JP5592677B2 - Biological nitrogen treatment method of ammonia containing wastewater - Google Patents

Description

  The present invention relates to a water treatment method for efficiently removing ammonia nitrogen contained in ammonia-containing wastewater.

  An ammonia stripping method (Non-patent Document 1, p412) is used as a method for removing ammonia in wastewater containing ammoniacal nitrogen.

  Ammonia stripping method uses slaked lime or sodium hydroxide to raise the pH of wastewater, adjust the water temperature as necessary to increase the proportion of free ammonia in the wastewater, and then fill the wastewater in various ways In this method, water is sprinkled from the upper part of the stripping tower filled with the material, and a large amount of air is blown from the lower part so that free ammonia in the wastewater is diffused into the air. The ratio of the amount of wastewater to be treated and the amount of air to be blown (hereinafter referred to as “gas-liquid ratio”) is an important factor affecting the ammonia removal rate, and is usually several thousand times higher. .

  However, the ammonia stripping method has a problem that the running cost is high. In order to increase the removal rate of ammonia, it is necessary to considerably increase the water temperature and pH. Therefore, it is not a good idea to remove nitrogen in wastewater containing ammonia by the ammonia stripping method alone. Further, the ammonia stripping method has a problem that it is necessary to treat the ammonia gas to be diffused. As this processing method, there are methods such as recovery, combustion, catalytic combustion, etc. as ammonium sulfate after using ammonia water. However, both methods cause further increase in equipment cost and running cost.

  On the other hand, biological nitrification-denitrogenation methods using microorganisms (Non-patent Document 1, p413 to 416) are widely used for sewage treatment and the like. Biological nitrification and denitrification methods using microorganisms include biological oxidation by aerobic autotrophic bacteria (nitrifying bacteria such as nitrozomonas and nitrobacter) and biological by facultative anaerobic heterotrophic bacteria (such as Pseudomonas). Made of a combination of reductions. This principle is as follows.

  First, the nitrification step is carried out in an aerobic tank, and consists of a two-stage reaction represented by the following reaction formulas (1) and (2), and the types of nitrifying bacteria involved are different.

2NH ₄ ⁺ + 3O ₂ → 2NO ₂ ⁻ + 2H ₂ O + 4H ⁺ (1)
2NO ₂ ⁻ + O ₂ → 2NO ₃ ⁻ (2)

  The reaction shown in the formula (1) is brought about by an ammonia oxidizing bacterium (nitrite) having nitrozomonas as a representative species, and the reaction shown in the formula (2) is a nitrite oxidizing bacterium (nitrifying) having a nitrobacter as a representative species. Caused by fungi).

Next, the denitrification step is performed in an anaerobic tank, and the object to be treated is reduced according to the reaction formulas shown in the following formulas (3) and (4) under anaerobic conditions, and nitrogen oxide gas (N ₂ O) or nitrogen gas (N ₂ ) and diffused into the atmosphere.

2NO ₂ ⁻ +6 (H) → N ₂ + 2H ₂ O + 2OH ⁻ (3)
2NO ₃ ⁻ +10 (H) → N ₂ + 4H ₂ O + 2OH ⁻ (4)

  This denitrogenation reaction requires a hydrogen donor, and organic substances are usually used as the hydrogen donor. In municipal sewage, organic matter in sewage (BOD (biochemical oxygen demand) or COD (chemical oxygen demand) is displayed) is used as it is, and in wastewater that does not contain organic matter, methanol etc. It is often added from.

  By the way, bacteria that perform a nitrification reaction are susceptible to inhibition, and substances that suppress the nitrification reaction have been investigated relatively widely (for example, Non-Patent Document 2, Patent Document 1, and Patent Document 2).

  According to this, for example, phenol is reported to be reduced by 75% in the nitrification rate per unit microorganism when only 5.6 mg / l is present. In Patent Document 2, a bioreactor is used in which phenol is removed by phenol-degrading bacteria and then reacted with ammonia-oxidizing bacteria.

Nitrite-oxidizing bacteria, typically nitrobacter, are said to be susceptible to this inhibition when the concentration of ammoniacal nitrogen in the wastewater increases and the concentration of free ammonia (NH ₃ ) increases (non-patented). Reference 3, p298). In particular, if the pH becomes too high, the proportion of free ammonia increases, so that nitrite-oxidizing bacteria are likely to be inhibited, and nitrite tends to accumulate. In such a case, the nitrification reaction tends to stop in the reaction formula (1), and nitrite nitrogen tends to accumulate in water. In urban sewage (ammonia nitrogen concentration: 50 mg / l or less), such a phenomenon hardly occurs. However, nitrite nitrogen tends to accumulate in wastewater from factories and the like with high ammonia nitrogen concentration. Since nitrous acid is measured as COD, when nitrogen removal is not necessary, nitrification suppression operation is performed so that the reaction of the reaction formula (1) does not occur.

  In addition to the ammonia nitrogen concentration in the wastewater, dissolved oxygen (DO) (for example, Non-Patent Document 4), pH (for example, Non-Patent Document 5), water temperature (for example, Non-Patent Document 6), thiosulfuric acid, sulfurous acid, It has been known that sulfur compounds such as thiocyan (for example, Patent Document 3) inhibit nitrite-oxidizing bacteria and easily accumulate nitrite in water.

  Thus, in the biological nitrification-denitrogenation method, various conditions that inhibit the reaction of microorganisms are known, but when nitrogen removal is necessary, a method of conversely utilizing this characteristic is also conceivable. In particular, in the nitrification process, the nitrite-oxidizing bacteria are operated under the condition of inhibiting the activity, and as shown in the above formula (1), ammonia nitrogen is stopped by oxidation to nitrite, and the above formula (3) As shown in the figure, it is conceivable to perform denitrification from the nitrous acid.

