JPS5919760B2 - Sludge treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating sludge generated from purification processes of water, sewage and various industrial wastewater.

Since most of these sludges are usually difficult to permeate, conventionally, before dewatering, inorganic flocculants such as slaked lime and iron sulfate are added and mixed to form flocs, which improves the dewaterability or dewatering rate. The dehydration rate was previously improved, but in recent years, organic polymer flocculants, which are superior in various respects such as flocculation effects, are increasingly being used.

There are several methods of using this polymer flocculant, including a method of using a polymer flocculant alone and a method of using a polymer flocculant and an inorganic flocculant together.

There is also a method of improving the dewatering properties of sludge by using a polymer flocculant together with coal powder or the like.

Apart from these methods, there is also a method of adding only the above-mentioned coal powder to the sludge, but in order to achieve the same effect as a polymer flocculant with this method, it must be added in large amounts. First, it is not effective because the amount of sludge cake after dewatering increases.

This drawback also applies when an inorganic flocculant is used alone.

In comparison, methods for preparing sludge that use a polymer flocculant alone or in combination with other agents have many advantages, such as the addition amount being small and the rate of increase in sludge cake being extremely small.

However, generally speaking, when polymer flocculants are used, the dewatering rate of sludge tends to be lower than when using inorganic flocculants, and even when there is no such tendency, the dewatering rate of sludge tends to be lower than when using inorganic flocculants. In order to improve the properties even slightly, attempts are being made to develop the polymer flocculant itself and the conditions for mixing it with sludge water, with the aim of generating flocs with greater floc strength.

However, the strength of sludge flocs is stabilized when the addition amount is larger than when it is added in a small amount, so in reality, it is necessary to add a larger amount, that is, the minimum amount of 2 to 10 The reality is that flocs with good dewatering properties are produced by adding twice the amount.

In this case, the flocculating effect when a polymer flocculant is added to sludge is due to physical effects as well as chemical reactions, so even if the amount of polymer flocculant added is kept below the required amount, However, in reality, unreacted polymer flocculant remains on the separated water side of the sludge.

Moreover, the reaction between sludge and polymer flocculant takes a longer time for the flocculation reaction as the amount of polymer flocculant added to the sludge increases.
When a large amount of polymer flocculant is added, the solids in the sludge cannot absorb the added polymer flocculant, and even after a long reaction time, the solids in the sludge do not adsorb the solids. , a large amount remains on the water side without migrating.

This residual phenomenon also occurs in the case of the method in which a polymer flocculant and an inorganic flocculant or a substance such as coal powder are added to sludge in combination as described above.

Specifically, for example, when a polymer flocculant is added alone, separated water after dehydration by a normal dehydration method contains 5 to 50% of the added amount of unreacted polymer flocculant.

This can be easily estimated by measuring the viscosity of the separated water.

Discharging such separated water containing unreacted polymers poses a problem in terms of pollution prevention, and, for example, if it is sent back to the inlet of an aeration tank where activated sludge treatment is being carried out, it may cause harmful effects such as inhibiting the respiration of activated sludge. It is being

For this reason, conventionally, in the sewage treatment process, if a pre-sedimentation tank such as a primary sedimentation tank is provided, the sludge should be returned to the inlet of the tank, or if a sludge thickening tank is provided, the sludge should be returned to the inlet of the pre-sedimentation tank, and then returned to the treatment process other than the required aeration tank. Accordingly, a so-called recycling method has been adopted in which wastewater is brought into contact with solid matter and coagulated.

Although this method does not discharge unreacted polymer flocculant to the outside of the system, it is not preferable from the viewpoint of sludge dewatering.

In other words, in the recycling method, the separated water after dehydration containing unreacted polymer flocculant is returned, so the same type of polymer flocculant is added in two stages to the sludge containing the polymer flocculant. It turns out.

If the amount of polymer flocculant added to the solid material is the same, this two-stage addition method is more effective than the normal one-stage addition method.
It was confirmed that the strength of the flocs became much weaker and the dewaterability of the sludge deteriorated.

In addition, in this case, the same amount of polymer flocculant remains on the water side of the sludge as in the normal one-stage addition method, and the viscosity on the water side remains as high as in the one-stage addition method. This also causes deterioration of dehydration properties (mainly dehydration speed in this case).

In addition, as mentioned above, the strength of the flocs in the two-stage addition method is lower than that in the normal one-stage addition method, so in order to increase the strength of the sludge flocs, an even greater amount of polymer flocculant is added than in the case of one-stage addition. was added to the sludge, resulting in an even greater amount of polymer flocculant remaining on the water side, creating a vicious cycle.

The present invention solves these drawbacks, and the present invention is a method for adding and mixing a polymer flocculant to sludge to generate flocs, and then dewatering the flocs. It is a sludge treatment method characterized by adding and mixing cellulose powder and dewatering it, and the unreacted polymer flocculant remaining on the water side of the sludge that has formed flocs and wood flour or cellulose powder (hereinafter referred to as powdered The purpose of this method is to coagulate the sludge (substances referred to as "substances"), to make it possible to discharge separated water after sludge dewatering, and to improve the dewaterability of sludge.

To explain the present invention in detail below, the amount of polymer flocculant (usually about 2 to 30% based on the amount of solids in the sludge) is sufficient to form strong flocs in the sludge as in the conventional method. is added to the sludge and mixed to form flocs, and then a powdery substance is added to the sludge and mixed.

As the powdery substance used in the present invention, a suitable effect is recognized as long as it can undergo an aggregation reaction with the polymer flocculant.
If the particle size is too small, dehydration and filtration will be inhibited, so a particle size of about 0.1 mrn to 2 mm is optimal.

