JP2005230669A - Wastewater treatment method and wastewater treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an existing wastewater treatment process by performing sludge solubilizing treatment and forming a carbon source or a precursor substance for biological dephosphorization for the purpose of stabilizing the biological dephosphorization, achieving the recovery efficiency of phosphorus resources and reducing the discharge amount of excess sludge. <P>SOLUTION: The wastewater treatment system is provided with a high-temperature and high-pressure water treatment apparatus 11 receiving the inflow of primary wastewater containing hardly decomposable organic matter, a biological treatment apparatus 10, a sedimentation tank 12 and a phosphorus treatment device 13 for taking out phosphorus resources by an MAP method. An anaerobic tank 14, an oxygen-free tank 15 and an aerobic tank 16 are provided to the biological treatment apparatus 10. By this constitution, the reduction of the amount of excess sludge or the recycling of phosphorus resources can be attained only by increasing the high-temperature and high-pressure treatment apparatus (solubilizing equipment) without largely remolding existing equipment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wastewater treatment method and a wastewater treatment system.

  It is written in the Basic Law for the Promotion of Recycling-oriented Society that waste generation should be given the highest priority when treating and disposing of waste. That is, it is first required to suppress the generation of excess sludge generated from wastewater treatment facilities. Against this background, volume reduction of surplus sludge has been demanded. Currently, development of technology for suppressing the generation of surplus sludge by solubilizing surplus sludge and returning it to the biological reaction tank is underway. So far, ozone reaction, wet bead mill, high-speed rotating disk, ultrasonic wave, high-temperature and high-pressure water reaction, thermophilic bacteria, etc. have been studied as solubilization techniques.

  Among these, high-temperature and high-pressure water is attracting attention because it requires energy and equipment cost during the reaction, but only water is used as a reaction solvent and the reaction system is simple and the reaction time is short. In order to evaluate whether solubilization and substrate formation of surplus sludge can be a technology to reduce surplus sludge discharge, analysis of the activated sludge process behavior and material flow when the sludge after reaction is circulated is necessary. Necessary. However, until now, there have been many studies focusing on solubilization, and sufficient knowledge about the characteristics of post-reaction sludge has not yet been obtained.

  In the fifth total water quality regulation, nitrogen and phosphorus are regulated in addition to the conventional COD for eutrophication measures. Therefore, wastewater treatment at business sites is not limited to fulfilling the social responsibility of improving the quality of discharged water, but is required to reduce the overall environmental burden such as control of excess sludge generation. On the other hand, the scarcity of phosphorus resources is strongly conscious worldwide, and strategic efforts have been started in each country to combat phosphorus resource depletion. While phosphorus removal from wastewater is required, in order to efficiently recover phosphorus from excess sludge from wastewater, it is necessary to sufficiently accumulate phosphorus in the wastewater in the activated sludge. That is, it is essential to stably remove biological phosphorus.

  On the other hand, acetic acid and propionic acid, which are carbon sources for polyphosphate-accumulating bacteria that play a major role in biological phosphorus removal, are scarcely contained in wastewater. Acetic acid and propionic acid are produced by a fermentation process of microorganisms in an anaerobic state, but the proportion of fermentable organic substances that are precursors of these organic acids is low in the wastewater. Therefore, stable biological phosphorus removal is a difficult situation in current wastewater treatment facilities. Therefore, if surplus sludge solubilization treatment liquid can be supplied as a carbon source for biological phosphorus removal, biological phosphorus removal can be stabilized and phosphorus recovery efficiency can be improved, and the amount of surplus sludge generated can also be increased. Because it can be reduced, a new wastewater treatment system can be constructed.

