Two-section type PD / A coupling granular sludge process based on hydroxyapatite reinforced secondary effluent high-efficiency nitrogen and phosphorus removal

Abstract

The invention discloses a two-stage PD / A coupled granular sludge process for reinforcing efficient nitrogen and phosphorus removal of secondary effluent based on hydroxyapatite, and relates to the field of sewage treatment. The method comprises the following steps: firstly, regulating the concentration ratio of NO3 <->-N / NH4 < + >-N to be 1.0-1.4, then pumping into a PD-HAP reaction tank together with a carbon source, converting NO3 <->-N into NO2 <->-N, regulating the pH value of the PD-HAP reaction tank to be 7.5-10.0 by using calcium chloride and calcium hydroxide, so that calcium and soluble phosphorus form hydroxyapatite precipitates in granular sludge, and the settling property and stability of the granular sludge are enhanced while the soluble phosphorus is removed; and pumping the discharged water into an AMX-HAP reaction tank, and removing NO2 <->-N and NH4 < + >-N. And the phosphorus is further removed by utilizing a more suitable alkaline environment created by an Anammox process. According to the method, the phosphorus removal capacity of hydroxyapatite and the denitrification characteristic of a PD / A process are combined, deep reduction of nitrogen and soluble phosphorus in secondary effluent is achieved, and the method has the advantages of being high in denitrification efficiency, high in phosphorus removal capacity, high in system stability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a two-stage PD / A coupled granular sludge process based on hydroxyapatite-enhanced secondary effluent for efficient nitrogen and phosphorus removal. Background Art

[0002] With rapid economic development, water pollution is becoming increasingly severe, and the degradation of aquatic ecosystems needs to be curbed urgently. In recent years, to meet increasingly stringent effluent quality standards, many existing wastewater treatment plants have been forced to add tertiary treatment units. Against this backdrop, the development of efficient, low-carbon wastewater treatment technologies has become a top priority.

[0003] At present, the organic matter content in urban sewage is limited, and the secondary effluent of sewage treatment plants usually contains excessive nitrates. Denitrifying biological filters are widely used for deep removal of nitrates, but there are problems such as high carbon source demand and low denitrification efficiency. Anaerobic ammonia oxidation (Anammox) technology is a recognized green, efficient and economical biological denitrification process. This technology can reduce nitrite to nitrogen gas under anaerobic conditions using ammonia as an electron donor. Compared with traditional denitrification processes, it has low energy consumption, does not require an external carbon source, and significantly reduces sludge production. However, urban sewage contains almost no nitrite nitrogen. How to provide a stable nitrite nitrogen substrate for the Anammox process has become the key to its successful application. To this end, the short-cut denitrification (Partial Denitrification, PD) process, as the front-end process of Anammox, has the advantages of high stability, low energy consumption and low greenhouse gas emissions, and is an urban sewage treatment process with great application prospects.

[0004] Phosphorus is a non-renewable resource, and the world is currently facing a severe phosphorus crisis. However, the PD / A process itself is unable to remove or recover phosphorus. Traditional biological and chemical methods for phosphorus removal are cumbersome and ineffective, making it difficult to recover phosphorus resources and resulting in resource waste. Summary of the Invention

[0005] The purpose of the present invention is to provide a two-stage PD / A coupled granular sludge process based on hydroxyapatite-enhanced secondary effluent for efficient nitrogen and phosphorus removal, so as to solve the problems existing in the above-mentioned prior art.

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

[0007] The present invention provides a two-stage PD / A coupled granular sludge process for efficient nitrogen and phosphorus removal from secondary effluent based on hydroxyapatite enhancement, comprising the following steps:

[0008] (1) Containing NO3 - -N urban sewage secondary effluent and NH4 +-N and organic matter in the municipal sewage are pumped into the comprehensive regulating tank to balance the water quality and water volume, and control the NO3 - -N / NH4 + -N mass concentration ratio is 1.0-1.4;

[0009] (2) The mixed sewage from the comprehensive regulating tank and the carbon source are pumped into the PD-HAP reaction tank. The pH of the PD-HAP reaction tank is adjusted to 7.5-10.0 using calcium chloride and calcium hydroxide, so that calcium and soluble phosphorus form hydroxyapatite precipitation inside the granular sludge, and NO3 - -N is converted to NO2 - -N and removal of dissolved phosphorus;

[0010] (3) Pump the effluent from the PD-HAP reaction tank into the AMX-HAP reaction tank to remove NO2 - -N、NH4 + -N and dissolved phosphorus, the effluent is discharged or reused.

