MEMBRANE AERATED SECONDARY CLARIFIER

Abstract

Provided is a clarifier unit of wastewater treatment system and a system comprising the unit, the unit including a treatment tank having a bottom wall, side walls, influent inlet, clarified water outlet and a sludge discharge outlet; wherein the unit has an oxygen supply assembly, including one or more oxygen supply elements confined to a bottom portion of the tank, each of which includes (i) a water-tight enclosure including oxygen-permeable membranes permitting oxygen permeation by, for example, a diffusion from the enclosure to a surrounding medium, and (ii) a gas inlet for receiving an oxygen-containing gas and a gas outlet for removal of gas.

Claims

1.-24. (canceled)

25. A clarifier unit of wastewater treatment system, comprising: a treatment tank having a bottom wall, side walls, influent inlet, clarified water outlet and a sludge discharge outlet; wherein the unit has an oxygen supply assembly, comprising one or more oxygen supply elements confined to a bottom portion of the tank, each of which comprises: a water-tight enclosure comprising oxygen-permeable membranes permitting oxygen permeation from the enclosure to a surrounding medium, and a gas inlet for receiving an oxygen-containing gas and a gas outlet for removal of gas.

26. The unit of claim 25, comprising one or both of a scraper adjacent the bottom wall for scraping sludge off the bottom wall and a conveyor for feeding the sludge sediment to the sludge outlet.

27. The unit of claim 26, wherein the one or more oxygen supply elements are situated above a scraper or conveyor situated at the bottom of the tank.

28. The unit of claim 25, wherein the at least one oxygen supply element is positioned such that it is entirely below the clarified water outlet.

29. The unit of claim 25, being a secondary clarifier.

30. The unit of claim 25, wherein the enclosure is defined between two oxygen-permeable membranes.

31. The unit of claim 30, wherein the two oxygen-permeable membranes are essentially parallel to one another.

32. The unit of claim 30, wherein the enclosure comprises one or more spacer elements between the two oxygen-permeable membranes.

33. The unit of claim 30, wherein the oxygen-permeable membranes are essentially vertically oriented.

34. The unit of claim 33, wherein the one or more oxygen supply elements are generally planar elements.

35. The unit of claim 33, wherein the one or more oxygen supply elements are configured as elongated sleeves.

36. The unit of claim 32, wherein the one or more oxygen supply elements define a generally circular path.

37. The unit of claim 36, comprising a plurality of concentric oxygen supply elements.

38. The unit of claim 36, comprising one or more spirally-arranged oxygen supply elements.

39. The unit of claim 25, wherein the oxygen permeable membranes comprise on their external, aqueous-facing face at least one of alkyl-acrylate or poly-methyl-pentene.

40. The unit of claim 25, comprising a plurality of oxygen supply elements configured as plates.

41. The unit of claim 40, wherein the oxygen supply element plates are arranged in an array, in which one or more oxygen supply element plates is oriented parallel to one or more other supply element plates.

42. The unit of claim 40, wherein the oxygen supply element plates have a radial orientation, optionally the oxygen supply element plates are fixed on one or more revolvable radial arms.

43. The unit of claim 40, wherein the one or more oxygen supply element plates are integral with a scraper adjacent the bottom wall for scraping sludge off the bottom wall and a conveyor for feeding the sludge sediment to the sludge outlet.

44. A water treatment system comprising a water treatment unit of claim 25.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0030] FIGS. 1A-1E are schematic illustrations of an exemplary embodiment of a clarifier unit of this disclosure, comprising a plurality of planar oxygen supply elements that revolve within a bottom portion of a clarifier tank. In these Figures:

[0031] FIG. 1A is an upper perspective view of a clarifier unit;

[0032] FIG. 1B is an upper perspective cross-sectional view of the unit of FIG. 1A, with the walls drawn partially transparent to permit the illustration of some internal elements;

[0033] FIG. 1C shows, in isolation, a revolving assembly of the unit including a plurality of oxygen supply elements fitted on two radial arms at its bottom end;

[0034] FIG. 1D shows an enlarged portion of the revolving assembly illustrating more details of the plurality of oxygen supply elements and of the gas feed and drain, with the orientation of the plates versus the arms on which they are fitted being slighted altered to illustrate an alternative orientation to that shown in FIG. 1C; and

[0035] FIG. 1E shows a single oxygen supply element unit in isolation.

