Method for recovering phosphorus in excess sludge by coupling anaerobic fermentation with sulfate reduction system

Abstract

The invention discloses a method for recovering phosphorus in excess sludge by coupling anaerobic fermentation with a sulfate reduction system, and belongs to the technical field of solid waste treatment. The method comprises the following steps: concentrating and sieving residual sludge of an urban sewage treatment plant; adding sulfate into inoculated sludge of the anaerobic tank, and carrying out domestication culture; and mixing the excess sludge and the inoculated sludge according to a volume ratio of 9: 1 to obtain mixed sludge, adding a sodium sulfate solution to enable the molar ratio of the added sulfur to the total iron element in the mixed sludge to be 1.5, and carrying out anaerobic fermentation under the conditions that the temperature is 37 + / -1 DEG C and the pH value is 5.5 to realize the release of inorganic phosphorus in the excess sludge. According to the method, the sludge is fermented under the weak acid condition of the anaerobic fermentation coupling sulfate reduction system, efficient release of iron phosphorus, calcium phosphorus and the like in organic phosphorus, polyphosphate and inorganic phosphorus in the residual sludge is rapidly achieved, the method is economical and environmentally friendly, and meanwhile, the method has important significance on sludge reduction, recycling and harmlessness.

Description

Technical Field

[0001] The invention relates to a method for recovering phosphorus in excess sludge by coupling an anaerobic fermentation system with a sulfate reduction system, and belongs to the technical field of solid waste treatment. Background Art

[0002] Phosphorus is one of the essential nutrients for life and is closely related to food supply and biogeochemical cycles on land and in the ocean. As humans mine phosphate ore in large quantities for the production of chemical fertilizers, a large amount of phosphorus resources eventually flow into the ocean and deposit on the seabed. The limited and one-way mobility of phosphorus resources has caused the shortage of phosphorus resources to become increasingly serious. Some researchers have estimated that global phosphorus resources will be exhausted within 100-200 years, so the problem of phosphorus shortage has attracted more and more attention. Based on the material flow analysis of phosphorus, people consider seeking renewable phosphorus resources from waste streams. Among them, about 90% of the phosphorus in urban waste streams will be enriched in residual sludge after passing through the centralized sewage treatment system. The residual sludge is large in volume and complex in composition. If it is not properly treated and disposed of, it will not only pollute the environment, but also pose a threat to human health. If its various forms of phosphorus are released and recycled through effective methods, it can not only bring certain economic benefits to sewage treatment plants and reduce the overall cost of sludge treatment and disposal; it can also achieve the reduction and resource utilization of residual sludge. Therefore, from the perspective of phosphorus resource circulation and sustainable development of sewage treatment plants, recovering phosphorus resources from sludge has great application potential.

[0003] Anaerobic fermentation of excess sludge can effectively achieve its reduction, resource utilization and harmlessness. The phosphorus forms in excess sludge mainly include organic phosphorus (OP), inorganic phosphorus (IP), and polyphosphorus (Poly-P). In the process of anaerobic fermentation phosphorus release, the effective release of OP in microbial cell components (RNA, DNA, cell membrane) and IP precipitated by metal ions (Fe, Al, Ca, Mg, etc.) from the solid phase to the liquid phase is a bottleneck problem.

[0004] At present, anaerobic fermentation of excess sludge uses external addition of negative divalent sulfide ions (S 2- ) or coupled with sulfate-reducing bacteria to reduce SO 4 2- Generate S 2- The iron precipitate in the iron phosphorus is combined to generate FeS, which is more insoluble, to release phosphorus. There is also a method of fermenting by adjusting the pH to weakly acidic conditions to dissolve and release calcium phosphorus. However, at present, these two methods can only target a single inorganic phosphorus in inorganic phosphorus, which is extremely unfavorable for the effect of the entire phosphorus release and its recovery, greatly reducing its utilization efficiency and scope of application. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method for recovering phosphorus from excess sludge by coupling anaerobic fermentation with a sulfate reduction system.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention proposes a method for recovering phosphorus from excess sludge by using an anaerobic fermentation coupled with a sulfate reduction (AF-SR) system. The method utilizes an anaerobic fermentation coupled with a sulfate reduction system to adjust the pH of the excess sludge to be weakly acidic, and fermentation promotes phosphorus release. The method specifically comprises the following steps:

[0008] (1) The excess sludge from the municipal sewage treatment plant was concentrated by gravity sedimentation for 24 hours and passed through a 100-mesh sieve;

[0009] (2) The supernatant of the inoculum sludge in the anaerobic tank was discarded, and the sludge was passed through a 100-mesh sieve. The pH of the sludge was adjusted to 10, sulfate was added every 7 days, and the sludge was acclimated and cultured at 37°C for two weeks to make the inoculum sludge have a strong sulfate reduction ability;

[0010] (3) The residual sludge treated in step (1) and the inoculated sludge obtained in step (2) are mixed in a volume ratio of 9:1 to obtain mixed sludge, sodium sulfate solution is added so that the molar ratio of the added sulfur to the total iron in the mixed sludge is 1.5, and anaerobic fermentation is carried out at 37±1°C and pH=5.5 to release inorganic phosphorus in the residual sludge.