  This nitrous acid generation-nitrite denitrification method (formula (1) + (3)) is compared with nitric acid formation-nitrate denitrification method (formula (1) + (2) formula + (4)), There is an advantage that the required oxygen amount in the nitrification process is 75% and the required COD amount is about 60% (Patent Documents 4 and 3).

  Furthermore, an anaerobic ammonia oxidation (anammox) reaction in which denitrification reaction is performed under anaerobic conditions using nitrous acid accumulated by the above formula (1) as an electron acceptor and ammonia in the influent wastewater as an electron donor has recently been put into practical use. It is expressed as (5). (For example, Non-Patent Document 7)

NH ₄ ⁺ +1.32 NO ₂ ⁻ +0.066 HCO ₃ ⁻ + 0.13H ⁺
→ 1.02N ₂ + 0.26NO ₃ ⁻ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O
... (5)

  This anaerobic ammonia oxidation reaction is inexpensive because it does not require COD, and since nitrous acid does not flow into the treated water, there is an advantage that the increase in COD of the treated water can be suppressed.

JP-A-8-141552 JP 2007-160236 A JP-A-2005-211832 JP 2004-230338 A

Water treatment management manual, Maruzen, 1998 Historical considerations of biological denitrification, water and wastewater, Vol. 13, no. 11, P1362-1374, 1974 Water treatment engineering (2nd edition), Gihodo Publishing, 1990 Biodegradation, (2008) 19: P303-312. Rev Environ Sci Biotechnol (2007) 6: P285-313 Process Biochemistry, 43 (2008): P154-160 Appl. Microbiol. Biotechnol. , (1998) 50, P589-596.

  Thus, in the treatment of wastewater containing ammoniacal nitrogen, the use of nitrous acid generation-nitrous acid denitrification method or anaerobic ammonia oxidation method can reduce the amount of oxygen and organic matter (COD) required for the treatment. It is advantageous. However, in order to carry out these methods, it is important to control the production of nitric acid in the nitrification process so that nitrous acid is stably produced. Since there are many conditions that inhibit the activity of nitrate oxidizing bacteria, there is a problem that the production of nitric acid cannot be controlled and nitrogen in wastewater cannot be removed efficiently.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to optimize the production of nitric acid to reduce nitrogen in wastewater in wastewater containing ammonia nitrogen. It is an object of the present invention to provide a biological nitrogen treatment method for ammonia-containing wastewater that can be efficiently removed.

  In order to solve the above-mentioned problems, the present inventors have conducted various studies on a method for more stably and efficiently treating wastewater containing ammonia nitrogen, and as a result, it has been demonstrated that it is active against ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. When inhibition is applied, the time required for the recovery of activity differs between ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, and nitrite is controlled by optimally controlling the method of providing activity-inhibiting conditions and sludge retention time. Compared with oxidizing bacteria, it can promote the growth (recovery of activity) of ammonia oxidizing bacteria and succeeded in controlling the production of nitric acid.

The gist of the present invention is the following (1) to (5).
(1) After performing nitrification and denitrification processes on ammonia-containing wastewater using the main reactor, the treated water and activated sludge are separated in the final sedimentation basin, and the activated sludge is returned to the main reactor as return sludge. In the biological treatment method of the ammonia-containing wastewater to be returned, a part of the activated sludge is taken out from the main reactor into another reaction vessel A, and the part of the removed activated sludge is converted into nitrite oxidizing bacteria. After adding a substance that inhibits activity to a predetermined concentration, it is returned to the main reactor, and the flow rate Qs _{1 of the} activated sludge taken out to the other reaction vessel A is SRT (Solid Retention Time) A biological nitrogen treatment method for ammonia-containing wastewater, characterized in that it is set so as to fall within a range of values calculated by formula (1).
1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₁ / Q) / T} (1)
However, μ ₁ : Specific growth rate of ammonia oxidizing bacteria (1 / day), μ ₂ : Specific growth rate of nitrite oxidizing bacteria (1 / day), Qs ₁ : Flow rate taken out from main reactor to another reaction vessel A ^{(m 3 / day), Q} : amount of waste water flowing into the main reactor ^{(m 3 / day), T} : Ri reaction time (day) der the main reactor, [1 / {mu in the formula (1) ₂ − (Qs ₁ / Q) / T} −1 / μ ₁ ]> 0 .
(2) After performing the nitrification process and denitrification process on the ammonia-containing wastewater using the main reactor, the treated water and the activated sludge are separated in the final sedimentation basin, and the activated sludge is returned to the main reactor as the returned sludge. In the biological treatment method of the ammonia-containing wastewater to be returned, a part of the returned sludge is taken out in another reaction vessel B, and the nitrite oxidizing bacteria are inhibited from activity against the part of the returned return sludge. After the substance is added to a predetermined concentration, it is returned to the main reactor, and the flow rate Qs _{2 of the} return sludge taken out to the other reaction vessel B is expressed by the following equation (2) as SRT (Solid Retention Time) A biological nitrogen treatment method for ammonia-containing wastewater, characterized in that it is set so as to fall within a range of values calculated in (1).
1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₂ / Q) · (M _r / M) / T}
... (2)
However, μ ₁ : Specific growth rate of ammonia-oxidizing bacteria (1 / day), μ ₂ : Specific growth rate of nitrite-oxidizing bacteria (1 / day), Qs ₂ : A part of the returned sludge is sent to another reactor B Amount to be taken out (m ³ / day), Q: Amount of waste water flowing into the main reactor (m ³ / day), T: Reaction time of the main reactor (day), M: Concentration of activated sludge in the main reactor (mg / l), _{M r:} Ri return activated sludge concentration (mg / l) der, the formula (2) in _{[1 / {μ 2 - (} Qs 2 / Q) · (M r / M) / T} - 1 / μ ₁ ]> 0 .
(3) After performing the nitrification process and denitrification process on the ammonia-containing wastewater using the main reactor, the treated water and the activated sludge are separated in the final sedimentation basin, and the activated sludge is returned to the main reactor as the returned sludge. In the biological treatment method of ammonia-containing wastewater to be returned, a preliminary reactor is provided upstream of the main reactor, and the ammonia-containing wastewater is supplied to the preliminary reactor, and a part of the return sludge is supplied to the preliminary reactor. After returning to the reactor, the waste water and a part of the returned sludge are brought into contact with the preliminary reactor, and a substance that inhibits the activity of nitrite oxidizing bacteria is added to the preliminary reactor to a predetermined concentration. fed into the main reactor, and the amount Qs ₃ of the return sludge to be returned to the pre-reactor, SRT (Solid Retention Time) is set to be in the following formula (3) Wherein, the biological nitrogen treatment method wastewater containing ammonium.
1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₃ / Q) · (M _r / M) / T}
... (3)
However, μ ₁ : Specific growth rate of ammonia-oxidizing bacteria (1 / day), μ ₂ : Specific growth rate of nitrite-oxidizing bacteria (1 / day), Qs ₃ : Part of the return sludge is introduced into the preliminary reactor. Amount (m ³ / day), Q: amount of wastewater flowing into the pre-reactor (m ³ / day), T: reaction time (day) of the main reactor, M: concentration of activated sludge in the main reactor (mg / l), _{M r:} Ri return activated sludge concentration (mg / l) der, the formula (3) in _{[1 / {μ 2 - (} Qs 3 / Q) · (M r / M) / T} -1 / Μ ₁ ]> 0 .
(4) In the main reactor, using the nitrite generation method for the nitrification step and using the nitrous acid denitrification method for the denitrification step, or using the nitrous acid generation method for the nitrification step, The biological nitrogen treatment method of ammonia-containing wastewater according to any one of (1) to (3), wherein an anaerobic ammonia oxidation reaction method is used.
(5) The substance that inhibits the activity is at least one of a sulfur compound, phenol, and ammoniacal nitrogen having a concentration after addition to wastewater of 60 mg / l or more (1) to (4) The biological nitrogen treatment method of ammonia-containing wastewater as described in any one of 1).

