GB2073165A - Submerged Filter Bed for Treating Liquid Waste - Google Patents

Abstract

A submerged-filter-beds tank 1 for treating liquid waste has a removable stack of shelves 10, which may be removed from the unit from the tank 1 e.g. for cleaning. The shelves comprise two intermeshing sets 3,4 arranged to form a zigzag downflow path in the tank. Each shelf may be spaced from a sidewall, thereby to form a gap 6a,6b for the flow of liquid, or provided with holes 37,37%. An air-lift pipe 8 for recirculating the waste liquid and an effluent riser 9 may also form part of the removable stack. <IMAGE>

Description

SPECIFICATION Submerged-Filter-Beds Tank for the Treatment of Foul Liquid Waste The pollution of rivers, lakes, swamps and seas is attributable to foul liquid wastes discharged from factories, dwellings, restaurants, assembly halls, etc. Treatment apparatus for purifying such foul waste water into clear water by the utilization of the biological activity of micro-organisms living in sludge have been heretofore used. The present invention relates to a submerged-filter-beds tank for carrying out a method in which a foul liquid waste of human body wastes and miscellaneous liquid wastes discharged from the abovementioned sources is purified by the use of the biological activity of micro-organisms.

In general, treatment processes for a foul liquid waste include a primary treatment, a secondary treatment, etc. A sedimentation tank or a screen is used as a primary-treatment apparatus to separate relatively coarse suspended solids from a foul liquid waste, and then a submerged-filter beds tank is employed as a secondary-trnatment.

apparatus to purify further the effluent from the sedimentation-tank or screen into clear water.

This secondary treatment apparatus is of great importance in that the superiority or inferiority in its function determines the waste-water treatment capacity of the whole treatment plant.

In a submerged-filter-beds tank of the invention, a plurality of horizontal, quadrangular or circular, flat or corrugated, irrigated shelves which form the bases for developing active biomembranes and which can be made up of plastics, especially of polyvinyl chloride, or of asbestos-cement, etc., are placed above one another at regular intervals.

According to investigations carried out by the present inventor, the proliferation and biological activity of micro-organisms scarcely depend on the kind of the materials of which the irrigated shelves are made. According to one aspect of the present invention, there is provided a submerged filter-beds tank having a removable, horizontal irrigatedshelves stack which comprises:: (a) vertical supporting bars; (b) two intermeshing sets of horizontal irrigated shelves amounted on the vertical supporting bars at substantially regular intervals, each irrigated shelf of one set forming a downflow gap at a part or the whole of its periphery, jointly with a part or all of walls of the vertical tank respectively, or having at least one downflow hole, each irrigated shelf on the other set forming a downflow gap at a part of its periphery, jointly with a part of walls of the vertical tank, or having at least one downflow hole, the shelves of each set being arranged alternately so that the downflow gaps of one shelf and an adjacent shelf, or the downflow gaps of one shelf and the downflow holes in the adjacent shelf, or the downflow holes in one shelf and an adjacent shelf are not in vertical alignment, whereby there is at least a downward zig-zag flow path; and (c) an air-lift pipe which is incorporated into the two intermeshing sets of the horizontal flat irrigated shelves to raise a combined foul liquid waste from the bottom to upper sections of the submerged filter-beds tank. When a foul liquid waste from a sedimentation tank or a screen is charged at the upper most irrigated shelf, it flows towards the downflow gap, or one or more downflow holes, where it falls to the irrigated shelf below. Here it flows in the opposite horizontal direction(s) towards the staggered downflow gap or the one or more staggered downflow holes from which it falls to the third irrigated shelf. This continues down the submerged filter-beds tank to the bottom. Since the submerged filter-beds tank is filled with a foul liquid waste in practice, it flows slowly.The removable, horizontal-irrigated-shelves stack may incorporate an air-lift pipe, adjacent thereto or passing vertically through the shelves. The foul liquid waste is raised by the air-lift pipe from the bottom to uppermost sections and recirculated downward between the spaces between the individual horizontal irrigated shelves in a zigzag manner, as mentioned above, and discharged as purified liquid from an effluent riser which may be similarly incorporated into the removable, horizontal-irrigated-shelves stack as to pierce each horizontal irrigated shelf, or attached to the vertical tank.

