JP7705754B2 - Wastewater treatment device and method for cleaning the same - Google Patents

Description

The present invention relates to a wastewater treatment device and a method for cleaning the wastewater treatment device.

Anaerobic membrane separation (anaerobic MBR: Membrane Bio Reactor) is known as a wastewater treatment technology for treating industrial wastewater, domestic wastewater, etc. Anaerobic membrane separation is an excellent wastewater treatment technology that uses microorganisms to perform solid-liquid separation using a separation membrane, and can break down organic matter in wastewater into methane and carbon dioxide.

In wastewater treatment equipment using anaerobic membrane separation, contaminants such as sediment and dirt adhere to the surface and pores of the separation membrane with continued use, causing clogging (fouling), and therefore the separation membrane must be cleaned. Membrane fouling reduces the permeation flux and has a significant impact on wastewater treatment performance.
Conventionally, methods for cleaning separation membranes include cleaning with an air diffuser and cleaning with a chemical solution (see, for example, Patent Documents 1 and 2).

Cleaning with an aeration tube involves placing an aeration tube below the separation membrane to generate air bubbles, and then bringing the gas-liquid mixture of the bubbles and wastewater (water to be treated) formed by the rising of the bubbles into contact with the surface of the separation membrane, thereby removing contaminants that have adhered to the surface of the separation membrane. Cleaning with an aeration tube is usually performed continuously while the wastewater treatment device is in operation. On the other hand, cleaning with a chemical solution involves immersing the separation membrane in a chemical solution of a specified concentration, and is performed, for example, periodically. In this case, the separation membrane is sometimes removed from the tank and immersed in the chemical solution.

Japanese Patent Application Publication No. 09-117646 Japanese Patent Application Publication No. 09-117789

However, the above-mentioned cleaning using an aeration tube utilizes the upward flow of the gas-liquid mixture caused by the rising of air bubbles, and therefore has the problem that contaminants tend to accumulate on the upper side of the separation membrane, making it difficult to remove the accumulated contaminants.
In addition, cleaning with chemical solutions affects the anaerobic bacteria in the tank during cleaning, so there are hopes for the development of a separation membrane cleaning technology that does not use chemical solutions.

The present invention aims to solve the above problems and provide a wastewater treatment device and a method for cleaning the wastewater treatment device that can clean the separation membrane using wastewater (water to be treated) and also effectively remove contaminants that have accumulated on the upper side of the separation membrane.

To solve the above problems, the wastewater treatment device of the present invention is characterized by comprising at least two anaerobic wastewater treatment tanks installed adjacent to each other, a separation membrane installed in each of the two anaerobic wastewater treatment tanks for filtering wastewater, an aeration pipe arranged below each of the separation membranes for supplying gas bubbles toward each of the separation membranes, a communication passage connecting the two anaerobic wastewater treatment tanks below the separation membranes, and a pressure difference generating means for generating a pressure difference between the two anaerobic wastewater treatment tanks.

In the wastewater treatment device of the present invention, a water level difference can be created by generating a pressure difference between one anaerobic wastewater treatment tank and the other anaerobic wastewater treatment tank, and a water flow can be formed that flows through a communication passage from the anaerobic wastewater treatment tank with a high hydraulic head to the anaerobic wastewater treatment tank with a low hydraulic head. This water flow creates a powerful downward water flow in the anaerobic wastewater treatment tank with a high hydraulic head, opposite to the upward flow of the gas-liquid mixed flow caused by the rising air bubbles in the aeration pipe, and the pollutants accumulated on the upper side of the separation membrane are peeled off downward. This allows the pollutants accumulated on the upper side of the separation membrane to be suitably removed by using the wastewater (water to be treated).
Therefore, the frequency of cleaning with chemicals can be reduced.

The pressure difference generating means preferably includes a gas recovery pipe connected to each of the two anaerobic wastewater treatment tanks, a recovery side on-off valve provided in the gas recovery pipe, a gas supply pipe connected to each of the two aeration pipes, a supply side on-off valve provided in both of the gas supply pipes, and a control unit that controls the opening and closing of both of the recovery side on-off valves and both of the supply side on-off valves.

