JPS58146495A - Treatment of organic waste liquid - Google Patents

Abstract

PURPOSE:To remove BOD, N and P at high rates from org. waste liquid by conducting only the nitrified liquid mixture to be conducted into a final settling basin into an oxygen enriching tank and subjecting the same to an oxygen enriching treatment then to solid-liquid sepn. in the final settling basin. CONSTITUTION:Liquid 11 to be treated contg. BOD, PO<3->4, NH<+>4, etc. is conducted into an anaeration tank 1, where the liquid is mixed with return sludge 17, and is anaerated. The anaerated liquid mixture 12 formed by said treatment is conducted to a denitrification tank 2, where the liquid is mixed with circulating liquid 18 contg. NO<->x fed from the terminal of a nitrification tank 3 to denitrify the liquid. The denitrified liquid mixture 13 formed by said treatment is conducted into the tank 3, where the liquid is aerated with the air 20 from air diffusion pipes 3' and is thus nitrified. Part of the nitrified liquid mixture 14 formed by the treatment is used as circulating liquid 18 and the rest is conducted into an oxygen enriching tank 4 where the liquid is aerated with the air 20 from an air diffusion pipe 4'. The oxygen enriched liquid mixture 15 is conducted to a final settling basin 5, where the liquid is separated to treated liquid 16 and settled activated sludge. The greater part of the sludge is used as return sludge 17 and the rest as excess sludge 19.

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 to a method for producing activated sludge with a high phosphorus content. This paper relates to an improvement of a circulating nitrification and dechambering method called the anaerobic-aerobic activated sludge method, which removes not only BOD and nitrogen but also phosphorus from organic wastewater.

In general, the modified cyclic nitrification and denitrification method is a biological treatment method developed in the Federation of South Africa around 1975. This is a technology that involves simply attaching an anaerobic tank in which neither PO nor NOx exists to the inflow end of the treated liquid and returned sludge in the nitrification-denitrification method, and stirring the treated liquid and returned sludge there for a fixed period of time before transferring the treated liquid and returned sludge to the denitrification tank KIL. Report (A, R, Mc Laren et al.
al: Effective Phosphorus
Removal from SewagebyBio
Logical Means l Wat8r 8.
)'-Vo12 Nn (1976)), this more simple ζ modification selectively produces activated sludge with a high phosphorus content, and can remove not only BOD and nitrogen but also phosphorus from organic wastewater with high efficiency. It is said that it can be removed by

In order to apply this technology to urban sewage treatment in Japan, the inventors conducted a follow-up experiment using domestic wastewater discharged from residential complexes as the liquid to be treated, and were able to confirm the effectiveness of the technology. At the same time, this experiment revealed that the BODil was 11 degrees lower and the nitrogen concentration was lower than that of the sewage in South Africa.
It has been found that it is inconvenient to apply this technology in its original form to Japan's sewage, which has a low OD/N ratio. is circulated back to the denitrification tank as a circulating fluid, and the NO contained in the circulating fluid is denitrified using the HOD of the treated fluid or activated sludge intracellular organic matter caused by it as a hydrogen donor. The advantage of this method is that it eliminates the need for chemical hydrogen donors such as methanol. If the circulating fluid contains a large amount of DO as well as NOx, the BOD of the treated fluid will increase.

The amount of NO7 that can be denitrified decreases as it is used for consumption.
The denitrification rate will also decrease. This does not become a problem when the liquid to be treated is waste liquid in which both OD and nitrogen are present in high concentrations, such as raw human waste, or sewage with a high BOD/N ratio, such as sewage in the Federation of South Africa. However, when the wastewater to be treated is wastewater that is generally dilute and has a low BOD/N ratio, such as sewage in Japan, this is a very big problem.To prevent this, at least the Do
It is customary to control this at a low level.

Even in additional experiments of the modified circulating nitrification and denitrification method conducted by the inventors, it was not possible to obtain a high nitrogen removal rate without such control, confirming the validity of this conventional technique. However, at the same time, it was also found that performing such sub-control of DO at the end of the nitrification tank in the modified circulating nitrification-denitrification method impairs phosphorus removal and the cleanliness of the treated solution. That is, when the DO at the end of the nitrification tank is controlled, when the nitrified mixed treated liquid flows into the final settling tank, the activated sludge contained therein immediately becomes anaerobic and begins to release the phosphorus held within the cells.