By the way, the present inventors have continued to elucidate the mechanism of the high-temperature and high-pressure water reaction and to study its application. For example, Japanese Patent Application Laid-Open No. 2003-251374 discloses a method of performing a high-temperature and high-pressure water reaction on wastewater containing a hardly decomposable substance. This research and development can be advanced to build a more effective wastewater treatment system.
JP 2003-251374 A

  The inventors of the present invention aimed to perform a high-temperature and high-pressure water treatment before biological treatment of wastewater to cause a structural change of a hardly decomposable organic substance and to convert it into a form capable of biological treatment. That is, the present invention introduces a high-temperature and high-pressure water reaction into an existing wastewater treatment process, solubilizes excess sludge, and generates a carbon source for biological phosphorus removal or a precursor thereof, The purpose is to improve the existing wastewater treatment process that can stabilize biological phosphorus removal and improve the efficiency of phosphorus resource recovery, and also reduce the amount of excess sludge discharged.

Means for solving the problems, action of the invention, and effect of the invention

The wastewater treatment method for solving the above-mentioned problem is, after subjecting wastewater containing a hardly decomposable organic substance to a high-temperature and high-pressure water reaction, changing the hardly decomposable organic substance to an easily decomposable organic substance or a slowly decomposable organic substance, The wastewater is characterized by performing microbial treatment under anaerobic conditions and microbial treatment under aerobic conditions.
The “hardly decomposable organic substance” means a general substance that is difficult for microorganisms to treat, and examples thereof include high molecular organic compounds and cyclic compounds. In this specification, it is defined as the total COD minus BOD5 (note that the meaning of each symbol will be described in detail later). Moreover, in order to consider the influence on the quality of treated water, the hardly decomposable organic substance was further classified into two components, a soluble hardly decomposable organic substance (S _I ) and a solid hardly decomposable organic substance (X _I ). All COD _Cr in sludge treatment liquid, BOD5, OUR, and oxygen demand (hereinafter S _I) was determined on solubility flame degradable organic substances with COD _Cr, the S _S from the OUR, subtracts S _S from BOD5 the X _S by, the total COD _Cr in sludge treatment liquid was determined X _I by subtracting the _{S S, X S, S I} .

“Easily degradable organic substances” are organic substances that can be easily decomposed by microorganisms. Specifically, Gujer et al. (Wat. Sci. Tech. 25 (6), 25-139, 1992.).
“Slowly decomposable organic matter” is defined herein as BOD5 minus the readily decomposable organic matter concentration.
“High-temperature high-pressure water” means that the temperature condition is about 300 ° C. as the lower limit and about 500 ° C. (preferably about 400 ° C.) as the upper limit, and the pressure condition is equal to or higher than the saturated vapor pressure of water at the above temperature. This means water that exhibits such temperature and pressure. Further, the time of the high-temperature and high-pressure water treatment depends on the reaction temperature, but a sufficiently good result can be obtained with a treatment time of about 7 minutes or more at about 350 ° C. or more and about 27 minutes or more at about 300 ° C. .

Microbial treatment is performed under two conditions: anaerobic conditions and aerobic conditions. This is because (1) an organic acid such as acetic acid / propionic acid is generated from a biodegradable organic substance (easy-degradable organic substance and slow-degradable organic substance) by an microbial fermentation process under anaerobic conditions, and then (2) This is because a method of removing phosphorus by microorganisms using these organic acids under aerobic conditions is taken.
According to the present invention, by performing high-temperature and high-pressure water treatment on waste water containing hardly decomposable organic matter, the total amount of organic matter is reduced, and the hardly decomposable organic matter is changed into easily decomposable organic matter and slowly decomposable organic matter. Therefore, the degradation amount by microorganisms can be increased and the sludge amount can be decreased. Moreover, phosphorus removal can be performed by microbial treatment of wastewater in two stages, anaerobic conditions and aerobic conditions.

Further, in the present invention, it is preferable that the waste water after the microbial treatment is subjected to a precipitation treatment, the precipitate at that time is subjected to a high-temperature high-pressure water reaction, and the microbial treatment is performed again.
Phosphorus is an essential component for treating wastewater using microorganisms. For this reason, in the current wastewater treatment facility, it is necessary to separately add a phosphorus content to the wastewater with a low phosphorus content at the time of microbial treatment. However, according to the present invention, since the precipitates (such as dead bodies of microorganisms) that have been subjected to microorganism treatment are subjected to a high-temperature and high-pressure water reaction, Process. For this reason, a so-called phosphorus content recycling system is formed in the system. This method is particularly effective for wastewater with low phosphorus content.

