Preparation method of biological capsule similar to aerobic granular sludge and application of biological capsule in sewage treatment

Abstract

The invention relates to a preparation method of a biological capsule similar to aerobic granular sludge and a method for treating domestic sewage by using the biological capsule. The preparation method of the biological capsule comprises the following steps: (a) preparing a gel solution; (b) mixing the gel solution with microorganisms to form a mixture; (c) dropwise adding the mixture into a cross-linking agent solution, so that a gel network is formed and microorganisms are fixed in the gel network to form a biological capsule; and (d) placing the biocapsule in a cross-linking agent solution for 12-24 hours to further enhance the gel strength, and then rinsing with water. The sewage treatment method comprises the following steps: (i) adding a biological capsule into a reactor; and (ii) operating the reactor in a sequencing batch mode. Although the biological capsule is broken at the initial stage of operation of the reactor, the fragments of the biological capsule can realize stability recovery within two weeks. Similar to aerobic granular sludge, the biological capsule fragments have a compact structure, good settling performance and capability of synchronously removing organic matters and nutrient substances. The technical problems that the aerobic granular sludge culture process is long and culture conditions are severe are solved, and the application prospect is good.

Description

Technical Field

[0001] The invention relates to a method for preparing a biological capsule similar to aerobic granular sludge and a method for treating sewage using the biological capsule, belonging to the technical field of sewage treatment. Background Art

[0002] Aerobic granular sludge (AGS) is considered to be one of the most promising wastewater biological treatment technologies due to its advantages such as high pollution removal efficiency, small footprint in engineering applications and low operating costs. AGS is a special biofilm structure that gradually forms granular biopolymers through the self-agglomeration of microorganisms. Compared with traditional activated sludge, it has the advantages of compact structure, good sedimentation performance and high biodiversity. Thanks to this, the biomass concentration in the AGS reactor is high, the mud-water separation effect is good, and organic matter and nutrients in sewage can be removed simultaneously in a single treatment reactor. However, the cultivation of AGS faces great challenges, especially when treating low-intensity sewage (such as domestic sewage). At present, sludge granulation is mostly completed in a sequencing batch reactor (SBR) with activated sludge, but this process is relatively complicated and is subject to many operating conditions, such as substrate composition, organic load, feeding strategy, fluid mechanics shear force, dissolved oxygen concentration, reactor operation, etc. The operating "window" for successful cultivation of aerobic granular sludge is relatively small, which limits the application of this technology.

[0003] Various methods have been studied in an attempt to promote the rapid formation of granular sludge. Chinese Patent No. CN104884608 discloses a method for accelerating the growth of AGS by adding crushed AGS. However, AGS is a scarce, slow-growing, and difficult-to-cultivate commodity. In actual engineering applications, the large amount of AGS required for reactor startup often lacks sufficient sources. Chinese Patent No. CN102502953 discloses a method for promoting AGS cultivation by adding a metal oxide carrier to a reactor inoculated with activated sludge. This method can shorten the sludge granulation time to 4 weeks, but the sewage concentration configured is much higher than that of typical domestic sewage (biochemical oxygen demand COD 1000mg / L relative to COD 200-400mg / L of typical domestic sewage). Chinese Patent No. CN106242045 also discloses a method for accelerating AGS cultivation by adding lanthanum compounds and neodymium compounds as activated sludge promoters, and the granular sludge formation time is 25 days. However, due to the poor settling properties of activated sludge, even with the rapid granulation method, it usually takes several weeks to achieve complete granulation. For the same reason, a large amount of sludge loss from the system is also a common phenomenon in the early stage of reactor operation, which also leads to low pollutant removal efficiency at this stage. Therefore, quickly starting the AGS system while maintaining a high pollutant removal rate is a huge challenge in practical applications. Summary of the invention

[0004] The present invention aims to alleviate one or more of the aforementioned problems and provide an efficient wastewater treatment method that accelerates the formation of aerobic granular sludge while achieving effective removal of organic matter and nitrogen. The present invention relates to the production of biocapsules having properties similar to aerobic granular sludge (AGS) and wastewater treatment methods relying on biocapsules.