  As described above, according to the present invention, it is possible to stably and efficiently treat waste water containing ammoniacal nitrogen.

It is explanatory drawing which shows Embodiment 1 based on this invention. It is explanatory drawing which shows Embodiment 2 based on this invention. It is explanatory drawing which shows Embodiment 3 based on this invention. In Embodiment 1 of this invention, it is a graph which shows the relationship between the amount of surplus sludge drawing-out, and the 3 state nitrogen concentration of an aerobic tank. In Embodiment 2 of this invention, it is a graph which shows the relationship between the quantity of the return sludge introduce | transduced into another reactor, and the three state nitrogen concentration of an aerobic tank. In Embodiment 3 of this invention, it is a graph which shows the relationship between the quantity of the returned sludge made to flow into another reactor, and the tri-nitrogen concentration of an aerobic tank.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

In FIG. 1, the flow sheet of the biological treatment method of the wastewater containing ammonia nitrogen which concerns on Embodiment 1 of this invention is shown.
First, waste water 1 containing ammonia nitrogen is caused to flow into a main reactor 2 having biological nitrogen removal ability. Main reactor 2 converts ammonia nitrogen into nitrate nitrogen by nitrifying bacteria in the nitrification process (aerobic condition), and then uses the nitrogenous nitrogen inflow wastewater organic matter in the denitrification process. To remove as nitrogen gas. Here, the nitrification step and the denitrification step may be arranged in one reactor, or a plurality of reactors may be used by dividing the reactor for each step.

  At this time, in the present embodiment, a part 6 of the activated sludge in the main reactor 2 is continuously extracted into the separate reactor (A) 7 to give the nitrite-oxidizing bacteria activity inhibitory substance 8, and then the main reaction. Return continuously to device 2.

  By this method, it is possible to preferentially hold ammonia-oxidizing bacteria in the main reactor 2 only by inhibiting the activity of a part of the nitrite-oxidizing bacteria. It was found that control with nitrogen was possible.

  After the waste water 1 containing ammonia nitrogen is reacted in the main reactor 2, the activated sludge and the treated water 4 are solid-liquid separated in the final sedimentation basin 3, and the separated activated sludge is the main reaction as the return sludge 5. Return to vessel 2. The activated sludge thus proliferated is drawn out of the system as surplus sludge 9 from the final sedimentation basin 3. Thus, in the present embodiment, a process of extracting a part of the activated sludge from the main reactor 2 to the separate reactor (A) 7, adding the activity inhibitor 8 and returning it to the main reactor 2, The activated sludge and the treated water 4 that have flowed into the final sedimentation basin 3 from the reactor 2 are subjected to solid-liquid separation in parallel.

  As a result of detailed examination of this treatment method, the present inventors have found that the activity inhibitor 8 of nitrite oxidizing bacteria provided in the separate reactor (A) 7 also inhibits the activity of ammonia oxidizing bacteria. We found that nitrite-oxidizing bacteria and ammonia-oxidizing bacteria differ in the time required for recovery of activity after being inhibited.

  As the activity inhibiting substance 8, for example, when phenolic or sulfur compounds and ammonia nitrogen corresponding to an amount of 60 mg / l or more in the waste water after addition are added, both nitrite-oxidizing bacteria and ammonia-oxidizing bacteria are active. Inhibited. Here, since this activity inhibiting substance 8 is decomposed and removed in a short time due to aerobic conditions in the nitrification step, when the activity inhibiting substance 8 is removed, ammonia oxidizing bacteria are more preferred than nitrite oxidizing bacteria. The activity recovers quickly.

