residual activated sludge (WAS) rich in organic matter is produced. Based on the dual demands of sludge stabilization and resourceization, anaerobic digestion / fermentation has become an important direction for sludge treatment under the background of double carbon. This process not only helps to achieve sludge reduction and stabilization, but also recovers valuable resources such as volatile fatty acids (VFAs) and methane, which has significant environmental and economic significance. Among them, VFAs are of great concern due to their wide application potential. VFAs can not only be used for the production of polyhydroxyalkanoates and bioenergy, but also as a supplemental carbon source for wastewater denitrification and phosphorus removal, thereby reducing the operating cost of wastewater treatment plants. Therefore, improving the yield of VFAs is crucial for promoting WAS resource utilization.

[0003] In addition to the recycling of carbon resources, the recovery of phosphorus from sludge is also a highly valuable work. Related data shows that the phosphorus recovered from sludge can meet nearly 20% of China's demand for phosphate fertilizer, which is an important way to achieve effective recovery of phosphorus resources. The simultaneous recovery of phosphorus in the process of anaerobic biological treatment of sludge provides the possibility for the resource production and application of phosphorus in sludge. Compared with struvite and Ca-P precipitation, vivianite not only can be used as a raw material for phosphate fertilizer, but also can be used as a raw material for lithium battery electrodes, which has high economic value. The anaerobic treatment environment of residual sludge provides the conditions for the formation of vivianite. Vivianite can be formed spontaneously in the anaerobic system of residual sludge by using the iron contained in the sludge and phosphate and dissimilatory metal-reducing bacteria. Therefore, the recovery of phosphorus in digested sludge in the form of vivianite has attracted international attention. However, how to strengthen the formation of phosphorus (mainly mineral precipitation and extracellular polymeric substance-bound phosphorus) in sludge to form vivianite in the anaerobic process, and how to separate vivianite from digested sludge are two major problems faced by the recovery of vivianite from digested sludge.

[0004] Studies have shown that the dosage of iron is a decisive factor in the proportion of vivianite formation. Directly adding ferric chloride to the anaerobic digestion system of sludge is a common method to improve the in-situ formation of vivianite. The in-situ formed vivianite in the anaerobic digestion sludge can be recovered by magnetic separation and other methods. However, this method has obvious shortcomings: on the one hand, the metal-bound phosphorus in sludge such as calcium, magnesium, and aluminum is difficult to release in the anaerobic digestion process and cannot form vivianite with iron; on the other hand, the addition of ferric chloride and the formation of vivianite to some extent inhibit the hydrolysis of sludge, affecting the recovery efficiency of carbon resources in sludge. In addition, although the magnetic separation of vivianite in anaerobic digestion sludge has good application efficiency in pilot tests, it is greatly affected by factors such as sludge matrix, and the effect is different and unstable.

[0005] In summary, the prior art still has many problems in the simultaneous realization of phosphorus recovery in the form of vivianite and efficient utilization of carbon resources during sludge anaerobic treatment, and a technical solution is urgently needed to solve the above problems to promote the resource utilization of sludge. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide a method for strengthening sludge carbon-phosphorus synchronous resource utilization based on ferric chloride pretreatment, which adjusts and restructures the occurrence form of phosphorus and organic matter in the sludge by ferric chloride, directionally drives the release and transformation of metal-bound phosphorus and extracellular polymeric substance-bound phosphorus in the sludge into vivianite, simultaneously induces the high-efficiency anaerobic acid production process of the sludge, finally realizes the clean extraction and recovery of vivianite by recycling the pretreatment acid solution, so as to achieve the economic and efficient separation of vivianite in residual digested sludge.

