JPH0457400B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention uses, for example, an anaerobic fluidized bed,
The present invention relates to a method for treating wastewater, which is characterized in that nitrate and nitrite nitrogen in wastewater are removed biologically, and at the same time, phosphorus in the wastewater is removed by insolubilizing phosphorus and fixing it on the surface of a fluidized bed. [Prior Art] Various methods have been disclosed for the removal of nitrogen and phosphorus from wastewater, in which denitrification and dephosphorization are performed in separate treatment steps, and none of them have been put to practical use. It has been served to Regarding nitrogen removal, or denitrification, organic nitrogen and ammonia nitrogen are oxidized to nitrate and nitrite nitrogen by nitrifying bacteria (ammonia oxidizing bacteria, nitrite oxidizing bacteria, etc.) under aerobic conditions. Next, it has been common practice to treat wastewater by decomposing these nitrate and nitrite nitrogen into nitrogen under anaerobic conditions by the action of denitrifying bacteria. Furthermore, it is known that anaerobic fluidized bed biological treatment can provide a high nitrogen removal effect under high nitrogen loads. In this process, microbial carriers with small particle diameters are kept in a fluid state under anaerobic conditions and brought into contact with wastewater, thereby forming a microbial film on the surface of each particle, and denitrifying bacteria in this microbial film. Nitrogen treatment in wastewater is carried out by this action. According to this method, the A/V value (microbial membrane area per unit volume) can be about 5 to 20 times higher than that of submerged filter bed or rotating disk type biological treatment. Compared to these biological treatments, the nitrogen load can be several to ten times higher. Regarding the removal of phosphorus, that is, dephosphorization, metal salts such as iron salts, aluminum salts, and calcium salts are added to wastewater and reacted with phosphoric acid in the wastewater to form water-insoluble phosphates, which are then coagulated. Phosphorus is removed by precipitation or coagulation flotation, or by adding calcium salts to wastewater and bringing them into contact with hydroxyapatite, which is calcium phosphate crystals, to remove phosphorus from the wastewater. A crystallization method is used in which calcium phosphate is precipitated and removed. [Problems to be solved by the invention] However, in such conventional denitrification and dephosphorization treatment of wastewater, a method is adopted in which the treated water is dephosphorized after denitrification treatment. Unavoidably, the wastewater treatment process is not only complicated as it is a two-step treatment process of denitrification and dephosphorization, but also requires the installation of separate facilities for each separate treatment, which increases the construction cost. The problem was that the amount of data would become enormous. The object of the present invention was disclosed in order to solve the above-mentioned problems, and it is configured such that denitrification and dephosphorization treatments can be performed at the same time, for example, in a single treatment device, and the same treatment device is used. The present invention provides a wastewater treatment method that can biologically denitrify and dephosphorize simultaneously in a treatment tank. This invention aims to achieve this objective by examining various types of biological carrier particles used in the fluidized bed in microbial treatment using an anaerobic fluidized bed for denitrification. They discovered that by using particles of this type, phosphorus can be removed at the same time as nitrogen, and they aimed to achieve this goal by focusing on this point. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a method in which, for example, biological carrier particles on which denitrifying bacteria are deposited on the surface are maintained in a fluid state by upward flow. In a fluidized bed biological treatment method in which organic wastewater is treated under anaerobic conditions by forming a fluidized bed, the main component of the biological carrier particles is calcium carbonate, and raw water or the fluidized bed is treated with iron salts or aluminum salts. A wastewater treatment method characterized by adding one or more metal salts and further maintaining the pH of the fluidized bed at 8.5 to 9.5 to simultaneously remove nitrogen and phosphorus from organic wastewater. It is. The addition of iron salts or aluminum salts into raw water or the fluidized bed is carried out to improve the removal efficiency of phosphorus by fixing phosphorus on the particle surface as calcium phosphate. Examples of iron salts include: ferric chloride, ferrous sulfate,
Ferric sulfate, etc., and as aluminum salt,
For example, aluminum sulfate, polyaluminum chloride, sodium aluminate, etc. can be used. The reason why the pH of the fluidized bed is maintained within the range of 8.5 to 9.5 is that a higher pH value is preferable for denitrification and dephosphorization, but if the pH is higher than 9.5, the growth rate of denitrification will decrease, or bacteria will It is undesirable because it will die. Also, the more preferable PH is
The experimental results also showed that it was in the range of 9.0 to 9.5. . Specifically, as a microbial carrier for a fluidized bed containing calcium carbonate as a main component, it is effective to use marble, coral fossil, shells, etc., which have been pulverized and adjusted to a size of about 2 mm to about 20 mm. In particular, coral fossils have a porosity of approximately
It is as large as 30% to about 40%, and can exhibit excellent denitrification and dephosphorization effects. [Operation] According to the wastewater treatment method of the present invention having such a configuration, nitrite nitrogen and nitrate nitrogen in wastewater are removed by the action of denitrifying bacteria deposited on the surface of biological carrier particles in the fluidized bed. Decomposed into nitrogen gas.
In addition, phosphorus dissolved in the form of phosphoric acid in wastewater forms calcium phosphate salts on the surfaces of particles mainly composed of calcium carbonate used as biological carriers, and is fixed on the surfaces of particles such as iron salts or aluminum salts. is added, iron and aluminum ions combine with phosphate ions to form poorly soluble iron and aluminum phosphates, which further form complex salts with calcium on the surface of the biological carrier in the fluidized bed. and fixed on the surface of the carrier. A part of the insoluble phosphoric acid compound fixed on the carrier surface is utilized by microorganisms living on the carrier surface and taken into the microorganism body, but the insoluble phosphoric acid compound fixed on the carrier surface is mixed with other carriers in a fluidized bed. They are separated from the surface by the friction and abrasion caused by the collision, and at the same time, they are flowed out into the fluidized bed along with the microbial film that peels off from the carrier surface, and they are transferred to the subsequent treatment process, which is a solid-liquid separation process using settling tanks, flotation tanks, etc. will be removed. [Example] FIG. 1 shows an example of a wastewater treatment apparatus including a fluidized bed for carrying out the wastewater treatment method according to the present invention. A gas blowing port 3 and a raw water supply port 4 are provided at the bottom of the fluidized bed 1, and a still water section 6 and a treated water overflow weir 7 are provided at the top of the fluidized bed 1 to prevent the carrier from flowing out. A pump 5 for recycling a portion of the treated water into the fluidized bed 1 tank in order to ensure the upward flow rate necessary to maintain the microbial carriers 2 in the fluidized bed 1 in a fluidized state.
and a piping system for communicating the pump 5 and the fluidized bed 1. A gas inlet 3 is provided at the bottom of the fluidized bed 1;
Blocked sludge can be cleaned by blowing air or oxygen-free gas through the tank. The treated water containing peeled pieces from the carrier surface containing insoluble phosphoric acid compounds and microorganisms flowing out from the anaerobic fluidized bed 1 is transferred to the aeration tank 8.
The soluble BOD components remaining in the treated water are decomposed by aerobic bacteria, and the sludge flocs are subjected to sedimentation separation, that is, solid-liquid separation, in the sedimentation tank 10. In the diagram,
Reference numeral 9 indicates an air inlet provided at the lower part of the aeration tank 8, and 11 indicates a discharge channel through which treated water from which solids have been removed is discharged from the upper part of the settling tank 10. Example 1 A portion of the treated water flowing out from the overflow weir 7 at the bottom of the fluidized bed 1, which has an upper inner diameter of 200 mm, a lower inner diameter of 60 mm, a conical part with a height of 100 mm, and a straight body part with a height of 1000 mm, is transferred to the lower raw water supply port. An anaerobic fluidized bed 1 having a structure that allows supply from 4 is used. A fluidized bed 1 is filled with 2.5 pieces of crushed coral fossil having a particle size of about 2 meshes to about 8 meshes. 2. Synthetic wastewater shown in Table 1
/hour and fluidized bed overflow water is supplied from the raw water supply port 4 at the bottom of the fluidized bed 1 at a rate of 4/hour. Add caustic soda to the raw water so that the pH of fluidized bed 1 is maintained at 9-9.5. Methyl alcohol is added to raw water in an amount 2.2 times the amount of nitrate nitrogen as a hydrogen donor for denitrifying bacteria. The treated water flowing out of the fluidized bed 1 was introduced into an aeration tank 8 (volume 8) for air aeration, and then flowed into a settling tank 10, and the supernatant water was analyzed for water quality. After confirming that the nitrogen content in the treated water is below 5ppm, add 10mg/ferric chloride as iron to the raw water.
The quality of the treated water was measured by adding 20 mg/, 50 mg/, and 100 mg/, and the results are shown in Table 2.

