JPH02284695A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To increase MLSS in an aerobic contact tank by separating sludge produced in the aerobic contact tank by precipitation in a precipitation tank, returning part of the precipitated sludge to the aerobic contact tank and returning part of the supernatant water to an anaerobic contact tank as circulating water. CONSTITUTION:Part of drained water as supernatant water in a precipitation tank 3 is returned to an anaerobic contact tank 1 and denitrified by anaerobic treatment. Part of sludge separated in the tank 3 is returned to an aerobic contact tank 2. Since MLSS in the aerobic contact tank can be increased by the return sludge and the lowering of nitrification efficiency can be prevented, waste water can stably be treated independently of external environment.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a wastewater treatment method that more effectively removes organic matter and nitrogen in a wastewater circulation denitrification method in which an anaerobic contact tank and an aerobic contact tank are installed. It is about the method.

(Conventional technology) Recently, anaerobic contact using an anaerobic filter bed has been introduced as a treatment method that generates less sludge, is easy to maintain, reduces electricity costs required for aeration, and can perform denitrification treatment. A cyclic denitrification method using an aerobic contact tank that uses contact aeration for secondary treatment has attracted attention and is widely used as a treatment system for community wastewater, such as agricultural community wastewater, fishing community wastewater, and domestic wastewater.

(Problems to be Solved by the Invention) However, the above treatment method relies on microbial reactions for organic matter removal, nitrification, and denitrification, and
It has the disadvantage that it is easily influenced by the amount of dissolved oxygen, pH, etc. In particular, the nitrifying bacteria that contribute to the nitrogen removal reaction in biological nitrification and denitrification are said to have a slower growth rate than other microorganisms that are involved in organic matter removal and denitrification. Because the capacity is about 172 cm compared to an anaerobic contact tank, it is difficult to increase the amount of nitrifying bacteria, and when the water temperature drops, the action of nitrifying bacteria is inhibited, and although there is no problem with organic matter removal, nitrification is There are many problems where progress is not made.

A method for improving this nitrification performance is to increase the amount of biomass (nitrifying bacteria) in the aerobic contact tank by increasing the amount of contact material filled. Alternatively, methods such as increasing the water tank capacity and prolonging the processing time have been considered, but this requires equipment costs and
It will be economically disadvantageous.

In addition, in treatment methods using suspended sludge such as the activated sludge method, there is a return sludge operation, in which the sludge separated in the settling tank is returned to the aeration tank, and the suspended sludge concentration in the tank (hereinafter referred to as ?+1) is returned to the aeration tank.
, called SS. ) is being maintained. However, when this operating method is applied to the above-mentioned cyclic denitrification method that incorporates an anaerobic contact tank and an aerobic contact tank, even if an attempt is made to increase the MLSS in the tank by returning the precipitated and separated sludge to the aerobic contact tank, the aerobic Since there is circulation from the contact tank to the anaerobic contact tank, and there is no stirring in the anaerobic contact tank, MLSS is
Precipitates in a gas contact tank. For this reason, the MLS of the anaerobic contact tank
It was difficult to increase S.

(Means for Solving the Problems) In order to solve the above problems, the inventors of the present invention have conducted extensive research and have arrived at the present invention.

That is, 1 the present invention provides a method for treating sewage in which inflow sewage is subjected to anaerobic treatment in an unstirred anaerobic contact tank and then subjected to aeration treatment in an aerobic contact tank, in which sludge generated in the aerobic contact tank is Separate in a sedimentation tank.

Along with returning a portion of the settled sludge to the aerobic contact tank.

The gist of the present invention is a wastewater treatment method characterized by returning a portion of the supernatant water to an anaerobic contact tank as circulating water.

First, a flow sheet of the conventional cyclic denitrification method is shown in FIG. The wastewater first flows into the anaerobic contact tank (1),
Anaerobic treatment is performed by passing through the filter bed, and the treated water that has completed the anaerobic treatment enters the aerobic contact tank (2).1 The inflowing wastewater is brought into contact with the filter bed through aeration and agitation by a blower. Afterwards, it is released into the river. Note that a part of the treated water is circulated from the outlet side of the aerobic contact tank (2) to the anaerobic contact tank il+.

Furthermore, the lη mud separated in the settling tank is discharged to the sludge treatment facility, but a portion is returned to the anaerobic contact tank (1).

However, as mentioned above, the nitrifying bacteria that contribute to the nitrification reaction are affected by the external environment (water temperature, dissolved oxygen g, p++, etc.) and are likely to cause problems in which nitrification does not proceed. Therefore, we propose the method of the present invention as a method for improving the nitrification reaction under the influence of the external environment.
The flow sheet is shown in Figure 1. In the present invention, unlike the conventional cyclic denitrification method, the sedimentation tank (3) in the sedimentation tank (3) is
Anaerobic contact of some of the discharged water, which is the supernatant water of I! It is returned to (1) for denitrification treatment by anaerobic treatment, and is also sent to the sedimentation tank (
A portion of the sludge separated in step 3) is returned to the aerobic contact tank (2).

