JP5936774B2 - Waste water treatment method and waste water treatment system - Google Patents

Description

The present invention relates to a method for treating industrial wastewater, domestic wastewater, human waste and other wastewater, and a wastewater treatment system.
This application claims priority on June 13, 2013 based on internationally filed PCT / JP2013 / 066393, the contents of which are incorporated herein by reference.

Conventionally, it is known that biological treatment is effective as a treatment method for wastewater such as industrial wastewater, domestic wastewater, and human waste. Among these, the activated sludge method is most widely adopted (for example, Non-Patent Document 1).
In the activated sludge method, waste water is aerated in an aeration tank (aerobic tank), and organic matter (hereinafter referred to as “BOD”) in the waste water is decomposed by oxygen respiration of aerobic microorganisms in the activated sludge to treat the waste water. It is a method to do.

In addition to BOD, wastewater may contain organic nitrogen (eg, proteins, amino acids, urea, etc.), nitrogen such as ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and phosphorus. In some cases, it is necessary to remove the.
Methods for treating wastewater containing BOD, nitrogen, and phosphorus include nitrification denitrification, anaerobic / aerobic (AO), anaerobic, An anaerobic / aerobic method (A2O method), anaerobic / nitrification endogenous denitrification method (AOAO method) and the like are known (for example, Non-Patent Document 2).
Further, as a method for treating waste water containing BOD and nitrogen, a method has been proposed in which the dissolved oxygen concentration is controlled to 1 mg / L or less and microorganisms having different metabolism are treated in a single tank (for example, patents). References 1, 2).

  In addition, biofilm treatment methods such as a carrier method, a catalytic oxidation method, and a rocking bed method are known as techniques for enhancing the capacity of the treatment tank. The biofilm treatment method is a technique for enhancing treatment capacity by attaching microorganisms in an aeration tank to an artificial filter medium (for example, a carrier, a filter bed, a rocking bed, etc.) and increasing the number of microorganisms in the aeration tank.

By the way, bacteria in activated sludge produce extracellular polysaccharides (EPS) in water, and it is known that characteristic structures including other bacteria and microorganisms are formed (formation of biofilm). (For example, nonpatent literature 3). An example of the characteristics of the biofilm is shown below.
(I) Since EPS in a biofilm is produced by microorganisms, its composition, that is, physical and chemical properties, varies in various ways.
(Ii) In the biofilm, microorganisms are inhabiting at an extremely high density (a closed colony with a high density of inhabitants is formed) in comparison with the surrounding environment, and homeostasis (in the microorganism, the internal environment is constant. The function of maintaining the state) is easily maintained.
(Iii) The oxygen concentration and ion concentration in the biofilm differ depending on the distance from the water channel and the distance from the biofilm surface, and form an oxygen concentration gradient and ion concentration gradient on the order of μm. Therefore, various niches (ecologic status) are created, and it becomes possible to sort microorganisms of different metabolic systems (for example, aerobic microorganisms and anaerobic microorganisms) on the order of μm.
(Iv) Biofilms also have a function of protecting and protecting microorganisms against various stimuli, such as increasing the resistance of internal microorganisms to drugs and increasing the protection from the toxicity of heavy metals and organic solvents.
(V) Within a biofilm, many types of microorganisms exchange metabolites, energy, and information with each other to create functions not found in a single microorganism (such as those that cannot be metabolized by a single species). It is possible to cope with various environmental changes.
(Vi) Microorganisms inside the biofilm have a lower growth rate than surface microorganisms.
(Vii) When the bacteria are subjected to stress such as nutrient deficiency such as nitrogen and phosphorus and oxygen deficiency, the production of EPS increases.

"Technology for enhancing activated sludge process", November 1, 1979, published by Science and Technology Development Center, Chapter 1 Measures for improving activated sludge process, pages 1-1 to 1-3 Supervised by the Sewerage Department, City Bureau, Ministry of Construction "Sewerage Facility Planning and Design Guidelines and Explanation, Part 1994", October 25, 1994, Japan Sewerage Association, Chapter 5, Water Treatment Facilities, pages 126-139 “Introduction to Biofilms-New Microorganisms in the Century of the Environment”, October 17, 2005, Japanese Society for Microbiological Ecology, Biofilm Research Group, Chapter I Biofilms as a place for microbiology, Chapters 1-10

JP 59-90696 A JP 2011-5354 A

However, in the case of the activated sludge method, since the BOD volume load of the aeration tank is usually controlled at about 0.3 to 0.8 kg-BOD / m ³ · d and the dissolved oxygen concentration is about 1 to 2 mg / L, aeration is performed. The tank capacity is increased, a large amount of air (oxygen) supply is required, and power consumption of the blower and the like is large. Moreover, in the activated sludge method, a large amount of excess sludge is generated, and the treatment costs of the excess sludge (dehydration costs, drying costs, industrial waste disposal costs, etc.) increase.
In the activated sludge method, a small amount of BOD is decomposed by respiration (sulfate respiration) or fermentation of anaerobic microorganisms in an anaerobic part such as the inside of the formed floc and a dead space where the aeration tank cannot be stirred. . At this time, substances that cause odor, such as organic acids, alcohols, and hydrogen sulfide, are generated.
Furthermore, in the activated sludge method, bulking may occur when the dissolved oxygen concentration in the aeration tank becomes low due to rapid load fluctuations (particularly rising) or BOD component changes in the wastewater. Once bulking occurs, it becomes difficult for the sludge to settle, and it becomes difficult to separate the treated water from the sludge in the sedimentation tank located downstream of the aeration tank.