[0007] The above purpose of the present application is realized by the following technical scheme:

[0008] A method for strengthening sludge carbon-phosphorus synchronous resource utilization based on ferric chloride pretreatment, comprising the following steps:

[0009] (1) adding ferric chloride to the sludge, adjusting the pH of the sludge to 2-3 to obtain acidified sludge;

[0010] (2) performing solid-liquid separation on the acidified sludge obtained in step (1) to obtain supernatant and residual sludge;

[0011] (3) recovering metal ions in the supernatant obtained in step (2) and obtaining residual acid solution; resuspending the residual sludge obtained in step (2) with water to a solid content of 5-10%, adjusting the pH of the sludge to 6.5-7.5 for high-solid anaerobic acid production, and performing solid-liquid separation on the sludge after the high-solid anaerobic acid production to obtain supernatant containing volatile fatty acids (VFAs) and anaerobic residual sludge containing vivianite;

[0012] (4) recycling the supernatant containing volatile fatty acids obtained in step (3) to a wastewater treatment plant as a carbon source for denitrification and phosphorus removal; mixing the anaerobic residual sludge containing vivianite obtained in step (3) with the residual acid solution obtained in step (3), adjusting the pH of the mixture to 2.5-3.5 for solid-liquid separation to obtain supernatant containing phosphate and divalent iron ions and residual digested sludge, and recovering phosphorus from the supernatant by vivianite crystallization method.

[0013] The present application realizes the directional regulation of the occurrence form of carbon and phosphorus in the sludge by ferric chloride pretreatment, and the core mechanism is reflected in the synergistic association of three dimensions:

[0014] Firstly, the acidification effect (pH regulation to 2-3) of ferric chloride and the Fe3+ The chemical combination ability of calcium, magnesium, aluminum and other metals forms a synergistic effect: in an acidic environment with pH 2-3, the metal-bound phosphorus of calcium, magnesium, aluminum and other metals is dissolved to release phosphate and calcium, magnesium, aluminum and other metal ions; at the same time, Fe 3+ By high affinity with phosphate, it preferentially combines with released phosphorus to form unstable iron-phosphorus complexes. The released calcium, magnesium, aluminum and other metal ions in the supernatant are centrifuged to avoid the recombination of free phosphate with calcium, magnesium and other metals during the anaerobic process, thereby reducing the interference of metal impurity ions in the formation of blue vitriol. This process not only realizes the efficient release of phosphorus, but also solves the problem of "low blue vitriol formation rate caused by insufficient iron source" in traditional processes through the reserve effect of Fe 3+

[0015] Secondly, the solid-liquid separation and water resuspension of the pretreated sludge create a key node for carbon and phosphorus diversion: the residual sludge obtained by step (2) is resuspended and pH-adjusted to enter the high-solid anaerobic acid-producing stage. The acidic conditions with pH 2-3 are close to the isoelectric point of the sludge, at which time only a small amount of dissolved organic matter is present in the supernatant, i.e., a large amount of organic matter still exists in the sludge residue. When the solid-liquid separation is resuspended with water, the sludge residue is resuspended in the liquid, and a large amount of organic matter (mainly extracellular polymeric substances) in the solid phase will be hydrolyzed to the liquid phase due to the removal of metals and changes in electrostatic interactions in the sludge system. The hydrolysis of extracellular polymeric substances promotes the release and conversion of phosphorus combined with extracellular polymeric substances to blue vitriol. 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, thereby solving the contradiction between "iron addition inhibiting hydrolysis" and "carbon and phosphorus recovery interference" in traditional processes. The VFAs yield is increased by more than 2 times, and the phosphorus recovery rate in blue vitriol can reach more than 80%.

[0016] Finally, the acid liquid circulation and product reuse form a closed loop advantage: the remaining acid liquid (pH≤3) after metal recovery in step (3) is recycled for the dissolution of blue vitriol in step (4), which not only avoids the burden of acid liquid treatment, but also realizes the efficient dissolution of blue vitriol in anaerobic residual sludge under acidic conditions by replacing the addition of a large amount of additional acid, thereby obtaining a high-concentration phosphate and divalent iron ion solution, which is finally crystallized into high-purity blue vitriol (purity≥90%) under anaerobic conditions. The supernatant containing VFAs is reused as a carbon source in a wastewater treatment plant, which can directly replace traditional chemical carbon sources such as methanol and sodium acetate.

