JP5581872B2 - Method and apparatus for denitrification treatment of ammoniacal nitrogen waste liquid - Google Patents

Description

  The present invention relates to nitrogen removal from ammonia and nitrogen-containing organic and inorganic waste liquids. Concentrated dewatered liquid of sewage digested sludge, methane fermentation sludge and separated liquids such as organic sludge and livestock waste liquid, leachate and industrial waste water. It relates to nitrogen removal.

By anaerobic digestion of liquid waste with high organic matter concentration such as organic sludge and sewage sludge, the carbon source that is organic matter can be recovered as methane gas (CH ₄ ), and the sludge volume reducing effect is also high, This is an effective means of reducing waste and recovering energy. However, in anaerobic digestion, nitrogen in the stock solution is not removed, so high-concentration nitrogen remains in the concentrated sludge and dehydrated filtrate of digested sludge. In addition to the above, waste leachate and petrochemical factory wastewater may have a low BOD and a high concentration of ammoniacal nitrogen. Both require nitrogen removal.

  Conventionally, a biological nitrification denitrification method is often used as a denitrification treatment method for nitrogen-containing waste liquid. The biological nitrification denitrification method is usually composed of a nitrification process and a denitrification process. In the nitrification process of the first process, ammonia nitrogen in the raw water is first oxidized to nitrite nitrogen by ammonia-oxidizing bacteria in an aerobic reaction tank, commonly called a nitrification tank, and then nitrite-oxidized by nitrite-oxidizing bacteria. Nitrogen is oxidized to nitrate nitrogen. In the denitrification process after the nitrification process, the treatment liquid (nitrification liquid) from this nitrification tank is introduced into an anaerobic reaction tank, commonly known as a denitrification tank, and nitrate nitrogen and nitrite nitrogen in the nitrification liquid are heterotrophic. By the denitrifying bacteria, it is reduced to harmless nitrogen gas in the presence of an electron donor. As this electron donor, an organic substance in the liquid to be treated is usually used. When the amount of organic substances is small, it is necessary to add methanol as an electron donor from the outside.

  In this biological nitrification denitrification treatment, ammonia nitrogen in the inflow raw water is finally oxidized into nitrate nitrogen via nitrite nitrogen in the nitrification tank. For this reason, it is necessary to supply oxygen necessary for ammoniacal nitrogen oxidation to the nitrification tank. However, the required oxygen amount is 4.57 times higher than that of the raw water ammonia nitrogen, and the supply power cannot be ignored. Further, in the denitrification tank, an organic substance that becomes an electron donor is required in a dependent denitrification reaction in which nitrate nitrogen becomes an electron acceptor. When the organic water is small in the raw water, it is necessary to add methanol as an electron donor necessary for denitrification. In order to obtain stable denitrification performance, the amount of methanol added is usually required to be about 2.5 to 3 times the amount of nitrate nitrogen flowing into the denitrification tank. Thus, the aeration power of the nitrification process and the amount of methanol added in the denitrification process are enormous, and the running cost is high. These reductions have become a major issue that must be solved to spread the nitrification denitrification process.

  In recent years, a denitrification treatment method using an autotrophic denitrifying bacterium that is completely different from the conventional denitrifying mechanism using the heterotrophic denitrifying bacterium has been disclosed (for example, Patent Document 1). This utilizes an autotrophic microorganism with ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor, and reacts ammonia nitrogen and nitrite nitrogen in an anaerobic state to convert them into nitrogen gas. It is an ammonia oxidation treatment method (Anaerobic Ammonium Oxidation Process), a nitrogen removal method by a so-called ANAMOX reaction, or an ammonia denitrification treatment method. The following formula (1) shows a reaction formula of this ammonia denitrification.

In the case of ammonia denitrification represented by formula (1), ammonia nitrogen and nitrite nitrogen react directly, so that it is not necessary to add organic substances such as methanol, and the chemical cost is greatly reduced. Further, in the denitrification reaction, 1 mol of ammonia nitrogen (NH ₄ -N) is reacted at a ratio of 1.32 mol of nitrite nitrogen (NO ₂ -N). Unlike the conventional nitrification process, it is not necessary to oxidize all of them to nitrite and nitrate nitrogen, and only a part of them should be oxidized to nitrite nitrogen. If a part of the raw water NH ₄ -N is oxidized to nitrite nitrogen from the above ammonia denitrification reaction, in the ammonia denitrification treatment, a mixture of NO ₂ -N and NH ₄ -N is obtained. A reaction as shown is obtained, and it is possible to eliminate both NH ₄ —N and NO ₂ —N of the treated water.

In the denitrification treatment using ammonia denitrification as described above, it is first necessary to oxidize a part of ammonia nitrogen in the inflow raw water to nitrite nitrogen in the nitrification process. In order to obtain a high rate of denitrification performance by the ammonia denitrification reaction, it is desired that 57% of the raw water NH ₄ —N is changed to NO ₂ —N and 43% NH ₄ —N is left. In this case, the NO ₂ —N / NH ₄ —N ratio of nitrite-treated water is 1.32, which matches the NO ₂ —N / NH ₄ —N ratio required for the ammonia denitrification reaction shown in Formula (1). To do.
However, in general, as shown in the following reaction formula in the nitrification process, NH ₄ -N in raw water undergoes ammonia oxidation reaction and nitrite oxidation reaction under aerobic conditions, and finally nitrate nitrogen (NO _3- N). Since the ammonia oxidation reaction and the nitrite oxidation reaction occur almost simultaneously, it is usually difficult to advance only the ammonia oxidation reaction.

  In recent years, research and development of this nitritation process has been advanced as a pretreatment for ammonia denitrification, and several treatment methods have been disclosed. For example, as disclosed in Patent Document 2, both ammonia nitrogen and nitrite nitrogen in the nitrification tank are maintained at a high level, and due to the toxicity of ammonia nitrogen and nitrite nitrogen, nitrite nitrogen is nitrated. It is said that the nitrite oxidation reaction that is converted to basic nitrogen can be suppressed. Furthermore, it is proposed to adjust the nitrification tank pH to 6 to 8 by adjusting the raw water flow rate.

In Patent Document 3, the amount of oxygen supplied to the nitrification tank is suppressed, that is, the nitrous acid oxidation reaction is suppressed by keeping the dissolved oxygen in the liquid (hereinafter referred to as “DO”) low in the nitrification tank, It has been proposed that nitrite-type nitrification can be maintained, and Patent Document 4 lowers DO in the nitrification tank, and when ammonia-oxidizing bacteria adhere to the biofilm, DO is 1.5 mg / L or less. In the case of suspended activated sludge, it is proposed that the nitrite oxidation reaction can be suppressed and the nitrite type nitrification can be maintained by setting DO to 1.0 mg / L or less.
Moreover, in patent document 5, by adjusting the amount of sludge returned to a nitritation tank, pH in a nitritation tank is controlled to a predetermined value, and free NH ₃ -N or free HNO in the nitritation tank is controlled. ₂ was maintained above a predetermined value, it is described that stable nitrite treatment is obtained.

Japanese Patent No. 3460745 JP 2003-24983 A JP 2003-10883 A Japanese Patent Laid-Open No. 2004-298441 JP 2010-5554 A

However, when nitrogen removal by ammonia denitrification (ANAMOX reaction) is applied to nitrogen-containing wastewater as described above, partial nitritation treatment that converts 57% of raw water NH ₄ —N to NO ₂ —N only is performed. Although desirable, in the control of pH and DO disclosed in the above prior art, fluctuations occur depending on the raw aqueous state to be supplied, the supply amount, etc., and it is difficult to stably perform denitrification over a long period of time.

