JPH047094A - Treatment of excessive sludge in activated sludge treatment - Google Patents

Abstract

PURPOSE:To effectively reutilize inorg. activated sludge solid carriers by circulating the same by concentrating and dehydrating the excessive sludge generated in the activated sludge treatment using the inorg. activated sludge solid carriers to incinerate the same and subsequently returning the obtained incineration ash to an aeration tank. CONSTITUTION:The excessive sludge generated from activated sludge treatment using inorg. activated sludge solid carriers is separated into overflow and underflow by a liquid cyclone. The underflow is returned to an aeration tank as it is and the overflow is conc., dehydrated and incinerated to obtain incineration ash which is, in turn, returned to the aeration tank. Concretely, about 85-98% of the carriers and about 50-70% of activated sludge can be introduced into the underflow and about 2-15% of the carriers and about 30-50% of activated sludge can be introduced into the overflow. By this method, almost 100% of the inorg. activated sludge solid carriers can be recovered and the treatment cost of waste water can be reduced to a large extent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for treating surplus sludge generated when an inorganic activated sludge immobilization carrier is used in activated sludge treatment of wastewater, etc.

(Prior art) For example, JP-A-63-42796 and JP-A-63-
As shown in Publication No. 126599, as a method for biologically treating wastewater, etc., activated sludge is treated in an aeration tank containing activated sludge, and then activated sludge and treated water are separated by sedimentation, and the treated water is discharged. However, it is known that the settled sludge can be reused in an aeration tank.

In the aeration tank, activated sludge is extracted from wastewater. ), phosphorus compounds, ammonia compounds, etc., but the amount of activated sludge increases with the treatment, so it is necessary to separately treat it as excess sludge.

Traditionally, this surplus sludge has been treated by:
After thickening and dewatering excess sludge, use it as is for landfill, etc.
The waste was digested and decomposed through methane fermentation to reduce its weight and then used for landfilling, etc., or it was incinerated and the incinerated ash was used for landfilling.

(Problem to be solved by the invention) By the way, Japanese Patent Laid-Open No. 63-42796 and Japanese Patent Laid-open No. 63
As shown in Publication No. 126599, recently, in order to improve the efficiency of activated sludge treatment in an aeration tank, a method has been adopted to immobilize activated sludge and increase its concentration by adding an inorganic carrier. It's becoming like this. Examples of the inorganic activated sludge solidification carrier include granulated blast furnace, zeolite, silica sand, and cristobalite.

When these inorganic activated sludge solidification carriers are used, the carrier is also included in what is separated as surplus sludge. In this case as well, if the excess sludge is treated as described above, it is difficult to reuse the solidified carrier, and there is a problem that the running cast of the solidified carrier becomes high.

The present invention provides a method for treating surplus sludge by reusing the carrier when an inorganic activated sludge immobilization carrier is used in activated sludge treatment of wastewater or the like.

(Means for Solving the Problems) The present invention is characterized in that surplus sludge generated from activated sludge treatment using an inorganic activated sludge immobilization carrier is concentrated, dehydrated and then incinerated, and the incinerated ash is returned to the aeration tank. A method for treating surplus sludge in activated sludge treatment, and separating surplus sludge generated from activated sludge treatment using an inorganic activated sludge immobilization carrier into overflow and underflow using a liquid cyclone, returning the underflow as it is to the aeration tank, Overflow is a method for treating excess sludge in activated sludge treatment, which is characterized by thickening, dehydrating, incinerating, and returning the incinerated ash to the aeration tank.

(Function) When inorganic immobilization carriers such as granulated blast furnace, zeolite, silica sand, cristobalite, etc. are added to the aeration tank of uniformly mixed activated sludge treatment, treatment efficiency can be improved by shortening treatment time, and the quality of treated water can be improved. In addition, the dewaterability of excess sludge is improved. For example, if 3% by weight of granulated blast furnace sludge is added to the aeration tank based on the aeration Wi capacity, excess sludge will be dehydrated in vacuum with the addition of a commercial molecular flocculant, resulting in a cake with a moisture content of approximately 60%. 6. The moisture content of the cake when granulated blast furnace water is not added is about 85 to 90%.

