JPS6254074B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention removes solids present in wastewater (hereinafter simply referred to as wastewater) after microbial treatment of wastewater such as activated sludge using a particle group with a specific gravity lighter than water as a material, and uses the filter material to The present invention relates to a method and apparatus for regenerating a filter layer by treating captured solids in wastewater without using washing water. Generally, when separating solids in wastewater by filtration,
A filter layer is formed using particles such as sand and anthracite that have a specific gravity greater than the specific gravity of the wastewater, and the wastewater is passed downward, upward, or horizontally to remove solids within the filter layer. Captured and removed. In such cases, when the pressure loss increases due to solids trapped in the filter layer, the supply of wastewater to the filter layer and the flow of treated water from the filter layer are stopped, and water or air and water are removed from the filter layer. The filter layer is caused to expand and the particles collide and mix, thereby discharging the trapped solids and cleaning the filter layer. The cleaning wastewater produced by this cleaning operation requires separate treatment equipment or the like to remove solids contained in the cleaning wastewater. These equipment costs can be so large that they account for approximately 50% of the total cost of the filtration equipment, and when considering the treatment of washing wastewater, including the disposal of the solids contained in the wastewater, the cost of water treatment is much lower. occupied a large proportion of the top. In particular, this trend showed that the smaller the water treatment capacity, the more limited the treatment and disposal methods, and the more significant the cost increase. In addition, solids that are generally present in wastewater that has been treated with microorganisms, such as activated sludge method, trickling filter bed, or rotating disk method, are simply separated by sedimentation in a sedimentation tank, or in some cases. In some cases, a flocculant or the like is added and removed by coagulation separation, etc. After these treatments, the wastewater is fed to a general filtration device to remove fine solids remaining in the wastewater. The solids captured in the filter layer by this method are contained in the wastewater generated by cleaning the filter layer by the method described above, and the wastewater containing these solids is Although solids and wastewater can be easily separated by returning the solids to a sedimentation tank, etc., the amount of sludge generated does not decrease, and generally 40% of the amount of BOD flowing into the microbial treatment equipment is It is said to be equivalent to ~80%. In order to dispose of such sludge separately, it is necessary to install new equipment. In addition, since these sludges are mainly composed of organic solids, they have disadvantages such as poor concentration ratio and large sludge volume compared to inorganic solids, and are extremely difficult to dewater due to their compressibility. had. As a method for solving the above-mentioned problems, the applicant of the present invention previously proposed ``filtration method'' in Japanese Patent Application Laid-open No. 56-33013 (hereinafter referred to as the prior invention). That is, particles having a specific gravity smaller than the specific gravity of wastewater are used as a filter medium, and the particles float to form an upper end opening of a draft tube below the upper surface of the filter layer formed by a water-permeable retaining plate provided at the top of the filtration device. When waste water is filtered using a filtration device having a filter, and when the pressure loss in the filter layer becomes large, the flow of waste water is stopped and air is blown out from below the draft tube to generate a circulating flow within the filter layer. We proposed a method to remove solids from wastewater. However, in the prior invention, the circulating flow does not pass water through the retaining plate, so in large equipment, the entire filter layer does not expand uniformly, resulting in a shot path, and the circulating flow occurs only in the vicinity of the draft tube, making it impossible to effectively clean the filter layer. It may not be done. In addition, since the floating particles circulate through the draft tube, the air introduced into the draft tube creates a pressure difference in this area while passing through the buoyant particle layer and the holding plate. requires large back pressure. Furthermore, floating particles may block the clearance between the holding plate and the upper end of the draft tube, which may prevent particles from circulating through the draft tube or may cause uneven flow or shot paths in the circulating water. Therefore, in the prior invention, it was not always possible to effectively wash the filter layer. In addition, in the prior invention, the main purpose is to expand the buoyant particle layer that has been formed and peel off the solid matter attached to the particles by colliding with each other. This method involves sedimentation and separation, followed by extraction. Therefore, after stopping the blowing of air, the separated solids must be allowed to settle and separate at the bottom of the equipment by allowing the equipment to stand for a predetermined period of time, and then be extracted to the outside of the equipment, and the discharged solids must be collected separately. I needed to do some processing. The present inventors have conducted various studies in order to further improve the above-mentioned problems. As a result, we have found a method and device that solve these problems. The method of the present invention involves filtering wastewater containing solids that has been subjected to microbial treatment, etc.
