JP2001009495A - Treatment of organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate and recover a phosphorus component in a short time by separating wastewater after aeration-treatment into primary treatment water and sludge, concentrating the obtained sludge and heating the concentrated sludge under specified conditions to release phosphorus and separate into secondary treatment water containing the released phosphorus component and the secondary sludge free from phosphorus component. SOLUTION: Raw wastewater A is fed from an anaerobic treatment tank 7 to an aeration treatment tank 1 to subject to aerobic treatment by an aeration means 12. The aeration-treated liquid is separated into phosphorus component-concentrated sludge and primary treatment water (a) by a solid-liquid separation means 2. The obtained sludge is concentrated by a concentration means 3 to obtain primary sludge (x) and phosphorus component-free separated water, which is discharged together with the primary treatment water (a). The obtained primary sludge (x) is heated by passing through a heat exchanger 11 and then heated at 60-90 deg.C for 10-120 minutes using a heating means 10 in a phosphorus releasing tank 4 to release the phosphorus component. The heated sludge is separated into treated water secondary treatment water) (b) rich in the phosphorus component and secondary sludge (z) by a solid-liquid separation means 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low-cost, high-yield method for treating organic wastewater discharged from a sewage treatment process such as a sewage treatment plant, a human waste treatment plant, or a food factory or a chemical factory. The present invention relates to a method for treating phosphorus that can separate and recover phosphorus components by using the method, and a method for treating organic wastewater employing the treatment method.

[0002]

2. Description of the Related Art As a method for treating organic wastewater, surplus sludge consisting of microbial biomass mainly composed of microbial cells and untreated residual sludge generated by biological digestion of organic wastewater is known. 2. Description of the Related Art A method has been widely adopted in which a treated sludge containing solids is separated into solid and liquid in a sedimentation tank or the like and treated water obtained as a supernatant is appropriately discarded, while excess sludge is treated by dumping in the ocean or land reclamation.

[0003] However, depending on the organic wastewater to be treated, a high content of phosphorus components (ie, orthophosphoric acid (orthophosphoric acid), polyphosphoric acid, phosphate) is contained in the treated water and excess sludge generated by such treatment. , Phosphate esters,
Phosphoproteins, glycerophosphate, phospholipids, etc.) in some cases. Disposal of these is regarded as a direct cause of environmental pollution, and in particular, when treated water containing such a large amount of phosphorus is discharged into lakes and marshes, phytoplankton remarkably grows due to eutrophication of water. Not preferred.

Accordingly, there has been a case in which a method is employed in which the following coagulant is added to the treated water from the precipitation apparatus to reduce the phosphorus component and then the treated water is discharged. In order to perform such a coagulation operation on water, a large-scale processing apparatus must be added, which increases the processing cost, the required time, the required number of personnel, etc., and causes a disadvantage. In addition, the efficiency of aggregation is low, and the removal of the phosphorus component may be insufficiently completed. At present, phosphorus components in excess sludge must be discarded without any means to remove them.

[0005] Incidentally, conventionally known processes for removing phosphorus contained in wastewater include a flocculant addition method, a crystallization dephosphorization method, and an anaerobic-aerobic activated sludge method (sewerage facility planning).・ Design guidelines and explanations (Part 2) 1
994 edition, published by Japan Sewer Association, No. 131-1
See page 36).

The coagulant addition method utilizes the fact that trivalent metal cations such as aluminum ions and iron ions react with orthophosphate ions to form poorly water-soluble phosphates. The flocculant is mixed with the wastewater, and the floc (including biologically derived floc) formed from the hardly soluble phosphate is precipitated and separated. According to this method, an increase in excess sludge of about 5 to 20% has been recognized, and it is hard to say that large-scale disposal of excess sludge containing a large amount of phosphorus component is preferable in recent years, as environmental conservation is being called for.

The crystallization method is based on the formation of hardly soluble hydroxyapatite by the reaction of orthophosphate ions and calcium ions, and is preferable in that it does not involve an increase in excess sludge. Since the conditions required for crystallization must be strictly controlled (for example, removal of crystallization-interfering substances such as carbonate ions by pretreatment, pH adjustment, temperature adjustment, etc.), application is limited and cost increases. It is not a preferable method as a means in wastewater treatment because it includes the cause of inducing.

