GB2303083A

GB2303083A - Apparatus for aggregation of particles suspended in liquid

Info

Publication number: GB2303083A
Application number: GB9614413A
Authority: GB
Inventors: Peter Daniel Anthony Pearce
Original assignee: Thames Water Utilities Ltd
Current assignee: Thames Water Utilities Ltd
Priority date: 1995-07-10
Filing date: 1996-07-09
Publication date: 1997-02-12
Also published as: GB9514064D0; GB9614413D0

Abstract

Apparatus for aggregation of particles suspended in a liquid, such as sewage, comprises a mass of buoyant, discrete flocculating means 3, such as polypropylene spheres, held between two pervious sheets 7 between an inlet 4 and an outlet 5 for the liquid, and positioned in the downward flow path of the liquid by impervious side walls 2. The flocculating means may be periodically cleaned by bursts of air. The apparatus may be positioned within a settling tank.

Description

APPARATUS FOR AGGREGATION OF PARTICLES SUSPENDED IN A LIQUID The invention relates to apparatus for aggregation of particles suspended in a liquid, and more particularly to apparatus including flocculating means.

According to the invention there is provided apparatus for aggregation of particles suspended in a liquid, comprising means defining a flow path for the liquid, and discrete flocculating means in the flow path for aggregation of suspended particles in the liquid, the discrete flocculating means being disposed between an inlet and an outlet for liquid from the apparatus.

It is preferred that the discrete flocculating means is buoyant in the liquid.

There may be retaining means for retaining the discrete flocculating means in position in the flow path. The retaining means may comprise spaced means disposed above and below the flocculating means to retain it in a desired position It is preferred that each retaining means comprises a substantially planar, mesh or grill member extending substantially horizontally across the flow path.

The inlet of the apparatus may comprise a conduit passing substantially vertically through the flocculating means. This helps prevent disruption of the formed floc by turbulence from inflow of liquid into the apparatus. It is preferred that the outlet of the apparatus comprises an opening or openings at a lower, in use, part of the apparatus, so that the formed flocs may leave the apparatus mainly by gravity, obviating the need for mechanical removal.

The majority of the flocculating means each may have a substantially smooth outer surface, and may be substantially spherical. It is preferred that the majority of media have a diameter of from 10 to 100mm, and more preferably of about 25mm. One preferred material for the flocculating means is polypropylene.

The flocculating means may comprise spheres, and the spherical media may have means to enhance or enlarge their respective surface areas, such as through bores, or a surface relief profile.

The defining means may comprise walls of the apparatus and the walls may be substantially vertically disposed in use. This allows for the flocculation at hydraulic rates in use in existing water treatment apparatus. It is further preferred that the walls are substantially planar.

According to a second aspect of the invention there is provided a settlement tank for use in water treatment, including apparatus as hereinabove defined.

According to a third aspect of the invention, there is provided a water treatment system including a settlement tank as defined above, or apparatus as defined above.

Apparatus embodying the invention is hereinafter described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic illustration of a first embodiment of apparatus according to the invention; Fig.2 is a schematic representation of a settlement tank including the apparatus of Figure 1; Fig.3 is a second embodiment of apparatus according to the invention; Fig.4 is to an enlarged scale a view of a sparge pipe used in the embodiment of Figure 3 and Fig.5 is a flow profile of liquid flow through the apparatus of Figure 1 or Figure 3.

Referring to the drawings, there is illustrated apparatus 1 for aggregation of particles suspended in a liquid, comprising means 2 defining a flow path for the liquid, and discrete flocculating means 3 in the flow path for aggregation of suspended particles in the liquid, the discrete flocculating means 3 being disposed between an inlet 4 and an outlet 5 for liquid from the apparatus 1.

In Fig. 1 and 2, the apparatus 1 consists of a cylindrical or square body having vertical walls 2 which define a flow path for liquid to be treated, which enters the apparatus via conduit 6.

