JPS5854639B2 - Sludge thickening method and its equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sludge thickening method and apparatus for sludge treatment.

For example, sludge generated in the process of sewage treatment contains more than 98% water, and is generally disposed of after undergoing processes such as thickening the sludge, pre-treatment by injection of chemicals, dehydration, drying, and incineration.

Today's sludge, which is generated in large quantities due to changes in environmental conditions such as pollution regulations and sanitation, has a high moisture content, so it is necessary to concentrate it first to reduce the burden of treatment in subsequent processes. There is a need.

The currently widely used sludge thickening method uses a thickener, which is based on the fact that the average apparent specific gravity of solid valves in sludge is approximately 1.03. This method attempts to separate solid valves by sedimentation.

However, with this method, sedimentation takes time and the degree of concentration is not satisfactory.

On the other hand, as a prior art, a pressure flotation method has also been proposed in which solid valves in sludge are adsorbed and floated to air bubbles generated by dissolution and precipitation of pressurized air.

According to this method, the floating speed of the solid valves adsorbed to air bubbles is faster than the settling speed of the solid valves in the sludge due to gravity, so the separation efficiency is superior to that of the thickener type.

However, in the case of the pressurized flotation method, water and air are introduced into a pressurized tank as a foaming mechanism, and 3 to 5 kg/a? Air is dissolved in the water by pressurizing it to about i, and then when the water in which the air has been dissolved is mixed with the inflowing sludge, the pressure in the mixing tank is returned to atmospheric pressure to precipitate excess dissolved air. Air bubbles are generated in the mixing tank.

Therefore, (i) the power consumption required to pressurize to dissolve the air is large; (11) the mechanism for pressurization and depressurization is complicated, making operation unstable; and (iii) the amount of air bubbles is small because the amount of air dissolved is small. (1v) Since the bond between solid content and gas is physical adsorption, the bonding force is weak (V)
Ultrafine bubbles are necessary because adsorption with solid content is proportional to the surface area of the bubbles. It has drawbacks such as not being able to determine the exact location, so it cannot be said to be very practical.

It is therefore an object of the present invention to provide a method that eliminates the above-mentioned drawbacks of conventional pressurized levitation systems.

As a result of various studies on the bubble generation mechanism of the conventional pressurized flotation method, the present inventors found that foam formation can be achieved by using an appropriate foaming agent without necessarily adopting a pressurization-decompression mechanism. The present inventors have discovered that this is possible under normal pressure, and that the size and amount of foam can be adjusted simply by mechanical stirring, and that even such foam can adsorb and float solids in sludge, and have completed the present invention. .

Furthermore, the present inventors focused on the fact that the solid content in sludge is negatively or positively charged on the surface, and if electrochemical adsorption (chemical adsorption) with the foam is performed, the foam and solid content can be separated. In the conventional pressurized levitation method, the use of water as a carrier for the bubbles was indispensable due to the fact that the bond was more stable, and because of the bubble generation mechanism. The present invention was completed based on the discovery that a foam with a high degree of elasticity can be obtained, and there is no need to use water as a carrier for the bubbles.

Therefore, the present invention generates foam by introducing a foaming agent, a polymer flocculant, and a gaseous liquid phase, mixes the generated foam with inflowing sludge, and floats the resulting foam-sludge mixture. This is a sludge concentration method in which the solid content of sludge introduced into a zone and adsorbed by the foam is floated and separated.

By charging the surface of the foam, the formation and adsorption action of the foam are further stabilized.

The principle of flotation according to the present invention is similar to the conventional pressure flotation method, in that the flocs or solid content in sludge (apparent specific gravity is about 1.
02 to 1.30), and the apparent specific gravity of the floc is 1 or less, and this difference in specific gravity from water is used to float the solid content from the water.

However, according to the conventional method, since the adsorption form of air bubbles and solid content is physical adsorption that depends on the surface area of the air bubbles, the air bubbles are required to be sufficiently small compared to the floc diameter, and such fine bubbles are It is actually quite difficult to control the production of by pressurization/depressurization operation.

In addition, pressurized water is used as a carrier for air bubbles, and when mixed with inflowing sludge, the pressure is reduced to generate air bubbles, so the sludge cannot be diluted, and the equipment must be increased in size accordingly.

According to the present invention, a foam generating device, that is, a foaming zone is provided separately from the mixing device with the sludge, and by using a foaming agent as appropriate, fine foam can be obtained, and only such foam can be mixed into the sludge. Furthermore, at that time, the surface of the foam is treated with chemicals to be positively or negatively charged, and the form of adsorption with the flocs is chemical adsorption (i.e., a flocculation reaction between the foam and the solid content). This makes the bond with the foam even stronger.

In addition, the above solid content is, when the sludge consists of organic matter,
Its surface is negatively charged; on the other hand, if it is made of an inorganic substance, it is positively charged.

Therefore, depending on the sludge being treated, the surface of the resulting foam is charged either positively or negatively so that it has an opposite charge.

