JP7181078B2 - Water treatment method and water treatment equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water treatment method and a water treatment apparatus, and more particularly to a water treatment method and a water treatment apparatus suitable for application to water treatment employing a nitrification/denitrification treatment method.

BACKGROUND ART Various water treatment apparatuses for treating organic wastewater containing BOD (Biochemical Oxygen Demand) and N (Nitrogen), such as night soil, nitrified liquid, industrial wastewater, etc., are conventionally known.

For example, Japanese Patent Application Laid-Open No. 6-335698 (Patent Document 1) discloses that organic wastewater containing nitrogen compounds is first aerated in an aeration tank in the preceding stage to substantially remove the BOD component, and then the sludge is separated. It is described that the nitrification is carried out by introducing into the nitrification tank in the latter stage without dehydration, and performing aeration in the presence of the carrier.

Japanese Patent Application Laid-Open No. 11-267690 (Patent Document 2) discloses a method for detecting the oxidation-reduction potential (ORP) of a nitrifying liquid in a denitrification tank in a nitrification/denitrification apparatus, and determining the supply amount of methanol based on the obtained ORP value. An example of a controlled water filtration circulation treatment system is described. In Japanese Patent No. 2912905 (Patent Document 3), raw water is supplied to a contact stabilization tank together with return sludge, ORP is controlled to -100 to 0 mV by aeration, sludge is activated, and organic matter in organic wastewater is turned into sludge. A treatment method for adsorption is described.

JP-A-6-335698 JP-A-11-267690 Japanese Patent No. 2912905

In the nitrification-denitrification treatment, which is performed in the order of denitrification and nitrification after storing organic wastewater, a circulating nitrification-denitrification method in which the nitrification liquid obtained in the nitrification tank is circulated in the denitrification process is used to Further denitrification can be performed in the denitrification tank using the derived BOD source, so the addition cost of the BOD source and the number of reaction tanks can be reduced, and more efficient water treatment can be performed.

However, when starting up a treatment apparatus that requires a long residence time, the nitrification process may not be stable for a long period of time by allowing the raw water to flow directly into the denitrification tank, and it may take a long time to start up. be.

Furthermore, when connecting the anaerobic ammonium denitrification treatment to the latter stage of the denitrification tank, it is necessary to maintain partial nitritation in the nitrification tank. need to keep above. In order to maintain the concentration of free ammonia, it is necessary to maintain a high ammonia concentration in the nitrification tank, which is in equilibrium with this, and to maintain a high ammonia concentration in the nitrification tank, it is necessary to reduce the circulation ratio. However, when the circulation ratio is decreased, the residence time becomes longer, and good nitrification activity may not be obtained.

In addition to the purpose of maintaining partial nitritation, for example, when it is necessary to operate at a low circulation ratio due to restrictions on the facility area and facility structure, or when operating with a reduced circulation rate for energy saving A decrease in nitrification activity of activated sludge may appear.

All of Cited Documents 1 to 3 have a certain effect as a method for efficiently decomposing and removing BOD and N in organic matter, but when the processing flow rate is small such as at the time of start-up No appropriate countermeasures have been proposed for any of the problems of lowering of nitrifying activity that may occur in the treatment, etc., when the nitrifying solution is operated at a low circulation ratio.

In view of the above problems, the present invention provides a water treatment method and a water treatment apparatus that can improve nitrification activity and realize early stabilization of the treatment apparatus.

As a result of intensive studies by the present inventors in order to solve the above problems, in the circulating nitrification-denitrification method in which organic wastewater is stored, denitrification and nitrification are performed in this order, sulfide is added to the water tank preceding the nitrification tank. We have found that it is effective to supply a sulfide inhibitor to suppress the generation of

In one aspect of the water treatment method according to the embodiment of the present invention, which has been completed based on the above knowledge, after storing organic wastewater, denitrification treatment and nitrification treatment are performed in order, and the nitrification liquid obtained by the nitrification treatment is In a water treatment method using a circulating nitrification and denitrification method that circulates to denitrification treatment, a sulfide inhibitor is supplied to a water tank preceding the nitrification tank for suppressing the inflow of sulfide into the nitrification tank in which nitrification treatment is performed. It is a water treatment method that

In one embodiment of the water treatment method according to the embodiment of the present invention, the sulfide inhibitor is supplied to a tank in which the hydraulic retention time is 2 hours or more and/or the circulation ratio of the nitrifying liquid is 5 times or less. Including.

