JPH0714519B2 - Sewage treatment method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to biochemical oxygen demand (hereinafter referred to as BOD and BOD) in the treatment of organic sewage containing suspended solids such as domestic sewage, sewage, and food factory wastewater. ), Suspended solids (hereinafter referred to as SS), and a method for treating sewage that enables removal of phosphorus in a short time and an apparatus therefor.

(Prior Art) As a method for treating organic sewage containing suspended solids, biological treatment with aerobic microorganisms mainly based on the activated sludge method has been conventionally applied.

These methods are widely applied in the field of sewage treatment, etc., and if properly designed and operated and managed, high quality treated water of BOD 10 mg / l or less and SS 20 mg / l or less can be obtained. There's a problem.

(1) Residence time of the processing facility is long.

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

(2) It is necessary to blow a large amount of air for supplying oxygen to the activated sludge and for mixing and stirring in the aeration tank.

About 40% of the energy (electricity) consumption at a sewage treatment plant that employs an activated sludge treatment system is dominated by the blower operation for this air supply.

By blowing a large amount of air and stirring the aeration tank,
It is unsanitary because there is foaming in the tank and scattering of them.

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

(4) The MLSS may settle down in the settling tank that is installed after the aeration tank, and the consolidation may deteriorate (expanding, hereinafter referred to as bulking), and good treatment may not be continued in some cases.

(5) The sludge generated by the activated sludge process is extracted as excess sludge from the settling tank, but the extracted sludge has an MLSS concentration of about 8,000 mg / l, which is due to sludge treatment such as dehydration associated with the facility. Requires a concentration operation such as weight concentration or mechanical concentration.

(6) Phosphorus, which is one of the causative substances of eutrophication phenomenon such as red tide, is hardly removed by the usual activated sludge system.

The present invention is intended to solve the problems found in the conventional techniques as described above.

(Means for Solving Problems) The feature of the sewage treatment method according to the present invention for solving the above-mentioned conventional problems is that organic sewage containing suspended matters such as domestic sewage, sewage, and food factory wastewater. A rapid stirring step of adding an inorganic coagulant such as PAC to rapidly stir, and a step of flocculating suspended matter, colloidal substances and phosphorus compounds in the wastewater by gentle stirring after the rapid stirring, and forming by this A primary solid-liquid separation step of solid-liquid separating the flocs thus prepared by pressure floating separation, and the primary treated water treated by the step is introduced into a filtration tank filled with a filter medium having a particle size of about 2 to 10 mm, and the primary Oxygen required for the action of the activated sludge-like aerobic microorganisms growing on the surface of the filter medium is supplied to the filter tank by using the soluble organic matter and NH ₄ ⁺ -N contained in the treated water as nutrient sources, and the primary treatment is performed. Solubility B remaining in water OD, SS,
It is in combination with a reprocessing step for removing phosphorus.

Further, the feature of the sewage treatment apparatus according to the present invention is to store organic sewage containing suspended solids such as domestic sewage, sewage, food factory wastewater, etc., to which inorganic coagulant such as PAC is added and rapidly stirred. A rapid stirring tank for mixing and mixing, a slow stirring tank for gently stirring the mixed wastewater that has been stirred and mixed in the rapid stirring tank, and large growth of fine flocs, and a mixed wastewater from the slow stirring tank are introduced. Then, the pressurized flotation separation tank provided with a pressurized water nozzle for injecting pressurized water in which air is excessively dissolved by pressurization and the growth floc group floated and separated on the pressurized flotation separation tank are discharged to the outside of the tank. Sludge removing means and the primary treated water from which flocs have been removed in the pressure floating separation tank are continuously supplied, and a filter medium having a particle size of 2 to 10 mm and having an aerobic microflora in the form of activated sludge grown on the surface is obtained. The packed filter layer is placed inside and the filter layer is empty. A filter tank equipped with a blower for blowing air, a backwashing means for cleaning the filter layer of the filter tank for a certain period of time by blowing air and feeding treated water, and a state of progress of clogging in the filter layer. Is detected by the pressure loss of the upper and lower parts of the filter bed, and a water level differential pressure transmitter for instructing the start of the operation of the backwash means, and the treated water flowing out from the filter tank are stored and sent to the pressure floating separation tank. And a treated water tank for supplying the pressurized pressurized water for bubble generation and the water for backwashing the filter layer.

