JPH09108692A - Treatment of organic waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of treating organic waste water in which nitrogen compounds, phosphorus compounds and organic materials are stably, effectively, easily and highly reduced by simple constitution. SOLUTION: Night soil base sewage is caused to flow in a high load reaction tank 1 and is aerated to subject easily decomposable organic materials and nitrogen compounds to biological nitrification and denitrification treatment by microorganisms of returned sludge. In a nitrification and denitrification tank 4, the easily decomposable organic materials and nitrogen compounds remaining at >=0.5mg/l DO and -100-50mV ORP lower than that in the high load reaction tank 1 are highly removed by the microorganisms of the returned sludge. Corresponding to the phosphate concentration and COD concentration in organic waste water flowing in the nitrification and denitrification tank 4, iron chloride and powdery activated carbon are added. The iron chloride makes phosphoric acid ions react with insoluble iron phosphate, and is secondarily flocculated and adsorbed with high molecular soluble organic materials. The powdery activated carbon adsorbs hydrophobic low molecular organic materials to make them insoluble. Membrane separation is performed by a UF membrane separator 7 to return sludge to the high load reaction tank 1 and the nitrification and denitrification tank 4, and filtrate is discharged as treated water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic wastewater treatment method and apparatus for purifying organic wastewater containing nitrogen compounds and phosphorus compounds.

[0002]

2. Description of the Related Art Conventionally, as a method of treating this type of organic wastewater, for example, a structure disclosed in Japanese Patent Publication No. 3-24280 is known.

The method for treating organic wastewater described in this Japanese Patent Publication No. 3-24280 discloses a method for treating organic wastewater with returned sludge containing BOD-oxidizing bacteria, nitrifying bacteria and denitrifying bacteria obtained by biological BOD removal and nitrogen removal. Wastewater is introduced into a high-load reaction tank, air is appropriately aerated to reduce BOD by aerobic organisms and nitrogen compounds by nitrifying bacteria and denitrifying bacteria, and then flow into the nitrifying and denitrifying tank to remain BOD. And nitrogen compounds are highly removed as nitrogen gas and carbon dioxide gas by nitrifying bacteria and denitrifying bacteria by biological nitrification reaction and biological endogenous respiratory denitrification reaction, and further generated in the nitrification denitrification tank in the sedimentation tank. The sludge is subjected to solid-liquid separation, the separated sludge is returned to the high-load reaction tank, and the filtrate is transported to the subsequent process as treated water.

However, the above Japanese Patent Publication No. 3-24280.
In the conventional method for treating organic wastewater described in Japanese Patent Publication,
BOD oxidizing bacteria, nitrifying bacteria, and denitrifying bacteria cannot highly reduce the chemical oxygen demand (COD) due to the phosphate ions contained in the organic wastewater and dissolved bio-hardly degradable organic substances. Furthermore, since nitrogen compounds such as organic wastewater night soil and septic tank sludge are contained at a high concentration, the nitrogen compounds cannot be removed stably, and suspended solids (SS), BOD, CO
It is difficult to stably reduce D and the like. For this reason,
Membrane separation may be performed instead of the sedimentation basin in order to remove phosphate ions and organic substances that are hardly biodegradable, which cannot be removed by BOD-oxidizing bacteria, nitrifying bacteria, and denitrifying bacteria. If only added, the membrane is clogged in a short time due to sludge and hardly decomposable organic matter generated in the high-load reaction tank and the nitrification / denitrification tank, and the treatment cannot be performed efficiently.

Therefore, for example, the water to be treated that has been dehydrated with a coagulant is biologically treated, and the treated water is added with powdered activated carbon in a downstream reaction tank and further with a coagulant in a downstream reaction tank. Then, a method of separating and removing aggregates by precipitation is known.

[0006]

However, the above-mentioned conventional method of adding powdered activated carbon and a flocculant requires a tank for biological treatment, a tank for adding powdered activated carbon, and a tank for adding a flocculant. However, there is a problem that the structure is complicated, the equipment is large, and a large installation space is required.

The present invention has been made in view of the above-mentioned problems, and it is stable, efficient, and easy to use a nitrogen compound with a simple structure.
It is an object of the present invention to provide a method for treating an organic wastewater capable of highly reducing phosphorus compounds and organic substances and an apparatus therefor.

[0008]

A method for treating organic wastewater according to claim 1, wherein the organic wastewater containing nitrogen compounds and phosphorus compounds is treated biologically, wherein the organic wastewater is treated organically. Powdered activated carbon and iron chloride are added to the organic wastewater, and the organic wastewater to which the powdered activated carbon and iron chloride is added is kept in contact with oxygen while maintaining the dissolved oxygen at 0.5 mg / l or less to remove the organic wastewater. Membrane separation after biological nitrification and denitrification treatment by microorganisms. Phosphorus dissolved in iron chloride to be added to the organic wastewater by microorganisms is biologically nitrification and denitrification treatment in one tank. While reacting the compound with insoluble iron phosphate, the residual high-molecular-weight organic compounds are coagulated and adsorbed, and the residual hard-to-decompose hydrophobic low-molecular-weight organic compounds are adsorbed and removed with powdered activated carbon, and these treatments are performed. After film Since it is separated, soluble organic substances due to chemical oxygen demand that forms a gel layer on the membrane surface with a simple structure are highly removed before the membrane separation, reducing the load of the membrane separation and reducing the efficiency. Good processing is possible. Further, when the dissolved oxygen of the organic waste water is higher than 0.5 mg / l, denitrification by the denitrifying bacteria does not occur and the nitrogen compound remains, so that the dissolved oxygen of the organic waste water should be removed efficiently in order to remove the nitrogen compound. Is set to 0.5 mg / l or less.

The treatment apparatus for organic wastewater according to claim 2 is
A biological treatment means in which oxygen is brought into contact with an organic wastewater containing a nitrogen compound and a phosphorus compound, and the organic wastewater is subjected to biological nitrification denitrification treatment by a microorganism to use the organic wastewater as a first treated water. Raw water inflow means connected to the biological treatment means for flowing the organic wastewater into the biological treatment means, and membrane separation means for membrane separation of the first treated water connected to the biological treatment means and flowing out of the biological treatment means. And a treatment agent adding means for adding powdered activated carbon and iron chloride to the organic wastewater, which is connected to at least one of the raw water inflow means and the biological treatment means, and the organic wastewater by microorganisms Biological nitrification and denitrification treatment, the phosphorus compound that dissolves in the added iron chloride is reacted with the insoluble iron phosphate, and the residual polymer soluble organic matter is secondarily aggregated and adsorbed. And a process of adsorbing and removing the persistent low-degradability hydrophobic low-molecular organic matter with powdered activated carbon are performed in one tank, and a chemical oxygen demand for forming a gel layer on the membrane surface with a simple structure is required. Soluble organic substances due to the amount are highly removed before membrane separation, reducing the load on membrane separation,
Efficient processing is possible.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of one embodiment of the method for treating organic wastewater of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 is a high-load reaction tank as a biological treatment means. In this high-load reaction tank 1, there is a raw water pipe 2 as a raw water inflow means for inflowing organic wastewater such as human waste and septic tank sludge. An aeration device (not shown) for aerating air is provided while being connected. Further, a nitrification denitrification tank 4 as a biological treatment means is connected to the high load reaction tank 1 via a carrier pipe 3. The nitrification and denitrification tank 4 is connected to an iron chloride addition device 5 as a treatment agent addition means for adding a predetermined amount of iron chloride and powdered activated carbon and a powdered activated carbon addition apparatus 6 as a treatment agent addition means. The powdered activated carbon does not require unnecessary stirring or aeration power, and has a true specific gravity of 1.9 to 2.2 and a particle size of 150 μm.
Use m or less. Further, in the nitrification / denitrification tank 4, for example, ultrafiltration (UF:
An UF membrane separation device 7 using an ultrafiltration membrane is connected via a transport pipe 8. Then, the sludge separated and removed by the UF membrane separation device 7 is returned to the high load reaction tank 1 and the nitrification denitrification tank 4, and a part of the sludge is transported to the dehydration step for treatment. Further, the filtered filtrate is discharged to a river as treated water or further purified in a post process.

