JPS6253799A - Method for concentrating organic sludge - Google Patents

Abstract

PURPOSE:To highly concentrate sludge, by adding not only an oxidizing agent but also a cationic polymer flocculant to sludge to be concentrated and separating them by gravity. CONSTITUTION:An oxidizing agent such as hydrogen peroxide, sodium peroxide or sodium hypochlorite and a cationic polymer flocculant [e.g., acid salt or quaternized agent of dimethylaminoalkyl (meth)acrylate or dimethylaminoalkyl (meth)acrylamide] are added to the sludge to be concentrated such as final sedimentation base sludge or excessive activated sludge of sewage under stirring in an amount of 0.05-0.2wt% of SS. Subsequently, the sludge is concentrated by gravitational separation. By this method, dehydratability is enhanced and the lowering in the water content of a dehydrated cake; accordingly, the enhancement of the releasability of said cake become possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] 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 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.
is a common name. Design guidelines of Japan Sewage Works Association (197
According to the Sewerage System Certification 1 Guidelines and Explanations published in 2013, the solid content of input sludge is 1% and the concentration of concentrated sludge solids is 4% with a residence time of 12 hours, but the organic content of sludge has increased in recent years. As a result, the ability to thicken 1.1 sludge has decreased, and many treatment plants are only able to thicken it to around 2%. Particularly in summer fisting, the sludge rises to the surface due to decomposition, making it difficult to thicken the sludge. A low sludge concentration has the disadvantage of reducing the efficiency of dewatering, digestion, etc.゛In order to solve such problems, a method has been proposed to increase the concentration of sludge by adding acid to the sludge to reduce the PI (PI) to 4 or less (Sewage/Sidewater Treatment Guide) Book, 1971, published by IK Kyoto Gijutsu Kenkyukai, p. 395).

[Problems that Kojimei tries to solve]

However, the above method of adding acid has problems in that the concentration tank is exposed to strong acidity and is adversely affected, and a large amount of alkaline agent for neutralization is required in the subsequent process.

This invention is intended to solve the above-mentioned problems, and aims to propose a method for concentrating organic sludge that can make sludge highly concentrated without using acids.

[Means for solving problems]

This invention adds an oxidizing agent to the sludge to be thickened, and
Cationic polymer flocculant 0.2% by weight or less (relative to Sq)
This is a method for concentrating organic sludge, which is characterized in that the organic sludge is concentrated by 1 gravity separation after addition.

The sludge to be concentrated in the present invention is an organic sludge containing organic matter. 11t
i'' constant sludge, surplus activated sludge, or a mixture of these sludges.

The oxidizing agent to be added to these sludges to be thickened is not particularly limited, but peroxides such as hydrogen peroxide and sodium peroxide, and hypochlorites such as sodium hypochlorite are preferred, and these include 111 alone. Alternatively, two or more types can be used in combination.

The cationic polymer flocculant used in the present invention is not particularly limited, but preferable cationic polymer flocculants include: (1) a monopolymer of a quaternized product or an acid salt of dialkylaminoalkyl (meth)acrylate; Ha (meta)
Copolymer with acrylamide 1, ■ Homopolymer of quaternized product or acid salt of dimethylaminoalkyl (meth)acrylamide or copolymer with (meth)acrylamide, ■ Mannich modified product of poly(meth)acrylamide,
(2) Hoffmann decomposition products of poly(meth)acrylamide are mentioned, and these can be used alone or in combination, or in combination with other cationic polymer flocculants.

The cationic polymer flocculant used has a colloidal equivalent value (pi(4) of 3@1!q/ or less, preferably 2
．． 6 maq/g or less is suitable. Further, it is suitable that the intrinsic viscosity is 30° C. [η) 1N-NaNg, 4-5 (da/IC) or more, preferably 5.0 (di/g) or more.

Cationic polymer flocculants with low cation density and high molecular weight are suitable for the present invention because they have good flocculating properties even when added in low amounts. Aminoalkyl (meth)acrylamide acid salts or quaternizing agents (methyl chloride, benzyl chloride, dimethyl sulfate, etc.)
A copolymer of (meth)acrylamide and a quaternary ammonium salt with a (meth)acrylamide content of 8.
There are some with 0+mo1% or more.

The sludge thickening method involves adding the oxidizing agent to the sludge to be thickened, and adding a cationic polymer flocculant to 0.2% by weight or less (based on SS), preferably 0.05 to 0.2% by weight (based on SS).
S) Concentrate by 1 gravity separation after addition and stirring.

Although the order of addition of the chemicals is not limited, it is preferable to add the oxidizing agent and the cationic polymer flocculant simultaneously to the brown substance introduced into the concentration tank, or to add the cationic polymer flocculant after adding the oxidizing agent. It is best to avoid adding an oxidizing agent after adding a cationic polymer flocculant, as the addition of the oxidizing agent may generate bubbles from the sludge and adhere to the flocs, causing some of the sludge to float to the surface.

