JPS5916516B2 - Fluidized bed biological treatment method and treatment equipment for wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluidized bed biological treatment method and treatment device for wastewater, and in particular, it maintains biofilm attached to a carrier stably and active, and achieves consistently high treatment efficiency in continuous operation. The present invention relates to a biological treatment method and treatment device that can achieve the following.

A method of decomposing and removing organic substances in wastewater by fluidizing a carrier with a biofilm attached thereto has been widely used in recent years because of its relatively high BOD removal efficiency.

However, during treatment, the biofilm grows excessively and aggregates or peels off from the carrier, producing floating sludge.

Japanese Patent Publication No. 52-38669 describes that floating sludge can be prevented from flowing out together with treated water by mechanically destroying agglomerates that are excessive bacterial growth and increasing specific gravity. There is.

However, in this method, since the agglomerates are only broken down by mechanical force such as a stirrer, the amount of exfoliated sludge increases in the treatment tank.

According to our research, an increase in the amount of exfoliated sludge in the treatment tank is an important cause of a decrease in the activity of biofilms attached to carrier particles and in the organic matter removal performance.

Further, Japanese Patent Application Laid-open No. 53-18252 describes that a partition plate is provided at the upper part of the treatment tank to prevent the carrier from flowing out and to allow floating surplus sludge to overflow together with the treated water.

However, in order to carry out this method, it is necessary that the inflow of raw water is always sufficient and that excess sludge can be discharged together with the treated water before it increases too much.

However, in actual wastewater treatment, the amount of raw water often fluctuates, and the inflow of raw water may sometimes stop.

If the inflow of raw water is insufficient or stopped, it is not possible to flow out a sufficient amount of treated water to fully remove floating surplus sludge. Therefore, surplus sludge increases in the treatment tank, and Processing efficiency is significantly reduced.

The present invention is capable of reducing the amount of exfoliated sludge suspended in the fluidized bed even if there are fluctuations in the amount of inflow of raw water, and can always maintain high activity of biofilm attached to carrier particles and performance of removing organic matter. The purpose of the present invention is to provide a treatment method and treatment device that can consistently and efficiently treat water and produce treated water of stable quality.

In the present invention, by using final treated water that does not contain sludge as circulating water, the flow rate at the upper part of the treatment tank near the separation date of the treated water allows the suspended detached sludge, that is, excess sludge, to flow out together with the treated water, but the carrier is The above objective is achieved by keeping the liquid within a range that does not allow it to flow out.

That is, in the method of the present invention, by circulating the final treated water to the treatment tank as needed, the flow velocity near the inlet of the treated water separation section in the treatment tank is made smaller than the sedimentation velocity of the carrier at the maximum water load, and the surplus is reduced. The floating excess sludge generated in the fluidized bed is maintained at a range higher than the settling rate of the sludge, and the floating surplus sludge generated in the fluidized bed is discharged into the solid-liquid separation tank together with the treated water.The excess sludge is removed in the solid-liquid separation tank by a conventional method to obtain the final treated water. It is characterized by obtaining.

The equipment used to carry out the method of the present invention mainly consists of a fluidized bed wastewater treatment tank and a solid-liquid separation tank, and the cross-sectional area of the inlet of the treated water separation section provided at the top of the treatment tank is the maximum of the treatment tank. A separation pipe that is set to produce a flow velocity that is lower than the sedimentation rate of the carrier and higher than the sedimentation rate of the suspended surplus sludge under water load, and flows out the treated water and the suspended surplus sludge from the treated water separation section to the solid-liquid separation tank; The present invention is characterized by being provided with a circulation path for circulating the final treated water to the lower part of the treatment tank and a circulation amount control device for circulating the final treated water in accordance with fluctuations in the inflow amount of raw water.

The fluidized bed treatment tank and solid-liquid separation tank used in this device may be of any conventional type, but in order to prevent the carriers with biofilms from flowing out, there is a baffle plate on the top of the treatment tank. etc. to form a separation section for the treated water, and the cross-sectional area of the inlet of the separation section is set so that at the maximum water load of the treatment tank, a flow velocity is smaller than the sedimentation rate of the carrier and greater than the sedimentation rate of suspended excess sludge. It is necessary to.

Next, the present invention will be explained in detail based on the drawings, but the present invention is not limited thereto. FIG. 1 is a schematic cross-sectional view of a conventional fluidized bed processing apparatus.

This device mainly consists of a treatment tank 1, a gas lift pipe 2, and a solid-liquid separation tank 3. Wastewater flows into the treatment tank 1 through an inflow pipe 4, and is attached to oxygen or air supplied from an aeration pipe 5 and carrier particles. The treated water is purified by the action of the biofilm and flows out from the treated water outflow pipe 6.

The sludge deposited at the bottom of the solid-liquid separation tank 3 is discharged from the sludge pipe 7.