When treating wastewater by the nitrification denitrification method, AO method, A2O method, AOAO method, etc., the metabolism (breathing) of microorganisms that treat BOD, nitrogen, and phosphorus is different. An anaerobic tank, an oxygen-free tank, and an aerobic tank are needed. Therefore, the installation area of a processing tank becomes large and operation management becomes complicated.
In addition, in the biological treatment methods described in Patent Documents 1 and 2 at a dissolved oxygen concentration of 1 mg / L or less, the processability tends to be lost due to small changes in raw water conditions and operating conditions, and it is difficult to maintain the processability and continue the operation. It was. Furthermore, in the methods described in Patent Documents 1 and 2, the treatment of BOD and nitrogen is described in a single tank, but the treatment of waste water that contains little or no nitrogen relative to BOD is described. It has not been. Moreover, it does not describe about simultaneous removal of BOD, nitrogen, and phosphorus in a single tank when phosphorus is also included.
In addition, the biofilm treatment method can enhance the processability by increasing the amount of microorganisms in the treatment tank by adhering microorganisms in the treatment tank to the filter medium (fixed bed, fluid carrier, rocking fiber filter medium, etc.). However, even if microorganisms of different metabolism are attached to one filter medium, if the treatment tank is an aerobic tank, it is difficult to simultaneously enhance the action of the number of anaerobic microorganisms. Therefore, when treating wastewater containing BOD, nitrogen, phosphorus, the number of treatment tanks cannot be reduced even though the capacity of each treatment tank can be reduced by adopting the biofilm treatment method. .

  In the conventional water treatment technology, among the characteristics of the biofilm described above, microbial cohesion and high density retention have been used in the activated sludge method and the biofilm treatment method. There is no water treatment technology using

The present invention has been made in view of the above circumstances, and when treating wastewater containing BOD, it is possible to simultaneously achieve enhancement of treatment capacity, reduction of power consumption and excess sludge amount, suppression of odor generation and bulking, An object of the present invention is to provide a wastewater treatment method and a wastewater treatment system capable of continuing stable operation and maintaining the treatment performance.
Another object of the present invention is to provide a wastewater treatment method and a wastewater treatment system that can be treated in a single treatment tank even when treating wastewater containing BOD and containing either or both of nitrogen and phosphorus. .

In the present invention, attention is paid to a biofilm (a community of microorganisms) composed of EPS produced by microorganisms. Here, the biofilm in the biological treatment tank refers not only to a part formed on the surface where the solid surface such as the wall of the treatment tank is in contact with water but also to a whole formed in the liquid in the treatment tank. The latter is in a floating dispersion state in the treatment tank.
In biofilms, microorganisms of different metabolic systems (for example, aerobic microorganisms and anaerobic microorganisms) can coexist, so if biofilm is used, all of BOD, nitrogen and phosphorus can be obtained in one treatment tank. The idea was that it could be processed at the same time.
In addition, biofilms that effectively coexist with microorganisms with different metabolisms in biological treatment tanks are composed of highly viscous EPS that is produced when microorganisms feel stress in the standard activated sludge method and causes viscous bulking. It was discovered that a biofilm composed of EPS produced by microorganisms during nitrate respiration (hereinafter referred to as “biofilm during nitrate respiration”) is more suitable than a biofilm to be produced.
Furthermore, it was difficult to maintain treatability at a dissolved oxygen concentration of 1 mg / L or less, but it was difficult to cope with small changes in raw water conditions and operating conditions. However, the addition of nitrate and alkali greatly changed raw water conditions and operating conditions. In contrast, the present inventors have found that stable operation can be continued and processability can be maintained, and the present invention has been completed.

That is, this invention has the following aspects.
[1] Waste water for aeration of the waste water in the biological treatment tank so that the oxidation-reduction potential in the biological treatment tank for biological treatment of waste water containing organic matter is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less. in the processing method, the to waste water or the biological treatment tank, nitrate activate the denitrification reaction by adding, to activate the added alkali nitrification, the amount of nitrogen needed for metabolism of the biological treatment tank A method for treating wastewater, in which organic matter in the wastewater is decomposed by bringing it into a circulating state, and there are denitrifying bacteria, nitrogen-fixing bacteria, and nitrifying bacteria in the biological treatment tank .
[ 2 ] In the biological treatment tank, the denitrification bacteria decomposes the BOD in the wastewater to generate nitrogen gas (N ₂ ) from nitrite ions (NO ₂ ⁻ ) and nitrate ions (NO ₃ ⁻ ). Reaction, a nitrogen fixation reaction that generates ammonia (NH ₃ ) from the nitrogen gas (N ₂ ) by the nitrogen-fixing bacteria, and the ammonia becomes ammonium ions (NH ₄ ⁺ ) in the treatment liquid, and the nitrifying bacteria , A nitrification reaction that generates nitrite ions (NO ₂ ⁻ ) and nitrate ions (NO ₃ ⁻ ) from the ammonium ions (NH ₄ ⁺ ) is performed in parallel, and nitrogen (N) is generated in the biological treatment tank. The method for treating wastewater according to [ 1 ], wherein the wastewater is recycled.
[ 3 ] Wastewater for aeration of the wastewater in the biological treatment tank so that the oxidation-reduction potential in the biological treatment tank for biologically treating the wastewater containing organic matter is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less. A processing system,
Biological treatment of the wastewater and the biological treatment tank having denitrifying bacteria, nitrogen-fixing bacteria, and nitrifying bacteria therein, and nitrate addition means for adding nitrate for activating a denitrification reaction to the wastewater or the biological treatment tank; An alkali addition means for adding an alkali that activates the nitrification reaction to the wastewater or the biological treatment tank, and by making the amount of nitrogen necessary for metabolism in the biological treatment tank circulate, Wastewater treatment system that decomposes organic matter in a single tank.