Next, the operation of the above embodiment will be described.

First, the organic wastewater is introduced into the high load reaction tank 1 through the raw water pipe 2 and aerated by an aerator (not shown) while maintaining the redox potential (ORP) at 0 to 300 mV. By this aeration, biological nitrification and denitrification treatment by microorganisms contained in sludge, which returns easily decomposable organic matter related to biochemical oxygen demand (BOD) in organic wastewater,
That is, it is aerobically decomposed by BOD oxidizing bacteria, which are microorganisms in the returned sludge, and organic substances at the time of nitrifying and denitrifying nitrogen compounds by nitrifying bacteria and denitrifying bacteria, which are microorganisms in the returning sludge. BOD is reduced by consumption.
Even if the ORP is set higher than 300 mV, there is almost no difference in degradability of easily decomposable organic matter and the operating cost for aeration increases, so the value is set to 300 mV or less. Also, OR
When P is lower than 0 mV, it becomes reductive and aerobic decomposition is not performed by BOD-oxidizing bacteria, and the functions of nitrifying bacteria and denitrifying bacteria also deteriorate. Therefore, ORP is 0 to 3
Set to 00 mV.

The aerated organic wastewater in which the organic substances and nitrogen compounds have been biologically nitrified and denitrified by the BOD oxidizing bacteria, nitrifying bacteria and denitrifying bacteria is transferred to the nitrifying and denitrifying tank 4 via the carrier pipe 3. Inflow. The organic wastewater flowing into the nitrification / denitrification tank 4 has a dissolved oxygen (DO) of 0.5 mg / l or less and an ORP of -100 to 50 mV.
Control below the ORP of. As a result, nitrate ions and nitrite ions are generated by nitrifying bacteria and nitrite bacteria as microorganisms contained in sludge that returns nitrogen compounds such as easily decomposable organic matter and ammonia (NH ₄ ) remaining in organic wastewater. In addition to nitrification, nitrate denitrifying bacteria, which are microorganisms in the returned sludge, reduce nitrate ions and nitrite ions to nitrogen gas and carbon dioxide gas by endogenous respiration and release them. If the ORP of the high load reaction tank 1 is lower than the ORP of the nitrification denitrification tank 4, the organic wastewater flowing into the nitrification denitrification tank 4 becomes reductive, and if the ORP of the nitrification denitrification tank 4 is kept at a predetermined value, nitrification will occur. Oxidation by a large amount of aeration is required in the denitrification tank 4. Due to this large amount of aeration, it is difficult to adjust DO to a low value of 0.5 mg / l. Therefore, the high-load reaction tank 1
If the ORP of is set higher than the ORP of the nitrification / denitrification tank 4, the nitrification / denitrification tank 4 can easily do 0.5 mg of DO without aeration.
Since it can be adjusted to a low value of / l, the ORP of the nitrification denitrification tank 4 is controlled to be lower than the ORP of the high load reaction tank 1, that is, the ORP of the high load reaction tank 1 is increased.

