JPH0716674B2 - Wastewater treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of a wastewater treatment method by an activated sludge method.

[Conventional technology]

The activated sludge method has been developed as a high-grade treatment technology for municipal sewage and industrial wastewater, and has been widely adopted as a method for biologically decomposing and removing BOD from wastewater. This method mixes and contacts wastewater with a suspension of microorganisms called activated sludge,
It aerobically aerobically decomposes the BOD of wastewater in the aeration tank. Then, in the aeration tank, the microorganisms are continuously cultured in the presence of oxygen using BOD in the wastewater as a culture medium. The mixed liquid from the aeration tank is introduced into a sedimentation basin, where microorganisms are settled and separated, and purified wastewater is discharged to the outside of the system. Most of the microorganisms that have settled in the sedimentation tank are returned to the aeration tank as activated sludge, and the specified microorganisms are present in the system.
A part of it is discharged out of the system.

In the activated sludge method as described above, there is substantially no growth of filamentous microorganisms such as filamentous fungi, the selective production and maintenance of highly active microorganisms are enhanced, and the sedimentation performance of microorganisms in a sedimentation pond is improved, A method has been proposed in which phosphorus can be substantially removed and also nitrogen can be removed (see JP-A-52-124768, etc.). In this method, before the aeration tank (aerobic zone),
Adding an anaerobic zone maintained under anaerobic conditions,
As well as inserting a denitrification zone between the anaerobic zone and the aerobic zone. The addition of the anaerobic zone avoids the propagation of fibrous species such as filamentous fungi that do not settle properly in the precipitation zone, and the BOD in the influent wastewater is adsorbed by the microorganisms that can act under the aerobic condition. Then, in the anaerobic zone, the release of phosphorus from the activated sludge is promoted, and the subsequent breeding of microbial species having an increased phosphorus uptake capacity in the aerobic zone is promoted. The anaerobic zone is followed by an aerobic zone in which the adsorbed BOD is oxidized and the remaining BOD is adsorbed and oxidized. In this aerobic zone, phosphorus is excessively ingested by microorganisms having an increased phosphorus uptake ability, and phosphorus is removed from wastewater. In the denitrification zone, anoxic condition is maintained,
The internal circulating fluid from the mixture and aerobic zone from the anaerobic zone is contacted, nitrate ion and nitrite ion (NOx ^-) is reduced to elemental nitrogen is released. These NOx ⁻ are formed by the oxidation of nitrogen such as ammonia contained in the inflowing wastewater in the aerobic zone, and are introduced into the denitrification zone in a state of being contained in the internal circulating liquid.

[Problems to be solved by the invention]

The present inventor has conducted various studies in the treatment of wastewater by the activated sludge method comprising the above-mentioned anaerobic zone / aerobic zone / sedimentation zone, and optionally adding a denitrification zone. It has been found that BOD plays an important role and that the ratio of phosphorus to BOD in the anaerobic zone has a great influence on phosphorus removal performance. That is,
In order to remove phosphorus efficiently (the total phosphorus content in the treated water flowing out of the precipitation zone should be 1 mg / l or less), the ratio of total phosphorus content / total BOD content at the anaerobic zone inlet should be controlled to 0.04 or less. is important. In the wastewater treatment by the activated sludge method, the content of phosphorus and BOD in the raw wastewater is not always constant, and since activated sludge that excessively ingests phosphorus is returned, the above-mentioned ratio at the anaerobic zone inlet is It is difficult to maintain by controlling the amount of sludge introduced. For example, if the total phosphorus content at the anaerobic zone entrance is
Assuming 5 mg / l, it is necessary to introduce raw wastewater having a BOD of 125 mg / l or more, and the above specific ratio can be secured only with raw wastewater to ensure stable and efficient phosphorus removal for a long period of time. It's difficult to go.

As a result of further studies, the present inventor has found that return water derived from various wastewater treatment systems, such as supernatant of sludge concentration tank, desorption solution of digestion tank, and heat treatment separation solution, has a relatively high BOD. It has been found that the above specified ratio can be ensured smoothly and advantageously by mixing such return water with the raw waste water and the returned sludge.

