JPH01242199A - Controlling method for intermittent aeration in aeration tank - Google Patents

Abstract

PURPOSE:To make nitration operation and denitirification operation at a low load stage stable by suspending an aeration apparatus when an initial pH after aeration, which is sensed by a sensor, attains a predetermined value, and operating the aeration apparatus when an initial pH after the suspension attains a predetermined value. CONSTITUTION:A pH in an aeration tank 1 is sensed by a pH sensor 5 after sending an aerated liquid in the aeration tank 1 to a pH sensor box 2 with a suction pump 3. An electric voltage sensed by the pH sensor is amplified by an amplifier 4, and an aeration device 6 is controlled by a controller S. Aeration reaction does not proceed and nitrogen in a feed water is not removed when the pH is biased to one side in an intermittent operation in a same aeration tank since both nitration reaction and denitrification reaction are influenced by pH. Accordingly, the pH in an aeration tank is preferred to be 6.5-8.0. When the pH attains <=6.5, the aeration is suspended, and when it attains <=8.0, the aeration is resumed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for controlling intermittent aeration in an aeration tank.

(Prior art) In the conventional intermittent operation of an aeration tank, the adjustment between aeration and non-aeration can be achieved by measuring the dissolved oxygen concentration in the aeration tank with a DO sensor, or by adjusting the difference between aeration and non-aeration. This was done by setting a timer in advance.

(Problems to be solved by the invention) Current DO sensors suffer from deterioration of the oxygen permeable membrane, obstruction of oxygen permeation due to dirt on the membrane surface, deterioration of the lead electrode which is the cation electrode, and deterioration of the potassium chloride solution which is the internal electrolyte. Because of this, the reliability of the Do concentration measurement value was low, and the oxygen permeable membrane, lead electrode, and internal electrolyte had to be replaced frequently.In addition, setting a timer requires extremely low load. In this case, due to excessive aeration, only nitrification progressed unilaterally. That is,
The pH change in the aeration tank during intermittent operation is due to the nitrification reaction (1
) and denitrification reaction (2) as shown in Figure 1.

Nitrification reaction: NH: +20. →No; +H, O+2H1
,・,(1) Denitrification reaction + 2NO; +I OH → 4H
*o+2oH-10N*7...(2) However, at extremely low loads, as shown in Figure 2, the IJO in the aeration tank increases even during the same aeration period, and the aerobic time becomes longer, causing nitrification. As the disease progresses, the pH decreases. For this reason, an anaerobic region is not formed, and furthermore, the efficiency of the denitrification reaction decreases due to a decrease in pH, so that the conversion of nitrate ions to nitrogen gas does not proceed.

(Means for Solving the Problems) The present invention uses a PH sensor to repeatedly aerate and stop aeration in a nitrogen removal method using intermittent aeration.

As shown in equation (1), FIGS. 1 and 2, aeration causes the PH to decrease, and as aeration continues, the PH decreases to 5 or less as shown in FIG. 3.

When the pH is 5 or less, the denitrification reaction rate reaches the maximum value of about V5, and the desired value cannot be reached unless the reaction time is increased by 5 times.

Generally, the nitrification reaction takes place at a pH of 6.5 to 8, as shown in Figure 3.
．． 0. It is desirable that the denitrification reaction be carried out at a pH of 5° to 8.5.

Therefore, it is preferable to process at pH 5.5 to 8.0 in the same tank. In order to efficiently repeat the nitrification and denitrification reactions under these conditions, the pH of the aeration tank should be 0.2 to 0.5 below the initial pH value (usually 7°0).
Stop the aeration device when the temperature drops 1. In other words, after the nitrification reaction is stopped and the aeration is stopped, the pH becomes 8.0 due to the denitrification reaction.
When the pH reaches 0.2 or more or after the aeration stops
Operate the aeration system when the temperature rises by 0.5.

The PH sensor can be installed directly in the aeration tank, or as shown in Figure 4, in the PH sensor storage box 2.
There is a method in which a pump 3 is provided in the box to suck the aeration liquid from the aeration tank 1, but the latter method is preferable in order to prevent the PH sensor from becoming contaminated. The supply liquid sucked into the PH sensor storage box 2 may be the supernatant liquid of the sedimentation tank.