The apparatus 1 contains flocculating means 3 in the flow path in the form of media such as a plurality of bodies or particles (not shown) which may be hollow, substantially spherical polypropylene balls, or other such granular media, all of which are buoyant in the liquid. Each particle or granule has a substantially smooth surface in order to minimise head loss across the apparatus. The flocculating means is held in place in the apparatus partly by the walls 2, and partly by retaining means 7 fixed to the walls 2 above and below the flocculating means 3 which retain it at a constant depth relative to the liquid in the apparatus.

The retaining means 7 are in the embodiment a suitable mesh or grille.

The conduit 6 enters the apparatus 1 as shown by arrow A, below the level of the flocculating means 3, and passes substantially vertically up through it, as shown by arrow B, terminating in a trumpet-shaped inlet which aids even distribution of liquid entering the apparatus 1.

The apparatus is particularly well suited for installation in existing settling tanks, as illustrated in Figure 2. The walls 2 of the apparatus may be provided by the existing diffuser drum of the settlement tank. As illustrated in Figure 2 the apparatus is positioned substantially centrally in the tank.

In use, liquid to be treated feeds into the apparatus 1 through conduit 6 in the direction of arrow A. It passes upwardly out of the inlet (arrow B) and on to the upper retaining mesh 7. The level of the liquid above the flocculating means 3 is varied by varying the rate of inflow of liquid. As the apparatus is particularly suited for operation at hydraulic rates in existing diffuser drums in operational settlement tanks, and in this usage it is advantageous that the walls 2 are of sufficient height to prevent overspill of untreated liquid during periods of increased inflow. The liquid passes into the flocculating means 3 and suspended particulate matter in the liquid is aggregated by virtue of the sinuous flow path through the voids in the flocculating means 3.The constant splitting and rejoining of flow streams through the flocculating means results in an increased number of suspended particle/particle collisions, some of which lead to a combined particle of larger size. The increased particle collision frequency is aided by a degree of solids entrapment which occurs within the flocculating means. This locally increases the solids concentration which further increases the number of particle collisions and consequently leads to a higher degree of flocculation. The flocculated particles enter the settlement tank through the open mesh of the lower (as shown) retaining means 7 (arrow C) and enter the settlement tank with the minimum of sheer and hence floc disruption.Due to the fact that the flocculating means 3 is retained at a constant level in the apparatus 1 relative to the walls 2, by the retaining means 7, the apparatus has fixed flocculation characteristics for a given flow rate of liquid.

Referring now to Figures 3 and 4, there is shown in Figure 3 a settling tank 20 to which has a centrally located apparatus 1 in the form of a centrally located flocculator of the kind shown in Figures 1 and 2, so a description of the construction thereof would not be repeated like parts being indicated by like references. The settling tank 20 has a scraper 21 a scraper support 22 including legs 23 depending from a scraper bridge 24, and a safety device for operating personnel in the form of a hand railing 25. There is a support device in the form of a tripod 26 for the scraper bridge. In the use described above with reference to Figures 1 and 2, there would be, in continuous operation, a build up of flocculated or other material in the medium of the apparatus 1, which tends to block the flow path and hence there can be a head loss.It is therefore advantageous to be able to dislodge or break up any build up of debris in the medium so in the embodiment of Figure 3 there is provided a suitable means 27 in the form of sparge pipe for air which is connected to, for support, a leg of the scraper at 28, the sparge pipe 27 being shown in greater detail in Figure 4. As shown the pipe 27 is of generally L-shape and extends under the flocculator to the inlet pipe 6, a leg or limb 29 thereof being of a length substantially equal to the radius of the apparatus 1 (when it is cylindrical). The sparge pipe 27 may alternatively be hand held rather than secured as shown in Figure 3. In either case, it is used intermittently to clean the flocculator 1 by admitting air to the tank 20 to accomplish which the limb 29 of the pipe has downwardly facing air sparge holes 30 of 1.5 mm diameter at 70 mm spacing in the embodiment. The holes 30 are also countersunk to 2.5 mm to aid air bubble release. An upright leg or limb 31 of the pipe 27 has a connector 32 for temporary connection to an air supply for example a Schraeder air supply (not shown). The length of the limb 31 is adjustable or adjusted to accommodate a particular tank depth and/or bridge height to enable safe access to the air connection 32 by operating personnel. Thus the connection is above the water level. As shown in Figure 3, the limb 31 is attached to a scraper leg when the scraper rotates or it can be attached to the tank if this rotates and the scraper 21 is stationary. When hand held, the air sparge pipe or land 27 can be manoeuvred from the scraper bridge 24.In all embodiments the air passes out of the holes 30 and bubbles up evenly and through the flocculating means in the flocculator to break up debris by "jostling" the media gently, so opening up the flow paths through the media, so this flocculating action can be continued.

