JP4101348B2 - Biological nitrogen removal method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological nitrogen removal method in which water to be treated containing a nitrogen component is biologically nitrified and denitrified.
[0002]
[Prior art]
Conventionally, a biological nitrification denitrification treatment method has been used as a treatment method for removing nitrogen from wastewater containing a nitrogen component.
[0003]
In such a biological nitrification and denitrification treatment method, when the nitrification tank and the denitrification tank are of a floating type, first, the water to be treated is supplied to the nitrification tank, where it is aerated together with the suspended sludge and aerobic. Perform nitrification under the conditions. Next, while supplying a nitrification liquid with sludge to a denitrification tank, a hydrogen donor is added and denitrification process is performed here under anaerobic conditions. And a denitrification process liquid is supplied to a sedimentation tank, a solid-liquid separation is performed here, supernatant water is discharged | emitted as process water, and a sedimentation sludge is returned to a nitrification tank. A part of the precipitated sludge is discharged out of the system as surplus sludge.
[0004]
The problem with this treatment method is that the growth rate of nitrifying bacteria is slower than that of denitrifying bacteria, so that the nitrifying bacteria cannot be maintained at a high concentration and the load on the nitrifying tank cannot be increased. That is, since a part of the precipitated sludge containing nitrifying bacteria and denitrifying bacteria is discharged as excess sludge, the nitrifying bacteria in the sludge in the treatment system cannot be maintained at a sufficient concentration.
[0005]
As a method for improving this, there is a method in which a precipitation tank is provided after each of the nitrification tank and the denitrification tank. However, this method has a problem that the number of precipitation tanks increases, and that precipitation separation is difficult in the subsequent precipitation tank of the nitrification tank. That is, nitrification alone consisting of nitrifying bacteria makes it difficult for flocs to occur and makes it difficult to separate precipitates.
[0006]
Further, there is an adhesion type method in which a nitrification tank and a denitrification tank are filled with a filler, and sludge is retained as a biofilm. However, nitrifying bacteria are difficult to adhere to the filler, and again sludge cannot be retained at a high concentration in the nitrifying tank. In addition, the pH changes because ammonia is oxidized to nitric acid, but when there is a filler, pH distribution can be made in the nitrification tank at the part near and far from the raw water inlet, and the entire nitrification tank is nitrified. The pH optimum for the fungus cannot be maintained, which adversely affects nitrification. In addition, when calcium is contained in the waste water, scales of calcium compounds (calcium carbonate, hydroxyapatite phosphate, etc.) are likely to occur at high pH parts, which can cause clogging of the filler. There is a problem.
[0007]
Furthermore, an upflow sludge blanket method has been developed as a method for treating nitrate nitrogen. This is a denitrifying bacterium that is agglomerated and agglomerated and held at a high concentration called granule, which is drained mainly containing nitrate nitrogen and a hydrogen donor in an upward flow, and held in the tank. This is a highly efficient denitrification method.
[0008]
In this method, if there is a lot of SS (floating solids) in the wastewater to be treated containing nitrate nitrogen, granule flows out along with SS, or SS precipitates and granule flows out. Or granule is destroyed by SS.
[0009]
[Problems to be solved by the invention]
Thus, various biological nitrogen removal apparatuses have been proposed in the past, but each has advantages and disadvantages, and a sufficiently efficient treatment cannot be performed.
[0010]
This invention is made | formed in view of the said subject, and it aims at providing the biological nitrogen removal method which can remove efficiently the nitrogen component in waste_water | drain.
[0011]
[Means for Solving the Problems]
The present invention provides a sludge floating type nitrification tank that oxidizes water to be treated containing nitrogen components to nitric acid and nitrous acid under aerobic conditions, and a nitrification liquid obtained in this nitrification tank by membrane separation, A biological separator having a desulfurization treatment tank of the upflow sludge blanket type in which the permeated water obtained by the membrane separation apparatus flows in together with the hydrogen donor and denitrifies under anaerobic conditions In the chemical nitrogen removing apparatus, the pH in the nitrification tank is maintained so that the Langeria index of water in the nitrification tank is 0 or less .
[0012]
Thus, in the present invention, the nitrification tank is a sludge floating type. Therefore, the problem based on the occurrence of the pH distribution like the above-described adhesion formula is solved. Next, nitrifying sludge composed of nitrifying bacteria with poor deposition and sludge adhesion to the filler can be efficiently separated by membrane separation of the nitrification treatment liquid. Therefore, by holding this separated sludge in the nitrification tank, the nitrifying bacteria can be kept at a high concentration in the nitrification tank. Furthermore, SS is not contained in the permeated water of membrane separation. For this reason, in an upward flow sludge blanket (USB) type denitrification tank, it is possible to perform the treatment while maintaining the granules in a suitable state. Accordingly, the water to be treated containing nitrogen components can be treated very efficiently. Note that methanol is generally used as the hydrogen donor, but other biodegradable organic substances may be used.
