JPS6347518B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a biological treatment method for removing BOD from nitrogen-containing organic wastewater by a long-term aeration method, and particularly for wastewater in which the ratio of nitrogen concentration to BOD does not fluctuate drastically, such as domestic wastewater. This invention relates to a biological treatment method suitable for treating wastewater, human waste, etc. [Prior art and problems to be solved by the invention] Operational factors when treating nitrogen-containing organic wastewater using an activated sludge method including a long-time aeration method include (a) water quality (BOD load); These include the amount of inflowing wastewater, (c) the amount of air blown into the aeration tank, (d) the amount of microorganisms in the aeration tank (the amount of sludge held in the system), (e) the amount of returned sludge, and (f) the daily sludge age, etc. It is known that the amount of air blown into the aeration tank (hereinafter referred to as aeration amount) is an important factor. Conventionally, this aeration amount has been determined empirically or by calculation from the BOD load to the aeration tank, the MLSS amount, etc. In actual equipment, once the aeration amount is determined, the aeration amount is not often changed in response to fluctuations in the inflow BOD amount. For this reason, there are times or periods when too much air is blown into the tank, and there are times or periods when too little air is blown into the tank, and processes such as oxidation and decomposition of organic matter are not being carried out very efficiently. There is. Furthermore, if the amount of aeration is too high or too low, it will generally have an adverse effect on the microorganisms present in the aeration tank. That is, when the amount of aeration is excessive, as shown in FIG. 7, the nitrification reaction is promoted (a), the pH is reduced (b), and the biological activity is reduced (c). On the other hand, if the amount of aeration is too low, the nitrification reaction will stop, the process will become anaerobic, the BOD removal activity will decrease, and in extreme cases, microorganisms will die. In addition, if the amount of aeration is excessive, the self-digestion of sludge will progress excessively1, resulting in aging and deterioration of sludge properties2, and a decrease in biological activity, as well as a decrease in so-called sludge that flows into the treated water. Carry over phenomenon 3 is likely to occur. Also, in case of overaeration, MLSS
(sludge volume) does not increase, and sometimes decreases4, which leads to a decrease in SV (activated sludge)5 and BOD-
Excessive MLSS loading leads to the above-mentioned decrease in biological activity, which in turn makes the plant vulnerable to fluctuations in inflow water quality and water volume.6 Also, as the sludge age becomes extremely long, the ability to decompose sewage decreases7. The quality of treated water deteriorates8. Furthermore, if the amount of aeration is excessive, the nitrification reaction will become significant;a, depending on the operating method, denitrification may occur in the settling tank9, and it will float up with the generated nitrogen gas and mix in the treated water in the form of scum. Treated water quality deteriorates10
Sometimes I do. By the way, in order to deal with the above-mentioned problems, there are some examples in which attempts have been made to control the amount of aeration by controlling the dissolved oxygen concentration (DO) in the aeration tank in large-scale equipment. However, when controlling based on DO detection values, the equipment is quite large because it requires constant maintenance of the DO meter and a mechanism to exclude abnormal detection values in order to accurately detect the dissolved oxygen concentration at all times. Become something. Furthermore, due to the characteristics of the device, if the DO meter is not thoroughly maintained, correct values cannot be obtained, which often causes various problems. Furthermore, in the conventional method of controlling based on the detected value of DO, the DO is kept within a predetermined range, for example 1.5 to
Since the main focus is on keeping the level at 2.5 ppm, when treating organic wastewater such as domestic wastewater or human waste containing ammonia nitrogen and/or organic nitrogen, the nitrogen content should be kept at 2.5 ppm. As a result, the pH decreased beyond the appropriate value for the microorganisms, leading to a decrease in the purification ability of the microorganisms, which had an adverse effect on BOD removal processing. This is the lower limit of 1.5ppm for DO.
This is due to the fact that nitrification reactions can occur at concentrations of 0.3 to 0.5 ppm or higher. [Background of the Invention] In view of the above circumstances, the present inventors conducted intensive research and found that when organic wastewater containing nitrogen is treated with biological treatment methods such as activated sludge method and catalytic oxidation method, organic nitrogen (Org−N) is ammonia nitrogen (NH ₄ −
While the ammonia nitrogen that originally exists is oxidized as it is and becomes nitrate nitrogen through nitrite nitrogen (NO ₂ -N), the pH of the sludge mixture in the aeration tank increases. We focused on the decrease. The progress of the nitrification reaction, that is, the pH
We found that the status of treatment such as BOD removal can be understood by the value, and we also found that it is easy to understand the general state of the biological treatment system by the PH. By controlling the aeration amount according to the PH of the sludge mixture in the aeration tank or the supernatant water of the settling tank,
We found that biological treatment including BOD removal can be performed efficiently. [Means for Solving the Problems] In the first invention, when treating nitrogen-containing organic wastewater by a long-time aeration method, the pH of the sludge mixture in the aeration tank or the supernatant water of the settling tank is detected. The above problem was solved by controlling the amount of air blown into the aeration tank based on the detected PH value or a value that takes into account the rate of change. Further, in the second invention, the basic amount of air blown into the aeration tank is controlled by the detected pH value, and the remaining adjustment amount is controlled by at least the detected value of the dissolved oxygen concentration in the aeration tank. , attempted to solve the above problems. Here, the long-time aeration method means that the BOD load is approximately 0.15.
