JPS6213043B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of backwashing a layer using air lift action of compressed air introduced into a draft tube in a method in which buoyant lightweight particles are used as a material and the liquid is passed through in an upward flow. The purpose is to simplify equipment, complete automatic backwashing, and significantly reduce backwash wastewater. The method of the present invention is effective in treating various types of liquids, and is characterized in that it functions extremely effectively regardless of the type of liquid. Even though it is simply referred to as material waste, the actual processing conditions vary, and the state in which the layer becomes occluded also varies depending on the type of liquid, material, etc. For example, when a pressure difference occurs between layers, simply loosening the layers will not be enough to clean the filled material, and some solid matter may adhere to the surface of the material. In the case of biological water treatment, the material is used not only to handle suspended matter but also to act as a carrier for the attachment of microorganisms. Therefore, cleaning materials in normal water treatment is often more difficult than in other cases, so water treatment will be used as a representative example in the following description. Generally, filtration equipment is a batch operation consisting of a water passage process and a backwashing process, and most of the advances in technology to date have been aimed at streamlining each of these processes. For example, in improving the water flow process, the water flow method can be started with downward flow, followed by upward flow, up/down flow, cross flow, radial flow, etc., and with regard to materials, simple methods such as sand flow can be considered. From phase filtration, multi-layer filtration using anthracite, garnet, etc. was considered and put into practical use.Furthermore, microfloc filtration, chemical injection, etc. were carried out as a result of studies on methods of injecting chemicals such as coagulants, and to a certain extent, Improvements have been made. On the other hand, since the passing process is originally a batch operation, a backwashing process is essential, and if this is to be operated automatically,
This requires complicated control circuits and valve operations, making the overflow device complicated. The present invention is a method of processing in an upward flow using lightweight particles as material, and is characterized by extremely effective cleaning of the layer. In other words, lightweight particles with a specific gravity smaller than that of water are used for the material, and these particles are floated inside the device and maintained under a water-permeable retaining plate such as grit, perforated plate, or wire mesh installed at a certain position below the water surface. This is a method in which water is passed through this in an upward flow. The particles form a layer under the retaining plate in close proximity to each other due to buoyancy. Filtration occurs when the stock solution passes through the layers thus formed in an upward flow. In addition, when the raw solution contains biological sludge, biological treatment is performed through contact with a biofilm layer that grows on the surface of the material over time.
Due to the increase in solids in the bed and the growth of biofilms, the pressure drop in the bed increases after a certain processing time, making it necessary to clean the bed. In conventional backwashing methods, backwashing water alone or in combination with gas is injected into the layer, causing the layer to flow, opening blockages in the layer, and removing biofilm, etc. on the surface of the material. ,
In addition to requiring a treatment device for discharging a large amount of backwash water, in cases where the layer is thick, satisfactory results cannot be obtained with backwashing for a short time. The inventors introduced compressed air from below a draft tube provided in the bed to form an upward flow in the draft tube, and also to form a circulation flow that violently flows the entire bed, thereby discharging the cleaning water. This method achieves a greater effect than conventional backwashing without any introduction. First, when the pressure loss in the layer increases, the flow of raw water is temporarily interrupted, and then the upper end opens into the layer, the lower end opens near the bottom of the device, and the tank is installed almost vertically inside the device. Compressed air is introduced from below the draft tube.
