JPS5950398B2 - Wastewater treatment method using batch activated sludge method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wastewater treatment method using a batch activated sludge method, and in particular, increases and decreases the amount of aeration into the aeration tank and the internal pressure of the aeration tank as appropriate throughout the treatment period. The present invention relates to a wastewater treatment method using a batch activated sludge method that makes it possible to supply the required amount of oxygen to activated sludge at each point in time.

Conventional batch activated sludge methods include, for example, the oxidation method developed by Passfire, in which wastewater is introduced into a single tank that functions as both an aeration tank and a sedimentation tank, left to stand, and then aeration is performed. A limited aeration method (Nihon Kogyo Shimbun, October 5, 1978 issue), and a pressurized aeration method that pressurizes the aeration tank to increase the rate of oxygen transfer into wastewater and supply sufficient oxygen to activated sludge. Method according to [Kyoshi Shinohara,
Taiji Dan: Water Treatment Technology, Vol. 16, p. 449 (1975)
] etc. are known.

All of these conventional methods are excellent wastewater treatment methods, but when we examine their aeration methods in detail, we find that in each method, the maximum oxygen level during the wastewater treatment period is An aeration method of constant air flow operation is adopted in which oxygen is supplied from the start of the treatment in an amount corresponding to the amount of oxygen required at the time when the intake rate is indicated, and this state is maintained until the end of the treatment.

The oxygen uptake rate of activated sludge growing under batch conditions is
It shows a relatively low value in the early stages, but then gradually increases and reaches the maximum oxygen uptake rate after a certain period of time (usually 5 to 6 hours), after which it gradually decreases and becomes significant in the final stage. This decreases rapidly, and the intake of oxygen is only as much as is necessary for endogenous respiration.

Considering that there is a change over time in the oxygen uptake rate of activated sludge, various conventional batch activated sludge processes supply excess oxygen than is required by activated sludge during most of the treatment period. As a result, the actual situation is that the blower power is wasted.

The purpose of the present invention is to provide a wastewater treatment method that improves the above-mentioned drawbacks of the conventional batch activated sludge method, reduces the aeration ratio to the liquid to be treated, improves oxygen absorption efficiency, and enables efficient batch treatment. In particular, this makes it possible to treat wastewater that is discharged only during the daytime, such as in small and medium-sized factories, or wastewater that fluctuates over time, such as in food factories, at a high load in a small land area. It is something to do.

The present invention aims to improve the oxygen uptake rate of activated sludge by adjusting the amount of aeration to the aeration tank and the internal pressure of the aeration tank in order to obtain high-quality treated water under conditions of a small aeration ratio when treating wastewater using the batch activated sludge method. It was completed after confirming through experiments that it is sufficient to increase or decrease the amount in response to changes over time.

That is, the gist of the present invention is that when wastewater and activated sludge are introduced into a closed aeration tank and the wastewater is treated, the pattern of changes over time in the oxygen uptake rate of the activated sludge is measured in advance for each wastewater to be treated, and the A wastewater treatment method using a batch activated sludge method is characterized in that the amount of air flow to the aeration tank and the internal pressure of the aeration tank are controlled in accordance with the pattern.

Unlike conventional pressurized aeration systems, the present invention does not operate with the aeration volume and internal pressure of the tank fixed at the start of treatment until the end of treatment; By increasing and decreasing the internal pressure in a histogram manner using a pressure regulating valve and an exhaust valve attached to the aeration tank, the aeration magnification is reduced and the oxygen absorption efficiency is increased.

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

FIG. 1 shows a wastewater treatment device used in carrying out the present invention. In this figure, only one closed aeration tank 1 is shown, but it is also possible to provide multiple tanks. If so, it goes without saying that these can be operated at the same time, but if they are operated alternately, wastewater can be treated continuously.

Furthermore, if it is difficult to directly treat wastewater with activated sludge, it is preferable to provide a regulating tank for preliminary treatment.

Since the present invention is a batch-type wastewater treatment method, it can also be operated under heated conditions. Therefore, a heat insulating material or a heat insulating jacket is attached to the peripheral wall of the aeration tank 1 to prevent fluctuations in treatment capacity due to changes in temperature. is preferred.

