JPS58143890A - Purification of organic waste water - Google Patents

Abstract

PURPOSE:To obtain the SS-decreased limpid purified water from which phosphorus and BOD are removed with high efficiency, by letting an overflowing liquid from the precipitation pool of an anaerobic-aerobic active sludge process flow through a sand filter cell, and returning a part of captured SS to an anaerobic or aerobic cell. CONSTITUTION:An organic waste liquid as a liquid 11 to be purified is agitated and mixed with precipitating sludge 12 returned from the third step in an anaerobic cell 1 under the anaerobic condition that any of dissolved oxygen, nitric acid and nitrous acid does not exist substantially. The mixed outflow liquid 13 from the anaerobic cell in which soluble phosphorus is increased but BOD is reduced by said first step is introduced into an aerobic cell 2 and aerated with O2-contg. gas through a sparger 2' to oxidize and decompose residual BOD components and to digest soluble phosphorus with active sludge. A mixed outflow liquid 14 from the second step is let flow into a precipitating pool 3, and its overflow liquid 15 is let flow through a sand filter 4. Lightweight flocks retained in the filter 4 are exfoliated by backwashing water, and its part or whole is returned to the cell 1 or 2. On the other hand, the purified liquid 16 is drained as such or after being highly purified in succession.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing organic matter and phosphorus, such as domestic sewage, industrial wastewater, and similar organic wastewater, and particularly relates to an anaerobic-aerobic-activated sludge method. This is related to the improvement of biological dephosphorization technology.

In general, the anaerobic-aerobic activated sludge method refers to the inflow end of the raw solution in the aeration tank in conventional activated sludge facilities to an anaerobic state in which there is virtually no dissolved oxygen (Do) or nitrate or nitrite (NOX). zone (hereinafter referred to as the anaerobic tank), where the liquid to be treated and the returned sludge are mixed, and then this mixed liquid is led to the subsequent aerobic zone (hereinafter referred to as the aerobic tank). This technology involves aeration, followed by solid-liquid separation in a settling tank. The process configuration of the anaerobic-aerobic activated sludge method, which has such characteristics, produces activated sludge that has a higher phosphorus uptake capacity than the activated sludge produced by the standard activated sludge method, and removes pollutants such as BOD and SS. At the same time, most of the soluble phosphorus present in the stock solution can be absorbed into the activated sludge.

The inventors also conducted an experimental study using a pilot plant in which domestic sewage was treated at s M3/i per day. As long as the ratio of the amount of BOD (F) flowing into the aerobic tank and the amount of activated sludge (MLSS amount) (M) existing in the aerobic tank, that is, the F/M ratio, is maintained at 02 to 0.7 (7 days). It was confirmed that it was possible to obtain a treatment solution in which almost no soluble phosphorus was present in the treatment water, and also to remove BOD.

However, on the other hand, the inventors also discovered that the activated sludge produced by this single method exhibits specific behavior during gravity sedimentation, and that the treated liquid flowing out from the settling tank is therefore likely to become cloudy. In other words, most of the blocks of this activated sludge are more dense than those produced by the conventional activated sludge method, and have a settling rate of more than 50 M/day, but because of their poor cohesiveness, they do not easily settle during settling. It is not possible to capture the light flocs that exist around the heavy flocs. For this reason, although the returned sludge drawn from the bottom of the settling tank is so thick as to exceed 4.5%, the SSa degree of the overflow liquid is often 501n9.
Exceed /l.

The visibility will be 10 crrL or less. Due to this phenomenon, almost no soluble phosphorus is detected in the overflowing liquid.5- Even though the total phosphorus amount, including solid phosphorus, is measured, there is a large difference from the total phosphorus amount in the liquid to be treated. What is even more undesirable is that it becomes something without.

If the liquid to be treated is a diluted waste liquid such as domestic sewage that generates a small amount of surplus sludge per amount of treated liquid, if this type of SS outflow continues, it will eventually become impossible to maintain the required amount of activated sludge in the aerobic tank. As a result, the F,/'M ratio in the aerobic tank also exceeded the appropriate range.

