JPH0220319B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wastewater treatment method for purifying industrial wastewater, human waste, sewage, and the like.

[Conventional technology]

In recent years, when phosphorus contained in wastewater discharged from sewage treatment plants, human waste treatment plants, factories, etc. is discharged into closed public water bodies, eutrophication of the water bodies progresses, leading to algae and blue-green algae. It poses various social problems such as the occurrence of red tide.

Under these circumstances, various treatment technologies have been developed for the purpose of removing phosphorus from these wastewaters.
Mainly, physicochemical methods and biological treatment methods are used.

In addition to the conventional coagulation-precipitation method, physicochemical methods include catalytic dephosphorization method and crystallization method. In addition, in places where biological treatment methods are used, phosphorus removal has been achieved to a certain extent compared to existing biological dephosphorization methods using aeration tanks, forest stripping methods, and flocculation methods in which flocculants are added.

However, the former requires a sand filtration tank in the latter stage, requires capital investment and site area, and therefore requires significant modification or expansion of existing facilities.

In addition, the latter is caused by BOD in inflow water during heavy rain or rainfall.
Stable removal is difficult, as problems such as a significant drop in removal efficiency occur due to the effects of
Its removal rate is about 50-80%.

Therefore, it is known that a high removal rate of phosphorus can be obtained by coagulating filtration of phosphorus by a direct filtration method using a sand filter.

[Problem that the invention seeks to solve]

However, with this direct filtration method using sand filtration, the addition of a flocculant causes an increase in SS, which causes problems such as premature clogging of the filter layer and setting of the optimum injection rate of the flocculant.

Incidentally, as a wastewater treatment method, the method shown in FIG. 9 is known.

According to this method, after the inflowing wastewater is removed from sand and impurities in the settling tank equipment 1, the solids that tend to settle are first removed in the settling tank 2. Thereafter, fine solid matter and soluble organic matter are adsorbed and decomposed by microorganisms in an aeration tank 3, and converted into large flocs that are easy to settle, and then settled in a final settling tank 4 to obtain clear treated water.

However, this process cannot be expected to remove much of the phosphorus contained in wastewater, so after this, coagulation-sedimentation methods or biological dephosphorization methods using an aeration tank may be used. . However,
In each method, it is difficult to achieve stable dephosphorization with high removal rate.

[Purpose of the invention]

The present invention was made to solve these conventional problems, and its purpose is to supplement SS by using the entire filter layer through direct filtration of an upflow moving bed type continuous sand filter and microfloc. It is an object of the present invention to provide a method for removing phosphorus from wastewater, which controls the amount of phosphorus to be large and prevents the entire filter layer from being suddenly clogged even when a flocculant is added to achieve a target phosphorus concentration in treated water.

[Means for solving problems]

The method for removing phosphorus from wastewater according to the present invention is a method for solid-liquid separation of low-concentration phosphorus present in treated water after physical treatment or biological treatment at a wastewater treatment facility by coagulation treatment. The process of measuring and calculating the phosphorus concentration contained in the water, determining the optimal amount of flocculant to be injected, and injecting it into the wastewater, mixing and stirring; A process of flowing into a moving bed type continuous sand filter, forming flocs that efficiently capture phosphorus in the sand filter and attaching them to sand particles, and separating flocs containing phosphorus attached to sand particles. This includes a process for

[Action of the invention]

In the present invention, by using an upflow moving bed continuous sand filter and direct filtration with micro flocs, the entire filter layer is used to increase the amount of SS captured, thereby achieving the target phosphorus concentration in the treated water. No sudden blockage occurs even when the agent is added. Furthermore, in response to changes in the phosphorus concentration in raw water, the amount of SS generated can be estimated by keeping the addition rate of flocculant constant.
By continuously pulling out and cleaning the filter sand in an amount that does not cause clogging of the sand layer, a clean sand layer is always maintained in the filtration part. Regarding this point, we use an upflow moving bed continuous sand filter to control the amount of sewage circulation by measuring the raw water phosphorus concentration (including continuous measurement) under the conditions of constant filtration rate and constant flocculant addition rate. The target treated water phosphorus concentration and stable operation can be achieved.
This method is also advantageous in that it can be easily installed as additional equipment in existing facilities.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a principle diagram showing an example of a wastewater treatment method applied to the present invention.

The steps up to the step of treating the inflowing wastewater in the final settling tank 4 are the same as in the conventional example (see FIG. 9).
That is, the inflowing wastewater is treated with sand and impurities in the settling tank equipment 1, first in the settling tank 2 where solids that tend to settle are removed, and then in the aeration tank 3 where microorganisms remove fine particles. The solids and dissolved organic matter are adsorbed and decomposed into large flocs that are easy to precipitate, and are precipitated in the final sedimentation tank 4 to produce clear treated water.

