CA1190174A - Wastewater treatment method and system - Google Patents

Abstract

Abstract of the Disclosure A wastewater treatment process is provided in which organic impurities such as oil, organic brighteners, and chlorinated solvents are removed from the upper surface of wastewater from an industrial process and metal values are precipitated and withdrawn from the wastewater. The remaining clear liquid containing dissolved salts is used to generate working steam in a boiler for an industrial purpose. The wastewater is heated in the boiler to produce an aqueous phase having an increased concentration of impurities and a steam component which is used for the industrial purpose and condensed to pro-duce water which is recycled for use in the industrial process and/or boiler.
The accumulated impurity component is removed from the boiler periodically or continuously .

Description

There has beell a growirlg concern on the part of naturalists, industrialists, federal, sta-te, and local legislative bodies, and the general population about controlling industrial pollution of the enviro~ment.
Pollution of air and surface waters by direct emission of wastes rom indus-trial plants into the air or into lakes and streams has been of concern for many years. More recently~ pollution of underground waters as well as of air and surface waters as a result of storing solid and liquid wastes at land disposal sites has been recognized as a serious problem. Federal and state statutes, municipal ordinances3 and regulations issued by agencies such as the EPA increasing the stringency of pollution standards are almost continuously being enacted and promulgated. While the ideal standard from the standpoint of pro*ection of the environment is ~ero discharge oE pollutants, for many areas of technology, it is widely believed at present that this standard is not practical, and standards have been accordingly established at levels which are considered feasible.
The present methods o~ treating industrial wastewater effluents include ion exchange, reverse osmosis, e~aporation, filtration, and chemical destruction of contaminants. The use of these processes, which are discussed in more detail below, has been unsuccessful in economically reaching the

2~ ultimate goal of ~ero discharge of liquid effluent.
In ion exchange processes the effluent i5 passed through a bed of solid ion exchange resins. A reversible chemical reaction takes place between the ion exchange resins and the effluent by means of which the harmful ions contained in the effluent are interchanged with non-polluting ions from the ion exchange resins. The purified effluent can then be discharged or returned to the process which generates the effluent. In time, the ion exchange resins become contaminated and must be decontaminated and regenerated by back-7~

washing. In the process o-f backwashing the ion exchange resins, wastewater is generated which is more highly contaminated than the original wastewater and which must be disposed of by some method. Also, the method is expensive and the ion exchange resins have to be replaced periodically.
Reverse osmosis is effective in some cases but is limited in the types of applications to which it may be applied because calcium salts deposit in the semi-permeable membranes and most industrial processes include a lime treatment which introduces additional calcium to furtller Eoul the membranes.
Moreover, chromic acid and high pH cyanide baths attack and destroy the membranes.
In evaporation processes the effluent passes through one or more evaporator units which concentrate it for further handling. An example of one such evaporation process is disclosed in the United States Patent No.

3,973~987, issued August 10, 1976, to Hewitt et al. Evaporation processes have the disadvantages that the evaporator units are relatively expensive and use considerable amounts of energy. As energy becomes less abundant and more expensive, it will be even more difficult to justi~y using this method than it is now. ~oreover, if the efflueTIt contains cyanide at relatively high concen-trations and sufficiently high hydrogen ion concentrations, carry-over o~
cyanide into the "purified" water is a problem.
Chemical destruction methods are perhaps the most com~lon, and lend themselves to both continuous and batch type operations and can be used on small or large volumes of ef1uent. Most toxic contaminants are reduced to an acceptable level but some, such as cadmium, cause problems whereby the present and anticipated pollution control standards cannot be met. Substantially zero discharge can be accomplished or a short period of time by chemical destruct methods by reclrculating the treated effluent. However, soluble salts build up in the treated e~-~luent, and consequently the treated effluent can be recycled only relatively few times. At some point, it is necessary to dump the recirculated effluent in which soluble contaminants have built up to a high concentration.
~ iltration methods have long been used to separate contaminants from industrial wastewater, but dissolved contaminants must first be precipit-ated to remoye them. Use of chemical precipitants can introduce additional con-taminants into the "purified" water. Consequently, this method is not only limited to precipitable contaminan-ts, but can also be slow, costly, and/or partially self-defeating.
It is accordingly one object of this invention to provide a pro-cess and system for economically removin~ impurities from industrial waste-water.
It is another object to provide an economically feasible proce~s for substantially ~ero discharge of contaminants in liquid effluent.
It is another object to m;ni~;ze the energy cost of removing impurities from industrial waste~ater.
It is another object to proYide a process and system for recycling effluent within an industrial process $or extended periods of time.
In accordance with this i.nyention, there is provided a process for purifying wastewater from an industrial process comprising introducing said wastewater into a steam boiler, heating said wastewater within said boiler to produce a steam component and a liquid component concentrated in impurities, removing steam rom said boiler and using it for an industrial purpose such as for heat or a source of energy to provide mechanical motion, and removing from the boiler at least a portion of the liquid component con-taining a high concentration of dissolYed salts and possibly precipitated solids.

~ ~3~'7~

The condensed steam is recycled to the boiler or for use in the industrial process.
~ n the preferred method of carrying out this invention suspended solids, and soluble and/or insoluble organics such as oil are removed from the wastewater before it is introduced into the boiler.
The use of a steam boiler to concentrate impurities and concomitant-ly produce steam for use as an energy source meets the objects set forth above.
Unexpectedly, industrial wastewater can be used as a feedwater to a steam boiler safely and without harm to the boiler. This flies in the face of conven-tional wisdom on feedwater quality requirements for a boiler, which teaches that boiler Eeedwater should be as pure as possible to prevent corrosion and scale formation in the boiler. Scale formation not only reduces the rate of heat transfer and increases the amount of fuel required, but it may cause hot spots resulting in burnout of the heat transfer surface.
Tlle process described herein is ~ery adaptable to existing equip-mcnt in most industrial operations, being usable with existing steam boilers in the plant. ~ery little extra energy is required by the boiler to produce steam from the contaminated industrial wastewater as compared to the usually very pure boiler feedwater. Thus, the process and sys-tem are relatively economical and energy efficien-t, and adds only a few percent to the cost of energy consumed in an industrial plant. SigniEicant economies also result from recycling the treated wastewater to the industrial process which produces the wastewater.
Thus, in most cases, the treated water is sufficiently pure to use as all or a part of the make-up water required for the industrial process. In addition, valuable chemicals may be recovered from the aqueous phase containing high concentrations of salts formed in the steam generating unit. The concentrated aqueous phase formed in the steam generating unit which may contain precipit-

