JPS6221597B2 - - Google Patents

Description

[Detailed description of the invention] The present invention automatically controls the amount of air supplied to the aeration tank and the amount of raw water (BOD amount) supplied to the aeration tank in aerobic activated sludge treatment using an automatic redox potential control device for wastewater treatment. This article relates to a method for automatically controlling the oxidation-reduction potential (hereinafter referred to as ORP) of an aeration tank.

Aerobic activated sludge treatment is an oxidation reaction in which microorganisms (hereinafter referred to as activated sludge) use oxygen in water to decompose pollutants such as organic matter in wastewater into carbon dioxide, water, and the like. In addition, if ammonia compounds and the like coexist in the wastewater, the ammonia compounds may be oxidized to nitrate compounds and/or nitrite compounds by the action of nitrifying bacteria.

As described above, the basic reaction is an oxidation reaction that occurs using oxygen by microorganisms. Generally, aerobic activated sludge treatment evaluates the dissolved oxygen concentration (hereinafter referred to as DO) in the aeration tank, sludge concentration, sludge properties (e.g. SV ₃₀ , SVI,
MLVSS), BOD load, etc. are used as indicators for operational management. However, even with such management, it is not possible to completely prevent problems such as deterioration of treated water quality due to decreased decomposability of pollutants, bulking of activated sludge, floating of activated sludge due to nitrification and denitrification, and outflow. This seems to be because these control items are insufficient or inappropriate for activated sludge treatment.

Therefore, the inventors investigated what should be used as an indicator for the management of aerobic activated sludge treatment, and found that the method of managing the ORP of the aeration tank was optimal.

That is, in aerobic activated sludge treatment, even if the above-mentioned operating conditions are maintained constant, the quality of the treated water may deteriorate for unknown reasons, and undecomposed components of pollutants may be detected in the treated water. This is because the types and concentrations of pollutants in wastewater are diverse and diverse, so the difficulty of decomposition by each type of activated sludge is different, and if the activity of activated sludge decreases for some reason, it has not been possible to decompose until now. It is thought that certain pollutants are detected in the treated water without being decomposed.

The fact that there are differences in the difficulty of decomposition by activated sludge depending on the type of pollutant in wastewater suggests that there are also differences in decomposition reaction energy, and this decomposition reaction energy is closely related to ORP. This suggests that stable activated sludge treatment is possible if the ORP of the aeration tank is controlled.

In addition, in the activated sludge treatment using the conventional management method, the quality of the treated water is unstable, as explained in Example 1.

From this perspective, the inventors investigated the relationship between the ORP of an aeration tank in activated sludge treatment and the quality of treated water using waste gas liquid (hereinafter referred to as ammonium water) generated when producing coke from coal, and published the results in the first paper. As shown in the figure.

The composition of ammonium water is based on the organic chemical oxygen demand (hereinafter referred to as
COD (represented as COD) mainly contains phenol, and compounds such as cresol, xylenol, and pyridine, and their derivatives; inorganic COD includes compounds such as rhodan, thiosulfuric acid, and sulfide, and other ammonia compounds.

The content of these compounds is 5000 as COD
~10000ppm, phenol 1500~2500ppm, rhodan compound 300~600ppm, thiosulfate compound 5000~
Contains about 10000ppm, sulfide compounds 30-60ppm.

This ammonium water is made of seawater and/or freshwater.
If the treated water is diluted twice and subjected to aerobic activated sludge treatment, the COD of the treated water will be around 50 to 150 ppm. Figure 1 shows
This ammonium water was treated with activated sludge, and the ORD in the aeration tank was adjusted from -200 mV to +250 mV (measured with a gold-silver/silver chloride composite electrode at PH7.0 and 30.0°C. The ORP values in the text below are calculated using this method. This is the result of examining the relationship between ORP and the COD, rhodan ion, and nitrite nitrogen concentrations of the treated water.

{COD=-0.561 [ORP] +269.4 (empirical formula) (V=0.8665)} As a result, there is a first-order correlation between the COD and ORP of treated water, and the higher the ORP, the lower the COD. When the ORP of a rhodan compound is higher than 0 mV, it is almost decomposed, but when it is lower than 0 mV, the decomposition of the rhodan compound decreases. On the other hand, since nitrite ions were detected at +150mV to +200mV, it became clear that the nitrification reaction occurs at a potential higher than +150-200mV.

As mentioned above, in activated sludge treatment using ammonium water, if the ORP of the aeration tank is maintained at around +150 mV, COD decomposition is good and nitrification reaction hardly occurs, allowing stable operation. It became.