This is a treatment method in which the amount of excess sludge is reduced to ~0.25 BODKg/m ³ days, and the grown sludge is decomposed and mineralized by self-oxidation to reduce the amount of excess sludge, that is, the usual long-time aeration method. In the long-time aeration method, the residence time is set to be long. The residence time when treating general domestic wastewater is usually about 16 hours or more. [Function] First, the process of wastewater treatment by the treatment method of the present invention will be explained step by step, taking a batch treatment reaction as an example. When wastewater that contains ammonia nitrogen and organic nitrogen and whose ratio of nitrogen concentration to BOD does not change drastically, such as domestic wastewater or human waste, flows into the aeration tank, Due to the influence of ammonia nitrogen and organic nitrogen,
The sludge mixture in the aeration tank or the supernatant liquid in the settling tank becomes a neutral or weakly alkaline liquid. When aeration is carried out, the action of microorganisms first oxidizes organic matter.
That is, BOD removal is performed. And this
At the point when BOD removal has progressed to a high level, organic nitrogen is decomposed into ammonia nitrogen by the action of microorganisms (hereinafter referred to as deamination reaction), and some of the resulting ammonia nitrogen is oxidized. The nitrification reaction progresses to some extent to form nitrite ions as shown in equation (1) and further to nitrate ions as shown in equation (2). NH ₄ ⁺ +3/2O ₂ →NO ₂ ^- +2H ⁺ +H ₂ O...(1) NO ₂ ^- +1/2O ₂ →NO ₃ ^-... (2) As a result, the sludge mixture in the aeration tank or the supernatant water of the settling tank PH decreases. Therefore, by observing this PH, it is possible to detect the completion of BOD removal. Then, when BOD removal approaches the end and the pH approaches the lower limit of the set value, the aeration amount is reduced. This prevents the BOD removal reaction from proceeding excessively. At the same time, the nitrification reactions of formulas (1) and (2) are also suppressed, and the decrease in the pH of the sludge mixture is stopped. In actual wastewater treatment, wastewater continuously flows into the aeration tank, so the amount of aeration is adjusted to keep the pH constant. Then, stable BOD removal can be performed. Moreover, as a result, aeration can be carried out without excess or deficiency, so that the properties of the sludge can be maintained in good condition. Furthermore, in the treatment method of the present invention, the pH of the sludge mixture is maintained at a predetermined value, so that good sludge properties can also be maintained from this point of view. Furthermore, by appropriately setting the pH value, it is possible to control the degree of activated sludge digestion and the amount of surplus sludge generated. In the case of the treatment method of the second invention, the basic amount is controlled by the PH value, and the remaining amount is controlled by at least the detected value of the dissolved oxygen concentration in the aeration tank, so that the inflow load that occurs in a short period of time is It can easily and quickly respond to large changes. In this case as well, the base aeration amount is set to PH
Since the treatment method is controlled by the above-mentioned method, it is possible to obtain the same effect as the treatment method of the first invention. [Example] The processing method of the present invention was carried out using a processing apparatus having the specifications shown in FIG. This treatment equipment uses a rectangular complete mixing aeration tank.
The output signal is taken out from the PH meter 21 installed around 2/3 of 20, passes through the instruction adjustment section 22, and adjusts the opening degree of the air bypass electric valve 23 by PID operation to control the aeration amount. A DO meter 25 is also attached, but this time the DO meter 25 was only used as a supplement for confirmation purposes. Processing conditions The main processing conditions are as follows. Mainly, long-time aeration method was used. Residence time was set to approximately 24 hours. The MLSS of the influent raw water was about 1300-3500 mg/. The amount of returned sludge was approximately 75% to 150%, and the PH was set to a slightly acidic level of 6.8 and operated automatically. The inflow raw water is comprehensive wastewater consisting of kitchen, gray water, sewage, etc. The data processed under the above conditions for over a year was statistically processed for BOD, COD, and SS, and the results are shown in Table 1. Figure 2 shows the data obtained regarding the relationship between inflow BOD and nitrification rate. Furthermore, during this period, DO was measured and the results are shown in Figure 3. Note that DO measurement is performed using DO that has been cleaned at each measurement time.
A meter was used, and when the flow rate was slow, the DO meter was moved appropriately. For reference, the relationship between nitrification rate and inflow BOD concentration when operating automatically with pH set to approximately 6.3.
The observed results of DO values are shown in Figures 2 and 3. Also, regarding the BOD, COD, and SS of the treated water in the case of manual operation, which was conventionally performed with the same treatment equipment,
The measurement results are statistically processed and listed in Table 1. The manual operation that was being performed at this time was
The concentration was maintained at 0.8 ppm. The reason for adopting the value of DO = 0.8 ppm here is that when we investigated the correlation between constant DO control and treated water quality in a separate basic experiment, we found that in the long-term aeration method, as shown in Table 2, This is because it has been confirmed that the best BOD removal can be achieved by controlling the amount by setting it to around 0.8 ppm.