- 4 -ates may be further concentrated by driving off nontoxic constitllents so that there will only be a small amount of toxic constituents remaining which can be easily and safely disposed of. ~letal salts in the form of substan-tially pure crystals can be obtained by evaporating water from the concentrated aqueous phase removed from the boiler.
For a better understanding of the invention, reference is made to the following descriptiDn of a preferred embodiment thereof, taken in conjur.c-tion with the figures oE the accompanying drawing in which:
Figure 1 is a schematic diagram of a system in accordance with this invention and which illustrates a process also in accordance therewith;
Figure 2 is a sectional view of a fire-tube boiler usable with a system in accordance with the present invention;
Figure 3 is a schema*ic diagram showing modifications to the system shown in Figure 1.
In carrying out this in~ention, liquid wastewater from an industrial process is introduced into a steam boiler to produce steam and a liquid component enriched in impurities. The feed to the boiler may be any industrial waste and this invention is not restricted to but is particularly useful for those industrial wastes containing a high concentration of heavy metal salts. The invention will accordingly be described in detail with particular reference to metal processing, including metal surface finishing, metal plating, pickling and similar processes wherein the wastewater contains high concentrations of heavy metal salts.
~aterials which may be present in the wastewater include but are not limited to salts of one or more of the elements including aluminum, cobalt, copper, nickel, cadmium, zinc, chromium, gold, silver, antimony, lead, rhodium, iridium, palladiul~, molybden~m, iron, tin, arsenic, ~arium, boron, calcium, lithium~ magnesium, manganese, mercury, potassium, sodium and -titaniwm. The anions which may be present include but are not limited to fluoride, chloride, sulfate, nitrate, cyanate and cyanide. Carbon powder may also be present.
The concentration of impurities in the feedwater may be at any level; however~ for most efficient operation of an industrial plant, it will range from a level where the impurity concentration is almost too high to be useful in the industrial process to its saturation point under ambient con-ditions~ While a feed containing solids could be introduced into the boiler, in the preferred operating mode solids are separated from the liquid, such as by settling, and the clari-fied liquid is fed to the boiler. Such a clarified liquid will normally be saturated with at least the component forming the solids at ambient temperatures, e.g. about 10 to about 30C. Typically, the wastewater fed to the boiler will contain from about 200 ppm by weight to about 10,000 ppm by weight, and usually about 2,000 ppm by weight of dissolved salts, but amounts of dissolved salts as high as 30,000 ppm and higher may be present.
In the preferred ~ethod of carrying out this invention the feed to the boiler is wastewater which at least in part has been sub~ected to repeated precipitation of heavy metals with suitable precipi-tating agents. Lime and sodium hydroxide are suitable precipitating agents and the selection of one or the other, or even another agent will depend on the specific conditions under which the process Is carried out. The use of lime has the advantage that the concentration of dissolved salts will increaseata relatively slow rate in view of the low solubility oE calcium salts, especially the carbonate. Lime has the disadvantage that it maintains the concentration of calcium at a level at which some scale may form in the boiler.
On the other hand, the use of sodium hydroxide as a precipitating 0~

agent permits t}-e invention to be c~rried out virtually free of sca]e-forming materials. ~lowever, in view of the high solubility of sodium compounds the concentration of dissolved salts increases more rapidly than when lime is used.
The boiler can readily keep the concentration of the sodium salts at an accep-table level; however, during periods in which the boiler may not be needed to produce energy, as in the summertime when -the boiler is not used to produce steam for heat, lime may be the chemical of choice, at least during the off-period for the boiler.
~ any wastewaters, especially those from metal plating processes, contain water-miscible and/or water-immiscible organic compounds and/or materials such as acetone, rust-preventive oils, organic brighteners, such as benzaldehyde, chlorinated solvents such as perchloroethylene and trichloro-ethylene, and organic-metallic compowlds. I~ these organic impurities are introduced into the boiler they steam distill and appear in the condensate, and thus to some extent contaminate the purified water. In the preferred method of carrying out this invention the organic impurities are removed from the wastewater before it is introduced into the boiler. In the preferred method of removing organic impurities from wastewater before it is in~roduced into the boiler the wastewater i5 contacted with a water-immisicible organic compolmd in which the organi.c impurities are soluble, thereby stripping the organic impurities from the water. Oil is the pre-ferred organic stripping agent since it may~already be in the sys;tem, for example as a result of its use as a rust-preventing agent, and advantage can be taken of its water--immisci-bility, density, and miscibility with organic impurities. Surprisingly, organics soluble in water, such as brighteners as exemplified by benzaldehyde, as well as the water-immiscible ones are removed by the oil. In the preferred method of removing organic impurities wastewater containing the organic impurities is passed through a layer of oil floating on a body oE wastewater as is discussed in detail below in the discussion of Fi~ure 3.
This method of removing organic compounds from wastewater may be used with purification methods other than those involving use of a boiler to separate inorganic impurities, such as reverse osmosis, and is not limited to the use of a boiler to concentrate impurities.
In order to reduce corrosion in the boiler the feed should be ad-justed to a pH so that the pll of the wastewater in the boiler is in the range of 8 to lO. Suitable compounds to control pH level and to minimize scale development are discussed in more detail below.
The boiler may be operated at any pres;sure for which the boiler was des-igned and the operating pressure wlll usually be determined by the nature of the steam usage. ~or ins~ance, if steam is used for heating the boiler may operate below about 15 psig, while if steam is used to supply mechanical energy the pressure may be as high as that for which the boiler was designed.
It has unexpectedly been discovered that the presence oE cyanide in a low concentration within the boiler has a beneficial effect in helping preyent corrosion. While the mechanism is not known, it is believed that the cyanide acts as a scayenger for oxidizing agents ~Yhich may be present. Con-sequently, in the preferred method of carrying out this process a low concen-tration of cyanide is maintained within the boiler.
In order to keep the cyanide from distilling over with the steam~
it is necessary to keep the pH of the wastewater in the alkaline range. At a pH of 6 all cyanide will distill over. At a higher pH the amount distilling over will depend upon the concentration of the cyanide. ~or example, at a cyanide concentration o~ 200 ppm by w-eight some cyanide wlll distill at a pH
of 7.5, while none will distill at a pH ~reater than 8Ø At a concentration 'f7~

