JPS61254300A - Method for concentrating organic sludge - Google Patents

Abstract

PURPOSE:To concentrate sludge to a high degree, by adding 0.2% or less by wt. of SS of a cationic polymer flocculant and an alkali agent to sludge to be conc. before concentrating said sludge. CONSTITUTION:0.2% or less by wt. of SS in sludge of a cationic polymer flocculant (e.g., a quaternized compound of dialkylaminoalkyl acrylate or a quaternized compound of dimethylaminoalkylacrylamide) and an alkali agent such as sodium hydroxide, potassium hydroxide or calcium hydroxide in an amount capable of holding pH of sludge to 7 or more are added to sludge to be concn. The reacted sludge is introduced into a solid-liquid separation tank and naturally sedimented. The solid component is subjected to dehydration/ digestion treatment and the separated solution is returned to a water treatment system. By this method, the generation of gas is suppressed and dehydration property can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for concentrating organic sludge, particularly to a method for concentrating sewage sludge by gravity separation.

[Conventional technology]

In sewage treatment, excess activated sludge is generally returned to the initial settling tank to form mixed raw sludge, or mixed sludge of excess activated sludge and initial settling tank sludge is concentrated by gravity separation. Design guidelines of Japan Sewage Works Association (1972)
According to the Sewerage Facility Design Guidelines and Explanations (published in 2013), the concentration of solid sludge in the input sludge is 1% and the concentration of solids in the thickened sludge is 4% with a residence time of 12 hours.However, with the increase in organic content of sludge in recent years Because the ability to thicken sludge has declined, many treatment plants only thicken it to around 2%. Particularly in the summer, sludge decomposes and floats to the surface, making it difficult to thicken the sludge. A low sludge concentration has the disadvantage that the efficiency of dehydration, digestion, etc. decreases.

In order to solve these problems, a method has been proposed to increase the concentration of sludge by adding an alkaline agent to the sludge to raise the pH to 9 or more (Sewage/Wastewater Treatment Guidebook, Published by Environmental Technology Research Group, No. 395 in 1972.
page).

[Problem that the invention seeks to solve]

However, the above-mentioned method of adding an alkaline agent has a problem in that the sludge cannot be concentrated sufficiently.

This invention is intended to solve the above-mentioned problems, and aims to propose a method for concentrating organic sludge that can highly concentrate sludge.

[Means for solving problems]

In this invention, zero cationic polymer flocculant is added to the sludge to be thickened.
．． 2% by weight or less (relative to SS), and after adding the alkaline agent necessary to maintain the pH of the sludge to be thickened at 7 or higher.1
This is a method for concentrating organic sludge, which is characterized by concentration by gravity separation.

The sludge to be thickened in the present invention is an organic sludge containing organic matter, and includes, for example, primary sedimentation tank sludge of sewage, excess activated sludge, or a mixed sludge thereof.

The cationic polymer flocculant to be added to these sludges to be thickened is not particularly limited, but preferred cationic polymer flocculants include: Union or copolymer with (meth)acrylamide, ■ Homopolymer of quaternized product or acid salt of dimethylaminoalkyl (meth)acrylamide or copolymer with (meth)acrylamide, ■ Mannich modified product of polyacrylamide, etc. These can be used alone or in combination, or in combination with other cationic polymer flocculants.

A cationic polymer flocculant having a high molecular weight is suitable for the present invention because it has good flocculating properties even when added in a small amount.

Such substances include acid salts of dimethylaminoalkyl (meth)acrylate or dimethylaminoalkyl (meth)acrylamide, or quaternizing agents (methyl chloride, pencil chloride, dimethyl sulfate, etc.) to form quaternary ammonium salts. A homopolymer of these and (meth)acrylamide, [η)
30'ClN-NaN0. ” 5.0 (dj2/g) or more is particularly preferred.

In addition, alkaline agents include bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide, sodium carbonate,
Basic salts such as sodium silicate, sodium aluminate, or mixtures thereof can be used.

