JPS586558B2 - Sewage treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating all wastewater containing nitrogen compounds, such as sewage, industrial waste, and human waste, and particularly relates to an improvement in a denitrification treatment method.

Conventionally, in order to purify sewage containing nitrogen compounds by denitrification treatment, as shown in Figure 1, sewage is first introduced from line 1 to BOD oxidation tank 2, where it is treated with BOD oxidizing bacteria and line 31.
The organic matter in the wastewater is oxidized and decomposed into CO2 and H20 by the air supplied from the wastewater.

At this time, some nitrogen compounds in the wastewater are taken up by BOD oxidizing bacteria as a nutrient source.

The wastewater treated in the BOD oxidizing tank 2 is sent to the settling tank 4, where it is separated into activated sludge containing BOD oxidizing bacteria and a supernatant liquid.

The activated sludge is returned to the BOD oxidation tank 2 from the line 5 (the above process is referred to as the BOD oxidation process, 1 in the figure).

The supernatant liquid is introduced into the nitrification tank 6, and most of the nitrogen compounds in the supernatant liquid are nitrified by nitrifying bacteria to nitrate nitrogen (NO3-N).

In order to maintain this function, air is supplied from line 32 and a pH adjuster is introduced from line 7.

The sewage treated in the nitrification tank 6 is introduced into the nitrification sedimentation tank 8, where it is separated into activated sludge containing nitrifying bacteria and supernatant liquid, and the activated sludge is returned to the nitrification tank 6 from the line 9 (the above is This process is called the nitrification process (■ in the figure).

The supernatant liquid is introduced into the denitrification tank 10, and the nitrate nitrogen (N03-N) in the supernatant liquid is reduced to nitrogen gas (N2) by the denitrification bacteria inserted in the tank 10 in advance. Ru.

In order to perform this function efficiently, an organic carbon source such as methanol is added through line 11.

The wastewater treated in the denitrification tank 10 is introduced into the denitrification aeration tank 12 as needed, and after being sufficiently aerated with air supplied from the line 33, it is introduced into the denitrification precipitation tank 13, where it is denitrified. The activated sludge is separated into an activated sludge containing nitrogen bacteria and a supernatant liquid, and the activated sludge is returned to the denitrification tank 10 through the line 14 (the above process is referred to as the denitrification process, indicated by ■ in the figure).

The supernatant liquid is discharged from the system through line 15 as treated water.

The conventional method described above has the following drawbacks.

(1) Since the organic matter in the wastewater is used as an organic carbon source in the denitrification process (2), the wastewater cannot be directly input into the process (2).

This is because nitrogen compounds (ammonia nitrogen) present in wastewater are not decomposed by denitrifying bacteria, and therefore remain in the treated water as they are.

Therefore, (2) BOD oxidation process is carried out to remove organic matter from wastewater.
There is a waste of having to remove similar organic substances in the subsequent denitrification process (2) even though they are removed in the next process.

Therefore, (3) running costs become high.

Furthermore, the amount of organic carbon source added in (4) denitrification step (2) needs to be commensurate with the amount of nitrate nitrogen (NO3-N) produced in nitrification step (2).

This is because if there is too much, it will flow into the treated water as BOD,
This is because if the amount is too small, the denitrification reaction will be insufficient.

Therefore, if the amount of nitrate nitrogen obtained in the nitrification step (2) changes due to the influence of changes in wastewater quality, water temperature, etc., it is extremely difficult to adjust the amount of organic carbon source added in the denitrification step (2).

In addition, (5) Especially in the denitrification process ■, there are problems such as sludge floating because a floating method is adopted, and (6)
) The upper limit of sludge concentration must be 1000 ppm.

The present invention has been made in view of the above points, and its purpose is (1) to make wastewater in a form that can be used in the denitrification process in order to use the organic matter in the wastewater as an organic carbon source in the denitrification process. To this end, (2) separating organic matter and nitrogen compounds (ammonia nitrogen) in wastewater, (3) repeatedly using the substances that participate in the separation, (4) increasing the sludge concentration in the denitrification process, (5) To reduce the amount of organic carbon source added to the denitrification process and to reduce BOD leakage.

That is, the present invention provides a first step of (1) passing a portion of sewage containing nitrogen compounds through a trickling filter to adsorb organic matter in the sewage to the trickling filter sludge, and then separating the trickling filter sludge. ,(
2) a second step of oxidizing and decomposing the organic matter remaining in the wastewater that has passed through the first step, and the organic matter in the remaining wastewater that has bypassed the first step, using BOD oxidizing bacteria in an aerobic atmosphere;
(3) A third step in which nitrogen compounds in the wastewater that has passed through the second step are nitrified into nitrate nitrogen by nitrifying bacteria in an aerobic atmosphere;
4) Nitrate nitrogen in the wastewater that has passed through the third step is reduced to nitrogen gas by denitrifying bacteria in an anaerobic atmosphere in the presence of the trickling filter sludge separated in the first step, and organic matter is removed in this step. The present invention relates to a sewage treatment method comprising a fourth step of circulating a part of the desorbed trickling filter sludge to the denitrification step and the remainder to the first step.