In this way, it has become clear that the ORP management method for aerobic activated sludge treatment is much more effective for stabilizing operation than the conventional DO management method in the aeration tank.

Next, an automatic control system for ORP in the present invention will be explained.

The ORP of the aeration tank varies depending on the amount of air supplied, the amount of BOD supplied, the activity of activated sludge, the concentration of activated sludge, PH, temperature, etc. The ORP of the aeration tank is automatically controlled by the pH, and if the temperature is constant, the aeration amount and/or
It is best to control it by BOD amount.

The reason for this will be explained using an example of activated sludge treatment of ammonium water.

When the activity level of activated sludge (BOD assimilation capacity, oxygen absorption rate) is normal, the ORP of the aeration tank can be easily controlled automatically by simply controlling the amount of aeration or the amount of raw water supplied using the method shown in Figure 2. It is. In other words, if the aeration tank is set to the desired ORP value, if the ORP of the aeration tank detected by the composite electrode 6 is on the reducing side than the set value, the aeration will be started according to the instructions from the ORP automatic control device 5 for wastewater treatment. Proportional control of ORP is performed such that the damper 9 of the pipe opens and the aeration amount increases, the ORP shifts to a higher value, and as it approaches the set value, the damper 9 closes and the aeration amount decreases. Note that when the ORP exceeds the set value by +50 mV or more, the amount of raw water supplied by the supply raw water pump 8 is increased by 5 to 10% compared to the steady state in order to quickly return the ORP to the set value. All of these controls are automatically performed according to instructions from the ORP automatic control device 5, and the ORP accuracy is 5 to 10 mV above the set value.

However, in actual activated sludge treatment, raw water is
Because there are frequent changes in BOD content, raw water composition, and the contamination of toxic substances into activated sludge, the activity level of activated sludge constantly fluctuates, and for this reason, it is not possible to automatically control ORP by simply controlling the aeration amount or feed raw water as described above. It may not be possible to control it. Therefore, the feature of the present invention is that it can sufficiently follow such fluctuations.
It also enables automatic control of ORP.

First, when the activity of activated sludge decreases,
The automatic control method of ORP will be explained.

Activated sludge contains heavy metals, nitrite compounds,
If cyanide compounds or the like are contained, or if the load of pollutants fluctuates significantly, the function of the activated sludge will be inhibited and the activity will decrease. In such a case, even if the aeration amount is increased, the ORP will be lower than the set value,
It is difficult to recover to the set value, and the aeration amount alone is insufficient.
Automatic control of ORP is quite difficult. The reason for this is that when the activity of activated sludge decreases, the ability to decompose pollutants that require a lot of energy to assimilate and decompose, that is, pollutants that can only be broken down in a place with a high ORP (oxidizing agent), is reduced, so the amount of aeration is reduced. Even if the amount is increased, these persistent substances will not decompose within the specified time and the ORP will be lower than the set value.

In such a case, in order to recover the ORP to the set value, an activated sludge treatment device as shown in FIG. What is necessary is to use a method that simultaneously controls the amount of air and the amount of aeration.

In other words, ORP is lower than the set value for some reason.
If it becomes lower than about 50mV, supply raw water pump 19
A good control method is to reduce the amount of supplied raw water by adjusting the aeration damper 17 and at the same time increase the amount of aeration by adjusting the aeration damper 17.

However, even with this control method, if the recovery of ORP to the set value is slow, or if it becomes lower than 100 mV, the supply raw water pump 19 can be stopped, the supply of raw water can be stopped, and only aeration can be performed. .

By using this control method, the ORP, which has dropped by about 100 mV, will easily recover to the set value in about 10 to 20 hours, and the activated sludge's ability to assimilate and decompose pollutants (activity) will also recover. The quality of treated water also improves. Once the ORP has recovered to the set value, activated sludge treatment can be carried out under normal conditions.

In addition, if activated sludge becomes extremely active, or the amount of pollutants supplied (amount of raw water supplied x concentration of pollutants)
If the value decreases, the ORP may become higher than the set value. This is when the decomposition of pollutants is proceeding smoothly and there is almost no undecomposed pollutant remaining in the aeration tank. When ORP is higher than the set value, for example +200 to 250 mV, nitrification reaction occurs and nitrite and nitrate compounds are generated, inhibiting the function of activated sludge, or causing sludge to float up or flow out in the sludge settling tank. On the contrary, it reduces the activity of activated sludge and causes malfunction.

