JPS6130839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for monitoring the amount of sludge in a settling tank of a sewage treatment plant, which monitors the amount of sludge accumulated in a settling tank in a water treatment system that uses activated sludge to treat sewage. It is.

In sewage treatment equipment that purifies general sewage and organic wastewater using activated sludge, which is a collection of microorganisms, the sewage that flows into the aeration tank or its primary treated water is treated with activated sludge (hereinafter referred to as "activated sludge") returned from the settling tank. When the mixed liquid is aerated, most of the pollutants are absorbed into the sludge, and this sludge is separated from water in a settling tank to become clear.

In this way, water treatment using activated sludge is a method of purifying organic wastewater that uses biological action in the aeration tank and solid-liquid separation action in the settling tank as the main processes.
The aeration conditions in the aeration tank as well as the condition of the sludge in the settling tank are important factors that affect the purification effect and operational safety.

By the way, if the amount of sludge accumulated in the settling tank becomes excessive, the effective volume of the settling tank will be reduced, and the sludge will not separate from the water and will flow out together with the treated water, and the retention time of the sludge will also become longer, causing the sludge to increase. When the sludge becomes anaerobic and rots to a severe degree, a denitrification reaction occurs and the precipitated sludge floats to the surface, making purification impossible. Furthermore, if the amount of sludge is too small, when the amount of sewage increases, it will not be possible to supply the amount of sludge necessary for purification to the aeration tank, and the sewage will be discharged through the settling tank with insufficient purification. In this way, the amount of sludge in the settling tank is the most important factor in the operation of activated sludge water treatment, and it is necessary to monitor the amount of sludge in the settling tank in order to maintain high treatment efficiency and stable operation. .

Conventionally, a method using a sludge interface detector has been proposed as a method for monitoring the amount of sludge. This method applies the principle of an optical or ultrasonic sludge densitometer to detect a sludge surface with a predetermined concentration. However, since the sludge in the settling tank is not evenly distributed throughout the settling tank, it is completely impossible to monitor the amount of sludge.

The present invention was made in view of the above circumstances, and whereas the conventional method described above was a static method that simply detected the sludge interface, the present invention was made based on the flow rate of inflow sewage, return sludge flow rate, excess sludge flow rate, or It is characterized by dynamically predicting the amount of sludge in the settling tank by analyzing time-series data of the flow rate of the settling tank and the sludge concentration of the mixed liquid flowing out from the aeration tank using a simulation model. The purpose of this study is to share information on how to monitor the amount of sludge in sedimentation tanks at sewage treatment plants, which can monitor the amount with high accuracy.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of the settling tank 10 showing the sedimentation state and sedimentation state of the settling tank sludge. In the figure, reference numeral 11 denotes a water conduit, which guides the mixed liquid after the microbial reaction from the aeration tank to the settling tank 10. This sedimentation tank 10
A rectifying wall 12 is vertically provided in the vicinity of the discharge port 11a of the headrace 11 to straighten the mixed liquid, and the sedimentation basin is connected to a vertical portion A on the side of the headrace 11 with this straightening wall 12 as a boundary. , and the other part is divided into cross-flow part B. Further, the sedimentation basin 10 is provided with a hopper 10a at the lower part of the space sandwiched between the discharge port 11a of the water conduit 11 and the rectifying wall 12, that is, at the lower part of the vertical part A. In addition, the sedimentation tank 10 includes the cross flow section B.
A scraper 13 is provided (over the whole except for the position of the hopper 10a) to scrape the sediment deposited on the bottom surface of the settling tank onto the hopper 10a. This raking machine 13 has a plurality of rakes 13b for raking sediments arriving at a predetermined interval on a belt 13a, and also has a belt 13a.
is held by a pulley 13c, and the belt 1
By driving 3a, the sediment is collected. 14 is a trough for receiving the supernatant water of the settling tank 10, and 15 is a sludge pipe provided in the hopper 10a for discharging the sludge in the hopper 10a to the outside.

In such a sedimentation tank, the mixed liquid after the microbial reaction is sent from the aeration tank to the sedimentation tank 10 via the water conduit 11. This sent mixed liquid is discharged from the discharge port 11a of the water conduit 11 to the upper part of the hopper 10a, but since there is a rectifying wall 12 here, it is divided into a vertical part A and a horizontal part B. At this time, the water flows gently into the cross-flow section B due to the action of the rectifying wall 12, and the water in the cross-flow section B is prevented from being disturbed. Cross flow part B
The sludge part of the mixed liquid that has flowed into the tank is precipitated here.
Separated into solid and liquid. Then, the supernatant water is trough 1
It is released from 4. The sludge left in the cross-flow section B starts to settle and then settles, but exists as settled sludge C in the upper layer and as settled sludge D in the lower layer. The settled sludge D has a density that is sufficient to be scraped up by the rake 9 of the scraper 13, and by driving this scraper 13, the hopper 1 of the vertical section A is
It is moved to within 0a. Then, the sludge E is accumulated in the hopper 10a together with the sludge E in the mixed liquid flowing down the vertical portion A. This accumulated sludge is drawn out through the sludge pipe 15.

