JPS6012197A - Treatment of phosphorus-containing organic waste liquid - Google Patents

Abstract

PURPOSE:To effectively perform dephosphorization, by a method wherein a part of a phosphorus-containing org. waste liquid is subjected to aeration treatment to be mixed with return sludge along with the remainder of the waste liquid while the resulting mixture is successively subjected to anaerobic treatment and aerobic treatment and, after solid-liquid separastion, a part of activated sludge is used as the return sludge. CONSTITUTION:A part of a phosphorus-containing waste liquid 6 is subjected to aeration treatment in an aeration tank 1 and the treated liquid is introduced into an anaerobic tank 2 along with the remainder of the waste liquid 6. At the same time, return sludge 7 from a solid-liquid separation tank 4 to be mixed with the waste liquid and the resulting mixture is subjected to anaerobic treatment. After treatment, the treated mixture is introduced into an aerobic tank 3 to be aerobically treated while the treated one is introduced into the solid-liquid separation tank 4. The treated water 8 from which org. substances and phosphorus are removed is discharged and a part of the separated sludge 9 is used as return sludge 7 while the remainder is discharged as excessive sludge 10.

Description

[Detailed Description of the Invention] This invention relates to a method for treating organic waste liquid containing phosphorus, in particular, the waste liquid is mixed with returned sludge and treated anaerobically, and then a part of the activated sludge that is separated into solid and liquid is treated by aerobic treatment. This is related to the processing method for returning the item.

As a method for treating organic wastewater containing phosphorus, the wastewater is mixed with return sludge and subjected to anaerobic treatment, followed by aerobic treatment, followed by solid-liquid separation, and a portion of the separated activated sludge is returned as return sludge. is being carried out. This method is a method to efficiently remove organic matter and phosphorus by placing activated sludge in an anaerobic-aerobic environment to cause excessive intake and release of phosphorus. It is applied to the treatment of organic wastewater containing

However, when this treatment method is applied to some waste liquids such as raw human waste, activated sludge maintains its organic matter absorption activity, but may lose its ability to absorb excess phosphorus, making phosphorus removal extremely unstable. There were problems such as lack of reproducibility, and sometimes excessive phosphorus intake did not occur at all.

This invention is intended to solve the above-mentioned problems, and involves aerating a portion of organic wastewater containing phosphorus, mixing it with the rest of the wastewater and returning sludge for anaerobic treatment, and then aerobic treatment. By doing so, we have developed a method for treating organic wastewater containing phosphorus that maintains a high excess phosphorus uptake capacity of activated sludge and can stably increase the phosphorus removal rate over a long period of time, even for wastewater that could not be treated conventionally, such as human waste. is intended to provide.

This invention aerates a part of organic wastewater containing phosphorus, mixes it with the rest of the wastewater and returns sludge, performs anaerobic treatment, performs aerobic treatment, then solid-liquid separation, and collects the separated activated sludge. There is a method for treating an organic waste liquid containing phosphorus, which is characterized in that a part of the waste liquid is returned as the return sludge.

When we investigated the cause of the reduced ability of activated sludge to overtake phosphorus when human waste is treated by anaerobic and aerobic treatment, we found that lower fatty acids, which are BOD components in human waste, are the cause.

Lower fatty acids are components of soluble nOD, and in the case of sewage, total B
It accounts for less than 10% of the OD and its influence is small, but in the case of human waste, about 50% of the total BOD is lower fatty acids, which make up the main part of the organic matter absorbed into activated sludge during anaerobic treatment, and It has a great influence on the properties of sludge. For this reason, wastewater other than night soil that contains a large amount of lower fatty acids exhibits a phenomenon similar to human urine.

゛It is not clear why activated sludge loses its ability to take in excess phosphorus when it absorbs a large amount of lower fatty acids during anaerobic treatment, but if anaerobic and aerobic treatments are repeated, activated sludge will absorb excess phosphorus for a period of time. Obtain the ability to ingest. However, if the cycle of absorbing a large amount of lower fatty acids in anaerobic treatment and then oxidizing and decomposing the absorbed lower fatty acids in aerobic treatment is repeated for a long time, only the organic matter absorption activity is maintained, but the ability to overtake phosphorus is reduced. The bacteria that have been lost will multiply preferentially, and even if these bacteria divide and multiply, they will only produce bacteria that do not have the ability to overtake phosphorus.