[0011] As a further preferred embodiment of the present invention, during the operation of step (2), the sludge concentration of the PD-HAP reaction tank is controlled to be 15.0-40.0 g / L.

[0012] As a further preference of the present invention, the carbon source in the step (2) is sodium acetate, and the COD quality of the carbon source entering the PD-HAP reaction tank is controlled to be mixed with the NO3 of the wastewater entering the PD-HAP reaction tank. - -N mass concentration ratio (ie COD / NO3 - -N) is 2.0-2.5.

[0013] As a further preferred embodiment of the present invention, during the operation of step (2), the Ca / P mass concentration ratio pumped into the PD-HAP reaction tank is controlled to be 2.0-5.0.

[0014] As a further preferred embodiment of the present invention, when the PD-HAP reaction tank effluent NO3 - When -N is greater than or equal to 1.0 mg / L, increase the COD mass of the carbon source entering the PD-HAP reaction tank in step (2) or increase the hydraulic retention time until the PD-HAP reaction tank effluent NO3 - -N is less than 1.0 mg / L.

[0015] As a further preferred embodiment of the present invention, during the operation of step (3), the sludge concentration of the AMX-HAP reaction tank is controlled to be 8.0-30.0 g / L.

[0016] As a further preferred embodiment of the present invention, when the AMX-HAP reaction tank effluent NO2 - -N and NH4+ -N is greater than or equal to 2.0 mg / L, extend the hydraulic retention time of the AMX-HAP reactor until the NO2 - -N and NH4 + -N is less than 2.0mg / L; when only NH4 + -N is greater than or equal to 2.0mg / L, reduce the ratio of urban sewage and urban sewage secondary effluent pumped into the comprehensive regulating tank until NH4 + -N is less than 2.0 mg / L.

[0017] As a further preferred embodiment of the present invention, when the dissolved phosphorus in the effluent of the AMX-HAP reaction tank is greater than or equal to 1 mg / L, it is adjusted by the following methods:

[0018] Increase the calcium source dosage to raise the mass concentration ratio of calcium to dissolved phosphorus in the PD-HAP reactor influent within the range of 2.0-5.0 until the dissolved phosphorus in the AMX-HAP reactor effluent is less than 1 mg / L; or

[0019] Reduce the addition ratio of calcium chloride to calcium hydroxide in the calcium source, and increase the pH of the PD-HAP reaction tank within the range of 7.5-10.0 until the dissolved phosphorus in the effluent of the AMX-HAP reaction tank is less than 1 mg / L.

[0020] Hydroxyapatite (HAP), with a structure and composition similar to natural phosphate rock, is widely used in a variety of fields. The coupling of hydroxyapatite with granular sludge enhances the granular sludge's settling properties, mechanical strength, and impact resistance. At the same time, by forming Ca-P precipitates within the particles, nitrogen and phosphorus are simultaneously removed, enabling phosphorus resource recovery. Considering that the phosphorus content in urban sewage is low and difficult to remove and recover, the present invention promotes the formation of hydroxyapatite crystals by adding a calcium source and creating alkaline conditions, providing an effective method for removing and recovering phosphorus during urban sewage treatment.

[0021] The present invention also provides a two-stage PD / A coupled granular sludge device for efficient nitrogen and phosphorus removal based on hydroxyapatite-enhanced secondary effluent, comprising a comprehensive regulating tank, a PD-HAP reaction tank and an AMX-HAP reaction tank connected in sequence;

[0022] The comprehensive regulating tank is used to regulate the sewage quality;

[0023] The PD-HAP reaction tank is used to remove the dissolved phosphorus in the effluent of the comprehensive regulating tank and convert NO3 - -N is converted to NO2 - -N;

[0024] The AMX-HAP reaction tank is used to remove NO2 from the effluent of the PD-HAP reaction tank. - -N、NH4 + -N and dissolved phosphorus.

