Method for forming nitrification sludge granule

Abstract

To provide a method for forming nitrification sludge granules, which is capable of forming granules useful for a biological treatment of nitrogen-containing wastewater in a short period of time.SOLUTION: A method for forming nitrification sludge granules of the present invention is characterized in that nitrifying bacteria are dispersed in a nitrogen-containing artificial substrate of a predetermined concentration contained in a sealed container, and the nitrogen-containing artificial substrate is nitrified by the nitrifying bacteria under a gravity range of less than 1 G.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for forming nitrifying sludge granules. [Background technology]

[0002] Conventionally, biological treatment of nitrogen-containing wastewater has been known to involve two steps: a process in which ammonia nitrogen is converted to nitrate nitrogen in a nitrification tank, and a process in which the nitrate nitrogen is converted to nitrogen in a nitrification tank.

[0003] In the nitrification tank, ammonia nitrogen in the nitrogen-containing wastewater is converted to nitrate nitrogen by the action of nitrifying bacteria, and the wastewater containing nitrate nitrogen is supplied to the nitrification tank. In the nitrification tank, the nitrate nitrogen in the wastewater is converted to nitrogen by the action of nitrifying bacteria and released into the atmosphere, while the purified wastewater is discharged. However, in the nitrification tank, there is a problem that the nitrification performance is reduced when nitrification sludge containing nitrifying bacteria is discharged together with the wastewater.

[0004] In order to solve the above problems, the use of nitrifying sludge granules has been considered (for example, see Non-Patent Document 1). According to Non-Patent Document 1, it is known that microorganisms self-granulate under certain conditions to form particles called granules, and it is said that these granules have a very high settling property compared to normal activated sludge flocs, and have very good solid-liquid separation. Therefore, it is considered that by making the nitrifying bacteria contained in nitrifying sludge form granules, it becomes possible to settle the granules in the nitrification tank and retain them at a high concentration, and it is possible to construct a wastewater treatment system in which nitrification performance is less likely to decrease.

[0005] As a method for forming the granules, for example, a method is known in which a semi-batch reaction tank is used, and the following steps are repeatedly carried out: an inflow process for inflowing organic matter-containing wastewater containing organic matter; a biological treatment process for biologically treating the target substance in the organic matter-containing wastewater with microbial sludge; a sedimentation process for settling the microbial sludge; and a discharge process for discharging the biologically treated biologically treated water (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-193384 A [Non-patent literature]

[0007] [Non-Patent Document 1] Yoshiaki Hasebe et al. "Nitrogen removal by aerobic granular sludge", Journal of Environmental Biotechnology, Vol. 15, No. 2. 2016, pp. 57-61 Summary of the Invention [Problem to be solved by the invention]

[0008] When using the granules to treat wastewater, it is considered advantageous for the granules to have a particle size of about 0.5 to 3.0 mm in order to facilitate settling of the granules in the nitrification tank and facilitate solid-liquid separation.

[0009] However, the method described in Patent Document 1 has the disadvantage that it takes several months until granules having a desired particle size are formed.

[0010] An object of the present invention is to provide a method for forming nitrifying sludge granules which can eliminate such inconveniences and form granules useful for biological treatment of nitrogen-containing wastewater in a short period of time. [Means for solving the problem]

[0011] In order to achieve this objective, the method for forming nitrifying sludge granules of the present invention is a method for forming nitrifying sludge granules, which is characterized in that nitrifying bacteria are dispersed in a nitrogen-containing artificial substrate of a predetermined concentration contained in a sealed container, and the nitrogen-containing artificial substrate is nitrified by the nitrifying bacteria under a gravity range of less than 1 G.