Although the treatment is carried out through the above-mentioned process, from Fig. 1, the total amount of sludge Z(t)
Considering this, this total sludge volume Z(t) is
, the amount of sludge shown by C (this is taken as Z ₁ (t)), the amount of settled sludge shown by C in cross flow section B (this is taken as Z ₂ (t)), and the amount of sludge shown by D (this is taken as Z ₃ (t)), it can be expressed as Z(t)=Z ₁ (t)+Z ₂ (t)+Z ₃ (t)...(1).

However, the flow rate Q _c of the mixed liquid flowing into the settling tank from the aeration tank and its sludge concentration X _a are the flow rate Q _s of the sewage, the flow rate of returned sludge Q _r , the flow rate of excess sludge Q _w , the flow rate Q _o drawn from the settling tank, and the inflowing sewage. If the concentration of the precipitating substance changes, it will change naturally. Therefore, the amounts of sludge in the settling tank Z ₁ , Z ₂ , and Z ₃ also change accordingly, but according to the inventor's research, the following facts have been found to be responsible for these changes in the amount of sludge. are doing. That is, (a) there is always a time delay when the settled sludge C transfers to the settled sludge D.

(b) The amount of settled sludge D transferred from the horizontal section B to the vertical section A is proportional to the amount of settled sludge.

(c) The mixed liquid in the vertical section A and the sludge from the horizontal section B are completely mixed in each tank of the vertical section.

This is a fact.

From the above (a), the amount Z ₂ (t) of settled sludge at time t can be given by the following equation, where t _d is the delay time.

Here, I and F represent the integer part and decimal part of the delay time _td , respectively, and h represents the measurement period.

Also, the speed at which settled sludge becomes settled sludge ω ₁
It can be seen that (t) becomes as follows.

ω ₁ (t)=Z ₁ (t)−Z ₁ (t−h) =F/h{Q _s (t−I)−Q _w (t−I)} X _a (t−I)+h−F /h _{ Q _s (t-I+h)-Q _w (t-I ₊ h)} t) is given by the following formula.

Z ₂ ′(t)=Z ₂ (t-h)ω ₁ (t) …(4) If the proportionality constant mentioned in (b) above is b, settling tank 1
The velocity ω ₂ (t) of sludge moving from the horizontal flow section B to the vertical section A at 0 can be expressed by the following equation.

ω ₂ (t)=b×Z ₂ ′(t)=b
{Z ₂ (t-h) + ω ₁ (t)} ...(5) Also, the concentration X _r (t) of the sludge drawn out from the point (c) above through the sludge drainage pipe 15 is expressed by the equation for a completely mixed flow. It is given by the following equation.

X _r (t)=X _o (t) + R _o (t)/h{Y _o (t-h)-X _o (t)} {1-exp(-h/R _o (t))}... _{( 6 ) _ _ _ _ _ o} (t)=V _o /Q _r (t) + Q _w (t) ... (8) Here, Y _o , Y _o - ₁ is the vertical part A of the settling tank 10
is the mixed liquid sludge concentration in the final tank (hopper 10a) and the tank immediately before the final tank, and V _o and R _o (t) are the volume and residence time of the final tank.

In the first to eighth equations, the unknown variables are the model parameters, namely the delay time _td , the proportionality constant b, and the number n of tanks in the vertical section. While constantly measuring Q _s , Q _r , Q _w and _{X a , the} return sludge concentration It can be easily determined by searching for a value that minimizes the error with _r '.

In this way, the amount of sludge in the sedimentation tank 10 can be determined by the first equation from the sludge amounts Z ₁ , Z ₂ , Z ₃ determined by the second to eighth equations.

An example in which the above-described method for calculating the amount of sedimentation tank sludge is actually applied will be described with reference to FIG. 2.