In the anaerobic-aerobic activated sludge method, microorganisms that have released polyphosphoric acid as orthophosphoric acid in an anaerobic state for energy acquisition accumulate as polyphosphoric acid after excessive intake and metabolism of orthophosphoric acid in an aerobic state. In this method, wastewater is subjected to repeated treatment in an anaerobic tank, an aerobic tank, and a sedimentation basin so that excess sludge contains a phosphorus component and the phosphorus component in the treated water is removed. Although the phosphorus component can be effectively removed from the treated water by this method, the excess sludge is rich in the phosphorus component and contains various other organic components and heavy metal components. And although the phosphorus component may be effectively used for producing fertilizers and phosphorus compounds, for example, it is inevitably discarded in a sludge state mixed with such miscellaneous components.

Therefore, for the purpose of recovering phosphorus from the sludge generated by the biological treatment and effectively using the sludge, the sludge is anaerobically treated to elute the phosphorus component in the sludge, and the eluted phosphorus component is aggregated. A method for adding and recovering an agent has been developed (see JP-A-9-267099), and more recently, an ozone treatment method (see JP-A-9-26999).
No. 4596), an alkali addition method (Japanese Patent Laid-Open No. 8-3).
No. 9096), and a method of recovering phosphorus in sludge by a method of mechanical pulverization (see Japanese Patent Application Laid-Open No. 11-57791).

[0010]

However, in the ozone treatment method, although there are few problems caused by chemicals and wastes, facility costs and running costs are very high, so that it can be practically used from an economical point of view. Absent. According to the alkali addition method, an alkali waste liquid is generated, and further cost is required for treating the waste liquid. According to a method including a step of releasing phosphorus components from microorganisms by exposing sludge to an anaerobic treatment step, phosphorus can be collected and reused at a relatively low cost, Processing time is required, and the recovery rate of phosphorus is 50
%, And the amount of the coagulant added increases because it is recovered as phosphoric acid. In the method using mechanical pulverization, a special device such as rotating metal blades at a high speed or rotating beads at a high speed is required, and maintenance of the device requires considerable cost and time.

In recent years, the achievement rates of the environmental standards of COD for lakes, marshes and closed sea areas have been 40% and 65%, respectively.
This is thought to be due to endogenous substances such as blue-green algae and plankton. For this reason,
The Environment Agency consulted the Central Council in February 1999 regarding the total emission control of nitrogen and phosphorus, which causes eutrophication, and a report on these regulations will be made in March 2000. There is a continuing need for a treatment method that efficiently and recyclably recovers the phosphorus component contained in the organic wastewater and that can be implemented at low cost without adversely affecting the environment.

Further focusing on the demand for the phosphorus component,
Currently, more than 900,000 tons (equivalent to more than 10 billion yen) of phosphorus ore are imported from other countries in Japan. However, it is becoming increasingly difficult to extract high-grade phosphate ore from its place of origin due to long-term consumption, and it is not clear whether it can be supplied to Japan in a stable manner in the future. Also,
Currently, about 3,000 tons (equivalent to more than 400 million yen) of polyphosphate are imported to Japan from Asia, Europe and the United States each year, and the amount of this import is increasing year by year. This is because polyphosphoric acid can be a raw material for the production of ATP and for the production of mineral fiber, which is expected to be a substitute for asbestos having carcinogenicity, and tripolyphosphoric acid is a synthetic detergent, detergent, sequestering agent, food It is considered that this is because it is used as a raw material of an additive and in a reagent raw material used for papermaking, dyeing, photographic technology and the like.

Therefore, in order to meet such a high demand in Japan, phosphate (calcium phosphate), which is a main component of phosphate ore, is contained in extremely high purity, or in a state of high purity as polyphosphate, If the phosphorus component derived from organic wastewater is recovered, it will be possible to use phosphorus component, which caused environmental pollution by disposal, very effectively, which will greatly contribute to various industries. It is.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide an organic wastewater treatment method which can efficiently separate and recover a phosphorus component in a short time, and require a chemical agent for precipitation as a solid. It is an object of the present invention to provide a treatment method that achieves an effect of reducing the amount, and is advantageous in reusing the phosphorus component.