Foam generation in the present invention can be achieved by simply introducing a foaming agent, a polymer flocculant, and a gas (e.g., air, oxygen) into the liquid phase, and fine foam can be easily made by simply stirring the foam mechanically. It is done.

Typical foaming agents include cationic surfactants such as alkyl amines and quaternary ammonium salts, which differ from the bubbles found in conventional pressurized flotation systems (which require the presence of water as a carrier). There are no particular restrictions on the material as long as it forms foam (does not require a carrier).

The liquid phase to which the foaming agent is added is generally water, which can be utilized by taking a portion of the clear water in the flotation valve zone.

As a means of adding the foaming agent to the liquid phase, in addition to the method of directly adding the foaming agent to the liquid phase, the foaming agent may be accompanied by the gas introduced into the liquid phase and supplied to the liquid phase together with the gas. .

In addition to powdered foaming agents, liquid foaming agents may also be used.

According to the present invention, the size of the foam can be adjusted by mechanically stirring the liquid phase to which the foaming agent is added, for example, by mechanically stirring with a homogenizer or a turbine type stirring device. In general, the diameter of the foam decreases as the rotational speed increases, but from the economical point of view, it is preferable that the foam has a diameter of 300 to 500 μm.

In addition, the diameter of conventional pressure levitation bubbles is approximately 100-1
It is 30 μm.

The foam thus generated is itself stable;
Only the necessary amount can be mixed depending on the amount of solids in the incoming sludge.

In addition, by using a cationic or anionic polymer flocculant together with a foaming agent during foaming, the surface of the foam is charged with a positive or negative charge, improving the stability of the foam.
It is also possible to strengthen the bonding force with the solid content of sludge.

As for the mixing operation, it is sufficient to simply mechanically extrude and stir.

The generated air bubbles can also be mixed with the sludge by simply extruding them into the incoming sludge flow path.

Specifically, mixing with sludge may be carried out by a screw conveyor or pneumatic transport if a mixing tank with sludge is provided, or by an ejector if the sludge is directly added to the inflowing sludge. Foam may be sucked into the sludge.

The invention will now be further described with reference to the accompanying drawings.

FIG. 1 is a schematic flow sheet of a known pressurized flotation method.

Sludge supplied from line 1 is mixed with flocculant from line 3 in mixing tank 2, and suspended solids in the sludge are flocculated into flocs.

This sludge is then sent to flotation tank 5 via line 4.

On the other hand, a portion of the clear water taken out from the flotation tank 5 via the line 6 is separated and pressurized by the pressure pump 7.

Air supplied from the compressor 8 is mixed with the clear water in the mixer 9, and then pressurized and dissolved in the pressure tank 10.

The pressurized water in which air has been dissolved under high pressure is released from the line 11 through the pressure reducing valve 12 into the inflowing sludge in the line 4.

The air dissolved in the pressurized water is precipitated by the pressure release at this time, becomes bubbles, and is adsorbed to the solid content in the sludge.

The obtained sludge-bubbles mixture is sent from line 4 to flotation tank 5, where the solid content is floated and separated due to the difference in specific gravity.

The floating solids are taken out from line 13 and subjected to the next treatment.

FIG. 2 is a schematic flow sheet of the method according to the invention.

The inflow sludge from the line 21 is transferred to the mixing zone (mixing tank) 22
At , it is mixed with the foam supplied from line 23 .

The mixing zone is suitably equipped with a stirring device (not shown).

The foam mixed in the sludge is adsorbed on the surface of the solid content (apparently having a specific gravity of about 1.02 to 1.3) in the sludge, and is further taken into the solid content divided by stirring.

The apparent specific gravity of the resulting sludge-foam mixture is K 0.4.
It becomes small to about 0.6.

The sludge-foam mixture is sent from line 24 to flotation zone 25.

The flotation separation of solids in the flotation zone 25 is K 0.5
The process is completed in a timely manner, and the floated and separated solids are recovered from line 26 and subjected to the next treatment.

The recovery rate for the solid content of the inflow sludge is approximately 100%, and the solid content concentration is approximately 9%.

On the other hand, the clarified water from the flotation zone 25 is recovered from the line 27, but a portion of it is fractionated and mixed with the foaming agent and polymer flocculant from the line 29 in the conditioning zone 28.

The amount of foaming agent added is xo, 1sfI/ for the amount of water collected.
It is l.

In addition, the polymer flocculant is 0.3 to o, t? /l.

Foaming agent (and polymeric agent) delivered via pump 30
The clarified water contained therein is introduced into a foaming zone 31 with gas (air or oxygen) from line 32 to form foam.

According to the present invention, sufficiently fine bubbles can be obtained by simply introducing gas, but by providing a stirring means in this bubble zone and stirring, the size of the obtained bubbles can be adjusted.

The resulting foam is sent to the mixing zone via line 23 as described above.

According to the present invention, since water is not used as a carrier unlike in the case of the conventional pressure flotation method, the foam can be
For example, when the mixing zone 22, that is, the mixing tank is provided as in the illustrated example, the mixing zone 22 is
extruded and mixed.

Note that when the foam is directly mixed with the inflowing sludge without providing a mixing tank, the foam may be sucked into the sludge by an ejector.

