JPS6010798B2 - Sewage treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention suspends so-called Kjeldahl nitrogen compounds, 80D components, and phosphates, which are measured by the Kjeldahl quantitative method such as ammonia nitrogen and organic nitrogen compounds in wastewater, in a treatment tank. This invention relates to a method for treating wastewater that removes wastewater using a microbial film that grows on the surface of suspended solid particles.

Up until now, various removal methods have been proposed for each of the components to be removed in wastewater, but wastewater usually contains multiple target components to be removed at the same time, and in this respect, there is a need for space for treatment equipment or for the use of chemicals. Mainly for economical reasons such as the amount used, there is a demand for a wastewater treatment process that can simultaneously remove a plurality of target components to be removed from wastewater in as few steps as possible.

In recent years, treated water is supplied into a treatment tank in which solid particles that have grown biofilm are suspended and suspended under aerobic or anaerobic conditions, and the solid particles are mixed with the solid particles to create aerobic conditions. Biological treatment methods include oxidative decomposition of BOD components and/or conversion of ammonia nitrogen into nitrate nitrogen (nitrification) under conditions, and decomposition of nitrate nitrogen into nitrogen gas (denitrogenization) under anaerobic conditions. It is attracting attention because of its advantages such as being able to treat BOD and nitrogen compounds at the same time, compact equipment, and high treatment efficiency. However, even with this method, the removal of nitrogen compounds actually involves two steps: nitrification and denitrification, and it is actually impossible to remove phosphorus, which is an important target removal component in other wastewater. there were.

In addition, a method focusing on phosphate removal utilizes the phenomenon that under aerobic conditions, phosphorus-deficient microorganisms take in too much phosphorus, and when these microorganisms are placed under anaerobic conditions, they release the ingested phosphorus. A method has been proposed that consists of a flow sheet that combines an aeration tank and an anaerobic dephosphorization tank.

According to this method, since the flocculant is added to the phosphorus concentrated liquid, the amount of flocculant added can be reduced. However, the treatment process is complicated, the treatment speed is extremely slow, it takes a long time, and therefore large-capacity equipment is required, and a phenomenon called bulking occurs, which worsens the settling properties of the sludge. , the water flows out with the treated water, causing a decline in the quality of the treated water, and in severe cases, there are cases where it is difficult to maintain and manage stable operation, such as when there is no sludge in the sludge and biological treatment is no longer carried out. There is a problem that Furthermore, in order to remove nitrogen compounds from wastewater, a separate process for removing nitrogen must be provided, further complicating the treatment process.

An object of the present invention is to solve the above problems and provide a wastewater treatment method for removing phosphates, nitrogen compounds, and BOD components from wastewater, which enables efficient and stable operation and maintenance. This was done as a.

The gist of the present invention to achieve this object is to supply water to be treated into a treatment tank in which solid particles on which a biofilm has grown are suspended and suspended under aerobic conditions. When contacting, the BOO volume load in the processing tank is set to 20
~50k9 BO town/day, BO in treated water
The objective is to simultaneously remove component D, phosphates, and nitrogen compounds.

In the present invention, the volume load of 80D is 20 to 50 [9-
BOD/ is assumed to be a high load of ・day.

The reason for this is that the growth of the microbial film on the surface of the solid particle is promoted by the decomposition of the BOD component, and the exfoliation of the microbial film itself due to the enlargement of the microbial film is promoted.As a result, the microbial film on the surface of the solid particle and the detached microorganism This is to enhance the uptake effect of phosphate and nitrogen compounds by both membranes. The 80D volume load in the conventional activated sludge method is 0.3~
The removal time of biological BOO components and nitrogen compounds using solid particles is approximately 0.8k9-day.
~10kg-BOD/day, biological dephosphorization method is 0
．． It is about 3 to 0.8ks-80D/day.

For example, in the activated sludge method, if the BOD volume load is increased, the amount of BOD components removed increases, but at the same time, the amount of sludge produced also increases, causing the bulking phenomenon described above, so the limit is inevitably around 0.8. The same is true for biological dephosphorization methods.