  As described above, the ammonia-oxidizing bacteria are also temporarily inhibited by the activity-inhibiting substance of the nitrite-oxidizing bacteria. However, since there is a difference in the time required for the subsequent recovery of the activity, in the present invention, in the main reactor 2 In order to preferentially retain the activity of the ammonia-oxidizing bacteria, the solid retention time (sludge retention time, hereinafter referred to as SRT) was the same as or longer than the growth time of the ammonia-oxidizing bacteria, and the activity was inhibited. The adjustment time was shorter than the growth time of nitrite-oxidizing bacteria.

  In the present invention, the wastewater treatment capacity is restored by recovering the activity of the microorganism that has been inhibited by the activity, and the wastewater treatment capacity is restored by the growth of the microorganism that has not been inhibited by the activity. However, since details of these are not yet elucidated, these are collectively referred to as recovery of activity.

In this SRT, the amount 6 of activated sludge to be extracted to another reactor (A) 7 is Qs ₁ (m ³ / day), the amount of waste water flowing into the main reactor is Q (m ³ / day), and the ratio of ammonia oxidizing bacteria When the growth rate is expressed as μ ₁ (1 / day), the specific growth rate of nitrite-oxidizing bacteria is expressed as μ ₂ (1 / day), and the reaction time of the main reactor is expressed as T (day), the following equation (1) It can be expressed as

1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₁ / Q) / T} (1)

  Here, SRT indicates the average number of days that microorganisms stay in the system, and is a value calculated by the following equation (a). In addition, the value of SRT represented by the following formula | equation (a) can be adjusted by changing the extraction amount of excess sludge.

  SRT (day) = reactor sludge amount (kg) ÷ (excess sludge amount (kg / day) + SS amount in treated water (kg / day)) Equation (a)

In the present invention, first, since the SRT needs to be equal to or longer than the time required for the growth of the ammonia-oxidizing bacteria, the reciprocal of the specific growth rate μ ₁ between the SRT and the ammonia-oxidizing bacteria is used (1) The leftmost side of the formula was derived. The specific growth rate is the growth rate per unit microorganism concentration, and 1 / μ ₁ represents the time required for the growth of ammonia-oxidizing bacteria.

A part of the ammonia-oxidizing bacterium is proliferated (activated from the time when it is not affected by the activity inhibitor in the main reactor after being inhibited by the addition of the activity inhibitor 8 in the separate reactor (A). Start recovering). At this time, since the activity-inhibiting substance 8 used in the present invention is oxidized in a relatively short time in the main reactor, the influence on the specific growth rate of the ammonia-oxidizing bacteria subjected to the activity inhibition is small and can be ignored. It has been confirmed that the time required for the growth of ammonia-oxidizing bacteria in the present invention is 1 / μ ₁ and there is no problem.

Next, in the present invention, it is necessary to set SRT to be less than the time required for the growth of nitrite-oxidizing bacteria. Assuming that activity inhibition is given to the activated sludge in the main reactor whose reaction time is T at a ratio of Qs ₁ / Q, the specific growth rate of nitrite-oxidizing bacteria present in the activated sludge is [μ ₂ − (Qs ₁ / Q) / T]. That is, since the reciprocal indicates the time required for the growth of the nitrite-oxidizing bacteria in the present embodiment, the SRT is less than the reciprocal of the specific growth rate of the nitrite-oxidizing bacteria in the present embodiment ( 1) The rightmost side of the equation was derived.

That is, in this embodiment, the amount of surplus sludge drawn, the amount of activated sludge Qs ₁ to be extracted to another reactor, the amount of waste water Q flowing into the main reactor, and the reaction time T of the main reactor are changed (1) Is set to a value that satisfies the above, ammonia-oxidizing bacteria are preferential in the main reactor 2, and the oxidation of ammonia nitrogen can be stopped with nitrite nitrogen.

  The specific growth rate for each microorganism is expressed as follows in the logarithmic growth phase. Therefore, a sufficient amount of substrate and necessary inorganic salts are added to the culture vessel to culture the target microorganism. Then, the microorganism concentration X can be obtained as a slope when plotted against the elapsed time t on a semi-log scale.

dX / dt = μX

Here, X: microorganism concentration (mg / l), t: time (day), and μ: specific growth rate (1 / day).

The biological treatment method for wastewater containing ammonia nitrogen according to Embodiment 2 of the present invention is shown in FIG.
In the present embodiment shown in FIG. 2, the activity inhibitor 8 of nitrite oxidizing bacteria is given to a part of the returned sludge 5 returned from the final sedimentation basin 3 to the main reactor 2. A part 6 of the returned sludge 5 is extracted into a separate reactor (B) 7, and the nitrite oxidizing bacteria 8 are given to the extracted nitrite oxidizing bacteria, and then returned to the main reactor 2, thereby oxidizing nitrite. It was found that bacterial growth can be suppressed and ammonia oxidizing bacteria can be preferentially retained in the main reactor 2.

At this time, the SRT uses Qs ₂ (m ³ / day) as the amount 6 of activated sludge to be extracted to the separate reactor (B) 7, Q (m ³ / day) as the amount of waste water flowing into the main reactor, and ammonia-oxidizing bacteria. Specific growth rate μ ₁ (1 / day), specific growth rate μ ₂ (1 / day) of nitrite-oxidizing bacteria, reaction time T (day) of the main reactor, M: concentration of activated sludge in the main reactor ( If _{expressed as} mg / l), _Mr : return activated sludge concentration (mg / l), it can be expressed as the following equation (2).

1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₂ / Q) · (M _r / M) / T}
... Formula (2)

The derivation of equation (2) is the same as equation (1), but in the embodiment shown in FIG. 2, the activated sludge concentration and main reaction in the separate reactor (B) 7 that gives the activity inhibiting substance 8. Since the activated sludge concentration in the vessel 2 is different, Qs ₂ / Q multiplied by the value of each activated sludge concentration is used. In the present embodiment, the amount of excess sludge withdrawn, the amount of activated sludge Qs ₂ withdrawn to another reactor, the amount of waste water Q flowing into the main reactor, and the reaction time T of the main reactor are changed to satisfy equation (2). By setting to such a value, ammonia oxidizing bacteria are preferential in the main reactor 2, and it becomes possible to stop the oxidation of ammonia nitrogen with nitrite nitrogen.

