Simulation device for researching release rule of water body bottom mud pollutants

Abstract

The invention discloses a simulation device for researching the release law of water body sediment pollutants, which comprises a static simulation area and a dynamic simulation area, the static simulation area is provided with a hydraulic disturbance / temperature simulation area, an aeration simulation area and a depth / pH value change simulation area, a stirring motor drives a stirring device and cooperates with an electric heating rod and a temperature controller to control the temperature, and the dynamic simulation area is provided with an aeration simulation area and a depth / pH value change simulation area. The aeration pump is connected with a plurality of aeration heads, and the basket screw adjusts the upper and lower plates to simulate depth / pH value changes. The dynamic simulation area comprises a placement area for placing a peristaltic pump, a hydraulic mixing area, a pollutant release area and a water outlet area. The peristaltic pump enables water to flow in each area through a circulating pipe (15), the hydraulic mixing area is communicated with the releasing area through different water passing openings, the pollutant releasing area is communicated with the water outlet area through different water passing openings, and the pollutant releasing area and the water outlet area are provided with sampling opening water taking devices and portable multi-parameter testers. According to the invention, static simulation and dynamic simulation are combined in the same device, and the influence of various environmental conditions on the release of sediment pollutants is simulated in the same device.

Description

Technical Field

[0001] The invention relates to the technical field of river, lake, reservoir and pond ecological research equipment, and in particular to a simulation device for studying the release law of water body bottom mud pollutants. Background Art

[0002] In recent years, with the rapid development of my country's economy, large amounts of pollutants such as nutrients and heavy metals have been discharged into water bodies through industrial and domestic wastewater, municipal waste, and atmospheric deposition. This has led to environmental deterioration and degradation of aquatic ecosystems in most rivers, lakes, reservoirs, and ponds nationwide. A complete aquatic ecosystem is composed of overlying water, suspended and dissolved matter, sediment, aquatic organisms, and the surrounding environmental conditions. Sediment is a crucial component of aquatic ecosystems, providing a substrate for aquatic plants and a breeding ground for benthic animals. It is also a major reservoir for nutrients and pollutants entering rivers. Sediment in rivers, lakes, reservoirs, and ponds is primarily composed of clay, silt, organic matter, and various minerals deposited at the bottom of the water body. These substances primarily originate from soil erosion, the decomposition of plant and animal life, and pollutants entering the water body. Numerous pollutants enter rivers, lakes, reservoirs, and ponds through various means, including atmospheric deposition, wastewater discharge, and rainwater leaching and erosion. Some of these pollutants are deposited in the sediment and gradually accumulate. Due to this continuous accumulation, the concentration of pollutants in the sediment is often several times higher than that in the overlying water, resulting in severe sediment pollution. Contaminated sediments can affect the growth and reproduction of submerged plants and benthic animals. Furthermore, pollutants in the sediments are absorbed by these organisms and can be biomagnified through the food chain, accumulating in fish, shellfish, and mammals, ultimately entering the human body and threatening human health. Therefore, sediments can serve as indicators of water pollution, and their environmental quality, to a certain extent, reflects the pollution status of the water body.

[0003] As the primary reservoir of pollutants in rivers, lakes, reservoirs, and ponds, sediments not only directly reflect the pollution history of water bodies, but also, with the continued advancement of water environment management and the control of external pollution sources, sediments can release various pollutants into overlying water bodies under certain changes in the external environment, causing "secondary pollution." A dynamic balance of absorption and release exists between sediments and overlying water bodies. The material exchange process between the two is highly complex, often involving biological recycling of substances, settling and resuspension of particles, adsorption and desorption of dissolved substances, precipitation and dissolution, and so on. Numerous factors influence this process, which can be broadly categorized as intrinsic and extrinsic. Intrinsic factors primarily include sediment properties and composition, while extrinsic factors primarily include water temperature, pH, dissolved oxygen, hydraulic disturbance conditions, and microorganisms. Using sediment release experiments to assess the impact of pollutants in sediments on overlying water bodies is an effective approach to accounting for endogenous pollution. Therefore, a set of experimental simulation devices was designed to simulate the enrichment and release of pollutants in water sediments under different environmental conditions, study the static and dynamic release processes of pollutants, and clarify their adsorption and release laws, which plays an important role in further management and control of pollutants in river, lake, reservoir and pond sediments.

