JPH0231895A - Process and apparatus for treating filthy water - Google Patents

Abstract

PURPOSE:To obtain treated water having good quality having a value of BOD and SS each specified value or below in a short time by flocculating org. filthy water by adding an inorganic flocculant and stirring the mixture, separating the liquid phase from the solid phase primarily and transporting the liquid phase to a filtration tank, and treating with activated sludge again. CONSTITUTION:Org. filthy water is introduced into a stirring tank 1, mixed with an inorganic flocculant such as PAC injected quantiatively thereinto and stirred with a rapid stirring device 2, then fed to a flow stirring tank 3 where it stirred slowly with a slow stirring device 4. Flocs of SS, colloidal matters, and P, etc., are grown, and allowed to contact with fine bubble group from a reduced pressure bubble generating apparatus 8 in a floating separation tank 5. Thus, a floated sludge layer 10 is formed by the floc floated by the effect of adhered bubbles, and discharged by a discharging device 9. The water is then introduced into a biological filtration tank 14 with a pump 13 through a water level adjusting tank 11 and a primary water storage tank 12, and then treated with aerobic microorganisms deposited to a filtration layer 15 on a supporting gravel layer 16 and air from an air diffusing pipe 18. By this process, satisfactory treated water having improved value of BOD and SS each specified level or below is obtd. is a short time.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to biochemical oxygen demand (hereinafter referred to as BOD) in the treatment of organic sewage containing suspended matter such as domestic sewage, sewage, and food factory wastewater. The present invention relates to a method and apparatus for treating wastewater that enables the removal of suspended solids (hereinafter referred to as SS), and phosphorus in a short period of time.

(Prior Art) As a method for treating organic wastewater containing suspended matter, biological treatment using aerobic microorganisms, mainly an activated sludge method, has conventionally been applied.

These methods are widely applied in fields such as sewage treatment, and with proper design and operation management, BODl 0■
Although it is possible to obtain high-quality treated water with a concentration of 5S20/2 or less and 5S20/2 or less, there are the following problems.

(1) Residence time in the treatment facility is long.

There are various methods for the activated sludge method, but the residence time in the aeration tank, which is the main part of the treatment, is about 8 hours for the standard activated sludge method, about 24 hours for the long aeration method, and about 24 hours for the long aeration method.
In the case of the ``oxidation ditch method'', the treatment time is 30 to 40 hours, so the capacity of the aeration tank is large, and therefore the facility site area is also large, making it difficult to locate new sewage treatment plants in large areas.

(2) A large amount of air needs to be blown for supplying oxygen to activated sludge and for mixing and stirring in the aeration tank.

Approximately 40% of the energy (electricity) consumption in sewage treatment plants that employ the activated sludge treatment method is accounted for by blower operation for this air supply.

By blowing in a large amount of air and stirring the aeration tank,
It is unhygienic due to foaming inside the tank and the scattering of foam.

(3) It is necessary to appropriately manage the activated sludge (hereinafter referred to as MLSS) concentration in the aeration tank. For this purpose, it is necessary to appropriately control the amount of sludge returned from the settling tank installed after the aeration tank and the amount of MLSS drawn out, and skilled operation management tools are required.

(4) Sedimentation of MLSS in a settling tank installed after the aeration tank may cause deterioration of compaction (swelling, hereinafter referred to as bulking), and it may not be possible to continue good treatment.

(5) The sludge generated during activated sludge treatment is extracted from the settling tank as surplus sludge, but the MLSS concentration of the sludge that is extracted is approximately 8,000 ■/Q, and sludge treatment such as dewatering that is attached to the facility This requires concentration operations such as gravity concentration and mechanical concentration.

(6) In the normal activated sludge method, phosphorus, which is one of the causative substances of eutrophication phenomena such as red tide, is hardly removed.

The present invention aims to solve the problems seen in the conventional techniques as described above.

(Means for Solving the Problems) The sewage treatment method according to the present invention for solving the conventional problems as described above is characterized in that organic sewage containing suspended matter such as domestic sewage, sewage, food factory wastewater, etc. A rapid stirring step in which a non-molecular flocculant such as PAC is added to the wastewater and rapidly stirred; and after the rapid stirring, a step in which suspended matter, colloidal substances, and phosphorus compounds in the wastewater are flocculated by gentle stirring; A primary solid-liquid separation step in which the formed flocs are solid-liquid separated by pressure flotation, and the primary treated water treated in this step is introduced into a filtration tank filled with filter media with a particle size of about 2 to 10 W. Oxygen necessary for the action of activated sludge-like aerobic microorganisms growing on the surface of the filter medium is supplied to the filter tank using dissolved organic matter and NH4''-N contained in the primary treatment water as nutritional sources, and This method is combined with a reprocessing process that removes soluble BOD, 33, and phosphorus remaining in the water.

