JP2882045B2 - Backwash control method for downflow type biological activated carbon treatment tower - Google Patents

Description

The present invention relates to a backwashing control method for removing clogging of a gap of activated carbon in a downflow type biological activated carbon treatment tower in advanced water purification treatment.

B. Summary of the Invention In the present invention, in a downflow type biological activated carbon treatment using an activated carbon treatment tower of an advanced water purification facility, the level meter detects that the water level in the activated carbon treatment tower during the activated carbon treatment has reached a predetermined level. Automatically starts backwashing, detects the expansion level of activated carbon at the time of backwashing with an interface meter, and automatically controls the flow rate of the backwashing treatment water to maintain this expansion level at a constant level. It is often done automatically.

C. Prior Art A water purification process that is currently generally performed will be described with reference to FIG. Raw water taken from rivers and lakes enters landing well A. Next, the mixture enters the floc formation pond C through the mixing pond B in which the coagulant is injected and mixed for the purpose of removing the turbid components (sand, clay, organic substances of algal sugar, etc.) in the raw water. In the floc formation pond C, the floc is gradually grown by the stirring force and the residence time. The floc which has grown to the maximum enters the sedimentation basin D and is separated. Further, the fine floc which cannot be removed by the sedimentation basin D is removed by the filtration basin E.

In this process, algicidal treatment, iron, manganese, chromaticity decomposition,
Chlorination for removal is incorporated. In particular,
In the suburbs of large cities, rivers and lakes are extremely polluted, have a high ammonia content, and have high chromaticity components including humic substances, which are precursors to the carcinogenic substance THM (trihalomethane). When chlorination is performed on both of the high contents, they react with ammonia to produce chloramine and consume more chlorine than necessary. As a result, the chlorine injection rate increases and TH
Increases the ability to produce M (THMFP). Against this background, in recent years, a method of incorporating advanced treatment into a general water purification process for the purpose of removing the above-mentioned substances has been used.

Advanced treatments include ozone treatment alone as an alternative to chlorination and activated carbon treatment to remove trace substances harmful to health. Further, there is a combination process utilizing the characteristics of both. F is an advanced water treatment system that performs a combined treatment of the two, and is composed of an activated carbon treatment tower G and an ozone contact tower. However, ammonia can hardly be removed even when both treatments are performed, and biological treatment (mainly nitrifying bacteria) must be performed to remove ammonia. In the biological treatment currently being performed, air is sent to raw water that has been withdrawn, microorganisms are propagated by aeration treatment (aerobic treatment), and ammonia is removed by the metabolic ability of microorganisms. However, this method is a good method if there is room in the facilities of the water purification plant, but this method cannot be adopted if the facilities are limited. As a result, the method considered as the best means was biological activated carbon treatment.

Biological activated carbon treatment is a modification of the activated carbon treatment in the advanced treatment process, in which microorganisms are propagated on the activated carbon surface, ammonia in the inflow water is removed, and trace organic substances can be adsorbed and removed. This method has not been established yet. In other words, there is a limit to the adsorptivity of activated carbon (breakthrough: total water flow when the target substance removal threshold is exceeded or water flow time at a constant water flow), and how highly efficient and long life can be maintained. Is an issue.

This biological activated carbon treatment method is roughly classified into a downward fixed bed through which the target water is passed from above the activated carbon treatment tower and an upward flow bed through which water is passed from below. As for each feature, the former has high removal efficiency of the target substance, but the filter bed is easily clogged by SS components and the like, and the cleaning cycle is short. On the other hand, the latter has lower removal efficiency of the target substance than the former, but is less likely to cause clogging of the filter bed due to SS components and the like, and both have advantages and disadvantages. When the filter bed is clogged, the gap between the filled activated carbons becomes clogged and the head rises,
Water flow capacity is reduced.

In particular, the control method of the backwash process, which is indispensable for the activated carbon treatment, is an important technique for operation management of the activated carbon treatment tower.

When using a downflow type biological activated carbon treatment in an advanced water purification facility, the flow resistance gradually increases due to suspended substances accumulated in the activated carbon layer and the biofilm attached to the activated carbon particle surface as water flows. . This is confirmed as a rise in the water level above the activated carbon filling section. When the head loss becomes large in this way, it becomes difficult to pass water, so that a backwashing operation for washing the activated carbon packed bed and reducing flow resistance is required. The frequency of backwashing depends on the amount of activated carbon treated water, the nature of suspended substances in the treated water, the concentration, the size of activated carbon particles, and the like.

