JPH07116691A - Treatment of drainage - Google Patents

Abstract

PURPOSE:To simultaneously remove nitrogen and phosphorus contained in drainage in an intermittent aeration activated sludge treatment method by introducing drainage into an anaeration tank and returning a part of settling sludge in a precipitation tank and also agitating drainage, and thereafter introducing drainage into an intermittent dispersion aeration tank and applying activated sludge treatment to drainage. CONSTITUTION:An anaeration tank 2 in which anaerobic treatment is performed for drainage 1 is equipped with a pump 8 and an agitator 10. The pump 8 is interlocked with an oxidation-reduction electrometer 6 to introduce primary settling sludge automatically when oxidation-reduction potential of drainage in the tank 2 is regulated to >=-150mV. Further an intermittent aeration tank 3 into which drainage 1 anaero-bically agitated in the anaeration tank 2 is sent is equipped with an aeration device 12 interlocked with a dissolved oxygen meter 9 through a timer 11 and with an agitator 10. Drainage 1 is introduced into the anaeration tank 2 and a part of sludge precipitated in a precipitation tank 4 is returned into the tank 2. After mechanical agitation treatment is performed in a specified retention time, drainage is introduced into an intermittent aeration tank 3. Aeration and nonaeration are alternately repeated herein and solid-liquid separation is applied to the mixed liquid of activated sludge in the precipitation tank 4. Supernatant liquid is discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater which can simultaneously remove nitrogen and phosphorus together with organic pollutants in wastewater.

[0002]

2. Description of the Related Art In controlling eutrophication of closed water areas such as lakes and inner bays, nitrogen and phosphorus as nutrient chlorine in domestic wastewater, which is the main cause, can be removed at the same time at low cost and with maintenance management. It is important to establish and disseminate easy processing technology. Although many techniques have been developed and introduced as a treatment technology for organic substances and nitrogen, biological treatment is the mainstream due to the reduction of operating costs and the ease of maintenance, and one of the processes is intermittent aeration. There is an activated sludge method.

FIG. 5 shows a processing flow of a conventional intermittent aerated activated sludge method. In the conventional intermittent aerated activated sludge method, the aeration / non-aeration time ratio is set by setting the timer 11, so it is possible to cope with load fluctuations due to the amount of water in the drainage 1, the water quality, and the sludge concentration in the intermittent aeration tank 3. However, there is a case where ammoniacal nitrogen is left due to insufficient nitrification or nitrate nitrogen is left due to overaeration, and the treatment performance is deteriorated.

Therefore, in order to cope with these load fluctuations,
A dissolved oxygen (hereinafter referred to as DO) automatic control intermittent aeration activated sludge method shown in FIG. 6 has been developed. This is because the upper limit value and the lower limit value of the DO concentration and the anaerobic stirring time are set by using the DO meter 9 and the timer 11 to automatically control the ON / OFF of the aeration device 12 without being influenced by the load fluctuation. Since the anaerobic / aerobic state can be secured, the nitrification / denitrification reaction is stable and the maintenance is easy.
However, a satisfactory phosphorus removal performance is not always obtained with only the intermittent bubbling tank 3, so that for the purpose of more advanced nitrogen / phosphorus removal, the operation / control of conventional biological phosphorus removal should be performed. It is necessary to incorporate it.

[0005]

In the prior art shown in FIG. 6, the DO meter 9 and the timer 11 are used to set the upper and lower limits of the DO concentration and the anaerobic stirring time, and the aeration operation is performed.
By the control method that automatically controls the DO concentration in the intermittent aeration tank 3 by stopping, it is possible to perform a stable nitrification / denitrification reaction by repeating the anaerobic / aerobic state without being affected by the load change in the intermittent aeration tank 3. It is possible. However, since the conditions of biological denitrification and dephosphorization are different, notable biological release and excessive intake of phosphorus do not necessarily occur in the intermittent aeration tank 3, and it is particularly suitable for the release of phosphorus. There is a problem that high phosphorus removal performance cannot be expected unless the anaerobic state is maintained.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for treating wastewater which can simultaneously remove nitrogen and phosphorus in the wastewater.