Furthermore, in the organic wastewater in the nitrification denitrification tank 4,
Iron chloride and powdered activated carbon are appropriately added by the iron chloride addition device 5 and the powdered activated carbon addition device 6. In addition, iron chloride is
An equivalent amount of phosphate is added to the organic wastewater flowing into the nitrification / denitrification tank 4. Further, the amount of powdered activated carbon added is as follows: The amount of powdered activated carbon added = COD of treated water / C of powdered activated carbon
It is calculated from the OD adsorption amount. Here, the COD adsorption amount of the powdered activated carbon is obtained from the adsorption isotherm of the powdered activated carbon shown in FIG. Here, when the organic wastewater is human waste or human wastewater-type wastewater such as septic tank sludge, the concentration of the phosphorus compound hardly exceeds 300 mg / l and the COD concentration hardly exceeds 500 mg / l. Therefore, as shown in FIGS. 3 and 4, the addition amount of iron chloride is 1500
The amount of activated carbon powder added may be 3000 mg / l or less.

The iron chloride, which is added appropriately, reacts with the phosphate ions in the organic waste water to produce insoluble iron phosphate. In addition, iron chloride is secondarily coagulated and adsorbed with the polymer-soluble organic matter in the organic waste water to reduce the COD of the organic waste water. Furthermore, the powdered activated carbon added is dissolved in the organic wastewater in which the microorganisms are difficult to decompose in the high load reaction tank 1 C
It absorbs and insolubilizes hydrophobic low molecular weight organic substances, which are difficult-to-decompose organic substances due to OD, and reduces the COD of organic wastewater.

The ORP of the nitrification / denitrification tank 4 is -100 mV.
When it is lower than the above, the reducing state is brought about, and when the amount of dissolved phosphoric acid in the organic wastewater flowing into the nitrification denitrification tank 4 is equal to the added amount of iron chloride, the phosphoric acid is eluted again as shown in FIG. Resulting in. Further, when the ORP of the nitrification denitrification tank 4 becomes higher than 50 mV, nitrification due to the oxidation of nitrogen compounds such as ammonia progresses, and the concentration of nitric acid and nitrite increases,
Nitric acid and nitrous acid cannot be completely denitrified at the rate of denitrification by endogenous respiration of denitrifying bacteria and remain. Further, if nitric acid and nitrous acid remain at a high concentration, the pH becomes low and becomes acidic, which hinders the removal of nitrogen compounds such as ammonia by oxidation. Therefore, the ORP of the nitrification denitrification tank 4 is set to -100 to
By adjusting to 50 mV, nitrogen compounds can be removed well without phosphorus elution. In addition, by adjusting the ORP of the nitrification / denitrification tank 4 to -100 to 50 mV, the UF of the subsequent process
It is also possible to prevent the elution of iron ions that deposit on the membrane surface of the membrane separation device 7 and reduce the membrane permeability.

The easily decomposable organic substances and nitrogen compounds remaining in the nitrification and denitrification tank 4 and the biologically nitrifying and denitrifying treatment were not treated, and iron chloride and powdered activated carbon removed the hardly decomposable organic substances and phosphate ions. The organic wastewater is subjected to membrane separation in the UF membrane separation device 7, a part of the sludge is dehydrated in the dehydration step, and the rest is returned to the high load reaction tank 1 and the nitrification denitrification tank 4. Further, the filtrate is discharged as treated water to rivers or the like, or is further highly purified.

Here, the results of measurement of the permeability of the UF membrane separation device 7 using the apparatus of the first embodiment in the case of adding only iron chloride and the case of not adding both iron chloride and powdered activated carbon are shown in FIG. 6 shows.

From the results shown in FIG. 6, when neither iron chloride nor powdered activated carbon was added, the permeation rate declined quickly, and the treated water due to the permeation rate declined unless the membrane was washed about once / month. However, when only iron chloride is added, the permeation rate is increased and the permeation rate is gradually decreased, and the cleaning can be performed about once every three months. Furthermore, it can be seen that the permeation rate is further increased when the iron chloride and powdered activated carbon according to the present embodiment are added.

