JPS5990690A - Treatment of water containing organic substance and phosphate - Google Patents

Abstract

PURPOSE:To remove efficiently org. substances and phosphates by treating water contg. the org. substances and phosphate in a biological dephosphorization process, bringing it into contact with crystal seeds contg. calcium phosphate at >=6 pH under the presence of Ca ions, and crystallizing the org. substances and phosphates. CONSTITUTION:A liquid mixture in which nitrate ions and nitrite ions are consumed is transferred to an anaerobic tank 3 to treat anaerobically. In the anaerobic tank 3, facultative anaerobia including denitrification bacteria usually consume phosphorus in the body as the energy source, and release phosphorus to adsorb or to absorb BOD. The liquid mixture in the anaerobic tank 3 is transferred partly to an aeration tank 4 through a connecting pipe 11. After treated aerobically by aeration through an aeration pipe 4a, the liquid is sent to a solid-liquid separation tank 5 to carry out precipitate separation. The supernatant is taken out from the connecting pipe 14, sent to a crystallization tank 6 after a calcium agent or the like is injected from an injection pipe 15, and brouhgt into contact with seed crystals contg. calcium phosphate in the presence of Ca ions at >=6 pH.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water containing organic matter and phosphates by a biological dephosphorization process and a crystallization process.

Biological dephosphorization methods have been proposed to remove organic matter and phosphorus from water containing organic matter and phosphorus, such as sewage and wastewater. In this method, raw water containing phosphorus such as phosphate is mixed with returned sludge, retained in an anaerobic tank for 60 minutes, and then retained in an aeration tank for 90 to 6 days.
B'OD is removed together with phosphorus, and the aeration liquid is separated into treated water and settled sludge in a settling tank. A part of this settled sludge is returned and the remainder is discharged as surplus sludge.

The mechanism for removing phosphorus and BOD in this one method is estimated to be as follows9. In other words, when sewage is mixed with returned sludge and stirred in an anaerobic tank, microorganisms in the sludge consume phosphorus compounds (magnesium salt of phosphoric acid) stored in the body as an energy source, and produce phosphorus (normal phosphorus). However, in the next aeration tank, the absorbed BOD is oxidized through respiration, and the released phosphorus and inflow phosphorus are absorbed and absorbed into the body in the form of phosphorus compounds as an energy source. store. The sludge that has accumulated phosphorus is returned to the anaerobic tank, where it undergoes the same action. In the normal activated sludge treatment method, the phosphorus content of excess sludge is 1.5 to 2.5% based on the dry weight of sludge. The content may be about 8 parts per dry weight of sludge. For this reason, phosphorus in wastewater is often removed at a high removal rate.

However, in such a biological dephosphorization method, the treatment effect varies depending on the quality of raw water, flow rate, etc. In particular, if the ratio of the BOD concentration to the phosphorus concentration (BOD/P ratio) in the raw water flowing into the anaerobic tank is not 20 or more, there is a problem that the dephosphorization effect is reduced.

On the other hand, the treated water from such a biological dephosphorization process is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions under conditions of pH 6 or higher to perform crystallization to remove residual phosphates. However, there was a problem in that the crystallization load fluctuated due to fluctuations in the phosphorus concentration of the water treated in the previous biological dephosphorization process, making it impossible to perform stable treatment. In addition, residual organic matter flowing out from the biological dephosphorization process contaminates the crystal seeds, reducing the dephosphorization activity of the crystal seeds, and if this is reactivated, treatment of the reactivation waste liquid is required. There were also problems.

This invention is intended to improve the above-mentioned conventional problems, and it is possible to reactivate the crystal seeds by reactivating them with an organic acid and supplying the reactivated waste liquid to a biological dephosphorization process. Provides a method for treating organic, mobile, and phosphate-containing water that can treat activated waste liquid, adjust the BOD/P ratio of raw water, and stably and efficiently remove organic matter and phosphates. It is intended to.