Furthermore, the sewage treatment equipment according to the present invention is characterized by storing organic sewage containing suspended matter such as domestic sewage, sewage, and food factory wastewater, and adding an inorganic flocculant such as PAC to this and rapidly stirring it. A rapid stirring tank is used to mix the wastewater, a slow stirring tank is used to gently stir the mixed wastewater in the rapid stirring tank to grow fine flocs, and the mixed wastewater from the slow stirring tank is introduced. Then, there is a pressurized flotation separation tank equipped with a pressurized water nozzle at the bottom that injects pressurized water in which air is dissolved in excess by pressurization, and a group of grown flocs floated and separated on the pressurized flotation separation tank is discharged to the outside of the tank. A sludge removal means and the primary treated water from which flocs have been removed in the pressurized flotation tank are continuously supplied, and a filter medium with a particle size of 2 to 10 m+ having activated sludge-like aerobic microorganisms grown on the surface is formed. A filtration tank with a filled wave layer installed inside and equipped with a blower to blow air into the wave layer, and when the wave layer in the filtration tank becomes clogged, it is cleaned for a certain period of time by blown air and treated water. a water level differential pressure transmitter that detects the progress of clogging in the filter layer by pressure loss between the upper and lower parts of the wave layer and instructs the start of operation of the backwashing means; The present invention is provided with a treated water tank for storing treated water flowing out from the filtration tank and supplying it to the pressurized flotation separation tank as circulation pressurized water for generating bubbles and water for backwashing the wave layer.

(Function) BOD in organic wastewater such as sewage containing suspended matter is composed of SS components, colloidal components, and soluble components.

The BODJ degree of untreated sewage is approximately 200/2, but by adding the Tll'a-free collector described above to such sewage and stirring rapidly and slowly, almost all of the SS components are removed. By precipitating some of the colloidal components as flocs and separating them by pressure flotation, approximately 1% of the BOD in wastewater is removed.
/2 is removed.

Phosphorus in wastewater reacts with an inorganic flocculant, for example, as described below, and is precipitated as flocs, and most of it is removed in substantially the same manner as the SS component.

AI"10PO4'-→A I PO, ↓・・・・・・(
1) Fe'+MoPO4'--+Fe PO4↓--・-
(2) The above phosphorus removal rate depends on the amount of inorganic flocculant added as shown in equations (1) and (2). Since biological treatment is carried out using aerobic microorganisms, the amount of phosphorus required for the survival and activity of these microorganisms is intentionally left in the primary treatment water. Adjust the amount of agent added.

Taking sewage as an example (assuming the phosphorus concentration in sewage to be 5r&t/ffi and the phosphorus concentration in primary treated water to be 1.5111!/ffi), the amount of inorganic flocculant to be added that meets the above objectives is as follows: When liquid sulfuric acid band is used as the agent, it is about 160 ■/β, in case of PAC it is 125 ■/g, and in the case of ferric chloride it is about 20 ■/2.

After such primary treatment, a filter medium with a thickness of 1 to 100 ml made of a natural material such as zeolite, a coal-based material, or a plastic-based artificial material with a particle size of 2 to 10 IllI, on which aerobic microorganisms are grown attached, is prepared. A biological filtration device with a 2m wave layer removes soluble BOD components and SS remaining in the primary treatment water.
, phosphorus is removed by the action of the above aerobic microorganisms, and BOD
, 33, final treated water with good water quality of less than 10 /2 and 1 /2 phosphorus can be obtained.

In this way, in the primary treatment that does not involve biological reactions, BO
Since approximately 1/2 of D, part of the colloidal components, and part of the phosphorus are removed, the load on the biological filtration device that performs the biological reaction is reduced, and the residence time is shortened. In addition, the pressure flotation method for solid-liquid separation requires approximately 10% less time than the sedimentation method.
/2o, which is extremely short, so the residence time of the entire apparatus is about 115 to 1/8 of that of the standard activated sludge method.

In addition, in the present invention, the amount of air that serves as a source of dissolved oxygen (hereinafter referred to as DO) for aerobic microorganisms that grow attached to the filter layer is reduced by primary treatment in the pressure flotation separation process. In the pressure flotation separation process, fine bubbles generated for solid-liquid separation result in Do
Since it also serves as replenishment, if the wastewater to be treated is sewage, the amount of air required for the amount of sewage supplied is approximately 2.
This is less than twice as much, and is reduced to less than 1/3 compared to the conventional technology.