Therefore, the treatment liquid contains soluble phosphorus at a higher concentration than the soluble phosphorus contained in the nitrified mixed treatment liquid, and the phosphorus removal rate decreases accordingly. Also, although the causal relationship is not yet clear, such low Do control will reduce the SS of the processing liquid.
If the concentration is high in pine trees, the problem arises that the treatment solution becomes extremely cloudy.

An object of the present invention is to provide an improved cyclic nitrification-denitrification method that eliminates the trade-offs of these conventional modified cyclic nitrification-denitrification methods.

In the present invention, only the nitrified mixed liquid is led to the final settling tank.
The oxygen-enriched mixture is introduced into an oxygen enrichment tank that is exposed to air in a dynamic state where a higher concentration of Do is present, and the resulting oxygen-enriched mixed solution is sent to a final settling tank to form a solid-liquid. It is characterized by separate processing.

That is, the returned sludge and liquid to be treated from the final settling tank are led to an anaerobic tank for anaerobic treatment, and the anaerobically treated mixed liquid obtained there is led to a denitrification tank, where it is sent from the subsequent nitrification tank. The denitrification treatment is carried out by contacting and mixing with the circulating fluid containing NO7, and the denitrification-treated mixed liquid obtained therein is led to a nitrification tank exposed to oxygen-containing gas to carry out the nitrification treatment.

A part of the obtained nitrified mixed liquid is returned to the denitrification tank as a circulating liquid, and the remaining part is led to an oxygen enrichment tank where it is aerated with an oxygen-containing gas, and then subjected to final precipitation after being buried. This is a method for simultaneously removing BOD, nitrogen, and phosphorus from organic waste liquid, which is characterized by solid-liquid separation into a treated liquid sent to a pond and concentrated activated sludge for return.

One embodiment of the present invention will be described with reference to FIG.
The liquid to be treated 11 containing reducing nitrogen compounds such as OD, PO4, and NH4 is led to the anaerobic tank 1, and mixed with the returned sludge 17 by the stirrer 10 in a state where neither DO nor NOl is substantially present.

undergo anaerobic treatment. During this anaerobic treatment process, the activated sludge converts its intracellular phosphorus into pony and then releases it into the solution. Coupled with this phosphorus release, B present on the solution side
At least a portion of the OD is ingested into the activated sludge in a non-oxidative manner, where it is converted into intracellular organic matter and N, which is sent from the subsequent 6 terminals of the nitrification tank.
It is mixed with the circulating liquid 18 containing O; and undergoes denitrification treatment while being aerated with an oxygen-containing gas such as air 20 supplied from the diffuser 6'. In this denitrification treatment process, the activated sludge oxidizes the organic matter through a denitrification reaction using the intracellular organic matter and BOD remaining on the solution side as hydrogen donors, while converting NOf, which was sent together with the circulating fluid 18, into N2. At the same time as it is converted to Neo etc., at least a part of P07 present in the solution is taken into the cells and accumulated as intracellular phosphorus. The denitrified mixed liquid 13 generated in this way is transferred to air or a similar oxygen-containing gas 20 to the diffuser 5'.
It is guided to an aerated nitrification tank 6 supplied from the nitrification tank 6, where it undergoes nitrification treatment. In this nitrification process, NH: or an equivalent reducing nitrogen compound coexists with the activated sludge, and due to the nitrification action, NO'x (NOl or No. 1) is produced.
oxidized to In addition, in parallel with nitrification, activated sludge further oxidizes intracellular organic matter and solution-side BOD that could not be oxidized during the denitrification process, and conjugates with this to cause uningested solution-side P.
O;- is taken into cells and accumulated as intracellular phosphorus.

The nitrified mixed liquid thus generated is sent to the oxygen enrichment tank 4 instead of the final settling tank 5.

In this case, it is important to control the Do at the end of the nitrification tank 3, particularly in the vicinity where the circulating fluid 18 is taken out, to a low level within a range that does not adversely affect nitrification. The optimal DO control range when applying nature to urban sewage treatment is 0.2 to 0.8 ■/
However, if the liquid to be treated is waste liquid with a high BOD/N ratio or waste liquid of human waste with high concentrations of both BOD and N, the range is 0.2 to 1.8 m9/l TLC fraud can.