In this configuration, cleaning can be easily performed using the head pressure by controlling the opening and closing of both recovery side valves and both supply side valves by the control unit. For example, when cleaning one anaerobic wastewater treatment tank, the control unit opens the recovery side valve of that tank and closes the supply side valve. Then, the control unit closes the recovery side valve in the other anaerobic wastewater treatment tank and opens the supply side valve. Then, the air pressure continues to increase in the other anaerobic wastewater treatment tank, and the water level in the other tank drops due to the increased gas. As the water level drops, wastewater (water to be treated) flows from the other anaerobic wastewater treatment tank through the communication passage to the one anaerobic wastewater treatment tank, and the water level in the one anaerobic wastewater treatment tank rises. When the water level in the one anaerobic wastewater treatment tank rises to a predetermined height, the control unit opens the recovery side valve in the other anaerobic wastewater treatment tank. This allows the wastewater (water to be treated) to flow vigorously from one anaerobic wastewater treatment tank to the other anaerobic wastewater treatment tank through a connecting passage, and contaminants that have accumulated on the upper side of the separation membrane of one anaerobic wastewater treatment tank are effectively removed by the wastewater (water to be treated).

It is also preferable that the gas recovered in both gas recovery pipes is supplied to both gas supply pipes through a blower device.

In this configuration, the gas recovered in both gas recovery pipes is circulated and supplied again to both anaerobic wastewater treatment tanks, enabling efficient cleaning of the separation membrane.

In order to solve the above problems, the method for cleaning a wastewater treatment device of the present invention is a method for cleaning a wastewater treatment device that includes at least two anaerobic wastewater treatment tanks installed adjacent to each other, a separation membrane installed in each of the two anaerobic wastewater treatment tanks for filtering wastewater, an aeration pipe arranged below both separation membranes for supplying gas bubbles toward both separation membranes, and a communication passage that connects the two anaerobic wastewater treatment tanks below both separation membranes. The method includes a water level difference forming step of forming a water level difference between the two anaerobic wastewater treatment tanks by generating a pressure difference between the two anaerobic wastewater treatment tanks, and a water flow forming step of forming a water flow that flows through the communication passage from the anaerobic wastewater treatment tank with a higher water head to the anaerobic wastewater treatment tank with a lower water head.

In the method for cleaning a wastewater treatment device of the present invention, a water level difference can be created between two anaerobic wastewater treatment tanks by the water level difference creating step, and a water flow can be created through a communication passage from the side with a higher head to the side with a lower head by the water flow creating step. This water flow is a downward flow opposite to the upward flow of the gas-liquid mixed flow caused by the rising of air bubbles in the aeration tube, and therefore acts to scrape off pollutants accumulated on the upper side of the separation membrane in a downward direction. This allows the pollutants accumulated on the upper side of the separation membrane to be suitably removed by using wastewater (water to be treated).
Therefore, the frequency of cleaning with chemicals can be reduced.

The wastewater treatment device and method for cleaning the wastewater treatment device of the present invention can use wastewater to clean the separation membrane and can also effectively remove contaminants that have accumulated on the upper side of the separation membrane.

1 is a configuration diagram showing a wastewater treatment device according to an embodiment of the present invention. FIG. 1 is a diagram showing a method for cleaning a wastewater treatment device according to an embodiment of the present invention, and is a diagram showing a water level difference forming step. FIG. 1 is a diagram showing a method for cleaning a wastewater treatment device according to an embodiment of the present invention, and is a diagram showing a water flow forming process. 1 is a schematic plan view showing an example of the layout of a wastewater treatment device according to an embodiment of the present invention.

The embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the up-down direction refers to the vertical direction perpendicular to the surface on which the anaerobic wastewater treatment tank of the wastewater treatment device is installed.

As shown in FIG. 1, the wastewater treatment device 1 includes anaerobic wastewater treatment tanks 2A and 2B, membrane units 10 and aeration pipes 11. The wastewater treatment device 1 also includes a pressure difference generating means 6 that generates a pressure difference between the two anaerobic wastewater treatment tanks 2A and 2B. Details of the pressure difference generating means 6 will be described later.