A description will be given of the biological activity of micro-organisms living in sludge. In the submerged-filter-beds tank of the invention, when air is supplied by the air-lift pipe to the foul liquid waste which flows slowly in a zigzag manner, and oxygen in the air is mixed with and dissolved into the foul liquid waste by the agitation of fine airbubbles, allowing aerobic bacteria contained in the foul liquid waste to respire and promoting their proliferation, micro-organisms adhere to both faces of each irrigated shclf to form biomembranes. The micro-organisms proliferate more and more by adsorbing and taking in the polluting matter contained in the foul liquid waste, and exert their excellent purifying activity.

During this process, the foul liquid waste is rapidly purified into clear water. It is for the purpose of improving the purification efficiency by generating as many biomembranes as possible by increasing the contacting-surface area that a plurality of horizontal, flat or corrugated, irrigated shelves forming the bases for developing biomembranes are placed one above another. That is to say, it is for the purpose of developing the biomembranes in a stable state as well as increasing the amount of contact between the foul liquid waste and the biomembranes adhering to both faces of each irrigated shelf that a plurality of horizontal irrigated shelves are mounted one above another at regular intervals and parallel to one another.

Thus the incoming foul liquid waste is continually in contact with the biomembranes during its circulation and recirculation through the submerged filter-beds tank. On the other hand, the utilization of settlement action caused by the gravity during the flowing of the foul liquid waste leads to the promotion of the adsorption on the biomembranes, thus improving the purification efficiency of the submerged-filter-beds tank. As a result the purified liquid scarcely contains S. S.

(Suspended Solids) and sludge, and both B. O. D.

(Biochemical Oxygen Demand) and C. O. D.

(Chemical Oxygen Demand) are extremely low, which means the excellent purification efficiencies of the filter-beds tank according to the invention. The reason why the sludge is hardly contained is considered to be that the special bacteria within the bodies of the biomembranes adhering to the irrigated shelves live on the biomembranes and that thus the proliferation of the bacteria balances with that of the biomembranes. Extremely low suspended-solids content is attributable to the fact that the biomembranes have a great adsorptive power and that the micro-organisms prey satisfactorily upon suspended solids. A microscopic examination of the biomembranes shows more fully that Vorticelia and Opercuiaria representative of aerobic bacteria are propagated in great quantities.Philodina and Podophrya representative of the bacteria preying upon biomembranes (bacteria) also coexist with the foregoing bacteria. Since the biological activities of micro-organisms are great as stated above, increasing the area of each irrigated shelf facilitates both an improvement in treatment capacities and the attainment of an effluent's B.

O. D. of less than 10 p.p.m. This filter-beds tank is applicable to any large-scale treatments, and may be enlarged as necessary.

The invention will be further described by way of example and with reference to ther accompanying drawings wherein like reference characters are employed to designate like parts or like components.

Brief Description of the Drawings Figures 1, 2, and 3 are the schematic illustrations of a submerged filter-beds tank described in Example 1. More particularly, Figs. 1, 2, and 3 respectively area vertical sectional view of the submerged filter-beds tank, a plan view thereof, and a perspective view of a removable stack of horizontal irrigated shelves thereof.

Figures 4, 5, and 6 are the schematic illustrations of a submerged filter-beds tank described in Example 2. More particularly, Figs. 4, 5, and 6 respectively are a vertical sectional view of the submerged filter-beds tank, a plan view thereof, and a perspective view of a removable stack of horizontal irrigated shelves thereof.

Figures 7 and 8 are the schematic illustrations of a submerged filter-beds tank described in Example 3. More particularly, Figs. 7 and 8 respectively are a vertical sectional view of the submerged filter-beds tank and a schematic illustration of corrugated irrigated shelves thereof.

Figures 9 and 10 are the schematic illustrations of a submerged filter-beds tank described in Example 4. More particularly, Figs. 9 and 10 respectively are a vertical sectional view of the submerged filter-beds tank and a perspective view of a removable stack of horizontal irrigated shelves thereof.

Figures 1 1 and 12 are the schematic illustrations of a submerged filter-beds tank described in Example 5. More particularly, Figs.

1 1 and 12 respectively are a vertical sectional view of the submerged filter-beds tank and a plan view thereof.

Figure 13 is a vertical sectional view of a submerged filter-beds tank described in Example 6.

Figure 14 is a vertical sectional view of the principal parts of a submerged filter-beds tank described in Example 7.