In the sludge thickening method, the cationic polymer flocculant is added to the sludge to be thickened to 0.2% by weight or less (based on ss), preferably 0.2% by weight or less (based on ss).
05 to 0.2% by weight (based on Ss) and an alkali agent are added and stirred, followed by concentration by gravity separation.

It is preferable to add the alkaline agent at once in the entire amount necessary to maintain the pH of the sludge to be thickened at 7 or higher, preferably 7 to 8, during the concentration process, that is, until it is drawn out as thickened sludge.

The required amount of the alkaline agent, which may be added in portions, is determined depending on the residence time, and is added so that p87 or higher is maintained during the residence time in the concentration tank.

The order of addition of the chemicals is not limited, and either the cationic polymer flocculant or the alkaline agent may be added to the sludge introduced into the thickening tank first, or both may be added at the same time.

The stirring method is also not particularly limited, and may be agitation using a stirring blade in a stirring tank, agitation by flow in piping, agitation by passing through a pump, or the like. There is no limit to the stirring intensity, and it is sufficient that the sludge and the chemical are sufficiently mixed and reacted.

The means of concentration is gravity separation, in which the reaction sludge is introduced into a solid-liquid separation tank and allowed to settle naturally. The concentrated solid sludge is led to a dehydrator, a digestion tank, etc., and subjected to treatments such as dehydration and digestion. The separated liquid is also returned to the water treatment system.

Although the concentration method of the present invention is effective for low-temperature sludge, it is particularly effective for sludge that easily generates gas due to decomposition at 18° C. or higher.

[For production]

Add 0.2% by weight of cationic polymer flocculant to the sludge to be thickened (
If you add the following (for SS) and react, and adjust the pH to 7 or higher, even in the case of sludge at a temperature that is too hot to putrefy,
Gas generation is reduced, preventing sludge from floating, and bridging of sludge is reduced, increasing sludge concentration. On the other hand, pH adjustment alone does not increase the sludge concentration, and adding only a cationic polymer flocculant to the sludge improves the settling properties of the sludge, but gases generated by putrefaction may adhere to the sludge. If the amount added is large, the sludge concentration will not become high because the generated flocs will cause bridging.

The reason why organic sludge has poor thickening properties is presumed to be that carbon dioxide gas generated by putrefaction adheres to sludge particles and floats to the surface.1 In the present invention, by adding an alkaline agent, the pH of sludge is increased. Become.

It is presumed that carbon dioxide gas dissolves into the sludge and prevents it from floating. When an alkali agent is added to the sludge to be thickened, the pH
pH increases, but the pH decreases due to the dissolution of organic acids and carbon dioxide gas generated by decay.

The pH is maintained at 7 or higher until it is extracted as thickened sludge.

If the pH during concentration exceeds 8, it may adversely affect dehydration and digestion, so it is preferable to maintain the pH at 7 to 8.

In this way, according to the method for concentrating organic sludge of the present invention, sludge can be concentrated to a high concentration. By increasing the sludge concentration, dewatering performance improves, making it possible to reduce the required amount of dehydrating agent, lower the water content of the dehydrated cake, and improve peelability.

〔Example〕

Examples of the present invention will be described below. In each example, % indicates weight %, and the cationic polymer flocculant used is as shown in Table 1. The sludge thickening test method is as follows.

Sludge Concentration Test Method Take the sludge 11 to be thickened in a 20ffi polyethylene container, add a predetermined amount of cationic polymer flocculant and alkaline agent, and stir with a stirrer.The sludge is transferred to a transparent acrylic resin cylinder with a picket fence. (1000m HX 1
50 mmφ) and measure the change in sludge volume over time. The concentration test rotates the picket fence (0,1
After the start of settling, the change in the sludge interface height over time is measured, and the S of the sludge phase is determined from the sludge volume and the SS concentration of the raw sludge.
Calculate the S concentration and use this as the sludge concentration at each time.

In addition, the time (hr) when sludge starts to float is measured and defined as the sludge floating time, and if the sludge does not float within 25 hours,
The above shall apply.