In addition, surplus sludge from activated sludge treatment using a non-1F1 immobilized carrier such as blast furnace granulation is processed using a liquid cyclone to
98% of the inorganic immobilized carrier is recovered. That is, when surplus sludge is treated with a liquid cyclone, it is separated into an underflow and an overflow, and the underflow has a higher concentration of blast furnace water granulation and a lower concentration of organic sludge than the overflow. Therefore, the underflow is returned to the aeration tank as return sludge, and the overflow is treated as surplus sludge. In addition, using granulated blast furnace water as an inorganic immobilization carrier,
Table 1 shows an example of recovering blast furnace granules from excess sludge using a liquid cyclone.

Table 1 Liquid cycling from sludge containing granulated blast furnace granules In this way, a cake with a low moisture content can be easily obtained from surplus sludge to which an inorganic immobilization carrier such as granulated blast furnace sludge has been added using a vacuum dehydrator or the like.

In addition, as explained above, it is difficult to recover inorganic immobilized carriers using conventional surplus sludge treatment methods, and if inorganic immobilized carriers are disposed of, the cost of wastewater treatment will increase. For this reason, inorganic immobilization carriers are as shown in Table 1.
Although most of the wastewater is recovered by cyclones, it is necessary to significantly increase the recovery rate in order to further reduce the cost of wastewater treatment.

Therefore, as a result of examining methods to increase the recovery rate of inorganic immobilized carriers, it became clear that the optimal method was to burn the excess sludge and the dehydrated cake of the overflow water of the hydrocyclone.

The dehydrated cake containing the inorganic immobilization carrier has a moisture content of 60
Since the amount of heavy oil used as a combustion improver is significantly lower than that of a dehydrated cake that does not contain an inorganic immobilization carrier, it is difficult to determine whether the incineration ash can be used again as an activated sludge immobilization carrier. There's a problem. Therefore, we measured the particle size distribution of surplus sludge containing blast furnace granules before and after incineration.
Incineration Mif is 20-200μm, 50% average particle size is 6
Incineration ash is 10-200μm, 5()% for 5μm
The average particle size is 55 μm, which is slightly finer. With this level of fineness, there is almost no carryover from the sludge settling tank even when it is used as an immobilization carrier for activated sludge.
Furthermore, the immobilization performance of activated sludge did not deteriorate, but rather tended to improve.

From these facts, the method of the present invention allows for easy treatment of surplus sludge from homogeneous mixed activated sludge treatment using inorganic immobilization carriers, and also allows for recovery of almost 100% of the inorganic immobilization carriers. This will greatly reduce the cost of wastewater treatment.

In the present invention, excess sludge is concentrated, dehydrated, and then incinerated, and the incinerated ash is returned to the aeration tank for reuse. The inorganic activated sludge solidification carrier undergoes almost no change even when incinerated, so it can be reused as is. Furthermore, about 20% of the activated sludge ash remains, but this will be incorporated into the activated sludge if it is added to the aeration tank, so it is sufficient to simply return the entire incinerated ash to the aeration tank.

In this way, it is possible to reuse the solidified carrier by simply returning the incinerated ash to the aeration tank, but in order to reduce the incineration cost, it is necessary to separate the excess sludge into overflow and underflow using a liquid cyclone. The underflow can be directly returned to the aeration tank, the overflow can be concentrated, dehydrated and then incinerated, and the incinerated ash can be returned to the aeration tank.

Liquid cyclone (underflow 1) can have a high carrier content, and overflow can have a high sludge content, for example, about 85 to 98% of the carrier and about 5 to 70% of the activated sludge. Place in underflow, about 2 to 15% of carrier and 30 to 50% of activated sludge
degree can be put into overflow. Therefore,
The underflow containing a large amount of carrier is directly returned to the aeration tank, and only the overflow containing a large amount of sludge is concentrated.
If the sludge is dehydrated and incinerated, and the incinerated ash is returned to the aeration tank, the amount to be incinerated will be small, allowing surplus sludge to be disposed of and the carrier to be reused.

