JPH08318292A - Waste water treatment method and apparatus - Google Patents

Abstract

PURPOSE: To remove a nitrogen compd. and a phosphorus compd. along with bacteria decomposable org. matter from waste water by replenishing waste water with sludge and mixing the circulating soln. from an aerobic treatment process to anaerobically decompose the same and subjecting a clarified soln. obtained by removing solid matter to aerobic decomposition treatment and removing suspended solid matter from the obtained soln. CONSTITUTION: Waste water to be treated, a phosphorus fixing flocculant and sludge are stirred and mixed in a flocculation and mixing tank 1 to form phosphorus- containing flocs. Subsequently, this flocculated waste water is supplied to an anaerobic tank 2 from the bottom part thereof. At this time, a high polymer flocculant is added to the flocculated waste water on the downstream side of the pump 51 of a flocculated waste water pipe 5 from a polymer flocculant supply pipe 52 to accelerate the growth of phosphorus-containing flocs. A circulating soln. is circulated and supplied to the anaerobic tank 2 by a circulating soln. supply pipe 4 and raised in the tank 2 to be anaerobically decomposed. Solid matter is separated in a solid separation part 22 and the remaining soln. is supplied to the bottom part of an aerobic tank 3 to be aerobically decomposed. A part of the decomposed soln. is circulated by the circulating soln. supply pipe 4 to be used and the remainder thereof is sent to a sand filter 36 to be filtered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method for treating wastewater having a very high total nitrogen concentration and therefore a low content of microbial degradable organic matter compared to the content of total nitrogen. Relates to a wastewater treatment method capable of efficiently removing not only microbial degradable organic substances but also nitrogen compounds and phosphorus compounds from such wastewater.

[0002]

2. Description of the Related Art A so-called activated sludge method, which uses activated sludge as a conventional treatment method for sewage and industrial wastewater (both of which may be collectively referred to simply as "wastewater" hereinafter), is a so-called activated sludge method. is there. In this way, in general,
Microbial degradable organic matter contained in wastewater (hereinafter B
Although the removal rate of OD component) is as high as 80 to 95%, the removal rate of each of nitrogen compounds and phosphorus compounds (hereinafter also referred to as nitrogen removal rate and dephosphorization rate) is extremely low, and The processing time is as long as ten hours or more, and various equipment therefor is expensive, and a large installation area and installation volume are required.

At present, as part of environmental protection, prevention of eutrophication in lakes and closed seas is being called for. When sewage treatment plants are allowed to discharge treated water to these waters, phosphorus and nitrogen There are regulations for each emission concentration, and more stringent regulations are imposed. Nevertheless, for example, the effluent discharged from a sewage treatment plant, which is represented by a desorbed liquid from a sludge digestion tank and a returned liquid, contains a large amount of residual nitrogen. It becomes difficult to remove nitrogen from such discharged liquid because the ratio of
It is a problem.

In the case of highly treating nitrogen components and BOD components in waste water to reduce it to a high degree, conventionally, a denitrification process in which methanol is added as a carbon source in order to remove nitrates in secondary treated water is used. Although the treatment process which it has was general, there is a so-called circulation method as a method that has been recently performed. One of the circulation methods is to first supply the treated water from which sediment has been removed in a settling tank to a denitrification tank that anaerobically treats it, and then introduce the treated water to a nitrification tank and treat it aerobically, and finally treat it. At the same time as leading to the settling basin, part of the nitrification solution is circulated to the above denitrification tank, while the sludge in the final settling tank is mixed with the treated water in the first settling tank as return sludge, and this mixed solution is supplied to the denitrification tank. It is the method of processing.

In this method, the nitrogen removal rate in the entire treatment process having a denitrification tank which is a biological reaction tank is 70 to 80%.
Is relatively high and is relatively effective in removing nitrogen,
On the other hand, the residence time is generally as long as 13 to 16 hours, and phosphorus is not removed to a practically satisfactory level. Further, the phosphorus compound is once fixed in the excess sludge, but in the anaerobic state, the phosphorus compound is released from the excess sludge, and as a result, the discharge liquid contains a large amount of the phosphorus compound. Moreover, since the sludge concentration cannot be increased, the capacity of the reaction tank must be increased.

As another method of the above circulation method, an anaerobic tank is provided in front of the denitrification tank, and the returned sludge from the final settling tank and the treated water in the first settling tank are mixed to thereby circulate the circulating water. By mixing the high-concentration BOD component in the wastewater before mixing with the returned sludge, the phosphorus compound in the sludge is released by contact between the BOD component and the returned sludge under anaerobic conditions, and the sludge under aerobic conditions There is a method in which the uptake of phosphorus by microorganisms in the inside is promoted, then denitrification and aerobic nitrification are performed, and denitrification and dephosphorization are simultaneously performed. However, this method has an advantage that phosphorus can be removed from the wastewater without using a chemical such as a phosphorus fixative, but on the other hand, the nitrogen removal rate and the dephosphorization rate are both sufficient for practical use. It is not so high, the problem that a large-scale denitrification tank and nitrification tank are required has not been solved, and a large amount of phosphorus compounds remains in the effluent due to the release of phosphorus compounds from sludge. There is a drawback that.

