JPH0375239B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater, and more specifically, a biochemical treatment method that combines anaerobic biological treatment and aerobic biological treatment for low-concentration wastewater after solid-liquid separation in a settling basin or the like. Relating to a method of purification by.

Biochemical treatment of wastewater has the great advantage of low energy consumption, unlike physicochemical treatments such as solid-liquid separation by adding flocculants, wet oxidation of waste liquid, dewatering, drying and incineration of sludge. Therefore, biochemical treatment using aerobic microorganisms is currently the mainstream method of purifying sewage, which is mainly miscellaneous wastewater such as kitchen wastewater and flush toilet wastewater, in urban areas.

This biochemical treatment using aerobic microorganisms can be roughly divided into two types: the suspended organism method and the fixed biofilm method. The suspended organism method further includes the standard activated sludge method and the long-time aeration method. The former is suitable for large-scale, high-grade treatment, but requires advanced technology to operate and requires a great deal of labor and expense for maintenance. The latter is suitable for medium-scale treatment and generates a small amount of sludge, but
The disadvantages are that the residence time is long and the processing performance is not very good. In addition, fixed biofilm methods include the trickling filter method, rotating disk method, and contact oxidation method, all of which have strong load fluctuations because the biofilm forms a food chain made up of a combination of various microbial films. Although it is easy to maintain and manage and is suitable for small-scale processing, it has the disadvantage of not being able to handle increases in processing volume. in this way,
Biochemical treatment using aerobic microorganisms has various advantages and disadvantages, but a further problem is the treatment of nitric acid and nitrite produced by the action of aerobic microorganisms.

In view of the above problems, the inventors of the present invention have investigated various wastewater treatment methods that combine aerobic biological treatment and anaerobic biological treatment. In addition, aerobic biological treatment uses a contact oxidation tank that is resistant to load fluctuations and is easy to maintain, and a part of the treated product in the contact oxidation tank is returned to the contact digestion tank. The present inventors have discovered that not only can the advantages of aerobic biological treatment and aerobic biological treatment be fully utilized, but also that the amount of sludge generated can be significantly reduced, leading to the completion of the present invention.

That is, in the wastewater treatment method according to the present invention, low-concentration wastewater after solid-liquid separation in a settling basin or the like is treated by providing multiple stages of anaerobic filter beds and a partition wall in the center to change the flow direction from the downward flow. The water is supplied to a contact digestion tank with an upward flow for purification treatment, the treated water is further supplied to a contact oxidation tank for oxidation treatment, and a part of the treated product obtained in the oxidation treatment is It is characterized in that it is returned to the contact digestion tank and purified again together with the low concentration wastewater.

According to the method of the present invention, while wastewater passes through each tank, it is alternately subjected to anaerobic treatment and aerobic treatment to decompose organic polymers into low molecular weight molecules, decompose low molecular weight molecules into carbon dioxide gas, water, etc. Since denitrification through reduction of nitrate ions and other efficient purification treatments are carried out, and stable and high-grade treatment is performed that is resistant to load fluctuations, maintenance costs and construction costs can be significantly reduced.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, A shows a contact digestion tank and B shows a contact oxidation tank. The contact digestion tank A has a hopper-shaped part 2 at the bottom of a cylindrical body 1, and an inflow part 3 that communicates with a sand settling pond (not shown) is opened on one side of the top plate 4 at the upper end of the body 1. ing. A partition wall 5 is vertically installed on this top plate 4 to partition the left and right sides, and its lower end is connected to the main body 1.
It reaches the bottom of the wall, and the left and right sides are connected. In the contact digestion tank A, a plurality of anaerobic filter beds 6, 6, . Further, a sludge withdrawal pipe 8 is provided at the lower end of the tank A, and a treated water withdrawal pipe 9 communicating with the contact oxidation tank B is provided at the upper end.