When the pressure loss in the layer became large, we removed the solids in the layer without using washing water and regenerated the layer, and the organic solids in the solids were treated with aerobic digestion to reduce the discharged solids. This method greatly reduces the amount of waste, and by combining it with microbial treatment such as the activated sludge method, it is possible to carry out continuous wastewater treatment. In the method of the present invention, a water-permeable retaining plate that is made of particles having a specific gravity smaller than the specific gravity of wastewater and prevents floating or outflow of particles is provided at one location on the upper part of the filter device and the side wall of the filter device, or at one location facing each other. They are provided at two positions in a positional relationship, and the upper end protrudes above the upper retaining plate and the lower end protrudes below the layer, respectively, in the layer formed by the particle group in the water-permeable retaining plate in the device, and each has an opening. Using a filtration device equipped with a vertical draft tube, the waste water is passed horizontally from one side wall to an opposite side wall equipped with a retaining plate to filter out the solid content in the waste water. When the pressure loss in the layer increases due to solids trapped in the device, the flow of wastewater is stopped, the liquid level in the device is maintained near the upper end of the draft tube, and air is blown out from below the draft tube. By forming a circulating flow of upward flow of water due to the rise of air bubbles in the tube and downward flow of water in the layer, the layer is expanded to eliminate solids trapped in the layer and to the particle surface. This is a method for removing solids in microbial-treated water, which is characterized by removing and cleaning attached solids and reducing organic solids by aerobic treatment with dissolved oxygen. That is, in the present invention, a filter layer is formed using the method described above, and wastewater that has been subjected to microbial treatment is passed horizontally through the filter layer, solids in the wastewater are filtered and separated, and the filter layer is formed. When a predetermined pressure loss is reached due to solids trapped in the filter, air is introduced into the draft tube installed in the filtration device to create a downward flow in the filter layer without introducing new water for washing. The solids trapped in the filter layer are removed by tightening and expanding the filter layer, and the organic solids among the solids are subjected to aerobic digestion treatment to reduce the amount of sludge generated. There is. In other words, in order to filter solids present in wastewater, a filter layer is created using particles lighter than water using a water-permeable retaining plate made of grids, perforated plates, wire mesh, etc. under the water surface in the filtration device. A filter layer is formed, and wastewater is passed through this filter layer in a horizontal flow. In this case, since the particles are brought close to each other by buoyancy and form a filter layer by the holding plate, the solids in the waste water can be filtered and separated. The wastewater from which the solid content has been removed passes through a water-permeable retaining plate on the side wall of the filtration device, and is taken out as treated water from the treated water outlet. Furthermore, since the wastewater contains microorganisms, a microbial film is formed on the surface of the filter medium particles over time, and residual BOD can be treated by dissolved oxygen in the wastewater. At the same time, the cells of the organic solids trapped in the filter layer are reduced due to basic biological metabolism, and the increase in pressure loss within the filter layer is slowed down, allowing long-term filtration processing. When the pressure loss within the filter layer increases as the filtration process continues, cleaning of the filter layer becomes necessary. In general, in conventional cleaning methods, these fluids are introduced into the lower part of the filter layer, either alone or in combination with air, to expand the filter medium and cause particles to collide with each other, removing solids trapped within the filter layer. Materials were peeled off and disposed of along with cleaning water. As a result, a large amount of cleaning wastewater was generated, which required treatment.
