Combined flow constructed wetland treatment system for treating polluted water body

Abstract

The invention discloses a combined flow constructed wetland treatment system for treating polluted water, which is composed of an adjusting pond, a stabilizing pond, an enhanced treatment area, a deep treatment area and a buffer area, and the water inlet end of the adjusting pond is provided with a grid structure; a first three-stage drop structure is arranged between the water outlet end of the adjusting pond and the water inlet end of the stabilizing pond; a submerged overflow mechanism is arranged between the water outlet end of the stabilization pond and the water inlet end of the enhanced treatment area, and a bio-membrane reactor is arranged in the enhanced treatment area; a plurality of groups of vertical flow treatment units are arranged in the deep treatment area; and a second three-stage drop structure is arranged between the drainage end of the deep treatment area and the water inlet end of the buffer area. The whole system is composed of the adjusting pond, the stabilizing pond, the enhanced treatment area, the deep treatment area and the buffer area, suspended solids are treated, then COD, ammonia nitrogen and total nitrogen are treated, and then total phosphorus is further treated, so that rural domestic sewage and agricultural non-point source sewage are treated.

Description

Technical Field

[0001] The invention relates to the field of wetland treatment systems, and in particular to a composite flow artificial wetland treatment system for treating polluted water bodies. Background Art

[0002] The wetland treatment system is an artificially constructed and supervised swamp-like surface that purifies sewage through the synergistic effects of physical, chemical and biological factors in the natural ecosystem.

[0003] Rural domestic sewage and agricultural non-point source pollution are important sources of water pollution in rural areas. At present, there are insufficient treatment facilities for such polluted water sources in rural areas. If the existing pond water surface cannot be utilized to form a multi-stage composite flow treatment system to effectively solve the problem of water pollutants, it will cause a large amount of waste of rural water resources. Therefore, a composite flow artificial wetland treatment system for treating polluted water bodies is proposed. Summary of the invention

[0004] The object of the present invention is to provide a composite flow artificial wetland treatment system for treating polluted water bodies to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a composite flow artificial wetland treatment system for treating polluted water, which is composed of a regulating pond, a stabilization pond, an enhanced treatment area, a deep treatment area and a buffer zone, wherein the water inlet end of the regulating pond is provided with a grid structure for inlet water filtration; A first and third step waterfall structure is provided between the water outlet of the regulating pond and the water inlet of the stabilization pond; A submerged overflow mechanism is provided between the water outlet of the stabilization pond and the water inlet of the enhanced treatment zone, a biofilm reactor is provided in the enhanced treatment zone, and the drainage end of the submerged overflow mechanism is connected to the water inlet of the biofilm reactor; A plurality of vertical flow treatment units are arranged in the deep treatment area, and a first-level waterfall structure is arranged at the drainage end of the biofilm reactor and the water inlet end of the plurality of vertical flow treatment units; A second and third level waterfall structure is provided between the drainage end of the deep treatment zone and the water inlet end of the buffer zone for connecting the two.

[0006] Preferably, a first shallow area is also provided in the enhanced treatment zone, and the water inlet end of the first shallow area is connected to the discharge end of the biofilm reactor. A plurality of habitat islands are provided in the first shallow area, and the discharge end of the first shallow area is connected to the water inlet end of the vertical flow treatment unit. The depth of the first shallow area is 20-60 cm.

[0007] Preferably, the grid structure comprises: A grill frame, wherein a cleaning cavity is provided in the middle of the grill frame, a water inlet is provided on the front of the grill frame, and a plurality of water outlets are provided on the inner wall of the back of the cleaning cavity along the horizontal transverse direction; A cleaning mechanism, wherein a plurality of groups of the cleaning mechanisms are arranged horizontally at the water inlet, and the plurality of groups of the cleaning mechanisms are used for once blocking floating garbage in the water body.

[0008] Preferably, a plurality of diversion holes are provided on the inner wall of the back side of the cleaning chamber and between the adjacent sides of the plurality of water outlets, and the diversion holes are used for secondary blocking of floating garbage in the water body.