In another embodiment of the water treatment method according to the embodiment of the present invention, the oxidation-reduction potential and/or dissolved oxygen concentration of a denitrification tank in which denitrification is performed is measured, and the oxidation-reduction potential is a predetermined value or more and/or It includes controlling the supply amount of the sulfide inhibitor so that the dissolved oxygen concentration is below a predetermined value.

In still another embodiment of the water treatment method according to the embodiment of the present invention, the oxidation-reduction potential and/or dissolved oxygen concentration of a storage tank for storing organic wastewater is measured, and the oxidation-reduction potential is a predetermined value or more and and/or controlling the amount of sulfide inhibitor supplied such that the dissolved oxygen concentration is below a predetermined value.

In yet another embodiment of the water treatment method of the present invention, the sulfide inhibitor comprises an oxygen-containing gas.

In still another embodiment of the water treatment method according to the embodiment of the present invention, the nitrification treatment is partial nitritation treatment.

In still another embodiment of the water treatment method according to the embodiment of the present invention, start-up treatment is performed in which the amount of organic wastewater treated is increased stepwise until the amount of organic wastewater treated reaches the rated treatment amount. and supplying the sulfide inhibitor during the start-up process.

In one aspect, a water treatment apparatus according to an embodiment of the present invention comprises a raw water tank for storing organic wastewater, a denitrification tank for denitrifying the organic wastewater to obtain a denitrifying liquid, and a nitrifying process for the denitrifying liquid. a nitrification tank to obtain a nitrifying liquid, a circulation line for circulating the nitrifying liquid to the denitrification tank, and a raw tank and denitrification tank having a hydraulic retention time of 2 hours or more and/or a circulation ratio of the nitrifying liquid of 5 times or less. and an inhibitor supplying means for supplying a sulfide inhibitor for suppressing the inflow of sulfide into the nitrification tank.

In one embodiment of the water treatment apparatus according to the embodiment of the present invention, the oxidation-reduction potential and/or the dissolved oxygen concentration of the denitrification tank are measured, and the oxidation-reduction potential is a predetermined value or more and/or the dissolved oxygen concentration is a predetermined value or less. A control means is provided for controlling the supply amount of the sulfide inhibitor so that

ADVANTAGE OF THE INVENTION According to this invention, the water-treatment method and water-treatment apparatus which can suppress the fall of the nitrification activity of a nitrification tank, and can realize early stabilization of a treatment apparatus are provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows the example of the water treatment apparatus which concerns on embodiment of this invention. It is a flowchart which shows another example of the water treatment apparatus which concerns on embodiment of this invention. It is a flowchart which shows the modification of the water treatment apparatus which concerns on embodiment of this invention. It is a flowchart which shows another modification of the water treatment apparatus which concerns on embodiment of this invention. 2 is a graph showing the relationship between the nitrification rate and the ammoniacal nitrogen volumetric load with respect to the number of days elapsed in Example 1 and Comparative Example 1 at the start-up of the apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings below, the same or similar parts are denoted by the same or similar reference numerals. The embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention. It does not specify anything.

(Water treatment method)
The water treatment method according to the embodiment of the present invention is a circulating nitrification-denitrification method in which organic wastewater is stored, then denitrification treatment and nitrification treatment are performed in order, and the nitrification liquid obtained in the nitrification treatment is circulated to the denitrification treatment. includes supplying a sulfide inhibitor to a water tank upstream of the nitrification tank for suppressing the inflow of sulfide into the nitrification tank in which the nitrification process is performed.