  For example, in the method described in Patent Document 5, the pH of the nitritation tank is adjusted by adjusting the amount of sludge returned to the nitritation tank. In a fixed case, even if the return sludge flow rate is changed, the MLSS (activated sludge suspended matter) concentration in the nitritation tank temporarily changes, but it is difficult to greatly change the MLSS in a long time. Especially when the sludge sedimentation is good, reducing the return sludge flow rate will increase the sludge retention time in the sedimentation basin, the return sludge MLSS will rise, and the amount of sludge returned to the nitritation tank will be almost the same, The nitritation tank MLSS concentration is approximately the same as before the return sludge amount change. The same applies when the return sludge flow rate is increased. Since the amount of sludge in the sedimentation basin is limited, it is difficult to increase the amount of sludge returned to the nitrification tank even if the return flow rate is increased. Furthermore, the return sludge concentration decreases due to the increase in the amount of inflow water in the sedimentation basin, and the amount of sludge returned to the nitritation tank does not increase greatly, and it is likely that it will remain at the same level as before the return flow rate change. Furthermore, the nitrification performance of activated sludge is proportional to the number of nitrifying bacteria present in the activated sludge. When there are many organic substances such as SS and BOD in the influent raw water, the number of nitrifying bacteria in the activated sludge is small, and even if the MLSS in the nitritation tank is increased, improvement in nitrification performance may be hardly expected.

  Even if the amount of returned sludge is adjusted as described above, even if there is a temporary change in the MLSS concentration in the nitrification tank, it is difficult to change greatly over the long time than before adjusting the amount of returned sludge. When the fluctuation is large, it is difficult to control the nitritation pH to a predetermined value only by adjusting the return sludge flow rate.

  The present invention solves the above-mentioned problems of the prior art. When the above nitrogen-containing wastewater is denitrified by nitrogen removal by ammonia denitrification (ANAMMOX reaction), the denitrification treatment is stable over a long period of time. It is intended to provide a denitrification treatment method for ammonia nitrogen-containing waste liquid and a treatment apparatus therefor.

As a result of continuous water flow experiments using actual wastewater, the present inventors previously measured the M-alkaliness and NH ₄ -N concentration of the treated water with respect to the treated water containing ammonia nitrogen, and activated sludge and Predetermined amount of alkali or acid so that the M-alkalinity / NH ₄ -N ratio of the treated water flowing into the nitritation treatment tank coexisting with the ammonia-oxidizing bacteria adherent biological carrier is 3.7 to 4.4. And then adjusting the aeration air volume or both the aeration air volume and the return sludge volume so that the nitritation tank pH is 6.0 to 6.9, a stable nitritation treatment can be obtained. In addition, it was confirmed that the NO ₂ —N / NH ₄ —N ratio of nitrite-treated water was around 1.3, which is necessary for the ammonia denitrification reaction, and the present invention was achieved. That is, this invention consists of the structure of following (1)-(7).

(1) A liquid to be treated containing ammonia nitrogen (NH ₄ -N) is introduced into a nitritation tank in which activated sludge and a microbial carrier adhering to ammonia-oxidizing bacteria coexist, and ammonia nitrogen in the liquid to be treated A part of (NH ₄ -N) is converted into nitrite nitrogen (NO ₂ -N), and then concentrated and separated in a solid-liquid separation tank, and a part of the separated activated sludge is converted into the nitritation tank. In the denitrification method of the ammoniacal nitrogen-containing liquid to be returned to the nitrite,
Ammonia nitrogen concentration (NH ₄ -N) and M-alkalinity of the liquid to be treated are measured in advance,
From the measurement results, a predetermined amount of alkali or acid was injected into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio was 3.7 to 4.4 , and
The pH of the nitritation tank is 6.0 to 6.9,
When the pH is 6.0 or less, the aeration air volume is reduced to lower the dissolved oxygen (DO) in the tank, the nitrification rate is lowered, and the return amount is reduced to lower the activated sludge concentration in the tank. When the pH is 6.9 or more, the aeration air volume is increased to increase the dissolved oxygen (DO) in the tank to improve the nitrification rate, and the return amount is increased to increase the activated sludge concentration in the tank. A denitrification treatment method for an ammoniacal nitrogen-containing liquid to be treated, which is controlled so as to lower the pH.

(2) the monitored concentration and the concentration of _NO 2 -N of _NH 4 -N nitrite reduction vessel treated _water, the concentration ratio of _{NO 2 -N / NH 4 -N (} NO 2 -N / NH 4 -N Ratio) is 1.3 or less, the alkali injection amount into the nitritation tank is increased or the acid injection amount is decreased, and when the NO ₂ —N / NH ₄ —N ratio is 1.3 or more, the alkali injection amount The method for denitrifying an ammoniacal nitrogen-containing liquid to be treated according to (1), wherein the injection amount is decreased or the acid injection amount is increased.
(3) The treated water treated in the nitritation treatment process is introduced into an ammonia denitrification tank filled with a biocarrier attached with ammonia denitrifying bacteria, NH ₄ -N is an electron donor and NO ₂ -N is an electron acceptor. The denitrification treatment method for an ammoniacal nitrogen-containing liquid to be treated according to the above (1) or (2), wherein the denitrification treatment is performed with an autotrophic denitrifying bacterium.

(4) Return the treated water treated in the ammonia denitrification tank and a part of the activated sludge separated from the solid-liquid separation tank to the raw water tank for introducing the treated water into the nitritation tank. The method for denitrifying an ammoniacal nitrogen-containing liquid to be treated according to (3) above, wherein
(5) The oxidation-reduction potential (ORP) of the ammonia denitrification tank is monitored, and when the ORP reaches 50 mV or more, an organic substance is added directly to the ammonia denitrification tank, or nitrogen gas (N ₂ ) is circulated to a denitrification tank, and the denitrification method for an ammoniacal nitrogen-containing liquid to be treated according to the above (3) or (4).

(6) A part of ammonia nitrogen (NH ₄ -N) in the water to be treated introduced from the raw water tank is treated with nitrite nitrogen (NO ₂ -N) in the presence of activated sludge and a microorganism carrier adhering to ammonia oxidizing bacteria. A nitritation tank that converts to
A solid-liquid separation tank for separating activated sludge from the effluent from the nitritation tank;
A sludge return line for returning a part of the separated activated sludge to the nitritation tank;
Ammonia in which effluent from the solid-liquid separation tank is denitrified by an autotrophic denitrifying bacterium in which ammonia nitrogen (NH ₄ -N) serves as an electron donor and nitrite nitrogen (NO ₂ -N) serves as an electron acceptor. A denitrification tank and a measuring instrument for measuring the concentration of NH ₄ -N and M-alkalinity of the liquid to be treated introduced into the nitritation tank, and obtaining measurement values;
An injection mechanism for injecting a predetermined amount of alkali or acid into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio is 3.7 to 4.4 according to the measured value;
A pH meter provided in the nitritation tank for measuring a pH value;
A mechanism for adjusting the amount of aeration air or the amount of returned sludge so that the pH value of the pH meter is 6.0 to 6.9;
A treated water circulation line for returning a part of the treated water treated in the ammonia denitrification tank to the raw water tank;
A raw water tank sludge return line for returning a part of the activated sludge separated from the solid-liquid separation tank to the raw water tank,
Ammonia, characterized in that the treatment of the nitritation tank is stabilized with respect to the raw water having a high ammoniacal nitrogen (NH ₄ -N) concentration by the treated water circulation line and the raw water tank sludge transport line. Denitrification treatment equipment for nitrogen-containing treatment liquid.
(7) A part of ammonia nitrogen (NH ₄ -N) in the treated water introduced from the raw water tank is treated with nitrite nitrogen (NO ₂ -N) in the presence of activated sludge and a microorganism carrier adhering to ammonia oxidizing bacteria. A nitritation tank that converts to
A solid-liquid separation tank for separating activated sludge from the effluent from the nitritation tank;
A sludge return line for returning a part of the separated activated sludge to the nitritation tank;
Ammonia in which effluent from the solid-liquid separation tank is denitrified by an autotrophic denitrifying bacterium in which ammonia nitrogen (NH ₄ -N) serves as an electron donor and nitrite nitrogen (NO ₂ -N) serves as an electron acceptor. A denitrification tank and a measuring instrument for measuring the concentration of NH ₄ -N and M-alkalinity of the liquid to be treated introduced into the nitritation tank, and obtaining measurement values;
An injection mechanism for injecting a predetermined amount of alkali or acid into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio is 3.7 to 4.4 according to the measured value;
A pH meter provided in the nitritation tank for measuring a pH value;
A control mechanism for adjusting the amount of aeration air or the amount of sludge returned so that the pH value of the pH meter is 6.0 to 6.9,
By the control mechanism, the pH of the nitritation tank is 6.0 to 6.9,
When the pH is 6.0 or less, the aeration air volume is reduced to lower the dissolved oxygen (DO) in the tank, the nitrification rate is lowered, and the return amount is reduced to lower the activated sludge concentration in the tank. When the pH is 6.9 or more, the aeration air volume is increased to increase the dissolved oxygen (DO) in the tank to improve the nitrification rate, and the return amount is increased to increase the activated sludge concentration in the tank. The denitrification apparatus of the ammoniacal nitrogen containing liquid to be processed characterized by controlling so that pH may be lowered by making it.

