JPS6279894A - Method for discriminating timing for backwashing of sewage cleaning-up device - Google Patents

Abstract

PURPOSE:To automatically and exactly know the timing for backwashing by calculating the weight of suspended matter to be captured by contact filter media from the concn. of the suspended matter in tanks and the flow rate at which sewage flows into the tanks and emitting a command for backwashing when the calculated value is higher than a set value. CONSTITUTION:The coated filter media 2a, 2b are installed in the tanks 1a, 1b and the sewage is circulated and fluidized to the contact filter media. The command for backwashing is delivered to the inside of the tank when the contact filter media capturing the suspended matter contained in the sewage attain the threshold of the treating capacity. The weight of the suspended matter to be captured by the above- mentioned contact filter media is calculated from the concn. of the suspended matter in the tanks and the flow rate at which the sewage flows into the tank in the above- mentioned method for discriminating the timing for backwashing of a sewage cleaning-up device. The command for backwashing is emitted when the calculated value is higher than the preset value. As a result, the additional decrease of the treating capacity of the contact filter media for cleaning-up of the sewage is obviated and the efficient backwashing operation is continued.

Description

Detailed Description of the Invention (Technical Field to which the Invention Pertains) The present invention is directed to the treatment of residual suspended solids after organic substances in circulating wastewater are oxidized and decomposed by the action of microorganisms that settle on a contact filter medium in a tank. The present invention relates to a method for determining backwash timing, which performs reverse '/fc operation so as not to reduce the purification capacity of the contact filter medium due to deposition and stacking.

[Prior art and its problems]

Conventionally, in purifying wastewater, a fixed bed method is well known in which wastewater is purified by utilizing the action of microorganisms contained in the wastewater. This fixed-bed method sewage purification equipment has a contact filter made of corrugated plastic plates, nets, tubes, etc. installed in the tank, and circulates and flows through the action of microorganisms that settle on the contact filter. It oxidizes and decomposes organic substances in sewage, and is suitable for sewage treatment and purification of domestic wastewater because it is easy to maintain, generates little surplus sludge, and is resistant to load fluctuations. and
It is liked and widely used.

By the way, this type of sewage treatment method can be roughly divided into the aerobic fixed bed method and the anaerobic fixed bed method. is circulated, organic substances are removed as described above,
It purifies sewage. In addition, the latter method anaerobically digests organic substances in wastewater without diffusing air into the tank.

Regarding the aerobic fixed bed method mentioned above, I would like to add:
There are methods to mainly remove organic substances in wastewater and methods to mainly remove suspended solids in wastewater, and these methods are used depending on the need, but in either case, suspended solids cannot be removed sufficiently. As a result, floating substances may come into contact with and stack on the contact filter medium, resulting in so-called clogging, which may reduce the purification performance.

Conventionally, a sewage purification apparatus as shown in FIG. 5, for example, has been proposed as a means for removing suspended solids from sewage.

Here, in the figure, the symbol (1) indicates a septic tank, and the - side of the septic tank (1) has a wastewater inlet (4), and the other side has a purified water outlet (5). are provided for each.

In addition, a contact filter medium (2) is installed in the septic tank (1), which allows microorganisms contained in the wastewater to settle and multiply, and also captures some of the suspended solids. 2)
A diffuser pipe (3) extends along the axis.

The air diffuser pipe (3) circulates and flows the wastewater in the tank in the direction of the arrow, and utilizes the air lift effect of air bubbles to circulate and flow the wastewater. This diffuser pipe (3)
is connected to the proa (11) via the aeration supply valve (9), and on the other hand, the proa (11) is connected to the aeration supply valve (9).
A branch conduit (6) is provided on the way to the backwash aeration pipe (8) via a backwash aeration supply valve (1O).

Therefore, when mainly removing suspended solids from wastewater (organic substances are mostly removed by a separate purification device), the wastewater is circulated and flowed by aeration from the aeration pipe (3). As it passes through the contact filter medium (2), it traps suspended solids, and the purified water is sent out through the outlet (5).

