JPS61171598A - Treatment of separated solution from digestion tank - Google Patents

Abstract

PURPOSE:To reduce the concn. of the org. substance of return water, by returning the separated solution separated from digested sludge in a digestion tank to a gravitational concn. tank along with the withdrawn sludge from a first sedimentation basin. CONSTITUTION:The separated solution of a digestion tank 15 is charged in a gravitational concn. tank along with the withdrawn sludge 8 from a first sedimentation basin 6. The high concn. separated solution of the digestion tank 15 is diluted to concn. receiving no sedimentation interference by the withdrawn sludge 11 from the first sedimentation basin 4 being the inflow sludge of the gravitational concn. tank 12 and excessive sludge 10. Flocs of sludge are formed so as to be grown on the solids contained in the separated solution as nuclei to promote the solid-liquid separation of the gravitational concn. tank 12. Therefore, the generation amount of digestion gas is increased to promote digestion.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for treating a digester separated liquid in a sewage treatment facility that employs a digestion method for sludge treatment.

[Conventional technology]

In general, many sewage treatment plants use the digestion method for sludge treatment, and a typical flow is shown in Figure 2. To explain this, the inflow water (1) and the return water (2) from the sludge treatment system are combined and flow into the first settling tank (4) as the first settling tank inflow water (3). Solid-liquid separation is performed in the first settling tank (4), the liquid phase is sent to the aeration tank (5), and the solid phase is transferred to the first settling tank drawn sludge (11).
It is discharged as. The liquid phase is stored in an aeration tank (5
In step 1, it is subjected to biological treatment using an activated sludge method, and solid-liquid separation is carried out in the final settling tank (6). This liquid phase is sterilized and discharged outside the facility as effluent water (7). The solid phase is discharged as sludge drawn from the final settling tank (8) and divided into sludge (9) returned to the aeration tank (5) and surplus sludge (10). The sludge drawn from the initial settling tank (11) and the excess sludge (10) are stored in the gravity thickening tank (12).
), and the liquid phase is returned to the water treatment system as gravity thickener overflow water (13). The solid phase is gravity thickened sludge (14)
The sludge is discharged as sludge and put into the digestion tank (15), where the sludge is mineralized and solid-liquid separated. The liquid phase after the solid-liquid separation is returned to the water treatment system as a desorbed liquid (16), and the solid phase is discharged as digested sludge (17). This lη mud is then subjected to treatments such as dewatering, drying, and incineration.

In a sewage treatment plant with the treatment flow described above, it is said that the return load from the sludge treatment system affects the water treatment system, causing deterioration of the quality of the effluent water.

According to the results of an investigation by the inventors into the factors contributing to variations in organic matter concentration in effluent water at a certain sewage treatment plant, as shown in Table 1, approximately 60% of the variation was due to return water from the sludge treatment system. Among these, it was found that the influence of the amount of the digester desorbed liquid or the amount of solids contained therein is extremely large.

Table 1 Factors for variation in organic matter concentration in effluent water [Problems to be solved by the invention] As mentioned above, in the conventional method, the digester desorbed liquid (16
) are non-biodegradable
Since this desorbed liquid (16) is returned to the initial settling tank (4), it places a heavy burden on the water treatment system and has a large effect on the quality of the effluent water.

The purpose of the present invention is to reduce the mobile concentration in return water in sewage treatment equipment that uses a digestion method for sludge treatment, and to prevent the impact of return load on the quality of effluent water. be.

[Means for solving problems]

The present invention provides the aforementioned sewage treatment equipment in which the digester desorbed liquid is charged into the gravity thickening tank along with the sludge drawn from the initial settling tank, thereby promoting solid-liquid separation in the gravity thickening tank. be able to·
11 [Example] Hereinafter, the present invention will be explained based on the example shown in FIG. 1.The difference between the present invention and the conventional treatment method is that
Conventionally, the desorbed liquid (16) of the digester (15) is directly returned to the water treatment system as return water (2), but in the present invention, the desorbed liquid (16) of the digestion tank (15) is first returned to the sedimentation tank (6). Sludge extracted from (8)
At the same time, it is also put into the gravity concentration tank (12). Other processing flows are the same as before.

[Effect]

By configuring this way, a high-concentration digestion tank (1
The desorbed liquid (16) of 5) flows into the gravity concentration tank (12).
Sludge (11) drawn from the initial settling tank (4), which is η mud;
The excess sludge (10) is diluted to a concentration that does not interfere with sedimentation, and the solids contained in the desorbed liquid (16), such as minerals and sediment, become cores and form sludge flocs. Solid-liquid separation in the gravity concentration tank (12) can be promoted.

Therefore, the concentration of gravity-thickened sludge increases, which increases in the digester (
15), the amount of digestive gas produced increases and digestion is promoted.

In addition, undecomposed organic matter in the desorbed liquid (16) tends to settle due to the above-mentioned reasons.
Compared to the case where the desorbed liquid (16) is directly returned to the water treatment system, the proportion of undecomposed organic matter returned to the water treatment system is reduced, the return load to the water treatment system is reduced, and the quality of the effluent water is improved. It will improve.

In addition, it is not conceivable that there would be any inconvenience caused by changing the conventional sewage treatment system due to such a change in the treatment flow.

〔Effect of the invention〕

As described above, the present invention provides the following effects.

■ Solids load in the initial settling tank is reduced.

■ The desorbed liquid with a high concentration of solids is diluted, and inorganic substances and sediments, which are originally easy to settle, settle out, and these become cores to form flocs, increasing the sedimentation property of the gravity thickening tank.

■ By diluting the desorbed liquid with a high concentration of solids, undecomposed organic matter becomes easier to settle, reducing the impact on water treatment and systems, and improving the quality of the effluent water.

[Brief explanation of the drawing]

FIG. 1 is a processing flowchart of the method according to the present invention;
The figure is a processing flowchart of the conventional method (1): Inflow water (2): Return water (3): Inflow water to the primary sedimentation tank + 4): Flt primary sedimentation tank (5): Aeration tank (6): Final settling tank (7): Effluent water (8): Sludge drawn from the final settling tank (9): Returned sludge (10): Surplus sludge (11): Sludge drawn from the first settling tank (12): Gravity thickening tank (13): 'Overflow water from gravity thickener (14):
Gravity thickening sludge (15): Digestion tank (16): Desorption liquid (17): Digested sludge

Claims (1)

[Claims] 1. A primary sedimentation tank that stores inflow water, an aeration tank that biologically processes the liquid phase from the primary sedimentation tank using the activated sludge method, and a final sedimentation tank that separates solid-liquid inflow from the aeration tank. , in a sewage treatment facility equipped with a gravity thickening tank for concentrating the sludge drawn from the first settling tank, and a digestion tank for digesting the gravity thickened sludge concentrated in the thickening tank, the digested sludge is decomposed in the digestion tank. A method for treating digested and desorbed liquid, characterized in that the separated desorbed liquid is returned to a gravity thickening tank together with the sludge drawn from the initial settling tank.