JP2011143363A - Method and apparatus for treating nitrogen in waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an economical method and apparatus for treating nitrogen in waste water which can reduce oxygen demand for nitrification and hydrogen donor demand for denitrification by carrying out nitrous acid type nitrification. <P>SOLUTION: In the method for treating nitrogen in waste water which includes a nitritation process 6 for oxidizing reduced nitrogen compounds in the waste water to nitrous acid by an activated sludge mixed liquor, and a denitrification process 5 for reducing and denitrifying the nitrous acid, a heat treatment process 7 for subjecting the activated sludge mixed liquor to heat treatment under an oxygen-free condition, and a solid-liquid separation process 8, the heat treatment of the activated sludge mixed liquor of the process 6 or 8 is carried out by alternately switching between a moderate temperature condition of 40-55°C for selectively inactivating nitrite-oxidizing bacteria and a high temperature condition of 60°C or higher for modifying the activated sludge mixed liquor to hydrogen donors for denitrification, or by alternately switching between a moderate temperature condition of 40-55°C for deactivating the activated sludge mixed liquor of the process 6 and a high temperature condition of 60°C or higher for modifying the activated sludge mixed liquor of the process 5, in the process 7 and then the activated sludge mixed liquor subjected to the heat treatment is introduced into the process 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and apparatus for biologically denitrifying nitrogen in wastewater by performing nitrite-type nitrification.

The biological denitrification method uses the action of nitrifying bacteria (nitrite bacteria, nitrate bacteria) to nitrify (oxidize) nitrogen compounds to NOx (NO2 + NO3) under aerobic conditions. Using this action, NOx is reduced and removed to N2 gas under anaerobic conditions. The reaction process until the completion of denitrification is expressed stoichiometrically as follows.
Nitrification reaction (aerobic condition)
NH4 ++ 1.5O2 → NO2-++ 2H ++ H2O (Nitrite bacteria) (1)
NO2- + 0.5O2-> NO3- (nitric acid bacteria) (2)
Denitrification reaction (anaerobic condition)
NO3- + H2 → NO2 ++ H2O (denitrifying bacteria) (3)
NO2- + 1.5H2-> 0.5N2 ↑ + OH- + H2O (denitrifying bacteria) (4)

  The conditions of the nitrification reaction are that the dissolved oxygen, water temperature, and pH are appropriately maintained, as in other aerobic microbial reactions, but the nitrification reaction is different from the case of oxidizing a carbon compound ( As shown in the formula (1), since this is a bioacid reaction that generates 2 equivalents of H + with respect to 1 equivalent of ammonia, the pH decreases as nitrification proceeds. However, the optimum pH range of nitrifying bacteria is 7.8 to 8.8, and when the pH is lowered to about 4, nitrification is almost stopped. For this reason, in order for a smooth nitrification reaction to be performed, the pH of the wastewater must be maintained near neutrality.

  As shown in the above formulas (1) to (4), oxygen is required for nitrification, and a hydrogen donor is required for denitrification. However, when a large amount of nitrogen contained in wastewater is treated, In addition, a large amount of valuable industrial chemicals such as oxygen supply power cost, methanol used as a hydrogen donor, and alkaline agent for pH control are consumed, which is a big problem in terms of operating cost of the denitrification apparatus.

  In the nitrification process of the denitrification apparatus, ammonia is normally nitrified to NO3. However, as can be seen from the above formulas (1) to (4), it is more effective to perform nitrification by keeping nitrification at NO2. The oxygen supply and denitrification hydrogen donor supply amount is small, which is advantageous in terms of operating costs. That is, the oxygen amount of NO2 type nitrification is 3/4 of NO3 type nitrification (1.5O2 / 2O2), and the amount of hydrogen donor consumed for the reduction of NOx is 3/5 of NO3 (1.5H2 / 2). 2.5H2) is sufficient. Thus, despite the obvious advantages of the NO2 type nitrification denitrification treatment, most of the actual denitrification treatment is carried out in the NO3 type. This is because it is extremely difficult to maintain NO2 type nitrification in the denitrification apparatus. However, there is a report that the higher the pH and ammonia concentration, the more likely it becomes NO2 type nitrification (Sewerage Association Vol.7, No.74, 1970/7, Yasunori Toya “Study on Biological Denitrification Method (1)”). Has been made.

From this chemical equilibrium equation, it can be easily estimated that free NH3 inhibits the activity of nitrate bacteria that nitrify NO2 to NO3.
NH4 ++ OH- ← → NH3 + H2O (5)
NH3: Free ammonia
From this equation (5), the higher the ammonia concentration and pH, the higher the free NH3 concentration and the range of conditions for NO2 type nitrification, but performing nitrification under such conditions is the nitrogen removal rate and the supply cost of the alkaline agent. It is difficult from the top.
In the biological denitrification method, in addition to the above-mentioned power costs for supplying oxygen for nitrification and alcohol costs for denitrification, excess sludge generated in biological treatment (activated sludge microorganisms, contained in wastewater) It is a heavy burden of processing and disposal costs (consisting of refractory suspended solids).