Such purification treatment is normally carried out continuously for several weeks, but in this case, suspended solids may be deposited on the contact filter medium (2).
If they are stacked and left as they are, the contact filter medium (2) will eventually become clogged, which is one reason for reducing the purification capacity. For this reason, a diffuser supply valve for backwashing (10
) is opened, air is sent from the proa (11) through the branch conduit (6) to the backwashing diffuser pipe (8), and the contact filter medium (2) is
A so-called backwashing operation is carried out to remove suspended solids that have settled in the septic tank (1) and become the I-layer. Afterwards, the mud is discharged to the outside from a drainage valve (12).

By the way, when performing a backwash operation of this type of device, if the timing is not properly grasped, the cleanliness level of the water after purification treatment may be adversely affected. In other words, although the contact filter medium still has sufficient ability to capture suspended solids, because the backwashing period was brought forward, even the suspended solids that had been deposited and layered on the contact filter medium were not absorbed into the purified water. Contaminants may enter the water and worsen the cleanliness of the water.

In addition, although this type of equipment is primarily intended to remove suspended solids, sewage still contains a large amount of microorganisms, and microorganisms can colonize and multiply on the contact filter media, removing organic substances from the sewage. Considering that oxidation and decomposition contribute to wastewater purification, advancing the backwashing period will strip microorganisms that have not yet grown sufficiently from the contact filter media, and will actually reduce the cleanliness of the water. It has a negative impact and is undesirable. In particular, when nitrifying bacteria settles and grows on the contact filter media, the growth of the bacteria is extremely slow, even though the bacteria have an extremely excellent ability to nitrify ammonia nitrogen to nitrate nitrogen. It is also slow - requiring a long period of time to regenerate exfoliated microorganisms.

On the other hand, if the backwashing period is missed, the contact filter medium becomes clogged due to excessive deposition and stacking of suspended solids, further reducing the wastewater purification ability.

In this way, if there is no means to properly grasp the timing of backwashing, it will have a great negative impact on the above-mentioned sewage purification processing ability, so various studies have been conducted to find the best timing for backwashing. Methods for determining this include visually checking for clogging of the contact filter medium, and using a timer to set a time and periodically perform automatic backwashing.

However, these methods are unfavorable from a labor-saving point of view because they require labor from operators, and the concentration of suspended solids in wastewater changes depending on the season, weather, time, etc.
It has the disadvantage that it cannot always guarantee a constant level of water cleanliness. Recently, a method has been proposed in which the concentration of suspended solids in the tank is detected by a sensor, and if the detected value exceeds a certain value, it is determined that the contact filter media is clogged and automatic backwashing is performed. (Refer to Special Publication No. 58-54875)
. However, although this method achieves good results when the concentration of suspended solids in wastewater is relatively stable, if the suspended solids increase or decrease by 1 degree or change rapidly, or if the suspended solids increase or decrease by 1 tf,
Despite the fact that the fa level itself has not changed much, the amount of wastewater has increased, so it appears that the suspended solids concentration has increased (detected, which often leads to incorrect backwashing orders being issued). have

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide a method for determining the backwashing time of a sewage purification device, which allows the backwashing time to be automatically and appropriately determined.

[Key points of the invention]

In order to achieve the above object, the present invention calculates the weight of suspended solids captured by the contact filter medium based on the suspended solid concentration in the tank and the amount of wastewater flowing into the tank, and this calculation is based on a preset value. The present invention is characterized in that a backwashing command is issued when either the weight of suspended solids is higher than the suspended solids weight, or the capture rate is determined from the calculated value of the suspended solids weight, and this value is lower than a preset suspended solids trapping rate.

When determining when to backwash a sewage purification system, it depends entirely on the weight of suspended solids that are deposited and layered on the contact filter media. Therefore, the present invention automatically detects the weight of suspended solids deposited and stacked on the contact filter medium. That is,
First, the concentration of suspended solids contained in wastewater is detected and this detection signal is applied to the control device, while a detection signal of the amount of wastewater flowing into the purification tank is also applied to the control device. Here, the product of the suspended solids concentration signal and the sewage amount signal is calculated, and the actual weight of suspended solids deposited and stacked on the contact filter medium is calculated. Next, the actual weight of suspended solids is compared with a preset weight of suspended solids, and if the actual weight of suspended solids is higher, a backwash command is sent to the sewage septic tank through a transmitter.