Anaerobic wastewater treatment tanks 2A, 2B (hereinafter referred to as "treatment tanks 2A, 2B") are adjacently arranged with a partition wall 2a formed in the center of the left and right. Each treatment tank 2A, 2B is sealed and configured to receive wastewater W1 as the water to be treated. The wastewater W1 is supplied to the treatment tanks 2A, 2B by a liquid delivery pump (not shown) installed midway through the wastewater supply line. Examples of wastewater W1 include industrial wastewater discharged from factories and domestic wastewater (sewage). In each treatment tank 2A, 2B, the water level W1a of the wastewater W1 is set to a height at which the entire membrane unit 10, 10 is immersed.

A communication passage 5 is formed in the lower part of the partition wall 2a to connect the treatment tanks 2A, 2B to each other. The communication passage 5 allows the flow of wastewater W1 between the treatment tanks 2A, 2B, and has an opening area that does not provide resistance to the flow of wastewater W1 between the treatment tanks 2A, 2B. The communication passage 5 is formed at an opening at a position below the membrane units 10, 10 of each treatment tank 2A, 2B.
A space is formed in the upper interior space of the treatment tanks 2A and 2B to allow the water level of the wastewater W1 to rise. The treatment tanks 2A and 2B are also provided with a discharge path (not shown) for discharging excess sludge.

The membrane unit 10 includes a plurality of membrane elements made of known separation membranes. The membrane units 10 used in each of the treatment tanks 2A and 2B have the same specifications. The membrane elements have a flat shape that allows for high integration. However, membrane elements of different shapes, such as a cylindrical shape, may also be used.
As the separation membrane, it is preferable to use a microfiltration membrane (MF membrane). Examples of the shape of the separation membrane include a hollow fiber membrane, a flat membrane, a tubular membrane, a bag-shaped membrane, etc., and a hollow fiber membrane having a large membrane area when compared on a volume basis is preferable.
Examples of the material for the separation membrane include organic materials (cellulose, polyolefin, polysulfone, polyvinyl alcohol, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, etc.) The material for the separation membrane is appropriately selected depending on the properties of the water to be treated.

The membrane unit 10 is, for example, a frame holding multiple membrane elements. A permeate discharge channel 12 for discharging the permeate W2 from the multiple membrane elements is connected to the top of the membrane unit 10. The permeate discharge channels 12, 12 of each membrane unit 10, 10 merge into one downstream. A suction pump (not shown) is provided in the middle of the merged channel. The permeate W2 is sucked into the suction pump and discharged to the outside, and is sent to a downstream advanced treatment facility (nitrogen treatment method) or anammox treatment device (not shown) to remove nitrogen.

The aeration pipes 11 are disposed below each of the membrane units 10. The aeration pipes 11 discharge biogas, which is supplied from the blower device 19, toward the membrane elements of the membrane unit 10. The aeration pipes 11 are provided with a plurality of discharge holes for discharging gas. A gas supply pipe 13 is connected to each of the aeration pipes 11. Each of the gas supply pipes 13 is connected to a main pipe 18 connected to the blower device 19, and is configured to receive gas supply through the main pipe 18. The bubbles generated in the aeration pipes 11 rise to form a gas-liquid mixed flow of the bubbles and wastewater W1. The biogas is a gas containing methane gas, carbon dioxide, nitrogen, hydrogen sulfide, etc.

The pressure difference generating means 6 includes gas recovery pipes 15 , recovery side on-off valves 16 , gas supply pipes 13 , supply side on-off valves 14 , and a control unit 30 .
The gas recovery pipes 15, 15 have one end connected to the treatment tanks 2A, 2B, and recover biogas from the interior of the treatment tanks 2A, 2B. The recovery side on-off valves 16, 16 are provided midway through the gas recovery pipes 15, 15, and are operated under the control of the control unit 30. The recovery side on-off valve 16 allows biogas to be recovered when open, and prevents biogas from being recovered when closed. The other end of each of the gas recovery pipes 15, 15 is connected to a recovery side main pipe 17. The downstream end of the recovery side main pipe 17 is connected to a gas folder 20. The gas folder 20 has the function of storing surplus biogas when it is generated. An end of a main pipe 18 is connected to the recovery side main pipe 17.