Example 1 Referring now to Figs. 1, 2, and 3, a treated liquid waste which has been separated as supernatant liquor or screened effluent, respectively, within a sedimentation tank or a screen for the first treatment (not shown in the drawings flows through a transporting pipe 2 into a submerged filter-beds tank 1 where it is purified. The purified liquid is discharged from the submerged filter-beds tank 1 through an effluent pipe 14 into a disinfection tank. A removable stack of horizontal irrigated shelves 10 as shown in Figs. 1 and 3 may be lifted out as a unit from a vertical tank 1' for a foul liquid waste for cleaning or other maintenance work. The removable stack of a plurality of the horizontal irrigated shelves with a shelf spacing b comprises two intermeshing sets of horizontal quadrangular flat irrigated shelves 3, 4.Each irrigated shelf 3 of one set forms a downflow gap 6b at its second side 3b, jointly with a second wall 5b of the vertical tank 1', and is in close contact with the other three walls 5a, 5c, 5d at its other three sides 3a, 3c, 3d respectively. Each irrigated shelf 4 of the other set forms a downflow gap 6a at its first side 4a, jointly with a first wall 5a opposite to the second wall 5b, and is in close contact with the other three walls 5a, 5c, 5d at its other three sides 4b, 4c, 4d respectively, so that the downflow gaps 6b, 6a of the one set and the other set are staggered along the vertical tank 1', whereby the flow path down across the submerged-filter-beds tank 1 is zigzagged. The two sets of the intermeshing horizontal irrigated shelves 3, 4 are mounted with a shelf spacing b on vertical supporting bars 7, an air-lift pipe 8, and an effluent riser 9, all of which pierce them. A compressed-airtpipe 11 to which an air-spout member 11' is attached at the lower end thereof is inserted in the centre of the air-lift pipe 8 which has an inlet hole 12 in its lower section. An effluent pipe 14 is connected to the upper end of the effluent riser 9 which has an inlet hole 13 in its lower section. Spacers 16 each of a given length are slipped on the vertical supporting bars 7 between the irrigated shelves 3, 4, to hold them at a given distance (a shelf spacing b) from one another.The removable stack 10 of the horizontal irrigated shelves 3, 4 may be lifted out as a unit by handles 7' mounted on the tops of the vertical supporting bars 7. From the lower section of the submerged-filter-beds tank 1, the air-lift pipe 8 leads up into the upper section thereof.

The air-lift pipe 8 returns the foul liquid waste W2 from the lower to upper sections of the submerged filter-beds tank 1 through the inlet hole 12 by the use of compressed air supplied to the compressed-air pipe 11 by the operation of an air-lift pump (not shown in the drawings). As mentioned above, in the submerged-filter-beds tank, the horizontal quadrangular irrigated shelves 3, 4 each of thickness 3 mm are placed one above another at regular shelf spacings b in staggered arrangement. The shelf spacing b is taken to be 3-10 cm, which permits the foul liquid waste filling the submerged filter-beds tank 1 to flow therethrough easily. The size of each of the aforementioned downflow gaps is 4-8 cm.The quantity of the foul liquid waste leaking at each of contacting surfaces (side 3wall, 5a, 3c-5c, 3d 5d for one set of the irrigated shelves 3; side 4bwall 5b, 4c-5c, 4d-5d for the other set 4) between the irrigated shelves and the inner surfaces of walls of the vertical tank 1' is very little on account of the fact that the contact is close, as seen from Fig. 2.

In the operation of the above described submerged filter-beds tank, the foul liquid waste W, which has passed through the transporting pipe 2 enters the submerged-filter-beds tank 1 where it falls to the uppermost irrigated shelf 3 while dispersing, flows thereon while spreading horizontally, and thus comes in touch with the air.

The foul liquid waste flows to a downflow gap 6b where it falls to the next irrigated shelf 4, and flows in opposite direction through a space between the uppermost and next irrigated shelves 3, 4 to the next downflow gap 6a from which it falls to a third irrigated shelf 3. These alternate with each other until the foul liquid waste reaches a bottom plate 1 5, namely, the foul liquid waste W, which has entered the submerged-filter-beds tank 1 at its upper section flows downward alternately through the downflow gaps 6b, 6a and through the spaces between the irrigated shelves 3, 4 to the bottom section in a zigzag manner. The foul liquid waste which has fallen to the bottom plate 1 5 is raised to the upper section by the operation of the air-lift pipe 8, and falls to the uppermost irrigated shelf 3 where it joins the incoming foul liquid waste W,.The mixed foul liquid waste W2 incessantly flows downward alternately through the individual downflow gaps 6b, 6a and through the individual spaces between the irrigated shelves 3, 4, as mentioned above.

