JPS6038095A - Treatment of organic sewage - Google Patents

Abstract

PURPOSE:To simultaneously remove BOD, nitrogen and phosphorus in sewage, by a method wherein org. sewage is subjected to aerobic reaction due to a fixed microorganism and a floated microorganism and guided to a solid-liquid separation apparatus to obtain treated water while a part of the separated sludge is returned to an anaerobic region. CONSTITUTION:After org. sewage 55 and sludge are introduced into an anaerobic tank 51 to be subjected to anaerobic reaction due to a floated microorganism, the treated sewage is introduced into an aerobic tank 52 to receive the supply of oxygen and aerobic reaction is performed by the microorganism fixed to a filter material 56 and the floated microorganism in the aerobic tank 52. Subsequently, the treated sewage is guided to a precipitation tank 53 to obtain treated water 57 and a part of the separated sludge 54 is returned to the anaerobic tank 51. In this case, it is desirable that the contact of org. sludge 55 and sludge are accelerated in the anaerobic tank 51 and both of them are stirred and mixed by a stirrer or a pump in order to prevent sludge precipitation. As the filter material 56 for holding a biological membrane, a granular material or a honeycomb tube can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for treating organic wastewater, particularly methanol,
? ) (This is a treatment method that can simultaneously remove BOD, nitrogen, and phosphorus from wastewater with a simple device without using chemicals such as conditioners or coagulants, and which is necessarily easy to operate and manage.) .

Measured as BOD in waste water such as sewage and human waste.

It contains organic pollutants that are often displayed, as well as nitrogen and phosphorus, which are substances that cause eutrophication in closed water bodies.

Biological treatment methods play an important role in removing these pollutants.

Regarding the removal of BOD, biological treatment methods such as the activated sludge method, the ladder method, the sprinkled P bed method, and the double rotating disk method have been widely used.

For nitrogen removal, there are biological treatment methods. This biological denitrification reaction is a two-step reaction. That is,
The first stage is due to the action of nitrifying bacteria under aerobic conditions.
Ammonia nitrogen (Nf (4”-N) in wastewater is converted to nitrite nitrogen < No2-N) and nitrate nitrogen (No3”-N)
) is the so-called nitrification process. This reaction can be expressed as follows.

NH4" + 1.50., →NO2-+ 1 (20+
2) I+ ... (1) No −+ 0.502 → No
3- ・・・・・・・・・(2) Formula (1), (2)
From NH4++202→NO3-+■I20+2H+...
...(3) The following @2 stages are No2-N, N05
-N is reduced to nitrogen gas (N2) by the action of denitrifying bacteria under anaerobic conditions, and this N2 is released into the atmosphere to complete the denitrification treatment of wastewater, and is called the denitrification process. It can be shown as the following formula.

2NO-+ 6H-+N↑+2H,,O+20H-...
...(4)2 2 NO3-+ l0H-+N2↑+4 N20 +
20H''' (5) As the nitrification reaction occurs, the pH decreases as shown in equations (1) and (3), so an alkali agent is added as necessary in the nitrification process. In the denitrification reaction, since a reducing agent is required as shown in equations (4) and (5), a necessary amount of an organic carbon source such as methanol is added. In the denitrification process, the pH increases.

Methods for biologically removing phosphorus have also been developed. When sewage containing BOD and phosphorus is treated with activated sludge, the sludge is repeatedly exposed to anaerobic and aerobic conditions to enhance the uptake of phosphorus into the sludge. Phosphorus in wastewater is removed by removing sludge with a large amount of phosphorus from the system as surplus sludge. 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, and there are various conventional treatment flows.

Figure 1 shows a conventional 7
0-sheet diagram. This method c. Treats the primary treated water 1 with an activated sludge device consisting of an aeration tank 2, a settling tank 3, and 1.
First, BOD is 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. Denitrification treatment is carried out in a device consisting of a settling tank 9,
Thus, nitrogen-removed treated water 10 is obtained. If necessary, an alkali agent 11 is added in the nitrification step, and an organic carbon source 12f such as methanol is added in the denitrification step.

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. For this reason, water temperature fluctuations,
Even if changes in water quality or quantity occur, it is easy to respond to these changes, 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 in the denitrification process is required to be approximately 2.5 times or more than the amount of No and -N to be denitrified, resulting in high costs. There are drawbacks.