In this embodiment, an upflow moving bed continuous sand filter 5 is provided after the final sedimentation tank 4, and phosphorus is removed after adding a flocculant through direct filtration using a microfloc filtration method. It is.

The feature of this embodiment lies precisely in this part.
Hereinafter, its specific configuration and operation will be explained.

First, in this embodiment, when installing the upward flow moving bed continuous sand filter 5 behind the final settling tank 4,
As shown in FIG. 2, a step A is inserted in which the concentration of phosphorus contained in the waste water is measured and calculated, the optimum amount of flocculant to be injected is determined, and this is injected into the waste water and stirred.

Next, the waste water that has passed through this step A flows into an upward flow moving bed type continuous sand filter 5 shown in FIG. Here, flocs that efficiently capture phosphorus are formed in the sand filter, and flocs are attached to the sand particles, and flocs containing phosphorus attached to the sand particles are separated, and the wastewater from which the phosphorus has been removed is processed. , and are sent to a sterilization pond 6.

Therefore, first, the upward flow moving bed continuous sand filter 5
The flow of removing phosphorus using the method will be explained based on FIGS. 2 to 4.

When a flocculant is added to phosphorus and removed by direct filtration, the flocs do not need to have a particularly large diameter, and a small diameter allows for more effective filtration, so it is possible to avoid the flocculant in the middle of the inflow pipe. In many cases, the method of adding is used.

In this embodiment as well, a phosphorus concentration meter 11 for automatically measuring the phosphorus concentration is provided in the middle of the raw water pipe, and this phosphorus concentration meter 11 communicates with the control panel 12 to determine the amount of flocculant added to the target phosphorus concentration of the treated water. is calculated, and the flocculant in the flocculant storage tank 8 is added by the injection pump 9. At this time, the amount of SS that will increase due to the addition of a flocculant is calculated in advance from theoretical and actual values,
of the filtration filler in the upflow moving bed continuous sand filter 5.
The amount of sludge to be removed for cleaning is determined based on the SS capture ability, and this amount is controlled according to the phosphorus concentration in the raw water.

A strainer 7 and a mixing device 10 are connected to the raw water pipe between the final settling tank 4 and the upflow moving bed continuous sand filter 5.
0, a flocculant is injected into the raw water and mixed in a mixing device 10.

The flocculant used in this step A is PAC (polyaluminum chloride), aluminum sulfate, iron salt, or the like. Therefore, the reaction between the flocculant and phosphorus can be easily calculated, and other products can also be confirmed on an experimental scale.

Next, a method of calculating the required amount of flocculant to be added to the target phosphorus concentration of treated water based on the phosphorus concentration in wastewater will be explained.

For example, when adding PAC as a flocculant,
A reaction similar to that in a coagulation sedimentation pond occurs. The reaction with ortholine (PO ₄ ^3- ) and alkalinity (mainly bicarbonate ions) in wastewater produces AlPO ₄ (aluminum phosphate) and Al as the final products, as shown below.
(OH) ₃ (aluminum hydroxide) floc is produced.

Al ³⁺ +PO ₄ ^3- →AlPO ₄ ↓ Al ³⁺ +3HCO ₃ ^- →Al(OH) ₃ ↓3CO _2Usually , in the case of treated water from the final sedimentation tank of a sewage treatment plant,
Since most of the phosphorus is in the form of orthophosphoric acid, it becomes a floc of AlPO ₄ , but other soluble phosphorus (polyphosphoric acid) is incorporated into agglomerated flocs such as Al(OH) ₃ .

In addition to the above, the consumption of flocculants is due to colloidal properties and partially soluble organic matter, etc.
The amount of flocculant added is influenced by these factors. However,
Although there are differences in the type of wastewater, location, etc., the above-mentioned substances are characterized by small fluctuations in concentration in specific wastewater or in certain areas.

Therefore, if the amount of flocculant added to reach the target phosphorus concentration in treated water is constant in terms of molar ratio to the phosphorus concentration in wastewater, controlling the amount added can reduce the amount below a certain value. The phosphorus concentration of treated water is obtained.

This relationship can be easily obtained in a laboratory if the facility is in operation. In addition, for newly constructed facilities, the above relationship can be estimated based on the type of wastewater, etc., and the optimum value for actual operation can be selected.

Furthermore, it can be confirmed that this relationship becomes as shown in FIG. 7 when PAC is added as a flocculant.

Based on the above, if the target phosphorus concentration of the treated water is to be lower than that shown in Figure 7, the Al molar ratio of the flocculant to the phosphorus concentration P in the wastewater is the above, and in the following cases, the above addition amount is It would be good if it could be controlled.

