JPS6328679B2 - - Google Patents

Description

[Detailed Description of the Invention] Description of the Technical Field The present invention is applied to a water treatment device that purifies wastewater by an activated sludge method, and the total amount of sludge retained in the so-called secondary treatment system and the secondary treatment The present invention relates to a sludge amount control method that controls the amount of sludge stagnant in a dusting tank and a settling tank in a system so as to maintain the balance in a state for effective purification.

Description of the Prior Art The activated sludge method is a type of biological treatment method that purifies organic matter in wastewater through the action of microorganisms such as bacteria. This group of microorganisms also ingests dissolved organic matter in wastewater as food, multiplies and converts it into a solid form called activated sludge. The wastewater is then purified by separating it into solid and liquid in a sedimentation tank. Therefore, by purifying wastewater using the activated sludge method, a large amount of activated sludge (hereinafter abbreviated as sludge) can be produced.
occurs. Of this sludge, the amount other than the amount necessary for purifying sewage must be drawn out of the secondary treatment system as surplus (hereinafter referred to as surplus sludge). In order to effectively purify sewage, it is necessary to supply organic matter in the sewage, ie, sludge in an amount suitable for food, to the dust tank.

Conventionally, to control the extraction of excess sludge in the former case, the amount of sludge stagnant in the settling tank is determined by using a sludge interface meter or by analyzing the input/output characteristics of the settling tank sludge. There is a method of extracting excess sludge so that the value becomes the desired value. However, this conventional method focuses only on the amount of sludge in the settling tank and does not take into account the amount of sludge in the dusting tank, so the extraction of excess sludge is extremely inaccurate, and is often due to over-extraction or under-extraction. This made the purification of sewage unstable. Therefore, to improve the shortcomings of these conventional methods, we have developed a method called total sludge retention control, in which excess sludge is extracted so that the total amount of sludge retained in the settling tank and the sludge tank reaches the desired value. There are ways to do it. According to this control of the total amount of sludge held, the amount of sludge held in the secondary treatment system can be almost completely maintained at the desired value. However, if the flow rate of inflowing sewage, which fluctuates daily and weekly, changes, the balance between the amount of sludge remaining in the dusting tank and settling tank will be disrupted, and when the flow rate of sewage increases, there will be no sufficient amount of sludge. There is a risk that the water will not be supplied to the dust tank, resulting in incomplete purification.
Therefore, in order to deal with fluctuations in the flow rate of wastewater,
It is easily understood that the ratio of the return sludge flow rate (hereinafter referred to as return sludge rate) to the flow rate of sewage flowing into the dusting tank may be controlled.

Conventionally, the above-mentioned control of the return sludge rate includes constant return sludge rate control, which controls the return sludge flow rate by keeping the value constant. However, the inventor's research has revealed that when this constant return sludge rate control is performed in combination with the above-mentioned total sludge holding amount, the following problem occurs. In other words, since the return sludge flow rate changes in proportion to the amount of inflowing sewage, the flow rate extracted from the settling tank (the sum of the return sludge flow rate and the surplus sludge withdrawal flow rate) changes, and as a result, the surplus to be removed changes. The sludge concentration changes and disrupts (interfere with) the total sludge retention control. Therefore, there is a problem that excess or insufficient amount of excess sludge is removed.

In addition, the return sludge rate is not controlled as a constant;
For example, there is a conventional method of correcting the return sludge rate in accordance with a target value of the concentration of sludge flowing into a dusting tank or a dusting tank (hereinafter referred to as MLSS concentration). However, even in this conventional method, the flow rate of returned sludge changes, and then the flow rate withdrawn from the settling tank also changes, so problems similar to those described above occur, interfering with the control of the total sludge holding amount, and preventing excessive or insufficient removal of excess sludge. It was something that made me wake up.

