JPH0336590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sludge thickening method. Conventionally, sludge with a high water content, such as surplus sludge generated in sewage treatment plants, has been concentrated by gravity sedimentation, flotation, or the like. The flotation method can obtain a higher concentration rate than the gravity sedimentation method, and among the flotation methods, the normal pressure flotation concentration method has stable separation efficiency and low operating costs, so it is gradually being adopted. It's coming. The normal pressure flotation concentration method involves mixing gas such as air into an aqueous solution containing a foaming agent and a polymer flocculant to generate bubbles.
This method consists of mixing air bubbles with sludge to electrochemically adsorb the air bubbles onto the surface of solid content in the sludge, and then floating and concentrating the solid content combined with the air bubbles in a flotation tank. In the flotation concentration method, sufficient flotation concentration can be achieved by reducing the apparent specific gravity of the sludge-air bubble mixture to approximately 0.9 or less, but in the conventional normal pressure flotation concentration method, all of the solid content in the sludge is directly converted to air bubbles. As a result, the apparent specific gravity of the thickened sludge was around 0.5, making it difficult to achieve stable flotation concentration by reducing the gas-solid ratio. As a result of intensive research into the bonding mechanism between air bubbles and solid content, the present inventors used a suspension containing solid content instead of clear water, mixed this with a foaming agent and a polymer flocculant, and created bubbles. When the bubbles are generated, the surface of the bubbles becomes electrically charged, and at the same time, the polymer flocculant is uniformly adsorbed on the surface of the solid content.When these mixtures are mixed with sludge, the solid content in the sludge becomes electrochemically charged with the bubbles whose surface is electrically charged. It also binds to the solid matter on which the polymer flocculant is uniformly adsorbed on the surface. That is, the solid content in the sludge forms a large floc through the bubbles whose surface is electrically charged and the solid content adsorbed by the polymer flocculant.
It was found that the solid content in sludge can be indirectly combined with air bubbles, and that it is even more effective if a part of the sludge to be treated is separated and used as a suspension containing the solid content. The present invention was completed based on this knowledge. That is, the present invention diverts inflowing sludge; mixes one of the diverted sludge, gas, a foaming agent, and a polymer flocculant to generate a bubble-solid mixture; This sludge concentration method consists of the following steps: mixing the sludge with a mixture; introducing the resulting mixture into a flotation zone to float and separate the thickened sludge; The present invention will be explained in detail below. The foaming agent used is not particularly limited, but in the case of sewage sludge, it is a cationic surfactant such as an alkylamine or a quaternary ammonium salt, with lauryltrimethylammonium chloride being a particularly preferred foaming agent. Further, the polymer flocculant used is a cationic polymer flocculant. When such a polymer flocculant is used, the surface of the generated bubbles becomes positively or negatively charged. In the case of sludge made of organic matter such as sewage sludge, the surface of the solid content is negatively charged, so a cationic polymer flocculant is used; in the case of sludge made of inorganic matter, the surface of the solid content is positively charged. Therefore, an anionic polymer flocculant is used. This allows the bubbles and the solid content to be strongly bonded electrochemically.
Methacrylic acid ester polymers are preferred polymer flocculants in the treatment of sewage sludge. The sludge to be treated is divided, and one of the divided sludges, a foaming agent, a polymer flocculant, and a gas are mixed to generate a foam-solid mixture. The sludge to be treated is surplus sludge or digested sludge, etc.
These usually have a moisture content of 98-99%. Although any type of gas can be used, air is preferred because it is easily available and economical. The method for generating the foam-solid mixture is not particularly limited, and for example, a foaming agent and a polymer flocculant are introduced into the sludge, then air is blown into the sludge, and the mixture is further mixed using an appropriate stirring means to form the foam-solid mixture. can occur. The amount of sludge used in this generation step is 5 to 50%, preferably 10 to 35% of the amount of sludge to be treated. This diversion ratio is 10 or
