JPS59199098A - Treatment of organic filthy water - Google Patents

Abstract

PURPOSE:To reduce BOD, nitrogen and phosphorus simultaneously by providing a biological filter bed to at least a part of the anaerobic zone in a reaction system comprising an aerobic zone and an anaerobic zone and introducing org. filthy water to the anaerobic zone and aerobic zone repeatedly. CONSTITUTION:Organic filthy water 57 is introduced into an anaerobic tank 51 held in an anaerobic zone and is treated with anaerobic bacteria deposited on a filter medium 56. The slurry mixture treated in the anaerobic tank 51 is treated in an aerobic tank 52 held in an aerobic zone and a part of the slurry mixture is returned to the anaerobic tank 51 through a return pipe 54, and the rest is separated to liquid and solid in a settling tank 53 and a part of the separated sludge is returned to the anaerobic tank 51. Although suspended organisms can exist in the anerobic tank 51 and the aerobic tank 52 where the sludge mixture circulates, the organisms are restricted as preferential species to aerobic bacteria and facultative anaerobic bacteria. The BOD is reduced by both anaerobic reaction and aerobic reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for biologically removing BOD, nitrogen, and phosphorus from organic wastewater such as sewage and human waste.

This type of wastewater contains organic pollutants that are often measured and displayed as BOD, as well as nitrogen and phosphorus, which are substances that cause eutrophication of closed water bodies. Biological treatment methods play an important role in removing these pollutants.

For example, as biological treatment methods for removing BOD, activated sludge method, lagoon method, watering hearth method, two rotating disk method, etc. have been widely used.

The following methods are also available for biologically processing nitrogen. In the first step, this method converts ammonia nitrogen (NH4+-N) in wastewater into nitrite nitrogen (NO2) by the action of nitrifying bacteria under aerobic conditions.
--N), oxidizes to nitrate nitrogen (NO3--N). This reaction is a so-called nitrification reaction and is expressed as follows.

NH4" +1.502→NO□-+ H2o + 2
H+・・・・・・・・・(1) No ”-+ 0.50
−+ NO3−・・・・・・・−・・・・(2)2 Formula (1), (2) NH4−+202→No, −+H20+ 2H+ ・
・・・・・・・・・・・・(3) Next, in the second stage, No.
--N, NO3--N, by the action of denitrifying bacteria under anaerobic conditions, nitrogen power (N
2) and dissipate the N2 into the atmosphere to complete the denitrification treatment of wastewater. This reaction is called a denitrification reaction and is expressed by the equation below.

2NO2-l-6H-+N2↑+2H20+ 20H-
... Concave curve ... (4) 2NO3'-+10H-+ N2↑
+4H20+ 20H-・Track...Track (5) With the nitrification reaction, Pll decreases as shown in equations (1) and (3). To prevent this, an alkaline agent is added as necessary in the nitrification step. In addition, in the denitrification reaction, formula (4)
, As shown in (5), a cyclic agent is required. For this purpose, a necessary amount of an organic carbon source such as methanol is added. In the denitrification process, the pH increases.

Furthermore, methods for biologically removing phosphorus have also been developed.

When treating sewage containing BOD and phosphorus with activated sludge, the method of death,
Sludge with a high phosphorus content is taken out of the system as surplus sludge, thereby removing phosphorus from the wastewater. However, the details of this biological phosphorus removal mechanism are currently unknown.

As described above, it is possible to remove various pollutants by utilizing biological effects, but the conventional treatment flow has some drawbacks.

FIG. 1 is a flow sheet diagram of a conventional biological treatment method for removing BOD and nitrogen. In this method, primary treated water 1 is treated with an activated sludge device consisting of an aeration tank 2 and a settling tank 3, and BOD is first removed. This treated water 4 is led to an activated sludge system consisting of an aeration tank 5 and a settling tank 6, where it is subjected to nitrification treatment, and then to a denitrification tank 7. Re-aeration tank (deaeration tank) 8,
A device consisting of a settling tank 9 is used to remove the room, thereby obtaining nitrogen-removed treated water 10. If necessary, add 1 part of an alkali agent in the nitrification process and 1 part of an organic carbon source such as methanol in the denitrification process.
Add 2.