When the level of the top horizontal section of the effluent riser 9 which leads to the lower section of the submerged-filter-beds tank 1 is made to be slightly high above the level of the uppermost irrigated shelf 3, the foul liquid waste filling the tank 1 can be circulated in a state that its surface is kept high above the uppermost irrigated shelf 3.

Therefore, if the level of the top horizontal section of the effluent riser 9 is made to be high above the level of the uppermost irrigated shelf 3, but slightly low below the level of the transporting pipe 2, then the circulation is satisfactory. The same quantity of the foul liquid waste as that of the foul liquid waste flowing through the transporting pipe 2 into the submerged filter-beds tank 1 turns to the purified liquid, which is discharged from the tank through the inlet hole 13 to the effluent riser 9, the effluent riser 9, and the effluent pipe 14; that is to say, when the foul liquid waste is recycled through the tank 1 and the air-lift pipe 8 over and over again in a state that it fills the tank, then organic substances contained in the foul liquid waste are disintegrated by the biological activity of the biomembranes formed on both surfaces of each irrigated shelf and thus the foul liquid waste is purified.

Example 2 Referring to Figs.4,5, and 6, the apparatus described in this example is a battery 30 of a plurality of adjacent submerged-filter-beds tanks 21,22 for purifying a combined liquid waste, which are held together as a unit in such a way that effluent troughs 28, 29 are formed between two opposed walls of any two adjacent filter-beds tanks 21,22 arranged in a series.Within each of vertical tanks 21 22' of quadrangular cross section for the combined liquid waste, there is housed a removable, horizontal-irrigated-shelves stack 20 comprising: (a) vertical supporting bars 7; (b) two intermeshing sets of horizontal quadrangular irrigated shelves 3, 4 mounted on the vertical supporting bars 7 at regular intervals b, each irrigated shelf 3 of one set forming a downflow gap 6b at its second side 3b, jointly with a weir plate 24 or 26 of the vertical tank 21' or 22', each irrigated shelf 4 of the other set forming a downflow gap 6a at its first side 4a, jointly with a first wall 23 or a weir plate 25 opposite to the weir plate 24 or 26 so that the downflow gaps 6b, 6a of the one set and the other set are alternated, whereby a flow path is zigzagged down across the submerged filter-beds tank 21 or 22; and (c) an air-lift pipe 8 which pass through the two sets of horizontal quadrangular irrigated shelves 3, 4. A container 30' for housing a battery of the submerged filter-beds tanks 21,22 may be enlarged and partitioned with partition plates 34 into compartments in order to arrange a large number of them within the container 30', each compartment housing a proper number of the submerged-filter-beds tanks in a series arrangement. Effluent-trough spacers 33 required to form the effluent troughs 28, 29 are positioned between two opposed weir plates 24-25, 26- 27 of any two adjacent filter-beds tanks 21, 22 arranged in a series within one compartment, or are attached in places to the partition plates 34.

The waste W2 which has been subjected to purification treatment in the first submergedfilter-beds tank 21 flows through an effluent trough inlet hole 31 made in the lower section of the weir plate 24 and through the effluent trough 28 into the next submerged-filter-beds tank 22, where it is further purified. The purified liquid waste W3 is discharged from the filter-beds tank 22 through an effluent-trough inlet hole 32 made in the lower section of the weir plate 26, through the effluent trough 29, and through an effluent pipe 14.

Example 3 Referring to Figs. 7 and 8, the removable stack 26 of horizontal irrigated shelves of this example is one in which horizontal irrigated shelves 35, 35' of corrugated cross section are used instead of the horizontal flat irrigated shelves 3, 4 of Example 1 or Example 2. In this example, the removable stack 36 is the same as that of Example 1 or Example 2 in the horizontal parallel arrangement of irrigated shelves and in other constructional features.