At 35%, the amount of air blown can be reduced relative to the amount of sludge to be treated, and when the sludge mixes with the remaining sludge that has been diverted and forms a large floc with the solid content of air bubbles, flotation concentration is performed. A sufficient apparent specific gravity can be obtained. The generated bubble-solid mixture is mixed with the remaining separated sludge. The mixing means may be a conventional stirring tank, or the bubble-solid mixture may be introduced into the sludge channel and mixed within the pipe. The mixture obtained by mixing the sludge and the bubble-solid mixture is floated and concentrated in a flotation tank. The flotation tank may be provided with an overflow wall at its upper part, and may also be provided with means for raking up concentrated sludge. Next, the present invention will be explained with reference to the accompanying drawings. A part of the inflowing sludge 1 is diverted, and one of the diverted sludges 2 is sent to the bubble-solid mixture generation zone 3. Here, the foaming agent 4, air 5, and polymer flocculant 6 are mixed to generate a foam-solid mixture 7. The remaining separated sludge 8 is mixed with the bubble-solid mixture 7 in a mixing zone 9, and then floated and separated in a flotation zone 10, and the thickened sludge is discharged from line 11 and the separated water is discharged from the system from line 12. . In the present invention, whereas in the conventional method all of the solid content in sludge was directly combined with air bubbles, the solid content in sludge forms large flocs through the air bubbles and solid content of the air bubble-solid content mixture. This enabled indirect bonding of air bubbles and solid content. As a result, the amount of air blown only needs to be the amount necessary to obtain a sufficient apparent specific gravity for flotation concentration, which is approximately 1/1/1 compared to the conventional method.
It became possible to reduce the number to 5. In the conventional normal pressure flotation concentration method, the foaming device corresponding to the bubble-solid mixture generation zone in the present invention consumes more than 50% of the power of the entire device, but in the present invention, the amount of blown air is approximately 1 /5, this can be significantly reduced. In addition, in the conventional method,
In the bubble generation process, clear water such as separated water was used to dilute the foaming agent, but in the present invention, there is no need to use such clear water, so the water load (sludge treatment amount (m ³ /h)/effective cross-sectional area of flotation tank (m ² )) can be increased, making it possible to downsize the flotation tank. Example: Extra sludge from a certain sewage treatment plant is extracted at a rate of 1.3 m ³ /h, of which 0.3 m ³ /h is diverted and treated with a polymer flocculant (methacrylic acid ester polymer) and a foaming agent (lauryl). After adding trimethylammonium chloride), air was blown to generate a mixture of fine bubbles and solids. The remaining surplus sludge after separating the air bubbles and solids mixture is 10 m ³ /h.
After mixing with water, it was floated and concentrated in a flotation tank. Floating tank effective cross-sectional area 0.5024m ² , polymer flocculant addition amount 0.002
Kg/Kg-DS, air injection amount 0.06Kg/Kg-DS,
The amount of foaming agent added is 0.003Kg/KgD.S. The results are shown in the table below. In addition, in the comparative example, the excess sludge used in the bubble-solid mixture generation process was 0.3
Separated water discharged from flotation tank instead of m ³ /h
0.3 m ³ /h was used to generate air bubbles. The amount of air blown was 0.012Kg/Kg-DS. Other conditions are the same as in the example. 【table】

[Brief explanation of drawings]

FIG. 1 is a flow sheet illustrating the method of the present invention. 1...Inflow sludge, 3...Bubble-solid mixture generation zone, 9...Mixing zone, 10...Flotation zone.

Claims (1)

[Claims] 1. Dividing the inflowing sludge; mixing the separated sludge, gas, foaming agent, and polymer flocculant to form air bubbles.
generating a solids mixture; mixing the separated sludge with the bubble-solids mixture; introducing the resulting mixture into a flotation zone to float and separate the sludge;
A sludge thickening method consisting of each process. 2. The method according to claim 1, wherein the amount of sludge in one side is 10 to 35% of the amount of inflowing sludge.