The organic wastewater is not particularly limited as long as it is organic wastewater containing BOD and N such as night soil, digestive fluid, and industrial wastewater, but the organic wastewater with a BOD of 500 mg/L to 3000 mg/L is treated. Furthermore, the higher the BOD concentration is from 1000 mg/L to 3000 mg/L, the higher the effect can be obtained. Organic waste water containing ammonia nitrogen of 30 mg/L or more is suitable for treatment, and the higher the concentration, 500 mg/L or more, the higher the effect. The organic waste water may or may not contain sulfide, but preferably contains sulfate ions. There are no restrictions on the concentration of sulfate ions, but the effect is particularly high when it is 100 to 5000 mg/L.

Examples of water tanks before the nitrification tank include raw water tanks that store organic wastewater, denitrification tanks that denitrify and denitrify organic wastewater, anaerobic tanks that are placed before the denitrification tanks, and raw water tanks. A regulating tank or the like arranged in the front stage of the . Although there are no particular restrictions on the position at which the sulfide inhibitor is supplied, it is preferably supplied to at least one of the denitrification tank arranged immediately before the nitrification tank and the raw water tank arranged immediately before the denitrification tank.

There are no restrictions on the addition of additional treatment after the nitrification treatment in the nitrification tank and its method. In particular, in the water treatment using the circulating nitrification and denitrification method, a part of nitrogen remains after the nitrification treatment, so finishing treatment of nitrogen is often provided. For example, as a post-treatment after nitrification treatment, methanol denitrification, endogenous denitrification, anaerobic ammonium oxidation, or the like can be added. In particular, when anaerobic ammonium oxidation is applied in the latter stage, the effect of this embodiment can be obtained more remarkably.

The sulfide inhibitor is preferably supplied in an aquarium with a hydraulic retention time (HRT) of 2 hours or more and/or a nitrifying liquid circulation ratio of 5 times or less. By supplying a sulfide inhibitor to a tank with a hydraulic retention time of 2 hours or more, it is possible to suppress the generation and anaerobicization of sulfide in the tank with a relatively long retention time. It is possible to suppress the inflow of toxic substances including sulfides, which affect the nitrification activity of the nitrification tank, into the nitrification tank, and suppress the decrease in the nitrification activity of microorganisms in the nitrification tank.

In particular, water tanks with an HRT of 8 hours or more, or even 2 days or more, are likely to become anaerobic in the water tank, decomposing organic wastewater, and easily generating toxic substances such as sulfides. By supplying a sulfide inhibitor to such a water tank, the water quality of the treated water flowing into the nitrification tank can be more properly maintained, and early start-up and stabilization of the water treatment equipment can be realized. .

When a partial nitritation treatment is used as a nitrification tank, it may not be possible to increase the circulation ratio of the nitrification liquid in order to stably maintain the partial nitritation treatment. For example, when the amount of influent water flowing into the nitrification tank is Q, in order to perform the partial nitritation treatment more stably, the circulating water amount of the nitrifying liquid to be circulated back to the denitrification treatment should be 5Q or less, or even 2Q or less. That is, it is necessary to set the circulation ratio of the nitrifying liquid to 5 times or less, further to 2 times or less.

By supplying the sulfide inhibitor to the water tank in which the circulation ratio of the nitrifying liquid is 5 times or less, or further 2 times or less, the ammonia concentration in the nitrification tank in which partial nitritation is performed is increased. Since the inflow of sulfide into the nitrification tank can be suppressed, the decrease in the nitrification activity of the nitrification tank can be suppressed and the water treatment apparatus can be stabilized at an early stage.

The sulfide inhibitor is not particularly limited as long as it can reduce the sulfide concentration of the treated liquid in the denitrification tank without inhibiting the nitrification activity of the nitrification tank. For example, microorganisms such as sulfur-oxidizing bacteria, or oxidizing agents such as iron salts, oxygen-containing gases, hydrogen peroxide, calcium peroxide, anthraquinone compounds, molybdenum compounds, and ozone can be used as sulfide inhibitors.