Oxidized nitrogen generated by nitrification in known wastewater biological denitrification methods such as nitrification liquid circulation can be used for denitrification using the BOD component of the wastewater as a hydrogen donor. It is desirable that it is about 2.86 times or more (2.86> = BOD / NO3-N, stoichiometric value not including cell growth) with respect to nitrogen. Wastewater with a small BOD / N requires valuable industrial chemicals such as industrial alcohol to make up for the shortage of BOD. On the other hand, the stoichiometric value of the BOD concentration of denitrification relative to nitrite nitrogen is 60% of nitrate nitrogen, which is about 1.71.
Furthermore, nitrous acid has a high denitrification rate because the amount of bound oxygen is 60% compared to nitric acid. In the nitrification liquid circulation method, most of the denitrifying bacteria constituting the activated sludge of the treatment apparatus are BOD-utilizing denitrifying bacteria in waste water, and some are alcohol (methanol) -utilizing denitrifying bacteria. is there. In order to improve the denitrification reaction rate of activated sludge from the bacterial cell composition ratio and the metabolic rate, it is much more effective to supply BOD components other than alcohol. Solubilization of a part of activated sludge and conversion to BOD material not only provides a hydrogen donor, but also greatly improves the denitrification rate and greatly reduces the denitrification tank volume. Effects can be obtained.

  Regarding nitrite-type nitrification, for example, in Japanese Patent Laid-Open No. 62-286598, the nitrification step under aerobic conditions is divided into two, and the former stage is adjusted intermittently or continuously to 40 to 45 ° C. Discloses a method for controlling nitrite type nitrification. However, in this publication, there is a problem that the heat loss due to the latent heat of evaporation of aeration is extremely large in order to maintain the aerobic conditions of the nitrification process of the water temperature adjustment part, and it is difficult to implement unless the wastewater itself is sufficiently hot. there were. In addition, when the BOD concentration of the wastewater itself is low, the injection amount is small compared to nitric acid nitrification, but it is necessary to inject industrial chemicals such as alcohol from the outside.

As a method for reducing chemicals for denitrification from the outside, for example, in Japanese Patent Application Laid-Open No. 2007-222830, a part of sludge is extracted from a denitrification step and / or a nitrification step, and after a solubilization treatment, And / or return to the nitrification process. This uses the increased BOD component for denitrification by using solubilized sludge as a hydrogen donor for denitrification. In addition, as an effect, reduction of excess sludge generation amount is disclosed. However, this publication does not disclose controlling the nitrification reaction to the nitrite type. For this reason, when the nitrification process is operated in the nitric acid type, the BOD / N ratio in the denitrification process is higher than that in the nitrous acid type, and the addition of an external organic substance such as methanol is necessary. The problem of high chemical costs remains.
JP-A-62-286598 JP 2007-222830 A Journal of Sewerage Association Vol. 7, no. 74, 1970/7

  In the present invention, in view of the background art, focusing on heat as a control factor common to nitrite type nitrification and sludge reforming, by performing nitrite type nitrification, oxygen demand for nitrification, for denitrification It is an object of the present invention to provide an economical wastewater nitrogen treatment method and apparatus that can reduce the amount of hydrogen donor required.

In order to solve the above problems, in the present invention, a nitritation step of oxidizing a reduced nitrogen compound of wastewater into nitrous acid by an activated sludge mixed solution, a denitrification step of reducing and denitrifying the nitrous acid, and activated sludge In the method for removing nitrogen from wastewater having heat treatment steps in which the mixed solution is heat-treated under oxygen-free conditions, the activated sludge mixed solution in the nitritation step is selectively deactivated in the heat treatment step. After heat treatment at an intermediate temperature of 40 to 55 ° C. for causing the mixture to be introduced, the heat-treated mixture is introduced into the denitrification step, and the activated sludge mixture in the nitritation step is used as a hydrogen donor for denitrification. After the heat treatment at 60 ° C. or higher for reforming, the operation of introducing the heat-treated mixed liquid into the denitrification step is performed by alternately switching the wastewater nitrogen treatment method. Is.
Further, in the present invention, a nitritation step of oxidizing the reduced nitrogen compound of wastewater into nitrous acid with an activated sludge mixed solution, a denitrification step of reducing and denitrifying the nitrous acid, and an activated sludge mixed solution with oxygen-free conditions In the nitrogen removal method of wastewater having each step of the heat treatment step that is heat-treated below, in the heat treatment step, 40 to 55 for selectively deactivating the nitrite oxidizing bacteria in the activated sludge mixed solution of the nitritation step An operation for introducing the heat-treated mixed liquid into the denitrification step after heat treatment at a medium temperature condition of 60 ° C., and 60 ° C. for reforming the activated sludge mixed liquid in the denitrogenation step to a denitrification hydrogen donor. After the heat treatment under the above high temperature conditions, the operation for introducing the mixed liquid subjected to the high temperature conditions into the denitrification step is performed by alternately switching the waste water nitrogen treatment method.