The biological treatment method for wastewater containing ammonia nitrogen according to Embodiment 3 of the present invention is shown in FIG.
In this embodiment shown in FIG. 3, the waste water 1 is first caused to flow into another reactor (C) 7 which is an example of a preliminary reactor. In another reactor (C) 7, a part 6 of the returned sludge is returned and an activity inhibitory substance 8 of nitrite oxidizing bacteria is given. After the reaction in the separate reactor (C) 7, the main reactor 2 undergoes a nitrification step and a denitrification step, and then the solid sludge is separated into activated sludge and treated water in the final sedimentation basin 5. The activated sludge is returned sludge. 5 is returned to the separate reactor (C) 7 and the main reactor 2. The separate reactor (C) 7 only needs to give activity inhibition to nitrite-oxidizing bacteria, and may be aerobic or anaerobic.

  In the embodiment shown in FIG. 3, when the wastewater 1 contains an activity inhibiting substance of nitrite oxidizing bacteria, the activity inhibiting substance in the wastewater 1 can be used as it is, and the nitrite is separated in the separate reactor 7. You may interrupt | providing the activity inhibitory substance 8 of oxidation bacteria.

At this time, the SRT uses Qs ₃ (m ³ / day) as the amount of activated sludge extracted to the separate reactor 7, Q (m ³ / day) as the amount of wastewater flowing into the main reactor, and specific growth of ammonia-oxidizing bacteria. Rate μ ₁ (1 / day), specific growth rate of nitrite-oxidizing bacteria μ ₂ (1 / day), reaction time T (day) of the main reactor, M: concentration of activated sludge in the main reactor (mg / l ), _Mr : Return sludge concentration (mg / l), it can be expressed as the following formula (3).

1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₃ / Q) · (M _r / M) / T}
... Formula (3)

The way of deriving the equation (3) is the same as the equation (2). In this embodiment, the amount of excess sludge withdrawn, the amount of activated sludge to be extracted to another reactor Qs ₃ , the amount of waste water Q flowing into the main reactor By changing the reaction time T of the main reactor and setting it to a value that satisfies the equation (3), ammonia oxidizing bacteria are preferential in the main reactor 2, and the oxidation of ammoniacal nitrogen is reduced to nitrous acid. It is possible to stop with active nitrogen.

  Here, nitrite nitrogen is stably accumulated in the nitrification step by the method shown in each embodiment of FIG. 1, FIG. 2, and FIG. Or an anaerobic ammonia oxidation reaction method can be used.

  In the main reactor, when the nitrite generation method is used for the nitrification process and the nitrous acid denitrification method is used for the denitrification process, an anaerobic tank and an aerobic tank are used as the main reactor, and the organic matter in the inflowing waste water 1 is used. In order to utilize as an electron acceptor, waste water is first introduced into an anaerobic tank and then carried into an aerobic tank, and a part of the treated water in the aerobic tank is circulated to the anaerobic tank. When the method according to each embodiment of the present invention is used, ammonia-oxidizing bacteria are given priority in the aerobic tank, and the nitrification process of the aerobic tank can be stopped in the nitrite production process, and the amount of oxygen necessary for the nitrification process Can be reduced by about 25%. As a result, since the nitrous acid produced in the aerobic tank is circulated to the anaerobic tank, the denitrification process becomes a nitrous acid denitrification reaction, and the amount of organic substances required for the denitrification process is smaller than that in the case of the nitric acid denitrification reaction. Since about 40% is sufficient, even when the amount of organic matter in the wastewater is insufficient, the amount of organic matter such as methanol to be added is small, and ammonia nitrogen in the wastewater can be efficiently removed.

  On the other hand, when using the nitrite generation method in the nitrification process and the anaerobic ammonia oxidation reaction process in the denitrification process, an aerobic tank and an anaerobic tank are used as the main reactor, and the waste water is first introduced into the aerobic tank. And then carry it into the anaerobic tank. When the method according to each embodiment of the present invention is used, ammonia-oxidizing bacteria are preferential in the aerobic tank, and ammonia in the aerobic tank is converted into nitrous acid. Nitrous acid produced in the aerobic tank and unreacted ammonia are allowed to flow into the anaerobic tank in the subsequent stage to perform an anaerobic ammonia oxidation reaction. At this time, the concentration of ammonia and nitrous acid is preferably a ratio of about 1: 1.32, and the pH, DO, ORP (oxidation-reduction potential), water temperature, etc. are controlled in the nitrous acid production step so that this value is obtained. Adjust the amount of nitrous acid produced. In this way, a part of the ammonia nitrogen in the inflowing wastewater is converted to nitrite nitrogen and an anaerobic ammonia oxidation reaction is performed. Therefore, by adjusting the amount of nitrite nitrogen produced by the above method, It is also possible to adjust to an arbitrary nitrogen removal amount. In this aerobic tank, ammonia nitrogen is not oxidized to nitrate nitrogen but is stopped with nitrite nitrogen, so that the required oxygen amount in the nitrification process in the aerobic tank can be reduced by about 25%.

  Here, as the activity inhibitor of nitrite-oxidizing bacteria used in each embodiment of the present invention, for example, at least sulfur compound, phenol, ammonia nitrogen corresponding to an amount of 60 mg / l or more in wastewater, Add one or more to give. Depending on the properties of the wastewater, a plurality of inhibition conditions may be given simultaneously.

