JP2002301499A - Water treatment method and apparatus using acid fermentation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method, and apparatus using acid fermentation which can raise disposal capacity by reducing the concentration of persistent SS in a biological treatment to shorten the retention time and producing soluble BOD from removed SS to return the BOD of a denitrification process in the biological treatment as a hydrogen donor. SOLUTION: Water-to-be-treated is subjected to solid-liquid separation in a first settling basin 1, where at least iron or aluminum-based inorganic flocculant is added, and the separated upper layer water is introduced into a biological treatment tank 2 to be biologically treated. The separated persistent SS is introduced into an acid fermentation tank 6 to produce organic acids by the acid fermentation. Fermentation sludge conditioned so as to have a pH of 4.5-6.5, preferably 5.0-6.0, in a sludge conditioning tank is dewatered by a dehydrater 14, and then the dehydrated filtrate containing the organic acids is supplied to the biological treatment tank 2 as an organic carbon source or a hydrogen donor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water treatment method and apparatus utilizing acid fermentation, and more particularly to a technique for treating wastewater.

[0002]

2. Description of the Related Art Conventionally, sewage is generally treated firstly through a sedimentation basin, a biological treatment tank, and a final sedimentation basin in this order. In the biological treatment of biological treatment tanks, activated sludge microorganisms dissolve B in wastewater by biochemical reactions of oxidation and assimilation.
OD is used as a nutrient for biological growth, and the reaction rate is affected by the influence factors of the aeration time, the amount of activated sludge microorganisms, and the amount of organic nutrients.

[0003] The denitrification activated sludge method of biological treatment combines the physiological actions of nitrifying bacteria and denitrifying bacteria that inhabit the activated sludge, and the BOD component of the substrate and the activated sludge are combined in the system. This is a treatment process for decomposing a substrate by contacting it, and comprises a nitrification step and a denitrification step.

In the nitrification step, ammonia nitrogen in wastewater and ammonia nitrogen converted from organic nitrogen by catabolism of BOD oxidizing bacteria are oxidized by nitrifying bacteria to nitrite nitrogen or nitrate nitrogen.

In the denitrification step, nitrite nitrogen or nitrate nitrogen in the wastewater nitrified in the nitrification step is reduced to nitrogen gas by denitrifying bacteria under anaerobic conditions without dissolved oxygen. In recent years, in order to prevent eutrophication of public water bodies, advanced removal of nitrogen and phosphorus is required in addition to organic matter. Has been removed.

[0006]

In recent years, it has been required to remove nitrogen from sewage in order to prevent eutrophication of public water bodies. Particularly in some areas, it is often required to remove nitrogen more than ever before. In nitrogen removal, the BOD in the incoming sewage is generally used as an organic carbon source for nitrogen removal. However, since this BOD is not present in excess in the sewage, it is necessary to perform more advanced nitrogen removal than before. In this case, the BOD is insufficient, and it is necessary to supply water from sources other than inflow sewage.

On the other hand, the organic SS component in the incoming sewage is
Under aerobic conditions, it gradually oxidizes and decomposes, eventually resulting only in water and carbon dioxide. However, in anaerobic digestion, the influent sewage or organic SS components therein undergo acid fermentation under anaerobic conditions. During the acid fermentation period, mainly carbohydrates are decomposed, and acetic acid, propionic acid, butyric acid are contained in the fermentation broth. ,
Organic acids such as valeric acid are generated, and the decomposition of organic acids and nitrogen-containing organic compounds starts during the acid decline period, the BOD value reaches the maximum, and the acid fermentation period occurs during the final alkaline fermentation period Various organic acids and undecomposed amino acids are decomposed into methane, carbon dioxide, and ammonia.

