JPS59109209A - Deaerating and defoaming method of sludge - Google Patents

Abstract

PURPOSE:To improve gas-liquid contact efficiency and to improve defoaming efficiency by running the raw liquid of sludge which is adjusted pH to an acid side in the form of film flow along the inside wall from the circumference at the peak of an inverted circular cone shaped vessel which is internally maintained in a vacuum and bringing the film flow into collision against the surface of the inside wall. CONSTITUTION:The raw sludge which is mixed with a chemical soln. by a line mixer 3 and is thus made acidic in the midway of feeding is defoamed in a vacuum vessel 4 which is internally maintained under the negative pressure by a vacuum unit 5. The sludge admitted into the vessel 4 enters a sludge well 41, from which the sludge flows downward through a slit or weir 42 along the wall 43 at the peak of the vessel, thereby forming film flow. Foam is quickly driven off from the surface of the film as the vacuum is maintained in the vessel. The downflowing sludge collides against a land part 44 by which the defoaming is further accelerated and the defoamed sludge is discharged from the bottom. The factor for generating gas and air foaming in the liquid is eliminated by adjusting the pH to acidity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved defoaming method in sludge treatment and the like.

Sludge generated from sewage and industrial wastewater is digested and then concentrated (decanted) to separate it into thickened sludge and supernatant liquid. In recent years, the inflow form of sewage has changed and the content of organic matter has increased, and sewage or suspended solids have accumulated in the pipes for a long time due to inadequate pipe maintenance and connection of each discharge destination. Significantly putrid sludge is now produced, and inevitably more gas bubbles are generated from the sludge and adhere to it. In particular, sludge floats to the surface in the thickening tank, reducing both the recovery rate and concentration concentration, which has become a major hindrance in subsequent treatment processes. Furthermore, the sludge discharged from the digestion tank inevitably contains bubble gas, but before it is dehydrated, a washing process (elution) is traditionally performed.
This has been dealt with by adding water to the digested sludge to wash and remove substances that impede deaeration, but due to operational and cost issues, in recent years this washing step has been omitted and concentrated dehydration treatment has been performed instead, which inevitably necessitates deaeration. Air defoaming has become increasingly important.

A further practical problem is that the operating speed of the dewatering machine (filter press) during sludge treatment is significantly reduced.As a result of investigating the cause, we found that in addition to the deterioration and alteration of the sludge, carbon dioxide gas due to rotting sludge It was found that the adhesion of air bubbles mainly caused by the adhesion of air bubbles significantly inhibited the function of the thickening tank, and this reduced the dewatering efficiency.

On the other hand, conventional methods for degassing and defoaming in sludge treatment have mainly been agitator methods such as the paddle type shown in Figure 1 and the lattice type shown in Figure 2. Above the scraping rake at the bottom of the sedimentation tank or sludge thickening tank
Some are equipped with a picket fence (called a picket fence). 1 to 3, explanations are omitted since they are based on public and private methods.

However, these conventional degassing and defoaming methods have the following drawbacks.

(1) Incomplete degassing: As mentioned above, for sludge that has come to contain a lot of violet gas, the conventional method has a high residual rate of bubble gas, so after (pre-) treatment Immediately after that, the sludge settles and thickens, but due to long-term stagnation, the newly decomposed gas and residual gas combine to cause the sludge to rise to the surface again.

(2) Bad working environment: With conventional methods, the water surface is open, so there is a bad odor, and if you want to deodorize the area around this workplace, you will need a huge cover.

(3) Required power is large: Since it is a mechanical stirring method, only a part of the given energy contributes to degassing, so the power is inevitably large.

Therefore, the present inventors have been conducting research to provide a method for efficiently degassing and defoaming in sludge treatment. It was discovered that sludge defoaming can be efficiently carried out through the agitation and contact of gas and liquid by a turbulent bed generated by colliding the film flow against a wall surface. So this is HC
O3'→H20+CO□ is the cause of bubbles, so during the defoaming process, the pH is lowered and HCO3-→
The present invention was completed based on the discovery that defoaming can be promoted as a synergistic effect by actively expelling CO2 gas by causing the OH-Co2↑ reaction.