[0009] Preferably, a plurality of rotating openings are opened at the top of the water inlet, and support rods are provided on the inner walls on both sides of the plurality of rotating openings, and a plurality of groups of cleaning mechanisms are rotatably inserted and connected in the water inlet through the plurality of support rods.

[0010] Preferably, the cleaning mechanism comprises: A blocking column, wherein a plurality of first blocking rods are arranged in a vertical direction on the front side of the blocking column, and a plurality of second blocking rods are arranged in a vertical direction on both sides of the blocking column; A connecting ring is fixedly connected to the top of the blocking column, the connecting ring is rotatably sleeved on the outer wall of the supporting rod, and a toggle tube is arranged on the top of the connecting ring.

[0011] Preferably, the submerged overflow mechanism comprises a grid frame, a plurality of square chambers are opened in the middle of the grid frame, and a plurality of expanded clay particles are respectively filled in the plurality of square chambers.

[0012] Preferably, the vertical flow treatment unit is configured as a plurality of hollow square structures with open tops, the square structures comprising a first longitudinal wall, a first transverse bottom plate, a partition wall, a second transverse bottom plate and a second longitudinal wall, the bottom of the first longitudinal wall is fixedly connected to one end of the first transverse bottom plate, the other end of the first transverse bottom plate is fixedly connected to one end of the second transverse bottom plate, and the first transverse bottom plate and the second transverse bottom plate are connected to form a stepped shape, the partition wall is arranged above the connection between the first transverse bottom plate and the second transverse bottom plate, a descending water flow outlet is formed between the bottom end of the partition wall and the top end of the connection between the first transverse bottom plate and the second transverse bottom plate, the other end of the second transverse bottom plate is fixedly connected to the bottom end of the second longitudinal wall, and an ascending water flow outlet is formed on the top of the second longitudinal wall opposite to the bottom of the partition wall.

[0013] Preferably, a plurality of second shallow areas are arranged in the buffer zone, the second shallow areas are arranged as long strip structures arranged along the horizontal and longitudinal directions, and the plurality of second shallow areas are arranged in a staggered manner.

[0014] Preferably, a natural purification area is provided at the drainage end of the buffer zone, and the natural purification area includes a plurality of third shallow areas, and the third shallow areas are arranged as long strip structures along the horizontal transverse direction, and the plurality of third shallow areas are arranged at equal intervals along the horizontal longitudinal direction, and the depths of the second shallow areas and the third shallow areas are 20-60 cm.

[0015] Technical effects and advantages of the present invention: The overall system of the present invention is composed of a regulating pond, a stabilization pond, an enhanced treatment area, a deep treatment area and a buffer zone, wherein the suspended matter and some COD, ammonia nitrogen and total nitrogen are firstly treated by the regulating pond and the stabilization pond, and then the COD, ammonia nitrogen and total nitrogen are centrally treated by the enhanced treatment area, and then the COD, ammonia nitrogen, total nitrogen and total phosphorus are further treated by the vertical flow treatment unit of the deep treatment area; finally, by utilizing the terrain advantage, a three-stage waterfall is manufactured to further filter out impurities and suspended matter, so that rural domestic sewage and agricultural non-point source sewage are treated, thereby protecting water resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the composition of the system of the present invention.

[0017] Figure 2 It is a schematic diagram of the internal structure connection of the system composition of the present invention.

[0018] Figure 3 It is a schematic diagram of the overall structure of the grid structure of the present invention.

[0019] Figure 4 It is a front view of the overall structure of the grid structure of the present invention.

[0020] Figure 5 It is a top view of the overall structure of the grid structure of the present invention.

[0021] Figure 6 It is a structural schematic diagram of the grid frame of the present invention.

[0022] Figure 7 It is a structural schematic diagram of the cleaning mechanism of the present invention.

[0023] Figure 8 It is a structural schematic diagram of the submerged overflow mechanism of the present invention.

[0024] Fig. 9 It is a structural cross-sectional view of the vertical flow processing unit of the present invention.

