JPH0734914B2 - Sewage treatment method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sewage treatment method and apparatus for purifying sewage containing organic substances.

(Prior Art) Conventionally, a batch reaction tank is equipped with a stirrer for agitating sewage and an aerator, and the sewage is stored in the reaction tank and stirred, aerated, and then allowed to stand to settle to obtain supernatant water There is known a sewage treatment method by a batch activated sludge method in which the sludge is discharged and the sludge that has settled is extracted.

(Problems to be Solved by the Invention) The conventional batch activated sludge method has the following problems. First, since the sludge that has settled is drawn out of the water, its volume is large and it is necessary to install a sludge thickening tank. Secondly, a special device is required to prevent the deterioration of the quality of the treated water by drawing out a part of the sludge settled at the same time when the supernatant water is taken in and the scum is removed. Third, the separated water helin is eluted from the sludge in the concentration tank that processes the sludge after it is extracted.

The present invention has an object to provide a sewage treatment method and an apparatus for the same, which solves various conventional problems.

(Means for Solving the Problem) The characteristics of the sewage treatment method of the present invention for solving the conventional problems as described above are characterized by removing raw water from which a large specific gravity of sand or the like and lightweight impurities such as dust are removed, By intermittently accommodating a fixed amount in a batch reaction tank and adjusting the installation position of a level meter and an intermediate treated water discharge pump, etc., the sludge required to maintain the sludge concentration required in the batch reaction tank can be stored. After accommodating the sewage to be treated in the state of being left in the batch reaction tank, the batch reaction process is performed by alternately performing the stirring step and the aeration step, and after further standing sedimentation for primary solid-liquid separation, A step of leaving as much sludge as necessary to maintain the required sludge concentration in the batch reaction tank, and temporarily storing intermediate treated water composed of a mixture of the excess sludge and supernatant water. It is stored in a tank and the intermediate treated water in that tank is rapidly stirred. The water is continuously fed to a rapid stirring tank for carrying out, and the inorganic coagulant such as PAC is added to the intermediate treated water in the rapid stirring tank to rapidly stir, and then the intermediate treated water is gently stirred. With the process of conducting water to the pressure flotation separation tank via a slow stirring tank for flocculating suspended solids, colloidal substances and phosphorus compounds, and separating the formed flocs into secondary solid-liquid separation by pressure flotation separation. In combination.

Further, the feature of the apparatus according to the present invention is that the raw water from which a large specific gravity such as sand or light contaminants such as dust is removed is intermittently accommodated in a fixed amount, and a stirring step, an aeration step and a stationary sedimentation step are performed. In addition, a batch reaction tank equipped with a level meter to know the amount of sludge required to maintain the required sludge concentration and an intermediate treated water drainage pump installed at the position required to obtain the required amount of sludge. And an intermediate treated water storage tank for temporarily storing intermediate treated water consisting of a mixed liquid of surplus sludge other than sludge necessary for the batch reaction tank and supernatant water, and an inorganic coagulant such as PAC in the intermediate treated water. A rapid stirring tank for adding and rapidly stirring and mixing, and a slow stirring tank for gently stirring the mixed intermediate treated water that has been stirred and mixed in the rapid stirring tank to greatly grow fine flocs. , Introduce the intermediate treated water from the slow stirring tank, and pressurize Pressure flotation separation tank having a pressurized water nozzle at the bottom for injecting pressurized water with excessively dissolved air, and sludge removing means for discharging the growth floc group floated and separated on the surface of the pressure flotation separation tank to the outside of the tank. The treatment water tank for storing the treated water flowing out from the pressurized flotation separation tank and supplying it to the pressurized flotation separation tank as the circulating pressurized water for generating bubbles.

(Operation) This sewage treatment method and its apparatus store a fixed amount of raw water in a batch reaction tank, and perform an agitation process and an aeration process by setting an appropriate cycle in a state where the required sewage concentration is controlled. . Then, it is allowed to stand for sedimentation for primary solid-liquid separation. Of the settled sludge, the amount of sludge necessary to maintain the required sludge concentration is left in the batch reaction tank by detecting with a level meter and adjusting the installation position of the intermediate treated water discharge pump, and the excess sludge and supernatant water are mixed. The intermediate treated water consisting of liquid is sent to the intermediate treated water storage tank. In other words, since only the supernatant water is not taken in, a special device for removing the supernatant water and removing scum in the reaction tank is unnecessary.

In this batch reaction step, most of the organic substances and nitrogen, which are based on the biochemical oxygen demand (hereinafter referred to as BOD) in the raw water, are removed, and a part of phosphorus is also removed.

By adding an inorganic coagulant such as PAC to the intermediate treated water sent to the intermediate treated water storage tank and stirring the mixture rapidly and slowly,
Almost all of the suspended matter (hereinafter referred to as SS) components and colloidal components in the intermediate treated water can be deposited as flocs. Further, phosphorus remaining in the intermediate treated water can be precipitated as flocs by reacting with the inorganic coagulant as described below, for example.