[0015]

According to a first aspect of the present invention, there is provided a method for treating organic wastewater, comprising: (1) an aeration treatment step in which the wastewater is subjected to aerobic treatment;
(2) a solid-liquid separation step in which wastewater after aeration treatment is separated into primary treated water and sludge; (3) a concentration step in which separated sludge is concentrated; and (4) a phosphorus component from the concentrated sludge. A phosphorus release step of performing a heat treatment at 60 to 90 ° C. for 10 to 120 minutes to release into the phase, and (5) secondary treated water containing the released phosphorus component, and secondary sludge from which the phosphorus component has been removed And a solid-liquid separation step of separating the wastewater into organic wastewater. According to this method, the phosphorus component is accumulated in the microorganisms in the wastewater in the aeration treatment step (1), and this treated water is separated into the primary treatment water and the sludge in which the phosphorus component is concentrated in the next solid-liquid separation step (2). The concentrated sludge is then separated and further concentrated (3), and then heated for a short time. In a phosphorus releasing step (4) which does not require any special equipment or reagent, the phosphorus component is released from the concentrated sludge into a liquid phase and solid-liquid separation is performed. By doing so, a small volume of treated water with high phosphorus content (secondary treated water)
And secondary sludge from which the phosphorus component has been removed. Since the phosphorus component released here is mainly in the form of polyphosphoric acid, the required amount of a coagulant such as a metal salt required for coagulation and precipitation is significantly lower than in the conventional method. Become. By reducing the sludge volume in the concentration step (3), the volume of the tank required for the subsequent phosphorus release step (4) can be reduced. This leads to a reduction in the energy required for heating in the process and a reduction in the volume of the processing tank thereafter, so that equipment and maintenance costs can be significantly reduced.

The second invention of the present application is characterized in that the concentration step (3) in the first invention of the present application is performed by a floating concentration method. The flotation concentration utilizes the fact that sludge floats by adding an air bubble to the sludge to reduce the apparent specific gravity of the sludge. For example, in the case of sedimentation concentration, there is a limit to the concentration rate, and the concentration can be limited to only about 2% of the sludge concentration. Further, depending on the residence time of the sludge, microorganisms are exposed to an anaerobic state, and in the aeration treatment step (1), the internal The accumulated phosphorus component is released again, so that the return water contains phosphorus, and the phosphorus removal rate of the water treatment system may be reduced. Therefore, the sludge can be substantially kept in an aerobic state, sufficient concentration of 4% or more of the sludge concentration can be realized while preventing the re-release of the phosphorus component, and the advantages associated with the above-mentioned sludge concentration can be achieved. Possible flotation enrichment methods are preferably employed in the present invention.

In the third invention of the present application, heat exchange between the sludge obtained in the concentration step (3) and the treatment liquid after the phosphorus release step (4) is performed, and the heat recovery efficiency in the treatment step is reduced. Provide a method that is good and has little heat loss. Further, if the heat exchange is performed in this manner, the solid-liquid separation step (5) is performed after the treatment liquid obtained after the release of phosphorus is cooled.
Therefore, there is also an advantage that the options of the solid-liquid separation means at this time are expanded.

The fourth invention of the present application is directed to the solid-liquid separation step (5).
After the step (2), the method further comprises a phosphorus coagulation step (6) of precipitating the released phosphorus component from the liquid phase by adding a coagulant to the secondary treatment water generated in the step. If the component precipitated by this method is recovered, the phosphorus component is obtained as a very concentrated solid component, so that it can be easily used for producing fertilizers and phosphorus compounds, and is advantageous in terms of transportation and handling.

In the treatment method according to the fifth invention of the present application, the phosphorus aggregating step (6) is carried out under basic conditions of pH 8.0 to 10.5. Under such conditions, the phosphorus component efficiently coagulates both the phosphoric acid component and the polyphosphoric acid component into a form that can be easily separated as a solid.