[0004] At present, the research on the release of pollutants in sediments usually adopts relatively simple devices or glass instruments. These devices can usually only be used to study the release of pollutants under certain single conditions. It is not possible to simultaneously study the release patterns of sediment pollutants under multiple different environmental conditions in the same device. In addition, there is currently no comprehensive simulation device on the market that is complete, easy to move, rational in structure, and rich in functions, and can be used to simultaneously study the effects of different conditions on the release of pollutants in sediments. Summary of the Invention

[0005] The present invention aims to provide a simulation device for studying the release patterns of sediment pollutants in water bodies. This device is capable of simultaneously studying the release patterns of sediment pollutants under a variety of different environmental conditions. Furthermore, this device can be used to study both the static and dynamic release processes of pollutants in sediment. This invention overcomes the shortcomings of current research by combining static and dynamic simulations in a single device, allowing simulation of the effects of multiple environmental conditions on sediment pollutant release.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions: a simulation device for studying the release pattern of sediment pollutants in water bodies, comprising a device body, a plurality of base rollers are provided at the lower end of the device body, the device body comprises a static simulation area and a dynamic simulation area, the static simulation area is divided into a hydraulic disturbance / temperature simulation area, an aeration simulation area, and a depth change / pH value change simulation area, and the dynamic simulation area is divided into a placement area, a hydraulic mixing area, a pollutant release area, and a water outlet area; A stirring motor is installed at the upper end of the hydraulic disturbance / temperature simulation area, and a power output shaft of the stirring motor is connected to a stirring device extending into the hydraulic disturbance / temperature simulation area. An electric heating rod and a temperature probe are also provided in the hydraulic disturbance / temperature simulation area. A temperature controller is provided in the hydraulic disturbance / temperature simulation area, and the electric heating rod and the temperature probe are both electrically connected to the temperature controller. An aeration pump is provided outside the aeration simulation area, an aeration device is provided inside the aeration simulation area, and the aeration device is provided with a plurality of aeration heads connected to the outlet end of the aeration pump; Two opposing inner walls of the depth change / pH value change simulation area are provided with a turnbuckle threaded connecting rod, the opposing turnbuckle threaded connecting rods are cooperatively connected to an upper support plate, the lower end of the upper support plate is threadedly connected to a lower pressure plate, and the interior of the depth change / pH value change simulation area is provided with a built-in scale along its height direction; A peristaltic pump is placed in the placement area, the outlet end of the peristaltic pump is connected to the hydraulic mixing area, the inlet end of the peristaltic pump is connected to the water outlet area through a circulation pipe, the hydraulic mixing area is connected to the pollutant release area through a water port, the pollutant release area is connected to the water outlet area through a water port, and the pollutant release area and the water outlet area are both provided with a sampling port water intake device and a portable multi-parameter measuring instrument; It also includes a control panel, and the stirring motor, the temperature controller, the aeration pump, the peristaltic pump, the sampling port water intake device and the portable multi-parameter measuring instrument are all controlled by the control panel.

[0007] The present invention is further configured as follows: the sampling port water intake device includes a vertical telescopic tube arranged vertically and a horizontal telescopic tube connected to the lower end of the vertical telescopic tube, the vertical telescopic tube and the horizontal telescopic tube are connected through an elbow, the vertical telescopic tube is provided with a vertical electric telescopic rod for driving the telescopic operation thereof, and the horizontal telescopic tube is provided with a horizontal electric telescopic rod for driving the telescopic operation thereof, and both the vertical electric telescopic rod and the horizontal electric telescopic rod are controlled by the control panel.