Therefore, if we constantly supply bacteria (aerobic bacteria or facultative anaerobic bacteria) that live in activated sludge before acquiring the ability to take in excess phosphorus, the newly supplied bacteria will acquire the ability to take in excess phosphorus after a predetermined period of time. As a result, the activated sludge as a whole maintains a high capacity for excess phosphorus uptake. Sewage contains many such bacteria, but the bacteria contained in human waste are anaerobic bacteria such as intestinal bacteria.
It does not grow in an anaerobic-aerobic environment.

Therefore, in the present invention, by aerating a portion of the waste liquid to be treated in advance, bacteria that can become dominant in the activated sludge are allowed to grow, and then anaerobic treatment is performed along with the remaining waste liquid to reduce the ability to overtake phosphorus. maintain.

Hereinafter, the present invention will be explained with reference to the drawings. Figures 1 to 3
Each figure is a system diagram showing an embodiment of the present invention, and 1
2 is an anaerobic tank, 3 is an aerobic tank, 4 is a solid-liquid separation tank, and 5 is a denitrification tank.

In either treatment method, a part of the waste liquid 6 is aerated in advance in the pre-aeration tank 1, and then introduced into the anaerobic tank 2 together with the remainder of the waste liquid 6 and the return sludge 7 for anaerobic treatment. The waste liquid 6 to be treated is an organic waste liquid containing phosphorus, but may also contain nitrogen and other components. Among these waste liquids, waste liquids containing a large amount of lower fatty acids such as human waste are suitable for this treatment, but waste liquids such as sewage that have a low content of lower fatty acids can also be treated. When raw human waste is treated as waste liquid 6, it is preferable to treat it in the form of filtered human waste from which solids have been removed, and the treatment can be carried out by diluting it with fresh water or seawater as necessary.

The aeration treatment in the pre-aeration tank 1 is performed to multiply the bacteria living in the activated sludge, and if the aeration treatment is performed with a residence time of about 2 to 24 hours, activated sludge will be generated in the pre-aeration tank 1. However, a part of it flows out into the anaerobic tank 2 together with the aeration liquid. The dispensing ratio of the waste liquid 6 to the pre-aeration tank 1 and the anaerobic tank 2 is about i:o,s~4, which allows bacteria to grow in the pre-aeration tank 1 and to perform anaerobic treatment in the anaerobic tank 2. It can be arbitrarily selected within a range that can supply the required OD.

The anaerobic treatment in the anaerobic tank 2 is carried out by gentle stirring with the supply of oxygen cut off and maintained in an anaerobic state for about 10 minutes to 4 hours. Through the anaerobic treatment, the bacteria contained in the returned sludge Z take in BOD in the waste liquid and release orthophosphoric acid using energy from hydrolysis of polyphosphoric acid stored in the body. Although the bacteria introduced from the pre-aeration tank 1 do not have this remarkable ability, they gradually acquire this ability by repeating anaerobic treatment and aerobic treatment. ML8S in anaerobic tank 2 is 2,000 to 20,000 ■/
The BOD to be introduced is 0.05 to 3”p BOD/
'&-8S/aay degree is desirable.

There are differences in the treatment after anaerobic treatment between Figures 1 and 6, but
After performing aerobic treatment in each aerobic tank 6, solid-liquid separation is performed in a solid-liquid separation tank 4 into treated water 8 and activated sludge 9,
A part of activated sludge 9 is used as return sludge 7, and the rest is used as surplus sludge 1.
Eject as 0.

The aerobic treatment in Figure 1 involves blowing air (oxygen) into the mixed liquid introduced from anaerobic tank 2 to aerobic tank B, and performing aeration treatment for a residence time of about 60 minutes to 24 hours to decompose organic matter. . At this time, activated sludge contains BOD absorbed during anaerobic treatment.
and T in liquid; OD is oxidized and decomposed by respiration, and phosphorus is taken into the body and stored in the form of polyphosphoric acid. This intake of phosphorus stores boronic acid as an energy source in preparation for an anaerobic environment, and the pre-aeration tank 1
Bacteria newly supplied from the environment will also acquire the ability to overtake phosphorus as they undergo repeated anaerobic-aerobic environmental changes.