According to this method, since the sludge is divided according to function, there are many operational factors such as return ratio, aeration air volume, and amount of sludge drawn out, and their positions are clear. This waste, water temperature fluctuation,
Even if changes in water quality or amount occur, operational responses to these changes are easy and stable treated water can be obtained.

However, on the other hand, the equipment cost is high due to the large number of equipment, and the amount of methanol added and IJII in the denitrification process is required to be approximately 2.5 times or more than No3--N to be denitrified. , has the disadvantage of high cost.

FIG. 2 is another example of a conventional method for removing BOD and nitrogen. In this method, two volumes of the primary treated water are put into the first denitrification tank 22 and then put into the nitrification tank 23, a part of the sludge mixture 24 is returned to the first denitrification tank 22, and the sludge mixture is The sludge is put into the second denitrification tank 25, subjected to denitrification treatment using methanol 26 as an organic carbon source, and further put into the sedimentation tank 28 via the re-aeration tank 27, and a part of this sludge 29 is transferred to the first denitrification tank 2.
2. This is the method of sending it back. That is, this method circulates the sludge mixture between the first denitrification tank 22 and the nitrification tank 23,
Denitrification is caused in the first denitrification tank 22 using BOD in the primary treated water, and for the water that cannot be completely denitrified here, methanol is supplementarily added in the second denitrification tank 25 for denitrification. This is a way to complete nitrogen.

This method has the advantage that methanol costs can be reduced as compared to the method shown in FIG. 1, and the number of facilities can also be reduced.

However, since nitrifying bacteria and denitrifying bacteria, which have completely different growth rates and actions, are cultured and mixed under exactly the same environmental conditions, it is difficult to manage operations in response to external conditions such as drops in water temperature and fluctuations in raw water quality. This is a difficult situation. Moreover, as the sludge is mixed and diluted with each other, both the nitrification rate and denitrification rate per unit amount of mixed sludge are small.For this reason, the volumes of both the nitrification tank and denitrification tank must be increased. There is a problem.

Figure 3 shows one of the conventional methods for removing BOD and phosphorus.
This is an example. In this method, primary treated water 31 and returned sludge 32 are brought into a contact reaction in an anaerobic tank 33 to achieve anaerobic decomposition of BOD and elution of phosphorus from the sludge. After that,
The sludge mixture is led to the aerobic tank 34 to aerobically decompose BOD and incorporate phosphorus into the sludge. The sludge mixture is then led to a settling tank 35 for solid-liquid separation to remove BOD and phosphorus to obtain treated water 36 and separated sludge 37.

This method can remove BOD and phosphorus from wastewater using a relatively simple device without using any agents such as flocculants. However, this method has a weak nitrogen removal function.

The method shown in FIG. 4 is an improvement on the processing method shown in FIG. 3, and is intended to remove BOD1 phosphorus and nitrogen. The method shown in FIG. 4 differs from the method shown in FIG. 3 in that a portion 38 of the sludge mixture discharged from the aerobic phase 34 is returned to the anaerobic tank 33. That is, this return helps the stirring and mixing of the anaerobic tank 33 and the aerobic tank 34, prevents short-circuit flow, increases the pH resulting from the denitrification reaction [see equations (4) and (5)], and reduces nitrification. It is possible to average out and neutralize the decrease in shear as a result of the reaction [see formulas (1) and (3)], thereby promoting the progress of anaerobic and aerobic reactions.

According to this method, BOD, nitrogen, and phosphorus can be removed from wastewater using a relatively simple device without using chemicals such as methanol or flocculants.

However, in this method as well, as in the conventional method shown in FIGS. 2 and 3, bacteria having different functions and properties are all used in a suspended mixed state, and therefore the operation is technically difficult. i.e. water temperature, water quality.

When the amount of water fluctuates, in the activated sludge treatment method, the return ratio is adjusted to control the sludge concentration in the reaction tank so that the load on the sludge falls within the processing capacity of the sludge. This is the basis of driving response.