The aeration tank 1 is equipped with a pressure gauge 11 and an exhaust valve 8 at its top, a treated liquid discharge valve 9 at a height of 172 to 1/4 from the bottom, and an excess sludge extraction valve 1 at its bottom.
It is equipped with 0.

The liquid to be treated is introduced by a pump 6 into the aeration tank 1 in which activated sludge that has been sufficiently acclimated to the liquid to be treated exists, and after this reaches a predetermined amount, the compressor 3 and the pressure regulating valve 4 are introduced.
An oxygen-containing gas (for example, air) is blown into the aeration tank 1 through.

In order to effectively carry out the present invention, the amount of aeration that corresponds to the oxygen uptake rate of the activated sludge existing in the aeration tank 1 after a certain period of time is estimated in advance, and this value is sequentially set.
It is usually necessary to vary the aeration rate 2 to 20 times during the entire treatment period.

For this purpose, the oxygen uptake rate at a predetermined BOD load on the liquid to be treated is measured, for example, in accordance with sewage test method i, and its changes over time are ascertained to determine the amount of aeration to the aeration tank and when to switch it. Confirmation is fundamental when implementing the present invention.

We also attempted small-scale batch processing using a small amount of liquid to be processed.
Calculate the α value, β value, dissolved oxygen, oxygen absorption efficiency, etc.', convert the oxygen uptake rate of activated sludge to the oxygen transfer rate in fresh water at 20℃, and further convert this to the air flow rate to determine the approximate aeration. Determining the amount is one method, and it is preferable to properly determine the amount of aeration based on this rough aeration amount in relation to the quality of the treated water.

Based on the above preliminary experiment, by adjusting the pressure regulating valve 4 and the exhaust valve 8, the aeration amount can be adjusted from 2 to 3 after the start of wastewater treatment.
The first aeration is performed at an amount that corresponds to the oxygen uptake rate of the activated sludge after a certain period of time.

Thereafter, by adjusting the pressure regulating valve 4 and the exhaust valve 8, the throughflow amount is set to an amount corresponding to the oxygen uptake rate of the activated sludge 3 to 4 hours after the start of treatment, and a second aeration is performed. Such aeration is sequentially performed a predetermined number of times.

□ The oxygen uptake rate of activated sludge gradually decreases at some point during the wastewater treatment period. is gradually decreased in response to the oxygen uptake rate.

When carrying out the present invention, the internal pressure of the aeration tank 1 is 0 to 10
．． 0 kg/cIT12G is adopted, but economically it is preferably 0 to 5.0 kg/cITI.G, more preferably θ to 3.0 kg/cm2G.

A mixed solution of 3.51 g of wastewater discharged from a food factory and 0.51 g of suspended water containing 24 g of activated sludge (initial BOD 1600 ppm) is placed in a closed aeration tank with a height of 300 mm and a diameter of 160 mm.
Table 1 shows the results when the method of the present invention and the conventional method using the pressurized aeration method were implemented.

FIG. 2 shows the increase/decrease fluctuations A and B in the aeration amount and the internal pressure of the aeration tank when the method of the present invention is carried out, as well as the progress C of BOD removal.

In summary, the present invention has provided a wastewater treatment method using a batch activated sludge method in which the amount of aeration is smaller than in conventional methods, and the quality of the resulting treated water is comparable to that of conventional methods.

[Brief explanation of the drawing]

Figure 1 shows an example of a wastewater treatment system for carrying out the present invention, and Figure 2 shows changes in the amount of ventilation into the aeration tank and the internal pressure of the aeration tank when the present invention is carried out. BOD
It shows the progress of removal. 1... Closed aeration tank, 2... Sand filter, 3
...Compressor, 4...Pressure regulating valve, 5...
Flow meter, 6... Pump, 7... Treated liquid supply valve, 8... Exhaust valve, 9... Treated liquid discharge valve, 10... Excess sludge extraction valve, 11... Pressure gauge .

Claims (1)

[Claims] 1. When introducing wastewater and activated sludge into a closed aeration tank and treating the wastewater, for each wastewater to be treated, the pattern of changes over time in the oxygen uptake rate of the activated sludge is measured in advance, and the aeration is performed in accordance with that pattern. A wastewater treatment method using a batch activated sludge method characterized by controlling the amount of aeration into the tank and the internal pressure of the aeration tank.