In the method of the present invention, air is introduced under a draft tube provided in the device to generate an upward flow in the draft tube and a downward flow in the filter layer, thereby creating a circulating flow of water in the device. The filter layer is expanded by the downward flow from the top to the bottom of the filter layer without using new washing water, and the solids trapped in the filter layer are released, and the solids attached to the particle surface are removed. This system also removes the solids contained in the solids, and by introducing air, a liquid with a high dissolved oxygen concentration is circulated within the device, and the organic solids are aerobically removed from the solids. This will greatly reduce the amount of sludge generated through digestion. When the aerobic digestion of the sludge is completed, the supply of air into the draft tube is stopped to stop the circulating flow, and the solids remaining in the circulating flow are allowed to settle to the bottom of the device, allowing the circulating flow to continue. The filter media particles that had expanded due to the heat transfer are floated again to form a filter layer under the water-permeable retaining plate installed above. The solid matter that has settled and accumulated at the bottom is extracted from the device using a pump or the like as appropriate and returned to the microbial treatment device, which is a pretreatment device. In some cases, it may be extracted and stored in a sludge tank or the like outside the system. As is clear from the above explanation, in the method of the present invention, when solid matter is trapped in the filter layer and the filter layer is being cleaned, the inflow of wastewater and the outflow of treated water are stopped, and the inflow of wastewater and the outflow of treated water are stopped, and solid matter is trapped in the filter layer. All you have to do is start supplying air to the filter, and there is no need for water for washing during washing in conventional filtration devices, and there is no need for incidental equipment for processing the washing water. At the same time, since the captured solids are reduced by performing aerobic digestion treatment, the amount of sludge is also reduced. Particles used to form the filter layer in the present invention are suitable if they have an apparent specific gravity of 1.0 or less and do not absorb water even if they exist in water. Natural materials such as perlite and shirasu balloons, which are generally used as lightweight aggregates, and artificial materials such as plastics and foamed plastics with a specific gravity of 1.0 or less are used. Among these, foamed plastics are most desirable as they allow arbitrary selection of specific gravity, shape, uniformity coefficient, etc. In particular, it is possible to arbitrarily change the specific gravity of foamed plastics by adding one or more inorganic substances such as calcium carbonate, barium sulfate, and magnesium oxide as fillers during their manufacture, and they also have good microbial adhesion. It is extremely desirable because it has high particle strength, can be used semi-permanently, and is inexpensive. When particles with a specific gravity of 1.0 or more become trapped in the filter layer, and the pressure loss increases, the wastewater tries to flow to other parts, causing the flow velocity to locally increase, forming a filter layer. This causes the trapped solids to easily flow out, leading to a deterioration in the quality of the treated water. Specific gravity 1.0
This does not happen with the following particles because a water-permeable retaining plate is provided on the top. The representative diameter of the particles used in this device is preferably in the range of 1 to 20 mm, taking into account the formation of a microbial film on the surface. The apparatus used in the method of the present invention uses particles having a specific gravity smaller than the specific gravity of wastewater as a filter medium, and a water-permeable retaining plate for preventing floating or outflow of the particle group is installed at the upper part of the filtration apparatus and at one place on the side wall of the filtration apparatus. It is provided at two locations facing each other, and is further equipped with a mechanism for horizontally inflowing and outflowing waste water and treated water, and the upper end protrudes above the upper water permeability retaining plate, and the lower end is a filter layer. Vertical draft tubes are provided that project downward and are open, and a nozzle is provided below the draft tubes to blow air upward. In the device of the present invention, the upper end opening of the draft tube is located near the water level of the drainage inlet, and the lower end opening of the draft tube is located at least 1/3 of the layer thickness below the lowest layer of the filter layer during filtration operation. It is desirable that you do so. It is desirable that the position of the nozzle for supplying air be directly below the opening at the lower end of the draft tube. Further, the area of the draft tube used is one corresponding to 1/100 to 1/3 of the horizontal cross-sectional area of the filter layer. An example of a mechanism for causing drainage to flow in and out in a horizontal flow is shown in FIGS. 1 and 2. In other words, in the case of a rectangular filtration device, the filtration layer has a double wall structure as shown in FIGS.