Example 4 Referring to Figs. 9 and 10, within a vertical tank 1' of quadrangular cross section for a combined foul liquid waste, there is housed a removable, horizontal-irrigated-shelves stack 39 comprising: (a) two intermeshings sets of horizontal flat quadrangular irrigated shelves 38, 38' mounted on vertical supporting bars 7 at regular intervals b, each of the irrigated shelves 38, 38' being in close contact with all of verticaltank walls at its whole periphery, each irrigated shelf of one set 38 having in its centre a larger central downflow hole 37, each irrigated shelf of the other set 38' having at least two smaller downflow holes 37' at places other than its center so that the larger central downflow holes 37 of the one set 38 the smaller downflow holes 37' of the other set 38' are not vertically aligned, whereby flow paths are complicatedly zigzagged down across the submerged filter-beds tank; and (b) an air-lift pipe 8 and an effluent riser 9 both of which pass through the two sets of thoroughly intermeshing horizontal flat quadrangular irrigated shelves 38, 38'. The two sets of the irrigated shelves 38, 38' which are the elements out of which the foregoing removable, irrigated shelves stack 39 is formed are of the same shape or size. Since the larger central downflow holes 37 of the one set 38 are not aligned vertically with the smaller downflow holes 37' of the other set 38', the falling liquid waste impinges against an irrigated shelf 38 or 38', and flows to the larger central downflow hole 37 or the smaller downflow holes 37 from which it falls to a next irrigated shelf 38' or 38.The resulting, complicated zigzag flow paths permit the bacteria to function satisfactorily. In the submerged filter beds tank 1 of this example, instead of the effluent riser 9, a weir plate as that described in Example 2 can be established in the tank, spaced a short distance away from a second wall of the vertical tank 1' for the purpose of forming, jointly with the second wall, an effluent trough through which the purified liquid waste is discharged.

Example 5 Referring to Figs. 11 and 12, within a cylindrical tank 44' for a combined foul liquid waste. there is housed a removable, horizontalirrigated-shelves stack 43 comprising: (a) two intermeshing sets of horizontal circular flat irrigated shelves 40. 42 mounted on vertical supporting bars 7 at regular intervals b. the irrigated shelves 40 of one set having a smaller diameter than those of the other set each irrigated shelf 40 of the one set forming an annular downflow gap 45 at its whole periphery, jointly with all of walls of the cylindrical tank 44', each irrigated shelf 42 of the other set having a larger diameter and a central downflow hole 41 in its center so that the annular downfiow gaps 45 of the one set 40 are not aligned with the central downflow holes 41 in the other set 42, whereby flow paths are zigzagged down across the cylindrical submerged filter-beds tank 44;; (b) an air-lift pipe 8 and an effluent riser 9 both of which pass through the two sets of the intermeshing horizontal circular flat irrigated shelves 40, 42. The incoming liquid waste through a transporting pipe 2 falls to the uppermost irrigated shelf 40, and flows outward to the annular downflow gap 45 where it falls to a second irrigated shelf 42. Here it flows inward to the central downflow hole 41 from which it falls to a third irrigated shelf 40. Here it again flows outward to the annular downflow gap 45. This continues down the cylindrical submerged filterbeds tank 44. The purified liquid waste W2 is discharged from the cylindrical submerged filterbeds tank 44 through the effluent riser 9 and an effluent pipe 14.

Example 6 Referring to Fig. 13, within a vertical tank 49' of quadrangular cross-section (or circular crosssection if desired) which has at its side an effluent trough 48 formed with its second wall 5b and an effluent-trough plate 46, there is housed a removable, horizontal-irrigated-shelves stack 47 comprising:: (a) two intermeshing sets of, horizontal, quadrangular (or circular), flat irrigated shelves 38, 38' mounted on vertical supporting bars 7 at regular intervals b, the whole peripheral surface of each irrigated shelf 38 or 38' being in close contact with all of walls of the vertical tank 49', each irrigated shelf 38 of one set having a plurality of downflow holes 37, each irrigated shelf 38' of the other set having a plurality of downflow holes 37' so that the downflow holes 37 in the one set 38 are not aligned vertically with the holes 37' in the other set 38', whereby flow paths are complicatedly zigzagged down across a submerged filter-beds tank 49; and (b) an air-lift pipe 8 which tunnels the two sets of the thoroughly intermeshing, horizontal, quadrangular (or circular), flat irrigated shelves 38, 38'. It is desirable to arrange scatteringly a large number of downflow holes in each irrigated shelf in order to make the flow of a combined foul liquid waste slow.

