JPH047098A - Batchwise activated sludge treatment method - Google Patents

Abstract

PURPOSE:To keep the concn. of the phosphorus compound in treated water low by transferring to a process discharging supernatant water when the ORP measured value of a sedimentation sludge tank in a still standing process separating waste water into settled sludge and supernatant water becomes -150mV or less. CONSTITUTION:The first anaerobic process injecting waste water in a reactor having activated sludge present therein under mechanical stirring and discharging a phosphorus compound from activated sludge and the first aerobic process performing aeration to control ORP to +100 to +120mV or more to carry out the oxidative decomposition of BOD and the oxidation of an ammonia compound and allowing activated sludge to excessively take in a phosphorous compound are carried out. Next, the second anaerobic process distributing a part of waste water using a hydrogen donor to stirr the same mechanically or to aerate the same under mechanical stirring to control ORP to -50 to -150mV and reducing nitrogen oxide to nitrogen gas is applied.

Description

Detailed Description of the Invention (Industrial Application Field) This invention is a method for removing eutrophic substances such as pollutants (BOD), ammonia compounds, and phosphorus compounds from wastewater, which are indicated by biochemical oxygen demand, in sea areas, rivers, and lakes. The present invention relates to a method for removing substances that cause oxidation by batch activated sludge treatment.

(Prior Art) Conventionally, activated sludge treatment has been used as a method for removing eutrophic substances mentioned in RIi.
n l+II OJ method-(, J, L, Ba
rnard, W ater W ast, esEng
g, 33 (1974)) or JP-A-54-2
There are the A10 method and the A2/O method described in 4774.

Furthermore, A210 described in Japanese Patent Publication No. 61-17558
As a modification of this method, a method that incorporates a rotating disk to immobilize organisms in the nitrification tank is known.

In these methods, BOD is mainly processed by aerobic oxidative decomposition, nitrogen compounds are released by nitrification-denitrification method, phosphorus compounds are released from activated sludge in an anaerobic environment, and excess phosphorus is released into activated sludge in an aerobic environment. It is removed by ingestion.

Further, JP-A No. 62-42796 discloses a method for removing BOD, ammonia compounds, and phosphorus compounds by a batch activated sludge treatment consisting of five stages. That is, the first
In the step, wastewater is injected into a biochemical reactor containing activated sludge with gentle agitation.
<P is brought to an anaerobic state of -200 to 3 Tl Om V to release phosphorus compounds from the activated sludge, and in the second stage, aeration is performed to increase ORP to +10 (1 to +120 clear\1 or more and aerobic state to BOD , removal of phosphorus compounds, and oxidation of ammonia compounds), and the third step is to reduce nitrogen oxides to nitrogen gas by reducing ORP to -5() to -150 mV anaerobic state without injecting a hydrogen donor. In the f:tS4 stage, aeration is carried out to bring the ORP to an aerobic state of +50 to +150 degrees to oxidize and decompose excess hydrogen donor, and in the fifth stage, aeration and stirring are stopped to allow the activated sludge to settle and WQ. This is a batch activated sludge treatment method in which supernatant water is discharged.

(Problem to be Solved by the Invention) However, in this fifth stage, the anaerobic degree of the sludge that has been deposited after settling increases, and as a result, phosphorus compounds are released from the sludge, resulting in an increase in the concentration of phosphorus compounds in the supernatant water. there were. That is, in the upper stages of sludge settling, mechanical stirring and aeration cannot be performed to separate the sludge by settling, and the anaerobic degree of the settled sludge layer increases over time. For example, in a process that only considers sludge sedimentation, in which the supernatant water is discharged after a predetermined period of time has passed, the anaerobic degree increases and phosphorus compounds are released, causing the treated water to be discharged. It is not possible to effectively prevent the phosphorus compound concentration from becoming quotient, and it is difficult to meet the strict phosphorus compound concentration standards.

The present invention provides a method that can maintain a low concentration of phosphorus compounds in treated water by improving the treatment in the sludge settling step of a method for batchwise activated sludge treatment of wastewater.