Above all, by using an oxygen-containing gas as a sulfide inhibitor, there is no need to install a separate reaction tank for desulfurization treatment, and the cost of adding chemicals is eliminated, simplifying water treatment equipment. Moreover, it is possible to provide a water treatment apparatus that can be made smaller and that is economically advantageous. As the oxygen-containing gas, any gas containing oxygen can be used, and oxygen gas, air, or the like can be used.

The supply amount of the sulfide inhibitor is such that the sulfide concentration in the influent flowing into the nitrification tank is 25 mg/L or less, more preferably 20 mg/L or less, still more preferably 10 mg/L or less, still more preferably 5 mg/L or less. is preferably adjusted to The sulfide concentration in water may be measured and confirmed with a detector, or the sulfide concentration in water may be estimated by measuring the hydrogen sulfide concentration in the gas phase of the water tank. Also, these values may be continuously monitored and measured and used for control. As a result, the nitrification process can be performed more stably without inhibiting the nitrification activity of the microorganisms flowing in the nitrification tank.

Regarding the supply control of the sulfide inhibitor, measure the oxidation-reduction potential (ORP, reference electrode: composite electrode (platinum electrode + reference electrode)) and dissolved oxygen concentration (DO) of the denitrification tank where denitrification treatment is performed immediately before the nitrification tank. However, it is preferable to control the supply amount of the sulfide inhibitor so that the ORP is a predetermined value or more and the DO is a predetermined value or less. That is, with respect to the appropriate supply amount of the sulfide inhibitor, the lower limit of the supply amount is determined by the ORP of the denitrification tank, and the upper limit of the supply amount is determined by the DO of the denitrification tank. By controlling the supply amount of the sulfide inhibitor based on both the ORP and DO in this way, the supply amount of the sulfide inhibitor can be adjusted more appropriately.

It is preferable to control the supply amount of the sulfide inhibitor so that the ORP of the denitrification tank is −400 mV or more, more preferably −300 mV or more. The upper limit of the oxidation-reduction potential is not particularly limited, but excessive supply of the sulfide inhibitor to promote oxidation may inhibit the denitrification reaction. Control is preferred.

When controlling the supply of the sulfide inhibitor based on the DO of the denitrification tank, the supply amount is controlled so that the DO of the denitrification tank is 0.5 mg/L or less, further 0.2 mg/L or less. is preferred. Furthermore, when the sulfide inhibitor is supplied to the raw water tank preceding the denitrification tank, the DO of the raw water tank is 5 mg/L or less, further 3 mg/L or less, and further 1 mg/L. It is preferable to control the supply amount. The sulfide inhibitor may be supplied by measuring the sulfide concentration in the influent water flowing into the nitrification tank and increasing or decreasing the supply amount according to the measurement result.

By applying the supply of the sulfide inhibitor to the start-up process in which the processing amount of organic wastewater is gradually increased until it reaches the rated processing amount, the nitrification activity of the nitrification tank is prevented from decreasing. By suppressing this, it becomes possible to realize early stabilization and early startup of the processing equipment.

When starting up the equipment, for example, starting with a treatment amount of about 1/10 of the rated treatment amount, the treatment amount may be increased step by step by about 1.5 to 2 times. Liquid retention time tends to be longer. Therefore, by adopting this method at the start-up time, a particularly advantageous effect is exhibited as a water treatment method and a water treatment apparatus capable of reaching the rated treatment capacity at an early stage.

In addition, when the amount of organic wastewater to be treated is relatively small, for example, during construction of treatment facilities, during consecutive holidays when the collection amount of human waste is decreasing, and for industrial wastewater during the shutdown period of factories, etc. This method can be preferably used.

When the present inventors performed start-up operation while maintaining various conditions such as pH and DO using a plant of nitrification and denitrification treatment equipment as described in Japanese Patent Application Laid-Open No. 2017-144402, it took about half a year. However, the activity of the sludge did not increase, and the nitrifying bacteria did not adhere to the carrier. Therefore, the processing flow rate could not be increased step by step, and the start-up operation was sometimes prolonged.