[0008] The present invention is further configured as follows: a water stop valve is provided on the vertical telescopic pipe.

[0009] The present invention is further configured as follows: the stirring device includes a main body rod, a plurality of stirring rods threadedly connected to the main body rod, and each stirring rod is connected to a rotatable fan blade.

[0010] The present invention is further configured as follows: the lower end of each stirring rod is connected to an arc-shaped baffle.

[0011] The present invention is further configured as follows: the temperature probe is connected to the lower end of the electric heating rod.

[0012] The present invention is further configured as follows: the outlet end of the peristaltic pump is connected to a water injection pipe, the water injection pipe is connected to multiple water distribution pipes connected to the hydraulic mixing zone, and each water distribution pipe is provided with a water stop valve.

[0013] The present invention is further configured as follows: a drain outlet is provided at the lower portion of the water outlet area.

[0014] The present invention is further configured as follows: the device body is provided with a storage platform between the static simulation area and the dynamic simulation area; the bottom of the storage platform is hollow, and the circulation pipe passes through the bottom of the storage platform.

[0015] The present invention is further configured as follows: the water outlet at the hydraulic mixing zone is higher than the water outlet at the water outlet zone.

[0016] In summary, the present invention has the following beneficial effects: the present invention realizes the convenient movement of the entire simulation device by installing a bottom pulley; realizes the static simulation and dynamic simulation of the release of sediment pollutants in the same device at the same time, and realizes the simultaneous simulation of the effects of multiple environmental conditions on the release of sediment pollutants in the same device; solves the problem of single flow rate in dynamic simulation, connects the water inlet and outlet with an adjustable constant speed peristaltic pump, and controls the water inlet flow by adjusting the pump, thereby achieving the purpose of controlling the water flow rate in the pollutant release area; solves the problem of excessive water flow velocity caused by the height difference of the water inlet and lifting the surface sediment in front of the pollutant release area by setting a hydraulic mixing zone; the sampling port water taking device The movement of the sampling tube is controlled by a telescopic panel, enabling the collection of water samples at different depths and locations. A curved baffle is threaded onto the bottom of the stirring rod in the stirring device, solving the problem of water swirling during stirring. The aerator and aeration head in the aeration device are evenly distributed in layers in a rectangular parallelepiped structure, ensuring sufficient contact between the overlying water and the air, solving the problem of high dissolved oxygen levels in the water near the aeration head and low dissolved oxygen levels in the water far from the aeration head during a single aeration process. In the depth change / pH change simulation area, the upper support plate and lower pressure plate are fixed by a basket thread connection, conveniently achieving the up and down movement of the bottom plate. A built-in scale is provided on the inner wall of the device, enabling precise depth adjustment. This invention enables the study of the release patterns of sediment pollutants under different environmental conditions and parameters within the same device. This has high practical value for studying and understanding the endogenous pollution mechanism of sediments, and helps guide pollution (siltation) removal in rivers, lakes, reservoirs, and ponds. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the overall structure distribution diagram of the present invention; Figure 2 It is a top view of the overall structure of the present invention; Figure 3 It is a rear view of the overall structure of the present invention; Figure 4 This is a front view of the overall structure of the present invention; Figure 5 It is a front view of the temperature control system of the present invention; Figure 6 This is a front view of the sampling port water intake device of the present invention.

[0018] Figure: 1. Static simulation area; 2. Hydraulic disturbance / temperature simulation area; 3. Aeration simulation area; 4. Depth change / pH value change simulation area; 5. Dynamic simulation area; 6. Placement area; 7. Hydraulic mixing area; 8. Pollutant release area; 9. Water outlet area; 10. Placement platform; 11. Stirring device; 12. Aeration device; 13. Upper support plate; 14. Lower pressure plate; 15. Circulation pipe; 16. Peristaltic pump; 17. Water injection pipe; 18. Water stop valve; 19. Water distribution pipe; 20. Water outlet; 21. Stirring motor; 22. Water sampling port Device; 23. Portable multi-parameter measuring instrument; 24. Aeration pump; 25. Threaded connection; 26. Stirring rod; 27. Fan blade; 28. Arc baffle; 29. Simulated release reaction mud area; 30. Aeration head; 31. Flower basket threaded connection rod; 32. Built-in scale; 33. Base roller skates; 34. Temperature controller; 35. Heating rod; 36. Temperature probe; 37. Vertical telescopic tube; 38. Vertical electric telescopic rod; 39. Elbow; 40. Horizontal telescopic tube; 41. Horizontal electric telescopic rod; 42. Control panel; 43. Drain outlet. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings.

