JPH03157196A - Treatment of organic sewage - Google Patents

Abstract

PURPOSE:To obtain a sludge treatment method to decrease excess sludge by subjecting org. sewage to a solid-liquid sepn. after an aerobic biological treatment, then making the separated sludge alkaline and agitating and stagnating the sludge for a prescribed period of time and supplying the sludge to an aerobic biological treatment stage to lower the pH of the sludge. CONSTITUTION:The sewage 1 passes thereof an aeration stage 2, flows into a solid- liquid sepn. stage 4 and a part of the separated activated sludge 5 is made into the excess sludge 7. The remaining greater part is added with an alkaline agent 9, such as NaOH, to have about pH9 to 12 alkalinity. The sludge is introduced to an agitating tank 10 and is agitated for about 2 to 60 minutes under such conditions; thereafter, the sludge is recycled to the aeration stage 2. The extracellular polymers of microorganisms are produced when the recycled activated sludge is made alkaline and the eluted biopolymers are metabolized to the activated sludge by the microorganism in the aeration stage 2. A certain change arises in the metabolism of the microorganisms and the propagation rate decreases if the cycle of making the activated sludge alkaline, then returning the sludge to low pH is repeated. The treating method for the org. sewage which drastically decreases the amt. of the excess sludge to be generated is obtd. by this method.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to sewage, human waste, garbage exuding sewage, septic tank mud,
A new biological treatment method for organic wastewater such as various industrial wastewater,
In particular, the present invention relates to a method for significantly reducing the amount of surplus sludge that inevitably occurs with aerobic biological treatment.

[Conventional technology]

Conventionally, activated sludge methods and nitrification-denitrification methods have been widely used as typical aerobic biological treatment methods for organic wastewater.

[Problem to be solved by the invention]

However, the biggest problem with the conventional aerobic biological treatment method for organic wastewater is that it generates a large amount of surplus sludge and has poor dewatering properties. Therefore, processing and disposal of surplus sludge requires a large amount of expense and equipment.

An object of the present invention is to provide a new process that can significantly reduce excess sludge generated during aerobic biological treatment of organic wastewater.

[Means to solve the problem]

In the present invention, organic wastewater is subjected to aerobic biological treatment, then solid-liquid separated, an alkaline agent is added to the separated sludge, and the separated sludge is stirred and retained for a predetermined time under alkaline conditions, and then supplied to the aerobic biological treatment process. This is a method for treating organic lη water, which is characterized by lowering the pi+ of cough lη mud.

[For production]

The effects of the present invention will be explained in the first section by taking activated sludge treatment of sewage as an example.
This will be explained in detail below with reference to the figures.

The sewage 1 is led to the aeration process 2, where it is aerated by the blower 3 for the required time in the coexistence of BOD-assimilating bacteria, and then flows into the solid-liquid separation process 4 where activated sludge is separated and separated into separated activated sludge 5. This becomes treated water 6.

In this solid-liquid separation step 4, in addition to precipitation separation, known means such as flotation, centrifugation, and membrane separation can be employed.

Now, while a part of the separated activated sludge 5 is supplied as surplus sludge 7 to the sludge dewatering step 8 and dehydrated, the separated activated sludge 5
The remainder, which is the majority of
is added, and under the alkaline conditions, the mixture is led to the stirring tank 10 and stirred for about 2 to 60 minutes, and then recycled to the aeration step 2.

This recycling process of the separated activated sludge 5 is the most important point of the present invention. Separated activated sludge 5 after addition of alkaline agent 9
The pH of is alkaline, but if the pH is less than 9, the desired effect of reducing excess sludge will be small.
It is preferable to set it in the range of H9-12. Alkaline agent 9
The stirring time after addition is important; if it is too short, it will be difficult to obtain an effect, and if it is too long, the activity of the activated sludge will deteriorate.

Since the appropriate stirring time varies depending on the type of raw water to be treated and the properties of the active 7η mud, it is necessary to determine it in advance by experiment. Roughly speaking, 5-120
Often within the range of minutes.

In cases where the amount of inflow water is large, such as in sewage treatment, methods other than precipitation (membrane separation, centrifugation, etc.) cannot be used for solid-liquid separation of activated sludge due to economic constraints due to the high power cost. However, the sludge concentration in sedimentation separation is usually 1 to 2%.
If the alkaline agent 9 is added directly to this waste sludge, the amount of alkaline agent 9 required to maintain the required p)I will be reduced because the amount of water on the receiving side is large. A big practical problem arises in that the amount of energy increases.