On the other hand, various treatments have been applied to the soluble BOD.
There is known a method of increasing the BOD component concentration of the waste water to be treated by adding sludge having increased components and the supernatant of such sludge to increase the ratio to the nitrogen concentration. That is, in the biological denitrification method of organic wastewater consisting of a nitrification step and a denitrification step, for example, sludge in the first settling basin and organic sludge such as surplus activated sludge that are produced from the treatment step of the wastewater are subjected to acidic fermentation to dissolve them. The method of adding a fermentation liquor with an increased BOD component to the organic wastewater (Japanese Patent Publication No. 57-12437) and the method of biologically denitrifying the nitrogen-containing organic wastewater into excess sludge generated, For example, a method of irradiating ionizing radiation such as alpha rays and deuteron rays to convert the sludge into a soluble organic substance, and then using the solution of the soluble organic substance as a hydrogen donor in the denitrification step (special feature Japanese Patent Publication No. 60-20076).

However, in these methods, the BOD
Sludge itself is not used as a component, and some treatment is required for sludge, which is complicated. Thus, one of the reasons that the sludge itself is not used as the BOD component in the conventional method is that the large amount of suspended solids contained in the sludge causes the SRT of the sludge in the nitrification tank.
(Sludge age or sludge retention time) is shortened, and the activated sludge in the nitrification tank is diluted over the course of operation, and the amount of microbial cells such as nitrifying bacteria involved in nitrification is gradually reduced. It is presumed that this is due to the fact that the bacterial cell concentration becomes diluted and so-called washing out occurs, resulting in insufficient nitrification in the nitrification tank. Then
It is preferable that the sludge itself can be added to supplement the BOD component in the wastewater to be treated, because the wastewater can be treated easily and efficiently.

Regarding the removal of phosphorus compounds from wastewater,
Conventionally, the following method is effective. That is,
A method in which an aluminum compound or a calcium compound is directly charged into an aeration tank and reacted with a phosphorus compound to remove it as a precipitate. Waste water is passed through a column tank filled with an adsorbent such as activated alumina to adsorb the phosphorus compound. And a crystallization dephosphorization method in which phosphorus is deposited on various particles by changing the pH of waste water containing phosphorus compounds to a metastable supersaturated state of phosphorus compounds. However, all of these methods can remove only phosphorus compounds, but such methods alone cannot remove other pollutants in wastewater, such as various nitrogen compounds. Naturally, it is impossible, and there are many technologies that cannot remove BOD components.

Further, not only BOD components, which are pollutants, but also suspended solid components (hereinafter referred to as SS components), nitrogen compounds and phosphorus compounds can be removed from the wastewater in a short time with a high removal rate. Moreover, a wastewater treatment method which does not cause bulking (Japanese Patent Application Laid-Open No. 5-1
No. 85091) is known. In this method, a dephosphorization coagulant addition step, an anaerobic treatment step and an aerobic treatment step are sequentially arranged, and a liquid containing a nitrate and / or a nitrite obtained in the aerobic treatment step is introduced into the anaerobic treatment step. It is a method of circulating to.

However, although this method has various advantages as described above, the total nitrogen concentration is extremely high by this method, and therefore the BOD component content is higher than the total nitrogen content. Low, BOD for total nitrogen
When treating a wastewater in which the ratio of components is less than the theoretical equivalent of microbial degradable organic matter to total nitrogen in the treatment of anaerobic wastewater, it is necessary to lengthen the residence time in the anaerobic treatment process and the aerobic treatment process. However, even if the residence time is increased, the BOD required for nitrogen removal is
It was found that the components were deficient and, accordingly, the removal of total nitrogen was essentially inadequate, and as a result of extensive studies on this measure, the addition of sludge to such wastewater resulted in The present invention has been achieved based on the new finding that it can be substituted as a shortage of BOD component.

[0012]

[Means for Solving the Problems] That is, the first aspect of the present invention relates to wastewater containing at least a suspended solid component, a microbial degradable organic substance, a nitrogen compound and a phosphorus compound,
A phosphorus-fixing flocculant is added to generate floc-containing flocs (the same applies hereinafter to flocs containing at least a phosphorus compound), and this wastewater is then sequentially passed through an anaerobic treatment process and an aerobic treatment process to remove the wastewater from the wastewater. In a wastewater treatment method for removing suspended solids components, microbial degradable organic matter, nitrogen compounds and phosphorus compounds, a) the inflowing wastewater has a ratio of microbial degradable organic matter to total nitrogen, and microbial degradable organic matter to total nitrogen in anaerobic wastewater treatment B) replenishing the wastewater with sludge before the formation of phosphorus-containing flocculant flocs by the addition of a phosphorus-fixing flocculant to the wastewater, and c) at least phosphorus-containing flocculant flocs and sludge. Mixing the containing wastewater with a circulating liquid containing at least nitrate and / or nitrite from the aerobic treatment process To obtain a circulating liquid mixed wastewater containing phosphorus-containing floc,

E) The circulating liquid mixed wastewater is introduced into an anaerobic process in which at least denitrifying bacteria are present, where nitrates and nitrites are converted into nitrogen gas and microbially degradable organic substances are anaerobically decomposed to produce gas. At most, these gas components are discharged to the outside of the anaerobic process, f) solids are removed from the liquid treated in the anaerobic treatment process to obtain a clarified liquid, and g) the clarified liquid from the anaerobic treatment process. To an aerobic treatment process in which at least nitrifying bacteria are present, where the ammonium compound contained in the clarified liquid is converted to nitrate and / or nitrite, and aerobically decomposes residual microbial degradable organic matter. To produce a gas which is discharged from the process to obtain an aerobically treated liquid in the process or to remove suspended solids from the aerobically treated liquid. To obtain a clarified liquid, and h) circulate at least a part of the aerobically treated liquid or the clarified liquid from which the suspended solids component has been further removed as a circulating liquid to the inlet of the anaerobic treatment process. It is a characteristic wastewater treatment method.