[0007]

The structure of the present invention for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The present invention provides a waste water containing an organic substance, a nitrogen compound and a phosphorus compound. In the intermittent aerated activated sludge treatment method of continuously treating, the anaerobic tank 2 and the settling tank 4 are installed in the preceding stage of the intermittent aeration tank 3, and the wastewater 1 flows into the anaerobic tank 2 and precipitates in the settling tank 4. A part of the sludge is returned and a mechanical agitation process for promoting the reaction is carried out to guide the wastewater to the aeration tank 3 with intermittent aeration, and aeration and non-aeration are alternately repeated in the aeration tank 3 to activate sludge. In the anaerobic tank 2, the treatment and mechanical stirring treatment for promoting the reaction are carried out, the mixed liquid of the activated sludge treatment is introduced into the sedimentation tank 4 for solid-liquid separation, and the supernatant liquid is discharged as treated water. Promotes the release of phosphorus from sludge In which it took technical means to promote overdose biological nitrification and denitrification and phosphorus in Rutotomoni intermittent punishment Kiso 3.

In the intermittent aeration tank 3, aeration and non-aeration are repeated intermittently under the control of the DO meter and the timer 11. When this control detects and confirms the upper limit set value of the DO concentration in the tank 3, aeration is stopped, and aeration is resumed after the anaerobic set time has elapsed. Below, this aeration / non-aeration operation is repeated. The inside of the tank 3 is constantly stirred by the stirrer 10 in order to improve the reaction efficiency while being returned. At that time, instead of the upper limit value of the DO concentration, the start point of the rapid increase of the DO concentration is detected, and if the aeration is stopped, energy can be saved.

Further, by dividing the anaerobic tank 2 into two or more tanks in the flow direction of the waste water so that the flow approaches the plug flow type, the release of phosphorus is promoted and the phosphorus removal performance is improved.

Further, the redox potential of the anaerobic tank 2 (hereinafter referred to as O
(Referred to as RP) is always -150 m or less so that sludge releases phosphorus. If it exceeds this value, the ORP value is lowered by introducing the first sludge and the like.

[0011]

[Function] The biological dephosphorization process is as follows: Activated sludge (dephosphorization bacteria) releases phosphine when stored in the body by activated sludge (dephosphorization bacteria) in an anaerobic state. It is known to consume too much phosphorus and excessively ingest more phosphorus than is released in an anaerobic state. In addition, ORP is used as an index as a condition for phosphorus release in an anaerobic state,
The value is reported to be in the range of -150 mV to -250 mV.

In the anaerobic tank according to the present invention, the sludge returned from the settling tank 4 containing phosphorus accumulating bacteria is mixed with the inflowing wastewater to increase the BOD (organic matter) concentration and the anaerobic concentration, thereby increasing the ORP value. Decreases to -200 mV or less. This satisfies the conditions for securing organic substances and ORP necessary for dephosphorization bacteria to release phosphorus. The sludge that has released phosphorus in the anaerobic tank 2 is simultaneously excessively ingested in the intermittent aeration tank 3 where biological nitrification and denitrification are performed by DO control. At that time, the release of phosphorus was not confirmed in the anaerobic state due to the non-aeration state. This is because the ORP value at which phosphorus is released is lower than the ORP value at which denitrification is performed, and phosphorus is released in the intermittent aeration tank 3. This is because the ORP does not decrease.

In the DO control method of the intermittent aeration tank 3, D
It is possible to improve the nitrification efficiency and save energy by stopping the aeration using the start point of the rapid increase of the DO concentration instead of the O concentration upper limit set value. This utilizes the fact that the ammonia concentration in the liquid completely disappears during the nitrification process and the DO concentration starts to rise at the same time. Further, in the nitrification / denitrification reaction of a single tank, it is possible to improve reaction efficiency by performing aeration / non-aeration as diligently as possible. Therefore, if the DO concentration rises, it is considered that nitrification is completed and the process proceeds to the denitrification step, whereby it is possible to prevent waste of energy and aeration and at the same time improve the treatment efficiency.

By dividing the anaerobic tank 2 into two or more tanks in the flow direction of the wastewater and bringing the flow closer to a plug flow type, the ORP in the anaerobic tank 2 is further lowered, the release of phosphorus is promoted, and the removal performance of phosphorus is increased. Is improved.

