JPS6345275B2 - - Google Patents

Description

[Detailed description of the invention]

The purpose of the present invention is to provide the most rational method for removing phosphorus and ammonia nitrogen.
In particular, this removal process is suitable for advanced treatment of secondary treated sewage water. Conventionally, it is known that biological nitrification and denitrification of ammonia nitrogen is carried out using a bed packed with granular filter media.
Additionally, a method for removing phosphorus using granular solids containing calcium phosphate is also known, but these were only carried out separately as unrelated processes, and we focused on the organic relationship between the two processes. At present, the concept of rational combination has not been reached at all. The present invention was completed based on the discovery that when a biological denitrification reaction occurs in the presence of a calcium phosphate-containing solid, phosphorus removal proceeds in parallel extremely effectively. That is, the present invention
A first step of carrying out at least a nitrification reaction by introducing wastewater containing phosphorus and ammonia nitrogen into a granular solid packed bed to which nitrifying bacteria are attached and allowing it to flow through in an aerobic atmosphere; The effluent was treated in the presence of calcium ions and organic carbon sources.
This is a method for removing phosphorus and nitrogen, which comprises a second step of contacting a solid containing calcium phosphate under anaerobic conditions. Next, one embodiment of the present invention will be described with reference to FIG. 1. Wastewater 1 containing ammonia nitrogen and phosphorus, such as activated sludge treated water of sewage, is made of granular solids such as sand, anthracite, and activated carbon. 2 is made to flow into a filling tank 3 which uses it as a filling material. A diffuser pipe 4 is provided at the bottom of the filling tank 3, and an oxygen-containing gas 5 such as air is supplied into the filling tank 3, so that the inside of the tank is maintained under aerobic conditions. As the inflow water flows through the packed tank 3 filled with granular solids 2, SS is removed, and at the same time, ammonia nitrogen is oxidized to nitrate due to the biological action of nitrifying bacteria that have grown in the packed bed. It becomes an ion. A typical reaction formula for the nitrification reaction by nitrifying bacteria is shown below. NH ⁺ ₄ +20 ₂ +OH ^- +HCO ₃ ^- →NO ₃ ^- +3H ₂ O+
CO ₂ ...(1) In the nitrification reaction, as shown in equation (1),
Bicarbonate ions (HCO ₃ ⁻ ) are also consumed to produce carbon dioxide gas, which is entrained in the bubbles of the oxygen-containing gas 5 supplied to the filling tank 3 and dissipated into the atmosphere. Also, in the nitrification reaction, hydroxide ions (OH ^- )
Since ammonia nitrogen is also consumed at the same time, if the content of ammonia nitrogen is large, it is necessary to add alkaline agent 1' to the liquid. As the alkali agent 1', caustic soda (NaOH), soda carbonate (Na ₂ CO ₃ ), etc. are usually used, or slaked lime [Ca(OH) ₂ ], quicklime (CaO), etc.
The use of a calcium-containing alkaline agent such as the following is effective and also serves the purpose of replenishing calcium ions required in the next phosphorus removal step. The effluent water from the filling tank 3 flows into the denitrification and dephosphorization tank 8, and anaerobically contacts the calcium phosphate-containing solid 9 filled in the tank, thereby removing nitrate ions (NO ₃ ^- ), nitrite ion (NO ₂ ^- )
and removal of phosphate ions (PO ₄ ^3- ). An organic carbon source 7 (hydrogen donor) and calcium agent 6 are added to the inflow water as necessary. The outflow water from the filling tank 3, which becomes the inflow water to the denitrification and dephosphorization tank 8, is
is removed, and ammonia nitrogen (NH ₄ −
N) also decreases and changes to nitrate nitrogen (NO ₃ -N), and carbonic substances decrease with the nitrification reaction. Therefore, an organic carbon source 7 and a calcium agent 6 are added to the outflow water from the filling tank 3, and a denitrification and dephosphorization tank 8 is added.
When an anaerobic condition is maintained in the tank, denitrifying bacteria that reduce nitrate ions (NO ₃ ^- ) to nitrogen gas (N ₂ ) will grow on the surface of the calcium phosphate-containing solid 9 filled in the tank, and the denitrifying bacteria will grow. A microbial film is formed. Along with the formation of this microbial film, a denitrification reaction progresses inside the biofilm, and nitrate ions (NO ₃ ⁻ ) in the liquid are reduced and removed to nitrogen gas (N ² ).
This reaction is shown in the following formula. 2NO ₃ ^- +5H ₂ →N ₂ ↑+2OH ^- +4H ₂ O ……(2) In this reaction, as shown in equation (2), hydroxyl ions are generated as denitrification occurs, and therefore hydroxide ions are generated inside the biofilm. , the pH will be higher than in the liquid. Along with this, the solubility of the calcium phosphate salt on the surface of the calcium phosphate-containing solid decreases. Therefore, the phosphate ions and calcium ions in the liquid diffuse through the microbial membrane on the surface of the calcium phosphate-containing solid 9 in the denitrification/dephosphorization tank 8 to the internal surface of the calcium phosphate-containing solid, and on this surface, phosphate ions are removed. Ions move from the liquid phase to the solid phase, and the phosphate ions in the liquid decrease. This precipitation reaction of phosphate ions is shown in the following equation. 5Ca ²⁺ +OH ^- +3PO ^3- ₄ →Ca ₅ (OH) (PO ₄ ) ₃
...(3) Along with this phosphorus removal reaction, hydroxide ions (OH ^- ) are consumed, so the denitrification reaction in equation (2) above also proceeds in the right direction, and the denitrification reaction is also promoted. Therefore, denitrification and dephosphorization are effectively carried out in the present invention. The amount of calcium that must be present in the water flowing into the denitrification/dephosphorization tank 8 of the present invention must be 0.7 times or more the phosphate ion concentration in the liquid. Therefore, if there is not enough calcium in the liquid, it is necessary to add a calcium agent. The amount of calcium added is at least 0.7 times the phosphorus concentration of the liquid, as shown in the previous equation (3), and the types of calcium agents added are calcium chloride (CaCl ₂ ), calcium nitrate (CaSO ₄ ), or slaked lime [Ca( Any water-soluble material such as OH) ₂ ] may be used. Of these, Ca(OH) ₂
It is also good to use it in combination with an acid so as not to raise the pH too much.
Further, it is more advantageous to use a calcium-containing alkali agent such as quicklime (CaO) or slaked lime [Ca(OH) ₂ ] as the alkaline agent added to the inflow water of the filling tank 3. The alkaline agent may be added directly into the filling tank 3 or within a pipe flowing into the filling bed 3. The calcium agent may be added directly into the denitrification/dephosphorization tank 8 or into the inflow pipe. As mentioned above, a calcium-containing alkaline agent may be added to the water flowing into the filling tank 3 as an alkaline agent. The organic carbon source 7 (hydrogen donor) may be added directly into the denitrification/dephosphorization tank 8 or in the inflow pipe, and the amount of addition is the hydrogen donor per mol of NO ₃ -N.