[Means for solving problems]

The present invention has been completed based on the above findings, and a mixture of wastewater containing phosphorus and BOD and activated sludge, a complete anaerobic zone containing neither molecular oxygen nor bound oxygen, and dissolved oxygen. The phosphorus is released from the activated sludge in the anaerobic zone by sequentially exposing it to the aerobic zone under the contained condition, and the BOD is adsorbed to the activated sludge, the BOD is oxidized and decomposed in the aerobic zone, and phosphorus is excessively ingested in the activated sludge. Let
Then, in the wastewater treatment method, which comprises discharging treated water from the sedimentation zone and returning a part of the sedimented sludge to the anaerobic zone as activated sludge, return water containing BOD at a high concentration derived from the wastewater treatment system is obtained. Introduced into the anaerobic zone,
The ratio of total phosphorus amount / total BOD amount at the inlet of the anaerobic zone
The present invention newly provides a method for treating wastewater, which is characterized by keeping it at 0.04 or less.

In the present invention, it is important to maintain the ratio of total phosphorus content / total BOD content at 0.04 or less. By doing so, the release of phosphorus from the activated sludge in the anaerobic zone is promoted, and as a result, the phosphorus uptake ability from the activated sludge in the aerobic zone is enhanced and the phosphorus removal effect from the wastewater is enhanced. Further, by ensuring the above-mentioned specific ratio, when the denitrification zone is inserted between the anaerobic zone and the aerobic zone, an effect that the denitrification efficiency is enhanced by the action of the increased BOD is also achieved.

Therefore, the present invention provides a mixture of wastewater containing phosphorus, nitrogen and BOD and activated sludge in a complete anaerobic zone under the condition that neither molecular oxygen nor bound oxygen is contained, and denitrification under anoxic condition. Zone and the aerobic zone under the dissolved oxygen-containing state to release phosphorus from the activated sludge in the anaerobic zone and adsorb BOD to the activated sludge, and in the denitrification zone the mixture from the anaerobic zone and the aerobic zone described later. contacting the internal circulating liquid from NOx ^- the so reduced to nitrogen and released out of the system, to oxidize and decompose BOD under aerobic zone, nitrogen NOx ^- is overdose activated sludge phosphorus causes oxidized to Then, sludge is precipitated from the mixture from the aerobic zone in the precipitation zone, treated water is discharged from the precipitation zone, and part of the precipitated sludge is returned to the anaerobic zone as activated sludge. In the wastewater treatment method
A method for treating wastewater, characterized in that return water derived from a wastewater treatment system and containing BOD at a high concentration is introduced into the anaerobic zone, and the ratio of total phosphorus amount / total BOD amount in the anaerobic zone is maintained at 0.04 or less. Is also newly provided.

Hereinafter, the present invention will be described more specifically with reference to the drawings.
The drawing is a schematic side sectional view for explaining a wastewater treatment method by the activated sludge method. FIG. 1 is a specific example of anaerobic zone / aerobic zone / sedimentation zone, and FIG. 2 is an anaerobic zone /
Specific examples of denitrification zone / aerobic zone / sedimentation zone are shown below. In these figures, A is an anaerobic zone, B is a denitrification zone, C is an aerobic zone, and D is a precipitation zone.

The anaerobic zone A is maintained in a completely anaerobic state in which neither molecular oxygen nor bound oxygen is contained. By maintaining the zone A as an airtight structure with gas or mechanical stirring, the complete anaerobic state is maintained. In the illustrated example, the anaerobic zone A
Is divided and divided into three sections 10, 11, 12.
It does not have to be particularly divided, or is not limited to three and may be divided into two or more. Further, each section of the anaerobic zone A is provided with a stirring means 7, and three sections are provided.
10, 11, 12 are connected in series. The influent wastewater containing phosphorus and BOD or the influent wastewater containing phosphorus, nitrogen and BOD is introduced into the anaerobic zone A from the line 1 and stirred and mixed with the activated sludge returned from the precipitation zone D through the lines 4 and 2. . In the drawing, the inflow wastewater 1 has three sections 10,
Although it is distributed and injected into 11 and 12, it may be injected into only the first compartment 10 without distribution. And anaerobic zone A
In the concrete example of FIG. 1, the mixed liquid from
In the specific example shown in FIG. 2, it is transferred to the denitrification zone B.