(Function) In other words, in the method of the present invention, organic matter in wastewater comes into contact with the anaerobic biofilm attached to the filter bed in the anaerobic contact tank, and is anaerobically decomposed and converted into organic acids and other low-molecular substances. Furthermore, following the production of organic acids, methanogens act and convert these substances into methane gas, carbon dioxide, etc.

At this stage of gasification, ROD in wastewater decreases, so 1
The load on the aerobic contact tank (hereinafter sometimes referred to as contact aeration tank), which is the next step, is reduced. In addition, by returning some of the clear liquid after the precipitation treatment to the anaerobic contact tank and circulating it through the aerobic contact tank and then the settling tank, the nitrate nitrogen generated in the aerobic contact tank in the circulating fluid can be removed. is converted into nitrogen gas and denitrified. Note that the sludge accumulated in the anaerobic contact tank is decomposed and reduced in volume by putrefaction.

Next, the water treated in the anaerobic contact tank flows into the aerobic contact tank, where sufficient oxygen is supplied and the organic matter remaining in the wastewater is removed by the aerobic biofilm that has grown on the contact material. Furthermore, the ammonia nitrogen in the wastewater is simultaneously oxidized to nitrate nitrogen.

In the conventional method, the biomass in the aerobic contact tank was increased by returning the returned sludge to the anaerobic contact tank, but the anaerobic contact tank did not require stirring.

Because MLSS settles in the tank, as a result, the MLSS in the aerobic contact tank? I couldn't raise my H degree. On the other hand, in the method of the present invention, suspended solids S after precipitation treatment are
S-poor water is circulated, while sludge generated in the aerobic contact tank is separated in a settling tank, and a portion of the sludge is returned to the aerobic contact tank. At this time, the SS of the aerobic contact tank can be controlled by changing the amount of sludge drawn out according to external environmental conditions.

(Example) Next, the present invention will be specifically explained using examples.

Example 1 Square anaerobic contact tank (dimensions 20cm x 20cm x
60cm H, aquarium capacity! 24 / Filler Niblastic honeycomb contact material, filling rate 60%) is used as an anaerobic filter bed, and an aerobic contact tank connected to it (dimensions 15 cm x 1
7cm x 55cm H, tank capacity 141. Filler Niblastic honeycomb contact material, filling rate 55%) was used as an aerobic filter bed, and then a settling tank (water tank volume FJ 31
) was connected to perform continuous treatment of wastewater. Continuous aeration is performed using a blower.

Along with returning a portion of the settled sludge to the aerobic contact tank.

A certain amount of supernatant water is circulated to the anaerobic contact tank481
I sent it back only / day.

Domestic wastewater was used as the raw water, and the treatment amount was 241/day (total) and the residence time was 41 hours. (24 hours of residence time in the anaerobic contact tank, 14 hours of residence time in the aerobic contact tank, and 3 hours of residence time in the settling tank) Note that some of the settled sludge generated in the sedimentation treatment.

The gate LSS of the aerobic contact tank was maintained at 120 (1 to 2300 mg/(!) by automatic withdrawal using a timer.

The inflow quality of raw water is ll0D 212mg//! ,
COD 98mg/β.

SS 185mg/! l, total nitrogen was 41 mg/1. This raw water was treated with the wastewater treatment equipment mentioned above.

1300? +ng/E, COD 12n+g/
I! , SS 5 mg/l, total nitrogen 8.6 mg/l
After testing this system for about one year, we found that the quality of the treated water was stable with little seasonal variation, and the BOD was 20mg/1.
Below, COD 20mg/1 or less and total nitrogen 15mg/
l! It was found that treated water with the following quality was obtained and could be fully used in the treatment of domestic wastewater.

(Effects of the invention) The present invention applies to two methods of cyclic denitrification using an anaerobic filter bed method using an unstirred anaerobic contact tank as the primary treatment of wastewater treatment and a contact aeration method using an aerobic contact tank for the secondary treatment. By using this method, it is possible to increase the MLSS of the aerobic contact tank using the sludge returned, and as a result, it is possible to prevent a decline in nitrification efficiency, so wastewater treatment can be carried out in a stable state without being affected by the external environment. It can be carried out.

[Brief explanation of drawings]

Figure 1 is a flow sheet of the wastewater treatment method of the present invention.
The figure shows a flow sheet for a conventional circulating aeration process. 1 - Anaerobic contact tank 2 - Aerobic contact tank 3 - Sedimentation tank (Kaya) mouth

Claims (1)

[Claims] (1) In a sewage treatment method in which inflowing sewage is subjected to anaerobic treatment in an unstirred anaerobic contact tank, and then aerated treatment is performed in an aerobic contact tank, the sludge generated in the aerobic contact tank is transferred to a settling tank. A wastewater treatment method characterized in that part of the precipitated sludge is returned to an aerobic contact tank, and part of the supernatant water is returned to an anaerobic contact tank as circulating water.