JPS59230688A - Sludge concentrating method - Google Patents

Abstract

PURPOSE:To miniaturize an apparatus scale, by controlling the thickness of a float sludge zone from the gas solid ratio of the amount of air supplied to a float concn. tank and the amount of a solid substance supplied thereto and the sludge staying time and concn. sludge concn. of the float sludge zone. CONSTITUTION:Four interface meters 7 for detecting the lower surface level of a float sludge zone 6 are provided in a float concn. tank 3 and a flow control valve 8 is provided to the outlet of separated water. The interface meters 7 and the flow control valve 8 are respectively connected to a control apparatus 9 and a sludge densitometer 10 for measuring the concn. of the sludge supplied to the float concn. tank 3 is arranged in a raw water tank 1. When the control apparatus 9 receives the measured signals from the sludge densitometer 10 and a flow meter 11 and successively operates the thickness index of the float sludge on the basis of said signals. Subsequently, the control apparatus 9 compares the position of the actual lower surface level of the float sludge zone 6 detected by the interface meters 7 and the aforementioned index and the valve 8 is controlled so as to adjust the difference thereof to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing sludge to zero through a pressure flotation process.

In recent years, with the spread of sewage systems, the issue of treatment and disposal of sludge, including sewage sludge, is now subject to reexamination from both technical and economic perspectives.

The treatment and disposal methods for these sludges generally consist of three methods.
After concentrating to about 4 parts and rc, digestion, medicine injection, dehydration, and incineration.
Chemical injection - dehydration - incineration, heat treatment - dehydration, - incineration, marc is processed by methods such as wet oxidation - dehydration, and then disposed of in a landfill, or dehydrated sludge without going through the incineration process is disposed of in green areas or farmland. It is being effectively used and returned to the public. In these treatment methods, the amount of sludge determines the construction and maintenance costs of the equipment, and when treating the same amount of sludge solids, the higher the concentration, the lower the construction cost of the equipment. Maintenance costs will be lower.

Furthermore, if the concentration into the sludge treatment process is unstable,
This will cause problems in terms of management.

Therefore, the establishment of a technology that can supply sludge as highly concentrated and stable thickened sludge will be extremely advantageous in terms of both performance and economy for the sludge treatment process as a whole.

The pressurized flotation concentration process attaches fine air bubbles to the solid matter such as sludge to be treated, and the apparent specific gravity of the solid material is lighter than that of accompanying fluids such as water, and its buoyancy is used to separate and concentrate the solid matter. This technology is said to be advantageous in principle compared to the gravity sedimentation forging process, which relies solely on gravity.

By the way, sewage sludge includes primary sedimentation tank sludge (raw sludge) that has been sedimented and separated in the primary sedimentation tank, surplus activated sludge generated in the aeration tank, etc., and the more organic components these sludges have, the more difficult it is to thicken them. This is because most of the organic components are made up of microorganisms, and there is almost no difference in specific gravity compared to water, and since it is a hydrophilic colloidal sol, it is not susceptible to compaction.

When sludge containing a large amount of organic components, such as surplus activated sludge, is concentrated using a pressure flotation concentration process, more microbubbles are attached to the sludge, and the microbubbles 5 are
Although it is necessary to allow the sludge to remain in the flotation concentration tank for a long time, there is a theoretical limit to increasing the amount of microbubbles generated in the flotation/condensation tank. Therefore, in order to make more microbubbles adhere to the sludge, the sludge to be treated is significantly diluted, and the amount of solid matter in the sludge supplied to the flotation thickening tank is reduced relative to the amount of microbubbles. Therefore, there was a problem that the floating image tank became large and uneconomical.

In addition, the conventional processing flotation concentration process has the drawback that the removal of the reduced sludge is not accurate, so the stable thickened sludge with a high degree of foundation cannot be chewed.