[0036] FIGS. 2A-2F are schematic illustrations of an exemplary embodiment of a clarifier unit of this disclosure having a stationary oxygen supply element assembly, constituted by a plurality of concentric sleeves, fixed at the bottom portion of the clarifier tank. In these Figures:

[0037] FIG. 2A is a top perspective view of the unit;

[0038] FIG. 2B is a top perspective cross-sectional view with side walls drawn partially transparent to permit the illustration of some internal elements;

[0039] FIG. 2C shows a side view of the stationary oxygen supply element assembly and the scraper below it, in isolation;

[0040] FIG. 2D is a top perspective view of the stationary oxygen supply element assembly;

[0041] FIG. 2E is a side perspective view of one of the circular oxygen supply elements; and

[0042] FIG. 2F is an enlargement of portion of FIG. 2E.

DETAILED DESCRIPTION OF EMBODIMENTS

[0043] In the following description, the invention will be illustrated with reference to the two specific embodiments, illustrated in the annexed Figures.

[0044] In accordance with one of these embodiments, illustrated schematically in FIGS. 1A-1E, a plurality of oxygen-supply elements are fixed on radial arms and at a bottom portion of the treatment tank that revolve in an essentially horizontal plane thereby diffusing oxygen throughout the bottom portion of the tank.

[0045] In the other embodiment, illustrated schematically in FIGS. 2A-2F, a plurality of static oxygen supply elements in the form of circular sleeves are used, fixed and confined at the bottom portion of the tank.

[0046] As will be appreciated these embodiments are exemplary of the broader scope of the invention as disclosed above, all sharing the general principle of diffusing oxygen to a bottom portion of a clarifier tank, ensuring oxygen supply and hence aerobic conditions so as to degrade organic matter without the undesired generation of gas bubbles, known to cause scum to elevate to upper portions of the tank, thereby reducing the quality of the effluent water.

[0047] Concentration of dissolved oxygen of 1 mg/l or more promotes an aerobic bacterial degradation of available biodegradable organic matter, rather than denitrification typically occur under anaerobic conditions; and the oxygen supply assembly is preferably designed to have working parameters intended to achieve such an oxygen concentration in the bottom portion, particularly in the sludge blanket. Such working parameters include, without limitation, the rate of oxygen diffusion out of the membrane, the number of oxygen supply elements, the total surface area of the oxygen permeable membranes, the rate of revolution in the event of revolving plates, etc. During the biological reaction of the biodegradable matter under aerobic conditions, CO.sub.2 is produced which dissolves in water and thus does not form bubbles.

[0048] As should appreciated, there can be a large variety of different configurations of the oxygen supply element disclosed herein, which can be revolving or stationary, fixed on more than two radial arms; and there can be other configurations of static oxygen supply element configured as sleeves forming, for example, a plurality of concentric enclosures, each formed in a spiral configuration, etc.

[0049] In a clarifier tank, the organic matter settles at the bottom of the tank forming a sludge blanket and most of the organic matter oxidation occurs in that sludge blanket. Therefore, the oxygen supply elements in a unit of this disclosure are preferably placed in or at least partially in the sludge blanket level.

[0050] Reference is now made first to FIGS. 1A-1E where the unit includes a revolving array of oxygen supply elements.

[0051] The unit 100, generally seen in FIGS. 1A and 1B, has a cylindrical tank 102 with influent inlet port 104 and effluent outlet 106, a scum disposal outlet 108 and sludge outlet 110 at the end of a sludge outlet conduit 110A, the floor 111 at the bottom of the tank may generally be inclined towards the sludge outlet 110. Influent inlet port 104 leads into an inlet conduit with a horizontal section 104A and a vertical section 104B, opening into a feed well compartment 112, from which the influent water spreads within the tank, with liquids flowing mostly upward and solids mostly settle downward. Disposed within the tank is a scum baffle 114 that forms a vertical barrier separating between a central surface area of the water within the tank and a peripheral portion draining into the clarified water trough 116. The central surface area holds the scum, whilst the peripheral portion is fed by clarified water that flows into the peripheral portion from a level lower than that in which the scum accumulates and is, thus, mostly free of scum. The water entering trough 116 drains out through effluent outlet 106.

[0052] Formed on top of the tank is a monitoring rack 120 which permits operators to inspect the tank.

[0053] The unit also includes a revolving assembly 130, best seen in isolation in FIG. 1C, which revolves horizontally about a vertical axis through the operation of motor 132 coupled to a shaft 134 integral with the revolving assembly.