FIG. 3 is an explanatory view of an activated carbon treatment apparatus using water washing as a backwash washing method in a conventional downflow activated carbon treatment. In FIG. 3, the normal treatment flow is as follows. The treatment tower inflow water 14 flows in from the upper part of the activated carbon treatment tower 1 and the activated carbon filling part 2 which is a fixed bed held by the activated carbon support part 3 flows down. A water substance is purified by adsorbing a substance such as a substance to be removed. The treated water that has passed through the activated carbon filling section 2 flows into the treated water collecting section 13 and flows out as treated water 16 in the treatment tower. When the flow into the activated water treatment tower 1 is continued, the flow resistance is increased due to the adsorption of organic substances and the like in the treatment tower inflow water 14 into the activated carbon filling section 2, and the water level above the activated carbon filling section 2 rises. The maintenance manager confirms that the water level has reached the set water level, and causes the system control unit 12 to perform a backwash operation.

 The operation at the time of the backwash will be described below.

At the start of backwashing, the inflow water electric valve 8 and the treated water electric valve 9
, The backwash pump 10 is operated, and the treated water 15 for backwashing flows into the activated carbon treating tower 1 from below the activated carbon treating tower 1, thereby expanding the activated carbon filling unit 2 with the water flow to fluidize the activated carbon particles. Then, the activated carbon filling unit 2 is washed. The washing wastewater is discharged from the upper part of the activated carbon treatment tower 1 as wastewater 18 during backwashing. At this time, the backwashing speed at the time of backwashing differs depending on the activated carbon to be used.
That is, the expansion is performed at a layer expansion rate of 30 to 40%. For example, if the water temperature is 20 ° C and the layer expansion rate is 40%, the backwashing speed is
Approximately 50 m / hr for coal-based granular activated carbon with an average particle size of 1.5 to 1.7 mm
Becomes

At the time of backwashing, the backwashing speed is set in the system control unit 12 in advance, and the backwashing pump control unit 11 is controlled by the backwashing water flow rate measuring unit 17 and the backwashing pump control unit 11 so as to have this set value. Controls the motor speed of the backwash pump 10.

D. Problems to be Solved by the Invention However, the conventional activated carbon treatment system has the following problems.

(1) It is necessary for the maintenance manager to confirm the time of backwashing, and if care is not taken, water may not be able to pass. Also,
Even when backwashing is performed periodically regardless of whether the head loss reaches the upper limit, it is necessary to check that the head loss does not exceed the upper limit during normal operation.

(2) In some cases, the layer expansion rate cannot be set to 30 to 40% simply by adjusting the backwashing speed to the set value at the time of backwashing. This is because the layer expansion coefficient is affected not only by the backwashing speed but also by the water temperature.

(Refer to Fig. 4, Document name: Technical data of advanced water purification facility (Activated carbon treatment facility) March 1988, Japan Water Works Association) Also, if the bed expansion rate is increased, washing water is required more than the removal effect by backwashing. Therefore, if the efficiency is poor, and if the coefficient of layer expansion is too small, the effect of backwashing cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to automatically start backwashing when a gap in activated carbon of a treatment tower is clogged. The present invention is to provide a backwashing control method for a downflow type bioactive carbon treatment tower in which a backwash flow rate is automatically adjusted so as to maintain a bed expansion coefficient, and an efficient backwash can be automatically performed. .

E. Means for Solving the Problems To achieve the above object, a method for controlling backwashing of a downflow type biological activated carbon treatment tower according to the present invention comprises a downflow type biological activated carbon treatment tower using an activated carbon treatment tower of an advanced water purification facility. In activated carbon treatment,
The level meter detects that the water level in the activated carbon treatment tower has reached a predetermined level during activated carbon treatment, and automatically starts backwashing. The expansion level of activated carbon during backwashing is detected by an interface meter and this expansion level is detected. The backwashing treatment water flow rate is automatically controlled so as to keep the water constant.

F. Action If the gap of the activated carbon filled in the activated carbon treatment tower is clogged, the flow of inflow water through the treatment tower becomes worse,
Since the water level rises, by detecting this water level with a level meter, the backwashing treatment water is automatically flowed to start backwashing. When backwashing starts, the activated carbon filling section expands. By detecting the expansion level and controlling the flow rate of the backwashing treatment water so that the expansion level is constant, the backwash can be performed with a constant efficiency. Thus, efficient backwashing can be automatically performed by appropriately setting the level detection position of the interface meter.

G. Embodiment An embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows a configuration diagram of an activated carbon treatment device. The same components as those shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will not be repeated.

