JP2002301500A - Water treatment method and apparatus using acid fermentation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method, and an apparatus using acid fermentation where the retention time in a biological treatment is shortened and soluble BOD is produced from SS to return the BOD to a denitrification process as a hydrogen donor. SOLUTION: Water-to-be-treated is subjected to solid-liquid separation in a first settling basin 1, where a flocculant is added, and the separated upper layer water is introduced into a biological treatment tank 2 to be biologically treated. The separated SS is introduced into an acid fermentation tank 6, and while keeping the pH of sludge in the tank between 4.5 and 6.5, preferably between 5.0 and 6.0, organic acids are produced by acid fermentation. Fermentation sludge in the acid fermentation tank 6 is dewatered by a dehydrater 13. The hydrated 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]

In order to solve the above-mentioned problems, a water treatment method using acid fermentation according to the present invention according to the first aspect of the present invention provides a method for solid-liquid separation of water to be treated in a sedimentation tank to which a flocculant is added. Then, 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 adjust the pH of the sludge in the tank to 4.5 to 6.5, preferably 5.0 to 6.5. Organic acid is produced by acid fermentation while maintaining at 6.0, the fermented sludge in the acid fermentation tank is dehydrated by a dehydrator, and the dehydrated filtrate containing the organic acid is supplied to the biological treatment tank as an organic carbon source or a hydrogen donor. Is what you do.

[0010] With the above configuration, since SS and phosphorus are removed by coagulation sedimentation treatment in the sedimentation basin, the amount of SS flowing into the biological treatment tank is reduced, and the operation is performed with a short average residence time of sewage in the biological treatment tank. SS in treated water that is difficult to oxidize and decompose by activated sludge microorganisms
Is converted into an organic acid which is a soluble BOD by acid fermentation in an acid fermentation tank, thereby enabling treatment in a biological treatment tank, 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.

When the fermentation process in the acid fermenter ends the acid fermentation period, the decomposition of organic acids generated during the acid fermentation period, ie, methanation, starts, so that the pH of the sludge in the acid fermenter is adjusted to 4.5.
By maintaining the pH at -6.5, preferably 5.0-6.0, the shift to methanation can be suppressed, and the most organic acid generated in the acid fermenter can be recovered. Further, the pH of the sludge in the tank is 4.5 to 6.5, preferably 5.0 to 6.5.
By maintaining it at 6.0, it is possible to prevent all phosphorus from being re-eluted from the flocculated sludge floc, and to prevent phosphorus from flowing into the biological treatment tank.

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. A biological treatment tank, an acid fermentation tank for acid fermentation of the sedimentation SS in the sedimentation basin, a dehydrator for dehydrating fermented sludge in the acid fermentation tank, and a dehydration filtrate containing organic acids separated by the dehydrator are supplied to the biological treatment tank. A dewatered filtrate supply system, an acid supply system for supplying acid to the acid fermentation tank, and an alkali supply system for supplying alkali to the acid fermentation tank,
PH measuring means for measuring the pH of the sludge in the acid fermentation tank,
The amount of sludge in the acid fermentation tank is controlled by controlling the supply amount of the acid supply system or the alkali supply system based on the measurement value of the pH measurement means.
And a control device for maintaining H at a set value.

[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. In the acid fermentation tank 6, the pH of the sludge in the tank is measured by the pH sensor 7, and based on the measured value, the controller 8 controls the acid supply pump 10 of the acid supply system 9 or the alkali supply pump 12 of the alkali supply system 11. The pH of the sludge in the acid fermentation tank 6 is maintained at a set value by controlling the driving to adjust the amount of the acid or alkali to be added.
The setting range of pH is 4.5 to 6.5, and preferably set to 5.0 to 6.0.

The fermented sludge in the acid fermentation tank 6 is dehydrated by a dehydrator 13, and a dehydrated filtrate containing an organic acid is supplied to a denitrification tank 3 of a biological treatment tank 2 through a dehydration filtrate supply system 14, and an organic carbon source or hydrogen is supplied. Serve as 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 in the denitrification tank 3 as an organic carbon source or a hydrogen donor. 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, in which the activated sludge microorganisms are difficult to assimilate by oxidation and decomposition, is converted into an organic acid, which is a soluble BOD, by acid fermentation in the acid fermentation tank 6, and the biological treatment tank is used. 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.

When the fermentation process in the acid fermenter 6 shifts to the acid decline period through the acid fermentation period, decomposition of organic acids generated during the acid fermentation period, that is, methanation starts, and as shown in FIG. PH of the sludge in the tank of 4.5 to 6.5,
Preferably, the shift to methanation is suppressed by maintaining it at 5.0 to 6.0, and the most organic acid generated in the acid fermenter can be recovered. In addition, by maintaining the pH of the sludge in the tank at 4.5 to 6.5, preferably 5.0 to 6.0, it is possible to prevent all phosphorus from re-eluting from the flocculated sludge floc, The flow of phosphorus into the processing tank can be reduced. Also, the SRT in the acid fermenter 6
(Sludge residence time) or HRT (hydraulic residence time)
Is from 0.5 to 5 days, preferably from 1 to 3 days.

[0022]

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. Furthermore, the pH of the sludge in the acid fermentation tank
Is maintained at 4.5 to 6.5, preferably 5.0 to 6.0, whereby the shift to methanation can be suppressed, the most organic acid can be recovered, and the flocculated sludge floc Can be prevented from being re-eluted, and the phosphorus can be prevented from flowing into the biological treatment tank.

[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.

FIG. 3 is a graph showing a relationship between pH in an acid fermentation tank and an organic acid production rate 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 pH sensor 8 Control device 9 Acid supply system 10 Acid supply pump 11 Alkaline supply system 12 Alkaline supply pump 13 Dehydrator 14 Dehydration Filtrate supply system

Continued on the front page (72) Inventor Tomohiro Katata 1-47, Shikitsu-Higashi 1-chome, Namiwa-ku, Osaka-shi, Osaka Prefecture (72) Inventor Hitoshi Yanase 2-1-2, Shikitsu-Higashi, Naniwa-ku, Osaka, Osaka No. 47 F-term in Kubota Corporation (Reference) 4D015 BA23 BB12 CA02 DA02 DA12 DB01 EA32 FA02 FA26 4D040 BB05 BB14 BB57 4D059 AA06 BA11 BF12 DA01 DA31 EA05 EB05

Claims (2)

[Claims] 1. A sedimentation tank to which a 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. The pH of the inner sludge is 4.5 to 6.5, preferably 5.0 to 6.5.
Organic acid is produced by acid fermentation while maintaining at 6.0, the fermented sludge in the acid fermentation tank is dehydrated by a dehydrator, and the dehydrated filtrate containing the organic acid is supplied to the biological treatment tank as an organic carbon source or a hydrogen donor. A water treatment method using acid fermentation, which comprises: 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, a dehydrator for dehydrating the fermented sludge in the acid fermentation tank, a dehydration filtrate supply system for supplying the dehydration filtrate containing the organic acid separated by the dehydrator to the biological treatment tank, and supplying the acid to the acid fermentation tank An acid supply system, an alkali supply system for supplying alkali to the acid fermenter,
PH measuring means for measuring the pH of the sludge in the acid fermentation tank,
The amount of sludge in the acid fermentation tank is controlled by controlling the supply amount of the acid supply system or the alkali supply system based on the measurement value of the pH measurement means.
A water treatment device using acid fermentation, comprising: a control device for maintaining H at a set value.