In FIG. 2, 20 is a settling tank, 20A is a vertical part thereof, 20B is a settling part of a cross-flow part, and 20C is a settling part of a cross-flow part. 20A-U is the upper tank of the vertical section 20A, 20A-M is the middle tank, and 20A-L is the lower tank, which is a hopper. 21 is a sludge storage tank that stores the sludge pulled out from the hopper 20A-L, 22 is a pump that sends out the sludge in this sludge storage tank 21, 23 is a return sludge distribution groove, and 24 is the sludge storage tank 21 and this return sludge distribution groove 23. 25 is a valve provided in this pipe 24 for opening/closing the pipe and adjusting the flow rate, and 26 is a return sludge flow meter for detecting the sludge flow rate in the pipe 24. 27 is a pipe line for sending out excess sludge in the sludge storage tank 21 to the sludge treatment facility;
8 is a valve provided in this pipe line 27, and 29 is an excess sludge flow meter for detecting the flow rate of sludge flowing inside this pipe line 27. 30 is an aeration tank, 31
is the return sludge distribution groove 23 sent to this aeration tank 30.
32 is a mixed liquid sludge concentration meter provided in the aeration tank 30 for detecting the mixed liquid sludge concentration in the aeration tank; 33 is a mixed liquid sludge concentration meter installed in the aeration tank 30; 34 is a flow path that leads the sewage to the aeration tank 30, and 35 is a meter that measures the flow rate of the sewage in this flow path 34.

Next, a method for monitoring the amount of sedimentation tank sludge in the above system will be explained.

The sewage or its primary treated water flowing from the flow path 34 is injected into the aeration tank 30 together with the return sludge from the return sludge distribution groove 23 to form a mixed liquid. The mixed liquid undergoes a biochemical reaction by aeration in the aeration tank 30, and then is led to the settling tank 20 through the distribution groove 33 at a distribution ratio _a3 . The mixed liquid led to the settling tank 20 is transferred to the vertical section 2 at a ratio d ₃ corresponding to the flow rate of sludge drawn out from the settling tank.
0A, and the rest is distributed to the settling section 20B of the cross-flow section. Solid-liquid separation occurs in the settling section, and the sludge falls into the settling section 20C with a delay time _Td . The amount of settled sludge in the settling section 20C multiplied by a coefficient _b3 is transferred to the vertical section 20A. In this example, since the settling tank is a two-story type, the ratio of the flow rate of sludge in the upper stage and the flow rate of sludge in the lower stage is set, and the rate at which the sludge in the upper stage falls into the middle tanks 20A-M of the vertical section 20A is determined by e. It was set to ₃ . The vertical section 20A consists of n stages of complete mixing tanks, in which sludge is drawn from the settling tank 20 through the lowest stage hopper 20A-L, and is combined with the sludge drawn from other settling tanks to form the N stage complete mixing tank. The sludge is collected in a sludge storage tank 21. The sludge in the sludge storage tank 21 is returned to the sludge distribution groove 2 via a pipe 24 by a pump 22.
I am guided by 3. Further, a part of the sludge introduced by the pump 22 is drawn out through a pipe line 27 and sent to a sludge treatment facility. The return sludge distribution groove 23 is connected to the aeration tank 3
The mixed liquid sludge is returned to the aeration tank 30, in which the mixed liquid sludge concentration meter 32 is installed, at a flow rate distribution ratio _c3 .

Although the treatment is carried out in this way, the aeration tank 30
The flow rate of sewage flowing into the sewage tank Q _s , the flow rate of return sludge from the sludge storage tank 21 to the sludge distribution groove 23 Q _r , and the flow rate of excess sludge sent from the sludge storage tank 21 to the sludge treatment facility Q _w are determined by flow meters 35, 26, and 29, respectively. has been detected, and also from the aeration tank 30 to the sedimentation tank 2.
Since the sludge concentration X _a of the mixed liquid sent to 0 is detected by the mixed liquid concentration meter 32, the above equation 1 ~
In order to calculate the amount of sludge in the settling tank 20 using the eighth equation, it is sufficient to know the parameters lag time t _d , proportionality constant b, and number n of vertical tanks.
Among these, n is determined by the actual plant. Also,
T _d and b are determined by actually measuring the return sludge concentration X _r ' several times while constantly measuring Q _s , Q _r , Q _w , and X _a and checking whether X _r in equation 6 is equal to this X _r '. Search and find a value that minimizes the error with _r ′.

Using these numerical values, the second to eighth equations are calculated to obtain the sludge amounts Z ₁ , Z ₂ , Z ₃ , and then the first equation is calculated to determine the sludge amount in the settling tank.