(Means for Solving the Problems) The present invention provides at least BOL), an ammonia compound,
This is a batch activated sludge treatment method for wastewater containing phosphorus compounds as eutrophic substances, in which wastewater is injected into a reactor containing activated sludge with mechanical stirring, and phosphorus compounds are released from the activated sludge. Then, perform aeration and OR
P is controlled within the range of +100 to +120 mV or higher (based on silver-silver chloride electrodes) to perform oxidative decomposition of BO) and oxidation of ammonia compounds, as well as an aerobic one-hour cycle in which phosphorus compounds are excessively ingested into activated sludge. , using a part of the wastewater as a hydrogen donor and dispensing it with mechanical stirring or mechanical stirring and aeration to increase the ORP from -50 to 15+1 m'i/
(Silver-silver chloride electrode standard) Anaerobic and aeration are performed to convert nitrogen oxides into nitrogen gas.
RP +50-+150mV1. ,: two aerobic steps in which the excess hydrogen donor 801) is oxidized and decomposed and nitrogen gas is bubbled and removed, and the sludge is settled from the activated sludge mixture, and the settled sludge and supernatant liquid are separated. In the batch activated sludge treatment method, which consists of a standing step in which the supernatant water is separated into two, and a discharge step in which the supernatant water is discharged as treated water, the ORP of the settled sludge layer in the standing step was measured, and the measured value was 1150 II.
This is a batch-type activated sludge treatment method characterized by shifting to the discharge stage in which supernatant water is discharged when it becomes below Iv (according to silver-silver chloride electrode standards). No flP, addition of granulated blast furnace, zeolite, silica sand or cristobalite as an activated sludge immobilization carrier to the 7 ctor, water-soluble reacts with phosphorus compounds to form insoluble phosphorus-metal compounds in the aerobic 2nd stage. It is preferable to add a metal compound and to control ORP to +100 to +150 mV in the two aerobic steps.

(Function) In the present invention, the activated sludge is used in the anaerobic process using an agitator, an underwater agitator, etc. Mixing and stirring are carried out by mechanical stirring and, in the aerobic process, by aeration of air. In addition, the anaerobic degree and aerobic degree of each process are measured with an ORP sensor immersed in the reactor, and if the ORP of each process decreases below the predetermined ORP value, the aeration rate of the air and the aeration amount are measured, except for the anaerobic 1 process. Increase by 1 (,) RP is increased, and when it recovers to the predetermined value, short-buy aeration is stopped or the aeration amount is reduced. The ORP sensor immersed in the reactor is best made of a composite 1tWi of gold or gold alloy and silver chloride/silver.

First, in the anaerobic first step, wastewater is injected into a reactor containing activated sludge while being mechanically stirred.
RP gradually decreases]ζ, and finally ORP becomes 200-
The voltage drops to -300 mV (hereinafter referred to as a silver-silver chloride electrode standard), and it becomes clearly anaerobic. If this state is maintained for a predetermined period of time, the phosphorus compounds in the activated sludge will be released into the wastewater. Phosphorus compounds release phosphorus from activated sludge under anaerobic conditions, and then when placed in aerobic conditions, activated sludge takes in excess phosphorus, and the activated sludge that has taken in too much phosphorus is removed as surplus sludge, which improves the quality of treated water. Since the phosphorus concentration can be reduced, it is removed by a combination of the anaerobic conditions in this first anaerobic step and the aerobic conditions in the next aerobic step.

In the next aerobic step 1, BOD is decomposed.

According to the inventors' research, the BOD of sewage is the O of the reactor.
It has been shown that 95% or more of RP is decomposed at 0 to 100 mV.
If this step is maintained above mV for 1 to 2 hours,
It disintegrates completely.

Next, ammonia nitrogen compounds and organic nitrogen compounds are removed by a nitrification/denitrification method. In this case, ammonia nitrogen compounds, organic nitrogen compounds, etc. are biologically oxidized,
Nitrate and nitrite nitrogen compounds (hereinafter referred to as NOx N
(abbreviated as ). According to research by the inventors, this nitrification reaction has an ORP of 80 to 100 in the case of dehydrated water.
It has been shown that the nitrification reaction occurs at mV or more, so it is best to perform the nitrification reaction in one aerobic step. Therefore, the ORP for aerobic one should be +100-+120 TIIV! +! ! ! If controlled, the nitrification reaction of ammonia nitrogen compounds and organic nitrogen compounds as well as the decomposition reaction of BOD will occur.