Next, Examples 6 (Example) of the present invention will be described Example 1 In activated sludge treatment using granulated blast furnace granules as an immobilization carrier for activated sludge, granulated blast furnace granules were used in an amount of 3% by weight based on the aeration tank capacity. The initial input was used to treat sewage. This treatment equipment generates surplus sludge of approximately 3 (6 (Ig) on dry matter basis) per 1 m' of sewage, and its concentration is approximately 20,0OOn6H/1 (organic sludge:
Approximately 6000mg/l, blast furnace granulation: approximately 14,000+u
r/l).

After adding ferric chloride as a flocculant and calcium hydroxide as a flocculating aid to this excess sludge, it was dehydrated by vacuum dehydration sprinkling, resulting in a cake with a moisture content of 60.5%. The waste was incinerated at ~600°C, and the incinerated ash was returned to the aeration tank for activated sludge treatment of sewage.6 As a result,
No incineration ash was observed in the treated water, and there was no decrease in treatment efficiency or treated water quality, showing treatment performance equivalent to that of blast furnace granulation that was initially introduced. In addition, the particle size distribution of the initially charged blast furnace granulated water is 20 to 200 μm, and the 50% average particle size is approximately 65 μm.
In contrast, the particle size distribution of incinerated ash is 15~2 +
The particle size is 10 μm, and the 50% average particle size is approximately 55 μm, which is slightly finer.

Example 2 In activated sludge treatment using granulated blast furnace granules as an immobilization carrier for activated sludge, 3% by weight of aerated ffi' was initially added to the granulated blast furnace granules to treat dead water. Approximately 61 g of concentrated #ri:"j mud (corresponding to the undiluted solution in Table 1) per 1 + n" of F water is extracted from the sludge settling tank of this treatment plant, and this is treated with a hydrocyclone to recover blast furnace granules. I did it. The properties of the stock solution supplied to the hydrocyclone, underflow and overflow are shown in Table 1. The underflow was returned to the aeration tank as return sludge.

When iron chloride and calcium hydroxide were added to the overflow surplus sludge and dehydrated using a vacuum dehydrator, the water content was 6.
A 6% cake was obtained. 500-600 for this cake
'C to obtain incineration ash. This incinerated ash has a particle size distribution of 10 to 200 μm and a 50% average particle size of 55 μm, which is slightly fine.

As a result of recycling and using only incinerated ash without supplementing granulated blast furnace granules, no deterioration in the treatment efficiency of activated sludge treatment or the quality of treated water was observed, and it was clear that incinerated ash could be used as an activated sludge immobilization carrier for 1 minute. Became.

(Effects of the Invention) According to the present invention, the inorganic activated sludge solidification carrier can be effectively circulated and reused while disposing of surplus sludge, and the running cost of the carrier can be reduced. Further, since the process does not require expensive equipment such as methane fermentation and requires a lot of work to bury the sludge, the cost of processing the excess sludge itself is low.

Claims (3)

[Claims] (1) A method for treating surplus sludge in activated sludge treatment, which comprises concentrating, dewatering, and incinerating surplus sludge generated from activated sludge treatment using an inorganic activated sludge immobilization carrier, and returning the incinerated ash to an aeration tank. (2) Excess sludge generated from activated sludge treatment using an inorganic activated sludge immobilization carrier is separated into overflow and underflow using a liquid cyclone, the underflow is returned to the aeration tank as it is, and the overflow is concentrated, dehydrated, and then incinerated. A method for treating surplus sludge in activated sludge treatment, characterized by returning incinerated ash to an aeration tank. (3) The method for treating surplus sludge in activated sludge treatment according to claim 1 or 2, wherein the inorganic activated sludge immobilization carrier is granulated blast furnace.