The second aspect of the present invention has a mixing tank provided with a waste water supply pipe and a phosphorus fixed coagulant supply pipe, a solids separating means is provided and a gas discharge port, and anaerobically polluted substances in waste water. An anaerobic tank for biodegradation, and at least three tanks of an aerobic tank for biologically oxidizing pollutants in the anaerobic clarified liquid from the anaerobic tank having a gas discharge pipe and an oxygen-containing gas blowing means, and the mixing tank. The anaerobic tank is connected to each other by a coagulation wastewater pipe, a sludge supply pipe is connected to the wastewater supply pipe, the mixing tank or the coagulation wastewater pipe, and the anaerobic tank and the aerobic tank are the anaerobic tanks. The wastewater treatment apparatus is characterized in that the tank is connected to each other by a pipe for sending a clear liquid, and the aerobic tank and the inlet of the anaerobic tank are connected to each other by a circulating liquid supply pipe.

The wastewater treated in the present invention (hereinafter sometimes referred to as treated wastewater or inflow wastewater) contains at least an SS component, a BOD component, a nitrogen compound and a phosphorus compound, and a BOD component with respect to total nitrogen. The ratio of total nitrogen in anaerobic wastewater treatment (mg mg / l
There is no particular limitation as long as it is less than the theoretical equivalent of BOD component (mg / l) to l) (hereinafter sometimes simply referred to as theoretical equivalent). This theoretical equivalent is calculated to be 2.86. However, B for total nitrogen in wastewater
Considering the analytical error of each of the total nitrogen and the BOD component when obtaining the actual ratio of the OD component, the upper limit of the actual ratio corresponding to this theoretical equivalent of the BOD component to the total nitrogen in the wastewater is usually Is in the range of about 2.8 to 2.9.

The wastewater treated in the present invention is a sludge treated in advance, for example, an effluent from a sludge treatment facility such as a sewage treatment plant represented by a desorbed liquor from a sludge digestion tank and the effluent of these effluents. The supernatant is preferred. In addition to this, the present invention can also treat wastewater such as factory wastewater, industrial wastewater, and domestic wastewater that lacks BOD components necessary for biological denitrification. Representative examples of factory wastewater include coke factory wastewater, natural gas well drainage, synthetic resin factory wastewater and fertilizer factory wastewater. The present invention does not prevent its application to treatment of wastewater obtained by subjecting these wastewaters to treatments such as filtration and activated carbon treatment in advance.

The typical composition of the wastewater treated in the present invention is, for practical use, for example, per liter of wastewater BOD component: 1000 mg or less Total nitrogen (TN): 10 to 1000 mg Total phosphoric acid (T- P): 0.5 to 100 mg Suspended solid component (SS): 1000 mg or less Organic suspended substance (VSS): 700 mg or less. The analysis of the amounts of these components is based on “Sewage Test Method (Japan Sewerage Association-1984 version)” (the same applies below).

The sludge added to the wastewater to be treated includes, for example, the first settling sludge from the first settling tank, the first settling sludge from the first settling tank, and the surplus sludge from the final settling tank of other wastewater sludge processing plants. The mixed thickened sludge and the like are preferably used, but a solid substance settled in each of the anaerobic treatment process and the aerobic treatment process in the present invention can also be used. This sludge preferably has a low water content,
For the convenience of operation, it is most preferable that the water content is the minimum that can maintain fluidity. In the present invention, as a part or all of the shortage of BOD components until the ratio of BOD components to the total nitrogen content in the treated wastewater reaches 2.8 to 2.9, which corresponds to the theoretical equivalent, Sludge is replenished.

The amount of sludge to be added is deficient in the amount of BOD component in the wastewater to be treated, the ratio of the amount of BOD component to the amount of SS component of sludge (hereinafter also referred to as BOD component / SS component), nitrate of circulating liquid and It depends on the concentration of nitrite, the circulation ratio, etc., and cannot be specified unconditionally, but the addition amount of sludge can be calculated from these.
At most, the amount of BOD component in the sludge is made equal to the amount of insufficient BOD component in the wastewater to be treated. For example, when the circulation ratio is about 3, BO in the wastewater to be treated after addition of sludge is
To the extent that the amount of D component is about 75% of the theoretical equivalent, that is, to the extent of not exceeding the theoretical equivalent to the sum of the amount of nitrate nitrogen and the amount of nitrite nitrogen contained in the circulating fluid. It may be added. The sludge may be added until the start of anaerobic treatment and until the phosphorus-containing flocculant flocs are formed, and it is preferable to add the phosphorus-fixing flocculant before or at the time of addition. Can be added even after the addition of, until the phosphorus-containing aggregated flocs are formed. That is, sludge can be supplied from a wastewater supply pipe, a mixing tank, or a coagulation wastewater pipe.