One end of the gas supply pipes 13, 13 is connected to the aeration pipes 11, 11, and supplies biogas to the aeration pipes 11, 11. The other end of each of the gas supply pipes 13, 13 is connected to a main pipe 18. The supply side opening/closing valves 14, 14 are provided midway through the gas supply pipes 13, 13, and are operated under the control of the control unit 30. When the supply side opening/closing valve 14 is open, it allows biogas to be supplied to the aeration pipe 11, and when it is closed, it prevents the supply to the aeration pipe 11. The upstream side of the main pipe 18 is connected to the recovery side main pipe 17.

The control unit 30 is a device that controls the opening and closing of the recovery side opening and closing valves 16, 16 and the supply side opening and closing valves 14, 14. The control unit 30 is configured with, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), input/output circuits, etc. The control unit 30 executes control by performing various processes based on inputs from input devices, programs stored in the ROM, data, etc.

Next, a method for cleaning the wastewater treatment device, which is executed under the control of the control unit 30, will be described. Figure 2 shows the method for cleaning the wastewater treatment device, and is a diagram showing the water level difference formation process. Figure 3 shows the method for cleaning the wastewater treatment device, and is a diagram showing the water flow formation process.

During normal operation without a pressure difference, as shown in FIG. 1, the water level W1a, 1a is set in the treatment tanks 2A, 2B so that the entire membrane units 10, 10 are immersed. During normal operation, the recovery side opening/closing valves 16, 16 and the supply side opening/closing valves 14, 14 are all opened under the control of the control unit 30, and the biogas discharged from the blower device 19 is diffused into the treatment tanks 2A, 2B from the diffuser pipes 11, 11 through the main pipe 18 and the gas supply pipes 13, 13. The biogas diffused into the treatment tanks 2A, 2B is discharged into the inner space of the treatment tanks 2A, 2B, recovered by the gas recovery pipes 15, 15, flows from the recovery side main pipe 17 into the main pipe 18, and is discharged again into the main pipe 18 by the blower device 19. In other words, during normal operation, the biogas circulates through such a circulation path, thereby maintaining the treatment tanks 2A, 2B in an environment suitable for the habitation of anaerobic microorganisms.

The method for cleaning the wastewater treatment device 1 includes a water level difference forming step and a water flow forming step. In the following, the left treatment tank 2A will be described as the target to be cleaned.
The water level difference forming step is a step of forming a water level difference by generating a pressure difference between the treatment tanks 2A and 2B. Specifically, in the treatment tank 2A, the recovery side on-off valve 16 is opened and the supply side on-off valve 14 is closed. On the other hand, in the treatment tank 2B, the recovery side on-off valve 16 is closed and the supply side on-off valve 14 is opened. In this way, in the treatment tank 2B, biogas continues to be supplied from the aeration pipe 11 with the gas recovery pipe 15 closed, so that the internal volume of the treatment tank 2B increases due to the accumulation of biogas, and the internal pressure increases. As a result, the water level W1a of the treatment tank 2B, which is at the height shown in FIG. 1 during normal operation, is pushed down to the low water level W1c shown in FIG. 2.

As a result, the wastewater W1 stored in the treatment tank 2B flows into the treatment tank 2A through the connecting passage 5, and the water level W1a in the treatment tank 2A, which is at the height shown in Figure 1 during normal operation, is pushed up to the high water level W1b shown in Figure 2.
This creates a water level difference between the treatment tanks 2A and 2B.

The water flow forming step is a step of forming a water flow that flows from the treatment tank 2A with the higher water head to the treatment tank 2B with the lower water head through the communication passage 5 based on the water level difference formed between the treatment tanks 2A and 2B by the water level difference forming step. The peak of the water level difference can be detected, for example, by monitoring the water level of the treatment tank 2A with a sensor or the like.
In the water flow forming process, the recovery side on-off valve 16 on the treatment tank 2A side is kept open, and the supply side on-off valve 14 is kept closed. On the other hand, on the treatment tank 2B side, the recovery side on-off valve 16 is switched to an open state, and the supply side on-off valve 14 is kept open. In this way, the biogas that has been retained in the inner space of the treatment tank 2B is recovered through the gas recovery pipe 15, and the pressure in the inner space of the treatment tank 2B drops suddenly. As a result, the water level in the treatment tank 2B rises from the low water level W1c to the normal operation water level W1a.