The present invention solves the above-mentioned problems, and separates and removes organic SS components from inflowing sewage, and acid-ferments the organic SS components to dissolve soluble BOD components (such as the organic acids described above). And a water treatment method utilizing acid fermentation, which can improve the denitrification treatment capacity by returning to the denitrification step of the biological treatment as a hydrogen donor, thereby providing a water treatment method and apparatus. And

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, a water treatment method using acid fermentation according to the present invention according to claim 1 is directed to a sedimentation tank to which at least an iron or aluminum-based inorganic coagulant is added. The water to be treated is solid-liquid separated, the separated upper layer water is guided to a biological treatment tank for biological treatment, and the separated SS is guided to an acid fermentation tank to produce an organic acid by acid fermentation. .5, preferably 5.0-6.
The dewatered fermented sludge is dehydrated by a dehydrator, and a dehydrated filtrate containing an organic acid is supplied to a biological treatment tank as an organic carbon source or a hydrogen donor.

[0010] According to the above-described structure, the coagulation and sedimentation treatment with an iron or aluminum-based inorganic coagulant in the sedimentation basin is performed.
Since S and phosphorus are removed, S flowing into the biological treatment tank
The amount of S decreases, and the average residence time of sewage in the biological treatment tank can be shortened to operate. The treatment in the biological treatment tank is enabled by changing to an organic acid that is a soluble BOD, and the activated sludge microorganisms grow using the soluble BOD as a nutrient. Therefore, the sludge load that can be treated in the system increases due to the decrease in the SS amount and the increase in the sludge concentration, and the amount of discharge to the outside of the system decreases.

In an acid fermenter, acetic acid, propionic acid, butyric acid,
Since various organic acids such as valeric acid are generated, by using this organic acid as an organic carbon source or hydrogen donor necessary for biological treatment (denitrification treatment), methanol and other substances supplied from outside the system The cost can be reduced by suppressing the hydrogen donor, and the types of activated sludge microorganisms that can be assimilated can be diversified and their proliferation can be promoted.

[0012] Fermented sludge contains iron or aluminum hydroxide added as an inorganic coagulant, and these hydroxides contain a large amount of water, which lowers the dewatering property of the fermented sludge. For this reason, fermented sludge is pH 4.5-
By refining to 6.5, preferably 5.0 to 6.0, a part of the hydroxide of iron or aluminum is solubilized to increase the dewatering property of the fermented sludge in the dewatering machine, and The water content can be reduced, and the amount of organic acid recovered as a dehydrated filtrate can be increased. Refining of the fermented sludge may be performed in an acid fermentation tank, or a separate sludge conditioning tank may be provided.

According to a second aspect of the present invention, there is provided a water treatment apparatus utilizing acid fermentation, wherein a sedimentation basin for solid-liquid separation of water to be treated flowing into the system and a biological treatment of the separation upper layer water of the sedimentation basin. Biological treatment tank, acid fermentation tank for acid fermentation of sedimentation SS in sedimentation basin, sludge refining tank for refining fermented sludge in acid fermentation tank, dehydrator for dewatering fermented sludge in sludge refining tank, dehydration Filtrate supply system to supply dewatered filtrate containing organic acids separated by the machine to the biological treatment tank, coagulant supply system to supply coagulant to sludge conditioning tank, and supply of acid to sludge conditioning tank An acid supply system, an alkali supply system for supplying alkali to the sludge conditioning tank, a pH measuring means for measuring the pH of the sludge in the sludge conditioning tank, and an acid supply system or Control to maintain the pH of sludge in the sludge conditioning tank at a set value by controlling the supply amount of the alkali supply system It is that a location.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2, the wastewater is first introduced into a sedimentation basin 1 to which an iron or aluminum-based inorganic coagulant and an organic polymer coagulant are added, and SS and phosphorus in the wastewater are removed by coagulation sedimentation treatment.

The separated upper layer water, which has been separated into solid and liquid in the first sedimentation basin 1, is guided to the biological treatment tank 2 for biological treatment, and discharged through the final sedimentation basin (not shown). In this process, the amount of inert SS contained in the separated upper layer water flowing into the biological treatment tank 2 is small, and the operation can be performed with a short average residence time of the activated sludge in the biological treatment tank 2.