When measures were taken to temporarily increase the treatment flow rate in order to promote the supply of ammonia, which is also a substrate, ammonia remained in the treated water, leading to a vicious cycle in which the concentration of beneficial ammonia, which inhibits nitrifying bacteria, increased. . Furthermore, as measures for increasing the rate of nitrification by nitrifying bacteria and promoting the adhesion of nitrifying bacteria to the carrier, phosphorus, which is an essential element for nitrifying bacteria, is added to the nitrification tank, and alkali necessary for promoting the nitrification reaction is added. An attempt was made to add a nitrifying agent to the nitrification tank, but the effect of increasing the rate of nitrification and promoting adhesion of nitrifying bacteria was hardly obtained.

The inventors of the present invention carried out further intensive studies, carried out laboratory tests in parallel with the above-mentioned nitrification and denitrification treatment plant, and compared the conditions and conditions of each water tank of the water treatment equipment in detail. As a result, while the color tone of the raw water and the denitrification tank did not change in laboratory tests using raw water with aeration, it was extracted that the color of the sludge in the denitrification tank at the plant turned black. From this situation, it was presumed that one of the causes of the decrease in the nitrification activity of the nitrification tank was the contamination of sulfides in the influent water flowing into the nitrification tank due to the retention time of the organic waste water.

According to the water treatment method according to the embodiment of the present invention, a sulfide inhibitor for suppressing the inflow of sulfides into the nitrification tank is supplied to the tank upstream of the nitrification tank. For example, by aerating the raw water tank and/or the denitrification tank under conditions that do not interfere with the treatment in each water tank, it is impossible to obtain the desired results even after optimizing various conditions such as pH and DO and taking various measures for about half a year. It is possible to increase the activity of the sludge in the nitrification tank, which was not present, and to quickly attach the nitrifying bacteria to the outer surface of the carrier, thereby stabilizing the treatment apparatus at an early stage.

(water treatment equipment)
FIG. 1 shows an example of a water treatment apparatus to which the water treatment method according to the embodiment of the invention can be applied. The water treatment apparatus includes a raw water tank 1 for storing organic waste water, a denitrification tank 2 for denitrifying the organic waste water to obtain a denitrifying solution, and a nitrification tank 3 for obtaining a nitrified solution by nitrifying the denitrifying solution. , a solid-liquid separation tank 4 for solid-liquid separation of the digestive liquid, a circulation line 5 connected to the nitrification tank 3 or a pipe in the latter stage of the nitrification tank 3 to circulate the nitrification liquid to the denitrification tank 2, and a solid-liquid separation tank 4. A return line 6 connected to the bottom of the solid-liquid separation tank 4 for returning the sludge solid-liquid separated in the solid-liquid separation tank 4 to the denitrification tank 2 as return sludge, and a sulfide suppression for suppressing the inflow of sulfides into the nitrification tank 3 Inhibitor supply means 7 for supplying an agent may be provided.

The denitrification tank 2 is provided with an ORP meter 21 for measuring the ORP of the water to be treated in the denitrification tank 2, a DO meter 22 for measuring DO, a thermometer 23 for measuring temperature, and a pH meter 24 for measuring pH. there is Furthermore, stirring means 25 for stirring the water to be treated in the denitrification tank 2 is arranged. The nitrification tank 3 is provided with a DO meter 32 for measuring the DO of the denitrification liquid flowing into the nitrification tank 3 to be treated, a thermometer 33 for measuring temperature, and a pH meter 34 for measuring pH. Furthermore, 35 for stirring the denitrification liquid in the nitrification tank 3 is arranged. The nitrification tank 3 contains a macromolecular biological carrier 34 capable of adhering nitrifying bacteria to its outer surface. A screen 36 is provided in the nitrification tank 3 to prevent the macromolecular biocarriers 34 from flowing out. The solid-liquid separation tank 4 may be provided with stirring means 45 for stirring the inside of the tank.