o-f 2000 ppm some cyanide will distiLl ove-r at a pH of 8 while none will distill at a pll oE 9. The cyanide concentration is preferably kept below 2000 ppm, since in higher concentrations cyanide may attack portions of the boiler as, for example, welds. Ihe most preferred cyanide concentration is within the range of from about 1 ppm to about 200 ppm.
Many plating wastes contain cyanide, and it may be necessary to treat the wastewater to prevent the cyanide from building up within the boiler to too high a level. Cyanide may be maintained at a proper level within the boiler by adding calcium hypochlorite to oxidize it to carbon dioxide and nitrogen. However, it has unexpectedly been discovered that oxidation of cyan-ide with H202 results in a significant reduction of solids being carried over with the steam. ~or example, when cyanide was destroyed with calcium hypo-chlorite, solids were present in the condensed steam at a level of about 40 ppm by weight. When the oxidizing agent was H2Q2 the concentration of solids in the condensed steam was reduced to about 4 ppm by weight. The concentration oE solids in the condensate in a system having a steam trap was reduced even further, to about 1 ppm by using stainless steel or CP~C pipe after the steam trap. The use of oxidizers in a boiler containing steam is believed to the contrary to usual boiler operating practice.
In the preferred ~ethod of carrying out this process chromate is present in a concentration of at least about S ppm by weight and preferably in a concentration of at least about 10 ppm. Concentrations of about 10 ppm to about 2000 ppm are most typical, but the concentration may range to 5000 ppm or higher. Chromate helps reduce corrosion o:E metal within the boiler, and it may be added if it is not already present in the wastewater fed to the boiler.
It has unexpectedly been folmd that for use in treating wastewater from a ~etal plating process where the heavy metals comprise cadmium, copper, _ ~ _ nickel, tin, zinc, chromium and iron, the amount of scale -formed ~Jithin the boiler is negligible and dissolved solids can accumulate to a level greater than about 40 percent by weight at the temperatures within the boiler. The absence of a significant amount of materials having an inverted solubility curve, such as calcium and magnesium sal~s, may explain the low incidence of scale information. In the preferred method of carrying out this invention the concentration of ~a is maintained at a level below about 200 ppm by weight, more preferably below about 100 ppm by weight, and in the most preferred me~hod CA is maintained ~elow about 10 ppm. The total concentration of material having an inverted solu~ility curve is preferably kept below about 300 ppm and most preferably ~elow about 20 ppm by weight.
The concentration of metal salts in the boiler, dissolved plus precipitated, may suitably range from a level slightly higher than that of the wastewater feed to a level of about 55 percent by weight. Inasmuch as zero liquid effluent from the industrial plant is the ultima-te goal, and a necessary adjunct to that goal is the productlon of the impurities in the form of solids, in the preferred method of carrying out this invention the salts are concen-trated in the steam boiler to as high a level as possible consonant with safe and efficient operation of the boiler. The preferred concentration of solids, dissolved and precipitated, is in the range of about 5 percent to about 30 percent by weight and the most preferred concentration is from about 10 percent to about 20 percent ~y weight. Tae concentrated solids are removed as by blowdown when the dcsired concentration is reached, and the re~oval may be either batch or continuous~.
In this process of treating wastewater and recycling the substan-tially pure water produced in accordance with this invention, the industrial process requires little or no make-up water from other sources. This feature ~ lQ -has the advantages -~hat not only is the cost of make-up water drastically reduced, but calci~lm does not acc~nulate in the system as it would if continu-ously added in make-up water. In order to keep calcium and magnesium concen-trations low, make-up water is pre~erably softened or it may consist of rain-water which has been captured and added.
The invention may be embodied in various forms, and the embodiments shown in the drawings are only provided to illustrate the invention.
Referring to Figure 1 of the drawing, an industrial process which produces contaminated wastewater ef~luent is generally designated as 10. The industrial process may include just about any industrial process which pro-duces contaminated wastewater effluent, but the process according to the present invention will be described with particular reference to metal processing, including metal surface finishing, metal plating, pickling and the like. It is to be understood that the present invention has application to a wide range of other industrial processes providing an e$~1uent with a relatively high concen-tration o impurities and the reference to metal processing is merely by way o example.
The wastewater eE1uent from the lndustrial process 10 preferably eikher does not contain extremely large amounts of corrosive chemicals or it contains corrosion-resisting chemicals. The ~aste~ater from a chrome plating process, wherein the effluent contains chromium ions which aid in protecting boiler tubes Erom corrosion, is an example o:E e~1uent containing corrosion-protecting chemicals.
The wastewater eEfluent from process 10 is conducted by means of conduit 12 through ~al~e 13 directly into a steam boiler 1~. Steam boiler 1 may be of any conventional construction and may include, for example, fire-tube, water-tube or package-type boilers. In steam hoiler 1~, the ~astewater -- 11 ~

e:E:Eluent is heated to produce a steam component thereby concentrating the impurities in the boiler in the aqueous phase. Although the impurities are concentrated to a level exceeding their solubility at ambient temperature, they may either remain in solution at the temperature within the boiler, or they may precipitate~
Standard boiler compounds may be introduced into the wa.stewater effluent before it enters boiler 1~ to inhibit or minimize the build-up of scale and to reduce corrosion in the boiler. Alternatively, the boiler com-pounds can be added to the boiler. ~here the boiler compounds are added direct-ly to boiler 1~, they are i.ntroduced through entry duct 16 by means of pump 18 since these boilers are pressurized vessels. In using these compounds i~ is desirable to adjust the pH of the wastewater within the boiler to be within a range of about 8 to la.
Suitable boiler compounds are well known to those skilled in the art. The choice and appropriate a~ount oE a proper boiler compound or compounds may easily be determined by mere routine experimentation, taking into considera-tion the type of wastewater ef1uent. Suitable boiler compounds include, for example, sodium phosphate, soda ash, am~nonia, volatile amines, such as morpholine ,md cyclohexylamine, chelating agents, such as EDTA, and polyacryl-amides of the type made according to United States Patent 3,~63,730, issued August 26, 196.~, to Booth et al.
~hile the heat transer sur$aces within the boiler are not harmed by the wastewater, it has unexpectedly been found. that the conventional level controls made of brass may corrode and it is preferred to use level controls made of stainless steel.
The concentrated i~puritie$, which may~contain p~ecipitates, will accumulate in the boiler 1~ and may ~or.m a slud~e which can be removed by - 12 ~