If the ORP becomes higher than the set value, it can be restored to the set value by reducing the aeration amount. However, when aeration is used to stir activated sludge, when the amount of aeration decreases, the activated sludge accumulates in the dead space of the aeration tank, becomes anaerobic, decomposes, and generates harmful gases such as hydrogen sulfide. , which can actually cause discomfort. For this reason, aeration is limited to reducing activated sludge to the extent that it does not accumulate or rot. Therefore, controlling the aeration amount alone will result in an ORP higher than the set value.
may not recover.

Even in such cases, automatic control of ORP has become possible by using the activated sludge treatment equipment shown in Figure 3.

That is, when the ORP becomes higher than the set value, the amount of supplied aeration can be reduced to an extent that activated sludge does not accumulate or rot, and the amount of supplied pollutants (BOD) can be further increased. All of these controls were made possible by using the ORP automatic control device 23.

However, for activated sludge, such as sewage from residential complexes, wastewater with relatively low toxicity can recover the ORP to the set value by increasing the amount of raw water supplied when the amount of pollutants increases.

However, in the case of industrial wastewater containing pollutants that are toxic to activated sludge, such as wastewater where wastewater from a coal chemical factory is mixed with cheap water, it is not possible to lower the ORP to the set value by increasing the amount of raw water supplied. is not desirable.
This is because in activated sludge treatment of industrial wastewater, if the load of raw water to be supplied changes, the activity will decrease or bulking will occur due to function-inhibiting substances in the wastewater.

Therefore, in the case of industrial wastewater, as a method to increase the amount of BOD supplied, an aqueous solution of organic matter that does not have a negative effect on activated sludge and has good decomposability, such as ammonium water - coal chemical factory wastewater, is recommended. It is preferable to use an aqueous solution of a phenol compound or the like or an aqueous solution of a benzene extracted component of ammonium chloride.

In other words, for some reason ORP is 50 less than the set value.
If the voltage rises to 100mV or more, industrial wastewater such as cheap water is passed through at a predetermined load amount, and ORP control is performed by adjusting the aeration damper 17 using the ORP automatic control device 23 shown in Figure 3 to reduce the aeration amount. It is only necessary to control the aeration tank so that the aqueous solution is supplied from the organic matter aqueous solution tank to the aeration tank by the supply pump 20 at the same time as the organic matter is reduced.

As explained above, in the activated sludge treatment of industrial wastewater such as ammonium water, there are significant fluctuations in the activity of the activated sludge, the type of pollutants in the wastewater, the concentration, etc., and the ORP of the aeration tank cannot be automatically controlled only by the aeration amount. is quite difficult,
Therefore, it is better to automatically control ORP using both the supplied BOD amount and the aeration amount.

Note that when an aqueous solution of organic matter that is easily decomposed by activated sludge is used to control ORP, there is an advantage that not only the accuracy of ORP control is improved, but also the activity, proliferation, etc. of activated sludge are significantly improved.

Therefore, one or two ORP automatic control devices 23 used in FIG. 3 may be used depending on their performance. For example, if two ORP automatic control devices are used, one device will control the ORP within a range of ±20mV of the ORP setting value, and the other device will control the ORP value for some reason.
If the value deviates significantly from the set value by ±50mV or more,
It may also be used for control to quickly recover ORP to a set value.

When activated sludge treatment is carried out using the ORP automatic control method of the aeration tank of the activated sludge treatment apparatus of the present invention, very stable activated sludge treatment becomes possible as explained in the examples.

In particular, when the treated water is subjected to higher-level treatment such as activated carbon adsorption treatment, reverse osmosis, and desalination treatment such as electrodialysis after activated sludge treatment, applying the activated sludge treatment of the present invention will stabilize the higher-level treatment. can.

Next, examples of the present invention will be described.

Example 1 An activated sludge treatment experiment was conducted using an activated sludge treatment apparatus having a treatment flow as shown in FIG. 3 for mixed wastewater of ammonium water and wastewater generated from a coal chemical factory.

Mixed wastewater of cheap water and wastewater generated from a coal chemical factory is diluted with seawater and fresh water to a COD of about 2000 to 2500 ppm and stored in a raw water storage tank 3. On the other hand, an aqueous solution containing 1000 ppm of phenol is stored in tank 4.

Raw water to aeration tank 1 COD0.3~0.5Kg/MLSS・
Quantitatively supplied by raw water pump 19 so that the amount is kg/day. The activated sludge concentration in aeration tank 1 is approximately
5000ppm, SVI is about 50. ORP in the aeration tank was set to +150 mV, and ORP automatic control was performed using ORP automatic control device 23.