Figure 5 shows schematically flow through the apparatus 20 which shows an even flow with settlement of solids at the centre "C" passage out of the tank and liquid escaping at the top "T" (as viewed) periphery of the tank.

Apparatus embodying the invention thus provides flocculation without the need for addition of coagulating chemicals (such as trivalent metal salts or polymers), and requires no power for operation. Furthermore the apparatus is virtually maintenance free, as back-washing or draining is not required. It will be understood that the flocculating means, when in the form of a plurality of spheres, suitably polypropylene spheres of 25 mm diameter, has the effective flocculating surface area enhanced by for example providing for through apertures in the spheres, or a surface relief profile on each sphere. Also, in view of the substantial lifting force provided by the buoyant media, there is means to strengthen connections between the conduit 6, and the mesh 7, suitably a spider, and means to retain the upper mesh 7 in position. Not only are, in apparatus described herein with reference to the drawings, settling characteristics enhanced, but there is an increase of "capture" of solids and therefore a better quality of effluent. There is an even down flow and favourable flowpath modifications, a lower velocity of liquid through the apparatus and a longer retention time, which leads to better flow, an increase in flocculating time and an enhanced quiescent zone (see Figure 5) which therefore maintains the integrity of the floc produced.

There may have valves such as rubber flap vales over the holes, to keep them clean.

Claims

CLAIMS:

1. Apparatus for aggregation of particles suspended in a liquid, comprising means defining a flow path for the liquid, and discrete flocculating means in the flow path for aggregation of suspended particles in the liquid, the discrete flocculating means being disposed between an inlet and an outlet for liquid from the apparatus.

2. Apparatus according to claim 1, the discrete flocculating means being buoyant in the liquid.

3. Apparatus according to claim 2, comprising retaining means for retaining the discrete flocculating means in position in the flow path.

4. Apparatus according to claim 3, the retaining means comprising spaced means disposed above and below the flocculating means.

5. Apparatus according to claim 4, each retaining means comprising a substantially planar, mesh or grille member extending substantially horizontally across the flow path.

6. Apparatus according to any preceding claim, the inlet comprising a conduit passing substantially vertically through the flocculating means.

7. Apparatus according to any preceding claim, the outlet comprising an opening at a lower, in use, part of the apparatus.

8. Apparatus according to any preceding claim, the majority of the flocculating means each comprising a medium having a substantially smooth outer surface.

9. Apparatus according to claim 8, the majority of media being substantially spherical.

10. Apparatus according to either of claims 8 or 9, the majority of media having a diameter of from 10 to 100mm.

11. Apparatus according to any of claims 8 to 10, the majority of media having a diameter of about 25mm.

12. Apparatus according to claim 11, the flocculating means comprising polypropylene.

13. Apparatus according to any of claims 9 to 12, the spherical media having means to enhance their respective surface areas.

14. Apparatus according to claim 13, the said means comprising through bores or a surface relief profile.

15. Apparatus according to any preceding claim, wherein the defining means comprises walls of the apparatus.

16. Apparatus according to claim 16, wherein the walls are substantially vertically disposed in use and/or are substantially planar.

17. Apparatus according to any preceding claim, comprising means to clean the flocculating means.

18. Apparatus according to claim 17, the device comprising an air sparge pipe.

19. Apparatus, substantially as hereinbefore described with reference to the accompanying drawings.

20. A settlement tank for use in water treatment, including apparatus according to any preceding claim.

21. A settlement tank, substantially as hereinbefore described with reference to the accompanying drawings.

22. A water treatment system, including a settlement tank according to claim 20 or claim 21, or apparatus according to any of claims 1 to 19.