On the other hand, in the method using solid particles, the bulking phenomenon is relatively less likely to occur due to the specific gravity of the solid particles, so it is possible to increase the BOD volume load compared to the activated sludge method.
When attempting to remove BOD and nitrogen compounds at the same time, the BOD volume load must be 10k9-BOD/〆・day or more because the mechanism is to first nitrate or nitrify the ammonia nitrogen in the wastewater and then perform nitrogenization and denitrification. If the load is too high, the nitric oxidation reaction will stop, making it impossible to remove BOD at the same time. On the other hand, in the solid particle suspension method of the present invention, the nitrification reaction of nitrogen is stopped as in the solid particle method, but since the uptake reaction of nitrogen compounds by the microbial membrane occurs, BOD components and phosphates are Similarly, nitrogen compounds are removed. The condition of BOD volume loading in the present invention is of critical significance, i.e., the present invention is suitable for high 80D volume loading when using solid particles, e.g.
In the case of D/day, phosphates and nitrogen compounds were hardly removed, resulting in 20k9-BOD/〆.

This was done based on the knowledge that phosphates and nitrogen compounds can be dramatically removed when the lower critical point is 1 day or more. If the particle size is smaller than 20k9-BOD/day, the growth of the microbial film on the solid particle surface will not be promoted even by long-term contact with the water to be treated, and as a result, the removal effect of phosphates and nitrogen compounds will be negligible. There is no such thing. On the other hand, if it is above the lower limit, the growth of the microbial film on the surface of the solid particle is promoted, the microbial film becomes enlarged, and is peeled off from the surface of the solid particle. That is, phosphates and nitrogen compounds are removed by actively repeating the growth and peeling of the microbial film. Moreover, it is noteworthy that above the lower limit, nitrogen compounds in the wastewater, such as ammonia nitrogen, are taken up by the microbial membrane in their unchanged form, which usually occurs under aerobic conditions at low BOD volume loads. Since conversion from ammonia nitrogen to nitrate nitrogen does not occur, a treatment step under anaerobic conditions for decomposing nitrate nitrogen is not required for post-treatment.

The upper limit for the BOD volumetric load is 50k9 - BOO/thousand day.

If it exceeds the upper limit, the growth of the microbial film will be excessive and a bulking phenomenon will occur as in the general activated sludge method. In addition, due to fluctuations in the concentration of target removal components such as BOD components in the water to be treated, their removal rate or removal efficiency and operational stability may deteriorate, so the BOD volume load should be increased by 20%.
It is preferable to set it as ~40k9-BOD/day. Note that if the 80D load is 20 kg-BOD/rudder-day or more, 80D may leak into the treated water, but in this case, it is sufficient to provide a warming tank to remove one more leaked BOO. The solid particles to be used in the present invention may be those that have phenotypic organisms growing on their surfaces and have a terminal velocity of 5-300/hour in the wastewater to be treated, such as sand, coke, coal, crushed brick particles, alumina, etc. Examples include organic particles such as silicates, zeolites, activated carbon inorganic particles, and synthetic resins, and those that are inexpensive and resistant to abrasion or crushing are preferred.

Appropriate BOD oxidizing bacteria etc. grow attached to the surface of the solid particles, and the particles usually have a particle diameter of 0.05 to 0.5 ribs.
・Because particles are used, the biofilm surface area in the reaction tank can be easily obtained, which is much larger than in the submerged bed method, so the biological reaction is extremely rapid and treatment can be completed in a very short time. The volume may also be relatively small. In addition, by adjusting the terminal velocity of the solid particles within a certain range, the treated water and the solid particles can be easily separated, and the solid particles on which the microbial film has grown can always remain in the tank without flowing out. It does not cause problems such as bulking, and does not require operations such as returning sludge, allowing stable operation and maintenance.

Next, an example of a flow sheet when the present invention is applied to sewage treatment is shown in FIG.

First, sewage containing BOD components, phosphates, and nitrogen compounds is introduced into the fly litter chamber 4 of the aeration tank 1 through the pipe 9.

In the rope room 4, the solid particles 6 on which microbial films have grown and the introduced sewage are held in a suspended state by the mechanical rope means 3 using rotary blades, and the room is made aerobic by the air introduced through the piping 2. be placed under conditions. In this state, the 80D volume load of the aeration tank is 20 to 50k.
Since it is 9-BOD/day, the microbial film on the surface of the solid particle 6 actively proliferates as the BOD component decomposes, and the microbial film itself becomes enlarged.

The enlarged microbial film is sequentially peeled off from the surface of the solid particles 6 by the diaphragm action, and by repeating this multiplication, enlargement, and peeling, the amount of the microbial film in the diaphragm chamber increases as a whole. When the 80D component is further oxidized and decomposed by the growing and enlarged microbial film on the solid particles and the microbial film peeled off from the solid particles (hereinafter referred to as peeled sludge), both
Phosphate, nitrogen compounds (NH3-N, K-N, etc.) are taken up in the microbial film and in the stripped sludge.