Although the biological treatment tank 2 can be constituted only by an aerobic tank, in the present embodiment, in order to remove nitrogen, it is constituted by a denitrification tank 3 and a nitrification tank 4 as shown in FIG. A nitrification liquid circulation system 5 is provided between the denitrification tank 3 and the nitrification tank 4, and guides the separated upper layer water and a dehydration filtrate described later to the denitrification tank 3. In addition to the above, the biological treatment tank 2 can be configured such that the denitrification tank 3 and the nitrification tank 4 are alternately arranged in multiple stages. In this case, the dehydrated filtrate is supplied to the second or third stage denitrification tank 3. I do.

First, the sedimentation SS separated into solid and liquid in the sedimentation basin 1 is led to the acid fermentation tank 6 to generate an organic acid by acid fermentation. Organic acids generated in the acid fermenter 6 include acetic acid, propionic acid, butyric acid, valeric acid and the like.

The fermented sludge in the acid fermentation tank 6 is guided to a sludge conditioning tank 7, and a flocculant is added to the sludge conditioning tank 7 using a flocculant supply pump 17, while the pH of the sludge in the tank is measured by a pH sensor 8. Then, based on the measured value, the controller 9 controls the acid supply pump 11 of the acid supply system 9 or the alkali supply system 12.
By controlling the drive of the alkali supply pump 13 to adjust the amount of acid or alkali to be added, the pH of the sludge in the sludge conditioning tank 7 is maintained at a set value. pH setting range is 4.5
To 6.5, and preferably set to 5.0 to 6.0.

The fermented sludge in the sludge conditioning tank 7 is dewatered by a dehydrator 14, and the dehydrated filtrate containing an organic acid is removed from the denitrification tank 3 of the biological treatment tank 2.
And supplied through a dehydration filtrate supply system 15 to serve as an organic carbon source or a hydrogen donor.

In the biological treatment tank 2, the nitrification liquid is returned from the nitrification tank 4 to the denitrification tank 3 through the nitrification liquid circulation system 5, and the organic acid is used as an organic carbon source or a hydrogen donor in the denitrification tank 3 as described above. A denitrification treatment is performed by the action. Thus, the cost can be reduced by suppressing a hydrogen donor such as methanol supplied from outside the system.

As described above, the SS in the water to be treated, which is difficult for the activated sludge microorganisms to utilize by oxidation and decomposition, is converted into an organic acid, which is a soluble BOD, by acid fermentation in the acid fermentation tank 6. By using the soluble BOD composed of various organic acids such as acetic acid, propionic acid, butyric acid, and valeric acid as a nutrient in 2, the types of activated sludge microorganisms that can utilize them are diversified, and the activated sludge microorganisms proliferate.

Iron or aluminum hydroxide added as an inorganic coagulant is present in the fermented sludge, and these hydroxides contain a large amount of water, which lowers the dewatering property of the fermented sludge. Therefore, the fermented sludge is adjusted to pH 4.5 to 6.5, preferably 5.0 to 6.5, in the sludge conditioning tank 7.
By tempering to 0, a part of the hydroxide of iron or aluminum is solubilized to increase the dewatering property of the fermented sludge in the dehydrator 14 and reduce the water content of the dewatered cake, which is recovered as a dewatered filtrate. The amount of organic acids recovered can be increased. Further, by maintaining the pH of the sludge in the tank at 4.5 to 6.5, preferably at 5.0 to 6.0, it is possible to prevent all phosphorus from being re-eluted from the flocculated sludge floc, and the biological The flow of phosphorus into the treatment tank 2 can be reduced.

The conditioning of the fermented sludge may be performed in an acid fermenter. In this case, the following operation and effect can be obtained. That is,
When the fermentation process in the acid fermentation tank 6 shifts to the acid decline period after the acid fermentation period, decomposition of the organic acid generated during the acid fermentation period, that is, methanation starts.
Is maintained at 4.5 to 6.5, preferably 5.0 to 6.0, whereby the shift to methanation can be suppressed, and the most organic acid generated in the acid fermentation tank can be recovered. The SRT (sludge residence time) or HRT (hydraulic residence time) in the acid fermenter 6 is 0.5 to 5 days, and preferably 1 to 3 days.

