AU618454B2

AU618454B2 - Waste water treatment

Info

Publication number: AU618454B2
Application number: AU50547/90A
Authority: AU
Inventors: Robert Kovac
Original assignee: SYSKILL Pty Ltd
Current assignee: Syskill (australia) Pty Ltd
Priority date: 1990-02-28
Filing date: 1990-02-28
Publication date: 1991-12-19
Anticipated expiration: 2010-02-28
Also published as: AU5054790A

Description

COMMONWEALTH OF AUSTRALIA Form PATENTS ACT 1952 COMPLETE SPECIFICATION (OR IGM AL) FOR OFAiCE USE Class Application Nu-nbew: Lodged: Int. Class 0 t Compiete %encification-Lodged: to Accepted: Published: Priority: Related Art: 0 0 0 ~TO BE COMPLETED BY APPLICAiNT 9 Name of Applicant: SYSKILL PTY. LTD.

~,Address of Applicant: 5 5 Brush Road, West Lenistone, New South Wales, Aus tralia Actual Inventor: Robert Kovac Address for Service: SMITH SHELSTON B3EADLE Suite 8, 207 Great North Road FIVE DOCK NSW 2046 Complete Specification for the invention entitled: "WASTE WATER TREATMENT" The following statement is a full description of this invention, including the best method of performing it known to me r. This invention relates to the treatment of waste water for the removal of particulates, fatty residues and other non-soluble pollutants. Typically the invention is applied to the treatment of industrial process effluents before the discharge of the treated effluent into municipal sewer systems and the like.

More particularly, the invention relates to such treatment by the so called air flotation process in which small air bubbles are released into a treatment tank holding the waste water to be treated, to, carry the pollutants to the surface, where they form or are held within a froth or scum which is mechanically removed before the remainder of the waste water is discharged.

i Hitherto it has been usual to liberate the air from nozzles on pipes submerged in the treatment tank and fed with air by an air ;compressor. Much development and experimentation has gone into the design of the nozzles in attempts to liberate the air as a dispersion of small bubbles, because the finer the bubbles the trlore efficient, they are at entraining the pollutants and maintaining a stable froth or scum at the surface. Nevertheless the bubbles usually coalesce to some extent on the nozzles, leading to the rapid rise of some large bubbles through the liquid and undesirable disturbance of the surface.

Therefore an object of the present invention is to provide a waste water treatment apparatus of the air flotation type, wherein the bubbles of air are very small indeed and substantially remain so during their rise through the liquid.

3 A second deficiency of prior known air flotation apparatus is the accumulation of dense sludges on the floor of the treatment tank.

Conventionally, the air is mixed into the stream of effluent to be treated some distance above the floor of the treatment tank or close to the surface so as to minimise the coalescing of bubbles before resching the surface. This results in some particles failing t be entrained with or caught by the air bubbles and sinking quickly to the bottom. This requires the apparatus to be shut down periodically or frequently for the removal of the sediment.

Thus another object of the present invention is to extend the times between shut downs for sludge removal.

The invention achieves its prime object by dissolving the air in !water under pressure and liberating streams or jets of the solution into the treatment tank. As a result minute, widely spaced bubbles of air are formed as the air comes out of solution because of the drop in liquid pressure. The bubble formation is quite analogous to that commonly observed upon the removal of the cap from a bottle of soda I water or other, so called, aerated beverage.

Furthermore, the solution is released in streams flowing over the floor of the treatment tank so as to disturb any sludge thereon and promote its entrainment by the bubbles.

The invention consists in an air flotation apparatus, for the treatment of waste water and like liquids, of the kind comprising a treatment tank to hold a quantity of the liquid, means to liberate air bubbles within the liquid and means to remove surface froth or scum -L ~from the liquid, characterised in that the air liberation means 11 -I111-I-I i d_ I i or r comprise means to dissolve air under pressure in water to form a solution, and means to release at least one stream of said solution into the liquid in the treatment tank for the formation of bubbles as the air comes out of solution due to the drop in pressure, and in that id stream, or each of them, sweeps over the floor of the tank.

By way of example, an embodiment of the above described invention is described in more detail below with reference to the accompanying drawings.

r S Figure 1 is a plan view of an air flotation apparatus according -li: 10 to the invention.

Figure 2 is a side elevation of the apparatus of figure 1 with portion of a treatment tank wall cut away.

I Icrui a 3 is a diagrammiatic sectional side elevation of the baffles and solution delivery pipes of the apparatus of figure 1, drawn to a larger scale.

Figure 4 is a sectional view taken on line 4 4 of figure 3.

Figure 5 is a diagrammatic elevation of a retention pressure vessel and air induction means, being components of the apparatus of figure 1, The illustrated apparatus comprises a treatment tank comprising a main operating chamber 11 in which the air flotation process takes place, an input chamber 12, to receive waste water to .be treated from supply hoses 13, separated from the operating chamber 11 by an adjustable weir 14, an auxiliary mixing chamber 15 in which detergents, flocculants or other chemical additives may be mixed for later addition to the input chamber 11, a return well 16 open to the operating chamber 11 and an outlet chamber 17 separated from the well 16 by an adjustable weir 18 which determines the liquid level in the operating chamber 11.