The treatment method of the sixth invention of the present application further includes an anaerobic treatment step (7) before the aeration treatment step (1). By this anaerobic treatment, the anaerobic sludge decomposition and the release of the phosphorus component to the liquid phase are performed prior to the excessive intake of the phosphorus component to the microorganisms, so that the excess intake of the phosphorus component in the aeration treatment is performed more efficiently. Become.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for treating organic wastewater of the present invention, sludge is treated at 60 to 90 ° C. for 10 to 120 minutes.
Preferably, heat treatment is performed at 70 to 80 ° C. for 20 to 60 minutes, and the phosphorus component in the sludge is released to the liquid phase by the heat treatment. When heating is performed under such conditions, it becomes possible to release the phosphorus component mainly as polyphosphoric acid, as will be apparent from the examples described later. Then, as compared with the case where the phosphorus component is released as orthophosphoric acid or other phosphoric acid derivatives according to the conventional method, a flocculant such as a metal salt necessary for recovering the phosphorus component as a precipitate from the liquid phase is required. The amount is significantly reduced. This is based on the number of phosphorus atoms,
This is because polyphosphoric acid has a small number of free phosphate residues to which a flocculant can bind. In addition, since the metal salt of polyphosphoric acid forms a larger granular sediment than the metal salt of phosphoric acid, in the subsequent recovery treatment, for example, the time required for precipitation separation or centrifugation is reduced, and the volume is reduced. This is advantageous because it is possible to reduce the volume and reduce the number of revolutions of centrifugation. If the treatment temperature is lower than 60 ° C., it is difficult to release the phosphorus component as polyphosphoric acid, and 9
If the temperature exceeds 0 ° C., polyphosphoric acid is decomposed into phosphoric acid immediately after release, so that the amount of a flocculant required for recovery is increased and the heating cost is undesirably high.

After performing the treatment for releasing phosphorus, the sludge after the treatment is separated into solid and liquid by ordinary means such as sedimentation, filtration (including membrane separation), and centrifugation, and contains the released phosphorus component. Add a coagulant such as polyaluminum chloride, aluminum sulfate, ferric chloride, ferrous sulfate, calcium chloride, calcium oxide, calcium hydroxide, magnesium chloride, magnesium sulfate, magnesium oxide, magnesium hydroxide, etc. to the liquid phase To precipitate the phosphorus component.
In order to cause precipitation from the phosphorus release treatment solution according to the above method, it is sufficient to add not more than half of the required amount of the flocculant in the same step as in the conventional method. It can be said that the production amount of the compound can be suppressed, which is preferable from the viewpoint of environmental conservation. After the precipitation, the obtained solid component is recovered by a conventional method, subjected to a purification treatment if necessary, and provided as a fertilizer, a phosphorus compound, and other raw materials for producing various drugs.

An embodiment of the method for treating organic wastewater of the present invention will be described below with reference to the schematic flow charts of FIGS.

That is, in the method shown in FIG.
Is first applied to the anaerobic treatment tank 7 to cause anaerobic digestion and release the phosphorus component stored as polyphosphoric acid granules in the microorganism. At this time, the phosphorus component is generally hydrolyzed and released as orthophosphoric acid into the liquid phase. Next, this treatment liquid is applied to an aeration treatment tank 1 provided with an aeration means 12 of an air pump, where decomposition of organic substances by aerobic microorganisms and ingestion of phosphorus components by the microorganisms (storage in the body) are performed. The phosphorus component released in the anaerobic treatment is concentrated in the microorganisms in this step. After that, the aeration treatment liquid is applied to the solid-liquid separation means 2 to separate sludge in which the phosphorus component is concentrated and primary treatment water a. As the solid-liquid separation means 2, conventionally known filtration including precipitation and membrane separation can be appropriately employed. A part of this sludge is appropriately returned to the anaerobic treatment tank 7 to adjust the amount of sludge to be subjected to the following steps, and to sufficiently decompose organic substances in the anaerobic and aerobic treatments and take in phosphorus components by microorganisms. It may be performed.

Next, the sludge obtained from the solid-liquid separation means 2 is subjected to a concentration means 3 for further concentration to a high concentration. When a high concentration of sludge is obtained by the concentrating means 3, it is possible to reduce the volume of an apparatus and energy required for the process after the subsequent phosphorus release. As the concentration means 3, filtration including centrifugation, precipitation, membrane separation, centrifugation, flotation concentration and the like can be used. Can effectively keep the sludge aerobic,
Since sufficient concentration of 4% or more sludge concentration can be realized while preventing re-release of the phosphorus component, it is preferable to employ floating concentration as the concentration means 3. A preferred condition for carrying out the flotation concentration is to dissolve about 2-3% air in the circulating water in a circulating system using about 4 times the amount of circulating water of the sludge volume. While the primary sludge x is obtained by the concentrating means 3, the separated water containing no phosphorus component can be discharged together with the primary treated water a.