blowdown through condu;t 20 and conventional blowdown valve 21. A combination of sluclge and seale may accumulate and can be removed by blowdown valve 20 and~or scraper devices.
~ rom boiler 1~, the steam component is conducted through conduit 22 as working steam used for any industrial purpose as indicated at 24, such as heating a plant or heat exchanger or for driving turbines. As the steam is used for the industrial purpose lt condenses forming relatively pure water which is conveyed through the conduit 26 to a condensate return tank 28.
The condensed water can be selectively pumped from condensate return tank 28 directly to boiler 14 by pump 35 through conduit 31 and valve 33 when there is insufficient untreated or pretreated wastewater effluent entering the boiler. Preferably, valve 33 is controlled by a standard water level sensing means in the water tank.
Alternatively, the water may be conducted from condensate return tank 28 through conduit 30 to a storage tank 32. The water from storage tank 32 is conducted through conduit 34, valve 36, pump 38 and check valve 43 bac~
to the original industrial process to be used therein. Where pump 38 is necessary, an accumulator device 45 should be used to compensate for any surge in line pressure resulting from the starting of the pump and otherwise help to maintain uniformity of pressure. The accumulator device may be any standard device incorporating a piston, diaphragm, or bello~s. Pump 38 may be unneces-sary where gravity feed may transfer ~ater from storage tank 32 to industrial process la. Another variation would be to let the condensate go directly to the industrial process 10 or to the process from the condensate return tank 28.
~any industrial processes yield ~:astewater effluents containing insoluble materials. In this case, a process according to the present in-vention can include some pretreatment o$ the ~aste~ater effluent. One such ~ 13 -process is described with reference again to Figure 1 of the drawing.
Wastewater effluent containing dissolved ions and solids produced by industrial process 10 is conducted through conduits ~0, 42 and 44 and valves 46 and 48 into settllng tanks 50 and 52. Of course, depending upon the system, any number of settling tanks may be used.
For the purpose of illustration, assume that the wastewater effluent contains 1,000 ppm suspended and dissolved solids. Suitable flocculents or precipitating agents, such as lime, are added to the wastewater effluent in settling tanks 50 and 52. Lime is useful as an agent to remove calcium or magnesium present as bicarbonates forming insoluble carbonates as illustrated by the equation:
Ca(011)2 ~ Ca(llC03~2 -~ 2CaC03 ~ ~ 2~12Q
~lowever, the concentration o~ calcium is preferably minimized as by using an-other agent such as sodium hydro~ide instead of lime.
The tanks 50 and 52 are preferably used alternately, that is, one tank is filled then the other, so that the process is a ~atch type process. A
continuous system can also be used if desired. A~ter a period of time, the effluent separates into two components, a relatively clear component 54 and 56 containing only dissolved solids, such as sodium and potassium chlorides, nitrates, sulfates, etc. in a concentration o~ about l,OQ0 ppm, and a sludge or precipitated component 58 and 60, having a concentration of solids of about 2-5%.
In many instances, the wa$tewater e~fluent may be recycled back to the industrial process for use therein after the suspended solids are removed.
Thus, the component ~ and 56 containing the dissolved solids is removed through cond~its 62 and 6~ and through valYes 66 and 68 from settling tanks 50 and 52, respectively. Conduits 62 and 64 are connected to tanks 50 and 52, -- 1~ -respectively, at a point above the allticipated level of sludge 58 and 60 so that only components 5~ and 56 are removed. The component containing the dis-solved solids is then conveyed through conduit 70 to storage ta-nk 72.
The le~el of li.quid in tank 72 can be raised and the concentration of dissolved solids therein diluted by adding water fr~m condensate return tank 28. Water is selectively conveyed from tank 28 to tank 72 through con-duit 37, valve 3~ and pump 41. The pump and valve can be controlled by level sensing devices and concentration sensing devices known to those ski.lled in the ar~. The liquid containing the dissolved solids in tank 72 is recycled through conduit 74, valve 78, pump 82, check Yalve 87 and conduit 86 back to industrial process 10. Of course, where gravity feed is available, pump 82 is ~mnecessary.
Where the pump is used, accumulator device 89 is also used for maintaining uniformity of pressure.
The recycling o~ the ~astewater effluent component containing only dissolved salts aids in greatly reducing the amount of water necessar~ from primary sources, such as the municipal water system, thus conserving water, a valuable natural resource. In addition, many of the dissolved chemicals con-tained in the component containing the dissolved salts are heneficial for the industrial purpose. Thus, there may be a two-way cost savings. Typically, the component containing the dissolved salts may be recyled for a long period of time, such as, for example, one year. ~he recycled component will eventual-ly contain too large a concentration of dissolved salts to be useful in *he industrial proc0ss. ~t tha-t time, it is introduced into boiler 14 through conduit 76, valve 80, pump 84 and conduit 8%. Boiler compounds are not necessa.ry, but in the pref0rred method of carrying out this invention they are added to the pretreated, recycled component be~ore it is introduced into the boiler. The boiler produces steam for an industrial use during which the '7~

steam is condensed and the resulting water is recycled to industrial process 10 and/or boiler 1~ as set forth hereinabove.
Preferably a portion of the component containing the dissolved salts in tank 72 is continuously rec~cled to the industrial process while a smaller portion is being conveyed continuously to the boiler. In this manner, the industrial process receiyes a recycled component containing dissolved salts and a substantially pure component ~hich has gone through the steam and conden-sation cycle as set ~orth hereinbe~ore. Processes that require high quality water can receive condensate continuously and this method can eliminate ion exchange Ullits.
Sludge 58 and 60 in tanks 50 and 52 may be pumped through condui-ts 90, 92, 9~ and through valves 94 and 96 by a pump 98 to a concentrator tank 100. The sludge 58 and 60 from settling tanks 50 and 52 may typically have a concentration of about 2-5% solids. The sludge is trans~erred to concentrator tank 100 and a~ter standing oyernight produces a relatively clear component 102 containing dissolved salts and a concentrated sludge component 104 which may over a period of time build to 15% solids content. Component 102 is recycled to tank 50 through conduit 108 and valve lQ~ ~or recycling to industrial process 10 and~or to be con~eyed -to boiler 14 as described hereinbe~ore. ~h~TI concen-2Q trated sludge 10~ becomes too concentrated or builds up to a predetermined level in tank 100, it is~ discharged -through concluit 106 and valve 107.
Concentrated sludge la4 and any sludge or scale ~ormed in boiler 14 may be concentrated ~urther by any suitable process. The more concentrated sludge and scale is reduced to a very small volume and may be readily dis-carded, or recycled to metal processors.
The energy in the boiler stack gases may be used to concentrate sludge by heat exchange between the hot gases which are the combustion products o-f the boiler fuel and the sludge, and a process wherein the sludgo fr~n the boiler is introduced into the boiler stack and water is removed from the sludge by evaporation is highly energy efficient. The water content can thus readily be reduced to less than about 2 percent by weight.
In practicing this invention it has been found that the nature of the industrial wastewater Eed to -the boiler 14 may cause a foaming problem in the boiler and the liquid would then haye a tendency to surge up and down there-in. As a result, the hoiler 14 may shut down and/or discharge the wastewater instead of steam from the boiler. It is thus an important aspect of this invention to provide headroom when necessary at the top of the boiler to accommodate the foam and to relieye the prohlem of discharging water ins-cead of steam. For most boilers it is belieyed that there should be provided at least about one -foot of space between the top of the wastewater and the top of the boiler 14. I~ necessary a conventional ~loat switch can b& provided at the desired water level in the boiler 1~ and can operate a valve at the inlet to the boiler to prevent over-loading the boiler with wastewater.
~ith reference to I~igure 2, boiler 10a represents a standald fire-tube boi]er ~or use with this inyention. In this boiler heat travels from hot combustion gases within the tubes through the tube walls to water within the boiler's water tank. The direction of temperature drop across the tube wall i5 from the combustion gases to the ~astewater. The transfer of heat is represented by ~he equation Q - ~IA ~T
where Q is the amount of heat ~ransferred per unit time, A i5 the area of the surface through ~hich th& heat is transferred, is the oyerall heat trans$er coefficient, and AT is the difference in -temperature between the fluid being heated and the hot combustion gases.
The QT for steam boilers is high relative to that of evaporators where the heat required for eyaporation usuaily is supplied by condensing steam~ and consequently the heat transfer area and thus the size of the boiler can be much smaller than that of an evaporator having an equivalent capacity for converting water to steam. An additional disadvantage of an evaporator which increases the cost of a syste~ using an evaporator is that it needs a source of energy, which in most cases is a steam boiler.
Roiler lOa includes outer side walls 12a and l~a, outer bottom wall 16a and outer top wall 18a which may be integral or contiguous with water tank top wall 20a. In addition to top wall 20a, tank 12a comprises bottom wall 22a and side ~alls 24a and 26a. No novelty is claimed in the precise construction of the boiler or the water -tank. The drawing is merely representa-tive of standard fire-tube boilers in which the present invention is operable.
~ater is pumped into tank 12a through conduit 12 and valve 1~ which may be control]ed by a standard water level detector associated with tank 12a.
Conduit 12 is also provided with check valve lla. ~hen the boiler is ~Jsed to purify industrial waste~ater, conduit 12 is connected to a source of industrial wastewater such as industrial process 10 shown in Pigure 1. The wastewater may be conveyed directly to boiler lOa or may be pretreated in accordance with the process previously described or any other desired process. The water is introduced into the tank to a level 27a just above the uppermost row of ~oiler tubes 50a so as to allow space in the tank for steam 29a. Steam produced by the boiler exits through conduit 22 and its flow is controlled by any conven-tional valve, not shown. The boiler may include any conven~ional blowdown valve and conduit, not shown~ and any conventional valved inlet port, not shown, = 18 -for the addition o~ standard boiler compounds to minimize scalc bwild-up and corrosion.
Burner 28a may he any suitable, conventional burner of the type used in boilers, s~ch as a gas burner, oil burner, coal burner or a combination thereof. Heat from burner 28a travels through chamber 30a between ~he outer boiler walls and the water tank walls. The heat is then routed by baffle 32a through fire tubes 34a, 36a and 38a into a chamber 42a. Chamber ~2a is defined by boiler outer wall ]4a, tank wall 26a and baffles ~Oa and ~a. ~rom there, the heat progresses through fire -tu~es ~6a, 48a and 50a into chamber 54a bounded by boiler outer wall 12a, tank wall 2~a and curved baffle 52a. In its path through the boiler, hot gases transer their heat through the fire tubes to the water and then are e~hausted through -flue 56a.
Attached to tank l~a is scale receptacle 58a for receiving any scale scraped fro~ tank 19a. Suitable conventional gasket material or sealing means may be used to prevent water fro~ leaking out of tank 19a or scale receptacle 58a.
~ccording to a prefexred embodiment which is particularly helpful when the wastewater contains water-immiscible organic liquid contaminants, especially those having a higher specific gravity than the wastewater, ~ith or without undissolved metal salts, the wastewater is vigorously agitated, prior to passage of the waste~ater through the oil layer, such as by injecting bubbles of a gas ~including gas mixtures~, for example oxygen, nitrogen, carbon dioxide and preferably air. Por example the liquid may be agitated in a first body of liquid and be passed through the oil layer in a second, separate body of liquid. ~he operations of agitating liquid in the first body of liquid and transEerring liquid from the first to the second body of liquid may each occur continuously or nonconti.nuously, and during certain periods these operations ~ 1~) ~