5.0 mol, for methanol _CH3OH / _NO3 -N
=2.0 to 3.0 [g/g]. In the above description of the filling tank 3, the inflow water was passed in a downward flow, but it may be passed in an upward flow as long as SS can be removed, that is, as long as there is no leakage of SS due to fluidization of the filling. In addition, the inflow water in the denitrification/dephosphorization tank 8,
The method of contact with the calcium phosphate-containing solid 9 may be an upward flow or a downward flow. Further, the calcium phosphate-containing solid 9 may be in the form of granules or plates, and its type may be minerals containing calcium phosphate such as phosphate rock or bone char, or it may be a solid that does not contain calcium phosphate and supports calcium phosphate or a substance containing it. remains unchanged. The gist of the present invention is that when a biological denitrification reaction occurs in the presence of a calcium phosphate-containing solid, phosphorus and nitrogen removal proceed in parallel extremely efficiently, accelerating each reaction. In the first step, ammonia nitrogen (NH ₄ -N) and SS are removed, in the second step denitrification and dephosphorization are performed, and in the second step, calcium ions and The presence of an organic carbon source is essential, and the great effects were achieved by carefully selecting the operating conditions. In other words, in the first step, along with the nitrification reaction,
SS removal and bicarbonate ion removal occur simultaneously. Removal of SS suppresses clogging in the second process,
Removal of bicarbonate also has the effect of preventing calcium ions from reacting and producing calcium carbonate, thereby preventing calcium from being consumed. In the second step, by performing the denitrification and dephosphorization processes in the same tank, the hydroxide ions consumed in the dephosphorization process as shown in equation (3) are converted to the denitrification reaction shown in equation (2). and can accelerate each other's reactions. According to the present invention, the following important benefits can be obtained, and phosphorus and nitrogen can be removed from wastewater in an extremely rational manner. (1) An example of the conventional treatment process is shown in Figures 2 and 3.
An example of the processing steps of the present invention is shown in FIG. Second
The figure shows biological nitrification using granular media followed by granular media denitrification treatment, but phosphorus is not completely removed in this process. Furthermore, FIG. 3 shows that after the processing steps in FIG.
A dephosphorization step is installed in which the dephosphorization step is brought into contact with a calcium phosphate-containing solid, but here a sand filtration step is required between the denitrification step and the dephosphorization step. Also, a large amount of alkaline agent was required to increase the pH of the water flowing into the dephosphorization process. In the present invention, as shown in FIG. 4, nitrification and SS removal are performed in the first step, and denitrification and dephosphorization can be performed simultaneously in the second step, so the equipment is simple and the amount of alkaline agents can be saved. Furthermore, when the present invention is applied to the treatment process shown in Figure 5, the organic matter in the wastewater can be used as the organic carbon source in the first denitrification process, and the alkali produced in the first denitrification process can be used as the alkali in the nitrification process. Alkaline sources and organic carbon sources can be further saved. (2) In addition, in the method of removing phosphorus by bringing wastewater containing phosphate ions into contact with a solid containing calcium phosphate, increasing the pH of the liquid to 8 to 9 by adding an alkaline agent etc. increases the efficiency of phosphorus removal. However, in the present invention, the pH of the wastewater is 6 to 7.
However, when a denitrifying biofilm is attached, the pH of the calcium phosphate-containing solid surface is adjusted to 8 to 9, so phosphorus is efficiently removed. (3) When treating phosphoric acid in normal liquid, a large amount of insolubilized solid phosphoric acid is produced as sludge.
Treatment and disposal of this is a problem, but in the present invention, phosphorus is deposited on the solid surface, so no sludge is generated. Furthermore, since a microbial film of denitrifying bacteria adheres to the surface of the calcium phosphate-containing solid and forms a cushion, even if the calcium phosphate-containing solids rub against each other, the precipitated phosphorus compounds will peel off and flow out of the system. There isn't. (4) When denitrification is performed by attaching a biofilm to a solid, the density of the particles decreases due to excessive biofilm attachment, which often causes the problem of the particles flowing out of the device. By precipitating a phosphorus compound in a solid state, the decrease in density due to biofilm adhesion is suppressed. The benefits obtained by the present invention as described above can be summarized as follows. (1) The processing process can be simplified. That is, dephosphorization and denitrification are performed in the same tank, and each reaction accelerates each other, so the time required for the treatment can be shortened. (2) There is no need to adjust the pH of the influent water in the dephosphorization and denitrification process. (3) Since the insolubilized phosphorus compound precipitates on the calcium phosphate-containing solid and does not peel off, no sludge is generated during the dephosphorization process. (4) Trouble with carrier outflow due to excessive biofilm adhesion can be suppressed. Next, examples will be shown. Example 1 Denitrification and dephosphorization treatments were performed using secondary treated water from a small sewage treatment plant. The processing steps are shown in FIG. After adding slaked lime 40mg/ to raw water, 1mm
Water was flowed downward at a LV of 60 m/day into a column with a diameter of 400 mm and a height of 3000 mm filled with 2 m of sand. Air was supplied from the bottom of the column to 1/2 of the raw water flow rate. After adding methanol in an amount three times the amount of NO ₃ -N to the effluent water, the dephosphorization tank was filled with 0.4 mm of North African phosphate rock for 2 m, and the top was sealed to create a dephosphorization tank with a diameter of 380 mm and a height of 3000 mm.
Water was flowing downward at a LV of 5m/hour to 6m/hour. Table 1 shows the quality of the raw water and the quality of the treated water after biofilm is attached to the process and a steady state has been reached.