[0012] According to the method for forming nitrifying sludge granules of the present invention, nitrifying bacteria are dispersed in a nitrogen-containing artificial substrate containing a predetermined concentration of nitrogen, preferably in the range of 0 to 1000 mg / L, and the nitrogen-containing artificial substrate is nitrified by the nitrifying bacteria under a gravity of less than 1 G, preferably in the range of 0.001 to 0.3 G, thereby making it possible to form nitrifying bacteria granules in the range of 0.8 mm or more, for example, in the range of 0.8 to 1.6 mm, in a short period of time, in the range of 12 to 96 hours. [Brief description of the drawings]

[0013] [Figure 1] A photograph showing the change over time in nitrification sludge undergoing nitrification treatment under a gravity of 0.001 G. [Diagram 2] A photograph showing the change over time in nitrification sludge undergoing nitrification treatment under 1G gravity. [Diagram 3] Graph showing the change over time in particle size of granules formed by nitrification sludge subjected to nitrification treatment under gravity of 0.001 G. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0015] In the method for forming nitrifying sludge granules of this embodiment, nitrifying bacteria are dispersed in a nitrogen-containing artificial substrate of a predetermined concentration contained in a sealed container, and the nitrogen-containing artificial substrate is nitrified by the nitrifying bacteria under gravity in the range of less than 1 G, preferably in the range of 0.001 to 0.3 G, for example, 0.001 G. Note that the gravity on Earth is set to 1 G.

[0016] In this embodiment, the sealed container may be any container that is capable of containing and sealing the nitrified sludge and the artificial substrate, but in a laboratory setting, for example, a vial with a screw cap can be used.

[0017] The artificial substrate may contain nitrogen in the range of 0 to 1000 mg / L, for example, 30 mg / L. As such an artificial substrate, for example, ammonium chloride (NH 4 Cl) 57.6 mg / L, ammonium sulfate ((NH 4 ) 2 SO 4 ) 72.7 mg / L, sodium bicarbonate (NaHCO 3 ) 530 mg / L, calcium chloride 29.1 mg / L, sodium chloride 60.6 mg / L, magnesium sulfate heptahydrate (MgSO 4 7H 2 O) 121 mg / L, potassium dihydrogen phosphate (KH 2 PO 4 ) 84.8 mg / L to which pure water is added to make the total concentration 30 mgN / L.

[0018] As the nitrifying bacteria, nitrifying sludge obtained from a sewage treatment facility, a sludge treatment facility, etc. can be used. The nitrifying sludge specifically contains, as the nitrifying bacteria, for example, Nitronmonas, Nitronlobus, Nitrosococcus, Nitronspira, Nitrospira, Nitrobacter, Nitrococcus, Nitrospina, etc.

[0019] The nitrifying sludge and the artificial substrate contained in the sealed container can be subjected to gravity of less than 1 G using a gravity control device (e.g., Gravité (registered trademark) manufactured by Space Bio Laboratories, Inc.). Conventionally, a clinostat is known as a device that can change the direction of gravity by rotation, but the gravity control device can simulate a microgravity environment of less than 1 G, for example, 0.001 G, by rotating a sample 360° around two orthogonal axes and dispersing the gravity vector in the XYZ axis directions.

[0020] In the method for forming nitrifying sludge granules of this embodiment, when the nitrifying bacteria are allowed to nitrify the nitrogen-containing artificial substrate under gravity within the above-mentioned range, the nitrifying bacteria are subjected to a load, which causes them to secrete extracellular polymeric substances (EPS), and the extracellular polymeric substances cause multiple nitrifying bacteria to adhere to and aggregate with each other, thereby forming nitrifying bacteria granules with particle sizes in the range of 0.8 mm or more, for example, 0.8 to 1.6 mm, in a short period of time, such as 12 to 96 hours.

[0021] In the method for forming nitrifying sludge granules in this embodiment, granules are formed using nitrifying bacteria, which are aerobic bacteria. However, anaerobic bacteria may be used instead of aerobic bacteria to form anaerobic granules.