In the water treatment apparatus shown in FIG. 1, when an oxygen-containing gas is used as a sulfide inhibitor, an existing oxygen or air supply device such as a blower can be used as the sulfide inhibitor supply means 7 arranged in the raw water tank 1. Can be used in combination. When aeration is used as the sulfide inhibitor supply treatment, it is preferable to adjust the amount of aeration air in the raw water tank 1 so that the ORP of the denitrification tank 2 is -400 mV or more, and more preferably -300 mV or more.

In particular, when the ORP of the organic wastewater, which is the raw water, is as low as −300 mV or less and contains a large amount of reducing substances, based on the measurement results of the ORP meter 21 arranged in the denitrification tank 2, the sulfide inhibitor in the raw water tank 1 For more efficient treatment, it is preferable to adjust the supply amount of .

When the sulfide inhibitor is supplied to the raw water tank 1, the combined use of heating may change the properties of the organic waste water, and the nitrification and denitrification treatment may not be performed stably. Therefore, it is preferable that the supply of the sulfide inhibitor to the raw water tank 1 is carried out with as little heat as possible such as heating or steaming. For example, it is more preferable to adjust the water temperature of the organic waste water in the raw water tank 1 to 4 to 30° C., the pH to 6.5 to 8.5, and the ORP to −400 mV or more.

A DO meter (not shown) may be arranged in the raw water tank 1 to control the DO of the raw water tank 1 . It is preferable to adjust the amount of aeration by the inhibitor supply means 7 so that the DO in the raw water tank 1 is 5 mg/L or less, further 3 mg/L or less, further 1 mg/L or less.

In the denitrification tank 2, nitrogen gas is generated by using denitrifying bacteria, which are heterotrophic bacteria in the activated sludge, and using BOD derived from organic wastewater, which is raw water, and NO _x -N generated in the nitrification tank 3. Heterotrophic denitrification proceeds. The water temperature is adjusted to 15-35°C and the pH is adjusted to 7.5-8.5. As shown in FIG. 2 , an inhibitor supply means 7 may be arranged in the denitrification tank 2 for supplying a sulfide inhibitor for suppressing the inflow of sulfides into the nitrification tank 3 . If the denitrification tank 2 has an existing facility for supplying stirring gas or the like, that facility may be used to supply the oxygen-containing gas as the sulfide inhibitor.

As in the water treatment apparatus shown in FIG. The addition of sulfide inhibitors can be omitted. On the other hand, the HRT of the denitrification tank 2 is 2 hours or more, 8 hours or more, or 2 days or more, or the circulation ratio of the nitrifying liquid returned to the denitrification tank 2 is 5 times or less, or 2 times or less. When the residence time of the treatment liquid is long, it is preferable to supply the denitrification tank 2 with a sulfide inhibitor.

In the denitrification tank 2, as shown in FIG. 2, the ORP and DO of the denitrification tank 2 are measured using an ORP meter 21 and a DO meter 22. is 0.5 mg/L or less, more preferably 0.2 mg/L or less. The sulfide inhibitor feed rate may be controlled based on either ORP or DO.

In the nitrification tank 3, nitrifying bacteria act to oxidize the ammoniacal nitrogen contained in the organic waste water into NO ₂ —N or NO ₃ —N. In the nitrification tank 3, there are cases where only activated sludge is used, and there are cases where activated sludge and a carrier are used together. When partial nitritation treatment is performed in the nitrification tank 3, in order to stably maintain the ammonia-oxidizing bacteria in the nitrification tank 3, 10 macromolecular biological carriers 34 capable of adhering and fixing ammonia-oxidizing bacteria are provided on the outer surface. About ~30% v/v is accommodated.

In order to perform the partial nitritation treatment in a more stable manner, coexistence of the macromolecular biological carrier 34 to which the ammonia-oxidizing bacteria are adhered and the suspended activated sludge is desirable. Due to the coexistence of suspended activated sludge, even if the water quality of the influent flowing into the nitrification tank 3 fluctuates, it can be averaged by the activated sludge treatment, and the impact of adhesion of ammonia-oxidizing bacteria on the macromolecular biological carrier 34 is almost negligible. Therefore, a stable nitritation treatment can be obtained, and early start-up and early stabilization of the entire water treatment apparatus can be promoted.