  Furthermore, in the present invention, a nitrification step of oxidizing the reduced nitrogen compound of wastewater into nitrous acid by the activated sludge mixed solution, a denitrification step of reducing and denitrifying the nitrous acid, and the activated sludge mixed solution under anoxic conditions In the method for removing nitrogen of wastewater having a heat treatment step for heat treatment and a solid-liquid separation step, in the heat treatment step, part or all of the activated sludge mixed liquid separated in the solid-liquid separation step is oxidized with nitrous acid. An operation for introducing the heat-treated mixed liquid into the denitrification step after heat treatment at a medium temperature of 40 to 55 ° C. for selectively inactivating the bacteria, and the activated sludge mixing separated in the solid-liquid separation step An operation of heat-treating a part or all of the liquid under a high temperature condition of 60 ° C. or higher for reforming into a denitrification hydrogen donor, and then introducing the heat-treated mixed liquid into the denitrification step. Switch alternately Ukoto is obtained by the nitrogen treatment method of the waste water, characterized in.

  In the nitrogen treatment method of wastewater, in the heat treatment step, the heat treatment time is such that the length of the heat treatment is high temperature condition time> medium temperature condition time, and the water temperature in the medium temperature condition time zone is 40 to 55 ° C. The heating time is set so that the heat treatment temperature is 60 ° C. or higher in the high temperature condition time zone, and the inflow amount of the activated sludge mixture liquid in the medium temperature condition time zone is the inflow amount of the activated sludge mixture liquid in the high temperature condition time zone. The denitrification step is preferably introduced after mixing the high temperature heating mixture from the heat treatment step with the effluent mixture of the nitritation step, and the waste water , A digestion liquid that flows out from the anaerobic digestion process that generates methane-containing biogas, and uses a heat generated from the biogas combustion device from the anaerobic digestion process as a heat source for the heat treatment process Kill.

  Further, in the present invention, nitritation means for oxidizing the reduced nitrogen compound of waste water to nitrous acid with an activated sludge mixed solution, denitrifying means for reducing and denitrifying the nitrous acid, and the activated sludge mixed solution with oxygen-free In the nitrogen removal apparatus of wastewater having each means of heat treatment means for heat treatment under conditions, the heat treatment means has an inflow path for flowing in the activated sludge mixed liquid from the nitritation means, and the activated sludge mixed in The heat treatment conditions of the liquid are alternately changed to a medium temperature condition of 40 to 55 ° C. for selectively deactivating nitrite oxidizing bacteria and a high temperature condition of 60 ° C. or more for reforming to a denitrification hydrogen donor. The wastewater nitrogen treatment apparatus is characterized by having a heating means for performing heat treatment by switching to a heat treatment, and an outflow path for allowing the heat-treated mixed liquid to flow out to the denitrification means.

  Further, in the present invention, nitritation means for oxidizing the reduced nitrogen compound of waste water to nitrous acid with an activated sludge mixed solution, denitrifying means for reducing and denitrifying the nitrous acid, and the activated sludge mixed solution with oxygen-free In a nitrogen removal apparatus for wastewater having each means of heat treatment means for heat treatment under conditions, the heat treatment means includes an inflow path for flowing the activated sludge mixed solution from the nitritation means, and the denitrification means. An inflow path for injecting the activated sludge mixed liquid, and an intermediate temperature condition of 40 to 55 ° C. for selectively deactivating the activated sludge mixed liquid flowing in from the nitritation means, Heating means for alternately heat-treating the activated sludge mixed liquid flowing in from the denitrification means to a high temperature condition of 60 ° C. or higher for reforming to a hydrogen donor for denitrification, and the heat-treated mixture Remove the liquid It is obtained by a nitrogen treatment apparatus wastewater and having an outflow path for flowing the element unit.

  Furthermore, in the present invention, nitritation means for oxidizing most of the reduced nitrogen compounds of wastewater to nitrous acid by the activated sludge mixed solution, denitrification means for reducing and denitrifying the nitrous acid, and the activated sludge mixed solution are not used. In a nitrogen removal apparatus for wastewater having heat treatment means for heat treatment under oxygen conditions and solid-liquid separation means, the heat treatment means includes a part or all of the activated sludge mixed liquid separated by the solid-liquid separation means. The inflow route for injecting the activated sludge and the heat treatment conditions of the activated sludge mixed solution into the intermediate temperature conditions of 40 to 55 ° C. for selectively deactivating the nitrite oxidizing bacteria and the hydrogen donor for denitrification A heating means for alternately heat-treating to a high temperature condition of 60 ° C. or higher for reforming, and an outflow path for flowing out the heat-treated mixed liquid to the denitrification means Waste water It is obtained by the hydrogen processing unit.