Although the denitrification zone B is maintained under anoxic condition, the same means as in the anaerobic zone A can be adopted as the maintaining means. In the specific example of FIG. 2, the zone B has an airtight structure, and the anoxic state is maintained by mechanical stirring. The amount of dissolved oxygen in denitrification zone B is usually 0.
It is kept below 5 mg / l, preferably below 0.3 mg / l. Further, the denitrification zone B is usually divided into two or more compartments, and in the specific example, is divided into three compartments 13, 14, 15. Further, each section of the denitrification zone B is provided with a stirring means 8, and the three sections 13, 14, 15 are connected in series. The mixed liquid from the anaerobic zone A is introduced into the denitrification zone B, where it is brought into agitating contact with the internal circulating liquid recirculated from the aerobic zone C through the line 6. In the specific example of FIG. 2, the internal circulating fluid is divided into three compartments 13, 14, 15
However, it may be injected only into the first compartment 13. Then, the mixed liquid from the denitrification zone B is transferred to another aerobic zone C.

The aerobic zone C is also preferably divided into two or more compartments and is preferably divided into four compartments 16, 17, 18, 19 which are connected in series in the embodiment shown in the drawing. The compartment is aerated. Aeration in the aerobic zone C is performed by introducing an oxygen-containing gas. Usually, air is introduced from the bottom of the aerobic zone C by the aeration device 9 provided for each section. The dissolved oxygen amount in the aerobic zone C is usually maintained at 1 mg / l or more, preferably 2 mg / l or more. Then, the mixed liquid from the aerobic zone C is transferred to the precipitation zone D in the specific example of FIG. 1, and in the specific example of FIG. 2, a part of the mixed liquid is used as an internal circulating liquid from the line 6 to the denitrification zone B. The other part is introduced into the precipitation zone D.

In the embodiment as shown in FIG. 2, the amount of the internal circulating liquid recirculated through the line 6 is usually 100 to 400 of the mixed liquid transferred from the anaerobic zone A to the denitrification zone B.
%, Preferably 100 to 200%.

In the sedimentation zone D, the sludge is separated into treated water and sedimented sludge. Part of the settled sludge is returned to the anaerobic zone A as activated sludge through the lines 4 and 2, and the treated water is discharged from the settling zone D through the line 3. It is desirable that the amount of activated sludge returned by the lines 4 and 2 is usually selected from the range of 20 to 150% of the inflowing wastewater 1, preferably about 30 to 100%. Other processing conditions in each of the zones A, B, and C, such as the staying time, can be appropriately selected.

In the method of the present invention, the total phosphorus amount in the anaerobic zone A / total
The high-concentration BOD-containing return water is introduced into the anaerobic zone A through the line 20 so that the ratio of the BOD amount becomes 0.04 or less.
By such means, the amount of BOD in the system is kept above a predetermined amount, the release of phosphorus from the activated sludge in the anaerobic zone A is promoted, and as a result, the excessive intake of phosphorus by the activated sludge in the aerobic zone C is increased. Therefore, the removal efficiency of phosphorus from the wastewater is stably enhanced. Further, the denitrification efficiency in the denitrification zone B is improved by increasing the BOD amount in the system. In the present invention, the high-concentration BOD-containing return water can be introduced into the anaerobic zone A and separately into the denitrification zone B.

Further, in the method of the present invention, as described in the specific example of the drawing, by distributing and injecting the wastewater and the internal circulating liquid to the anaerobic zone and the denitrification zone, respectively, the BO
Since the D concentration was constant in each section, the release of phosphorus from sludge became large overall, the excessive intake of phosphorus by sludge in the aerobic zone was further promoted, the phosphorus removal rate increased, and the denitrification zone Then, the nitrogen addition becomes constant in each section, and the denitrification effect increases.