However, the amount of sludge to be added is, as a guide, practically, usually about 2000 mg (mg) or more, preferably 25 per 1 liter (l) of waste water to be treated.
It is set to about 00 to 4000 mg. Further, in the present invention, the liquid in the apparatus can be analyzed at any time during the operation, and the addition amount of sludge can be adjusted as desired, and it is preferable.

In the present invention, before the anaerobic treatment of the wastewater to be treated (hereinafter sometimes referred to as a sludge mixture) to which sludge has been added, a flocculating agent for dephosphorization is added and mixed to produce a flocculated floc containing flocs. Is generated. The phosphorus-fixing flocculant is not particularly limited as long as it is a substance capable of reacting with a phosphorus compound to form a water-insoluble precipitate, and representative examples thereof include the following substances. That is, (1) aluminum-based coagulant-polyaluminum chloride, sulphate earth, etc. (2) Iron-based flocculants-polyiron, ferric chloride, ferrous sulfate, etc. (3) Calcium compound-calcium carbonate, calcium hydroxide, calcium oxide and the like. (4) Other metal salts-respective compounds such as Mg, Zn and Ba. (5) Substances containing (1) to (4) -such as blast furnace slag, coal ash and dolomite. And so on.

The amount of the phosphorus-fixing coagulant used may be a stoichiometric amount or more with respect to the amount of the phosphorus compound contained in the inflowing wastewater, but in practice, it is about 2 mole times or more with respect to the phosphorus compound. Is preferable, and it is particularly preferable that the amount is about 3 to 5 times or more. In order to improve the contact between the phosphorus-fixing flocculant and the inflowing wastewater and to smoothly generate the phosphorus-containing floc, it is preferable to stir vigorously. In order to further grow the phosphorus-containing floc, it is preferable to further use another flocculant such as a polymer flocculant. For example, anionic polymer flocculants such as anionic polyacrylamide and sodium polyacrylate are preferably used. This polymer flocculant is added so that the concentration in the inflowing wastewater is usually about 0.1 to 20 ppm.

By the formation of the phosphorus-containing aggregated flocs,
The amount of phosphorus compounds dissolved in the wastewater is extremely reduced and becomes extremely small. A large amount of water is contained in the phosphorus-containing floc. When both the phosphorus-fixing coagulant and the polymer coagulant are used in combination, the order of addition is not particularly limited, but it is preferable to add the dephosphorization coagulant first in practice. In order to generate this phosphorus-containing floc, the pH and temperature of the inflowing wastewater are set to about 5 to 9 and 5 to 40 ° C, respectively, but the pH and the temperature of the inflowing wastewater are usually within this range. Therefore, it is not necessary to artificially control pH and temperature. Prior to feeding to the anaerobic tank, it is preferable to provide a coagulation tank in the coagulation wastewater pipe in order to substantially complete the formation of coagulation flocs. The mixing tank can also be used as a coagulation tank.

The thus obtained influent wastewater containing at least phosphorus-containing coagulated flocs and sludge (hereinafter sometimes referred to as coagulated wastewater) contains at least nitrate and sub-atom from the aerobic treatment process of the second stage. A circulating liquid containing nitrates (hereinafter sometimes simply referred to as circulating liquid) is mixed (the liquid after mixing the circulating liquid is sometimes referred to as circulating liquid mixed wastewater). The ratio of the amount of the circulating liquid added to the coagulation wastewater to the amount of the coagulation wastewater (hereinafter referred to as the circulation ratio) is the liquid treated in the next anaerobic treatment process, that is, the circulating liquid derived from the circulating liquid dissolved in the circulating liquid mixed wastewater. The ratio of the amount of BOD component to the sum of the amount of nitrate nitrogen and the amount of nitrite nitrogen is determined so as not to exceed the theoretical equivalent of 2.8 to 2.9.

The circulation ratio (volume ratio) is changed according to the respective compositions of the inflowing wastewater and the circulating liquid. The larger the circulation ratio, the higher the nitrogen removal rate according to the invention of the inflowing wastewater tends to be. However, when the circulation ratio exceeds a certain limit, the nitrogen removal rate of the inflowing wastewater according to the present invention does not become higher as the circulation ratio increases. Therefore, in practice, this circulation ratio is usually about 0.5 to 5, preferably about 0.5.
It is about 5 to 4, and about 3 is optimal. For example, when the circulation ratio is 3, the nitrogen removal rate of the waste water to be treated according to the present invention is theoretically about 75%. In the calculation of this theoretical value, (1) the denitrification rate in the anaerobic treatment process (the same applies to the conversion rates from nitrate nitrogen and nitrite nitrogen to nitrogen gas) is substantially 100%. (2) In the aerobic treatment process, the conversion rate from ammonia nitrogen to nitrate nitrogen and / or nitrite nitrogen is substantially 100%.
Is. It is based on the assumption that. However, the respective values of (1) and (2) above are 100% in reality.
However, in consideration of this, the nitrogen removal rate is actually about 70%. The circulating liquid mixed waste water containing at least the phosphorus-containing floc and sludge and the circulating liquid obtained here is sent to the next anaerobic treatment process.