[0022] Next, examples of the present invention and comparative examples will be described. EXAMPLES

[0023] Example 1 In this example, first, nitrified sludge obtained from a sludge treatment facility and ammonium chloride (NH 4 Cl) 57.6 mg / L, ammonium sulfate ((NH 4 ) 2 SO 4 ) 72.7 mg / L, sodium bicarbonate (NaHCO 3) 530 mg / L, calcium chloride 29.1 mg / L, sodium chloride 60.6 mg / L, magnesium sulfate heptahydrate (MgSO 4 7H 2 O) 121 mg / L, potassium dihydrogen phosphate (KH 2 PO 4 An artificial substrate with a composition of 84.8 mg / L of nitrogen per 100 ml was added, and pure water was added to adjust the total volume to 250 mL, the nitrification sludge concentration to 0.25 g-VSS / L, and the nitrogen concentration to 30 mg-N / L. Pure oxygen was then introduced at 1 kgf / cm 2 The sample solution was prepared by aeration at a pressure of 1000 psi for 3 minutes.

[0024] Next, the sample solution was dispensed in 6.5 mL portions into 6 mL screw-capped vials, filled to the brim to prevent air from entering and sealed, and the nitrogen-containing artificial substrate was nitrified by the nitrifying bacteria under a gravity of 0.001 G using the gravity control device. The change over time in the nitrifying sludge in the sample solution contained in the vial is shown in Figure 1.

[0025] The particle size and number of nitrifying bacteria granules formed in the sample solution were measured by image analysis using an image size measurement software (Click measure (free software)). The particle size of the nitrifying bacteria granules measured and the ratio of the number of nitrifying bacteria granules of each particle size to the total number over time are shown in Figure 3.

[0026] Comparative Example 1 In this comparative example, the sample solution prepared in exactly the same manner as in Example 1 was dispensed in 6.5 mL portions into 6 mL screw-capped vials, filled to the brim to prevent air from entering, sealed, and placed on a flat surface at a temperature of 25±2° C., and the nitrogen-containing artificial substrate was allowed to nitrify by the nitrifying bacteria under a gravitational force of 1 G. The change over time in the nitrifying sludge in the sample solution contained in the vial is shown in FIG.

[0027] 1 and 2, it is clear that in Example 1, where nitrification treatment was carried out under a gravity of 0.001 G, granule formation was observed 12 hours after the start of the experiment, and the particle size of the granules gradually increased thereafter, whereas in Example 1, where nitrification treatment was carried out under a gravity of 1 G, no granule formation was observed even 48 hours after the start of the experiment.

[0028] Furthermore, from FIG. 3, it is clear that in Example 1, in which the nitrification treatment was carried out under gravity of 0.001 G, the particle size of the granules increased over time, and the proportion of granules with large particle sizes increased; 48 hours after the start of the experiment, it is clear that 66.4% of the total number of granules had a particle size in the range of 0.8 to 1.6 mm. [Explanation of symbols]

[0029] Unsigned.

Claims

1. A method for forming nitrifying sludge granules, comprising the steps of: A method for forming nitrifying sludge granules, comprising dispersing nitrifying bacteria in a nitrogen-containing artificial substrate of a predetermined concentration contained in a sealed container, and allowing the nitrifying bacteria to nitrify the nitrogen-containing artificial substrate under gravity in the range of less than 1 G.

2. 2. The method for forming nitrifying sludge granules according to claim 1, wherein the nitrification treatment is carried out under a gravity range of 0.001 to 0.3 G.

3. 2. The method for producing nitrifying sludge granules according to claim 1, wherein the nitrification treatment is carried out for a period of time ranging from 12 to 96 hours.

4. 2. The method for forming nitrifying sludge granules according to claim 1, wherein the artificial substrate contains nitrogen in the range of 0 to 1000 mg / L.

5. 2. The method for forming nitrifying sludge granules according to claim 1, wherein the formed granules have a particle size in the range of 0.8 to 1.6 mm.

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