Water purification system

Waste water is reclaimed for re-use by emulsifying with a water insoluble (or oil soluble), high molecular weight, anionic surface active oil, then breaking the emulsion by physical or chemical methods, thereby producing a coherent floc which occludes insoluble matter suspended in the water, then separating the floc from the purified water in a coherent mass.

This invention relates to a process of reclaiming waste water and to an 
apparatus suitable for use in said process. Heretofore, many attempts have 
been made to reclaim waste water, including that produced from laundry 
operations, particularly where there is a shortage of water, the cost of 
water is high; or to re-use heated water before it cools. Likewise, 
discharge of such waste water into streams and lakes has resulted in a 
pollution menace. Before the advent of syndets, i.e., synthetic 
detergents, primarily the alkyl aryl sulfonates and nonionics, laundry and 
similar wash operations were conducted with soaps of fatty acids, usually 
sodium oleate, stearate, palmitate and fatty acids in general as their 
sodium or potassium salts. Sodium carbonate, sodium borate, trisodium 
phosphate, tetrasodium pyrophosphate and sodium silicate were also often 
present with the soaps to reinforce and accelerate their detergent action 
in removing soil from fabrics. The waste water from these operations could 
be recovered when desired, by simply neutralizing the alkalinity of the 
water with, for instance, aluminum sulfate, thereby separating the fatty 
acids along with aluminum soaps and aluminum hydroxide when alum was used 
as the neutralizing agent. 
With the advent of the syndets, particularly the sodium alkyl aryl 
sulfonates of ten to sixteen carbon atoms and sodium lauryl sulfates and 
lauryl sulfates of 12 carbon atoms and the nonionics, such as ethoxylated 
alcohols, the previous methods of water reclaiming and purification were 
found ineffective owing to the water soluble nature of the metal salts of 
the organic sulfonates and sulfates employed in the syndets. When waste 
water from such operations is treated with alum, or other floccing agents, 
the carbonates and alum reactive chemicals are rendered insoluble but the 
clarification is slow and incomplete because the syndets remain active 
surfactants, suspending the soils and insoluble chemicals. Likewise when 
such wash waters containing syndets are purified by ultra filtration, the 
insoluble solids, bacteria and larger organic molecules are removed, but 
the syndets carry through with the purified effluent rendering such water 
unsatisfactory for effective rinsing. When electro-chemical purification 
is employed, that method also is unable to or requires excessive time to 
break the bond between the syndet and water, so the effluent is too 
"sudsy" for use as an effective rinse water. 
Suspended contaminates or dissolved contaminates that can be made insoluble 
by chemical reaction have been separated from water by allowing the 
suspended or reaction-produced contaminates to settle out over a period of 
time. Baffles, parallel plates and dissolved air tend to hasten the 
removal but used alone often do not do a fast enough or complete enough 
job. Settling has been further accelerated by coagulants such as the 
inorganic electrolytes, alum, calcium oxide, or iron compounds and the 
organic polymeric electrolytes (polyelectrolytes). The inorganic and 
organic electrolytes are often used together with the inorganic added 
first to produce a precipitate and the organic polyelectrolyte added last 
to build and strengthen the floc just prior to settling. However, there 
are many instances where the contaminates are resistant to polyelectrolyte 
floculation, where the most efficient polyelectrolyte dosage is too 
expensive or where the residual polyelectrolyte left in the clarified 
water is harmful to subsequent uses for the water or floc. Some examples 
of the latter case are waters that are to be reused for washing and 
rinsing where the polyelectrolyte causes redeposition of soils back onto 
the washed surfaces, waters that are to be treated subsequently by 
molecular filtration or ion exchange resins which are fouled by 
polyelectrolytes and flocs that must be saved in a pure state for animal 
feed. 
A search of the patent literature revealed a number of patents directed to 
the solution of this problem, but none provided a process which met the 
requirements for a commercially satisfactory process, namely: (1) rapid 
action to allow recycle, involvement of minimum volumes of water, 
preferably a recycle rate equal to the use demand rate; (2) separation of 
opaque suspended matter providing water of rinse water quality; (3) low 
cost of reagents; (4) simple, inexpensive apparatus. Among the patents 
studied were the following: U.S. Pat. Nos. 2,613,180; 2,695,710; 
2,762,681; 3,147,217; 3,200,069; 3,389,081; 3,583,909; 3,817,870; 
2,793,185; 3,510,001; 3,583,090; 3,733,265; 3,764,013; RE 28,323; 
3,259,567; 3,434,968; 3,673,065. 