[0017] In summary, the present application realizes the synergistic recovery of blue vitriol (high-value-added phosphorus product) and VFAs (low-cost carbon source) through the whole-process correlation design of "pretreatment directional regulation-carbon and phosphorus diversion and conversion-product recycling", greatly reduces the operating cost through resource recycling, solves the technical problems of incomplete phosphorus release, carbon and phosphorus recovery conflict, and large reagent consumption in traditional processes, and highlights the technical advantages of "waste treatment and resource utilization".​

[0018] Further, in step (1), the sludge is the residual activated sludge from biological phosphorus removal, from a sewage treatment plant.

[0019] Further, in step (1), the sludge has a solid 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 any range formed by any two of these values. The amount of ferric chloride added is affected by the solid content of the sludge.

[0021] Ferric chloride is not only a pH regulator, but also a key medium for phosphorus form conversion: its hydrolysis produces Fe 3+ which can combine with free phosphate in the sludge, and at the same time, the acidic conditions promote the release of calcium-magnesium-aluminum-bound phosphorus. If the amount added is too low (<10 mM), the pH cannot be effectively adjusted to the target range (2-3), and the Fe 3+ is not enough to cause incomplete release of phosphorus, affecting the subsequent formation of blue vitriol; if the amount added is too high (>30 mM), excessive Cl - will be introduced, inhibiting the activity of subsequent anaerobic microorganisms, and at the same time, increasing the cost of reagents.

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

[0023] Further, in step (2), the solid-liquid separation is performed by 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, and free acid (providing raw materials for subsequent metal recovery and acid recycling); the residual sludge is rich in degradable organic matter (providing substrates for anaerobic acid production).

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

[0026] Further, in step (3), ion exchange resins or adsorbents are used to recover the metal ions in the supernatant obtained in step (2).

[0027] Further, 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 recovery of metal ions, free acid (pH≤3) remains in the supernatant, which does not need to be neutralized and can be directly used for the subsequent dissolution of blue vitriol, achieving acid recycling and reducing reagent consumption.

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

[0030] Further, in step (3), the pH of the sludge is adjusted to 6.5-7.5 by using a sodium hydroxide solution with a concentration of 2-4 M, which is the optimal pH range for the acid-producing bacteria; if the pH <6.5, the activity of the acid-producing bacteria is inhibited and the VFAs production is reduced; and if the pH >7.5, the activity of the methanogenic bacteria is promoted, the VFAs produced is consumed, and the carbon source recovery rate is reduced.

[0031] Further, in step (3), the high solid content anaerobic acid production is specifically performed by mixing the resuspended sludge with the inoculated sludge at a volatile solid (VS) mass ratio of 1:(0.5-1) and performing the high solid content anaerobic acid production at 33-37°C for 7-12 days.

[0032] Further, the inoculated sludge is selected from the acclimated sludge rich in acid-producing functional microorganisms (such as acid-producing bacteria and hydrolytic bacteria), and the VS mass ratio of 1:(0.5-1) can ensure that there is sufficient amount of microorganisms in the system; if the ratio is too low (<1:0.5), the microorganisms are insufficient and the hydrolysis and acid production efficiency is low; and 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 VFAs production.

[0033] In step (4), the solid content of the mixture obtained by mixing the anaerobic residual sludge containing blue vitriol obtained in step (3) with the remaining acid liquid obtained in step (3) is 3-5%, and when the pH of the mixture is insufficient to reach 2.5-3.5, a hydrochloric acid solution with a concentration of 2-4 M is used for supplementary adjustment.

[0034] In step (4), the pH of the mixture is 2.5-3.5; if the pH <2.5, the blue vitriol will be excessively dissolved and the iron-phosphorus ratio will be imbalanced; and if the pH >3.5, the dissolution of phosphate and divalent iron will be incomplete, reducing the recovery rate.

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

[0036] Further, the anaerobic conditions are as follows: nitrogen or argon is introduced to maintain the dissolved oxygen (DO) <0.5 mg / L; the anaerobic environment can avoid the oxidation of divalent iron to trivalent iron (trivalent iron is easy to form iron hydroxide precipitate, which interferes with the purity of blue vitriol).