The stirring method is not particularly limited, and may include stirring using a stirring blade in an Mt stirring tank, stirring by flow in piping, stirring by passing through a pump, and 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 solid content of the concentrated sludge is led to a dewatering device, digestion tank, etc. for dewatering.

Used for processing such as digestion. In addition, the separated liquid is a water treatment system.
・It will be returned to.

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]

Adding an oxidizing agent to the sludge to be thickened suppresses the putrefaction of the sludge and prevents it from floating, increasing the sludge concentration. In addition, an oxidizing agent was added and a cationic polymer flocculant was added at 0.2
If it is added in an amount less than % by weight (relative to SS), the sedimentation properties of the sludge will be improved, so the sludge concentration will be higher than in the case of only the oxidizing agent. Note that if the amount of the cationic polymer flocculant added is increased, the sludge concentration may not become high because bridging occurs in the generated flocs. On the other hand, when only a cationic polymer flocculant is added, gases generated by putrefaction tend to adhere and float, and the sludge concentration does not increase.

In this way, according to the method for concentrating organic sludge of the present invention, sludge can be concentrated to a high concentration without using acid. As the sludge concentration increases, 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〕

Five embodiments of the present invention will be described below. In the examples, % indicates weight %, and the drugs used are as shown in Table 1. The sludge thickening test method is as follows.

Sludge thickening test method: Place sludge 17Q to be thickened in a 20Ω polyethylene container.
A predetermined amount of oxidizing agent and cationic polymer flocculant are added, and the sludge is stirred using a stirrer.
150 mmφ) and measure the change in sludge volume over time. The concentration test rotates the picket fence (0,
After the start of sedimentation, the SS concentration in the sludge phase was calculated from the sludge volume and the SS concentration in the raw sludge by measuring the change in the sludge interface height over time.

This is taken as the sludge concentration at each time.

In addition, the time (hr) when the sludge begins to float is measured and defined as the sludge floating time, and if the sludge does not float within 25 hours, it is counted as 2.
5 or more.

Mixed sludge of sewage initial settling tank sludge and excess activated sludge (mixing ratio (SS conversion)... initial settling: surplus = 1 = 1, sludge water temperature 2
4°C, pi 6.8. Electric conductivity 1480μs71,
S S 1.18%, V S S/S S 83.1%
) The results of the Nitsuite sludge concentration test are shown in Table 2.

In Table 2, test Na4.5 is when the oxidizing agent and cationic polymer flocculant are added at the same time, and test &6 is when the oxidizing agent is added after the cationic polymer flocculant is added. &8 to 10 are cases where the cationic polymer flocculant was added after the oxidizing agent was added.

From the results in Table 2, in the case of raw sludge (test Nα1), 11
150mg/L of hydrogen peroxide solution
Or the next layer sodium chlorate f00+++g/! t
When T was added (test Nα2.7), sludge floating was prevented, and the sludge SS concentration after 25 hours was 2.5%. On the other hand, when 150 mg/Q of hydrogen peroxide solution and cationic polymer flocculant C10.2% vs. The sludge SS concentration reached approximately 3.1%, but C
When 1' was added first (test Ha 6 ), some flocs floated to the surface. Furthermore, when 0.3% of C1 was added to SS (test Nα5), the sedimentation properties of the sludge improved, but bridging occurred and the sludge concentration did not increase. When sodium hypochlorite 200mg/Q and cationic polymer flocculant C20, 1% vs. SS were used together (test Na8), sludge sedimentation was also improved, and the sludge SS concentration was 3.0% after 25 hours. reached. C3 as a cationic polymer flocculant
, C4 (test Nα9.10) also concentrates to a higher concentration than when using only sodium hypochlorite.

However, since the actual thickness is about 1 to 2 m, the sludge SS concentration is much higher than that in this example.

[Effects of the Invention] According to the present invention, an oxidizing agent is added to the sludge to be thickened, and a cationic polymer flocculant is added to perform gravity separation. It can be concentrated to a high concentration without using acid.

Claims (4)

[Claims] (1) Concentration of organic sludge characterized by adding an oxidizing agent and 0.2% by weight or less (relative to SS) of a cationic polymer flocculant to the sludge to be thickened, and then concentrating by gravity separation. Method. (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 oxidizing agent is a peroxide or a hypochlorite. (4) The cationic polymer flocculant has a colloid equivalent value of 3 meq/g or less at pH 4 and an intrinsic viscosity [η]^3
＾0＾℃_1_N_-_N_a_N_O___34.5(
dl/g) or more. The concentration method according to any one of claims 1 to 3.