In the nitrification treatment, M-alkalinity is consumed as NH ₄ -N in raw water is oxidized to NO ₂ -N, and M consumed in nitrification of 1 mg / L NH ₄ -N. -The alkalinity is 7.1 mg / L. When the ratio of M-alkalinity to the NH ₄ —N concentration of the raw water is low, the nitrification ratio of the raw water NH ₄ —N is small, and the treated water NO ₂ —N / NH ₄ —N ratio is far below the target value of 1.3. It will be. Conversely, when the M-alkalinity with respect to the NH ₄ -N concentration of the raw water is high, nitrification proceeds, the residual amount of the treated water NH ₄ -N decreases, and the treated water NO ₂ -N / NH ₄ -N ratio is the target value. It will greatly exceed 1.3.
_NO 2 -N / _NH 4 -N ratio of nitrite treatment water by a change in the M- alkalinity / _NH 4 -N ratio in the raw water varies greatly, _NO 2 -N / NH required ammonia denitrification It may deviate significantly from the _4- N ratio of 1.3, and a stable denitrification treatment cannot be obtained. In the above prior art, even if the nitrification tank pH is controlled to a predetermined value by adjusting the raw water flow rate, the raw water M-alkalinity / NH ₄ -N ratio depends on the raw water state, so treated water NO ₂ -N It is difficult to control / NH ₄ -N around the target 1.3.

In the present invention, M-alkalinity and NH ₄ -N concentration of water to be treated are measured in advance with respect to the water to be treated containing ammoniacal nitrogen, and nitritation treatment in which activated sludge and ammonia-oxidizing bacteria adherent biocarrier coexist is present. The first step is to inject a predetermined amount of alkali or acid into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio of the water to be treated flowing into the tank is 3.7 to 4.4. It is a feature.

Furthermore, the nitrification performance of the biocarrier adhering to the ammonia-oxidizing bacteria depends on DO of the nitrification tank, that is, the aeration air volume, and as shown in FIG. The nitrification rate of the carrier increases as DO increases. In particular, if DO is 3 mg / L or more, the nitrification rate increases rapidly, and if DO is 5 mg / L or more, the nitrification rate of the carrier is almost the same. It became clear that it reached 90% of the maximum value. It was also revealed that the carrier nitrification rate decreased to 20% or less of the maximum value when DO was 2 mg / L or less, and that the carrier nitrification rate was greatly reduced at low DO.
In the present invention, as a second feature, the pH of the nitrite tank is adjusted based on the following technical idea using a reaction tank in which activated sludge and a biological carrier adhering to ammonia-oxidizing bacteria are mixed in a nitrification tank. Yes.

  In the nitritation tank of the present invention, ammonia oxidizing bacteria are attached to the biological carrier and coexist in the activated sludge. The nitrification performance of the nitrification tank can be considered as the sum of the biological carrier nitrification performance and the activated sludge nitrification performance. Therefore, from the above findings, the nitrification activity of the biological carrier increases when the amount of aeration air is large. The nitrification performance of activated sludge depends on the activated sludge concentration in the nitritation tank, and the nitrification performance increases as the activated sludge concentration increases. The activated sludge is an aggregate of microorganisms, and the ratio of nitrifying bacteria varies greatly depending on the raw water state and sludge residence time. When raw water containing a large amount of organic matter such as BOD or SS or SS flows, the ratio of nitrifying bacteria in the nitritation tank activated sludge is extremely reduced, and it is expected that there is almost no nitrifying ability. On the other hand, the microorganisms adhering to the biological carrier are basically only nitrifying bacteria, and in the present invention, only ammonia oxidizing bacteria. Therefore, it is the biological carrier that mainly contributes to the nitrification performance.

On the other hand, in a nitritation tank, the pH decreases as nitrification proceeds. In normal nitrification, the optimum pH value is around 8. However, in the present invention, as a result of various studies, the amount of aeration air or the amount of aeration air and the amount of sludge returned to a nitrification tank in which a biological carrier and activated sludge coexist. By adjusting both of these parameters, the pH of the nitritation tank is controlled to 6.0 to 6.9, so that NH ₄ -N is stably converted to NO ₂ -N and partially nitritized at an ideal ratio. This is what we can do.
That is, if pH becomes 6.9 or more, nitrification will advance and pH will fall by increasing the aeration air volume and making DO high, improving the nitrification speed of a biological carrier. Similarly, if the return sludge flow rate is increased, the activated sludge concentration in the nitritation tank temporarily increases, contributing to an improvement in the nitrification rate of the nitritation tank and lowering the pH.
Similarly, if the nitritation tank pH is 6 or less, the carrier nitrification rate is decreased and the nitritation tank pH is increased to 6 or more if the aeration air volume is reduced and the DO is lowered. At the same time, if the amount of returned sludge is reduced, the concentration of activated sludge in the nitritation tank temporarily decreases, the nitrification performance of the nitritation tank decreases, and the pH can similarly rise to 6 or more. .

Even when the NH ₄ -N load exceeds a predetermined value, such as when the flow rate of raw water flowing into the nitritation tank increases or the concentration of NH ₄ -N increases, the pH is adjusted to 6.0 to 6.9. In order to obtain a stable nitritation treatment, if possible, the nitritation tank DO should be 3 mg / L or more, preferably 4 mg / L or more.
On the other hand, even when the NH ₄ -N load falls below a predetermined value, such as when the flow rate of raw water flowing into the nitrification tank decreases or the NH ₄ -N concentration falls, the pH is adjusted to 6.0 to 6. 9, in order to obtain a stable nitritation treatment, the nitritation tank DO should be 3 mg / L or less, preferably 2 mg / L or less if possible.

According to the present invention, the M-alkalinity / NH ₄ -N ratio of the inflow raw water is adjusted to a predetermined value, and even if the inflow NH ₄ -N load fluctuates in the nitritation tank, the aeration air volume or aeration By adjusting the air volume and the return sludge volume, the pH of the nitritation tank can be controlled to 6.0 to 6.9, stable partial nitritation treatment can be performed, and nitritation water NO ₂ —N / NH ₄ The -N ratio is about 1.3, which is the target, and stable denitrification performance and a high nitrogen removal rate can be obtained in the ammonia denitrification treatment in the subsequent stage. Furthermore, since the ammonia oxidizing bacteria in the nitrating tank can be kept at a high concentration by allowing the microbial carrier adhering to the ammonia oxidizing bacteria and activated sludge to coexist in the nitrating treatment tank, a high NH ₄ -N load can be obtained. In addition, the lower the nitritation water DO supplied to the ammonia denitrification tank, the less DO brought into the ammonia denitrification tank and the less adverse effect on the denitrification activity. The nitritation water DO solid-liquid separated from the activated sludge in the sedimentation basin is lower than the nitritation tank DO, and the amount of DO brought into the ammonia denitrification tank is reduced, so that the treatment performance of the ammonia denitrification tank can be stably obtained.

Furthermore, the NH ₄ —N concentration and the NO ₂ —N concentration of the nitritation tank treatment water are monitored, and when the measured NO ₂ —N / NH ₄ —N deviates from 1.3, it is injected into the nitritation tank. By finely adjusting the amount of alkali or acid injected, the nitrite-treated water NO ₂ —N / NH ₄ —N becomes approximately 1.3. Nitrogen treatment and good water quality can be obtained.