[0025] Furthermore, the two-stage PD / A coupled granular sludge device for efficient nitrogen and phosphorus removal based on hydroxyapatite-enhanced secondary effluent also includes a carbon source storage tank and a calcium source storage tank connected to the PD-HAP reaction tank.

[0026] 1. About the PD-HAP reaction pool of the embodiment of the present invention:

[0027] By precisely controlling the carbon source dosage, calcium source composition, and Ca / P mass ratio, efficient conversion of nitrate nitrogen to nitrite nitrogen (conversion rate > 90%) is achieved, and partial removal of phosphorus is achieved by forming hydroxyapatite inside the granular sludge.

[0028] 2. About the AMX-HAP reaction tank of the embodiment of the present invention:

[0029] The alkalinity generated by the Anammox process is used to achieve NH4 + -N and NO2 - -N removal (total nitrogen removal rate>90%) while further removing phosphorus (total removal rate>80%), breaking through the technical difficulties of traditional PD / A process in achieving phosphorus removal and resource recovery, and forming a new model of "denitrification-phosphorus removal" synergistic effect.

[0030] By coupling hydroxyapatite within the granular sludge, the mechanical strength and settling performance of the granular sludge are improved, ensuring phosphorus removal efficiency while avoiding the risk of sludge loss. Compared with traditional PD / A reactors, it has higher stability.

[0031] The present invention mixes urban sewage and urban sewage secondary effluent in a certain proportion in a comprehensive regulating tank and then pumps them into the PD-HAP reaction tank to convert NO3 - -N is reduced to NO2 - -N, then reacts with NH4 in the AMX-HAP reaction cell + -N is removed simultaneously. Dissolved phosphorus in the raw water is further removed in the PD-HAP and AMX-HAP reactors by forming hydroxyapatite precipitation inside the granular sludge.

[0032] The present invention combines the excellent phosphorus removal ability of hydroxyapatite and the efficient denitrification characteristics of the PD / A process to achieve a deep reduction of nitrogen and phosphorus in the secondary effluent. It has the advantages of high denitrification efficiency, strong phosphorus removal ability, high system stability, and low external carbon source consumption.

[0033] The present invention discloses the following technical effects:

[0034] (1) Compared with traditional denitrifying biological filters, the PD-HAP / AMX-HAP process of the present invention saves 100% of aeration energy consumption and more than 80% of carbon source dosage. At the same time, it has excellent high-load treatment capacity, significantly reduces sewage treatment costs and carbon dioxide and nitrogen oxide emissions, and effectively promotes environmental protection, energy conservation and sustainable development.

[0035] (2) The present invention utilizes the PD-HAP / AMX-HAP process to overcome the technical difficulties of the PD / A process in simultaneously removing phosphorus and realizing phosphorus resource recovery. By utilizing the alkaline environment generated during the PD and Anammox processes, combined with the external addition of a calcium source to supplement calcium ions and further adjust the pH, the soluble phosphorus in the sewage and calcium form hydroxyapatite within the granular sludge, achieving the simultaneous removal of nitrogen and phosphorus. At the same time, phosphorus resource recovery is achieved by regularly discharging the large-sized coupled granular sludge in the reaction tank and collecting the inner core.

[0036] (3) The present invention couples higher-density hydroxyapatite with PD and Anammox granular sludge, thereby enhancing the settling performance of the granular sludge and maintaining the microbial biomass retention level in the reaction tank, thereby ensuring the treatment efficiency and system stability.

[0037] (4) The present invention utilizes a two-stage PD-HAP / AMX-HAP process to carry out the short-range denitrification process and the anaerobic ammonium oxidation process in two independent reaction tanks, creating the most suitable living environment for each microorganism, which is conducive to maintaining an efficient and stable denitrification effect.

[0038] (5) By adjusting the calcium source composition and carbon source dosage, the present invention allows most of the dissolved phosphorus to be converted into hydroxyapatite by the faster-growing heterotrophic short-range denitrifying bacteria in the PD-HAP reactor. Furthermore, the AMX-HAP reactor further utilizes the more favorable environment for hydroxyapatite formation to achieve deep phosphorus removal, fully ensuring that the effluent quality meets standards while avoiding the inhibition of the activity of the anammox bacteria, which have a slower doubling time, caused by the rapid precipitation of inorganic matter in the anammox system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 is a process flow chart of the present invention;

[0041] Figure 2Schematic diagram of the device of the present invention. DETAILED DESCRIPTION

[0042] 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 rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice 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 any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0048] Example 1

[0049] The water quality of the municipal sewage used in the present invention is as follows: the average COD concentration is 156.5 mg / L, NH4 + The average -N concentration was 47.8 mg / L, the average dissolved phosphorus concentration was 7.8 mg / L, and the pH was 7.1.