In addition, the wastewater treatment system according to the present invention includes a high-temperature high-pressure water treatment device into which primary wastewater containing a hardly decomposable organic substance flows in, and secondary wastewater treated by the high-temperature high-pressure water treatment device into the secondary wastewater. A biological treatment apparatus for treating the wastewater with microorganisms, and a sedimentation tank for allowing the wastewater discharged from the biological treatment apparatus to flow in and precipitating solids to discharge the treated solution portion as treated wastewater. The biological treatment apparatus is provided with an anaerobic tank and an aerobic tank in order from the side into which the secondary wastewater flows.
According to this wastewater treatment system, when the wastewater is subjected to microbial treatment, high-temperature and high-pressure water treatment is performed in advance, and the microbial treatment is performed in two tanks, an anaerobic tank and an aerobic tank, so that the organic matter treatment ratio in the wastewater And the phosphorus content can be recovered.

  Next, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited by these embodiments, and various forms are possible without changing the gist of the invention. Can be implemented. Further, the technical scope of the present invention extends to an equivalent range.

<Test method>
1. Surplus sludge Anaerobic and aerobic activated sludge from a wastewater treatment facility installed in a simmering factory in Aichi Prefecture was collected from the end of the aerobic tank. The MLSS (sludge concentration in the reaction tank) of this sludge was about 16000 mg-SS / L. Here, this sludge was concentrated by gravity sedimentation and adjusted to 22000 mg-SS / L.

2. FIG. 1 shows a high-temperature and high-pressure water treatment apparatus 1 (hereinafter simply referred to as “treatment apparatus 1”) used in the examples. The processing apparatus 1 includes a temperature-controllable molten salt bath 2 (for example, a TSC-006 type made by Hastelloy (pressure glass industry)) and a heat-resistant A pressure-resistant sealed processing container 3 (for example, the above TSC-006 type made of Hastelloy) and a pressure sensor 4 are provided.

  Inside the molten salt tank 2, a heater 6 and a rotary blade 5 are provided. By rotating the rotary blade 5 with the heater 6 attached, the liquid in the molten salt tank 2 is mixed, A uniform temperature can be obtained. The heater 6 is provided with a computer (not shown), and the temperature in the molten salt tank 2 can be controlled within a predetermined range. In this processing apparatus 1, the temperature inside the molten salt bath 2 can be controlled within a range of about 150 ° C to about 500 ° C.

Moreover, the processing container 3 can be comprised from Hastelloy (Ni, Cr, Mo etc.), for example, The volume is 65.9 ml. A lid is attached to the upper part of the processing container 3, and an appropriate temperature can be obtained with the internal space of the processing container 3 sealed. At the time of the test, a sample diluted at an arbitrary magnification is put into the processing container 3, and the upper lid is placed on the container and sealed. Thereafter, the processing container 3 and the pressure sensor 4 are connected.
After sealing the processing container 3, the processing container 3 is put into the molten salt tank 2 that has been heated to a preset temperature in advance, and this time is set to 0 minutes to start the high-temperature and high-pressure water treatment. In addition, the pressure was adjusted by appropriately changing the sample volume put into the processing container 3.

After the target processing time has elapsed, the processing container 3 is pulled up from the molten salt bath 2, the entire processing container 3 is immersed in water, and cooled to about room temperature. Then, the sample in the processing container 3 was collect | recovered and the subsequent process was performed.
In addition, although said processing apparatus 1 is a batch type thing, a continuous type thing can also be used.