In other words, the present invention uses sludge stock solution whose pH has been adjusted to the acidic side,
A method for degassing and defoaming sludge, which is characterized by causing a film to flow down along the inner wall of the container from the circumference of the top of an inverted conical container whose interior is kept in a vacuum, and causing this film flow to collide with the inner wall surface. The main points are as follows.

In the method of the present invention, the collision of the sludge stock solution film flow against the inner wall surface of the container is caused by the collision of the film flow against a portion such as a land portion in the middle portion of the inner wall, as shown in FIG. 4, which will be described later.

The method of the present invention has the following features.

(1) Adopts a vacuum defoaming method, which has not been used conventionally in sludge treatment; (2) Improves gas-liquid contact efficiency and improves defoaming efficiency by forming a falling film and a flowing colliding mixed flow section. (3) Add pH control to reduce HCO3-+H→
The amount of defoaming can be reduced by removing not only the bubbles that have caused the reaction H, co, -+ H, ○10 CO, ↑, but also the carbon dioxide gas that has become M alkali. Enlarge.

And the following effects can be achieved.

(1) It has a large degassing effect and eliminates thickening tank troubles caused by floating sludge. (2) The device is compact and hygienic to handle. (3) It has a wide range of uses and applications, and is already installed on existing lines. (4) Low power consumption; (5) pH control allows for less chemical injection in subsequent processes.

The method of the present invention will be explained using FIG.

In Fig. 4, 1 is a liquid feeding pump, 2 is a chemical injection pump, and 3 is a liquid feeding pump.
4 is a line mixer, 4 is a vacuum container, 5 is a vacuum generation unit (such as a vacuum pump), 6 is a discharge pump, and 7 is a pH detection device. Raw sludge is sent to a vacuum container 4 by a pump 1, and during the delivery, the pH inside the container 4 is detected by a detection device 7, and a chemical solution such as HCl or FeCl2 is mixed in a line mixer 3 through a chemical injection pump 2. and into container 4. At this time, pHFi is 5 to 5, preferably 35 to 4. The container is connected to a vacuum unit 5 to form a vacuum of approximately 550 to 600 mH5', and the liquid defoamed in this vacuum is under negative pressure, so it is discharged with positive pressure. Pump 6 has been installed. However, if the container 4 is installed at a sufficiently high position, the discharge pump 6 is not necessary. The sludge flowing into the vacuum container 4 enters the sludge sump 41 and from there flows down along the wall 46 at the top of the container through a slit or weir 42 to form a film stream. Air bubbles are quickly removed from the film surface because the inside of the container is solid.

The wall of the container has an inverted conical shape to provide an appropriate flow rate and film thickness for defoaming. The flowed sludge is transferred to the land section 44.
Defoaming is further promoted by colliding with the gas, being disturbed there, and being exposed to a vacuum atmosphere. The sludge that has passed through the land portion 44 is further discharged from the bottom while being degassed.

Furthermore, as mentioned above, the gas concentration in the liquid is increased by CO2 converted from M alkali by acidic pH adjustment, and by contact with the vacuum state where the gas partial pressure is low, degassing is performed vigorously, causing gas bubbles in the liquid. and remove factors that cause bubbles.

In this way, by removing gas from the liquid and reducing M-alkali, the adhesion of air bubbles to the sludge is reduced, the obstruction in the thickening tank is eliminated, and the M-alkali is lowered. It is possible to gradually reduce the amount of chemical injection required for dewatering, and the performance of sludge dewatering can be improved overall.

[Brief explanation of the drawing]

Figure 1.2.3 is a diagram showing the conventional deaeration method, and the fourth
The figure is a diagram showing the degassing method of the present invention. Sub-agents 1) Meifuku agent Ryo Hagiwara -

Claims (1)

[Claims] A sludge stock solution whose pH has been adjusted to the acidic side is caused to flow down in a film form along the inner wall of the container from the top circumference of an inverted conical container whose interior is kept in a vacuum, and this film flow collides with the inner wall surface. Features a sludge degassing and defoaming method.