JPH01297200A - Agricultural reduction method for organic sludge - Google Patents

Abstract

PURPOSE:To highly concentrate sludge and to prevent the generation of secondary public nuisance by adding chlorous acid or chlorite and a cationic polymer flocculant to sludge to be conc. and subsequently concentrating said sludge by gravitational separation. CONSTITUTION:After chlorous acid or chlorite and a cationic polymer flocculant are added to sludge to be conc. such as first sedimentation basin sludge of sewage, excessive activated sludge or sludge mixture thereof, said sludge is conc. by gravitational separation. As chlorous acid or chlorite, a stable easily soluble salt such as sodium chlorite is pref. and the addition amount thereof is pref. 25-100mg/l. As an embodiment of the cationic polymer flocculant, a quaternized compound of dialkylaminoalkyl (meth)acrylate is designated and the addition amount thereof is pref. 0.1-0.4wt.%. The gravitational separation being a concn. means is performed by introducing the sludge into a solid-liquid separation tank to perform natural sedimentation.

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 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. According to the sewerage maintenance and management guidelines (Japan Sewage Works Association), the concentration of thickened sludge in gravity thickening tanks is 2 to 4%.
The average concentration is around 3%, but according to the results of a survey on the actual situation of each sewage system by the Japan Sewage Works Association [1], there are treatment plants with extremely poor concentration conditions, where the concentration of thickened sludge is less than 2%. Especially in the summer, CO□ gas bubbles generated by sludge decomposition adhere to the sludge, causing the sludge to float to the surface and making it difficult to thicken the sludge. A low sludge concentration has the disadvantage of reducing the efficiency of subsequent processes such as dewatering and digestion.

In order to solve these problems, a method has been proposed in which sludge is concentrated by adding chlorine or a free chlorine agent such as calcium hypochlorite (Sewage/Wastewater Treatment Guidebook, 1972). (Published by Environmental Technology Research Group, p. 395).

However, the above-mentioned method of adding a free chlorine agent has a problem in that even if a large amount is added, the effect is not significant and secondary pollution occurs due to residual chlorine.

Subsequently, a method using oxidizing agents such as hypochlorite and hydrogen peroxide was proposed (Japanese Patent Laid-Open No. 197200/1983). However, since hypochlorite and hydrogen peroxide are also decomposed to generate chlorine and oxygen gas, it is necessary to carry out sufficient deaeration treatment, and there is also a desire to further increase the concentration of sludge.

[Problem to be solved by the invention]

This invention is intended to solve the above-mentioned problems, and aims to propose a method for concentrating organic sludge that can thicken sludge to a higher degree than conventional methods and has fewer problems of secondary pollution. There is.

[Means to solve the problem]

This invention is a method for concentrating organic sludge, which comprises adding chlorite or chlorite and a cationic polymer flocculant to sludge to be concentrated, and then concentrating the mixture by gravity separation.

The sludge to be thickened in the present invention is:

It is organic sludge containing organic matter, such as primary sedimentation tank sludge of sewage, surplus activated sludge, or mixed sludge thereof.

The chlorite or chlorite to be added to the sludge to be thickened is not particularly limited, but stable and easily soluble salts such as sodium chlorite are preferred, and these salts can be used singly or in combination of two or more. is possible. The amount of these additions varies depending on the type and properties of the sludge, but is 5 to 500 mg/
Q, preferably about 25 to 1100 II1/Q.

Cationic polymer flocculants that can be used in the present invention include:
Although not particularly limited, preferred cationic polymer flocculants include: (1) a homopolymer of a quaternized product or acid salt of dialkylaminoalkyl (meth)acrylate or a copolymer with (meth)acrylamide; (2) dimethylaminoalkyl ( Examples include quaternized products of meth)acrylamide or homopolymers of acid salts or copolymers with (meth)acrylamide, ■Mannich-modified products of poly(meth)acrylamide, and ■Hoffmann decomposition products of poly(meth)acrylamide. , these can be used alone or in combination or with other cationic polymeric flocculants.

The cationic polymer flocculant used has a colloid equivalent value (pH 4) of 3 meq/g or less, preferably 2.
6 meq/g or less is suitable. Also, the intrinsic viscosity [
9130°C lN-NaNo = 4.5 (dQ/g) or more, preferably 5.0 (clQ/g) or more is suitable.

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, and examples of such agents include dimethylaminoalkyl (
meth)acrylate or dimethylaminoalkyl(
A copolymer of (meth)acrylamide and an acid salt of meth)acrylamide or a quaternary ammonium salt made with a quaternizing agent (methyl chloride, benzyl chloride, dimethyl sulfate, etc.), with a (meth)acrylamide content of 80
There are some with mo1% or more.

The amount of cationic polymer flocculant added is 0.05 to 1% by weight.
(vs. SS), preferably 0.1 to 0.4% by weight (vs. SS), preferably 0.1 to 0.4% by weight (vs. SS)
).

The method for concentrating organic sludge is to add chlorite (salt) to the sludge to be thickened.
and a cationic polymer flocculant are added, stirred and mixed, and concentrated by gravity separation.

Although the order of adding the chemicals is not limited, it is desirable to add the cationic polymer flocculant after adding chlorite (salt) to the sludge fed into the thickening tank.

The method of stirring and mixing after adding the drug is not particularly limited.