3. Solubilization treatment conditions As conditions for solubilization treatment of excess sludge, (1-1) 200 ° C., 6.9 minutes, (1-2) 200 ° C., 26.9 minutes, (2-1) 250 ° C., 7.4 Minutes, (2-2) 250 ° C., 27.4 minutes, (3-1) 300 ° C., 7.4 minutes, (3-2) 300 ° C., 27.4 minutes, (4) 350 ° C., 7.4 And (5) 400 ° C. for 7.4 minutes. The treatment temperature was set to 200, 300, 350 ° C. under subcritical water conditions and 400 ° C. under supercritical water conditions. The pressure in each treatment condition was saturated water vapor pressure under subcritical water conditions and 30 MPa under supercritical water conditions. The treatment time was defined as the elapsed time from when the inside of the reaction vessel reached 90% of the target temperature.

4). Analytical method For the determination of the soluble component, a sample filtered using a GF / C filter (pore size 1.2 μm, Whatman) before analysis was used. A COD analysis kit (DR2000, HACH) was used for measurement of chemical oxygen demand (CODcr). The biochemical oxygen demand (BOD) and MLSS were measured according to the Japan Sewerage Association sewage test method (1997). A total organic carbon meter (Shimadzu Corporation, TOC-VE) was used for the measurement of total organic carbon (TOC) and dissolved organic carbon (DOC). High performance liquid chromatography (Shimadzu Corporation, LC-VP) was used for the measurement of acetic acid and propionic acid. As a high-performance liquid chromatography column, two columns of Shim-Pack SCR-102H (Shimadzu Corporation) were connected.

5). Fractionation of organic component In this example, from the viewpoint of biodegradability, T-CODcr of the solubilized treatment liquid is easily degradable organic matter, slow degradable organic matter, soluble hardly degradable organic matter, and solid hardly degradable organic matter. It was fractionated into four components. The method of Guyer et al .: Wat. Sci. Tech. 25 (6), 25-139, 1992. was followed for the measurement of readily degradable organic substances. When an oxygen consumption rate (OUR) test is performed using the solubilized solution as a substrate, a curve as shown in FIG. 2 is obtained. By dividing the area value Sso enclosed in the figure by (1-Y), the readily decomposable organic substance concentration is estimated. Here, the growth yield Y used was a reference value of 0.63 (Henze, M. et al., Activated Sludge Model No. 2, Scientific and Technical Report No. 3, International Association on Water Quality, 1995). .

For the measurement of slow-degradable organic matter, Guyer et al. Have proposed estimation by simulation using a part of the activated sludge model for sewage, but the solubilization treatment solution of food processing wastewater treatment sludge is proposed. There are concerns about application. Therefore, in this example, the value obtained by subtracting the readily decomposable organic substance concentration from BOD5 was defined as the slow decomposable organic substance concentration.
A method for quantifying soluble hardly decomposable organic matter (S _l ) will be described. First, after measuring sludge processing liquid and MLSS, activated sludge from which organic substances in the liquid phase were removed using centrifugation was put into an Erlenmeyer flask. Each concentration was adjusted so that the F / M ratio was 0.1. Next, the easy-decomposable and slow-decomposable organic substances were removed by treating for 8 hours under aerobic conditions. Thereafter, a filter (pore size: 0.45 [mu] m) was filtered using a COD _Cr of the resulting filtrate was quantified as S _I.
The solid flame-degradable organic substances, minus the BOD5 and S _l from T-CODcr (i.e., minus the easily decomposable organic matter concentration and slow degradable organic substances the concentration and solubility flame degradable organic substances from total organic concentration ).
So far, solubilization of sludge using high-temperature and high-pressure water has been studied, but an example of examining the proportion of persistent organic substances in sludge treatment liquid in both solid phase and liquid phase Absent. When persistent organic substances are present in the solid phase, they can be removed from the wastewater by solid-liquid separation using a precipitation tank. However, when it was present in the liquid phase, it simply changed the form of the hard-to-decompose organic matter that was originally present in the solid phase into the liquid phase. Since this is not possible, there is a possibility of being discharged into the environment together with the discharged water when the subsequent treatment is not performed. When river water containing these soluble organic materials is used again as clean water, there is a possibility that it may become a substance that generates carcinogenic trihalomethane (trihalomethane precursor) by chlorine disinfection. To do. Examining the existence form of persistent organic substances is very important not only for designing wastewater treatment processes but also for examining the impact on the environment and human body.