According to the present invention, by performing nitrite-type nitrification, the oxygen demand for nitrification and the hydrogen donor demand for denitrification can be reduced, so that economical denitrification treatment can be performed.
Further, in the present invention, the activated sludge mixed solution is heated and reformed to a denitrification hydrogen donor, so that the hydrogen donor for denitrification is replenished in the process and used as a hydrogen donor. Since the amount of sludge generated can be reduced, a synergistic economic effect can be achieved, and the control factors for nitritation and sludge reforming are unified to heat, and both intermediate and high water temperatures are achieved by intermittent operation. Since the treatment in the water temperature region can be performed in a single process, the configuration of the treatment apparatus can be simplified.
Furthermore, according to the present invention, since the supply of the hydrogen donor has become economically easy, the risk of nitrous oxide (N2O: dinitrogen monoxide) generation due to residual nitrous acid in the denitrification step is avoided, and the earth Contributes to the prevention of global warming. This nitrous oxide is one of the greenhouse gases, and the global warming coefficient indicating the degree of impact on global warming is 310 times that of carbon dioxide (CO2). It has become an issue.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flow sheet showing an outline of the steps of an example of the present invention.
In FIG. 1, the raw water 1 containing ammonia is introduced into the denitrification step 5 under anaerobic conditions together with the return sludge 2, the circulating water 3, and the heated circulating water 4-2. Similarly, reductive denitrification is performed by a hydrogen donor such as a BOD substance contained in the raw water flowing into the denitrification step 5. Ammonia hardly changes under anaerobic conditions. Next, the effluent from the denitrification process 5 flows into the nitritation process 6, and after ammonia is oxidized to nitrous acid, most of the effluent from the nitritation process 6 is circulated in the denitrification process 5. It is circulated as water 3 and heat circulating water 4-1 in the heat treatment step 7. The remaining portion is introduced into the solid-liquid separation step 8 and separated into the separated water 9 and MLSS, a part is returned to the denitrification step 5 as the return sludge 2, and the remaining portion is discharged outside the treatment system as the excess sludge 10. Is done. For solid-liquid separation, known solid-liquid separation methods such as gravity natural sedimentation, centrifugal concentration, and membrane separation can be used. When membrane separation is adopted as the solid-liquid separation method and the membrane is installed in the nitritation step 6, the return sludge line can be omitted.

  Biological nitrification denitrification is usually performed in the nitric acid type, and in order to switch to the nitrite type, it is only necessary to selectively deactivate nitric acid bacteria that oxidize nitrous acid to nitric acid. Nitric acid bacteria are less resistant to high temperature water than nitrite bacteria, and are selectively deactivated depending on the temperature range of 40 to 55 ° C. and the contact time at the water temperature. However, it is not reproduced in a strict temperature range, and the water temperature for selection varies considerably and is not uniform. This is due to the fact that nitrate bacteria in activated sludge are composed of multiple genera with slightly different characteristics, and the water temperature of nitrate bacteria and nitrite bacteria depends on the water quality (pH, water temperature, salt concentration, etc.) of the activated sludge mixture. This seems to be because resistance is different. If left at a water temperature of 40 degrees or more for a long time, nitrification activity may be inactivated and nitrifying bacteria may be destroyed. The standard is around 40-55 ° C, but the higher the water temperature, the greater the deactivation rate, so the nitrogen (NH3-N, NO2-N, NO3-N) concentration is analyzed over time and the activity of nitrifying bacteria The water temperature and contact time can be adjusted while confirming the above.

  When nitrate bacteria are inactivated and become nitrite type, even if the water temperature is lowered to around 30 ° C, the nitrite type is maintained for several months, but after that, nitrate bacteria gradually grow and become nitrate type. The activated sludge mixed liquid water temperature in the heat treatment step 7 may be adjusted to an intermediate temperature (40 to 55 ° C.) to selectively deactivate nitric acid bacteria so that the nitrite type is obtained again. Heated circulating water 4-2 heated to an intermediate temperature is circulated to the denitrification step 5. Switching from the high temperature condition (60 ° C. or higher) to the medium temperature condition (40 to 55 ° C.) may be performed when NO 2 −N / NO x −N = 0.9 (NO x −N = NO 2 −N + NO 3 −). N). That is, (1) switching from the medium temperature condition to the high temperature condition in the heat treatment process, and (2) switching from the high temperature condition to the medium temperature condition, the switching in the case of (1) is performed by changing the nitritation process from the nitrate type to the nitrite type. If it is stable with nitrous acid (NO2-N / NOx-N = 0.9 or more), switching to the case of (2) changes the nitritation process from nitrite type to nitric acid type This is performed in the first case (when NO2-N / NOx-N = 0.9 or less).

For example, when starting up a plant using activated sludge accustomed to the nitric acid type as seed sludge, the heat treatment process starts at medium temperature, the nitritation process changes to the nitrite type, At a stable stage, the heat treatment process is then switched to a high temperature condition for operation. In addition, when the heat treatment process is operated for several months under a high temperature condition and the nitritation process starts to change from the nitrite type to the nitric acid type, the heat treatment process is switched from the high temperature condition to the medium temperature condition.
In order to grasp the switching time, it is preferable to analyze the concentration of NH3-N, NO2-N, NO3-N in the nitritation step 6 several times a week to confirm the transition state to the nitric acid type. The number of days required for switching to nitritation is preferably 4 to 7 days. Moreover, the state of the nitric acid type and the nitrous acid type in the nitrification step can be evaluated by the ratio of NO3-N and NO2-N in NOx-N of the activated sludge treated water. That is, when the NO2-N / NOx-N ratio is 0.9 or more, preferably 0.98 or more, nitrite type, and the NO3-N / NOx-N ratio is 0.9 or more, preferably 0.98 or more. In the case, it can be said to be a nitric acid type.