One object of my invention is to provide a process for reclaiming waste 
wash water which will meet the foregoing requirements with a minimum of 
apparatus and at a cost which will compete with purchased city water. 
Another object is to provide a process which will reclaim water while at 
elevated washing temperatures, thereby producing warm water for recycle 
and saving part of the fuel required to heat it for the washing operation, 
for laundry purposes usually about 140.degree. F. Another object of the 
invention is to produce a floc which, owing to its concentrated form, can 
be easily used or disposed of, for example, by burning in a furnace with 
other fuel, removed as a solid suitable for land fill, or used as animal 
feed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The foregoing objects can be achieved by injecting into the waste water a 
small controlled amount of an oil, comprising a water insoluble surface 
active agent which is a high molecular weight organic acid or its metal 
salt. Oil soluble sodium salts, or other Group 1 metal salts such as 
potassium salts, are particularly useful, as I have discovered. Suitable 
acids can be selected from the class of the sulfonic acids, and their 
byproduct green acids, the phosphonic acids, the alkyl phenates and the 
carboxylic acids, the acids having upward of 18 carbon atoms, generally 20 
to 40 carbon atoms. Suitable sodium, or other Group 1 metal, salts may 
have upward of 18 carbon atoms, generally 20 to 40 carbon atoms, and an 
average molecular weight of above about 300. Hereinafter these substances 
are referred to as "surfactant". 
In the presence of a synthetic detergent component in the water, the 
surfactant forms an emulsion aided by agitation at and immediately after 
the point of the injection and by the presence of the synthetic detergent. 
This operation can be carried out batchwise, but the rapid separation 
possible with this invention lends itself to continuous flow treating. I 
therefore prefer to operate continuously, injecting the surfactant into a 
stream of waste water entering a mixer. The amount of surfactant required 
can vary somewhat, depending on the amount of detergent in the waste 
water. Usually the volume of surfactant added is related to the weight of 
the active detergent present by a factor of 0.2 times to an upper limit of 
about 100 times (at which point the emulsion may invert). An effective 
amount being a ratio of 1 part of surfactant to up to 2 parts of active 
detergent content by weight or 3 parts of floc removed. In general, when 
treating a mixture of waste wash water and rinse water, e.g., rejected 
from the usual laundry operation, the amount of surfactant required will 
be about 100 to 250 mg. per liter of water treated. If insufficient 
surfactant is used, the floc later produced will possess insufficient 
adhesiveness and fail to separate from the water rapidly and completely. 
Accordingly, it is desirable to add just the minimum amount to produce a 
coherent floc, up to the point of inversion. Except for cost, excess 
surfactant is not harmful. 
The emulsion is next broken by treating with commonly used floccing 
chemicals, such as alum (aluminum sulfate), zinc chloride, calcium oxide, 
or iron chloride or combinations of these with polyelectrolytes or by 
electrochemical or ultra filtration methods well known in the art. In each 
case, the surfactant has captured or sequestered the synthetic detergent 
by mutual solubility so that as the emulsion is broken, the synthetic 
detergent is carried from the water with the surfactant. 
I have also discovered that if a surfactant, for example, an oil soluble 
sodium sulfonate, having a suitable hydrophilic-lipophilic (HLB) is 
chosen, it can also be used to flocculate and clean waste water which does 
not have any appreciable syndet content. An oil soluble surfactant is 
chosen which can be emulsified in the waste water. The emulsified oil 
soluble (water insoluble, but emulsifiable) surfactant is separated from 
the waste water, preferably by flocculation with divalent and trivalent 
metal salts such as alum (aluminum sulfate). When separated, the 
surfactant (and floc, is used) removes soils and suspended matter 
contained in the waste water. It is believed that the multivalent metal 
ions used to flocculate the emulsion react with the emulsified surfactant 
to further greatly reduce its solubility and to break the emulsion and 
flocculate out the surfactant and occluded soils. 