By the way, the relationship between the COD concentration and the permeation rate of the soluble organic matter flowing into the UF membrane separator 7 is that the soluble organic matter forms a gel layer on the membrane surface. As shown in FIG. 7, the membrane permeation rate decreases as the COD concentration increases. Therefore, it is understood that the addition of the powdered activated carbon that adsorbs the soluble organic matter related to the COD concentration suppresses the growth of the gel-like layer formed on the film surface and increases the permeation rate.

According to the above embodiment, after the easily decomposable organic matter and the nitrogen compound of the organic wastewater are biologically nitrified and denitrified by the BOD oxidizing bacteria, nitrifying bacteria and denitrifying bacteria in the high load reaction tank 1. , Nitrogen denitrification tank 4 easily removes easily decomposable organic substances and nitrogen compounds remaining in the nitrification denitrification tank 4, and iron chloride is added to react the phosphate ion with the insoluble iron phosphate, and high load reaction Polymer-dissolved organic substances that are not oxidatively decomposed in tank 1 are secondarily aggregated and adsorbed, and powdered activated carbon is added to them, and they are non-degradable hydrophobic low molecules that are not oxidatively decomposed by BOD oxidizing bacteria and are not aggregated and adsorbed by iron chloride. The high-load reaction tank 1 and the nitrification denitrification tank 4 are obtained by adsorbing and removing organic substances and further separating the remaining nitrogen compounds and organic substances into membranes by a membrane separator
Since it is returned to the membrane and treated again, the soluble organic substances due to the chemical oxygen demand forming the gel layer on the membrane surface can be highly removed before the membrane separation, the load of the membrane separation can be reduced, and the efficiency can be reduced. Can handle well.

In the above embodiment, the high-load reaction tank 1 and the nitrification / denitrification tank 4 may be divided into one tank so as to communicate with each other.

Further, the nitric denitrification tank 4 is provided with the iron chloride addition device 5 as a treatment agent addition means and the powdered activated carbon addition device 6 as a treatment agent addition means, but the high load reaction tank 1 and the raw water pipe 2 are provided. Even if it is provided directly, the same effect can be obtained. Then, the iron chloride and the powdered activated carbon may be appropriately mixed, and the mixture of the iron chloride and the powdered activated carbon may be added. The amount of iron chloride and powdered activated carbon added can be minimized by performing nitrification and denitrification in the nitrification and denitrification tank 4 and adding iron chloride and powdered activated carbon after the treatment in the high-load reaction tank 1. Therefore, the processing cost can be reduced.

[0025]

EXAMPLE An experiment in which the organic wastewater is purified by using the apparatus having the configuration of the above-described embodiment will be described. As a comparative example, the organic wastewater was similarly purified by a conventional apparatus for solid-liquid separation in a sedimentation tank without using iron chloride and powdered activated carbon. Table 1 shows the results.

[0026]

[Table 1] First, as the organic wastewater, human waste sewage, which is a mixture of human waste of 40% by weight and septic tank sludge of 60% by weight, is used. The properties of this organic wastewater are shown in Table 1. Then, the organic wastewater was introduced into the high-load reaction tank 1 at a rate of 1 kl / day, aerated while maintaining the ORP at 0 to 300 mV and retained for one day, and then introduced into the nitrification denitrification tank 4, and DO was reduced to 0. 0.5 mg / l or less, ORP of -100 to 50 mV, OR of high load reaction tank 1
It is controlled to be lower than P and allowed to stay for 1 day. This nitrification denitrification tank 4
530 ppm, which is an amount equivalent to the solidification of the soluble phosphate in the organic wastewater flowing into the nitrification and denitrification tank 4 during the retention
The amount of powdered activated carbon added is increased / decreased as the residual COD is increased / decreased while observing the residual COD of the treated water filtered in the membrane separation in the subsequent step. The average amount of powdered activated carbon added was 300 ppm. And 1
After staying for a day, solid-liquid separation is performed by the UF membrane separation device 7, sludge is returned to the high load reaction tank 1 and nitrification denitrification tank 4, and the filtrate is discharged as final treated water as treated water. The properties of this treated water are shown in Table 1.