  In each embodiment of the present invention, when phenol is given as an activity inhibitor, for example, the effect of the present invention can be obtained by adding and adjusting so that the concentration is 20 mg / l or more and 200 mg / l or less. Can do. Moreover, as a sulfur compound, sulfurous acid, thiosulfuric acid, and thiocyan are suitable, and the effect of the present invention can be obtained by adding and adjusting so that it is 40 mg-sulfur / l or more and 200 mg-sulfur / l or less. It becomes possible. Moreover, it becomes possible to acquire the effect of this invention by adding and adjusting ammonia nitrogen so that it may become 60 mg-N / l or more and 700 mg / l or less.

  Here, the amount of addition described above is an example, and varies depending on the components of the wastewater and the type of microorganism, and the value also changes when a plurality of activity inhibitory substances coexist. Therefore, the value which causes activity inhibition can be confirmed by using the following method.

Prepare multiple 500 ml beakers, add activated sludge containing ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, and a medium containing (NH ₄ ) ₂ SO ₄ , NaNO ₂ and inorganic salts to make 500 ml. Perform a formula experiment. For each beaker, the experiment is performed by changing the concentration of the inhibitor to be added, and the changes in ammonia nitrogen concentration and oxidized nitrogen concentration after the start of the experiment are observed. For example, after 20 hours from the start of the experiment, each beaker is allowed to stand and the supernatant is removed. Then, the precipitated activated sludge is transferred to another 500 ml beaker, and the same medium as described above is added, and no inhibitor or inhibitor is added. Hold and observe for activity recovery. By this method, conditions under which the inhibitor acts on ammonia-oxidizing bacteria and nitrite-oxidizing bacteria can be confirmed.

  The conditions for inhibiting the activity of nitrite-oxidizing bacteria include pH, dissolved oxygen concentration, water temperature, etc. in addition to the addition of phenol, sulfur compounds and high-concentration ammoniacal nitrogen. For example, pH is 7.5 to 8.5. In the case of dissolved oxygen concentration, activity inhibition occurs at less than 0.5 mg / l, and in the case of water temperature at 25 ° C. or higher, but in the case of activity inhibition due to pH, dissolved oxygen concentration, water temperature, those inhibition conditions disappear. Since the activity of nitrite-oxidizing bacteria is immediately recovered, it is not effective as an activity inhibition condition of the present invention, and is not a target of a substance that inhibits the activity of the present invention.

  On the other hand, phenol and sulfur compounds added to another reaction vessel are oxidized and decomposed in a relatively short time in an aerobic tank in the main reactor when flowing into the main reactor from another reaction vessel. In the case of nitrogen, since it is converted to nitrite nitrogen by nitrification in the aerobic tank in the main reactor, ammonia is continuously added without affecting the activity of ammonia oxidizing bacteria in the main reactor. Biological treatment of wastewater containing natural nitrogen becomes possible.

  The wastewater treated in the present invention can be applied to all wastewater containing ammonia nitrogen at a concentration exceeding the wastewater discharge standard value, but is particularly effective when applied to wastewater containing high concentration ammoniacal nitrogen. is there.

  Therefore, the present invention is suitable for biological treatment of wastewater containing low-concentration water generated in a coke factory of a steel mill, high-concentration ammoniacal nitrogen generated from a chemical factory or a food factory. In particular, when it is applied to low water generated at a coke plant, waste water contains phenol, sulfur compounds, and other nitrite-oxidizing bacteria activity inhibitors, so these activity inhibitors should be used effectively. Is possible.

  Examples of the present invention will be described below, but the present invention is not limited to the examples.

Example 1
2 shows an example of the embodiment shown in FIG.
Artificial sewage was used as the target wastewater. In addition, phenol was added as an activity inhibitor of nitrite oxidizing bacteria. The wastewater properties and activity inhibition conditions are shown below.

<Properties of wastewater>
BOD: 120mg / l
NH ₄ -N: 40 mg / l
TP: 5 mg / l
Amount of phenol added: 80 mg / l

  In the main reactor, continuous treatment was performed using nitrite production-nitrite denitrification method. An outline of the apparatus and processing conditions are shown below.

<Outline of device and processing conditions>
Main reactor Anaerobic tank 200L
Aerobic tank 300L
MLSS average 3,460mg / l
Separate reactor 50L
Amount of activated sludge withdrawn to another reactor Qs ₁ 43 L / day
Waste water flowing into the main reactor Q 792L / day
Specific growth rate of ammonia oxidizing bacteria μ ₁ 0.6 1 / day
Specific growth rate of nitrite-oxidizing bacteria μ ₂ 0.312 1 / day
Sludge return rate 100% (= 792L / day)
Mixing liquid circulation rate 200%
Treated water SS average 360mg / l
Excess sludge concentration average 8,280mg / l
Excess sludge extraction amount Set arbitrarily

FIG. 4 shows the measurement results of the tristate nitrogen concentration in the aerobic tank when the SRT is changed by adjusting the amount of excess sludge withdrawn. In the above operating conditions, 1 / μ ₁ is 1.67 day and 1 / {μ ₂ − (Qs ₁ / Q) / T} is 4.42 day.

As shown in FIG. 4, when the sludge extraction amount of the excess sludge was operated in the range of 14 L / day to 90 L / day, the nitrite oxidizing bacteria were inhibited, and nitrite nitrogen could be accumulated in the aerobic tank. . The excess sludge extraction amount 14 L / day corresponds to SRT = 4.3 day, and 90 L / day corresponds to SRT = 1.7 day. Therefore, the SRT is adjusted to 1 / μ ₁ and 1 by adjusting the sludge extraction amount. / {Μ ₂ − (Qs ₁ / Q) / T}, the nitrification reaction in the aerobic tank could be stopped up to nitrite nitrogen. In addition, this method reduced the amount of aeration in the aerobic tank by about 25%.

