CA1091830A - Wastewater flotation - Google Patents
Wastewater flotationInfo
- Publication number
- CA1091830A CA1091830A CA293,867A CA293867A CA1091830A CA 1091830 A CA1091830 A CA 1091830A CA 293867 A CA293867 A CA 293867A CA 1091830 A CA1091830 A CA 1091830A
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- water
- wastewater
- bubbles
- catch basin
- flocs
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- Separation Of Suspended Particles By Flocculating Agents (AREA)
- Physical Water Treatments (AREA)
Abstract
WASTEWATER FLOTATION
Abstract of the Disclosure:
A flow of wastewater is adjusted to near zero streaming potential by injecting a combination of a mineral acid and a multivalent metal coagulant into the wastewater.
The potential is measured in streaming detector units. The thus adjusted flow enters a coagulation cell for contacting the flow with dense quantities of small bubbles to form an initial floc. The flow then passes to a basin where a combined floc is separated and skimmed along the surface of the basin to a location generally above the entrance to the basin. A supplemental supply of bubbles preferably is maintained below the surface of the skimmings at this location in order to decrease the water content of the skimmings.
Abstract of the Disclosure:
A flow of wastewater is adjusted to near zero streaming potential by injecting a combination of a mineral acid and a multivalent metal coagulant into the wastewater.
The potential is measured in streaming detector units. The thus adjusted flow enters a coagulation cell for contacting the flow with dense quantities of small bubbles to form an initial floc. The flow then passes to a basin where a combined floc is separated and skimmed along the surface of the basin to a location generally above the entrance to the basin. A supplemental supply of bubbles preferably is maintained below the surface of the skimmings at this location in order to decrease the water content of the skimmings.
Description
lO9i830 Specification:
This invention relates to an improved method and appara-tus for floating particulates from wastewater.
The use of small diameter bubbles to float impurities rom a wastewater has been known as a valuable tool in reducing the level of particulates in minicipal and industrial waste-waters. For example, in the Ramirez, U.S. Patent No. 4,012,313 issued March 15, 1977 for Wastewater Treatment, there i8 dis-closed the use of a decreasing gradient of bubble densities to float particulates. This patent also recognizes that most wastewaters, especially those from meat treating operations or edible oil plants, have one common characteristic which must be overcome in clarifying these wastewaters. These wastewaters contain suspended, charged particulate matter which will not settle out on thelr own even if allowed to stand or months on ~i end. These particulates u~ually carry an electrostatic charge, ~ and it i~ recognized that in order to coalesce these particu-`~ latea, their charge must be substantially reduced.
-' In publications such as Komline et al, U.s. Patent ~ 20 No. 3,723,712 and Carlson, U.S. Patent No. 3,594,313, negative-. .
- ly charged wastewater particles are reduced to particles having approximately zero charge by adding to the wastewater quantities of coagulants that provide positive charges, such as metal chlorides, sulfates or salts. It is al~o known, for example from these two patents, that optimum particle charge reduction ;^ is accomplished when the zeta potential of the wastewater is ."~ ~
adjusted and maintained near a zero value. Generally, in these ~` patents the metal coagulants serve to neutralize the charge on the particles and then to coalesce them. It is also kno~n that these coalesced particles will form a buoyant floc when brought into contact with small bubbles. The buoyant floc may then be removed from the surface of the thus clarified wastewater.
These floc that are removed may be referred to as skimmings.
It has been found that systems that use significant amounts of metal coagulants are hampered in their effectiveness by the for-mation of large amounts of metal hydroxides that are collected in the skimmings. These metal hydroxides unfortunately bind not only the particulates but also substantial quantities of water so that the skimmings contain about 95 per cent water, meaning that the solids content of the skimmings is especially low. These binding properties also tend to increase the effort needed to "render" the skimmings when it is desired to recover valuable materials such as minerals, proteins, ~ats and oils ; present in the raw wastewater. Metal coagulants used in large quantitie3 also tend to taint the recovered materials with - residue from the metal coagulants and result in recovered pro-dùcts that may have an undesirable color.
When using only metal coagulants in many primary treat-ment system3, a relatively large volume of skimmings, on the order of 2 to 8 volume per cent of the wastewater treated, are produced. Likewise, the metal coagulants themselves are parti-~; 20 culate matter which add to the total suspended solids content , of the wastewater. Another disadvantage is that the cost of metal coagulants is high when compared with the cost of inorganic acids.
It i8 also known from another development of E.R.
Ramirez relating to Wastewater Clarification Utilizing Stream-.~
~ ing Potential Adjustment, that these disadvantages may be re-.;; .
duced significantly for certain types of wastewaters by adjust-ing their streaming potentials to near zero with only an inor-ganic acid or base that is not traditionally used as a coagulant.
~he above-noted Ramierez development is necessarily limited to certain wastewaters having soluble or insolulizable charged particulates. The invention of the present application is cap-
This invention relates to an improved method and appara-tus for floating particulates from wastewater.
The use of small diameter bubbles to float impurities rom a wastewater has been known as a valuable tool in reducing the level of particulates in minicipal and industrial waste-waters. For example, in the Ramirez, U.S. Patent No. 4,012,313 issued March 15, 1977 for Wastewater Treatment, there i8 dis-closed the use of a decreasing gradient of bubble densities to float particulates. This patent also recognizes that most wastewaters, especially those from meat treating operations or edible oil plants, have one common characteristic which must be overcome in clarifying these wastewaters. These wastewaters contain suspended, charged particulate matter which will not settle out on thelr own even if allowed to stand or months on ~i end. These particulates u~ually carry an electrostatic charge, ~ and it i~ recognized that in order to coalesce these particu-`~ latea, their charge must be substantially reduced.
-' In publications such as Komline et al, U.s. Patent ~ 20 No. 3,723,712 and Carlson, U.S. Patent No. 3,594,313, negative-. .
- ly charged wastewater particles are reduced to particles having approximately zero charge by adding to the wastewater quantities of coagulants that provide positive charges, such as metal chlorides, sulfates or salts. It is al~o known, for example from these two patents, that optimum particle charge reduction ;^ is accomplished when the zeta potential of the wastewater is ."~ ~
adjusted and maintained near a zero value. Generally, in these ~` patents the metal coagulants serve to neutralize the charge on the particles and then to coalesce them. It is also kno~n that these coalesced particles will form a buoyant floc when brought into contact with small bubbles. The buoyant floc may then be removed from the surface of the thus clarified wastewater.
These floc that are removed may be referred to as skimmings.
It has been found that systems that use significant amounts of metal coagulants are hampered in their effectiveness by the for-mation of large amounts of metal hydroxides that are collected in the skimmings. These metal hydroxides unfortunately bind not only the particulates but also substantial quantities of water so that the skimmings contain about 95 per cent water, meaning that the solids content of the skimmings is especially low. These binding properties also tend to increase the effort needed to "render" the skimmings when it is desired to recover valuable materials such as minerals, proteins, ~ats and oils ; present in the raw wastewater. Metal coagulants used in large quantitie3 also tend to taint the recovered materials with - residue from the metal coagulants and result in recovered pro-dùcts that may have an undesirable color.
When using only metal coagulants in many primary treat-ment system3, a relatively large volume of skimmings, on the order of 2 to 8 volume per cent of the wastewater treated, are produced. Likewise, the metal coagulants themselves are parti-~; 20 culate matter which add to the total suspended solids content , of the wastewater. Another disadvantage is that the cost of metal coagulants is high when compared with the cost of inorganic acids.
It i8 also known from another development of E.R.
Ramirez relating to Wastewater Clarification Utilizing Stream-.~
~ ing Potential Adjustment, that these disadvantages may be re-.;; .
duced significantly for certain types of wastewaters by adjust-ing their streaming potentials to near zero with only an inor-ganic acid or base that is not traditionally used as a coagulant.
~he above-noted Ramierez development is necessarily limited to certain wastewaters having soluble or insolulizable charged particulates. The invention of the present application is cap-
-2-, .
lO9i830 :
able of satisfactorily clarifying a wider variety of wastewaters. ~-It adjusts the streaming potential thereof to near zero by the combination of an inorganic acid and relatively small amounts of a multivalent metal coagulant, thereby lessening the diffi-culties encountered when metal coagulants only are used and ., , thereby removing many of the limitations of using only inorgan-ic acid or bases.
The above-noted Ramireæ development recognizes the re-lationship between streaming potential values and wastewater clarification. When used-herein, streaming potential values refer to streaming detector units which are qualitative approxi-mations of zeta potential values measured on a detector manu-facturea by Water Associates, Inc. of Framingham, Massachusetts.
There i~ a precise relationship between streaming units and zeta values, d~sclosed, for example, in Encyclopedial of Electrochemistry, editor Clifford A. Hampel, Rehinhold Publish-ing Corporation, New York, N.Y., 1964, at page 384.
The Ramirez and Johnson U.S. Patent No. 4,031,006 of June 21, 1977 for Vortex Coagulation Means and Method for Wastewater Clarification recognizes that superior initial floc ~ formation is achieved with a vortex chamber upstream of a -~ flotation basin. This patent does not, however, deal with the advantageous streaming potential adjustment of the present ,. lnvention.