Next, a method for extracting dirty sand from the upflow moving bed type continuous sand filter 5 will be explained based on FIG. 3.

This upflow moving bed continuous sand filter 5 includes a cylinder 30 that is open at the top and can be opened and closed via a drain 31 at the bottom, and is provided at the bottom of this cylinder 30. Header 32 into which treated water is injected
and a plurality of riser pipes 33 communicating with this header 32 and having a distributor 34 on the upper part.
An air lift pipe (sand pumping pipe) 35 that stands up coaxially with the cylinder 30 inside the cylinder 30, a sand drainage trough 37 surrounding the upper opening 36 of the air lift pipe 35, and a lower part of the sand drainage trough 37. a guide pipe 38 provided at The sand layer 40 is filled in the cylinder 30 so that the upper part is on the lower side.
and an overflow weir 41 for sending the treated water that has passed through the sand layer 40 to the sterilization pond 6.

In this upward flow moving bed type continuous sand filter 5, raw water is supplied to the header 32, and air is sent to the air lift pipe 35 in the center to lift sand from the bottom to the upper part of the cylinder 30 by the air lift effect. As a result, the raw water rising inside the sand layer 40 attaches flocs to the sand and flows from the overflow weir 41 to the sterilization pond 6.
sent to. On the other hand, sand with flocs attached is
Due to the air lift effect by the air lift pipe 35,
It is sent to the upper sediment drainage trough 37. Here, when the sand with flocs attached is discharged, the flocs are separated and fall downward through the guide pipe 38. Then, at the part of the dispersion umbrella 39, the sand layer 4
distributed to 0.

In this treatment step, the air lift pipe 35 lifts the sand from the bottom to the top, so the amount of air and the amount of sand lifted are closely related. Therefore, by increasing or decreasing the amount of air, the amount of sand will also increase or decrease, and the relationship is known in advance.For example, if an air lift pipe 35 with an inner diameter of 36Φ is used, the amount of sand will increase or decrease at an air amount of 60/min.
It is possible to pump sand at a rate of 29/min.

As described above, it becomes possible to control the amount of flocculant added and the amount of sand pumped (the amount of circulating sand) based on the phosphorus concentration in the raw water and the phosphorus concentration in the treated water. Regarding the amount of sand lifted, increasing the number of air lift pipes 35 is effective when the phosphorus concentration is high.

Incidentally, since the upward flow moving bed type continuous sand filter 5 used here is of the upward flow type, the flocs are captured using the entire sand layer. Since it is a moving bed type, the filter layer is always filled with clean sand that is continuously washed, keeping the SS capture capacity constant. The present invention is suitable because it has the advantage of being able to maintain stable performance even when the quality of raw water changes by changing the amount of filthy sand that is continuously pulled out from the bottom of the sand filter.

Next, the amount of sand movement relative to the amount of SS generated due to the addition of flocculant will be explained.

The theoretical value and actual value of the amount of SS that increases with the addition of flocculant are calculated as follows.

According to the above reaction formula, first, for every 1 mole of phosphorus (molecular weight 31) in the wastewater, 1 mole of Al (molecular weight 27) is
moles react to form 1 mole of AlPO ₄ (molecular weight 122). Therefore, the amount of AlPO ₄ produced is
per, AlPO ₄ production amount = 1 mg/×122/31×1 (=Al
/P molar ratio)≒3.9mg/.

Next, according to the reaction formula, Al(OH) ₃ (molecular weight 78)
The increase due to the generation of Al(OH)3 can be calculated by excluding the consumption amount in the previous section from the amount of Al added, and the amount of Al(OH) ₃ generated = [Added Al amount - Al consumption amount (AlPO ₄ )] x 78/27 It is expressed as

The amount of increase in products due to colloidal substances and some soluble organic substances contained in other wastewater can be sufficiently estimated by laboratory-scale tests.

Due to the above ++, due to the addition of flocculant
The increase in SS can now be calculated, and the total amount of SS to be removed, Y, is as follows: Y=X+C (where C=inflow SS amount of wastewater).

Next, the amount of sand movement relative to the amount of SS generated is determined as follows. In the case of organic wastewater, the specific gravity of flocs is small, approximately 1.0. When using an upflow moving bed continuous sand filter, the filter layer will always be clean as long as the amount of sand moved (amount of filthy sand removed) for this type of wastewater is greater than a certain value relative to the amount of inflow SS. It is clear from various achievements that this value is maintained at 0.5Kg・SS/m ³・sand.

Therefore, the moving sand amount S is expressed by the following formula.

S=X (Kg・SS)/0.5 (Kg・SS/ ^m3・sand) Based on the above, for the total amount of SS after adding flocculant,
The required amount of sand movement is determined, and the amount of air required for sand lifting is determined from FIG. 8, and the required amount is controlled.