(Function) BOD in organic wastewater such as sewage including suspended solids is
It is composed of colloidal components and soluble components. The BOD concentration of untreated sewage is about 200 mg / l, but by adding the above-mentioned inorganic coagulant to such sewage and stirring rapidly and slowly, almost all SS components and colloidal components About half of BOD in wastewater is removed by precipitating a part of it as flocs and separating it by pressure floating.

The phosphorus in the wastewater reacts with the inorganic coagulant in the following manner, for example, to precipitate as flocs, and most of the phosphorus is removed in the same manner as the SS component.

Al ³⁺ + PO ₄ ^3- > AlPO ₄ ↓ (1) Fe ³⁺ + PO ₄ ^3- > FePO ₄ ↓ (2) The above phosphorus removal rate is shown in equations (1) and (2). Thus, it depends on the addition amount of the inorganic coagulant. In the present invention, since the biological treatment with aerobic microorganisms is performed after the primary treatment by the pressure floating separation, it is possible to intentionally allow phosphorus to remain in the primary treated water to the extent necessary for the survival and activity of these microorganisms. First, the addition amount of the inorganic coagulant is adjusted according to the phosphorus concentration in the wastewater to be treated.

The amount of inorganic flocculant added to meet the above purposes is, for example, sewage (phosphorus concentration in wastewater is 5 mg / l, phosphorus concentration in primary treated water is 1.5 mg / l) 160 mg / l with liquid sulfuric acid band, 125 m with PAC
g / l, about 20 mg / l for ferric chloride.

After performing such a primary treatment, aerobic microorganisms adhered and grown on the surface, a natural product such as zeolite having a particle diameter of 2 to 10 mm, a coal-based material, and a thickness of a filter material prepared from a plastic-based artificial material 1 to 1 In a biological filtration device having a filter layer of 2 m, soluble BOD components remaining in the primary treated water, SS, phosphorus is removed by the action of the aerobic microorganisms, both BOD, SS 10 mg /
l, Phosphorus 1 mg / l or less, and finally treated water of good quality can be obtained.

Thus, in the primary treatment without biological reaction, BOD
Approximately one half of the above, a part of the colloidal component and a part of phosphorus are removed, so that the load on the biological filtration device for carrying out the biological reaction is reduced and the residence time is shortened. In addition, the pressure flotation method for solid-liquid separation requires a remarkably short time of about 1/20 as compared with the precipitation method, so the residence time of the entire device is 1/5 to 1 compared to the standard activated sludge method. It will be about / 8.

Further, in the present invention, the amount of air as a supply source of dissolved oxygen (hereinafter referred to as DO) to the aerobic microorganisms that adhere and grow on the filter layer is
The primary treatment is carried out in the pressure floating separation process to reduce the load, and the fine bubbles generated for solid-liquid separation in the pressure floating separation process also serve as DO supply to the primary treated water. As a result, when sewage to be treated is sewage, the required air volume is approximately twice or less than the supplied sewage volume, and is reduced to 1/3 or less as compared with the conventional technology.

Further, the solid-liquid separation in the present invention is pressure floating separation before biological reaction and filtration accompanied by biological reaction, and there is no trouble in operation of the apparatus due to the influence of bulking.

Further, the sludge solid-liquid separated by the pressure floating separation has a high concentration of about 30,000 mg / l as SS, and therefore, the concentration operation in the sludge treatment is unnecessary.