[0050] The water quality of urban sewage after secondary treatment is as follows: the average COD concentration is 23.5 mg / L, NO3- The average concentration of -N was 22.7 mg / L, and the NH4 + The average -N concentration was 1.3 mg / L, the average dissolved phosphorus concentration was 4.2 mg / L, and the pH was 7.1.

[0051] The processing process is as follows:

[0052] (1) The urban sewage and the secondary effluent of urban sewage were pumped into the comprehensive regulating tank in a volume ratio of 1:3. The water quality was regulated in the comprehensive regulating tank. The average COD concentration of the effluent was 56.8 mg / L, and the NO3 - The average concentration of -N was 17.2 mg / L, and NH4 + The average -N concentration was 12.9 mg / L, the average dissolved phosphorus concentration was 5.1 mg / L, and the pH was 7.1.

[0053] (2) Pump the effluent from the comprehensive regulating tank and the carbon source organic matter (sodium acetate) in the carbon source storage tank into the PD-HAP reaction tank to reduce most of the nitrate nitrogen to nitrite nitrogen and induce the formation of hydroxyapatite, control the COD quality of the carbon source organic matter in the carbon source storage tank entering the PD-HAP reaction tank and the NO3 - -N mass concentration ratio is 2.1, and calcium chloride and calcium hydroxide are added at a mass ratio of 2:1 to adjust the Ca / P mass concentration ratio in the reactor to 2.5 and the pH to about 8.0.

[0054] During the operation, the sludge concentration of the PD-HAP reactor was 23.8 g / L, the sludge retention time was 7 days, and the hydraulic retention time was 1.5 hours. - -N and NO2 - The average concentrations of -N were 0.9 mg / L and 15.1 mg / L, respectively, and the conversion rate of nitrate to nitrite exceeded 90%. The average concentration of dissolved phosphorus was 1.6 mg / L, and the average COD concentration was 27.8 mg / L.

[0055] (3) The effluent from the PD-HAP reactor was pumped into the AMX-HAP reactor for total nitrogen reduction and deep phosphorus removal. During operation, the sludge concentration of the AMX-HAP reactor was 15.6 g / L, the hydraulic retention time was 3 h, and the sludge retention time was 25 days.

[0056] The average COD concentration of the effluent from the long-term operation AMX-HAP reactor is 15.4 mg / L, and NO3 - The average concentration of -N is 0.5mg / L, NO2 - The average concentration of -N is 0.3 mg / L, and the NH4+ The average -N concentration is 1.1mg / L, the average TN concentration is 2.0mg / L, the total nitrogen removal rate is over 90%, the average dissolved phosphorus concentration is 0.8mg / L, the dissolved phosphorus removal rate is over 80%, and the pH is around 8.1. + -N, TN and phosphorus and other effluent indicators all stably meet the national Class A standards.

[0057] Regarding the PD-HAP reaction pool of the embodiment of the present invention:

[0058] By precisely controlling the amount of carbon source added (COD:NO3 - -N mass ratio of 2.1) and Ca / P mass ratio of 2.5, achieving efficient conversion of nitrate nitrogen to nitrite nitrogen (conversion rate > 90%), and partial removal of phosphorus (soluble phosphorus reduced from 5.1 mg / L to 1.6 mg / L) by forming hydroxyapatite inside the granular sludge.

[0059] Regarding the AMX-HAP reaction tank part of the embodiment of the present invention:

[0060] The alkalinity generated by the Anammox process is used to achieve NH4 + -N and NO2 - While removing -N (total nitrogen removal rate>90%), it also achieves further removal of phosphorus (soluble P reduced to 0.8 mg / L, removal rate>80%), breaking through the technical difficulties of traditional PD / A process in achieving phosphorus removal and resource recovery, and forming a new model of "denitrification-phosphorus removal" synergistic effect.