In the anaerobic treatment process, as in the conventional anaerobic wastewater treatment process, various anaerobic microorganisms including denitrifying bacteria (both facultative anaerobic microorganisms and obligate anaerobic microorganisms are included. ) Exists,
BOD components, nitrates, nitrites, etc. are anaerobically reduced and decomposed by these microorganisms, respectively, and finally gas components are produced. Further, the SS component is hydrolyzed and solubilized by these microorganisms. The BOD component dissolved in the circulating liquid mixed wastewater and the solubilized BOD component are converted into a gas such as carbon dioxide through an organic acid.

Nitrate and nitrite are finally converted to nitrogen gas by nitrate respiration and nitrite respiration of facultative anaerobic microorganisms, respectively. This nitrogen gas is discharged from the anaerobic treatment process, and the wastewater to be treated is denitrified. Further, the BOD component in the circulating liquid mixed waste water acts as a hydrogen donor at this time. Here, ammonium compounds in the circulating liquid mixed wastewater (organic nitrogen such as urea nitrogen is also included below)
Is only consumed as a nutrient source for various microorganisms in the anaerobic treatment process, and is substantially not chemically changed.

Further, a trace amount of the phosphorus compound eluted from the phosphorus-containing coagulated flocs, a trace amount of the phosphorus compound dissolved in the circulating liquid mixed wastewater, and part of nitrates and nitrites are also consumed as nutrient sources for various microorganisms in the anaerobic treatment process. To be done. In the anaerobic treatment process, each substance is decomposed in this way and microorganisms are also proliferated. Here, normally, the circulating liquid mixed wastewater can be treated as it is, so that it is not particularly necessary to artificially control the pH and the temperature.

In this way, the solid matter is separated from the liquid treated by the anaerobic treatment process (hereinafter also referred to as anaerobic treatment liquid) by a usual solid-liquid separation means such as sedimentation separation, centrifugation and filtration. After being removed, a clarified liquid (hereinafter sometimes referred to as an anaerobic-treated clarified liquid) is obtained.
The solid matter removed here mainly contains phosphorus-containing flocs and microbial cells. The solid separating means may be provided integrally with the tank body of the anaerobic tank in the anaerobic process, or may be provided separately from the tank body. This anaerobic treatment clarified liquid contains BOD components, ammonium compounds, and trace amounts of phosphorus compounds.

This anaerobic treatment clarified liquid is sent to the next aerobic treatment process. In this aerobic treatment process, as in the conventional aerobic wastewater treatment process, aerobic microorganisms such as nitrifying bacteria such as nitrite bacteria and nitric acid bacteria are present, and the BOD component and ammonium compound are oxygen-containing gas. Aerobically oxidised by microorganisms in the presence of
Finally, carbon dioxide gas and nitrate and nitrite are produced, respectively. The oxygen-containing gas only needs to contain molecular oxygen, and air, air enriched with oxygen gas, oxygen gas, or the like is used. Above all, air is preferred. The carbon dioxide gas generated here is discharged to the outside of the aerobic treatment process together with the oxygen-containing gas. B
The OD components, traces of unoxidized ammonium compounds, some of the nitrates and nitrites and traces of residual phosphorus compounds are consumed as nutrients for various microorganisms in this aerobic treatment process.

In this aerobic treatment process, an oxygen-containing gas is passed through the liquid and agitated, and if desired, further mechanically agitated to supply oxygen into the liquid so that dissolved oxygen is not deficient. I won't. In this aerobic treatment process, the clarified liquid from the anaerobic treatment process in the previous stage can usually be treated as it is, so that there is no particular need to control the pH and temperature of the liquid. In addition, as described above, in general, when the water content of the added sludge is excessive, in the aerobic treatment process, the bacterial cell amount of the microorganisms involved in this aerobic process decreases with the progress of operation. However, so-called washing out occurs, and there is a high risk that the progress of nitrification here will decrease.

However, in the present invention, even if a large amount of water is contained in the sludge added to the treated wastewater,
Since this moisture is contained and removed in the solid matter removed in each of the anaerobic treatment process and the aerobic process, the risk of so-called washing out is reduced. Further, in order to substantially completely prevent the occurrence of so-called washing out in the aerobic treatment process, aerobic microbial cells involved in the aerobic treatment process are used by being immobilized on various carriers. It is preferable.

Immobilization of microorganisms can be carried out by a conventional method. It is preferable to use a fixed bed in which microorganisms are fixed. As the carrier for the fixed bed, for example, a filter bed using a filler, a honeycomb structure, and a disk body such as a fixed disk and a rotating disk are preferable. As a typical example of the filler,
Examples include anthracite (anthracite) and plastic moldings. As the honeycomb structure and the disc body, those made of a porous body and those made of a multi-foam body are preferable. Further, for example, a cord-shaped carrier made of a plastic fiber such as polyvinylidene chloride can be used, and is preferable. In addition, in this aerobic treatment process, the floating activated sludge method is not obstructed if the risk of occurrence of washout is accepted. However, in this case, in order to prevent the occurrence of bulking, 0.0
It is preferable to add a cationic polymer flocculant so as to be 1 to 0.05 ppm.