Purpose of the Invention The purpose of the present invention is to control the amount of sludge in a water treatment equipment that purifies sewage using the activated sludge method by controlling the amount of excess sludge in a water treatment system so as not to over-extract or under-extract the sludge, and to maintain the balance of the amount of sludge in the sludge tank and settling tank. The purpose is to provide a method.

Summary of the Invention Here, the present invention will be summarized and explained based on the flow rate and quality of sewage flowing into the dusting tank, the flow rate of sludge returned from the settling tank, and the sludge concentration, including the dusting tank and the settling tank. Applied to water treatment equipment that can determine the total amount of sludge held in the treatment system by analyzing the behavior of sludge stagnant in the treatment system over time, and controls the total amount of sludge held to a desired value. At the same time, a setting value is given to control the ratio of the flow rate of sludge returned from the settling tank to the dusting tank to a target value to the flow rate of sewage flowing into the dusting tank. When the flow rate of inflowing sewage increases, the set value for the total sludge holding amount is increased and the set value for the ratio of the return sludge flow rate is lowered, and when the flow rate of inflowing sewage to the dusting tank decreases, the set values are set as above. A method for controlling a sludge flow rate in an activated sludge method, which is characterized by changing the flow rate in the opposite direction to when it increases.

Embodiment of the Invention An embodiment of the present invention will be described below with reference to the drawings. Sewage or primarily treated sewage sent from pipe A flows into a dusting tank 3 via a sewage flow meter 1 and a turbidity meter 2. Sedimentation tank 4 is in dust tank 3
Return sludge flows from the pipe B through a return sludge valve 5, a return sludge flow meter 6, and a return sludge concentration meter 7. The inflowing sewage and the returned sludge are supplied to the dusting tank 3 through the pipe C, and are mixed by dusting by the air ejected from the aeration pipe 8. Therefore, pollutants such as organic matter in the sewage react with the sludge and are absorbed into the sludge. At the end of the reaction, the mixture in the smoking tank (below
MLSS) is led to the sedimentation basin 4 where it is sedimented and separated, and the supernatant water is discharged as treated water from the secondary treatment system via pipe D. The silt settled here is collected in the hopper portion 9 of the settling tank 4 and concentrated. The concentrated sludge in the hopper section 9 is drawn out by the drawing pipe E, and some of it becomes the return sludge mentioned above.
The remaining portion is discharged from the pipe F to the outside of the secondary treatment system via an excess sludge extraction valve 10 and an excess sludge extraction flow meter 11.

Reference numerals 20 and 21 indicate setting devices for setting the flow rate of sludge passing through the corresponding valves 10 and 5 to a predetermined value, which receives set values by signals from converters 18 and 19, which will be described later, and which also connects the corresponding flowmeters 11 and 6. The opening degrees of the corresponding valves 10 and 5 are feedback-controlled by the signals from the valves 10 and 5.

Sewage flow meter 1, turbidity meter 2, return sludge flow meter 6,
Return sludge concentration meter 7 and excess sludge extraction flow meter 1
The signals generated by 1 are respectively sent to a computer 12 having a program capable of analyzing the behavior of the sludge in the sludge tank and settling tank. The computer 12 analyzes the MLSS concentration at each point in the flow direction of the dusting tank 3 and the sludge concentration at each point in the settling tank 4 according to the program from the signals of the above-mentioned measuring meters, and The amount of sludge retained in each pond 4 and the total amount of sludge held W(t), which is the sum thereof, are calculated. This process may be performed using a method similar to the conventional method for controlling the total amount of sludge retained, and a detailed explanation will be omitted. Further, the computer 12 calculates the return sludge rate R(t) from the wastewater flow rate Q _s (t) and the return sludge flow rate Q _R (t) according to the following formula.

R (t) = Q _R (t) ÷ Q _s (t) ... (1) The above total sludge holding amount W (t) is sent to the first controller 13, and the above return sludge rate R (t) is It is transmitted to the second controller 14.