[0061] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A two-stage PD / A coupled granular sludge process for efficient nitrogen and phosphorus removal from secondary effluent based on hydroxyapatite enhancement, characterized in that: The following steps are involved: (1) Pump the secondary effluent of urban sewage and urban sewage into the comprehensive regulating tank together to control the NO3 content of the sewage in the regulating tank. - -N / NH4 + -N mass concentration ratio is 1.0-1.4; (2) The mixed sewage and carbon source from the comprehensive regulating tank are pumped into the PD-HAP reaction tank together, and the pH of the PD-HAP reaction tank is adjusted to the range of 7.5-10.0 using calcium chloride and calcium hydroxide, so that calcium and soluble phosphorus form hydroxyapatite precipitation inside the granular sludge, and NO3 - -N is converted to NO2 - -N and remove dissolved phosphorus; (3) Pump the effluent from the PD-HAP reaction tank into the AMX-HAP reaction tank to remove NO2 - -N、NH4 + -N and dissolved phosphorus, the effluent is discharged or reused.

2. The process according to claim 1, characterized in that During the operation of step (2), the sludge concentration in the PD-HAP reaction tank is controlled to be 15.0-40.0 g / L.

3. The process according to claim 1, characterized in that During the operation of step (2), the carbon source is sodium acetate, and the COD quality of the carbon source entering the PD-HAP reaction tank is controlled to mix with the wastewater in the comprehensive regulating tank and enter the PD-HAP reaction tank. - -N mass concentration ratio is 2.0-2.

5.

4. The process according to claim 1, characterized in that During the operation of step (2), the Ca / P mass concentration ratio pumped into the PD-HAP reaction tank is controlled to be 2.0-5.

0.

5. The process according to claim 1, characterized in that When the PD-HAP reaction tank effluent NO3 - When -N is greater than or equal to 1.0 mg / L, increase the COD mass of the carbon source entering the PD-HAP reaction tank in step (2) or increase the hydraulic retention time until the PD-HAP reaction tank effluent NO3 - -N is less than 1.0 mg / L.

6. The process according to claim 1, characterized in that During the operation of step (3), the sludge concentration in the AMX-HAP reaction tank is controlled to be 8.0-30.0 g / L.

7. The process according to claim 1, characterized in that When the AMX-HAP reactor effluent NO2 - -N and NH4 + -N is greater than or equal to 2.0 mg / L, extend the hydraulic retention time of the AMX-HAP reactor until the NO2 - -N and NH4 + -N is less than 2.0mg / L; when only NH4 + -N is greater than or equal to 2.0mg / L, reduce the ratio of urban sewage and urban sewage secondary effluent pumped into the comprehensive regulating tank until NH4 + -N is less than 2.0 mg / L.

8. The process according to claim 4, characterized in that When the dissolved phosphorus in the effluent of the AMX-HAP reactor is greater than or equal to 1 mg / L, adjust it in the following ways: Increasing the dosage of calcium chloride and calcium hydroxide in step (2) to increase the mass concentration ratio of calcium to dissolved phosphorus in the influent of the PD-HAP reaction tank within the range of 2.0-5.0 until the dissolved phosphorus in the effluent of the AMX-HAP reaction tank is less than 1 mg / L; or The addition ratio of calcium chloride and calcium hydroxide in step (2) is reduced, and the pH of the PD-HAP reaction tank is increased within the range of 7.5-10.0 until the dissolved phosphorus in the effluent of the AMX-HAP reaction tank is less than 1 mg / L.

9. A two-stage PD / A coupled granular sludge device for efficient nitrogen and phosphorus removal based on hydroxyapatite-enhanced secondary effluent, characterized in that: It includes a comprehensive regulating pool, a PD-HAP reaction pool and an AMX-HAP reaction pool connected in sequence; The comprehensive regulating tank is used to regulate the sewage quality; The PD-HAP reaction tank is used to remove the dissolved phosphorus in the effluent of the comprehensive regulating tank and convert NO3 - -N is converted to NO2 - -N; The AMX-HAP reaction tank is used to remove NO2 from the effluent of the PD-HAP reaction tank. - -N、NH4 + -N and dissolved phosphorus.

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