The Ramirez U.S. Patent No. 3,969,203 issued November 13, 1976, for Dewatering of Wastewater Treatment Wastes, recognizes the advantages of dewatering ~kimmings. This particular patent iB restricted to dewatering operations carried out after the skimmings are removed from the apparatus in which they are formed. This can be at times disadvantageous by requiring an extra handling step. It has now been determined that dewatering can usually be accomplished in situ; that is, the skimmings can
lO9i830 :
able of satisfactorily clarifying a wider variety of wastewaters. ~-It adjusts the streaming potential thereof to near zero by the combination of an inorganic acid and relatively small amounts of a multivalent metal coagulant, thereby lessening the diffi-culties encountered when metal coagulants only are used and ., , thereby removing many of the limitations of using only inorgan-ic acid or bases.
The above-noted Ramireæ development recognizes the re-lationship between streaming potential values and wastewater clarification. When used-herein, streaming potential values refer to streaming detector units which are qualitative approxi-mations of zeta potential values measured on a detector manu-facturea by Water Associates, Inc. of Framingham, Massachusetts.
There i~ a precise relationship between streaming units and zeta values, d~sclosed, for example, in Encyclopedial of Electrochemistry, editor Clifford A. Hampel, Rehinhold Publish-ing Corporation, New York, N.Y., 1964, at page 384.
The Ramirez and Johnson U.S. Patent No. 4,031,006 of June 21, 1977 for Vortex Coagulation Means and Method for Wastewater Clarification recognizes that superior initial floc ~ formation is achieved with a vortex chamber upstream of a -~ flotation basin. This patent does not, however, deal with the advantageous streaming potential adjustment of the present ,. lnvention.
The Ramirez U.S. Patent No. 3,969,203 issued November 13, 1976, for Dewatering of Wastewater Treatment Wastes, recognizes the advantages of dewatering ~kimmings. This particular patent iB restricted to dewatering operations carried out after the skimmings are removed from the apparatus in which they are formed. This can be at times disadvantageous by requiring an extra handling step. It has now been determined that dewatering can usually be accomplished in situ; that is, the skimmings can
-3-be reduced in water content while being increased in relative solids content before they are removed from the apparatus that forms them.
It ha~ also been determined that, quite unexpectedly, an embodiment of the method and apparatus of this invention can cause ~ignificant reduction in the content of ions in waste-waters by transferring significant amounts thereof into the skimmings. While it is believed that this phenomenon itself had been at work, unrecognized, in systems of the type disclosed in said U.S. Patent No. 4,012,313 and in U.S. Patents No.
3,959,131, No. 3,969,245, and No. 3,975,269, this particular embodiment o the present invention accomplishes even better ion removal than that of these ~ystems.
Aacordingly, an object o thi~ invention i3 an improved method and apparatus for the flotation removal of charged par-ti¢ulates rom a wa~tewater while using relatively lower concen-trations of multivalent metal coagulants to form skimmings that are readily renderable, of increased solid to liquid ratio, and . .
of reduced relative volume.
It is a further object of the invention to provide an ~- improved method and apparatus to clarify wastewaters by means of forming skimmings having improved color and odor properties.
One other object of this invention is an improved method ~',!' and apparatus for clarifying wastewater by separating out skim-mings containing a large percentage of particulates and for in-creasing that percentage of particulates even further by dewater-... .
~ ing the skimmings in situ.
,
It ha~ also been determined that, quite unexpectedly, an embodiment of the method and apparatus of this invention can cause ~ignificant reduction in the content of ions in waste-waters by transferring significant amounts thereof into the skimmings. While it is believed that this phenomenon itself had been at work, unrecognized, in systems of the type disclosed in said U.S. Patent No. 4,012,313 and in U.S. Patents No.
3,959,131, No. 3,969,245, and No. 3,975,269, this particular embodiment o the present invention accomplishes even better ion removal than that of these ~ystems.
Aacordingly, an object o thi~ invention i3 an improved method and apparatus for the flotation removal of charged par-ti¢ulates rom a wa~tewater while using relatively lower concen-trations of multivalent metal coagulants to form skimmings that are readily renderable, of increased solid to liquid ratio, and . .
of reduced relative volume.
It is a further object of the invention to provide an ~- improved method and apparatus to clarify wastewaters by means of forming skimmings having improved color and odor properties.
One other object of this invention is an improved method ~',!' and apparatus for clarifying wastewater by separating out skim-mings containing a large percentage of particulates and for in-creasing that percentage of particulates even further by dewater-... .
~ ing the skimmings in situ.
,
-4-10 ~ i~ 3 0 An obj'ect of one embodiment of this invention is the provision of an apparatus and process that acc'omplishes significant reductions in thé content of certain adsorbable ions in wastewater ~imultaneously with:the'removal of par-ticulates~
This invention is an improved method:and apparatus for clarifying Mastewaters by flotation. A flow of wastewater containing charged particulate matter is adjusted to near its zero streaming potentiaL value'by adding an inorganic acid in combination with a metal coagulant. The adjusted wastewater flow'is thén directed to a confined flow path' ,that is .supplied with dense .quantities of 'small bub~les to form.an initial, or 'embryo,: IocO The mixed wastewater ~and embryo floc ,then passes,into a flotation zone'for fur~hér c'omb~ning thé,'embryo floc into a larger'more buoyant floc.
Positioned ab.ove.'.the.flotation zone'is a skimming means, , which'directs.,this floc toward ,the upstre'am:end of .thé
flotation zone,: thé'cl'arified wastewater exiting from thé, do.wnstre'am,end of thé flotation zonev' Preferabl'y, a.supple-' mental bubb'Ie',supply is pos.itioned:in said up.stream :end to thereby, dewater ,thé collected floc skimmings just before they pass .out of the flotation zoneO
~ dditi~nal obj'ects, if not aet fo,rth'specifically herein, will be'readily apparent to .those'skilled in thé art from *he'detailed description of the..invention which'follows and from ,thé.'d~awings, in which:' FIGURE 1 is a perspective view o thé,preferred apparatus of this.invention.
FIGURE 2.is a sch~matic. view 'of thé.apparatus of this:inventionO
FIGURE,3'is a plot o the tests discussed in Example'II, _5_ 1091~330 The method of this invention removes particulates from a flow of wastewater. The wastewater to be treated is mixed with a quantity of a multivalent metal coagulant to adjust the streaming potential toward zero, but still short of zero or almost zero. Ad~ustment to zero or almost zero is completed with an inorganic acid. The'thus adjusted wastewater pas~es through a confined flow path wherein it is intimately mixed with a dense supply of small bubbles that form an embyro floc of gas-particulate composites. The wastewater and embryo floc then flow together out of the confined flow path and into a long flotation zone. A larger, more buoyant combined floc is formed along the'top surface of the long flotation zone. This larger combined floc is ; skimmed along said surface toward its inlet end A supple-mental bubble supply i5 preferably provided below the'surface at said inlet end to dewater the skimmed floc before'it -~
leaves the flotation zone.
The preferred method clarifies industrial waste-' waters, the majority of which include negatively ch æ ged particulates. This -create~ a wastewater in which the re-pulsive forces of the charges maintain the particulates in ~;
suspension for extended periods of time.
A source'of multivalent metal ions is added to an industrial water to be'brought toward its zero streaming potential in order to significantly lower the repulsive forces. The preferred source of multivalent ions is ferric sulfate. Others include alum, ferric chloride and aluminum chloride.' For waters that are not exceptionally emulsified, '' the concentration of the multivalent ions is very low, on ' 30 the order of from about 0.1 to 2 millimolar, usually 0.1 to 1.0 millimolar, with respect to the multivalent ion.
However, for waters that are particularly difficult to treat, such as highly emulsified waters from laundries, '' ~O ~ i ~ 3 0 significantly greater concentrations of the added chemicals, especially the multivalent metal coagulant, are needed.
This will break the emulsion as well as lower the charges on the particulates. Concentrations as high as 15 millimolar, or even higher, may be required for satisfactory primary treatment of such waters. Thus, the concentration of added multivalent metal coagulant could be between about 20 ppm and 4000 ppm or more.
- Between about 100 ppm and 1500 ppm of a mineral acid is also added to act in combination with the multivalent ions to achieve the final streaming potential ad;ustment to :~ near zero~ The preferred mineral acid is-su~phuric acid.
Other suitable mineral acids include hydrochloric acid. The acid i8 added to bring the hydrogen ion concentration between ~; about 2 to 30 millimolar, usually 4 to 12 millimolar.
This combination of inorganic acid and multivalent coagulant brings with it two important advantages: the extent of clarification is increased, and the treatment time is decreased when compared with processes that use only a mineral acid to adjust the charge. Additionally, when - the subsequent steps of this method utilize electrolytic means to supply the bubbles, the amount of electric power - needed to clarify a ~olume of wastewater is decreased, ., usually by greater ~han 50 per cent.
On a ~olar basis, the ratio of multivalent ions to hydrogen ions usually will be no greater than 1 to 1 even for highly emulsified water and can be as low as 1 to 100 for waters that exhibit very little emulsification. Generally, ~ most waters can be treated successfully with a molar ratio ;~ 30 of trivalent metal ions to hydrogen ions between 1 to 50 and 1 to 2.
With the streaming potential near zero, the parti-culates are no longer charged or carry only very low charges.
lOgl~3~
This means that the charge repulsion present among the particulates prior to treatment has been removed or at least substantially lessened. Without this adjustment, the parti-culates will remain dispersed throughout the wastewater and will be resistant to the bubble treatments of the subsequent steps. The streaming potential adjustment markedly increases the tendency of the particulates to unite and grow with the small bubbles to readily form the desired floc.
In the next step of this method, the streaming potential adjusted wastewater flows into the confined flow path, for forming the initial, or embryo, floc, depicted in FI~URE 1. The preferred confined flow path is an upward vortex, but other path configurations that enhance mixing ; and coagulation may be used, such as those mentioned in U.S.
Patents No~ 3,959,131 and No. 3,969,245.
A dense supply of small bubbles also flows into the'confined flow path. The density of this supply is such that the bubbles comprise 1/2 to 6 volume per cent of the ' wastewater in the confined flow path'for adequate embryo, floc formation, generally within about 1 to 5 minutes.
These bubbles may be provided by the in-line dispersing of ' air bubbles, by electrolytic decompostion of water, or by pressurized gas dissolution. The bubbles should have a diameter of between 30 to 500 microns, preferably 50 to 200 microns. They should be provided in densities preferably between about 106 and 109 bubbles per liter of water being `' treatedO Dispersion techniques often are the most cost efficient.
In an optional step, a polymer flocculant may be ' 30 added after the embryo floc and wastewater flow together ; out of the confined flow path'and into the long flotation zone. This feature usually noticeably improves the consistency of the overall process by increasing the stability of the - ~09i83~
floc composites formed, making them less susceptible to being damaged during the subsequent separation procedure.
A~y po}ymer flocculant (anionic, cationic, or nonionic) may be uQed in concentrations between about 1/2 and 15 ppm. The preferred polymers are polyelectrolytes in the form of polyacrylic acrylamides, which are copolymers of from about 50 to 90 weight per cent acrylamides or methacrylamides, and from about 10 to 50 weight per cent acrylic or methacrylic acid or water soluble salts thereof. These polymers are characterized by weight average molecular weights of about 2 million and usually the molecular weights range between about 7 to 12 million a~ measured by light scattering techniques The preferred concentration range for the polymer flocculant is between about 1 to 3 ppm, although it could be as high as 20 ppm or higher for highly emulsified waters Irrespective of the makeup of the gas-solid composites formed in the preceding steps, the next step in the present method begi~s the`process of separating the two-phase composites from the`wastewater. Thé wastewater and the composites mixed therein flow together into the long flotation zone.
Preferably, additional bubbles are provided from the bottom of at least the upstream portion of the zone for assisting ; in the flotation separation of the buoyant floc composites These additional bubbles may be supplied by electrolytic , decompostion of water. They also may be provided by gases dissovled in water. These bubbles can be provided in a pattern that gradually decreases in density in the downstream direction. The decrease may be geometric.
The use of electrolytic bubbles, particularly in the long flotation zone, often has a particular advantage of reducing the amount of certain adsorbable ions that might be present in the raw wastewater. Such ions include _g_ ' 109i83~
ammonia-nitrogen, cyanide, phenols, polybrominated biphenyls, and various other organic toxic pollutants. The reduction ifl significant, with these ion values being enriched in the floc. The degree of reduction may be reported as a partition coefficient, defined as the concentration of ions in the fLoc phase over the concentration of ions in the mother liquor, here the wastewater. This feature results in a partition coefficient in excess of 30/1.
The reason for this highIy beneficial phenomenon 10 is not presently known. The following is offered as an ` hypothesis. Hydrogen bubbles appear to act as a catalyst in ; that they attach to the particulates to form some of the two-phase composites, hydrogen being the gas phase. It is postulated that ions are thén adsorbed, either physically, chemically, or by ion exchange, onto the solids at the gas-solid interphase. When these two-phase composites enter the skimmings later on in this method, these values are thus removed from the wastewater. It is further postulated that ^` some ions that are not so adsorbed are destroyed by electro-20 lytic action.
- Within thé long flotation zone as a whole, the r combined floc, which is depicted in FIGURE 1, rises to thesurface to form the skimmings, and the clarified wastewater flows the length of the zone and out at its downstream end.
` As an optional feature, this operation may be assisted by ~ vertical, perforated baffles placed transverse to the flow ; throughout the long flotation zone. Such baffles have from about 30 to 80 per cent, prefera~ly from 50 to 60 per cent uniform free passage therethrough as the wastewater flows 30 downstream through the zoneO They usually significantly reduce turbulence, channelling and back diffusion within the zone which would deveIop if the baffles were not present and - which would cause disruption of the separation process to :
10 ~ i 8 3 0 decrease the final clarity of the wastewater.
The in situ dewatering method of this invention provides a supplemental supply of bubbles at a location that i~ below the accumulation of skimmings at the inlet end of the long flotation zone. Adequate dewatering of the skimmings to a solids content between about 15 and 30 weight per cent usually takes place if the bubbles are supplied in the approximate range of about 0.1 to 2 cubic feet of bubbles per hour per square foot of the horizontal area of the supplemental supply.
For most efficient operation, the bars of the skimmer must be below the surface of the water for substantially the entire length of the long flotation zone, which surface can be kept generally at the same height by a weir structure.
m e skimmer may be tilted slightly, but the bars themselves should not be above the surface of the accumulated skimmings in order to prevent the bars from forcing the skimmings down into the basin. There should be no substantial obstruction between the bars so the skimmings can be'free to have appreci-able vertical movement. The skimmer should move at a slow speed, generally no faster than 3 feet per minute and prefer~
ably on the order of 5 to 12 inches per minute, so the skimmings will remain in the'dewatering region for a significant length'of time to increase the ability of the supplemental bub'bles to displace water from the skimmings which can rise to well above the water surface to be skimmed off by the bars. For particularly effective dewatering, the skimmer can be advanced intermittently only. This permits batches of skimmings to be dewatered in situ for extended periods of time when they are not being moved horizontally through the dewatering region The polymer flocculant that is added can be increased to between 2 and 25 ppm to further improve dewatering. Thé preferred range is 4 to 10 ppm -` 1091~30 ' A further optional step in the method of this inven- ~-tion i8 the addition of a strong base such as lime into the water after the completion of the streaming potential adjustment to approximately zero and before the water enters the confined flow path. Thi8 step, which raises the pH, can bring about three distinct advantages. It brings the pH back up to a value that is within acceptable'governmental pH discharge standards, usually between 6 and 9. It significantly reduces acid damage to the equipment~ When the water being treated contains heavy metals, the higher pH will enhance the'formation of hydroxides o many of the heavy metals, which'hydroxides are usually in-soluble particùlates that will be passed into the skimmings.
The concentration of strong base added for this third advantage should be adequate to raise'the'pH to between about 7 and 10, preferably between 7,5 and 9, The FIGURE 1 perspective view of the preferred appar-' atus, génerally referred to ~y reference numeral ll, illustrates the' bubble formation means 12, 13 and 14 as electrode'pairs.
Other methods of bubble'formation, discussed elsewhere herein, }~.
, 20 are intended to be'depicted by reference numerals 12, 13 and 14.
Also as diseussed herein, bubble formation means-13 is provided when in situ dewatering is to be'performed, and bubble formation means 14 is optional. Generally, the water to be treated enters '' inlet 15; the clarified water exits through outlet 16; and the ' skimmings are collected in trough'l7.
Inlet 15 preferably opens into a holding tank 18 op-tionally outfitted with'a mixing means 19 or promoting unifor-' mity in the makeup of ~he water within holding tank 18. Both `' tank 18 and means 19 increase the efficiency of the overall process by permitting more'consistent and accurate streaming potential adjustments, which'may be monitored by a probe 21.
Probe'21 is preferably a streaming detector; it may also be a .
10~1830 p~ reading device if used in conjunction with other means (not ShOWIl) for correlating the near zero zeta or streaming potential reading of the incoming water with pH values.
Opening into holding tank 18 are injectors 22 and 23, one for adding the mineral acid and another for adding the multi-valent metal coagulant. A conduit 24 communicates the streaming potential adjusted water with a coagulation cell 25. CeIl 25 contacts and mixes this water with dense quantities of small bubbles, preerably in the upward vortex motion depicted, to thereby form the embryo floc. Another conduit 26 communicates the coagulation cell 25 with the catch basin 27. A further in-jector 28 may open into conduit 26. It optionally opens either into the basin 27 through its upstream wall 29 or into both conduit 26 and through wall 29. Injector 2~ adds polymer floc-culant when included to assist in situ dewatering and/or to form the combined floc as depicted.
When bubble formation means 13 is desired, it is at the upstream end of basin 27 and i8 below the surface of the water and skimmings in basin 27. When means 13 i8 below conduit 26, bubbles supplied théreby also help in floating the floc in the basin 27. This is -generally acceptable when means 13 sup-plies dissolved air bubbles, which resist coalescing as they rise the height of basin 27. Electrolytic bubbles have a greater tendency to coalesce into bubbles that are too large for effective dewatering if they have to travel substantial heights through water. When means 13 is electrolytic, it should be at a depth not in excess of about 3 feet. ~1hen means 13 is above conduit 26, it should not excessively obstruct the flow of floc. One way of reducing any obstruction is by mounting the electrodes longitudinally of the flow into basin 27.
Optionally present for assisting in the flotation of the combined floc may be the bubble formation means 14, 109i830 which is located near the bottom surface of basin 270 Means 14 is less likely to be needed if means 13 is below conduit 26. A skimmer 31 moves the skimmings up the angled beach toward trough 17. This allows additional water to run down the beach lnto basin 27 to increase skimmings dewatering. A
recycle member 32 may be provided for supplying clarified water for use in the bubble formation means 12.
FIGURE 2 is a schematic view of the apparatus. It '' shows a bubble formation mean~ 12 that is an in-line'disperser which economically and effectively disperses a gas supply as small bubbles into a liquid supply. The short arrow line to means 12 is the'gas supply, preferably a supply of air.
, The drawing shows different paths by which the "-, liquid supply can be provided to means 12. The liquid supply may be from the recycle member 32, which recycles as much as abou~ 50, often about 10 to 20 volume per cent of ~' , the water flowing through'the total apparatus 11, preferablyabout 15 per cent. The'liquid supply may be from conduit 24 ', 20 through by-pass 33. When conduit 24 does not open into cell 25, such as by closing a valve 34, the entire flow ~,` through inlet 15 passes through means 12. Otherwise, it is -' possible to have'only a portion of the flow pass into means 12 to provide the liquid supply.
"'' The means 12 may supply the required density and ~,' size'of bubbles by dissolving gas bubbles under pressure ~' within the liquid. Such a structure is depicted for bubble ~ . .
formation means -13'in FIGURE 2. The bubble'supply surface formed by means 13'has a length L that is about one-fourth the length of the entire basin 27. A tilt of skimmer 31 is depicted. Also shown is a phantom line drawn between ;~, the outer tips of skimmer bars 41. The tilt is such that '' this phantom line is below the skimmings surface for a dlstance "a" at the upstream end and is below the skimmings surface for a distance "b" at the downstream end of basin -;
27. Preferably, distances a and b are relatively small, on t~e order of one inch for a and no more than the depth of a skimmer bar for b. When the in situ dewatering is in operation, it i8 common for the dewatered skimmings to bunch up approxi-mately along length L, often until they actually cover portions of the skimmer bars 41 at the inlet end. A weir box 42 helps maintain these relative distances that assist the dewatering function. Weir box 42 may include a height-adjustable wall 43O' ' In the structure shown in FIGURE 2, the floor of basin 27 has a depression 44. An optional bottom drag member 45 operates to pass any especially large or heavy materials from the bottom of basin 27 into the depres~ion ' 44. An angular barrier 46 preferably is provided. It ,~ allows clearnace for drag member 45 and improves the'flotation - efficiency of the basin 27 and of the means 13. Perforated ba~fles 47 may also be located transverse'to the flow through ~' 2Q the basin 27.
;" The following Examples are set forth as illustrative ' embodiments of the invention and are not to be'taken in any manner as limiting the scope théreof as defined by the appended claims.
E X A M P L E
A packinghouse'wastewater was used to demonstrate '' on a bench'scale the effects of the combination of mineral acid and trivalent ions on streaming potential readings and on subsequent electrolytic purification. The physical characteristics of this raw wastewater varied with numerous collections between the'following values: total BOD, from 1500 to 2500 ppm; suspended solids, from 1200 to 1800 ppm; hexane extractables, from 600 to 1,000 ppm; and .' , .
turbidity (in Jackson turbidity units), from 800 to 1,100units. The pH of the raw wastewater was 7.5. This was treated by a series of chemical additions varying from pure slllfuric acid to pure ferric sulfate as a means of adjusting the wastewater to a zero streaming potential. It was found that the pH value observed at zero streaming potential of the treated wastewater varied depending upon the chemicals used to attain zero streaming potential.
This Example illustrates results that may be obtained when minimum quantities of metal coagulants are added in conjunction with the inorganic acid in adjusting to near zero streaming potential. The combinations are listed below, along with an indication of the pH recorded at zero streaming potentialO Also recorded are the turbidity values (in Jackson turbidity units) achieved when using electrolysis at a relatively low total value o 4.0 ampere-minùtes per gallon of wastewater. Runs No. 2 and 3 used the process of this invention. The results show improved turbidity of the treated water when compared with Run No. 1, which used only mineral acid. The results also show significantly lower volumes of skimmings for Runs No. 2 and 3 when compared , with Run No~ 4, which used only a trivalent metal coagulant instead of the combination of this invention. It should be emphasized that these were bench scale tests when looking at the skimmings volumes below. The reported volumes are for relative comparisons between Runs 1-4. The reportèd absolute ~ values are significantly higher than those observed during :~! full-scale operations.
Sulfuric Ferric pH at Skimmings-Volume %
Run Acid Sulfate Zero Zeta Turbidity Wastewater . 30 No. Added Added Potential (JTU) Treated 1 400 ppm 0 ppm 4.7 540 1.2 , 2 325 ppm50 ppm 4O8 360 2.5 3 300 ppm100 ppm 4.9 90 3.1 4 0 ppm 600 ppm 5.2 20 7O5 .: ~
109~830 E X A M P L E II
Using the same wastewater of Example I, tests similar to those of Example I were conducted, this time ~arying the total electrolysis power used in the process.
The following results were tabulated:
Sulfuric Ferric Power Input Run Acid Sulfate (Amp. Min./ Turbidity No. Added ~dded Gal.) (JTU) -5a 300 ppm 0 ppm 4 500 5b " " ~ 270 5c " " 12 80 6a 250 ppm 100 ppm 4 90 6b " " 8 80 6c " " 12 35 ; 7a 0 ppm 600 ppm 4 50 ; 7b " " 8 35 7c " " 12 20 These same resultæ are also plotted in FIGURE 3.
The initial pH of the water at the time these tests were run was 7.8. Its initial streaming potential was -20Ø The turbidity reading before treatment was 800 JTU. Run Nos. 6 were in accordance with the process of this invention.
- FIGURE 3 dramatically illustrates the increased power use to turbidity reduction efficiency that results in Run Nos. 6 when compared with Run Nos. 5. In addition, a corresponding efficiency comparison between Run Nos. 7 and Run Nos. 6 is rather favora~le. Run Nos~ 6, however, did not exhibit the ~, undesirable increase in skimmings volume shown in Run Nos.
7, which were on the order of Run No. 4 of Example I.
E X A M P L E III
Water from another meat packinghouse was treated in accordance with the preferred process and in the preferred apparatus. The raw water had averaged analyses of 3000 mg/l ; BOD, 1300 mg/l suspended solids, 1000 mg/l FOG (fats, oils iO~1830 and greases) and a p~l of 7.6. The streaming potential was adjusted to near zero with treatments that varied with the surging flow through this full-scale, on-stream operation.
~he treatment ranges were: 50-125 mg/l ferric sulfate and 100-225 mg/l sulfuric acid, the pH after adjustment being an average of 4.50 Electrolysis using between 1300-2100 amperes of current provided the bubbles into the coagulation cell, followed by 2-4.5 mg/l of the preferred polymer. The influent pumping rate of the water treated was between 800-850 gallons ~ 10 per minuteO Dissolved air bubbles were supplied into the ; catch basin below the inlet for dewatering and floc flotation, the water for dissolving being recycyled clarified water in a volume of about 400 gallons per minute, the pressurization being 60 psi. Averaged samples of the clarified water had , . . .
398 mg/l BOD, 105 mg/l total suspended sollds, and 18 mg/l FOG. The in situ dewatered s~immings had a solids content '; of between 15 and 30 weight per cent.
r~ E X A M P L E IV
Tests not in accordance with this invention were 20 carried out in the same manner, on the same apparatus, and t on the same industrial effluent as Example III. The combination of mineral acid and multivalent metal coagulant was not - used. Used was 75-225 mg/l of sulfuric acid to adjust to ., ,' near zero streaming potential, the pH being 5.4. Also added was about 2 mg/l of the preferred polymer. Averaged samples of the clarified water analyzed as 797 mg/l BOD, 470 mg/l total suspended solids, and 166 mg/l FOG.
, E X A M P L E V
; Another series of tests not in accordance with 30 this invention were conducted as in Example III. The treatment prior to the coagulation cell was with 100-400 mg/l ferric ` ~- sulfate, and the near zéro s-treaming potential was at a pH
of about 6.5. The preferred polymer was added in concentrations ; -18-lO 9 i 8 ~ 0 between 3 and 4.5 mg/l. The treated water showed 327 mg/l BOD, 85 mg/l total suspended solids, and 31 mg/l FOG.
E X A M P L E VI
A further set of tests similar to tho~e of Example V
were conducted, this time using 150-400 mg/l of alum instead of the ferric sulfate, the adjusted pH being 6O7. Between 2-4 mg/l of the preferred polymer was added. The clarified water showed 611 mg/l BOD, 537 mg/l total suspended solids, and 311 mg/l FOG.
E X A M P L E VII
' Pilot plant tests were run at about 10 gallons perminute on a very highly emulsified water from a commercial t laundry for industrial shop towels. The equipment used was along the lines of FIGURE 1, except that the water flowed through the electrodes in the coagulation cell, which was tubular in shape, The water had a pH of 12, had 14,000 ppm COD, had 3,478 ppm suspended solids, had 2,869 ppm hexane extractables (Fats, Oils and Greases), had 11 ppm of lead, had 4 ppm of zinc, and had a turbidity reading of 18,000 JTU. The'streaming potential was -2Q streaming units.
The current to the'cell was 75 amps at 12 volts. The current to the basin was 35 amps at 6 volts.
First 3000 ppm alum was added. When 1,000 ppm of sulfuric acid was thén added, the pH was lowered to about 4, ~' at which time the streaming potential was approximately zero, and most of the charge was removed fr~m the particulates.
The pH was then raised with'500 ppm of lime in order to meet governmental discharge pH standards; in order ta prevent acid damage to the coagulation cell, the basin and other portions of the apparatus; and in order to enhance the formation of heavy metal hydroxides which could be passed into the skimmings. Between the ceIl and the basin, 15 ppm '~ polymer was injected into thé'flow of embryo floc and water.
109~30 : The thus treated water had a pH of 7.5, had 605 ppm COD, had 155 ppm suspended solids, had 13 ppm hexane extractables, had 0.17 ppm of lead, had 0.06 ppm of zinc, and had a turbidity reading of 300 JTU.
E X A M P L E ' VIII
Pilot tests along the lines of Example VII were ~' run on a laundry water from painters' and printers' towels .' which had a pH of 11.5, had 16,000 ppm COD, had 3,980 ppm ~.
'.~ suspended solids, had 2,.543 hexane extractables J had 9.1 ppm ~:
; 10 lead, had 4.0 ppm zinc, and had a turbidity reading of ' 25,000 JTU. Treatment used 4,000 ppm alum and 1,500 ppm ~ :' ';.~ sulfuric acid to adjust .the' streaming potential to -l streaming units. Also added were 700 ppm lime, and 2Q ppm of the . ~-~- preferred polymer flocculantO Thé'clarified water had a pH
... . ..
:.'. o 7.9, 1,490 ppm COD, 57 ppm ~uspended solids, 92:ppm ~ :`
hexane'extractables, 0.60 ppm lead, 0.16 ppm zinc, and turbidity readings of between 300 and 500 3TU.
-" E X A M P L' E IX .
Additional pilot tests according to Example'VII ' .' 20 were.'conducted on a water that combined flows of Example' i VII water, of Example'VIII water, and of a general wastewater.
"~; ~ It had a pH of ll.6, 6480 p'pm COD, 1610 ppm suspended solids, ' 1540 hexane'extractables, 6.9 ppm lead, and 2.0'ppm zinc.
- .
In this series of tests, the ~object was to bring the'hexane extractables to below municipal standarda of 250 ppm. Added were'2,.000 ppm alum, 800-ppm .sulfuric acid, to adjust to .
. ~ -0.5 streaming units, followed by 250 ppm lime, and 15 ppm . of the polymer fl'occulant. The'clarified water had a pH of 7.8, 925 ppm COD, 250 ppm suspended solids, 110 ppm hexane . 30 extractables, 0.4 ppm lead, 0.4 ppm zinc, and turbidity readings between 500 and 600 JTU.
-- Ob~iously, many difications and variations of the invention as hereinbefore set forth may be made without . -20-. . ~
10~31~330 departing from the spirit and scope thereof, and only such llmitations should be imposed as are indicated in the appended claims.
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This invention is an improved method:and apparatus for clarifying Mastewaters by flotation. A flow of wastewater containing charged particulate matter is adjusted to near its zero streaming potentiaL value'by adding an inorganic acid in combination with a metal coagulant. The adjusted wastewater flow'is thén directed to a confined flow path' ,that is .supplied with dense .quantities of 'small bub~les to form.an initial, or 'embryo,: IocO The mixed wastewater ~and embryo floc ,then passes,into a flotation zone'for fur~hér c'omb~ning thé,'embryo floc into a larger'more buoyant floc.
Positioned ab.ove.'.the.flotation zone'is a skimming means, , which'directs.,this floc toward ,the upstre'am:end of .thé
flotation zone,: thé'cl'arified wastewater exiting from thé, do.wnstre'am,end of thé flotation zonev' Preferabl'y, a.supple-' mental bubb'Ie',supply is pos.itioned:in said up.stream :end to thereby, dewater ,thé collected floc skimmings just before they pass .out of the flotation zoneO
~ dditi~nal obj'ects, if not aet fo,rth'specifically herein, will be'readily apparent to .those'skilled in thé art from *he'detailed description of the..invention which'follows and from ,thé.'d~awings, in which:' FIGURE 1 is a perspective view o thé,preferred apparatus of this.invention.
FIGURE 2.is a sch~matic. view 'of thé.apparatus of this:inventionO
FIGURE,3'is a plot o the tests discussed in Example'II, _5_ 1091~330 The method of this invention removes particulates from a flow of wastewater. The wastewater to be treated is mixed with a quantity of a multivalent metal coagulant to adjust the streaming potential toward zero, but still short of zero or almost zero. Ad~ustment to zero or almost zero is completed with an inorganic acid. The'thus adjusted wastewater pas~es through a confined flow path wherein it is intimately mixed with a dense supply of small bubbles that form an embyro floc of gas-particulate composites. The wastewater and embryo floc then flow together out of the confined flow path and into a long flotation zone. A larger, more buoyant combined floc is formed along the'top surface of the long flotation zone. This larger combined floc is ; skimmed along said surface toward its inlet end A supple-mental bubble supply i5 preferably provided below the'surface at said inlet end to dewater the skimmed floc before'it -~
leaves the flotation zone.
The preferred method clarifies industrial waste-' waters, the majority of which include negatively ch æ ged particulates. This -create~ a wastewater in which the re-pulsive forces of the charges maintain the particulates in ~;
suspension for extended periods of time.
A source'of multivalent metal ions is added to an industrial water to be'brought toward its zero streaming potential in order to significantly lower the repulsive forces. The preferred source of multivalent ions is ferric sulfate. Others include alum, ferric chloride and aluminum chloride.' For waters that are not exceptionally emulsified, '' the concentration of the multivalent ions is very low, on ' 30 the order of from about 0.1 to 2 millimolar, usually 0.1 to 1.0 millimolar, with respect to the multivalent ion.
However, for waters that are particularly difficult to treat, such as highly emulsified waters from laundries, '' ~O ~ i ~ 3 0 significantly greater concentrations of the added chemicals, especially the multivalent metal coagulant, are needed.
This will break the emulsion as well as lower the charges on the particulates. Concentrations as high as 15 millimolar, or even higher, may be required for satisfactory primary treatment of such waters. Thus, the concentration of added multivalent metal coagulant could be between about 20 ppm and 4000 ppm or more.
- Between about 100 ppm and 1500 ppm of a mineral acid is also added to act in combination with the multivalent ions to achieve the final streaming potential ad;ustment to :~ near zero~ The preferred mineral acid is-su~phuric acid.
Other suitable mineral acids include hydrochloric acid. The acid i8 added to bring the hydrogen ion concentration between ~; about 2 to 30 millimolar, usually 4 to 12 millimolar.
This combination of inorganic acid and multivalent coagulant brings with it two important advantages: the extent of clarification is increased, and the treatment time is decreased when compared with processes that use only a mineral acid to adjust the charge. Additionally, when - the subsequent steps of this method utilize electrolytic means to supply the bubbles, the amount of electric power - needed to clarify a ~olume of wastewater is decreased, ., usually by greater ~han 50 per cent.
On a ~olar basis, the ratio of multivalent ions to hydrogen ions usually will be no greater than 1 to 1 even for highly emulsified water and can be as low as 1 to 100 for waters that exhibit very little emulsification. Generally, ~ most waters can be treated successfully with a molar ratio ;~ 30 of trivalent metal ions to hydrogen ions between 1 to 50 and 1 to 2.
With the streaming potential near zero, the parti-culates are no longer charged or carry only very low charges.
lOgl~3~
This means that the charge repulsion present among the particulates prior to treatment has been removed or at least substantially lessened. Without this adjustment, the parti-culates will remain dispersed throughout the wastewater and will be resistant to the bubble treatments of the subsequent steps. The streaming potential adjustment markedly increases the tendency of the particulates to unite and grow with the small bubbles to readily form the desired floc.
In the next step of this method, the streaming potential adjusted wastewater flows into the confined flow path, for forming the initial, or embryo, floc, depicted in FI~URE 1. The preferred confined flow path is an upward vortex, but other path configurations that enhance mixing ; and coagulation may be used, such as those mentioned in U.S.
Patents No~ 3,959,131 and No. 3,969,245.
A dense supply of small bubbles also flows into the'confined flow path. The density of this supply is such that the bubbles comprise 1/2 to 6 volume per cent of the ' wastewater in the confined flow path'for adequate embryo, floc formation, generally within about 1 to 5 minutes.
These bubbles may be provided by the in-line dispersing of ' air bubbles, by electrolytic decompostion of water, or by pressurized gas dissolution. The bubbles should have a diameter of between 30 to 500 microns, preferably 50 to 200 microns. They should be provided in densities preferably between about 106 and 109 bubbles per liter of water being `' treatedO Dispersion techniques often are the most cost efficient.
In an optional step, a polymer flocculant may be ' 30 added after the embryo floc and wastewater flow together ; out of the confined flow path'and into the long flotation zone. This feature usually noticeably improves the consistency of the overall process by increasing the stability of the - ~09i83~
floc composites formed, making them less susceptible to being damaged during the subsequent separation procedure.
A~y po}ymer flocculant (anionic, cationic, or nonionic) may be uQed in concentrations between about 1/2 and 15 ppm. The preferred polymers are polyelectrolytes in the form of polyacrylic acrylamides, which are copolymers of from about 50 to 90 weight per cent acrylamides or methacrylamides, and from about 10 to 50 weight per cent acrylic or methacrylic acid or water soluble salts thereof. These polymers are characterized by weight average molecular weights of about 2 million and usually the molecular weights range between about 7 to 12 million a~ measured by light scattering techniques The preferred concentration range for the polymer flocculant is between about 1 to 3 ppm, although it could be as high as 20 ppm or higher for highly emulsified waters Irrespective of the makeup of the gas-solid composites formed in the preceding steps, the next step in the present method begi~s the`process of separating the two-phase composites from the`wastewater. Thé wastewater and the composites mixed therein flow together into the long flotation zone.
Preferably, additional bubbles are provided from the bottom of at least the upstream portion of the zone for assisting ; in the flotation separation of the buoyant floc composites These additional bubbles may be supplied by electrolytic , decompostion of water. They also may be provided by gases dissovled in water. These bubbles can be provided in a pattern that gradually decreases in density in the downstream direction. The decrease may be geometric.
The use of electrolytic bubbles, particularly in the long flotation zone, often has a particular advantage of reducing the amount of certain adsorbable ions that might be present in the raw wastewater. Such ions include _g_ ' 109i83~
ammonia-nitrogen, cyanide, phenols, polybrominated biphenyls, and various other organic toxic pollutants. The reduction ifl significant, with these ion values being enriched in the floc. The degree of reduction may be reported as a partition coefficient, defined as the concentration of ions in the fLoc phase over the concentration of ions in the mother liquor, here the wastewater. This feature results in a partition coefficient in excess of 30/1.
The reason for this highIy beneficial phenomenon 10 is not presently known. The following is offered as an ` hypothesis. Hydrogen bubbles appear to act as a catalyst in ; that they attach to the particulates to form some of the two-phase composites, hydrogen being the gas phase. It is postulated that ions are thén adsorbed, either physically, chemically, or by ion exchange, onto the solids at the gas-solid interphase. When these two-phase composites enter the skimmings later on in this method, these values are thus removed from the wastewater. It is further postulated that ^` some ions that are not so adsorbed are destroyed by electro-20 lytic action.
- Within thé long flotation zone as a whole, the r combined floc, which is depicted in FIGURE 1, rises to thesurface to form the skimmings, and the clarified wastewater flows the length of the zone and out at its downstream end.
` As an optional feature, this operation may be assisted by ~ vertical, perforated baffles placed transverse to the flow ; throughout the long flotation zone. Such baffles have from about 30 to 80 per cent, prefera~ly from 50 to 60 per cent uniform free passage therethrough as the wastewater flows 30 downstream through the zoneO They usually significantly reduce turbulence, channelling and back diffusion within the zone which would deveIop if the baffles were not present and - which would cause disruption of the separation process to :
10 ~ i 8 3 0 decrease the final clarity of the wastewater.
The in situ dewatering method of this invention provides a supplemental supply of bubbles at a location that i~ below the accumulation of skimmings at the inlet end of the long flotation zone. Adequate dewatering of the skimmings to a solids content between about 15 and 30 weight per cent usually takes place if the bubbles are supplied in the approximate range of about 0.1 to 2 cubic feet of bubbles per hour per square foot of the horizontal area of the supplemental supply.
For most efficient operation, the bars of the skimmer must be below the surface of the water for substantially the entire length of the long flotation zone, which surface can be kept generally at the same height by a weir structure.
m e skimmer may be tilted slightly, but the bars themselves should not be above the surface of the accumulated skimmings in order to prevent the bars from forcing the skimmings down into the basin. There should be no substantial obstruction between the bars so the skimmings can be'free to have appreci-able vertical movement. The skimmer should move at a slow speed, generally no faster than 3 feet per minute and prefer~
ably on the order of 5 to 12 inches per minute, so the skimmings will remain in the'dewatering region for a significant length'of time to increase the ability of the supplemental bub'bles to displace water from the skimmings which can rise to well above the water surface to be skimmed off by the bars. For particularly effective dewatering, the skimmer can be advanced intermittently only. This permits batches of skimmings to be dewatered in situ for extended periods of time when they are not being moved horizontally through the dewatering region The polymer flocculant that is added can be increased to between 2 and 25 ppm to further improve dewatering. Thé preferred range is 4 to 10 ppm -` 1091~30 ' A further optional step in the method of this inven- ~-tion i8 the addition of a strong base such as lime into the water after the completion of the streaming potential adjustment to approximately zero and before the water enters the confined flow path. Thi8 step, which raises the pH, can bring about three distinct advantages. It brings the pH back up to a value that is within acceptable'governmental pH discharge standards, usually between 6 and 9. It significantly reduces acid damage to the equipment~ When the water being treated contains heavy metals, the higher pH will enhance the'formation of hydroxides o many of the heavy metals, which'hydroxides are usually in-soluble particùlates that will be passed into the skimmings.
The concentration of strong base added for this third advantage should be adequate to raise'the'pH to between about 7 and 10, preferably between 7,5 and 9, The FIGURE 1 perspective view of the preferred appar-' atus, génerally referred to ~y reference numeral ll, illustrates the' bubble formation means 12, 13 and 14 as electrode'pairs.
Other methods of bubble'formation, discussed elsewhere herein, }~.
, 20 are intended to be'depicted by reference numerals 12, 13 and 14.
Also as diseussed herein, bubble formation means-13 is provided when in situ dewatering is to be'performed, and bubble formation means 14 is optional. Generally, the water to be treated enters '' inlet 15; the clarified water exits through outlet 16; and the ' skimmings are collected in trough'l7.
Inlet 15 preferably opens into a holding tank 18 op-tionally outfitted with'a mixing means 19 or promoting unifor-' mity in the makeup of ~he water within holding tank 18. Both `' tank 18 and means 19 increase the efficiency of the overall process by permitting more'consistent and accurate streaming potential adjustments, which'may be monitored by a probe 21.
Probe'21 is preferably a streaming detector; it may also be a .
10~1830 p~ reading device if used in conjunction with other means (not ShOWIl) for correlating the near zero zeta or streaming potential reading of the incoming water with pH values.
Opening into holding tank 18 are injectors 22 and 23, one for adding the mineral acid and another for adding the multi-valent metal coagulant. A conduit 24 communicates the streaming potential adjusted water with a coagulation cell 25. CeIl 25 contacts and mixes this water with dense quantities of small bubbles, preerably in the upward vortex motion depicted, to thereby form the embryo floc. Another conduit 26 communicates the coagulation cell 25 with the catch basin 27. A further in-jector 28 may open into conduit 26. It optionally opens either into the basin 27 through its upstream wall 29 or into both conduit 26 and through wall 29. Injector 2~ adds polymer floc-culant when included to assist in situ dewatering and/or to form the combined floc as depicted.
When bubble formation means 13 is desired, it is at the upstream end of basin 27 and i8 below the surface of the water and skimmings in basin 27. When means 13 i8 below conduit 26, bubbles supplied théreby also help in floating the floc in the basin 27. This is -generally acceptable when means 13 sup-plies dissolved air bubbles, which resist coalescing as they rise the height of basin 27. Electrolytic bubbles have a greater tendency to coalesce into bubbles that are too large for effective dewatering if they have to travel substantial heights through water. When means 13 is electrolytic, it should be at a depth not in excess of about 3 feet. ~1hen means 13 is above conduit 26, it should not excessively obstruct the flow of floc. One way of reducing any obstruction is by mounting the electrodes longitudinally of the flow into basin 27.
Optionally present for assisting in the flotation of the combined floc may be the bubble formation means 14, 109i830 which is located near the bottom surface of basin 270 Means 14 is less likely to be needed if means 13 is below conduit 26. A skimmer 31 moves the skimmings up the angled beach toward trough 17. This allows additional water to run down the beach lnto basin 27 to increase skimmings dewatering. A
recycle member 32 may be provided for supplying clarified water for use in the bubble formation means 12.
FIGURE 2 is a schematic view of the apparatus. It '' shows a bubble formation mean~ 12 that is an in-line'disperser which economically and effectively disperses a gas supply as small bubbles into a liquid supply. The short arrow line to means 12 is the'gas supply, preferably a supply of air.
, The drawing shows different paths by which the "-, liquid supply can be provided to means 12. The liquid supply may be from the recycle member 32, which recycles as much as abou~ 50, often about 10 to 20 volume per cent of ~' , the water flowing through'the total apparatus 11, preferablyabout 15 per cent. The'liquid supply may be from conduit 24 ', 20 through by-pass 33. When conduit 24 does not open into cell 25, such as by closing a valve 34, the entire flow ~,` through inlet 15 passes through means 12. Otherwise, it is -' possible to have'only a portion of the flow pass into means 12 to provide the liquid supply.
"'' The means 12 may supply the required density and ~,' size'of bubbles by dissolving gas bubbles under pressure ~' within the liquid. Such a structure is depicted for bubble ~ . .
formation means -13'in FIGURE 2. The bubble'supply surface formed by means 13'has a length L that is about one-fourth the length of the entire basin 27. A tilt of skimmer 31 is depicted. Also shown is a phantom line drawn between ;~, the outer tips of skimmer bars 41. The tilt is such that '' this phantom line is below the skimmings surface for a dlstance "a" at the upstream end and is below the skimmings surface for a distance "b" at the downstream end of basin -;
27. Preferably, distances a and b are relatively small, on t~e order of one inch for a and no more than the depth of a skimmer bar for b. When the in situ dewatering is in operation, it i8 common for the dewatered skimmings to bunch up approxi-mately along length L, often until they actually cover portions of the skimmer bars 41 at the inlet end. A weir box 42 helps maintain these relative distances that assist the dewatering function. Weir box 42 may include a height-adjustable wall 43O' ' In the structure shown in FIGURE 2, the floor of basin 27 has a depression 44. An optional bottom drag member 45 operates to pass any especially large or heavy materials from the bottom of basin 27 into the depres~ion ' 44. An angular barrier 46 preferably is provided. It ,~ allows clearnace for drag member 45 and improves the'flotation - efficiency of the basin 27 and of the means 13. Perforated ba~fles 47 may also be located transverse'to the flow through ~' 2Q the basin 27.
;" The following Examples are set forth as illustrative ' embodiments of the invention and are not to be'taken in any manner as limiting the scope théreof as defined by the appended claims.
E X A M P L E
A packinghouse'wastewater was used to demonstrate '' on a bench'scale the effects of the combination of mineral acid and trivalent ions on streaming potential readings and on subsequent electrolytic purification. The physical characteristics of this raw wastewater varied with numerous collections between the'following values: total BOD, from 1500 to 2500 ppm; suspended solids, from 1200 to 1800 ppm; hexane extractables, from 600 to 1,000 ppm; and .' , .
turbidity (in Jackson turbidity units), from 800 to 1,100units. The pH of the raw wastewater was 7.5. This was treated by a series of chemical additions varying from pure slllfuric acid to pure ferric sulfate as a means of adjusting the wastewater to a zero streaming potential. It was found that the pH value observed at zero streaming potential of the treated wastewater varied depending upon the chemicals used to attain zero streaming potential.
This Example illustrates results that may be obtained when minimum quantities of metal coagulants are added in conjunction with the inorganic acid in adjusting to near zero streaming potential. The combinations are listed below, along with an indication of the pH recorded at zero streaming potentialO Also recorded are the turbidity values (in Jackson turbidity units) achieved when using electrolysis at a relatively low total value o 4.0 ampere-minùtes per gallon of wastewater. Runs No. 2 and 3 used the process of this invention. The results show improved turbidity of the treated water when compared with Run No. 1, which used only mineral acid. The results also show significantly lower volumes of skimmings for Runs No. 2 and 3 when compared , with Run No~ 4, which used only a trivalent metal coagulant instead of the combination of this invention. It should be emphasized that these were bench scale tests when looking at the skimmings volumes below. The reported volumes are for relative comparisons between Runs 1-4. The reportèd absolute ~ values are significantly higher than those observed during :~! full-scale operations.
Sulfuric Ferric pH at Skimmings-Volume %
Run Acid Sulfate Zero Zeta Turbidity Wastewater . 30 No. Added Added Potential (JTU) Treated 1 400 ppm 0 ppm 4.7 540 1.2 , 2 325 ppm50 ppm 4O8 360 2.5 3 300 ppm100 ppm 4.9 90 3.1 4 0 ppm 600 ppm 5.2 20 7O5 .: ~
109~830 E X A M P L E II
Using the same wastewater of Example I, tests similar to those of Example I were conducted, this time ~arying the total electrolysis power used in the process.
The following results were tabulated:
Sulfuric Ferric Power Input Run Acid Sulfate (Amp. Min./ Turbidity No. Added ~dded Gal.) (JTU) -5a 300 ppm 0 ppm 4 500 5b " " ~ 270 5c " " 12 80 6a 250 ppm 100 ppm 4 90 6b " " 8 80 6c " " 12 35 ; 7a 0 ppm 600 ppm 4 50 ; 7b " " 8 35 7c " " 12 20 These same resultæ are also plotted in FIGURE 3.
The initial pH of the water at the time these tests were run was 7.8. Its initial streaming potential was -20Ø The turbidity reading before treatment was 800 JTU. Run Nos. 6 were in accordance with the process of this invention.
- FIGURE 3 dramatically illustrates the increased power use to turbidity reduction efficiency that results in Run Nos. 6 when compared with Run Nos. 5. In addition, a corresponding efficiency comparison between Run Nos. 7 and Run Nos. 6 is rather favora~le. Run Nos~ 6, however, did not exhibit the ~, undesirable increase in skimmings volume shown in Run Nos.
7, which were on the order of Run No. 4 of Example I.
E X A M P L E III
Water from another meat packinghouse was treated in accordance with the preferred process and in the preferred apparatus. The raw water had averaged analyses of 3000 mg/l ; BOD, 1300 mg/l suspended solids, 1000 mg/l FOG (fats, oils iO~1830 and greases) and a p~l of 7.6. The streaming potential was adjusted to near zero with treatments that varied with the surging flow through this full-scale, on-stream operation.
~he treatment ranges were: 50-125 mg/l ferric sulfate and 100-225 mg/l sulfuric acid, the pH after adjustment being an average of 4.50 Electrolysis using between 1300-2100 amperes of current provided the bubbles into the coagulation cell, followed by 2-4.5 mg/l of the preferred polymer. The influent pumping rate of the water treated was between 800-850 gallons ~ 10 per minuteO Dissolved air bubbles were supplied into the ; catch basin below the inlet for dewatering and floc flotation, the water for dissolving being recycyled clarified water in a volume of about 400 gallons per minute, the pressurization being 60 psi. Averaged samples of the clarified water had , . . .
398 mg/l BOD, 105 mg/l total suspended sollds, and 18 mg/l FOG. The in situ dewatered s~immings had a solids content '; of between 15 and 30 weight per cent.
r~ E X A M P L E IV
Tests not in accordance with this invention were 20 carried out in the same manner, on the same apparatus, and t on the same industrial effluent as Example III. The combination of mineral acid and multivalent metal coagulant was not - used. Used was 75-225 mg/l of sulfuric acid to adjust to ., ,' near zero streaming potential, the pH being 5.4. Also added was about 2 mg/l of the preferred polymer. Averaged samples of the clarified water analyzed as 797 mg/l BOD, 470 mg/l total suspended solids, and 166 mg/l FOG.
, E X A M P L E V
; Another series of tests not in accordance with 30 this invention were conducted as in Example III. The treatment prior to the coagulation cell was with 100-400 mg/l ferric ` ~- sulfate, and the near zéro s-treaming potential was at a pH
of about 6.5. The preferred polymer was added in concentrations ; -18-lO 9 i 8 ~ 0 between 3 and 4.5 mg/l. The treated water showed 327 mg/l BOD, 85 mg/l total suspended solids, and 31 mg/l FOG.
E X A M P L E VI
A further set of tests similar to tho~e of Example V
were conducted, this time using 150-400 mg/l of alum instead of the ferric sulfate, the adjusted pH being 6O7. Between 2-4 mg/l of the preferred polymer was added. The clarified water showed 611 mg/l BOD, 537 mg/l total suspended solids, and 311 mg/l FOG.
E X A M P L E VII
' Pilot plant tests were run at about 10 gallons perminute on a very highly emulsified water from a commercial t laundry for industrial shop towels. The equipment used was along the lines of FIGURE 1, except that the water flowed through the electrodes in the coagulation cell, which was tubular in shape, The water had a pH of 12, had 14,000 ppm COD, had 3,478 ppm suspended solids, had 2,869 ppm hexane extractables (Fats, Oils and Greases), had 11 ppm of lead, had 4 ppm of zinc, and had a turbidity reading of 18,000 JTU. The'streaming potential was -2Q streaming units.
The current to the'cell was 75 amps at 12 volts. The current to the basin was 35 amps at 6 volts.
First 3000 ppm alum was added. When 1,000 ppm of sulfuric acid was thén added, the pH was lowered to about 4, ~' at which time the streaming potential was approximately zero, and most of the charge was removed fr~m the particulates.
The pH was then raised with'500 ppm of lime in order to meet governmental discharge pH standards; in order ta prevent acid damage to the coagulation cell, the basin and other portions of the apparatus; and in order to enhance the formation of heavy metal hydroxides which could be passed into the skimmings. Between the ceIl and the basin, 15 ppm '~ polymer was injected into thé'flow of embryo floc and water.
109~30 : The thus treated water had a pH of 7.5, had 605 ppm COD, had 155 ppm suspended solids, had 13 ppm hexane extractables, had 0.17 ppm of lead, had 0.06 ppm of zinc, and had a turbidity reading of 300 JTU.
E X A M P L E ' VIII
Pilot tests along the lines of Example VII were ~' run on a laundry water from painters' and printers' towels .' which had a pH of 11.5, had 16,000 ppm COD, had 3,980 ppm ~.
'.~ suspended solids, had 2,.543 hexane extractables J had 9.1 ppm ~:
; 10 lead, had 4.0 ppm zinc, and had a turbidity reading of ' 25,000 JTU. Treatment used 4,000 ppm alum and 1,500 ppm ~ :' ';.~ sulfuric acid to adjust .the' streaming potential to -l streaming units. Also added were 700 ppm lime, and 2Q ppm of the . ~-~- preferred polymer flocculantO Thé'clarified water had a pH
... . ..
:.'. o 7.9, 1,490 ppm COD, 57 ppm ~uspended solids, 92:ppm ~ :`
hexane'extractables, 0.60 ppm lead, 0.16 ppm zinc, and turbidity readings of between 300 and 500 3TU.
-" E X A M P L' E IX .
Additional pilot tests according to Example'VII ' .' 20 were.'conducted on a water that combined flows of Example' i VII water, of Example'VIII water, and of a general wastewater.
"~; ~ It had a pH of ll.6, 6480 p'pm COD, 1610 ppm suspended solids, ' 1540 hexane'extractables, 6.9 ppm lead, and 2.0'ppm zinc.
- .
In this series of tests, the ~object was to bring the'hexane extractables to below municipal standarda of 250 ppm. Added were'2,.000 ppm alum, 800-ppm .sulfuric acid, to adjust to .
. ~ -0.5 streaming units, followed by 250 ppm lime, and 15 ppm . of the polymer fl'occulant. The'clarified water had a pH of 7.8, 925 ppm COD, 250 ppm suspended solids, 110 ppm hexane . 30 extractables, 0.4 ppm lead, 0.4 ppm zinc, and turbidity readings between 500 and 600 JTU.
-- Ob~iously, many difications and variations of the invention as hereinbefore set forth may be made without . -20-. . ~
10~31~330 departing from the spirit and scope thereof, and only such llmitations should be imposed as are indicated in the appended claims.
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Claims (19)
1. A method for removing particulates from waste-waters by flotation, comprising: obtaining a supply of waste-water; adjusting the streaming potential of particulates in the wastewater to approximately zero, said adjusting step in-cluding adding a multivalent metal coagulant in combination with a mineral acid; forming a confined flow path of the thus adjusted water; supplying dense quantities of small bubbles within said confined flow path; forming embryo flocs within said wastewater while it is within said confined flow path;
flowing the wastewater containing the embryo flocs into a long flotation zone; forming combined flocs from a plurality of embryo flocs; and removing the combined flocs from the water.
flowing the wastewater containing the embryo flocs into a long flotation zone; forming combined flocs from a plurality of embryo flocs; and removing the combined flocs from the water.
2. The method of claim 1, wherein the streaming potential adjusting step adds the combination of coagulant and acid at a molar ratio between about 1 to 1 and 1 to 100, based on the concentrations of the metal ions and the hydro-gen ions, respectively.
3. The method of claim 1, wherein the step of re-moving the combined flocs from the water includes: slowly skimming the combined flocs toward a dewatering region at the inlet end of the long flotation zone; dewatering in situ the combined flocs skimmed to the dewatering region, said de-watering step including adding a supplemental bubble supply from below said dewatering region; and then removing the de-watered skimmings from the inlet end of the long flotation zone.
4. The method of claim 1, wherein said adjusting step includes: first adding the multivalent metal coagulant at a concentration between 0.1 to 15 millimolar based on the metal ion concentration to bring the wastewater toward its zero stream-ing potential and to break emulsions, if present in the waste-water; and then adding the mineral acid at a concentration be-tween 2 to 30 millimolar based on the hydrogen ion concentration to complete said adjusting of the streaming potential to approx-imately zero, the resulting pH being between 3 and 6.5.
5. The method of claim 1, wherein said step of supply-ing bubbles within the confined flow path supplies the bubbles to a density of 1/2 to 6 volume percent of the water within the confined flow path.
6. The method of claim 1, wherein the step of forming a confined flow path forms an upward vortex having a duration of from 1 to 5 minutes.
7. The method of claim 1, wherein the step of remov-ing combined flocs from the water is assisted by providing electrolytic bubbles within at least a portion of the long flo-tation zone, said assisting step also reducing the amount of certain absorbable ions in the water by passing said ions into the skimmings.
8. The method of claim 1, further comprising raising the pH of the water between the streaming potential adjusting step and the confined flow path forming step, said pH being raised to between 7 and 10 within as quickly as 5 to 60 seconds and as long as days after said adjusting step.
9. The method of claim 1, further comprising partial-ly baffling water flowing through the long flotation zone by permitting free passage of about 30 to 80 percent of the flow through the long flotation zone.
10. The method of claim 1, wherein the step of supplying dense bubbles to the confined flow path includes forming the bubbles by electrolytic decomposition, by dis-persion of gas into water, or by pressurized dissolving of gas into water.
11. The method of claim 1, further comprising supplying bubbles into the long flotation zone by electroly-tic decomposition or by pressurized dissolving of gas into water.
12. An apparatus for removing particulates from wastewater by flotation, comprising: a coagulation cell having an inlet and an outlet; injector means located up-stream of said coagulation cell inlet for adding, in combin-ation, a multivalent metal coagulant and a mineral acid to adjust the streaming potential of a wastewater to approxi-mately zero; a bubble formation means for supplying bubbles to said coagulation cell; a catch basin; a conduit communi-cating said cell outlet with an inlet of the catch basin;
and a means for removing floated particulates from the water in the catch basin.
and a means for removing floated particulates from the water in the catch basin.
13. The apparatus of claim 12, wherein said means for removing floating particulates includes a skimmer along the surface of said catch basin, and a supplemental bubble formation means for supplying bubbles to form a dewatering region along a length at the inlet end of the catch basin, such bubbles entering the basin below said length.
14. The apparatus of claim 13, wherein said supple-mental bubble formation means includes a plurality of elec-trodes that are located at a depth not in excess of about 3 feet, said depth being from the surface of the catch basin to the upper surface of said electrodes.
15. The apparatus of claim 13, wherein said supple-mental bubble formation means is a pressurized gas dissolving means.
16. The apparatus of claim 13, wherein said dewater-ing region has a length that is about 1/4 the total length of the catch basin.
17. The apparatus of claim 12, further comprising a plurality of transverse baffles spaced along a majority, of the length of said catch basin, said baffles having perforations in about 30 to 80 per cent of their surface area.
18. The apparatus of claim 12, further comprising a depression at the inlet end of the floor of the catch basin, a drag member along the floor of the catch basin downstream of said depression, and a barrier along the width of the catch basin generally separating the volume of the basin above the depression from the remaining volume of the tank.
19. The method of claim 4 wherein said resulting pH
is between 4 and 5.5.
is between 4 and 5.5.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US76781777A | 1977-02-11 | 1977-02-11 | |
| US767,817 | 1977-02-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1091830A true CA1091830A (en) | 1980-12-16 |
Family
ID=25080682
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA293,867A Expired CA1091830A (en) | 1977-02-11 | 1977-12-23 | Wastewater flotation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1091830A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2003086977A1 (en) | 2002-04-09 | 2003-10-23 | Institut National De La Recherche Scientifique | Methods and apparatus for treating animal manure |
-
1977
- 1977-12-23 CA CA293,867A patent/CA1091830A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2003086977A1 (en) | 2002-04-09 | 2003-10-23 | Institut National De La Recherche Scientifique | Methods and apparatus for treating animal manure |
| US7156999B2 (en) | 2002-04-09 | 2007-01-02 | Institut National De La Recherche Scientifique | Methods and apparatus for treating animal manure |
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