Even if the effluent from the heat treatment step 7 is allowed to flow into the nitritation step 6 only when the treatment is performed under a medium temperature condition, the same effect can be obtained. Is set to a high water temperature range (60 ° C.). It was confirmed that when the activated sludge was reformed by heating the activated sludge mixed liquid at 60 ° C., the BOD component effective as a denitrification hydrogen donor was eluted.
Table 1 shows the elution concentration of soluble BOD (S-BOD) by heat treatment under anaerobic conditions. The target sludge is activated sludge in a nitrification tank (MLSS concentration 14000 mg / L), and the heat treatment time is 8 hours.

  The higher the temperature, the higher the reforming speed and the higher the elution BOD concentration. However, when the temperature reaches around 160 ° C, the activated sludge mixture becomes extremely brown and the biodegradable COD concentration also increases and the quality of the treated water deteriorates. To do. In addition, high temperature treatment at 100 ° C. or higher is uneconomical when the fuel is expensive and requires a national qualified person for the pressure vessel for handling, so it is desirable to adjust the temperature to 60 ° C. to 100 ° C. . The activated sludge is an aggregate of microorganisms, but when the treatment target wastewater contains a high concentration of bioinert suspended matter, the content of the bioinert substance in the activated sludge increases. Since the bioinert substance has a higher reforming temperature than microorganisms, the activated sludge having a high bioinert substance content has a relatively high temperature range of 80 to 100 ° C. and a microbial aggregate content. What is necessary is just to modify | reform in a comparatively low temperature range of 60 to 80 degreeC with respect to high activated sludge.

The total amount of the return water sludge of the circulating water amount and the heated circulating water amount is preferably an amount in which the raw water ammoniacal nitrogen is diluted to about 100 mg / L so that the pH of the nitritation step is kept neutral.
Z0 · Q / (Q + R + NC + HC) = 100 mg / L
Raw water volume Q (m3 / day), return sludge volume R (m3 / day), circulating water volume NC (m3 / day), heated circulating water volume HC (m3 / day), raw water nitrogen concentration Z0 (mg / L)
Since nitrite bacteria are also deactivated at high water temperatures (over 60 ° C), the amount of heated circulating water at high water temperatures does not cause nitrite bacteria to be washed out of the process. It is necessary to set it to ˜3.5 days (the reciprocal of the specific growth rate of nitrite bacteria) or more, and it may be determined using Equation (6) as a guide. In conditions where sludge age can be secured, the solid-liquid separation process 8 and the return sludge 2 are omitted, and the activated sludge mixed liquid in the nitritation process 6 is discharged as treated water as it is, so-called transient (One Through) process. Can also be done.
HC (m3 / day) <0.3Vn / 1 / day (6)
Heated circulating water volume HC (m3 / day), nitritation process volume Vn (m3)

The inflowing liquid residence time in the heat treatment step 7 at a high temperature may be 1 hour or longer although it depends on the water temperature and the properties of the activated sludge. In the heat treatment step 7 at high temperature, air agitation was studied for mixing, but the effect of denitrification of the heat reforming mixture as a hydrogen donor decreased. This is considered to be because a part of the hydrogen donor was biologically oxidatively decomposed at 60 to 80 ° C. and a part was released. Therefore, contact with air is not preferable.
As a heating method of the heat treatment step 7, a known heating method such as high-temperature steam, an electric heater (such as a charging type, a ribbon heater), an underwater gas burner, or a heat pump can be used. Automatic control is safe for water temperature control.
When heated circulating water 4-2 that has been heat-reformed under high temperature conditions is mixed with circulating water 3 in a pipe or the like and then introduced into the denitrification step 5, the local water temperature rises in the denitrification step and the accompanying bacteria Can be prevented from being deactivated.
Part of the activated sludge mixed liquid flowing out from the nitritation step 6 is separated into separated water 9, return sludge 2, and excess sludge 10 in the solid-liquid separation step 8. For solid-liquid separation, known separation techniques such as conventional gravity sedimentation separation and membrane separation can be used.

  Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 2, the activated sludge mixed liquid is circulated as circulating water 4-1 from the nitritation step 6 to the heat treatment step 7 in the intermediate temperature condition time zone, and the circulating water 4-1 is stopped and removed in the high temperature condition time zone. This is a method of circulating the activated sludge mixed liquid from the nitrogen step 5 as the circulating water 4-3. In FIG. 2, since the oxygen-free activated sludge mixed solution [dissolved oxygen concentration = 0] can be introduced into the heat treatment process in the high temperature condition time zone, the oxygen-free condition of the heat treatment process 7 is compared with the above-described invention of FIG. It is advantageous to maintain.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 3, a part or all of the returned sludge 2 from the solid-liquid separation step 8 is introduced into the heat treatment step 7, and the returned sludge is subjected to intermediate temperature conditions (40 to 55 ° C.) and the activated sludge mixed solution is denitrogenated. This is a method of intermittent heat treatment under high temperature conditions (60 ° C. or higher) for reforming to a hydrogen donor. After heating, the effluent mixed solution from the heat treatment step 7 is returned to the denitrification step 5. In order to prevent the nitrite bacteria in the return sludge 2 from being killed in the high temperature condition time zone, if a part of the return sludge is introduced into the heat treatment step 7 and then returned to the denitrification step 5 in the intermediate temperature time zone good.
FIG. 4 is another embodiment of the present invention for improving the nitrogen removal rate of treated water.
In FIG. 4, since the effluent from the nitritation step 6 contains nitrous acid, in order to improve the nitrogen removal rate and prevent sludge from rising during sedimentation separation, the nitritation step 6 and the solid liquid A hydrogen donor such as alcohol 22 may be added by interposing a denitrification step 20 between the separation steps 8. The activated sludge mixed solution in the denitrification process can be mixed by a known stirring mechanism.