[0037] The beneficial effects of the present application are:

[0038] 1、The present application significantly improves the formation efficiency and quality of the blue vitriol in the sludge anaerobic digestion system through the directional restructuring of ferric chloride and the circulation control of acid liquor: on the one hand, the conversion rate of phosphorus in the sludge to the blue vitriol is increased by more than 2 times compared with the traditional process, solving the bottleneck of the difficulty of releasing and converting the calcium-magnesium-aluminum combined state phosphorus; on the other hand, through the selective dissolution of acid liquor and the solid-liquid separation of calcium, magnesium, aluminum and other metal ions, the content of coexisting interfering metal ions in the blue vitriol is reduced by more than 90%, and the product purity can reach more than 90%, laying a foundation for its high-value application as a phosphate fertilizer or lithium battery electrode raw material.

[0039] 2、In the dimension of carbon resource recovery, the present application eliminates the inhibition of traditional iron salt addition on sludge hydrolysis through the directional destruction of EPS in the pretreatment stage, greatly improves the utilization efficiency of organic matter by microorganisms in the anaerobic acid production process, and increases the maximum volatile fatty acid (VFAs) production by more than 2 times compared with the prior art, thereby strengthening the practical value of carbon source.

[0040] 3、The present application has a recovery efficiency of more than 90% for multivalent metal ions (calcium, magnesium, aluminum, iron) through ion exchange resin or adsorbent, and the recovered iron source can be recycled for the pretreatment stage, thereby reducing the consumption of reagents; at the same time, the content of heavy metals (such as lead and cadmium) in the residual digestion sludge is reduced by more than 50% after being dissolved by acid liquor and removed from the sludge through solid-liquid separation, which not only improves the environmental safety of the sludge, but also realizes the cascade utilization of metal resources, thereby significantly reducing the operation cost of the process. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The present application is a process schematic diagram of the sludge carbon-phosphorus co-resource method based on ferric chloride pretreatment. DETAILED DESCRIPTION

[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 the present application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0043] The present application will be further described below with reference to the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting of the present application.

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

[0045] The application provides a method for simultaneously recycling carbon and phosphorus of sludge based on iron chloride pretreatment, comprising the following steps:

[0046] (1) adding iron chloride to the sludge, adjusting the pH of the sludge to 2-3 to obtain acidified sludge;

[0047] (2) performing solid-liquid separation on the acidified sludge obtained in step (1) to obtain supernatant and residual sludge;

[0048] (3) recycling metal ions in the supernatant obtained in step (2), and obtaining residual acid liquor; resuspending the residual sludge obtained in step (2) in water to a solid content of 5-10%, adjusting the pH of the sludge to 6.5-7.5 to perform high-solid anaerobic acid production, and performing solid-liquid separation on the sludge after the high-solid anaerobic acid production to obtain supernatant containing volatile fatty acids (VFAs) and anaerobic residual sludge containing blue vitriol;

[0049] (4) recycling the supernatant containing VFAs obtained in step (3) to a sewage treatment plant as a carbon source for denitrification and phosphorus removal; mixing the anaerobic residual sludge containing blue vitriol obtained in step (3) with the residual acid liquor obtained in step (3), adjusting the pH of the mixture to 2.5-3.5 to perform solid-liquid separation, obtaining supernatant containing phosphate and divalent iron ions and residual digestion sludge, and recycling phosphorus from the supernatant by a blue vitriol crystallization method.

[0050] In the specific embodiment, a flowchart of the method for simultaneously recycling carbon and phosphorus of sludge based on iron chloride pretreatment is shown in Figure 1 , comprising the following steps:

[0051] (1) adding iron chloride to the sludge from a sewage treatment plant, adjusting the pH of the sludge to 2-3 to obtain acidified sludge;

[0052] (2) performing solid-liquid separation on the acidified sludge obtained in step (1) to obtain supernatant rich in metals and residual solid (i.e., residual sludge);