Al ³⁺ + PO ₄ ^3- > AlPO ₄ ↓… (1). Fe ³⁺ + PO ₄ ^3- → FePO ₄ ↓ (2) By separating these precipitated flocs by pressure floating separation, final treated water of good water quality with extremely low concentrations of BOD, nitrogen, and phosphorus can be obtained.

Further, the floc group separated by floating is collected in the air by the mud collecting means. In this way, the sludge is not collected in water and the sludge concentration is high, and the sludge is aerobically collected, so that solid-liquid separation and sludge concentration are simultaneously performed in a short time.
The sludge thickening tank is unnecessary because the volume of recovered sludge is reduced.
As described above, since phosphorus is removed by physicochemical treatment with an inorganic coagulant and sludge concentration in the sludge concentration tank is not performed, there is almost no possibility of redelution of phosphorus.

(Embodiment) Next, an embodiment of the present invention will be described with reference to the drawings.

In the figure, 1 is a batch reaction tank, and two tanks are used in this embodiment. Raw water from which impurities such as sand and light dust have been removed beforehand is alternately fed into the batch reaction tank 1. Batch reaction tank 1
Is equipped with an aeration nozzle 3 to which compressed air is supplied from an aeration blower 2 and an underwater stirrer 4. In this batch reaction tank 1, the biochemical treatment is performed in a state where the raw water is stored up to a predetermined water level by the batch treatment. At this time, the sludge concentration is maintained in a fixed range because it can be controlled by the level meter 5 so as to leave a necessary sludge amount in the batch reaction tank 1 after the sedimentation in the batch reaction tank 1.

The amount of residual sludge at this time may be adjusted by adjusting the height of the water intake port of the intermediate treated water discharge pump 6 without using the level meter 5.

The biochemical treatment is performed by alternately setting aeration and agitation by setting an appropriate cycle, and performs denitrification along with BOD removal. The processing efficiency can also be improved by using a plurality of batch reaction tanks 1 and 1 while shifting them temporally.

After completion of the biochemical treatment, static sedimentation was performed to perform primary solid-liquid separation, and the sludge amount necessary to keep the sludge concentration in the batch reaction tank 1 within the required range was set at a level meter 5 or a required position. By the action of the intermediate treated water discharge pump 6, the intermediate treated water left in the batch reaction tank 1 and made of a mixed liquid of excess sludge and supernatant water is sent to the intermediate treated water storage tank 7 by the intermediate treated water discharge pump 6. The pump 6 is automatically stopped when it descends to a certain water level. This intermediate treated water storage tank 7 is a batch reaction tank 1, 1
It has a function of performing adjustment for connecting the batch processing step and the continuous processing step after the next step.
An aeration nozzle 9 to which air is supplied from an adjusting tank blower 8 is inserted in the intermediate treated water storage tank 7.

The intermediate treated water in the intermediate treated water storage tank 7 is continuously and quantitatively supplied by the intermediate treated water supply pump 10 to the rapid stirring tank 11 in the next step. The intermediate treated water and an inorganic coagulant such as PAC which is quantitatively injected into the rapid stirring tank 11 are mixed by the rapid stirring tank device 12. By the above operation, SS, colloidal substances, phosphorus, etc. remaining in the intermediate treated water are formed as fine flocs by chemical or electrochemical action. Slow stirring tank for intermediate treated water containing these flocs
It is introduced into 13 and is slowly stirred in the tank by a slow stirring device 14. In this step, the fine flocs formed in the previous step are made to collide with each other and adhere to each other to grow into flocs having a diameter of about 1 mm. The intermediate treated water containing the grown flocs is supplied to the pressure-floating separation tank 15, and the diameter is generally generated through a reduced pressure bubble generator 17 installed at the bottom of the inflow section formed by a vertical partition 16 in the tank. Mix and contact with 30-60μ fine bubbles. Pressurized water is supplied to the depressurized bubble generator 17. This pressurized water is supplied from the treated water storage tank 23 storing the final treated water according to the method of the present invention into the pressurized water adjusting tank 25 via the pressurized water pump 24, and the pressure inside the tank 25 is approximately 4 kg / cm ² . Filling material installed in the tank while keeping it 2
By contacting with the pressurized air continuously supplied from the compressor 27 via 6, the air is excessively dissolved as compared with under normal atmospheric pressure.

The flocs and bubble aggregates in which fine bubbles are attached 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 wall 18 installed diagonally in the pressure floating separation tank 15. After rising, reach the water surface of the tank 15,
Separated from intermediate treated water. These flocs separated on the water surface of the tank 15 accumulate to form a floating sludge layer 19. The sludge layer 19 is continuously or intermittently scraped to the outflow side of the pressure flotation separation tank 15 by a flotation sludge discharge device 20, and discharged to a flotation sludge discharge tank 21 provided adjacent to the pressure flotation separation tank 15. ,
Carry out to the outside.