[0005] In some embodiments, the technical problem to be solved by the present invention is how to shorten the startup time of the AGS process while maintaining effective removal of pollutants. The solution to this technical problem is to prepare biocapsules with similar properties to AGS outside the reactor and inoculate the pre-prepared biocapsules into the reactor to treat the sewage.

[0006] In one embodiment, the present invention provides a method for preparing a biocapsule similar to aerobic granular sludge, the method comprising the steps of: (a) preparing a gel solution; (b) mixing the gel solution with microorganisms to form a mixture; (c) dripping the mixture into a crosslinker solution to form a gel network and fix the microorganisms therein to form a biocapsule; and (d) placing the biocapsule in the crosslinker solution for 12-24 hours to further strengthen the gel strength, and then washing with water. The biocapsule is used to be inoculated into a reactor for sewage treatment.

[0007] In another embodiment, the present invention provides a method for treating sewage, comprising the steps of: (i) adding a biocapsule to a reactor; and (ii) operating the reactor in a sequencing batch mode. The biocapsule is prepared according to any of the methods for preparing the biocapsule in the embodiments of the present invention.

[0008] Other example embodiments are discussed herein.

[0009] The present invention has many advantages. In some embodiments, compared with the existing AGS technology, the present invention has the following beneficial effects:

[0010] (1) The present invention provides an effective method to accelerate the granulation process of sludge while ensuring the removal effect of pollutants. The method includes preparing biocapsules with properties similar to AGS outside the reactor and inoculating such biocapsules directly into the reactor. The system is started up after two weeks of operation, at which time the biomass is mainly composed of fragments produced by the initially added biocapsules. In some embodiments, the present invention can remove organic matter and nitrogen at the same time. In some embodiments, the removal rates of COD, ammonia nitrogen and total nitrogen can reach 95%, 84% and 80%, respectively.

[0011] (2) During the sewage treatment process, the biocapsules and their fragments already have a granular structure, so a higher organic loading rate (OLR) is not required to promote particle formation. No external carbon source needs to be added to the original sewage. The present invention can effectively reduce the cost of adding carbon sources.

[0012] (3) In the sewage treatment process, the biocapsule and its fragments already have a granular structure, so a higher superficial gas velocity is not necessary for particle formation. In some embodiments, a dissolved oxygen (DO) level of 3 mg / L is sufficient for pollutant removal. The present invention can effectively reduce energy consumption costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The features and advantages of the present invention may be further understood by reference to the remainder of this specification and the accompanying drawings; the same reference numerals are used for the same components in the drawings. In some cases, a sub-label is placed after a reference numeral and a hyphen to indicate one of a number of similar components. When a reference numeral is mentioned without specifying an existing sub-label, all of these similar components are referred to.

[0014] Figure 1 SA-Ca biocapsules prepared under different conditions

[0015] Figure 2 . Changes in biocapsules under conditions of Example 2

[0016] Figure 3 .The removal effect of pollutants by the biocapsule reactor under the conditions of Example 2

[0017] Figure 4 . Changes in biocapsules under conditions of Example 3

[0018] Figure 5 . Pollutant removal effect of biocapsule reactor under the conditions of Example 3 DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] In the present invention, “comprising” means including the following elements, but does not exclude other elements.

[0021] One aspect of the present invention provides a method for preparing a biocapsule similar to aerobic granular sludge, the method comprising the steps of: (a) preparing a gel solution; (b) mixing the gel solution with microorganisms to form a mixture; (c) dripping the mixture into a crosslinker solution to form a gel network and fix the microorganisms therein to form a biocapsule; and (d) placing the biocapsule in the crosslinker solution for 12-24 hours to further strengthen the gel strength, and then washing it with water.

[0022] In an optional embodiment, the size of the biocapsule is between 2.9-3.6 mm, and the sedimentation velocity is greater than 53 m / h.

[0023] In an optional embodiment, the gel material in step (a) includes sodium alginate, polyvinyl alcohol or a mixture thereof.

[0024] In an optional embodiment, the viscosity of the sodium alginate solution is 100-150 cps when the concentration is 1 w / v%, and the degree of polymerization of the polyvinyl alcohol is 1650-1750.

[0025] In an optional embodiment, the concentration of the sodium alginate solution is 1-4 w / v% of the mixture, and the concentration of the polyvinyl alcohol is 5-10 w / v% of the mixture.