[0053] (3) recycling metals in the supernatant rich in metals obtained in step (2) by using ion exchange resin or adsorbent, recycling the water (i.e., residual acid liquor) after the metal recycling for subsequent processes; resuspending the residual solid obtained in step (2) in water to a solid content of 5-10%, adjusting the pH of the sludge to 6.5-7.5 to perform high-solid anaerobic acid production, and performing solid-liquid separation on the sludge after the high-solid anaerobic acid production to obtain supernatant rich in VFAs and residual sludge rich in blue vitriol;

[0054] (4) The VFA-rich supernatant obtained in step (3) is returned to a sewage treatment plant for carbon recovery; the residual sludge rich in blue vitriol obtained in step (3) is mixed with the residual acid liquor 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 rich in phosphate and divalent iron and residual digested sludge (i.e. residual sludge), and the supernatant is subjected to blue vitriol crystallization recovery.

[0055] The sludge in the following examples is from a sewage treatment plant in Shanghai, with a solid content of 2% and a pH of 7, wherein the content of phosphorus is 23.5 mg / g TS, and the contents of calcium, magnesium, aluminum and iron are 25.4, 5.6, 25.9 and 15.6 mg / g TS, respectively, and the contents of heavy metals arsenic, chromium, copper, nickel, lead and zinc are 0.0007, 0.0626, 0.140, 0.0208, 0.0446 and 0.798 mg / g TS, respectively.

[0056] Example 1

[0057] A method for simultaneous carbon and phosphorus resource recovery from sludge based on ferric chloride pretreatment, comprising the following steps:

[0058] (1) Ferric chloride is added to the residual activated sludge (the addition amount is 10 mM), and after stirring and mixing for 30 min, the pH of the sludge is adjusted to 3 to obtain acidified sludge.

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

[0060] (3) The supernatant is subjected to metal ion recovery using a 732 type strong acid cation exchange resin, and calcium ions, magnesium ions, aluminum ions and iron ions are recovered (the total recovery rate of calcium ions, magnesium ions, aluminum ions and iron ions is 80%), and residual acid liquor is obtained; the residual sludge is resuspended in water, and the solid content is adjusted to 7%; a 3M sodium hydroxide solution is used to adjust the pH of the sludge to 7.0; the resuspended sludge is mixed with inoculated sludge at a VS mass ratio of 1:0.8, and placed in a 35°C constant temperature water bath reactor for high-solid anaerobic acid production for 10 days; the sludge after high-solid anaerobic acid production is subjected to solid-liquid separation to obtain supernatant containing VFAs and anaerobic residual sludge containing blue vitriol, and the conversion rate of phosphorus to blue vitriol in the sludge reaches 80%.

[0061] (4) The supernatant containing VFAs (VFAs production of 220.6 mg COD / g VS, in which acetic acid is the main component, accounting for 60%) is transported to a sewage treatment plant as a supplemental carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing blue vitriol is mixed with the residual acid liquor obtained in step (3), and the pH of the mixture is adjusted to 3 for solid-liquid separation to obtain supernatant containing phosphate and divalent iron ions and residual digested sludge (the heavy metal content is reduced by 50% compared with before treatment), and the supernatant is placed in an anaerobic reaction device (nitrogen is introduced to maintain the dissolved oxygen DO <0.5 mg / L), 3M sodium hydroxide solution is used to adjust the pH to 7.0, and the mixture is statically crystallized for 24 h to recover phosphorus by the blue vitriol crystallization method, and finally the blue vitriol product (the purity is 90% after detection) is obtained.

[0062] Example 2

[0063] A method for simultaneous carbon and phosphorus resourceization of sludge based on iron chloride pretreatment, comprising the following steps:

[0064] (1) Iron chloride is added to the residual activated sludge (the addition amount is 15 mM), and after stirring and mixing for 20 min, the pH of the sludge is adjusted to 2.5 to obtain acidified sludge.