A possible reason for this is that the flow rate of the thickened sludge cannot be accurately measured due to bubbles in the removed ft-Dt% reduced sludge sludge. As a means to partially solve this drawback,
As seen in U.S. Pat. However, even with this method, levitation 0
It is not possible to cope with changes over time in the flow rate and concentration of sludge supplied to the reduction tank, resulting in The problem of not being able to obtain stable and highly concentrated sludge remains unsolved.

In this way, when concentrating sludge using the conventional pressurized flotation concentration process, it is not possible to obtain reduced sludge in a highly concentrated and stable state, and there are many problems in practical application. te fc.

The present inventor has conducted intensive research in order to continuously extract sludge, such as sewage sludge, in a stable state and higher than the attained O variation of thickened sludge in a method of concentrating sludge such as sewage sludge using a pressure flotation concentration process. As a result, the inventors discovered the correlation between the gas-solid ratio between the amount of air supplied to the flotation thickening tank and the amount of solids supplied, the sludge residence time in the floated sludge zone, and the thickened sludge concentration, and the present invention was accomplished.

The present invention will be explained below.

In the present invention, in order to concentrate sludge by flotation under pressure, the floated sludge is separated, a part of the separated water after 7c is circulated, and after pressurizing it, air of approximately the same pressure is supplied, and the air is A circulation pressurization method in which fine bubbles are generated by dissolving the sludge and then reducing the pressure, supplying the sludge to be treated, allowing the generated bubbles to adhere to the sludge, flotation separation and θ compression in a flotation concentration tank,
The sludge to be treated is either as it is or the slurry diluted with separated water is pressurized, air of approximately the same pressure is supplied to this, the pressure is reduced after it is dissolved, and fine bubbles are generated and at the same time sludge particles are Various methods are employed, such as a fully pressurized method in which the material is deposited, separated by flotation, and concentrated in a flotation concentration tank.

Note that the shape of the tank for reducing the floating γt can be vertical, horizontal, or round.
Various shapes such as circular or rectangular shapes are used for c.

In the present invention, when concentrating engineered sludge in such a flotation concentration process, the air-solid ratio between the amount of supplied air supplied to the flotation concentration tank and the amount of solid matter in the supplied sludge, the WSO shrinkage sludge concentration, and the floated sludge zone Calculate the thickness of the floating sludge zone so that the surface of the floating sludge zone in the flotation concentration tank becomes 0 degrees, which is the target value of the sludge artist, based on the correlation between the residence time and This is a method of controlling the actual thickness of the floated sludge zone in the flotation thickening tank, and furthermore, the thickness of the floated sludge zone, that is, the lower surface of the floated sludge zone is separated from the floated sludge so that it is at a predetermined level. This process is performed by controlling the discharge flow rate of separated water.

A method for controlling the discharge flow rate of separated water so that the lower surface of the floating sludge zone reaches the predetermined level calculated above is as follows:
A sensor such as a sludge concentration meter or turbidity meter is installed at the interface between the floating sludge zone and separated water in the flotation concentration tank, and the lower surface of the floating sludge zone is detected by the sensor.
Squeeze the flow rate adjustment valve of the separated water outlet provided at the bottom of the flotation concentration tank so that the lower surface reaches the level calculated above, gradually reduce the discharge flow rate of separated water, or open the flow rate adjustment valve, There is a method of gradually increasing the discharge flow rate of separated water. Note that a plurality of the sensors are installed at a position that provides sufficient residence time in the floating sludge zone, for example, at a location 0.5 to 1.5 m from the upper part of the sludge zone. First, to estimate the thickness of the floating sludge zone where the flotation tank should be located, measure the flow rate and concentration of sludge supplied to the flotation thickening tank with a flow meter or sludge concentration meter, and use these measured values to estimate the thickness of the floated sludge zone where the flotation tank should be located. The amount of solids to be supplied is calculated, and then the amount of solids to be supplied is calculated from the amount of solids to be supplied and the target thickened sludge concentration value.