may occur simultaneously~ alternately or in other time relationships. Pre-ferably the liquid which is passed ~hrough the oil layer is withdrawn from an upper portion or the surface of the first body of liquid in a first vessel and is transferred from that vessel to a second vessel which contains the second body of liquid and in which the oil layer constitutes at least the upper portion of the second body of liquid. ~oreover, it i.s desirable that the first body of liquid exhibit a gradient with respect to the mass of precipitated metal salts per unit volume of liquid which is positive ~i~h increased depth of liquid. Thus, there are more suspended and~or settled metal salts so~ids in a lower portion of the first body or vessel as compared to its upper portion.
The desired gradient may be produced in any convenient way, such as for ex-ample by providing less vigorous agitation in the upper portion of the first body or vessel and~or by discontinuing the agitation operation during at least a portion o:E ~he time when the transferring operation is being conducted.
According to a particularly preerred embodiment the liquid is transferred only after a period of reduced or no agitation su$$icient to cause appreciable or substantial settling o suspended solids, and this is preferably but not necessarily combined with withdra~ing liquid from onlr the surface of the first body.
~0 ~egardless of the point o withdrawal and sequence of agitating a.nd transferring, the transferred liquid is caus-ed to flow into and through at least a portion of the thickness of the oil layer ~hile su~ficiently restricting agitation of the oil layer or ~aintaining it substantiallr intact. Accll-îng the oil layer has a lowex speciic gravity than any other liquid which may be present in the second body, which is usuall~ the case, organics from the firsl body of liquid ~e~en thcse which may~be hqaYier than water~ beco~e dispersed or disso]ved in the oil layer o-~ the second body of liquid, while the aqueous _ 2Q ^

portion of the first body Eorms or passes into a lower aqueous layer in the second body. One convenient and preferred -techni~ue for effecting transfer is to withdraw liquid from the last-mentioned aqueous layer and to propel such withdrawn liquid into contact with an upper portion or the surface of the first body of liquid in the direction of a dam or weir over which the li~uid at the surface of the first body is thus caused to flow. The li~uid overflow may then be passed downwaTdly, pre$erably along a downward-directed surface upon which it flows, to the oil layer.
A system of recycling wastewater from a metal plating process showing portions of the system of ~igure 1 with modifications is given in Figure 3. In this system, the wastewater from the industrial process is added through line 40 and yalves 46 or 48 to either tank 5Q or tank 52 where it is treated as by adding a precipitating agent. The resulting mixture is agitated by air introduced rom an air source (not shownl through line 124 or line 125.
A~ in ~igure 1~ tanks 50 and 52 are used alternately, i.e , when one tank is full and the wastewater therein is ready to be treated the other tank is empty and ready to rece~ve wastewater from the industrial process. Oil and other organic compounds often found in wastewater, such as chlorinated solvents and brighteners, are removed Erom the wastewater hy passing che waste-water through oil layer 130 within recirculation tank 136. This is accomplished by adding enough liquid tv tanks 50 or 52 either from line 40 or from recircula-tion tank 136 through lines 128 or 12~ to cause wastewater to over10w into recirculation tank 136.
The oil layer 130 is effective in re~oving from ~astewater organic compounds soluble in the oil including water-soluble organics such as brighteners as well as wat~r-immiscible compounds, and is effective in remoying emulsiied particles which ~ould be difficult to separate from water by differences in L'~