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

[0066] (3) The supernatant is subjected to metal ion recovery by using 732 type strong acid cation exchange resin, and calcium ions, magnesium ions, aluminum ions and iron ions are recovered (the total recovery rate is 85%), and residual acid liquor is obtained; the residual sludge is resuspended in water, and the solid content is adjusted to 6%, and the pH of the sludge is adjusted to 6.8 by using 3M sodium hydroxide solution, and the resuspended sludge is mixed with inoculated sludge at a VS mass ratio of 1:0.6, and is placed in a 34°C constant temperature water bath reactor for high-solid anaerobic acid production for 9 days, and the sludge after high-solid anaerobic acid production is subjected to solid-liquid separation to obtain supernatant containing VFAs and anaerobic residual sludge containing blue vitriol, and the conversion rate of phosphorus to blue vitriol in the sludge reaches 85%.

[0067] (4) The supernatant containing VFAs (VFAs production of 225 mg COD / g VS was detected, and acetic acid was the main component, accounting for 60%) was transported to a sewage treatment plant as a supplemental carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing blue vitriol was mixed with the residual acid liquor 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 divalent iron ions and residual digested sludge (the heavy metal content was reduced by 60% compared with before treatment), and the supernatant was placed in an anaerobic reaction device (nitrogen was introduced to maintain the dissolved oxygen DO <0.5 mg / L), 3M sodium hydroxide solution was used to adjust the pH to 7.0, and the mixture was statically crystallized for 24 h to recover phosphorus by the blue vitriol crystallization method, and finally the blue vitriol product (the purity was 93% detected) was obtained.

[0068] Example 3

[0069] A method for strengthening sludge carbon-phosphorus synchronous resourceization based on ferric chloride pretreatment, comprising the following steps:

[0070] (1) Ferric chloride was added to the residual activated sludge (the addition amount was 20 mM), and after stirring and mixing for 40 min, the pH of the sludge was adjusted to 2.0 to obtain acidified sludge.

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

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

[0073] (4) The supernatant containing VFAs (VFAs production of 225 mg COD / g VS was detected, and acetic acid was the main component, accounting for 60%) was transported to a sewage treatment plant as a supplemental carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing blue vitriol was mixed with the residual acid liquor 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 divalent iron ions and residual digested sludge (the heavy metal content was reduced by 95% compared with before treatment), and the supernatant was placed in an anaerobic reaction device (nitrogen was introduced to maintain the dissolved oxygen DO <0.5 mg / L), 3M sodium hydroxide solution was used to adjust the pH to 7.0, and the mixture was statically crystallized for 24 h to recover phosphorus by the blue vitriol crystallization method, and finally the blue vitriol product (the purity was 95% detected) was obtained.

[0074] Comparative Example 1

[0075] A method for strengthening sludge carbon-phosphorus synchronous resourceization based on ferric chloride pretreatment, comprising the following steps:

[0076] (1) Ferric chloride was added to the residual activated sludge (the addition amount was 6 mM), and after stirring and mixing for 30 min, the pH of the sludge was 4, and acidified sludge was obtained.

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

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

[0079] (4) The supernatant containing VFAs (the VFAs yield is 145 mg COD / g VS, and acetic acid is the main component, accounting for 50%) is transported to a sewage treatment plant as a supplementary carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing blue vitriol is mixed with the residual acid liquor obtained in step (3), the pH of the mixture is adjusted to 3 for solid-liquid separation, and the supernatant containing phosphate and divalent iron ions and anaerobic digestion sludge (the heavy metal content is reduced by 20% compared with before treatment) are obtained; and the supernatant is placed in an anaerobic reaction device (nitrogen is introduced to maintain the dissolved oxygen DO < 0.5 mg / L), 3M sodium hydroxide solution is used to adjust the pH to 7.0, and the supernatant is statically crystallized for 24 hours to recover phosphorus by the blue vitriol crystallization method, and finally the blue vitriol product (the purity is 60% after detection) is obtained.

[0080] Comparative Example 2

[0081] A method for strengthening sludge carbon-phosphorus synchronous resourceization based on iron chloride pretreatment, comprising the following steps:

[0082] (1) Iron chloride is added to residual activated sludge (the addition amount is 10 mM), and after stirring and mixing for 30 min, the pH of the sludge is adjusted to 3 to obtain acidified sludge.