Example 7 Referring to Fig. 14, within a vertical tank 54' which has at its side wall an effluent trough 51 and to which a liquid-lifting pump 57 is attached at its outside, there is housed such a removable stack of irrigated shelves as would remain after the air-lift pipe 8 and an effluent riser 9 are omitted from the horizontal-irrigated-shelves stack described in each of the foregoing Examples, for example, a removable, horizontalirrigated-shelves stack 50 which comprises two sets of intermeshing horizontal quadrangular flat irrigated shelves 3, 4 mounted on vertical supporting bars 7 with a shelf spacing b, each irrigated shelf 3 of one set forming a downflow gap 6b jointly with a weir plate 53 at its second side 3b, each irrigated shelf 4 of the other set forming a downflow gap 6a jointly with a first wall 5a of the vertical tank 54' at its first side 4a so that the downflow gaps 6b, 6a of the one set are not in vertical alignment with those of the other set, whereby a flow path is zigzagged down across a submerged filter-beds tank 54. The liquid waste W2 is raised from the bottom section 58 to upper section of the submerged-filter-beds tank by means of the liquid-lifting pump 57, sprinkled over the uppermost irrigated shelf, and purified during its recirculations through the submerged filter-beds tank 54.

In the submerged filter-beds tank 54, the liquid-lifting pump 57 and the effluent trough 51 respectively act as an air-lift pipe 8 and an effluent riser 9 described in each of the foregoing Examples, and the purified liquid is discharged from the submerged-filter-beds tank 54 through an upper outlet hole 59. The liquid waste W2 is elevated from the bottom section 58 of the tank 54 through a lower, liquid-lifting pipe 55, the liquid-lifting pump 57 and an upper, liquid-lifting pipe 55 to a sprinkler 56 attached to the top end of the liquid-lifting pipe 55, from which sprinkler 56 it is sprinkled over the uppermost irrigated shelf 3. Thus the liquid waste is purified during its recirculations through the submerged filter-beds tank 54.

The submerged filter-beds tank according to the present invention is operated as described in each of the preceding Examples; however, the quantities of foul liquid wastes from kitchens, miscellaneous liquid wastes, human body wastes, etc., and the qualities of a combined liquid waste of these liquid wastes vary with the season, day of the week, time, etc. Therefore, in working the present invention, it is preferable to keep the average mixing ratios and the average rate of flow by attaching a flow-regulating device to a transporting pipe 2 which provides liquid communication from a sedimentation tank used for a primary treatment to the submerged-filterbeds tank.

The present invention is worked as described above, and the substantial advantages in carrying out the invention are as follows: 1. The use of irrigated shelves (plate-like articles) of high surface area results in a compact design for an apparatus for purification treatment, and the floor space occupied by the apparatus is thereby considerably reduced.

2. The horizontal parallel arrangement of irrigated shelves leads to stability of the biomembranes, thus the biomembranes multiply very rapidly and do not fall off.

3. The content of suspended solids (S. S.) after a purifying treatment is smaller, and sludge is scarcely produced during the purifying treatment.

Plants for purifying treatment heretofore in use are in difficulties in the disposal of sludge which is produced in large quantities, and thus a great cost is incurred in its disposal. The submerged filterbeds tank according to the present invention mitigates such conventional drawbacks and difficulties.

4. The purification efficiency of the submerged filter-beds tank according to the invention hardly depends on the atmospheric or liquid-waste temperature. According to the results of the investigation carried out by the inventor, no decrease in the purification efficiency is recognized even in the cold season in which the atmospheric and liquid-waste temperatures are 00C and 4-50C respectively.

5. Because no technical means is required for maintenance and management, the submerged filter-beds tank according to the invention is simple and easy to handle. Running costs also are lower compared with those for other treatment processes or treatment apparatus.

6. The purification efficiency of the submerged filter-beds tank according to the invention is superior to that of apparatus heretofore in use.

7. The submerged filter-beds tank according to the invention is suitable also for such a smallscale liquid-waste treatment as used in individual dwellings, small assembly halls, etc.