[0026] In an optional embodiment, the microorganism in step (b) is concentrated activated sludge or a culture of a bacterial strain, and the suspended solids concentration of the mixed liquor is 15,000-20,000 mg / L.

[0027] In an optional embodiment, the cross-linking agent solution in step (c) comprises a calcium, magnesium, iron and / or aluminum salt solution with a concentration of 1-10 w / v%, saturated boric acid or a mixture thereof.

[0028] One aspect of the present invention provides a method for treating wastewater, comprising the steps of: (i) adding a biocapsule to a reactor; and (ii) operating the reactor in a sequencing batch mode. The preparation of the biocapsule is carried out according to any of the methods for preparing the biocapsule in the embodiments of the present invention.

[0029] In an optional embodiment, the batch reaction operation cycle of step (ii) is 4-6 hours, and each reaction cycle includes the following steps: (a) static water inlet to the reactor; (b) aeration reaction, during which the dissolved oxygen concentration is maintained above 3 mg / L; (c) stopping aeration, and the sludge settling time does not exceed 6 minutes per meter of water depth; and (d) drainage, with a drainage ratio of 30-50%.

[0030] The following further describes various aspects of the present invention in conjunction with the accompanying drawings:

[0031] In some embodiments, the present invention aims to solve the problems of long aerobic granular sludge (AGS) formation time and low pollutant removal efficiency when starting the AGS reactor.

[0032] The solution provided by the present invention is to prepare a biocapsule having similar characteristics to AGS, such as high biomass concentration and dense microbial structure, and then directly inoculate the prepared biocapsule into a reactor for sewage treatment. According to a first aspect of the present invention, a simple and rapid method for preparing a biocapsule is provided, which comprises the following steps: (a) preparing an aqueous solution of a gel material, (b) mixing the solution in step (a) with a concentrated solution of microorganisms to form a mixture, (c) adding the mixture dropwise to a crosslinker solution to form a biocapsule having a structure of a gel network encapsulating the microorganisms, and (d) strengthening the biocapsule. The biocapsule can be formed within one day and has some characteristics similar to AGS, such as a larger particle size (2.9-3.6 mm) and a good settling velocity (>53 m / h).

[0033] According to another aspect of the present invention, there is provided a method for treating sewage with a short startup time and a high pollutant removal rate, which comprises the following steps: (a) inoculating the prepared biocapsule into a reactor, and (b) operating the reactor in a sequencing batch reactor (SBR) mode. The system observed the breakage of the biocapsule in the early stage of operation, but it soon stabilized, at which time the fragments of the biocapsule dominated. The fragments of the biocapsule also have some characteristics similar to AGS, such as a larger particle size (about 1 mm) and a good settling velocity (>13 m / h). The biocapsule system was started up within two weeks, and the removal rates of COD, ammonia nitrogen and total nitrogen could reach 95%, 84% and 80%, respectively.

[0034] The technical problem to be solved by the present invention is how to shorten the formation time of AGS while maintaining the removal of pollutants. In some embodiments, the solution to this technical problem is: AGS-like sludge is prepared by a fast and stable method outside the reactor, and then the pre-prepared AGS-like sludge is directly inoculated into the reactor to treat the sewage.

[0035] Compared with AGS formed by the self-condensation process, fixing microorganisms in gel materials can effectively shorten the time to form a compact structure. Suitable gel materials should have the characteristics of fast gel formation, good stability and non-toxicity to microorganisms, such as alginate, polyvinyl alcohol (PVA) and a mixture of alginate and PVA. When using appropriate cross-linking agents, both alginate and PVA can quickly form a cross-linked network. The structure of alginate consists of α-L-glucuronic acid (G block) and β-D-mannitol acid (M block). When multivalent ions (such as calcium ions) interact with the G block sequence, thermally irreversible hydrogel beads are formed, thereby forming a cross-linked complex. The gelation of PVA can be completed by instantaneous polymerization using boric acid. In some embodiments, when preparing PVA / alginate gel, a calcium chloride solution containing boric acid can be used for cross-linking. In the method for preparing a biocapsule, the gel material is first dissolved in water and thoroughly mixed with the concentrated microorganisms. The mixture is then dripped into the cross-linking agent solution. The carboxyl groups of alginate or the hydroxyl groups of PVA enable the bonding process, thereby quickly forming a strong gel structure and fixing the microorganisms inside. In some embodiments, a longer curing time may be required to fully complete the cross-linking reaction. The biocapsule is then removed, cleaned and prepared for further use.