Moreover, the solid-liquid separation in the present invention involves pressurized flotation separation before performing a biological reaction and filtration accompanied by a biological reaction, and there is no trouble in operating the apparatus due to the influence of bulking.

In addition, since the sludge separated into solid and liquid by pressure flotation has a high concentration of about 30,000 μ/β in terms of SS, a concentration operation in sludge treatment is not necessary.

Furthermore, since the present invention combines a treatment consisting only of biological reactions, such as the activated sludge method, with a physicochemical treatment using an inorganic flocculant, phosphorus, which is difficult to remove by biological reactions alone, can be removed by chemical reactions as explained above. removed.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a first embodiment. In this embodiment, organic wastewater containing suspended matter, such as domestic sewage, sewage, and food factory wastewater, is continuously and quantitatively supplied to a rapid stirring tank 1. , is mixed with an inorganic flocculant such as PAC which is quantitatively injected into the tank using a rapid stirring device 2. By the above operation, SS, colloidal substances, phosphorus, etc. in the wastewater are formed as fine flocs by chemical or electrochemical action. The wastewater containing these flocs is made to flow into the slow stirring tank 3,
Slow stirring is performed in the tank using a slow stirring device 4. In this step, the fine flocs formed in the previous step are caused to collide and adhere to each other, and grow into flocs with a diameter of about 1 inch. The wastewater containing the grown flocs is supplied to the pressure flotation separation tank 5, and bubbles with a diameter of approximately 30~ Mix and contact with a group of 60μ fine bubbles. Pressurized water is supplied to the reduced pressure bubble generator 8.

This pressurized water is supplied from the treated water storage tank 25 that stores the final treated water according to the method of the present invention into the pressurized water adjustment tank 28 via the pressurized water pump 26, and maintains the internal pressure of the tank 28 at approximately 4 kg/-. While filling material 30 installed in the tank
By contacting with pressurized air that is continuously supplied from the compressor 29 via the compressor 29, air is dissolved in excess compared to normal atmospheric pressure.

The floc/bubble aggregates, in which fine air bubbles are attached to the flocs formed in the previous step, behave as a unit and their density is lower than that of water, so they move along the partition wall 7 installed diagonally in the pressure flotation tank 5. After rising, it reaches the water surface of nuclide 5 and is separated from the wastewater. These flocs separated on the water surface of the nuclide 5 accumulate to form a floating sludge layer 10. The sludge layer 10 is continuously or intermittently scraped up to the outlet side of the pressurized flotation tank by the floated sludge discharge device 9, and is discharged to the floated sludge discharge tank 32 provided adjacent to the pressurized flotation tank 5 to the outside. Let it drain.

The primary treated water that has completed the pressurized flotation separation process is made to flow into the primary treated water storage tank 12 via the water level adjustment weir 11 provided for the purpose of adjusting the water level in the pressurized flotation separation tank 5, and is stored there. In this primary treated water, most of the SS and phosphorus and approximately 1/2 of the BOD in the inflowing wastewater have been removed at the end of the above process. In addition, the Do concentration is increased by mixing and contacting for approximately 15 to 20 minutes with a group of fine bubbles that contribute to pressure flotation separation.

The primary treated water is continuously and quantitatively supplied to the biological filtration tank 14 via the primary treated water supply pump 13. The tank 14
There is a water collecting device 17 inside to collect filtered water evenly at the bottom.
is accommodated, on top of which is a support gravel layer 16 for physically supporting the filter medium, and on top is a layer of natural or artificial gravel so as to have a relatively even particle size distribution in the range of 2 to 10 particles. Wave layers 15 filled with filter media made of plastic to a thickness of 1 to 2 m are housed in a stacked manner.

The primary treated water supplied to the biological filtration tank 14 flows out of the tank via the wave layer → supporting gravel layer → water collection device due to the water head pressure above the filter layer 15 . In this process, wave layer 1
Due to the action of aerobic microorganisms grown on the surface of the filter medium constituting 5, soluble BOD components, NH4-N, and phosphorus remaining in the primary treated water are removed. The wave layer 15 is necessary for the reaction of removing these pollutants by aerobic microorganisms.
Air supplied from a blower 19 through an aeration pipe 18 installed at the interface between the support gravel layer 16 and the support gravel layer 16 is sheared while rising through the wave layer, and is dissolved in the water.