According to the wastewater treatment method and wastewater treatment system of the present invention, when treating wastewater containing BOD, it is possible to simultaneously achieve treatment capacity enhancement, power consumption and reduction of excess sludge, odor generation and bulking suppression, In addition, stable operation can be continued and processability can be maintained.
Moreover, according to the wastewater treatment method and wastewater treatment system of the present invention, even when wastewater containing BOD and containing either or both of nitrogen and phosphorus can be treated in a single treatment tank.
Moreover, if it is the installation using the existing activated sludge method, conversion while operating (maintaining processability) is possible.

It is a schematic block diagram which shows an example of the wastewater treatment system of this invention. It is a chart which shows the mechanism by which wastewater is biologically processed.

Hereinafter, description will be given with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of a wastewater treatment system of the present invention. The wastewater treatment system 1 of this example includes an adjustment tank 10, a biological treatment tank (hereinafter also simply referred to as "treatment tank") 20, a precipitation tank 30, a nitrate addition means 41, an alkali addition means 42, and wastewater. A flow path 51, a transfer flow path 52, a treated water flow path 53, an excess sludge flow path 54, and a return sludge flow path 55 are provided.

The adjustment tank 10 is a tank that adjusts the flow rate of waste water and the like, and includes a tank body 11 that stores the waste water and a pump 12 that supplies the waste water to the treatment tank 20.
The tank body 11 is not particularly limited as long as it can store wastewater, and examples thereof include a wastewater tank.

The treatment tank 20 is a tank that biologically treats the wastewater supplied from the adjustment tank 10 and includes a tank body 21 that stores the wastewater and aeration means 22 that supplies air and aerates the inside of the treatment tank.
The aeration means 22 includes an air diffuser 22a, a blower 22b, an air supply pipe 22c, a manometer 22d, and a flow meter 22e. The air diffuser 22 a is disposed at the bottom of the tank body 21. The blower 22b supplies air to the air diffuser 22a. The air supply pipe 22c connects the air diffuser 22a and the blower 22b. The manometer 22d and the flow meter 22e are provided between the air diffuser 22a and the blower 22b.
The tank body 21 is not particularly limited as long as it can store wastewater, but is preferably made of a material that is not easily deteriorated by nitrate or alkali.
The aeration means 22 is not particularly limited as long as it can aerate wastewater, and for example, a known aeration apparatus can be used.

The sedimentation tank 30 is a tank for solid-liquid separation of treated water obtained by biological treatment of wastewater in the treatment tank 20 and sludge (microorganism group), and is separated from a tank body 31 for storing treated water and sludge. A scraper 32 for scraping the sludge and a pump 33 for returning a part of the sludge to the treatment tank 20.
The structure of the tank body 31 is not particularly limited.
The scraper 32 is not particularly limited as long as it can scrape sludge.

The nitrate addition means 41 in this example is a means for adding nitrate to the wastewater batchwise or continuously in the treatment tank 20.
The nitrate addition means 41 is not particularly limited as long as nitrate can be added to wastewater.

The alkali addition means 42 in this example is a means for adding alkali to the wastewater batchwise or continuously in the treatment tank 20.
The alkali adding means 42 is not particularly limited as long as alkali can be added to wastewater.

The waste water channel 51 is a channel through which waste water is supplied from the adjustment tank 10 to the treatment tank 20.
The transfer channel 52 is a channel through which a mixed solution of treated water and sludge that has been biologically treated in the treatment tank 20 is transferred from the treatment tank 20 to the sedimentation tank 30.
The treated water channel 53 is a channel through which treated water that has been separated into solid and liquid in the settling tank 30 is discharged from the settling tank 30 to the outside of the system.
The surplus sludge channel 54 is a channel through which a part of the sludge separated into solid and liquid in the settling tank 30 is discharged from the settling tank 30 to the outside as surplus sludge.
The return sludge flow path 55 is a flow path in which a part of the sludge separated into solid and liquid in the settling tank 30 is returned from the settling tank 30 to the treatment tank 20 as return sludge.

The wastewater treatment method using the wastewater treatment system 1 shown in FIG. 1 includes the following steps (a) to (c).
Step (a): A step of making the flow rate and concentration of wastewater uniform in the adjustment tank 10.
Step (b): A step of biologically treating the wastewater supplied from the adjustment tank 10 in the treatment tank 20.
Step (c): A step of solid-liquid separation of the mixed liquid of treated water and sludge into treated water and sludge in the precipitation tank 30.

<Waste water>
The wastewater to be treated in the present invention is not particularly limited as long as it is organic wastewater, and examples thereof include industrial wastewater, domestic wastewater, and human waste. In addition, the wastewater may contain nitrogen, phosphorus, etc. in addition to BOD.

<Process (a)>
In step (a), the flow rate, load component, and load concentration of wastewater are made as uniform as possible in the adjustment tank 10.

<Step (b)>
In the step (b), nitrate is added to the wastewater from the nitrate addition means 41, and alkali is added from the alkali addition means 42. Further, the wastewater to which nitrate and alkali are added is aerated by the aeration means 22 in the treatment tank 20 so that the redox potential is ± 0 mV or more and the dissolved oxygen concentration (DO) is 1 mg / L or less (hereinafter, “ Also called “low aeration”.) Thereby, the waste water is biologically treated. The mechanism by which wastewater is biologically treated will be described with reference to FIG.
The oxidation-reduction potential is measured at a liquid temperature of 25 ° C. using an oxidation-reduction potentiometer (for example, “D-13” manufactured by Horiba, Ltd.). The dissolved oxygen concentration is measured at a liquid temperature of 25 ° C. using a dissolved oxygen concentration meter (for example, “OM-51” manufactured by Horiba, Ltd.).