It is a graph which shows the relationship between the biological carrier nitrification rate relative ratio of a nitrification tank, and DO. It is the schematic (flow sheet) which shows the one aspect | mode of the denitrification processing method of this invention. It is the schematic (flow sheet) which shows the other aspect of the denitrification processing method of this invention.

  The water to be treated which is the subject of the present invention is sewage containing a high concentration of ammonia nitrogen, and may contain organic substances, carbonates, nitrite nitrogen and other substances. When organic nitrogen is present, it may be put into the present invention as it is, but organic nitrogen may be converted to ammonia nitrogen by anaerobic treatment or aerobic treatment in advance. Moreover, even in the case of sewage with BOD 3 times or more that of ammonia nitrogen, it may be put into the present invention as it is. Even better. Examples of target sewage include human waste, sewage, anaerobic digestion dehydrated filtrate, waste leachate, fertilizer factory effluent and the like.

Hereinafter, the denitrification method of the present invention will be described in detail with reference to the drawings showing an example of an embodiment of the present invention. However, the present invention is not limited only to these embodiments.
First, an example of the treatment according to the present invention for the concentrated dewatered filtrate of sewage digested sludge will be described with reference to the flow sheet shown in FIG.

A denitrification treatment apparatus shown in FIG. 2 which is an embodiment of the present invention includes a raw water tank 2 and a microbial carrier 8 to which a part of ammonia nitrogen (NH ₄ -N) in treated water adheres activated sludge and ammonia oxidizing bacteria. A nitritation tank 4 that converts to nitrite nitrogen (NO ₂ -N) in the presence of a solid, a solid-liquid separation tank (precipitation basin) 11 that separates activated sludge from the effluent from the nitritation tank, The sludge return line 14 for returning a part of the activated sludge separated from the solid-liquid separation tank 11 to the nitritation tank, and the NH ₄ -N as an electron donor and the effluent from the solid-liquid separation tank 11 It has an ammonia denitrification tank 16 that denitrifies by an autotrophic denitrifying bacterium in which NO ₂ -N becomes an electron acceptor, and the NH ₄ -N concentration (mg / mg) of the liquid 3 to be treated introduced into the nitritation tank 4 L) and a meter (not shown) for measuring M-alkalinity (mg / L), A mechanism for injecting alkali or acid into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio is 3.7 to 4.4 according to the measured value, and a pH in the nitritation tank 4 A mechanism for adjusting the amount of aeration air or the amount of aeration air and the amount of sludge returned to the nitrite tank so that the pH is 6.0 to 6.9 according to the measured value of the pH meter 6 I have.

As shown in FIG. 2, the concentrated dehydrated filtrate 1 of digested sludge is introduced into the raw water tank 2 as inflow raw water, and the liquid 3 to be treated is supplied from the raw water tank 2 to the nitritation tank 4. In the nitrification tank 4, a part of ammonia nitrogen (NH ₄ -N) contained in the supplied liquid 3 to be treated is caused by the action of the biological carrier 8 attached to the ammonia oxidizing bacteria and the ammonia oxidizing bacteria in the activated sludge. is oxidized to nitrite nitrogen _(NO 2 -N). After the treatment, the mixed liquid in the nitritation tank is separated by the nitritation tank separation screen 20 and the nitritation tank effluent 10 flows into the settling tank (solid-liquid separation tank) 11, and after sludge sedimentation separation. A supernatant is obtained as nitrite-treated water 12.

NH ₄ -N and M-alkalinity are measured in advance for the liquid 3 to be treated flowing into the nitritation tank, and the M-alkalinity / NH ₄ -N ratio is calculated. When the M-alkalinity / NH ₄ -N ratio is 3.7 or less, an alkali is injected into the nitritation tank when the ratio is 4.4 or more. In this case, the addition amount is set so that the liquid M-alkalinity / NH ₄ -N ratio after injection is 3.7 to 4.4, preferably 3.9 to 4.1. Also, on demand water, preferably only 4.0 near as possible M- alkalinity / _NH 4 -N ratio.

  Here, examples of the neutralizing agent 5 to be added include sodium hydroxide, sodium carbonate, sodium bicarbonate and the like as alkali, and sulfuric acid and hydrochloric acid as the acid.

A pH meter 6 and a DO meter 7 are installed in the nitritation tank 4, and the aeration air volume or aeration air volume and the aeration air volume are adjusted so that the pH is 6.0 to 6.9, preferably 6.4 to 6.7. Adjust the amount of sludge returned to the nitrous acid tank. If pH becomes 6.9 or more, DO in a tank will be raised by increasing the amount of aeration air from the aeration blower 9. As DO increases, the nitrification rate of the biological carrier 8 increases, and the pH of the nitritation tank 4 decreases to 6.9 or less. At the same time, if the return amount 14 of the sludge settled in the sedimentation basin (solid-liquid separation tank) 11 is temporarily increased, the activated sludge concentration in the nitritation tank 4 increases, and the same effect is obtained.
Conversely, if the pH is 6.0 or less when the NH ₄ -N load is low due to a decrease in the influent water volume or the raw water nitrogen concentration, the aeration air volume of the aeration blower 9 is reduced, and the DO in the nitritation tank is reduced. The nitrification rate of the carrier 8 is lowered and the pH of the nitrite tank is restored to 6.0 or more. Similarly, if the return sludge amount 14 is temporarily reduced at the same time and the activated sludge concentration in the nitritation tank 4 is lowered, the pH in the tank rises due to the decrease in the nitrification rate in the nitritation tank 4. .

In order to always obtain a high NH ₄ —N load in the nitritation tank 4, it is desirable to keep the nitritation tank DO constantly high. As shown in FIG. 1, in the case of a carrier, if the DO is 3 mg / L or less, the decrease in the nitrification rate accompanying DO decrease is large, and if the DO is 4 mg / L or more, 80% or more of the maximum nitrification rate is obtained. The DO in the nitritation tank 4 is usually 3 mg / L, preferably 4 mg / L or more.
Therefore, if the nitritation tank pH becomes 6.9 or more due to inflow nitrogen load fluctuation, it is effective to increase the aeration air volume so that the nitritation tank DO becomes 4 mg / L or more. Further, since the nitrification rate is low when the DO in the nitritation tank 4 is 2 mg / L or less, the DO in the nitritation tank 4 is 2 mg / L or less when the pH is 6.0 or less. It is effective to reduce the amount of aeration air.

In addition to activated sludge, in addition to the activated sludge, the polymer biological carrier 8 capable of adhering and fixing ammonia oxidizing bacteria can be stably attached to the nitrifying tank 4. Nitrification performance is obtained. As the polymer biological carrier 8 filled in the nitritation tank 4, synthetic polymers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyacrylamide, and photo-curing resin, polymers such as carrageenan and sodium alginate are used. Examples thereof include a gel carrier, a fluid carrier made of polyethylene, polyurethane, polypropylene, or the like.
As the shape of the carrier 8, any of a spherical shape, a square shape, and a cylindrical shape can be used, and the effective diameter is not particularly limited. However, in order to stably separate the carrier 8 by the separation screen 20 at the aeration tank outlet, 3 About 10 mm is preferable. The specific gravity of the carrier is preferably from 1.001 to 1.05 so that it can flow uniformly in the aerated state. Moreover, it is desirable that the carrier filling amount is 10 to 30 V% which enables uniform mixing flow.

In the schematic diagram shown in FIG. 2, the nitrite-treated water 12 is directly introduced into the ammonia denitrification tank 16. In the ammonia denitrification tank 16, NH ₄ -N in the inflow treated water becomes an electron donor and NO ₂ -N becomes an electron acceptor by the denitrification bacteria of the denitrification carrier 17, and is denitrified. In the mixed liquid after the denitrification treatment, the denitrification carrier is separated from the separation screen 21 to become ammonia denitrification treated water 22.

By filling the ammonia denitrification tank 16 with the polymer biological carrier 17 capable of adhering and fixing ammonia denitrifying bacteria, the ammonia denitrifying bacteria can be stably adhered, and stable denitrification performance can be obtained in the ammonia denitrifying tank 16. As the polymer carrier 17 filled in the ammonia denitrification tank 16, a synthetic polymer such as polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylamide, photocurable resin, or a polymer such as carrageenan or sodium alginate was used. Examples thereof include a fluid carrier made of a gel carrier, polyethylene, polyurethane, polypropylene or the like.
As the shape of the carrier 17, any of a spherical shape, a square shape, and a cylindrical shape can be used, and the effective diameter is not particularly limited, but in order to stably separate by the separation screen 21 at the outlet of the denitrification tank 16, About 3 to 10 mm is preferable. A carrier having a large number of fine pores on the surface, a sponge having a hollow inside, and a material having innumerable irregularities on the surface can quickly attach and fix ammonia denitrifying bacteria, and high denitrification performance can be obtained in a short period of time. Furthermore, since the ammonia denitrifying bacteria in the denitrification tank can be maintained at a high concentration for a long period of time, stable denitrification performance can be obtained.
The specific gravity of the carrier is preferably 1.00 to 1.10 which can flow uniformly by stirring in an anaerobic state. The carrier filling amount is desirably 10 to 30 V% so as not to cause local deposition in the denitrification tank.

  In the present invention, when the oxidation-reduction potential (ORP) of the ammonia denitrification tank 16 is measured by the ORP meter 18 and the ORP rises to 50 mV or more, the organic additive 15 is temporarily mixed in the nitrite-treated water 12. If the ORP drops to 50 mV or less, it is preferable to stop the supply. Further, if the nitrogen gas generated from the denitrification tank 16 is supplied to the bottom of the denitrification tank and circulated, the ORP similarly decreases.

The nitritation water 12 flowing into the ammonia denitrification tank 16 is better for the denitrification process as its DO is lower, and basically it is preferably 0 mg / L. When DO is high, there is a concern about inhibition of DO to ammonia denitrifying bacteria. If DO remains in the ammonia denitrification tank 16, the oxidation-reduction potential (ORP) increases. If the ORP is 50 mV or more, the ammonia denitrification activity is reduced. Therefore, if the denitrification tank ORP is 50 mV or more, the organic additive 15 is mixed with the nitrite-treated water 12 and added. A part of floc-forming bacteria that aerobically oxidatively decompose organic substances is attached to the denitrification carrier 17 together with the denitrification bacteria. The denitrification tank ORP is lowered by activating the floc-forming bacteria by supplying organic matter and consuming DO. Thereby, ammonia denitrifying bacteria activity is maintained high and stable denitrification performance is obtained.
On the other hand, since the growth rate of floc-forming bacteria is faster than that of ammonia-denitrifying bacteria, if the amount of organic substance 15 added is large, more floc-forming bacteria grow than ammonia-denitrifying bacteria, and the ratio of denitrifying bacteria in the denitrifying tank 16 decreases. It is preferable that the amount of organic substance added is as small as possible. Therefore, when the ORP of the denitrification tank 16 becomes 50 mV or less after the addition of the organic matter 15, the addition is stopped.

  Here, examples of the organic substance to be added include methanol, ethanol, acetic acid, sodium acetate, glucose, peptone, and the like.

  In the above example, the nitrite-treated water 12 is directly introduced into the ammonia denitrification tank 16, but when the DO of the nitrite-treated water 12 is high, an intermediate tank is provided in the middle, and the By introducing the nitrating water 12 to reduce the DO and then introducing it into the ammonia denitrification tank 16, a higher denitrification effect can be obtained. In this case, the same effect can be obtained even if the additive 15 is injected into the intermediate tank for the purpose of removing DO flowing into the ammonia denitrification tank 16.

A part of the ammonia denitrification treated water 22 is circulated to the raw water tank 2 through a circulation line 23 as necessary.
Necessarily a part of the ammonia denitrifying treatment water 22, need not be recycled to the raw water tank 1, for high _NH 4 -N concentration raw water, and reduction of _NH 4 -N concentration and _NO 2 -N concentration By circulating the ammonia denitrification treated water 22 to the raw water tank, the NH ₄ —N concentration of the water to be treated 3 flowing into the nitritation tank 4 is lowered, and the treatment of the nitritation tank 4 is stabilized. For example, the stock solution NH ₄ -N concentration is 1500 mg / L or more, such as methane fermentation liquid of livestock manure waste liquid, concentrated sludge, and methane fermentation liquid dehydrated filtrate of garbage, and it remains in the nitrification tank after partial nitritation treatment. The remaining NH ₄ —N concentration and NO ₂ —N concentration are as high as about 600 to 900 mg / L, respectively. In this state, both NH ₄ —N-derived free NH ₃ and NO ₂ —N-derived free HNO ₂ are highly toxic and are not preferable. When the NO ₂ -N concentration is 800 mg / L or more and the pH is 7 or less, the toxicity intensity of NO ₂ -N also has an adverse effect on ammonia oxidizing bacteria. As a result, the stable partial nitritation cannot be obtained, which causes a deterioration in processing performance. In this case, if a part of the ammonia denitrification treated water 22 having a low NH ₄ —N concentration and a low NO ₂ —N concentration is circulated to the raw water tank 2 (circulation line 23), NH ₄ —N in the liquid 3 to be treated. The concentration can be reduced, and the NO ₂ —N concentration and the NH ₄ —N concentration in the nitritation tank are in a range that does not adversely affect the activity of ammonia oxidizing bacteria, and a stable nitritation treatment can be obtained. Furthermore, since the M-alkalinity of the ammonia denitrification treated water 22 is high and the M-alkalinity / NH ₄ -N ratio is often higher than 4.4, the M-alkalinity / NH ₄ -N ratio is 3.7. In the case of raw water having a small ratio to the following, M-alkalinity is replenished, and the alkali injected into the nitritation tank can be reduced.

Further, as shown in FIG. 3, a part of the returned sludge from the sedimentation basin 11 after the nitritation treatment is returned to the raw water tank 2 through the return pipe 24 for the raw water having a high NH ₄ -N concentration. Thus, the organic matter in the raw water is used as a hydrogen donor by the action of the dependent denitrifying bacteria in the activated sludge in the raw water tank, and NO _x -N in the circulated ammonia denitrification treated water can be removed. The raw water T-N flowing into the water decreases, and the ammonia denitrification treated water TN serving as the final treated water is also reduced, thereby improving the TN removal rate of the entire treatment system. Further, organic substances flowing into the nitritation tank are reduced due to the reduction of organic substances accompanying NO _X -N removal in the raw water tank, and the nitrifying activity is maintained high, so that stable nitritation performance is obtained. .

  Examples of the present invention are shown below, but the present invention is not limited to these examples.

<Example 1>
According to the treatment flow shown in FIG. 2, the ammonia denitrification treatment of the sewage digested sludge dehydrated filtrate was performed. Table 1 shows the processing conditions of Example 1.

The nitrite treatment tank 4 was filled with 20 V% of a carrier 8 made of PEG having an average particle size of 4.2 mm. An average of 255 L / d was continuously passed from the raw water tank 2 to the nitritation tank 4. The M-alkalinity / NH ₄ -N ratio was determined in advance with respect to the inflow raw water, and the NaOH aqueous solution 5 was injected into the nitritation tank 4 so that the M-alkalinity / NH ₄ -N was 4.0. The output of the blower 9 was adjusted so that the DO in the nitritation tank 4 was 4 mg / L or more. In addition, priority was given to the output adjustment of the aeration blower 9 so that the pH of the nitritation tank 4 would be 6.0 to 6.9. Even when the output of the blower 9 was adjusted, the return sludge amount 14 was also adjusted when it was out of pH 6.0 to 6.9. The excess sludge 13 was extracted so that the MLSS in the nitritation tank was 3000 to 4000 mg / L.