The method for estimating the thickness of this floating sludge zone will be further explained using the gas-solid ratio and the thickened sludge concentration.

Figure 1 shows the correlation between the sludge retention time in the floating sludge zone and the zero shrinkage sludge concentration, and the relationship differs depending on the change in the gas-solid ratio between the amount of air attached to the sludge and the amount of solids supplied. The gas-solid ratio is the ratio of the weight of fine bubbles attached to the sludge to the weight of the sludge (solid content). However, this can be determined by dividing the weight of free air dissolved in water in the pressure flotation concentration process by the solid weight of the sludge.

By the way, the amount of microbubbles generated in the flotation 67 condensation tank has a limit as mentioned above, and can be considered to be constant if the pressure to pressurize and the temperature of the water to be pressurized are the same.
Once the amount of dissolved air is measured, it is not necessary to measure it continuously. Therefore, the gas-solid ratio is inversely proportional to the concentration of supplied sludge, and fluctuations in the gas-solid ratio during operation of the pressurized flotation concentration process can be translated into changes in the concentration of supplied sludge. As is clear from Figure 1, the sludge supplied to the flotation thickening tank reaches a certain concentration after a certain point in time, which corresponds to its gas-solid ratio. The volume of the floating sludge zone that the supplied sludge forms after a period of time! k (thickness - amount of solids supplied, / (temperature x surface area of floating sludge zone of nuclear device) is calculated.

Therefore, surfacing? The above-mentioned capacity ( thickness) is added (
(integration) to calculate the thickness of the floating sludge zone. Then, the actual thickness of the a sludge zone is controlled by making this calculation timely and using the calculated thickness of the floating sludge zone as a symmetry.

The above-mentioned index of the thickness of floating sludge can be determined instantly even if there are fluctuations in the concentration or flow rate of the supplied sludge by using the relationship shown in Figure 1 with a computer, etc., and the sample value P
The thickness of the sludge zone can be adjusted to the above-mentioned index by sending a control signal to a flow rate regulating valve or the like at the separated water outlet using a known control method such as an ID or a PID with a gear. In addition, thickened sludge is removed by overflowing the thickened sludge collection river overflow weir from the surface of the floating sludge zone of the floating thickening tank, and the amount of overflow is controlled by the flow rate of separated water. Separated water discharge stream,
By controlling the I-sludge as described above, it becomes possible to prevent the reduced sludge from flowing out without restriction and to stabilize the floating sludge zone. At this time, the purpose of the thickened sludge scraper is to scrape the thickened sludge so that it does not drift, and the scraping M degree of the scraper is adjusted so that the thickened sludge on the surface is scraped up uniformly, It is determined between 1 and 60 minutes depending on the tendency.

According to this method, when taking out the thickened sludge, it is possible to further reduce the influence of flow to the lower part of the floating sludge zone.

Conventionally, the means to increase the concentration level is to increase the gas-solid ratio, that is, to dilute the supplied sludge to lower its concentration, and to increase the solids load to 60 to 90 kg-8S/rIL.
This was done within 2 days, but all of these methods merely increased the size of the plant unnecessarily, and no economic effect could be expected.

In the present invention, by introducing floating sludge based on the correlation between the gas-solid ratio, the purse sludge concentration, and the residence time in the floating sludge zone, the equipment performance can be fully demonstrated and the equipment scale can be significantly reduced. can.

That is, according to the present invention, there is no need to unnecessarily dilute the concentration of the supplied sludge, and the solids load can also be reduced to 50 to 600 [l].
ry -887m, 2. 〕、Good bite is 100-3
00 [1cy-8S/door 2 days], it is possible to reduce the capacity 4 of the flotation 1 condensation tank, and it is possible to further stabilize the highly concentrated thickened sludge and continuously maintain it in a t state. You can get it.