Not only soluble phosphorus (even BOD) remains. To prevent this, the upward flow rate in the sedimentation tank must be made lower than the sedimentation rate of fine SS, but this requires a vast water area. The reality was that a sedimentation tank was required, and the facility was unsatisfactory due to the lack of feasibility due to the required area.

The present invention aims to solve these problems in the conventional anaerobic-aerobic activated sludge method, and the light flocs contained in the settling tank overflow of the anaerobic-aerobic activated sludge method are Sludge process The overflow of the anaerobic-aerobic activated sludge process was used at 360 M7 days, based on the fact that it is extremely sandy compared to the fine-grained SS contained in the treated water. Even when processed at overspeed, the amount of ss captured per P material is 12 to 9.
The purpose of this invention is to provide an effective processing method that is capable of removing 0 or more 88 characters.

In other words, the present invention passes the overflow from the settling tank of the anaerobic-aerobic activated sludge process to a sand filter, and at least part of the SS captured there is transferred to the anaerobic tank of the anaerobic-aerobic activated sludge process. It is characterized by returning the water to an aerobic tank. Through such operations, it is possible to obtain a clear treated liquid with low SS content and virtually no phosphorus (total phosphorus concentration of 0.3 μl or less), and it is also suitable for use with dilute waste liquids such as domestic sewage. However, the required amount of activated sludge can be easily maintained in the aerobic tank, thereby maintaining a stable and high rate of BOD.
removal can be achieved.

In addition, the sedimentation tank of the present invention does not require consideration for complete sedimentation separation of fine particulate SS, and has good sedimentation and concentration properties that are specifically produced by the anaerobic-aerobic activated sludge method. It is sufficient to have enough water area to sediment and separate activated sludge flocs, and even if a sand filter facility is included, the area required for solid-liquid separation is smaller than that of the conventional anaerobic-preferential method, which separates solid-liquid using only a sedimentation tank. Since it is smaller than the air activated sludge technology, it can be used in combination with a relatively small settling tank and sand filter.
As a solid-liquid separation method in the aerobic activated sludge process, it is extremely effective in terms of facility area and solid-liquid separation efficiency.

One embodiment of the method of the present invention will be described based on the drawings. In the first step, the liquid to be treated 11, which is an organic waste liquid such as domestic sewage, is led to the anaerobic tank 1 together with the sedimentation return sludge 12 and mixed by a stirrer 11'. will be processed. Activated sludge hydrolyzes the high molecular phosphorus compound (polyphosphoric acid) stored in its cells and releases it into the solution, and uses the energy obtained at this time to remove a portion of the BOD contained in the liquid to be treated. is taken into cells and becomes an intracellular stored organic matter. The scale of the anaerobic tank 1 in which these reactions in the first step are carried out varies depending on the composition and concentration C of the liquid to be treated (depending on the composition and concentration C of the liquid to be treated, but when domestic sewage is used as the liquid to be treated, the scale of the inflow of the liquid to be treated is 05 to 2.5 hours is enough.

The anaerobic tank effluent mixed liquid 13 in which soluble phosphorus has increased and -BOD has decreased in this way is led to the aerobic tank 2 which is partitioned in a continuous or communicating state. This aerobic tank 2 is aerated by supplying air 2'' or a similar oxygen-containing gas from an aeration diffuser 2'.The activated sludge contained in the mixed liquid 13 flowing out of the anaerobic tank is In the second step, the BOD components that cannot be ingested are ingested and oxidized and decomposed, and the organic matter stored in the cells is also oxidized and decomposed.