  Next, a method for securing a heat source for heat reforming at a high water temperature will be described. The aerobic digestion method used as a method for high-concentration wastewater is a method in which human waste is aerated for a long time, but the water temperature reaches 60 ° C. due to the heat of oxidation by microorganisms. However, since the BOD component is oxidatively decomposed by free oxygen even at 60 ° C., the activated sludge cannot be reformed into a hydrogen donor for denitrification. Thus, although the water temperature reaches a high temperature due to the oxidation heat of microorganisms, there is a limit to the rise in water temperature due to latent heat of vaporization and inactivation due to the high water temperature of microorganisms, and the oxidation reaction occurs in the entire reaction tank. The sludge mixture cannot be locally heated. Another embodiment of the present invention capable of locally heating such waste water, for example, organic waste, to a high temperature will be described with reference to FIG.

In FIG. 5, the organic waste 11 is introduced into a methane fermentation process 12 under anaerobic conditions, and after the organic matter is decomposed into a biogas 13 containing methane, carbon dioxide, etc., the gas is desulfurized. After the hydrogen sulfide is removed at 14, the hydrogen sulfide is once stored in the gas holder 15 and then used as a fuel for the heat treatment step 7. The method of directly heating the activated sludge mixture using an underwater gas burner is the simplest and the apparatus configuration is simple. In the nitrification and denitrification treatment of the effluent of methane fermentation, activated sludge can be locally heated to high water temperature using methane generated in methane fermentation, so that the activated sludge mixture can be easily modified. Smooth denitrification by the modified sludge and suppression of excess sludge generation amount are possible. Therefore, the denitrification treatment using the methane fermentation digestion desorption solution as raw water is one of the preferred applications of the present invention.
Since the mixed liquid having an increased BOD concentration flows from the heat treatment process 7 to the denitrification process 5 and the BOD / N ratio is increased, denitrification is promoted.

Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited to this embodiment. Here, an embodiment will be described in which the heat treatment process is operated under a high temperature condition, the nitritation process starts to change from the nitrite type to the nitric acid type, and the heat treatment process is switched from the high temperature condition to the medium temperature condition.
Example 1
An implementation process of the operation method according to FIGS. 1 to 3 of the present invention will be described.
Table 2 and FIG. 6 show the operation history of this example. As shown in FIG. 6, data was collected in the same manner as in the operation method of FIG. 1, the operation method of FIG. 2, and the operation method of FIG.

In this example, the activated sludge mixed liquid introduced into the heat treatment process was operated for 3 months under the high water temperature condition of the method of returning from the nitritation process to the denitrification process, and then the sublimation in the oxidized nitrogen of the nitritation process. Since the ratio of nitrate nitrogen became 90% or less, the heat treatment process was switched to a medium water temperature operation.
Since the ratio of nitrite nitrogen in the oxidized nitrogen in the nitritation process reached 90% or more on the sixth day after switching to medium water temperature operation, the heat treatment process was performed at high water temperature operation (according to the flow sheet in FIG. 1). (Hereinafter referred to as “method of FIG. 1”, the same shall apply hereinafter). High water temperature operation (method of FIG. 1) was performed for 6 days, and it was confirmed that the nitrogen water quality (NH4-N, NOx-N) was stabilized. Subsequently, high water temperature operation (method shown in FIG. 1) was conducted for 2 weeks, and measurement or analysis for a total of 6 times during this period (measurement etc. were carried out once every Monday, Wednesday and Friday. The same applies hereinafter. ) The experimental result data is the average value.

Similarly, in the method of FIG. 2, the activated sludge mixed liquid in the denitrification process is operated for 3 months after the heat treatment under the high water temperature condition and then returned to the denitrification process. Since the ratio of nitrate nitrogen became 90% or less, the heat treatment process was switched to a medium water temperature operation. Since the ratio of nitrite nitrogen in the oxidized nitrogen reached 90% or more on the 6th day after switching to medium water temperature operation, switching to high water temperature operation, this operation was performed for 6 days, and the treatment was stable After confirming the above, high water temperature operation was continued for 2 weeks, 6 measurements or analyzes (similar to the above) were performed, and the average value was adopted as experimental data.
Similarly, in the method of FIG. 3, after a part or all of the activated sludge mixed liquid separated in the solid-liquid separation process is heat treated under a high water temperature condition and returned to the denitrification process for 3 months, the oxidized nitrogen is then used. Since the ratio of the nitrite nitrogen in the inside became 90% or less, the heat treatment process was switched to a medium water temperature operation. On the 6th day after switching to medium water temperature operation, the ratio of nitrite nitrogen in the oxidized nitrogen reached 90% or more, and then switched to high water temperature operation for 6 days. After confirmation, the high water temperature operation was continued for 2 weeks, 6 measurements or analysis (similar to the above) were performed, and the average value was adopted as experimental data.
Here, the heat source used for the heat treatment was obtained by converting methane gas obtained by methane fermentation into steam with a boiler. In addition, the said high water temperature is 60 degreeC or more, and medium water temperature is 40-55 degreeC temperature conditions.