The first controller 13 has a contact point 15 through which a set value _Wsv of the total sludge holding amount W(t) can be input automatically or manually, and the change in excess sludge withdrawal △ is calculated by the following formula.
W is calculated and outputted to the upper controller 16.

E _w (t)=W(t)−W _sv ……(2) △W(t)=A _w・[K _wp・{E _w (t) −E _w (t−H _w )}+K _wI・E _w (t)〕
...(3) Here, H _w is the control period, K _wp , K _wI are the control gains,
A _w is a dead band element. In addition, the second controller 14 has a contact 17 that can automatically or manually input the set value R _sv of the return sludge rate, and calculates the change in the return sludge rate ΔR(t) using the following formula. The value is transmitted to the upper controller 16.

E _R (t)=R _sv −R(t) ……(4) △R(t)=Ar・[K _RP・{E _R (t) −E _R (t−H _R )}+K _RI・E _R (t)]
...(5) Here, H _R is the control period, K _RP , K _RI are the control gains,
_AR is a dead band element.

The controller 16 operates to increase the set value W sv of the total sludge holding amount of the first controller 13 when the amount of sewage flowing into the dusting tank 3 increases, and increases the set value W _sv of the total sludge holding amount of the second controller 14 . It is designed to operate to lower the rate setting value R _sv . Similarly, when the amount of inflowing sewage decreases, the set value of the total sludge holding amount is lowered and the set value of the return sludge rate is increased by the operation opposite to the above. That is, under control of a constant return sludge rate, as the inflow sewage volume increases, the return sludge flow rate also increases at a constant rate, but if the total sludge holding amount W is constant, as the return sludge flow rate increases, the return sludge concentration decreases. Therefore, the MLSS concentration in the dust tank 3 also decreases. The degree of this decrease depends on the total amount W of sludge held. Of course, if the total amount of sludge is retained sufficiently, the decrease in MLSS concentration will be slight. On the other hand, if the total sludge holding amount W is too small, most of the sludge will be accumulated in the sedimentation tank 4, and the MLSS concentration will drop sharply. Therefore, in order to prevent such a situation from occurring, as mentioned above, when the amount of inflowing sewage increases, the target value of the total sludge holding amount W is set high, and the MLSS concentration in the dusting tank is reduced. In addition, when the amount of inflowing sewage decreases, the target value of the total sludge holding amount W is set low, and the tank 3
It is necessary to prevent an increase in the MLSS concentration of

In addition, when the total sludge holding amount W is controlled to be constant, the amount of inflowing sewage increases and the dust tank 3
If we start to compensate for the decrease in the MLSS concentration by supplying sludge from the sedimentation tank 4 to the dusting tank 3 under constant return rate control, the residence time of the sludge in the sedimentation tank 4 will decrease, resulting in a low concentration rate. Become. For this reason, the concentration of returned sludge becomes diluted, and the MLSS concentration in the dusting tank 3 becomes low. At the same time, since the return sludge flow rate Q _R and the sewage inflow flow rate Q _s are also high, the reaction time of the sludge in the dusting tank 4 is also shortened, making it impossible to perform sufficient purification. Therefore, in order to prevent such a situation from occurring, as mentioned above, when the amount of inflowing sewage tends to increase, the return sludge rate R should be reduced, and when the former tends to decrease, the latter should be reduced. It would be better to increase it.

Upper controller 1 in the present invention used in this example
The specific configuration of 6 is such that the above operation can be performed without using the amount of inflowing sewage, that is, the signal from the sewage flowmeter 1. That is, the change ΔR _{sv in the set value R sv} of the return sludge rate R(t) for the second controller 14 is the change _ΔW in the total sludge holding amount W(t) output from the first controller 13 Using the value of (t), it is calculated and determined, for example, according to the following formula.

△R _sv = K _R・△W(t) ...(6) Also, the total sludge holding amount W(t) for the first controller
The change in the set value W _sv of △W _sv is determined by the second controller 14
Change amount △R of return sludge rate R(t) output from
Using the value of (t), it is calculated and determined, for example, according to the following formula.