The activated sludge utilizes a part of the energy generated during the oxidative metabolism of organic matter to absorb soluble phosphorus present outside the cells into the cells, while also converting intracellular polymeric phosphorus compounds (PoIJ IJ Synthesize phosphoric acid). At this time, an amount of soluble phosphorus greater than that released in the anaerobic tank 1 is ingested, and the concentration of soluble phosphorus in the mixed liquid becomes lower than that of the liquid to be treated. 9- In order to completely remove soluble phosphorus, the P/BOD of the liquid to be treated must be
It is necessary that the daily average value of the ratio be 0.06 or less, and most domestic sewage satisfies this condition. In this case, B.O.
In order to complete the oxidative decomposition of D and the removal of soluble phosphorus, the VM ratio of the aerobic tank should be controlled within the range of 0.2 to 0.7 (7 days), preferably 0.3 to 0.5 (7 days). There is a need to.

In addition, F is the amount of BOD per day (kg-BOD/day) that the liquid to be treated brings into the entire system, and 1M is the amount of activated sludge (K-MLSS) expressed by IJLss present in the aerobic tank.
). If the F/M ratio is too low, the amount of surplus sludge generated will be too small compared to the amount of inflowing phosphorus, making it impossible to completely remove soluble phosphorus, and if the F/M ratio is too high, the rate of Theoretically, the oxidative decomposition of BOD and the uptake of soluble phosphorus will be incomplete, so the F/M ratio should be within the range mentioned above.This optimal F/M ratio is also controlled by water temperature, and in winter A low F/M value is preferred, and a high F/M value is preferred in the summer. In the conventional anaerobic-aerobic activated sludge method, a large amount of activated sludge is unavoidably discharged as light flocs contained in the sedimentation tank overflow, and the required F/
Although it becomes difficult to maintain the M value, in the method of the present invention, the light flocs of the precipitate/(12 bath flow liquid) are recovered in the sand l:i filter described later and directly recycled as backwash return sludge. Alternatively, since it is returned to the aerobic tank via the anaerobic tank, the required F/M ratio can be easily maintained. Thus, the aerobic tank effluent mixed liquid 1 with reduced BOD and soluble phosphorus produced in the aerobic tank 2
4 is sent to a settling tank 6, where it undergoes solid-liquid separation 1.

That is, only heavy flocs that are easily settled and separated are separated in the settling tank 3, and are returned to the anaerobic tank 1 as settled return sludge 12. These easily settled flocs constituting the third step are separated and precipitated/l! 2 overflow liquid 15
There is still a lot of activated sludge in the form of fine flocs,
Total BOD concentration including solid BOD and SS concentration of this liquid.

Although the solid phosphorus concentration is extremely high, this is not a big problem in the present invention, where this liquid is not used as the final treatment liquid. -11- The structure of the sedimentation tank 6 may be a cross-flow type equipped with a flight conveyor, but the clarifier type is preferable because it allows easy control of the amount of settled sludge in the sedimentation tank and the ability to obtain thick return sludge. A circular settling basin is preferred. The amount of overflow liquid relative to the water area of the sedimentation tank, that is, the water area load is the ML of the aerobic tank outflow mixture.
Although it varies depending on the SS concentration, it may be considerably higher than the standard activated sludge method or the conventional anaerobic-aerobic activated sludge method. For example, if the MLSS concentration of the aerobic tank effluent mixture is 2500-3
000 rn9/l, the sedimentation basin water area load is 4
It may be 0 m/day or more. In the conventional anaerobic-aerobic activated sludge method, which cannot eliminate light flocs from the settling tank overflow, the water area load on the settling tank is limited to 25 m/day.
This will result in a significant reduction in the scale of the facility.

The sedimentation tank overflow liquid 15 generated by separating the easily-sedimentable heavy flocs in the sedimentation tank 6 in this way is
' is sent to a sand filter 4 filled with sand. All of the structures that have been used in the past can be used for this sand filter, but
When the amount of liquid to be treated is large, such as in the case of domestic sewage treatment, a gravity type as in this embodiment is preferable to a pressure type. Further, an upward flow type may be used when the amount of liquid to be treated is stable, but a downward flow type as in this embodiment is preferable when there is a large fluctuation.