[0025] In the figure: 1. Regulating pond; 2. Stabilizing pond; 3. Intensified treatment area; 4. Deep treatment area; 5. Buffer zone; 6. Grid frame; 7. Blocking column; 8. First and third level waterfall structure; 9. Submerged overflow mechanism; 10. Biofilm reactor; 11. First level waterfall structure; 12. Vertical flow treatment unit; 13. Second and third level waterfall structure; 14. Natural purification area; 31. First shoal area; 32. Habitat island; 51. Second shoal area; 61. Cleaning chamber; 62. Inlet Water inlet; 63, water outlet; 64, guide hole; 65, rotating port; 66, support rod; 71, first blocking rod; 72, second blocking rod; 73, connecting ring; 74, toggle tube; 91, grille frame; 92, expanded clay; 121, first longitudinal wall; 122, first transverse bottom plate; 123, partition wall; 124, second transverse bottom plate; 125, second longitudinal wall; 126, descending water flow outlet; 127, ascending water flow outlet; 141, third shallow beach area. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides Figure 1 and Figure 2 A composite flow artificial wetland treatment system for treating polluted water bodies shown in the figure is composed of a regulating pond 1, a stabilization pond 2, an enhanced treatment area 3, a deep treatment area 4 and a buffer zone 5. The water inlet end of the regulating pond 1 is provided with a grid structure for inlet water filtration; It should be noted that the regulating pond 1 in the whole system serves as the first water inlet structure, so a grid structure is provided in the present solution to carry out the first step of interception treatment of the treated sewage, that is, to intercept and filter the floating garbage impurities through the grid structure.

[0028] Specifically, refer to Figures 3 to 7 As shown, the grid structure includes: A grill frame 6, a cleaning chamber 61 is provided in the middle of the grill frame 6, a water inlet 62 is provided on the front of the grill frame 6, and a plurality of water outlets 63 are provided on the inner wall of the back of the cleaning chamber 61 along the horizontal transverse direction; Furthermore, a plurality of diversion holes 64 are provided on the inner wall of the back side of the cleaning chamber 61 and between the adjacent sides of the plurality of water outlets 63 . The diversion holes 64 are used for secondary blocking of floating garbage in the water body.

[0029] It should be noted that, by setting the grid frame 6, the water inlet structure of the regulating pond 1 is carried out, so that the sewage to be treated enters the grid frame 6 through the water inlet 62, and then is diverted into the regulating pond 1 through the water outlet 63 and the diversion hole 64 respectively. The top of the cleaning chamber 61 is an open structure, which is convenient for hollowing and cleaning the inside.

[0030] A cleaning mechanism, a plurality of cleaning mechanisms are arranged horizontally at the water inlet 62, and the plurality of cleaning mechanisms are used for once blocking floating garbage in the water body. The first step of blocking is performed by the cleaning mechanism, and after the floating garbage passes through the cleaning mechanism and enters the cleaning chamber 61, it is blocked once by the water outlet 63 and the diversion hole 64, so that the floating garbage remaining in the cleaning chamber 61 can be removed from the top of the cleaning chamber 61.

[0031] Furthermore, a plurality of rotating openings 65 are provided at the top of the water inlet 62, and support rods 66 are provided on the inner walls on both sides of the plurality of rotating openings 65, and the plurality of cleaning mechanisms are respectively connected to the water inlet 62 by rotating and inserting the plurality of support rods 66; Cleanup agencies include: A blocking column 7, wherein a plurality of first blocking rods 71 ​​are arranged in a vertical direction on the front side of the blocking column 7, and a plurality of second blocking rods 72 are arranged in a vertical direction on both sides of the blocking column 7; The connecting ring 73 is fixedly connected to the top of the blocking column 7 , and the connecting ring 73 is rotatably sleeved on the outer wall of the supporting rod 66 . A toggle tube 74 is provided at the top of the connecting ring 73 .

[0032] It should be noted that, by rotating and interlacing the connecting ring 73 and the support rod 66, the blocking column 7 can be rotated, wherein the first blocking rod 71 and the second blocking rod 72 are both round rod structures arranged obliquely upward. Through the oblique arrangement of the first blocking rod 71 and the second blocking rod 72, plastic bags and tree branches and twigs in the water body can be blocked and mounted. In this way, by rotating the blocking column 7, the first blocking rod 71 and the second blocking rod 72 can be used to lift these floating objects for cleaning. The structural arrangement of the toggle tube 74 makes it possible to connect a long rod when controlling the rotation of the blocking column 7, thereby increasing the lever arm, thereby facilitating the rotation adjustment of the blocking column 7.

