Water Purification System

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.

FIG. 1 is a schematic diagram of an apparatus for practicing the process of cleaning waste water; and,

FIG. 2 is a modification of the apparatus of FIG. 1.

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:

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

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.