Further, in the present invention, since the treatment consisting of only a biological reaction such as the activated sludge method and the physicochemical treatment with an inorganic coagulant are combined, phosphorus, which is difficult to remove only by the biological reaction, can be treated by the chemical reaction as described above. To be removed.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows a first embodiment. In this embodiment, organic sewage containing suspended solids such as domestic sewage, sewage, food factory wastewater, etc. is continuously and quantitatively supplied to the rapid stirring tank 1. The mixture is mixed with an inorganic coagulant such as PAC which is quantitatively injected into the tank by the rapid stirring device 2. By the above-mentioned operation, SS, colloidal substances, phosphorus, etc. in wastewater are formed as fine flocs by chemical or electrochemical action. Sewage containing these flocs is caused to flow into the slow stirring tank 3 and is slowly stirred by the slow stirring device 4 in the tank. In this process, the fine flocs formed in the previous process are made to collide with each other and adhere to each other to grow into flocs having a diameter of about 1 mm. The sewage containing the grown flocs is supplied to the pressure flotation separation tank 5 and is generated through a depressurized bubble generator 8 installed at the bottom of the inflow section formed by a vertical partition 6 in the tank. Mix and contact with microscopic bubbles of 60μ. Pressurized water is supplied to the depressurized bubble generator 8. This pressurized water is supplied from the treated water storage tank 25 storing the final treated water according to the method of the present invention into the pressurized water adjusting tank 28 via the pressurized water pump 26, and the pressure inside the tank 28 is approximately 4 kg / cm ² . While maintaining, by contacting with pressurized air continuously supplied from the compressor 29 through the filler 30 installed in the tank, the air is excessively dissolved as compared with under normal atmospheric pressure. .

The floc / bubble associations in which fine bubbles adhere to the flocs formed in the previous step behave as a unit and their density is lower than that of water. Therefore, along the partition walls 7 installed diagonally in the pressure floating separation tank 5. After rising, the water reaches the water surface of the tank 5 and is separated from waste water. These flocs separated on the water surface of the tank 5 accumulate to form a floating sludge layer 10. The sludge layer 10 is continuously or intermittently scraped by the floating sludge discharge device 9 toward the outflow side of the pressure floating separation tank, and the pressure floating separation tank 5 is discharged.
It is discharged to the floating sludge discharge tank 32 which is provided adjacent to and is discharged to the outside.

The primary treated water that has undergone the pressure floating separation step is flowed into the primary treated water storage tank 12 through a water level adjusting weir 11 provided for the purpose of adjusting the water level in the pressure floating separation tank 5, and is temporarily stored. This primary treated water is SS in the inflowing wastewater at the end of the above process,
Most of phosphorus is removed, and about 1/2 of BOD is removed. Also,
The DO concentration is increased by mixing and contacting with the micro-bubble group that contributes to the pressure floating separation for about 15 to 20 minutes.

The primary treated water is continuously and quantitatively supplied to the biological filtration tank 14 via the primary treated water supply pump 13. A water collecting device 17 for evenly collecting the filtered water is accommodated in the bottom of the tank 14, a supporting gravel layer 16 for physically supporting the filter medium on the upper part thereof, and a particle size of 2 to 10 mm at the uppermost part. The filter layers 15 each having a thickness of 1 to 2 m and filled with a filter material made of a natural product or an artificial product are sequentially stacked and housed so that the particle size distribution becomes relatively uniform in the range.

The primary treated water supplied to the biological filter tank 14 flows out of the tank through the route of filter layer → supporting gravel layer → water collecting device due to the head pressure of the upper part of the filter layer 15. In this process, due to the action of aerobic microorganisms that have adhered and grown on the surface of the filter medium that constitutes the filter layer 15, the soluble BOD component remaining in the primary treated water, NH ₄ ⁺
-N, phosphorus is removed. The DO required for the removal reaction of these pollutants by aerobic microorganisms is the filter layer 15 and the supporting gravel layer 16
The air supplied from the blower 19 via the air diffuser 18 installed on the boundary surface of the is sheared while rising in the filter layer and dissolved in water.

