JP3802186B2 - Sewage treatment equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sewage treatment apparatus, and more particularly, to a sewage treatment apparatus such as a combined treatment septic tank incorporating a dephosphorization treatment apparatus for removing phosphoric acid from sewage mixed with manure wastewater and domestic wastewater.
[0002]
[Prior art]
As this type of dephosphorization processing apparatus, an apparatus disclosed in JP-A-3-89998 (C02F 3/12, 1/58, 11/00) is known.
[0003]
This is provided with a liquid receiving tank such as a flow rate adjusting tank or a sedimentation separation tank, a biological treatment tank, and a sludge concentration tank, and at least one place in the path from the biological treatment tank to the liquid receiving tank contains insoluble phosphate-forming metal. Electrodes and noble metal electrodes are placed in a conductive state, or a pair of insoluble phosphate-forming metal electrodes are placed and a voltage is applied between them to form electrochemically insoluble phosphate. It is an apparatus that removes phosphorus by eluting metal ions into waste water.
[0004]
[Problems to be solved by the invention]
In such an apparatus, an insoluble phosphate-forming metal in which suspended matter (SS) contained in sewage to be treated or treated water, particularly SS having a relatively large particle diameter, is placed in a conductive state. There is a risk of entering between the electrodes of the metal and the noble metal electrode or between the electrodes of the insoluble phosphate forming metals.
[0005]
In that case, since the SS that has entered causes current leakage, the elution amount of insoluble phosphate-forming metal ions in the sewage fluctuates, resulting in inconvenience that the removal of phosphate precipitates becomes unstable. .
[0006]
The present invention has been made in view of such a situation, and a dephosphorization apparatus that prevents electrolysis instability caused by suspended substances contained in sewage and obtains a desired ion elution amount is provided. An object is to provide an integrated sewage treatment apparatus.
[0007]
[Means for Solving the Problems]
According to one aspect of the present invention, the iron ions or aluminum ions for divided phosphoric acid in wastewater eluting by electrolysis, a plurality of sets comprising a pair of electrode plates consisting of an anode and a cathode, respectively the electrode plate, its electrode face are arranged so as to be substantially parallel to the direction of flow to flow into and out of the wastewater, these plurality of sets of electrode plates, this a set of electrode surface of the electrode plate Are arranged in a direction intersecting with the flow direction so that the electrode surfaces of a set of electrode plates adjacent to each other face each other, and the electrode surfaces of the set of electrode plates and a set of adjacent ones thereof A sewage treatment apparatus is provided in which a partition plate having a larger surface area than the electrode surface of the electrode plate is provided between the electrode surface of the electrode plate and substantially parallel to the electrode surface of the electrode plate. .
[0008]
Electrode plate for example, a rectangular electrode surface, iron ions or aluminum ions are eluted by electrical degradation.
[0009]
A set of electrode plates, for example, are both composed of one of iron and aluminum, or one from one of iron and aluminum and the other of an insoluble metal. In the former case, it is possible to prevent the electrode from being passivated by preventing the ion elution from the electrode by reversing the polarity of the electrode as desired. In the latter case, an electrode composed of one of iron and aluminum is used as an anode, and an electrode composed of an insoluble metal is used as a cathode. Here, as an electrode comprised from the insoluble metal, there exist electrodes, such as silver and platinum, for example.
[0010]
Eluted ions is reacted with phosphoric acid in wastewater (orthophosphoric acid), a poorly soluble phosphorus compound _{(Fe (OH) x (PO} 4) y or _{Al (OH) x (PO 4} ) y) aggregation And precipitate.
[0011]
The electrode plate in this dephosphorization apparatus is arranged so that its electrode surface is substantially parallel to the direction of flow from inflow to outflow of sewage. By arranging the electrode plates in this way, the suspended matter (SS) in the sewage flows along the electrode surface of each electrode toward the outlet without any stagnation. Therefore, it is possible to reduce the possibility that the SS contained in the sewage enters and stays between the electrode plates.
[0012]
Electrode plate, a plurality of sets, because they are provided, the total surface area of the electrodes surface is to be the same as that in the pair of electrodes, Ru increases the flexibility of the plurality of sets of electrodes arranged. In addition, since the weight of the electrode plate per set can be reduced, the inspection and replacement work of the electrodes becomes easy.