[0054] The revolving assembly includes a frame 140 with two scum scraper, generally radial, arms 136 at its upper end. These arms are positioned above the bottom portion of the scum baffle 114 such that during their revolutions they scrape the upper surface of the water within the tank, thereby scraping and channeling the scum into the scum trough 138 from which the scum is fed into and discharged from scum disposal outlet 108.

[0055] Frame 140 includes two radial arms 142 at its bottom end, extending radially outward from annulus 144 that is fitted around tube section 104B. Arms 142 holds a plurality of planar oxygen supply elements 146 which may, by one embodiment be fitted to the arms at an off-tangential angle, as shown in FIG. 1C; or may be arranged tangentially, as shown in FIG. 1D.

[0056] Rigid oxygen supply elements in configured as plates fixed to at bottom end of a frame of a revolving assembly, of the kind shown in the exemplary embodiment of FIGS. 1A-1E, may each serve a dual function of an oxygen supply element and that of a scraping blade for scraping sludge off the tank's floor 111. For the scraper function, an angled orientation may be of advantage, since tangentially revolving plates will not permit sludge scraping. Thus, in this manner, the oxygen supply element function and the scraper are in fact integrated and no independent scraper device is needed.

[0057] It is also possible to include an additional scarper device with independent scraper blades below the revolving oxygen supply element plates, in which case the oxygen supply element plates may have a tangential orientation, that minimizes water turbulence, as shown in FIG. 1D.

[0058] As can be seen, particularly in FIG. 1E, each of the oxygen supply elements 146 has a water-tight enclosure 148 confined between two opposite, water-impermeable and oxygen-permeable membranes 150, a gas inlet 152 and gas outlet 154. Disposed within the enclosure 148 is spacer element 156, which has the form of a grid. It should be noted that the spacer element may have a variety of different forms and a grid structure is just an example. The membranes are typically made of a pliable or flexible material and the spacer element 156 hold the membranes from collapsing one versus the other even when the gas pressure inside the enclosure will be less than that of the surrounding hydrostatic pressure. The gridded spacer element 156 also serves as rigid skeleton and provides for an overall structural support and imparts some robustness to the oxygen supply element. As can be appreciated, the grid of element 156 is configured in a manner to permit flow of gas between gas inlet 152 and gas outlet 154 and distribute it via the various cells defined by the grid through the entire volume of the enclosure.

[0059] The oxygen supply elements receive a supply of oxygen-containing gas. A variety of such gases may be contemplated within the framework of this disclosure including pure oxygen, oxygen-enriched gas or air. Air is a specific embodiment and may be of advantage for practical considerations of availability and costs. In the following, the specific embodiments in the annexed drawings will be described with air being the oxygen-containing gas; and it being understood that it is an illustrative description and not a limiting one.

[0060] A fan 160 is fixed to the frame by means of a small ramp 182 situated on and fixed to the top of the frame and thus is elevated above the upper level of the water surface within the tank. The fan is electrically wired via a rotating electrical connector (not shown) that permit a constant supply of electricity throughout the revolution of frame 140. Fan 160 is configured to force air into a feed tube 162 that is fixed to and extends downwards along a frame beam to connect to a feed manifold tube 164 (one on each of the arms) fitted along and fixed to arms 142. The manifold tube 164 is linked through small pipes 166 to the gas inlet 152 to thereby channel air into the enclosure of the oxygen supply elements. Gas outlet 154 is linked through small pipes 168 to a drain manifold tube 170 that channel the gas through drain tubes 172 to a venting orifice 174 from which the air is vented into the atmosphere.

[0061] The water-impermeable and oxygen-permeable membranes 150 may, by one embodiment consist of a polymeric film or fabric. Such films or fabrics are generally known. The base fabric may be a non-woven polymeric fabric that may, for example, be a dense polyolefin, such as polyethylene or polypropylene or may be a polyester fabric coated by a water-impermeable layer. Such coating is preferably applied to the external water-facing face of the fabric and may have an overall thickness between 5-20 μm. Typically, the water-impermeable and oxygen-permeable membrane is of a known woven fabric formed from a first polymer such as Tyvek® (DuPont) and the second coating polymer may, for example, be alkyl-acrylate. While the first polymeric fabric imparts permeability, the function of the second, coating polymer is intended to substantially seal the fabric to the passage of water, while offering only small resistance to oxygen diffusion therethrough. Alkyl-acrylates are usually the convenient coating in the case of polyolefin fabrics and may be conveniently applied, as noted above, by a variety of coating techniques and extrusion. Where the fabric is made of a polyester, the second polymer coating is suitably poly-methyl-pentene. It should, however, be emphasized that the oxygen supply elements of this disclosure or not limited by a specific type of film or fabric and any film or fabric that may have the combined water impermeability and oxygen permeability may have utility as the oxygen permeable membrane of this disclosure.