However, if the time for backwashing cannot be properly determined using only the above functions, the suspended solids capture rate is calculated using a differentiator based on the actual suspended solid weight, which changes from moment to moment, and this calculated value is combined with a preset suspended solids weight. The substance capture rate is compared, and if the calculated value is lower, a backwash command is sent to the 7η water septic tank through the transmitter.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.
Prior to the explanation, the points of view that led to the creation of the present invention will be explained in detail.

Previously, this type of research has shown that the types of suspended solids deposited and stacked on contact filter media are due to differences in the shape and structure of the contact filter media, the impact that sewage has on the contact filter media during aeration, the number of aerations, etc. Considering the purification capacity, it is known that the weight of approximately 5 to 10 +r/m is the limit, although it depends on the amount of water.

On the other hand, the weight TSS of suspended solids deposited and laminated on the contact filter medium can be determined from the following theoretical formula.

Here, Q is the amount of sewage flowing into the septic tank, SS is the concentration of suspended solids remaining in the first septic tank, and S S z is the suspended solids Mt remaining in the second septic tank.

time and t indicate processing time.

When the suspended solid weight TSS determined from the above equation (1) is graphed, the theoretical suspended solid trapping characteristics as shown by the solid line in FIG. 2 are obtained. As can be easily understood from this figure, at the time of startup, the suspended solid weight Tss increases at an accelerating rate, but eventually the contact filter medium becomes clogged and eventually converges to a constant value.

It has been confirmed that the ability of the contact filter medium to capture suspended solids begins to deteriorate approximately one month after startup.

Considering these technical data comprehensively, the weight of suspended solids Tss deposited and laminated on the contact filter medium is determined by its upper limit TSSm.
Favorable results could be obtained by sending a backwashing command to the sewage purification tank when it was within the range of 60-70% of ax (=5-lokg/m).

Next, the inventor examined in detail the theoretical suspended solids trapping characteristic p shown by the solid line in FIG. 2, and found that the suspended solids trapping rate of the contact filter medium at startup (in FIG. (For convenience of explanation, this α is defined as the suspended solids capture rate.) is the theoretical suspended solids weight before reaching the suspended solids weight upper limit value TSSllIax. It was noticed that this difference naturally differs from the suspended solids capture rate determined from the capture characteristic r, and that this difference has a certain causal relationship with the purification processing ability of the contact filter medium.

In other words, the reason why the capture rate at startup is higher than the capture rate before reaching the upper limit of the weight of suspended solids is thought to mean that the phenomenon of clogging caused by suspended solids does not occur much in the contact filter medium. .

Therefore, the inventor calculated the theoretical suspended solids capture rate α from the solid line shown in FIG. 2 using the following formula.

t where TSS (t) is the weight of suspended solids captured, expressed as a function of the purification treatment time, and L indicates the purification treatment time.

The upper limit value αmax of the theoretical suspended solids capture rate α obtained from the above equation (2), that is, the upper limit value of the purification processing capacity of the contact filter medium, is determined in advance through experiments and research, and this upper limit value α
Actual suspended solids capture rate α within the range of 40 to 50% of max.
When b is input, by using this value as the backwash command signal αb, it is possible to know the preferred timing for backwashing.

However, the theoretical suspended solids capture rate α and the actual suspended solids capture rate α
As can be seen from the actual suspended solids trapping characteristics m and n shown by broken lines and chain lines in FIG. 2, b does not necessarily match. Examining this difference, we find that the range L of the characteristic m
The reason for this is that the concentration of suspended solids is low when the amount of inflowing sewage is large, so it is thought that the suspended solids ITTs captured by the contact filter medium do not increase much.