For speed of operation and simplicity and because of the helpfully 
adsorptive aluminum oxide produced, a specialized apparatus for using alum 
(aluminum sulfate) may be used in implementing the emulsion breaking 
function of this invention. In the apparatus, aluminum sulfate in a water 
solution of any convenient dilution is injected into the wash water 
surfactant emulsion. Being strongly acidic, the alum neutralizes the 
alkaline minerals (such as sodium carbonate and silicate) which have been 
left in the wash water from having been compounded into the syndet 
containing detergent formula. Sufficient alum is added to give the water a 
slightly acid reaction, e.g. pH 5 to 6.5. When carbonates have been 
included in the detergent formula a gelatinous precipitate of aluminum 
oxide is formed which acts as an adsorbant for dyes and other soils 
contained in the wash water. 
Simultaneously with the formation of aluminum hydroxide, the surfactant 
emulsion is broken and the collodial particles of the surfactant and 
associated oil and syndets along with the aluminum oxide become the 
coherent floc hereinabove referred to. From this it will be observed that 
the process involves a complex combination of chemical and physio-chemical 
reactions wherein the most important, from the standpoint of a successful 
process is the adsorption of the synthetic detergent -- usually, but not 
limited to, alkyl aryl sulfonate in combination with the added surfactant, 
through a mutual solubility or covalent bonding reaction. 
The water insoluble (or oil soluble) sulfonic acids employed in my 
surfactant can be made by sulfonating a petroleum lubricating oil fraction 
with oleum or SO.sub.3 in a manner well known to the art or by sulfonating 
an alkyl benzene of the desired molecular weight, e.g., benzene alkylated 
with butylene dimer or trimer. One such process is described in U.S. Pat. 
No. 2,746,980, the disclosure of which is incorporated by reference 
herein. A suitable oil fraction for this purpose may have a molecular 
weight of 400 to 600 and a yellow to red color; for some surfactants a 
molecular weight of the precursor oil fraction may be as low as about 300. 
A fraction commonly used is known as 480 neutral oil. After sulfonation, 
the oil is separated from acid sludge and the sulfonic acids extracted 
with alcohol and water, then neutralized with lime to form the calcium 
soap. The sulfonic acid can be neutralized with sodium hydroxide to form 
the sodium salt, which can be extracted from the oil with aqueous alcohol. 
If the Group 2 salt is desired, the sodium salt can be converted to the 
calcium, barium or magnesium salt by double decomposition with the 
corresponding Group 2 metal halide. The sulfonate obtained in this manner 
usually contains 50% to 60% by weight of unsulfonated petroleum 
hydrocarbon oil. To reduce the cost, additional oil can be added, reducing 
the sulfonate content to 15 to 30 percent. For this purpose I can use a 
non-volatile petroleum fraction such as 60 pale oil, deodorized kerosene, 
or "Iso-par M" (TM) which is an odorless petroleum fraction boiling at 
410.degree. to 480.degree. F. with a flash point above 170.degree. F. 
Addition of about 1 to 5 percent by weight of viscous polybutene of high 
molecular weight adds adhesiveness to the resulting floc, if desired. 
Other water insoluble surfactants are the phosphonic acids prepared by 
reacting an olefin such as polybutene or polypropylene with phosphorous 
sulfide then hydrolyzing the product to eliminate H.sub.2 S in a manner 
well known in the art. Oleic acid or calcium or barium oleate in mineral 
oil solution can also be used, as can phenyl stearic acid and the calcium 
salt of polymerized napthenic acids of 13 to 23 carbon atoms, the 
so-called "bicyclic acids," and the so-called green acid by-products 
formed in the sulfonation of petroleum fractions. All the above water 
insoluble surfactants are preferentially oil soluble owing to their high 
lipophylic character which can be expressed as a hydrophylic-lipophylic 
balance (HLB) of less than 1 on the scale in which the HLB of laundry 
detergent equals above 20. Oleic acid is 1 on the HLB scale. However, an 
oil soluble sodium or Group 1 metal salt, suitable for use in cleaning 
waste laundry water, or other waste water, as described herein, can have 
an HLB of up to about 10 or 12. Whichever chemical is used, our reference 
to "surfactant" is meant to also describe and include the one used as 
diluted ready for addition to the waste water. 
The following examples will demonstrate the process and its results: 
EXAMPLE 1 
To 25 gallons of hot water in the washing machine was added 100 gms. of 
detergent having the following formula: 
Sodium alkyl aryl sulfonate: 20% 
Sodium carbonate: 25% 
Sodium metasilicate: 6% 
Brightener: 1% 
Carboxy metal cellulose: 1% 
Water: 47% 
A ten pound load of soiled clothing was added and washing continued for 30 
minutes at about 140.degree. F. water temperature. The waste water was 
then withdrawn and spun from the clothes, after which the clothes were 
rinsed with 25 gallons of fresh water, either tap water or purified 
recycle water. The rinse water was spun from the clothes and combined with 
the waste wash water. About 500 gallons of discarded water was accumulated 
in this manner. It will be observed that the water will contain about 105 
milligrams per liter of the alkyl sulfonate syndet. 