In the present invention, biological treatment of wastewater is achieved by the following four stages. Metabolic activation (in the case of conversion from the activated sludge method, conversion of the metabolic pathway) is roughly divided into the following three stages: the first stage to the third stage. FIG. 2 shows an example in which an aerobic treatment that is an activated sludge method is provided as the following pre-stage, but the present invention also holds when there is no aerobic treatment.
First stage: Activation of denitrification reaction (in the case of conversion from activated sludge method, induction from oxygen respiration to nitrate respiration)
2nd stage: Activation of nitrogen fixation reaction 3rd stage: Activation of nitrification reaction

When the denitrification reaction is activated (denitrification by nitrate respiration) (in the case of conversion from the activated sludge method, the metabolic pathway is shifted from oxygen respiration to nitrate respiration), The reaction from the first stage to the third stage proceeds in parallel.
Stage 4: Microbiological symbiosis in the biofilm during nitrate respiration (symbiosis between living organisms)

(Previous stage)
In the activated sludge method, most of the parts are in an aerobic atmosphere, and the microorganisms decompose BOD by oxygen respiration. However, in a small part of the anaerobic part such as the inside of the floc, BOD is decomposed by sulfate respiration or fermentation.
(First stage)
When nitrate is added to the wastewater and aeration is performed such that the oxidation-reduction potential in the treatment tank is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less, the microorganisms in the treatment tank decompose BOD in the wastewater by nitrate respiration. (Denitrification reaction activation using BOD in wastewater as organic carbon source).
When converting from the activated sludge method, nitrate is added to the wastewater, and the aeration is changed so that the redox potential in the treatment tank is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less. Induced to breathing. Specifically, most of the aerobic microorganisms are induced from oxygen respiration to nitrate respiration, and a small portion of the anaerobic microorganisms are induced from sulfate respiration and fermentation to nitrate respiration.

As shown in FIG. 2, microorganisms that perform nitrate respiration (induced by nitrate respiration), such as denitrifying bacteria, decompose BOD to form nitrogen from nitrite ions (NO ₂ ⁻ ) and nitrate ions (NO ₃ ⁻ ). Gas (N ₂ ) is generated (denitrification reaction). At this time, alkali (carbonic acid (H ₂ CO ₃ ), hydrogen carbonate ion (HCO ₃ ⁻ ), etc.) is also generated, and a biofilm during nitrate respiration described later is also formed.
Examples of the denitrifying bacteria include those belonging to Flavobacteriaceae, Sphingobacteriaceae, Rhodocyclaceae, Flexibacteraceae, Comamonadaceae and the like.
Some bacteria decompose BOD and generate nitrogen gas (N ₂ ) exclusively from nitrite ions (NO ₂ ⁻ ).

(Second stage)
Nitrogen gas (N ₂ ) generated by the denitrification reaction is converted into ammonia by a microorganism (nitrogen-fixing bacteria or the like) (activation of the nitrogen fixation reaction). Ammonia (NH ₃ ) produced by this reaction is ionized in water to become ammonium ions (NH ₄ ⁺ ).
Examples of the nitrogen-fixing bacteria include those belonging to Rhodocyclaceae, Rhodobacteriaceae, Rhodospirillaceae and the like.

(3rd stage)
If oxygen is dissolved in the wastewater in the presence of ammonium ions (NH ₄ ⁺ ) generated in the second stage and alkali generated in the first stage, microorganisms (nitrifying bacteria such as nitrite and nitrate bacteria) As a result, ammonium ions (NH ₄ ⁺ ) are oxidized to nitrate ions (NO ₃ ⁻ ) via nitrite ions (NO ₂ ⁻ ) (nitrification reaction).
The nitrification reaction proceeds with the alkali generated in the first-stage denitrification reaction, but the nitrification reaction proceeds efficiently by adding the alkali together with the nitrate in the step (b) in advance.
Examples of the nitrifying bacteria include those belonging to Nitrospiraceae, Nitrosomonadaceae and the like.

Nitrite ions (NO ₂ ⁻ ) and nitrate ions (NO ₃ ⁻ ) generated by the nitrification reaction in the third stage are used as nitrates for microbial nitrate respiration in the first stage. Thus, in the present invention, nitrogen (N) is transformed from nitrogen gas (N ₂ ) to ammonium ion (NH ₄ ⁺ ) to nitrite ion (NO ₂ ⁻ ) and further to nitrate ion (NO ₃ ⁻ ). Is changed and the first to third stages are circulated.

(Fourth stage)
During nitrate breathing, the amount of ATP synthesis is reduced compared to oxygen breathing. Thus, microorganisms produce EPS to collect more nutrients and form a biofilm (microbe community) during nitrate respiration by different microorganisms. As a result, the state changes to the following (α) to (γ).
(Α) Microorganisms having different metabolisms such as denitrifying bacteria, nitrogen-fixing bacteria, and nitrifying bacteria in the first to third stages are in a stable symbiotic state (symbiosis between living organisms) in the biofilm.
(Β) Nitrogen (N) is exchanged in the system by exchanging nitrogen gas (N ₂ ), ammonium ions (NH ₄ ⁺ ), nitrate ions (NO ₃ ⁻ ), etc., which are produced by microorganisms in the biofilm. Thus, the amount of nitrogen (N) necessary for the metabolism of microorganisms is stably circulated (in-system nitrogen circulation).
(Γ) A group of microorganisms in a symbiotic state is capable of metabolizing those that cannot be metabolized by microorganisms alone, thereby increasing the treatment of wastewater (eg, increasing the degradability of persistent substances).

Examples of the nitrate added to the waste water include sodium nitrate, potassium nitrate, magnesium nitrate, and calcium nitrate. These nitrates may be used alone or in combination of two or more.
As shown in FIG. 1, when adding nitrate to the wastewater in the processing tank 20, the addition amount of nitrate is preferably 0.1 mg-NO ₃ -N / L or more with respect to the amount of treated water, and 0.5 mg-NO _3. -N / L or more is more preferable. If the addition amount of the nitrate _0.1mg-NO 3 -N / L or more, microorganisms can be sufficiently guided to nitrate respiration in the first stage. Moreover, because it leads to an increase in drug costs When the amount of the nitrate increase, the amount of nitrate is preferably from _20mg-NO 3 -N / L, more preferably not more than _{10mg-NO 3 -N / L,} 5mg-NO _3- N / L or less is more preferable.
Moreover, when nitrate nitrogen is contained in the waste water to be treated in an amount of 0.5 mg-NO ₃ -N / L or more, there are cases where stable processability can be maintained without adding nitrate.