Oxygen-containing gas is supplied into the nitrification tank 3 by the stirring means 35 provided in the nitrification tank 3 . It is preferable that the DO in the nitrification tank 3 be maintained at 2 mg/L or less by the DO meter 32 .

(Modification)
3 and 4 show a modification of the water treatment device according to the embodiment of the present invention. The water treatment apparatus shown in FIGS. 3 and 4 shows an example of water treatment using an anaerobic-anoxic-aerobic method, and an anaerobic tank 9 is provided after the raw water tank 1 . The denitrification tank 2 downstream of the anaerobic tank 9 functions as an anoxic tank for nitrogen removal, and the nitrification tank 3 downstream of the denitrification tank 2 functions as an aerobic tank for decomposition of organic matter, removal of phosphorus, and nitrification of ammonia. Function. The anaerobic tank 9 is provided with an ORP meter 91, a thermometer 93, a pH meter 94, and the like, like the denitrification tank (anoxic tank) 2 and the nitrification tank (aerobic tank) 3. In the water treatment apparatus shown in FIGS. 3 and 4, a sulfide inhibitor is supplied to at least one of the raw water tank 1, the anaerobic tank 9 and the anoxic tank 2 to suppress the inflow of sulfide into the nitrification tank 3. Inhibitor supply means 7 may be provided for.

As described above, according to the water treatment apparatus according to the embodiment of the present invention, at least one of the raw water tank 1, the denitrification tank 2, and the anaerobic tank 9, in which the HRT is 2 hours or more and/or the circulation ratio of the nitrifying liquid is 5 times or less. In addition, an inhibitor supply means 7 for supplying a sulfide inhibitor for suppressing the inflow of sulfides into the nitrification tank 3 is provided, thereby reducing harmful substances including sulfides flowing into the nitrification tank 3. Therefore, it is possible to suppress the deterioration of the nitrification activity in the nitrification tank 3 and to stabilize the treatment equipment at an early stage.

Examples of the present invention are presented below along with comparative examples, which are provided for a better understanding of the invention and its advantages and are not intended to be limiting of the invention.

(Example 1, Comparative Example 1)
A water treatment test was performed on the apparatus shown in FIG. The raw water used was a dehydrated liquid separated from night soil treatment plant (average: NH ₄ -N: 650 mg/L, BOD: 400 mg/L, SO ₄ ^2- : 1500 mg/L, iodine consumption: 200 mg/L). The raw water was slightly aerated in the raw water tank and controlled so that the ORP in the raw water tank was -400 mV or more, the water temperature was 4 to 30°C, the pH was 6.5 to 8.5, and the DO was 5 mg/L or less. At that time, slight aeration was performed so that the ORP of the denitrification tank was −300 mV or higher.

The nitrification tank was filled with 20% polyethylene glycol carrier, and the capacity of the denitrification tank and the nitrification tank was 1 L. The nitrified liquid from the nitrification tank and the returned sludge from the solid-liquid separator were circulated to the denitrification tank for each 1Q of the raw water. The NH ₄ --N volume load was increased stepwise in the range of 0.3 to 1.0 kg/m ³ /d to increase the nitrification rate and to promote adhesion of nitrifying bacteria to the carrier. The results are shown in FIG.

In Example 1, the flow rate was increased weekly to increase the NH ₄ --N volume loading. In order to prevent the nitrification of the activated sludge from being suppressed due to the concentration of free ammonia, the operation was carried out while maintaining the concentration of free ammonia not exceeding 1 mg/L. As a result, in the system in which raw water was aerated, sulfide ions and hydrogen sulfide were not detected in the denitrification tank in Example 1. On the other hand, in Comparative Example 1 in which the raw water was not aerated, 2 to 10 mg/L of sulfide ions and 25 to 50 mg/L of hydrogen sulfide were detected in the denitrification tank. One month after the test, the nitrification rate increased to 0.8 kg/m ³ /d in Example 1, but it was about 0.4 kg/m ³ /d in Comparative Example 1, indicating a difference in the nitrification rate. was taken. In Example 1 _{, the NH 4 —N} volume load was gradually increased while stable treatment was performed. .