specific gravity.
I~ an oil layer does not form within one or two cycles after start-ing the process, enough oil sllould be added to form layer 130 from about 1/4 inch to about 3 inches thick. The oil layer is pre~erably maintained at a thickness of from about 1 to about 2 inches. While thicknesses greater than these may be used, there appears to be no advantage to thicker layers. The te~l "oil" refers to lighter petroleum fractions ordinarily used for rust preventive purposes or for lubrication such as oils designated as S~E No. 30.
By use of the air agitation system the water-immiscible organics which are heavier than water, such as chlorinated solvents as exemplified by perchloroethylene and trichloroethylene, are prevented from accumulating in the sludge by being dispersed throughout tanks 5Q and 52 and thus overflow into recirculation tank 136. The sludge for recycle to metal processors is t~lUs relatively free of organic compounds. In using the air agitation system to disperse the hea~y organics throughout tanks 5Q and 52 the agitation is prefer-ably intermittent to permit solids to setlle while wastewater overflows into tank 136.
Operation of the alr agitation system and recirculation pl~p keeps the concentration of total or~anic carbon in the condensed steam at a relative-ly low level. If hea~y organic5, such ax the chlorinated solvents, are not present, recirculatiQn alone will keep the concentration of total organic carbon in the steam condensate at a negligibly~l~w leyel.
The pre5ence o~ a heaYy organic impurity, such a~ trichloroethylene and perchloroeth~lene, in the wastewater may re~uire controlling the composition of oil layer 130 to maintain a density less than that of the wastewater. The density may be reduced, if necessary, by adding additional oil to the layer, either with or without a step of removing a portion of the material from layer 130. The specific gravity of the oil layer is preferably maintained below about 0.~.
The clearJ oil-free water 135 from the recirculation tank 136 is moved by pump 126 or 127 through conduits 128 or 129 into tank 50 or 52 through spray heads (not shown~. This recirculating water serves to provide water to tank 50 or 52 to float the oil and other organics into the recirculation tank, or to flush sludge 58 or oO from tanks 50 or 52 when they are being emptied.
Clear liquid from tanks 50 to 52 is pumped into s~orage tank 72 through line 70.
The treated wastewater from tank 72 may be recycled as is shown in Figure l.
The process according to the present invention provides for sub-stantially zero contaminated wastewater efflu~nt discharge. The wastewater effluent is treated in accordance with -the present invention and need not ever leave the system. The only contaminants which leave the system are in the form of oil ~organics), highly concentrated sludge and/or scale which are easier to dispose of than large amounts of dilute liquid efEluents, certain of which can be dried thus further concentrating them and placing them in a form 5Ui cable for processing by metal manuEacturers.
The process will now be illustrated using the following specific, nonlimiting examples:
Example l Approximately 500 gallons o-f recycled wastewater efluent were obtained from the wash and rinse baths of an electroplating process. The recycled wastewater effluent, which had been used in the baths for about one year, contained heavy metals, such as cadmium~ copper, nickel, tin, zinc and iron. In addition, it contained cyanide, hexavalent chrome, oil, alka~ine cleaner and various acids.
The cyanide was destroyed by normal chlorination. The hexavalent chrome was partially reduced by a hydrosulfite and the oil removed continuously with an oil separator. The heavy metals were precipitated with excess lime and polyamine flocculents. After this treatment, a sludge component and a clear component remained. The pH of the clear component was adjusted to approximate-ly 8 and it was pumped to a reservoir -for use in the electroplating process as needed. The clear component was recycled once or twice each week and after about a year the water became unusable due to a build-up of dissolved solids and interference with the plating operation. The dissolved solids, in a concentration of about 8,500 mg/l, seemed to consist mostly of sodium sulfate, sodium chloride and sodium nitrate. Other cations, such as potassium, calcium, magnesium and ammonia were present, but no e~forts were made to determine exact amounts. Organic ma-terials, such as wetting agents, were also present.
The recycled component containing the large concentration of dis-solved solids was then introduced into a small laboratory boiler for testing to see if the boiler would separate the contaminants from the steam and not damage the boiler.
The steam produced by the boiler at about 15 p.s.i.g. was condensed and the water condensate was relatively clean. It contained some ammonia and iron and had a p~l of 8.8. The sludge produced in the boiler was soft and oo~ed out of a control valve ~corresponding to a typical blowdown valve) and the experiment progressed. The boiler contained an average of about 4 gallons of the component containing the high concentration of dissolved solids as the 500 gallons of wastewater were passed through the boiler. When the boiler was dis-assembled, some hard scale was found and removed.

~xample 2 A 55 gallon drum of chrome waste was obtained from another plant that processed copper and copper alloys. The chrome was re~uced to the tri-valen-t state and the sludge represented ahout 50% of the solution by volume.
The p}l o the solution was adjusted to 8, the solution was agitated and allowed to stand for about 20 minutes. The sludge was still about 50% by volume and remained so af-ter leaving the sludge stand overnight. Solids by weight of the sludge were about 5~.
The waste was then introduced into the laboratory boiler. There was concern that the sludge would be difficult to concentrate in the boiler because of its voluminous nature. However, this did not prove to be the case.
The greensludge did not show up in the boiler sightglass or enter the steam port Difficulties, however, were encountered in other aspects. Even though the pH was adjusted and maintained at about 8~ the steam had a pH of 2.4 and badly corroded the boiler steam lines. Excess sodium sulfite was present, yielding corrosive sulfur dioxide and sulfurous acid. Hexavalent chrome was added to remove the excess sodium sulfite and the experiment repeated. When approximately 5 mg~l of hexayalent chrome was maintained in the boiler, no further sulfur dioxide was carried over with the steam and the pH of the conden-sate was about 8. There appeared to be no further corrosion of the boiler system.
Example ~
~nother experiment was carried out with the same chrome wastewater as used in Example 2. The conditions in the boiler were 5-10 ppm of hexavalant chrome and the pH ranged rom about 8 to about 10. Morpholine was added to the boiler to adjust the pH o the steam so that as the steam entered the conden-sate tcmk, the -~H wa$ between 7.5 and 8.5. The steam pressure was about 15 p.s.i.g.

:~L~ t~

Tile chrome sludge did not interfere with the normal boiler con-ditions. The condensate showed the presence of morpholine and a pH of about 8. No noticeable corrosion could be detected in the boiler or in the steam lines. The concentrated trivalent chrome was removed from the boiler through the control valve a-t about 60 percent dissolved salts and solids. No hard scale formed on the inside of the boiler.
A portion of the impurities removed from the boiler were further concentrated by placing the sludge on a cloth which was placed on a steam table.
More water was driven off and the solids were concentrated to about 97 percent by weight. The sludge was dark green in color and hard. It was crumbly and easily separated from the cloth.
Another portion of the 6~ percent solids removed from the boiler was placed in the exhaust stack for the boiler, ~here water was driven off and the solids concentrated to about ~8 percent.
Example 4 Sludge from the boiler ~ormed as in Example 3 and consisting of 60 percent solids were pumped from the boiler to a stainless steel conveyor designed to carry the sludge into the exhaust stack of the boiler. The exhaust gases, which were at a temperature rom about 350F ~o 45~F, further concen-trated the solids.
Example 5 The following example was conducted in the laboratory as part of an economic study. l`t is be]ieved that the economlc savings set forth below would be achieved.
Conditions at another plant were observed and samples of waste-water effluent taken. Particular emphasis was placed on the economics of this plant which illustrated the energy savings associated according to the present ~ ~ ~r~d ~