Due to the air lift effect of the introduced compressed air, the water in the tube flows upward, which forms a downward flow within the apparatus from the top of the bed. The material particles flow violently and, after releasing the solid matter trapped in the bed, the particles are further carried along with the flow to near the bottom of the device. Solid matter adhering to the surface of the particles while being fed near the bottom of the device is peeled off by contact with the water stream and contact between the particles. Further, the particles to which the solids that cannot be completely peeled off are sucked into the draft tube by the water flow, and while rising in the draft tube, the solids are further peeled off by contact with air bubbles. By repeating this movement, most of the biofilm that adheres to the material particles is peeled off, leaving only a faint surface coating that remains strongly attached, and the specific gravity of the particles returns to near its original value. recover to. Therefore, the amount of compressed air introduced into the draft tube is adjusted so that the downward flow velocity within the device is constant, and the downward flow velocity is set to be lower than the floating velocity of the particle group with biofilm attached. If you allow a slightly faster flow to form,
These particles circulate inside and outside the draft tube along with the flow, and the biofilm is effectively removed. When the biofilm is peeled off, the specific gravity of the material particles becomes close to the original value, so the floating speed becomes greater than the downward flow velocity of water, and the material particles stop entering the draft. Therefore, the material particles become in a fluidized bed state, and only water is circulated. In this way, in the cleaning method of the present invention,
By detecting the amount of material particles rising inside the draft tube, the completion of material particle cleaning can be determined very easily. When the introduction of compressed air is stopped after cleaning, the material particles in a fluid state float up again, forming a layer under the retaining plate, and the ss (suspended solid) separated from the material particles floats up again. , hereafter ss
) settles and accumulates at the bottom of the device. The deposited ss is extracted from the device using an appropriate method. If the ss settles poorly, you can add a flocculant to speed up the settling, or you can remove the water in the device at the same time as the ss is removed. As is clear from the above explanation, in the method of the present invention, the layer is cleaned only by introducing compressed air, so there is no need for cleaning water during backwashing in conventional equipment, and it is used for cleaning wastewater treatment. Since no additional equipment is required, and cleaning can be performed in a short time, the operating rate of the filter equipment is significantly improved, and there are great industrial benefits. In addition, in the method of the present invention, a mechanism is provided to detect changes in the internal pressure of the bed and changes in the amount of material particles rising inside the draft tube during cleaning, and these mechanisms are used to detect changes in the internal pressure of the bed and changes in the amount of material particles rising inside the draft tube during cleaning. If it is linked to the above, automation of layer cleaning can be easily achieved. As the material particles according to the present invention, pearlite, shirasu balloons, etc. which are generally used as lightweight aggregates, plastics with a specific gravity of 1.0 or less, foamed plastics, etc. can be used. Among them, foamed plastics are the most desirable material as the specific gravity, shape, coefficient of proximity, etc. can be selected arbitrarily.
In particular, foamed plastic particles obtained by adding inorganic substances such as calcium carbonate and talc (mainly composed of silicon oxide and magnesium oxide) as fillers during production have the advantage of being able to change the specific gravity arbitrarily, and of being uniform in biofilm. It is extremely desirable because it can be used for a long time, can be used semi-permanently, and is inexpensive. There are no particular restrictions on the shape of the particles, and any shape such as a spherical polygon can be used, but spherical or columnar shapes, which are suitable for mass production, are preferred. There is no particular limit to the size of the material, but a particle size of around 1 mm is recommended for capturing micro flocs made of agglomerated inorganic SS, and a particle size of around 1 mm is recommended for capturing biosolids, taking into account the formation of biofilm on the surface of the material. The desired thickness is 1 to 10 mm. The apparatus used in the method of the present invention is required to be equipped with a draft tube having a compressed air inlet in a filtration apparatus using a floating material. The upper end of the draft tube is located below the retaining plate, i.e.
Preferably, it is located within the bed, and its lower end is located near the bottom of the device and slightly spaced from the bottom to create a circulating flow throughout the device. If the device is very long due to design and the layers are not very thick, the length can be shortened accordingly. The compressed air inlet opens upward near the lower end of the draft tube. The shape of the draft tube is not particularly limited, and may be a vertical cylindrical body with a horizontal cross section of a circle, a polygon such as a quadrangle, a fan shape, etc., and a right cylindrical shape is most commonly used. The size of the draft tube is determined by the size of the water treatment equipment, the shape and size of the material particles used, etc. Generally, the ratio of the diameter d of the draft tube to the diameter D of the device, ie d/D, is 0.1.