This invention treats water containing organic matter and phosphates by a biological dephosphorization process including an anaerobic treatment process and an aerobic treatment process, and treats the treated water in the presence of calcium ions and with a pH of 6 or higher. Crystallization is performed by contacting crystal seeds containing calcium phosphate under the following conditions, and the crystal seeds with reduced dephosphorization performance are reactivated by contacting with an organic acid, and the resulting reactivated waste liquid is subjected to the biological dephosphorization. An organic substance characterized by being supplied to a process. This is a method for treating water containing biphosphates.

The present invention will be explained below with reference to the drawings. The drawing is a system diagram showing one embodiment of the present invention. In the drawing, 1 is a settling tank, 2 is a denitrification tank, 6 is an anaerobic tank, 4 is an aeration tank, 5 is a solid-liquid separation tank, and 6 is a crystallization tank, which are connected in series in the above order.

Although the sedimentation tank 1 is not necessarily required, the raw water flowing in from the raw water pipe 7 is sedimented and separated, and the solid matter is discharged from the sludge pipe 8 as settled sludge. The supernatant water of the settling tank 1 is supplied to the denitrification tank 2 from the raw water supply pipe 10 together with the return sludge from the anti-transfer pipe 9 .

The denitrification tank 2 and the anaerobic tank 6 have substantially the same configuration, and are capable of performing anaerobic treatment by gently stirring them while blocking air. The denitrification tank 2 is included in the anaerobic treatment process and is for denitrifying when nitrate ions or nitrite ions are contained in the returned sludge, and may be omitted when these are not contained. When the returned sludge containing nitrate ions or nitrite ions is mixed with raw water and kept in an anaerobic environment, denitrifying bacteria become dominant, consuming nitrate and nitrite ions and releasing them as desirable elements. .

The mixed liquid in which the nitrate ions and nitrite ions have been consumed in this manner is transferred to the anaerobic tank 6, and an anaerobic treatment step is performed in the same manner as denitrification. Since nitrate ions and nitrite ions are not present in the anaerobic tank 6, facultative anaerobes including denitrifying bacteria consume phosphorus in the body as an energy source and release phosphorus.
Adsorbs or absorbs BOD. A similar phenomenon occurs even when nitrate ions and the like are not present in the returned sludge and when the denitrification tank 2 is omitted. The mixed liquid in the anaerobic tank 6 is sent in portions 9 to the aeration tank 4 through the communication pipe 11, diffused in the aeration tank 4, and aerated through the pipe 4a to perform an aerobic treatment process. Here, the microorganisms in the activated sludge ingest phosphorus in the liquid and decompose BOD.

In this way, organic substances and phosphates in the mixed solution are removed. The aerated mixed liquid is sent in portions from the connecting pipe 12 to the solid-liquid separation tank 5 for sedimentation separation, and the precipitated solid content is sent to the solid-liquid separation tank 5 through the communication pipe 12.
A portion is returned from the return pipe 9 as return sludge, and the remainder is discharged as surplus sludge. This completes the biological dephosphorization process.

The supernatant water is taken out from the communication pipe 14, and a calcium agent and/or an alkaline agent are injected through the chemical injection pipe 15, and the crystallization tank 6 is
in the presence of calcium ions and at a pH of
The crystallization step is performed by contacting the crystal seeds containing calcium phosphate filled in the crystallization tank 6 under conditions of 6 or more.

The reaction that occurs when water containing phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions varies depending on the reaction conditions, but is usually expressed by the following formula.

SCa +3HPO4-1-40H-+ca5(OH
I(PO413+3H20=·(1)) As can be seen from the formula (1), in order to increase the removal rate of phosphate, it is necessary to advance the reaction to the right.

Crystal species containing calcium phosphate include hydroxyapatite [Ca5(OH)(PO4)3], fluoroapatite [Cas (F l ('PO4'l 3) or tricalcium phosphate (Ca 3 <PO4)2), etc. Crystal seeds containing calcium phosphate can be used. Natural phosphate rock or bone char has calcium phosphate as the main component and is suitable as a crystal seed. Crystal seeds with calcium phosphate precipitated on the surface of furnace materials such as sand can also be used. As a crystal seed, it is desirable that the main component is calcium phosphate of the same type as the calcium phosphate produced by the reaction.For example, in a system that produces hydroxyapatite, the use of hydroxyapatite facilitates the precipitation of new crystals. , phosphate removal is performed efficiently and the removal rate is increased.