As for the release of phosphorus from the activated sludge, since the ORP of the surrounding environment progresses well at -150 mV or less, the ORP in the anaerobic tank 2 is always maintained in the range of -150 mV or less. When the value exceeds the value (outside the range), the first sludge etc. is automatically flowed in to perform OR
Decrease the value of P. From this fact, a stable phosphorus release in the anaerobic tank 2 is always generated by the automatic control, and an excessive intake of phosphorus in the next intermittent aeration tank 3 is promoted, so that a stable phosphorus removal performance is always obtained. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. Reference numeral 2 denotes an anaerobic tank for introducing effluent 1 from the outside to perform anaerobic treatment. The tank 2 is interlocked with the redox potential meter (ORP meter) 6 for measuring the redox potential. A pump 8 for automatically injecting initially settled sludge and the like when the oxidation-reduction potential of wastewater in the tank 2 becomes −150 mV or more, and a stirrer 10 for stirring the inside of the tank 2 to promote the reaction. Is equipped with.

Reference numeral 3 is an intermittent aeration tank which is connected to the anaerobic tank 2 and introduces the effluent 1 which is anaerobically stirred in the anaerobic tank 2 to perform aeration and non-aeration to perform intermittent aeration treatment.
In the aeration tank 3, a dissolved oxygen meter (DO meter) 9 for measuring dissolved oxygen (DO) in the tank, a timer 11 interlocked with the DO meter 9, and an aeration device interlocked with the timer 11 and driven. 12
And a stirrer 10 that promotes the reaction by stirring the waste water in the tank during aeration / non-aeration.

Numeral 4 is connected to the intermittent aeration tank 3, and the tank 3
This is a settling tank in which the treated water 5 treated in step 2 is separated by precipitation and the supernatant liquid is allowed to flow out of the system. And settling tank 4 and anaerobic tank 2
A return sludge pipe 7 for returning the settled sludge from the settling tank 4 to the anaerobic tank 2 is connected between and.

The operation control of the aeration device of the intermittent aeration tank 3 is as follows.
DO in the intermittent spout air tank 3 using the DO meter 9 and the timer 11
The upper and lower limits of concentration and the anaerobic stirring time were set, and automatic control was performed. The aeration state is from the lower limit to the upper limit,
In the non-aeration state, the anaerobic / aerobic time was controlled by maintaining a constant stirring time after reaching the lower limit. Further, the inside of the intermittent aeration tank 3 and the inside of the anaerobic tank 2 were always stirred by the stirrer 10.

Using the above apparatus, BOD 200 mg /
l, total nitrogen 20 mg / l, total phosphorus 7 mg / l treated with waste water, BOD 10 mg / l or less, total nitrogen 12 mg / l or less,
Treated water containing less than 1 mg / l of total phosphorus is obtained, and organic pollutants,
Nitrogen and phosphorus could be removed simultaneously. FIG. 2 shows changes with time in water quality in the anaerobic tank 2 and the intermittent aeration tank 3. Anaerobic tank 2 O
The RP decreased to around -200 mV, and the phosphorus concentration was found to increase with the release of phosphorus from sludge, and phosphorus was stably excessively ingested in the next intermittent aeration tank 3. It is generally considered that the higher the sludge phosphorus content, the higher the phosphorus removal capacity. FIG. 3 shows a comparison of phosphorus content in sludge between the conventional intermittent aeration method and the anaerobic + intermittent aeration method of the present invention. In the present invention, it can be seen that by installing the anaerobic tank 2, a phosphorus content rate more than double that of the conventional case can be obtained.

FIG. 4 shows the changes over time in the DO concentration and the ammonia nitrogen in the intermittent aeration tank 3, showing a rapid increase in the DO concentration after the ammonia nitrogen disappeared due to nitrification (point A).
Can be seen. Therefore, by detecting this sudden rising start point and stopping the aeration, the aeration can be prevented and the process can quickly proceed to the next denitrification step, so that the reaction efficiency can be improved and energy saving can be achieved.

An experiment was conducted by reducing the volume of the anaerobic tank 2 in order to reduce the size of the anaerobic tank 2. However, if the residence time of the anaerobic tank 2 is too short, the ORP will not decrease and the phosphorus will not be released. However, by dividing the anaerobic tank 2 into two or more tanks, an environment suitable for the release of phosphorus was gradually formed, and the phosphorus removal performance was improved. Therefore, it was possible to reduce the size of the anaerobic tank 2 by dividing the anaerobic tank 2 and making the flow a plug flow type.