[0024]

As described above, according to the present invention, the SS is removed from the water to be treated in the preceding stage of the biological treatment tank, and the removed SS is converted to an organic acid which is a soluble BOD by acid fermentation. By supplying to the tank, the average sludge retention time of the activated sludge in the biological treatment tank can be shortened due to the decrease in the amount of SS and the operation can be performed. And the amount of SS discharged out of the system is reduced. In addition, by using an organic acid as an organic carbon source or a hydrogen donor required in a biological treatment (denitrification treatment), it is possible to reduce a cost by suppressing a hydrogen donor such as methanol supplied from outside the system. Activated sludge microbial species that can be assimilated by using soluble BOD composed of various organic acids as nutrients can be diversified and activated sludge microorganisms proliferate, and sludge load that can be treated in the system by increasing sludge concentration The amount increases. Further, the pH of the acid sludge is adjusted to 4.5 to 4.5.
By tempering to 6.5, preferably to 5.0 to 6.0 and dehydrating, a part of the hydroxide of iron or aluminum is solubilized to enhance the dehydration of fermented sludge in the dehydrator. The water content of the dehydrated cake can be reduced, and the amount of the organic acid recovered as the dehydrated filtrate can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a water treatment apparatus using acid fermentation according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a biological treatment tank in the water treatment apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First sedimentation tank 2 Biological treatment tank 3 Denitrification tank 4 Nitrification tank 5 Nitrification liquid circulation system 6 Acid fermentation tank 7 Sludge conditioning tank 8 pH sensor 9 Controller 10 Acid supply system 11 Acid supply pump 12 Alkaline supply system 13 Alkaline supply pump 14 Dehydrator 15 Dehydration filtrate supply system

Continued on the front page (72) Inventor Toshihiro Komatsu 1-47, Shikitsu Higashi 1-chome, Namiwa-ku, Osaka-shi, Osaka (72) Inventor Tomohiro Katata 1-chome 2, Shikitsu-higashi, Naniwa-ku, Osaka, Osaka No. 47 F-term in Kubota Corporation (Reference) 4D015 BA23 BB05 CA01 DA02 DA12 EA32 FA02 FA03 FA26 4D040 BB05 BB15 BB57 BB73 BB93 4D059 AA04 AA06 AA23 BA13 BE49 BE54 BF12 CA28 EA05 EB05 EB11

Claims (2)

[Claims] Claims: 1. A water to be treated is solid-liquid separated in a sedimentation tank to which at least an iron or aluminum-based inorganic coagulant is added, and the separated upper layer water is guided to a biological treatment tank for biological treatment. It is led to an acid fermentation tank to produce an organic acid by acid fermentation, and has a pH of 4.5 to 6.5, preferably 5.0.
Water using acid fermentation, wherein the fermented sludge conditioned to -6.0 is dehydrated with a dehydrator, and a dehydrated filtrate containing an organic acid is supplied to a biological treatment tank as an organic carbon source or a hydrogen donor. Processing method. 2. A sedimentation basin for solid-liquid separation of water to be treated flowing into the system, a biological treatment tank for biologically treating the separation upper layer water of the sedimentation basin, and an acid fermentation for acid fermentation of the sedimentation SS of the sedimentation basin. Tank, sludge refining tank for refining fermented sludge in acid fermentation tank, dehydrator for dewatering fermented sludge in sludge refining tank, and dehydration filtrate containing organic acid separated by dehydrator to biological treatment tank Dehydration filtrate supply system to supply, coagulant supply system to supply coagulant to sludge conditioning tank, acid supply system to supply acid to sludge conditioning tank, and alkali supply to supply alkali to sludge conditioning tank System, pH measuring means for measuring the pH of the sludge in the sludge conditioning tank, and a tank for the sludge conditioning tank by controlling the supply amount of the acid supply system or the alkali supply system based on the measured value of the pH measurement means. Water treatment utilizing acid fermentation, comprising: a control device for maintaining the pH of the internal sludge at a set value. apparatus.