The tank 10 is furnished with surface sweeping devices comprising endless conveyor chains 19 trained around sprocket wheels on a head shaft 20 driven by a geared motor 21, a tail shaft 22 and an intermediate shaft 23. At least one sweeper blade '(not shown) extends from one chain 19 to the other. The arrangement is such that as the chains 19 move the blade sweeps the surface froth or scum to and up an outlet ramp 24 into a chute i having an inclined floor terminating in a waste disposal duct 26.

Insofar as described above, apart from the presence of the i well 16, the illustrated apparatus is conventional and needs no further detailed description. However in accordance with the invention the apparatus includes air liberation means comprising a retention pressure vessel 27, a pump 28 drawing water from the well 16 and delivering it into the vessel 27, air induction means 29 whereby air is entrained in the water entering the vessel 27, to be dissolved therein, and a solution distribution system for delivering solution from the vessel 27 into the chamber 11.

The air induction means 29 may comprise a conventional venturi type inductor 30, pipe connected through valves 31 and 32 to the inlet and outlet pipes of the pump 28. The valves 31 and 32 X6,P 14 merely offer alternative ind)-ction rates as may be desired. Normally 6 only one or other valve is open at any one time. The operation of the induction means may be monitored by means of an air flow meter 33 and pressure gauge 34 showing the pressure within the vessel 27.

The pressure within the vessel 27, typically around 400 kPa, the air flow rate and the dwell time of water within the vessel (as determined by the vessel capacity and the pumping rate) are such that all of the inflowing air is dissolved in the water to form a solution in the vessel.

That solution is liberated in the chamber 11 by way of a solution supply pipe 35 and three distributor pipes 36 extending from the pipe 35 into the tank 10 across the floor of chamber 11. Each of I the distributor pipes 36 is slotted at 37 (see figure 4) to release streams of solution flowing along the floor of chamber 11 towards tlhe outlet end thereof. Control valves 38 and 39 are provided to regula': the flow of solution and provide the back pressure required in the vessel 27.

A

The solution streams from each pipe 36 are directed towards a bank of baffle plates 40, 41 or 42, as the case may be. Each bank of baffle plates comprises a main plate 43 extending upwardly from the floor of the chamber to completely block and redirect the impinging stream and a group of corrugated plates between which the liquid and air bubbles may ascend. It will be seen that the inclination of the baffle plates is such that the upflowing stream is directed partly counter to the general flow direction through the chamber 11. This promotes gentle mixing of the streams and the waste water and increases the dwell time of the bubbles below the surface.

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It will also be noticed that the spacing between the plates in each group decrease as the group approaches the outlet end of the tank. Typically, the spacing between plates in group 42 may be in group 41 it may be 70mm. and in group 40 it may be 50mm.. The effect of this is to progressively reduce the upflow speed with the object of producing increasingly calm conditions towards the outlet end of the chamber 11 to enhance the stability of the increasingly thick layer of surface froth or scum towards that end.

In other embodiments of the invention oxidising agents, for example ozone, or other disinfectants may be introduced into the retention pressure vessel 27. Because of the pressure in the vessel such agents dissolve readily, which helps avoid waste of agent due to it rei_ lining undissolved.

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Claims

1. An air flotation apparatus, for the treatment of waste water and like liquids, of the kind comprising a treatment tank to hold a quantity of the liquid, means to liberate air bubbles within the liquid and means to remove surface froth or scum from the liquid, characterised in that the air liberation means comprise means to dissolve air under pressure in water to form a solution, and means to release at least one stream of said solution into the liquid in the treatment tank for the formation of bubbles as the air comes out of solution due to the drop in pressure, and in that said stream, or each of them, sweeps over the floor of the tank. V 4

2. Apparatus according to claim 1 wherein said means to dissolve !comprise a retenti'ui pressure vessel, a pump drawing water from the tank through an input duct and delivering that vater into the vessel through an output duct, and a venturi type air inductor connected to one or other of those ducts. tit#

3. Apparatus according t' either claim 1 or claim 2 wherein said means to release comprise a distributor pipe extending across the floor of the tank having openings therealong from each of which a said stream emerges,

4. Apparatus according to any one of the preceding claims wherein the or each stream impinges on a bank of baffle plates which redirect the stream upwardly and partly counter to the general flow direction of waste water through the tank.

Apparatus according to claim 4 wherein there are a plurality of distributor pipes and corresponding banks of baffles, further characterised in that the spacing between the plates of each bank diminishes from bank to bank in the direction of the outlet end of the tank.

6. Apparatus for the treatment of waste water by the dispersed air process substantially as described herein with reference to the accompanying drawings. Dated this twenty-seventh day of September 1991. SYSKILL PTY.LTD. I Attorney: ROBERT G. SHELSTON Fellow Institute of Patent Attorneys of Australia l' I of CARTER SMITH BEADLE