[0013]
The plurality of sets of electrode plates are arranged in a direction intersecting with the direction of sewage flow so that the electrode surfaces of one set of electrode plates face each other. Yes. Furthermore, a partition plate having a surface area larger than the electrode surface of the electrode plate is substantially between the electrode surface of the electrode plate and the electrode surface of the pair of electrode plates adjacent thereto. It is provided in parallel, whereby a set of electrode plates of a set of electrode plates can be brought close to each other.
[0014]
More preferably, each electrode plate is provided with a plurality of terminals. If so provided, the current density distribution becomes more uniform and stable ion elution can be achieved compared to the case where each electrode is provided with one terminal.
[0015]
The dephosphorization processing apparatus which concerns on this invention means the thing provided with the power supply required for performing electrolysis, the control part of an electric current, the aeration tube etc. which were provided in the elution tank in the said elution tank.
[0016]
According to another aspect of the present invention, there is provided a sewage treatment apparatus incorporating the various dephosphorization treatment apparatuses. For example, a dephosphorization processing device is arranged in the upper part of the biofilm filtration tank (bacterial tank) of the merged processing septic tank or the next processing water tank (precipitation tank) adjacent to this, and the contaminant removal tank (first) There is provided a combined treatment septic tank configured to remove phosphoric acid from the treated water returned to the anaerobic filter bed tank).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, three embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to these.
[0018]
Embodiment 1
As shown in FIG. 1, dephosphorization processing apparatuses D ₁ according to one embodiment of the present invention is used incorporated into a small combined treatment septic tank 1 as sewage treatment apparatus with a flow rate adjusting function.
[0019]
The inside of the septic tank 1 is arranged in the order of the sewage purification process from the side of the inflow pipe 2 into which sewage mixed with urine wastewater and domestic wastewater flows to the side of the discharge pipe 3 that discharges sewage treated water to the outside. Accordingly, a tank structure is formed in which a plurality of tanks are partitioned.
[0020]
Reference numeral 4 denotes a contaminant removal tank that is partitioned and formed in the forefront portion on the inflow pipe 2 side. In this foreign matter removal tank 4, the foreign matter which is mixed in human waste water and domestic waste water and cannot be purified is separated and removed.
[0021]
An inflow guide 5 is defined on the inflow pipe 2 side of the contaminant removal tank 4. Between the inflow guide 5 and the inflow pipe 2, a rectangular or cylindrical downflow passage 6 that guides the inflow water toward the lower side of the contaminant removal tank 4 is formed.
[0022]
The contaminant removal tank 4 is provided with an anaerobic filter bed 7 which is a filter bed for anaerobic microorganisms, and anaerobic treatment is performed by causing the anaerobic filter bed 7 to inhabit the microorganisms. The anaerobic filter bed 7 suppresses the sediment from being rolled up by the water flow when inflow water or backwash wastewater flows in temporarily, and flowing out to the next tank as a floating substance, thereby reducing the load on the next tank. Can be lowered.
[0023]
Reference numeral 8 denotes a next anaerobic filter bed tank formed adjacent to the contaminant removal tank 4. In the anaerobic filter bed tank 8, anaerobic treatment is performed by causing the anaerobic filter bed 9 to inhabit anaerobic microorganisms.
[0024]
Reference numeral 10 denotes a next biofilm filtration tank that is formed adjacent to the anaerobic filter bed tank 8. The biofilm filtration tank 10 is provided with an aerobic filter bed 11 which is a filter bed of aerobic microorganisms, and aerobic microorganisms are inhaled in the aerobic filter bed 11 to perform aerobic treatment. ing.
[0025]
Reference numeral 12 denotes a next treated water tank formed adjacent to the biofilm filtration tank 11. In the treated water tank 12, the treated water that has been aerobically treated in the biofilm filtration tank 11, filtered, and transferred is stored stationary.
[0026]
Reference numeral 13 denotes a disinfection tank that is partitioned on the upper portion of the treated water tank 12. The sterilization tank 13 is usually configured to sterilize the supernatant water that has been treated in the treatment water tank 12 and discharge the supernatant water from the discharge pipe 3 to the outside.