  Table 3-1 and Table 3-2 show the experimental conditions and experimental results of nitrification denitrification (nitric acid type treatment: conventional method) in which the nitrification type is nitric acid type, as the implementation result 1. Table 4-1 and Table 4-2 show the experimental conditions and experimental results of nitrification denitrification (nitrite type treatment: conventional method) in which the nitrification type is nitrite type as the implementation result 2. Table 5-1 and Table 5-2 show FIG. 1 of the present invention as execution results 3 (nitrification type-high water temperature / intermediate water temperature intermittent treatment, nitrification denitrification performed by nitrite type, high water temperature heating) The experimental conditions and experimental results are shown respectively. In Table 6-1 and Table 6-2, FIG. 2 of the present invention is shown as an implementation result 4 (nitrite type—intermittent treatment of high water temperature / medium water temperature, nitrification denitrification carried out by nitrite type, high water temperature heating) The experimental conditions and experimental results are shown respectively. In addition, Table 7-1 and Table 7-2 show FIG. 3 of the present invention as an execution result 5 (nitrite type-high water temperature / intermediate water temperature intermittent treatment, nitrification type is nitrite type, and part of the returned sludge is high water temperature. The execution conditions of nitrification denitrification performed by heating and the results of nitrogen removal are shown respectively.

The specific effects of the present invention clarified from the implementation results are summarized in Tables 8 and 9 in comparison with the conventional method.
In Table 8, it can be seen that the amount of acetic acid added is remarkably reduced and the amount of surplus sludge generated is greatly reduced by the modification of activated sludge under high temperature conditions. Excess sludge requires an expensive organic polymer flocculant (polymer) at the time of dehydration, and is expensive for disposal of the dehydrated sludge. Such an expensive cost is reduced in proportion to a decrease in the amount of surplus sludge generated, so the economic effect is great. This effect is further enhanced synergistically by making the nitrification form the nitrite type. Moreover, since the scale of the dehydrator can be reduced, the purchase cost of the dehydrator can also be reduced.
Table 9 shows the relative ratio of the concentration of nitrous oxide (N2O: dinitrogen monoxide), which is an intense global warming gas, in the denitrification step 5 gas phase. In the present invention [FIGS. 1 and 2], the N2O concentration is low, and it has been found that it is effective in preventing global warming. This is presumed to be because there is a sufficient hydrogen donor in the denitrification step 5 and the oxidation-reduction potential (ORP) is stably maintained at a low level.

The flow sheet which shows the process of an example of the processing method of this invention. The flow sheet which shows the process of the other example of the processing method of this invention. The flow sheet which shows the process of the other example of the processing method of this invention. The flow sheet which shows the process of the other example of the processing method of this invention. The flow sheet which shows an example of the process combined with the methane fermentation process of the processing method of this invention. Explanatory drawing which shows the implementation background of the driving | running method of this invention.

1: raw water, 2: return sludge, 3: circulating water, 4: heated circulating water, 5: denitrification step, 6: nitritation step, 7: heat treatment step, 8: solid-liquid separation step, 9: separated water, 10: surplus sludge, 11: organic waste, 12: methane fermentation process, 13: biogas, 14: desulfurization process, 15: gas holder, 20: second denitrification process, 21: re-aeration process, 22: alcohol

Claims (10)