<Test results and discussion>
1. Solubilization rate The TOC and the solubilization rate of the sample before and after the high-temperature high-pressure water reaction are shown in FIG. In the figure, due to the space, the reaction time is rounded off (the same display may be used in other figures). The solubilization rate was defined as the ratio of DOC to TOC of the treatment liquid. Most of the TOC of the untreated sample was suspended organic carbon (POC), but DOC was generated after the high-temperature and high-pressure water reaction at 200 ° C. for 7.4 minutes, and the solubilization rate was about 0.6. Had reached. It was confirmed that the suspended components constituting the excess sludge turned into dissolved components by the high-temperature and high-pressure water reaction.

  Under temperature conditions of 250 ° C. or higher, TOC decreased with increasing temperature or reaction time. The reason for this is that the formation of black matter such as charcoal and tar was not visually confirmed in the sample after the high-temperature and high-pressure water reaction. It was considered that the constituent material of sludge was made low molecular or inorganic. The solubilization rate reached about 0.9 under the reaction conditions of 400 ° C. and 7.4 minutes, the most advanced mineralization.

2. Improvement of biodegradability FIG. 4 shows changes in TOC (horizontal axis) and BOD5 (vertical axis) in the sample before and after the high-temperature and high-pressure water reaction. Under the reaction conditions of 200 ° C. and 6.9 minutes, TOC was hardly reduced and BOD 5 was increased. That is, it can be said that biodegradability was improved without mineralization. However, under the reaction conditions of 200 ° C. and 26.9 minutes, an increase in BOD5 is observed as seen between the pre-treatment and 6.9 minutes reaction, even though the reaction time is increased by 20 minutes. There wasn't.

  Further, under the reaction conditions of 250 ° C. and 7.4 minutes, BOD 5 did not increase so much as compared with the reaction at 200 ° C., although TOC decreased and mineralization progressed. Under the reaction conditions of 250 ° C. and 27.4 minutes, mineralization further progressed, but BOD 5 decreased conversely. Although the hydrolysis reaction is dominant at the reaction temperature of 200 ° C. or 250 ° C., the mineralization reaction of the biodegradable component changes the structure from a component that is difficult to biodegrade to a component that can be biodegraded. This was thought to be faster than the reaction. Therefore, it was considered that a higher reaction temperature was required to promote this structural change and further improve biodegradability.

  Under the reaction conditions of 300 ° C., when the reaction time increased from 7.4 minutes to 27.4 minutes, a significant increase in BOD5 was observed. Under the reaction conditions of 350 ° C. and 400 ° C., the amount of decrease in TOC was remarkable despite the reaction time of 7.4 minutes. However, BOD5 under the reaction conditions of 350 ° C and 400 ° C showed almost the same value as that in the high-temperature high-pressure water reaction at 250 ° C for 27.4 minutes or 300 ° C for 7.4 minutes. From this, at the reaction temperatures of 350 ° C. and 400 ° C., the components that were difficult to biodegrade which were difficult to change the structure at the reaction temperature of 200 ° C. to 300 ° C. It was thought that it turned into a degradable component.

3. Effectiveness of solubilized solution as a carbon source for biological phosphorus removal Biophosphoric acid accumulating bacteria responsible for biological phosphorus removal are known to directly use lower fatty acids such as acetic acid and propionic acid as carbon sources. ing. Therefore, it is important to fractionate the total amount of organic substances in the solubilized solution from the viewpoint of biodegradability and to quantify each component in order to examine the applicability as a carbon source for biological phosphorus removal. . In this example, T-CODcr of the solubilized treatment liquid was fractionated into four components: an easily decomposable organic substance, a slow decomposable organic substance, a soluble hardly decomposable organic substance, and a solid hardly decomposable organic substance.