8. Since a removable stack of the irrigated shelves can be lifted out as a unit, its repairs and exchanges are easy. In a case where efficiency decreases during operation on account of the fact that miscellaneous things clog the submerged filter-beds tank, a removable stack of the irrigated shelves may be lifted out as a unit for cleaning.

Furthermore, there is the convenience that a removable stack of the irrigated shelves can be transported on its own.

9. A submerged filter-beds tank of the desired construction and configuration can be designed by combining adequately the types of the removable stacks of irrigated shelves described in the foregoing Examples.

Claims (21)

Claims

1. A submerged-filter-beds tank comprising a tank in which is housed a removable stack of horizontal-irrigated-shelves comprising: (a) supporting bars; (b) two intermeshing sets of irrigated shelves which are mounted at regular intervals on supporting bars, each irrigated shelf of one set having a portion or portions defining at least in part one means providing liquid communication from above the shelf to below it, each irrigated shelf of the other set having a portion or portions defining at least in part one means providing liquid communication from above the shelf to below it, the shelves being arranged so that the said communication means of one set are not in vertical alignment with those of the other set, such that there is provided a zig-zag flow path down the submerged-filter-beds tank; and (c) an air lift pipe, incorporated into the two intermeshing sets of horizontal flat irrigated shelves, to raise the combined foul liquid waste from the bottom to the upper section of the submerged-filter-beds tank.

2. A submerged-filter-beds tank as set forth in claim 1 , wherein said means for providing liquid communication from above a shelf to below it is a downflow gap which is defined by a part of the periphery of each of the horizontal flat irrigated shelves and a part of the walls of the vertical tank.

3. A submerged-filter-beds tank as set forth in claim 1, wherein said means for providing liquid communication from above a shelf to below it is a downflow hole which is made in each of the shelves.

4. A submerged-filter-beds tank as set forth in claim 1, wherein said means for providing liquid communication from above a shelf to below it for one set is a downflow gap which is formed with the whole periphery thereof and all of walls of the vertical tank, and the said means of each shelf of the other set is a downflow hole made therein.

5. A submerged-filter-beds tank as set forth in any of claims 1 to 4, wherein the shelves are flat.

6. A submerged-filter-beds tank as set forth in any of claims 1 to 4, wherein the shelves are corrugated.

7. A submerged-filter-beds tank for purifying a foul liquid waste, which comprises a vertical tank of quadrangular cross-section for the waste being treated, which vertical tank is adapted to communicate with a sedimentation tank or a screen by means of a transporting pipe, and a removable stack of horizontal-irrigated-shelves which is housed within the vertical tank and which is comprises:: (a) supporting bars; (b) two intermeshing sets of horizontal quadrangular irrigated shelves which are mounted on the vertical supporting bars with a predetermined shelf spacing, each irrigated shelf of one set forming a downflow gap at a second side, jointly with a second wall of the vertical tank, each irrigated shelf of the other set forming a downflow gap at a first side, jointly with a first wall of the tank opposite to said second wall so that the downflow gaps of one set are not in vertical alignment with those of the other set, whereby a zigzag flow path is provided down the submerged-filter-beds tank.

(c) an air-lift pipe which passes through the two sets of the horizontal quadrangular irrigated shelves and into which a compressed-air pipe is inserted; and (d) an effluent riser which passes through the two intermeshing sets of horizontal quadrangular irrigated shelves.

8. A battery of submerged-filter-beds tank for purifying a combined foul liquid waste, which comprises a plurality of submerged-filter-beds tanks which are held together as a unit so that an effluent trough is formed between the outer surfaces of two opposed tank walls of two adjacent submerged-filter-beds tanks, each of the submerged-filter-beds tanks comprising a vertical tank of quadrangular cross-section holding the liquid waste under treatment and a removable, horizontal-irrigated-shelves stack which is housed in the vertical tank and which comprises:: (a) supporting bars; (b) two intermeshing sets of horizontal quadrangular irrigated shelves mounted on the vertical supporting bar with a predetermined shelf spacing, each irrigated shelf of one set forming a downflow gap at a second side, jointly with a weir plate of the vertical tank, each irrigated shelf of the other set Forming a downflow gap at a first side, jointly with a tank wall or a weir plate opposite to the weir plate such that the downflow gaps formed by one set are not in vertical alignment with the downflow gaps formed by the other set, to form a zigzag flow path down the submerged-filter-beds tank; and (c) an air-lift pipe passing through the two intermeshing sets of horizontal quadrangular irrigated shelves.