When the aerobic treatment liquid is discharged from the aerobic treatment process, the anaerobic treatment clarified liquid is supplied to the aerobic treatment process, and the anaerobic treatment clarified liquid has a content rate of the SS component. May be low,
Since a small amount of SS component contained in these aerobic treatment liquids is precipitated in the aerobic treatment process,
It is a clear liquid. In addition, when the aerobic treatment liquid contains a considerable amount of SS components and in order to further reduce the content rate of the SS components in the aerobic treatment liquid, sedimentation and centrifugation are performed from the substantially clear liquid. Alternatively, the solid matter can be removed by an ordinary solid-liquid separation means such as filtration to obtain a clear liquid having a low content of SS components. At least a part of the aerobic treatment liquid or the clarified liquid thus obtained is circulated as a circulating liquid to the inlet of the anaerobic treatment process,
The remaining portion is discharged as it is or after being subjected to various treatments such as solid-liquid separation as necessary, or is reused. The wastewater treatment device of the present invention is preferably installed adjacent to another wastewater treatment facility serving as a sludge supply source, but may be installed independently of other wastewater treatment facilities.

[0035]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 Wastewater Treatment Device FIG. 1 shows a flow sheet of a representative example of the wastewater treatment device of the present invention. This wastewater treatment device has a coagulation / mixing tank 1, an anaerobic tank 2, and an aerobic tank 3. A wastewater supply pipe 11, a phosphorus fixed coagulant supply pipe 12 and a sludge supply pipe 13 are connected to the coagulation and mixing tank 1, and a stirrer 14 is built therein. The anaerobic tank 2 has a gas discharge pipe 21 connected to the upper portion thereof, and the bottom portion thereof has an inverted conical shape so that a solid matter separating portion is formed.
It is said to be 22. The solids separation section 22 at the bottom of this anaerobic tank 2
A sludge storage tank 221 is connected to the peripheral wall of the. Also, anaerobic tank
2 has a stirrer 23 built-in.

The aerobic tank 3 has a built-in fixed bed 31 in which aerobic microbial cells are fixed, a bottom has a built-in sparger 33 connected to an air blowing pipe 32, and an upper part has a sparger 33. A gas discharge pipe 34 and an overflow pipe 35 are connected to each other. The overflow pipe 35 is branched into two branch pipes 351 and 352 on the downstream side. By connecting the branch pipe 351 to the inlet of the pump 41,
Further, by connecting the circulating liquid supply pipe 4 to the coagulation wastewater pipe 5, the upper portion of the aerobic tank 3 and the bottom inlet of the anaerobic tank 2 are connected to each other. A sand filter 36 is arranged downstream of the aerobic tank 3. Upper part of aerobic tank 3 and sand filter 36
Are connected to each other by an overflow pipe 35 and a branch pipe 352. The coagulation and mixing tank 1 and the inlet at the bottom of the anaerobic tank 2 are the coagulation wastewater pipe 5 where a pump 51 is provided in the middle.
Are connected to each other via. A polymer coagulant supply pipe 52 is connected to the coagulation wastewater pipe 5. The upper portion of the anaerobic tank 2 and the aerobic tank 3 are connected to each other by an overflow pipe 6.

In the wastewater treatment apparatus of the present invention shown in FIG. 1, the wastewater to be treated is treated as follows. That is, the sludge for replenishing the deficient amount of the BOD component in the treated wastewater, the phosphorus fixed coagulant and the treated wastewater is passed through the wastewater supply pipe 11, the phosphorus fixed coagulant supply pipe 12 and the sludge supply pipe 13. It is supplied to the coagulation and mixing tank 1. Agglomeration mixing tank
In 1, the wastewater to be treated, the phosphorus-fixing coagulant and the sludge are agitated by a stirrer 14 and mixed with each other to produce phosphorus-containing floc, and at least a flocculated wastewater containing phosphorus-containing flocs and sludge. This coagulation wastewater is discharged from the coagulation and mixing tank 1, and a pump 51
It is supplied into the anaerobic tank 2 from the inlet at the bottom of the anaerobic tank 2 via the coagulation wastewater pipe 5 provided with. If desired, in order to further grow the above-mentioned phosphorus-containing floc in the flocculation wastewater discharged from the flocculation and mixing tank 1, the polymer is fed from the polymer flocculant supply pipe 52 downstream of the pump 51 of the flocculation wastewater pipe 5 as desired. A flocculant is added. In addition, a circulating liquid containing at least nitrates and nitrites from the aerobic tank 3 is added to this coagulated wastewater via a circulating liquid supply pipe 4 provided with a pump 41 in the middle of the condensed wastewater to obtain a circulating liquid mixed wastewater. To be done.

The circulating liquid mixed wastewater supplied from the inlet at the bottom of the anaerobic tank 2 to the inside of the anaerobic tank 2 is stirred by the stirrer 23 so as to rise inside the anaerobic tank 2, and during this time, the anaerobic tank 2 is degassed. It is brought into contact with anaerobic microorganisms such as nitrifying bacteria, and anaerobically reduced and decomposed by the action of the anaerobic microorganisms, and the BOD component in the liquid is finally converted into a gas such as carbon dioxide gas, nitrate and Both nitrate nitrogen and nitrite nitrogen such as nitrite are finally converted into gas such as nitrogen gas, and the SS component is solubilized. The gas component generated here is anaerobic tank 2
The gas is discharged from the gas discharge pipe 21 at the upper part of the.