[0011] Further, the sulfate is sodium sulfate or potassium sulfate. More preferably, the sulfate is sodium sulfate.

[0012] Furthermore, the amount of sulfate added in step (2) is 100 mg / L each time, so that the inoculated sludge has sufficient carbon source and a higher sulfate load.

[0013] Furthermore, the sulfate in step (2) is sodium sulfate or potassium sulfate, preferably sodium sulfate.

[0014] Furthermore, the volume ratio of the mixed sludge to the sodium sulfate solution is 1.6L:20mL.

[0015] Furthermore, during the anaerobic fermentation process, 4 mol / L hydrochloric acid solution was added to adjust the pH to 5.5.

[0016] The phosphorus forms in the residual sludge mainly include organic phosphorus (OP), polyphosphate (Poly-P), iron phosphorus (Fe-P), calcium phosphorus (Ca-P), etc. In the process of anaerobic fermentation coupled with sulfate-reducing bacteria system to treat sludge, polyphosphate bacteria in the sludge use OP and Poly-P in the cell as energy sources to decompose them into PO 4 3- , and released into the liquid phase, Fe-P is reacted by adding sulfur ions (S 2- ), to combine with Fe in iron phosphorus 2+FeS is generated, and Fe-P in the sludge is converted into soluble salts. By adjusting the weak acid environment of pH=5.5, Ca-P in the sludge is converted into hydrogen phosphate ions and calcium ions, so that various forms of inorganic phosphorus are effectively released from the solid phase to the liquid phase, thereby improving the fermentation release effect of phosphorus in the sludge.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] The present invention utilizes anaerobic fermentation coupled with a sulfate-reducing bacteria system to carry out anaerobic fermentation under weakly acidic conditions, which can realize the simultaneous release of iron phosphorus and calcium phosphorus in organic phosphorus, polyphosphorus, and inorganic phosphorus, greatly improving the ratio of sludge fermentation phosphorus released from the solid phase to the liquid phase. The method of the present invention is simple, efficient, energy-saving and environmentally friendly. Compared with the traditional additional addition of sodium sulfide reagents, or single regulation of weak acid fermentation, the present invention can make the sludge ferment under weakly acidic conditions of anaerobic fermentation coupled with a sulfate-reducing system, quickly realize the efficient release of iron phosphorus and calcium phosphorus in organic phosphorus, polyphosphorus and inorganic phosphorus in the residual sludge, realize sludge phosphorus recovery, which is economical and environmentally friendly, and at the same time has important significance for sludge reduction, resource utilization and harmlessness. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 The schematic diagram of the present invention is a schematic diagram of the recovery of phosphorus from excess sludge by an anaerobic fermentation coupled with a sulfate reduction system;

[0021] Figure 2 The results are as follows: the amount of phosphate (SIP) released from the solid phase to the liquid phase in the mixed sludge after being treated with Example 1 (experimental group B), Comparative Example 1 (blank group K) and Example 2 (experimental group A). DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] The present invention proposes a method for recovering phosphorus in excess sludge by coupling anaerobic fermentation with a sulfate reduction system. The method utilizes anaerobic fermentation coupled with a sulfate reduction system to adjust the pH of the excess sludge to be weakly acidic, and fermentation promotes phosphorus release. The method specifically comprises the following steps:

[0028] (1) The excess sludge from the municipal sewage treatment plant was concentrated by gravity sedimentation for 24 hours and passed through a 100-mesh sieve;

[0029] (2) The supernatant of the inoculum sludge in the anaerobic tank was discarded, and the sludge was passed through a 100-mesh sieve. The pH of the sludge was adjusted to 10, sulfate was added every 7 days, and the sludge was acclimated and cultured at 37°C for two weeks to make the inoculum sludge have a strong sulfate reduction ability;

[0030] (3) The residual sludge treated in step (1) and the inoculated sludge obtained in step (2) are mixed in a volume ratio of 9:1 to obtain mixed sludge, sodium sulfate solution is added so that the molar ratio of the added sulfur to the total iron in the mixed sludge is 1.5, and anaerobic fermentation is carried out at 37±1°C and pH=5.5 to release inorganic phosphorus in the residual sludge.