9. A submerged-filter-beds tank for purifying foul liquid waste, which comprises a vertical tank of quadrangular crosssection for containing liquid waste under treatment and a removable, horizontal-irrigated-shelves stack which is housed within the vertical tank and which stack comprises: (a) supporting bars; (b) two intermeshing sets of horizontal quadrangular flat irrigated shelves mounted on the vertical supporting bars with a predetermined shelf spacing, each irrigated shelf of one set having at least one downflow hole, each irrigated shelf of the other set having at least one downflow hole the arrangement being such that the downflow holes of one set are not in vertical alignment with those of the other set such that a zigzag flow path down the tank is formed; (c) an air-lift pipe which passes through the stack of shelves; and (d) an effluent riser which passes through the stack of shelves.

10. A submerged-filter-beds tank for purifying foul liquid waste, which comprises a cylindrical tank for containing the liquid waste and a removable, horizontal-irrigated-shelves stack which is housed within the cylindrical tank and which comprises: (a) vertical supporting bars; (b) two intermeshing sets of horizontal circular flat irrigated shelves mounted on the vertical supporting bars with a predetermined shelf spacing, each irrigated shelf of one set having a smaller diameter than those of the other set, each irrigated shelf of the said one set forming an annular downflow gap at its whole periphery with the walls of the cylindrical tank, each irrigated shelf of the other set having a larger diameter to form an effective seal against the tank wall and a central downflow hole in its centre so that the annular downflow gaps of the said one set and the central downflow holes of the other set form a zigzag flow path down the tank; (c) an air-lift pipe which passes through the stack of horizontal circular flat irrigated shelves; and (d) an effluent riser which passes through the stack of horizontal circular flat irrigated shelves.

11. A submerged-filter-beds tank for purifying foul liquid waste, which comprises a vertical tank of quadrangular cross-section having an effluent trough at a side thereof, and a removable, horizontal-irrigated-shelves housed within the vertical tank and comprised of; (a) supporting bars; (b) two intermeshing sets of horizontal quadrangular flat irrigated shelves mounted on the supporting bars with a predetermined shelf spacing, each irrigated shelf of one set having a plurality of downflow holes, each irrigated shelf of the other set having a plurality of downflow holes so that the downflow holes in the one set are not in alignment with those of the other set, thereby to form a zigzag flow path down the tank; and (c) an airlift pipe passing through the stack of shelves.

12. A submerged-filter-beds tank as set forth in claim 11, wherein the tank is of circular-crosssection and the shelves are circular.

13. A submerged-filter-beds tank for purifying foul liquid waste, which comprises: (a) a vertical tank of quadrangular crosssection having an effluent trough at a side wall and a liquid lifting pump attached outside thereof to raise the combined foul liquid waste from the bottom of the top of the tank to recirculate said waste; and (b) a removable, horizontal-irrigated-shelves stack housed within the vertical tank and comprising two intermeshing sets of horizontal quadrangular flat irrigated shelves mounted on vertical supporting bars with a predetermined shelf spacing, each irrigated shelf of one set forming a downflow gap jointly with a weir plate at a second side, each irrigated shelf of the other set forming a downflow gap jointly with a first wall at a first side of the tank, thereby to form a zigzag flow path down the tank.

14. A submerged-filter-beds tank as claimed in any preceding claim, wherein the shelves are sized to form a close fit with the walls of the tank so that downflow of liquid takes place substantially or wholly via the downflow holes or gaps.

15. A submerged-filter-beds tank, wherein irrigated shelves for the filter-beds comprise a unitary removable stack.

16. A submerged-filter-beds tank as claimed in claim 15, wherein the stack comprises two intermeshing sets of shelves.

17. A submerged-filter-beds tank as claimed in claim 15 or 16, wherein the stack includes an airlift pipe and/or an effluent discharge pipe.

18. A submerged-filter-beds tank as claimed in any of claims 1 to 17, wherein the shelves are of plastics or asbestos.

19. A submerged-filter-beds tank substantially as hereinbefore described in any one of the foregoing examples 1 to 7.

20. A stack of irrigated shelves as defined in any of claims 1 to 18.

21. The features herebefore disclosed or their equivalents in any novel combination.