In this case, from the viewpoint of reducing the power cost of the return pump, it is desirable to set the necessary minimum return ratio. However, the sludge in this method contains BOD removing bacteria, nitrifying bacteria, denitrifying bacteria, and dephosphorizing bacteria, and since these bacteria have different growth rates, reaction rates, growth conditions, etc., water temperature, water quality, When the amount of water changes, the abundance ratio of each microorganism in the mixed sludge also changes. However, the abundance ratio and activity of various microorganisms,
Since it is difficult to grasp the SS concentration (MLSS) of the sludge mixture in a short time, as in the conventional activated sludge method,
) or the activated sludge sedimentation rate (S3o) as an indicator for adjusting the load amount remains problematic. One! Since the composition of mixed sludge and the treatment capacity of that sludge vary greatly depending on external conditions, the treatment activity per unit amount of sludge also varies, making it technically difficult to adjust the amount of sludge in the tank to accommodate treatment movements. There is no escaping the drawback of being.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to use a simple device without using chemicals such as methanol, p'(141n agent, or flocculant).
The present invention provides a method for treating organic wastewater that can simultaneously remove BOD, nitrate, and phosphorus from wastewater and that is easy to operate and manage.

That is, the present invention provides a bio-fixing door material in at least a part of the anaerobic region of a reaction system that has formed an anaerobic region and an aerobic region, and repeatedly passes organic wastewater to the anaerobic region and the aerobic region. Denitrification, BOD removal, and phosphorus removal are performed using the sessile organisms that adhere to the P material and the suspended organisms exposed to the anaerobic and aerobic areas, and then solid-liquid separation is performed to form the separated sludge. It is characterized by returning the sample to the anaerobic area.

The present invention will be described below with reference to illustrative embodiments.

FIG. 5 is a flow sheet diagram showing an example of an organic wastewater treatment apparatus used in the method of the present invention.

This device has an anaerobic tank 51, an aerobic tank 52, and a sedimentation tank 53 arranged in this order, and a return pipe 54 is connected from the bottom of the sedimentation tank 53 to the inlet of the anaerobic tank 51, and from the outlet of the aerobic tank 52 to the sedimentation tank 53. Anaerobic tank 51
A return pipe line 55 is connected to the inlet of the pipe. This disgusting loquat・5
1 is provided with a biofixing reactor material 56 inside. This p
The material 56 is filled with wastewater and sludge so that they can freely flow in the vertical direction, horizontal direction, or both directions. As the cutting material 56, cylindrical furnace materials such as honeycomb chives, crushed stone, gravel, sand, granular or block materials such as Raschig rings, plate-shaped furnace materials such as plastic plates, etc. can be used. Although these furnace materials 56 can be installed in a fixed type or a movable type, a fixed type is preferable from the viewpoint of reducing operating power costs. It is preferable to use a movable type from the viewpoint of measuring. However, during water flow treatment operation, it is important to avoid excessive rubbing of the reactor materials against each other in order to prevent the attached biofilm from mechanically peeling off and failing to perform biological functions. desirable. In case a biological film develops excessively on the tear material and the flow of the sewage and sludge mixture is obstructed, pumps, piping, etc. are installed so that the anaerobic tank 51 can be cleaned with air, water, or both. It is practically safe to be prepared. In order to assist the stirring and mixing in the anaerobic tank 51,
It is also possible to use a method in which the inside of the anaerobic tank 51 is stirred using a stirrer, a pump, or the like.

According to the method of the present invention, the organic wastewater 57 first flows into the anaerobic tank 5 maintained in an anaerobic region.

Living organisms adhere to the furnace material 56 in the anaerobic tank 51. Since these sessile organisms are fixed in the anaerobic tank 51 and constantly exposed to anaerobic conditions, the dominant species are limited to facultative anaerobes and obligate anaerobes, and nitrifying bacteria cannot live under constant anaerobic conditions. It does not include aerobic bacteria such as This sessile organism becomes the main body of the denitrification reaction shown in equations (4) and (5) above. In this case, N02--N in the denitrification reaction
.

No. 3-N is the nitrification reaction in the aerobic tank 52 [formula (1)
, (2), (3)) and is supplied to the anaerobic tank 51 through return pipes 54 and 55.

In addition, the organic carbon source used in the denitrification reaction is the primary treated water 57
Use the BOD included in. In addition, sessile organisms are BOD
It also acts as the main body of the anaerobic removal reaction.