The ammonia denitrification tank 16 was controlled by injecting sulfuric acid so that the pH was 7.5. The denitrification tank 16 was filled with 20 V% of a carrier 17 made of PVA having an average particle diameter of 4 mm. Further, since there was almost no inorganic carbon in the nitritation water 12 flowing into the ammonia denitrification tank 16, about 300 mg / L of Na ₂ CO ₃ was added to the nitritation water 12 as an additive (inorganic carbon source) 15. .
Table 2 shows examples of raw water, nitrite-treated water, and ammonia denitrification-treated water quality in Example 1 during continuous water treatment for about one year.

Since the raw water M-alkalinity / NH ₄ -N ratio was adjusted to 4.0 in advance in the nitritation treatment, about 57% of NH ₄ -N was nitrified, and the treated water NO ₂ -N was 480 mg / L, the NO ₂ —N / NH ₄ —N ratio was 1.3, which was close to the ammonia denitrification requirement of 1.32. The NO ₂ —N ratio to the treated water NO _X —N was 99.6%, and a stable nitritation treatment was obtained.
In the ammonia denitrification treatment, the inflow nitritation water NO ₂ —N / NH ₄ —N is 1.3, which is almost equal to the ratio required for the ammonia denitrification reaction. As a result, the denitrification water NH ₄ —N and NO ₂ —N are both low, 10.5 mg / L and 12.3 mg / L, respectively. TN became 107.8 mg / L and the removal rate with respect to inflow raw | natural water TN was obtained 87.3%.

Further, in Example 1, an alkaline agent was continuously added to the nitritation tank in order to replenish the raw water deficiency M-alkalinity. Note that the same effect can be obtained by adding an alkali agent directly to the raw water tank. The same effect can be obtained by using any one of NaOH, Na ₂ CO ₃ and NaHCO ₃ as the alkali agent.

<Comparative Example 1>
The same sewage digested sludge dehydrated filtrate as in Example 1 was used as raw water 1, and M-alkalinity / NH ₄ -N adjustment by NaOH injection was not performed on the raw water, and the pH of the nitritation tank 4 was 7.5. Control by NaOH injection was performed so that The aeration volume and sludge return rate were both constant. Other conditions were the same as in Example 1.
Table 3 shows an example of the raw water and treated water quality results of Comparative Example 1.

As shown in Table 3, since the raw water M-alkalinity / NH ₄ -N ratio was not adjusted and the pH of the nitrite treatment tank was controlled to 7.5, the pH was 7.5 as nitrification progressed. When reduced to below, the raw water NH ₄ —N total nitrification was inadequate for M-alkaline replenishment from NaOH injection. As a result, the nitritation tank treated water NH ₄ -N decreased to 5.6 mg / L. Reduction of NH ₄ -N in the nitrification tank reduced the toxicity of free NH ₃ to nitrite oxidizing bacteria. Further, since the pH of the nitritation tank is as high as 7.5, the amount of free HNO ₂ is small, and the toxicity to nitrite oxidizing bacteria is low, nitrification proceeds to the nitric acid type, and the treated water NO ₂ -N is 3 It decreased to 0.5 mg / L, NO ₃ -N increased to 840 mg / L, and nitrite type nitrification could not be achieved.
As described above, since stable nitritation treatment could not be performed in the nitritation tank, and nitrification became nitric acid type nitrification, the treated water NO ₃ -N was as high as 835 mg / L in the ammonia denitrification tank. The water TN was 835 mg / L, which was almost the same as the raw water TN, and the nitrogen removal rate was only about 2%.

<Comparative example 2>
The raw water was the same as in Example 1. In this comparative example, neither raw water M-alkalinity / NH ₄ -N adjustment nor nitritation tank pH control was performed. The NH ₄ —N load and the ammonia denitrification tank TN load of the nitritation tank were the same as those in Example 1.
Table 4 shows an example of the raw water and treated water quality results of Comparative Example 2.

As shown in Table 4, since the M-alkalinity / NH ₄ -N was not adjusted with respect to the inflow raw water, the nitrite-treated water NH ₄ -N was 458 mg / L, which is 87 mg / L higher than Example 1. Moreover, NO ₂ —N was 398 mg / L, which was 82 mg / L lower than Example 1. As a result, the nitrite-treated water NO ₂ —N / NH ₄ —N ratio was 0.9, which was lower than 1.3 required for the ammonia denitrification reaction.
In the ammonia denitrification treatment, the treated water NH ₄ -N was as high as 145 mg / L, so the treated water TN was 229 mg / L, and the removal rate with respect to the raw water was 73%.
If the raw water M-alkalinity / NH ₄ —N is not adjusted as described above, the NO ₂ —N / NH ₄ —N of the nitrite-treated water greatly deviates from 1.3 required for the ammonia denitrification reaction. Therefore, a large amount of NH ₄ —N remains in ammonia denitrification, and the denitrification treated water TN becomes high, and good denitrification performance cannot be obtained.

<Comparative Example 3>
The raw water of Comparative Example 3 was the same as that of Example 1. Further, with respect to the raw water, M- alkalinity / _NH 4 -N ratio was injected NaOH to nitrite reduction vessel such that a 4.0. However, as in Example 1, the aeration air volume was not controlled so that the nitritation tank pH was 6.0 to 6.9, and aeration was performed with a substantially constant air volume. In addition, the return rate was changed so that the amount of returned sludge was pH 6.0 to 6.9 as in Example 1.
Table 5 shows an example of the raw water and treated water quality results of Comparative Example 3.

As shown in Table 5, the nitrite-treated water NH ₄ -N of Example 1 was as high as 425 mg / L while the nitrite-treated water NH ₄ -N of this comparative example was 371 mg / L. Moreover, NO ₂ —N is 365 mg / L, which is lower than Example 1, and NO ₃ —N is 72 mg / L, which is higher. As a result, the nitrite-treated water NO ₂ —N / NH ₄ —N greatly deviated from the target of 1.3, 0.8.
In Comparative Example 3, when the pH of the nitritation tank is as high as 6.9 or higher, even if the activated sludge return amount is increased, the aeration air volume does not increase and is constant, so the nitrification ability of the carrier that greatly contributes to nitrification performance Was not improved, M-alkaliness remained, and NH ₄ -N became high. As a result, the pH is 7.3, which is higher than that of Example 1, and NO ₂ -N is 365 mg / L, which is lower than that of Example 1. Therefore, free HNO ₂ is lower than that of Example 1, and free from nitrite oxidizing bacteria. Since the toxicity of HNO ₂ decreased, the activity of nitrite oxidizing bacteria increased slightly, and the treated water NO ₃ -N increased to 72 mg / L.
Since nitritation treatment was not stable and good treated water could not be obtained, NH ₄ -N was largely left at 132 mg / L and NO _x -N was 147 mg / L in the ammonia denitrification tank treated water. -N was as high as 281 mg / L, and the TN removal rate relative to the raw water was only 67%.

<Comparative example 4>
The raw water of Comparative Example 4 was the same as that of Example 1. Further, with respect to the raw water, M- alkalinity / _NH 4 -N ratio was injected NaOH to nitrite reduction vessel such that a 4.0. However, neither the aeration air volume nor the return sludge flow rate adjustment was performed so that the nitritation tank pH was 6.0 to 6.9 as in Example 1, and the return rate was almost 30% of the raw water amount. It was constant.
Table 6 shows an example of the raw water and treated water quality results of Comparative Example 4.

As shown in Table 6, also in Comparative Example 4, the nitritation tank treated water NH ₄ -N is as high as 510 mg / L. Moreover, NO ₂ —N is 285 mg / L, which is lower than that of Example 1. Furthermore, NO ₃ -N increased to 85 mg / L. As a result, the nitrite-treated water NO ₂ —N / NH ₄ —N was 0.6, greatly deviating from the target 1.3.
In Comparative Example 4, even when the nitritation tank inflow NH ₄ -N load is temporarily increased or the nitrification capacity of the nitrification tank nitrification carrier is lowered and the pH rises to 6.9 or more, Since the amount of returned sludge is constant, the nitrification capacity of the support in the nitrification tank and activated sludge does not increase, and the required nitrification capacity is insufficient, resulting in an increase in the treated water M-alkalinity and NH ₄ -N. . Further, pH is higher than 7.6 as in Example 1, since the _NO 2 -N is lower than in Example 1 and 285 mg / L, free HNO ₂ is lower than in Example 1, free HNO against nitritation oxidation bacteria _{2 Since the} toxicity decreased, the activity of nitrite oxidizing bacteria increased slightly, and the treated water NO ₃ -N increased to 85 mg / L.
Since the nitritation treatment was not stable and good treated water could not be obtained, NH ₄ -N remained large at 292 mg / L and NO _X -N at 146 mg / L in the ammonia denitrification tank treated water, and T -N was as high as 438 mg / L, and the TN removal rate relative to the raw water was only 48%.