~0.6, preferably 0.2~0.5 is used. If the cross-sections of the draft tube and the draft tube are other than circular, the above ratio is determined using their respective equivalent diameters. As one embodiment of the method of the present invention, two or more types of lightweight particles having different specific gravity are used as material particles,
A so-called multilayer structure is considered. That is, as mentioned earlier, it is extremely easy to make two or more types of material particles with different specific gravity and particle size, and by simply floating the particles made in this way on raw water, the specific gravity and particle size can be changed, respectively. A multilayered layer of particles with different diameters etc. can be easily formed. Moreover, even when backwashing the layers used in such a layered manner, the entire material can be washed at the same time using the method described above without considering the separation of each layer. It has the characteristic that by allowing it to float, a layer that is exactly the same as the state before backwashing can be formed. For example, lightweight particles with a relatively small specific gravity (0.5 to 2 mm),
When large particles (2 to 10 mm) and lightweight particles with relatively high specific gravity are simultaneously introduced into the filtration device, due to the difference in floating speed, small particles form an upper layer and large particles form a lower layer. After relatively large SS is captured in the lower layer, finer SS is captured in the upper layer, making it possible to perform extremely effective overtreatment with a long backwash interval. Furthermore, the fact that the layer state after backwashing is always the same layer with the same packing density without the need for special technical means is an extremely desirable method from the standpoint of continuously performing uniform overtreatment over a long period of time. . However, the introduction of compressed air when backwashing such a composite layer is determined based on the particles with the highest specific gravity, and the completion of cleaning must be determined based on the amount of rise of the particles with the highest specific gravity in the draft tube. It won't happen. Next, the present invention will be explained based on the drawings. The figures are action diagrams explaining the filtration process according to the filtration method of the present invention. Fig. 1 shows the water passing state, Fig. 2 shows the backwashing state, and Fig. 3 shows the biofilm being peeled off and particles passing through the fluidized bed. Figure 4 shows the state when the ss is formed and the state when the ss is discharged. In the water passing state shown in Fig. 1, raw water is introduced from the raw water inlet 1 at the bottom of the filtering device, passes through the packed bed 7 made of lightweight material, passes through the perforated plate 6, and is extracted from the treated water outlet 2. It can be done. When the pressure loss of the layer increases as the SS in the raw water is captured in the material layer, the flow of raw water is stopped by detecting the internal pressure of the filter, compressed air is introduced from the compressed air introduction pipe 3, and a backwashing process begins. The compressed air discharged from the air lift nozzle 8 rises in the draft tube 5 and has a lifting effect on the water and lightweight materials in the layer, and flows downward outside the draft tube, that is, in the layer portion, to remove buoyant lightweight particles. The material flows vigorously along with the circulating water currents that form inside and outside the tube, and during this time, microorganisms are detached from the material. In the backwashing state, the adhered ss is separated in the draft tube or in the fluidized bed of material and then moves downward, and a part of it settles to the bottom of the filter main body 9. As backwashing continues for a certain period of time, the specific gravity of the particles gradually decreases, and the material forms a fluidized bed in which only water circulates. When the supply of compressed air is stopped, the flow of the lightweight material stops and the material floats upward again and stands still to form a layer. At this time, by allowing a certain resting time, most of the exfoliated ss is sedimented and separated downward. In the backwash drainage state, the separated ss is discharged from the backwash drainage valve 4 as backwash wastewater, but when cleaning materials to a higher level, a part of the treated water is allowed to stay in the upper part of the filtration device. It is also possible to clean the material by leaving it in place and removing it at the same time as backwashing water. When the above backwashing process is completed, water flow is started again. The present invention will be explained below based on Examples. Example 1 An upflow filtration device ( ^6B transparent PVC column) equipped with normal backwashing equipment capable of water backwashing in a downward flow and an upflow filtration device according to the present invention ( ^6B
Activated sludge treated water was used as raw water in a transparent PVC column equipped with a 2 ^B draft tube, and continuous over-operation was performed in parallel. The ss concentration in the treated water is
The filtration device according to the present invention and a conventional upward flow filtration device are almost the same, and typical values of the ss concentration in raw water and the ss concentration in treated water in a steady state are listed in the table below.