[0036] In some embodiments, in the method for treating sewage, the biocapsule is directly added to the reactor as inoculum sludge. In some embodiments, the reactor is operated in accordance with the SBR mode. First, the sewage is added from the bottom of the reactor. Because the microorganisms of the present invention are directly added in the form of biocapsules, high OLR is not a necessary condition for forming granular sludge in the present invention. Low-concentration domestic sewage can enter the reactor directly without adding an external carbon source. Secondly, aeration allows the biocapsule to simultaneously carry out aerobic reactions (mainly in the outer layer) and anaerobic reactions (mainly in the inner layer). In view of the fact that the microorganisms are directly added in the form of biocapsules in the present invention, high superficial gas velocity is not a necessary condition for forming granular sludge in the present invention. Keeping the dissolved oxygen above 3 mg / L can ensure the aerobic and anaerobic reactions of the biocapsule. The third step of the operation is to stop aeration (oxygen supply) and allow the biocapsule to settle, followed by the fourth step of drainage. In some embodiments, the operation was repeated in a "water inlet, aeration, sedimentation and drainage" mode for a month, during which the biocapsules were observed to go through three stages: (I) intact original biocapsules (within the first week), (II) biocapsules were broken (within the second week), and (III) dense biocapsule fragments (after the second week). After two weeks of operation, the system returned to stability, and the biocapsule fragments with a size of 1 mm and a dense structure still had similar functions to AGS. The removal efficiencies of COD, ammonia nitrogen and total nitrogen can reach 95%, 84% and 80%, respectively.

[0037] Example 1

[0038] Materials and methods:

[0039] Preparation of biocapsules. Sodium alginate (SA) solution and microorganisms (concentrated activated sludge in this example) were mixed in equal volumes. The composition of the mixture varied in the following weight percentages: the ratios of SA and activated sludge were 1 / 0.45 and 1 / 0.9, respectively. The activated sludge was taken from a local sewage treatment plant and concentrated by centrifugation before use. The concentration of the activated sludge was expressed by the mixed liquor suspended solids concentration (MLSS). The mixture was then added dropwise to a CaCl2 solution (4 w / v%). The dropper sizes were 1 and 3 mm. The biocapsules were stored in the CaCl2 solution for another 12-24 hours and then rinsed with water several times before analysis. All biocapsules could be collected within 1 day.

[0040] result:

[0041] Figure 1 The appearance of SA-Ca biocapsules prepared under different conditions is shown. They are all brown spherical, with a size between 2.9-3.6 mm. The sedimentation velocity is greater than 53 m / h.

[0042] Example 2

[0043] Materials and methods:

[0044] The following biocapsules were used as inoculum sludge:

[0045] Mixture: 1% SA + 0.9% MLSS; Drip tip size: 3 mm; Biocapsule size: 3.6 mm.

[0046] After the reactor was inoculated with biocapsules, it was operated in accordance with the SBR mode. The initial MLSS concentration in the reactor was 3-4 g / L. The reactor was operated for one month, and each operation cycle was 4 hours, including 15 minutes of water inlet, 207 minutes of aeration, 3 minutes of sedimentation and 15 minutes of drainage. Artificial synthetic simulated domestic sewage was used as the inlet water, and its composition was 300 mg / L COD, 30 mg / L ammonia nitrogen and 42 mg / L total nitrogen. The volume exchange ratio was 30%-50%. The aeration rate during the reaction was 1.0 cm / s.

[0047] result:

[0048] The biocapsule system achieved complete granulation (i.e., more than 80% of the biomass was larger than 0.2 mm) immediately after inoculation. However, over time, the added biocapsules became unstable and biocapsule breakage was observed. Figure 2As shown, during the first week, the biocapsule remained intact and then began to break. Fragments were observed in the second week. After two weeks, the system was dominated by biocapsule fragments, and these newly formed fragments became stable. The stable biocapsule fragments were 0.8-1.0 mm in size, but still had a high biomass content and a dense microbial structure, with a sedimentation rate of 13m / h. At the end of one month of operation, the COD, NH3-N and total nitrogen concentrations in the effluent were 14.6mg / L, 4.8mg / L and 8.4mg / L, respectively, and the corresponding removal efficiencies were 95%, 84% and 80%, respectively ( Figure 3 ).