Easily degradable organic substances are classified as organic substances that are easily ingested by heterotrophic bacteria. In addition to lower fatty acids, precursors that can be converted to lower fatty acids by a fermentation process in an anaerobic state are also included. This readily decomposable organic matter becomes important as an index representing the potential of the polyphosphate-accumulating bacteria group as a carbon source.
Although slow-degrading organic substances cannot be directly ingested by heterotrophic bacteria, they are positioned as organic substances that can be ingested after undergoing a hydrolysis process by an extracellular enzyme. The carbon source of the polyphosphate accumulating bacteria group is produced from slow-degrading organic substances through a hydrolysis and fermentation process. Therefore, when the solubilized solution is used as a carbon source for biological phosphorus removal, it is desirable that the biodegradable organic substance contains a larger amount of easily decomposable organic substances.

The result of fractionating and quantifying the organic component of the solubilized solution into the above four components is shown in FIG. In the figure, persistent decomposition (solid phase) means a solid persistent organic substance, and persistent decomposition (liquid phase) means a soluble persistent organic substance.
In the untreated sample (pre-reaction sludge), the hardly decomposable organic matter (sum of solubility and solidity) accounted for about 90%, but the ratio decreased with increasing reaction temperature or reaction time, and biodegradation It turned into possible organic matter (easy-degradable organic matter and slow-degradable organic matter). Under the reaction conditions of 200 ° C. and 6.9 minutes, or 300 ° C. and 7.4 minutes, slow-decomposable organic substances were generated from the hardly-decomposable organic substances. In the reaction conditions of 300 ° C., 27.4 minutes, 350 ° C., 7.4 minutes, and 400 ° C., 7.4 minutes, easily decomposable organic substances were produced in addition to slow decomposable organic substances. In particular, under the reaction conditions of 400 ° C. and 7.4 minutes, easily decomposable organic substances and slow decomposable organic substances accounted for 67% and 31% of T-CODcr, respectively.
In addition, when classifying persistent organic substances into soluble persistent organic substances and solid persistent organic substances, almost all the persistent organic substances were in the solid phase before the reaction, but after the reaction, It was confirmed that the ratio of the liquid phase in the hardly decomposable organic substance was increased even under the above reaction conditions. The ratio of the liquid phase in the hardly decomposable organic substance increased with the increase of the reaction temperature, and reached the maximum at the reaction temperature of 300 and 350 ° C., but decreased when the reaction temperature increased to 400 ° C.

プロピオン酸は、３００℃、２７.４分間の反応条件で６２０ｍｇ／Ｌと最も多く、酢酸は４００℃、７.４分間の反応条件で７３０ｍｇ／Ｌと最も高い値を示した。易分解性有機物が最も多く含まれた４００℃、７.４ｍｉｎの可溶化処理液（４５００ｍｇ／Ｌ）には、酢酸およびプロピオン酸が、易分解性有機物のそれぞれ１６％、３％含まれていた。これらの結果より、高温高圧水反応後の可溶化処理液は、生物学的リン除去の炭素源として有効に機能し得ることが示された。 Table 1 shows acetic acid (Acetic) contained in the solubilized solution after treatment under the reaction conditions of 300 ° C., 27.4 minutes, 350 ° C., 7.4 minutes, and 400 ° C., 7.4 minutes. The concentrations of acid, propionic acid and other organic acids and ready biodegradable substrate are also shown.

Propionic acid was the most abundant at 620 mg / L under the reaction conditions of 300 ° C. and 27.4 minutes, and acetic acid was the highest value at 730 mg / L under the reaction conditions of 400 ° C. and 7.4 minutes. The solubilized treatment liquid (4500 mg / L) at 400 ° C. and 7.4 min, which contained the most easily decomposable organic substances, contained 16% and 3% of the easily decomposable organic substances, respectively. . From these results, it was shown that the solubilized treatment solution after the high-temperature and high-pressure water reaction can function effectively as a carbon source for biological phosphorus removal.