The crystallization conditions are the same as those of the conventional method, and when brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and at a pH of 6 or higher, calcium phosphate is produced according to the formula (1) above. is precipitated on the surface of the crystal seed, the crystal grows, and the phosphate ions in the water are removed.

Calcium ions and hydroxide ions to be present in water do not need to be added from the outside if they are present in the raw water from the beginning, but if they are not present in the raw water or are insufficient, they are added from the outside. The amount added should be in excess of the reaction equivalent, but if too much is added, fine precipitates may precipitate in areas other than the crystal seeds, and impurities such as calcium carbonate may be generated. It should be within the range where it will not be generated. That is, the amounts of calcium ions and hydroxyl ions are set to be higher than the solubility of hydroxyapatite produced in equation (1), but lower than the supersolubility, that is, the conditions are such that hydroxyapatite is produced at a concentration in the metastable range. Here, supersolubility is the concentration at which crystals begin to precipitate when no crystal seeds are present in the reaction system.

In other words, at a concentration higher than supersolubility, new crystals precipitate where crystal seeds do not exist, forming fine precipitates.
Although clogging of the hearth occurs, in the metastable region where the supersolubility is lower, new crystals precipitate on top of the crystal seeds, and only crystals grow and no precipitates are formed. In addition, crystals do not precipitate in systems with low solubility.

The amount of hydroxyapatite produced is controlled by the phosphate ion concentration, calcium ion concentration, and pH of the reaction system. The amount of calcium ions and the pH value that bring the amount of produced hydroxyapatite within the metastable range can be determined experimentally by changing these values for each reaction system. The approximate range is when the phosphate ion is 501n9/A or less, the calcium ion is 10 to 100
/A s pH is about 6 to 12, but varies depending on each condition.

The method of contacting the water containing phosphate with the crystal seeds containing calcium phosphate may be a fixed bed method or a fluidized bed method. The smaller the size of the crystal seeds, the larger the surface area, which makes it easier for new crystals to precipitate, but if the size of the crystal seeds is too small, it will be difficult to contact or separate the crystal seeds from water.

Furthermore, if the particle size is one size larger, the specific surface area per unit filling amount is small, so particles with a mesh size of about 9 to 600 are usually used. The larger ones are suitable for fixed beds, and the smaller ones are suitable for fluidized beds. In the case of a fixed bed, crystal seeds having a particle size of 9 to 65 mesh are packed, and water is passed upwardly or downwardly at a flow rate of SV1 to 5 hours to precipitate calcium phosphate crystals. Furthermore, a fixed bed and a fluidized bed may be combined.

If the crystal seed surface becomes clogged with sludge during water flow, periodically perform upward flow cleaning (backwashing) to spread out the crystal seed bed and clean it, and remove it from the surface. It is desirable to remove the impurities.

The water flow conditions during cleaning are 1 to 1, and the flow rate is 20 to 80 m/h.
The cleaning time is approximately 5 to 60 minutes.

Through the crystallization process in the crystallization tank 6 as described above, phosphates leaking into the supernatant water of the solid-liquid separation tank 5 are removed, and the final treated water flows out from the treated water pipe 16.

How, in the biological dephosphorization process, which includes anaerobic and aerobic treatment steps, most of the organic matter and phosphates in the raw water are removed, and the remaining phosphates are removed in the crystallization step. , treated water that can be discharged is obtained, but when the BOD/P ratio in the raw water is less than 2D, the dephosphorization effect in the biological dephosphorization process decreases. The general quality of sewage water is P: 3-5 m9/〃, BOD: 50-1
50 m9/A, and the B OD/P ratio is usually 20 or more, so the above operation can be sufficient for treatment, but due to seasonal factors, human factors, etc., the JBOD/P ratio is 20 or more.
Since the stability of the treatment is lost when the BOD/P ratio of the raw water goes into the anaerobic treatment process, an organic acid is used to reactivate the crystal seeds and the waste liquid is supplied to the raw water. 2
Adjust to 0 or more.