[0027]
The contaminant removal tank 4 and the anaerobic filter bed tank 8 are partitioned by a vertical partition 14. An advection port 15 penetrating the partition wall 14 is formed in the upper part of the partition wall 14. The advection port 15 is fitted with a rectangular or cylindrical advection tube 16. The lower end of the advection pipe 16 is located below the anaerobic filter bed 7 of the foreign matter treatment tank 4 and also serves as a cleaning port.
[0028]
The anaerobic filter bed tank 8 and the next biofilm filtration tank 10 are partitioned by an intermediate partition wall 17. An upflow passage 18 is fixedly provided on the anaerobic filter bed 8 side of the intermediate partition wall 17. The sewage that has flowed from the contaminant removal tank 4 through the advection pipe 16 to the anaerobic filter bed tank 8 passes through the anaerobic filter bed 9 in a downward flow, and then rises through the upflow passage 18.
[0029]
A water intake port of a metering pump (not shown) is provided in the upper part of the upflow passage 18. The metering pump transfers a certain amount of sewage from the anaerobic filter bed tank 8 to the biofilm filtration tank 10. That is, the sewage is taken into the metering pump from the water intake and is sent to the next biofilm filtration tank 10 by a certain amount.
[0030]
A certain amount of suspended matter (SS) is trapped in the anaerobic filter bed 9 in the anaerobic filter bed tank 8. The captured SS is gradually anaerobically decomposed to become soluble, or stored as sludge at the bottom of the anaerobic filter bed tank 8. In the anaerobic filter bed 9, organic nitrogen is anaerobically decomposed into ammonia nitrogen.
[0031]
In the vicinity of the bottom of the biofilm filtration tank 10, an air diffuser 22 of the air diffuser 21 is arranged in a horizontal state. The aeration device 21 performs an oxygen supply function for aerobic microorganisms living in the aerobic filter bed 11 of the biofilm filtration tank 10 by blowing air from the aeration tube 22.
[0032]
A filter medium is disposed in the aerobic filter bed 11 in the biofilm filtration tank 10, and microorganisms attached to the filter medium decompose the BOD component or the like, or convert it to SS and trap it on the filter medium. The biofilm filtration tank 10 also has a physical filtration action, and again captures SS. Moreover, in the biofilm filtration tank 10, ammonia nitrogen is changed to nitrate nitrogen by the action of nitrate bacteria and nitrite bacteria that change nitrogen to nitric acid.
[0033]
A partition wall 23 is provided between the biofilm filtration tank 10 and the next treated water tank 12. A communication portion 24 is provided below the partition wall 23. And the biofilm filtration tank 10 and the treated water tank 12 are connected by this communication part 24.
[0034]
In the treated water tank 12, the treated water that has flowed from the biofilm filtration tank 10 through the communication portion 24 is separated into a precipitate and a supernatant water. The bottom of the treated water tank 12 is inclined to return the sediment deposited there to the biofilm filtration tank 10 through the communication part 24.
[0035]
The bottom part of the biofilm filtration tank 10 and the upper part of the contaminant removal tank 4 are communicated with each other by an L-shaped first return pipe 25 composed of a vertical part 25a and a horizontal part 25b. A first air supply pipe 31 a is arranged inside the vertical portion 25 a of the first return pipe 25. The first air supply pipe 31 a is connected to the blower 30 outside the tank constituting the air lift pump 29 via the air lift supply pipe 31. Then, the air supplied from the blower 30 is blown out from the first air supply pipe 31 a so that the sludge accumulated on the bottom of the biofilm filtration tank 10 is sucked into the first return pipe 25 and returned to the contaminant removal tank 4. It has become.
[0036]
On the other hand, the supernatant water of the treated water in the treated water tank 12 is pumped up from the lift pipe 32 by the air blown out from the second air supply pipe 31 b disposed inside the lift pipe 32 and communicating with the air supply pipe 31. The first supply pipe 31a and the second supply pipe 31b can be switched to either one by a switching valve.
[0037]
A circulation path 26 is provided from the upper part of the treated water tank 12 to the upper part of the contaminant removal tank 4 for constantly returning the supernatant water of the treated water. The circulation path 26 is provided with a diversion meter 27, a dephosphorization device D ₁ , and an inlet 28 to the contaminant removal tank in the order of water flow from the treated water tank 12. Then, the supernatant water pumped up from the lift tube 32, diversion metering device 27, after being subjected to a dephosphorylation treatment device D _1, through the circulation path 26 back to the top of the descending flow path 6 of contaminant removal tank 4 It is.