Activated sludge that has acquired the ability to take in excess phosphorus has a phosphorus content of 4 to 6%, compared to about 2% in normal activated sludge.
The phosphorus content will be approximately 100%. Therefore, when solid-liquid separation is performed in the solid-liquid separation tank 4, the treated water 8 is separated into treated water 8 from which organic matter, phosphorus, etc. have been removed, and activated sludge 9 which has stored a large amount of phosphorus. By returning part of the activated sludge 9 as return sludge 7, the anaerobic-aerobic environmental change is repeated.

In the treatment method shown in Fig. 2, the aerobic treatment in the aerobic tank 6 is nitrification treatment, in which aeration is performed in excess of the aeration for BOD removal to make nitrifying bacteria predominant and to reduce nitrogen components in the mixed liquid. It becomes nitrified to nitrate ions and carbon dioxide ions (7). A denitrification tank 5 is provided between the anaerobic tank 2 and the aerobic tank 6 in order to perform denitrification treatment on the degraded mixed liquid.

The denitrification tank 5 has the same anaerobic structure as the anaerobic tank 2, and the mixed liquid that has undergone anaerobic treatment in the anaerobic tank 2 and the return liquid 11 that has been nitrified in the aerobic tank 6 are introduced, and the denitrification bacteria in the tank are Denitrification treatment is performed by mixing and stirring with activated sludge containing activated sludge. Here, ROD in the mixed liquid is used as a hydrogen donor, and the return liquid 11
Denitrifying bacteria that reduce nitric acid or carbon nitrite ions in the waste liquid to nitrogen become dominant, and the nitrogen components in the waste liquid are removed.

In this treatment method, nitrification and denitrification treatments for nitrogen removal are performed independently of phosphorus removal, and the denitrification mechanism is performed in the same manner as in the case of FIG. In other words, the phosphorus released in the anaerobic tank 2 and the IJ in the waste liquid 6 are taken up in excess into the activated sludge in the aerobic tank 6, and the BOD absorbed into the activated sludge in the anaerobic tank 2 is absorbed into the activated sludge in the aerobic tank 2. It is decomposed in tank 3.

The treatment method shown in FIG. 6 is a method in which the denitrification and nitrification treatments shown in FIG. A denitrification tank 5b and a final aerobic tank 3b are provided, the mixed liquid in the anaerobic tank 2 is dispensed into the denitrification tank 5 and the intermediate denitrification tank 5a, and the return liquid 11 is returned from the intermediate aerobic tank 3a to the denitrification tank 5. Organic substances 12 such as methanol are injected into the final denitrification tank 5b.

In this process, the nitrification process is carried out in the aerobic tank 3 and the intermediate aerobic tank 3a, and the anaerobically treated mixed liquid is dispensed into the denitrification tank 5 and the intermediate denitrification tank 5a for denitrification and treatment. In the denitrification tank 5b, organic matter 12 is injected and finally denitrified.
BOD remaining after re-aerating in the final aerobic tank 6b
remove. If the number of stages of the intermediate denitrification tank 5a and the intermediate aerobic tank 6a is increased, the denitrification effect will be further enhanced.

In this treatment method as well, nitrification and denitrification are performed independently of phosphorus removal, and the dephosphorization mechanism is performed in the same manner as in FIGS. 1 and 2. In other words, the phosphorus released in the anaerobic tank 2 and the phosphorus in the wastewater 6 are taken up in excess into the activated sludge in the aerobic tank 3, and the B absorbed into the activated sludge in the anaerobic tank 2 is
OD is decomposed in an aerobic tank 6. The subsequent nitrification and denitrification treatments do not affect phosphorus metabolism.

In addition to this, the treatment method can be changed in various ways, but in any case, after aerating a portion of the waste liquid, it is mixed with the returned sludge along with the rest of the waste liquid to perform anaerobic treatment and aerobic treatment. It is necessary.