Furthermore, the reason why the characteristic n is higher than the characteristic i is considered to be that the concentration of suspended solids contained in the wastewater is extremely high compared to the amount of wastewater.

Therefore, in Fig. 2, we set the lower limit standard suspended solids weight TSSn and the upper limit standard white suspended solids weight TSSh, and under the condition that suspended solids weight TSS<lower limit standard suspended solids weight TSSβ, the actual suspended solids capture rate αb≦theoretical In the case of suspended solids capture rate α (
In the case of characteristic m), it is assumed that the contact filter medium has sufficient ability to capture suspended solids, and no backwashing command is issued. Suspended solid weight T
It is sufficient to issue a reverse command when SS≧lower limit standard suspended solid weight TSSf.

On the other hand, as in characteristic n, if the actual suspended solids capture rate αb>theoretical suspended solids capture rate α, but the suspended solids weight TSS≧the suspended solids weight within the upper limit standard TSSh, the contact filter medium no longer captures suspended solids. Since the capacity has been lost, a backwashing command is issued.The value of the lower limit standard suspended solids weight TSS1 is about 50% of the above TSSmax, and the value of the suspended solids weight TSSh within the upper limit standard is , above T
This is about 80% of SSmax. These are empirically determined preferred applicable values.

An embodiment of the present invention based on the above-mentioned point of view will now be described, but the same components as in FIG. 5 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 1 shows a sewage purification device showing one embodiment of the present invention, which includes a first septic tank (la) and a second septic tank (1b) that are connected to each other. have

The first septic tank (1a) oxidizes and decomposes organic substances in wastewater through the action of microorganisms.
It also has the function of capturing some of the suspended solids in wastewater. Furthermore, although the second septic tank (1b) mainly captures suspended substances in wastewater, it also has the function of oxidizing and decomposing organic substances in wastewater. For this reason, the first
The structures and shapes of the contact filter media (2a) and (2b) installed in the second septic tanks (1a) and (1b) are different.

On the other hand, the first and second septic tanks (1a) and (1b)
is equipped with a detector (
15a) and (15b) are arranged, and the signals detected from these detectors (15a) and (15b) are applied to the control device (16) via the converter (14). There is. Further, an fL volume needle (13) for detecting the amount of wastewater inflow is provided at the inlet (4) of the first septic tank (1a), and the signal detected by the flow meter (13) is also The signal is applied to a control device (16).

As shown in FIG.
) and a transmitter (21), which are connected to each other by an electrical circuit.

In the control device (16) having such a configuration, the concentrations of suspended solids in the first and second septic tanks (1a), (1b) are detected by the detectors (15a), (15b), respectively. The detection signal passes through a converter (14) to determine the difference thereof, and the difference signal is applied to a multiplier (17). The sewage flow rate signal is also applied to the multiplier (17), where it is multiplied and the output signal is sent to the integrator (18). The integrator (18) determines the weight of the trapped suspended solids TSS based on the above-mentioned formula (1), and the integrated signal is sent to the setting signal from the setting device (19) through the operating end (20). When it is determined that the suspended solids weight TTS is higher than the set value, the backwashing command signal αb is sent from the transmitter (21) to the backwashing aeration supply valve ( 10) was sent to
This performs a backwash operation of the contact filter medium (26).

Note that the first septic tank (1a) also performs backwash operation,
Since this is a backwash operation using a timer circuit, it is treated as outside the scope of the present invention here.

The setting device (19) has an upper limit value T of the suspended solids weight TSS.
A set value of 60 to 70% of SSmax is cented.

FIG. 4 shows another embodiment of the control device according to the present invention, which is generally designated by the reference numeral (22). The 311 device (22) includes multipliers (1
7), integrator (18), differentiator (23), setter (24)
), and has a transmitter (26).