This water was next drawn into a centrifugal pump at the rate of 4.5 gal. 
per minute, along with surfactant, in this case a 25% active solution of 
high molecular weight neutral calcium sulfonate, at the rate of 250 
milligrams per liter or about 4.4 grams per minute. Emulsification takes 
place in the pump which forces the water into a reaction vessel of 8.0 
gallons capacity. Between the pump and the reaction vessel, a 20% solution 
of alum was added at the rate of 15.0 gms. per minute. The reaction vessel 
was maintained at about 20 lbs. per sq. in. pressure and air was injected 
therein in excess of that which will dissolve in the water at this 
pressure. The rate of feeding alum was maintained by a metering pump or 
proportioning pump to give an acidity to the water of about 5 to 6.5 pH. 
This was controlled automatically by a pH meter arranged to sample the 
reaction vessel. The volume of water in the reaction vessel was controlled 
to provide a residence time of one half to two minutes. 
The stream next flowed through a pressure reducing valve to a floc 
separator where dissolved air was released and the floc was floated to the 
surface, collecting there as a pasty, coherent layer containing 80 to 90 
percent of water, to be removed by scraping manually or mechanically. Care 
was taken to avoid the introduction of undissolved air to the separator 
because of excessive turbulence set up therein. The clear, reclaimed water 
was withdrawn from the bottom of the separator. It can be passed through a 
screen or coarse filter to remove any bits of accidental floc, then passed 
through a carbon filter to collect any trace of oil, dyes and other 
organic impurities and finally sterilized, for example, by ultraviolet 
light, ozone or chlorine. Following is an analysis of the purified water 
produced hereinabove: 
Suspended solids: 5 PPM 
Dissolved solids: 1.5% maximum 
Bacteria (culture): None 
Virus: None 
Odor (olefactory test): None 
pH: 6-7 
Hardness: None 
Softness (alum test): 0.005% 
Clarity (nephelometer): Clear 
Color: Water white 
Heavy metals: 2 PPM 
Mercury: None 
EXAMPLE 2 
The process of the invention was used in a commercial laundry which washed 
a combination of domestic laundry (shirts and jeans) and uniform (rental 
overalls and shop towels). The water usage was 20 gallons per minute 
during a 16 hour day or approximately 500,000 gallons per month. 
Water from all of the wash and rinse cycles was collected in a 2000 gallon 
sump where a pump mixed and equalized the water. The soil and detergent 
load and composition varied with the different wash operations. A second 
pump picked up the mixed water from the sump and sent it through the 
process. 120 to 200 mg/l. of surfactant was added to the waste water 
containing about 1500 PPM detergent. The surfactant was a sodium sulfonate 
(TM PETRONATE CR) having a molecular weight (equivalent weight) of about 
500. The surfactant was added just prior to the pump. The pump and a 
pressure relief recycle loop around the pump (recycle rate about two 
times) mixed the surfactant into the water to produce an emulsion with the 
water and syndets. The water (at 30 psi) next flowed through a 20 gallon 
per minute (at 10 psi pressure drop) nozzle into the top of a 60 gallon 
glass lined pressure reaction vessel maintained at 20 psi. An air space of 
about 30% of the vessel capacity was maintained at the top of the tank by 
means of a float valve which metered in pressurized air from a compressor. 
The water coming into the air space had a violent mixing action as it 
struck the surface of the water. Two metering pumps metered a solution of 
alum, about 28% Al.sub.2 (SO.sub.4).sub.3, into the vessel at the mixing 
area. The alum and air entrained by the jet of water were thoroughly mixed 
to dissolve and entrain the air into the water in the vessel. From the 
reaction vessel the exit water passed through a 20 psi orifice into a 
dissolved air flotation cell. A pH probe at the exit of the vessel sensed 
the pH of the treated water and controlled the two alum metering pumps to 
produce a pH as close to 5 as possible. In the flotation cell, the water 
insoluble reaction products coalesced to form floc particles which were 
buoyed by air effervescing from solution because of the drop in pressure. 