On the other hand, the phosphorus-containing agglomerate flocs in the liquid are further grown, and these agglomerate flocs are settled in the anaerobic tank 2 and reach the solid separation section 22 at the bottom of the anaerobic tank 2 where they are collected. The solid matter and the liquid content are separated from each other, and the solid matter is discharged to the sludge storage tank 221 connected to the peripheral wall of the solid matter separating section 22. In the upper part of the anaerobic tank 2, the anaerobic treated clarified liquid contains substantially no or very little phosphorus-containing floc. This anaerobic treatment clarified liquid is an anaerobic tank
Aerobic tank 3 from the top of 2 via overflow pipe 6
Supplied at the bottom of the.

The anaerobic-treated clarified liquid supplied to the aerobic tank 3 is
BOD in the liquid is contacted with aerobic microorganisms in the fixed bed of the aerobic tank, and in the presence of oxygen-containing gas released from the bottom of the aerobic tank by the action of the aerobic microorganisms.
The component and the ammonium compound are aerobically oxidized, and finally carbon dioxide gas and nitrate and nitrite are produced to obtain an aerobic treatment liquid. The oxygen-containing gas and the generated gas component are discharged from the gas discharge pipe 34 in the upper part of the aerobic tank 3. The aerobic treatment liquid obtained here is a substantially clarified liquid, and is passed through the overflow pipe 35 and the branch pipe 351 in order, and all or a part of the aerobic treatment liquid is used as a circulating liquid as a pump 41 and a circulating liquid supply pipe. Four
Is added to the coagulation wastewater that passes through the coagulation wastewater pipe 5 and is supplied to the anaerobic tank 2 from the inlet at the bottom of the anaerobic tank 2 as circulation liquid mixed wastewater and circulated to the anaerobic tank 2.

If desired, the substantial remainder of the clarified liquid, which is the aerobic treatment liquid from the aerobic tank 3, is sent to the sand filter 36, which is a solid separating means of the aerobic tank 3, where Floating solid components in the aerobic treatment liquid are substantially completely removed, and the rest is discharged out of the apparatus.

Example 2 Treatment of the supernatant of the desorbed liquid from the digestion tank The waste liquid treatment apparatus of the present invention shown in Example 1 was used to treat the supernatant of the desorbed liquid from the digestive tank. . As the phosphorus-fixing coagulant, polyaluminum chloride and calcined dolomite were used. The experimental conditions are shown below. The results are shown in Table 1. The results shown in Table 1 are average values of the results obtained by maintaining the conditions for a further month after reaching the steady state about one month after the experimental conditions were set. Anaerobic tank size: 80 mmφ x 2000 mmH (volume 10
L) Size of aerobic tank: 200 mm × 250 mm × 500 mm H (volume: 20 liters) Fixed bed: Biocord (manufactured by TBC Co., Ltd.), a cord carrier made of polyvinylidene chloride, carrying aerobic microbial cells As a string-shaped immobilization product, this string-shaped immobilization product is fixed to a rectangular stainless steel frame at both ends,
This string-like immobilization product is built in the anaerobic tank so as to be vertical. This string-like immobilization product is 350 m per 1 m ³ of the internal volume of the anaerobic tank.

Wastewater to be treated: The supernatant liquid of the desorbed liquid from the digestion tank. The composition is shown in Table 1. Temperature Normal temperature Added sludge: Raw sludge mixed with species A sludge concentrated from a sludge drawn from the first settling tank and a sludge drawn from the final settling tank of a conventional sewage treatment plant. Addition amount 120 g per 1 liter of treated wastewater as SS component Circulation ratio: 3 Residence time: Anaerobic tank 36 hours Aerobic tank 72 hours Amount of phosphorus-fixing coagulant: Polyaluminum chloride 200 mg per 1l treated wastewater Calcined dolomite 1l treated wastewater 500 mg per unit (also known as dolomite, dolomite, which is a double salt of calcium carbonate and magnesium carbonate, calcined at 800 to 1000 ° C and the particle size adjusted to 100 to 200 mesh) Polymer flocculant: Kind And usage amount In case of polyaluminum chloride Anion polymer 5mg per liter of treated wastewater In case of calcined dolomite Cationic polymer 5mg per liter of treated wastewater

[0044]

[Table 1]

Example 3 Treatment of the supernatant of the desorbed liquid from the digestion tank Using the wastewater treatment apparatus of the present invention shown in Example 1, The supernatant was processed. As the phosphorus-fixing coagulant, polyaluminum chloride and calcium hydroxide were used. The experimental conditions are shown below. The results are shown in Table 2. In addition,
The results shown in Table 2 are the average values of the results of treatment for one month after the experimental conditions were set and a steady state was reached, and then the conditions were maintained for another month. Anaerobic tank size: 80 mmφ x 2000 mmH (volume 10
L) Size of aerobic tank: 200mm × 250mm × 500mmH (volume 20 liters)

Wastewater to be treated: The supernatant liquid of the desorbed liquid from the digestion tank. The composition is shown in Table 2. Temperature Normal temperature Added sludge: Raw sludge mixed with species A sludge concentrated from a sludge drawn from the first settling tank and a sludge drawn from the final settling tank of a conventional sewage treatment plant. Addition amount 160g as SS component per liter of treated wastewater Circulation ratio: 3 Residence time: Anaerobic tank 18 hours Aerobic tank 36 hours Amount of phosphorus fixing coagulant: Polyaluminum chloride 200mg per 1l of treated wastewater Calcium hydroxide Treatment wastewater 700 mg per liter Polymer Flocculant: Type and amount Used In the case of polyaluminum chloride Anion polymer 5 mg per liter of treated wastewater Calcium hydroxide In the case of cation polymer 5 mg per liter of treated wastewater

[0047]

[Table 2]

[0048]

Industrial Applicability According to the present invention, it is possible to easily and efficiently treat wastewater having a very high total nitrogen concentration and therefore a low content of microbial degradable organic matter compared to the content of total nitrogen. .