  Further, as shown in FIG. 4, in the range where the excess sludge extraction amount exceeds 90 L / day, the concentration of nitrite nitrogen decreases and the concentration of nitrate nitrogen increases. In addition, the concentration of nitrite nitrogen is reduced in the range where the excess sludge extraction amount is 14 L / day or less. As is apparent from this result, it has been found that when the SRT is outside the range of the above formula (1), the nitrification reaction in the aerobic tank cannot be stopped by nitrite nitrogen.

(Example 2)
The example of embodiment shown in FIG. 2 is shown.
The same waste water as in Example 1 was used. The outline of the apparatus and processing conditions in Example 2 are shown below.

<Processing conditions>
Main reactor Anaerobic tank 200L
Aerobic tank 300L
MLSS 7,560mg / l
Separate reactor 50L
Amount of returned sludge withdrawn to another reactor Qs ₂ arbitrarily set Amount of wastewater flowing into the main reactor Q 792 L / day
Specific growth rate of ammonia oxidizing bacteria μ ₁ 0.6 1 / day
Specific growth rate of nitrite-oxidizing bacteria μ ₂ 0.312 1 / day
Sludge return rate 100% (= 792L / day)
Mixing liquid circulation rate 200%
Treated water SS average 288mg / l
Surplus sludge concentration (= returned sludge concentration) Average 15,640 mg / l
Pull out excess sludge: 10L / day

In order to inhibit the activity of nitrite-oxidizing bacteria, the amount of return sludge Qs ₂ withdrawn to another reactor is adjusted to obtain a value of 1 / {μ ₂ − (Qs ₂ / Q) · (M _r / M) / T}. FIG. 5 shows the measurement results of the trinitrogen concentration in the aerobic tank when changed. Under the above operating conditions, SRT is 9.8 day, and 1 / μ ₁ is 1.67 day.

As shown in FIG. 5, when the amount of returned sludge to be introduced into another reactor is operated within the range of 53 L / day or more, the activity inhibition of nitrite oxidizing bacteria becomes remarkable, and nitrite nitrogen can be accumulated in the aerobic tank. It was. The amount of returned sludge to be introduced into another reactor, 53 L / day, corresponds to 10.8 day of 1 / {μ ₂ − (Qs ₂ / Q) · (M _r / M) / T}, and the returned sludge that gives activity inhibition. By adjusting the amount and setting SRT <1 / {μ ₂ − (Qs ₁ / Q) · (M _r / M) / T}, the nitrification reaction in the aerobic tank can be reduced to nitrite nitrogen. I was able to stop. In addition, this method reduced the amount of aeration in the aerobic tank by about 25%.

Further, as shown in FIG. 5, the concentration of nitrite nitrogen decreases and the concentration of nitrate nitrogen increases in the range where the amount of returned sludge introduced into another reactor is less than 53 L / day. On the other hand, when the amount of surplus sludge withdrawn from the 10 L / day was changed from 10 L / day to 140 L / day with the return sludge amount Qs ₂ to be introduced into another reactor being 40 L / day, the SRT was 1.56 day, The concentration of ammonia nitrogen disappeared and the nitrification reaction did not proceed. As is clear from these results, it has been found that when the SRT falls outside the range of the above formula (2), the nitrification reaction in the aerobic tank cannot be stopped by nitrite nitrogen.

(Example 3)
4 shows an example of the embodiment shown in FIG.
The wastewater used was the coke plant's low water. The outline of the apparatus, waste water quality and treatment conditions in Example 3 are shown below.

<Properties of wastewater>
COD: 400 to 500 mg / l
NH ₄ -N: 400 to 700 mg / l
NO ₂ -N: <0.1mg / l
NO ₃ -N: <0.1mg / l
TP: <0.1 mg / l
Phenol: 60-180 mg / l
S ₂ O ₃ ²⁻ : 90 to 150 mg / l
SCN: 60-80 mg / l

<Processing conditions>
Main reactor Anaerobic tank 200L
Aerobic tank 300L
MLSS 5,200mg / l
Separate reactor 50L
Amount of returned sludge flowing into another reactor Qs ₃ arbitrarily set Amount of wastewater flowing into main reactor Q 720 L / day
Specific growth rate of ammonia oxidizing bacteria μ ₁ 0.6 1 / day
Specific growth rate of nitrite-oxidizing bacteria μ ₂ 0.312 1 / day
Sludge return rate 100%
Mixing liquid circulation rate 200%
Treated water SS average 170mg / l
Excess sludge concentration (= Return sludge concentration) Average 11,800mg / l
Pull out excess sludge 30L / day

A value of 1 / {μ ₂ − (Qs ₃ / Q) · (M _r / M) / T} by adjusting the amount of returned sludge Qs ₃ flowing into another reactor in order to inhibit the activity of nitrite oxidizing bacteria FIG. 6 shows the measurement results of the tri-state nitrogen concentration in the aerobic tank when the pressure is changed. Under the above operating conditions, SRT is 5.5 days, and 1 / μ ₁ is 1.67 days.

As shown in FIG. 6, when the amount of returned sludge flowing into another reactor was operated in the range of 30 L / day or more, the activity inhibition of nitrite oxidizing bacteria became remarkable, and nitrite nitrogen could be accumulated in the aerobic tank. . The amount of return sludge that flows into another reactor is 30 L / day, which corresponds to 1 / {μ ₂ − (Qs ₃ / Q) · (M _r / M) / T}, which is 5.7 day. By adjusting the amount and setting SRT <1 / {μ ₂ − (Qs ₃ / Q) · (M _r / M) / T}, the nitrification reaction in the aerobic tank can be reduced to nitrite nitrogen. I was able to stop. In addition, this method reduced the amount of aeration in the aerobic tank by about 25%.