The resulting floc, with the occluded surfactant, syndets and soils, was 
removed at the top of the flotation cell for dewatering and disposal. The 
clear water was removed from the bottom of the flotation cell, filtered to 
remove stray particles of floc and stored in a clean water tank for reuse 
in filling the washers. 
The quality of the clarified water was excellent, suitable for use as rinse 
water or detergent wash water. Operation of the process reduced water 
consumption by about 85% and fuel consumption (required to heat the wash 
water) by about 73%. 
Referring to FIG. 1, the flow chart for the process using wash water as 
described in Example 1, waste water is charged by line 10 to supply tank 
11 wherein a sufficient volume e.g., 500 gallons, is retained to average 
or equalize the supply which may vary in composition from time to time as 
the laundry machines are discharged periodically. The water then flows 
from tank 11 by line 12 through check valve 13 which prevents any reverse 
flow to the tank, thence by pump 14 and line 15 to circulating pump 16 and 
by line 17 to reaction zone 18. Reactor 18 may have a volume of about 50 
to 100 gallons in an average installation, providing a residence time of 
about one half minute to five minutes, one minute has been found very 
satisfactory. 
From an upper level in tank 18, the water is then recycled by lines 19 and 
15 back to the inlet of pump 16 which is preferably of the centrifugal 
type with sufficient capacity to recycle the water at a rate of 2 to 10 
times the rate of flow from feed tank 11. Air is injected into the 
circulating stream by line 20, controlled by metering valve 21 set to 
introduce air at a rate sufficient to saturate the water in reactor 18. 
Into the line leading to pump 14 is continuously fed a stream of 
surfactant oil from supply tank 22 by metering pump 23 through line 24. In 
pump 14 it becomes thoroughly emulsified with the water from line 12. 
Inasmuch as the amount of surfactant is quite small, e.g., 1 quart per 
1000 gallons of water treated, pump 23 provides an accurate control for 
the purpose and can be adjusted to provide any desired constant rate of 
injection. The surfactant is rapidly emulsified and dispersed in the water 
by the turbulence in pump 16 and by the dispersing action of the residual 
soaps and detergents in the waste water. 
There is next introduced into the stream, by line 25, a solution of alum 
(aluminum sulfate) from supply tank 26 controlled by metering pump 27. A 
20% solution of alum in water is convenient for the purpose. The rate of 
alum injection is adjusted in relation to an assumed five times recycle 
rate and the usual amount of detergent in the water or about 174 mg. per 
liter of waste water when the wash water detergent solids content is 
around 265 milligrams per liter. The alum coagulates the soaps and 
detergents in the waste water, forming a gelatinous precipitate of 
aluminum hydroxide and aluminum soaps which are insoluble in the water. 
These form a highly adsorbant floc which is less dense than water and 
floats to the top in reactor 18. This precipitate is recycled with air and 
water to pump 16 where it encounters additional surfactant and alum in 
line 17. 
The system, including the reactor 18, pump 16 and recycle lines 15, 17, and 
19, is maintained under pressure to accelerate the solution of air in the 
water and dispersed floc. A pressure of about one atmosphere gage is 
effective for this purpose, e.g., 10 to 20 psi gage. At a later stage in 
the process when pressure is released, the dissolved air escapes from 
solution in the form of microscopic bubbles which occlude the dispersed 
solids and oils on the bubble surfaces to form the floc which floats to 
the surface, leaving the water clarified. Feed pump 14 maintains the 
pressure on the system for this purpose. A centrifugal pump or other type 
equipped with a spring loaded bypass set at the desired pressure, can be 
used, as is well known in the art. Solution of the air is aided by the 
residence time in the reactor and by the high recycle ratio. 
Agitation and air adsorption in the reaction zone may also be affected by 
injecting the liquid stream into the top of the reaction zone through a 
high velocity nozzle impinging upon the surface of the liquid in the zone. 
The liquid in the zone may be maintained at a fixed level below the top of 
the pressurized apparatus by a float regulated injection of pressurized 
air. 
From the reactor 18 the water flows by line 28 to froth separator 29 which 
is a vertical tank or tower, preferably of rectangular cross section, 
wherein the floc or froth rises to the top and the clear treated water 
settles to the bottom. Water transferred to separator 29 is withdrawn from 
a mid-point of reactor 18 behind baffle 18A, which prevents escape of air. 