Examples of the alkali added to the waste water include sodium hydrogen carbonate, sodium carbonate, carbonic acid, and sodium hydroxide. These alkalis may be used alone or in combination of two or more.
As shown in FIG. 1, when adding an alkali to the waste water in the processing tank 20, the amount of alkali added is preferably 0.6 mg as CaCO ₃ / L or more in terms of M alkalinity with respect to the amount of treated water, and 3 mg as CaCO _3. / L or more is more preferable. If the amount of alkali added is 0.6 mg as CaCO ₃ / L or more in terms of M alkalinity, the nitrification reaction proceeds sufficiently in the third stage. Moreover, since the increase in the amount of alkali added leads to an increase in chemical cost, the amount of alkali added is preferably 50 mg as CaCO ₃ / L or less in terms of M alkalinity.
Moreover, when adding an alkali to the wastewater in the processing tank 20 as shown in FIG. 1, it is preferable to adjust so that the pH of the wastewater in the processing tank 20 and the sedimentation tank 30 may be 6.0-8.6. .
Further, when the M alkalinity of the raw water is 50 mg as CaCO ₃ / L or more, there are cases where stable processability can be maintained without adding alkali.

The redox potential in the treatment tank 20 due to low aeration is ± 0 mV or more, and the dissolved oxygen concentration is 1 mg / L or less. If the dissolved oxygen concentration in the treatment tank 20 is 1 mg / L or less, the activity of denitrifying bacteria is hardly inhibited, and aerobic microorganisms can be induced from oxygen respiration to nitrate respiration.
Further, as described above, dissolved oxygen in the wastewater is required for the third stage nitrification reaction, but may be as low as the oxidation-reduction potential is ± 0 mV or more.
Therefore, during biological treatment, it is preferable to perform aeration so that the oxidation-reduction potential in the treatment tank 20 is ± 0 mV or more and the dissolved oxygen concentration is 0.3 mg / L or less, and more preferably, the oxidation-reduction potential is ± 0 mV or more. The dissolved oxygen concentration is 0.1 mg / L or less.
However, when converting from the activated sludge method, the dissolved oxygen concentration in the wastewater may be 1 mg / L or more at the stage where the activation of the metabolism of microorganisms is not sufficiently advanced.

<Step (c)>
In the step (c), the biologically treated waste water is solid-liquid separated into sludge (microorganisms) and supernatant liquid (treated water) in the precipitation tank 30.
The supernatant liquid (treated water) separated in the precipitation tank 30 is discharged out of the system through the treated water channel 53.
The sludge separated into solid and liquid in the sedimentation tank 30 is returned to the treatment tank 20 through the return sludge flow path 55 as return sludge. Moreover, a part of sludge is discharged | emitted out of the system through the excess sludge flow path 54 as excess sludge.

<Effect>
According to the present invention, nitrate and alkali are added to the wastewater, and the redox potential in the treatment tank for biological treatment of the wastewater is low aerated so that the dissolved oxygen concentration is 1 mg / L or less. The microorganism performs nitrate respiration, and the denitrification reaction proceeds sufficiently to form a biofilm during nitrate respiration. In addition, different metabolic microorganisms (denitrifying bacteria, nitrogen-fixing bacteria, nitrifying bacteria, etc.) can coexist with biofilms during nitrate respiration, so even if wastewater contains BOD and nitrogen, It can process simultaneously with one processing tank.
Moreover, even when the wastewater does not contain nitrogen, a stable BOD treatment can be performed by adding a nitrate of about 0.1 to 20 mg-NO ₃ -N / L due to nitrogen circulation in the system.
In addition, phosphorus can be treated at the same time by coexisting with phosphorus-accumulating bacteria on the biofilm. In addition, the biofilm has a high adsorption / aggregation efficiency of the substrate and can efficiently treat wastewater.
Therefore, in the present invention, conventional biological nitrogen treatment and phosphorus treatment methods (nitrification denitrification method, anaerobic / aerobic method (AO method), anaerobic / anoxic / aerobic method (A2O method), anaerobic / nitrification Compared to biodenitrification methods (AOAO method, etc.), the number of treatment tanks can be reduced.

  In addition, according to the present invention, the biofilm plays a role of cushioning against microorganisms against a sudden increase or decrease of the load, so that it is resistant to load fluctuations. Also, since it plays a role of defense against bioinhibitors and poisons, resistance to bioinhibitors and poisons also increases. In addition, the decomposition of difficult-to-decompose organic substances that are difficult to process by the activated sludge method is promoted by the symbiosis between microorganisms. Therefore, it is possible to reduce the installation area because high load treatment is possible compared to the conventional method (activated sludge method). In addition, resistance to living organisms under harsh conditions is enhanced and bulking can be suppressed, so operation management is easy.

  In addition, according to the present invention, power consumption can be reduced because low aeration is required so that the dissolved oxygen concentration in the treatment tank is 1 mg / L or less.

  In addition, according to the present invention, since microorganisms change metabolism from oxygen respiration to nitrate respiration, the amount of ATP synthesized when the same amount of BOD is decomposed is reduced, so the amount of excess sludge generated is also reduced. it can.

  Moreover, if it is this invention, in order to suppress sulfate respiration and fermentation of microorganisms, since generation | occurrence | production of an organic acid, alcohol, hydrogen sulfide, etc. is suppressed, generation | occurrence | production of an odor can be reduced. In addition, by suppressing the generation of hydrogen sulfide, corrosion and deterioration of concrete water tanks, water channels and steel cans can be suppressed.

  Further, according to the present invention, by adding nitrate and alkali to waste water, stable operation can be continued and maintainability can be maintained even with large fluctuations in raw water conditions and operating conditions.

  In addition, according to the present invention, the biofilm during nitrate respiration collects insoluble fine suspended solids, thereby improving the transparency of treated water and improving the quality of treated water (floating of treated water). Substance concentration (SS concentration) decreases).

As described above, in the present invention, nitrogen (N) changes its form from nitrogen gas (N ₂ ) to ammonium ion (NH ₄ ⁺ ) to nitrate ion (NO ₃ ⁻ ), etc. Circulating the third stage. Further, the alkali necessary for the third stage nitrification reaction is produced by the first stage denitrification reaction. Therefore, the addition of nitrate and alkali to the wastewater in the step (b) may be performed at least at the start of operation of the wastewater treatment system. That is, nitrate and alkali may be added from the outside to at least wastewater to be biologically treated first. In the subsequent biological treatment, nitrate ions (NO ₃ ⁻ ) generated through the first stage to the third stage, nitrogen gas (N ₂ ) in the aerated air, and alkali generated in the first stage are in the system. Therefore, the reaction from the first stage to the third stage may proceed in parallel by the fourth stage without adding nitrate and alkali to the waste water from the outside.
However, when the nitrate concentration or alkali concentration in the system is lowered, a new nitrate or alkali may be added to the waste water.

<Other embodiments>
The wastewater treatment method of the present invention is not limited to the method described above. In the above-described method, as shown in FIG. 1, nitrate and alkali are added only to the waste water in the treatment tank 20, but the nitrate and alkali are either before the treatment tank 20 (the treatment tank 20 or upstream thereof). What is necessary is just to add at a point. That is, the nitrate may be added from the nitrate addition means 41 and the alkali may be added from the alkali addition means 42 only to the waste water in the adjustment tank 10. Further, nitrate may be added from the nitrate addition means 41 to the waste water in both the adjustment tank 10 and the treatment tank 20, and alkali may be added from the alkali addition means 42. Furthermore, nitrate may be added to the wastewater in the adjustment tank 10 from the nitrate addition means 41, and alkali may be added to the wastewater in the treatment tank 20 from the alkali addition means 42, or vice versa.
Further, the waste water at any point further upstream than the adjustment tank 10 (because it is the upstream side of the adjustment tank 10, if a plurality of waste water flows into the adjustment tank 10, one or more of them or Nitrate may be added from the nitrate addition means 41 to all waste water), and alkali may be added from the alkali addition means 42.

Moreover, in the method mentioned above, although the flow volume and density | concentration of wastewater are equalized in the adjustment tank 10 as process (a), process (a) may not be performed.
Also, before the step (a) or between the step (a) and the step (b), a step of removing large and small solids (screen, solid content removing device (coagulation precipitation, pressurized flotation, etc.), precipitation tank, etc. Other steps may be provided.
Moreover, in the method mentioned above, although the liquid mixture of treated water and sludge is solid-liquid separated into the treated water and sludge in the settling tank 30 as a process (c), the separation function of sludge and treated water, such as a membrane separator. It is good also as what substitutes for the sedimentation tank 30. In addition, when installing a membrane separator in the processing tank 20, the transfer flow path 52 and the return sludge flow path 55 become unnecessary, and the treated water flow path 53 and the excess sludge flow path 54 exit from the processing tank 20. It becomes a shape.
Furthermore, in the method described above, wastewater is biologically treated in one treatment tank 20, but a plurality of treatment tanks 20 may be used. As described above, according to the present invention, wastewater can be treated in one treatment tank even when wastewater containing BOD, nitrogen, and phosphorus is treated, but a plurality of treatment tanks 20 may be used.

The present invention can also be applied to biofilm treatment methods other than the trickling filter method (immersion filter method, fluidized bed method, immobilized carrier method, rotating disk method, rocking bed method, etc.).
When the present invention is applied to the biofilm treatment method, nitrate and alkali are added to the wastewater before the biofilm treatment tank (in the biofilm treatment tank or upstream thereof), and the biofilm treatment tank is subjected to low aeration (redox potential is ± 0 mV). As described above, the dissolved oxygen concentration may be 1 mg / L or less).
There is no limitation on the material and shape of the filter medium used in the biofilm treatment method.

Further, the present invention can be applied to a dispersal bacteria treatment method.
The dispersal bacteria treatment method is a treatment method in which BOD in waste water is oxidized and decomposed by non-aggregating bacteria (dispersing bacteria) and converted to non-aggregating bacteria in the substantial absence of protozoa and metazoans.
As a method for making protozoa and metazoans substantially non-existent and giving priority to non-aggregating bacteria, (1) Addition of dispersal bacteria preparations, (2) No addition of protozoa / metazoans (no return sludge) Etc.), (3) The retention time in the treatment tank is set so that protozoa and metazoans cannot grow, and (4) a filter medium (fixed filter medium, fluid carrier, rocking fiber filter medium) capable of holding and fixing dispersal bacteria or Installation, (5) Combinations of (1) to (4) above, and the like.
When the present invention is applied to the dispersal bacteria treatment method, nitrate and alkali are added to the wastewater before the dispersal bacteria treatment tank (or the upstream of the dispersal bacteria treatment tank), and the biofilm treatment tank is low aerated (redox potential is ± 0 mV). As described above, the dissolved oxygen concentration may be 1 mg / L or less).
In addition, there is no limitation in the material and shape of the filter medium thrown in in said (4).