- This control may be performed manually, but it is easy if a DO meter 8 is installed in the path of the circulating fluid 18 as shown in the example in Fig. 2, and the ventilation amount regulator 9 is automatically activated by the instruction signal from the DO meter 8. can be automatically controlled.

The nitrified mixed liquid 14 flowing down into the oxygen enrichment tank 4 is further subjected to aeration treatment in an aerator 4' which releases an oxygen-containing gas 20. The purpose of this aeration treatment is to prevent anaerobic conditions in the final sedimentation tank, and specifically, by aerating at a high Do concentration, the intracellular organic matter remaining in the activated sludge is reduced. .

In this case, the DO concentration is insufficient at 2.0 ■/l, and 4.01
Since 1 to 9/l is sufficient, it is preferable to use more than that. The scale of this oxygen enrichment tank 4 should not be determined simply by the residence time, but should be determined based on the F/M ratio 1, which takes into account the strength of the liquid 11 to be treated and the activated sludge (MLSS) concentration of the mixed liquid. It should be determined as follows. Here, F is the BOD amount jkp-B loaded on this entire system per day.
OD/day], M is 1, f present in the oxygen enrichment tank 4
Activated sludge amount displayed as LSS (4-h<Lss
). Kokii tends to be able to take very high numbers, but still up to 7 kg-BOQ/kf'-m
r, s s It is preferable to limit it to x days. Note that the oxygen enrichment tank 4 and the nitrification tank 3 do not necessarily have to be separated from the nitrification tank 3; for example, the oxygen enrichment tank 4 and the nitrification tank 3 need not be separated from each other; for example, an aeration tank whose shape ensures a plug flow type and which can ensure DO'a degrees in each zone is used. If so, the nitrification tank 6 and the oxygen enrichment tank [4] may be a physically integrated aeration tank.

The oxygen-enriched mixed liquid, which contains a high concentration of DO and which has more stabilized activated sludge, generated under these conditions is led to the final settling tank 5, where the treated liquid is Solid-liquid separation is performed into 16 and precipitated activated sludge. Most of this settled activated sludge is sent to the aeration tank 1 as return sludge 17.

The remainder is discharged outside the system as surplus sludge 19.

Next, examples of the present invention and comparative examples are shown below.

(Comparative Example) A supplementary test was conducted using a modified conventional circulating nitrification-denitrification method shown in FIG. 1 using domestic wastewater discharged from an EM housing complex as the liquid to be treated. The specifications and flow conditions of this test facility are shown in the first column.

In the first experimental section, the nitrification tank terminal, that is, the fourth compartment D O
When operated at 4.5 MVl to 5.2 m9/l, excellent treatment results were obtained in terms of phosphorus removal and treatment liquid cleanliness. However, the amount of Do brought into the denitrification tank is 4
2%, NOx remained in the denitrified mixed liquid at all times, and the overall nitrogen removal rate remained at 64 cm (see Table 2).Table 2 Operating conditions and water quality analysis average of the first experimental area value (w
V't) Note: Denitrification solution and nitrification solution are analyzed by placing the mixed solution on top. Therefore, in the second and third experiment sections, 00 in the fourth compartment of the nitrification tank was set to 2.7 to 1.8 TlVt, 0, respectively.゜8~
The operation was controlled within the range of 0.2"Q/l. As a result, the lower the Do, the higher the nitrogen removal rate was obtained.

Phosphorus removal and treatment liquid equipment performance deteriorated due to back pressure. Above all,
A notable phenomenon is phosphorus leaching in the final settling basin. In other words, even if the Do in the fourth compartment of the nitrification tank was lowered, the dissolved PO4 concentration in the nitrified mixed solution did not change from that in the first experimental section, but the lower the Do, the higher the dissolved PO4 concentration in the treated solution. The difference from that of the nitrified mixed liquid was large (see Tables 3 and 4). Further, the SS concentration of the treated liquid was acceptable as secondary treated water up to the -2 experimental group, but became extremely high in the third experimental group. Since this SS had a high phosphorus content, the total phosphorus concentration of the treatment solution also increased accordingly.

Table 3 Operating conditions and water quality analysis average values for the 2nd experimental area Note) Denitrifying and nitrifying solutions are analyzed for the mixed liquid supernatant Table 4 Operating conditions and water quality analysis average values for the 3rd experimental area Note) Derooming liquid , the nitrifying solution was analyzed by placing the mixed solution above. In order to solve this trade-off of the Do control value at the terminal of the nitrifying tank, a treatment test of the method of the present invention corresponding to the example in FIG. 2 was carried out in the fourth section. This was carried out in the 5th experimental area.

