JPS6229116B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for simultaneously removing nitrogen and phosphoric acid contained in wastewater. As a means of removing nitrogen contained in wastewater, ammonium ions are oxidized to NO ₂ ^- or NO ₃ ^- by the action of nitrifying bacteria in a nitrification tank, and then denitrifying bacteria are used in a denitrification tank. Due to the action,
Methods are being used to reduce NO ₂ ^- and NO ₃ ^- to N ₂ . On the other hand, as a method for removing phosphoric acid present in wastewater, by adding aluminum salt,
There are methods to precipitate AlPO ₄ and methods to precipitate Ca ₅ (OH) (PO ₄ ) ₃ by adding calcium salt. However, the denitrification and dephosphorization methods have only been carried out separately, and the current situation is that it has not been possible to efficiently process both in the same tank. In other words, when Al ³⁺ is added to the biological treatment process,
The optimal pH for precipitating AlPO ₄ is around 6, while the pH suitable for denitrification is between 7 and 9.
There are no conditions under which both denitrification and dephosphorization can be performed efficiently. Furthermore, when Ca ²⁺ is added to the biological treatment process, the optimal pH for precipitating Ca ₅ (OH) (PO ₄ ) ₃ is 10 or higher, so both denitrification and dephosphorization can be performed efficiently. There are no conditions. The present invention is extremely effective in causing biological denitrification reactions in the presence of calcium phosphate-containing solids.
This method was completed after discovering that the crystallization and removal of phosphoric acid proceeded in parallel effectively. Next, embodiments of the present invention will be described in detail. If necessary, add Ca(OH) ₂ to the effluent of the nitrification process,
Add calcium agents such as CaSO ₄ and CaCl ₂ to remove Ca/
Adjust P (calcium to phosphorus weight ratio) to 2.0 or more. However, if there is already a sufficient amount of calcium ions in the influent water, it is not necessary to add a calcium agent. Furthermore, after supplying an organic carbon source such as methanol as necessary, the solid particles containing calcium phosphate are introduced into a dephosphorization tank which accommodates solid particles and maintains an anaerobic state. The state of the calcium phosphate-containing solid particles in the dephosphorization tank may be a fixed bed, a fluidized bed, or a suspended state. When water is passed through the dephosphorization tank in this manner, denitrification bacteria begin to proliferate in the tank, and a denitrification biofilm is formed on the surface of the solid particles. Then, the denitrification reaction inside the biofilm (near the granular surface) increases 2NO ₃ ^- +5H ₂ →N ₂ +2OH ^- +4H ₂ O PH, creating a favorable environment for the phosphorus removal reaction. Therefore, phosphate ions in the inflow water diffuse to the surface of solid particles in the dephosphorization tank (some of them diffuse inside the biofilm), and a phosphorus removal reaction occurs on the surface of the solid particles.5Ca ²⁺ +OH ^- +3PO ₄ ^{3 -} →Ca ₅ (OH) (PO ₄ ) ₃ is effectively generated. In this case, the denitrification bacteria adhesion medium may include calcium phosphate-containing solid particles such as phosphate rock and bone charcoal.
Alternatively, use is made of particles of sand, activated carbon, etc. on which calcium phosphate is supported. As a medium, sand,
Denitrification methods using activated carbon and plastic particles have been conventionally used, but with this method,
Phosphoric acid is not removed. In other words, in order to efficiently perform denitrification and dephosphorization within a biofilm, it is necessary to support as many denitrifying bacteria as possible on the surface of solid particles and to maintain a high diffusion rate of phosphate ions to the surface of solid particles. In this case, if solid particles containing calcium phosphate are used, the difference between the phosphoric acid concentration in the liquid and the phosphorus concentration (solubility) on the surface of the solid particles acts as a concentration driving force and increases the diffusion rate. According to the present invention, the following important benefits can be obtained, and phosphoric acid and nitrogen in wastewater can be removed in an extremely rational manner. (1) Since denitrification and dephosphorization, which were originally performed separately, can be efficiently performed in the same tank, the installation space of the equipment can be greatly reduced. (2) Utilizes the increase in PH within the biofilm to provide a site for phosphorus removal reactions on the surface of solid particles.
Unlike the conventional lime flocculation and precipitation method, an alkaline agent to raise the pH is not required, or a large amount can be saved. (3) The pH within the biofilm is maintained at 8 to 9, and special pH control can be omitted. (4) Normally, when treating phosphoric acid in a liquid, a large amount of insolubilized solid phosphoric acid is generated as sludge, and the treatment and disposal of this becomes a problem, but in the present invention, phosphoric acid is There is no generation of sludge. (5) When denitrification is performed by attaching biofilm to solid particles, the density of the particles decreases due to excessive biofilm attachment, which often causes the problem of the particles flowing out of the device. However, in the present invention, The precipitation of phosphorus compounds on solid particles suppresses the decrease in density due to the adhesion of biological drugs. (6) Conventionally, a method is known in which the biological denitrification process is carried out in the presence of a granular medium, while a method in which phosphoric acid is removed by contacting with a granular solid containing calcium phosphate is also known, but each method is performed separately. The current situation is that the concept of rationally combining both processes has not yet been reached. In the present invention, denitrification and dephosphorization are performed in the same tank, but since denitrification occurs within the biofilm and dephosphorization occurs on the surface of the carrier, both processes are efficiently performed in parallel. It is done. Example 1 Raw water was prepared by adding sodium nitrate to activated sludge treated water of groundwater from a certain group containing 3 to 4 mg of phosphorus and 30 mg of calcium to make the nitrate nitrogen content 30 mg/. Methanol was added to this raw water in an amount approximately three times the amount of NO ₃ -N in the raw water, and CaCl ₂ was added at 50%
200mm inner diameter filled with North African phosphate rock with a particle size of about 0.4mm to a bed height of 2m.
Water was passed through the column having a height of 400 mm in a downward flow at a flow rate of 5 to 10 m/h in a sealed state with air blocked. For one week after the water flow started, biofilm did not adhere to the surface of the phosphate rock, and neither nitrogen nor phosphorus was sufficiently removed, but after two weeks, biological drugs began to adhere to it.
NO ₃ -N is below 1mg/, phosphorus concentration is 0.7mg/
Removed below. In parallel with this, a similar test was conducted using a column filled with sand of the same particle size, but NO ₃ -N was removed to less than 1 mg/day when biofilm was attached to the sand surface, but phosphorus At a concentration of 2 to 3 mg/ml, not much was removed. These results are summarized in the following table.