[0033] A first and third step waterfall structure 8 is provided between the outlet of the regulating pond 1 and the inlet of the stabilizing pond 2; It should be noted that the outlet of the regulating pond 1 is connected to the inlet of the stabilization pond 2 through the stepped first and third level waterfall structures 8, so that the first and third level waterfall structures 8 are utilized to allow the regulating pond 1 and the stabilization pond 2 to process suspended matter.

[0034] A submerged overflow mechanism 9 is provided between the water outlet of the stabilization pond 2 and the water inlet of the enhanced treatment zone 3. A biofilm reactor 10 is provided in the enhanced treatment zone 3, and the drainage end of the submerged overflow mechanism 9 is connected to the water inlet of the biofilm reactor 10. It should be noted that the outlet end of the stabilization pond 2 is connected to the inlet of the biofilm reactor 10 at the water inlet end of the enhanced treatment zone 3 through the submerged overflow mechanism 9. The submerged overflow mechanism 9 and the biofilm reactor 10 enable the enhanced treatment zone 3 to treat COD, ammonia nitrogen and total nitrogen. The biofilm reactor 10 is a reactor that combines membrane separation and biological treatment technology. It is widely used in water treatment, wastewater treatment, waste gas treatment and other fields. It utilizes the biofilm (activated sludge) formed by microorganisms on the membrane surface to degrade and remove pollutants in the water. At the same time, through the separation function of the membrane, the treated water and microorganisms are separated to achieve the purpose of water resource reuse or sewage treatment.

[0035] Specifically, a first shallow area 31 is also provided in the enhanced treatment zone 3, and the water inlet end of the first shallow area 31 is connected to the discharge end of the biofilm reactor 10. A plurality of habitat islands 32 are provided in the first shallow area 31, and the discharge end of the first shallow area 31 is connected to the water inlet end of the vertical flow treatment unit 12. The depth of the first shallow area 31 is 20-60 cm.

[0036] It should be noted that the hydraulic retention time of water flowing through the wetland is extended through the first shoal area 31, and the aquatic food chain is restored through the habitat island 32, thereby improving the self-purification function of the wetland. Specifically, refer to Figure 8 As shown, the submerged overflow mechanism 9 includes a grid frame 91, a plurality of square chambers are opened in the middle of the grid frame 91, and a plurality of ceramsite particles 92 are respectively filled in the plurality of square chambers.

[0037] It should be noted that the grille frame 91 is divided into four square chambers for filling with expanded clay 92. The expanded clay 92 in each square chamber has different properties. When the water flow is small, the water flows through the expanded clay 92 and then flows through the submerged overflow mechanism 9. When the water flow is large, the water flows through the top of the submerged overflow mechanism 9, and the submerged overflow mechanism 9 is set to a depth of 2-3 meters.

[0038] A plurality of vertical flow treatment units 12 are arranged in the deep treatment area 4, and a first-level water drop structure 11 is arranged between the drainage end of the biofilm reactor 10 and the water inlet end of the plurality of vertical flow treatment units 12; It should be noted that the outlet of the biofilm reactor 10 is connected to the inlet of the vertical flow treatment unit 12 of the deep treatment zone 4 through the primary waterfall structure 11, and the vertical flow treatment unit 12 is used to further treat COD, ammonia nitrogen, total nitrogen and total phosphorus.