[0049] Example 3

[0050] Materials and methods:

[0051] The following biocapsules were used as inoculum sludge:

[0052] Mixture: 1% SA + 0.9% MLSS; Drip tip size: 3 mm; Biocapsule size: 3.6 mm.

[0053] After the reactor was inoculated with biocapsules, it was operated according to the SBR mode. The initial concentration of MLSS in the reactor was 3-4 g / L. The reactor worked for one month, with an operation cycle of 6 hours, including 15 minutes of water inlet, 327 minutes of aeration, 3 minutes of sedimentation and 15 minutes of drainage. The composition of artificial synthetic simulated sewage was 300 mg / L COD, 30 mg / L NH3-N and 42 mg / L total nitrogen. The volume exchange ratio was 30%-50%. The aeration rate during the reaction was 0.5 cm / s.

[0054] result:

[0055] like Figure 4 As shown, a change from large to small size of biocapsules was observed during the operation of the reactor. At the end of one month of operation, the average size of the particles (i.e., biocapsule fragments) in the reactor was 1.0 mm. The sedimentation velocity was 19 m / h. The COD concentration dropped very quickly during operation, and the effluent was always below 50 mg / L. The reactor was started up within two weeks, after which the NH3-N concentration in the effluent remained below 5 mg / L and the total nitrogen concentration was below 20 mg / L. At the end of one month of operation, the removal rates of COD, NH3-N and total nitrogen were 83%, 83% and 52%, respectively.

[0056] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the present invention is not limited thereby. A person skilled in the art may implement the present invention in a variety of variations without departing from the scope and essence of the present invention, such as using a feature of one embodiment to obtain another embodiment. Any modification, equivalent substitution and improvement made within the technical concept of the present invention shall be within the scope of the present invention.

Claims

1. A method for preparing a biocapsule similar to aerobic granular sludge, the method comprising the following steps: (a) preparing a gel solution; (b) mixing the gel solution with microorganisms to form a mixture; (c) adding the mixture dropwise to a crosslinker solution to form a gel network and immobilize the microorganisms therein, forming a biocapsule; and (d) The biocapsules were placed in the crosslinker solution for 12–24 h to further enhance the gel strength and then rinsed with water.

2. The preparation method according to claim 1, wherein the size of the biocapsule is between 2.9 and 3.6 mm, and the sedimentation velocity is greater than 53 m / h.

3. The preparation method according to claim 1, wherein the gel material in step (a) comprises sodium alginate, polyvinyl alcohol or a mixture thereof.

4. The preparation method according to claim 3, wherein the viscosity of the sodium alginate solution is 100-150 cps when the concentration is 1 w / v%, and the degree of polymerization of the polyvinyl alcohol is 1650-1750.

5. The preparation method according to claim 3, wherein the concentration of sodium alginate solution is 1-4 w / v% of the mixture, and the concentration of polyvinyl alcohol is 5-10 w / v% of the mixture.

6. The preparation method according to claim 1, wherein the microorganism in step (b) is concentrated activated sludge or a culture of a bacterial strain, and the suspended solid concentration of the mixture is 15,000-20,000 mg / L.

7. The preparation method according to claim 1, wherein the cross-linking agent solution in step (c) comprises a calcium, magnesium, iron and / or aluminum salt solution, saturated boric acid or a mixture thereof with a concentration of 1-10 w / v%.

8. A method for sewage treatment, comprising the following steps: (i) adding biocapsules into a reactor; (ii) operating the reactor in sequencing batch mode, in, The biocapsule is prepared according to the method according to any one of claims 1-7.

9. The method for treating sewage according to claim 8, wherein the batch reaction operation cycle of step (ii) is 4-6 hours, and each reaction cycle comprises the following steps: (a) static water feeding into the reactor; (b) aeration reaction during which the dissolved oxygen concentration is maintained above 3 mg / L; (c) aeration is stopped and the sludge settling time does not exceed 6 minutes per metre of water depth; and (d) Drainage, the drainage ratio is 30-50%.

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