[0013]
It is also preferable to use an immersion membrane as the membrane separation means. The inside of the nitrification tank is aerated, and if an immersion film is disposed here, deposits on the film surface can be removed by aeration from the lower part. Therefore, the amount of permeated water can be stably obtained over a long period in the membrane separation apparatus. If the amount of permeated water has decreased, the membrane may be washed with chemicals (sodium hydroxide, hydrochloric acid, sodium hypochlorite, etc.).
[0014]
Then , the pH in the nitrification tank is maintained so that the Langerier index of water in the nitrification tank is 0 or less. Thereby, the pH in the nitrification tank can be controlled so as not to inhibit the nitrifying bacteria. Moreover, scale generation on the membrane surface of the membrane separator can be effectively prevented.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0016]
“First Embodiment”
FIG. 1 is a block diagram showing the overall configuration of an apparatus used in the method of the first embodiment. Waste water containing nitrogen (mainly ammoniacal nitrogen) flows into the nitrification tank 10. The nitrification tank 10 is supplied with air (oxygen gas or oxygen-enriched air) from its lower part, and the inside of the tank is aerated.
[0017]
A pH sensor 12 is provided to detect the pH of the mixed solution in the nitrification tank 10. The detected value of the pH sensor 12 is supplied to the pH adjuster supply device 14. The pH adjuster supply device 14 controls the supply of an acid or alkali pH adjuster into the nitrification tank 10 based on the supplied pH.
[0018]
An immersion type membrane separation device 16 is provided in the nitrification tank 10. A suction pump 18 is connected to the membrane separation device 16. Then, the suction pump 18 discharges the permeated water that has passed through the membrane, thereby discharging the nitrification water while leaving the sludge in the nitrification tank 10.
[0019]
An upflow sludge blanket type denitrification tank 20 is connected to the suction pump 18. The nitrification water from the suction pump 18 is supplied to the bottom of the denitrification tank 20 after a hydrogen donor (for example, methanol) is added. Then, the supernatant water is discharged from the upper part of the denitrification tank 20 as treated water.
[0020]
In such an apparatus, the inside of the nitrification tank 10 is kept under aerobic conditions by aeration. Nitrogen-containing wastewater is aerated with sludge, so that nitrogen in wastewater such as ammonia is nitrified to nitric acid or nitrous acid by nitrifying bacteria in the sludge. In this system, the sludge in the nitrification tank 10 is maintained in the nitrification tank 10 by the membrane separation device 16 in the tank. Therefore, the sludge concentration in the nitrification tank 10 can be controlled independently, the sludge in the nitrification tank 10 can be maintained at a high concentration, and the load on the nitrification tank 10 can be increased. Moreover, since the nitrification tank is a floating type, generation | occurrence | production of pH distribution in sludge can be prevented and nitrification can be performed effectively. Furthermore, the nitrification sludge in the nitrification tank 10 has poor sedimentation and adhesion, but can be effectively separated using the membrane separation device 16. Therefore, treated water with less SS can be supplied to the denitrification tank 20.
[0021]
In particular, in the present embodiment, an immersion type is used for the membrane separation device 16. Therefore, the membrane surface can be effectively cleaned by aeration in the nitrification tank. Moreover, since nitrifying bacteria with relatively little adhesion form a sludge from which membrane separation is performed, more suitable membrane separation is performed.
[0022]
Furthermore, since a pH adjuster (usually sodium hydroxide or the like) is added by the pH adjuster supply device 14 and the pH in the nitrification tank 10 is maintained at a suitable level, a suitable nitrification treatment can be performed.
[0023]
Here, the pH adjustment in this embodiment is performed so that the Langeria index is 0 or less.
[0024]
The Langeria index (saturation index) is the difference between the actual pH of water and the theoretical pH (pHs, the pH when the calcium carbonate in water is in an equilibrium state where it does not dissolve or precipitate). It is used as a guide. When the index is positive and the absolute value is large, calcium carbonate is more likely to precipitate. If it is zero, it is in an equilibrium relationship, and a negative value indicates that no calcium carbonate film is formed.
[0025]
The Langeria index is obtained from the following formula from the pH of water, the calcium ion concentration, the total alkalinity, and the amount of soluble substances.