The final treated water after the pressure floating separation process is SS, BOD,
The nitrogen and phosphorus concentrations are extremely low and have good water quality.The water is discharged to the treated water tank 23 through the water level adjusting weir 22 provided for the purpose of adjusting the water level in the pressure floating separation tank 15. It

(Effects of the Invention) The sewage treatment method and apparatus of the present invention configured as described above have the following effects.

By using the pressurized flotation method for solid-liquid separation, the generated sludge has a high concentration, there is no need for sludge concentration, and a sludge thickening tank is not required.

Phosphorus is re-eluted because it uses a method of reacting physicochemically with Al ³⁺ and Fe ³⁺ in the inorganic coagulant to precipitate as flocs and aerobically separating from wastewater in a short time. Does not happen.

The supernatant water intake device and the scum removal device, which had been an important technical issue in the batch activated sludge method, are not required because the wastewater from the batch reaction tank is treated as an intermediate treated water consisting of a mixture of supernatant water and excess sludge. Become.

There is no concern about carryover of solid-liquid separated sludge, maintenance is easy, and treated water is stable.

It is also suitable for separating sludge with a high SVI (sludge volume index), which is said to be prone to bulking.

Since the solid-liquid separation process is a continuous type, the amount of a fixed amount of pressurized water required for pressure floating separation per unit time can be reduced, and the pressurized water adjusting tank, the pressurized water pump, and the compressor may be compact.

[Brief description of drawings]

Drawing is a schematic block diagram of the Example of this invention. 1 ... Batch reaction tank, 2 ... Aeration blower, 3 ... Aeration nozzle, 4 ...
… Underwater agitator, 5 …… Level meter, 6 …… Intermediate treated water discharge pump, 7 …… Intermediate treated water storage tank, 8 …… Aeration blower, 9 …… Aeration nozzle, 10 …… Intermediate treated water supply pump,
11 …… Rapid stirring tank, 12 …… Rapid stirring apparatus, 13 …… Slow stirring tank, 14 …… Slow stirring apparatus, 15 …… Pressurization floating separation tank, 16
...... Partition, 17 ...... Decompression bubble generator, 18 ...... Partition, 19 ...
… Floating sludge tank, 20 …… Floating sludge discharging device, 21 …… Floating sludge discharging tank, 22 …… Pressurization floating tank Water level adjusting weir, 23 …… Treatment water tank, 24 …… Pressurized water pump, 25 …… Pressurized water adjusting tank , 26 ……
Filling material, 27 ... Compressor.

Claims (2)

[Claims] 1. Raw water from which high specific gravity such as sand and light contaminants such as dust have been removed is intermittently stored in batch reaction tanks in fixed amounts, and the concentration of wastewater is controlled in the batch reaction tanks. To perform a batch reaction process by alternately performing a stirring process and an aeration process,
The process of static sedimentation for primary solid-liquid separation, and the amount of sludge necessary to control the sludge concentration required in the batch reaction tank is left in the batch reaction tank, and excess sludge and supernatant water are removed. A step of temporarily storing the intermediate treated water consisting of a mixed liquid with the intermediate treated water storage tank, and adding an inorganic coagulant such as polyaluminum chloride (hereinafter referred to as PAC) to the intermediate treated water and rapidly stirring. And a step of flocculating the suspended solids, colloidal substances and phosphorus compounds in the intermediate treated water by gentle stirring after the rapid stirring step, and the flocs formed by this are separated by solid-liquid separation by pressure floating separation. A method for treating wastewater, which comprises a combination with a secondary solid-liquid separation step. 2. Raw water from which high specific gravity such as sand and light contaminants such as dust are removed is intermittently stored in a fixed amount, and the agitation step, aeration step and static sedimentation are controlled by controlling the concentration of sewage inside. From the batch reaction tank that performs the process, and the mixture of the excess sludge and the supernatant water after leaving the sludge in the batch reaction tank only for controlling the sludge concentration required in the batch reaction tank. The intermediate treated water storage tank for temporarily storing the intermediate treated water, the rapid stirring tank for adding the inorganic coagulant such as PAC to the intermediate treated water and rapidly stirring and mixing, and the rapid stirring tank By gently stirring the mixed and treated intermediate treated water to slowly grow fine flocs, and by introducing the intermediate treated water from the slowly stirred tank, pressurizing from a pressurized water nozzle provided at the bottom. Pressurized water with excessively dissolved air is sprayed Water contacting the fine bubbles and intermediate processing water produced by being once reduced pressure, and the pressure is solid-liquid separated into growth flocs and final treated water floatation separation tank,
Sludge removal means for discharging the growth floc group floated and separated on the surface of the pressure flotation separation tank to the outside of the tank, and the final treated water flowing out from the pressure flotation separation tank is stored, and bubbles are generated in the pressure flotation separation tank. A sewage treatment apparatus comprising a treated water tank for supplying as circulating pressurized water for use.