Baffles 30 in separator 29 assist in settling and clarification of the 
water by preventing turbulence. Flow through line 28 is controlled by a 
diaphragm valve 31 in response to pH meter 32 which senses the hydrogen 
ion concentration in the recycle line from reactor 18. For best operation, 
it is desirable to maintain the hydrogen ion concentration of the treated 
water in reactor 18 between pH 5 and pH 6.5. If the pH rises above 6.5, 
the meter 32 restricts the flow through discharge line 28 until the alum 
introduced at 25 reduces it to the acceptable range. 
At the top of separator 29 the froth collects in a layer and overflows at 
33, assisted by a travelling rake 34 or other device to urge the pasty 
mass into trough 35 leading to disposal. The froth level in 29 can be 
maintained by a float 36 in level box or reservoir 37 connected to the 
bottom of tank 29 by line 38. The float actuates discharge valve 39 
through connection 40. The clarified water flows by line 41 and pump 42 to 
filter 43. This can be a simple fabric or open cell sponge type filter to 
remove accidental bits of floc, etc., or it can be a sand type filter 
commonly used in water treating plants. Since the water at this point is 
clear, filter 43 serves no significant clarification function. From 43 the 
water flows to a final activated carbon or charcoal filter 44 where any 
residual odors resulting from traces of hydrocarbons, etc. are adsorbed. 
The completely purified water, free of detergents and all dispersed solids 
and insolubles, flows by line 45 leading to the water supply for further 
laundering operations or uses. For this purpose it may be heated and/or 
treated with disinfectants to insure freedom from trace amounts of 
pathogens which may have escaped the floc extraction stage of the process. 
Although I have described my invention with respect to a specific design of 
apparatus, I may employ other methods and devices for performing the 
process. Thus, the pH controller can actuate the metering pump for 
introducing alum solution to obtain the desired acidity in the reactor. I 
have also operated the reactor, flowing in at the top, preferably through 
a spray nozzle, and out the bottom, recycling from top to bottom and 
controlling the level therein at a mid point by means of a float operated 
valve. The level in the floc separator 29 can also be controlled by a 
simple overflow weir set at the desired level and connected to the bottom 
of the separator tower 29, thus eliminating the need for a float control. 
FIG. 2 shows a modification of the apparatus of FIG. 1 in which the liquid 
stream is injected into the top of the reaction zone 18 through a high 
velocity nozzle 47. The air is injected into the reaction zone 18 through 
line 20 and valve 21 which is controlled by float 49 to regulate the level 
of the liquid in reaction zone 18. 
Further modifications of my invention include the use of molecular 
filtration (ultra filtration or reverse osmosis) and electrochemical 
means. When employing ultra filtration (U/F) or reverse osmosis (R/O) I 
omit the step in which the inorganic electrolyte is added. The low HLB 
surface active agent and oil causes the high HLB detergent to form mycels 
so that they no longer remain dispersed as a colloidal solution. Both U/F 
and R/O reject only a fraction of high HLB detergent molecules when 
dispersed as a colloidal solution in the water. When, by my process, they 
are collected into mycels they no longer act individually and are 
therefore not present at the surface of the U/F or R/O membrane. As a 
result, the permeate so produced has a far lower concentration of surface 
active agents (detergents and soaps) than is found when detergent mixtures 
are treated without the addition of the low HLB mixture. I thus overcome 
the problem of organics and foaming in the permeate stream. 
When employing electrochemical means, I can either omit or include the step 
in which the inorganic electrolyte is added. If that step is included, a 
carbon cathode and noble metal anode (or noble metal plated anode) are 
used to treat the flocced effluent from the reaction zone. When current is 
passed through this system, the resultant formation of gaseous hydrogen 
and oxygen float the floc particles to the surface and a froth similar in 
nature to that obtained with dissolved air flotation is formed. If the 
addition of the inorganic electrolyte is omitted, an aluminum anode and 
carbon cathode is used. When current is passed through a surfactant-waste 
water emulsion, aluminum ions thereby produced react with the 
surfactant-detergent mycels to break the emulsion and produce a floc in a 
manner similar to the addition of an inorganic electrolyte. The 
simultaneous production of gaseous hydrogen and oxygen float these 
colloidal particles to the surface as described above. 
Other modifications can of course be readily made by one skilled in the art 
without departing from the spirit of the invention and the scope of the 
appended claims.