FIG. 2 is another conventional method for removing BOD and nitrogen. In this method, the primary treated water 21f is put into the first denitrification tank 22, then into the nitrification tank 23, and a part of the sludge mixture 24f is put into the nitrification tank 23.
f: While returning to the first denitrification tank 22, the sludge mixture is put into the second denitrification tank 25, denitrified using methanol 26 as an organic carbon source, and further passed through the re-aeration tank 27 to the sedimentation shaft 28.
A portion 29 of this sludge is returned to the first denitrification tank 22. That is, in this method, the first denitrification tank 2
The sludge mixture is circulated between the sludge tank 2 and the nitrification tank 23, and denitrification is caused in the first denitrification tank 22 using BOD in the primary treated water. is the second
This is a method in which methanol is supplementarily added in the denitrification tank 25 to complete denitrification.

This method has the advantage that methanol costs can be reduced compared to the method shown in FIG. 1, and the number of equipment can also be reduced. Since nitrifying bacteria and denitrifying bacteria, which have completely different effects such as 1 growth rate and 9 action, are cultured and mixed under exactly the same environmental conditions, operation management that responds to external conditions such as a drop in water temperature and fluctuations in raw water quality is possible. is technically difficult.

Moreover, as the sludge is mixed and diluted with each other, both the nitrification rate and the denitrification rate per unit amount of mixed sludge become small, resulting in the problem that the volumes of both the nitrification tank and the denitrification tank must be increased. There is.

FIG. 3 is an example of a conventional method for removing BOD and phosphorus. In this method, primary treated water 31 and returned sludge 32 are caused to contact and react in an anaerobic tank 33 to achieve anaerobic decomposition of BOD and elution of phosphorus from the sludge. Thereafter, 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 obtain treated water 36 from which BOD and phosphorus have been removed 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, the nitrogen removal capacity in this method is low.

BOD by improving the processing method in Fig. 3.

There is a method shown in FIG. 4 for the purpose of removing phosphorus and nitrogen. This method differs from the method shown in FIG. 3 in that a portion 38 of the sludge mixture discharged from the aerobic tank 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, and further increases the pH caused by the denitrification reaction [Equation (4)
), (5)] and the decrease in pif resulting from the nitrification reaction (see formulas (1), (3)), thereby promoting the progress of anaerobic and aerobic reactions. can do.

Therefore, with this method, the BOD of wastewater can be reduced using relatively simple equipment without using chemicals such as methanol or coagulants.
, nitrogen, and phosphorus can be removed.

However, in this method, as in the conventional method shown in Figures 2 and 3, all bacteria with different functions and properties are used in a suspended state, making operation technically difficult. be. i.e. water temperature, water quality.

When the amount of water fluctuates, in the activated sludge treatment method, it is best to control the sludge concentration in the reaction tank by adjusting all return holes so that the load on the sludge falls within the range of the sludge's processing capacity. This is the basics of driving support. in this case,
It is desirable to set the necessary minimum return ratio from the viewpoint of reducing the electricity cost of the return pump. However, the sludge in this state contains BOD removing bacteria, nitrifying bacteria, denitrifying bacteria, and dephosphorizing bacteria, and these have different growth rates, reaction rates, growth conditions, etc. Therefore, when the water temperature, water quality, water amount, etc. change, the abundance ratio of each microorganism in the mixed sludge also changes. However, since it is difficult to determine the abundance ratio and activity of various microorganisms in a short time, it is difficult to determine the abundance ratio and activity of various microorganisms in a short time. Problems remain in applying an index such as sedimentation rate (SV!1G) as an index for adjusting the total load amount. In other words, 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 to accommodate treatment operations. There is no escaping the drawback of being.

The present invention has been made in view of the above circumstances, and its purpose is to use a relatively simple device without using methanol, a regulator, a coagulant, or other chemicals.
BOD, nitrogen in wastewater.

Shiriki 1 provides a method for treating organic wastewater that can remove phosphorus at the same time and is easy to operate and manage.

That is, the method for treating organic sewage according to the present invention involves introducing organic sewage into an anaerobic area to cause an anaerobic reaction by suspended organisms, and then introducing it into an aerobic area provided with biofixation reactor material. It is characterized by supplying oxygen to cause an aerobic reaction by sessile and planktonic organisms, and then guiding it to a solid-liquid separator to obtain treated water, and returning a portion of the separated sludge to the anaerobic area.

The method of the present invention will be explained below with reference to the drawings.