In FIG. 1, reference numeral 4 denotes a level meter detecting portion provided at a position for setting a water level at the time of backwashing on the upper part of the activated carbon treatment tower 1; 5, a level meter converter; The interface meter detecting unit 7 provided at the activated carbon interface setting position is a converter for the interface meter, and the outputs of the converters 5 and 7 are drawn into the system control unit 12. Next, the operation of the activated carbon processing apparatus will be described.

Open the inflow water motorized valve 8 and the treated water motorized valve to open the treatment tower
14 is introduced from the upper part of the activated carbon treatment tower 1 and the activated carbon filling part 2 held by the activated carbon support part 3 is caused to flow down, thereby purifying the water quality by adsorption or the like of a removed substance such as an organic substance. The treated water that has passed through the activated carbon filling section 2 flows into the treated water collecting section 13 and exits as treated tower treated water 16. As the supply of the treatment tower inflow water 14 to the activated carbon treatment tower 1 continues, the accumulation and adsorption of suspended substances in the activated carbon filling section 2 increase, and the pressure loss in the activated carbon filling section 2 also increases. Appears as a rise in the water level at the top of part 2.
The point at which this water level is detected by the level meter detecting unit 4 whose position has been set in advance is defined as the start of backwashing. The level detection signal detected by the level meter detection unit 4 and converted by the level meter conversion unit 5 is sent to the system control unit 12, and the backwash operation is automatically started using this signal as a backwash start signal.

At the start of backwashing, the inflow water electric valve 8 and the treated water electric valve 9
Is closed and the backwashing pump 10 is operated to wash the activated carbon filling unit 2 by flowing treated water 15 for backwashing from the bottom of the activated carbon treating tower 1. The washing wastewater is discharged from the upper part of the activated carbon treatment tower 1 as wastewater 18 during backwashing.
At this time, the backwashing speed at the time of backwashing is such that the activated carbon interface fluidized by the backwashing of the activated carbon filling unit 2 is detected by the interface meter detection unit, and the signal from the interface meter converter 5 is received by the system control unit 12. The backwash pump 10 and the backwash pump control unit
11 controls the backwash flow rate and adjusts the backwash speed. This keeps the activated carbon interface at a constant level. In addition, the system control unit 12 determines whether the value of the flow velocity measured by the backwash water flow rate measuring unit 17 is within a range of a preset upper and lower limit value, and outputs an alarm if abnormal.

After the backwash operation is continued for a required time, the backwash pump 10 is stopped, the treated water electric valve 9 is opened, the sedimentation of the activated carbon and the discharge of the wash water are performed, and then the inflow water electric valve 8 is opened to supply water. To start.

If the interferometer detector 6 is of a movable type instead of a fixed type, a backwashing operation with an arbitrary layer expansion coefficient is possible.

H. Effects of the Invention Since the present invention is configured as described above, the following effects can be obtained.

(1) The activated carbon filling section can detect clogging based on the water level and automatically perform backwashing.

(2) Since the backwashing is performed by automatically adjusting the backwashing flow rate by an interface meter so as to maintain the layer expansion coefficient of the activated carbon, efficient backwashing can be performed automatically.

(3) By combining the above (1) and (2), the backwash operation can be automated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an activated carbon treatment device used in an embodiment of the present invention, FIG. 2 is an explanatory diagram of a configuration of a water purification plant, FIG. 3 is a configuration diagram of a conventional activated carbon treatment device, and FIG. It is a graph which shows an activated carbon expansion coefficient. DESCRIPTION OF SYMBOLS 1 ... Activated-carbon processing tower, 2 ... Activated-carbon filling part, 3 ... Activated-carbon support part, 4 ... Level meter detection part, 5 ... Level meter converter, 6 ... Interface meter detection part, 7 ... Interface meter Transducer, 8 ...
Inflow water electric valve, 9 ... treated water electric valve, 10 ... backwash pump, 11 ... backwash pump control unit, 12 ... system control unit
13 ... treated water collecting section, 14 ... treated tower inflow water, 15 ... treated water for backwash, 16 ... treated tower treated water, 17 ... backwash water flow measuring section, 18 ... backwashing Drainage.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 1 / 28,3 / 06

Claims (1)

(57) [Claims] In a downflow type biological activated carbon treatment using an activated carbon treatment tower of an advanced water purification facility, a level meter detects that the water level in the activated carbon treatment tower during the activated carbon treatment has reached a predetermined level, and automatically detects the water level. A downstream bioactive carbon characterized by automatically starting backwashing, detecting the expansion level of activated carbon during backwashing with an interface meter, and automatically controlling the flow rate of the backwashing treatment water so as to keep the expansion level constant. Control method for backwashing of treatment tower.