JPH07214089A - Waste water treatment - Google Patents

Abstract

PURPOSE:To effecively utilize the residual biological activity of excess sludge to lower BOD, etc., and to improve the efficiency in treating waste water by adding the excess sludge generated after activated-sludge treatment to the raw water in the initial settling basin while the biological activity of the excess sludge still remains. CONSTITUTION:Raw waste water is transferred from the initial settling basin to the final settling basin through an aerator. A part of the activated sludge separated from liq. in the final settling basin is recycled as return sludge in accordance with the operational condition of the aerator. Meanwhile, the remainder of activated sludge is dehydrated as return sludge, used in reclamation or incinerated. In this case, the excess sludge is added to the raw waste water in the initial settling basin when the biological activity of the sludge still remains. Consequently, the residual biological activity of the excess sludge is effectively utilized, BOD, etc., are lowered, and the efficiency in treating waste water is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a wastewater treatment method by the activated sludge method.

[0002]

2. Description of the Related Art Usually, in the wastewater treatment by the activated sludge method, a standard activated sludge method, a dispensing method, a complete mixing method, a re-aeration method and the like are used. In both cases, the main process is to pass the raw wastewater from the first settling tank to the final settling tank through the aeration tank.The activated sludge that is solid-liquid separated in the final settling tank is partially returned according to the operating conditions of the aeration tank. It is reused as sludge, but the rest is discharged as excess sludge to the sludge treatment process, and is dehydrated for landfill or incinerated.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to the use of surplus sludge from activated sludge wastewater treatment, and aims to improve the efficiency of wastewater treatment by fully utilizing the biological activity of excess sludge. It is intended.

[0004]

DISCLOSURE OF THE INVENTION It has been found that the present invention has an effect of mainly reducing numerical values such as BOD by simply adding excess sludge to raw wastewater without using means such as aeration. It has been completed.

[0005] Usually, in the wastewater treatment by the activated sludge method, operating conditions are set so as to keep the MLSS in the aeration tank substantially constant. Therefore, the generation of excess sludge is unavoidable. If all the activated sludge generated in step 2 is returned to the aeration tank, the retention time in the tank required for biological treatment will be shortened, and the amount of aeration will be insufficient and the amount of oxygen for living organisms will be insufficient. ,
On the contrary, the processing performance decreases.

[0006]

EXAMPLE The present invention is to maintain the aeration tank under the correct operating conditions, add excess sludge to the raw wastewater entering the first settling tank, mix it, and utilize the residual biological activity during the retention in the first settling tank. By reducing the load components in the drainage by
It improves the efficiency of wastewater treatment.

Therefore, the excess sludge can be added and mixed anywhere before the entrance of the sedimentation tank, and it can be easily handled by joining pipes or the like. When the pump is first used to transfer the liquid to the settling tank, joining to the inlet of the pump is preferable in terms of uniform mixing, but it is not limited to this.

During the initial residence time in the settling tank, the biological activity is maintained for a time period within which dissolved oxygen is effective, and the load components in the wastewater are biologically treated.
In D, there is a reduction of about 10 to 30%. This varies depending on the mixing ratio of excess sludge, water temperature, and residence time.

[Example 1] The results of the table test show that, when 5% by volume of excess sludge was added to the mixed wastewater of paper and board, 26.3% by residence time 1 hour,
When 31.7% was added in 2 hours and 10% was added, a BOD cut rate of 30.3% in 1 hour and 38.5% in 2 hours was obtained. The BOD of raw wastewater is 100 mg / l.

[Embodiment 2] The results of the table test show that the paperboard-based clarifter treated water (the original wastewater COD260
(mg / l), when 2% by volume is added, the residence time is 13.8% for 1 hour, 27.9% for 2 hours, and for 4%, the same is 15.3% for 1 hour and 2 hours. 29.4%
The COD cut rate of was obtained.

[Embodiment 3] The results of the table test show that wastewater from the waste paper pulp treatment process (raw wastewater COD 640 m
g / l), when 4% by volume% is added, the residence time is 4.7% for 1 hour, 3.1% for 2 hours, and 8% is added.
Similarly, 10.9% CO for 1 hour and 14.1% CO for 2 hours
The D cut rate was obtained.

[0012]

According to the present invention, since excess sludge can be effectively utilized and BOD and COD components can be reduced by a prior mixing process prior to the activated sludge process by a regular aeration tank, the aeration tank can be used. It is possible to reduce the load on the wastewater and increase the efficiency of the wastewater treatment process.

Claims (1)

[Claims] 1. Excess sludge generated after treatment of activated sludge is added to raw wastewater in the first settling tank of the activated sludge treatment process while the biological activity remains, and the residual biological activity of the excess sludge is utilized. A wastewater treatment method characterized by: