CA1186586A

CA1186586A - Treatment of waters with broad spectrum contaminants

Info

Publication number: CA1186586A
Application number: CA000394212A
Authority: CA
Inventors: James Keane
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-11-06
Filing date: 1982-01-15
Publication date: 1985-05-07
Also published as: US4417985A

Abstract

ABSTRACT OF THE DISCLOSURE
Industrial waters containing dissolved or suspended contaminants are treated by turbulently mixing the contaminated water with a composition comprising a discontinuous phase of gas in the form of surfactant-stabilized spherical bubbles having a narrowly distributed size in the range of from about 12 to about 100 microns and a half-life of at least about 2 minutes, each gas bubble being encapsulated in a double surfaced hydration layer containing water and a soluble surfactant having a HLB
ratio greater than about 10. The encapsulated gas bubbles are dispersed in a continuous water phase and each has an outer surface layer of collector ions movably held to the hydration layer by Coulomb forces and active to react with the contaminants. The surfactant is present in an amount up to about 3 times critical micelle concentration so as to stabilize the bubbles and impart to the hydration layer sufficient thickness and viscosity to retard migration of the collector ions through the hydration layer for a period of time sufficient to enable the collector ions to react with the contaminants and cause nucleation thereof directly at the surface layers of the bubbles. The reaction between the collector ions and the contaminants causes the bubbles to rupture and to release their entrapped gas as naked gas bubbles and forms an insoluble reaction product, the ruptured bubbles exposing the surfactant contained in the respective hydration layer thereof for reaction with any unreacted collector ions to form a further insoluble reaction product.
Both these reactions products are then allowed to separate from the water as a recoverable agglomerated material.

Description

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The present invention lies in the field of industrial waste water treatment and is particularly directed toward treating waters containing complex wastes, such as industrial laundry wastes. More particularly, the invention relates to a composition for the direct nucleation of con-taminants contained in a hydrogen-bonded liquid such as water, as well as to a method and apparatus for preparing same.
In most eases, an industrial waste water stream can be analyzed, predicted and even treated on a eonsistant basis. The diseharge from an indus-trial laundry is not however. In practical terms, there is yet no technology to treat such type of dise~large consistently, at reasonable cost, le-t alone recyele it. There are known waste water treatment systems whieh are aimed at specific ends, but none can handle the range of eonstituents, nor the range of variability that exists in industrial laundry wastes.
An industrial laundry supplies fabric clean-ing and rental services for uniforms, wiper rags, mats, mops, air filtration bags, etc., in fact any cleaning or cleanup item required that is made of fabric. The fi'tration bags are a newer service product for these 25 laundries, and in fact represent a transfer of an air pollution problem to one of water pollution. White linen or uniforms are not a part of their business, these are being done by a different elass of laundry.
A typieal industrial laundry has 20 ~ 000 to 30 200,000 gallons/day of diseharge water. It ean typi-cally represent 0. 2% of the hydraulie load on a municipal treatment plant, yet at the same time represent 15 to 20% of its treatment load. This load can be practically any oil, dirt or chemical that a customer list of 10,000 plant,s, typical for such an operation, can generate. The following table shows justfour typical customers from a single morn-ing's run by a laundry sales truck:
TABLE

Plant Fabric Item Contaminants . . . . .
Printer Wiper Rags Ink - Metall.ic Pigments - Oil Base - Surfactants Solvents - Toluene - Chlorinated Oils - Lube Oil - Grease _ _ _ .
Body Shop Uniforms Paint Wiper Rags Body Filler Dust Lube Oil Solvents Manufactur- Mats Mineral oils ing Mops Cutting Oils Wiper Rags Synthetic Oils Uniforms Metal particles Floor wax Cleaning Compounds etc.
. _ .
Research Wipers Confidential Company _. .......... _ _ .

,~
~1 A typical day might be 50 such plants, and a typical laundry might have 20 such trucks. It is to be noted that the last entry, under research company, -the contaminants are held confidential, often a waste item cannot be identified due to secrecy or more likely unwillingness of such companies to a~nit what it is.
rrhus~ it can be seen that as many as :L000 plants can indirectly feed a vast unidentified waste s-tream to a municipal treatment plant.
It was observed during work with a micro-gas emulsion (MGE) of the type described in U.S. patent no.
3,900,420 to Sebba that concentrated waste waters with complex mixtures such as those found in industrial laundry waste could not be floated using MGE bubbles, but required much larger bubbles similar to those used in the ion flotation method described in Canadian patent no, 708,215 also to Sebba. rrhus, MGE bubbles were made with a venturi generator according to the teaching of the Sebba patent and were introduced into a complex water waste stream containing a broad spectrum of contaminants. rrhere was a very little separation of the contaminants from the water, although with different surfactants there was variation in the type of contaminants that was partially collected. At

2~ very high surfactant concentrations, the bubble size was indeed small with long persistance but there were rela-tively a few bubbles in the expected 1-10 ~u range ~colloidal size). rrhese concentrations were in the range of 1,000 to 3,000 p.p.m. which were entirely out of the practical economic range for waste water stripp-ing~ At lower values of surfactant additions, the bubble size was much larger but the number of bubbles in the range 1-10 ,u became extremely small. Further inves-tiga-tions revealed that these sma:~ bubbles had at very short life at surEactant concentrations at about the critical micelle concentra-lion or below it.
The remaining larger bubbles behaved as specific contaminan-t collectors very similar to the ion flo-tation teaching of -the other Sebba patent, -thus requir-ing the selection of specific surfactants. In no case did these hubbles collect other than a narrow range of contaminants and were not therefore useful in the part-icular range of applications to which the present invention pertains.
In considering the problem of scale-up of bubble forming systems, it became evident that the method of using a recirculating system with a time delay loop to select out the long life bubbles was not a practical approach, and further raised the question as to the nature of the short life bubbles that were rejected. For every gallon of bubbles produced, 10 gallons had to be circulated at high pressure drop through a venturi. The venturi was only effective around its periphery, so that as scale-up in size was attempted, it was found that bubble production was proportional to ~J where ~ is the active throat aiameter, whereas the recirculation load on the pump was proportional to ~ d2. Clearly, when using a ven-turi-type bubble generator, large increases in capacity of bubble production would not be possible and still retain an economic power input per unit bubble area produced.

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It is an object of the present invention to clean contaminated waters containing a broad spectrum of contami-nants, in an effective and economic manner.
According to one aspec-t of the invention, there is provided a composition for the direct nucleation of materials which are dissolved or suspended in a hydrogen-bonded liquid, which comprises a discontinuous phase of gas in the form of surfactant-stabilized spherical bubbles having a narrowly distributed size in the range of from about 12 to about 100 microns and a half-life of at least about 2 minutes, each gas bubble being encapsulated in a double surfaced hydration layer containing the hydrogen--bonded liquid and a soluble surfactant having a HLB ratio greater than about 10. The encapsulated gas bubbles are dispersed in a continuous phase of the hydrogen-bonded liquid and each has an outer surface layer of collector ions movably held to the hydration layer by Coulomb forces and active to react with the materials to be nucleated. The surfactant is present in an amount up to about 3 times critical micelle concentration so as to stabilize the bubbles and impart to the hydration layer sufficient thickness and viscosity to retard migration of the collector ions through the hydration layer for a period of time sufficient to enabl.e the collector ions to react with the materials and cause nucleation thereof directly at the surface layers of the bubbles.
It has been found that when the bubbles rupture as a result of the nucleation reaction at the surface layers and of the collector ions having migrated in time through the respective hydration layer of unreacted bubbles and reacted with the surfactant, they release their entrapped gas as naked gas bubbles which coalesce with other naked gas bubbles to provide large gas buh~les which are effective for flotation of the nucleated materials.
Of course, if the materials contained in the hydrogen-bonded liquid are high density ma-terials, the nucleated materials will drop under gravity to form a sediment layer instead of a floating floc. For the sake of sim-plicity, the encapsulated gas bubbles of -the invention having a surface layer of nucleation centers formed of active collector ions will be hereinafter termed DNF
(Direct Nucleate Flotation) bubbles; it must be understood, however, that such terminology does not limit in any way the application of these bubbles to the separation of nucleated materials only by flo-tation.
The spherical yas bubbles forming the DNF
bubbles of the invention must have a narrowly distributed size of at least about 12 ~u since it has been found that the lifetime of the DNF bubbles is strongly dependent on the size of the gas bubbles. Below about 12 ~u, they rapidly shrink and disappear~ In the 12-15)u range, they are extremely stable, the gas bubbles are static, that is, they neither grow nor shrink, and thus last for hours.
Above about 15~u, the bubbles become dynamic, that is, they slowly increase in size. The bubble sizes must also be narrowly distributed since a narrow distribution yields the best compromise between lost of bubbles due to un-economically short life and loss of effective surface area due to uneconomically large bubbles. By the expression "bubbles having a narrowly distributed size" are meant those bubbles whose size is greater than one half or less than twice the size of the most frequently occurin~ bubbles and comprising about 68% of all the bubbles formed.
The gas bubbles preferably have a narrowly distributed size in the range of from about 12 to about 100 ~, where the half-life of such bubbles is from about 2 minutes to more than 2 hours. In the particularly preferred range of about 12 to about 20 ,u, the bubbles have half-lives of at least about one hour. The term "half-life" refers to the time it takes for a bubble to half or double its size (diameter).
The gas is generally air and may be present in an amount of up to about 80% by volume, preferably between about 5 to about 80% by volume.
'rhe hydrogen-bonded liquid can be any liquid containing hydrogen bonds such as, for example, water, alcohols and glycols.
Where the hydrogen-bonded liquid is water, the surfactant can be any water soluble anionic, cationic or non-ionic surfactant having a HLB (Hydro-philic-Lipophilic-Balance) ratio greater than about 10, preferably of about 16 to about 18. A surEactant with a HLB ratio of above 10 is necessary for effect-ively forming the required hydration layer. Such surfactants are preferably selected from -the group consisting of alkali metal and ammonium lauryl sulfates such as sodium lauryl sulfate (HLB : 40) and ammonium lauryl sulfate (HLB : 18~, poly-oxyethylene derivatives of fatty acid partial esters of sorbitol anhydrides stlch as TW~EN 20 (trade mark, polyoxyethylene sorbitan monolaura-te with HLB of 16.7) and surfactants based on alkylaryl ~ r?

polyether alcohols, sulfonates and sulfates such as TRITON X-100 (trade mark, isooctophenoxypolyethoxy-ethanol wi-th HLB o-f 13~5).
The surEactant is present in an amount to stabilize the gas bubbles and also to impart to the hydration layer the required thickness and viscosity.
In practice, this amount is usually at or slightly above (e.g~ 10%) critical micelle concentration (CMC).
This concentration of surfactant corresponds to the maximum depression of the gas to liquid interfacial tension which occurs when the surfactant forms a monolayer at the interface, -thls monolayer when it is completely formed will develop a deep hydra-tion layer.
The CMC for many surfactants is in the range of about 100 to about 300 p.p.m~ It is also possible for the surfactant to be in an amount which is slightly less ( e . g. 10%) than the CMC, in which case the gas bubbles are less stable and will more readily release their entrapped gas 50 as to assist in the flotation of the nucleated materials.
The double-sur~aced hydration layer which covers each gas bubble is a "deep" layer which is ~nown in the literature as having a thickness of about 10 to about 100 A. As will be hereinbelow explained in greater detail, when the hydrogen-bonded liquid is water, this water is present in the hydration layer in the form of soft ice having a viscosity of the order of 10 poises. This soft ice may comprise a plurality of successive layers of po-larized water molecules. In the case where theamount of water soluble surfactant greatly exceeds the ~ _~

CMC, that is, when it reaches an amount up to about 3 times the CMC, the hydration layer will be multi-layered and contain an innermost mono-molecular layer of surfactant and a double-molecular layer of sur-factant spaced therefrom with an inner soft ice layerbetween the surfac-tant layers and an outermost soft ice layer surrounding the double-molecular layer of surfactant.
It has also been observed that when the hydra-tion layer further contains an oil soluble surfactant, there exists a second critical size at about 25 ~ where the bubbles rupture and then collapse. It has been further observed that when such DNF bubbles contain-ing a mixture of water soluble surfac-tan-t and oil soluble surfactant (for example, in a weight ratio of about 1:1) rupture as a result of the nucleation reaction at the surface layers and of unreacted bubbles having a size above about 15 microns slowly increasing in size and reaching a size of about 2~ 25 microns, other unreacted bubbles also rupturing in time as a result of the collector ions having migrated through the respective hydration layer thereof and reacted with the water soluble surfactant, residual globules of the oil soluble surfactant with no residual gas core are formed which have a size of about 1 micron. These very small globules of oil soluble surfactant act as further collectors of any oil soluble materials present in the water, and thus advantageously serve to extend the range of materials to be collected.
The collector providing the collector ions is preferably present in an amount of about - ~L~ 7~

100 to about ~00 p.p.m~ Such collector can be any suitable ionizable floccula-ting agent, coagulating agent or precipitating agent which is soluble in the hydrogen-bonded liquid. Where -the hydro~en-bonded liquid is water, the collector can be selec-ted from the group consisting of aluminu1n sulfate, alkali metal hydroxides and bicarbonates. Excellent results have been ohtained with aluminum sulfateO The surface layer of collector ions has no bonding beyond the Coulomb forces holding it in place and the collector ions are thus movably held to the hydration layer.
Where the layer of collector ions is positively or negatively charged, it acts as a Faraday cage to elec-trically screen the hydration layer.
The composition of thè invention is pre-pared by a novel method which comprises the s-teps of.
a) providing a flowing stream comprising a two phase mixture of the gas and a solution containing the hydrogen-bonded liquid and a soluble surfactant which has an HLB ratio greater than about 10 and which is present in an amount up to about 3 times critical micelle concentration, b) imparting to the stream a rota-ting laminar flow so as to form in -the hydrogen-bonded liquid a plurality of micro-vortices centrifugally entrapping the gas therein and allowing the micro-vortices to break into surfactant-stabilized spherical gas bubbles, the micro-vortex forming being carried under conditions -to provide bubbles haviny a narrowly distributed size in the range of from about 12 to about 100 microns and a half-life of a-t 1east about 2 minutes' c) providing a time delay so as to a:Llow the hydration layer to completely deve.lop on each of the surfactant-stabilized gas bubbles formed, d) adding the collector p:roviding the col]ector ions and allowing these ions to form an outer su.rface layer on the respective hydration layer of each surfactant-stabilized gas bubble, the collector ions being movably held to the hydration layer by Coulomb -forces.
In one preferred embodiment, the micro-vortex forming step ~b) is carried ou-t by subjecting the s-tream to micro-vor-tex forming and shedding means comprising a plurality of spaced apart substantially parallel stationary rods of circular cross-section disposed transversely to the direction of flow, under conditions to provide a Reynolds number in the range of from about 500 to about 5,000.
In another preferred embodiment, the micro-vortex forming step (b) is carried out by subjecting the strea~n to micro-vortex forming and shedding means comprising a plurali-ty,of radially arranged rods of circular cross-section rotating about a central axis and disposed transversely to the direction of flow, also under condi-tions to provide a Reynolds number in the range of from about 500 to about 5,000.

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As will be seen hereinbelow, the Reynolds number is governed by the stream velocity upstream of the micro-vortex forming and shedding means, -the vis-cosity of the liquid medium and the rod diameter and, a-t Reynolds numbers o:E about 500 to about 5,000, -the size of the bubbles formed is nearly constant. It has also been determined empirically that with a rod diameter of at least 0.005 inch, the bubble size is at least about 12 ~. When using rods having diameters in the range of from about 0.005 to about 0.02 inch, the bubbles formed have a narrowly distributed size in - lla -the range of frorn about 12 to about 100 ~. The bubble size is of course related not only -to the rod dia-meter but also to the amount of surfactan-t used and a decrease in the surfactant amount for a cons-tant rod diameter will increase the size of the bubbles pro--duced.
The useful total effective length defined by the rods is generally in the range of from about 100 to about 10,000 inches.
The time delay provided for allowing the hydration layer to completely develop on each of -the surfactant-stabilized gas bubbles is preferably in the range of from abou-t 10 to abou-t 100 milliseconds.
The invention further provides an apparatus for carrying out a method as defined above, which com-prises first feed means for providing the aforesaid flowing stream' micro-vortex forming and shedding means arranged in the flow path of the stream for imparting to the stream a rotating laminar flow so as to form the aforesaid micro-vortices, means for providing the required time delay, and second feed means for adding the collector.
According to another aspect of the invention, there is also provided a bubble generator for producing a mixture of surfactant-stabilized spherical gas bubbles having a narrowly distributed size and dispersed in a hydrogen-bonded liquid, This bubble generator comprises feed means for providing a flowing stream comprising a two phase mixture of the gas and a solution containing a sta-bilizing amount of the surfactant in the hydrogen-bonded liquid, and micro vortex forming and shedding means compris-~12-ing a plurality of rods arranged in the flow path of thestream and disposed transversely to -the direction of flow for impartiny to the strearn a rotatirlg laminar flow so as to form in the hydrogen-bonded liquid a plurality of micro-vortices which cen-trifugally entrap the gas -therein and break into surfactant-stabilized spherical bubbles of a narrowly distributed size. The rods are adapted to provide a ~eynolds nurnber in the range of from about 500 to abou-t 5,000.
According to yet a further aspect of the invention, there is provided a method of treating water containing dissolved or suspended materials to separate these materials therefrom, which comprises turbulently mixing the water with a composition as previously defined in which the hydrogen-bonded liquid is water so as to cause nucleation of the materials at the surface layers of the bubbles. The reaction between the collector ions and the materials causes the bubbles to rupture and to release their entrapped gas as naked gas bubbles and forms an insoluble reac-tion product, the ruptured bubbles exposing the sur-factant contained in the respective hydration layer thereof for reaction with any unreacted collector ions to form a further insoluble reaction product, any unreacted bubbles also rupturing in time as a result of the collector ions having migrated through the respective hydration layer thereof and reacted with the surfactant to form the aforesaid further insoluble reaction product. Bo-th the insoluble reac-tion product and further reaction product are thenallowed to separate from the water as a recoverable agglomerated material.
In one preferred embodiment of the water treatment method of the invention, the treated water containing the insoluble reaction product and further insoluble reaction product is passed to a quiescent flotation chamber wherein both reaction products are allowed to separate as a floc which is buoyed to the surface of the water with large gas bubbles formed by the coalescence of the naked bubbles with one another.
In another preferred embodiment of the water treatment method, the treated water containing the inso-luble reaction product and further insoluble reaction product is passed to a settlement chamber having a bottom, wherein at least the insoluble reaction product is allowed to separate under gravity to form a sediment layer at the bottom of the chamber.
Examples of complex wastes that can be treated according to the invention are industrial laundry waste with oils, greases, metals, dyes, deter-gents and water conditioning chemicals in highly solu-bilized form. Another example is a mixture of crude oil, clay and water, with or without surfactants used to solu~ilizethe crude oil and various chemicals to condition the water. A further example is a mixture of clays and minerals such as phosphate slime, in which case the water treatment method is multi-staged where a DNF bubble mixture having a first collector is used to collect one specie of clay in a first stage, and another DNF bubble mixture with a second collector is used to collect the other species in a second stage.

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The invention will now be fur-ther under-stood by the following detailed descrip-tion of preferred embodiments thereof, wi-th reference to the appended drawings, wherein:
Fig. l schematically represents a DNF
bubble generator according to a first preferred e-mbo-di~ent of the invention' Fig. 2 is an enlarged schematic represen-tation of a micro-vortex forming and shedding rod as used in the apparatus of Fig. l, showing the formation of micro-vortices, Fig. 3 is another schematic representation of a DNF bubble generator according to a second preferred embodiment of the invention' Fig. 4 is a diagram showing the relation-ship between the Reynolds number and the Strouhal number, Fig. 5 is another diagram showing the relationship between the bubble half-life and the size thereof, Fig. 6a, 6b and 6c are fragmen-tary schematic representationsof a DNF bubble with anionic, cationic and non-ionic surfac-tants, respectively, Fig. 7 is another fragmentary schematic representation of a DNF bubble having a multilayered hydration layer, Fig. 8 is a flow diagram illus-trating a waste water treatment method according to a preferred embodiment of the invention, and Fig. 9 is another flow diagram illustrat~
ing a two-stage waste water treatment method according . ~ ;',.\`. _,~

5~
to a further preferred embodiment of the invention.
Referring to Fig~ 1, there is shown a DI~F
bubble generator comprising a longitudinally extending conduit 10 for carrying a flowing stream, the conduit having a portion 12 thereof adapted to form and shed micro-vortices, An aqueous solution of surfactant 1~
is fed at a controlled flow rate via the inlet 16, by means of a pump (not shown~. Air 18, also controlled for flow rate and àdditionally for pressure, is introduced by means of the injector 20. Baffle plates 22 cause the stream to turbulently flow in the region 24 so as to ensure the formation of a uniform two phase mixture upstream of the micro-vortex forming and shedding por-tion 12 of the conduit. In the conduit portion 12, there is arranged a plurality of spaced apart substan-tially parallel stationary rods 26 of circular cross-section which are disposed transversely to the direction of flow. me rods 26 shed micro-vortices when the Reynolds number lies between 50 and 5,000. At a Reynolds number below 50, the flow does not separate for the sur-faces of the rods, whereas above 5,000 the flow is turbulent.
As best shown in Fig. 2, the rod 26 impartes to the two phase mixture a rotating laminar flow which entrains the air bubbles 18' around the rod in both the clockwise and counterclockwise directions. As a result, a plurality of cylindrical micro-vortices 28 are formed which centrifugally entrap the air therein, each cylin-drical micro-vortex having an air core 30 surrounded by a surfactant film 32. As shown, the micro-vortices 28 are formed in a pair of upper and lower layers which are spaced by the distance d and each have a sinusol-dal wave motiorl, the respective micro-vortices of the upper and lower layers being spaced rela-tive -to one another by the dis-tance 1 with the micro-vortices of one layer being disposed intermediate two successive micro-vortices of the other layer. Once a cylindrical micro-vortex 28 is formed and breaks away from the rod, frictional forces in the water will dissipate the rotational energy and the cylindrical micro-vortex will stop rotating. Before it does 90 however, the cylinder will become unstable and break up into short segments that close to form surEactant-stabilized air bubbles 28', It should be noted that the ratio d/l is an indicator of the stability of the micro vortex formi~g and shedding process. At d/l = 0.28, optimum stability occurs which gives the least dispersion of bubble size and the greatest number of bubbles at the size determined by the parameters of the system.
As is known, the distribution of the bubble size is related to the stream velocity Vo upstream of the micro-vortex forming and shedding region 12, to the viscosity V of the liquid medium and to the rod diameter D by the following relations:
Reynolds number (Re) = Vo D
and Strouhal number (S) = n D
Vo where n is the micro-vortex frequency defined by the ratio 2 Vo/l. The relationship be-tween the Reynolds number and the Strouhal number is shown in Fig. 4, ac published in "Fluid Dynamics", James W. Daily, Addison Wesley Pub., Reading, Mass~, 1966, Libxary of Congress, number 65-23029, page 381. Over the ranye Re = 50 to 500, the bubble size is decreasing since the frequency n is increasing. Over the range Re = 500 to 5,000, the bubble size is nearly constant and thus by con-trolling the parameters Vo, V and D to have a Reynolds 10 number in this range, the size of the bubbles produced will be restricted to a narrow size range.
Fig. 5 shows that -the half-life of the bubbles is a function of size. 'rhe critical lower size limit is at about 12 ~u, as below such size the 15 bubbles rapidly shrink and disappear. In the 12-15 ,u range, the bubbles are extremely stable and last for hours. The useful bubble sizes exhibiting adequate half-lives are therefore from about 12 ~1 upwards, with the micro-vortex forming and shedding parameters 20 set to produce as many bubbles at the critical size as possible and as few below i-t as possible. ~his leads to an optimum selection for the maximum of a normal distribution curve to be set at about 15 ,u, with at least 95% of the bubbles produced being over 10 ~u.
25 This in turn ensures the best compromise between loss of bubbles due to uneconomically short life, and loss of effective surface area due to uneconomically large bubbles.
In the conduit portion 12 of the DNF bubble 30 generator illustrated in Fig. 1, several hundred rods 26 are provided so as to define a useful total effec-tive ~ S~h~

length of about lO0 to about 500 inches, preferably 200 to 300 inches. The surfactant-stabilized air bubbles 28' produced are then allowe~ to travel a length sufficient to provide the necessary time delay (about lO - lO0 milliseconds) for the desired hydration layer to completely develop, before a solution of collector 34 is added via the inlet 36. The resulting aqueous DNF bubble mixture 38 with collector ions forming the surface layers of the bubbles is discharged at the outlet 40 and is active for treating indus-trial waste waters~
As an example, if the DNF bubble generator just described is designed to convert 1 gallon/minute for an air and water mixture in a volume ratio of l:l to a DNF bubble mixture, -the parameters of such a gene-rator may be the following:
Reynolds number : 500 Micro-vortex shedding frequency : 51 x 103/sec.
Rod diameter : 0.005 irch Total effective rod length : 100 inches The total active surface area available for treating waste waters and defined by the surfaces of the DNF
bubbles produced is 1864 sq. ft./min. If the flow rate is increased to lO0 gal~min., the Reynolds number in-creases to 5,000 and the total active surface area defined by the ~NF bubbles becomes 18,640 sq. ft./min~

Fig. 3 illustrates another embodiment of a DNF bubble generator. The apparatus illustrated com-prises a micro-vortex chamber 50 to which are connected /''l ~ 3 a feed conduit 52 and a discharge conduit 54. :[n the chamber 50, a pluxality of rods 56 of circlllar cross-section are radially arranged ~or ro-tation about a central axis; they are supported by a circular rnounting plate 58 which is connected to the rotor 60 of motor 62.
An aqueous solution of surfactant 64 is introduced via the inlet 66 and is circulated into the system at a controlled flow rate by means of the purnp 68. The feed conduit 52 is provided wi-th four successive angularly bent portions 70, 72, 74 and 76, each o~ about 45.
The first angularly bent portion ~0 serves to impart to the stream a counter-rotating double macro-vortex.
A vane 78 is provided downstream oE the first bent por-tion 70 whereby to select one of the macro--vortices of the double macro-vortex. The three other bent por-tions 72, 74 and 76 serve to increase the rotational velocity of the selected macro-vortex. For low Reynolds nun~ers, the selected macro-vortex has a direc~ion of rotation which is the same as the direction of rotation of the rods 56, whereas for high Reynolds numbers the direction of rotation of the selected macro-vortex is opposite the direction of rotation of the rods 56.
Air is injected into the eye of the selected macro-vortex by means of the injector 80 in~ediately prior to the impingement on plate 58, resulting in a uniform two phase mixture in the region 82~ As the mixture enters the chamber 50, it is radially dis-persed by the rotating plate 58 and contacted by the rotating rods 56 which move transversely through the fluid. The micro-vortices are formed in the same manner as in the en~odiment of Fig. 1 and schemati-cally illustrated,in Fig. 2. The surfactant-stabi lized air bubbles 84 discharged from the chamber 50 are similarly allowed to travel a length 1, sufficient to provide the necessary time delay fc,r the hydration layer to completely develop, before a solution of collector 86 is added via the inlet 8~,~ The resulting aqueous DNF bubble mixture 90 is discharged at the outlet 92.
In the embodiment illustrated in Fig~ 3, i-t is possible to arrange several thousand rods 56 such that the total effective length lies in the range of from about 1,000 to abou-t lO,OQ0 inches.
As previously mentioned, the hydrat:ion layer in which the gas bubble is encapsulated contains water and a surfactant. When the amount of surfactant is at or slightly above the critical micelle concentration, the surfactant forms a monolayer at the gas to water inter-face. Since water is polar, it will become oriented in the vicinity of the surfactant layer to form one or more layers of polarized water molecules. Such layers of polarized water molecules are known to be in a form of ice, called "soft ice", having a densi-ty of 1.1 as compared with 1.0 for free water and 0.9 for the crystalline ice formed on freezing ("~nterfacial Phenomena", J. D. Davies and E. K. Rideal, Academic Press, 1961, page 364). The viscosity of "sof-t ice"
is of the order of 104 poises, decreasing away from the surface.
The properties of water when bound at a surface layer have been explored by several investi-gators. As noted above, the density of this water is ~1 _ ~

1.1 and its entropy of formation is 2.2 e.u. as com-pared with about 5 e,u, for ordinary ice, Perhaps the most striking evidence for the existance o-f -this extremely dense water is -the work of Dukhin and Shilov which have measured the dialectric constant of -the water film ("Dielec-tric Phenomena and the Double Layer in Disperse Syste~s and Polyelectrolytes", trans. by D. Lederman, John Wiley and Sons, New York, 1974).
The static value of the dialectric constant increases greatly as the layers of polarized water molecules form, when measured at low frequencies of the order of lOHz to lOKHz. This shows tha-t as in many systems such as quartz grains covered with a polar water layer, the relaxation time of the water molecules changes from that of water to that of ice as the layers of polarized water molecules form, and that each indivi-dual layer can be easily detected as it is formed.
Given the existence of an extemely viscous region in the hydration layer, one can see that the mi-gration of collectcr ions through such a layer would besubstantially impeded. Figs. 6a, 6b and 6c schema-tically illustrate the structure of a DNF bubble where the collector ions resulting from the dissociation of for example, alum (A12 (S04)3 18H20) are represented by the symbols ~ for A1~3 and ~ for S04 . As seen in Fig. 6a, the DNF bubble with a center at 100 has a spherical air core 102 surrounded by a monolayer 104a of anionic surfactant. The negatively charged heads of the anionic surfactant molecules polarize the kidney-shaped water molecules (probability model) _~/

'b resulting in the formation of a soft ice layer 106. The polarized water molecules impart to the Stern layer 108 (defined by the transition layer between bound and unbound rnolecules) a negative charge which attracts the A1~3 ions, resultiny in the formation of a mono-layer 110 thereof which is surrounded by a diffused layer or cloud 112 of the S04 ions~ It is to be noted that the stronger the charge of the surfactant heads is,the more layers 106 of polarized water molecules there would be and the longer would be the time delay until the collector ions reach the surfactant heads and react therewith.
Thus, the soft ice layer 106 allows a layer 110 of Al+ ions to form an exterior surface oE an anionic surfactant-stabilized bubble, which is held in place temporarily by the soft ice and located perhaps 10 water molecule layers above the actual surfactant layer 104a . Such an ionic layer would have no bonding beyond the Coulomb forces holding it in place. There would thus be a large tangential mobility for the collector ions so that the surface would tend to fill with like ions, and the oppositely charged ions would then form a cloud 112 outside this layer. It is to be ~urther noted that these collector ions are physically located to directly nucleate whatever species of con-taminant are introduced into the bubble region.
Exactly the same arrangement applies to the cationic surfactant-stabilized bubble represented in Fig. 6b and having a monolayer 104b of cationic sur-factant, except that the negative S04 ions would be _~

attracted by -the positivelycharge~ Stern layer instead of the A1~3 ions, forming -the monolayer 110'~ The Al~ ions would then be in the cloud ]12' around the bubble.
Similarly for the non-ionic surfactant-stabilized bubble shown in Fig~ 6c and having a mono-layer 104c of non-ionic surfactant, the layer 106 would consist of bound water molecules due to the combined charge in the surfactant heads and the hydrogen bonding that can form. In this case, the layer 114 of attracted ions would be a mixture, preserving the charge balance at neutral as is xequired.
When the surfactant concentration is raised considerably above the critical micelle concentra-tion so that sufficient surfactant is present to form much more surface area that is possible with the quantity of air present in the two phase mixture entering the micro-vortex forming and shedding system, then a plural-ity of layers of surfactant and soft ice can form. A DNF
bubble with such an arrangement of layers is schematic-ally represented in Fig. 7. The layers of surfactant always form in odd numbers due to the asymmetrical nature of the surfactant molecules. If, for instance, this surfactant has an oil soluble tail and a water soluble head then the gas to liquid interface would have a monolayer 104 of surfactant molecules interposed, with the oil soluble tails in -the gas and water soluble heads in the water forming one soft ice layer 106. A second layer 104' of surfactant can now form outside the first by having the water soluble heads of this second layer immersed in the soft ice layer 106 ou-tside -the -first surfactant layer 10~ and oriented oppositely to i-t, with the oil soluble tails directed ou-twardly. The oil soluble tails cannot rernain in -the outwardly di-rected position unless there is a third layer 104" ofsurfac-tant molecules with their oil soluble -tails in-wardly directed, coexisting in an oily region formed by the tails themselves and having outwardly directed water soluble heads immersed in an additional soft ice layer 106'~ Thus, one can make a bubble wi-th a sur-factant laden surface with one or three layers of sur-factant with a soft ice layer associated with the heads of each surfactant layer.
It will be realized that it is not possible to make a bubble with two surfactant layers, with oil soluble tails, since the outer layer must necessarily have its surfactant tails either in the soft ice layer developed by the innermost surfactant layer or in the water surrounding the outermost surfactant layer, neither event is possible and the same discussion holds true for any even number of surfactant layers.
Such a bubble configuration has the very great advantage that it can withstand the disruptive effects of waste species to collector reaction or collector to surfactant reaction, thus delaying the destruction of the bubble and even-tually providing much more surfactant which can be selected to have an affi-nity for specific species in the waste stream after -the collector ions have been used up. The ability to deliver a controlled amount of collector followed by a controlled amount of surfactant as a specific ion collector is advantageous in the trea-tment of water containing large amoun-ts of one specie of contaminant and smaller amounts of many others.
The application of the DNF bubbles -to the treatment of industrial waste waters is schema-tically shown in Fig. 8. The flow diagram of Fig. 8 represents a single stage water treatmen-t method. Surfactant-stabilized bubbles are produced by the ~ubble generator200 which is fed with an aqueous solution of surfactant and air via feed lines 202 and 204. The bubble mixture produced is passed through a delay lengt}l 206 so as to allow the hydration layer to completely develop before the collector is added via line 208, rrhe resulting DNF bubble mixture is passed to the turbulent mixer 210 where it is turbulently mixed with the contami-nated water which is fed via line 212. Prior to being mixed with the DNF bubble mixture, the pH of the con-taminated water is adjusted by adding a suitable saltvia line 214. The resulting mixture containing inso-luble reaction products is passed to the quiescent flotation chamber 216 where the insoluble reaction products separate as a floc which is buoyed to the surface of the water by large flotation bubbles pro-duced by the coalescence of smaller naked air buhbles which are released by the DNF bubbles upon rupturing.
rrhe floc is discharged via line 218 and clean water is recovered via line 220. A clean water recycle stream 222 can be provided to dilute the waste water so as to increase the effectiveness o:E -the water stripping process, if required.
It has been observed that when -the pH
adjustment is performed with a particular sal-t such as sodium hydroxide and when the collector used is a salt which will coat the surfactan-t-stabilized bubbles and also react with the salt used to adjust the pH of the waste water, a water repellant floc results which is highly effective in removing waste water contami-nants. Thus, if the pH adjust salt is sodium hyd:roxideand the collector is aluminum sulfate, and if the alu-minum sulfate and sodium hydroxide are presen-t in proportionsto completely collect the waste species and react with each other residues, a water repellant floc will result which will remain stable for several hours to several days~
Experiments with benzene ring compounds from waste water residues used in the manufacture of dye intermediate compounds showed color concentration of -~99%, but over two days, the dyes which were ini-tially collected diffused out of the floc. This illustrates that if two types of collector are used together, then a water repellant floc can be obtained which is stable long enough to effect a separation of the waste species from the water.
Fig. 9 schematically illustrates -the appli-cation of the DNF bubbles in a two-stage water treat-ment method. Waste water is fed via line 300 and is passed to the pH adjustment tank 302 where the pH is adjusted with a chemical addition to the inlet side v~

~3~

of the circulating pump 304 from a signal provided by the pH probe 306~ This pump recircu:Lates the contents of tank 302 to mix the chemicals used for pH adjust-ment with the waste stream and to provide a time delay S for the pH adjustment reactions to comp1eteO Since a complex waste s-tream at high concentration often con-tains strong buffering agents, a second similar pump 308 and tank 310 with pH probe 312 are provided to adjust the pH a second time. The preferred chemical for the pH adjustment is NaOH and the pH point to which the adjustment is to be made is determined empirically for each waste stream, based on the results of flota-tion tests. ~he discharge of the tank 310 is passed to the turbulent mixer 314 where a DNF bubble mixture from the gene.rator 316 is turbulently rnixed with the waste stream. The DNF bubble generator 316 is an embodiment of the invention such as the one shown in Fig. 3, wherein an aqueous solution of surfactant, air and collector are fed via lines 318, 320 and 322, respectively. Following the mixer 314, the combined waste and bubble mixture streams are passed to the quiescent flotation tanlc 324 where separation is effected by the coalesced residual naked ~ir bubbles left after the collector and waste species or the collector and surfactank have reacted and destr~yed the DNF bubbles. The water is discharged as partially c.leaned water via line 326 and the fLoc is discharged via line 328, containing a large portion of the contaminants.
The partly cleaned water is subjected to a second stage treatment and is passed via the line 326 to the -tank 310', where pump 308' and pH pro~e 312' are used to effect a pH adjustment to a second pH value also found by empirica] tests by means of flotation tests using the DNF bubble mix-ture. The presence of strong pH buffers in tank 310' is un:Likely, so only one pH adjustmen-t system would normally be used. ~he waste water partiall.y cleaned and pH adjusted for the second time is fed to turbulent mixer 314 7 where it is combined with a DNF bubble mixture formed in a se-cond DNF bubble generator 316' similar to generator316 of the first stage. The choice of surfactants and collectors for generators 316 and 316' depend only on the characteristics of the waste stream and can be any combination of anionic, cationic or non-ionic surfactants or mixtures thereof in either generator independently of the other. Following a similar reaction series in the mixer 314' to that which occurred in the mixer 314 modified by the choice of surfactants and collectors, the combined waste and bubble mixture streams are passed to the quiescent flotation tank 324' where the cleaned water and a second floc residue are discharged via lines 326' and 328'. The cleaned water which exists via line 326' is passed to .the tank 302' where the pH probe 306' and pump 304' effect a final pH adjustment, as required for the finally cleaned water which is discharged via line 330.
If alum is used as the collector or if a polyelectrolyte is used that like alum has a tendency to coat the interior surfaces of the system, then a system cleaning line 332 must be included. The inlet line 300 and outlet line 330 are closed when line 332 i5 open so that -the entire water c~ntent of the system is recirculated. The pH probe 306, 312 or 312' is used to raise the pH so as to return any solids deposited on the interior surfaces to the solut:ion state, from which they can be precipitated or collected and removed via the floc discharge lines 328 and 328' at a latter time.
The following non-limiting examples of preparation of DNF bubbles further illustrate the invention:

Use was made of a DNF bubble generator as illustrated in E'ig. 1, with the following parameters:
air/water ratio (volume) : 1:1 surfactant : 300 p.p.m. of Reynolds number : 500 rod diameter : 0,005 inch total effective rod length: 180 inches.
Collector : 100 p.p.m. of aluminum sulfate A DNF bubble mixture was ob-tained, in which the air buhbles had a size of about 12 to 20 ,u.

Use was made of the same DNF bubble gene-rator as in Example 1 with the same parameters, except that the rod diameter was increased to 0.01 inch and the total effective rod length to 222 inches.
As a result, a DNF bubble mixture was ob-tained in the air bubbles had a size of about 20 to 30 JU.

In order to obtain DNF bubbles having a narrowly distributed size in the range of from about 30 ;u to about 100 y, the rod diameter can be increased to about 0.02 inch or the amount of surfactant can be decreased from 300 to abou-t 150 p.p.m~

Use was made of a DNF bubble generator as illustrated in Fig. 3, with the following parameters:
air/water ratio (volume~
surfactant : 300 p.p.m. of speed of pump : 1840 rev./min.
direction of macro-vortex : the same as that of the rotor Reynolds number : 500 - 600 rod diameter : 0.005 inch total effective rod length : 3,500 inches revolution speed of rotor : 1840 rev./min.
rotor size ~ 5 inches time delay length : 2 feet collector : 100 p.p.m. of aluminum sulfate 20 gal./min. of a D~F bubble mixture were produced, in which the air bubbles had a size of about 12 to 20 jU,

Claims

The embodiments of the invention, in which an exclusive property or privilege is claimed, are defined as follows:-

1. A composition for the direct nucleation of materials which are dissolved or suspended in a hydrogen-bonded liquid, which comprises a discontinuous phase of gas in the form of surfactant-stabilized spherical bubbles having a narrowly distributed size in the range of from about 12 to about 100 microns and a half-life of at least about 2 minutes, each said gas bubble being encapsulated in a double surfaced hydration layer containing said hydrogen-bonded liquid and a soluble surfactant having a HLB ratio greater than about 10, said encapsulated gas bubbles being dispersed in a continuous phase of said hydrogen-bonded liquid and each having an outer surface layer of collector ions movably held to said hydration layer by Coulomb forces and active to react with said materials, said surfactant being present in an amount up to about 3 times critical micelle concentration so as to stabilize said bubbles and impart to said hydration layer sufficient thickness and viscosity to retard migration of said collector ions through said hydration layer for a period of time sufficient to enable said collector ions to react with said materials and cause nucleation thereof directly at said surface layers of said bubbles.

2. A composition as claimed in claim 1, wherein said gas is air and is present in an amount of up to about 80% by volume.

3. A composition as claimed in claim 2, wherein the amount of air is comprised between about 5 to about 80% by volume.

4. A composition as claimed in claim 1, wherein said gas bubbles have a size of about 12 to about 20 microns.

5. A composition as claimed in claim 4, wherein said gas bubbles have a half-life of at least about 1 hour.

6. A composition as claimed in claim 1, wherein said hydrogen-bonded liquid is water.

7. A composition as claimed in claim 6, wherein said surfactant is a water soluble anionic, cationic or non-ionic surfactant.

8. A composition as claimed in claim 7, wherein said surfactant is selected from the group consisting of alkali metal and ammonium lauryl sulfates, poly-oxyethylene derivatives of fatty acid partial esters of sorbitol anhydrides and surfactants based on alkylaryl polyether alcohols, sulfonates and sulfates.

9. A composition as claimed in claim 8, wherein said surfactant is a non-ionic surfactant available under the trademark TRITON X-100.

10. A composition as claimed in claim 7, wherein said water soluble surfactant has a HLB ratio of about 16 to about 18.

11. A composition as claimed in claim 7, wherein said gas bubbles have a size of about 12 to less than about 25 microns and wherein said hydration layer further contains an oil soluble surfactant, whereby when said bubbles rupture as a result of the nucleation reaction at said surface layers and of unreacted bubbles having a size above about 15 microns slowly increasing in size and reaching a size of about 25 microns, other unreacted bubbles also rupturing in time as a result of said col-lector ions having migrated through the respective hy-dration layer thereof and reacted with said water solu-ble surfactant, residual globules of said oil soluble surfactant with no residual gas core are formed which have a size of about 1 micron and act as further collec-tors of any oil soluble materials present in said water, thereby extending the range of materials to be collected.

12. A composition as claimed in claim 1, wherein said surfactant is present in an amount at or slightly above critical micelle concentration.

13. A composition as claimed in claim 12, wherein said surfactant is present in an amount of about 100 to about 300 p.p.m.

14. A composition as claimed in claim 12, wherein said surfactant is present in an amount of about 10%
above critical micelle concentration.

15. A composition as claimed in claim 1, wherein said surfactant is present in an amount of about 10%
less than critical micelle concentration.

16. A composition as claimed in claim 1, wherein said hydration layer has a thickness of about 10 to about 100 .ANG..

17. A composition as claimed in claim 7, wherein said hydration layer contains water in the form of soft ice having a viscosity of the order of 104 poises.

18. A composition as claimed in claim 17, wherein said hydration layer contains a plurality of successive layers of polarized water molecules.

19. A composition as claimed in claim 17, wherein said water soluble surfactant is present in an amount equal to about 3 times the critical micelle concentration thereof, whereby said hydration layer is multilayered and contains an innermost mono-molecular layer of surfactant and a double-molecular layer of surfactant spaced there-from with an inner soft ice layer between said surfactant layers and an outermost soft ice layer surrounding said double-molecular layer of surfactant.

20. A composition as claimed in claim 1, wherein said surface layer of collector ions is positively or nega-tively charged and acts as a Faraday cage to electri-cally screen said hydration layer.

21, A composition as claimed in claim 1, wherein the collector providing said collector ions is present in an amount of about 100 to about 500 p.p.m.

22. A composition as claimed in claim 1, wherein said hydrogen-bonded liquid is water and the collector providing said collector ions is a water soluble collec-tor selected from the group consisting of aluminum sulfate, alkali metal hydroxides and bicarbonates.

23. A composition as claimed in claim 22, wherein said collector is aluminum sulfate.

24. A method of preparing a composition for the direct nucleation of materials which are dissolved or suspended in a hydrogen-bonded liquid, which comprises the steps of:
- providing a flowing stream comprising a two phase mixture of gas and a solution containing said hydrogen-bonded liquid and a soluble surfactant which has a HLB ratio greater than about 10 and is present in an amount up to about 3 times critical micelle concentration;
- imparting to said stream a rotating laminar flow so as to form in said hydrogen bonded liquid a plurality of micro-vortices centrifugally entrapping said gas therein and allowing said micro-vortices to break into surfactant-stabilized spherical gas bubbles, said micro-vortex forming step being carried out under conditions to provide bubbles having a narrowly distributed size in the range of from about 12 to about 100 microns and a half-life of at least about 2 minutes, - providing a time delay so as to allow a hydration layer to completely develop on each of said sur-factant-stabilized gas bubbles formed;
- adding a collector providing collector ions active to react with said materials and allowing said ions to form an outer surface layer on the respective hydration layer of each said surfactant-stabilized gas bubble, said collector ions being movably held to said hydration layer by Coulomb forces.

25, A method as claimed in claim 24, wherein said gas is air and is present in said mixture in an amount comprised between about 5 to about 80% by volume.

26. A method as claimed in claim 24, wherein said hydrogen-bonded liquid is water.

27. A method as claimed in claim 26, wherein said surfactant is a water soluble anionic, cationic or non-ionic surfactant.

28. A method as claimed in claim 27, wherein said surfactant is selected from the group consisting of alkali metal and ammonium lauryl sulfates, polyoxyethylene derivatives of fatty acid partial esters of sorbitol anhydrides and surfactants based on alkylaryl polyether alcohols, sulfonates and sulfates.

29. A method as claimed in claim 28, wherein said surfactant is a non-ionic surfactant available under the trademark TRITON X-100.

30. A method as claimed in claim 27, wherein said water soluble surfactant has a HLB ratio of about 16 to about 18.

31. A method as claimed in claim 27, wherein said mixture further contains an oil soluble surfactant and the micro-vortex forming step is carried out under conditions to provide bubbles having a size of about 12 to less than about 25 microns.

32. A method as claimed in claim 31, wherein said water soluble surfactant and said oil soluble surfactant are present in said mixture in a weight ratio of about 1:1.

33. A method as claimed in claim 24, wherein said surfactant is present in said mixture in an amount at or slightly above critical micelle concentration.

34. A method as claimed in claim 27, wherein said water soluble surfactant is present in said solution in an amount equal to about 3 times the critical micelle concentration so as to provide a hydration layer which is multilayered and contains an innermost mono-molecular layer of surfactant and a double-molecular layer of sur-factant spaced therefrom with an inner soft ice layer between said surfactant layers and an outermost soft ice layer surrounding said double-molecular layer of sur-factant.

35. A method as claimed in claim 24, wherein said collector is added in an amount of about 100 to about 500 p.p.m.

36. A method as claimed in claim 24, wherein said hydrogen-bonded liquid is water and said collector is a water soluble collector selected from the group consisting of aluminum sulfate, alkali metal hydroxides and bicarbonates.

37. A method as claimed in claim 36, wherein said collector is aluminum sulfate.

38. A method as claimed in claim 24, wherein said micro-vortices are formed in a plurality of pairs of layers, each pair of layers comprising respective first and second layers which are spaced by a distance d, the respec-tive micro-vortices of said first and second layers being spaced relative to one another by a distance 1 with the micro-vortices of one of said layers being disposed inter-mediate two successive micro-vortices of the other layer.

39. A method as claimed in claim 38, wherein the distances d and l are selected such that the ratio d/l is equal to about 0.28.

40. A method as claimed in claim 24, wherein the micro-vortex forming step is carried out by subjecting said stream to micro-vortex forming and shedding means comprising a plurality of spaced apart substantially parallel stationary rods of circular cross-section disposed transversely to the direction of flow, under conditions to provide a Reynolds number in the range of from about 500 to about 5,000.

41. A method as claimed in claim 40, wherein said stream is caused to turbulently flow upstream of said micro-vortex forming and shedding means so as to provide a uniform two phase mixture.

42. A method as claimed in claim 40, wherein said rods have diameters of at least about 0.005 inch.

43. A method as claimed in claim 42, wherein the diameters of said rods are in the range of from about 0.005 to about 0.02 inch so as to provide gas bubbles having a narrowly distributed size in the range of from about 12 to about 100 microns.

44. A method as claimed in claim 42, wherein said rods define a total effective length in the range of from about 100 to about 500 inches.

45. A method as claimed in claim 40, wherein said two phase mixture comprises a mixture of air and water in a volume ratio of about 1:1 containing about 300 p.p.m.
of a non-ionic surfactant having a HLB ratio of about 13.5, and wherein the micro-vortex forming step is carried out at a Reynolds number of about 500 using rods having diameters of about 0.005 inch, whereby air bubbles having a size of about 12 to about 20 microns are obtained.

46. A method as claimed in claim 45, wherein said rods define a total effective length of about 180 inches.

47. A method as claimed in claim 40, wherein said two phase mixture comprises a mixture of air and water in a volume ratio of about 1:1 containing about 300 p.p.m.
of a non-ionic surfactant having a HLB ratio of about 13.5, and wherein the micro-vortex forming step is carried out at a Reynolds number of about 500 using rods having diameters of about 0.01 inch, whereby air bubbles having a size of about 20 to about 30 microns are obtained.

48. A method as claimed in claim 47, wherein said rods define a total effective length of about 222 inches.

49. A method as claimed in claim 24, wherein the micro-vortex forming step is carried out by subjecting said stream to micro-vortex forming and shedding means comprising a plurality of radially arranged rods of circular cross-section rotating about a central axis and disposed transversely to the direction of flow, under conditions to provide a Reynolds number in the range of from about 500 to about 5,000,

50. A method as claimed in claim 49, wherein said stream is caused to flow in the form of a macro-vortex up-stream of said micro-vortex forming and shedding means.

51. A method as claimed in claim 50, wherein said macro-vortex is caused to rotate in a direction which is the same as the direction of rotation of said rods.

52. A method as claimed in claim 50, wherein said macro-vortex is caused to rotate in a direction which is opposite the direction of rotation of said rods.

53. A method as claimed in claim 49, wherein said rods have diameters of at least about 0.005 inch.

54. A method as claimed in claim 53, wherein the diameters of said rods are in the range of from about 0.005 to about 0.02 inch so as to provide gas bubbles having a narrowly distributed size in the range of from about 12 to about 100 microns.

55. A method as claimed in claim 53, wherein said rods define a total effective length in the range of from about 1000 to about 10,000 inches.

56. A method as claimed in claim 51, wherein said two phase mixture comprises a mixture of air and water in a volume ratio of about 1:1 containing about 300 p.p.m. of a non-ionic surfactant having a HLB ratio of about 13.5, and wherein the micro-vortex forming step is carried out at a Reynolds number of about 500 to about 600 using rods having diameters of about 0.005 inch, whereby air bubbles having a size of about 12 to about 20 microns are produced.

57. A method as claimed in claim 56, wherein said rods define a total effective length of about 3,500 inches.

58. A method as claimed in claim 38, wherein said time delay is in the range of from about 10 to about 100 milliseconds.

59. A method of treating water containing dissolved or suspended materials to separate said materials therefrom, which comprises turbulently mixing said water with a composition as defined in claim 6 so as to cause nucleation of said materials at said surface layers of said bubbles, whereby the reaction between said collector ions and said materials causes said bubbles to rupture and to release their entrapped gas as naked gas bubbles and forms an insoluble reac-tion product, said ruptured bubbles exposing the sur-factant contained in the respective hydration layer thereof for reaction with any unreacted collector ions to form a further insoluble reaction product, any unreacted bubbles also rupturing in time as a result of said collector ions having migrated through the respective hydration layer thereof and reacted with said surfactant to form said further insoluble reaction product, and allowing both said insoluble reaction product and said further reaction product to separate from said water as a recoverable agglomerated material.

60. A method as claimed in claim 59, wherein the treated water containing said insoluble reaction pro-duct and said further insoluble reaction product is passed to a quiescent flotation chamber wherein both said reaction products are allowed to separate as a floc which is buoyed to the surface of the water with large gas bubbles formed by the coalescence of said naked bubbles with one another.

61, A method as claimed in claim 59, wherein the treated water containing said insoluble reaction product and said further insoluble reaction product is passed to a settlement chamber having a bottom, wherein at least said insoluble reaction product is allowed to separate under gravity to form a sediment layer at the bottom of said chamber.

62. A method as claimed in claim 59, wherein use is made of a composition in which said gas is air, said surfactant is a non-ionic surfactant having a HLB
ratio of about 13.5 and in which said air bubbles have a narrowly distributed size in the range of from about 12 to about 20 microns.

63. A method as claimed in claim 62, wherein said composition contains aluminum sulfate as collector providing said collector ions.

64. A method as claimed in claim 59, wherein use is made of a composition in which said gas bubbles have a size of about 12 to less than about 25 microns and in which the respective hydration layer of said bubbles contains in addition to a water soluble surfac-tant an oil soluble surfactant, whereby when said bubbles rupture as a result of the nucleation reaction at said surface layers and of unreacted bubbles having a size above about 15 microns slowly increasing in size and reaching a size of about 25 microns, other un-reacted bubbles also rupturing in time as a result of said collectors ions having migrated through the res-pective hydration layer thereof and reacted with said water soluble surfactant, residual globules of said oil soluble surfactant with no residual gas core are formed which have a size of about 1 micron and act as further collectors of any oil soluble materials present in said water, thereby extending the range of materials to be collected.

65. A method as claimed in claim 60, wherein use is made of a composition in which some of said encapsulated gas bubbles contain in the respective hydration layer thereof an amount of said surfactant which is slightly less than critical micelle con-centration, whereby said bubbles release more readily their entrapped gas so as to assist in the flotation of said reaction products.

66. A method as claimed in claim 60, wherein the pH of said water containing said materials is adjusted prior to being turbulently mixed with said composi-tion.

67. A method as claimed in claim 66, wherein said pH
adjustment is effected by adding to said water a water soluble salt which also reacts with the collector pro-viding said collector ions, whereby a water repellant floc is obtained.

68. A method as claimed in claim 67, wherein said water soluble salt is sodium hydroxide and said collector is aluminum sulfate.