[Table] Example 2 In Example 1, 40mg/NaOH was added to the solution in which the calcium concentration of the raw water was adjusted to 0mg/
After adding methanol and passing water through the nitrification process, calcium chloride was added to the effluent water at the same time as methanol, and the water was passed through the dephosphorization process. The relationship between the calcium concentration of the inflow water during the dephosphorization process and the phosphorus concentration of the treated water was determined by varying the amount of calcium chloride added and is shown in FIG. Without the addition of calcium ions, phosphorus was hardly treated at 1.8 mg per liter, but we decided to increase the amount of calcium ions in the inflow to the dephosphorization tank to more than twice that of phosphorus (0.7 times that of phosphate ions). As a result, the phosphorus concentration in the treated water was below 1.0mg/. Example 3 Treated water amount 500m ³ / for secondary treated urban sewage water
Denitrification and dephosphorization treatments were carried out within days. Diameter 2400mm height filled with 1m of anthracite 2mm thick after adding 40mg/NaOH to raw water
Water was passed through the 6000 mm column at a LV of approximately 60 m/day. Air was supplied from the bottom of the column at an amount 1.5 times the flow rate of raw water. Furthermore, after adding methanol three times the amount of NO ₃ -N to the effluent water, 2 m ³ of 0.3 mm phosphate rock from North Africa was filled, and the top was sealed to form a 1000 mm diameter container.
Water was passed through the 4300 mm column in an upward flow at a water flow rate of 20 m/hour. The phosphate rock was suspended in a fluidized bed. After the water flow started, biofilms started to adhere to the solid particles in the column, and the quality of the raw water and treated water after reaching a steady state is shown in Table 2.