[0083] (2) The acidified sludge is placed in a 35℃ constant-temperature water bath reactor for high-solid anaerobic acid production for 10 days, and after the acid production is completed, the sludge is subjected to solid-liquid separation to obtain supernatant containing VFAs and anaerobic residual sludge containing blue vitriol, and the conversion rate of phosphorus to blue vitriol in the sludge reaches 60%.

[0084] (3) The supernatant containing VFAs (the VFAs yield is 75 mg COD / g VS) is transported to a sewage treatment plant as a supplementary carbon source for denitrification and phosphorus removal; the anaerobic residual sludge containing blue vitriol is mixed with acid liquor, the pH of the mixture is adjusted to 3 for solid-liquid separation, and supernatant containing phosphate and divalent iron ions and residual digestion sludge are obtained; the supernatant is placed in an anaerobic reaction device (nitrogen is introduced to maintain the dissolved oxygen DO < 0.5 mg / L), 3M sodium hydroxide solution is used to adjust the pH to 7.0, and the supernatant is statically crystallized for 24 hours to recover phosphorus by the blue vitriol crystallization method, and finally the blue vitriol product (the purity is 40% after detection) is obtained.

[0085] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Those skilled in the art should understand that on the basis of the above description, other different forms of changes or variations can also be made. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for simultaneous resource utilization of carbon and phosphorus in sludge based on ferric chloride pretreatment strengthening, characterized in that, The method comprises the following steps: (1) adding ferric chloride into sludge, adjusting pH of the sludge to 2-3 to obtain acidified sludge; (2) performing solid-liquid separation on the acidified sludge obtained in step (1) to obtain supernatant and residual sludge; (3) recovering metal ions in the supernatant obtained in step (2) and obtaining residual acid liquor; resuspending the residual sludge obtained in step (2) in water to obtain a solid content of 5-10%, adjusting pH of the sludge to 6.5-7.5 to perform high-solid-content anaerobic acid production, and performing solid-liquid separation on the sludge after the high-solid-content anaerobic acid production to obtain supernatant containing volatile fatty acids and anaerobic residual sludge containing blue vitriol; (4) using the supernatant containing volatile fatty acids obtained in step (3) as a carbon source to perform denitrification and phosphorus removal in a sewage treatment plant; mixing the anaerobic residual sludge containing blue vitriol obtained in step (3) with the residual acid liquor obtained in step (3), adjusting pH of the mixture to 2.5-3.5 to perform solid-liquid separation, obtaining supernatant containing phosphate and divalent iron ions and residual digestion sludge, and recovering phosphorus from the supernatant by a blue vitriol crystallization method.

2. The method of claim 1, wherein, In step (1), the sludge is residual activated sludge for biological phosphorus removal, and the solid content of the sludge is 1.5-3% and the pH is 6.5-7.

5.

3. The method of claim 1, wherein, In step (1), the ferric chloride is added in an amount of 10-30 mM.

4. The method of claim 1, wherein, In step (2), the solid-liquid separation is performed by plate-and-frame filtration or centrifugal separation.

5. The method of claim 1, wherein, In step (3), the metal ions mainly 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), the metal ions in the supernatant obtained in step (2) are recovered by using ion exchange resin or adsorbent.

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

8. The method of claim 1, wherein, In step (3), the high-solid-content anaerobic acid production is performed by mixing the resuspended sludge with inoculated sludge at a volatile solid mass ratio of 1:(0.5-1), and the high-solid-content anaerobic acid production is performed at 33-37℃ for 7-12 days.

9. The method of claim 1, wherein, In step (4), the solid content of the mixture obtained by mixing the anaerobic residual sludge containing blue vitriol obtained in step (3) with the residual acid liquor obtained in step (3) is 3-5%, and when the pH of the mixture is insufficient to reach 2.5-3.5, a hydrochloric acid solution with a concentration of 2-4 M is used for supplementary adjustment.

10. The method of claim 1, wherein, In step (4), the supernatant containing phosphate and divalent iron ions is adjusted to a pH of 6-8 under anaerobic conditions to recover phosphorus by a blue vitriol crystallization method.

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