[0039] Specifically, refer to Fig. 9As shown, the vertical flow treatment unit 12 is configured as a plurality of hollow square structures with open tops, the square structures comprising a first longitudinal wall 121, a first transverse bottom plate 122, a partition wall 123, a second transverse bottom plate 124 and a second longitudinal wall 125, the bottom of the first longitudinal wall 121 is fixedly connected to one end of the first transverse bottom plate 122, the other end of the first transverse bottom plate 122 is fixedly connected to one end of the second transverse bottom plate 124, and the first transverse bottom plate 122 and the second transverse bottom plate 124 are connected to form a stepped shape, the partition wall 123 is arranged above the connection between the first transverse bottom plate 122 and the second transverse bottom plate 124, a descending water flow outlet 126 is formed between the bottom end of the partition wall 123 and the top end of the connection between the first transverse bottom plate 122 and the second transverse bottom plate 124, the other end of the second transverse bottom plate 124 is fixedly connected to the bottom end of the second longitudinal wall 125, and an ascending water flow outlet 127 is formed on the side opposite to the top of the second longitudinal wall 125 and the bottom of the partition wall 123.

[0040] It should be noted that the top height of the first longitudinal wall 121 is lower than the top height of the isolation wall 123. At this time, the top of the first longitudinal wall 121 forms a water inlet, and the top height of the second longitudinal wall 125 is less than the top height of the first longitudinal wall 121, thereby forming a rising water flow outlet 127. The vertical flow treatment unit 12 ensures that the sewage is not short-circuited, extends the reaction process, and allows the sludge to be suspended, fully mixed and reacted with the sewage and sludge, thereby improving the effects of denitrification and dephosphorization.

[0041] A second and third level waterfall structure 13 is provided between the drainage end of the deep treatment zone 4 and the water inlet end of the buffer zone 5 for communicating the two.

[0042] It should be noted that the outlet of the vertical flow treatment unit 12 is connected to the buffer zone 5 through the second three-stage waterfall structure 13, so that the terrain advantage is fully utilized to create a three-stage waterfall to filter out impurities and suspended matter.

[0043] Specifically, a plurality of second shallow areas 51 are arranged in the buffer zone 5 . The second shallow areas 51 are arranged as long strip structures arranged along the horizontal and longitudinal directions, and the plurality of second shallow areas 51 are arranged in a staggered manner.

[0044] Furthermore, a natural purification area 14 is provided at the drainage end of the buffer zone 5, and the natural purification area 14 includes a plurality of third shallow areas 141, and the third shallow areas 141 are arranged as long strip structures along the horizontal transverse direction, and the plurality of third shallow areas 141 are arranged at equal intervals along the horizontal longitudinal direction, and the depths of the second shallow areas 51 and the third shallow areas 141 are 20-60 cm.

[0045] It should be noted that, by providing the second shallow area 51 and the third shallow area 141, the hydraulic retention time of water flowing through the wetland is prolonged.

[0046] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite flow artificial wetland treatment system for treating polluted water, characterized in that: It is composed of a regulating pond (1), a stabilization pond (2), an enhanced treatment area (3), a deep treatment area (4) and a buffer area (5), wherein the water inlet end of the regulating pond (1) is provided with a grid structure for filtering the inlet water; A first and third step waterfall structure (8) is provided between the water outlet of the regulating pond (1) and the water inlet of the stabilization pond (2); A submerged overflow mechanism (9) is provided between the water outlet of the stabilization pond (2) and the water inlet of the enhanced treatment zone (3); a biofilm reactor (10) is provided in the enhanced treatment zone (3); and the drainage end of the submerged overflow mechanism (9) is connected to the water inlet of the biofilm reactor (10); A plurality of groups of vertical flow treatment units (12) are arranged in the deep treatment zone (4), and a first-level waterfall structure (11) is arranged at the drainage end of the biofilm reactor (10) and the water inlet end of the plurality of groups of vertical flow treatment units (12); A second and third level waterfall structure (13) is provided between the drainage end of the deep treatment zone (4) and the water inlet end of the buffer zone (5) for communicating the two.

2. A composite flow artificial wetland treatment system for treating polluted water according to claim 1, characterized in that: A first shallow area (31) is also provided in the enhanced treatment area (3), the water inlet end of the first shallow area (31) is connected to the water outlet end of the biofilm reactor (10), a plurality of habitat islands (32) are provided in the first shallow area (31), the water outlet end of the first shallow area (31) is connected to the water inlet end of the vertical flow treatment unit (12), and the depth of the first shallow area (31) is 20-60 cm.