invention. ApprQximately 750,000 pounds of steam were generated daily in the winter for heating and proccssing in -the plant. In the summcr, about 200,000 pounds of steam were used daily. The water discharge varied between 100,000 and 140,000 gallons per day throughout the year. About 75 percent of the water was used in the electroplating department. Even though the water was cleaned by chemical treatment before being discharged to a stream, it was not considered clean enough for recycling to the plating department. Samples o~ the chemical-ly treated wastewater effluent were run through the laboratory boiler and the water condensed ~rom the steam produced by the boiler provided to be of high quality and satisfactory for the plating operation.
If the wastewater effluent from the plating operation only were run through a separate evaporator, the additional cost for energy would be in excess of $2,000 per day, which would double the budget cost. However, if the wastewater effluent were introduced into the existing plant boiler, the energy costs would be only slightly increased. For illustration, Gn a cold ~inter day, 765,000 pounds of steam were generated and 583,440 pounds (78,000 gallons) of steam were used in the plating area. By passing all of the wastewater through the existing boiler in accordance with the present invention, there would be more than enough water for daily usage. A further advantage would be that the condensate would be warm (75-100F), which would facilitate rinsing in the plating operation.
~ince the steam had to be generated anyway, the only additional costs would be hea-ting the condensate return water more than previously done. It was estimated that 10 percent additional energy would be required for this purpose, but this would be offset by less blowdown, so that the net energy loss would be only 4 to 5 percent.
In the summer, not enough steam would be generated to process the ~ 27 ~

q~

water according -to the present inyention ~ach cycle. A determination would have to be made as to W~iC}I process in the plant was most critical and would require the pure high quality condensate produced in accordance with the pre-sent invention. The rest of the operation would use recycled water from normal chemical destruc-t methods. The net reslllt would be a substantially closed loop system and substantially no water would ever leave the system in liquid form containing pollutants, except in the concentrated sludge from the boiler.
Example 6 Seyeral 55 gallon drums of water effluent were collected from a plant before waste treatment procedures were carried out on the waste effluent.
The cost of chemicals at this plant was very high for reducing hexavalent chromium and precipitating heavy metals. The only pretreatment before passing the waste through the boiler was to adjust the pH to 9 and add polyamines to prevent the scale formed from sticking to the boiler plate. Hexavalent chromium was maintained in the boiler. The water which was condensed from the steam produced by the boiler was of excellent quality, bu-t the scale did adhere somewhat and mechanical scraping was necessary.
E~ample 7 Trichloroethylene was introduced into the recycled water in the system of Figure 3 to determine whether it would appear in the condensate if it were introduced into the boiler and to determine whether it would be removed by passing the recycled water through an oil layer. Trichloroethylene was selected since it has been found in ground waters and is considered to be a carcinogen.
~hen trichloroethylene wa$ a component of the wastewater introduced into the boiler, the condensed steam ~as blue in color. The reason for the color is not known~ but it made for easy visual detection of the presence of trichloroe-thylene. The air agitation system and the recirculation pumps were then turned on ~or about 30 n~inutes eorcing the water over the overflow through a 3 inch thick layer of oil. 'I'he wastewater was permitted to settle overnight and clear water was drawn lnto the boiler. The condensate was clear indicating the absence of significant amounts of trichloroethylene.
Example 8 The experiment of E~ample 7 was repeated without air agitation.
The condensed steam from the boiler was blue, indicating the presence of tri-chloroethylene in the condensate.
~ample 9 Drawing oils and organic plating brighteners, but without any chlorinated solvents, were introduced into the recycled water introduced into the boiler. No blue color appeared in the condensate; however, analysis showed a significant concentration of total organic carbon in the condensate.
The present invention may be embodied in other specific forms without departing rom the spirit or essential attributes thereof. For example, the industrial wastes may be from sources other than metal processes, as for example chemical processes~ biological processes, mining industries, or pharmaceutical industries. The pressure at which the boiler is operated is determined by its capability and the use to which the steam is put. Pressures as high as 150 p.s.i. may be desirable for processing waste Erom the pharma-ceutical industry or for biological wastes to ensure destruction o~ all viruses and thermophiles. ~ccordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

- 2~ -

Claims (66)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for substantially zero discharge of polluting impurities in wastewater comprising the steps of introducing said wastewater having a first concentration including dissolved impurities into a boiler having a heat trans-fer surface in contact with said wastewater, raising the temperature of said surface to produce a steam component and a component having a second concen-tration of impurities, said second concentration being greater than said first concentration, and removing said steam component from said boiler.

2. The process of claim 1 wherein said steam removed from said boiler is used for an industrial purpose resulting in formation of condensate, and at least a portion of said condensate is recycled for use in said industrial process.

3. The process of claim 2 wherein a portion of the condensate is recycled to said steam boiler.

4. The process of claim 1 wherein the wastewater fed into said boiler contains from about 200 to about 5,000 ppm by weight of impurities.

5. The process of claim 1 wherein the liquid component within said boiler contains from about 5 percent to about 30 percent by weight impurities.

6. The process of claim 1 wherein the liquid component within said boiler contains from about 10 percent to about 20 percent by weight impurities.

7. The process of claim 1 wherein the impurities in the wastewater com-prise at least one salt of alkali, alkaline earth, and heavy metals.

8. The process of claim 7 wherein the heavy metals are selected from the group consisting of cadmium, copper, nickel, tin, zinc, chromium, iron and alu-inum.

9. The process of claim 1 wherein compounds having an inverted solubility curve comprise no more than about 300 ppm by weight of impurities in the wastewater.

10. The process of claim 1 wherein calcium ions in the wastewater comprise no more than about 200 ppm by weight.

11. The process of claim 1 wherein the pH of the wastewater is adjusted to a value within the range of about 8 to about 10.

12. The process of claim 1 wherein the wastewater contains at least one organic impurity and the process includes a step of removing said organic impurity from said wastewater before introducing said wastewater into said boiler.

13. A process for substantially zero discharge of polluting impurities in wastewater effluent as in claim 1 further comprising the steps of precipi-tating a portion of said impurities separating the resulting precipitated impurities from the resulting aqueous phase forming a partially purified aqueous waste, and then processing at least a portion of the partially purified aqueous waste in said boiler.

14. The process of claim 13 wherein said impurities also include undissolved impurities.

15. The process of claim 13 wherein a portion of said partially purified aqueous waste component is recycled to an industrial process prior to processing in said boiler.

16. The process of claim 12 wherein said impurity is removed from said wastewater by passing said wastewater through a layer of a water-immiscible solvent for said impurity.

17. The process of claim 16 wherein said layer of a water-immiscible solvent comprises an oil.

18. The process of claim 16 wherein said impurity is selected from the group consisting of oils, organic plating brighteners, and chlorinated solvents.

19. The process of claim 12 wherein at least a portion of said organic impurities are water-soluble organic compounds.

20. The process of claim 12 wherein at least a portion of said organic impurities are substantially water-immiscible.

21. The process of claim 12 wherein at least a portion of said organic impurities are substantially water-immiscible and have a specific gravity greater than that of water.

22. The process of claim 16 wherein the step of passing said waste-water through a water-immiscible organic solvent is carried out by passing said wastewater through a layer of said solvent disposed on the surface of an aqueous body.

23. The process of claim 22 further comprising the step of agitating said wastewater prior to its passage through said solvent.

24. The process of claim 23 wherein said agitation is accomplished by injecting gas bubbles into said wastewater.

25. The process of claim 1, further comprising the step of removing at least a portion of said component having a second concentration from said boiler.