As a comparative example, an organic wastewater having the properties shown in Table 1 was similarly introduced into the high-load reaction tank at an input rate of 1 kl / day, and was aerated for one day, and then was aerated in a nitrification denitrification tank. The solution is allowed to stay for a day and solid-liquid separated in a sedimentation tank to obtain treated water having the properties shown in Table 1.

From the results shown in Table 1, it can be seen that particularly COD, phosphorus and suspended solids (SS) are highly removed as compared with the comparative example.

[0029]

According to the method for treating organic wastewater according to the first aspect, the organic wastewater is biologically nitrified and denitrified by microorganisms and dissolved in iron chloride added in one tank. After reacting the phosphorus compound with the insoluble iron phosphate, the residual polymer soluble organic matter is secondarily aggregated and adsorbed, and the residual hard-to-decompose hydrophobic low molecular weight organic matter is adsorbed and removed with powdered activated carbon, and then the membrane is formed. Since it is separated, a soluble organic substance due to a chemical oxygen demand that forms a gel layer on the membrane surface can be highly removed before membrane separation with a simple structure, reducing the load of membrane separation and efficiently. It can be processed.

According to the organic wastewater treatment apparatus of claim 2, treatment for aerobic decomposition / nitrification denitrification by microorganisms in one tank, insolubilization of phosphorus compounds by iron chloride and residual polymer solubility Chemistry for secondary coagulation and adsorption of organic substances, and adsorption and removal of persistent non-decomposable hydrophobic low-molecular organic substances by powdered activated carbon, which can be simplified in structure and forms, for example, a gel layer on the film surface. The soluble organic substances due to the specific oxygen demand can be highly removed before the membrane separation, the load of the membrane separation can be reduced, and the treatment can be efficiently performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a method for treating organic wastewater according to the present invention.

FIG. 2 is a graph showing an adsorption isotherm of the above powdered activated carbon.

FIG. 3 is a graph showing the relationship between the COD concentration and the amount of powdered activated carbon added.

FIG. 4 is a graph showing the relationship between the phosphorus concentration and the amount of iron chloride added.

FIG. 5 is a graph showing the relationship between phosphorus concentration and ORP.

FIG. 6 is a graph showing changes in membrane permeation rate due to the additive.

FIG. 7 is a graph showing the relationship between the soluble COD concentration flowing into the membrane separation device and the membrane permeation rate.

[Explanation of symbols]

 1 High-load reaction tank as biological treatment means 2 Raw water pipe as raw water inflow means 4 Nitrification denitrification tank as biological treatment means 5 Iron chloride addition device as treatment agent addition means 6 Activated carbon addition device as treatment agent addition means 7 UF membrane separation device which is a membrane separation means

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Claims (2)

[Claims] 1. A method for treating an organic wastewater containing a nitrogen compound and a phosphorus compound, which biologically treats the organic wastewater, wherein powdered activated carbon and iron chloride are added to the organic wastewater, and the powdered activated carbon and The organic wastewater to which iron chloride has been added is contacted with oxygen while maintaining the dissolved oxygen at 0.5 mg / l or less, and the organic wastewater is subjected to biological nitrification and denitrification treatment by microorganisms and then subjected to membrane separation. A method for treating organic wastewater, comprising: 2. An organic wastewater containing a nitrogen compound and a phosphorus compound is contacted with oxygen, and the organic wastewater is subjected to biological nitrification and denitrification treatment by a microorganism to make the organic wastewater the first treated water. Biological treatment means, raw water inflow means connected to the biological treatment means for flowing the organic wastewater into the biological treatment means, and the first treated water connected to the biological treatment means and flowing out of the biological treatment means into a membrane Membrane separation means for separating, and comprising at least one of the raw water inflow means and the biological treatment means, a treatment agent addition means for adding powdered activated carbon and iron chloride to the organic wastewater, Treatment equipment for organic wastewater.