[0038]
The diversion meter 27 is installed in the upper part of the treated water tank 12, and is integrally formed in a rectangular box-shaped bottomed structure from the front and rear plate portions, the left and right side plate portions, and the bottom plate portion. The inside of the box is partitioned into an inflow chamber, a water diversion chamber, and an intermediate chamber between the two.
[0039]
In the inflow chamber, an inflow pipe through which the supernatant water pumped from the lift pipe 32 of the air lift pump 29 flows is installed. The inflow chamber and the intermediate chamber are partitioned by a partition wall formed so that the lower side can be communicated, and the treated water that has flowed into the inflow chamber is diverted and transferred to the intermediate chamber.
[0040]
The diversion chamber is divided into two chambers, a first diversion chamber and a second diversion chamber. The partition wall between the first water diversion chamber and the intermediate chamber has a lower end fixed to the bottom plate and an upper end opened in a V shape. The partition wall between the second water diversion chamber and the intermediate chamber has a lower end fixed to the bottom plate and an upper end opened in a concave shape. And the overflow dam plate which can adjust the open dimension is attached to the partition opened to this concave shape.
[0041]
An outflow pipe for allowing treated water to flow out to the circulation path 26 is connected to the first diversion chamber, and an outflow pipe for letting out treated water to the biofilm filtration tank 10 is connected to the second diversion chamber. Has been. Therefore, the treated water that has flowed into the inflow chamber passes through the intermediate chamber and is divided into a circulation path and a biofilm filtration tank in the two water diversion chambers by adjusting the height of the overflow weir plate.
[0042]
As shown in enlarged views in FIGS. 2 and 3, the dephosphorization processing device D ₁ includes an elution tank 39, a pair of iron electrode plates 40 and 41 having a rectangular plate shape disposed in the elution tank 39, and these A DC power source 42 for applying a current between the electrode plates 40 and 41 and a control unit 43 are provided. The electrode plates 40 and 41 use iron for both the anode and the cathode.
[0043]
The elution tank 39 is provided in the upper part of the biofilm filtration tank 10, and is integrally formed in a rectangular box-shaped bottomed structure from the front and back plate portions, the left and right side plate portions, and the bottom plate portion. An inflow port 44 and an outflow port 45 are provided in the front and back plate portions, respectively.
[0044]
The sewage flowing out from the outflow pipe 37 flows in from the inflow port 44, and the sewage supplied with the iron ions eluted from the iron electrode plates 40 and 41 flows out from the outflow port 45 into the circulation path 26. The controller 43 controls the amount of iron ions eluted in the elution tank 39 by controlling the current applied between the electrode plates 40 and 41.
[0045]
The elution tank 39 is provided with an aeration tube 46 for aerobing the electrode plates 40 and 41 from below and a blower 47 disposed outside the tank for supplying air to the aeration tube 46. The aeration tube 46 supplies air to the sewage, thereby cleaning the electrode surfaces of the electrode plates 40 and 41 with bubbles, preventing the sludge from adhering, and causing the sludge to float and flow out from the outlet 45.
[0046]
The electrode plates 40 and 41 are arranged so that the rectangular electrode surfaces thereof are substantially parallel to the flow direction from the inlet 44 to the outlet 45 in the elution tank 39. By arranging the electrode plates 40 and 41 in this way, SS in the sewage that has flowed into the elution tank 39 flows toward the outlet 45 along the electrode surfaces of the electrode plates 40 and 41 without any stagnation. Therefore, it is possible to reduce the possibility that SS contained in the sewage to be treated or the treated water after treatment enters between the electrode plates 40 and 41 and stays behind.
[0047]
Each electrode plate 40/41 is provided with a plurality of terminals 48 at the upper end thereof. When a plurality of terminals 48 are provided in this manner, the current density distribution becomes more uniform and stable ion elution can be achieved compared to the case where one terminal is provided on each electrode plate. .