26. The process of claim 25 wherein said boiler has an exhaust stack for evacuating hot gases generated from raising the temperature of said heat transfer surface, further comprising the steps of introducing said removed component to said stack and concentrating said removed component using the heat from said hot gases.

27. The process of claim 25 wherein said removed component is retained within said stack for a period of time sufficient to reduce the water content to less than about 2 percent by weight.

28. The process of claim 27 wherein at least one of the impurities is a metal salt which is crystallized in substantially pure form upon evaporation of the water in said liquid component.

29. The process of claim 27 wherein the impurities are metal salts.

30. A process for substantially zero discharge of polluting impurities in wastewater effluent from an industrial process comprising the steps of separating said effluent into components including a first component con-taining dissolved solids, recycling a portion of said first component for use in said industrial process, and processing a portion of said first component in said boiler as in claim 1.

31. The process of claim 30, wherein said recycling step is performed for a predetermined period of time prior to any processing in said boiler.

32. The process of claim 31, wherein said predetermined period of time is that time wherein the recycled component can no longer be used beneficially in said industrial process.

33. The process of claim 30, wherein said recycling step and said step of processing in said boiler is proceeding continuously, further comprising the steps of condensing said steam removed from said boiler to form a condensate and recycling said condensate for use in said industrial process.

34. The process of claim 33 further comprising the step of combining said condensate with said first component prior to said use in said industrial process.

35. A process for substantially zero discharge of polluting impurities in wastewater from metal processing operations wherein said wastewater contains high concentration of heavy metal salts, comprising the steps of introducing said wastewater having a first concentration including dissolved impurities into a boiler having heat transfer surfaces in contact with said wastewater, raising the temperature of said surface to produce a steam component and a component having a second concentration, said second concentration being greater than said first concentration, and discharging said steam component from said boiler.

36. The process as in claim 35, wherein said wastewater further includes an organic impurity selected from the group consisting of oils, organic brighteners and chlorinated solvents, further comprising the step of passing said organic impurity through an organic solvent for said impurity.

37. The process as in claim 35, further comprising the steps of separating said effluent into components including a first component containing dissolved salts and a second component and recycling said first component to said metal processing operations for a predetermined time period prior to introducing said wastewater into said boiler.

38. The process as in claim 37, wherein said wastewater further includes cyanide further comprising the step of adding an oxidizing agent to said wastewater prior to introducing said wastewater into said boiler.

39. The process as in claim 38 wherein said oxidizing agent is hydrogen peroxide.

40. The process as in claim 35, wherein said wastewater from said metal processing operations consists essentially of plating wastes.

41. A process of processing wastewater effluent from an industrial process for substantially zero discharge of polluting impurities wherein the effluent contains dissolved solids including metal values, the process comprising the steps of settling out solids to form a settled sludge component and a relatively clear component, separating said clear component from the settled sludge component, continuously feeding a major proportion of the clear component to said industrial process for recycling and a minor proportion of the clear component to a boiler so that the clear component contacts a heat transfer surface of the boiler, regulating the pH of said minor proportion to the range of 8 to 10 before feeding the minor proportion to the boiler, heating the clear component in the boiler under pressure of at least 15 psig (1.0 Kg/cm2) to produce steam and a boiler sludge, removing the steam and condensing it to form a purified component, removing the boiler sludge, and removing the settled sludge component.

42. A process of processing wastewater effluent from an industrial process for substantially zero discharge of polluting impurities, wherein the effluent contains dissolved solids including metal values, the process comprising the steps of settling out solids to form a settled sludge component and a relatively clear component, continuously recycling the clear component through said industrial process and said settling process until the concentration of dissolved solids reaches a predetermined level, feeding the recycled clear component to a boiler, so that the clear component contacts a heat transfer surface of the boiler, regulating the pH of the clear component to 8 to 10 before feeding the component to the boiler, heating the clear component in the boiler under pressure of at least 15 psig (1.0 kg/cm2) to produce steam and a boiler sludge, removing the steam and condensing it to form a purified component, removing the boiler sludge, and removing the settled sludge component.

43. A process according to Claim 41 or 42, wherein the concentration of compounds with inverted solubility curves in the clear component being fed to the boiler is regulated to no more than 300 ppm.

44. A process according to Claim 41 or 42, wherein the concentration of compounds with inverted solubility curves in the clear component being fed to the boiler is regulated to less than 20 ppm.

45. A process according to claim 42 or 43, wherein at least a portion of the condensed steam is recycled in said industrial process.

46. A process according to Claim 41 or 42, wherein at least a portion of the condensed steam is used as a diluent for said liquid component.

47. A process according to claim 41 or 42, wherein the boiler sludge is removed when the concentration of impurities is from 5 to 30 per cent by weight.

48. A process according to claim 41 or 42, wherein the settled sludge component has a concentration of 2 to 5 per cent by weight of impurities.

49. A process according to claim 41 or 42, in which the clear component fed to the boiler has a dissolved solids concentration of 5000 to 30,000 ppm.

50. A process according to claim 41 or 42, wherein the removed settled sludge component is fed to a tank for further settling into a concentrated part until the concentrated part has at least 15% by weight of solids.

51. A process according to claim 41 wherein the industrial process is a metal plating process having rinsing operations and the recycled clear component is utilized in the rinsing operations.

52. A process according to Claim 51, wherein the concentration of cyanide in the boiler is kept below 2000 ppm.

53. A process according to Claim 52, wherein said concentrations of cyanide is kept from 1 to 200 ppm.

54. A process according to Claim 41, wherein the wastewater effluent contains cyanide and the pH of the clear component fed to the boiler is adjusted to a level such that distillation of cyanide is substantially prevented.

55. A process according to Claim 54, wherein said pH is 8 where the cyanide concentration is 200 ppm or less.

56. A process according to Claim 54,wherein said pH is 9 where the cyanide concentration is from 200 to 2000 ppm.

57. A process according to Claim 54, 55 or 56, wherein the cyanide is oxidised in the boiler by hydrogen peroxide.

58. A process according to claim 41 or 42, wherein the clear component fed into the boiler contains from 200 to 5,000 ppm by weight of impurities.

59. A process according to claim 41, wherein the impurities in the wastewater comprise at least one salt of alkali, alkaline earth, and heavy metals.

60. A process according to Claim 59, wherein the heavy metals are cadmium, copper, nickel, tin, zinc, chromium or iron.

61. A process according to claim 41, wherein the wastewater contains at least one organic impurity and the process includes a step of removing said organic impurity from said wastewater before introducing said waste-water into said boiler.

62. A process; according to Claim 61 wherein the organic impurity is removed by passing the wastewater through a layer of water-immiscible solvent for said impurity.

63. A process according to Claim 62, wherein the organic impurity is an oil, organic plating brightener or chlorinated solvent.

64. A process according to Claim 61, 62 or 63, wherein the step of passing the wastewater through a water-immiscible organic solvent is carried out by passing said wastewater through a layer of said solvent disposed on the surface of an aqueous body.

65. A process according to claim 41, in which chromate is kept in the boiler at a concentration of at least 5 ppm.

66. A process according to Claim 65, in which said chromate concentra-tion is at least 10 ppm.