[0020] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", "front", "back", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0021] Furthermore, terms such as "horizontal" and "vertical" do not necessarily mean that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0022] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections, direct connections, indirect connections via an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0023] Example, see Figure 1-6 A simulation device for studying the release patterns of pollutants from bottom sediments in water bodies includes a device body, the lower end of which is provided with multiple base rollers 33. The device body includes a static simulation area 1 and a dynamic simulation area 5. The static simulation area 1 is divided into a hydraulic disturbance / temperature simulation area 2, an aeration simulation area 3, and a depth change / pH value change simulation area 4. The bottoms of the hydraulic disturbance / temperature simulation area 2 and the aeration simulation area 3 are both filled with sludge simulated release reaction mud areas 29. The dynamic simulation area 5 is divided into a placement area 6, a hydraulic mixing area 7, a pollutant release area 8, and a water outlet area 9. A placement platform 10 is provided between the static simulation area 1 and the dynamic simulation area 5. The bottom of the placement platform 10 is hollow.

[0024] A stirring motor 21 is mounted at the top of the hydraulic disturbance / temperature simulation zone 2. The power output shaft of the stirring motor 21 is connected to a stirring device 11 extending into the hydraulic disturbance / temperature simulation zone 2. The stirring device 11 comprises a main rod, four stirring rods 26 threaded 25 onto the main rod, each of which is connected to a rotatable fan blade 27. The lower end of each stirring rod 26 is connected to an arc-shaped baffle 28, which is used to prevent the water from swirling during the stirring process. Four electric heating rods 35 are also provided within the hydraulic disturbance / temperature simulation zone 2. Each electric heating rod 35 is connected to a temperature probe 36 at its lower end. A temperature controller 34 is also provided within the hydraulic disturbance / temperature simulation zone 2. The electric heating rods 35 and the temperature probe 36 are both electrically connected to the temperature controller 34. The hydraulic disturbance / temperature simulation area 2 is used to simulate and study the release pattern of sediment pollutants under different hydraulic agitation or temperature conditions. The stirring device 11 used to study hydraulic disturbance and the temperature control system used to study temperature conditions are both movable and can be replaced according to the experimental conditions.

[0025] An aeration pump 24 is located outside the aeration simulation area 3. Inside, an aeration device 12 is installed. The aeration device 12 is connected in layers to form a rectangular parallelepiped structure and is evenly distributed. Multiple aeration heads 30 are installed on the aeration device 12. This distribution ensures sufficient contact between the overlying water and the air to achieve the desired dissolved oxygen level. This prevents high dissolved oxygen levels near the aeration heads 30 and low levels farther from the heads. The aeration simulation area 3 is used to simulate the release of sediment pollutants under varying dissolved oxygen conditions. The aeration device 12 is used to control dissolved oxygen levels. The aeration device 12 is removable and can be detached.

[0026] Two reaction zones are located within the depth change / pH change simulation zone 4. Built-in scales 32 are located on both walls of the reaction zones to facilitate observation and depth adjustment. Each reaction zone has a threaded basket connecting rod 31 located on each inner wall. The opposing threaded basket connecting rods 31 are connected to an upper support plate 13. The lower end of the upper support plate 13 is threadedly connected 25 to a lower pressure plate 14. The depth change / pH change simulation zone 4 is used to study the release patterns of sediment pollutants under different dredging depths or pH conditions. The depth of the reaction zones can be adjusted to meet experimental requirements. When conducting experiments at different dredging depths, the bottom plate can be fixed by adjusting the threaded basket connecting rods 31 to achieve the desired depth. When conducting experiments at different pH values, the bottom plate can be adjusted to the bottom of the reaction zone, and then filled with experimental mud and water.