[Table] Example 4 The nitrified water of Example 1 was collected at 3 m ³ /day,
After adding 3 times the amount of methanol as NO ₃ -N, honeycomb of PVC board (thickness 0.3 mm, distance across flats 10 mm) 200
Water was sprinkled from the top of the column, which was packed with 400 mm in diameter and 2000 m in height, with a sealed top, using a distributor, and water was passed through the column at a water flow rate of 1.0 m/h. In parallel, a PVC honeycomb was prepared using an alkaline solution of potassium hydrogen phosphate (50 mg phosphorus/, PH 8.5) and an alkaline solution of calcium chloride (Ca 200 mg/, PH 8.5).
8.5) and water was passed under the same conditions through a column filled with artificially precipitated calcium phosphate crystals on the honeycomb surface.
The processing results are shown in Table 3. With normal honeycomb, denitrification occurred but almost no phosphorus was removed, but with honeycomb loaded with calcium phosphate, the treated water had a phosphorus concentration of 0.8 to 1.2 mg/, and good water quality was obtained.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1...An explanatory diagram showing one embodiment of the present invention,
Figures 2 and 3...Explanatory diagram of the process of the conventional method, Figure 4...
An explanatory diagram of the process of the present invention, Fig. 5. An explanatory diagram of another process of the present invention, Fig. 6. Relationship between the amount of calcium added and the phosphorus concentration of treated water in the dephosphorization process. 1... Wastewater, 2... Granular solid, 3... Filling tank,
4... Diffuser pipe, 5... Oxygen-containing gas, 1'... Alkaline agent, 6... Calcium agent, 7... Organic carbon source, 8... Dephosphorization tank, 9... Calcium phosphate-containing solid.

Claims (1)

[Claims] 1. By introducing wastewater containing phosphorus and ammonia nitrogen into a granular solid packed bed to which nitrifying bacteria are attached, and allowing it to flow through in an aerobic atmosphere,
Phosphorus, characterized in that it consists of a first step of at least carrying out a nitrification reaction, and a second step of contacting the effluent of the step with a calcium phosphate-containing solid under anaerobic conditions in the presence of calcium ions and an organic carbon source. How to remove nitrogen. 2. The method according to claim 1, wherein an alkaline agent is added to the first step inflow water. 3. The method according to claim 2, wherein the alkaline agent is a calcium-containing alkaline agent. 4. The method according to claim 1 or 2, wherein a calcium agent is added to the second step inflow water. 5. The method according to claim 1, 2, 3 or 4, wherein the amount of calcium ions present in the liquid is 0.7 times or more the concentration of phosphate ions in the liquid.