This problem can be solved by introducing a new method in which the waste sludge after sedimentation is reduced to a solid content of about 4 to 6% using a centrifugal concentrator, and then an alkali agent is added.

The separated activated sludge 5 to which the alkaline agent 9 has been added and stirred for a predetermined time in the stirring tank 10 is recycled to the aeration process 2, where it is uniformly mixed with a large amount of activated lη mud in the aeration process 2 and diluted. At the same time, the H present in the aeration process 2
°Ions lower the pH. pH in aeration step 2
Since the separated activated sludge 5 to which the alkaline agent 9 has been added flows in, the pH of the separated activated sludge 5 normally rises a little higher than the pH of the inflowing sewage droplets, but the separated activated sludge 5 has a circulation system of high pH-0 low PU. It will be a cycle.

In this way, it has been experimentally shown that when activated sludge is subjected to a circulation system in which high pl=O and low pl+, the amount of surplus sludge generated is reduced to 2/3 to 1/2 of the conventional activated sludge method. was confirmed. This reduction in the amount of surplus sludge generated is due to the fact that the recycled activated sludge is made alkaline.
The extracellular polymer of the microorganisms is eluted, the eluted biopolymer is assimilated by the microorganisms in the aeration step 2, and when the cycle of making the activated sludge alkaline and then returning it to low pH (neutral) is repeated, the microorganisms are It is presumed that this is due to some change in metabolism and a decrease in the proliferation rate.

〔Example〕

Examples and comparative examples of the present invention will be described below.

Overflow sewage of the first settling tank of the present invention (BOD 120-180■/β
SS 130-180■/1) is supplied to the aeration tank, aeration time is 6 hours, activated sludge MLSS 1800-2500■
Activated sludge treatment was carried out at /l. Thereafter, the activated sludge discharged from the aeration tank was introduced into a settling tank (water area load: 12 m/m/day) and separated by precipitation to obtain settled sludge (solids concentration: 1.1 to 1.4%).

Most of this settled sludge R (m/day) was added with Na0tl to set the pH to an alkaline condition of about 10 to 12, stirred for about 5 to 20 minutes, and then recycled to the aeration tank.

Here, the set flow rate of R was determined by the following equation.

γ-Madashi, Q... Sewage flowing into the aeration tank 1 (m/day) Q4...
Excess sludge removal! <m/day) (kg/kir) As a result of continuing operation for one month under these conditions, the pH of the aeration tank was
is 7.6 to 8.2, the water quality of treated sewage, which is the settling tank effluent, is BOD 13 to 22 呵/β, 5S 23 to 33 ■/1, and excess sludge generation is 0.033 to 0.037 kzss.
/11 (・It was sewage. Also, the SVI of activated sludge is 1.
20 to 135, and the sedimentation 'I:i shrinkability was excellent.

Comparative Example A treatment experiment was conducted under the same conditions as in the example of the present invention except that the addition of NaOH to the settled Fl sludge and the stirring step were omitted, and the water quality of the treated sewage was the same except for the pH. However, the amount of surplus sludge generated was 0.1 to 0.
15 kgSS/n?・The amount of wastewater was significantly larger than that of the present invention. Also, the svr of activated sludge is 22
0 to 235, indicating that the precipitated Ls concentrating property was inferior to that of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, high pi+-5
By experiencing the low 1) H circulation system, the amount of surplus sludge generated can be significantly reduced, and the dewatering performance of lη mud can be improved, making it extremely easy to process and dispose of surplus lη mud. .

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. 1...Sewage, 2...Aeration process, 3...Blower-1
4... Solid-liquid separation step, 5... Separated activated sludge, 6...
- Treated water, 7... Surplus lη mud, 8... Sludge dewatering process, 9... Alkaline agent, 10... Stirring tank.

Claims (1)

[Claims] (1) After subjecting organic wastewater to aerobic biological treatment, solid-liquid separation is performed, an alkaline agent is added to the separated sludge, and the separated sludge is stirred and retained for a predetermined period of time under alkaline conditions, after which it is supplied to the aerobic biological treatment process. A method for treating organic sewage, characterized by lowering the pH of the sludge.