In addition, when the amount of liquid to be treated is small, a parallel flow type or moving bed type sand filter can also be used. The most important point in designing this sand filter is the selection of the grain size of the sand forming the center of the P material 4'.

For example, the light flocs contained in the sedimentation tank bath liquid 15 are solid substances that can be easily filtered through sand.

Effective diameter 05 ~ as used in conventional sand 1-pass technology
There is no need to use 071rnn fine sand as one material.

Relatively coarse sand with an effective diameter of about 0.9 to 2.0 mm may be used.

By selecting such f-materials, it is possible to secure an overspeed of 360 m/day or more, and even if the SS capture amount per f-material becomes 8 kg/1 or more without increasing the water head loss. It is possible to secure an SS capture rate of about 90 inches. In other words, the SS concentration in the sedimentation tank overflow is 5o'''v.
-13- Even if light flocs of about t are included, a treatment solution with an SS concentration of 3 m9/ or less can be obtained by backwashing about twice a day using a P material with a height of 1 m. The treated liquid 16 thus produced by removing light flocs from the sedimentation tank overflow is either discharged as is or undergoes further advanced treatment if necessary.

On the other hand, the light flocs retained in the sand filter 4.

During the backwashing process, it is peeled off from the f material 4' by backwashing water. All of this backwash wastewater, or a portion of it that contains a high concentration of SS, is returned to the aerobic tank 2 either directly as backwash return sludge 17 or via the anaerobic tank 1, and the F/M ratio there is adjusted to the required value. The fourth amount to be attributed as part of the sludge amount to be maintained below.
It is processed through a process. In this case, the backwash return sludge 17 may be sent directly to the anaerobic tank 1 or the aerobic tank 2, but it is more preferable to send it via the storage tank 5 in order to equalize the amount of water.

Note that when a large amount of light flocs is retained in the sand filter 4, the liquid in the filter becomes anaerobic -14= during one water flow process, and as a result, soluble phosphorus is released from the retained activated sludge. The concentration of soluble phosphorus in the treatment liquid 16 may be higher than that in the sedimentation tank overflow liquid 15. As a preventive measure, it is also effective to pre-aerate the sedimentation tank overflow liquid 15 with oxygen-containing gas, but if the type of sand filter is a gravity counterflow type, one material A method of venting oxygen-containing gas from the bottom is also effective.

Next, Examples and Comparative Examples of the present invention will be shown.

(Comparative Example) A treatment experiment using the conventional anaerobic-aerobic activated sludge method was conducted using domestic sewage discharged from a housing complex as the liquid to be treated. This experimental facility has an aerobic tank and an aerobic tank.

It consisted of a settling tank, and the specifications of each device were as shown in Table 1.

Table 1 Comparative example (conventional anaerobic-aerobic activated sludge method) experimental facility j□ -15- Using such a facility, the amount of liquid to be treated was 5.45 m/day,
Sedimentation tank return sludge flow rate 0.63 When treated for 7 days, 40 to 50 m9/l of SS (light activated sludge floc) was constantly washed away in the sedimentation tank overflow liquid.

Despite not discharging any excess sludge, the MLSS concentration in the anaerobic tank and aerobic tank was 85 o m971~11
K could only be maintained in the range of 00 m9/l (average 950 m9/7), and the F/M ratio of the aerobic tank was around 1.1 (7 days). The treatment results at this time are shown in Table 2.

Table 2 Treatment results of comparative example (Example-1) In view of such deterioration in treatment results, in order to recover light activated sludge flocs in the sedimentation tank overflow, the facilities in Table 1 and the facilities in Table 3 were installed. Equipped with a gravity counterflow type sand filter as shown,
Backwashing was performed at intervals of 16 hours using backwash water of 0 and 2 nl/7 of the sand 1 filter specifications of Examples 1 and 2 in Table 3, and the wastewater (backwash return sludge) was stored and used for preferential treatment. It was quantitatively returned to the air tank. As a result, the MLSS concentration in the aerobic tank gradually increased. After that, the MLSSi degree is 2100m9/l
When the sludge discharge from the sedimentation tank was controlled so that the F/M ratio of the aerobic tank was around 0.4 (7 days), the results were as shown in Table 4. Obtained processing results.