Further, the present invention can be applied to an alternative process of the anaerobic treatment method.
When the present invention is applied to an alternative treatment of an anaerobic treatment device, nitrate and alkali are added to wastewater before the anaerobic treatment vessel (upstream and anaerobic treatment tank), an aeration device is attached to the anaerobic treatment tank, and the anaerobic treatment tank is lowered. Aeration may be performed (the redox potential is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less). If there is a pre-oxidation treatment tank in front of the anaerobic treatment tank, add nitrate and alkali to the wastewater before the pre-oxidation treatment tank (pre-oxidation treatment tank and its upstream), and lower the pre-oxidation treatment tank and the anaerobic treatment tank. Aeration is enough.
In addition, when supplying a filter medium to an anaerobic treatment tank, there is no limitation in the material and shape of the filter medium to input.

In addition, the present invention places a high-load treatment device (anaerobic treatment method, biofilm treatment method, dispersal bacteria treatment method, etc.) in the previous stage, and uses an activated sludge treatment device or biofilm treatment apparatus in the subsequent stage as a finishing treatment. It can be applied to an alternative process at a later stage.
In the case where the present invention is applied to an alternative treatment of a post-stage biological treatment apparatus in which a high-load treatment apparatus is placed in the front stage, in a post-stage biological treatment tank (an activated sludge treatment tank or a biofilm treatment tank) before (the latter stage biological treatment tank and its upstream) Nitrate and alkali are added to the wastewater, and the latter biological treatment tank is aerated (the redox potential is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less).
In addition, when a back | latter stage biological treatment tank is a biofilm treatment tank, there is no limitation in the material and shape of a filter medium to introduce | transduce.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

"Example 1"
The wastewater treatment system 1 shown in FIG. 1 was used, the wastewater was artificial sewage, and the sewage sludge was returned sludge from the sewage treatment plant. A 60 L waste water tank was used as the tank body 11 of the adjustment tank 10. Moreover, the capacity | capacitance of the tank main body 21 of the processing tank 20 was 10L, and the capacity | capacitance of the tank main body 31 of the sedimentation tank 30 was 10L.
Waste water is supplied from the waste water tank to the treatment tank 20 under the condition of a treatment water amount of 3.5 L / day, and the concentration of calcium nitrate in the waste water in the treatment tank 20 is 2 mg-NO ₃ -N / L with respect to the treatment water amount. 8 mg as CaCO ₃ / L of 5 mass% sodium hydrogen carbonate aqueous solution was added. Furthermore, the wastewater was biologically treated by aeration of the treatment tank 20 with the aeration means 22 so that the oxidation-reduction potential in the treatment tank 20 was 0 mV or more and the dissolved oxygen concentration was 1 mg / L or less. At this time, the temperature in the treatment tank 20 was adjusted to 25 ° C., and the amount of aeration air was adjusted while confirming the dissolved oxygen concentration. Subsequently, the mixed liquid of treated water and sludge was separated into treated water and sludge in the sedimentation tank 30, the treated water was discharged out of the system, and part of the sludge was returned to the treatment tank 20 as return sludge. The return sludge rate was 100% of the treated water volume. Excess sludge was discharged out of the system in batches while confirming the sludge interface of the settling tank.
In addition, the addition method of calcium nitrate and sodium hydrogencarbonate aqueous solution was a batch, and there was a period when it was not added during the test period. Further, during the treatment period, the oxidation-reduction potential in the treatment tank was 40 to 250 mV, the dissolved oxygen concentration was 0.36 mg / L or less, and the average aeration air volume was 270 NmL / min. The oxidation-reduction potential is measured using an oxidation-reduction potentiometer ("D-13" manufactured by Horiba, Ltd.), and the dissolved oxygen concentration is measured using a dissolved oxygen concentration meter ("OM-51" manufactured by Horiba, Ltd.). Measured.
Table 1 shows chemical amounts and properties (results of water quality analysis) of artificial sewage used as wastewater, and Table 2 shows treatment conditions (operation conditions) of wastewater.

  The treated water carried out under the above test conditions was collected and analyzed for properties. Moreover, the removal rate of BOD and total nitrogen (TN), the BOD sludge conversion rate, and the estimated sludge reduction rate were calculated | required with the following method. These results are shown in Table 3.

BOD removal rate (%) = {(BOD amount in wastewater before treatment−BOD amount in treatment water) / BOD amount in wastewater before treatment} × 100
Total nitrogen (TN) removal rate (%) = {(total nitrogen amount in wastewater before treatment−total nitrogen amount in treated water) / total nitrogen amount in wastewater before treatment} × 100
BOD sludge conversion rate (%) = {(increase amount of sludge in the treatment tank and settling tank in the specific period + amount of excess sludge withdrawn in the specific period) / treatment BOD amount in the specific period} × 100
Estimated sludge reduction rate (%) = (average BOD sludge conversion rate during this test / BOD sludge conversion rate in activated sludge (40-50%)) × 100

In Tables 1 and 3, “BOD” is biochemical oxygen demand, “TN” is total nitrogen, “Org-N” is organic nitrogen, and “NH ₄ -N” is ammonia. is nitrogen, "NO 2 _-N" is the nitrite nitrogen, "NO 3 _-N" is the nitrate nitrogen, "SS" is a floating material.

As is clear from Table 3, in Example 1, almost 100% of BOD and about 55% of nitrogen could be treated in one treatment tank.
Moreover, the excess sludge could be reduced by 50 to 60%.