[0031] In some embodiments of the present invention, the amount of sulfate added in step (2) is 100 mg / L each time, so that the inoculated sludge has sufficient carbon source and a higher sulfate load.

[0032] In some embodiments of the present invention, the sulfate in step (2) is sodium sulfate or potassium sulfate, preferably sodium sulfate.

[0033] In some embodiments of the present invention, the volume ratio of the mixed sludge to the sodium sulfate solution is 1.6L:20mL.

[0034] In some embodiments of the present invention, during the anaerobic fermentation process, 4 mol / L hydrochloric acid solution is added to adjust the pH to 5.5.

[0035] In some embodiments of the present invention, the total phosphorus (TP) in the mixed sludge is 610.5±19.69 mg / L, of which the calcium phosphorus (AP) concentration is 130.26±6.93 mg / L, the inorganic phosphorus (IP) concentration is 492.7±20.91 mg / L, the non-calcium phosphorus (NAIP) concentration is 368.9±16.58 mg / L, and the organic phosphorus (OP) concentration is 103.6±8.49 mg / L, and the calcium phosphorus (AP) accounts for about 21.3%.

[0036] The concentrations of iron (Fe), aluminum (Al), calcium (Ca) and magnesium (Mg) in the mixed sludge are 1200.38±25.02 mg / L, 322.11±19.91 mg / L, 386.22±16.6 mg / L and 84.26±12.95 mg / L, respectively, among which iron accounts for a relatively high proportion, about 60%.

[0037] In some embodiments of the present invention, the iron concentration of the mixed sludge is about 1200.38 mg / L, and the sodium sulfate solution is added according to the volume ratio of the mixed sludge to the sodium sulfate solution of 1.6L:20mL, so that the molar ratio of the externally added sulfur (S) to the total iron element (Fe) in the mixed sludge is 1.5, corresponding to the added sulfate (SO 4 2- ) concentration is 3094.98 mg / L.

[0038] The phosphorus forms in the excess sludge of the present invention mainly include organic phosphorus (OP), polyphosphorus (Poly-P), iron phosphorus (Fe-P), calcium phosphorus (Ca-P), etc. In the process of anaerobic fermentation coupled with sulfate reduction system, phosphorus is effectively released from the solid phase to the liquid phase through three pathways, thereby improving the fermentation release effect of phosphorus in the sludge. The principle diagram is shown in Figure 1 :

[0039] ① Release pathways of organic phosphorus and polyphosphate

[0040] Under anaerobic conditions, polyphosphate bacteria in sludge use OP and Poly-P in the cell as energy sources to decompose them into PO 4 3- , and released into the liquid phase.

[0041] ②Iron and phosphorus release pathway

[0042] Fe-P is achieved by adding sulfide ions (S 2-), to combine with Fe in iron phosphorus 2+ FeS is generated and the Fe-P in the sludge is converted into soluble salts, thereby releasing phosphorus into the liquid phase.

[0043] ③ Calcium and phosphorus release pathway

[0044] By regulating the weak acid environment of pH=5.5, the calcium phosphate in the sludge is converted into hydrogen phosphate ions and calcium ions, thereby releasing Ca-P from the solid phase to the liquid phase.

[0045] All raw materials used in the examples of the present invention are commercially available.

[0046] The technical solution of the present invention is further illustrated by the following embodiments.

[0047] Example 1

[0048] (1) The excess sludge from the municipal sewage treatment plant was concentrated by gravity sedimentation for 24 hours and passed through a 100-mesh sieve;

[0049] (2) The supernatant of the inoculum sludge in the anaerobic tank was discarded, and the sludge was passed through a 100-mesh sieve, and the pH of the sludge was adjusted to 10. Sodium sulfate was added at a dosage of 100 mg / L every 7 days, and the sludge was acclimated and cultured at 37°C for two weeks to make the inoculum sludge have a strong sulfate reduction ability;