Then, the wastewater W1 stored at the high water level W1b in the treatment tank 2A returns to the treatment tank 2B through the connecting passage 5. At this time, the water flow generated in the treatment tank 2A flows downward, opposite to the upward flow of the gas-liquid mixture flow caused by the air bubbles in the aeration pipe 11, and acts to scrape off the pollutants accumulated on the upper side of the membrane unit 10 in a downward direction. As a result, the pollutants accumulated on the upper side of the membrane unit 10 and the upper side of the membrane element in the treatment tank 2A can be suitably removed using the wastewater W1 (water to be treated).

When cleaning the membrane unit 10 in the treatment tank 2B, the opposite of the cleaning method described above is performed: the pressure inside the treatment tank 2A is increased to create a water level difference, and a water flow is formed that flows from the treatment tank 2B with the higher water head to the treatment tank 2A with the lower water head through the communication passage 5. This allows the pollutants that have accumulated on the upper side of the membrane unit 10 and the upper side of the membrane element on the treatment tank 2B side to be effectively removed using the wastewater W1 (water to be treated).

In the wastewater treatment device 1 of the present embodiment described above, a water level difference can be formed by generating a pressure difference between the treatment tanks 2A and 2B, and for example, a water flow can be formed that flows from the treatment tank 2A with a high water head to the treatment tank 2B with a low water head through the communication passage 5. In the treatment tank 2A, this water flow is a downward flow opposite to the upward flow of the gas-liquid mixed flow caused by the air bubbles in the aeration tube 11, and therefore acts to peel off the pollutants accumulated on the upper side of the membrane unit 10 and the membrane elements in a downward direction. This allows the pollutants accumulated on the upper side of the membrane unit 10 and the membrane elements to be suitably removed by using the wastewater W1 (water to be treated).
Therefore, the frequency of cleaning with chemicals can be reduced.

Furthermore, cleaning utilizing the hydraulic head pressure can be easily performed by controlling the opening and closing of both recovery side on-off valves 16, 16 and both supply side on-off valves 14, 14 by the control unit 30. For example, cleaning can be performed by the control unit 30 in a predetermined cycle, such as once a day or once a week.
In addition, the suction pressure of the suction pump may be detected by a sensor or the like, and when the suction pressure exceeds a predetermined value, it may be determined that the membrane unit 10 is dirty, and cleaning may be automatically performed by the control unit 30.

In addition, the biogas recovered in both gas recovery pipes 15, 15 is supplied to both gas supply pipes 13, 13 through a blower device 19, enabling efficient cleaning of the membrane unit 10.

In the method for cleaning the wastewater treatment device 1 of this embodiment, a water level difference can be formed between the treatment tanks 2A, 2B in the water level difference forming step, and a water flow can be formed through the communication passage 5 from the side with a higher water head to the side with a lower water head in the water flow forming step. This water flow is a downward flow opposite to the upward flow of the gas-liquid mixed flow caused by the air bubbles in the aeration pipe 11, and therefore acts to peel off pollutants accumulated on the upper side of the membrane unit 10 and the membrane elements in a downward direction. This allows the pollutants accumulated on the upper side of the membrane unit 10 and the membrane elements to be suitably removed by using the wastewater W1 (water to be treated).
Therefore, the frequency of cleaning with chemicals can be reduced.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit of the present invention.
For example, in the above embodiment, a water level difference is created between the treatment tanks 2A and 2B by the biogas sent to the aeration pipe 11 by the blower device 19. However, this is not limited to this, and the pressure in the interior may be increased by storing biogas that is naturally generated from the stored wastewater W1 without using the blower device 19.

In the above embodiment, a water level difference is created between two adjacent treatment tanks 2A, 2B to perform cleaning. However, this is not limited to this. The membrane unit 10 can also be suitably cleaned by utilizing the water level difference in a wastewater treatment device 60 having three treatment tanks 61-63 and a reserve tank 55 as shown in FIG. 4.
4 includes a membrane unit 10, and each of the two partition walls 2a, 2a includes a communication passage 5. Similarly, each of the treatment tanks 61 to 63 includes a gas recovery pipe 15, a recovery side on-off valve 16, a gas supply pipe 13, and a supply side on-off valve 14, and a control unit 30 for controlling the opening and closing of these.