[Brief description of drawings]

FIG. 1 is a flow sheet of a representative example of a wastewater treatment device of the present invention.

[Explanation of symbols]

 1 Coagulation / mixing tank 11 Waste water supply pipe 12 Phosphorus fixed coagulant supply pipe 13 Sludge supply pipe 14 Stirrer 2 Anaerobic tank 21 Gas discharge pipe 22 Solids separation section 221 Sludge storage tank 23 Stirrer 3 Aerobic tank 31 Fixed bed 32 Air blowing pipe 33 Sparger 34 Gas discharge pipe 35 Overflow pipe 351 Branch pipe 352 Branch pipe 36 Sand filter 4 Circulating liquid supply pipe 41 Pump 5 Coagulation wastewater pipe 51 Pump 52 Polymer coagulant supply pipe 6 Overflow pipe

Claims (9)

[Claims] 1. A phosphorus-fixing flocculant is added to wastewater containing at least suspended solids, microbial-degradable organic matter, nitrogen compounds and phosphorus compounds to produce phosphorus-containing floc, and then the wastewater is anaerobically treated. In a wastewater treatment method for removing suspended solids components, microbial degradable organic matter, nitrogen compounds and phosphorus compounds in the wastewater by sequentially passing through a process and an aerobic treatment process, a) the inflowing wastewater is microbially decomposed to total nitrogen. The ratio of volatile organics to less than the stoichiometric equivalent of microbial degradable organics to total nitrogen in the treatment of anaerobic wastewater, and b) the addition of a phosphorus-fixing flocculant to the wastewater, before the phosphorus-containing flocculant flocs are produced. And c) wastewater containing at least phosphorus-containing floc and flocs and at least nitric acid from the aerobic treatment process. Mixing a circulating liquid containing salt and / or nitrite to obtain a circulating liquid mixed wastewater containing phosphorus-containing floc, and e) guiding the circulating liquid mixed wastewater to an anaerobic process in which at least denitrifying bacteria are present, Here, the nitrate and nitrite are changed to nitrogen gas and the microbial degradable organic matter is anaerobically decomposed to generate gas, and these gas components are discharged to the outside of the anaerobic process, and f) in the anaerobic treatment process. Solids are removed from the treated liquor to obtain a clarified liquid, g) leading the clarified liquid from the anaerobic treatment process to an aerobic treatment process in which at least nitrifying bacteria are present, where it is contained in the clarified liquid. The ammonium compounds present in the process to nitrates and / or nitrites and aerobically decomposes residual microbial degradable organic matter to produce a gas, which is removed from the process. Effluent to obtain an aerobically treated liquid in the process, or a suspension liquid component is further removed from the aerobic treated liquid to obtain a clarified liquid, h) the aerobically treated liquid or the suspended solid A wastewater treatment method, characterized in that at least part of the clarified liquid from which the product components have been further removed is circulated as a circulating liquid to the inlet of the anaerobic treatment process. 2. The wastewater treatment method according to claim 1, wherein a high-molecular flocculant is used together with the dephosphorization flocculant in the inflowing wastewater. 3. The volume ratio of the circulating liquid to the inflowing wastewater is 0.
The method for treating wastewater according to claim 1 or 2, which is 5 to 5. 4. The pH and temperature of the agglomeration process are substantially 5-9 and 5-40 ° C., respectively.
The wastewater treatment method according to any one of 1 to 3. 5. The wastewater treatment method according to claim 1, wherein immobilized microorganisms are used as aerobic microorganisms in the aerobic treatment process. 6. An anaerobic anaerobic biodegradation of pollutants in wastewater, which has a mixing tank provided with a wastewater supply pipe and a phosphorus fixed coagulant supply pipe, a solids separating means is provided, and which has a gas outlet. A mixing tank and an anaerobic tank having at least 3 tanks, an aerobic tank for biologically oxidizing pollutants in the anaerobic clarified liquid from the anaerobic tank, which has a gas discharge pipe and an oxygen-containing gas blowing means. Are connected to each other by a coagulation wastewater pipe, and a sludge supply pipe is connected to the wastewater supply pipe, the mixing tank or the coagulation wastewater pipe,
Further, the anaerobic tank and the aerobic tank are connected to each other by a pipe for sending a clarified liquid of the anaerobic tank, and the aerobic tank and the inlet of the anaerobic tank are connected to each other by a circulating liquid supply pipe. A wastewater treatment device characterized in that 7. The wastewater treatment device according to claim 6, further comprising an aerobic tank containing a fixed bed in which microbial cells are fixed. 8. The coagulation wastewater pipe is provided with a coagulation tank for coagulating and settling the phosphorus-containing coagulation flocs.
Alternatively, the wastewater treatment device according to 7. 9. The wastewater treatment apparatus according to claim 6, wherein a polymer coagulant supply pipe is connected to the wastewater supply pipe, the mixing tank, or the coagulation wastewater pipe.