Hereinafter, the method of the present invention will be explained in detail using FIG. 2.

FIG. 2 is a flow sheet showing an embodiment of the method of the present invention.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts as in FIG.

In the first step, a part of the sewage is introduced from the line 1 into the trickling filter tower 21, and organic matter in the sewage is adsorbed or assimilated by the trickling hearth sludge.

Nitrogen compounds (ammonia nitrogen) in wastewater are also consumed in accordance with the amount of assimilation.

The sprinkled hearth sludge and sewage are then introduced into the sprinkled hearth settling tank 22, where they are separated into the sludge and sewage as a supernatant liquid.

The wastewater that has passed through the first step is introduced into the BOD oxidation tank 2 in the second step, and along with the wastewater introduced from line 1' bypassing the first step, BOD oxidizing bacteria and line 3
The organic matter in the wastewater is oxidized by the air supplied from No. 1 and decomposed into CO2 and H2O.

This can be expressed as a formula as follows.

After that, the wastewater is sent to the BOD oxidation sedimentation tank 4, and the BOD
It is separated into sludge containing oxidizing bacteria and wastewater as a supernatant liquid.

The BOD oxidizing bacteria-containing sludge is circulated from the line 5 to the BOD oxidizing tank 2, and the sewage as a supernatant liquid is sent to the next third step.

In the third step, the wastewater is introduced into the nitrification tank 6, and nitrogen compounds (ammonia nitrogen) in the wastewater are nitrified to nitrate nitrogen by nitrifying bacteria.

This can be expressed as a formula as follows.

In order to maintain the above-mentioned nitrification effect, air is introduced through line 32 and a pH adjuster (alkali in this case) is introduced through line 7.

Thereafter, the sewage is introduced into the nitrification sedimentation tank 8, where it is separated into sludge containing nitrifying bacteria and sewage as a supernatant liquid.

The nitrifying bacteria-containing sludge is circulated and supplied to the nitrification tank 6 from the line 9, and the sewage as a supernatant liquid is sent to the next fourth step.

In the fourth step, the sewage is introduced into the denitrification tank 10 and separated from the organic carbon source supplied from the line 11 and the trickling filter sludge separated by the trickling filter sedimentation tank 22 of the first step and introduced through the line 23. At the same time, it is stirred in an anaerobic atmosphere.

In the tank 10, when the denitrifying bacteria decomposes and assimilates organic matter adsorbed or assimilated by the trickling filter sludge, it takes in oxygen from nitrate nitrogen in the wastewater and reduces the nitrate nitrogen to M2. The denitrification reaction occurs.

The reaction can be expressed as follows, for example, when the organic substance is glucose.

It is produced through a two-step reaction.

Thereafter, the sprinkled hearth sludge and sewage containing denitrifying bacteria are introduced into the aeration tank 12, aerated with air supplied from the line 33, and then introduced into the denitrification settling tank 13.

The sludge is sedimented and separated in the tank 13, and a part of the sludge is circulated through the line 24 to the denitrification tank 10, and the rest to the trickling filter sludge of the first step.

The purified wastewater is discharged from line 15.

The effects of the method of the present invention explained above are listed below.

(1) In the first step, the organic matter in the sewage is removed to some extent by adsorption or assimilation by the watering bed sludge;
The BOD oxidation tank in the second step can be downsized.

(2) In the fourth step, the denitrifying bacteria take in only the amount of organic matter that corresponds to the amount of nitrate nitrogen in the wastewater, and
Since bed sludge is inert in an anaerobic atmosphere, excess organic matter does not flow out, and the inconvenience of BOD flowing into the treated water does not occur.

(3) In the fourth step, since the trickling filter sludge has good settling properties, the settling properties of the sludge in the denitrification settling tank can be improved.

(4) In the fourth step, the amount of organic carbon source supplied can be reduced or zero.

EXAMPLE Sewage treatment was carried out according to the flowchart shown in FIG.

The results are shown in Table 1.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing a conventional sewage treatment method, and FIG. 2 is a flow sheet showing an embodiment of the method of the present invention.

Claims (1)

[Claims] 1. A first step of passing at least a portion of the sewage containing nitrogen compounds through a trickling filter to adsorb organic matter in the sewage to the trickling filter sludge, and then dispersing the trickling filter sludge; (2) the first step; 1
a second step of oxidizing and decomposing the organic matter remaining in the wastewater that has passed through the process and the organic matter in the remaining wastewater that has bypassed the first step using BOD oxidizing bacteria in an aerobic atmosphere; (3) the wastewater that has gone through the second step; (4) a third step of nitrifying the nitrogen compounds inside to nitrate nitrogen by nitrifying bacteria in an aerobic atmosphere;
A trickling filter in which the nitrate nitrogen in the wastewater that has gone through the process is reduced to nitrogen gas by denitrifying bacteria in an anaerobic atmosphere in the presence of the trickling filter sludge separated in the first step, and organic matter is removed in this step. A sewage treatment method comprising a fourth step of circulating a part of the bed sludge to the denitrification step and the remainder to the first step.