In the 4th experimental area, the circulating fluid was directly taken out from the 4th compartment of the nitrifying cypress, and 15 t (apparent F.
/M ratio is equivalent to 6.6kf-BODA-ML88X days)
A cylindrical aeration tower was installed as an oxygen enrichment tank, and its DO concentration was controlled at 4.5 to 5.5 μ/l. However, as shown in Table 5.

The processing situation did not improve much. From this, in order to prevent phosphorus elution in the final sedimentation tank.

It is not enough to simply increase the Do concentration in the effluent mixture; it is necessary to stabilize the activated sludge at a high temperature of 11 degrees Celsius, which requires an oxygen enrichment tank of a certain size. It was judged.

(Example-2) Therefore, in the fifth experiment [3 compartments (0, 0,
47m') and the DO at its end (3rd @ Room J)
was controlled at 0.2 to 0.8119/l, and the circulating fluid was taken from there. Also, the 4th compartment of the former nitrification tank (0, 1
7m') will be used as an oxygen enrichment tank.

The concentration was controlled at 4.2-5.5'l'9/l. In the oxygen enrichment chamber at this time? The apparent F/M ratio is 0.6'f-
Corresponds to BOD/J-MLSSX day. Tables 5 and 6
As shown in the table, the treatment status was satisfactory in terms of all water items.

Table 5 Operating conditions and water quality analysis average values (my
7t) Table 6 Operating conditions and water quality analysis average value (rIVt) of the 5th experimental area The present invention can solve the conventional problems in the conventional canned-aerobic activated sludge method, - The soluble phosphorus contained in the treated water can be greatly reduced, the phosphorus removal rate can be significantly improved, and the SS concentration can also be lowered.
Less S? * It is possible to obtain a processing solution that is vibrant and substantially free of phosphorus (total phosphorus concentration of 0.3 mm/l or less).

Even for dilute waste liquids such as domestic sewage.

The activated septic equipment required for the aerobic tank can be easily maintained.

As a result, it is possible to achieve a stable and high rate of BOD removal, and there is no need to consider complete sedimentation separation for fine particulate SS. It is extremely effective in terms of solid-liquid separation efficiency.

[Brief explanation of the drawing]

Figure 1 is a flow sheet for the conventional cyclic nitrification process;
The figure is a flow sheet of the method of the present invention. 1... air tank, 2... denitrification rosewood, 6... nitrification tank,
4...Oxygen enrichment tank, 5...Final sedimentation tank, 6,7...
- Circulation pump, 8... Do meter, 9... Aeration amount regulator, 10... Stirrer, 11... Liquid to be treated, 12.
1.5.14.15...Mixed liquid, 16...Treatment liquid 1
7...Return sludge, 18...Circulating liquid, 1ν...Excess sludge, 20...Oxygen-containing gas.

Claims (1)

[Claims] 1. The sludge returned from the final settling tank and the liquid to be treated are mixed and treated under an aerobic condition, and the anaerobically treated mixed liquid is
In a device that performs denitrification treatment by contacting and mixing with a nitrification circulating liquid containing Ox, the nuclear denitrified mixed liquid is nitrified while being aerated with oxygen-containing gas, and a part of the nitrified mixed liquid is transferred to the circulating liquid. It is then returned to the denitrification process. A method for treating an organic waste liquid, which comprises carrying out an oxygen enrichment treatment while aerating the remainder with an oxygen-containing gas, leading it to the final settling tank, and performing solid-liquid separation into a treated liquid and concentrated activated sludge for return. 2. The treatment method according to claim 1, wherein the oxygen enrichment treatment step is performed by controlling the amount of DO to 4.0 or more. 6. The oxygen enrichment treatment step is loaded per day with 6 HO
Dt (kf-BOD/day) (F) Amount of activated sludge present in the oxygen enrichment treatment process (1w-uLss) (M)
The treatment method according to claim 1 or 2, wherein the treatment is carried out by controlling the k ratio to 7 kg-B ODA "MLSS · days or less. 4. The nitrification treatment step comprises: The process is carried out in a nitrification tank where air is removed, and the end of the nitrification tank is
A processing method according to at least one of claims 1 to 3, wherein the processing is carried out under kC control in the range of 08 to /l.