【table】

〔Effect of the invention〕

As explained above, in the first invention, PH
Nitrogen-containing organic wastewater is biologically treated using a long-term aeration method while controlling the amount of air blown into the aeration tank based on detected values. Therefore, the following advantages (1) to (6) can be obtained. (1) BOD removal can be carried out to an appropriate stage, and excessive progress of nitrification reaction and excessive aeration can be prevented. Therefore, according to the biological treatment method for nitrogen-containing organic wastewater of the present invention, BOD can be removed to a high degree, sludge properties can be kept good, and good and stable wastewater treatment can be performed. (2) Since the status of the biological treatment system can be reliably grasped by the PH, by controlling the amount of air blown into the aeration tank based on this PH detection value, it is possible to set the biological treatment system to a specified level. etc. can be processed in a highly stable manner. (3) Since the air is controlled to be blown in a predetermined amount, the nitrification reaction is appropriate, the pH is set to a predetermined value, biological activity is improved, and biological treatment can be carried out efficiently. . (4) According to the first invention, the amount of aeration is controlled based on the detected pH value, etc., resulting in an appropriate biological treatment system, so that self-digestion of sludge does not substantially occur or occurs only to an appropriate extent. do not have. (5) According to the first invention, since the nitrification reaction can be set appropriately, denitrification is unlikely to occur in the settling tank, and problems such as scum generation do not occur. (6) Even with existing technology, the PH meter used can provide sufficiently accurate detection values with some maintenance, is reliable, and has low equipment costs, so it can be easily incorporated into automatic control systems. . In addition, in the case of the treatment method of the second invention, the basic amount is
Since it is controlled by the PH value, and above it is controlled by at least the detected value of dissolved oxygen concentration in the aeration tank, in addition to the same effect as the first invention,
It has the advantage of being able to easily and quickly respond to large fluctuations in the inflow load that occur in a short period of time.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the structure of the processing equipment used in the example, and Figure 2 is the nitrification rate and inflow in the example.
Figure 3 is a graph showing the relationship between BOD concentration, Figure 3 is a graph showing the relationship between DO and PH in the same example, and Figure 4 is a graph showing the relationship between DO and PH in the same example.
The figure shows the inflow total nitrogen concentration and inflow BOD in a comparative example.
Figure 5 is a graph showing the relationship between nitrification rate and inflow BOD concentration in a comparative example. Figure 6 is a graph showing the relationship between nitrification rate and inflow BOD concentration in a comparative example.
A graph showing the relationship with the BOD concentration, FIG. 7, is an explanatory diagram showing the causal relationship when the amount of air blown into the aeration tank is excessive.

Claims (1)

[Scope of Claims] 1. When treating nitrogen-containing organic wastewater by a long-term aeration method, the PH of the sludge mixture in the aeration tank or the supernatant water of the settling tank is detected, and the detected PH value or its fluctuation rate is determined. A biological treatment method for nitrogen-containing organic wastewater, characterized in that the biological treatment process including BOD removal is controlled by adjusting the amount of air blown into an aeration tank according to a value that takes into account. 2. When treating nitrogen-containing organic wastewater by a long-term aeration method, the pH of the sludge mixture in the aeration tank or the supernatant water of the settling tank is detected, and the basics of the air blown into the aeration tank are determined based on the detected pH value. In addition to adjusting the amount,
A biological treatment method for nitrogen-containing organic wastewater, characterized in that a biological treatment process including BOD removal is controlled by adjusting the amount of residual adjustment based on at least a detected value of dissolved oxygen concentration in an aeration tank.