Stirring using a stirring blade in a stirring tank, stirring by flow in piping, stirring by passing through a pump, etc. can be used. There is no particular limit to the stirring intensity, but it is desirable to stir sufficiently to mix the chemicals and remove the gas accumulated in the sludge.

The means of concentration after stirring and mixing is gravity separation.
The reacted 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, a digestion tank, etc. for dewatering.
Used for processing such as digestion.

The separated liquid is also returned to the water treatment system.

Although the concentration method of the present invention is effective for sludge at low temperatures, it is particularly effective for sludge that is susceptible to gas generation due to decomposition at 18° C. or higher.

[For production]

Sludge flotation occurs because gas generated by sludge decay accumulates within the sludge phase in the thickening tank.

When chlorite (salt) is added to the sludge to be thickened, the putrefaction of the sludge is suppressed and floating is prevented, thereby increasing the sludge concentration. In addition, when chlorite (salt) is added and a cationic polymer flocculant is added at 0.05 to 1% (relative to SS),
Because the settling properties of sludge are improved, the sludge concentration is higher than when using only chlorite (salt).

When the chlorine fi (salt) of the present invention is mixed with sludge to be thickened, it does not decompose and generate chlorine unlike conventional free chlorine agents, and is a stable compound near neutrality, so it There is no generation of harmful gases that would cause the surface to float. As for the mechanism of action, it is assumed that bacteria are oxidized and sterilized during the nascent stage through oxygen, and the sludge concentration can be increased compared to conventional agents.

In addition, when the amount of cationic polymer flocculant added is increased,
The sludge concentration may not become high because the generated flocs cause bridging. On the other hand, when only the cationic polymer flocculant is added.

Gases generated due to decomposition stick to the surface and float to the surface.
Sludge concentration will not increase.

In this manner, according to the method for concentrating organic sludge of the present invention, sludge can be concentrated to a higher concentration than conventional methods without substantially changing the properties of the sludge, such as ρ■. As the sludge concentration increases, dewatering performance improves, reducing the amount of dehydrating agent needed to be added, lowering the water content of the dehydrated cake, improving dewatering performance such as improving peelability, increasing the amount of sludge treated, and promoting digestion efficiency. etc. become possible.

〔Example〕

Examples of the present invention will be described below. In the examples, % indicates weight %.

Example 1 Mixed sludge (pH
=7.0.5S=0.90%, VSS/SS = 65
%, temperature = 25°C), a sludge thickening test was conducted using an oxidizing agent or an oxidizing agent and a cationic polymer flocculant (CP).

The oxidizing agents used were sodium chlorite solution (25%) and sodium hypochlorite solution (12%), and the cationic polymer flocculant CP was a copolymer of methyl chloride quaternary product of dimethylaminoethyl methacrylate and acrylamide. 30°C [η]lN-NaN03 = 9.0'', colloid equivalent value = 2.0 meq/g (at pH = 4), acrylamide content = 80 mo1%).

The sludge thickening test method is as follows.

Sludge Concentration Test Method Sludge to be thickened 11 was placed in a 20Q capacity polyethylene container, a predetermined amount of oxidizing agent was added, and then a predetermined amount of cationic polymer flocculant was added either directly or further, mixed and stirred, and then this sludge was mixed and stirred. Transparent acrylic resin cylinder (1000n++eH
x 200m+mφ) and measure the change in sludge volume over time. After the start of sedimentation, the change in the sludge interface height over time was measured, and the SS concentration for sludge was calculated from the sludge volume and the SS concentration of the raw sludge.

This is taken as the sludge SS concentration at each time.

In addition, the time (hr) when sludge begins to float is measured and defined as the sludge floating time, and if the sludge does not float within 24 hours,
The above shall apply.

Mixing and stirring after addition of the oxidizing agent and the cationic polymer flocculant is performed using a stirrer on the ILQ sludge to be thickened at a circumferential speed of 1. The test was carried out for 3 minutes at Om/sec (25 Orpm). The results are shown in Table 1. In Table 1.

Nα1-4 show comparative examples, and N05-7 show examples.

Example 2 Next, mixed sludge of sewage primary sedimentation tank sludge and surplus activated sludge (
pi (~6.0.5S=1.2%, VSS/5S=8
Regarding hard-to-thicken sludge consisting of 0%, temperature = 25℃),
The test was conducted in the same manner as in Example]. The results are shown in Table 2. In Table 2, Nnl-4, 8, and 9 represent comparative examples, and Na 5 to 7 represent examples.

From the above results, primary chlorite or hydrogen peroxide is insufficient to improve the concentration of both easily thickening sludge and difficult-to-thicken sludge, but chlorite has a large concentration improvement effect. I know that it will happen.

Note that in this example, the thickness of the sludge phase is several tens of cm;
The thickness of the thickening tank to be implemented is 2 to 3 m, so the sludge SS
The concentration is even higher than that in this example.

〔Effect of the invention〕

According to the present invention, sludge to be thickened is separated by gravity by adding chlorite (salt) and a cationic polymer flocculant, so even in the case of high-temperature, perishable sludge, the properties of the sludge are almost unchanged. It can be concentrated to a high concentration without changing it, and there is little secondary pollution.

Agent: Patent attorney Sei Yanagi Hara

Claims (1)

[Claims] (1) A method for concentrating organic sludge, which comprises adding chlorite or chlorite and a cationic polymer flocculant to sludge to be concentrated, and then concentrating by gravity separation.