[0048]
In the elution tank 39, iron ions Fe ²⁺ are dissolved from the electrode plates 40 and 41, and oxygen (air) is supplied to the sewage through the aeration tube 46. Fe ²⁺ is oxidized using dissolved oxygen to form Fe ³⁺ and sent to the contaminant removal tank 4, reacts with orthophosphoric acid PO ₄ ^3−, and is hardly soluble iron phosphate Fe (OH ) _X (PO ₄ ) _y . The iron phosphate salt Fe (OH) _x (PO ₄ ) _y aggregates with the SS present in the contaminant removal tank 4 as a nucleus, becomes a large floc, precipitates, and accumulates at the bottom of the tank.
[0049]
Contaminants containing iron phosphate deposited on the bottom of the contaminant removal tank 4 are periodically (usually once a year) from the portion of the contaminant removal tank 4 where there is no anaerobic filter bed 7. Pumped out at a rate)
[0050]
Embodiment 2
As shown in FIGS. 4 and 5, a dephosphorization processing device D _{2 according to} another embodiment of the present invention is incorporated in a small combined processing septic tank (not shown) as a sewage processing device having a flow rate adjusting function. It is used.
[0051]
This dephosphorization processing device D ₂ applies an electric current between the elution tank 49, three sets of iron electrode plates 50, 51 having a rectangular plate shape arranged in the elution tank 49, and these electrode plates 50, 51. A DC power supply 52 and a control unit (not shown) are provided. The electrode plates 50 and 51 use iron for both the anode and the cathode.
[0052]
The elution tank 49 is provided in the upper part of the biofilm filtration tank 10, and is integrally formed in a rectangular box-shaped bottomed structure from the front / back plate part, the left and right side plate parts, and the bottom plate part. An inflow port 54 and an outflow port 55 are provided in the front and back plate portions, respectively.
[0053]
The sewage flowing out from the outflow pipe 37 flows from the inflow port 54, and the sewage supplied with iron ions eluted from the iron electrode plates 50 and 51 flows out to the circulation path 26 from the outflow port 55.
[0054]
The elution tank 49 has an aeration pipe (not shown) for aeration of the electrode plates 50 and 51 from below and a blower (not shown) arranged outside the tank for supplying air to the aeration pipe. It is attached.
[0055]
The three sets of electrode plates 50 and 51 have their rectangular electrode surfaces substantially parallel to the direction of flow from the inlet 54 to the outlet 55 in the elution tank 49, and are longitudinal to the direction of the flow. It is arranged in one row. By arranging the electrodes 50 and 51 in this way, SS in the sewage flowing into the elution tank 49 does not stagnate toward the outlet 45 along each electrode surface of the three sets of electrode plates 50 and 51. Flowing. Therefore, it is possible to reduce the possibility that SS contained in the sewage to be treated or the treated water after treatment enters between the electrodes 50 and 51 and is stagnated.
[0056]
Embodiment 3
As shown in FIGS. 6 and 7, a dephosphorization processing device D _{3 according to} still another embodiment of the present invention is used in a small combined treatment septic tank (not shown) as a sewage treatment device having a flow rate adjusting function. It is incorporated and used.
[0057]
The dephosphorization processing device D ₃ includes an elution tank 69, three sets of rectangular plate-like iron electrode plates 70 and 71 arranged in the elution tank 69, and iron adjacent to the set of iron electrode plates 70 and 71. A partition plate 80 that partitions the electrode plates 70 and 71, a DC power source (not shown) for applying a current between the electrode plates 70 and 71, and a control unit (not shown) are provided. The electrode plates 70 and 71 use iron for both the anode and the cathode.
[0058]
The elution tank 69 is provided in the upper part of the biofilm filtration tank 10, and is integrally formed in a rectangular box-shaped bottomed structure from the front and back plate parts, the left and right side plate parts, and the bottom plate part. An inflow port 74 and an outflow port 75 are provided in the front and back plate portions, respectively.
[0059]
The sewage flowing out from the outflow pipe 37 flows from the inflow port 74, and the sewage supplied with iron ions eluted from the iron electrode plates 70 and 71 flows out from the outflow port 75 to the circulation path 26.
[0060]
The elution tank 69 has an aeration pipe (not shown) for aeration of the electrode plates 70 and 71 from below and a blower (not shown) arranged outside the tank for supplying air to the aeration pipe. It is attached.