Table 4 Treatment Results of Example-1 (Example-2) When the sedimentation property of the activated sludge was investigated in Example-1, the 1 isokinetic sedimentation rate was as high as 45-/min, that is, 65 m/day. Therefore, among the facilities listed in Table 1, only the settling pond has a water volume of 0.1.
5&, it was replaced with a circular clarifier with a water area of 0.125 m''.This result.

Although the upward flow rate of the sedimentation tank was 46 m/day, the SS concentration of the sedimentation tank overflow was almost the same as in Example-1, and the operation of the sand filter was not affected in any way.

-18- (Example-3) In Example-1 and Example-2, as shown in Table 4, a slight increase in soluble phosphorus was observed in the sand filter.

On the other hand, when measuring the redox potential of the sand filtration solution, Eh-
-170ZV (-400771 with platinum-calomel electrode
V,). Therefore, the sand filter listed in Table 3 was replaced, and a perforated plate was installed under the bottom support bed, and 99% oxygen was passed through the perforated plate at a rate of 60 seconds/m/m/n every 30 minutes. A sand filter according to Table 5 was installed to supply gas.

Table 5 Sand filter specifications of Example 3 As a result, the oxidation-reduction potential of the sand 1 overtreated liquid is Eh = +3
20mV (+5[177ZV at platinum-force Romel electrode)
-19-, and the soluble phosphorus concentration of the sand filtration solution at that time is 005~o, o7'', and no increase in soluble phosphorus in the sand filter is observed at all.

1...Anaerobic tank, 2...Aerobic tank, 6...Sedimentation tank, 4
... sand filter, 5 ... storage tank, 11 ... liquid to be treated, 12 ... sedimentation return sludge, 16 ... effluent mixed liquid, 1
4... Effluent mixed liquid, 15... Overflow liquid, 16... Treated liquid, 17... Backwash return sludge - now''/reverse ↓)K.

Patent applicant Go Hatayama, patent attorney representing Ebara Infilco Co., Ltd. - Patent attorney Sen 1)
Minoru

Claims (1)

[Scope of Claims] 1. A first step of mixing the liquid to be treated and the sedimentation return sludge returned from the third step described below in an anaerobic state in which dissolved oxygen, nitric acid, and nitrous acid are substantially absent. and a second step of aerating the liquid mixture produced in the first step with an oxygen-containing gas. A third step in which the mixed liquid produced in the second step is separated by sedimentation and a small amount of the settled sludge (some of which is supplied to the first step as settled return sludge), and a settling tank treatment liquid in the third step is A method for treating organic wastewater, comprising a fourth step of performing sand filtration and returning at least a portion of the activated sludge captured by the sand filtration to the first step or the second step.2. The second step is the ratio of the daily BOD amount (lkcq-BOD/day) (F) to which the liquid to be treated is brought in and the activated sludge amount (ky-MLSS) σ) present in the second step. ~o, 7 (7 days), preferably 0.3-0.5 (
7 days). 6. The method according to claim 1 or 2, wherein in the third step, the upward flow rate in the settling tank is set to 40 m/day or more. 4. The fourth step is sand filtration using a gravity downward counterflow type sand filtration device filled with P material, and the treatment is carried out by aerating oxygen-containing gas from the bottom of the swamp material. , the method according to item 2 or 3. 5. The fourth step is performed using a sand filter, and the effective diameter of the sand filter is set to 09 to 2. [] The method according to claim 1, 2, 3, or 4, wherein one material is subjected to water flow treatment in the range of ms.