JPH06238295A - Drain treatment - Google Patents

Abstract

PURPOSE:To obtain a method for treating drained water for efficient organic substance removal and nitrification by performing nitrification using a back-stage tank filled with a porous carrier which is best suited for the growth of nitrification bacterium after removing an organic substance using a front-stage tank of a multi-stage divided biotreatment tank. CONSTITUTION:In a drain treatment method, a treatment tank consists of a biotreatment tank 1 divided by a diaphragm 9 in a multi-stage fashion as the front stage being the first stage 4 of an organic substance removal tank and the second stage 5 of an organic substance removal tank, and the back stage being the first stage 6 of a nitrification tank and the second stage 7 of a nitrification tank. In addition, the organic substance removal tanks 4, 5 are filled with a plate-like vinyl chloride carrier 2, for example, which is best suited for the growth of BOD oxidation bacterium for removal of the organic substance. On the other hand, the nitrification tanks 6, 7 are filled with a granulated ceramic carrier 8, for example, which is best suited for the growth of nitrification bacterium as a porous carrier. In addition, each tank 4 to 7 is equipped with arranged air diffusion pipe 3 for aeration, and waste water is purified by nitrification in the nitrification tanks 6, 7 after the removal of an organic substance in the organic substance removal tanks 4, 5. Thus water purification takes place and the treated water is discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method for removing organic substances and nitrifying.

[0002]

2. Description of the Related Art As a method for decomposing and removing organic matter contained in human waste, sewage, various industrial wastewaters, etc., a biological treatment method utilizing microorganisms is widely used. The problem becomes serious, and not only organic substances but also advanced treatment of nitrogen and phosphorus in these wastewater is desired. In order to perform nitrogen removal using biological treatment technology, nitrification must first be performed. That is, nitrifying bacteria
Nitrite nitrogen (hereinafter, NO ₂ −) from ammonia nitrogen (hereinafter, NH ₄ —N) due to (generic term for nitrite bacteria and nitric acid bacteria)
N) or nitrate nitrogen (hereinafter, NO ₃ —N).
Further, in order to further remove nitrogen, it is necessary to reduce these to nitrogen gas by denitrifying bacteria growing in an anaerobic atmosphere.

[0003]

The conventional biological treatment techniques for nitrification are roughly classified into an activated sludge method using suspended microorganisms and a biofilm method in which a tank is filled with a carrier to capture the microorganisms. . In the activated sludge method, organic matter is removed B
The OD-oxidizing bacteria and the nitrifying bacteria grow in a suspended state while being mixed. However, the growth time of nitrifying bacteria is short, and the doubling time is as long as 10 to 70 hours as compared with several 10 minutes of BOD-oxidizing bacteria. Therefore, the conventional activated sludge method has a drawback in that nitrifying bacteria are easily washed out from the tank and nitrification does not occur at this time. There are various biofilm methods depending on the shape and material of the carrier to be filled. Among them, a treatment method using a plate-shaped carrier made of a synthetic resin such as vinyl chloride has been widely used. This is B on the surface of the carrier.
The OD-oxidizing bacteria are formed into a slime shape to remove organic substances, and nitrification is carried out by nitrifying bacteria growing inside the carrier. However, when external environmental conditions change, organisms are separated from the surface of the carrier and flow out of the treatment tank, which has a drawback that nitrification does not proceed.

As another biofilm treatment method, there is a treatment method using a porous carrier. The porous carrier may be an inorganic material such as granular ceramic or a synthetic resin such as polyethylene. The shape of these porous carriers provides an environment suitable for the growth of nitrifying bacteria. That is, the porous carrier has the effect of buffering the characteristics of nitrifying bacteria that are weak against changes in external environmental conditions. However, in wastewater having a high organic matter load, BOD-oxidizing bacteria become predominant, and the carrier surface may be covered with slime-like substances derived from bacterial cell components, metabolites, etc., thereby inhibiting the growth of nitrifying bacteria inside the surface layer. This is due to the following reasons. Nitrifying bacteria are autotrophic bacteria that perform cell synthesis using carbon dioxide as the sole carbon source. Therefore, the heterotrophic bacterium B
There is no substrate competition with OD-oxidizing bacteria,
Oxygen is required to oxidize NH ₄ —N and NO ₂ —N when obtaining energy for growth, so that competition for oxygen occurs. At this time, nitrifying bacteria are known to be inferior to BOD-oxidizing bacteria, and it is said that growth and activity thereof are suppressed.