[Table] Example 2 Table 3 shows the results of changing the PH in the fluidized bed by adding 20 mg of iron in the same treatment process using the same equipment as in Example 1.

[Table] Example 3 Crush oyster shells into a fluidized bed tank and make 2 meshes.
The same equipment as in Example 1 was used, except that 2.5 times the particle size of mesh was filled, and the same treatment was carried out.

[Table] The process was carried out and treatment was carried out by adding 20 mg of iron/ferric chloride. The pH in the treatment tank is adjusted using caustic soda.
Adjust to 9-9.5. The processing results are shown in Table 4. Comparative Example 1 Approximately 2 meshes of anthracite in a fluidized bed tank
Other than filling 2.5 particles with a particle size of about 8 mesh.

【table】

〔Effect of the invention〕

As is clear from the above description, according to the present invention, in the anaerobic fluidized bed biological treatment method for organic wastewater, the main component of the biological carrier particles is calcium carbonate, and iron salts or Adding one or more metal salts selected from aluminum salts,
Furthermore, since we decided to treat organic wastewater by maintaining the pH of the fluidized bed at 8.5 to 9.5, we could biologically treat the nitrogen content in the wastewater using denitrifying bacteria, and at the same time remove the phosphorus content from the wastewater using calcium carbonate, which is a carrier. The wastewater treatment process can be carried out simultaneously in the same fluidized bed tank, which simplifies the wastewater treatment process by requiring only the construction cost of a single tank. The extremely effective effect of being able to do this can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a wastewater treatment apparatus including a fluidized bed for carrying out the wastewater treatment method according to the present invention. 1...Fluidized bed, 2...Microbial carrier, 3...Gas inlet, 4...Raw water supply port, 5...Pump for recycling treated water, 6...Static water section, 7...Overflow weir, 8
... Aeration tank, 9 ... Air inlet, 10 ... Sedimentation tank, 11 ... Outlet channel.

Claims (1)

[Claims] 1. A fluidized bed biological treatment method for treating organic wastewater under anaerobic conditions by forming a fluidized bed in which biological carrier particles are maintained in a fluidized state by upward flow, comprising: The main component is calcium carbonate,
One or more metal salts selected from iron salts or aluminum salts are added to raw water or a fluidized bed, and the pH of the fluidized bed is maintained at 8.5 to 9.5, and nitrogen and phosphorus in organic wastewater are simultaneously removed to produce wastewater. A wastewater treatment method characterized by treating.