FIG. 2 shows one embodiment of the 7 to 3 reduction method of the present invention, in which 1 is a raw water tank, 2 is a pressurized tank, and 3 is a floating d-contraction tank. The sludge is transferred from this raw water tank 1 through a pressurized tank 2 to a flotation concentration tank 3, where it is floated, separated, and contracted in a flotation tank 3.
It is well known that while being transferred from the pressurized tank 2 to the pressurized tank 2, it is pressurized by the pump 4 and air is introduced, and that the pressure is reduced by the valve 5 while being transferred from the pressurized tank 2 to the flotation concentration tank 3. That's right.

In this embodiment, in the flotation concentration tank 3, there are four interface meters 7 and 7 for detecting the lower surface of the flotation sludge zone 6.
..., and the separated water outlet of the flotation concentration tank 3 is equipped with a flow rate adjustment valve 8. These interfaces total 7・
..., each of the flow rate regulating valves 8 is connected to a control device 9. In addition, the raw water tank 1 is equipped with a sludge concentration meter lO that measures the 9 degrees of sludge supplied to the floating 8-fan tank 3, and the pipe that transfers sludge from the raw water tank 1 to the pressurized tank 2 is equipped with a sludge concentration meter lO. A flow meter 11 is equipped to measure the flow rate.

The control device 49 includes a sludge concentration meter 10 and a flow meter 11.
When a dFIJ constant signal is received from each of the above, an index of the thickness of the floated sludge is calculated from this signal based on the relationship shown in FIG. Next, the control device 9 controls the interface meter 7...
Compare the actual lower surface of the floating sludge zone 6 detected with the above index and make sure that the difference is zero.
The flow rate adjustment valve 8 is controlled to drain the separated water.

According to the above-mentioned sulfurization apparatus, the flow rate of separated water discharged from the flow rate regulating valve 8 installed in the control device 9 is accurately regulated.
It is easy to adjust the lower surface of fJy4 to a predetermined level, and automation is possible without requiring manual labor.

The present invention '5r will be specifically explained below with reference to Examples.

(Example) When sludge was treated in a fully pressurized pressure flotation device using the method described above while changing the supply flow rate of the Eri flotation concentration tank from 10 to 20-/hr, each result shown in the table below was obtained. I was stunned. , the volatile substances in the sludge are 79~
The ratio was 32 (relative to total solids).

Table As is clear from this table, despite the high solids load, the sludge was concentrated to the extent of 3'6 to 6.
For comparison, when the above sludge was concentrated using a normal gravity sedimentation method, the concentration was only 2.111.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the small line sludge concentration and the floating sludge zone 71α, and FIG. 2 is a flow sheet showing an example of the method of the present invention. 1...Raw water tank, 2...Pressure tank, 3...Floating crimping tank, 6...Floating sludge zone, 7...・Interface meter, 8...Flow f AI'J valve control, 9...Control device, 10...
...Sludge concentration meter, 1] ...Flowmeter.

Claims (3)

[Claims] (1) Sludge is subjected to pressure flotation first contraction process.
In the F method, the correlation between the amount of air supplied to the flotation tank and the amount of solids in the supplied sludge, the concentration of thickened sludge, and the residence time in the flotation zone is determined by A method for shrinking sludge characterized by determining the thickness of a floating sludge zone and controlling the actual thickness of the floating sludge zone in the flotation thickening tank based on the thickness. (2) The thickness of the floated sludge zone is controlled by controlling the discharge flow rate of separated water from which floated sludge has been separated so that the lower surface of the floated sludge zone is at a predetermined level. The method for concentrating sludge as described in paragraph 1. (3) The thickness of the floating sludge zone is controlled by sensors such as a sludge meter and turbidity meter installed at the interface between the floating sludge zone and the separated water, and at the separated water outlet of the flotation concentration tank.
2. The method for reducing ε3 of sludge according to claim 1, characterized in that tl'' is carried out using a weight adjustment valve.