Moreover, as shown in FIG. 6, in the range in which the amount of returned sludge is less than 30 L / day, the concentration of nitrite nitrogen decreases and the concentration of nitrate nitrogen increases. On the other hand, in a state where the return sludge amount Qs ₃ was 20L / day to be introduced into another reactor, where the withdrawal of excess sludge was changed from 30L / day to 130L / day, SRT is next 1.57Day, in the waste water The decrease in ammonia nitrogen concentration disappeared and the nitrification reaction stopped. As is clear from these results, it has been found that when the SRT is outside the range of the above formula (3), the nitrification reaction in the aerobic tank cannot be stopped by nitrite nitrogen.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Waste water 2 Main reactor 3 Final sedimentation tank 4 Treated water 5 Return sludge 6 Extraction to another reactor 7 Separate reactor 8 Activity inhibitor of nitrite oxidation bacteria 9 Extraction of excess sludge

Claims (5)

After the nitrification process and denitrification process are performed on the ammonia-containing wastewater using the main reactor, the treated water and activated sludge are separated in the final sedimentation basin, and the activated sludge is returned to the main reactor as return sludge. In the biological treatment method of contained wastewater,
A part of the activated sludge is taken out from the main reactor into another reaction vessel A, and a substance that inhibits the activity of nitrite oxidizing bacteria is added to the part of the extracted activated sludge so as to have a predetermined concentration. The activated sludge flow rate Qs ₁ which is later returned to the main reactor and taken out to the other reaction vessel A is set so that the SRT (Solid Retention Time) is within the range of values calculated by the following equation (1). A biological nitrogen treatment method for ammonia-containing wastewater, characterized in that

1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₁ / Q) / T} (1)

However,
μ ₁ : Specific growth rate of ammonia-oxidizing bacteria (1 / day)
μ ₂ : Specific growth rate of nitrite-oxidizing bacteria (1 / day)
Qs ₁ : Flow rate (m ³ / day) taken out from the main reactor to another reaction vessel A
Q: Amount of waste water flowing into the main reactor (m ³ / day)
T: reaction time of the main reactor (day)
Der is, the formula (1) in _{[1 / {μ 2 - (} Qs 1 / Q) / T} -1 / μ 1]> 0. After the nitrification process and denitrification process are performed on the ammonia-containing wastewater using the main reactor, the treated water and activated sludge are separated in the final sedimentation basin, and the activated sludge is returned to the main reactor as return sludge. In the biological treatment method of contained wastewater,
A part of the returned sludge is taken out into another reaction vessel B, and a substance that inhibits the activity of nitrite oxidizing bacteria is added to the part of the returned returned sludge to a predetermined concentration, and then the main reaction is performed. The flow rate Qs _{2 of the} return sludge that is returned to the vessel and taken out to the other reaction vessel B is set so that the SRT (Solid Retention Time) falls within the range of values calculated by the following equation (2) A method for biological nitrogen treatment of ammonia-containing wastewater.

1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₂ / Q) · (M _r / M) / T}
... Formula (2)

However,
μ ₁ : Specific growth rate of ammonia-oxidizing bacteria (1 / day)
μ ₂ : Specific growth rate of nitrite-oxidizing bacteria (1 / day)
Qs ₂ : Amount of part of the returned sludge to be taken out to another reactor B (m ³ / day)
Q: Amount of waste water flowing into the main reactor (m ³ / day)
T: reaction time of the main reactor (day)
M: concentration of activated sludge in the main reactor (mg / l)
M _r : Return activated sludge concentration (mg / l)
Der is, the formula (2) in _{[1 / {μ 2 - (} Qs 2 / Q) · (M r / M) / T} -1 / μ 1]> 0. After the nitrification process and denitrification process are performed on the ammonia-containing wastewater using the main reactor, the treated water and activated sludge are separated in the final sedimentation basin, and the activated sludge is returned to the main reactor as return sludge. In the biological treatment method of contained wastewater,
A preliminary reactor is provided on the upstream side of the main reactor, and ammonia-containing wastewater is supplied to the preliminary reactor, and a part of the return sludge is returned to the preliminary reactor, and the waste water and a part of the return sludge are returned. Is added to the preliminary reactor so that the concentration of the substance that inhibits the activity of the nitrite-oxidizing bacteria is reduced to a predetermined concentration, and then supplied to the main reactor, and to the preliminary reactor. A biological nitrogen treatment method for ammonia-containing wastewater, characterized in that the amount Qs _{3 of the} returned sludge to be returned is set so that SRT (Solid Retention Time) is represented by the following formula (3).

1 / μ ₁ ≦ SRT <1 / {μ ₂ − (Qs ₃ / Q) · (M _r / M) / T}
... Formula (3)

However,
μ ₁ : Specific growth rate of ammonia-oxidizing bacteria (1 / day)
μ ₂ : Specific growth rate of nitrite-oxidizing bacteria (1 / day)
Qs ₃ : Amount of part of the returned sludge introduced into the pre-reactor (m ³ / day)
Q: Amount of waste water flowing into the pre-reactor (m ³ / day)
T: reaction time of the main reactor (day)
M: concentration of activated sludge in the main reactor (mg / l)
M _r : Return activated sludge concentration (mg / l)
Der is, the equation (3) in _{[1 / {μ 2 - (} Qs 3 / Q) · (M r / M) / T} -1 / μ 1]> 0. In the main reactor,
A nitrous acid generation method is used for the nitrification step, a nitrous acid denitrification method is used for the denitrification step, or a nitrous acid generation method is used for the nitrification step, and an anaerobic ammonia oxidation reaction method is used for the denitrification step. The biological nitrogen treatment method according to any one of claims 1 to 3, wherein the ammonia-containing wastewater is used. 5. The substance according to claim 1, wherein the substance that inhibits the activity is at least one of a sulfur compound, phenol, and ammonia nitrogen having a concentration after addition to wastewater of 60 mg / l or more. A biological nitrogen treatment method for ammonia-containing wastewater according to item 1.