[Table] Example 2 Secondary treated water from sewage treatment plant A with NO ₃ -N 10 mg/, phosphorus concentration 1-2 mg/, and calcium 50 mg/ was used as raw water, and after adding methanol in an amount approximately three times that of NO ₃ -N, Water was passed through a column packed with the same phosphate rock as in Example 1 under the same conditions. In this way, denitrification and dephosphorization progress as a biofilm adheres to the surface of the phosphate rock, and after two weeks, the NO ₃ -N level of the treated water is 1
mg/or less, and the phosphorus concentration was maintained at less than 0.7 mg/. The results are summarized in the following table.

[Table] Example 3 To the same raw water as in Example 1, methanol was added in an amount approximately three times the amount of NO ₃ -N, and CaCl ₂ was added to 50 mg/day, and then a layer of North African phosphate rock with a particle size of 0.3 mm was added. Water was passed through a column with an inner diameter of 200 mm and a height of 4300 mm packed to a height of 1 m in an upward flow at a flow rate of 20 mg/h to bring the phosphate rock into a fluidized suspended state. The quality of the treated water about two weeks after the start of water flow was good, with NO ₃ -N and phosphorus concentrations of 1 mg/or less, as shown in the table below.

[Table] Example 4 To the same raw water as in Example 1, methanol was added in an amount approximately three times the amount of NO ₃ -N, and 70 mg of CaSO ₄ was added, and the mixture was fed into a stirring tank with a volume of 90 m/min at a rate of 3 times per minute ( residence time approximately 30 minutes). Fine grains of phosphate rock from North Africa with a grain size of 0.1 mm were added to the tank at a rate of 0.9
Stirred at 100 rpm. Approximately two weeks after the start of water flow, biofilms began to adhere to the surface of the phosphate rock, and the quality of the treated water was as shown in the table below, with both NO ₃ -N and phosphorus concentrations below 1 mg/.

【table】

Claims (1)

[Scope of Claims] 1. Denitrification of wastewater, which is characterized in that wastewater containing nitrogen and phosphoric acid in the nitrate and nitrite forms is brought into contact with solid particles containing calcium phosphate in the presence of calcium ions in an anaerobic state. , dephosphorization method. 2. The method for denitrifying and dephosphorizing wastewater according to claim 1, wherein a calcium agent is added as necessary. 3. The method for denitrifying and dephosphorizing wastewater according to claim 1 or 2, wherein an organic carbon source is added as necessary.