[0026]
Langeria index = pH of water-pHs
pHs = 8.313-log [Ca ²⁺ ] -log [A] + S
here,
8.131: Constant calculated from the solubility coefficient of calcium carbonate and the second dissociation constant of carbonic acid [Ca ²⁺ ]: Calcium concentration as Ca ²⁺ , unit mg / L
[A]: Total alkalinity as CaCO ₃ , unit mg / L
S: Correction coefficient obtained by the following equation S = 2√μ / (1 + √μ)
Here, μ = 2.5 × 10 ⁻⁵ Sd, and Sd is a soluble substance concentration (mg / L).
[0027]
Note that the Langeria index varies depending on the temperature. Takeo Sato: Water and drainage, Vol. 19, no. 2, (1977) shows a chart that can easily calculate the Langeria index.
[0028]
By maintaining the pH in the nitrification tank 10 (the pH of the above-mentioned water) so that the Langeria index calculated in this way is 0 or less, the pH in the nitrification tank 10 is always appropriate depending on the alkalinity. Can be kept on things. Furthermore, by maintaining the Langeria index at 0 or less, it is possible to prevent calcium precipitation on the membrane surface of the membrane separation device 16 and to eliminate adverse effects on membrane separation. The concentration of Ca ^{2+ in} the water to be treated may be measured with a calcium ion monitor, but may be a constant if the concentration change is small.
[0029]
As the separation membrane of the membrane separation device 16, an ultrafiltration membrane (UF), a microfiltration membrane (MF), or the like is employed. Examples of the material include polyolefin, cellulose acetate, and ceramic. Further, as the shape of the membrane, a tubular type or a flat membrane type that is resistant to sludge blockage is suitable. Furthermore, chemical cleaning may be performed periodically to prevent a decrease in the filtration flow rate. As cleaning chemicals, sodium hypochlorite, sodium hydroxide, surfactants, enzymes, oxalic acid, hydrochloric acid and the like are employed. This chemical cleaning may be performed while immersed in the nitrification tank 10, but may be performed once after being pulled up. Moreover, although the suction filtration using the suction pump 18 is employ | adopted as the filtration system in the membrane separator 16, it is also possible to employ | adopt the gravity filtration system which filters by gravity.
[0030]
Further, the amount of aerated air in the nitrification tank 10 is a flow rate corresponding to the BOD load (about 20 to 100 Nm ^{3 with} respect to 1 kg-BOD (including oxygen demand for nitrification of nitrogen content)), as well as blocking of the membrane surface. In order to reduce the flow rate, a flow rate for creating an upward stirring flow is required. Intermittent aeration may be performed so that the membrane surface can be cleaned intermittently. The suction pump 18 is preferably a self-contained pump.
[0031]
The denitrification tank 20 of the upflow sludge blanket type is supplied with nitrification water with less SS after membrane separation in an upward flow together with the hydrogen donor. The denitrification tank 20 is only stirred by the inflowing water, and there is almost no oxygen dissolution. For this reason, the inside of the denitrification tank 20 is maintained under anaerobic conditions, and denitrification treatment is performed to oxidize the hydrogen donor using oxygen of nitric acid (and / or nitrous acid). A sludge mass called le is generated. And this granule stays in the lower part of the denitrification tank 20 by dead weight, and denitrification process is performed continuously when the nitrification water to which the hydrogen donor was added passes here. Since granule has a relatively excellent sedimentation property, clear treated water with less SS can be obtained by the denitrification tank 20 of the upward flow sludge blanket type. Moreover, the sludge density | concentration in the denitrification tank 20 can be maintained at a high density | concentration, and an efficient denitrification process can be performed.
[0032]
In addition, the sludge in the nitrification tank 10 and the denitrification tank 20 is appropriately removed from the system as excess sludge. In the present invention, each tank is discharged independently, so that the residence time in the sludge system can be controlled, and nitrifying bacteria are not reduced in the nitrification tank.
[0033]
“Second Embodiment”
FIG. 2 is a block diagram showing the overall configuration of an apparatus used for the method of the second embodiment. In this example, the nitrification solution in the nitrification tank 10 is supplied by a pump 22 to a normal membrane separation device 24 provided separately from the nitrification tank 10. Then, the permeated water of the membrane separation device 24 is once stored in the intermediate tank 26 and then supplied to the denitrification tank 20 by the pump 28, and a part of the concentrated water of the membrane separation device 24 is returned to the nitrification tank 10. The other part is discharged out of the system as surplus sludge.
[0034]
Even in such a configuration, the sludge is effectively separated from the nitrification treatment liquid from the nitrification tank 10 by the membrane separation device 24. Therefore, the sludge concentration in the nitrification tank 10 can be maintained at a high concentration. Further, since pH control is performed based on the Langeria index, it is possible to effectively prevent generation of scale on the film. Furthermore, since the SS flowing into the denitrification tank 20 can be reduced, it is possible to prevent the adverse effect of the inflow SS from occurring in the denitrification tank 20.