Table 1 ■ Example 1 Sewage primary sedimentation tank sludge (pH 6.3, electrical conductivity 205
0p S/0m, S S 1.00%, V S S/
A sludge concentration test was conducted on SS 70.8% and sludge temperature 22-24°C.

The results are shown in Table 2.

In Table 2, the raw sludge (Test 1) hardly settled and floated to the surface in 7 hours. Sodium hydroxide 220mg/
When Q vs. slurry was added (Test & 2), the pH decreased to less than 7.0 during concentration and sludge floated to the surface. On the other hand, when more than 350 g/Q of sodium hydroxide was added to the slurry (test Nα3 to 4), the pH of the sludge after concentration was 7.0 or higher, preventing floating, and after 25 hours The SS concentration of the sludge was 2.5%.

On the other hand, add sodium hydroxide to 350 or 540
When adding mg/Q to slurry and adding 0.1% or 0.2% to SS of cationic polymer flocculant C1 (tests &7 to 9), flotation was prevented and sedimentation properties were improved. The SS after 25 hours reached 3.1 to 3.4%, which indicates that the effect is better than that of sodium hydroxide alone. Furthermore, when 0.3% of C1 was added to SS (test Nα10), sludge bridging phenomenon occurred, and the achieved concentration was lower than when the amount added was 0.1% to SS and 0.2% to SS. Ta.

On the other hand, flotation occurred when only C1 was added (Test &5) and when C1 was used in combination with sodium hydroxide in an amount of 220 mg/Q vs. slurry (Test Nα6).

Example 2 Mixed sludge of sewage primary sedimentation tank sludge and excess activated sludge (mixing ratio (SS conversion)... initial sedimentation: surplus = 1:1, pH 6.1
, electrical conductivity 1910 μS/am, SS 0.81%, V
S S/S S 80.3%, sludge temperature 21-23℃
) We conducted a sludge concentration test. The results are shown in Table 3.

From Table 3, the raw sludge (test Nα11) floated to the surface in 12 hours. Calcium hydroxide was added at 350 mg/Ω vs. slurry, and cationic polymer flocculant C3 was added at 0.1 or 0.
When 2% of SS was added (tests Nn12 to 13), the pH of the thickened sludge became 7.0 or higher, preventing flotation and improving sedimentation, so the SS concentration after 25 hours was 2.9% or more.
It reached 3.1%. When the amount of C3 added is 0.3% vs. SS (Test & 14), sludge bridging phenomenon occurs, and the SS concentration reached is 0.1% or 0.
It was stroked lower than in the case of 2% vs. SS.

In addition, as a cationic polymer flocculant, 30°C [η]lN-NaN0z is 3.2.4.4, respectively.
When using 0.2% of C2 and C4 vs. SS (test &
15-16) had worse sedimentation than when C3 was used, and the SS concentration reached was lower. Although sedimentation is improved by increasing the amount of C2 and C4 added, it becomes easier to float, so it is more effective to use C3.

〔Effect of the invention〕

According to the present invention, a cationic polymer flocculant is added to the sludge to be thickened, and an alkaline agent is added to maintain the pH at 7 or more for gravity separation, so that the sludge can be concentrated to a high concentration. I can do it.

Claims (5)

[Claims] (1) After adding 0.2% by weight or less of a cationic polymer flocculant (relative to SS) to the sludge to be thickened and the alkaline agent necessary to maintain the pH of the sludge to be thickened to 7 or higher, gravity separation is performed. A method for concentrating organic sludge, which is characterized by concentrating organic sludge. (2) The concentration method according to claim 1, wherein the sludge is sewage primary sedimentation tank sludge, surplus activated sludge, or a mixed sludge thereof. (3) The concentration method according to claim 1 or 2, wherein the pH is 7 to 8. (4) The amount of coagulant added is 0.05 to 0.2% by weight (relative to S
S) The concentration method according to any one of claims 1 to 3. (5) The concentration method according to any one of claims 1 to 4, wherein the temperature of the sludge is 18°C or higher.