JPS5935279B2 - Method for concentrating organic sludge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for flotation and concentration of sludge containing organic matter, such as surplus sludge generated when purifying human waste, sewage or industrial wastewater, and human waste septic tank sludge.

Flotation concentration is a method in which fine bubbles are attached to or entangled with the particles to be removed, and the particles are forcibly separated and concentrated using the power of the bubbles.

Conventionally, methods for generating bubbles during flotation concentration include pressure flotation and electrolytic flotation, but in these methods, the size of the bubbles generated is smaller than the size of the suspended particles to be floated. It is difficult to float and concentrate even relatively large and fine particles using a method of floating, and the suspended particles themselves are sticky colloidal particles, so when they float, they also take with them the moisture attached to their surroundings. be.

As a result, the concentration of flotation thickened sludge decreases, and the solid content recovery rate decreases due to an increase in treated water SS.In practice, this is done after adding a polymer flocculant to enlarge the particles before flotation concentration. is the current situation.

The present invention has been developed as a result of various studies to eliminate the drawbacks of these methods and to more effectively float and concentrate sludge. After adjusting the pH of sludge to 2 to 3, hydrogen peroxide is added and mixed, and then the sludge is stabilized. It is an object of the present invention to provide a novel method for concentrating organic sludge in which flotation concentration can be carried out efficiently by placing the sludge in the sludge.

Hereinafter, the present invention will be explained in detail based on examples.

The principle of the present invention is that hydrogen peroxide is decomposed in sludge, and particles are attached to microscopic oxygen bubbles generated at that time to float and concentrate.

In the present invention, as a first step, the pH of the sludge is adjusted to 4 or less, preferably 2 to 3, using an acid such as sulfuric acid or hydrochloric acid.

The purpose of this pH adjustment is that large amounts of catalase produced by microorganisms exist in sludge containing organic matter.
These have a catalytic effect on the redox reaction that decomposes hydrogen peroxide (H2O2) added in the second step into oxygen and water.

Therefore, in the pH range where the catalytic effect is exerted, the added hydrogen peroxide is decomposed very quickly, and the rate of bubble formation of oxygen gas generated by decomposition becomes greater than the rate of adsorption of microbubbles to sludge particles. becomes dynamic, and the generated bubbles are wastefully discharged out of the system.

Therefore, when performing flotation concentration using hydrogen peroxide, the PH
It is necessary to eliminate the catalytic action by setting the pH to 4 or less, preferably 2 to 3.

Further, in this PH region, the viscosity of high-viscosity polysaccharides in the organic matter, which is an obstacle to flotation and concentration, is reduced, and when flotation and concentration is carried out, a synergistic effect is brought about along with a reduction in catalytic activity.

In the second step, hydrogen peroxide is added and mixed to the sludge whose pH has been adjusted to 4 or less, preferably 2 to 3.

The amount of hydrogen peroxide added is 1.0% or more per solid matter, preferably in the range of 1.0 to 5%.If it is less than 1.0%, the effect of flotation concentration will be small, and if it is 5% or more, No further improvement in effectiveness was observed.

In addition, the standing time should be 4 hours or more, preferably 8 to 12 hours; if it is less than 8 hours, flotation concentration will not be completed, and if it is more than 24 hours, no further improvement in concentration will be observed. I can't.

In addition, although human waste septic tank sludge was shown as an example, it goes without saying that the same effect as the above-mentioned example can be obtained even if the method is applied to sludge containing organic matter such as sewage or surplus sludge.

Through the treatments in the first and second steps above, hydrogen peroxide is effectively decomposed, and the bubbles produced by the decomposition are extremely fine, comparable to or smaller than bubbles produced by electrolysis. It attaches to, captures, and captures even particles.
Since hydrogen peroxide is uniformly mixed in the sludge, it is possible to generate bubbles uniformly in each part of the sludge, resulting in effects such as high clarity of the separated liquid.

Furthermore, since the flotation operation itself is static, the concentration of separated solids can be made higher by appropriately designing the separation between the flotation concentration section and the clarified liquid section from an engineering perspective.

The optimum amount of H20□ to be added is determined by the viscosity and other physical properties of the sludge liquid.

Example 1 After adjusting the pH by adding sulfuric acid to human waste septic tank sludge (concentration 1.6%), hydrogen peroxide was added and mixed, left to stand for 24 hours to float and concentrate, and the results of measuring the concentrated sludge concentration were Shown in Table 1.

This result shows that good results can be obtained when the pH is 4 or less and hydrogen peroxide is added in an amount of 1.0% or more based on solid matter.

Example 2 Human waste septic tank sludge was adjusted to pH=2.5 with sulfuric acid, hydrogen peroxide was added in an amount of 5.0% based on the solid matter, and the mixture was allowed to stand. The results are shown in Table 2.

It can be seen from this that when the standing time is 4 hours or more, the degree of concentration is considerably improved.

□ Example 3 The results obtained by the method of the present invention (results after 24 hours of standing in Table 2) and the conventional method (15
Table 3 shows a comparison with the result of flotation concentration for 5 minutes).

From the above results, the method of the present invention has obtained superior results in both the floating concentrate concentration and the treated water SS compared to the conventional method.

Claims (1)

[Scope of Claims] 1. A method for concentrating organic sludge, which comprises adjusting the pH of sludge containing organic matter, adding hydrogen peroxide, and flotation concentration of suspended particles. 2. The method for concentrating organic sludge according to claim 1, wherein the pH is adjusted to 4 or less with an acid such as sulfuric acid or hydrochloric acid. 3. The method for concentrating organic sludge according to claim 1 or 2, which is carried out by adding hydrogen peroxide in an amount of 1.0% to 5% based on the solid matter.