The NOx -N generated in the aerobic 1st step is reduced to nitrogen gas through a denitrification reaction using wastewater organic matter as a hydrogen donor in the anaerobic 2nd step.7 As a hydrogen donor, the anaerobic 11
What is necessary is just to supply wastewater at the ratio of 1-3 parts to 4 parts of wastewater injected in step. At this time, anaerobic 2nd process (n ORP Ka1
50 m V to Fl: Naru! - Phosphorus is released from the activated sludge and the phosphorus concentration in the treated water increases, so when the ORP of the second anaerobic step becomes -15 (1 mV or less, aeration is performed from the bottom and a low In this way, ammonia and organic nitrogen compounds in the water can be easily removed by nitrification and denitrification methods.

In the aerobic 2nd step, aeration is performed to increase ORP by +50 to +150.
mV, and the excess hydrogen donor used in the anaerobic step 2 is decomposed with acid 1). In addition, in the water purification process in which nitrogen gas adhering to the activated sludge is also removed by aeration, neither aeration nor stirring is performed, the activated sludge is allowed to settle, and the activated sludge is separated into activated sludge and supernatant water. and,
In the final discharge step, the supernatant water is discharged as treated water.

One of the important issues to efficiently remove phosphorus compounds in the batch activated sludge treatment method is to suppress the re-release of phosphorus from activated sludge during the standing process, or to remove residual phosphorus compounds from the previous process. be.

In the present invention, first, the ORP of the activated sludge is measured in the standing step, and when the measured value becomes 1150 mV or less, the process moves to the discharge step in which supernatant water is discharged.

As mentioned above, in the standing process, neither aeration nor stirring is performed, so the anaerobic degree of the settled sludge layer increases over time, and eventually phosphorus compounds are released. It is best to use ORP. That is, as shown in the tIS1 diagram, ? From the relationship between the ORP of the settled sludge layer and the phosphorus concentration of the treated water in the RP equipment process, when the ORP of the settled sludge layer becomes 1160 mV or less, the lower the ORP, the higher the phosphorus concentration of the treated water tends to be. Therefore, the treated water in the standing process needs to be discharged before the ORP of the settled sludge layer reaches -1160 mV, thereby: (1) removing the phosphorus compounds in the treated water to 1/1 or less (as phosphorus); I can do it.

Therefore, the ORP of the settled sludge layer in the standing process was measured, and when the ORP reached -150 mV, the supernatant water was discharged. By measuring ORP in this manner, it becomes possible to discharge supernatant water before phosphorus compounds are released from activated sludge, and it is possible to maintain a low phosphorus compound concentration in treated water.

Second, in order to promote sedimentation of activated sludge and maintain activated sludge at a surface concentration to improve treatment efficiency, commercial furnace granulated water, zeolite 1, and silica sand are used as inorganic immobilization carriers for fluidized bed reactors. Mako adds cristobalite to the reactor. Activated sludge can be immobilized on the surface of these carriers, and the concentration of activated sludge can be increased, so that the efficiency of BOD decomposition, ammonia compound oxidation reaction, etc. can be increased. In addition, if activated sludge is immobilized on a carrier, the settling of activated sludge during the standing process will be promoted, and the sludge will settle sufficiently before the ORP of the sludge becomes -1150 mV or less, and the supernatant water will be separated from the activated sludge more completely. It becomes possible to release water.

In addition, the material used in the present invention? ! The activated sludge immobilization carrier has a particle size of 10 to 200 μm, and the amount added is preferably about 0.5 to 3% based on the capacity of the reactor. In the case of batch-type activated sludge treatment, if the particle size exceeds 2()0 μm, it is difficult to flow uniformly in the reactor, and if the particle size is less than 10 μm, it will not settle sufficiently and the particles will not settle as the treated water is discharged. leaked out,
This is because it causes the treated water quality to become low in F. In addition, the amount added has a sedimentation promotion effect and surface concentration of activated sludge of 0.5%.
The above is recognized, and it reaches a plateau of 3%'t', so 0.5~
A range of 3% is appropriate.

When removing phosphorus compounds using biological treatment methods, the phosphorus compounds may not be removed sufficiently due to many factors, resulting in the phosphorus concentration of the treated water becoming quotient.The causes are as follows.

■Since the ORP in the anaerobic 1st step does not decrease sufficiently, phosphorus is not sufficiently released from the activated sludge, and therefore phosphorus is not sufficiently taken up by the activated sludge in the next aerobic 1st step.

■If the denitrification reaction in the anaerobic 2nd process is insufficient, NOx
-N remains, which suppresses the release of phosphorus during the anaerobic first stage of the next cycle.