Therefore, in a biological treatment method using a porous carrier, in order to effectively promote nitrification, BO
It has a drawback that a slime-like substance derived from the growth of D-oxidizing bacteria must be frequently backwashed or withdrawn. As described above, the activated sludge method and the biofilm method have been conventionally performed in order to sufficiently promote nitrification in biological treatment tanks such as human waste, sewage, and various industrial wastewater. However, these remain problems such as insufficient supply of oxygen due to symbiosis with BOD-oxidizing bacteria and outflow of nitrifying bacteria to the outside of the tank, which is a cause of not exhibiting good nitrification. In view of the above problems, the present invention provides a wastewater treatment method for efficiently removing organic substances and nitrifying.

[0006]

DISCLOSURE OF THE INVENTION The present invention is directed to dividing a biological treatment tank into multiple stages, removing organic substances in the previous stage tank, and then filling a porous carrier suitable for growth of nitrifying bacteria with the latter stage tank. The present invention relates to a wastewater treatment method for nitrification. First, the processing flow will be described. In the treatment tank, the biological treatment tank is divided into multiple stages, so that the front stage is set as an organic matter removal tank and the rear stage is set as a nitrification tank, and organic matter removal and nitrification are performed in each tank. It is also possible to use a multi-phase treatment method in which both tanks are separated in advance. The volume ratio of each tank to the total tank and the number of tanks depend on the load conditions of organic matter and nitrogen in the inflowing waste water. By combining the treatment tank with an anaerobic treatment tank, it is possible to reduce the treated water in which nitrification has progressed to nitrogen gas and remove it.

Next, the carrier to be filled in the processing tank will be described. There are various types of carriers used in the biological treatment tank, and as their materials, there are synthetic resins such as polyethylene and polypropylene, inorganic substances such as anthracite and ceramics, and the shapes are plate-like, granular, saddle-like, and the like. In general, the growth of BOD-oxidizing bacteria that removes organic matter has no affinity for the selection of many of these carriers, and therefore does not limit the selection. It is necessary to avoid this, as it requires manipulation. Next, the carrier to be filled in the nitrification tank will be described. In the present invention, the organic substance components have already been removed in the organic substance removal tank in the preceding stage, and the inorganic water components such as NH ₄ —N occupy most of the wastewater flowing into the nitrification tank. For this reason, the nitrification tank has a BOD
Since the presence of oxidizing bacteria is low and nitrifying bacteria take precedence, the sludge generated in the organic matter removal tank is low.

In view of such a processing flow, in the present invention, a porous carrier is adopted as the carrier to be filled in the nitrification tank. It has been conventionally said that the porous carrier is suitable for the growth of nitrifying bacteria. This is because the porous carrier has characteristics such as good oxygen permeability and avoiding the risk of bacterial outflow to the outside of the treatment tank. However, as described above, in the conventional processing flow, such characteristics cannot be sufficiently brought out due to the generation of slime-like substances due to the symbiosis of BOD-oxidizing bacteria. INDUSTRIAL APPLICABILITY The present invention can solve the above-mentioned problems and bring out the characteristics of the porous carrier by dividing the organic substance removal tank and the nitrification tank in multiple stages.

[0009]

EXAMPLES Next, examples of the present invention will be described. First, a wastewater containing organic matter and organic nitrogen was artificially produced, and this was used as wastewater to be supplied to the multistage biological treatment tank 1 shown in FIG. 1 according to the present invention, and continuous treatment operation was performed. In FIG. 1, 2 is a plate-shaped vinyl chloride carrier housed in the first stage 4 and the second stage 5 of the organic substance removing tank, and 8 is a granular ceramic carrier filled in the first stage 6 and the second stage 7 of the nitrification tank. , 9 is 4,
Partition walls 3, 5 and 6 for partitioning each tank are air diffusers for feeding aeration air into each tank, and waste water is 4, 5, 6
Then, the water is moved in the order of 7 and 7 to be purified and discharged as treated water. Further, in order to determine the treatment characteristics of the multi-stage biological treatment tank, continuous treatment was applied to the one-phase biological treatment tank shown in FIG. In FIG. 2, the one-phase biological treatment tank 10 is filled with the granular ceramic carrier 8, and 3 is the same air diffuser as in the case of FIG. Wastewater is introduced from the left end, purified, and discharged as treated water from the right end. Table 1 shows the composition of the wastewater components, and Table 2 shows the specifications and load conditions of both treatment tanks. The temperature was about 25 ° C.