"Example 2"
The wastewater treatment system 1 shown in FIG. 1 was used, the wastewater was the wastewater from the seasoning factory, and the sludge for habituation was the return sludge from the sewage treatment plant. A 60 L waste water tank was used as the tank body 11 of the adjustment tank 10. Moreover, the capacity | capacitance of the tank main body 21 of the processing tank 20 was 10L, and the capacity | capacitance of the tank main body 31 of the sedimentation tank 30 was 10L.
Waste water is supplied from the waste water tank to the treatment tank 20 under the condition of a treatment water amount of 10 L / day, and calcium nitrate is added to the waste water in the treatment tank 20 at a concentration of 10 mg-NO ₃ -N / L and a concentration of 5 mass with respect to the treatment water amount. % Sodium hydroxide aqueous solution was added so that the pH in the treatment tank 20 would be 7 or more. Furthermore, the wastewater was biologically treated by aeration of the treatment tank 20 with the aeration means 22 so that the oxidation-reduction potential in the treatment tank 20 was 0 mV or more and the dissolved oxygen concentration was 1 mg / L or less. At this time, the temperature in the treatment tank 20 was adjusted to 25 ° C., and the amount of aeration air was adjusted while confirming the dissolved oxygen concentration. Subsequently, the mixed liquid of treated water and sludge was separated into treated water and sludge in the sedimentation tank 30, the treated water was discharged out of the system, and part of the sludge was returned to the treatment tank 20 as return sludge. The return sludge rate was 100% of the treated water volume. Excess sludge was discharged out of the system in batches while confirming the sludge interface of the settling tank.
In addition, the addition method of calcium nitrate is a batch, the addition method of sodium hydroxide is an automatic addition method using a pH controller, and there were times when it was not added during the test period. During the treatment period, the oxidation-reduction potential in the treatment tank was 55 to 261 mV, the dissolved oxygen concentration was 0.23 mg / L or less, and the amount of aeration air was 100 to 500 NmL / min. The oxidation-reduction potential is measured using an oxidation-reduction potentiometer ("D-13" manufactured by Horiba, Ltd.), and the dissolved oxygen concentration is measured using a dissolved oxygen concentration meter ("OM-51" manufactured by Horiba, Ltd.). The pH was measured using a pH meter (“D-24” manufactured by Horiba, Ltd.).
Table 4 shows the properties (results of water quality analysis) of the seasoning factory used as waste water, and Table 5 shows the treatment conditions (operation conditions) of the waste water.

  The treated water carried out under the above test conditions was collected and analyzed for properties. Moreover, the removal rate of COD (chemical oxygen consumption) was calculated | required with the following method. These results are shown in Table 6.

  COD removal rate (%) = {(COD amount in wastewater before treatment−COD amount in treated water) / COD amount in wastewater before treatment} × 100

In Tables 4 and 6, “COD _Cr ” is the oxygen demand by potassium dichromate, “COD _Mn ” is the oxygen demand by potassium permanganate at 100 ° C., and “BOD” is the biochemical oxygen demand. a quantity, "Org-N" is an organic nitrogen, _"NH 4 -N" is ammonia nitrogen, _"NO 2 -N" is nitrite nitrogen, _"NO 3 -N" is It is nitrate nitrogen, “SS” is a suspended substance, “TN” is total nitrogen, “PO ₄ -P” is phosphate phosphorus, and “TP” is total phosphorus. .

As is apparent from Table 6, in Example 2, 96% or more of COD _Mn could be processed in one processing tank.

  The wastewater treatment method of the present invention is useful as a wastewater treatment method containing BOD. Moreover, it is also useful as a wastewater treatment method in which either or both of nitrogen and phosphorus are contained in wastewater containing BOD.

DESCRIPTION OF SYMBOLS 1 Waste water treatment system 10 Adjustment tank 11 Tank main body 12 Pump 20 Biological treatment tank (treatment tank)
DESCRIPTION OF SYMBOLS 21 Tank main body 22 Aeration means 22a Air diffuser 22b Blower 22c Air supply pipe 22d Manometer 22e Flow meter 30 Precipitation tank 31 Tank main body 32 Scraper 33 Pump 41 Nitrate addition means 42 Alkali addition means 51 Waste water flow path 52 Transfer flow path 53 Treated water channel 54 Excess sludge channel 55 Return sludge channel

Claims (3)

A method for treating wastewater, wherein the wastewater is aerated in the biological treatment tank so that the redox potential in the biological treatment tank for biologically treating the wastewater containing organic matter is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less. in the the waste water or the biological treatment tank, nitrate activate the denitrification reaction by adding, to activate the added alkali nitrification, the amount of nitrogen is circulated required for the metabolism of the biological treatment tank A method for treating wastewater , wherein the organic matter in the wastewater is decomposed by making the state, and denitrifying bacteria, nitrogen-fixing bacteria, and nitrifying bacteria are present in the biological treatment tank . In the biological treatment tank, a denitrification reaction that decomposes BOD in wastewater by the denitrifying bacteria to generate nitrogen gas (N ₂ ) from nitrite ions (NO ₂ ⁻ ) and nitrate ions (NO ₃ ⁻ ); A nitrogen fixation reaction that generates ammonia (NH ₃ ) from the nitrogen gas (N ₂ ) by the nitrogen-fixing bacteria, and the ammonia becomes ammonium ions (NH ₄ ⁺ ) in the treatment liquid. A nitrification reaction for generating nitrite ions (NO ₂ ⁻ ) and nitrate ions (NO ₃ ⁻ ) from ions (NH ₄ ⁺ ) is performed in parallel, and nitrogen (N) is circulated and used in the biological treatment tank. The processing method of the wastewater of Claim 1 . In a wastewater treatment system, the wastewater is aerated in the biological treatment tank so that the oxidation-reduction potential in the biological treatment tank for biologically treating wastewater containing organic substances is ± 0 mV or more and the dissolved oxygen concentration is 1 mg / L or less. There,
Biological treatment of the wastewater and the biological treatment tank having denitrifying bacteria, nitrogen-fixing bacteria, and nitrifying bacteria therein, and nitrate addition means for adding nitrate for activating a denitrification reaction to the wastewater or the biological treatment tank; An alkali addition means for adding an alkali that activates the nitrification reaction to the wastewater or the biological treatment tank, and by making the amount of nitrogen necessary for metabolism in the biological treatment tank circulate, Wastewater treatment system that decomposes organic matter in a single tank.

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