3. A composite flow artificial wetland treatment system for treating polluted water according to claim 1, characterized in that: The grid structure comprises: A grill frame (6), wherein a cleaning cavity (61) is provided in the middle of the grill frame (6), a water inlet (62) is provided on the front of the grill frame (6), and a plurality of water outlets (63) are provided on the inner wall of the back of the cleaning cavity (61) along a horizontal transverse direction; A cleaning mechanism, wherein a plurality of groups of the cleaning mechanisms are arranged horizontally and transversely at the water inlet (62), and the plurality of groups of the cleaning mechanisms are used for once blocking floating garbage in the water body.

4. A composite flow artificial wetland treatment system for treating polluted water according to claim 3, characterized in that: A plurality of diversion holes (64) are provided on the inner wall of the back side of the cleaning chamber (61) and between the adjacent sides of the plurality of water outlets (63). The diversion holes (64) are used for secondary blocking of floating garbage in the water body.

5. The composite flow artificial wetland treatment system for treating polluted water according to claim 3, characterized in that: A plurality of rotating openings (65) are provided at the top of the water inlet (62), and support rods (66) are provided on the inner walls on both sides of the plurality of rotating openings (65). The plurality of cleaning mechanisms are rotatably inserted and connected in the water inlet (62) via the plurality of support rods (66).

6. A composite flow artificial wetland treatment system for treating polluted water according to claim 5, characterized in that: The cleaning mechanism comprises: A blocking column (7), wherein a plurality of first blocking rods (71) are arranged in a vertical direction on the front side of the blocking column (7), and a plurality of second blocking rods (72) are arranged in a vertical direction on both sides of the blocking column (7); A connecting ring (73) is fixedly connected to the top of the blocking column (7), the connecting ring (73) is rotatably sleeved on the outer wall of the support rod (66), and a toggle tube (74) is provided at the top of the connecting ring (73).

7. A composite flow artificial wetland treatment system for treating polluted water according to claim 1, characterized in that: The submerged overflow mechanism (9) comprises a grid frame (91), a plurality of square chambers are provided in the middle of the grid frame (91), and a plurality of ceramsite (92) are respectively filled in the plurality of square chambers.

8. The composite flow artificial wetland treatment system for treating polluted water according to claim 1, characterized in that: The vertical flow processing unit (12) is configured as a plurality of hollow square structures with open tops, the square structures comprising a first longitudinal wall (121), a first transverse bottom plate (122), a partition wall (123), a second transverse bottom plate (124) and a second longitudinal wall (125), the bottom of the first longitudinal wall (121) being fixedly connected to one end of the first transverse bottom plate (122), the other end of the first transverse bottom plate (122) being fixedly connected to one end of the second transverse bottom plate (124), and the first transverse bottom plate (122) and the second transverse bottom plate (125) being fixedly connected to each other. 24) are connected to form a step shape, the isolation wall (123) is arranged above the connection between the first transverse bottom plate (122) and the second transverse bottom plate (124), a descending water flow outlet (126) is formed between the bottom end of the isolation wall (123) and the top end of the connection between the first transverse bottom plate (122) and the second transverse bottom plate (124), the other end of the second transverse bottom plate (124) is fixedly connected to the bottom end of the second longitudinal wall (125), and an ascending water flow outlet (127) is formed on the side of the top of the second longitudinal wall (125) opposite to the bottom of the isolation wall (123).

9. The composite flow artificial wetland treatment system for treating polluted water according to claim 1, characterized in that: A plurality of second shallow areas (51) are arranged in the buffer zone (5), the second shallow areas (51) being arranged as long strip structures arranged in a horizontal and longitudinal direction, and the plurality of second shallow areas (51) are arranged in a staggered manner.

10. A composite flow artificial wetland treatment system for treating polluted water according to claim 9, characterized in that: A natural purification area (14) is provided at the drainage end of the buffer zone (5), the natural purification area (14) comprising a plurality of third shallow areas (141), the third shallow areas (141) being arranged as a long strip structure along a horizontal transverse direction, and the plurality of third shallow areas (141) being arranged at equal intervals along a horizontal longitudinal direction, and the depths of the second shallow areas (51) and the third shallow areas (141) being 20-60 cm.

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