[0010]

[Table 1]

[0011]

[Table 2]

(1) Organic matter removal and nitrification characteristics First, in order to see the organic matter removal and nitrification abilities of each treatment tank, the dissolved organic carbon concentration (hereinafter DOC) and the nitrification rate of the final treated water change with time. I asked. The result is shown in Figure 3.
Shown in. In the figure, ● and ○ are multi-stage biological treatment tanks (● is DOC, ○ is nitrification rate), ▲ and △ are single-phase biological treatment tanks (▲ is DOC, △ is nitrification rate) ) Is shown. The nitrification rate was calculated by the following calculation formula.

[0013]

[Equation 1] Nitrification rate (%) = {(treated water NOx-raw water NOx)
/ Treated water TN} × 100 However, NOx = NO ₂ ^2- -N + NO ₃ ^-- N

As a result, the removal of both organic substances proceeded similarly, but there was a difference in the rise of nitrification. That is, nitrification was expressed in the early stage of the culture in the multi-stage biological treatment tank, and then stable treatment was shown. When the carrier packed in the one-phase biological treatment tank was observed, its surface was covered with slime-like substances which might be derived from the bacterial cell components and metabolites of BOD-oxidizing bacteria. This is considered to be the reason why the growth of nitrifying bacteria was suppressed and nitrification did not proceed well as described above. As described above, it was confirmed that the treatment method had utility for nitrification.

Further, in order to determine the organic matter removal and nitrification characteristics in each tank of the treatment tank, the DOC and nitrification rate of each tank on the 100th day of culture were determined. The results are shown in Fig. 4. In the figure, ● indicates DOC and ○ indicates nitrification rate. From this result, it was found that almost DOC was removed in the first stage of the organic matter removal tank, and the organic carbon component was scarcely contained in the first stage of the nitrification tank. In addition, it became clear that nitrification started to progress from the second stage of the organic matter removal tank, and thereafter the nitrification rate gradually increased. Therefore, by the treatment by the treatment tank,
It was found that the BOD-oxidizing bacteria and the nitrifying bacteria were separated from each other, and the growth of the latter was not hindered, and efficient organic matter removal and nitrification could be performed.

(2) SS trapping characteristics In order to determine the SS trapping characteristics in each tank, culture 10
The SS in each tank on day 0 was determined. The results are shown in Table 3.

[0017]

[Table 3]

First, SS was generated in the first stage of the organic matter removing tank. It is considered that this is derived from liberated bacterial components and metabolites of BOD-oxidizing bacteria attached to the carrier filled in the tank. Next, SS was decreased in the second stage of the organic substance removal tank where DOC removal proceeded. This is probably because much of the SS generated in the first stage was captured by the carrier in the second stage. Furthermore, SS was hardly detected in the nitrification tank. It is considered that this is because most of the SS was already captured in the second stage of the organic matter removal tank and that there was no outflow of bacterial cell components or the like because there were no BOD-oxidizing bacteria in the nitrification tank. From the above, it was found that the present invention has an advantage that SS is generated and captured in the organic matter removal tank in many cases, and the operation for extracting excess sludge is limited and simple without extending over the entire tank. .

From the above examples, it was revealed that the multi-stage biological treatment tank according to the present invention efficiently promotes organic substance removal and nitrification, and further facilitates the operation of extracting excess sludge.

[0020]

EFFECTS OF THE INVENTION According to the present invention, the removal of organic substances and the nitrification proceed efficiently, and the operation of extracting excess sludge can be simplified.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a multistage biological treatment tank in a wastewater treatment method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a one-phase biological treatment tank.

FIG. 3 is a graph showing daily changes in DOC and nitrification rate.

FIG. 4 is a graph showing DOC and nitrification rate of each tank of the multi-stage biological treatment tank of FIG.

[Explanation of symbols]

1 ... Multi-stage biological treatment tank, 2 ... Plate-shaped vinyl chloride carrier, 3 ...
Air diffuser, 4 ... Organic matter removal tank first stage, 5 ... Organic matter removal tank second stage, 6 ... Nitrification tank first stage, 7 ... Nitrification tank second stage, 8 ... Granular ceramic carrier, 9 ... Partition wall, 10 ... 1 Phase-type biological treatment tank

Claims (1)

[Claims] 1. A biological treatment tank is divided into multiple stages, organic substances are removed in the former tank, and then nitrification is performed in the latter tank filled with a porous carrier suitable for growth of nitrifying bacteria. Wastewater treatment method.