△W _sv = K _w · △R (t) ... (7) Here, K _R and K _w are time constants.

In addition to calculating by the above equations (6) and (7), the change in the set value R _sv of the return sludge rate R and the change △ _{W sv in} the set value of the total sludge holding amount are calculated as the inflowing sewage. flow rate
It may be calculated directly from the value of Q _s , for example, as in the following formula. However, its application requires consideration of the characteristics of the behavior of sludge in the dusting tank 3 and settling tank 4, especially the mixing characteristics in the dusting tank 3, and the sludge concentration rate and maximum possible accumulation amount in the settling tank 4. It is necessary to give sufficient consideration.

△R _sv =K _R ′・Q _s (t)−Q _s (t−H)/H …(8) △W _sv =K _w ′・Q _s (t)−Q _s (t−H)/ H...(9) Here, K _R ′, K _w ′ are time constants, Q _s (t), Q _s (t−
H) is the flow rate of inflowing wastewater, and H is the control period.

As described above, the first controller 13 and the second controller 14
The amount of excess sludge extracted and the amount of change in the return sludge rate calculated by are input to converters 18 and 19, respectively.
They are output as changes in the values of the excess sludge withdrawal amount and the return sludge flow rate, respectively, and are transmitted to the setting device 20 and the setting device 21.

Effects of the Invention By applying the sludge amount control method of the present invention, the adjustment of the excess sludge extraction flow rate and the return sludge flow rate operate in conjunction with each other without interference in response to fluctuations in the amount of inflowing sewage. of the dust tank
The MLSS concentration is stabilized, the balance of sludge volumes in the dusting tank and settling tank is maintained, and the concentration rate of excess sludge is high, allowing it to be removed as excess sludge that can be easily treated.

[Brief explanation of the drawing]

The drawing is a flow diagram showing an example of a system configuration for executing the sludge amount control method according to the present invention. 1... Sewage flow meter, 2... Turbidity meter, 3... Dust tank,
4...Sedimentation tank, 5...Return sludge valve, 6...Return sludge flow meter, 7...Return sludge concentration meter, 8...Aeration pipe, 9...Sedimentation tank sludge hopper, 10...Excess sludge withdrawal valve, 11...Excess sludge withdrawal flow rate 12... Computer, 13... First controller, 14... Second controller, 15... Set value input contact, 16... Upper controller, 17... Set value input contact.

Claims (1)

[Claims] 1. Based on the flow rate and quality of sewage flowing into the dusting tank and the flow rate and sludge concentration of sludge returned from the settling tank, the stagnation in the treatment system including the dusting tank and the settling tank can be determined. applied to water treatment equipment that can determine the total amount of sludge held in the treatment system by analyzing the behavior of sludge in time series, and is a set value for controlling the total amount of sludge held to a target value. At the same time, a set value is given to control the ratio of the flow rate of sludge returned from the settling tank to the dusting tank to the flow rate of sewage flowing into the dusting tank to a desired value, and the flow rate of sewage flowing into the dusting tank is When increasing, the set value for the total sludge holding amount is increased and the set value for the ratio of the return sludge flow rate is lowered, and when the flow rate of sewage flowing into the dusting tank decreases, the above set values are changed from those when increasing. A method for controlling the amount of sludge in an activated sludge method, which is characterized by changing the amount in the opposite direction. 2. Claims characterized in that the set value for the ratio of the returned sludge flow rate is changed according to the change in the total sludge holding amount, and the set value for the total sludge held amount is changed according to the change in the ratio of the returned sludge flow rate The sludge amount control method according to item 1. 3 The set value for the total sludge holding amount and the set value for the ratio of the returned sludge flow rate are changed according to the rate of change of the flow rate of sewage flowing into the dusting tank. Sludge volume control method.