When the ORP in the aeration tank becomes approximately 20 to 50 mV lower than +150 mV, the aeration damper 17 is proportionally controlled by the ORP automatic control device 23 to increase the aeration amount.
ORP recovered to +150mV. Also, CRP is +
When the voltage falls below 100mV, the ORP automatic control device 23
As a result, the raw water pump 19 was stopped and the supply of raw water was stopped, and at the same time, the aeration damper 17 was opened and the amount of aeration increased. As a result, it took about 10 hours for ORP to recover from +80mV to the set value of +150mV.

Also, ORP is about 20~20mV higher than the set value of +150mV.
At 50 mV on the oxidation side, the aeration damper 17 was closed, the aeration amount was reduced, and the ORP was restored to the set value.

Furthermore, when ORP reaches +200 mV or more, the aeration damper is completely closed, and at the same time, the pump 20 for the phenol aqueous solution is operated to supply the phenol aqueous solution in addition to raw water such as ammonium water to the aeration tank.
It took about 4 hours for ORP to recover from +230mV to +150mV.

As a result, feed raw water (COD 2000~2500ppm phenol 300~500ppm, rhodan ion 100~
150ppm) is treated by the method of the present invention, the treated water2
The water quality in No. 6 was very good, with COD being removed to 50-100 ppm, rhodan ion to less than 2 ppm, and phenol to less than 0.1 ppm. At this time, the nitrite nitrogen generated in the aeration tank is 0 to 0.5 ppm, which is a level that hardly inhibits the function of activated sludge, so there is no problem.

Furthermore, if the same wastewater is treated with activated sludge and managed only with DO, the COD of the treated water will be 50 to 300 ppm, phenol 0.05 to 13 ppm, and rhodan ion 2 to 60 ppm.
However, the quality of the treated water was extremely unstable. In addition, nitrite nitrogen in the aeration tank is generated from 0 to 84 ppm, and when it exceeds 10 ppm, activated sludge floats up and flows out in the settling tank, and the activated sludge concentration in the aeration tank decreases.
It decreased to 1000-2000ppm. In this way, the DO management method is extremely unstable.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the ORP of the aeration tank and the quality of treated water. Figure 2 shows the relationship between the ORP of the aeration tank and the quality of treated water.
Moreover, FIG. 3 is an explanatory diagram of the activated sludge treatment apparatus in the present invention. 1...Aeration tank, 2...Activated sludge settling tank, 3...
Raw water storage tank, 4... Aeration blower, 5...
ORP automatic control device for wastewater treatment, 6... ORP composite electrode, 7... ORP recorder, 8... Ammonium water supply pump (proportional control by 5), 9... Damper with electromagnetic valve (proportional control by 5), 10... Electric damper, 11... Pump for return sludge, 12... Pump for removing excess sludge, 13... Treated water, 14, 15
... Diffusion hole, 16 ... Organic matter aqueous solution storage tank for ORP control, 17 ... Damper with solenoid valve (proportional control by 23), 18 ... Electric damper, 19 ...
...Raw water supply pump (proportional control by 23), 20
... Organic matter aqueous solution supply pump (proportional control by 23), 21 ... Return sludge pump, 22 ... Excess sludge removal pump, 23 ... ORP automatic control device, 24 ... ORP recorder, 25 ... ORP complex Potential, 26...treated water.

Claims (1)

[Claims] 1. In activated sludge treatment with ammonium water, a redox potential composite electrode made of gold and silver chloride/silver connected to a redox potential control device is immersed in an aeration tank, and a solenoid valve for aeration is connected to the redox potential control device. A damper and a raw water supply pump are connected, and the oxidation-reduction potential measured by the above-mentioned composite electrode is used as an index to automatically control the oxidation-reduction potential of the aeration tank to be within the range of +50 to +150mV. If the reduction potential rises by 50 mV or more above the set value, the aeration damper with solenoid valve is automatically operated and the degree of opening and closing of the damper is reduced to reduce the amount of aeration, or the ammonium water supply pump is automatically activated to supply ammonium water. Either increase the amount of ammonium water or automatically operate the aeration damper and ammonium water supply pump to simultaneously reduce the aeration amount and increase the ammonium water supply amount to restore the redox potential to the predetermined set value. On the other hand, if the oxidation-reduction potential drops by 50mV or more from the predetermined redox potential set value, the damper with an aeration solenoid valve is automatically activated and the damper is opened/closed to increase the amount of aeration, or the aeration damper and ammonium water are supplied. Automatic oxidation-reduction potential for aerobic activated sludge treatment, characterized by automatically operating a pump to simultaneously increase the amount of aeration and reduce the amount of ammonium water supplied, thereby restoring the oxidation-reduction potential to a predetermined set value. Control method.