Since the pH at the beginning of aeration is normally 7.0, when aeration starts, P f (decreases) (but the denitrification reaction
As shown in the figure, at PH5,Q the reaction rate is at its maximum value of 5.
096, PHHO25 can be suppressed by 70% by 1
The lower limit was set to 6.8, and the upper limit was set to 6.8 in consideration of measurement errors, that is, aeration was stopped when the pH decreased by 0.2 to 0.5. Further, since the pH increase value after the aeration is stopped is required to be repeated in the neutral range, it was similarly set to 0.2 to 0.5.

(action).

Both nitrification and denitrification reactions are affected by pH, as shown in Figure 3. In intermittent operation in the same tank, if the pH is one-sided, the reaction will not proceed, so nitrogen in the raw water will not be removed. For this reason, the pH inside the tank must be kept in the neutral range as shown in Figure 3.

The PH sensor is for keeping the pH inside the tank in the neutral range. When aeration is performed, the PH in the tank decreases as shown in equation (1), so the PH value after aeration is between 0.3 and 0.
．． 5 or below 6.5, stop aeration and switch to denitrification reaction. In the denitrification reaction, the pH increases by 1 as shown in equation (2), and after the aeration stops, the pH value decreases to 0.
Start aeration when the temperature rises by 2 to 0.5 or reaches 8.0 or higher. This operation is controlled by P1 (sensor) and repeated to keep the pH inside the tank in the neutral range.

(Example) An example of the present invention will be described below based on FIGS. 1 to 5.

The aeration liquid in the aeration tank 1 is sent to the PH sensor storage box 2 by the suction pump 3, and the PH in the aeration tank is detected by the PH sensor 5.

The voltage detected by the PH sensor is amplified by the amplifier 4, and the aeration device 6 is controlled by the controller 8.

A tap water 7 pipe for cleaning the PH sensor 5 is permanently installed in the PH sensor storage box 2.

Figure 1 shows that the intermittent operation of aeration/aeration stop for a set time under the design load allowed sufficient time for nitrification and denitrification, making it possible to remove nitrogen in the same tank.

Figure 2 shows the intermittent operation of aeration/aeration stop according to the set time at low load, but because of the low load, Do inside the tank increases during aeration, and even if aeration is stopped, the inside of the tank remains anaerobic. It took time to reach this state, and the set aeration stop time was too short for anaerobic time, resulting in insufficient denitrification reaction time and insufficient nitrogen removal.

In Fig. 2, when the aeration device is stopped at pH 5.8 using the PH sensor and started at pH 7.0, the O pattern as shown in Fig. 5 is obtained, and the nitrification time is
The denitrification time could be set in the same manner as shown in Figure 1, making it possible to remove nitrogen.

(Effects of the Invention) The present invention achieves the following effects with the above configuration.

1) Stable nitrification and denitrification time can be provided in the tank even under low load, making it possible to remove nitrogen.

2) By using a PH sensor, there is no membrane deterioration like in conventional Do sensors, and it can withstand long-term use.

[Brief explanation of the drawing]

Figure 1 shows the DO and PH changes in the aeration tank under the design load, and Figure 2 shows the DO and P in the aeration tank under low load.
Figure 3 shows the influence of PH on nitrification and denitrification rates, Figure 4 shows the flow sheet when installed in an aeration tank, and Figure 5 shows P at low load.
Glue when the aeration device is controlled by the H sensor. It is a figure showing the change of and PH. Explanation of symbols

Claims (1)

[Claims] 1. In an aeration tank control method that repeatedly performs intermittent aeration/aeration stop operations, the pH in the aeration tank or sedimentation tank is detected by a PH sensor, and the initial pH value after aeration is detected. Stop the aeration device when the pH value decreases by 0.2 to 0.5 or below 6.5, and when the pH value increases by 0.2 to 0.5 from the initial pH value after stopping the aeration or when the pH A method for intermittent aeration control of an aeration tank by PH sensor control, characterized in that the operation of operating an aeration device is repeated when the value becomes 8.0 or more.