The sludge mixture treated in the anaerobic tank 51 is treated in the aerobic tank 52 maintained in an aerobic region, a part of which is returned to the anaerobic tank 51 through the return pipe 54, and the remainder is sent to the settling tank 53. Solid-liquid separation is performed, and a portion of the separated sludge is returned to the anaerobic tank 51. In this way, floating organisms are present in the anaerobic tank 51 and the aerobic tank 52 in which the sludge mixture circulates.

These planktonic organisms are repeatedly exposed to aerobic and anaerobic conditions for a relatively short period of several hours, so the dominant species are limited to aerobic bacteria and facultative anaerobes. does not include obligate anaerobes that are killed by In the case of aerobic bacteria, repeated exposure to aerobic and anaerobic conditions is not the optimal habitat condition. However, by making the residence time under aerobic conditions equal to the residence time under anaerobic conditions, the BOD load on suspended sludge and NI
(By appropriately adjusting the 4+-N load to provide growth conditions for aerobic bacteria, it is possible to maintain aerobic bacteria as the dominant species in suspended sludge.

The floating organisms form and maintain an anaerobic state in the anaerobic tank 51 based on their oxygen consumption ability, and become the main agents of the reaction that anaerobically removes BOD and the denitrification reaction. B is still in the aerobic tank 52.
Main body of aerobic OD removal reaction and nitrification reaction. Furthermore, by circulating between the anaerobic tank 51 and the aerobic tank 52,
Repeated exposure to anaerobic and aerobic conditions acts to absorb phosphorus from wastewater.

By circulating and returning the sludge mixture through the return pipes 54 and 55, mixing and agitation are strengthened, and uniformity of PL (pl) and promotion of anaerobic and aerobic reactions are achieved.

After reacting in this manner, the sludge mixture is introduced into the total settling tank 53, and treated water 58 from which BOD, nitrogen and phosphorus have been removed can be obtained as solid-liquid separated supernatant water.

A part of the separated sludge is returned to the anaerobic tank 5 through the return pipe 54, and the remaining part of the separated sludge is discharged as surplus sludge 59 to the outside of the system.

In this method, however, BOD is removed by both anaerobic and aerobic reactions. In this case B.O.
The aerobic removal reaction rate of D may be different from the anaerobic removal reaction rate, but in this method, the residence time of the aerobic Fi 52 is usually set to be the same as the residence time of the anaerobic tank 51. be.

Therefore, the floating organisms in the aerobic tank 52 play a leading role in BOD removal in this method, and the sessile organisms and floating organisms in the anaerobic tank 51 play complementary roles.

The nitrification reaction is an aerobic reaction, and is carried out by the action of suspended organisms in the aerobic tank 52.

The denitrification reaction is an anaerobic reaction, and is performed by the action of solid organisms and suspended organisms in the anaerobic tank 51. The biomass of sessile organisms is stable, and the biota is still limited to anaerobic bacteria, so they perform a stable denitrification function. Since suspended organisms contain facultative anaerobes, denitrification reactions occur due to their action, but the abundance ratio of the suspended biota, that is, aerobic bacteria and facultative anaerobes, is different from that of the raw wastewater. Varies depending on water quality, etc. For this reason, the denitrification function per unit amount of suspended organisms also changes. However, the amount of suspended biomass is
It has the advantage that it can be read out by manipulating the return ratio through 4. In other words, sessile organisms and planktonic organisms act in a mutually complementary manner to obtain stable denitrification-treated water while external conditions such as water temperature, water quality, and eternity fluctuate.

The main body of the dephosphorization reaction is floating organisms, which take in phosphorus and multiply while circulating between the anaerobic tank 51 and the aerobic tank 52.

As described above, this method effectively combines the functions of sessile organisms and planktonic organisms to obtain treated water that is stable in BOD, nitrogen, and phosphorus removal even under fluctuating external conditions.

When designing the equipment, it is preferable to fill the furnace materials of the anaerobic tank so that the surface area load of No-N is 0.1 g/m2・day, and the gaps between the furnace materials should be filled with sludge mixture. The angle is preferably 10° or more to facilitate the flow of liquid.

The sludge load in the aerobic tank 52 is 0.2 to 9 BOD/
Yu・MLSS・Nittori, o, 1kg・NH4-N7kg
・It is preferable to use MLSS/Nichido.