The primary sludge x thus obtained is transferred to the heat exchanger 1
After heating through the heating device 1, in order to release the phosphorus component from the microorganisms contained in the sludge to the liquid phase, in the next phosphorus release tank 4, heating means 1 such as a heater and a steam generator are used.
By performing heat treatment at 60 to 90 ° C. for 10 to 120 minutes, preferably at 70 to 80 ° C. for 20 to 60 minutes using 0, the phosphorus component is released mainly from microorganisms as polyphosphoric acid. When the phosphorus component is released as polyphosphoric acid, a coagulant B such as a metal salt necessary for the treatment in the phosphorus coagulation tank 6 for recovering the phosphorus component as a precipitate from the liquid phase.
Is significantly reduced as compared to the case where the required amount of phosphoric acid is released as phosphoric acid by anaerobic treatment, ozone treatment, alkali treatment or the like as described above. Since the metal salt of polyphosphoric acid forms a large granular sediment, the time required for subsequent recovery treatment, for example, sedimentation separation or centrifugation, the volume, the number of revolutions, and the like can be advantageously reduced.

After completion of the treatment in the phosphorus release tank 4,
The solid-liquid separation means 5 separates the treated water (secondary treated water) b and the secondary sludge z having a relatively small volume and a high phosphorus content. As the solid-liquid separation means, for example, centrifugal separation, separation by a dehydrator and the like are suitable. Since the volume of the secondary treated water b is much smaller than that of treated water containing a phosphorus component, which is generated by a conventional wastewater treatment method, a phosphorus coagulation process for recovering the phosphorus component as described below is performed. Equipment for
Very small ones will suffice.

In the phosphorus coagulation step, a conventionally known method such as crystallization dephosphorization can be used, but generally, the secondary treatment water b is introduced into the phosphorus coagulation tank 6 and the coagulant B
Is added under stirring to coagulate the phosphorus component as a solid component. Here, since the phosphorus component contained in the secondary treatment water b is mainly obtained as polyphosphoric acid, it can be aggregated into a granular solid component that can be easily recovered even if a small amount of the coagulant B is used. . After adding the flocculant B, stirring and precipitating, the phosphorus component is recovered according to the following steps. Coagulant B
It is most preferable to determine the number of free phosphoric acid residues from the total amount of phosphorus components and polyphosphoric acid contained in the secondary treatment water b, and use only the amount of the number of moles that is sufficient. In order to improve the recovery rate of the phosphorus component as a solid component during the aggregation reaction in the phosphorus aggregation tank 6, the secondary treatment water b is prepared by adding an appropriate amount of a basic substance such as an aqueous sodium hydroxide solution. pH 8 or more, preferably 8.0-1
The basicity may be adjusted to 0.5, more preferably 9 to 10 basicity.

Next, the tertiary treated water c substantially free of the phosphorus component and the solid phosphorus component y are obtained by the solid-liquid separation means 8. This solid phosphorus component y is separated from the sludge, contains almost no other components contained in the raw wastewater, and is reduced in volume, and contains fertilizers, synthetic detergents, detergents, and metals. It is easy to use as a raw material for ion sequestering agents and food additives, as a raw material for reagents used in papermaking, dyeing, photographic technology, etc., and a raw material for producing phosphorus compounds. However, it is preferable that the phosphorus component p be recovered as a substantially dry solid by the additional phosphorus recovery means 9 so as to be in a form that is most easily distributed and transported. For example, freeze-drying, dehydration,
Drying and the like can be mentioned.

In FIG. 2 showing a particularly preferred embodiment, the primary sludge x obtained from the enrichment means 3 and the phosphorus release tank 4 are shown.
Is exchanged with the processing liquid obtained from the heat exchanger 11. This is advantageous in that heat recovery efficiency is improved and heat loss is reduced. Further, if the heat exchange is performed as described above, the processing liquid obtained after the release of phosphorus is cooled and then supplied to the solid-liquid separation means 5, so that the heat resistance of the solid-liquid separation means 5 is very low. The dehydrator such as a centrifugal separator, a membrane separator, a belt press, a filter press and the like can be widely used. In particular, when the use of a belt press type dehydrator is intended, problems such as shrinkage of the filter cloth due to high temperature can be avoided, and the life of the membrane can be extended.