[0061]
The three electrode plates 70 and 71 are arranged so that their rectangular electrode surfaces are substantially parallel to the flow direction from the inlet 74 to the outlet 75 in the elution tank 69 and transverse to the flow direction. Arranged in three rows. By arranging the electrode plates 70 and 71 in this way, SS in the sewage flowing into the elution tank 69 stagnates toward the outlet 75 along the electrode surfaces of the three sets of electrode plates 70 and 71. It flows without. Therefore, it is possible to reduce the risk that SS contained in the sewage to be treated or the treated water after treatment enters between the electrode plates 70 and 71 and stays there. In addition, work such as inspection and replacement of the electrode plates 70 and 71 is easier than when the electrode plates 70 and 71 are arranged vertically. Furthermore, the partition plate 80 is provided between the pair of electrode plates 70 and 71 and the adjacent electrode plates 70 and 71 so that the electrode plates 70 and 71 are close to each other, so that the elution tank 69 can be made more compact. The electrode exchange becomes easier.
[0062]
Each electrode plate 70/71 is provided with two terminals (not shown) at its upper end. When two terminals are provided in this way, the current density distribution becomes more uniform and stable ion elution can be achieved as compared with the case where one terminal is provided for each electrode.
[0063]
【The invention's effect】
According to the present invention, plate-shaped electrodes, so are arranged to be substantially parallel to the direction of flow to flow into and out of the electrode surface is dirty water, suspended matter in the sewage the electrode plates It flows smoothly along the electrode surface toward the outlet. Therefore, it is possible to reduce the possibility that the SS contained in the sewage enters and stays between the electrode plates, and it is possible to perform stable phosphorus removal by preventing fluctuations in the amount of ion elution caused by suspended substances.
[0064]
Further, the electrode plate is a plurality of sets, because they are arranged, the total surface area of electrode surface is to be the same as that in the pair of electrode plates, Ru increases the flexibility of the plurality of sets of electrodes arranged. In addition, since the weight of the electrode plate per set can be reduced, the inspection and replacement work of the electrodes becomes easy.
[0067]
Further, the plurality of sets of electrode plates are arranged in a direction intersecting the flow direction so that the electrode surfaces of the one set of electrode plates face each other. Therefore, work such as inspection and replacement becomes easy. In addition, a partition plate having a surface area larger than the electrode surface of the electrode plate is substantially equal to the electrode surface of the electrode plate between the electrode surface of the pair of electrode plates and the electrode surface of the pair of electrode plates adjacent thereto. Since they are provided in parallel, one set of electrode plates can be brought close to one set of adjacent electrode plates, and operations such as inspection and replacement become easier.
[Brief description of the drawings]
FIG. 1 is a vertical longitudinal sectional view of a small merged treatment septic tank incorporating a dephosphorization processing apparatus according to one embodiment of the present invention.
FIG. 2 is an enlarged side vertical sectional view of the dephosphorization processing apparatus of FIG. 1;
FIG. 3 is a rear vertical sectional view of the dephosphorization processing apparatus of FIG. 2;
FIG. 4 is an enlarged plan view of a dephosphorization processing apparatus according to another embodiment of the present invention.
5 is a side vertical sectional view of the dephosphorization processing apparatus of FIG. 4;
FIG. 6 is an enlarged plan view of a dephosphorization processing apparatus according to still another embodiment of the present invention.
7 is a side vertical sectional view of the dephosphorization processing apparatus of FIG. 6;
[Explanation of symbols]
39, 49, 69 Elution tank 40, 50, 70 Electrode plate 41, 51, 71 Electrode plate 44, 54, 74 Inlet 45, 55, 75 Outlet

Claims (1)

Iron ions or aluminum ions for divided phosphoric acid in wastewater eluting by electrolysis, a plurality of sets comprising a pair of electrode plates consisting of an anode and a cathode,
Each electrode plate is arranged so that its electrode surface is substantially parallel to the direction of flow from inflow to outflow of sewage ,
The plurality of sets of electrode plates are arranged in a direction intersecting the flow direction so that the electrode surfaces of the one set of electrode plates face each other. And
A partition plate having a surface area larger than the electrode surface of the electrode plate is substantially parallel to the electrode surface of the electrode plate between the electrode surface of the pair of electrode plates and the electrode surface of the pair of electrode plates adjacent thereto. A sewage treatment apparatus characterized by being provided .

Images