4). Substrate affinity for phosphorus release activity of solubilized treatment solution In anaerobic state, in order to confirm that easily degradable organic substances are converted into lower fatty acids by the fermentation process and used as a carbon source for polyphosphate-accumulating bacteria. Using a solubilized solution at 200 ° C., 300 ° C., and 400 ° C., a phosphorus release activity test from microorganisms was performed. The test results are shown in FIG.

  The phosphorus release rate was highest in the solubilized solution at 400 ° C., followed by 300 ° C. and 200 ° C. in this order. This result corresponded to the abundance of readily decomposable organic substances including acetic acid or propionic acid. In the solubilized solution at 400 ° C., rapid release of phosphorus was observed by 10 minutes immediately after the start of the test by using the lower fatty acid present in the solution. Thereafter, phosphorus release continued, although the rate of phosphorus release decreased. This was thought to be due to the fact that easily degradable organic substances other than lower fatty acids used the fermentation product of the fermentation process by the polyphosphate-accumulating bacteria. A similar tendency was observed in the solubilized treatment solution at 300 ° C. Thus, it was shown that the readily degradable organic substances defined in this study have substrate affinity for phosphorus release activity.

  On the other hand, in the solubilized treatment solution at 200 ° C. in which no readily decomposable organic matter was generated, no increase in phosphorus concentration was observed for 30 minutes immediately after the start of the phosphorus release test, and then phosphorus release was observed. This was thought to be because slow-degradable organic substances were reduced in molecular weight by the hydrolysis process, and some of them took a certain time to go through the fermentation process.

<Summary>
Improvement of biodegradability was observed as a result of high temperature and high pressure water reaction on wastewater. Moreover, the applicability of the high-temperature and high-pressure water reaction to wastewater treatment could be demonstrated.
A solubilization experiment was conducted using high-temperature and high-pressure water reaction for food processing wastewater treatment sludge. At this time, in order to examine the effectiveness of the surplus sludge solubilization treatment liquid as a carbon source for biological phosphorus removal, the organic components of the treatment liquid are classified into easily decomposable organic substances, slow decomposable organic substances and hardly decomposable organic substances. It was fractionated into 4 components. As a result, under the reaction conditions of 400 ° C. and 7.4 minutes, the polyphosphate-accumulating bacteria group responsible for phosphorus removal contained acetic acid and propionic acid that can be used as a carbon source. In addition, readily degradable organic substances including these lower fatty acids were observed to have substrate affinity for phosphorus release activity. From the above, it was revealed that this solubilized solution is effective as a carbon source for biological phosphorus removal. Moreover, it was shown that the evaluation of the treatment liquid as a substrate is important in the method of solubilizing excess sludge and then returning it to the biological reaction tank.

<Wastewater treatment system>
From the results so far, for example, the one shown in FIG. 7 can be proposed as a treatment system in the case where the high-temperature and high-pressure water reaction is applied to the activated sludge treatment process.
In this treatment system, a high-temperature and high-pressure water treatment device 11 into which primary wastewater containing a hardly decomposable organic substance flows, a biological treatment device 10 into which secondary wastewater treated by the treatment device 11 flows, and a downstream thereof are disposed. And a sedimentation tank 12 for precipitating solids. Further, a phosphorus treatment device 13 is provided downstream of the high-temperature and high-pressure water treatment device 11 to take out phosphorus immobilized on the polyphosphate-accumulating bacteria group by the MAP method.

In the sedimentation tank 12, solid matter is precipitated to become excess sludge, and the treated solution portion is discharged as final treated wastewater. Further, the route of sending the sludge in the sedimentation tank 12 to the processing apparatus 11 is branched, and the end thereof is directly connected to the anaerobic tank 14 of the biological treatment apparatus 10.
The processing apparatus 11 changes a hardly decomposable organic substance into an easily decomposable organic substance or a slow decomposable organic substance by treating the primary wastewater and excess sludge from the settling tank 12 with high-temperature and high-pressure water. Thereafter, the primary wastewater subjected to the high-temperature and high-pressure treatment is returned to the biological treatment apparatus 10 via the phosphorus treatment apparatus 13.