Further, the phosphorus component is converted to phosphate ions and polyphosphate ions or to phosphate salts by using ion exchange chromatography or the like before or after the treatment step in the phosphorus flocculation tank 6. Separation into a polyphosphate, ie, a phosphoric acid component and a polyphosphoric acid component, may be a supply form of both components that are considered to be used for different purposes.

In the present invention exemplified above, the respective structures of the aeration treatment tank 1, the solid-liquid separation means 8, and the anaerobic treatment tank 7 and the paths connecting them are not particularly limited, and are essentially used conventionally. What has been done can be used. For the device of the present invention, the aeration tank 1 is provided with a diffuser 13 capable of distributing the air sent from the aeration means 12 such as an air pump and a blower into the aeration tank 1. Preferably, any device provided with a stirring means or the like may be used. Also, the conditions and the like in these steps may be performed according to conventionally known aerobic treatment methods, solid-liquid separation methods, and the like (Japanese Patent Application Laid-Open No.
-10791 and the like).

In brief, the processing in the aeration tank 1 is performed at normal temperature. And solid-liquid separation means 2
For example, means such as precipitation and filtration including membrane separation are selected. Of these, sedimentation is preferred because the equipment and maintenance costs are inexpensive and the operation requires little labor. Further, as the solid-liquid separation means 8, for example, means such as precipitation, filtration (including membrane separation), or centrifugation can be selected. Of these, sedimentation or filtration is preferable because no specially expensive equipment or labor is required, and sedimentation in a sedimentation tank is most preferable if separation is easy depending on the properties of the treatment liquid. The processing temperature in the anaerobic processing tank 7 is not particularly limited, and may be preferably performed at normal temperature. Here, it is preferable that the anaerobic treatment tank 7 is provided with stirring means so that the phosphorus component released around the microorganisms does not stay and the release of phosphorus is not prevented.

Since the phosphorus component finally recovered as the phosphorus component p is not only concentrated but also considerably purified, as described above, the raw material phosphate ore in the production of fertilizers, various phosphorus compounds, chemicals, etc. It is suitable for being reused as.

[0035]

EXAMPLES Examples of the present invention will be described below, but should not be construed as limiting the scope of the present invention or these examples.

[Example 1] In a laboratory batch anaerobic aerobic activated sludge process, 500 ml of activated sludge derived from a sewage treatment plant was placed in a 1 L Erlenmeyer flask, and then had the composition shown in Table 1 below. And 500 ml of organic wastewater containing a phosphorus component.

[0037]

[Table 1]

An anaerobic treatment is applied to 1 L of this raw wastewater for 20 liters.
The aerobic treatment was carried out at 20 ° C. and an aeration amount of 20 vvm (using an aeration pump) at pH 7 and a residence time of 5 hours at pH 7 and a residence time of 2 hours. During this treatment, the liquid was continuously stirred with a stirrer so that the liquid volume was maintained at 1 L.

After completion of the aerobic treatment, 1 ml of the sludge was dispensed into 25 Eppendorf tubes, and each of the 5 sludges was allowed to stand in a thermostat set at 50 ° C., 60 ° C., 70 ° C., 80 ° C. and 90 ° C. . Sample one tube every 20 minutes, centrifuge each sample at 8,000 × g for 5 minutes, and determine the total amount of phosphorus, polyphosphate and phosphate in the supernatant according to the following method. did. Total phosphorus: Hydrothermal decomposition in the presence of ammonium persulfate (12
(1 ° C., 30 minutes), and then quantified as phosphoric acid by the following method. Polyphosphoric acid amount: Thermal decomposition (100) in the presence of 1N hydrochloric acid
(7 ° C., 7 minutes) and then quantified as phosphoric acid by the following method Phosphoric acid amount: Measurement of phosphate ion amount based on molybdenum blue (ascorbic acid reduction) absorption spectrophotometry according to JIS K0102 Then, the phosphorus components in these supernatants aggregate To determine whether separation can be achieved by precipitation, calcium chloride (Ca
Cl ₂ ) to a final concentration of 50 mM,
The total phosphorus content of the precipitate obtained by centrifugation at 8,000 × g for 5 minutes was measured by the above total phosphorus determination method.