Figure 2 shows the measurement results of the BOD of treated water when raw water with a BOD of 500 pya was treated using this device.

As is clear from FIG. 2, the BOD fluctuates between 15 and 30 fermentations at a BOD volumetric load of 7 KP-BOD/m3·d, and the treated water temporarily deteriorates.

In order to investigate the cause of the sludge, we carried out treatment for 10 days using the equipment shown in Figure 1, and investigated the relationship between the amount of biofilm attached to the carrier and the amount of floating exfoliated sludge, that is, the amount of excess sludge. investigated.

In addition, in reality, sometimes during wastewater treatment, the amount of raw water flowing in decreases and sludge cannot be removed, and in this case, the quality of the treated water is likely to deteriorate. Sludge was not drained from the solid-liquid separation tank.

In addition, the amount of excess sludge was determined gravimetrically according to JISKO101, but since it is difficult to completely peel off the biofilm attached to the carrier and measure it, the oxygen consumption rate)'r(ppm-02 /h ) values were determined and compared based on their magnitude.

The results are shown in A of FIG. As a result, the oxygen consumption rate of the carrier reached its maximum value about 2 days after the start of flowing raw water, confirming that the biofilm was well attached to the carrier.

However, the amount of excess sludge began to increase rapidly after 2 days and reached about 7000 p- after 7 days.

Furthermore, while the amount of excess sludge is increasing, the oxygen consumption rate of the carrier with biofilm attached is decreasing, indicating that the state of biofilm attachment is deteriorating.

Therefore, it is clear that the presence of excess sludge significantly impairs biofilm activity and organic matter removal performance.

On the other hand, the oxygen consumption rate coefficient Kr (
■・02/g・5s-h) was 10 to 14 for suspended surplus sludge, while it was 23 to 38 for biofilm attached to the carrier. The activity is clearly higher.

Therefore, an increase in excess sludge in the treatment tank deteriorates the decomposition efficiency of organic matter.

As described above, when the amount of inflow water decreases during treatment in the conventional apparatus and it becomes impossible to drain the sludge, excess sludge increases and the quality of the treated water deteriorates.

Fig. 4 is a schematic system diagram showing one embodiment of the device of the present invention.Even if there is a fluctuation in the amount of wastewater flowing in, the treated water separation section is designed to prevent excess sludge from accumulating in the treatment tank. This is a device that can set the flow velocity at a constant value.

In the apparatus shown in FIG. 4, the same parts as in FIG. 1 are designated by the same reference numerals.

In the apparatus shown in FIG. 4, a baffle plate 13 is installed in the upper part of the treatment tank 1, and a separation part for the treated water is formed between the baffle plate 13 and the wall of the treatment tank 1. Separation pipe 8 for draining treated water and excess sludge to solid-liquid separation tank 3
is installed.

The separation pipe 8 is provided at a position where the treated water can flow out at the maximum water load of the treatment tank 1.

In addition, the cross-sectional area between the lower end of the baffle plate and the tank wall, that is, the inlet of the separation section, is set so that at the maximum water load of the treatment tank 1, the flow velocity is smaller than the sedimentation rate of the carrier and larger than the sedimentation rate of suspended surplus sludge. Set it as follows.

Waste water is supplied to the treatment tank 1 through the inflow pipe 4, and the amount of water is measured by a flow meter 9 installed midway, and the flow rate value is constantly input to the control device 10.

This control device 10 controls when the water amount becomes lower than the maximum water amount load, that is, when the flow rate value measured by the flow pointer 9 is
If the water volume is insufficient to meet the maximum water load, a signal is output to the treated water circulation pump 12, the treated water is sucked into the treated water storage tank 11, and the total flow rate flowing into the fluidized bed is adjusted and kept constant. .

In this way, the maximum water load is always maintained, so the flow velocity near the inlet of the treated water separation section is also maintained within a range that is lower than the sedimentation rate of the carrier and greater than the sedimentation rate of excess sludge, and the excess sludge is collected at the same time as the treatment water cost. Of course, it flows out and flows into the solid-liquid separation tank 3 via the separation pipe 8.

In the solid-liquid separation tank 3, treated water and sludge can be separated by a conventional method. For example, the sludge is precipitated by coagulation and sedimentation and discharged from the sludge pipe 7, and the treated water is discharged from the treated water outlet pipe 6. It flows into the storage tank 11.

As described above, according to the apparatus of the present invention, the maximum water flow load is always maintained by the control device, and at the maximum water flow load, the flow velocity at the inlet of the separation section is within a range that is smaller than the sedimentation speed of the carrier and larger than the sedimentation speed of excess sludge. Therefore, even if there are fluctuations in the amount of raw water flowing in, excess sludge suspended in the fluidized bed will not accumulate, and therefore the biofilm attached to the carrier will be maintained stably, resulting in consistent Efficient BOD removal is achieved.