Also, as shown in Figures 1 and 2, only one side of the filter layer is
Some have a heavy wall structure, have a water-permeable retaining plate on the inner wall, and have a plurality of nozzles appropriately installed in a rake-shaped drainage distribution pipe inside the single wall facing the retainer plate. In the case of a cylindrical filtration device, the filtration layer has a double wall structure as shown in Figures 2 and 1, and water permeability retaining plates are provided on each of the inner walls at opposing positions, and the draft tube is A method in which pipes equipped with water-permeable retaining plates are tied together along the outer wall, and the wastewater flows into the pipes and the treated water flows out from the outer wall, or the wastewater flows in from the outer wall as shown in Figures 2 and 2. There is a method in which the treated water is drained from a pipe connected to the draft tube. It is necessary that the amount of air introduced is such that the expansion of the buoyant particle group becomes too large and the particles do not flow into the draft tube from the lower end of the draft tube. Next, in order to efficiently remove solids from wastewater, the present invention provides a plurality of the above-mentioned filtration devices, and while one or more of the filtration devices is performing filtration processing, the remaining devices are subjected to washing and aerobic digestion processing. By performing both operations alternately, it is possible to continuously remove solids from the waste water. That is, for example 3
Two of these filtration devices are connected in series for filtration, and the remaining one is used for cleaning the filter layer and aerobic digestion to continuously treat wastewater and perform filtration. If the pressure drop of the device on the upstream side increases, the filtration operation is switched to washing and aerobic digestion treatment. On the other hand, the other device that has completed the cleaning and aerobic digestion treatment can be switched to the subsequent filtration device to continuously remove solids from the waste water. Furthermore, after microbial treatment of wastewater is performed by the microbial treatment device in the first stage using a device that combines a microbial treatment device and a filtration device used in the method of the present invention, the treated water is treated to remove the solids contained therein. The solid content can be filtered by directly passing it through a subsequent filtration device without performing sedimentation separation. Furthermore, a microbial treatment device is installed in the first stage, and two or more filtration devices used in the method of the present invention are installed in the second stage, and the outlet of the treated water discharged from the first stage microbial treatment device and the waste water intake of the second stage filtration device are connected. After the wastewater is subjected to microbial treatment by the first-stage microbial treatment device using the connected wastewater treatment devices, the treated water is directly transferred to at least one of the second-stage filtration devices without sedimentation and separation of the solids contained therein. The solid content in the waste water is filtered through the filter layer, and when the pressure loss in the filter layer increases due to the solids trapped in the filter layer, the waste water from the filter is passed through the remaining filter devices. At the same time, air is blown into the draft tube of the above-mentioned filtration device, which has stopped the inflow and outflow, to remove solids trapped in the filter layer and to clean the filter layer to remove organic matter. By carrying out aerobic digestion treatment of the solid matter and using the device after this treatment again for the filtration operation, the filtration device is sequentially or alternately switched to filtration, filter layer washing, and aerobic digestion treatment. It is also possible to treat wastewater continuously, thereby omitting the sedimentation and separation equipment for solids that is provided in general microbial treatment, saving land for wastewater treatment equipment and making the equipment more compact. It's something you get. Next, the present invention will be explained based on the drawings. FIG. 1 illustrates a filtration operation for removing solids from wastewater according to the present invention. In the filtration operation shown in FIG. 1, wastewater is caused to flow from a microbial treatment device provided as a pre-treatment device into the device from the wastewater inlet 1 through the water-permeable retaining plate 6' on the side wall using the water level difference. Water is passed horizontally through the packed bed 7 of floating particles, passing through the water-permeable retaining plate 6'' on the side wall and being extracted from the treated water outlet 2. The existing solids are trapped in the layer and removed.As the solids in the wastewater are trapped in the filter layer, the pressure loss of the filter layer increases and the water level gradually rises, causing the draft tube to rise. When the water reaches near the upper end, the outflow of water from the treated water outlet 2 is stopped, and then when the water level in the device reaches the vicinity of the upper end of the draft tube, the inflow from the drainage inlet 1 is stopped.Then, the draft tube 5 Air is introduced into the draft tube from the air introduction pipe 3 provided at the bottom of the filter to start cleaning the filter layer.The air introduced from the nozzle of the air introduction pipe 3 rises inside the draft tube 5. This causes an air lift phenomenon, forming a circulation flow of water flowing upward in the draft tube 5 and in a downward direction through the external filter layer. Expands the solid matter trapped in the filter layer, and also peels off the solid matter adhering to the particle surface due to the collision action between the particles.At the same time,
Organic solids attached to particles and organic components present in circulating water are aerobically digested using dissolved oxygen in water to reduce organic sludge.