(■ In the standing process, the settled sludge becomes anaerobic, specifically, when the ORP becomes -1 (i0 mV or more), phosphorus is re-released from the activated sludge.

((For D, countermeasures can be taken using the methods mentioned above, but for ■ and ■, the cause is water quality fluctuations due to rainfall, etc.) Specifically, if the rain continues and pollutants The concentration is low [When water flows in, the OR of the anaerobic 1st step
If P is not sufficiently lowered or the m5fA degree of the sewage water used as a hydrogen donor in the anaerobic second step is low, denitrification reaction does not occur sufficiently and NOx-N remains.

For this reason, phosphorus is not removed sufficiently, causing an increase in the phosphorus concentration of the treated water. When phosphorus compounds are removed only by biological methods, it is impossible to avoid a decrease in phosphorus removal performance due to fluctuations in the quality of the influent water.

Therefore, in order to prevent a decrease in phosphorus removal performance due to changes in the water quality of the inflow water, in the aerobic 2nd step, Wl-free
l) Adding a water-soluble metal compound that reacts with the phosphoric acid compound to form an insoluble phosphorus metal compound.

Methods for removing phosphorus compounds from water such as carbon dioxide by adding water-soluble metal compounds, such as iron chloride, polyaluminum chloride (PAC), and sulfuric acid clay, are already known. However, this chemical phosphorus removal method is expensive, generates a large amount of surplus sludge, or
There are problems such as difficulty in removing organic phosphorus compounds, which contain as much as 50%. The present invention solves these problems by combining biological and chemical methods. In other words, in the case of batch activated sludge treatment, the upper %1 is due to oxidative decomposition of BOD, nitrification reaction, excessive intake of phosphorus,
It has the W1 ability to oxidatively decompose organic phosphorus compounds and convert them into inorganic phosphoric acid compounds. For this reason, most of the phosphorus compounds in the aerobic two-step process are inorganic phosphate compounds, most of which are removed biologically, and the remaining phosphorus compounds are at most 2 mH,/l (as phosphorus). ) is below. Therefore, if the phosphorus emission regulation is below Img/l, 1ug/l
1 or more, or 1, 5 if it is 0, 5 mg/l or less
It is sufficient to remove phosphorus of mFI/1 or more. To remove this residual phosphorus compound, aerobic two-step chlorination reaction with inorganic phosphorus compounds to easily form insoluble phosphorus compounds! 1 to 1.5 mg of water-soluble metal compounds such as iron, polyaluminum chloride, and sulfuric acid, and 1 to 1.5 mg of inorganic phosphorus compounds.
/ Just add the amount necessary to remove (as phosphorus). Therefore, the phosphorus removal method, which combines biological and chemical methods, requires significantly less water-soluble metal compounds than chemical removal methods, resulting in lower costs (I) and the generation of sludge. There is almost no increase in phosphorus, and compared to biological methods, phosphorus can be removed more stably and with higher efficiency.

In addition, when the water-soluble metal compound mentioned above is used in the aerobic 2-soil process, in addition to the action of removing phosphorus, it also has the action of promoting the settling of activated sludge in the standing process, so that the anaerobic state of the settled sludge layer progresses. There is also the advantage that the supernatant water can be discharged while the water is still in use.6 Also, in order to prevent the settled sludge layer from becoming anaerobic during the standing process, the ORP of the upper aerobic level is +10.
It is also preferable to maintain it between 0 and +150 mV.

Next, examples of the present invention will be described.

(Example) Example 1 The internal volume of the reactor is ',)! Using a batch type activated sludge treatment pilot plant equipped with an ORP control device, a sequencer for switching between anaerobic and aerobic processes, a slow stirrer, etc., B is extracted from sewage in three cycles a day.
An experiment was conducted to remove OD, nitrogen compounds, and phosphorus compounds at the same time6.The order in which the anaerobic and aerobic steps were combined and the processing time were as follows.