  A nitritation step in which reduced nitrogen compounds of wastewater are oxidized into nitrous acid by an activated sludge mixture, a denitrification step in which the nitrous acid is reduced and denitrified, and a heat treatment in which the activated sludge mixture is heat-treated under anoxic conditions In the nitrogen removal method of wastewater having each step, in the heat treatment step, an intermediate temperature condition of 40 to 55 ° C. for selectively deactivating the activated sludge mixed solution of the nitritation step in the nitrite oxidizing bacteria An intermediate temperature heated mixed liquid is obtained by heat treatment in the operation of introducing the obtained intermediate temperature heated mixed liquid into the denitrification step, and the activated sludge mixed liquid in the nitritation step is used as a hydrogen donor for denitrification. The heat treatment is performed under a high temperature condition of 60 ° C. or higher for reforming to obtain a high temperature heated mixed solution, and the operation of introducing the obtained high temperature heated mixed solution into the denitrification step is alternately performed. A method for nitrogen treatment of wastewater.   A nitritation step in which reduced nitrogen compounds of wastewater are oxidized into nitrous acid by an activated sludge mixture, a denitrification step in which the nitrous acid is reduced and denitrified, and a heat treatment in which the activated sludge mixture is heat-treated under anoxic conditions In the nitrogen removal method of wastewater having each step, in the heat treatment step, an intermediate temperature condition of 40 to 55 ° C. for selectively deactivating the activated sludge mixed solution of the nitritation step in the nitrite oxidizing bacteria An intermediate temperature heated mixed solution is obtained by heat treatment with the operation of introducing the obtained intermediate temperature heated mixed solution into the denitrification step, and the activated sludge mixed solution in the denitrification step is changed to a denitrification hydrogen donor. Heat treatment under a high temperature condition of 60 ° C. or higher to obtain a high temperature heated mixed liquid, and alternately performing the operation of introducing the obtained high temperature heated mixed liquid into the denitrification step. Nitrogen treatment method for wastewater.   A nitritation step of oxidizing the reduced nitrogen compound of waste water into nitrous acid by an activated sludge mixture, a denitrification step of reducing and denitrifying the nitrous acid, a heat treatment step of heat-treating the activated sludge mixture under anoxic conditions, And in the nitrogen removal method of wastewater having each step of the solid-liquid separation step, in the heat treatment step, a part or all of the activated sludge mixed liquid separated in the solid-liquid separation step is selectively used for nitrite oxidizing bacteria. In the operation of introducing an intermediate temperature heating mixed liquid into the denitrification step by heating at an intermediate temperature of 40 to 55 ° C. for inactivation to obtain the intermediate temperature heating mixed solution, and the solid-liquid separation step A part of or all of the separated activated sludge mixed solution is heat-treated at a high temperature condition of 60 ° C. or higher for reforming to a denitrifying hydrogen donor to obtain a high temperature heated mixed solution, and the obtained high temperature heated mixing The operation of introducing the liquid into the denitrification step Preparative, nitrogen treatment method of the waste water, which comprises carrying out alternately switched.   In the heat treatment step, the length of time for heat treatment is high temperature condition time> medium temperature condition time, and the heating time is set so that the water temperature in the intermediate temperature condition time zone is 40 to 55 ° C. The method for nitrogen treatment of wastewater according to claim 1, 2, or 3, wherein the heating time is set so that the heat treatment temperature is 60 ° C or higher.   5. The inflow amount of the activated sludge mixed liquid in the medium temperature condition time zone is larger than the inflow amount of the activated sludge mixed liquid in the high temperature condition time zone in the heat treatment step. The nitrogen treatment method of waste water as described in the item.   6. The denitrification step, wherein the high temperature heated mixed solution from the heat treatment step is introduced after being mixed with the effluent mixed solution of the nitritation step. The nitrogen treatment method of the wastewater as described.   The waste water is a digestion liquid that flows out from an anaerobic digestion process that generates methane-containing biogas, and a heat source of the heat treatment process is generated from a biogas combustion apparatus from the anaerobic digestion process. The nitrogen treatment method for wastewater according to any one of claims 1 to 6.   Nitriding means for oxidizing the reduced nitrogen compound of waste water to nitrous acid with an activated sludge mixture, denitrification means for reducing and denitrifying the nitrous acid, and heat treatment for heat-treating the activated sludge mixture under oxygen-free conditions In the nitrogen removal apparatus for wastewater having each means, the heat treatment means has an inflow path for flowing in the activated sludge mixed liquid from the nitritation means, and a heat treatment condition of the activated activated sludge mixed liquid, For heat treatment by alternately switching between a medium temperature condition of 40 to 55 ° C. for selectively deactivating nitrite oxidizing bacteria and a high temperature condition of 60 ° C. or more for reforming to a denitrification hydrogen donor. A wastewater nitrogen treatment apparatus, comprising: a heating means; and an outflow path for allowing the heat-treated mixed liquid to flow out to the denitrification means.   Nitriding means for oxidizing the reduced nitrogen compound of waste water to nitrous acid with an activated sludge mixture, denitrification means for reducing and denitrifying the nitrous acid, and heat treatment for heat-treating the activated sludge mixture under oxygen-free conditions In the nitrogen removal apparatus of waste water having each means, the heat treatment means includes an inflow path for flowing in the activated sludge mixed liquid from the nitritation means, and an activated sludge mixed liquid from the denitrification means. An inflow path for inflow, an activated sludge mixed solution flowing in from the nitritation means, an intermediate temperature condition of 40 to 55 ° C. for selectively deactivating nitrite oxidizing bacteria, and an inflow from the denitrification means And a heating means for alternately heat-treating the activated sludge mixed liquid to a high-temperature condition of 60 ° C. or higher for reforming the activated sludge mixed liquid to a denitrifying hydrogen donor; Leaked into Nitrogen treatment apparatus of the wastewater, characterized in that it comprises a fit of outflow pathways. A nitritation means for oxidizing most of the reduced nitrogen compounds of wastewater to nitrous acid by an activated sludge mixture, a denitrification means for reducing and denitrifying the nitrous acid, and heat treating the activated sludge mixture under oxygen-free conditions In the nitrogen removal apparatus for wastewater having each means of heat treatment means and solid-liquid separation means, the heat treatment means has an inflow for flowing a part or all of the activated sludge mixed liquid separated by the solid-liquid separation means. The route and the heat treatment conditions of the activated sludge mixture that has flowed in are modified to a medium temperature condition of 40 to 55 ° C. for selectively deactivating nitrite-oxidizing bacteria, and 60 for reforming into a denitrification hydrogen donor. Nitrogen treatment of wastewater characterized by having heating means for alternately heat-treating under high-temperature conditions of at least ° C. and an outflow path for flowing out the heat-treated mixed liquid to the denitrification means apparatus.

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