Figure 5 shows the amount of B contained in organic wastewater by the method of the present invention.
FIG. 2 is a flow sheet diagram showing an example of a processing device that simultaneously removes OD, nitrogen, and phosphorus. In this device, an anaerobic tank 51, an aerobic tank 52 in which P material 56 is installed, and a sedimentation tank 53 are arranged in order, and the bottom of the sedimentation tank 53 is connected to the inlet of the anaerobic tank 51 by a return pipe 54f. There is. In the method of the present invention, raw sewage 55 (organic sewage) and sludge are introduced into a gas tank 51 (anaerobic region) to cause an anaerobic reaction by suspended organisms.

Thereafter, it is introduced into the aerobic tank 52 (aerobic area) to supply oxygen, and an aerobic reaction is caused by the sessile organisms fixed on the furnace material 56 and the floating organisms floating in the aerobic tank 52. After sludge, the separated sludge is guided to a settling tank 53 (solid-liquid separator) to obtain treated water 57, and a portion 54 of the separated sludge is returned to the anaerobic tank 51.

In this method, in the anaerobic tank 51, in order to promote contact between the raw sewage 55 and the sludge and prevent the sludge from settling, it is preferable to mix the sludge with a stirrer or a pump. Do within the anaerobic tank 51 must be 0.5 my/lJ or less, but if this Do condition is satisfied, stirring and mixing may be performed by blowing nitrogen gas, digestive gas, carbon dioxide gas, or air, etc. is also possible. The aerobic tank 52 stirs and mixes the inside of the tank by blowing in oxygen-containing gas and mechanically aerating the tank to create an aerobic state. In this case, it is desirable that Do in the tank be 0.5 m9/1 or more.

The F material 56 installed in this aerobic tank 52 retains biofilm, and granular furnace material, honeycomb tube, string-like furnace material, plate-like F material, etc. can be used as this F material 56. can. However, it is desirable to select the shape of the furnace material in consideration of the raw water properties, etc. to prevent clogging due to thickened biofilm. As a method of installing the furnace material 56, any of fully submerged installation, semi-submerged and semi-aerial installation, and all-aerial installation can be selected. In the case of a semi-submerged type or a fully aerial type, it is also possible to perform spraying using a pump in order to promote contact between the sludge mixture and the furnace material. Furthermore, the furnace material 56 can be installed on the entire surface or a part of the surface of the aerobic tank 52 when viewed from the top surface of the aerobic tank 52. Alternatively, the installation location must take into account water flow caused by mechanical aeration. The installation position of the spastic material is closely related to the shape of the aerobic tank, but it is desirable to install the furnace material area so that the NH4-N load is 1.51 NH4-N/m2-day or less. Yorca and MLS are also used for the properties of raw sewage.
When the S concentration is 3000 mQ/l, it is desirable that the residence time in the anaerobic tank 51 be at least 1 hour and the residence time in the aerobic tank 52 be at least 4 hours. The treated water 57 is obtained as separated water, and precipitated sludge is obtained. A part of this settled sludge is returned to the anaerobic tank 51 through the return pipe 54,
The remainder of the settled sludge is discharged outside the system as surplus sludge 58 and is separately processed and disposed of.

When designing the settling tank 53, the water area load should be set at 20 to 3
Q m S 7m 2 /day dust, rJ1 when staying 2.
It is preferable to set it to about 5 hours, and it is preferable to set the sludge return flow rate to 01 to 0.5 Q with respect to the raw water flow rate Q.

In this method, BOD is reduced by adsorption to sludge in the anaerobic tank 51, anaerobic digestion, and consumption as an organic carbon source for denitrification, and sessile organisms and BOD due to assimilation and catabolism by planktonic organisms
Q is removed.

Further, nitrogen is nitrified by sessile organisms and floating organisms in the aerobic tank 52, and becomes No2-N.

The BOD in the organic wastewater 55 is converted into an organic carbon source by the action of denitrifying bacteria in the sludge in the anaerobic tank 51. denitrification as

In this method, the sessile organisms are allowed to act in the aerobic tank 52, and the reason for this is to retain the nitrifying bacteria in the sessile furnace material 56 to ensure the existing fKk of the nitrifying bacteria. That is, nitrifying bacteria have a slow growth rate, and in order to cause a nitrification reaction, it is necessary to maintain the sludge age for 10 days or more using a normal activated sludge method. Therefore, when the BOD load increases or the water temperature decreases, in a mixed culture of BOD removing bacteria and nitrifying bacteria, the ratio of the former increases and nitrification no longer occurs. However, sessile biofilms are almost fixed;
The sludge age is close to infinity and the nitrification reaction can be maintained. Therefore, in this method of using sessile organisms, it is possible to prevent the situation of suffocation and also to make the aerobic jfj52 compact.