The water level in the biological filter tank 14 rises as aerobic microorganisms grow on the filter medium. If 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 a preset lower limit water level, the treated water automatic valve 21 and the air supply automatic valve 24 are closed, the air cleaning automatic valve 23 is opened, and the air from the blower 19 is collected by the water collecting device 17. It is supplied from the lower part of the supporting gravel layer 16 and the aerobic microorganisms excessively grown on the surface of the filter medium are separated by physical shearing force due to the rise of bubbles. After continuing this process for about 2 minutes, the blower 19 is stopped, the air washing automatic valve 23 is closed, the backwash pump 20 is further operated, the backwash automatic valve 22 is opened, and the treated water storage tank 25 is opened. By supplying the final treated water stored in advance through the water collecting device 17 from the lower part of the biological filter tank 14 at a flow velocity sufficient to expand the filter layer 15, the separated aerobic microorganisms are treated as waste water. It is discharged to the outside of the tank through the trough 31. This discharged water is mixed with sewage and supplied to the rapid stirring tank 1 which is the inflow portion of the apparatus, and is reprocessed by the rapid stirring process, the slow stirring process, and the pressure floating separation process.

The required residence time in the device of the present invention is about 15 minutes for the rapid / slow stirring process, about 15 to 20 minutes for the pressure floating separation process, about 30 to 60 minutes for the biological filtration process, and a total of 1 hour to 1 hour 30 minutes. The wastewater can be treated in an extremely short time as compared with the prior art, and the wastewater treatment device becomes extremely compact.

FIG. 2 shows a second embodiment. In the present invention, the pressure flotation separation step which is the primary treatment of sewage and the biological filtration step which is the final treatment are carried out at the bottom of the pressure flotation separation tank 5. By integrally forming the tank 14, the device according to the present invention can be operated as described above in a single tank.

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

In the second embodiment, since the pressure floating separation tank 5 and the biological filtration tank 14 are integrally formed continuously in the vertical direction, the water level of the pressure floating separation unit is kept constant over time. Therefore, a differential pressure transmitter 27 is provided just above the filter layer 15 and just below the supporting gravel layer 16, and the difference between the top and bottom of the biological filter tank is provided via a controller 31 electrically connected to the transmitter. The opening of the treated water amount control valve 33 is sequentially and continuously changed in response to the increase in pressure to keep the water level in the levitation separation part constant.

Also in the second embodiment, the rapid stirring, slow stirring step, the step of adjusting the pressurized water for the generation of fine bubbles, the air washing due to the clogging of the biological filter layer, the back washing step and the opening / closing operation of the automatic valve,
It is similar to the first embodiment.

In the second embodiment, the floating sludge 10 formed on the water surface of the pressure flotation separation tank 5 during the normal treatment is operated by operating the floating sludge attracting device 9 intermittently or continuously so that the floating sludge storage tank It is discharged to the outside of the tank via 32 and used in the sludge treatment process.

In the step of backwashing the biological filtration tank 14, the backwash discharge containing the separated aerobic microorganisms is discharged from the top of the pressure floating separation tank 5 to the outside of the tank via the floating sludge storage tank 32, and the device of the present invention is provided. In the inflow part, it mixes with the inflowing wastewater, and is reprocessed through the rapid stirring / slow stirring and the pressure floating separation process. Further, in order to smooth the overflow of the discharged water in the backwashing step of the biological filtration layer, the floating sludge attracting device 9 is continuously operated. In this step, the inflow sewage automatic valve 34 is closed to stop the inflow of sewage, and also the injection of the inorganic coagulant into the rapid stirring tank 1 is stopped, but the pressurized water is not supplied through the reduced pressure bubble generator 8. continue.

Although not particularly shown in FIGS. 1 and 2,
When the physical strength of the flocs formed in the slow stirring step is insufficient, it is possible to inject a polymer flocculant of about 1 mg / l to the slow stirring tank with respect to the inflowing wastewater amount.

Table 1 is an example of the treated water quality in each step in the embodiment of the present invention in which sewage is the target sewage.

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

According to the method / apparatus of the present invention, the treated water having a good water quality of 10 mg / l or less for both BOD and SS and 1 mg / l or less for T-P can be obtained in a short time of 1 to 1.5 hours in total in the apparatus. .

Compared with the conventional method, the volume and installation area of the device can be significantly reduced, and the facility cost can be reduced. In particular, as shown in the second embodiment, by performing the pressure floating separation as the primary treatment and the biological filtration as the final treatment in a single tank integrally formed, the sewage treatment apparatus according to the present invention becomes extremely compact.