[0027] A peristaltic pump 16 is placed in the placement area 6. The peristaltic pump 16 can adjust the constant speed to adjust the water inlet flow rate. The outlet end of the peristaltic pump 16 is connected to a water injection pipe 17 through an adapter. The water injection pipe 17 is connected to multiple water distribution pipes 19 connected to the hydraulic mixing area 7. Each water distribution pipe 19 is provided with a water stop valve 18. The inlet end of the peristaltic pump 16 is connected to the water outlet area 9 through a circulation pipe 15. The circulation pipe 15 passes from the bottom of the placement platform 10. Each water distribution pipe 19 is provided with a water stop valve 18 to control the water inlet. The overlying water body is preferentially pumped into the hydraulic mixing area 7, and then enters the pollutant release area 8 through the water outlet 20, and then flows into the water outlet area 9 and is connected to the water inlet of the peristaltic pump 16 through the circulation pipe 15 to achieve an overall flow circulation. The hydraulic mixing zone 7 is connected to the pollutant release zone 8 through multiple water outlets 20, and the pollutant release zone 8 is connected to the water outlet zone 9 through multiple water outlets 20. The water outlet 20 at the hydraulic mixing zone 7 is higher than the water outlet 20 at the water outlet zone 9. The water outlets 20 on both sides have a certain height difference, the purpose of which is to make the water flow. A drain outlet 43 is opened at the bottom of the water outlet zone 9 to discharge excess water after the experiment.

[0028] A sampling port water intake device 22 is installed at the front, middle, and rear of the pollutant release zone 8 and at the water outlet zone 9, respectively, for collecting water samples from different areas for analysis. A portable multi-parameter measuring instrument 23 is placed at the front, middle, and rear water intake locations. The portable multi-parameter measuring instrument 23 is placed on the storage platform 10 and is used to measure parameters such as pH and dissolved oxygen in the water. The sampling port water intake device 22 includes a vertical telescopic tube 37 and a horizontal telescopic tube 40 connected to the lower end of the vertical telescopic tube 37. The vertical telescopic tube 37 and the horizontal telescopic tube 40 are connected by an elbow 39. The vertical telescopic tube 37 is equipped with a vertical electric telescopic rod 38 for driving its extension and contraction. The horizontal telescopic tube 40 is equipped with a horizontal electric telescopic rod 41 for driving its extension and contraction. A water stop valve 18 is installed on the vertical telescopic tube 37. The height of the vertical telescopic tube 37 is adjusted by controlling the extension and contraction of the vertical electric telescopic rod 38, and the length of the horizontal telescopic tube 40 is adjusted by controlling the extension and contraction of the horizontal electric telescopic rod 41, thereby enabling the collection of water samples at different depths and locations.

[0029] It also includes a control panel 42. The stirring motor 21, temperature controller 34, aeration pump 24, peristaltic pump 16, vertical electric telescopic rod 38, horizontal electric telescopic rod 41 and portable multi-parameter measuring instrument 23 are all controlled by the control panel 42. The control panel 42 has a built-in operating system for centralized control of the simulation device.