[0062] The overall required surface area of water-impermeable and oxygen-permeable membranes may be calculated taking into account the following parameters: mixed liquor volatile suspended solids concentration in the wastewater influent; hydraulic retention time in the clarifier; hydrolysis rate; biodegradable organic matter generated by hydrolysis; degradable fraction of the biodegradable organic matter; required biodegradable organic matter removal rate and oxygen permeability properties of the membrane.

[0063] For example, according to the calculation shown in the table 1 below, the fraction of volume used to install the membranes is 35% of the clarifier volume. 18 membrane brackets at a size of 1 m.sup.2 would be installed per each m.sup.3 used. The membranes would be spaced apart by a distance of 50.6 mm.

TABLE-US-00001 TABLE 1 # Parameter Value Units 1 Mixed Liquor Volatile Suspended 3000 mg/l Solids concentration 2 Hydraulic retention time in 2 h the clarifier 3 Hydrolysis rate 0.07 g/g/d 4 Biodegradable organic matter 17.5 mg/l generated by hydrolysis 5 Degradable fraction 80% 6 Required removal rate 168.0 g/d/m.sup.3 7 Oxygen permeability of membrane 14 g/d/m.sup.2 Required surface area 12.0 m2/m.sup.3 Example Fraction of volume used 35% Number of 1 m.sup.2 plates per 18.0 per m.sup.3 used each m3 used Spacing between membranes 50.6 mm

[0064] Reference is now being made to FIGS. 2A-2F showing, as already noted above, an embodiment with static oxygen supply elements secured at the bottom portion of the tank. Some elements in this embodiment are identical or similar to those shown in FIGS. 1A-1E and accordingly are given the same reference numeral shifted by a hundred. By way of example, tank 202 and scum outlet 208 in FIG. 2A are substantially the same and serve the same function as the respective elements 102 and 108 in FIG. 1A. The reader is referred to the above description for understanding their role or function.

[0065] Like the embodiments of FIGS. 1A-1E, the unit of FIGS. 2A-2F comprises a revolving assembly 230 that includes scum scraper arms 236 at the top of frame 240 having the function similar to that of the scum scraper arms 136. Formed at the bottom of frame 240 is a sludge scraper 235 with downwardly extending scraper blades 237. During revolution, sludge accumulates at the bottom of tank 202 toward the central vertex 239 of the conical floor 211 and sludge may then be discharged through conduit 210A and sludge outlet 210.

[0066] The stationary oxygen supply element assembly 245 is placed in the sludge blanket level adjacent to and above scraper 235. The assembly 245 comprises an array of concentric oxygen supply elements 247 which are typically held within a frame formed with annular and radial frame elements 249, 251 to the walls or to a central bean of the tank. It should be noted that the concentric array is formed with a clearance 282 between a more central group of oxygen supply elements 253 and a peripheral one 255 that permits passage therethrough and a space for unhindered revolution of beam 257 of frame 240.

[0067] FIG. 2E is a schematic illustration of a single circular oxygen supply element 247 having a gas inlet 252 and gas outlet 254 permitting the ingress and egress of supplied air. Portion 2F is shown in enlarged view in FIG. 2F and has functionally a similar structure to that of the oxygen supply element shown in FIG. 1E, particularly in that both comprise two parallel membranes with a spacer element therebetween.

[0068] The tank includes also two air feed ports 261 linked to and fed air by fan (not shown). Ports 261 are linked to manifolds 263, which are linked to a feed air into the enclosure of the circular permeable membrane elements 247. Oxygen from the air permeates by diffusion through membranes 250 to thereby support the biological oxidation of biodegradable organic matter in the sludge blanket.

[0069] Air outlet manifold 265 is linked to gas outlets 254, draining exhaust gas from within the enclosure 248 of oxygen supply elements 247 to air drain tubes 267, which extend out of the aqueous medium to an orifice 269 above water level or through the tank wall 202, and vented to the atmosphere.

[0070] It should be emphasized again that the above description of specific embodiments is illustrative only of the broader scope and teachings of this disclosure and the reader is referred to the general description for a full understanding of the scope of this disclosure.