In addition, in this method, the suspended sludge is repeatedly exposed to anaerobic conditions and aerobic conditions, so that a biological dephosphorization reaction can occur. In other words, the returned sludge releases the phosphorus contained in the sludge itself under anaerobic conditions in the anaerobic jiff 51, and then releases the commercially available phosphorus into the sludge under aerobic conditions in the aerobic tank 52. The phosphorus in the raw organic wastewater 55 is removed by taking it into the organic wastewater 55. This phosphorus is discharged outside the system in the form of excess sludge.

-1 decreases with the nitrification reaction, and PI decreases with the denitrification reaction.
I increases, but in this method 2
Since two reactions occur and the returned sludge and raw sewage are mixed together, the voice does not differ much from the original sewage, and if the raw sewage is around neutral, there is no need to add tone roughening. .

Since BOD in the raw wastewater is used as the organic carbon source for denitrification, it is usually unnecessary to add an organic carbon source agent such as methanol. However, if the BOD concentration in the raw wastewater is low compared to the nitrogen and phosphorus concentrations and the nitrogen and phosphorus concentrations in the treated water are to be eliminated very well, BOD such as methanol can be used.
An OD source may be supplementarily added to the anaerobic tank 5 or the aerobic tank 52 or both.

Furthermore, the equipment used in this method is relatively simple, and water droplets can be applied to existing activated sludge equipment for secondary treatment by simple modification. The only things that need to be managed during operation are the amount of air supplied and the amount of return, so similar to the conventional activated sludge method, advanced operation management technology is not required and water temperature can be controlled.

In response to fluctuations in water quantity and quality, treatment can be stabilized by using sessile organisms and circulation through return.

FIG. 6 shows another embodiment of the method of the invention. The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 5 in that a circulation path 59 is provided from the aerobic tank 52 to the anaerobic tank 51. According to this device, by performing circulation, stirring and mixing within the system can be promoted, stabilization and efficiency of biological reactions can be reduced, and the sludge flowing between the furnace materials in the aerobic tank 52 can be mixed. By increasing the flow rate of the liquid, clogging can be effectively prevented and the effect of thinning out living organisms can be obtained.

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 6.

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 The quality of the treated water obtained from Table 1 is BOD.

The nitrogen and phosphorus concentrations were extremely low, and it was confirmed that the treated water was superior to treated water obtained by conventional methods.

As is clear from the above explanation, according to the method of the present invention,
BOD, nitrogen, and phosphorus in wastewater can be removed simultaneously with a simple device without using chemicals such as methanol, PII regulators, or flocculants. This method uses sessile organisms and planktonic organisms in combination according to their functions, and since the composition and action of each type of sludge are clear, it can easily respond to changes in water temperature, water quality, load amount, etc. It is possible to handle operation management. In particular, since the biofixed furnace material is provided in the aerobic area, the nitrification reaction can be maintained well.

[Brief explanation of the drawing]

1 to 4 are flow sheet diagrams showing a conventional method for treating organic sewage, FIG. 5 is a flow sheet diagram showing an example of a method for treating organic sewage according to the present invention, and FIG. 6 is a flow sheet diagram showing an example of the method for treating organic sewage according to the present invention. It is a flow sheet diagram showing another example of the method for treating organic wastewater according to □. 51... Anaerobic tank, 52... Aerobic tank, 53... Sedimentation tank, 54... Return pipe, 55... Raw sewage, 56...
・Biosolidification 7 (f 'F material, 57...treated water, 58...
・Excess sludge, 59...Circulation route.

Claims (2)

[Claims] (1) Organic wastewater is introduced into an anaerobic area to cause an anaerobic reaction by floating organisms, and then introduced into an aerobic area equipped with biofixation reactor material to supply oxygen and cause sessile and floating organisms to react. A method for treating organic sewage, which is characterized by causing an aerobic reaction and then guiding it to a solid-liquid separator to obtain treated water, and returning a portion of the separated sludge to an anaerobic area. (2) The method for treating organic wastewater according to claim 1, characterized in that the sludge mixture is circulated between an anaerobic region and an aerobic region.