In general, injecting treated water into a treatment tank is considered undesirable because it lowers the loading efficiency of raw water.

However, according to the present invention, as described above, the activity of the activated sludge adhering to the carrier is increased, so the treatment efficiency of the entire plant is surprisingly increased.

In addition, as shown in Figure 4, if circulating water is distributed and supplied from the bottom of the fluidized bed, C1 deposits may occur when restarting the system after shutting down, which is a problem with fluidized bed biological treatment equipment. It can also be used as fluidization energy for carriers.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example 1 Raw water with a BOD of 500 pIIll was processed using the apparatus shown in Figure 4, but in order to clearly demonstrate the effect of the present invention, it was first treated for 10 days without sludge removal using the apparatus shown in Figure 1. Next, the contents of the treatment tank were directly transferred to the apparatus shown in FIG. 4 to continue treatment.

During the treatment, the amount of floating residue, excess sludge, and oxygen utilization rate were measured.

The results for the first 10 days are shown in A of FIG. 3, and the results for the next 10 days (results of Ansei 7) are shown in B of FIG.

...As is clear from comparing A and B in Fig. 3, when switching to the method of the present invention, the amount of floating surplus sludge decreased rapidly, and two days after implementing the method of the present invention, the amount of suspended surplus sludge decreased to 500.
pIII1 and did not increase thereafter.

Contrary to the amount of sludge, the rate of oxygen utilization by □adhesion and biofilm increased sequentially, and 5 days after switching to the method of the present invention, it became the same as that of the conventional method, and the treatment was continued thereafter. However, this value remains at approximately the same level.

In the conventional method, the BOD of treated water is 2.
BOD/m3・d 15-30pp [Q (see Figure 2)
However, according to the method of the present invention, it was 10 to 15 hemp,
Treated water with better quality than conventional methods can be obtained.

Furthermore, no deterioration in the quality of treated water was observed during the three-month continuous experiment.

Furthermore, when we conducted the same experiment as above by changing the amount of surplus sludge, we found that the amount of suspended surplus sludge in the fluidized bed was 2000p.
It has been found that when the pI is controlled to below 11, particularly below 1000p, a large amount of highly active biofilm can be stably maintained.

As described above, the present invention stably maintains a large amount of highly active biofilm, resulting in high wastewater treatment efficiency.
Treated water of good quality is consistently obtained.

[Brief explanation of the drawings] Figure 1 is a schematic cross-sectional view of a conventional fluidized bed biological treatment equipment, and Figure 2 shows changes in BOD of treated water when wastewater is treated with the equipment shown in Figure 1. Figure 3 is a graph showing the amount of suspended surplus sludge and oxygen utilization rate in the fluidized bed when wastewater is treated using the apparatus of Figures 1 and 4, and Figure 4 is a graph showing the amount of suspended surplus sludge and oxygen utilization rate of the apparatus of the present invention. FIG. 1 is a schematic system diagram illustrating one embodiment. Explanation of symbols: 1... Processing tank, 3... Solid-liquid separation tank, 5... Diffusion pipe, 8... Separation pipe, 9... ...flow meter, 10... control device, 12... treated water circulation pump, 13...
・Baffle board.

Claims (1)

[Claims] 1. In a fluidized bed biological treatment method for wastewater in which organic matter in wastewater is removed by attaching microorganisms to a granular carrier and fluidizing the carrier, the final treated water is transferred to a treatment tank as necessary. By circulating the water, the flow velocity near the inlet of the treated water separation section in the treatment tank is maintained within a range that is lower than the sedimentation velocity of the carrier and greater than the sedimentation velocity of excess sludge at the maximum water load, and the suspended surplus generated in the fluidized bed is A fluidized bed biological treatment method for wastewater, which is characterized in that sludge is discharged together with treated water into a solid-liquid separation tank, and excess sludge is removed in the solid-liquid separation tank by a conventional method to obtain final treated water. 2. The treatment method according to claim 1, wherein the amount of suspended surplus sludge in the fluidized bed is controlled to 2000 pp or less, particularly 11000 pp or less. 3 It mainly consists of a fluidized bed type wastewater treatment tank and a solid-liquid separation tank, and the cross-sectional area of the inlet of the treated water separation section provided at the top of the treatment tank is set to be smaller than the sedimentation velocity of the carrier at the maximum water load of the treatment tank, and the floating Separation pipe that is set to generate a flow velocity greater than the sedimentation velocity of the excess sludge and flows the treated water and floating excess sludge from the treated water separation section to the solid-liquid separation tank, and circulates the final treated water to the lower part of the treatment tank. A fluidized bed biological treatment device for wastewater, characterized in that it is equipped with a circulation path and a circulation amount control device that circulates final treated water according to fluctuations in the inflow amount of raw water.