FIG. 3 shows the results thus obtained. FIG.
(A) is 50 ° C., (b) is 60 ° C., (c) is 70 ° C., (d) is 80 ° C., (e) is a change with time of each quantitative value by heat treatment at 90 ° C., (F) shows the phosphorus composition (: phosphoric acid,: polyphosphoric acid and: the amount of other phosphoric acid compounds) in the activated sludge before the heat treatment.

FIG. 3 shows that the heat treatment of the activated sludge sample was performed for 50 hours.
It can be seen that when performed at ℃, the amount of phosphorus components released from the sludge is all small, and moreover, the amount released as phosphoric acid is larger than polyphosphoric acid (FIG. 3 (a)). At this temperature, the polyphosphoric acid granules in the sludge appeared to be hardly liberated. At a treatment temperature of 70 ° C. (FIG. 3 (c)), about 90% of the amount of polyphosphoric acid (FIG. 3 (f)) present in the activated sludge was released and released one hour after the start of heating. At this point, about 20% of polyphosphoric acid has been decomposed into phosphoric acid. When calcium chloride was added 2 hours after the start of heating and centrifugation was performed, most of the total amount of released phosphorus could be recovered as a precipitate. When the treatment temperature is 90 ° C. (FIG. 3 (e)), the release of polyphosphoric acid proceeds rapidly, and it ends in about 10 minutes under these conditions. At this time, the amount decomposed into phosphoric acid was about 10%. When the release of polyphosphoric acid ends,
This polyphosphoric acid was rapidly decomposed into phosphoric acid, and about 60% of the released polyphosphoric acid was phosphoric acid 2 hours after the start of heating. At this time, even if flocculation and precipitation were performed with calcium chloride, the amount of the phosphorus component that could be recovered was only about 20% of the released amount. Therefore, when the method of the present invention is carried out at a temperature of 90 ° C., it is indicated that it is preferable that the released polyphosphoric acid be subjected to flocculation and precipitation quickly.

Example 2 The sample collected in Example 1 was examined under visible light and with DAPI (4 ', 6-diamidino-
(2-Phenylindole) After fluorescence staining, microscopic examination under ultraviolet irradiation was performed to examine the presence of polyphosphate granules. Activated sludge sample before heat treatment (a), supernatant sample after treatment at 70 ° C. for 60 minutes (b) and calcium chloride precipitate from this supernatant (c)
Was used as a sample. Polyphosphoric acid granules can be easily identified because they emit yellow light specifically when irradiated with ultraviolet light (UV) after DAPI fluorescence staining. FIG. 4 shows the results. When the activated sludge sample (FIG. 4, (a)) before the heat treatment was irradiated with ultraviolet light after DAPI staining, yellow polyphosphate granules were observed. In addition, even if the same observation was performed on the supernatant before heating, no polyphosphate granules were observed at all. Yellow polyphosphate granules were also observed in the supernatant sample (FIG. 4, (b)) after treatment at 70 ° C. for 60 minutes and the calcium chloride precipitate (FIG. 4, (c)) from this supernatant. Therefore, it was confirmed that polyphosphoric acid according to the quantitative method of Example 1 was present as polyphosphoric acid granules.

Example 3 Activated sludge (total phosphoric acid amount: 2.76) prepared in the same manner as in Example 1 to examine the optimum pH when the phosphorus component is aggregated and collected as a solid component Mmol) at 90 ° C. for 15 minutes or 1
After treatment for 20 minutes, the phosphorus component was released into the liquid phase. This supernatant was subjected to various pHs shown in FIG. 5 (around 7, 7.5, 8.
0, 8.5 or 9.0) using Tris buffer, and then calcium chloride was added to a final concentration of 50 mM and stirred. FIG. 5 shows the results of quantifying the total amount of phosphoric acid recovered as a sediment. From these results, when the phosphorus component is recovered as a solid component in the phosphorus coagulation tank 6, the pH is adjusted to a basicity of 8 or more, preferably 8.0 to 8.0.
It became clear that the recovery of the phosphorus component can be achieved with excellent efficiency by adjusting to 10.5.