After the aerobic treatment is fully completed, air introduction pipe 3
The inflow of air is stopped, the particles are floated again to form a filter layer, and the remaining solids are allowed to settle to the bottom of the device. The sludge settled at the bottom is returned to the microbial treatment device installed as a pretreatment device or taken out of the system through the sludge extraction pipe 4 using a pump or the like. Thereafter, the outflow of treated water from the treated water outlet 2 and the inflow of waste water from the drainage inlet 1 are restarted, respectively, and normal filtration operation is started. Next, examples of the present invention will be described, but these examples do not limit the present invention. Example After pre-treating sanitary wastewater from a certain company using a microbial wastewater treatment device using granular carriers,
Wastewater was treated using the microbial filtration device shown in . The main device dimensions and experimental conditions used in this experiment are as follows. (1) Microbial wastewater treatment equipment using granular carriers
: 1000mmφ x 1750mmH (with draft tube 200mmφ x 1500mmL) Carrier particles used: Foamed polypropylene particles added with calcium carbonate 20mt% Shape 3.5mmφ x 4.0mmL Particle density 0.82g/cm ³ Filling amount in the device 1200 Waste water supply rate 240/hr ( 2) Flotation particle filling filtration device
:2000mmL×100mmW×2500mmH (with draft tube 50mmφ×1200mm) Filter layer volume
120 (800mmH x 100mmW x 1500mmL) Carrier particles used
: The properties are the same as the above (1) microbial wastewater treatment device using granular carriers Filling amount in the device: 120 Water flow rate: 240/hr Filtered wastewater obtained by treating sanitary wastewater using the above device and the present invention The properties of the treated water treated by the filtration device according to the above method were as shown in Table 1.

[Table] After 171 hours have passed since the filtration device started operating, when the filter layer differential pressure reaches 122 cmAq, filtration is stopped and air at 450N/min is passed through the draft tube of the filtration device for 170 hours to clean and clean the filtration layer. Pneumodigestion treatment was performed. The analysis results of water quality at the initial stage and when ventilation is stopped are as follows, and it can be seen that SS and COD have been reduced to about 1/2 or less.

[Table] After the ventilation was stopped, the amount of solid matter deposited at the bottom of the filtration device was approximately 30.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the filtration operation of the filtration device used in the present invention, and FIG. 2 is an explanatory diagram of the filtration operation of the filtration device showing another embodiment used in the present invention. 1... Drain inlet, 1'... Drain inlet, 2...
Treated water outlet, 2'... Treated water outflow section, 3... Air introduction pipe, 4... Sludge withdrawal pipe, 5... Draft tube, 6... Water permeable retaining plate, 6'... Water permeable retaining plate ( Drainage inflow part), 6''...Water permeable retaining plate (treated water outflow part), 7...Filter layer.

Claims (1)

[Scope of Claims] 1. A water-permeable retaining plate made of particles having a specific gravity smaller than the specific gravity of wastewater and preventing the floating or outflow of the particle group is provided at one location on the upper part of the filter device and the side wall of the filter device, or at one location opposite to each other. The upper end protrudes above the upper retaining plate and the lower end protrudes below the layer, respectively, in a layer formed by a group of particles in a water-permeable retaining plate in the device. The waste water is passed horizontally from one side wall to the opposite side wall provided with a retaining plate using a filtration device equipped with an opening vertical draft tube to filter out the solid content in the waste water and treat it. Water is extracted through the retaining plate on the side wall, and when the pressure loss in the layer increases due to solids trapped in the layer, the flow of wastewater is stopped and the liquid level in the device is lowered to the vicinity of the upper end of the draft tube. The draft tube is held at Microorganism-treated water is characterized by removing solids trapped in the layer, removing and cleaning solids attached to particle surfaces, and reducing organic solids by aerobic treatment with dissolved oxygen. How to remove solids. 2. A water-permeable retaining plate made of particles having a specific gravity smaller than the specific gravity of wastewater and preventing the floating or outflow of the particle group is provided at one location on the upper part of the filter device and the side wall of the filter device, or in a position facing each other. A vertical pipe is provided at two locations, and is further provided with a mechanism for horizontally inflowing and outflowing wastewater and treated water, and has an upper end protruding above the upper water-permeable retaining plate and a lower end protruding below the layer and openings respectively. An apparatus for removing solid matter from microbially treated water, which is provided with a draft tube and has a nozzle below the draft tube that blows air upward.