Further, the powdered substance to be added may be in the form of a powder or may be in the form of a slurry.

In the present invention, it is an important condition to add the powdered substance after the sludge has been flocculated as described above. At the same time, if a powdery substance is added and mixed as a coagulation aid, the number of substances that react with the polymer flocculant will increase by the amount added, which will not only increase the amount of polymer flocculant used, but also Since most of the powdered material coagulates with the solid content in the sludge and the polymeric flocculant, it is necessary to remove the unreacted polymeric flocculant remaining on the separated water side of the sludge after the powdery material has formed flocs. This is because we found that it becomes almost impossible to do so.

In the present invention, the time difference between adding the polymer flocculant to the sludge and then adding the powdered material after the mixing port varies from case to case, but first the polymer flocculant is added to the sludge and then the powder substance is added for 2 to 5 seconds. Continue stirring and mixing for about a minute to form flocs.

Any stirring method may be used.

Then, when it is determined that sufficient flocs have been generated for dehydration, the powdered material is added.

The amount of powdered material added varies depending on the properties of the sludge, the amount of polymer flocculant added, the type of powdered material, etc., but the optimum amount is such that the viscosity of the separated water after dewatering is equivalent to that of water conditioning. Generally, the optimum amount is added within the range of 5 to 50% of the solid substances in the sludge.

After adding the powdery substance, stir for 5 to 60 seconds, but as long as the powdery substance is dispersed in the sludge that has formed flocs, it is recommended to use the weakest stirring force possible so as not to destroy the flocs. preferable.

The stirring method here may be any method similar to the above-mentioned stirring.

By this stirring and mixing, the unreacted polymer flocculant and powdery substance remaining on the water side of the sludge that has formed flocs coagulate.

Immediately thereafter, the dehydration process begins, and a commonly used pressure dehydrator or the like is sufficient as the dehydrator used in this dehydration process.

The sludge cake after dewatering is then disposed of at a designated disposal site or incinerated.

Furthermore, if the main component of the sludge cake or the powdered adsorbent material added or mixed thereto has a high calorific value, it can be actively used as fuel or auxiliary fuel.

As explained above, according to the present invention, a polymer flocculant is added to sludge and mixed to form flocs, and then a powdery substance is added and mixed to prevent unreacted substances remaining on the separated water side of the sludge. Since the polymer flocculant and the powdered substance are flocculated, the unreacted polymer flocculant remaining on the water side of the sludge can be removed.

For this reason, it is possible to discharge the separated water after dewatering the sludge, and unlike conventional recycling methods, it is not necessary to add a polymer flocculant in two stages, so the strength of the flocs is greatly stabilized, and the sludge can improve dehydration properties.

In addition, the viscosity of the water in the sludge is significantly lowered by removing unreacted polymer flocculants, which primarily improves the dewatering speed during dewatering.

This improvement in dewatering performance is due to the simplification of the dehydrator,
Enables miniaturization and facilitates selection of dehydrator.

In addition, as explained in the prior art section, the conventional two-stage addition method of polymer flocculant using the recycling method is
If the addition amount is the same, the strength of the floc will be lower than that of the one-stage addition method, but according to the present invention, there is no need to use the recycling method, so there is no need to add the polymer flocculant in two stages, and the strength of the floc is lower. There are no sub-effects that would make it smaller.

In addition, if the separated water after dehydration contains a large amount of turbidity components, the separated water may be returned to the initial settling tank, etc. In this case, the separated water will contain almost no polymer flocculant. Because it is not recycled, it has many benefits, including eliminating the negative effects of conventional recycling methods.

Examples of the present invention are shown below.

Example 1 Mixed raw sludge generated from a sewage treatment plant (solid content concentration 4
．． 0%) was added to the sludge pipe at a rate of 8 kg/ton of dry solid cationic polymer flocculant Orufrock 5X-48 (trade name), stirred in the pipe for 15 seconds using pipe resistance, and then The flocculated sludge is taken into a rotating drum type agitator, and while rotating at a stirring speed of 3 rpm, 50 kg/) of wood powder having a diameter of 0.12 to 1 mm is added.
Added dry solids.

After continuing stirring with this stirrer for 30 seconds, the mixture was immediately supplied to a belt press type pressure dehydrator for dehydration.

In addition, as comparative examples, experiments were also conducted under the same conditions: ■ When only the polymer flocculant was added; ■ When the polymer flocculant was added after no wood flour was added; and ■ When the polymer flocculant and wood powder were added at the same time. The results are shown in Table 1.
Shown below.

Example 2 A cationic polymer flocculant Presedan C8-25 (trade name) 6 to 9/) was added to concentrated sludge (solid content concentration 3%), which is a mixture of anaerobic digested sludge and activated sludge generated from a human waste treatment plant.
70 kg of cellulose powder was prepared into a 10% slurry by adding dry solids and stirring for 60 seconds at a rotational speed of 50 rpm in a rotating drum type stirrer to form sludge flocs. was added and then stirred for 60 seconds.

Thereafter, it was immediately dehydrated using a filter press type dehydrator.

In addition, as comparative examples, under the same conditions, ■ when only the polymer flocculant was added, ■ when the polymer flocculant was added after adding cellulose powder, and ■ when the polymer flocculant and cellulose powder were added at the same time. conduct experiments,
The results are shown in Table-2.

Claims (1)

[Claims] 1. A sludge treatment method characterized by adding and mixing a polymer flocculant to sludge to generate flocs and then dewatering the sludge, which is characterized by adding and mixing wood flour or cellulose powder after generating flocs and dewatering the sludge. .