In such a wastewater treatment device 60, for example, when cleaning the membrane unit 10 of the treatment tank 61, the supply side opening/closing valve 14 of the treatment tank 61 is closed and the recovery side opening/closing valves 16 of the treatment tanks 62 and 63 are closed in the water level difference formation process to increase the pressure inside the treatment tanks 62 and 63. As a result, the water levels of the treatment tanks 62 and 63 are lowered, and instead the water level of the treatment tank 61 is raised, forming a water level difference between the treatment tank 61 and the treatment tanks 62 and 63.

When the water level difference is formed, the water flow forming process maintains the recovery side on-off valve 16 in the treatment tank 61 in an open state and the supply side on-off valve 14 in a closed state. On the other hand, in the treatment tanks 62 and 63, the recovery side on-off valves 16 are switched to an open state and the supply side on-off valves 14 are maintained in an open state. As a result, the pressure in the treatment tanks 62 and 63 drops, and the water levels of the treatment tanks 62 and 63 rise from the low water level to the water level during normal operation. This rise causes the wastewater W1 to flow vigorously from the treatment tank 61 through the communication passage 5 into the treatment tanks 62 and 63. The water flow generated in the treatment tank 61 at this time is a downward flow opposite to the upward flow of the gas-liquid mixed flow caused by the air bubbles in the air diffuser 11, so it acts to strip off the polluted materials accumulated on the upper side of the membrane unit 10 in a downward direction. This allows the pollutants accumulated on the upper side of the membrane unit 10 and on the upper side of the membrane elements in the treatment tank 61 to be suitably removed by using the wastewater W1 (water to be treated).
In addition, when cleaning each of the membrane units 10, 10 in the treatment tanks 62, 63, a water level difference is similarly created, so that contaminants can be suitably removed.
As described above, the wastewater treatment device 60 having three treatment tanks 61-63 and a reserve tank 55 has been described. However, this is not limited to this, and the membrane unit 10 can also be suitably cleaned by utilizing the water level difference in wastewater treatment devices having four or more treatment tanks or reserve tanks.

1 Wastewater treatment device 2A, 2B Anaerobic wastewater treatment tank (treatment tank)
5 Communication passage 6 Pressure difference generating means 10 Membrane unit 11 Aeration pipe 13 Gas supply pipe 14 Supply side opening/closing valve 15 Gas recovery pipe 16 Recovery side opening/closing valve 30 Control unit 60 Wastewater treatment device 61 to 63 Treatment tank W1 Wastewater

Claims (4)

At least two anaerobic wastewater treatment tanks installed adjacent to each other;
A separation membrane is installed in each of the two anaerobic wastewater treatment tanks and filters the wastewater;
an aeration tube disposed below each of the separation membranes and configured to supply gas bubbles toward each of the separation membranes;
a communication passage below the two separation membranes that communicates between the two anaerobic wastewater treatment tanks;
and a pressure difference generating means for generating a pressure difference between the two anaerobic wastewater treatment tanks. The wastewater treatment device according to claim 1, characterized in that the pressure difference generating means comprises a gas recovery pipe connected to each of the two anaerobic wastewater treatment tanks, a recovery side on-off valve provided in the gas recovery pipe, a gas supply pipe connected to each of the two aeration pipes, a supply side on-off valve provided in both of the gas supply pipes, and a control unit that controls the opening and closing of both of the recovery side on-off valves and both of the supply side on-off valves. 3. The wastewater treatment apparatus according to claim 2 , wherein the gas recovery pipes are connected to the gas supply pipes through a blower device. A method for cleaning a wastewater treatment device comprising at least two anaerobic wastewater treatment tanks installed adjacent to each other, a separation membrane installed in each of the two anaerobic wastewater treatment tanks for filtering wastewater, an aeration pipe disposed below each of the two separation membranes for supplying gas bubbles toward each of the two separation membranes, and a communication passage connecting the two anaerobic wastewater treatment tanks below the two separation membranes, comprising:
a water level difference generating step of generating a pressure difference between the two anaerobic wastewater treatment tanks to generate a water level difference between the two anaerobic wastewater treatment tanks;
a water flow forming step of forming a water flow that flows through the communicating passage from the anaerobic wastewater treatment tank with a higher water head to the anaerobic wastewater treatment tank with a lower water head.

Images