〔Example〕

Next, examples of the present invention will be described more specifically, but it goes without saying that the present invention is not limited to these examples.

Example 1 and Comparative Example 1 According to FIG. 1 of the accompanying drawings, wastewater was treated under the conditions shown in Table 1 below. In addition, as a comparative example, wastewater treatment was also performed when returning water was not introduced into the anaerobic zone. The results are shown in Table 1 below.

Example 2 and Comparative Example 2 According to FIG. 2 of the accompanying drawings, the wastewater was treated under the conditions shown in Table 2 below. In addition, as a comparative example, wastewater treatment was also performed when returning water to the anaerobic zone was not introduced. The results are shown in Table 2 below.

[Effect of the invention] The present invention has very good dephosphorization efficiency from wastewater, for example, has an excellent effect that the total phosphorus concentration in the treated water after treatment can be reduced to 1 mg / l or less, and contains BOD. Even in the treatment of wastewater whose amount is not always constant, it has an effect that a good dephosphorization efficiency can be stably ensured over a long period of time.
Further, also in the case of treating wastewater containing nitrogen such as ammonia, the advantage that good denitrification efficiency can be achieved is recognized.

[Brief description of drawings]

The drawing is a schematic side sectional view for explaining the wastewater treatment method by the activated sludge method. Fig. 1 shows a specific example of an anaerobic zone, an aerobic zone, and a precipitation zone, and Fig. 2 shows an anaerobic zone, a denitrification zone, and This is a concrete example of the air zone and the precipitation zone. A ... Anaerobic zone, B ... Denitrification zone C ... Aerobic zone, D ... Sedimentation zone 1 ... Wastewater inflow line 2, 4 ... Sludge return line 3 ... Treated water outflow line 6 ... Internal circulating fluid injection line 7, 8 ... Agitation Means, 9 ... Aeration device 10, 11, 12 ... Anaerobic zone section 13, 14, 15 ... Denitrification zone section 16, 17, 18, 19 ... Aerobic zone section 20 ... Return water inflow line

Claims (2)

[Claims] 1. A mixture of wastewater containing phosphorus and BOD and activated sludge is sequentially exposed to an anaerobic zone in the absence of molecular and bound oxygen and an aerobic zone in the presence of dissolved oxygen to anaerobically. Once phosphorus is released from the activated sludge in the zone, BOD is adsorbed, BOD is participated and decomposed in the aerobic zone and phosphorus is excessively ingested in the activated sludge, and then the mixture from the aerobic zone is solid-liquid separated in the precipitation zone. And let the treated water flow out from the precipitation zone,
In a wastewater treatment method, which comprises returning a part of the settled sludge to the anaerobic zone as activated sludge, introducing return water containing a high concentration of BOD to the anaerobic zone, which is derived from a wastewater treatment system. A method for treating wastewater, characterized in that the ratio of total phosphorus amount / total BOD amount as a phosphorus removal factor in 0.04 is maintained at 0.04 or less. 2. A mixture of wastewater containing phosphorus, nitrogen and BOD and activated sludge is sequentially passed to an anaerobic zone under the above-mentioned conditions, a denitrification zone under anoxic conditions and an aerobic zone under dissolved oxygen-containing conditions. Then, phosphorus is released from the activated sludge in the anaerobic zone and BOD is adsorbed to the activated sludge, and the mixture from the anaerobic zone and the internal circulating liquid from the aerobic zone described below are contacted with each other in the denitrification zone to leave the residual BOD ( NOx in the presence of a hydrogen donor) ^- the so reduced to nitrogen and released out of the system, the nitrogen is oxidized decompose BOD under aerobic zone NOx ^- causes oxidized, phosphorus is overdose in activated sludge and, Then, the treated water is discharged from the settling zone, and a part of the settling sludge is returned to the anaerobic zone as activated sludge.
A method for treating wastewater, comprising the step of introducing return water containing water into the anaerobic zone and maintaining the ratio of total phosphorus amount / total BOD amount as a phosphorus removal factor in the anaerobic zone at 0.04 or less.