Figure 3 shows the amount of sludge Z in the settling tank determined using the above method.
This is the weekly fluctuation of (Equation 1). The amount of sedimentation tank sludge obtained through calculation shows daily fluctuations that follow the amount of sewage inflow, and when the average residence time is calculated, it is in the range of 1 to 2 hours, which is almost the same as the design value of the water treatment equipment. The results obtained were of value. By the way, the optimal value of the parameters used to calculate the amount of sludge is a ₃ = 1.088,
T _d = 1, 59 hr (h is time hr), b =
0.596, d ₃ = 0.783, e ₃ = 0.426, n = 3, N = 1
(N is the number of sections in the sludge storage tank 21), c ₃ =1.015. These parameter values are consistent with those expected in the actual machine.

In this way, the flow rate of sewage, return sludge flow rate, excess sludge flow rate, or settling tank is calculated using parameters that minimize the deviation (error) between the simulation model calculation value and the actual measurement value of the return sludge concentration returned to the aeration tank. The amount of sludge accumulated in the settling tank can be determined by calculation from the time series of the measured value or representative value of the mixed liquid sludge concentration of the withdrawal flow rate and the aeration tank outflow, making it easy to monitor the amount of sludge in the settling tank. Therefore, the aeration tank and settling tank can be managed to match the sewage inflow characteristics.

In this way, sewage, etc. is mixed with activated sludge in the aeration tank, and this mixed liquid is sent to the settling tank to precipitate the solid content. In a facility that processes the sewage while discharging some of it from the settling tank to the outside, the amount of inflow of the sewage, the concentration of the mixed liquid, the amount of sludge removed from the settling tank, and the amount of sludge sent from the settling tank to the aeration tank. The amount of sludge in the settling tank is determined by calculating the amount of sludge settling in the settling tank according to a simulation model consisting of the amount of activated sludge and the time required for the solid content of the mixed liquid to settle in the settling tank. Since the amount is known, the amount can be known accurately, making it easier to monitor the amount of sludge in the settling tank, and managing the aeration tank and settling tank to match the inflow characteristics of sewage. It is possible to provide a method for monitoring the amount of sludge in a sewage treatment plant sedimentation tank, which has excellent features such as the ability to

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the settling tank to explain the sedimentation and sedimentation state of sludge in the settling tank, and Fig. 2 mainly shows a settling tank simulation model to explain one embodiment of the present invention. FIG. 3, a system diagram showing the flow of sludge, is a graph showing weekly fluctuations in the amount of sludge in the settling tank monitored by the method of the present invention. 10, 20... Sedimentation tank, 10a, 20A-L... Hopper, A, 20A... Vertical section, B, 20B... Cross flow section, 12... Straightening wall, 13... Scraping machine, 21... Sludge storage tank, 23... Return sludge distribution Groove, 24, 27...pipeline,
26, 29, 35...flow meter, 30...aeration tank, 32
...Mixed liquid sludge concentration meter, 33...Distribution groove.

Claims (1)

[Claims] 1. Sewage, primary treated water, etc. are mixed with activated sludge in an aeration tank, and this mixed liquid is sent to a sedimentation tank divided into a vertical section and a horizontal section to precipitate the solid content. The sludge is collected in the vertical section, a part of which is sent to the aeration tank as the activated sludge, and a part of which is removed from the settling tank to the outside. The concentration of the mixed liquid, the amount of sludge to be removed from the settling tank, the amount of activated sludge sent from the settling tank to the aeration tank, and the time required for the solid content of the mixed liquid to settle in the settling tank. A relational expression of a simulation model is set to determine the amount of sludge in the sedimentation tank, and the time required for the sedimentation is set as a parameter, and calculations are performed from the actual measured values of each amount and the concentration to determine the amount of settled sludge in the settling tank. A method for monitoring the amount of sludge in a sewage treatment plant sedimentation tank. 2. The method according to claim 1, characterized in that a relational expression of a simulation model is set by adding a ratio of the mixed liquid flowing into the settling tank to the vertical part and the horizontal part as a parameter. Method for monitoring sewage treatment plant sedimentation tank sludge volume. 3. Claims 1 and 3, characterized in that the relational expression of the simulation model is set by adding the distribution ratio of the amount of sludge transferred from the horizontal flow section of the settling tank to each tank of the vertical section as a parameter. A method for monitoring the amount of sludge in a sewage treatment plant sedimentation tank as described in Section 2. 4 Add the number of stages of the vertical part as a parameter,
A method for monitoring the amount of sludge in a sedimentation tank of a sewage treatment plant according to claim 1, characterized in that a relational expression of a simulation model is set. 5. In a case where there is a plurality of settling tanks, a relational expression of a simulation model is set by adding a ratio of the liquid mixture distributed from the aeration tank to each of the settling tanks as a parameter. A method for monitoring the amount of sludge in a sedimentation tank of a sewage treatment plant as described in item 1.