[0050] (3) the residual sludge treated in step (1) and the inoculum sludge obtained in step (2) are mixed in a volume ratio of 9:1 to obtain mixed sludge, wherein the total phosphorus (TP) in the mixed sludge is 610.5±19.69 mg / L, the calcium phosphorus (AP) concentration is 130.26±6.93 mg / L, the inorganic phosphorus (IP) concentration is 492.7±20.91 mg / L, the non-calcium phosphorus (NAIP) concentration is 368.9±16.58 mg / L, and the organic phosphorus (OP) concentration is 103.6±8.49 mg / L. In addition, the concentrations of iron (Fe), aluminum (Al), calcium (Ca) and magnesium (Mg) in the mixed sludge are 1200.38±25.02 mg / L, 322.11±19.91 mg / L, 386.22±16.6 mg / L and 84.26±12.95 mg / L, respectively;

[0051] (4) Add 1.6 L of mixed sludge to a 2 L fermenter, and then add 20 mL of sodium sulfate solution with a concentration of 3094.98 mg / L, so that the molar ratio of externally added sulfur (S) to the total iron (Fe) in the mixed sludge is 1.5. Fermentation was carried out at 37±1°C, and the pH was adjusted to 5.5 by adding 4 mol / L hydrochloric acid solution. Anaerobic fermentation was carried out for 2 h to release inorganic phosphorus in the residual sludge.

[0052] Comparative Example 1

[0053] The same as Example 1, except that the steps of adding sodium sulfate solution and adding hydrochloric acid solution to adjust pH are omitted, so that S / Fe=0, and pH is not adjusted throughout the process.

[0054] Comparative Example 2

[0055] Same as Example 1, except that S / Fe=1.5, the pH was adjusted to 7.5 by adding 4 mol / L hydrochloric acid solution, and the pH was maintained at 7.5 throughout the process.

[0056] Processing results

[0057] After treatment with Example 1 (experimental group B), Comparative Example 1 (blank group K) and Example 2 (experimental group A), the release amount of phosphate (SIP) from the solid phase to the liquid phase in the mixed sludge is shown in Figure 2 ,Depend on Figure 2 It can be seen that the treatment method of Example 1 (experimental group B) of the present invention can make the phosphate content in the treated liquid phase reach 357.6±5.9 mg / L at 15 days, which is 9.4 times (38±1.4 mg / L) of comparative example 1 (blank group K) and 1.4 times (249.3±3.6 mg / L) of Example 2 (experimental group A). ​​The experimental results show that the present invention can promote the release of inorganic phosphorus such as iron phosphorus and calcium phosphorus in excess sludge and thus promote the total phosphorus release rate.

[0058] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for recovering phosphorus from excess sludge by coupling anaerobic fermentation with a sulfate reduction system. It is characterized in that Anaerobic fermentation is coupled with a sulfate reduction system to adjust the pH of the remaining sludge to a weakly acidic state, and fermentation promotes phosphorus release.

2. The method for recovering phosphorus from excess sludge by anaerobic fermentation coupled with sulfate reduction system according to claim 1, It is characterized in that The specific steps include: (1) The excess sludge from the municipal sewage treatment plant was concentrated by gravity sedimentation for 24 hours and passed through a 100-mesh sieve; (2) The supernatant of the inoculated sludge in the anaerobic tank was discarded, and the sludge was passed through a 100-mesh sieve. The pH of the sludge was adjusted to 10, sulfate was added every 7 days, and the sludge was cultured at 37°C for two weeks; (3) The residual sludge treated in step (1) and the inoculated sludge obtained in step (2) are mixed in a volume ratio of 9:1 to obtain mixed sludge, sodium sulfate solution is added so that the molar ratio of the added sulfur to the total iron in the mixed sludge is 1.5, and anaerobic fermentation is carried out at 37±1°C and pH=5.5 to release inorganic phosphorus in the residual sludge.

3. The method for recovering phosphorus from excess sludge by anaerobic fermentation coupled with sulfate reduction system according to claim 1, It is characterized in that The amount of sulfate added in step (2) is 100 mg / L each time.

4. The method for recovering phosphorus from excess sludge by anaerobic fermentation coupled with sulfate reduction system according to claim 3, It is characterized in that The sulfate is sodium sulfate or potassium sulfate.

5. The method for recovering phosphorus from excess sludge by anaerobic fermentation coupled with sulfate reduction system according to claim 4, It is characterized in that The sulfate is sodium sulfate.

6. The method for recovering phosphorus from excess sludge by anaerobic fermentation coupled with sulfate reduction system according to claim 2, It is characterized in that The volume ratio of the mixed sludge to the sodium sulfate solution is 1.6L:20mL.

7. The method for recovering phosphorus from excess sludge by anaerobic fermentation coupled with sulfate reduction system according to claim 2, It is characterized in that During the anaerobic fermentation process, 4 mol / L hydrochloric acid solution was added to adjust the pH to 5.5.

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