1... Raw water tank 2... Denitrification tank (anoxic tank)
3... Nitrification tank (aerobic tank)
4 Solid-liquid separation tank 5 Circulation line 6 Return line 7 Inhibitor supply means 8 Control means 9 Anaerobic tank 21, 91 ORP meter 22, 32 DO meter 23, 33, 93 Thermometer 24, 34, 94 ... pH meter 25, 35, 45 ... Stirring means 34 ... Macromolecular biological carrier 36 ... Screen

Claims (6)

In a water treatment method using a circulating nitrification-denitrification method in which organic wastewater is stored, then denitrification treatment and nitrification treatment are performed in order, and the nitrified liquid obtained in the nitrification treatment is circulated to the denitrification treatment,
performing a start-up process in which the processing amount of the organic wastewater is increased stepwise until the processing amount of the organic wastewater reaches the rated processing amount;
During the start-up process, an oxygen-containing gas for suppressing the inflow of sulfide into the nitrification tank where the nitrification process is performed is supplied so that the oxidation-reduction potential of the water tank preceding the nitrification tank is -400 mV or more. ,
The nitrification treatment is a partial nitritation treatment in which a macromolecular biological carrier to which ammonia-oxidizing bacteria are attached and suspended activated sludge coexist, and the nitrification treatment is followed by an anaerobic ammonium oxidation treatment. water treatment method. 2. The water treatment method according to claim 1, comprising supplying the oxygen-containing gas into the water tank having a hydraulic retention time of 2 hours or more and/or a circulation ratio of the nitrifying liquid of 5 times or less. The oxidation-reduction potential and/or dissolved oxygen concentration of the denitrification tank in which the denitrification treatment is performed is measured, and the above-mentioned 3. The water treatment method according to claim 1 or 2, comprising controlling the supply amount of the oxygen-containing gas. The oxidation-reduction potential and/or the dissolved oxygen concentration of the storage tank for storing the organic wastewater is measured, and the oxygen The water treatment method according to any one of claims 1 to 3, comprising controlling the supply amount of the contained gas. The supply amount of the oxygen-containing gas is adjusted so that the sulfide concentration in the influent water flowing into the nitrification tank is 25 mg/L or less,
Immediately before the nitrification treatment, the oxidation-reduction potential and dissolved oxygen concentration of the denitrification tank in which the denitrification treatment is performed are measured. /L or less, and when the oxygen-containing gas is supplied to the raw water tank preceding the denitrification tank, the dissolved oxygen concentration in the raw water tank is controlled to 5 mg / L or less. 3. The water treatment method according to claim 1, wherein the supply amount of the oxygen-containing gas is suppressed. a raw water tank for storing organic wastewater;
a denitrification tank for denitrifying the organic wastewater to obtain a denitrification liquid;
a nitrification tank in which the denitrification solution in which the macromolecular biological carrier to which ammonia-oxidizing bacteria is attached and suspended activated sludge coexist is subjected to partial nitritation treatment to obtain a nitrification solution;
a circulation line for circulating the nitrifying liquid to the denitrification tank;
The hydraulic retention time is 2 hours or more and/or the circulation ratio of the nitrifying solution at the time of start-up treatment in which the treatment amount of the organic wastewater is increased stepwise until the treatment amount of the organic wastewater reaches the rated treatment amount. Sulfide to the nitrification tank so that the oxidation-reduction potential of at least one of the raw water tank and the denitrification tank is -400 mV or more. an inhibitor supply means for supplying an oxygen-containing gas for inhibiting the inflow of
an anaerobic ammonium oxidation treatment tank for anaerobic ammonium oxidation treatment of the nitrifying liquid;
A water treatment device comprising:

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