In addition, the biological treatment apparatus 10 is provided with an anaerobic tank 14, an anaerobic tank 15, and an aerobic tank 16 in order from the side into which the waste water that has undergone the reaction of high-temperature and high-pressure water flows. In addition, the arrow in a figure shows the direction through which waste water or sludge flows.
In this system, a part of the sludge extracted from the settling tank 12 is introduced into the high-temperature and high-pressure water treatment device 11 to be solubilized, and after the phosphorus resource is recovered as magnesium ammonium phosphate by the phosphorus treatment device 13 (MAP method), anaerobic Return to tank 14. In addition, the primary wastewater is improved in biodegradability by treatment in the high-temperature and high-pressure water reaction apparatus 11 and is introduced into the anaerobic tank 14 without applying the MAP method in the phosphorus treatment apparatus 13.
According to this configuration, it is possible to cope with the technique of the present invention only by adding solubilization equipment without greatly modifying existing equipment.

The features of this configuration are (1) reducing the amount of excess sludge generated from the activated sludge method, (2) drastically reducing industrial waste treatment costs, and (3) without major modifications to existing wastewater treatment facilities. (4) standardizing a small model and making it a unit type.
In business wastewater treatment, there is a situation that optimum maintenance management is not necessarily performed due to reasons such as an excessively small structure, a shortage of specialist engineers, cost savings, or undesirable wastewater conditions. In this way, advanced wastewater treatment measures are not limited to the introduction of nitrogen / phosphorus treatment, but are considered diverse, such as a combination of measures in the factory, improvement of existing facilities, and advancement of optimization of maintenance management. It is done. From the diversity, it is necessary to select and apply the advanced measures that are optimal for each business site and industry.

  Based on such a viewpoint, various advices can be given to each business establishment in conjunction with the fifth total water quality regulation, and the wastewater treatment process can be improved by using the present invention. At the same time, a business aimed at enhancing maintenance manpower through manager training can be realized. Furthermore, the running cost can be reduced by measuring the inflow / outflow wastewater and examining more appropriate operating conditions.

It is a figure which shows the outline | summary of a high temperature / high pressure water treatment apparatus. It is a graph which shows the relationship between the result of an oxygen consumption rate test, and an easily decomposable organic substance density | concentration. It is a graph which shows the TOC and solubilization rate of the excess sludge before and after a high temperature / high pressure water reaction. It is a graph which shows the change of TOC and BOD5 before and after high temperature high pressure water reaction. It is a graph which shows the change of the organic substance component (hard decomposition (solid phase), difficult decomposition (liquid phase), slow decomposition, easy decomposition) before and after a high temperature / high pressure water reaction. It is a graph which shows the result of having performed the phosphorus release activity test from microorganisms when using the solubilization process liquid at 200 degreeC, 300 degreeC, and 400 degreeC. It is a figure which shows the outline | summary of the wastewater treatment system in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... High temperature / high pressure water treatment apparatus 10 ... Biological treatment apparatus 12 ... Precipitation tank 14 ... Anaerobic tank 15 ... Anoxic tank 16 ... Aerobic tank

Claims (2)

The waste water containing the hardly-decomposable organic substance is subjected to a high-temperature and high-pressure water reaction to change the hardly-degradable organic substance into a biodegradable organic substance, an easily-degradable organic substance or a slow-degradable organic substance, and then the waste water is subjected to anaerobic conditions. A method for treating wastewater, characterized by performing microbial treatment under aerobic conditions. A high-temperature and high-pressure water treatment device into which primary wastewater containing persistent organic substances flows in, a biological treatment device into which secondary wastewater treated by this high-temperature and high-pressure water treatment device flows in and treats this secondary wastewater with microorganisms, and A wastewater discharged from the biological treatment apparatus, and a precipitation tank for precipitating solids and discharging the treated solution as treated wastewater. A wastewater treatment system comprising an anaerobic tank and an aerobic tank or an anaerobic tank, an anaerobic tank and an aerobic tank in order from the side into which the next wastewater flows.

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