[Table] Backwash operations were carried out whenever the pressure loss in the bed increased, but approximately once every three days. To give an example of the backwashing effect, in a conventional upward flow filtration device, backwashing was performed in a downward flow using filtered treated water. The flow rate at this time was 1.0m ³ /hr for 10 minutes, and the backwash drainage amount was
170, and the ss concentration in backwash wastewater is 1730mg/
It was hot. In the filtration apparatus equipped with the backwashing method according to the present invention, backwashing was performed by blowing compressed air at a flow rate of 1.2 m ³ /hr for about 10 minutes. At this time, the amount of drained water was 19, and the ss concentration in the backwash wastewater was 15,300mg/
It was hot. Moreover, no difference was observed in the pressure loss of the layer after backwashing depending on the backwashing method. As is clear from this example, according to the backwash method of the present invention, the amount of backwash water was small and the concentration was high, and the ss was removed well. Example 2 Amount of compressed air introduced from the draft tube,
The following experiment was conducted to clarify the relationship between the effects of backwashing. When the pressure loss in the layer reached 1 m-water column in the upflow device according to the present invention in Example 1, a backwashing operation according to the present method was performed, and the backwashing effect was measured by the degree of pressure loss recovery. The amount of compressed air introduced was determined in advance by measuring the amount of pumped liquid relative to the amount of compressed air introduced so that the downward flow velocity outside the draft tube would be a predetermined value. The table below shows the amount of compressed air introduced during backwashing, the flow rate in the bed, and the pressure loss in the bed when water flow resumes after backwashing.

[Table] From the above results, the amount of compressed air introduced during backwashing is
It has been found that it is effective when the flow rate is such that the downward flow velocity outside the draft tube is 1/10 or more, preferably 1/5 or more of the particle terminal velocity. Example 3 According to the filtration method of the present invention, when wastewater containing microorganisms is filtrated, a filtration film is formed on the material particles, so it has become clear that decomposition of residual organic matter and biological denitrification are possible. Ta. When activated sludge treated water is passed through a long-time aeration method using the same device as in Example 1, the film formed on the material particles becomes a biological film containing denitrifying bacteria because some of the layers become anaerobic. A denitrification reaction takes place using the remaining organic matter in the wastewater as a nutrient source, decomposing nitrate nitrogen and converting it into nitrogen gas. The nitrate nitrogen concentration and COD value corresponding to the results of Example 1 in which denitrification reaction was observed are shown in the table below.

【table】 [Brief explanation of the drawing]

FIGS. 1 to 4 are explanatory views of the state of particles in the filtration apparatus during the filtration and backwashing steps in the method of the present invention. FIG. 1 shows the state during the passing process, FIG. 2 shows the state during backwash processing, FIG. 3 shows the state when backwashing is completed, and FIG. 4 shows the state at the time of ss discharge.

Claims (1)

[Scope of Claims] 1. In a method in which particles having a specific gravity smaller than that of the concentrated stock solution are used as a material, and the layer formed under the retaining plate at the top of the device by floating particle groups is passed through the stock solution in an upward flow. When the pressure loss in the bed increases, after stopping the inflow of raw liquid, compressed air is blown out from below the draft tube whose upper end opens below the upper surface of the bed and whose lower end opens near the bottom surface of the filter device. An upward flow is formed by the rise of air bubbles in the draft tube, and a circulation flow is formed throughout the liquid in the drafting device.At this time, by adjusting the amount of compressed air introduced into the draft tube, the inside of the device is The downward flow velocity of the liquid is set to be faster than the floating velocity of particles with solid matter attached, but slower than the floating velocity of clean particles, and the circulation flow stirs the layer and entrains the particles, and the draft tube By coming into contact with the air bubbles while rising inside the layer, the solids trapped in the layer are released and the solid substances attached to the particle surface are peeled off. After cleaning, the inflow of compressed air is stopped and the particle group is removed. A filtration method using a floating material, characterized in that the supply of the undiluted solution is restarted after the layer is formed again by levitation of the material. 2. The method according to claim 1, wherein the end point of the cleaning of the two layers is determined based on the amount of material particles rising in the draft tube in a circulating flow. 3. The method according to claim 1 or 2, in which the material particles include two or more types of particles having different specific gravity. 4 Plastic particles whose material particles are foamed;
Alternatively, the method according to claim 1, 2, or 3, wherein the particles are formed by adding an inorganic substance to foamed plastic, and the raw solution is waste water.