The apparent specific gravity of the sludge solids separated by the present invention is 0.
4 to 0.6, generally 0.5 or less, which is significantly smaller than 0.8 to 0.9 in the case of the conventional pressure flotation separation method.

The thickened sludge obtained in this way is spongy and compressible, so conventionally it was roll pressed after adding chemicals, but in the case of the present invention, the thickened sludge obtained can be directly put into the roll press. be able to.

Therefore, it is easy to handle and process, and there are great economic advantages such as no need for the use of chemicals.

In addition, even when performing centrifugal separation, separation of only water is difficult because the binding force between solids and foam is strong, and the apparent specific gravity of a mixture of solids and foam is generally low, 0.5 or less. It can be done easily.

Furthermore, when oxygen is used as the gas to be introduced, the sludge solids can be directly subjected to aerobic digestion treatment, making it possible to greatly simplify the treatment process.

Experimental Example 1 *Excess sludge produced by the activated sludge method was concentrated using the method of the present invention using the same apparatus as shown in FIG.

Treated sludge solid content Apparent specific gravity 1.03 pH 6.8 Using lauryltrimethylammonium chloride as a foaming agent, 0.15 per 11 pieces of clear water collected from the flotation tank
A polymer flocculant of 5' and vinylpyridine copolymer salt was added at 0.25f-0.51 per 11 parts of clear water, sent to a bubbler, and mechanically stirred using a homogenizer to remove the foam produced. Forcibly extrude into the mixing tank, 21/
It was mixed with the sludge flowing in at m1tt.

After mixing and stirring for about 10 minutes, send it to the flotation tank, and the
．． The solid content was floated and separated for 5 hours.

The results are as follows. According to the invention, therefore, only the required amount of foam needs to be mechanically mixed with the sludge at any given time.

In addition, the foam whose surface is electrically charged is very stable, and even when mixed and stirred, the foam does not aggregate together, but rather,
It has a tendency to penetrate into the interior of split flocs, and its apparent specific gravity can be reduced to about 0.4 to 0.5.

Experimental Example 2 Excess sludge produced by the activated sludge method was concentrated according to the method of the present invention using an actual apparatus similar to that shown in FIG.

The chemicals used were lauryltrimethylammonium chloride and a polymer flocculant of vinylpyridine copolymer salt as in Experimental Example 1, and 0.2 to 0.351 was added per 11 pieces of clear water taken from the flotation tank. This is sent to a foaming device, mechanically stirred using turbine blades, and the resulting foam is forcibly extruded into a mixing tank. It was mixed with the sludge flowing in at L.

The mixture is sent to a flotation tank with a surface area of 0.332i,
Solid content was floated and separated.

The water level in the table indicates the liquid level in the flotation tank, and is adjusted by a movable weir attached to the flotation tank to increase or decrease the residence time of the floating solids (fross).

In addition, the cross residence time was expressed relative to the volume of the cloth above the water level of the flotation tank.

The results are shown in Table 2.

As described above, according to the present invention, a flock with a strong bonding force is
A foam mixture is obtained, and since only the foam is added to the sludge, the solid content can be separated to r100% by arbitrarily changing the amount of foam.

Foam generation, transport and mixing can all be carried out under normal pressure, which simplifies the equipment, reduces power costs, improves operational stability, and significantly reduces capital investment.

The concentration rate is also improved by about 50% compared to the conventional pressure flotation method.

As described above, according to the present invention, surplus sludge generated from a water treatment device can be quickly and easily concentrated, the volume can be reduced, and the burden of the next process can be reduced.

Sources of sludge to be treated according to the present invention include sewage treatment plants, mine wastewater, water change wastewater from road construction, and even industrial wastewater, and the present invention is not particularly limited in these respects.

[Brief explanation of drawings]

FIG. 1 is a schematic flow sheet of the known pressure flotation method; and FIG. 2 is a schematic flow sheet of the method of the present invention. 22: Mixing zone, 25: Flotation separation zone, 31: Foaming zone.

Claims (1)

[Scope of Claims] 1. Generating foam whose surface is electrically charged by introducing a foaming agent, a polymer flocculant, and a gas into a liquid phase;
The generated foam is mixed with the inflowing sludge, and the solid content in the sludge is adsorbed by the foam, and the resulting foam-sludge mixture is led to a flotation zone, and the solid content adsorbed by the foam is floated. A sludge thickening method that consists of separating. 2. The method according to claim 1, wherein the gas is air or oxygen. 3 Consists of a mixing zone, a flotation zone and a foaming zone,
means for separating a portion of the clear water from the flotation zone and adding a foaming agent and a polymer flocculant; means for sending the clear water containing the foaming agent and polymer flocculant to the foaming zone; A sludge concentrator comprising means for foaming the clear water containing the foaming agent and polymer flocculant in the foaming zone by introducing a gas therein, and means for sending the resulting foam to the mixing zone. 4. The apparatus according to claim 3, wherein the foaming zone is provided with a mechanical stirring means, and the size of the generated foam is characterized.