Next, an example of the performance according to this embodiment will be shown. When using PAC as a flocculant, the filtration speed is 200m/
The addition rate is molar ratio to raw water phosphorus (Al/P) for raw water phosphorus concentration of 2.0 mg/or less,
By 2.7 times, the total phosphorus concentration in the filtrate can be reduced to 0.3 mg/or less, and by 3.7 times, the total phosphorus concentration can be reduced to 0.2 mg/or less (see Figure 5).

In the above case, when the PAC addition rate is 3 times or more in molar ratio (Al/P), the total phosphorus removal rate is stably obtained at 80% or more (see Figure 6).

With the addition of a flocculant, the generated solid SS increases due to the production of phosphates and hydroxides (2.5 to 4 times the Al ₂ O ₃ equivalent amount in the case of sewage), but the amount of sand circulation increases by 0.5
By keeping it below Kg・SS/ ^m3 ,
No blockage occurred in the filter layer.

Normally, in the case of a sewage treatment plant, the phosphorus concentration at the outlet of the aeration tank is 3 to 4 mg/kg, but the amount of flocculant added can be reduced by combining biological dephosphorization using existing facilities. I can do it.

When the SS content of the raw water is high (20 mg/min or more), installing a strainer device at the front stage to reduce the SS load can be an effective means to ensure stable operation.

〔Effect of the invention〕

As described above, according to the present invention, the following effects are achieved.

Compared to conventional methods, this method is easier to maintain and manage because it is possible to automatically maintain treatment performance by measuring only the raw water phosphorus concentration. The facilities are also simple.

Even with slight fluctuations in raw water phosphorus concentration, treated water with a stable high removal rate can be obtained, and the total phosphorus concentration can be maintained at all times.
It can be kept at 0.2-0.3mg/. Also, with this value, the AGP value (algae productivity) is 80~80 compared to raw water.
90% removed, sufficiently suppressing algae growth in public waters.

The amount of flocculant consumed when added to an aeration tank is the same as when using the coagulation-sedimentation method, but it can be reduced by about 50% if an existing aeration tank is used in conjunction with the biological dephosphorization method. In conventional methods, only phosphorus removal is targeted, but according to the present invention, it is possible to remove SS by 1 mg/less or less, COD by 30%, and chromaticity by 50%, which is highly effective in improving water quality. obtain.

In the case of the present invention, since it can be easily modified in the future, it has the advantage of being able to easily incorporate accessory equipment for odor removal, decolorization, etc., and is considered to have a wide range of applications in improving water quality.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing the main parts, Figure 3 is a cross-sectional view showing an example of an upflow moving bed continuous sand filter used in the above example, and Figure 4 shows the processing situation in the above example. Figure 5 is a graph showing the relationship between filtrate total phosphorus concentration and PAC addition rate;
Figure 7 is a graph showing the relationship between total phosphorus removal rate and PAC addition rate, Figure 7 is a graph showing the relationship between target phosphorus concentration in treated water and flocculant addition amount, and Figure 8 is a graph showing the relationship between sand removal rate and air supply rate. FIG. 9 is a diagram showing a conventional system. 1...Sedimentation basin equipment, 2...First sedimentation basin, 3...
Aeration tank, 4...Final sedimentation tank, 5...
...upward flow moving bed continuous sand filter, 6...sterilization pond,
7... Strainer, 8... Coagulant storage tank, 9...
Injection pump, 10... Mixing device, 11... Phosphorus concentration meter, 12... Control panel, 30... Cylinder part, 32...
Header, 33... riser pipe, 35... air lift pipe, 40... sand layer.

Claims (1)

[Claims] 1. In a method for solid-liquid separation of low-concentration phosphorus present in treated water after physical treatment or biological treatment at a wastewater treatment facility by coagulation treatment, the concentration of phosphorus contained in wastewater is reduced. A process of measuring and calculating, determining the optimum amount of coagulant to be injected, injecting it into the wastewater, mixing and stirring, and injecting the coagulant in the above process, and then passing the stirred wastewater through upward flow moving bed continuous sand filtration. The process includes a step of flowing into a sand filter to form a floc that efficiently captures phosphorus in the sand filter and attaching it to the sand particles, and a step of separating the floc containing phosphorus attached to the sand particle. A method for removing phosphorus from wastewater, characterized by: 2. In the process of separating phosphorus-containing flocs attached to sand particles, the phosphorus concentration is measured in advance,
In the waste water according to claim 1, the method is controlled so that an appropriate amount of sand particles are deposited by automatically changing the amount of sand movement in response to changes in phosphorus concentration. Phosphorus removal method.