The water level in the biological filter tank 14 rises as aerobic microorganisms on the filter medium grow. When the water level detector 27 installed in the tank 14 detects the preset upper limit water level in the tank 14, the primary treated water supply pump 13 is stopped. After that, when the water level drops to the preset lower limit water level,
After closing the treated water automatic valve 21 and the air supply automatic valve 24, the air cleaning automatic valve 23 is opened and air from the blower 19 is supplied from the lower part of the supporting gravel layer 16 through the water collection device 17, and the filter medium is The aerobic microorganisms that have grown excessively on the surface are removed by the physical shearing force caused by the rising air bubbles. This process takes about 2 minutes [j! After that, the blower 19 is stopped and the automatic air cleaning valve 23 is closed, and then the backwash pump 2 is turned on.
0, open the automatic backwash valve 22, and open the treated water storage tank 2.
The final treated water stored in advance in 5 is transferred to water collection device 1.
7 from the lower part of the biological filtration tank 14 at a flow rate sufficient to expand the wave layer 15, the detached aerobic microorganisms are discharged to the outside of the tank via the drainage trough 31. This discharged water is mixed with sewage and supplied to the rapid stirring tank 1 which is the inflow part of this device, and is used for rapid stirring process, slow stirring process,
Reprocess by pressure flotation separation process.

The required residence time in the apparatus of the present invention is approximately 15 minutes for the rapid/slow stirring process, approximately 15 to 20 minutes for the pressure flotation separation process,
The biological filtration process takes approximately 30 to 60 minutes, total time of 1 hour to 1 hour and 30 minutes, making it possible to treat wastewater in an extremely short time compared to conventional techniques, and making the wastewater treatment device extremely compact.

FIG. 2 shows a second embodiment, in which a pressure flotation separation process, which is the primary treatment of wastewater, and a biological filtration process, which is the final treatment, are carried out in the lower part of the pressure flotation tank 5. By integrally forming the tank 14, this device is capable of performing the functions of the present invention as described above in a single tank.

In addition, in FIG. 2, the same parts as in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

In this second embodiment, the pressure flotation tank 5 and the biological filtration tank 14 are vertically continuous and integrally formed, so that the water level in the pressure flotation section is maintained constant over time. Therefore, the area directly above the wave layer 15 and the supporting gravel layer 1 must be
A differential pressure transmitter 27 is installed directly below the biological filtration tank 6, and a controller 31 electrically connected to the transmitter controls the opening of the treated water flow control valve 33 in response to an increase in the differential pressure between the upper and lower sides of the biological filtration tank. The water level of the flotation separation section is kept constant by changing the water level one after another.

In the second embodiment as well, the rapid stirring, slow stirring process, 11N pressurized water process for generating fine bubbles, air cleaning due to clogging of the biological filter layer, backwashing process, and automatic valve opening/closing operation are performed in the first embodiment. This is similar to the example.

In the second embodiment, the floated sludge 10 formed on the water surface of the pressurized flotation separation tank 5 during normal processing is removed from the floated sludge storage tank by operating the floated sludge scraping device 9 intermittently or continuously. 32 to the outside of the tank and subjected to a sludge treatment process.

In the backwash process of the biological filtration tank 14, backwash wastewater containing separated aerobic microorganisms is discharged from the top of the pressurized flotation separation tank 5 to the outside of the tank via the floatation sludge storage tank 32, and the device of the present invention In order to mix with the inflowing wastewater at the inflow part and perform reprocessing through rapid stirring, slow stirring, and pressure flotation separation processes, and to smooth the overflow of wastewater in the backwashing process of the biological filtration layer, The floating sludge scraping device 9 is operated continuously. In this process, the automatic inflow sewage valve 34 is closed to stop the inflow of sewage, and the injection of No-111 flocculant into the rapid stirring tank 1 is also stopped, but pressurized water is supplied via the decompression bubble generator 8. continues.

Although not particularly illustrated in both Figures 1 and 2,
If the physical strength of the flocs formed in the slow stirring process is insufficient, this can be dealt with by injecting about 1/2 of the amount of polymer flocculant into the slow stirring tank based on the amount of inflowing sewage. can.

Table 1 shows an example of the quality of treated water for each process in the embodiment of the present invention, in which sewage is the target wastewater.

Chapter 1 Table *T P hails total phosphorus.

(Effects of the Invention) The effects of the invention in treating organic sewage containing suspended matter by the sewage treatment method and apparatus of the present invention are as follows.

■According to the method and apparatus of the present invention, the total residence time in the apparatus is as short as 1 to 1.5 hours, and both BOD and SS are 10
Treated water with good water quality of 111 r/fl or less and T Plq/ffi or less can be obtained.

■Compared to the conventional method, the volume and installation area of the device can be significantly reduced, and the facility cost can also be reduced.

In particular, as shown in the second embodiment, the sewage treatment apparatus according to the present invention can be made extremely compact by carrying out the pressure flotation separation as the primary treatment and the biological filtration as the 'IfL final treatment in a single integrated tank.