The device of the present invention is capable of fully automatic operation and does not require skill and high technical experience in operation.

The amount of air as an oxygen supply source is less than 1/3 of the conventional method, and the required blower capacity is reduced.

Since the concentration of discharged sludge is about 3 times higher than that of the conventional method, the volume of generated sludge becomes about 1/3, which makes concentration operation unnecessary in the sludge treatment process, and The capacity can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention, and FIG. 2 is a schematic diagram showing a second embodiment of the present invention. 1 ... Rapid stirring tank, 2 ... Rapid stirring device, 3 ... Slow stirring tank, 4 ... Slow stirring device, 5 ... Pressurized floating 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 collecting device, 18 ……
Air diffuser, 19 …… Blower, 21 …… Automatic treated water valve, 22 ……
Backwash automatic valve, 23 …… Air cleaning automatic valve, 24 …… Air supply automatic valve, 25 …… Treated water storage tank, 28 …… Pressurized water adjusting tank, 29 ……
Compressor, 30 ... Filling material.

Claims (5)

[Claims] Claims: 1. Organic sewage containing suspended solids such as domestic sewage, sewage, food factory wastewater, etc.
Write as C. ) And the like, and a rapid stirring step of rapidly stirring and a step of flocculating the suspended matter, colloidal substance and phosphorus compound in the wastewater by gentle stirring after the rapid stirring, The primary solid-liquid separation step of solid-liquid separation of the flocs by pressure floating separation, and the primary treated water treated by the step is introduced into a filter tank filled with a filter medium having a particle size of about 2 to 10 mm, and the primary treatment is carried out. The oxygen necessary for the action of the aerobic microorganisms in the form of activated sludge that grows on the surface of the filter medium is obtained by using soluble organic matter and ammonia nitrogen (hereinafter referred to as NH ₄ ⁺ -N) contained in water as nutrients. A method for treating sewage, which is combined with a step of re-treating the primary treated water by supplying it to a filtration tank. 2. The method for treating sewage according to claim 1, wherein high-concentration oxygen air is used as a gas source for fine bubbles required for pressure floating separation and a gas source supplied to a filter layer. 3. A rapid agitation tank for accommodating organic sewage containing suspended solids such as domestic sewage, sewage, food factory wastewater, etc., to which inorganic coagulant such as PAC is added and rapidly agitated and mixed. , A slow stirring tank that gently stirs the mixed wastewater that has been stirred and mixed in the rapid stirring tank to grow fine flocs to a large extent, and a mixed wastewater from the slow stirring tank is introduced, and pressurized water provided at the bottom Pressurized water that jets pressurized water with excess air dissolved by pressurizing from the nozzle to bring mixed sewage into contact with fine air bubbles that are generated when the pressurized water is depressurized at once, and solid-liquid separation into growth flocs and primary treated water Separation tank, sludge removing means for discharging the growth floc group floated and separated on the pressure flotation separation tank to the outside of the tank, and primary treated water from which flocs have been removed in the pressure flotation separation tank are continuously supplied. Activated sludge that grew on the surface Of a filter tank having an aerobic microbiota having a particle size of 2 to 10 mm and having a blower for blowing air into the filter layer, and a filter layer of the filter tank. Backwashing means for washing for a certain period of time by blowing air and treated water when clogging, and the progress of clogging in the filter layer is detected by pressure loss in the upper and lower parts of the filter layer, and the backwashing means To store the treated water flowing out from the filtration tank and to supply it to the pressurized flotation separation tank as circulating pressurized water for bubble generation and as backwash water for the filtration layer. Sewage treatment equipment comprising the treated water tank of. 4. A pressure levitation separation tank is integrated with a filtration tank at a lower part to form a single tank, and sewage containing growth flocs supplied to the tank is pressure levitation separated at the top of the tank. The sewage treatment apparatus according to claim 3, wherein treatment with aerobic microorganisms is performed in the lower 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 floating separation and a gas source supplied to a filter layer. .