[0035]
In addition, as the operation method of the pump 22 to the membrane separation apparatus 24, there are a continuous operation in which the membrane is continuously separated, or an intermittent operation in which the operation and the pause are repeated, and any of them can be adopted. As the pump 22, a pump having a discharge pressure of 5 to 20 kPa is suitable.
[0036]
"Other"
Moreover, the apparatus of this embodiment is suitable for treatment of waste water from a semiconductor device manufacturing process containing a large amount of calcium and ammonia, exhaust gas desulfurization waste water, and the like. That is, in this embodiment, since precipitation of the calcium compound in the nitrification tank 10 can be prevented, there is no adverse effect on the membrane separation device 16. Moreover, since the waste water contains calcium, the amount of the pH adjuster (alkali) added to the nitrification tank 10 can be relatively reduced. Furthermore, since calcium ions are contained in the nitrification treatment liquid, the generation of granules in the denitrification tank 20 is promoted, and the effect of making it easier to maintain the sludge concentration in the denitrification tank 20 is obtained.
[0037]
【Example】
<Example>
A water flow experiment was conducted using the ammonia-containing waste water discharged from a certain semiconductor factory by the processing apparatus described in the above embodiment. The experimental specifications were as follows.
[0038]
Raw water NH ₄ —N concentration: 200 mg / L
Raw water PO ₄ -P concentration: 2 mg / L
Effective volume of nitrification tank: 2m ³
Nitrogen tank dissolved oxygen concentration: 2mg / L
Membrane specifications: Immersion membrane, membrane area 5.6 m ² , material: polyolefin hydrogen donor: 50% methanol hydrogen donor addition concentration: 800 mg BOD / L
Denitrification tank effective volume: 1m ³
The passing water 5~25m ³ / d, in the nitrification tank as the volume loading 0.5~2.5kgN / m ³ / d, was 1.0~5.0kgN / m ³ / d in the denitrification tank. As a result, the maximum removal rate per unit volume in the nitrification tank was about 2 kgN / m ³ / d. In the denitrification tank, it was about 4.5 kgN / m ³ / d.
[0039]
<Comparative example>
The same waste water as in the example was used, a floating type nitrification tank and a denitrification tank were used, a sedimentation basin was installed in the latter stage, and the precipitated sludge was returned to the nitrification tank. The effective volume was the same as in the example.
[0040]
The passing water 0.5 to 10 m ³ / d, in the nitrification tank as the volume loading 0.05~1kgN / m ³ / d, was 0.1~2kgN / m ³ / d in the denitrification tank. As a result, the maximum removal rate per unit volume in the nitrification tank was about 0.5 kgN / m ³ / d. In the denitrification tank, it was about 1.7 kgN / m ³ / d.
[0041]
That is, in the example, the maximum removal rate was 4 times in the nitrification tank and 3 times in the denitrification tank as compared with the comparative example. The maximum removal rate of the denitrification tank was examined by adding nitric acid to the water flowing into the denitrification tank.
[0042]
【The invention's effect】
As described above, according to the present invention, since the nitrification tank is a sludge floating type, the problem based on the occurrence of the distribution of pH in the tank as in the adhesion type is solved. Further, by membrane separation of the nitrification solution, nitrification sludge composed of nitrification bacteria with poor adhesion of sludge to the precipitate and filler can be efficiently separated, and the nitrification bacteria can be kept at a high concentration in the nitrification tank. Furthermore, since the permeated water of the membrane separation does not contain SS, the treatment can be carried out while maintaining the granules in a suitable state in an upward flow sludge blanket type denitrification tank.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an apparatus according to a first embodiment.
FIG. 2 is a block diagram showing an overall configuration of an apparatus according to a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Nitrification tank, 12 pH sensor, 14 pH adjuster supply apparatus, 16, 24 Membrane separation apparatus, 18, 22, 28 Pump, 20 Denitrification tank, 26 Intermediate tank.

Claims (1)

Sludge floating type nitrification tank that oxidizes treated water containing nitrogen component to nitric acid and nitrous acid under aerobic condition, and membrane that removes solid matter by membrane separation of nitrification liquid obtained in this nitrification tank Biological nitrogen removal comprising a separation device and an upflow sludge blanket type denitrification treatment tank in which the permeated water obtained in the membrane separation device flows together with a hydrogen donor and denitrification treatment is performed under anaerobic conditions In the device
A biological nitrogen removal method characterized by maintaining the pH in the nitrification tank so that the Langeria index of water in the nitrification tank is 0 or less .

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