When the ORP in the anaerobic tank 2 does not decrease due to load fluctuations and the release of phosphorus is suppressed, the phosphorus removal performance decreases. At that time, by detecting an increase in ORP and causing the first sludge 13 and the like to flow into the anaerobic tank 2 via the pump 8,
It can lower RP and accelerate the release of phosphorus.
As a result, the phosphorus removal performance can be stably maintained at a high level.

[0024]

EFFECTS OF THE INVENTION The wastewater treatment method of the present invention has the effect of simultaneously removing organic pollutants, nitrogen and phosphorus in wastewater.

[Brief description of drawings]

FIG. 1 is a process flow chart showing an embodiment of the present invention.

FIG. 2 shows phosphorus in an anaerobic tank and an intermittent aeration tank of the present invention,
The figure which shows the time change of ORP and DO.

FIG. 3 is a diagram showing a comparison of phosphorus content in sludge between the present invention and a conventional intermittent aeration method.

FIG. 4 is a diagram showing temporal changes of DO and ammonia nitrogen in the intermittent aeration tank of the present invention.

FIG. 5 is a flow chart of a conventional intermittent aeration tank.

FIG. 6 is a process flow chart of a conventional dissolved oxygen automatic control intermittent aeration tank.

[Explanation of symbols]

 1. Drainage 2. Anaerobic tank 3. Intermittent air tank 4. Settling tank 5. Treated water 6. ORP meter 7. Return sludge pipe 8. Pump 9. DO total 10. Stirrer 11. Timer 12. Aeration device 13. First sludge

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Makoto Yamamoto 3-1, 1 Kanda Sugawadai, Chiyoda-ku, Tokyo Inside Hitachi Chemical Techno Plant Co., Ltd. Shimodate Factory Co., Ltd. (72) Inventor Yuhei Inamori 2 of 16 Onogawa, Tsukuba City, Ibaraki Prefecture

Claims (5)

[Claims] 1. In an intermittent aerated activated sludge treatment method for continuously treating wastewater containing an organic substance, a nitrogen compound, and a phosphorus compound, an anaerobic tank 2 is installed in a stage before the intermittent aeration tank 3 and a precipitation tank 4 is installed in a latter stage. The anaerobic tank 2, the inflow of the wastewater 1 and the precipitation tank 4
Part of the sludge settled in step 1 is returned and the mechanical agitation process is carried out to guide the wastewater 1 to the aeration tank 3 with intermittent spitting, and in the aeration tank 3, aeration and non-aeration are alternately repeated to activate sludge. And the mechanical agitation treatment are carried out, the mixed liquid of the activated sludge treatment is introduced into the settling tank 4 for solid-liquid separation, and the supernatant liquid is discharged as treated water, whereby phosphorus is released from the sludge in the anaerobic tank 2. And a biological nitrification / denitrification reaction in the intermittent aeration tank 3 and an excessive intake of phosphorus. 2. The intermittent oxygen gas tank 3 has a dissolved oxygen meter 9 installed therein, and the upper and lower limits of dissolved oxygen and anaerobic stirring time are set to determine the dissolved oxygen concentration in the intermittent oxygen gas tank 3. The method for treating wastewater according to claim 1, wherein the method is automatically controlled by operating / stopping aeration. 3. An intermittent aeration tank 3 is provided with a dissolved oxygen meter 9 therein, and stops aeration by detecting a sudden rising start point of the dissolved oxygen concentration, and the dissolved oxygen concentration is further detected. The method for treating wastewater according to claim 1, wherein aeration operation is performed according to a lower limit value and an anaerobic stirring time set value. 4. The method for treating wastewater according to claim 1, wherein the anaerobic tank 2 is divided into two or more tanks in the flow direction of the wastewater. 5. The anaerobic tank 2 has an oxidation-reduction potentiometer installed therein so that the oxidation-reduction potential in the anaerobic tank 2 is -150.
The method for treating wastewater according to claim 1 or 4, wherein the first settling sludge or the like is supplied when the voltage becomes mV or less.