[0030] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed. However, as long as such modifications are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A simulation device for studying the release pattern of water sediment pollutants, comprising a device body, characterized in that: A plurality of base rollers (33) are provided at the lower end of the device body. The device body comprises a static simulation area (1) and a dynamic simulation area (5). The static simulation area (1) is divided into a hydraulic disturbance / temperature simulation area (2), an aeration simulation area (3), and a depth change / pH value change simulation area (4). The dynamic simulation area (5) is divided into a placement area (6), a hydraulic mixing area (7), a pollutant release area (8), and a water outlet area (9). A stirring motor (21) is installed at the upper end of the hydraulic disturbance / temperature simulation area (2), and a power output shaft of the stirring motor (21) is connected to a stirring device (11) extending into the hydraulic disturbance / temperature simulation area (2). An electric heating rod (35) and a temperature probe (36) are also provided in the hydraulic disturbance / temperature simulation area (2). A temperature controller (34) is provided in the hydraulic disturbance / temperature simulation area (2), and the electric heating rod (35) and the temperature probe (36) are both electrically connected to the temperature controller (34); An aeration pump (24) is provided outside the aeration simulation area (3), an aeration device (12) is provided inside the aeration simulation area (3), and the aeration device (12) is provided with a plurality of aeration heads (30) connected to the outlet end of the aeration pump (24); Two opposing inner walls of the depth change / pH value change simulation area (4) are provided with basket threaded connecting rods (31), the opposing basket threaded connecting rods (31) are cooperatively connected with an upper support plate (13), the lower end of the upper support plate (13) is threadedly connected (25) with a lower pressure plate (14), and the interior of the depth change / pH value change simulation area (4) is provided with a built-in scale (32) along its height direction; A peristaltic pump (16) is placed in the placement area (6), the outlet end of the peristaltic pump (16) is connected to the hydraulic mixing area (7), the inlet end of the peristaltic pump (16) is connected to the water outlet area (9) through a circulation pipe (15), the hydraulic mixing area (7) is connected to the pollutant release area (8) through a water outlet (20), the pollutant release area (8) is connected to the water outlet area (9) through a water outlet (20), and a sampling port water device (22) and a portable multi-parameter measuring instrument (23) are provided in the pollutant release area (8) and the water outlet area (9); It also includes a control panel (42), and the stirring motor (21), the temperature controller (34), the aeration pump (24), the peristaltic pump (16), the sampling port water intake device (22) and the portable multi-parameter measuring instrument (23) are all controlled by the control panel (42).

2. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: The sampling port water intake device (22) comprises a vertical telescopic tube (37) arranged vertically, and a horizontal telescopic tube (40) connected to the lower end of the vertical telescopic tube (37). The vertical telescopic tube (37) and the horizontal telescopic tube (40) are connected via an elbow (39). The vertical telescopic tube (37) is provided with a vertical electric telescopic rod (38) for driving the telescopic tube to extend and retract. The horizontal telescopic tube (40) is provided with a horizontal electric telescopic rod (41) for driving the telescopic tube to extend and retract. Both the vertical electric telescopic rod (38) and the horizontal electric telescopic rod (41) are controlled by the control panel (42).

3. The simulation device for studying the release pattern of water sediment pollutants according to claim 2, characterized in that: A water stop valve (18) is provided on the vertical telescopic tube (37).

4. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: The stirring device (11) comprises a main body rod, a plurality of stirring rods (26) threadedly connected (25) to the main body rod, and each stirring rod (26) is connected to a rotatable fan blade (27).

5. The simulation device for studying the release pattern of water sediment pollutants according to claim 4, characterized in that: The lower end of each stirring rod (26) is connected to an arc-shaped baffle (28).

6. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: The temperature probe (36) is connected to the lower end of the electric heating rod (35).

7. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: The outlet end of the peristaltic pump (16) is connected to a water injection pipe (17), and the water injection pipe (17) is connected to a plurality of water distribution pipes (19) connected to the hydraulic mixing zone (7), and each water distribution pipe (19) is provided with a water stop valve (18).

8. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: A drain outlet (43) is provided at the lower portion of the water outlet area (9).

9. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: The device body is provided with a storage platform (10) between the static simulation area (1) and the dynamic simulation area (5). The lower portion of the storage platform (10) is hollow, and the circulation pipe (15) passes through the lower portion of the storage platform (10).

10. The simulation device for studying the release pattern of water sediment pollutants according to claim 1, characterized in that: The water outlet (20) at the hydraulic mixing zone (7) is higher than the water outlet (20) at the water outlet zone (9).

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