[0044]

According to the present invention, the phosphorus component contained in the organic wastewater can be separated and recovered into a small-capacity liquid or solid state in a short time, so that the phosphorus can be easily reused. You. At this time, since the phosphorus component is concentrated as polyphosphoric acid, the amount of the required flocculant is
A much smaller amount is sufficient than previously known methods.

The method of the present invention is advantageous in that it enables low-cost treatment, since it requires no reagent or expensive equipment and has a high phosphorus component recovery rate.

Further, according to the present invention, it becomes possible to recover phosphorus components in a sludge treatment method which has a low heat loss and is highly economical.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a method for treating organic wastewater of the present invention.

FIG. 2 is a schematic structural view of one particularly preferred embodiment of the method for treating organic wastewater of the present invention.

FIG. 3 is a graph showing the change over time of the release of various phosphorus components when activated sludge is treated at a temperature in the range of 50 to 90 ° C.

FIG. 4 shows (a) activated sludge, (b) the supernatant after treatment at 70 ° C. for 60 minutes, and (c) the components precipitated by calcium chloride, which were observed by fluorescent staining of polyphosphoric acid with visible light and DAPI. It is a figure which shows a micrograph (1000 times magnification).

FIG. 5 is a graph showing the efficiency of phosphorus recovery by adding a flocculant at various pHs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Aeration treatment tank 2, 5, 8 ... Solid-liquid separation means 3 ... Concentration means 4 ... Phosphorus release tank 6 ... Phosphorus coagulation tank 7 ... Anaerobic treatment tank 9 ... Phosphorus recovery means 10 ... Heating means 11 ... Heat exchanger 12 ... Aeration means 13 ... Aeration means A ... Raw wastewater B ... Coagulant a ... Primary treatment water b ... Secondary treatment water c ... Tertiary treatment water x ... Primary sludge y ... Solid phosphorus component z ... Secondary sludge p ... Phosphorus component

Continuing on the front page (72) Inventor Junichi Kato 2-24-16 Minamizao, Fukuyama-shi, Hiroshima New Erdim Extension 104 (72) Inventor Retsushi Nishimoto 77-1-1, Tsujii, Himeji-shi, Hyogo Kenji Katsura 1-5-3-408 Ibukidai Nishimachi, Nishi-ku, Kobe City, Hyogo Prefecture (72) Inventor Susumu Hasegawa 4-17-1, Ibukidai Higashicho, Nishi-ku, Kobe City, Hyogo Prefecture F-term (reference) 4D028 BD06 BD16 4D038 AA08 AB43 BB01 BB13 BB19 4D040 BB01 BB32 4D059 AA01 AA08 BF02 BF11

Claims (6)

[Claims] In the method for treating organic wastewater, the following steps are carried out: (1) aeration treatment step in which wastewater is subjected to aerobic treatment; (2) wastewater after aeration treatment is treated as primary treated water and sludge. (3) a concentration step in which the separated sludge is concentrated; and (4) a concentration step at 60 to 90 ° C. for releasing the phosphorus component from the concentrated sludge to the liquid phase.
A phosphorus release step of performing a heat treatment for 120 minutes, and (5) a solid-liquid separation step of separating into secondary treated water containing the released phosphorus component and secondary sludge from which the phosphorus component has been removed. Organic wastewater treatment method. 2. The processing method according to claim 1, wherein the concentration step (3) is performed by a flotation concentration method. 3. The treatment method according to claim 1, wherein heat exchange is performed between the sludge and the treatment liquid after the phosphorus release step (4). 4. A phosphorus coagulation step (5) in which, after the solid-liquid separation step (5), the released phosphorus component is precipitated from the liquid phase by adding a coagulant to the secondary treatment water generated in the step. The processing method according to any one of claims 1 to 3, further comprising (6). 5. The method according to claim 1, wherein the phosphorus aggregating step (6) is carried out at pH 8.0.
The treatment method according to claim 4, which is carried out under a basic condition of from 1 to 10.5. 6. The treatment method according to claim 1, further comprising an anaerobic treatment step (7) before the aeration treatment step (1).