<Example 2>
Example 2 is an example of application of the present invention to a methane fermentation separated liquid of livestock waste liquid. Table 7 shows the processing conditions of Example 2.

In Example 2, the same processing apparatus as in Example 1 was used. However, since the target raw water NH ₄ -N is high, the amount of raw water is 80 L / d, which is smaller than that in Example 1. Here, ammonia denitrification treated water was circulated to the 80 L / d raw water tank. Moreover, 16 L / d equivalent to 20% of the amount of raw water was returned to the raw water tank from the nitrite treatment sedimentation basin. The MLSS in the tank became about 2000 to 3000 mg / L due to the inflow of the returned sludge from the sedimentation tank into the raw water tank. The average amount of raw water inflow into the raw water tank was 80 L / d, and the HRT based on the raw water was about 24H. Further, the inside of the raw water tank was constantly stirred with a stirrer.
NaOH was injected into the nitritation tank with respect to the raw water so that the M-alkalinity / NH4-N ratio was 4.0, as in Example 1. In addition, the aeration air volume and the return sludge flow rate were adjusted so that the nitritation tank pH was 6.0 to 6.9.
Table 8 shows an example of inflow raw water, raw water tank raw water, nitritation tank treated water, and denitrification tank treated water quality of Example 2.

The livestock dung waste liquid methane fermentation separation liquid NH ₄ -N in the raw water tank inflow was as high as 2580 mg / L, but the raw water tank NH ₄ -N became 1320 mg / L by the inflow mixing of the denitrified water. Despite the mixing of the high NO _X -N denitrification water, raw water tank in _NO X -N is 7.1 mg / L and less. Moreover, BOD fell significantly from 250 mg / L and 1100 mg / L of inflow raw | natural water. This is a result of the denitrification reaction proceeding in the raw water tank by using the BOD in the methane fermentation separation liquid as a hydrogen donor due to the activity of subordinate denitrifying bacteria in the inflow return sludge.
In the nitritation treatment, the treated water NH ₄ -N becomes 535 mg / L, NO ₂ -N becomes 705 mg / L, NO ₂ -N / NH ₄ -N becomes 1.3, and the ammonia denitrification required amount 1.32 A value close to was obtained. The NO ₂ —N ratio to the treated water NO _X —N was 98.6%, and a stable nitritation treatment was obtained.
In the ammonia denitrification treatment, the inflowing nitrite-treated water NO ₂ —N / NH ₄ —N is 1.3, which is substantially equal to the target value, so that the treated water NH ₄ —N is 8.5 mg / L, _NO 2 -N becomes low both with 15 mg / L. Further, _NO X -N is as low as 150mg / L, T-N is 159 mg / L, and the removal rate for the inflow raw water was about 93.8%.

<Comparative Example 5>
The same livestock dung waste liquid methane fermentation separation liquid as Example 2 was used. Here, unlike Example 2, only the inflow raw water was stored in the raw water tank, and the circulation of denitrification treated water and the injection of return sludge were not performed. Other conditions were the same as in Example 2.
Table 9 shows an example of raw water and treated water quality of Comparative Example 2.

As shown in Table 9, the influent raw water NH ₄ -N is as high as 2580 mg / L, and BOD also remains at 1100 mg / L. In the nitritation treatment tank, the treated water NH ₄ —N was as high as 1520 mg / L, and the NO ₂ —N was 1015 mg / L. As a result, the nitrite-treated water NO ₂ —N / NH ₄ —N was as low as 0.7, which was greatly reduced from the target value of 1.32. This is because the influent raw water NH ₄ -N is as high as 2580 mg / L, and a large amount of the nitritation tank NH ₄ -N remains, thereby increasing the toxicity of free NH ₃ and reducing the activity of ammonia oxidizing bacteria. It is done. As a result, the nitrification performance decreased and a large amount of NH ₄ -N remained.
In the ammonia denitrification tank, NO ₂ —N / NH ₄ —N is only 0.7 and NH ₄ —N is as high as 1520 mg / L, so even if denitrification proceeds, NH ₄ − Since N always remains as high as 750 mg / L or more, the amount of free NH ₃ that is toxic to ammonia denitrifying bacteria is also high, and as a result of the gradual decrease in the activity of ammonia denitrifying bacteria, the ammonia denitrified treated water finally becomes NH ₄ It became 1015mg / L at 1500 mg / L, in _NO 2 -N -N. This was almost the same level as the inflowing nitrite-treated water, and no denitrification performance was obtained.
As described above, even if high concentration NH ₄ -N raw water is not diluted, it is introduced directly into the nitrification tank and ammonia denitrification tank, and even if partial nitrite treatment and denitrification treatment are carried out, high concentration NH ₄ -N remains. Highly toxic free NH ₃ was high, and both ammonia-oxidizing bacteria and denitrifying bacteria were greatly reduced or stopped due to the influence of toxicity, and stable treatment could not be obtained.

According to the present invention, N-nitrite coexisting with activated sludge and ammonia-oxidizing bacteria-attached biological carrier is measured in advance for M-alkalinity and NH ₄ -N concentration of water to be treated containing ammoniacal nitrogen. A predetermined amount of alkali or acid is injected into the nitritation tank so that the M-alkaliness / NH ₄ -N ratio of the water to be treated flowing into the nitrification tank is 3.7 to 4.4, and nitrous acid is added. If the aeration air volume or both the aeration air volume and the return sludge volume are adjusted so that the pH of the nitrification tank becomes 6.0 to 6.9, a stable nitritation treatment can be obtained, and NO _{2 in the} nitritation water can be obtained. can be -N / _NH 4 -N ratio is around 1.3 required ammonia denitrification.
That is, since the ammonia oxidizing bacteria in the nitrifying tank can be kept at a high concentration by allowing the microbial carrier adhering to the ammonia oxidizing bacteria and the activated sludge to coexist with the activated sludge in the nitrating treatment tank, a high NH ₄ -N It was found that the load was obtained and the pH of the nitritation tank could be adjusted by adjusting the amount of aeration air in the nitrite oxidation layer. In addition, the lower the DO of nitritation water supplied to the ammonia denitrification tank, the less DO brought into the ammonia denitrification tank, and the less adverse effect on the denitrification activity. Therefore, if the nitritation water DO solid-liquid separated from activated sludge in the sedimentation basin is lower than the nitritation tank DO, the amount of DO brought into the ammonia denitrification tank is reduced and the treatment performance of the ammonia denitrification tank is stabilized. Obtained.

Also, the NH ₄ -N concentration and NO ₂ -N concentration of the nitritation tank treatment water are monitored, and when the measured NO ₂ -N / NH ₄ -N ratio deviates from 1.3, By finely adjusting the injection amount of the injected alkali or acid, the nitrite-treated water NO ₂ —N / NH ₄ —N becomes approximately 1.3, which is stable if supplied to the ammonia denitrification tank in the subsequent stage. Denitrification treatment and good water quality are obtained.

Furthermore, when the NH ₄ —N concentration of the inflowing raw water is as high as 1500 mg / L or more, the mixed solution NH ₄ flowing into the nitrification tank by circulating denitrification water having a low NH ₄ —N concentration to the raw water tank. -N is diluted and lowered. As a result, the residual NH ₄ -N concentration and NO ₂ -N concentration after partial nitritation are both suppressed to appropriate values, and free NH ₃ and free HNO ₂ concentrations that are toxic to ammonia oxidizing bacteria and ammonia denitrifying bacteria Becomes an appropriate value, and adverse effects on ammonia oxidizing bacteria and ammonia denitrifying bacteria can be reduced, and stable partial nitritation and denitrification treatment can be obtained. In addition, if BOD remains in the inflowing raw water, a part of the sludge returned to the nitritation tank sedimentation basin is returned to the raw water tank and stirred and mixed in the raw water tank. NO _X —N in the ammonia denitrification treated water can be reduced by denitrification using BOD. Thereby, TN of denitrification processing water becomes low, and the TN removal rate with respect to raw | natural water improves.