In the contact digestion tank A, it is important to provide multiple upper and lower anaerobic beds 6 with good biofilm adhesion. That is, in anaerobic filter beds, biofilms generally have weak adhesion, and if the flow rate is too high or the flow is disturbed, the biofilms will peel off and the treatment effect will be significantly reduced. Therefore, the filter media constituting the filter bed 6 are granular materials made of other plastic materials such as bamboo shinobu or crushed stone, or materials with good biofilm adhesion properties such as plate-like materials, cylindrical materials, and net-like materials. Then, the filter media are stacked to a required thickness to form several stages of filter beds 6, and each filter bed 6 is
A gap 7 of a required height is provided between them. By arranging the filter beds 6 in multiple stages and providing appropriate intervals between the filter beds in this manner, the wastewater uniformly contacts the filter media, the turbulent flow state is rectified, and the treatment effect is significantly enhanced.

In the contact oxidation tank B, like the contact digestion tank A, a vertical flow pipe 11 is vertically installed in the center of a cylindrical body 10 with a hopper section at the bottom, and an aerobic filter bed 12 is provided around it. The end of the air supply pipe 13 is opened at the lower end of the flow pipe 11. In addition, a purified water outflow pipe 14 is provided at the top of the tank B,
A purified water return pipe 15 that communicates with the inflow part 3 of tank A is branch-connected to a part of it, and a sludge withdrawal pipe 1 is further connected to the lower end.
6 is provided.

Next, the purification effect of wastewater will be explained.

Low-concentration wastewater after solid-liquid separation in sand settling ponds, etc.
It is supplied from the inflow part 3 to one of the upper parts of the contact digestion tank A, and flows downward as shown by the arrow to the anaerobic filter bed 6.
It passes sequentially from the upper stage to the lower stage and reaches the bottom of the tank, then becomes an upward flow and passes sequentially from the lower stage to the upper stage of the anaerobic filter bed 6, forming an anaerobic biofilm formed on the anaerobic filter bed 6. Upon contact, decomposition of high-molecular organic substances into low-molecular weight substances, generation of ammonium ions (NH ₄ ), etc. occur, resulting in purification. At this time, the wastewater whose flow is disturbed by passing through the upper or lower filter bed 6 is rectified by passing through the gap 7 between the filter beds before entering the next filter bed. 6 becomes uniform, and uniform contact conditions with the filter medium are obtained.

The purified wastewater then enters the aerobic contact oxidation tank B through the discharge pipe 9 at the top of the tank, and is circulated in the tank B by the air supply circulation flow from the air supply pipe 13 to the aerobic filter bed 12. When it comes into contact with the aerobic biofilm of the water, it is purified by oxidizing low-molecular organic matter, decomposing it into carbon dioxide gas and water, and oxidizing ammonium ions into nitric acid and nitrous acid. This purified water is discharged out of the system through a purified water outflow pipe 14, and a part of it is returned to the contact digestion tank A through a purified water return pipe 15 equipped with a pump P, where it undergoes anaerobic treatment along with newly supplied wastewater. is,
Denitrification occurs by reduction of nitric acid, nitrous acid, etc. generated in the catalytic oxidation tank B along with the decomposition of the high-molecular organic matter into low molecular weight.

Excess sludge generated in the contact digestion tank and oxidation tank A, B is normally discharged from each sludge withdrawal pipe 8, 16 through a sludge return pipe 17, and is treated together with the solids separated in the settling basin or the like or alone. However, a portion may be returned to the digestion tank A for reprocessing.

Thus, according to the method of the present invention, the wastewater is alternately subjected to anaerobic treatment and aerobic treatment while passing through each tank, and furthermore, the treated product from contact oxidation tank B is returned to the contact digestion tank, Since it is subjected to anaerobic and aerobic treatment alternately again, decomposition of organic polymers into low molecular weight molecules, decomposition of low molecular weight molecules into carbon dioxide gas, water, etc., and denitrification by reduction of nitrate ions, etc., are sufficiently carried out. The process progresses and a stable high-grade purification process is achieved.

It is more preferable to provide a plurality of each of the contact digestion tanks A, A', A'' and the contact oxidation tank B, and to treat the wastewater by flowing it through these tanks in series.

Figures 2A and 2B show other contact materials used in the anaerobic filter bed of the present invention.