In this configuration, the suspended matter concentration difference signal and the flow rate signal are applied to the multiplier (17) as in the first embodiment, and the output signal multiplied here is applied to the integrator (17).
8), and the suspended solid weight TSS is calculated from time to time. The calculated suspended solids weight ITss signal is sent to the differentiator (23), where it is differentiated based on the above-mentioned equation (2), and the actual suspended solids capture rate αb is calculated. This output signal of the actual suspended solids trapping rate αb is compared with the setting signal from the setting device (24) through the operating end (25), and when it is determined that the actual suspended solids trapping rate αb is lower than the set value, It is sent from the transmitter (21) as a backwash command signal αb to the backwash aeration supply valve (10) of the second septic tank (1b),
This performs a backwash operation of the contact filter medium (2b).

Note that the setting device (24) is set to a value of 40 to 50% of the upper limit value α+aax that allows the contact filter medium (2b) to perform purification processing.

Since this embodiment performs detailed calculations as described above, it is very convenient to apply it to cases where backwashing timing cannot be properly determined using only the first embodiment described above.

〔Effect of the invention〕

As explained above, according to the present invention, deposits and
The weight of suspended solids that accumulates is calculated from the suspended solids concentration of sewage and the amount of sewage inflow, and when it is determined that the value is higher than the set value, a backwash command signal is issued, so that the sewage purification process of the contact filter medium is Extremely efficient backwash operation can be continued without any further reduction in capacity. Further, according to the present invention, the clogging of suspended solids deposited and stacked on the contact filter medium is determined from the suspended solids capture rate of the contact filter medium based on the suspended solids concentration of wastewater and the amount of wastewater inflow, and the capture rate is determined from the suspended solids capture rate of the contact filter medium. Since the system determines that the value is lower than the set value and issues a backwash command signal, even if the suspended solids concentration in the wastewater changes rapidly, or even if the suspended solids concentration hardly changes, the amount of wastewater inflow will suddenly increase. It is expected that this will further contribute to the improvement of this type of technology, since it is possible to accurately judge when to backwash even if the amount of water increases.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the suspended solids trapping characteristics, which compares theoretical values and actual data, and Fig. 3 is a graph showing an embodiment of the present invention. FIG. 4 is a schematic block diagram showing yet another embodiment of the control device according to the present invention, and FIG. 5 is a schematic diagram showing a conventional embodiment. 1a: First septic tank, 18: Integrator lb...
Second septic tank, 19.24...Setter 2a, 2
b...Contact filter medium, 21.26...Transmitter 8...Aeration pipe for backwashing, 23...Differentiator 10...Aeration supply valve for backwashing,

Claims (1)

[Claims] 1) A contact filter medium is installed in the tank, and wastewater is circulated through the contact filter medium, and when the processing capacity of the contact filter medium to capture suspended solids contained in the wastewater reaches its limit, the contact filter medium is installed in the tank. In the method for determining backwashing time for sewage purification equipment that sends backwashing commands, the weight of suspended solids captured by the contact filter medium is calculated from the suspended solids concentration in the tank and the flow rate flowing into the tank, and this calculated value is set in advance. A method for determining backwashing timing for a sewage purification device, characterized in that a backwashing command is issued when the value is higher than a specified value. 2) The weight of suspended solids captured by the contact filter medium is determined by the difference between the suspended solids concentration in the first septic tank and the suspended solids concentration in the second septic tank, plus the flow rate of sewage flowing into the first septic tank. 2. A method for determining backwashing timing for a sewage purification device according to claim 1, wherein the calculation is performed by multiplying and integrating the multiplication formula. 3) A contact filter medium is installed in the tank, and sewage is circulated through the contact filter medium to capture suspended solids contained in the sewage.When the processing capacity of the contact filter medium reaches its limit, a backwash command is sent into the tank. In the method for determining when to backwash a purifier, the weight of suspended solids captured by the contact filter medium is continuously calculated based on the suspended solids concentration in the tank and the flow rate of sewage flowing into the tank, and the suspended solids captured from this calculated value is 1. A method for determining backwashing timing for a sewage purification device, characterized in that a backwashing command is issued when this value is lower than a preset suspended solids capture rate. 4) The method for determining backwashing timing for a sewage purification apparatus according to claim 3, wherein the suspended solids capture rate is determined by differentiating the weight of suspended solids by the purification treatment time.