From the above, according to the treatment method and treatment apparatus of the present invention, the NH ₄ —N concentration and the NO ₂ —N concentration of the treated water after the ammonia denitrification reaction are lowered to a very low concentration stably over a long period of time. It can be widely used in the technical field of treatment of sewage, leachate, livestock wastewater, industrial wastewater, organic wastewater and the like.

1: Concentrated dehydrated filtrate 2: Raw water tank 3: Liquid to be treated 4: Nitrite tank 5: Neutralizing agent 6: Nitrite tank pH meter 7: DO meter 8: Nitrite carrier 9: Aeration blower 10: Nitrite tank effluent 11: Sedimentation basin (solid-liquid separation tank)
12: Nitrite treated water 13: Waste mud line (excess sludge)
14: Return sludge 15: Additive 16: Ammonia denitrification tank 17: Denitrification carrier 18: ORP meter 19: Ammonia denitrification tank pH meter 20: Nitrite tank separation screen 21: Ammonia denitrification tank separation screen 22: Ammonia denitrification treatment Water 23: Circulating fluid 24: Raw water tank return sludge

Claims (7)

Liquid to be treated containing ammonium nitrogen (NH 4 _-N), was introduced into nitritation tank microbial carrier of activated sludge and ammonia-oxidizing bacteria attached coexist, ammonium nitrogen該被treatment solution (NH ₄ -N) is converted into nitrite nitrogen (NO ₂ -N), concentrated and separated in a solid-liquid separation tank, and a part of the separated activated sludge is returned to the nitritation tank. In the denitrification method of ammonia nitrogen containing liquid to be nitritized,
Ammonia nitrogen concentration (NH ₄ -N) and M-alkalinity of the liquid to be treated are measured in advance,
From the measurement results, a predetermined amount of alkali or acid was injected into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio was 3.7 to 4.4 , and
The pH of the nitritation tank is 6.0 to 6.9,
When the pH is 6.0 or less, the aeration air volume is reduced to lower the dissolved oxygen (DO) in the tank, the nitrification rate is lowered, and the return amount is reduced to lower the activated sludge concentration in the tank. When the pH is 6.9 or more, the aeration air volume is increased to increase the dissolved oxygen (DO) in the tank to improve the nitrification rate, and the return amount is increased to increase the activated sludge concentration in the tank. A denitrification treatment method for an ammoniacal nitrogen-containing liquid to be treated, which is controlled so as to lower the pH. To monitor the density of the density and _NO 2 -N of _NH 4 -N of the nitrite reduction vessel treated _water, the concentration ratio of _{NO 2 -N / NH 4 -N (} NO 2 -N / NH 4 -N ratio) When the ratio is 1.3 or less, the alkali injection amount into the nitritation tank is increased or the acid injection amount is decreased. When the NO ₂ —N / NH ₄ —N ratio is 1.3 or more, the alkali injection amount is increased. The method for denitrification of an ammoniacal nitrogen-containing liquid to be treated according to claim 1, wherein the denitrification treatment method comprises reducing the acid injection amount or increasing the acid injection amount. The treated water treated in the nitritation treatment process is introduced into an ammonia denitrification tank filled with an ammonia denitrifying bacteria-attached biological carrier, and NH ₄ -N becomes an electron donor and NO ₂ -N becomes an electron acceptor. 3. The denitrification method for an ammoniacal nitrogen-containing liquid to be treated according to claim 1 or 2, wherein the denitrification treatment is performed by a nutrient denitrifying bacterium.   The treated water treated in the ammonia denitrification tank and a part of the activated sludge separated from the solid-liquid separation tank are returned to the raw water tank for introducing the treated water into the nitritation tank. The method for denitrifying an ammoniacal nitrogen-containing liquid to be treated according to claim 3. Monitor the oxidation-reduction potential (ORP) of the ammonia denitrification tank, and when the ORP reaches 50 mV or more, add organic substances directly to the ammonia denitrification tank or use nitrogen gas (N ₂ ) obtained in the denitrification tank. The method for denitrification of an ammoniacal nitrogen-containing liquid to be treated according to claim 3 or 4, wherein the denitrification tank is circulated in a denitrification tank. Part of ammonia nitrogen (NH ₄ -N) in the water to be treated introduced from the raw water tank is converted to nitrite nitrogen (NO ₂ -N) in the presence of activated sludge and microbial carriers attached to ammonia oxidizing bacteria. A nitritation tank;
A solid-liquid separation tank for separating activated sludge from the effluent from the nitritation tank;
A sludge return line for returning a part of the separated activated sludge to the nitritation tank;
Ammonia in which effluent from the solid-liquid separation tank is denitrified by an autotrophic denitrifying bacterium in which ammonia nitrogen (NH ₄ -N) serves as an electron donor and nitrite nitrogen (NO ₂ -N) serves as an electron acceptor. A denitrification tank and a measuring instrument for measuring the concentration of NH ₄ -N and M-alkalinity of the liquid to be treated introduced into the nitritation tank, and obtaining measurement values;
An injection mechanism for injecting a predetermined amount of alkali or acid into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio is 3.7 to 4.4 according to the measured value;
A pH meter provided in the nitritation tank for measuring a pH value;
A mechanism for adjusting the amount of aeration air and the amount of returned sludge so that the pH value of the pH meter is 6.0 to 6.9;
A treated water circulation line for returning a part of the treated water treated in the ammonia denitrification tank to the raw water tank;
A raw water tank sludge return line for returning a part of the activated sludge separated from the solid-liquid separation tank to the raw water tank,
Ammonia, characterized in that the treatment of the nitritation tank is stabilized with respect to the raw water having a high ammoniacal nitrogen (NH ₄ -N) concentration by the treated water circulation line and the raw water tank sludge transport line. Denitrification treatment equipment for nitrogen-containing treatment liquid. Part of ammonia nitrogen (NH ₄ -N) in the water to be treated introduced from the raw water tank is converted to nitrite nitrogen (NO ₂ -N) in the presence of activated sludge and microbial carriers attached to ammonia oxidizing bacteria. A nitritation tank;
A solid-liquid separation tank for separating activated sludge from the effluent from the nitritation tank;
A sludge return line for returning a part of the separated activated sludge to the nitritation tank;
Ammonia in which effluent from the solid-liquid separation tank is denitrified by an autotrophic denitrifying bacterium in which ammonia nitrogen (NH ₄ -N) serves as an electron donor and nitrite nitrogen (NO ₂ -N) serves as an electron acceptor. A denitrification tank and a measuring instrument for measuring the concentration of NH ₄ -N and M-alkalinity of the liquid to be treated introduced into the nitritation tank, and obtaining measurement values;
An injection mechanism for injecting a predetermined amount of alkali or acid into the nitritation tank so that the M-alkalinity / NH ₄ -N ratio is 3.7 to 4.4 according to the measured value;
A pH meter provided in the nitritation tank for measuring a pH value;
A control mechanism for adjusting the amount of aeration air and the amount of sludge returned so that the pH value of the pH meter is 6.0 to 6.9,
By the control mechanism, the pH of the nitritation tank is 6.0 to 6.9,
When the pH is 6.0 or less, the aeration air volume is reduced to lower the dissolved oxygen (DO) in the tank, the nitrification rate is lowered, and the return amount is reduced to lower the activated sludge concentration in the tank. When the pH is 6.9 or more, the aeration air volume is increased to increase the dissolved oxygen (DO) in the tank to improve the nitrification rate, and the return amount is increased to increase the activated sludge concentration in the tank. The denitrification apparatus of the ammoniacal nitrogen containing liquid to be processed characterized by controlling so that pH may be lowered by making it.

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