Injection of sewage - Anaerobic 1st step (60 minutes 1ift) → Aerobic 1st step (2.5 o'clock flit) → Anaerobic 2nd step (3 hours) → Aerobic 2nd step (30 minutes) → Standing step (45 minutes) - Upper stage of discharge (15 minutes) The set values of ORP fltll Ill for each process are +120 mV for aerobic 1st process, 1150 mV for anaerobic 2nd process, +150mV for aerobic 2nd process, and the value just above IW is O When the temperature reaches 25 m, the upper layer water (25 m') is discharged as treated water. In the anaerobic upper stage, slow stirring was always performed, and when ORP fell below the set value, aeration was performed from the bottom of the reactor, and when it recovered to the set value, aeration was stopped and ORP control was performed. In addition, (in the process, stir constantly with a roots blower, and when the ORP is low, increase the rotation speed of the roots blower to increase aeration, and when it recovers to the set value, increase the rotation speed to reduce the amount of electricity exposed. As a result of this method of ORP control, the ORP in the standing step was approximately -100 mV even after 30 minutes of standing, and no re-release of phosphorus occurred. Under these conditions. The treatment performance is shown in Table 1.The sewage dispensing ratio is 4 steps for tLXl soil and 1 step for 2 steps of anaerobic water.
And so.

Table 1 Water quality of supply r water and treated water 100 ml of ferric aqueous solution (equivalent to 4 ml per 1st floor 3 of F water) was added, followed by anaerobic 2 steps for 3.5 hours in the same manner as in Example 2, and standing step 15. Ding water was processed in minutes.

The results are shown in Table 2 6 Table 2 Water quality of supply F water and treated water Example 2 Under the same conditions as Example 1, 0.5 kg (1% (equivalent) was added to conduct the experiment. As a result, it became clear that the sludge settling for about 1 time after standing still was completed in 15 minutes, so the anaerobic 2 steps were changed to 3 times.
．． The water was treated for 5 hours and the standing step was for 15 minutes. As a result, the T-P of the treated water was 0.12 to 0.48 g/l, and the K-N was 1.2 to 4.5 g/l. NO*
When N was 0.01 to 3.7 mg/l1), the denitrification reaction was promoted.

Example 3 Under the same conditions as Example 1, 30% salt was obtained in two aerobic steps (effects of the invention) By the present invention, the activated sludge in the f# stone step of the batch activated sludge treatment method, for which no measures had been taken in the past, was The problem of phosphorus compound release and biological or chemical dephosphorization methods can be accurately addressed, and the phosphorus compound concentration of the final treated water can be stably maintained at a low level.

[Brief explanation of drawings]

Figure 1 shows the ORP of the settled sludge layer in the standing process and the T-P (
It is a figure showing the relationship with total phosphorus) 1% degree. Figure 1

Claims (4)

[Claims] (1) A batch activated sludge treatment method for wastewater containing at least BOD, ammonia compounds, and phosphorus compounds as eutrophic substances, in which wastewater is injected into a reactor in which activated sludge is present while mechanical stirring is performed, and the activated sludge is Anaerobic step to release more phosphorus compounds and aeration to increase ORP by 1
An aerobic step in which BOD is oxidized and decomposed and ammonia compounds are oxidized while being controlled within the range of 00 to +120 mV or more (according to silver-silver chloride electrodes), and phosphorus compounds are ingested excessively into activated sludge, and a portion of the wastewater is was used as a hydrogen donor, and while dispensing it, the ORP was controlled in the range of -50 to -150 mV (based on silver-silver chloride electrode) by mechanical stirring or aeration in addition to mechanical stirring, and nitrogen oxides were removed. Two anaerobic steps to reduce to nitrogen gas and aeration to increase ORP +50 to +1
Aerobic 2 which maintains the voltage at 50 mV and oxidizes and decomposes the excess hydrogen donor BOD and removes nitrogen gas by forming bubbles.
In the batch activated sludge treatment method, which consists of a process, a standing process in which sludge is settled from an activated sludge mixture and separated into settled sludge and a supernatant liquid, and a discharge process in which the supernatant water is discharged as treated water. A batch activated sludge treatment method characterized by measuring the ORP of the settled sludge layer in the loading step, and moving to the discharge step in which supernatant water is discharged when the measured value is −150 mV or less (based on silver-silver chloride electrodes). . (2) The batch activated sludge treatment method according to claim 1, wherein granulated blast furnace, zeolite, silica sand, or cristobalite is added to the reactor as an inorganic activated sludge immobilization carrier. (3) The batch activated sludge treatment method according to claim 1, wherein in the two aerobic steps, a water-soluble metal compound that reacts with the phosphorus compound to form an insoluble phosphorus-metal compound is added. (4) ORP +100 to +150 in aerobic 2 steps
The circular activated sludge treatment method according to any one of claims 1 to 3, wherein the activated sludge treatment method is controlled to mV.