Regarding phosphorus removal, the residence time for the amount of inflow primary treated water is 1.0 hours or more in the anaerobic tank 51 and 3.0 hours or more in the aerobic tank 52.
It is preferable to set it as 0 hours or more. In this case, the amount of phosphorus removed is 40 to 50 m9T-P/
g-MLSS can be expected.

The water area load of the sedimentation tank is preferably 20 to 30 m3/m2°day. Depending on the quality of the raw water, the anaerobic treatment time of the denitrification tank and
The anaerobic treatment time for dephosphorization may not match. If more denitrification time is required, this can be solved by allowing more time for dephosphorization treatment, increasing the overall volume of the anaerobic tank 51, and increasing the residence time. If it is possible to use less water, as shown in FIG.
It is also possible to fill either one with the furnace material 56. In this case, the outlets of the return lines 54 and 55 can be the inlet of the first stage anaerobic tank 511 or the inlet of the second stage 512 of the anaerobic tank, or both. Anaerobic right second stage 51
2 is air diffusion to measure contact between sewage and sludge and prevent settling of sludge, 71? It is preferable to use pumping, stirring or mechanical stirring.

As a modification of the method shown in FIG. 5, there is a method in which the primary treated water is dispensed into an aerobic tank 52, as shown in FIG. Furthermore, as a modification of the method shown in Fig. 6, as shown in Fig. 8,
It is also possible to dispense the primary treated water into the second stage anaerobic tank 512, the aerobic tank 52, or both, and these modified methods are effective when the BOD is extremely high due to the composition of the raw water. be.

Furthermore, as a modification of FIGS. 5 and 9,
As shown in the figure and FIG. 10, it is also possible to return part of the treated water 58 to the anaerobic tank 51, the first stage 5111 of the anaerobic tank, the second stage 512 of the anaerobic tank, or both. .

This intensifies the agitation and mixing of the entire system.

Therefore, each pollutant removal reaction is carried out thoroughly, which is useful for improving the pollutant removal rate, and also helps to hydraulically absorb load fluctuations.

Next, an example in which organic sewage treatment of the present invention was carried out will be described based on the flows shown in FIGS. 5 and 9.

In this example, school lunch center wastewater was used as raw wastewater. Its composition is shown in Table 1. As a conventional method for comparison, experiments using the flows shown in FIGS. 2 and 4 were also conducted.

Table 1 As a result, as is clear from Table 1, the quality of the treated water obtained was extremely low in BOD, nitrogen, and phosphorus concentrations compared to treated water obtained by conventional methods. It was excellent.

As is clear from the above explanation, according to the method of the present invention,
BOD, nitrogen,
Phosphorus can be removed at the same time. Moreover, in this method, sessile organisms and planktonic organisms are used in combination according to their functions, and the composition and action of each sludge are clear, so it is easy to adapt to fluctuations in water temperature, water quality, load amount, etc. It is possible to handle operation management.

[Brief explanation of the drawing]

1 to 4 are flow sheet diagrams showing different conventional methods for treating organic sewage, FIG. 5 is an explanatory diagram showing an example of the organic sewage treatment flow used in the method of the present invention, and FIG. 10 through 10 are explanatory diagrams showing other different examples of the organic wastewater treatment flow used in the method of the present invention. 51... Anaerobic tank, 511... Anaerobic tank first stage, 512
...Anaerobic tank second stage, 52...Aerobic tank, 53...Sedimentation tank, 5''4...Return pipe line, 55...Return pipe line, 5
6... Biofouling ν material, 57... Primary treated water, 58.
...BOD, nitrogen, phosphorus removed treated water, 59...excess sludge.

Claims (2)

[Claims] (1) A biofixing reactor material is provided in at least part of the anaerobic zone of the reaction system that has formed an anaerobic zone and an aerobic zone, and organic wastewater is repeatedly introduced into the anaerobic zone and aerobic zone. Then, denitrification, BOD removal, and phosphorus removal are performed using sessile organisms fixed on the furnace material and floating organisms exposed to the anaerobic and aerobic areas. After that, solid-liquid separation is performed to separate a part of the separated sludge. A method for treating organic wastewater characterized by returning it to an anaerobic area. (2) A method for treating organic sewage according to claim 1, characterized in that a part of the solid-liquid separated water is returned to an anaerobic region.