If crystallization continues in the crystallization tank 6, the dephosphorization activity of the crystal seeds decreases and cannot be recovered even by normal washing operations. Therefore, the crystallization operation is stopped and the chemical injection pipe 17 is placed in the crystallization tank 6.
Organic acid is injected into the crystal and brought into contact with the crystal seeds to reactivate them. The timing of reactivation may be when the BOD/P ratio decreases, but there is no particular restriction.

The organic acid may be one that is biodegradable, such as acetic acid, propionic acid, butyric acid, lactic acid, oxalic acid, citric acid, glutamic acid, etc., and one or more of these acids is brought into contact with the crystal seeds in the form of a solution. . Acid concentration is a measure of the degree of contamination;
It varies depending on the frequency of acid treatment, etc., but usually 0.005 to 5
Mol/! The degree is a guideline.

The reactivation treatment may be carried out by simply bringing the crystal seeds into contact with an organic acid solution, and any method such as water passage through a packed bed or immersion method can be employed, but it is preferable to use a method that corresponds to the crystallization method.

For example, when performing crystallization using a packed bed water flow method, it is easy to perform reactivation using the same packed bed water flow method.In particular, when cleaning the crystal layer, it is recommended to treat it with an organic acid bath solution. It is efficient. Although the treatment time depends on the acid concentration, it is about several minutes to several hours, and if it is too long, the amount of leached phosphorus will increase, which is not preferable. Reactivation is usually performed once or twice a month.

After reactivating as described above, water is passed through the crystallization tank 6 again to restart the crystallization process. The reactivation waste liquid varies depending on the conditions, but it is usually 60 to 5000 m97! Contains a certain amount of phosphorus, and has a BOD/P ratio of 50 to 1o.

The connecting pipe 18 is taken out and stored in the storage tank 19, and when the BOD/P ratio of raw water becomes less than 20, the connecting pipe 2o is supplied to the raw water supply pipe 1o, and the BOD/P is
Adjust the ratio to 20 or more. BOD/P ratio of raw water is 20
In the above case, the waste liquid may be supplied from the branch pipe 21 to the aeration tank 4 for treatment;
Since the higher the D/P ratio, the higher the dephosphorization effect, the raw water may be constantly supplied to the raw water supply pipe 10 from the communication pipe 2o.

Part of the organic matter in the reactivation waste liquid injected into the raw water is adsorbed or absorbed in the denitrification tank 2 and the anaerobic tank 6, and the remainder is decomposed in the aeration tank 4. In addition, most of the phosphorus in the waste liquid is removed in the aeration tank 4 along with the phosphorus in the raw water, and the remainder is removed in the crystallization tank 6.
will be removed.

In this way, by supplying the reactivated waste liquid to the biological dephosphorization process, waste liquid treatment is carried out, and the BOD/P ratio of the first physical dephosphorization process is adjusted to an appropriate value, and biological The dephosphorization effect in the dephosphorization process can be maintained high, thereby stably processing can be performed, the load of the crystallization process can be averaged, and the process can be performed stably and efficiently as a whole.

In addition, in the above description, the detailed steps, operations, etc. of the biological dephosphorization step and the crystallization step can be changed. In addition, if multiple crystallization tanks 6 are provided and reactivation is performed sequentially, crystallization can be performed continuously without interrupting the crystallization process, and the generation of reactivation waste liquid can be averaged. Therefore, the storage tank 19 can be made smaller, or it can be omitted depending on the case.

The present invention is applicable to the case of removing organic matter and phosphorus from sewage, syneresis, and other water containing organic matter and phosphorus.

As explained above, according to the present invention, water containing organic substances and phosphates is treated in a biological dephosphorization process and a crystallization process, and the crystal seeds used in the crystallization process are reactivated with an organic acid. Since the waste liquid is supplied to the biological dephosphorization process, it is possible to easily treat the reactivated waste liquid and to efficiently remove organic substances and phosphates from the raw water.