■The device of the present invention is capable of fully automatic operation and does not require skill or advanced technical experience.■The amount of air as an oxygen supply source is less than 1/3 of the conventional method, and the blower is not required. Capacity becomes smaller.

■Since the concentration of the sludge discharged is about three times higher than that of conventional methods, the volume of sludge generated is reduced to about 1/3, eliminating the need for thickening operations in the sludge treatment process, and sludge treatment equipment. capacity can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a first embodiment of the invention, and FIG. 2 is a schematic diagram showing a second embodiment of the invention. 1... Rapid stirring tank, 2... Rapid stirring device, 3... Slow stirring tank, 4... Slow stirring device, 5... ...Pressure flotation separation tank, 6...
・Partition wall, 8... Decompression bubble generator, 9... Floating sludge discharge device, 12... Primary treated water storage tank, 14... Biological filtration tank, 15...Filter layer, 16...Supporting gravel layer, 17...Water collection device, 18...
・Diffuser pipe, 19...Blower-521...
・Treatment water automatic valve, 22... Automatic backwash valve, 23.
... Air cleaning automatic valve, 24 ... Air supply automatic valve, 25 ... Treated water storage tank, 28 ...
- Pressurized water adjustment tank, 29 - Old... Compressor 30...
...Filling material.

Claims (5)

[Claims] (1) A rapid stirring step in which an inorganic flocculant such as polyaluminum chloride (hereinafter referred to as PAC) is added to organic wastewater containing suspended matter such as domestic sewage, sewage, food factory wastewater, etc. and rapidly stirred; After the rapid stirring, a step of forming suspended matter, colloidal substances, and phosphorus compounds in the wastewater into flocs by gentle stirring, and a primary solid-liquid separation step of separating the flocs thus formed into solid-liquid by pressure flotation separation. The primary treated water treated in this step is introduced into a filter tank filled with filter media with a particle size of about 2 to 10 mm, and the soluble organic matter and ammonia nitrogen (hereinafter NH_4) contained in the primary treated water are removed. ^+-N) is used as a nutrient source to supply oxygen necessary for the action of activated sludge-like aerobic microorganisms growing on the surface of the filter medium to the filtration tank, and reprocessing the primary treated water. A wastewater treatment method consisting of a combination. (2) The wastewater treatment method according to claim 1, wherein high-oxygen air is used as a gas source for fine bubbles required for pressurized flotation separation and as a gas source to be supplied to the filter layer. (3) A rapid stirring tank that stores organic sewage containing suspended solids such as domestic sewage, sewage, and food factory wastewater, adds an inorganic flocculant such as PAC, and rapidly stirs and mixes the organic sewage. A slow stirring tank that gently stirs the mixed wastewater mixed in the rapid stirring tank to grow fine flocs,
The mixed sewage from the slow stirring tank is introduced, and pressurized water with excessively dissolved air is sprayed from the pressurized water nozzle installed at the bottom, and the mixed sewage and pressurized water are depressurized at once, resulting in fine bubbles generated. a pressurized flotation tank that separates the grown flocs and primary treated water into solid-liquid by contacting them, a sludge removal means that discharges the group of grown flocs floated and separated on the pressurized flotation tank to the outside of the tank, and the pressurized Continuously supply primary treated water from which flocs have been removed in a flotation separation tank, and produce activated sludge-like aerobic microflora grown on the surface with a particle size of 2 to 1.
A filter layer filled with a 0 mm filter medium is installed inside, and
a filtration tank equipped with a blower that blows air into the filtration layer;
A backwash means for cleaning the filter layer of the filter tank for a certain period of time by blowing air and water supply when the filter layer of the filter tank becomes clogged; A water level differential pressure transmitter that detects and commands the start of operation of the backwashing means, and a water level differential pressure transmitter that stores treated water flowing out from the filtration tank and circulates pressurized water for generating bubbles to the pressurized flotation separation tank and A sewage treatment device comprising a treated water tank for supplying water for backwashing. (4) A filtration tank is integrated in the lower part of the pressure flotation separation tank to form a single tank, and the wastewater containing the grown flocs supplied to the tank is separated by pressure flotation in the upper part of the tank, and the filtration tank is separated in the lower part of the tank. The sewage treatment device according to claim 3, wherein the sewage treatment device is configured to perform treatment using aerobic microorganisms in a filtration tank. (5) The sewage treatment apparatus according to claim 3 or 4, wherein high-concentration oxygen air is used as a gas source for fine bubbles required for pressure flotation separation and as a gas source to be supplied to the filter layer.