If the pH inside the pot is below 6.5 due to the quality of the sewage, a separate alkali addition means is installed and an alkali agent is added in advance or inside the pot to increase the pH of the bait to 7.5 or lower.
It is preferable to adjust it to 8.0.

The water and exfoliated sludge thus treated in the sludge chamber 4 are then separated from solid particles in the settling chamber 5.
At this time, the water area load of the sedimentation separation chamber 5 is increased from 3 to 8〆/〆'hr.
This is preferable in terms of separation efficiency. The treated water and exfoliated sludge discharged from the atomization tank 1 through a discharge passage 7 having a suitable separation means such as a gutter are then introduced into a settling tank 8 and separated, and the treated water A is discharged out of the system as an upper lighting liquid. At the same time, the stripped sludge is discharged from the lower part as surplus sludge B and is disposed of appropriately, such as by disposal or incineration. The water area load in the sedimentation tank is 12-24/d/day (0.5-1.0
It is preferable to set it as 〆/de/hour). The implementation of the present invention is not limited to the flow sheet described above; for example, the operation of solid particles, sewage, and gas (air) can be carried out by
Not only the mechanical fly-flying using the rotary blade, but also flying-flying (air lantern-hailing) using an air lift effect may be used.

Further, the separation operation of the exfoliated sludge and the treated water may be performed by an operation other than the sedimentation method, such as flotation separation. Any one of these may be selected as appropriate. Furthermore, when the amount of BOD components in wastewater or the amount of wastewater becomes large, it is also possible to increase the number of bomb tanks and process them in series or in parallel. Next, examples of the present invention will be described below.

Continuous treatment of wastewater was carried out under the following conditions based on the process flow shown in FIG. That is, using a rectangular eel tank with a side length of 22 m, a water depth of 22 m, and an internal volume of 10 m, the water surface load in the sedimentation separation chamber of the eel tank is 5 w/h.
, the water surface load of the sedimentation separation tank for treated water and exfoliated sludge is 0.5.
〆/de/day, the aeration chamber was filled with 1.5 tons of sand of 0.2 to 0.3 ◇, the particle concentration was set to 15% by apparent volume, and the treated water temperature was set to 25℃. However, the amount of air was set so that the dissolved oxygen concentration in the aeration tank was 3 to 4 feet. Primary treated water from a sewage treatment plant is used as wastewater to be treated (raw wastewater), and if necessary, Bebuton and meat extract are added as BOD sources to increase the BOD volume load to 7, 10, 20, 30.
, 40, 50, and k9-BOD/day.

Table 1 x Addition of pork beptone and meat extract in raw water as a BOD source. By separating and removing phosphorus, 70 to 95% or more of phosphorus is removed, and at the same time, it is possible to remove 10 to 20 TK-N.

In addition, since N03-N is hardly detected in the treated water, it is possible that N-N' in the raw water was not oxidized.
It is presumed that it was taken into the microbial membrane. As is clear from the above explanation, the present invention makes the process much simpler than the conventional biological dephosphorization process using activated sludge, and the equipment is easier to maintain and manage. Since no additives are required, significant savings in operating costs are possible.

Furthermore, denitrification and BOD removal proceed simultaneously with dephosphorization, and the surface area of the microbial membrane that contributes to microbial membrane purification can be increased, so a rapid purification effect can be obtained, making it possible to reduce the amount of sedimented sewage in sewage treatment plants. If applied to processing such as
It has the advantage of low operating costs and efficient processing.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the sewage treatment method according to the present invention. 1: Aeration tank, 2: Air piping, 3: Speech means, 4: Rope cassette chamber, 5: Sedimentation separation chamber, 6: Solid particles 7: Discharge channel, 8: Sedimentation tank, 9: Raw water piping, A; Treated water, B: Surplus sludge. Figure 1

Claims (1)

[Claims] 1. When supplying water to be treated into a treatment tank in which solid particles on which biofilm has grown are stirred and suspended under aerobic conditions and brought into contact with the solid particles, the BOD in the treatment tank is
A sewage treatment method characterized by simultaneously removing BOD components, phosphates, and nitrogen compounds from water to be treated at a volumetric load of 20 to 50 kg-BOD/m^3.day.