Next, examples of the present invention will be described.

Example p) 17.0, alkalinity 100■/! , phosphorus concentration 4”
';j, / AlB OD , (Habtong, /l/:
I-su) 100m9/! Synthetic wastewater was treated according to Figure 70-. However, the sedimentation tank 1 and denitrification tank 2 were omitted.

First, the wastewater was sent to the anaerobic tank 6, where it was retained at 0.85 br for anaerobic treatment, and then sent to the aeration tank 4 for aerobic treatment. MLSS of aeration tank 4 is 2,000 to 4,000 m9/
! , the residence time is 2. Ohr. Next, solid-liquid separation tank 5
The sludge was separated and a portion of it was returned to the anaerobic tank 3 so that the return rate was 30%. On the other hand, after adding slaked lime to the supernatant water of the solid-liquid separation tank 5 so that the pH becomes 8.5 with calcium ions 4CJm9/A1, the second crystallization tank 6 filled with 150 mIV of phosphate rock with a particle size of 16 to 62 meshes is added. 5V
Water was passed for 1 month at 2 hr-'.

After that, water flow was interrupted and 0.5 mol/! of acetic acid 0.75!
The phosphorus ore was reactivated using the phosphate rock, and the generated reactivation waste liquid was stored in a storage tank 19. I then resumed driving, but
At that time, the BOD of the synthetic wastewater mentioned above was determined to be peptone glucose 50m97! 100m97 consisting of and reactivated waste liquid 50 da/z (as BOD)! The treatment was carried out under the same conditions except for the water quality at each detection port after 18 months of Run 1 (
BOD and Total-El are shown in the following table.

As a comparative example, BO in synthetic wastewater after the above reactivation treatment was
The treatment was carried out under the same conditions except that D (peptone glycose) was changed to 50 μ/cm (Run 2).

Similarly, the water quality after one month is also recorded in the table.

From the results shown in the table above, in the biological dephosphorization method, the phosphorus removal rate deteriorates when the BOD/P ratio becomes less than 20, and the crystallization conditions must be extremely complicated in order to improve the quality of the final treated water. Recognize.

On the other hand, in Run 1 according to the method of the present invention, the BOD/P ratio is always kept at 20 or more by supplying reactivated waste liquid, so the processing conditions in each tank are almost constant.
It can be seen that the operation is simplified and the quality of the treated water obtained is also extremely good.

[Brief explanation of drawings]

The drawing is a system diagram showing one embodiment of the present invention, in which 1 is a precipitation tank, 2 is a denitrification tank, 6 is an anaerobic tank, 4 is an aeration tank, 5 is a solid-liquid separation tank, 6 is a crystallization tank, 7 15.17 is a raw water pipe, 15.17 is a chemical injection pipe, 16 is a treated water pipe, and 19 is a storage tank. Agent Patent Attorney Sei Yanagihara

Claims (1)

[Claims] (1) Water containing organic matter and phosphates is treated by a biological dephosphorization process including an anaerobic treatment process and an aerobic treatment process, and the treated water is treated in the presence of calcium ions. The reactivated waste liquid is obtained by contacting crystal seeds containing calcium phosphate under conditions of pH 6 or higher for crystallization, and reactivating the crystal seeds with low dephosphorization performance by contacting them with an organic acid. A method for treating water containing organic matter and phosphates, characterized in that the organic matter and phosphates are supplied to the biological dephosphorization step. (2) The water containing organic substances and phosphates according to claim 1, wherein the organic acid is one or more selected from acetic acid, propionic acid, butyric acid, lactic acid, oxalic acid, citric acid, and glutamic acid. Processing method. (6) The method for treating water containing organic acids and phosphates according to claim 1 or 2, wherein the crystal species containing calcium phosphate are hydroxyapatite, fluoroanotite, or tricalcium phosphate. (4) The method for treating water containing organic matter and phosphate according to any one of claims 1 to 6, wherein the anaerobic treatment step includes a denitrification step.