That is, the contact material C is a dish-shaped body 18 with different large and small diameters.
and 19 (for example, 5 to 10 cm in diameter) are provided vertically in multiple stages at appropriate intervals by connecting members 20. The dish-shaped bodies 18 and 19 are connected with each other with the central recess 21 facing upward, and each has a plurality of notches 22 at its outer peripheral edge. Dish-shaped body 1
8 and 19 are made of corrosion-resistant metal, plastic, or plate material, and the connecting member 20 may be made of any material capable of fixing the dish-shaped body, such as a rod, string, or rope shape.

When the anaerobic filter bed 6 shown in FIG. 1 is constructed using this contact material C, the following effects can be obtained. In other words, anaerobic microorganisms have weaker adhesion to the filter bed than aerobic microorganisms, and when a biofilm forms a layer,
It tends to peel off and fall off easily, reducing its ability to purify sewage. However, when the contact material C is used in the anaerobic filter bed as in this embodiment, there is no risk that the anaerobic biofilm will adhere to the central recesses 21 of the horizontal dish-shaped bodies 18 and 19 and be peeled off. More stable anaerobic treatment is performed. Furthermore, in the central recess 21,
When anaerobic biofilm forms beyond a certain limit,
The notch 22 on the outer periphery can prevent the lower layer from rotting due to excessive growth of the anaerobic biofilm layer. Moreover, unlike the so-called packed type anaerobic filter bed 6 shown in FIG.
Replacement is also extremely easy.

Next, the conventional method and the present invention will be compared.

Even with the standard activated sludge method, which is considered the highest grade of conventional sewage treatment, the BOD removal rate is limited to 90%, and if the BOD concentration of inflow wastewater is 200mg/, the treated water will
20mg/. Furthermore, if the BOD concentration is 200 mg/ or more or the water temperature is 10°C or less, or if the residence time is too long, it will be difficult to manage the activated sludge, and the BOD removal rate will drop significantly.

On the other hand, with the present invention, the BOD removal rate can always be maintained at 95% or higher, for example, BOD removal rate of inflow sewage.
is 200mg/, the BOD of treated water is 10mg/or less. In addition, even if the BOD of inflow wastewater reaches a concentration of 200 mg/or more, it is possible to change the residence time of contact digestion tank A and contact oxidation tank B by appropriately changing and combining them, or by changing the residence time of contact digestion tank A and contact oxidation tank B. By installing tank B in multiple stages, the BOD removal rate can be increased.
It is also possible to set it to 97% or more.

An example of this combination of residence time changes is:
When the BOD of inflow wastewater is 200mg/, the residence time in contact digestion tank A and contact oxidation tank B is 12.5% each.
If set as time, the BOD of treated water purified in tanks A and B will be 60 mg/, 6 mg/, respectively, and the BOD removal rate will be 97%.

Further, according to the present invention, in the contact digestion tank A,
Since the BOD removal rate is 70% or more, the amount of BOD removed in contact oxidation tank B is reduced, the amount of air required is small, and the power of the blower, which accounts for the majority of water treatment power, is reduced to about half of that of conventional methods. , power consumption can be significantly reduced.

Furthermore, even in the catalytic oxidation method, which is said to generate the least amount of sludge, the amount of excess sludge is 20 to 30% of the amount of BOD removed, but in the present invention, it is extremely small.
It accounts for only about 5-15% of the removed BOD.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of a purifying device for carrying out the present invention, Fig. 2 A and B show other contact materials for carrying out the present invention, A is its plan view, and B is its It is a sectional view along the aa line. A... Contact digestion tank, B... Contact oxidation tank, C... Contact material, 1... Cylindrical body, 2... Partition wall, 6... Anaerobic filter bed,
7... Spacing, 12... Aerobic filter bed, 15... Purified water return pipe, 18, 19... Dish-shaped body, 20... Connecting material.

Claims (1)

[Claims] 1 Low-concentration wastewater after solid-liquid separation in a settling pond, etc.
The water is purified by being supplied to a contact digestion tank with multistage anaerobic filter beds and a partition wall in the center to change the flow direction from downward flow to upward flow, and the treated water is further subjected to catalytic oxidation. Processing of low concentration wastewater characterized by supplying it to a tank for oxidation treatment, and returning a part of the treated product obtained in the oxidation treatment to the contact digestion tank and purifying it again together with the low concentration wastewater. Method.