According to the present invention, a part of organic waste liquid containing phosphorus is aerated, mixed with the remaining waste liquid and returned sludge for anaerobic treatment, and then a part of the activated sludge that has been subjected to aerobic treatment and solid-liquid separation is Since it is configured to be returned, bacteria that can acquire the ability to take up excess phosphorus are constantly supplied, and the ability of activated sludge to take up too much phosphorus is always maintained at a high level, resulting in a stable high removal rate over a long period of time. Phosphorus can be removed to lower the phosphorus concentration in treated water. This effect is remarkable in the case of wastewater with a high concentration of lower fatty acids such as human waste, but the phosphorus removal rate is maintained high even in the case of wastewater with a low concentration of lower fatty acids such as sewage. In the case of wastewater with a high concentration of lower fatty acids,
As lower fatty acids are decomposed by aeration of some of the wastewater,
The concentration of lower fatty acids becomes low, creating an environment in which it is easy to maintain the activated sludge's ability to take in excess phosphorus.

Next, examples of the present invention will be described.

Example Sodium acetate 2,000 μ/m, Yeast extract 150 μ
/i, ammonium chloride 800■/no, magne sulfate* Shira (heptahydrate) 150~/no, potassium phosphate 130
■/no, using synthetic human waste with 1,000 ■/i salt
Processing was performed using the processing method shown in the figure. The residence time of each type is 12 hours in pre-aeration tank 1, 2.6 hours in anaerobic tank 2, 10 hours in denitrification tank 5, and 15 hours in aerobic tank 6. The dispensing ratio of 6 is 1:1, the dissolved oxygen in pre-aeration tank 1 is 0 to 5 Wq/no, and the MLSS of anaerobic tank 2 is 5.
ODD~B, Ll Ll O■/i, the return rate of the return sludge 7 is 200%, and the return rate of the return liquid 11 is 400%.

Comparative Example For comparison, the pre-aeration tank 1 was not provided, the entire amount of wastewater 6 was introduced into the anaerobic tank 2, and the other conditions were the same as in the example.

As a result, there is no difference between the Example and Comparative Example regarding the removal of nitrogen and COD, and the nitrogen removal rate is approximately 90% in each case.
, the COD removal rate was 95%.

However, regarding the removal of phosphorus, in the comparative example, approximately 1 hour after the start of operation.
After the phosphorus removal rate reached almost 100% after a month, the monthly phosphorus removal rate continued to be 100%, but after that it gradually worsened, and two weeks after the deterioration started, the phosphorus removal rate was about 10%.
Stable at %. On the other hand, in the case of the example, the start of operation was approximately 1
After a month, the phosphorus removal rate reached almost 100%, and the phosphorus removal rate remained at 95% or higher for more than 6 months.

- From the above results, it can be seen that the treatment method of the present invention can remove phosphorus stably and at a high removal rate over a long period of time compared to the treatment method of the comparative example.

[Brief explanation of the drawing]

1 to 3 are system diagrams showing embodiments of the present invention, respectively. In each figure, the same reference numerals indicate the same or equivalent parts, 1 is a pre-aeration tank, 2 is an anaerobic tank, 3, 3a, 3b are aerobic tanks, 4 is a solid-liquid separation tank, 5.5a, 5b is a denitrification tank. Agent Patent Attorney Sei Yanagihara

Claims (5)

[Claims] (1) A part of the organic waste liquid containing phosphorus is aerated, and the rest of the waste liquid is mixed with returned sludge for anaerobic treatment.
A method for treating organic waste liquid containing phosphorus, which comprises performing aerobic treatment, followed by solid-liquid separation, and using a portion of the separated activated sludge as the return sludge. (2) The method for treating organic waste liquid containing phosphorus according to claim 1, wherein the aerobic treatment is an aeration treatment for decomposing organic matter. (3) The organic waste liquid containing phosphorus according to claim 1, wherein the aerobic treatment is a nitrification treatment for decomposing organic matter and nitrifying nitrogen components, and the nitrified liquid is subjected to a denitrification treatment. processing method. (4) The method for treating organic waste liquid containing phosphorus according to claim 3, wherein the denitrification treatment is provided between the anaerobic treatment and the nitrification treatment, and the nitrified liquid is returned. (5) A method for treating organic waste liquid containing phosphorus according to claim 6 or 4, wherein nitrification treatment and denitrification treatment are repeated in multiple stages.